A Study of the Structure and the Corrosion Behavior of Al Based Coatings Deposited with Low Pressure Cold Spray
R. G. Maev, D. Dzhurinskiy, J. Muller, E. Maeva, V. Leshchynsky, University of Windsor, Windsor, ON, Canada
Improvement of corrosion resistance of friction stir welded aluminum alloys is of great importance for aerospace applications. The paper presents first results about Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements (polarization curves, electrochemical impedance spectroscopy) in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the Al based coatings were investigated and compared with pure Al coating. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.The results reveal the corrosion resistance of friction stir welded aluminum alloys can be substantially improved by applying Al-based coatings made with LPCS.
TITANIUM for High-Power Energy Storage
G. E. Welsch1, D. McGervey1, J. W. Ki2, (1)Case Western Reserve University, Cleveland, OH, (2)formerly PhD student at CWRU, now at POSCO, Pohang, South Korea
High-purity titanium and tailored titanium alloys can serve as electrodes and dielectric substrate in electrolytic supercapacitors. Alloy composition and surface-modification processing play critical roles in the generation of titanium-supported dielectric film. Chemical stoichiometry and structural integrity at the atomic scale are essential for the formation of a dielectric with high field strength and low leakage current. These are requisites for high energy density. Additionally, a nanometer-scale open-porous titanium topography provides high specific surface area and a low series-resistance electrical connectivity. Design principles based on pure titanium and on Ti-alloys will be presented. Experimental data from first generation 'titanium spine electrodes' show their potential for high combined energy density and power. [Acknowledgement: Research support by NRO]
Conductive Nano and Macro Materials in Polymeric Composites for Lightning Strike Protection Applications
K. Kranjc1, J. C. Fielding1, T. Gibson2, (1)Materials and Manufacturing Directorate, Air Force Research Laboratories, Wright-Patterson AFB, OH, (2)University of Dayton Research Institute, Dayton, OH
Since composite materials are becoming increasingly integrated into aircraft structures, the need has arisen for a conductive composite that can disperse the charge incurred from a lightning strike with minimal to no damage to the composite itself. Nanomaterials with a high aspect ratio are electrically conductive as well as lightweight, which makes them ideal for integration into aircraft structures. Various conductive nanomaterials such as single-wall nanotube and multi-wall nanotube buckypapers and nickel nanostrand veils and films have thus been added to a traditional composite lay-up along with macro conductive materials such as nickel-coated carbon fibers and expanded copper mesh. The conductive composite panels were fabricated using a resin transfer molding process, and these panels were then lightning-strike-tested using a 100 kA current. The lightning strike test results including damage depth and damage area analysis using ultrasonic scan, X-ray, and optical microscopy will be presented as well as electrical conductivity test results using 4-point probe method. Correlation between the lightning strike results and electrical conductivity will be made.
Electrodeposited Nanocrystalline Metals and Alloys as Environmentally Compliant Alternative Coatings to Functional Hexavalent Chromium and Cadmium
D. Facchini, J. McCrea, I. Brooks, F. Gonzalez, G. Palumbo, Integran Technologies, Inc., Toronto, ON, Canada
Increasingly stringent environmental and emissions requirements are putting severe pressure on the metal finishing industry to shift away from coatings that are deemed unacceptable from environmental, health and safety standpoints. These include Cd and hexavalent Cr plating which are used to provide corrosion and/or wear protection to aerospace components. Electrodeposited Cd is used extensively by the aerospace industry to protect iron and steel from corrosion. Alternate coating technologies have found acceptance in various military and commercial Cd-replacement roles; however, there are still some technology gaps for specific applications, particularly regarding high-strength steel components which are prone to hydrogen embrittlement, a serious issue that commonly occurs in the corrosion-resistant coating process. Hard Cr plating from hexavalent chromium solutions is a technique that has been in commercial production for over 50 years. It is a process that is used to apply hard coatings to a variety of aircraft components in manufacturing operations and for general re-build of worn or corroded components that have been removed from aircraft during overhaul. In particular, Cr plating is used extensively on hydraulic and pneumatic actuator wear surfaces. While HVOF coatings show good potential, their use has been limited because they are not amenable to non-line-of-sight applications and they require a fairly substantial investment in capital equipment. Through microstructural design and engineering materials, Integran Technologies Inc. has recently developed several surface nanotechnology platforms as alternatives to existing functional Cr and Cd applications within the aerospace sector. An overview of nanocrystalline materials and their enabling structure/property relationships will be presented, with particular emphasis on processes and properties as they pertain to alternatives to Cr and Cd. For these examples the importance of application- and property-specific microstructural design and optimization is underscored.
Mechanical Behavior of Cast Titanium Alloy Lattice Block Structures
E. Y. Chen1, Q. Li2, D. R. Bice1, D. C. Dunand3, (1)Transition45 Technologies, Inc., Orange, CA, (2)University of Nevada, Reno, Reno, NV, (3)Northwestern University, Evanston, IL
Lattice block structures (LBS) - also called lattice block materials, lattice-truss structures, truss-core sandwiches, and cellular lattices - are three-dimensional-periodic reticulated materials that derive their outstanding mechanical performance from a high-symmetry arrangement of internal trusses connected at nodes. These engineered materials are innovations that offer tremendous opportunities for weight and cost reduction in future aerospace systems, both for commercial and military applications. In this presentation, the structural and mechanical characterization of individual struts and flat panel LBS produced using an aerospace quality investment casting process are reported for the titanium alloys Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo. Testing in compression, bending, and impact show that high strength, ductility and energy absorption are achieved for both individual struts and full panels. Elevated temperature testing results will also be discussed. Finally, the experimental compressive stress-strain behavior of the LBS panels will be compared to finite element modeling (FEM) predictions. This work was supported by NASA-Glenn Research
Al-SiC Composite for Cutting and Structural Applications
R. Sagar, IIT Delhi, Delhi, India
There are many commercial processes available for making a polymeric composite. These can be broadly divided into two categories primary and secondary manufacturing methods . The primary manufacturing methods include Hand Lay-up and Spray-up techniques, Resin Transfer Molding, Compression Moldings, Autoclave Molding, Injection Molding, Filament Winding, Pultrusion etc., while the secondary manufacturing methods include edge trimming, hole generation or drilling, grooves cutting,
The performance of the developed drill is evaluated by studying effect of various tool performance parameters
Advantages:
Limitations
Development and Property Evaluation of Aluminum-Alloy Reinforced with Chilled Nano-ZrO2 Metal Matrix Composites (CNMMCs) for Aerospace Applications
J. Hemanth, University, TUMKUR, India
In the present research nano- ZrO2 particulates were dispersed in aluminum alloy (LM 13) by chilled melt deposition technique followed by hot extrusion. The size of the particles dispersed varies from 50-80 nm and amount of addition varies from 3 to 15 wt.% in steps of 3%. Microstructural studies of the nano-composite developed indicate that there is uniform distribution of the reinforcement in the matrix alloy with significant grain refinement and retention of residual porosity. Mechanical properties reveal that presence of nano- ZrO2 particulates and chilling has improved significantly the strength and hardness with slight reduction in ductility as compared against the matrix alloy. Fractography of the specimens showed that the fracture behavior of matrix alloy has changed from ductile intergranular mode to cleavage mode of fracture. Results of the thermal and electrical tests on the composites developed indicate that, thermal conductivity and electrical resistance both decreased with increase in reinforcement content. Figs. 1 and 2 shows microstructure of extruded and fractured CNMMC containing 12 wt% reinforcement.
Fig.1 Optical microstructure of extruded Fig.2 SEM Fractograph of NMMC (12 wt%
NMMC containing 12 wt.% reinforcement. ZrO2,) (Magnification 100 μm, 500 X) (500 X Magnification)
Coating and Sealant Removal Using Cold Atmospheric Plasma
S. J. Hudak1, J. J. Cuomo1, A. J. McWilliams1, P. J. Yancey2, J. Waldrep2, R. Kestler3, J. Kingsley4, (1)North Carolina State University, Raleigh, NC, (2)AP Solutions, Inc., Cary, NC, (3)NAVAIR, Cherry Point, NC, (4)AFRL/RXSA, Dayton, OH
Atmospheric plasma is being investigated as an alternative technology to remove protective coating and sealant materials from aerospace structures. In collaboration with NAVAIR’s FRC-East Fleet Readiness Center at Cherry Point NC and the Air Force Research Laboratory Dayton, OH, researchers at NC State University and AP Solutions, Inc. have demonstrated the ability of AP Solutions’ Plasma Flux cold atmospheric plasma system to remove a variety of materials from different substrates. Atmospheric plasma is created using standard electrical outlet power combined with compressed air which is available in any shop. Electrical outlet power is converted to a higher frequency and is used to electrically excite the compressed air into a chemically active plasma state. The plasma is directed through a suitable nozzle to create a plume which is then moved across the substrate using manual or automated means. Ionized gas and chemically active species in the plasma react with component materials converting them into low molecular weight gasses and compounds which are collected and filtered for disposal. Rates of removal can be adjusted depending on application requirements and are competitive with conventional coating and sealant removal techniques. The condition of the surface remaining is dependent on the exposure conditions and material composition. With proper application of the plasma the substrate may be suitable for direct recoating.
Cold Spray Technology Update – Process Developments and Industrial Applications
D. Harvey, TWI Ltd., Cambridge, United Kingdom
Cold Spray is a recently commercialised technology, developed for the production of high quality, metallic coatings, spray-formed components and repairs. The process involves the rapid deposition of metallic layers using fine powders (typically 10- 50μm), propelled at target substrates or components at velocities between 500-1000ms-1 in a cold supersonic jet of compressed gas. Cold Spray offers manufacturing solutions where the properties of conventional metal-sprayed coatings (e.g. flame, arc, plasma and HVOF spraying) are not fit-for-purpose. Coatings are characterised by:
High strength resulting from excellent inter-particle cohesion and adhesion to the substrate.
Very low porosity and oxide content.
Superior corrosion and oxidation resistance.
High thermal and electrical conductivity
Materials that can be deposited by cold spray include:
Metals: Al, Cu, Sn, Ni, Ti, Ag, Zn, Ta, Nb, Zr, Ta.
Alloys: steels, Ni alloys, Ti alloys, MCrAlYs.
Composites (or blends): Cu-W, Al-SiC, Al-Al2O3.
The first part of the paper will summarise of the current technology position of the Cold Spray process and will include:
An overview of the Cold Spray process equipment and related facilities
Benchmarking with conventional thermal spray processes.
A summary of commercial systems.
The second part of the paper will provide an overview of current Cold Spray aerospace-related application developments, including:
Repair of Mg alloy components e.g. helicopter engine gearboxes.
MCrAlY coatings for gas turbines.
Copper and aluminium layers for electronic devices, heat sinks.
Cd-plating alternatives.
Fabrication of Smart Aerospace Materials with Ultrasonic Consolidation
G. K. M. Martin, K. Johnson, Solidica, Ann Arbor, MI
Ultrasonic Consolidation (UC) is a new welding process that permits unique and advanced part fabrication. Using a continuous, rolling process, layers of metal material can be welded together to encapsulate a variety of devices and geometries, including in situ strain sensors, thermocouples and conformal cooling channels. Together, these strengths can be combined to build smart, lightweight structures excellent for use in aerospace applications sensitive to weight and corrosivity.
This talk will discuss the fundamental processes and strengths of UC for creating these structures. Key components include the materials science associated with ultrasonic excitation, deformation and fabrication capabilities of the Solidica welding platform. Examples of in situ component embedding will be highlighted and a final case study presented.
Flexible Robotic Direct Printing of Aircraft Surface Electronics
J. W. Sears, V. Kalanovic, South Dakota School of Mines & Technology, Rapid City, SD
Direct Printing (Write) has been developed over the last ten year for direct fabrication of electronic devices that can be place on conformal surfaces. To the most part the technology has been applied for surface structures with the print head in a vertical orientation to the surface. Some system have the capability to manually adjust from the vertical position. This presentation presents how the Direct Printing technology can be applied within a Flexible Robotic Environment (FRE). With FRE, directly printed devices can be applied to air foils, hemispheres and other contoured shapes at accuracies of less then 10 microns. Flexible electrical devices have been developed using various direct write techniques to deposit micron-resolution conductive patterns onto various substrates ranging from glass to plastic or even paper. These direct write techniques use nanometer sized particles in a suspension or slurry that are deposited onto the substrate and cured or sintered to increase the cohesion of the particles to increase the physical and electrical properties of the deposition. The sintering of particles is driven by both temperature and time. So the desired properties of a given deposition can be achieve by either raising the deposition and the substrate to a high temperature for a shorter period of time or a low temperature for a longer period of time. The capabilities of both FRE and Direct Printing (Write) will be presented.
Solution Nitriding – a Cost Effective Case Hardening Process
P. Weymer, Ipsen, Inc., Cherry Valley, IL
Solution nitriding or the Ipsen SolNit® process is a newly developed thermo-chemical heat treating process for case-hardening stainless steels. If treated with normal nitriding or carburizing processes, stainless steels lose most of their corrosion resistance due to the formation of chromium nitrides or carbides. The Ipsen patented case hardening process is very different from the conventional nitriding process. It imparts a nitrogen rich case measuring up to 0.100” (2.5 mm) on parts made from either austenitic or martensitic stainless steels while at the same time preserves or improves the parts corrosion resistance. Attendees will learn about the background theory, microstructure, application, and results of solution nitriding in Ipsen’s high pressure gas quench furnaces.
Evaluation of Thermomecanical Processes on Alloy 909 Properties
O. Covarrubias, O. Elizarraras, Frisa Aerospace SA de CV, Santa Catarina, Mexico
Alloy 909 (UNS N19909) is a Ni-Fe-Co alloy used for jet-engine components manufacture due to its low thermal expansion properties and high-strength at elevated temperatures. Mechanical testing shall be performed for tensile, hardness and stress-rupture capabilities in order to fulfill requirements; this properties can be affected by manufacturing parameters like hot-working conditions and heat treatment procedures. This job summarizes evaluation of effects on mechancial properties of alloy 909 when several rings, made by forging procedures, are exposed to different forging and heat-treatment parameters on industrial conditions.
The Repair of Cracks in Thermoplastic Matrix Composite Materials by Microwave Heating of Carbon Nanotubes
S. C. Chang, T. H. Chen, T. H. Chiu, National Tsing Hua University, Hsinchu, Taiwan
The unique heating property of microwave irradiation on carbon nanotubes (CNTs) was used in the repairing of cracks in thermoplastic matrix composite materials. The drastic temperature rise of CNTs in response to microwave irradiation provides a strong bonding between the CNTs and polymer within a few seconds without thermal damage to the substrate. It is found that cracks in thermoplastic matrix composite materials can be “welded” by using microwave irradiation within a few seconds and the strength of the welded parts is even greater than that of the good composite.
Advance on the Design of New Material for Surface Thermal Response on High-Speed Vehicles
M. R. Reda, CanadElectrochim, Saskatoon, SK, Canada
Mike Reda Consultant Visiting prof. Engineering Physics Dept. University of Saskatchewan Canada Thermal insulation materials for sharp leading edges on hypersonic vehicles must be stable at very high temperatures (near 2000ºC). The materials must resist evaporation, erosion, and oxidation, and should exhibit low thermal diffusivity to limit heat transfer to support structures. The effect of the surface shear stresses is to induce high temperature and pressure surface oxidation. Surface oxidation can be considered as solid /gas heterogeneous chemical reaction.The high inter-facial temperature and pressure ( similar to hot working of the material) and in the presence of impurities which act as a dopant, a situation similar to doping of oxide at high temperature and pressures will subsequently induce phase change of the inter-facial layer and degradation. However, if the inter-facial layer is chosen properly so that the anticipated doping of impurities during high speed operation will lead to a phase change that have much lower thermal diffusivity. This can be done by dividing the inter-facial layer into two parts. In the interior part which will undergo a pseudo-liquid heterogeneous catalytic ( catalysis in the micro andnanochannels ) reaction which occurs at room temperature while at the exterior layer a high temperature and pressures non catalyzed heterogeneous reaction issimultaneously occurring.
Forging Advanced Systems & Technologies (FAST) Program
J. D. Tirpak, Advanced Technology Institute, North Charleston, SC
The Forging Advanced Systems & Technologies (FAST) program is a multi-year, multi-million dollar Defense Logistics Agency/US Army sponsored program. Elements of the program might appeal to many in the Aeromat community. For example the application of the National Forging Tooling Database results in daily location of forging dies that keep legacy systems flying. The application of the same data base in collecting new dies for current programs will ensure these future legacy systems will be supported by forging supply chains. The program constantly encounters the need for replacing old materials with new materials not unlike the materials discussed in other sessions at Aeromat. The presentation will explore current mechanisms for the introduction of these new materials into legacy systems. The program also promotes the use of rapid forging tooling, simulation, and problem solving - both technical and enterprise problem solving. In addition to looking at the future, the presentation will also touch upon the successes of the recently completed PRO-FAST Program.
Improving the Function and Surface Performance of Composites by Thermal Spray Coating
D. Harvey, M. Riley, P. Burling, TWI Ltd., Cambridge, United Kingdom
The use of composites as structural components in aerospace sector is increasing due to good strength to weight ratios. However, limited surface properties prevent use in applications where wear resistance, thermal management or electrical conductivity are required. To facilitate wider composite use, coatings are required to provide protection and increase functionality of the surface.
Thermal spraying processes offer a wide range of coatings with multiple functionality. However, due to the low melting point of resins, and the relatively high temperatures associated with thermal spraying, it has generally proven difficult to deposit well adhered coatings on composite substrates without damaging them.
Maximum adhesion is achieved through careful selection of coating materials, control of the surface preparation, and thermal spray process optimisation. Novel spraying techniques have been developed for depositing multi-layer and graded coatings. Hard coatings, such as WC-Co, can be deposited on CFRP following application of a bond coat. Other functional layers may also be incorporated e.g. for providing thermal insulation for protecting composites in high temperature applications.
Initial tests have shown, that in four point bending, coatings remain attached even after failure of the underlying composite. Promising fatigue results have also been achieved, with coatings surviving 0.5million cycles through significant deflection in four point bending.
Thermal spraying technology shows promise for applications within the defence and aerospace sectors, where coatings can provide multiple functions including wear resistance, thermal management, reduced IR emissions and analog absorption. This paper presents recent developments that demonstrate the feasibility of coating composite materials, such as carbon fibre reinforced polymers (CRFP), using thermal spraying processes.
In Situ Monitoring Ultrasonic Technique of Cold Spray Process
S. Titov, M. Lubrick, D. Dzhurinskiy, V. Leshchynsky, R. G. Maev, University of Windsor, Windsor, ON, Canada
A novel ultrasonic technology is developed to monitor the Low Pressure Cold Spray (LPCS) coating formation in real time. The multi-channel ultrasonic matrix transducer installed at an opposite sheet side generates the sound waves which penetrate both the plate and coating. The waves reflect off the substrate-coating interface and coating surface in the direction perpendicular to the plane of the plates. The pulse repetition is high enough to generate a picture showing the coating in various areas of the coating path , its evolution. Additionally, acoustic noise generation, an accompanying effect produced during LPCS, is examined. It is shown that spraying parameters strongly affect the thickness, microstructure and strength of coating, and in situ monitoring technique for coating process allows to control the coating performance.
In-Situ Aluminum Metal-Matrix Composites
S. Viswanathan, R. G. Reddy, The University of Alabama, Tuscaloosa, AL
Liquid state processing is the preferred route for the production of particulate reinforced Metal Matrix Composites (MMCs) due to the lower cost and the ability to form a variety of shapes. However, the disadvantages of liquid state processing include the cost of the reinforcement, reaction between the particulate and liquid alloy, and the entrapment of gas or air bubbles during stirring of the reinforcement into the liquid alloy. In this work, a reactive gas is bubbled through an aluminum alloy melt. The reinforcing particles nucleate and grow directly from in-situ chemical reactions between molten metal and a gas source. Since the particles are formed in situ, they are thermodynamically stable and free of surface contamination, thereby yielding better interfacial properties that will not degrade during service. The microstructure and properties of the resulting MMC are characterized.
Relating Microstructure and Machinability in Titanium Alloy Ti-5553
J. D. Cotton, M. L. Watts, The Boeing Company, Seattle, WA
Ti-5Al-5Mo-5V-3Cr-0.5Fe (Ti-5553) has exceptionally good strength-to-density ratio and fracture toughness in the beta-annealed, slow-cooled and aged condition, but exhibits typically challenging, near-beta alloy behavior in machining. In an effort to produce machined components at minimum cost, a study was carried out to relate microstructure and machinability for this alloy. Prior efforts to relate these parameters, in any alloy system, have been few and not particularly revealing. The present effort evaluated machinability for Ti-5553 in various metallurgical states and noted a strong tool life dependence on microstructure. This presentation will cover fundamental aspects of work-piece machinability as a function of microstructure, tool-workpiece interfacial reactions and chip formation mechanisms. Machinability was empirically assessed by quantifying cutting force and tool life characteristics in a controlled end milling operation at constant material removal rates. Microstructures were assessed via standard light and electron microscopy, thermal analysis and x-ray diffraction. The results indicate that tool life can be substantially increased by choosing beneficial microstructures in a given alloy.
Mechanism Controlling Thermal Conductivity and Coefficient of Thermal Expansion of Copper Metal Matrix Composite
D. E. Esezobor, S. O. Adeosun, S. O. Fatoba, University of Lagos, Lagos, Nigeria
An important consideration in copper metal matrix composite (CuMMC) production is the nature of the interface between the matrix and the reinforcement. This often depends on the processing route and since it occurs at high temperature, it is more chemical than mechanical. Understanding the mechanism controlling thermal conductivity of Cu-SiC particulate composite is of considerable current interest for microelectronic and thermo-electronic applications. In this paper, the effect of particle size, volume fraction and processing parameters on the thermal conductivity of Cu-SiC particulate composite produced by non-conventional liquid route is investigated. The development of microstructure suitable for high thermal conductivity and low coefficient of thermal expansion of copper alloy MMC is studied.
Repair and Restoration of Gas Turbine Components Using Direct Metal Deposition
B. Dutta, V. Singh, H. Natu, J. Choi, J. Mazumder, POM Group, Inc., Auburn Hills, MI
Direct Metal Deposition (DMD) is a Laser Aided Manufacturing (LAM) technique commercialized by The POM Group Inc. which is used in repair and restoration of high performance nickel and cobalt superalloys in the aerospace industry. DMD provides a promising solution for hard to weld gas turbine components which are manufactured from directionally solidified(DS) or single crystal (SX) alloys. Examples of such components are gas turbine blades and stator vanes segments. DMD can also be used in providing OEM solutions such as welding of Z-notches in new gas turbine blades. Recent developments in the DMD process has allowed extended capabilities to control microstructure, minimize the heat affect zone(HAZ)and provide near net shape with the integration of new technological advanced laser systems such as the disc laser. With the integration of disc lasers and proprietary POMs’ software, DMD can achieve fine laser cladding of features with magnitude of 200 microns. Moreover DMD with the use of proprietary sensor technology controls the heat input into the part in real time. This technology has proven its use in DS and SX alloys where issues such as recrytallization of the base alloy cannot be tolerated. Besides rebuilding and used component, DMD technology has also been proven in hardfacing applications for gas turbines such as Z-notch welding with alloys such as Stellite 6 and Stellite 694. The near neat shape and the minimum heat input keep the cost of post processing and distortion to a minimum in such restored parts.
Joining Concepts for Hybrid Aluminum – Composite Structures
J. C. Ehrstrom1, T. Crawford1, C. Hénon1, D. Hofmann2, K. P. Smith3, (1)Alcan, Voreppe, France, (2)Alcan NTC, Neuhausen, Switzerland, (3)Alcan Rolled Products, Ravenswood, WV
Carbon Fiber Reinforced Plastics (CFRP) were selected for the outer structure of aircraft wing and fuselage of Boeing 787 and Airbus 350. However, CFRP’s perform less well than metals in out of plane directions, so the internal components are often metallic. Aluminum represents a light weight low cost solution, but its electrochemical potential difference with carbon, its higher thermal expansion coefficient and lower Young’s modulus are issues when it is joined to CFRP. A straightforward solution is to use Titanium, which has more compatible properties but associated cost and manufacturing difficulties.
Prediction of Distortion in Thin-Walled Machined Components
L. Zamorano, T. Marusich, S. Usui, K. Marusich, S. Garud, Third Wave Systems, Minneapolis, MN
Machined monolithic components provide the foundation for modern aircraft structures requiring high performance designs in terms of weight, strength and fatigue properties. Part distortion and warpage arising from bulk material and machining-induced stresses frustrates manufacturing and assembly processes and necessitates expensive trial-and-error methods, shot peening and heat treating to minimize distortion. Strict weight requirements are exacerbated by thicker component section designs as a distortion control mechanism.
We present a physics-based model which takes into account the pre-machined bulk stress state and machining-induced stresses for monolithic parts. Sources of stresses include heat treatment, quenching, forging and machining operations. A customized solid model representation of the initial workpiece geometry is developed. Bulk stresses are mapped onto the solid model. CNC toolpath programs, along with corresponding tooling geometry, are read and analyzed. Bulk stresses are removed from the component as material is machined away, while machining-induced stresses are applied to the final surfaces. The final workpiece geometry is meshed automatically with finite elements and equilibrium solutions calculated. Minimum distortion configurations and strategies are analyzed. Distortion prediction, measurement and validation are presented for a number of monolithic, thin-walled components.
Property Analysis of a High Strength Cold Worked Cu-Ni-Sn Spinodal Alloy
W. R. Cribb1, F. C. Grensing2, (1)Brush Wellman Inc., Cleveland, OH, (2)Brush Wellman Inc., Elmore, OH
Different grades of spinodally-hardened Copper-Nickel-Tin alloys have been under development for over 40 years. A process utilizing a combination of hot and cold work followed by a spinodal decomposition thermal treatment yields the highest property combination. These alloys have become the material of choice in high performance wear-critical applications. This presentation reviews a new high-strength temper, ToughMet® 3 TS160U, which has significantly higher design strength. In preparation for AMS and MMPDS design allowables listing, substantial rod testing data were generated, including basic tensile and compression mechanical properties, pin bearing performance and shear strength.
Property performance will be described in detail. Initial findings relating to work hardening and fracture characteristics will be presented, including key inputs to modeling and design.
Ti6Al4V manufactured with Electron Beam Melting – Mechanical and Chemical properties
M. Svensson, S. Thundal, Arcam AB, Mölndal, Sweden
In recent years, Electron Beam Melting (EBM) has matured as a technology for rapid manufacturing of fully dense metal parts. The parts are built by additive consolidation of thin layers of metal powder, using an electron beam. With EBM, it is possible to create parts with geometries too complex to be fabricated by other methods, e.g. fine network structures, internal cavities and channels. A complete study of the mechanical and chemical properties has recently been made on both RAW and HIP condition, revealing the true benefit of using EBM in for example fatigue-critical components. With its production-like environment it delivers full traceability from ingot to the final part and complies with the industry-driven standards for aerospace applications. The EBM process is described in detail, with focus on mechanical properties of titanium alloys used for aerospace applications.
Semi-Solid Metal Processed by Inclined Cooling Plate; An Alternative for Aerostructural Materials
H. Mehrara, M. Nili-Ahmadabadi, S. Ashouri, J. Ghiasinejad, University of Tehran, Tehran, Iran
Micro-structural control of metallic materials through grain refining of alloy cast/wrought products is a key method to improve its properties. In solidification processing, the refinement is conventionally exercised by chemical and mechanical media to obtain fine and uniform equiaxed grains.
However, the predominant structure under common casting conditions is dendrite morphology which adversely affects materials performance. Although initial microstructure might be altered by later thermal and mechanical treatments, the dendritic pattern cannot be fully removed. Alternatively, performance improvement can be approached by alteration/control of growth morphology as well as refining. Concept of Semi-Solid Metal (SSM) processing (processing within mushy zone) has been introduced as a family of routes toward non-dendritic microstructure.
In this context, Inclined Cooling Plate (ICP) method is a recent solution where due to flowing of alloy melt down an inclined cold plate, a semi-solid mixture is produced with a fine, uniform and non-dendritic solid phase suitable for thixo-casting/forming processes.
In this paper, an ICP analog system is described that – by transparent model alloy – visualizes the behavior of the metal alloy. Experiments show that forced-convection across solid/liquid interface modifies the structure of mushy zone of the alloy compared with conventional casting processes. In detail, the cooling effect of plate generates numerous solid grains which are subjected to crossing melt flow. As a result, these grains are fragmented into myriad of fine particles and washed to downstream. Then, in thermally and compositionally uniform ambient main flow, these fragments can grow with cellular morphology in radial directions. Indeed, the combined effects of solidification and fluid flow are utilized in ICP to develop such microstructure with fine-and-uniformly-distributed-radially-grown-cells within liquid pool. The present study also clarifies how the ICP-processed alloys might be considered as alternative aerostructural material for either continuous ingot in subsequent forming or discrete part through near net shape manufacturing.
Carpenter's EXPERIMENTAL 290 ALLOY
P. Novotny1, M. Taheri2, M. Hartshorne2, (1)Carpenter Technology Corporation, Reading, PA, (2)Drexel University, Philadelphia, PA
Carpenter’s EXPERIMENTAL 290 ALLOY is a Co-free, high strength high toughness alternative to 300M. The EXPERIMENTAL 290 ALLOY has a 290 ksi minimum UTS combined with a 70 ksi√in. minimum KIC. The EXPERIMENTAL 290 ALLOY also has a rotating bending fatigue test run-out stress of 145 ksi. This presentation will discuss the metallurgy of the EXPERIMENTAL 290 ALLOY and compare its properties to 300M and Carpenter AerMet 100 alloy. Stress Corrosion Cracking resistance in 3.5% NaCl will also be discussed.
Stress Corrosion and Hydrogen Embrittlement Testing of Custom 465 Stainless Alloy
D. E. Wert, M. L. Schmidt, Carpenter Technology Corporation, Reading, PA
Custom 465 Stainless Alloy is becoming the alloy of choice for many aerospace applications due to its combination of high strength, good toughness, and good corrosion resistance. This presentation will cover recent results of stress corrosion cracking (KISCC) and hydrogen embrittlement (KIHE) testing of Custom 465 Stainless Alloy in the standard solution/refrigerated/aged condition, and in the solution/refrigerated/cold worked/aged condition, after aging at 950°F or 1000°F. Additionally, fine structure analysis of the alloy will be presented in order to correlate some of the mechanical property/stress corrosion results with structural observations.
The KISCC and KIHE values to be discussed were generated using the RSLTM Rising Step Load Bend Testing System, manufactured by Fracture Diagnostics International, LLC. This machine and test method (ASTM F1624-05) allows KISCC values to be determined on fracture mechanics bend samples per ASTM E399/E1290 in far less time than the standard double cantilever beam test approach (incorporating procedures from NACE TM0177), which has been proven to be somewhat unreliable with high-strength corrosion-resistant grades. In addition, KIHE values are easily obtained with this apparatus, as it allows testing to be run at various controlled applied potentials. The data to be presented will represent samples held at potentials ranging from open circuit, where the test sample is freely corroding in 3.5% NaCl test solution, to -1.10 Vsce, simulating cathodic charging while being galvanically coupled to zinc.
The results of fine structure TEM analysis of Custom 465 Stainless alloy developed in collaboration with
Strengthening of Cold-Worked Custom 465 Stainless Steel by Aging
E. Lee, NAVAIR-Naval Air Systems Command, Patuxent River, MD
The effect of aging on mechanical properties of cold-worked Custom 465 stainless steel was studied. Cold-worked Custom 465 stainless specimens were aged at temperatures, ranging from 900F to 1,025F. Subsequently, they were subjected to microstructure examination, measurement of threshold stress intensity for stress corrosion cracking in 3.5% NaCl solution Kiscc, and tests of hardness, tension, fracture toughness and fatigue. The results indicate that the aging-induced strengthening, indicated by UTS, YS and hardness, is peaked by 900F aging and reduced with increasing aging temperature. However, the elongation and conditional fracture toughness Kq increased with increasing aging temperature. It is noticeable that, by 950F aging, the mechanical properties become similar to those of AerMet 100 steel with better resistance to stress corrosion cracking.
The Effects of Heat Treatment On the Microstructure and Mechanical Properties of High Cobalt Martensitic Precipitation Strengthened Stainless Steels
W. M. Garrison, P. Komolwit, Carnegie Mellon University, Pittsburgh, PA
The objective of this work was to examine the effects of heat treatment on the mechanical properties and microstructure of two sets of high cobalt martensitic precipitation strengthened stainless steels which can achieve yield strengths of about 1650 MPa. The first series of alloys consisted of three compositions. The three alloys contained (in wt. %) about 0.005 carbon, 14 chromium, 5 molybdenum and 1.5 nickel and differed only in cobalt contents which were 18, 19.5 and 21 wt. %. The second series of alloys also consisted of three compositions. These three alloys all contained (in wt. %) 0.025 carbon, 14 chromium, 5 molybdenum, 1.5 nickel and 0.025 titanium and differed only in cobalt content which were 16, 17 and 18 wt. %. The carbon and titanium additions to the second series of alloys were made with the objective of gettering the sulfur as particles of titanium carbosulfides because particles of titanium carbosulfide are much more resistant to void nucleation than other types of sulfides and this greater resistance void nucleation has been to improve the toughness of other ultra-high strength steels. In this work the effects of tempering temperature, refrigeration after cooling from the austenitizing temperature, the rate of cooling from the austenitizing temperature, austenitizing temperature and of double austenitizing heat treatments on the Charpy impact energy, the tensile properties, fracture modes and microstructure were evaluated.
An Investigation of the Effects of Inclusion Type On the Toughness of Low Alloy Ultra-High Strength Steels
W. M. Garrison, P. Choudhary, Carnegie Mellon University, Pittsburgh, PA
In this work we have examined the effects of inclusion type on the toughness of two low alloy steels. The first composition considered was (in wt.%) 0.4 carbon, 1.5 nickel and 1 chromium. The second composition was identical except that it also contained 2 wt. % silicon. For each composition three heats were prepared. One heat was not modified with any additions to getter the sulfur. The sulfides in these heats were expected to be particles of CrS. One heat was modified by the addition of 0.025 wt. % titanium in order to getter the sulfur as particles of titanium carbosulfide. The third heat was modified by the addition of rare earths so that the sulfur and oxygen could be gettered as rare earth oxy-sulfides, sulfides and oxides. Previous work has shown that small titanium additions to steels such as HY180 and AF1410 can result in the sulfur being gettered as particles of titanium carbosulfide which results in significant improvements in toughness because the particles of titanium carbosulfide are very resistant to void nucleation. In addition, previous work has shown that rare earth additions significantly improve the toughness of HY180 and AF1410 steels because such additions result in large and widely spaced inclusions. The purpose of this work was to determine if these two approaches to gettering sulfur could be used to improve the toughness of low alloy steels. The Charpy impact energy, the fracture toughness and tensile properties of these heats have been determined and the toughness results will be discussed in terms of measured inclusion sizes, volume fractions, spacings and resistance to void nucleation.
The Superficial Quenching of Mecanical Piece
A Journey In the World of Structural Stainless Steels
A. Tronche, AUBERT & DUVAL, Gennevilliers, France
Stainlee steels are gaining importance in today's world because they represent a good alternative to low carbon steels protected with hazardous substances. Stainless steels can be martensitic, austenitic, with or withour carbon. The present document will focus on the precipitation hardening stainless steels, those commonly used for structural applications in the aerospace industry.
Precipitation hardening stainless steels conver a wide range of resistance typically from 100 MPa (145 ksi) to 1930 MPa (280 ksi) and above. Increasing the resistance of the grades implies compromising on other properties, namely toughness and stress corrosion resistance. Nevertheless the recent development tools have allowed to create simple precipitation hardening solutions with high resistance, controlled fracture toughness and good common and stress corrosion resistance. An example of such an achievement is MLX19 (280 ksi) from AUBERT&DUVAL.
The paper will therefore present the different grades, the technical approach for their development and the potential limitations which have to be taken into account.
Steels for Gears Applications
A. Tronche, AUBERT & DUVAL, Gennevilliers, France
AUBERT&DUVAL has developed over the years steel grades for gears applications. Carburized, nitrided and induction treated grades are available to provide designers with a large range of possiblities for overcoming a number of challenges, including, environmental, fabrication, weight, price, etc.
Advantages of using the alloys in various forms will be discussed; nitriding versus carbuzizing, low carbon steels versus precipitation hardened steels. A focus on a few grades will be mde; CX13VDW, a carburizing stainless steel, for replacing AISI9310 where corrosion resistance is required. FDG and FND, gas quenching steels, for reduction of distortion, machining and scrap compared to AISI9310 product fabrications. FND also allows high working temperatures. Carburized NC310YW and nitrided ML340 where very high strength is required. Deep nitrided GKH and GKP grades for very high fatigue limits. And finally XD16N, a grade showing higher corrosion resistance, fatigue limit than 440C and can be used at high temperatures.
Low Temperature Carburization of Austenite Stainless Steels
S. R. Collins, Swagelok Company, Solon, OH
Low-temperature colossal supersaturation (LTCSS) is a novel diffusional surface hardening process for carburization of austenitic stainless steels and other alloys without the precipitation of carbides. The formation of carbides is kinetically suppressed, enabling extremely high or colossal carbon supersaturation. As a result, surface carbon concentrations in excess of 12 at.% are routinely achieved. This treatment increases the surface hardness by a factor of four to five, improving resistance to wear, corrosion, and fatigue, with significant retained ductility.
LTCSS provides a uniform and conformal hardened gradient surface with a hardness layer is at least 25µm thick, with a near surface hardness of ≈HV1200 (over 70 HRC). The thickness of the hardened layer can be increased further by additional carburization treatments. In addition, because parts are treated at low temperature, they do not distort or change dimensions. In addition to austenitic stainless steels, research efforts are underway to extend the technology to other industrially important alloys, such as precipitation-hardening stainless steels, duplex alloys, nickel-based alloys, and cobalt-based alloys.
This talk will describe the technology, and will discuss research findings from a recent U.S. Department of Energy project that quantified the performance improvements for treated materials.
Materials Properties of Low-Temperature Carburized Alloy A286
F. J. Martin1, R. A. Bayles1, P. M. Natishan1, R. Rayne1, G. M. Michal2, F. Ernst2, H. Kahn2, A. H. Heuer2, M. Gaudette Koul3, (1)Naval Research Laboratory, Washington, DC, (2)Case Western Reserve University, Cleveland, OH, (3)U. S. Naval Academy, Annapolis, MD
Materials properties of Alloy A286 surface hardened by Low-Temperature Carburization (LTC) are discussed. Surface modification of Alloy A286 (UNS S66286) is performed using a LTC strategy, whereby a high concentration of carbon in solid solution (more than 10 at% directly below the surface) is diffused into near-surface portions the metallic structures. The depth of the carburized layer is on the order of 30µm. In spite of the tempering required for LTC, the bulk mechanical properties of the alloy appear to be unchanged. Surface hardness increases significantly and is accompanied by a large compressive biaxial stress. During mechanical testing, the carburized layer remains ductile and intact until the ultimate tensile stress is reached, after which strain localization and case cracking appear prior to specimen failure. Corrosion behavior of the carburized alloy surface is that of a passive material, more resistant to corrosion in seawater than that of the base Alloy A286 alloy. Corrosion fatigue resistance of LTC-altered coupons also increases, presumably due to the combined influence of surface compressive stress and improved corrosion resistance. The carburized case has a negligible influence on hydrogen embrittlement sensitivity, showing neither benefits from residual surface compressive stresses nor any signs of premature surface cracking despite the existence of post-UTS case cracking.
Induction Heating of Special Alloys
V. Rudnev, Inductoheat Inc., Madison Heights, MI
Presentation discusses different aspects of using induction for heating various special alloys including
Ø High production multi-station induction system for heating 210mm-440mm diameter and 1200mm long special alloy billets (including, Inconel, Incoloy, stainless steels, etc.) prior to piercing and direct extrusion.
Ø Heating of selective areas of special alloy parts
Ø Numerical computer modeling of induction heating of special alloys. Advanced numerical computer modeling ensures optimal process design and takes into consideration non-linear physical properties of billet materials. It in imperative to take into consideration electromagnetic end and edge effects as well as thermal edge effect when developing induction process.
Optimisation of Laser Direct Metal Deposition for Additive Manufacture and Repair of Alloy 718
R. Freeman1, C. Kong2, M. Dore1, L. Zhang1, (1)TWI Ltd, Cambridge, United Kingdom, (2)TWI Technology Centre (Yorkshire), Rotherham, United Kingdom
Direct metal laser deposition (DMLD) offers an increasingly attractive additive manufacturing/repair route that can offer advantages over other processes, such as those based on arc welding. In particular, heat input and distortion are low, and the sophisticated systems to accurately control the processing head to build up a deposit on the work piece give superb flexibility. For nickel alloys, the low heat input can prevent liquation cracking in the service exposed substrate and provide an enabling technology for significant life extension of damaged parts which might otherwise require replacement.
The main barrier to the wider implementation of laser based additive manufacture, is that engineers cannot easily design parts that are produced using these techniques because the mechanical properties and potential performance of the deposited metal are not fully understood. DMLD will only achieve its full potential when a link between the process parameters used, the microstructure created and the properties of the deposit is established, and can therefore be used for part design.
The work reported here was carried out as part of TWI’s Core Research Programme and assessed the performance of deposits of alloy 718 and established links between observed weld quality, detailed microstructure and mechanical test performance. Quantitative data was established, which can be used for modelling of the microstructural development of the direct metal leaser deposits, and to provide guidance for an effective strategy for DMLD additive manufacture and repair of alloy 718 and similar materials. The presentation will review the deposition parameters used, the quality of the deposits produced and their resultant tensile, fatigue and creep performance.
Direct Metal Laser Sintering (DMLS) of Heat Resistant Nickel and Cobalt Chrome Alloys for Aerospace Applications
T. Syvänen, L. Thorsson, J. Kotila, O. Nyrhilä, J. Hänninen, EOS Electro Optical Systems Finland Oy, Turku, Finland
Additive laser melting technologies have been used for manufacturing prototypes, functional metal components and prototype tools for more than 10 years. During this period the technology has advanced to a level where direct production of complex metallic parts for various applications is possible. High-end applications in aerospace and medical industry have special demands for materials, manufacturing technologies and supply chains. A New manufacturing technology has to be well proven before it can be widely accepted for critical metal part manufacturing. Therefore intensive research and development work, material testing, metallurgical characterization and validation procedures are ongoing to enter these industries with a technology such as Direct Metal Laser Sintering (DMLS).
New Cold Spray Based Technique of Nanostructured FeAl Intermetallic Compound Coating and Its Microstructural Characterization
R. G. Maev, E. Leshchinsky, D. Dzhurinskiy, E. Maeva, A. Chertov, University of Windsor, Windsor, ON, Canada
The FeAl intermetallic compound offers a combination of attractive properties such as a high specific strength, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures in hostile environments. However, commercialization of these intermetallics has been limited due to their low ductility at room temperature and low mechanical strength above 600oC. A main approach for improving their ductility is by reducing the crystallite size to the nanometer range. The aim of this paper is to present first results of FeAl intermetallic nanocrystalline compound synthesis with new technique. A combination of Cold spraying (CS) and Resistance Spot Weld Sintering (RSWS) is used. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. RSWS is shown to use microscopic electric discharges between the particles under pressure and to reduce significantly the synthesis and densification temperatures, limiting thereby the grain growth. The microstructures and properties of the sintered products were characterized by SEM, TEM and micromechanical tests to define structure and properties formation mechanisms. Application prospects will be discussed as well.
Laser Sintering of High Temperature Metals and Plastics
U. Behrendt, EOS GmbH Electro Optical Systems, Krailling, Germany
Laser Sintering with new high temperature materials. A long time the use of layer manufacturing technologies for production purpose was strictly limited by the available materials. Step by step continuous development improved the technology and achieved higher productivity, better material properties, long lifetime of parts and the cost situation. Especially the low numbers and the long product life time in the aerospace market require new production methods. Applications like air duct's or jet engine parts are already used in the industry since a long time. New high temperature materials i.e. PEEK or Inconel 718 open up new market segments and are key factors for the break through of this technology. Advantages of fast and flexible production combined with excellent material properties help to reduce some of the problems with aging fleet's and spare part supply. Potential and vision for new material development in laser sintering technology.
Carbon Nanotube Reinforced Ultra-High Temperature Ceramics
A. Datye1, K. Wu1, S. Kulkarni1, W. Li1, H. T. Lin2, (1)Florida International University, Miami, FL, (2)Oak Ridge National Laboratory, Oak Ridge, TN
Currently there is a great need in developing advanced super-sonic and hypersonic flying vehicles. The continuous pushing for higher speeds has imposed an enormous demand to improve the thermal management for various heat-generating sources. The sharp leading edges of the hypersonic flying vehicles required for maneuvering at high speeds can experience temperatures greater than 2000C, especially at the reentry stage. Current thermal protection materials even ultra high temperature ceramics are not suitable for sustained operation at
these extreme temperatures. Carbon nanotubes (CNTs) have a unique combination of thermal mechanical and electrical properties which make them ideal reinforcing materials for ceramic systems. Addition of CNTs can increase the thermal conductivity of the ceramic system which can dissipate heat more quickly from the material and thus extend the operating time of the
material. However, even after 10 years of research into ceramic-CNT systems problems like uniform dispersion and interface bonding still persist.
In this research CNTs are grown in-situ on the surface of the SiC and ZrB2 particles, followed by Spark Plasma Sintering (SPS) to prevent significant grain growth of the ceramic matrix and to retain the CNTs. The unique process has proven to enhance the thermal properties along with the mechanical properties of the composite.
Formation of Different Generations of Gamma Prime Precipitates in Rene 88DT Nickel Base Superalloy
J. Hwang1, S. Nag1, S. Rajagopalan2, J. Tiley3, G. B. Viswanathan2, H. L. Fraser4, R. Banerjee1, (1)University of North Texas, Denton, TX, (2)The Ohio State University, Columbus, OH, (3)Air Force Research Laboratory, Wright-Patterson, AFB, OH, (4)Center for Accelerated Maturation of Materials, Columbus, OH
The compositional and microstructural evolution of different generations of γ’ precipitates during the continuous cooling, followed by isothermal aging, of a commercial nickel base superalloy, Rene 88DT, have been characterized by three dimensional atom probe tomography (3DAP) coupled with energy-filtered transmission electron microscopy (EFTEM) studies. After solutionizing in the single γ phase field, during continuous cooling at a relatively slow rate (~ 24°C/min), the first generation primary γ’ precipitates, forming at relatively higher temperatures, exhibit near-equilibrium compositions, while the smaller scale secondary γ’ precipitates, forming at lower temperatures, exhibit non-equilibrium compositions often consisting of excess Co and Cr, while being depleted in Al and Ti content. The compositions of the γ matrix near these precipitates also exhibit similar trends with the composition being closer to equilibrium near the primary precipitates as compared to the secondary precipitates. Subsequent isothermal aging at 760°C, leads to some coarsening of the primary γ’ precipitates, but does not affect their composition significantly. In contrast, the composition of the secondary γ’ precipitates is driven towards equilibrium during the isothermal aging.
Prediction of Grain Size in Ni-Base Disk Superalloys during Processing and Heat Treatment
E. Payton, Y. Wang, M. J. Mills, Ohio State University, Columbus, OH
Higher operating temperatures and dual microstructure disks are desired in the next generation of jet turbines. Accurate physical modeling of grain coarsening is needed to accelerate alloy and process development to achieve desired mechanical properties, including creep and fatigue behavior. The variation of distributions and volume fractions of secondary phases with thermal exposure control grain growth behavior and hence control grain coarsening. Materials simulation and characterization techniques are being integrated and used simultaneously to understand the microstructural features that control grain coarsening and to develop physics-based predictive models.
Influence of γ' Precipitated Phases on the Mechanical Properties of a Fe-Ni Superalloy
M. de la Garza Garza1, M. Guerrero-Mata1, V. Páramo-López2, (1)Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Mexico, (2)Frisa Aerospace S.A. de C.V., Santa Catarina, Mexico
The effect of different morphologies and sizes of g’ precipitates on the mechanical properties of a 909 incolloy was studied. Hot compression testing was carried out at different schedules, afterwards the samples were heat treated at various temperatures ranging from 960 to 1000ºC in order to vary the process conditions of the material, different size and morphology of g’ phase were obtained, the characterization of the samples was performed using SEM (scanning electron microscopy), TEM (transmission electron microscopy) and AFM (atomic force microscopy), some precipitates are spheroid shaped and 100 nm in size and other precipitates are needle type and 2 µm of size. The mechanical properties of the material were related to the morphology and distribution of the g’ phase, finding beneficial the presence of large precipitates inside the grains and detrimental the opposite, i.e., when these are at the boundary of the grains.
The Intermediate Temperature Deformation of Ni-Base Superalloys: Importance of Reordering
L. Kovarik1, R. R. Unocic1, J. Li2, M. J. Mills1, (1)The Ohio State University, Columbus, OH, (2)TWI Ltd, Cambridge, United Kingdom
A number of planar deformation mechanisms, such as microtwinning, a[112] dislocation ribbon and superlattice intrinsic and superlattice extrinsic stacking fault formation, can operate during the intermediate temperature deformation of Ni-base superalloys. The fundamental, rate-limiting processes controlling these deformation mechanisms are not fully understood. It has been recently postulated that reordering of atoms in the wake of the gliding partial dislocations as they shear the γ' precipitates within the γ/γ' microstructure is the limiting process. Experimental evidence that substantiates the validity of the reordering model for the microtwinning mechanism is provided. A conceptual approach to study reordering at the atomic scale using ab-initio calculation methods is also presented. The results of this approach provide a clear conceptualization of the energetics and kinetics of the reordering process, which may be generically important for the aforementioned planar deformation modes.
Variability In Microstructure and Its Effect On Fatigue Behavior In IN-100
W. J. Porter1, K. Li1, S. K. Jha2, M. J. Caton3, J. M. Larsen3, (1)University of Dayton Research Institute, Dayton, OH, (2)Universal Technology Corporation, Dayton, OH, (3)Air Force Research Laboratory, Wright-Patterson AFB, OH
An effort to understand the variability in fatigue behavior based upon location-to-location differences in the microstructure within two IN-100 pancake forgings is described. The microstructures used in this study come from two forgings, one heat treated to a subsolvus condition and the other to a supersolvus condition. In this investigation, fatigue specimens were extracted from inner-, mid-, and outer-radial positions of each forging. Multiple specimens from each location were tested under similar fatigue conditions (temperature, stress and frequency) to assess differences in performance. Detailed fractography was performed on all specimens to identify the type and location of fatigue initiation sites. Additionally, a location-based comparison of the distribution of microstructural features including grain size and gamma prime size was undertaken to illuminate their role in fatigue behavior. Finally, a comparison of the findings for each forging is made and their similarities and differences are discussed.
Fretting Fatigue Behavior of in-100
S. Mall, Air Force Institute of Technology, Wright-Patterson AFB, OH
In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out at room temperature and elevated temperature of 600 0C. The study includes both experiments and the analyses of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of two cylindrical pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN-100, and that increasing cylindrical pad radii does not have the any effect. The crack initiation location and orientation along the contact surface were determined using the Optical and Scanning Electron Microscopy (SEM). In all experiments, cracks were found to initiate near the trailing edge at the contact surface, and at an orientation of 45° with a scatter of +/-10°. Finite element analysis was conducted to obtain the contact region state variables such as stress, strain and displacement. These state variables were used to compute the critical plane based parameters. These parameters were evaluated based on their ability to predict the crack location, crack initiation angle and fatigue life without dependence on contact geometry. The comparison of the analytical and the experimental results showed that fretting fatigue life is not only governed by shear stress on the critical plane, but also the normal stress on the critical plane plays a role in the crack initiation mechanism. A modified shear stress range parameter is capable of predicting crack location, crack initiation angle and fatigue life in IN-100.
Effect of Microstructure on Alloy 909 Stress-Rupture Properties
O. Covarrubias, E. Osvaldo, Frisa Aerospace SA de CV, Santa Catarina, Mexico
Industrial applications of alloy 909 can include components made from seamless rings produced by forging/rolling procedures. Manufacturing conditions will affect microstructure and mechanical properties of metallic alloys, including alloy 909: forging/rolling procedures determine grain size, meanwhile heat treatment can promote or inhibit presence of intergranular and transgranular phases. Combination of processes, forging and heat treatment will have a direct effect on microstructure, affecting mechanical properties. Several forgings, made from 909 alloy, were produced considering industrial conditions. Samples from these rings were extracted and exposed to different heat treatments. Stress-rupture testing was performed, and microstructures from these samples were evaluated. Correlation between microstructures and stress-rupture properties is evaluated to determine which conditions promote better stress-rupture behavior for alloy 909.
Microstructural Features Leading to Enhanced Resistance to Grain Boundary Cracking in Allvac 718Plus
K. A. Unocic1, R. W. Hayes2, G. S. Daehn1, (1)The Ohio State University, Columbus, OH, (2)Metals Technology Inc., Northridge, CA
This study focuses on the microstructural features which enhance the resistance of Allvac 718Plus to grain boundary cracking during testing of samples at 704oC in both dry air and moist air. Fully recrystallized structures were found to be susceptible to brittle grain boundary cracking in both environments. Detailed TEM characterization was performed to reveal features that resist grain boundary cracking in the non-susceptible microstructures. Dislocation substructures found within the grains of non-susceptible structures are suggested to compete with the high angle grain boundaries for oxygen and thereby reducing the concentration of oxygen on grain boundaries and subsequent embrittlement. In addition EBSD misorientation maps also reveal that special boundaries (i.e. Σ3 boundaries) are not embrittled. This is in agreement with previous findings on the superalloy Inconel 718. Furthermore, it is observed that cracks propagate along high angle boundaries. This study also suggests that the presence of delta phase at the grain boundaries does not produce materials that are resistant to grain boundary cracking.
The Effect of γ' Precipitate Size on the Deformation Mechanism in An Advanced Disc Ni-Base Superalloy
E. M. Knoche1, B. M. B. Grant1, J. Quinta da Fonseca1, M. Daymond2, M. Preuss1, (1)University of Manchester, Manchester, United Kingdom, (2)Queen's University, Kingston, ON, Canada
Nickel based superalloys are extensively used in the aero-engine and power generation industries for high temperature regions of gas turbines. There is a drive to increase the operation temperature of engines in order to improve fuel efficiency. This has lead to the development of advanced polycrystalline disc alloys such as RR1000 with a γ′ volume fraction of nearly 50%. There has been a significant amount of work on low volume fraction Ni-base superalloys, however, the way in which the deformation mechanism changes with increased volume fraction is not well understood. Conventional microstructures of such alloys exhibit a bi- or tri-modal γ′ distribution making mechanistic studies very difficult. For this reason, model microstructures with simplified uni-modal γ′ distributions (80 nm, 120 nm and 250 nm) have been developed for RR1000. In-situ loading experiments using neutron diffraction were performed to investigate the elastic strain response of γ and γ′ during plastic deformation at room temperature 500°C and 750°C. The results show that the level of load partitioning between γ and γ′ generally increases with increasing particle size and higher test temperature. A two-site EPSC model has been employed to identify possible mechanisms for such changes in load transfer. Results indicate that the observed changes of load transfer can be understood in terms of changes of the γ′ slip mode from {111} to {100} with increasing temperature and an increase of critical resolved shear stress in γ′ with increasing particle size. The plasticity modelling results are supported by detailed post-mortem electron microscopy studies showing less particle shearing with increased particle size and test temperature.
Influence of γ′ Precipitate Morphology on Creep Deformation Mechanisms
R. R. Unocic, L. Kovarik, M. J. Mills, The Ohio State University, Columbus, OH
The influence of microstructure on the creep rate controlling deformation mechanisms in Ni-base disk superalloy Rene 104 has been investigated through a combination of creep experiments and TEM deformation mechanism characterization. Particular emphasis was placed on the role of the secondary and tertiary γ′ precipitate size scale, volume fraction and γ channel width spacing on the dislocation substructure that formed during creep deformation. A direct comparison was made by testing specimens with different initial microstructures at the same stress (724MPa) and temperature (677ºC). Furthermore, the evolution was tracked by characterizing creep specimens that were interrupted at varying levels of plastic deformation. The TEM results show that the less creep resistant microstructure possessed a greater secondary γ′ size, wider γ channel width, and higher volume fraction of tertiary γ′ precipitates. Deformation in this microstructure commences by way of a/2<110> dislocations that are concentrated in the γ matrix at lower strains, which then transition to a SISF related precipitate shearing mode at larger strains. The more creep resistant microstructure possessed a finer γ channel width spacing, which promoted a/2<110> dislocation dissociation into a/6<112> Shockley partials at lower strains and led to microtwinning at higher strains.
Study of Deformation Mechanisms Following Low Cycle Fatigue of a Ni-Based Superalloy
P. J. Phillips1, R. R. Unocic1, L. Kovarik2, M. J. Mills2, D. Mourer3, (1)Ohio State University, Columbus, OH, (2)The Ohio State University, Columbus, OH, (3)GE Aviation - Lynn, Lynn, MA
The effect of microstructure on the high temperature low cycle fatigue deformation mechanisms of an advanced Ni-based disk superalloy was studied using TEM characterization methods. In order to track the evolution of these mechanisms, specimens were interrupted after a limited number of cycles and were not run to failure. Both fine and coarse precipitate microstructures were examined, corresponding to a fast or slow cool, respectively, from the gamma prime solvus temperature. The operative deformation mechanisms are correlated with the precipitate structure, number of cycles and testing temperature. The observed mechanisms include stacking faults, dislocation bands, and microtwins. A rationale for the observed mechanisms in terms of time-dependent damage processes will also be discussed.
Hot Working of Platinum Group Metal-Modified Nickel-Base Superalloys
D. L. Ballard, D. S. Weaver, S. L. Semiatin, P. L. Martin, Air Force Research Laboratory, Wright-Patterson AFB, OH
Platinum- and iridium-modified γ-γ’ nickel-base superalloys are being evaluated for use at high-temperatures due to their superior oxidation resistance when compared to conventional nickel-base superalloys. Due to a higher γ’ solvus, these materials also retain excellent strength at temperatures in excess of 1100°C. However, because of their cost and density, sheet and foil applications are being pursued. Mechanical and other physical properties in these product forms will be compared to conventional nickel-base superalloys, such as Waspaloy and alloy 718.
A Comparison of Thermal Barrier Coatings with Platinum Aluminide and Platinum Diffused Bond Coats
M. Attia1, W. R. Chen2, C. Mandache2, J. R. Nicholls3, R. David1, R. Sikorski4, J. Thornton1, M. Winstone5, B. Withy6, (1)DSTO, Melbourne, Australia, (2)Institute for Aerospace Research, National Research Council of Canada, Ottawa, ON, Canada, (3)Cranfield University, Cranfield, United Kingdom, (4)Air Force Research Laboratory, Wright Patterson AFB, OH, (5)DSTL Porton Down, Salisbury, Wiltshire, United Kingdom, (6)Defence Technology Agency, NZDF, Auckland, New Zealand
The aim of this work was to use non-destructive evaluation (NDE) to identify precursors to failure in thermal barrier coatings (TBCs), and link this to changes in the microstructure. The work compares the performance, under thermal cycling, of two types of electron-beam physical vapour deposited (EBPVD) TBCs on the nickel superalloy CMSX-4. The difference between the two types was the bond coats: either a platinum modified aluminide bond coat or a platinum diffused bond coat. Samples were examined visually to determine on which cycle they failed, or if they survived intact, and then subjected to non-destructive evaluation techniques: thermography, ultrasound, eddy current and piezospectroscopic imaging. Subsequently, the discs were cross-sectioned and examined with electron microscopy using backscattered imaging and energy dispersive X-ray spectroscopy. The TBCs with the diffused bond coat survived longer than those with the aluminide bond coat. Both thermography and piezospectroscopic imaging showed anomalies scattered across some of their images. The anomalies were not in images of the lower durability aluminide TBCs, as might be expected, but in those of the more durable platinum diffused TBCs. Cross-sectioning showed that the platinum diffused TBCs contained patches of internal oxides within their bond coats and beneath the usual layer of thermally grown oxide on the bond coat surface. There are indications that thermography and piezospectroscopic imaging can see the patches of internal oxide that form in the platinum diffused bond coats before the delamination of the thermal barrier layer. If further work can establish the relationship between the degree of this internal oxidation and remaining life, and if thermography and piezospectroscopic imaging can reliably assess the degree of this internal oxidation, then these NDE techniques could help reduce maintenance costs.
Delivering Value to Customers through the Use of Friction Stir Welding for Stretch Forming Wide Aluminum Sheets
P. Ainsworth1, Y. Marchal2, P. Lassince1, (1)Kaiser Aluminum, Spokane, WA, (2)SONACA, Gosselies, Belgium
Abstract: Stretch-forming of wide aluminum sheets is commonly used to produce parts such as leading edges and fuselage panels. Typically, this process uses very wide high surface quality sheets (sometimes "polished skin sheets") that is cladded on both sides with a 1XXX series aluminum for corrosion resistance. Stretch forming operations for leading edges skins are typically performed in the transverse direction (perpendicular to the rolling direction). This process leads to a significant amount of expensive material that is wasted due to the fact that the stretching jaw marks are cut off upon completion of the stretch forming process. A collaborative project between SONACA and Kaiser Aluminum identified Friction Stir Welding, FSW, as an enabling technology to reduce the total cost of the manufacturing process from ingot casting and rolling through to stretch forming and final part preparation. This lower cost manufacturing method uses FSW to attach non-clad (bare) aluminum "tabs" on either side of a narrow polished skin sheet with cladding material on one side only. The bare aluminum "tabs" are placed inside of the stretcher jaws and the entire bare-clad-bare welded panel is stretch formed. Once the panel is formed the FSW regions and the bare aluminum "tabs" are removed producing a polished skin sheet part with cladding material on one side only. This paper will summarize the development of this lower cost process and the material properties and performance of the parts produced using this process.
The Thixo-Extrusion Behavior of Al-6.0wt%Zn-2.5w%Mg-0.1wt%Sc Alloy Billet Fabricated by Cooling Plate
S. Y. Shim, D. H. Kim, T. H. Kim, S. G. Lim, i-Cube Center, Gyeongsang National University, Jinju, South Korea
The Al-Zn-Mg alloys have been improved by demand to reducing weight for vehicles including automobile, trains and aircraft structural parts. However, their high strength has led to reduce formability in extrusion process. The Thixo-extrusion is one of solutions to solve the problem. For obtaining thixo-extrusion reasonable feedstock, we have fabricated a semi-solid billet by the cooling plate method which is able to form spherical grains as flowing melts on copper plate. For observing Thixo-extrusion behaviors, we carried out extrusion at various semi-solid ranges of the billets. Comparing with a conventional extrusion, the results have showed that Thixo-extrusion process using feedstock fabricated by cooling plate could improve the formability as concerning extrusion pressure, extrusion ratio and ram speed. Furthermore, the EPMA analysis gave us that addition of 0.1wt% Sc contents effectively prevented coarsen grain during reheating process of semi-solid feedstock because of forming Al3Sc precipitations.
Light Weight Titanium – Aluminum Laminate Structures Via Ultrasonic Consolidation
K. Johnson, L. A. Schwope, J. Sheridan, Solidica, Inc., Ann Arbor, MI
Light weight titanium – aluminum laminate structures fabricated via Ultrasonic Consolidation (UC) offer promise as a weight reduction strategy to improve the endurance or payload capacity of manned and unmanned vehicles. UC is an additive manufacturing technology that allows complex laminate geometries to be fabricated at low cost and high speed, and optionally supports enhanced ballistic protection, embedded structural fibers, and embedded sensors. Laminate properties can be varied during the building process. Layered composites with gradient functional properties can enhance structural performance, reduce weight, enhance constructional freedom, and consolidate parts. Certain parameters (such as sonotrode texture and weld speed) of the UC process can be modified to produce a significant strengthening effect in the material localized at each interface region. The strengthening effect is driven primarily from a significant ultrasonically induced sub-grain refinement phenomenon that is unique to solid state ultrasonic welding methods.
Al-SiCp Surface Composites by Friction Stir Processing-Effect of Initial Particle Size
A. Patil, P. R. Kalvala, R. R. Rangaraju, R. K.S., M. M., University of Nevada Reno, Reno, NV
Aluminum alloy (Al-2%Mg) surface composites were developed by incorporating silicon carbide (SiCP) particles by friction stir processing (FSP) using a high speed steel tool pin and shoulder. Two different sizes (100-250 μm and 2 -4 μm) of SiCP particles were used. FSP was carried out by applying 2000 rpm and a speed of 15 mm/min. After FSP, X-ray diffraction was carried out to find for any phase changes. Scanning electron microscopy (SEM) was used to characterize the particle distribution and their chemical compositions. Vickers hardness measurements were made. Pin-on-disk tests were conducted as per ASTM G-99.
The size of the coarser SiCP particles was reduced to ~ 1 μm or less by FSP from an initial size of 100 - 250 μm . In contrast, the size of the finer SiCP particles was not significantly different after FSP compared to their initial size. The distribution of particles was found to be more uniform on the surface as well in the cross sectional direction of the FSP specimens when coarser particles were used. In the case of finer particles, the density of particles was more at the bottom of FSP nugget than at the top.
XRD results showed presence of SiC and Al. SiCP particles which were distributed in aluminum matrix were found to be decorated with matrix material due to friction stirring. SEM and EDS results of FSP samples showed the presence of Fe and W in surface composite which was confirmed due to the wear of tool material. Hardness of aluminum alloy base material increased from 60 Hv to 258 Hv after FSP. Pin-on-disk tests showed that wear loss of FSP specimens was negligible compared to the extensive wear of base plate. There was no difference between the wear resistance of pins made of two sizes of SiCP particles.
The Effects of Contact Conditions and Hydrostatic Pressure on Cavitation Evolution during Superplastic Forming of Lightweight Alloys
M. A. Nazzal1, F. Abu-Farha2, (1)German Jordanian University, Amman, Jordan, (2)Penn State University/Erie, Erie, PA
It is well established that many superplastic alloys exhibit cavitation during deformation. Cavitation not only limits the superplastic ductility of the material, but also adversely affects the service properties and fatigue performance of the formed parts. In this paper, finite element simulations and experiments are carried out to study the effects of contact conditions and hydrostatic pressure on the evolution of cavities during superplastic forming of both the 5083 aluminium and AZ31 magnesium alloys. The finite element analysis is based on a three dimensional model, that uses experimentally calibrated microstructure-based equations, and takes both damage evolution and grain growth into account. Elements that can handle contact, large deformation and the generated triaxial stress state are used. An elevated temperature pneumatic forming setup, with both forward and back pressure forming capabilities, is also built to accommodate different amounts of hydrostatic pressure. The area fraction of voids is measured at different places across the formed sheet and correlated to the associated friction coefficient and hydrostatic pressure.
A Numerical and Experimental Investigation of Reverse Bulging of Lightweight Superplastic Sheets
M. A. Nazzal1, F. Abu-Farha2, (1)German Jordanian University, Amman, Jordan, (2)Penn State University/Erie, Erie, PA
One of the major drawbacks of superplastic forming is the non-uniform thickness distribution of the formed part, and the potentially severe thinning associated with large plastic strains. One approach to tackle the problem is by reverse free bulging of the sheet, before the actual forward forming into the desired die cavity. In this work, finite element simulations and experiments are carried out to study the merits of performing a reverse bulging step prior to the superplastic forming process. In the reverse bulging step, the sheet is blown away form the female die to selected heights, hence causing various levels of deformation in the polar region of the formed sheet. Then the forming pressure is reversed so that most of the deformation takes place in the region next to the clamping flange instead of the polar region. Thickness distributions were measured and then compared to those corresponding to conventional forward forming, and hence the effects of the initial reverse bulging heights were quantified. The study is carried out using both 5083 aluminium and AZ31 magnesium sheets.
Advanced Cast Aluminum Alloys
A. P. Druschitz, J. Griffin, University of Alabama at Birmingham, Birmingham, AL
Castable versions of the 7000 series aluminum alloys are being developed for the production of ultra-high strength (>500 MPa yield strength), lightweight, shaped castings. These castings can replace aluminum fabrications and hog-outs in industrial, automotive, aerospace and military applications. Due to the long freezing range of these alloys, special casting processes (solidification under pressure) and heat treatments (solution treatment followed by hot isostatic pressing) are being developed. These processes can also be used to enhance the properties of existing casting alloys.
A New Ultra High Strength Aluminium Alloy Applied In Small Rocket Motors
O. Jensrud, J. I. Moe, SINTEF Raufoss Manufacturing AS, Raufoss, Norway
The improvement of lightweight aerospace components indeed requires new development of the aluminium alloy used. The challenges in applying high strength aluminium alloys are corrosion resistance and ductility in the temper of maximum strength. In addition have an alloy suitable for plastic forming to manufacture semi parts, in the Raufoss case small rocket engines.
The main idea of the new development has been reduction of the elements Cu and Fe in comparison with older alloys like AA7278 and AA7050. It is strongly believed that constituents of AlCuFe play and key factor in corrosion behaviour and especially for anodised qualities. It is also known that addition of Zn gives rather high level of strength in hardened tempers without reduction of formability. The new alloy introduced in small rocket engines has higher Zn and lower Cu content compared with older qualified materials. In addition to chemical composition the microstructure in the final temper are as important as chemistry and especially the grain structure. To control grain structure during processing of the material from ingot casting to final shape and temper the elements Zr and Cr play an important role in combination with an exact defined thermo mechanical route. The microstructure controls the most severe corrosion phenomena’s like stress corrosion and grain boundary attacks.
The new alloy (Al+Zn8.8+Mg2.8+Cu0.5+Zr0.15+Cr0.18) gives a yields strength of 630MPa with an elongation of 10% for a cold extruded and heat treated tubular part.
The introduction of the new Raufoss Alloy RA7090 in the rocket motor engine has improved the performance of the Raufoss Nammo AS rocket system. The main improvements are corrosion resistance, better ductility as well as a significantly easier manufacturing chain from molten alloy to final engines.
An concluding a better performance of the rocket engine system.
High Strength and High Temperature Aluminum Alloy for High Performance Applications
A. B. Pandey1, J. E. Spowart2, (1)Pratt & Whitney Rocketdyne, West Palm Beach, FL, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH
There has been growing interest to develop high strength and high temperature aluminum alloys to reduce weight of high performance aerospace and space components. Typically, aerospace and space components are made out of nickel base superalloys and steels. The use of a high strength and high temperature aluminum alloy can reduce the weight of components providing a substantial increase in the system’s thrust-to-weight ratio. New aluminum alloys containing nanocrystalline L12 strengthening precipitate are being developed under a program funded by the Air Force Research Laboratory. Process development and scale up of L12 strengthened aluminum alloys are also being performed under an IR&D program. The present aluminum alloy is based on a novel Al-Sc based alloy system. Aluminum-scandium alloy forms Al3Sc based precipitate that has an L12 structure which is strong and thermally stable up to very high temperatures. The strength and thermal stability of Al3Sc precipitate can further be improved by additional elements. These dispersoids provide strengthening in the alloy through Orowan strengthening, antiphase boundary energy strengthening and grain size strengthening. The proposed P/M alloy has demonstrated very high strength for a range of temperatures up to 600°F. Process parameters have been optimized to produce optimal properties in the material. These alloys have demonstrated an excellent compatibility with high pressure gaseous hydrogen. High cycle fatigue and creep tests of these alloys were also conducted. Fatigue results of these alloys showed good endurance limits at room temperature. Creep resistances of these alloys were found to be significantly superior to the existing aluminum alloys. The dominant strengthening mechanisms in these materials are grain size strengthening, Orowan strengthening and antiphase boundary energy strengthening. The strengthening mechanisms will also be discussed. Friction stir welding of Pandalloy demonstrated weld joint with 95% of parent metal strength.
Fracture Behavior of Cryogenically Solidified Aluminum-Alloy (LM-13) Reinforced with Nano-ZrO2 Nano Metal Matrix Composites (CNMMCs)
J. Hemanth, University, TUMKUR, India
Abstract
Fracture behavior of LM-13 aluminum alloy reinforced with different wt.% of nano-ZrO2 particles, solidified under various cryogenically cooled chills (at -80oC), cast using DMD (Dis-integrated Melt Deposition) technique followed by hot extrusion were investigated. The use of nano particles and cryogenic chilling enabled in strengthening mechanical properties of the composite. These nano chilled composites were developed exclusively for aero space applications.
The size of the particles dispersed varies from 50-80 nm and amount of addition varies from 3 to 15 wt.% in steps of 3%. Cryo chills of thickness 25, 20, 15, 10 and 5 mm were used to study the heat capacity of the chill on mechanical behavior of the composite developed. Microstructural studies of the nano-composite developed indicate that there is uniform distribution of the reinforcement in the matrix alloy with significant grain refinement and retention of residual porosity. Mechanical properties reveal that presence of nano- ZrO2 particles as dispersoid (up to 12 wt.%) and chill thickness (25 mm) has improved significantly the strength, hardness and fracture toughness with slight reduction in ductility as compared against the matrix alloy. Fractography of the specimens showed that the fracture behavior of matrix alloy has changed from ductile intergranular mode to cleavage mode of fracture. Finally heat capacity of the cryo-chill is identified as an important parameter which affects mechanical properties.
Key Words: Nano, Composite, Al-alloy, Cryogenic, Fracture.
Kaiser 7XXX Select® Plate: Creating Value for Customers in Finished Parts
P. Ainsworth1, S. Jansen2, P. Lassince1, (1)Kaiser Aluminum, Spokane, WA, (2)Metal Technology Germany (EDSWOG), Bremen, Germany
The aerospace industry uses many monolithic parts machined out of aluminum 7XXX plates. A key issue for the cost-effectiveness of this process is the minimum distortion after machining. Any excessive machining distortion will result in the need for costly and time consuming re-work prior to installation of the component on the aircraft. To solve this problem Kaiser Aluminum has developed a manufacturing process that is capable of providing aluminum 7XXX plates that meet all mechanical properties requirements, together with considerably lower residual stress levels. These plates are now branded as Kaiser Select(r). The machining behavior of this material was evaluated with Airbus (Varel plant) on machined parts that typically required re-work due to machining distortion. The results of this evaluation show that the dimensional variation after machining was reduced to such a level that the need for rework was eliminated. The paper will present both the Kaiser improved process, and the Airbus Varel results.
Aleris' Advanced Aluminium Products for Aircraft Structural Components
S. Spangel, A. Buerger, I. Kroepfl, Aleris Aluminum Koblenz GmbH, Koblenz, Germany
In order to achieve the aggressive targets of increased passenger and cargo capacities as well as lower fuel burn and larger ranges the aircraft industry is constantly looking for new aluminium alloys offering improved performance. Furthermore the application of aluminium in future aircrafts being in competition with fibre reinforced composites requires that the performance capability of modern aluminium alloys is fully utilized. To meet these requirements Aleris Aluminum Koblenz is working on new AA7x81 and 2xxx type sheet and plate alloys which offer benefits in terms of performance, weight and cost savings compared to conventional alloys. This presentation covers the recent Aleris 7xxx and 2xxx developments including alloys currently being internationally registered as well as newly developed alloys and will outline some future developments. Focus will be placed on AA7x81 plate material available in a wide thickness range which offers superior strength combined with high fracture toughness. Applications may include wing components (spars) or fuselage frames. Additionally a property overview of the corresponding sheet development program will be part of the presentation.
Development of allowables on Al-Li alloy 2195
M. Niedzinski, Alcan Aerospace, Chicago, IL
Development of alloy 2195 and subsequent usage on the external tank of Space Shuttle allowed launch of heavier components into more difficult orbits thus facilitating construction of International Space Station. This high strength/modulus and low density Aluminum Lithium alloy is also characterized by excellent corrosion resistance and good cryogenic fracture toughness. Even thou two new space application has surfaced recently alloy 2195 was not very visible to designers for commercial applications due to the nonstandard and proprietary test methods and test planes/orientations used for certification and lot acceptance testing. To facilitate commercial usage large scale test program was started to develop mechanical properties and write an AMS specification (which is a precursor to MMPDS inclusion) for T3/T82 temper. Testing encompassed plate material in the range of .500”to 2.250”. Paper will provide full portfolio of the static and dynamic properties and current applications.
Overview of Advanced Aluminum Alloys for Aerospace
R. J. Rioja1, J. Witters2, E. Colvin2, L. Mueller2, (1)Alcoa, Inc., Alcoa Center, PA, (2)Alcoa, Inc, Alcoa Center, PA
Aluminum products continue to make improvements to reduce weight of aerospace structures. With the increase and volatility of the price of crude oil and the need to reduce CO2 emissions, new Aluminum-base products are needed to enable cost effective structural weight savings of aircraft components. In this presentation, the latest plate, sheet, extruded and forged products from Alcoa for the aerospace industry are presented. The performance of several plate and extruded new products available for upper wing, lower wing and fuselage applications is discussed. Progress developing new alloys with and without Li additions is reviewed. Metrics indicating potential weight savings are presented. The benefits of unitization/part reduction using new "large" 7085 and 2040 forgings from Alcoa Cleveland are discussed. It is concluded that advanced aluminum products continue to enable OEMs to reduce weight and cost of modern aircrafts.
Scalmalloy® = a Unique High Strength AlMgSc Type Material Solution Prepares the Path towards Future Eco-Efficient Aerospace Applications
F. Palm1, R. Leuschner2, T. Schubert2, (1)EADS Innovation Works Germany, Munich, Germany, (2)Fraunhofer Society, Institute for Manufacturing and Advanced Materials (FhG-IFAM), Dresden, Germany
At AEROMAT2006 in
“Freezing” of more than 1,0 wt% Sc in the Al-lattice is very difficult. Only improved melt spin procedures developed in close collaboration with the Fraunhofer Institute for Manufacturing and Advanced Materials (FhG-IFAM,
The patended ScalmalloySC sheet material manufacturing procedure differs significantly from “classically” rolled AlMgSc sheet materials known from
New Developments on AlMgSc Alloys for Advanced Aircraft Applications -Properties and Potentials-
S. Spangel1, A. Buerger1, I. Kroepfl1, G. Tempus2, J. Hackius3, (1)Aleris Aluminum Koblenz GmbH, Koblenz, Germany, (2)Airbus Deutschland GmbH, Bremen, Germany, (3)AIRBUS Deutschland GmbH, Bremen, Germany
In the past decade the demand for lighter structures and advanced manufacturing technologies has accelerated the development of AlMgSc alloys. These alloys are specially designed for optimum performance considering new manufacturing techniques such as laser beam welding, friction stir welding and creep forming. Focus will be placed on highly advanced AlMgSc alloys such as Ko8242 and Ko8542 with a density in the range of today’s Al-Li alloys for fuselage skin or other applications where sheet products in complicated shaped parts are used. With their excellent fatigue and damage tolerance properties, good corrosion performance eliminating the need for cladding, good weldability and their low density the AlMgSc alloys offer huge benefits in terms of weight and cost savings. This paper will give a property overview of Aleris’ latest AlMgSc alloys including the influence of heat treatment and will outline some future developments and trends.
Tensile Testing Aluminum Alloy 6061 Alloy at Different Strain Rates and Temperatures
S. Adedokun, FAMU-FSU College of Engineering, Tallahassee, FL
Aluminum alloy 6061 was tensile tested at different strain rates at different superplastic temperatures. The tested aluminum alloy 6061 was initially heavily cold rolled and heat treated.
Changes in the behavior of the alloy were quantified by the changes in the tensile properties. Tensile properties measured were yield strength, UTS, Young's modulus, ductility and percentage elongation.
Temperatures and the strain rates were found to have significant effects on the measured properties with significant changes occuring due to the previous deformation history of the alloy.
High Performance Sustainable Airframes Using Monolithic Structures
F. Eberl1, I. Bordesoules2, F. Bron3, J. C. Ehrstrom3, (1)Alcan Rhenalu, Issoire Cedex, France, (2)Alcan CRV, Voreppe, France, (3)Alcan, Voreppe, France
The use of monolithic structures shows a great interest for very competitive weight/cost performance balances in wing or fuselage aircraft structures. In particular for business jet wings, integral structures are widely used due to their stiffness and cost efficient manufacturing. Even for larger regional jets, monolithic structures were selected for their design flexibility.
For compression loaded upper wings, various buckling modes are the limiting property. Integral machining of monolithic plates allows to integrate particular design features in order to increase the stiffness of the wing and to optimize the buckling behavior.
Well selected design features are also of great interest for damage tolerant dominated areas. Although endurance fatigue is naturally improved compared to a built-up structure, the design needs to be optimized for the fatigue crack propagation performance. Innovative structural designs integrating low cost reinforcements allow to exploit the entire benefit of a full integral wing.
In order to optimize the material use by conserving the full advantage of monolithic structures, modern assembling techniques as friction stir or laser beam welding can be used. Even more competitive cost reduction can be reached by thinking of the global life cycle and the supply chain management. From construction to dismantling, aspects as recycling are taken into account.
Last not least, the choice of the advanced aluminum alloy plays a key role for the property balance of the part to be designed. A large alloy portfolio and particularly alloys developed for monolithic structures allow to reach a high performance balance for cost effective metallic aircraft structures.Examples illustrating the specific areas of design, recycling, supply chain and optimized materials choice will be shown for various aircraft structural parts. Comparisons to today’s flying structures will be mentioned as baseline in order to better appreciate the step-change which has been made in the last decade.
Future Aluminum Airframes by Concurrent Optimization of Innovative Material, Design and Manufacturing
F. Eberl1, F. Bron2, J. C. Ehrström2, (1)Alcan Rhenalu, Issoire Cedex, France, (2)Alcan, Voreppe, France
Achieving the ambitious weight-cost targets of the airframers will require non-conventional solutions. Material property improvements alone, whatever the material nature, are not likely to bring the gap the airline companies expect. Tomorrow’s aircraft will be an optimized combination of innovations in materials, design and manufacturing.
High performance aluminum alloys combined with innovative design and new manufacturing practices constitute a very interesting recipe for new airframes reducing significantly both cost and weight. Some solutions have already been proposed like stringer bonding (significant improvement in fatigue and damage tolerance), skin crenellations (cost-free improvement in crack propagation), top-hat stringers (reduced weight and cost in top wing covers), friction stir welding (reduced buy/fly). New solutions are also proposed such as 45° stringer layout (weight reduction).
In this presentation, the new combinations of alloy, design concept and manufacturing method proposed by Alcan are presented and the resulting weight reduction is assessed with a global fuselage model. The focus is also put in the use of optimization techniques to push each concept/material combination to its maximum potential.
Identifying Opportunities for Reduced Maintenance/Inspection Intervals Using Advanced Al-Cu-Li Products
A. Danielou1, C. Hénon1, J. C. Ehrstrom1, P. Lequeu2, K. P. Smith3, (1)Alcan, Voreppe, France, (2)Alcan Pechiney Rhenalu, Issoire, France, (3)Alcan Rolled Products, Ravenswood, WV
Al-Cu-Li alloys are well known for their benefits in reducing density and increasing modulus, proportionally to their Li content. In addition, third generation Al-Cu-Li alloys have excellent resistance to corrosion in accelerated testing and after seacoast exposure. The compositions and processing of these alloys have been optimized to offer different toughness/static balances depending on the application in aircraft: 2195 with high static properties for compression-dominated panels, 2050 with good toughness/static balance for medium to thick gauge plate for integral structures, 2196 with high damage tolerance and low density for lower wing skins, 2198 with high damage tolerance for fuselage sheet.
The opportunities offered by these improvements over incumbent alloys’ durability and damage tolerance with regard to inspection interval and design service life will be discussed.
Engineering An Efficient Zirconium Grain Refiner for Magnesium Alloys
P. Saha, S. Viswanathan, The University of Alabama, Tuscaloosa, AL
Zirconium is well known as an excellent grain refiner for magnesium alloys that do not contain aluminum. Currently, approximately 1% by weight of zirconium is added to magneisum alloys for grain refinement. In this work, a Design of Experiments (DOE) approach was used for a systematic study of the grain refinement of magnesium by zirconium. Variables included the amount of zirconium, the pouring temperature, and the holding time prior to casting. Samples were poured into a special “hockey puck” mold designed to reproduce the conditions in permanent mold casting. Optical metallography and quantitative image analysis were used to measure the resultant grain sizes. The effect of the various factors on the measured grain size and the interaction among the various factors is discussed. An approach for the development of an efficient Zr-based grain refiner is outlined.
Diamondoid Stabilized Nanocrystalline Aluminum
J. C. Earthman1, K. Maung1, K. Hung1, F. A. Mohamed1, C. Franks2, A. Yousefiani2, (1)University of California, Irvine, Irvine, CA, (2)The Boeing Company, Huntington Beach, CA
The use of nanocrystalline (nc) alloys at elevated temperatures has been severely limited by their inherent thermal instability. In order to better understand the effect of nanoscale particles on this behavior, grain growth in nanocrystalline Al alloys with 1 and 5 wt% diamantane diamondoid additions was investigated. Diamantane diamondoids are hydrocarbon molecules with a 14 C atom diamond cubic framework terminated by hydrogen atoms (C14H20). In the present work, as-cryomilled powders were sealed in glass tubes in an Ar atmosphere and then annealed at temperatures ranging from 423–773K for different hold times up to ten hours. The average grain size for nc Al + 1 wt% diamantane was limited to 55 nm or lees from an initial grain size of 22 nm for all of the exposures conducted. Similar results were obtained with nc Al + 5 wt% diamantane. The thermal exposure data also demonstrate that the average grain size following thermal exposure for nc Al with diamantane is substantially smaller than that for pure nc Al processed under the same conditions. Analysis of the grain growth data suggests that the presence of diamantine results in strong pinning forces on boundaries during heat treatment. The present work was initially supported by the National Science Foundation (Grant No. D-DMR-0304629), and is currently sponsored by the UC Discovery Program (Award No. GCP07-10250) in partnership with the Boeing Company (Award No. 247099).
Improved Properties of Light Alloys Produced by Cryomilling and Bulk Consolidation Processing
R. Gansert1, D. Grant2, C. Melnyk2, S. Schroeder2, (1)AMTS Incorporated, Simi Valley, CA, (2)California Nanotechnologies, Inc., Cerritos, CA
Near-nano and nano-grained materials show great potential for applications in the aerospace industry. The Hall-Petch relationship cites the strengthening of materials by reducing the average crystallite (grain) size. A study is proposed to investigate the increase in mechanical properties provided by near-nano and nano-grained powders used in powder metallurgical applications. Nanocrystalline powders of light alloys (aluminum, titanium) will be produced from cryomilling operations. Consolidated forms of near-nano and nanocrystalline materials will be produced using hot isostatic pressing (HIPing) and Spark Plasma Sintering (SPS). The mechanical properties of the near-nano and nanocrystalline materials will be compared to consolidated forms of conventional materials. Initial testing indicates an increase in hardness and shear by 2-3 times from use of near-nano and nano- crystalline materials. Cryomilled powders and consolidated forms of these powders will be examined using Field Emission Scanning Electron Microscopy. Macrohardness, microhardness and shear testing will be performed to examine the mechanical properties.
Advances in Ion Fusion Formation (IFF): An Alternative Solid Freeform Fabrication Process
R. J. Adams, Honeywell, Tempe, AZ
Honeywell continues to make steady progress with its entry into the Solid Free-form Fabrication manufacturing technology called Ion Fusion Formation (IFF), a Direct Metal Deposition (DMD) process. These direct metal deposition processes are also called additive manufacturing (AM). New advances have been made including equipment upgrades to extend the size range, new materials deposition capability and improved shielding. Furthermore, we have begun efforts to develop tooling manufacture & repair capability. We will describe those advances. This is a near-net-shape hardware manufacturing process that uses a very hot ionized gas to deposit metal in small discreet amounts and ultimately build a complete part. Components can be used as-deposited or post-deposition processed. The latter condition can give some improvement in properties for heat treatable materials just as conventional casting or forging heat treatable alloys currently undergo a final heat treatment for property improvement. The process has low initial capital, maintenance and operating cost and is user friendly.
Discussion of IFF capabilities will include efforts to improve surface finish, deposit new materials and improve properties. IFF efforts have been directed to build structures with commercially available materials i.e. existing castings or forging materials. Our most recent materials advances are with Al alloys and Ti 6-4 but many other materials have been studied. The properties of IFF deposits meet or exceed the conventional materials & therefore can be used as direct substitutes. Thus the entry of IFF into the manufacturing base can be facilitated by using the same materials as more conventional processes.
We will present mechanical properties for tooling materials as well as low alloy steels, stainless steel, titanium, aluminum alloys and high-temperature materials including their properties. In addition, we will review the requirements for shielding and its effect on properties as well progress in component manufacture will be discussed.
Aerodynamic Heat Treating Furnaces for Aerospace Applications
A. V. Sverdlin, A. R. Ness, Bradley University, Peoria, IL
AHTF furnaces, in which air or gas is heated to 500-700oC without electrical or other special heaters, have been developed and placed in operation in a number of plants for heat treating aluminum, magnesium, and titanium alloys, and also steels. The AHTF chamber furnace is thermally insulated without the use of fire bricks. It has a centrifugal fan with vanes having a special contour. The fan, operating in a closed system, converts, into heat, almost all the energy used to turn it; the heat is transferred to the parts by convection. In most machine building plants aluminum alloys are heat treated in ERF furnaces (electric resistance furnaces with forced air circulation) or in salt baths. This research deals with an investigation of the heating conditions for various semifinished products of aluminum alloys in the AHTF-3 in comparison with the ERF-2 furnace and a potassium nitrate bath of approximately the same working volume
Development of Alloy Recycling Indices for Aerospace Aluminum Alloys
S. K. Das1, J. G. Kaufman1, J. A. S. Green1, D. Emadi2, M. Mahfoud3, (1)Phinix, LLC, Lexington, KY, (2)McGill University, Ottawa, ON, Canada, (3)College of the North Atlantic - Qatar, Doha, Qatar
For many decades, thousands of obsolete private, civil, and military aircraft have been sitting in “graveyards” across the globe. The used aircraft at the end of their productive life provide an obvious source of valuable aluminum and many alloying elements such as copper and zinc. However cost-effective recycling of old aircraft is complex because aircraft alloys are (a) typically relatively high in alloying elements and (b) contain relatively higher levels of impurities than required of many newer aircraft alloys to optimize their toughness and other performance characteristics. Most aluminum alloys in commercial use today were developed primarily based upon the elemental alloying additions needed to achieve the target performance requirements, including such properties as strength, toughness, and/or corrosion resistance. It was taken for granted that whatever base metal requirements were needed would come from primary aluminum, to which the needed alloying elements were added. Little or no consideration was given to the recycling process: what will happen when a product made of the alloy reaches the end of its life, and becomes available for recycling. Today, for the first time, this approach is being replaced by one in which consideration of recycling characteristics are considered in alloy design; recyclability along with performance requirements are considered in designing new alloy compositions. This paper introduces a new approach by recognizing the relative recycle-friendliness of existing aerospace aluminum alloys, indicating which can be most easily recycled for direct reuse and which will require substantial reprocessing. The need for the recycling index is described, the basis of the Alloy Recycling Index documented, and some of the early conclusions that may be drawn from such an approach are laid out. The Alloy Recycling Index or ARI is proposed as an industry aid to recognizing the relative recyclability of aluminum alloys, with the goal of maximizing the industry contribution to a green environment. Initial development of ARI is based on the elemental alloy composition which can be latter be expanded to include the carbon footprint of individual alloys.
Recent Advancements in Mechanistic Materials Modeling for Dual Microstructure Heat Treated Aeroturbine Disc Alloys
H. J. Jou, QuesTek Innovations LLC, Evanston, IL
Dual Microstructure Heat Treatment (DMHT) technology optimizes nickel-based aeroturbine disks and achieves significant performance improvements for aeroturbine engines. DMHT generates gradient microstructures and a major hurdle to perfecting this technology is a lack of mechanistic microstructure and mechanical property modeling in the gradient region. Recent advancements in the development and refinement of physics-based model techniques for Ni-based superalloys extend the capabilities established in DARPA Accelerated Insertion of Materials (AIM) and ONR/DARPA D3D programs to address the gradient region of DMHT disks. These advancements include performance enhancements and the calibration/validation/implementation of PrecipiCalc® software to DMHT precipitation microstructure modeling for 3rd generation disc alloys through a NASA/QuesTek/Air Force/Rolls-Royce collaboration. The application of D3D 3D tomography techniques and a fatigue lifing model, developed in collaboration with Professor David McDowell of Georgia Institute of Technology, establishes a framework for the optimization of DMHT disks for next generation aeroturbines.
Porosity Reduction and Grain Size Prediction in Hot Rolling by FEM
V. Mendoza, Carpenter Technology Corporation, Reading, PA
The main goals of process simulation in manufacturing are to reduce manufacturing/part development time and cost as well as increasing quality and productivity. The usage of finite element analysis techniques for the modeling of the metal forming process has become well established in recent years and the techniques have been successfully developed and applied with the increased computational capability of modern computers. The current effort is to demonstrate metal forming analysis, using the FE method, to understand the ultrasonic performance of several hot rolling pass schedules. i.e., porosity reduction and the evolution of the grain size. Results are very helpful is selecting the optimum geometry and process parameters to achieve the required specifications.
Finite Element Simulation of the Electron Beam Freeform Fabrication Process: Residual Stresses and Distortion
U. Chandra1, G. Barot1, A. Chandra1, K. M. B. Taminger2, J. K. Watson3, (1)Modern Computational Technologies, Inc., Cincinnati, OH, (2)NASA Langley Research Center, Hampton, VA, (3)NASA Johnson Space Center, Houston, TX
This presentation discusses the application of the finite element method for the prediction of residual stresses and distortions in components made by the electron beam freeform fabrication (EBF3) process. Comparison of the computed values of residual stresses with their experimental counterparts is also included.
Three test specimens with varying levels of complexity were fabricated using the EBF3 process. Specimen 1 was a 6”x3”x1/4” plate and the material was deposited along one of its 6” long edge in a number of thin layers. Specimen 2 was in the form of a circular disc formed on a plate type substrate. Specimen 3 involved three adjacent straight lines of deposit each consisting of several layers of material. A commercial finite element code, ABAQUS - supplemented with a special user subroutine to model the heat source, was used for simulations. A combination of X-ray diffraction and incremental ring core techniques was used for stress measurement.
The presentation also highlights some of the challenges experienced during the fabrication of test specimens, their finite element simulation and experimental validation.
Design and Analysis Workflows for Advanced Simulation of Composite Structures
K. Indermuehle, A. Prior, SIMULIA, Providence, RI
In this paper we review the current capabilities in use for the design and analysis of composite structures, and identify the main advantages of high fidelity simulation in the aerospace and energy domains. The common difficulties encountered in using these methodologies will be highlighted, and solutions proposed. A typical workflow for the design and analysis of a generic aerodynamic blade will be examined with a focus on the integration of the tools and the robustness and efficiency of the overall process. A typical workflow would be initiated within the geometry tool (CAD), and at some point would require the transfer of accurate geometric and composite layup information to a modelling system. The modification and refinement of the layup is then carried out in the analysis modelling tool and advanced nonlinear structural simulation is used to assess the performance of the component. This may include draping analysis to confirm that the component can be manufactured to the design specification, and a range of structural analyses to cover assembly, in-service loads, and limit load cases with damage and failure. The paper will review these simulation capabilities and consider the integration into a coherent workflow. These analyses are initially carried out on the ‘as designed' model, but it is important to assess the sensitivity of the structural response to variations in design parameters. Typically, the analysis would consider the variation in dimensions due to manufacturing and assembly tolerances, as well as variations in the composite construction (layup angle, ply thickness, etc) due to process variability. The workflow example will be used to illustrate the capabilities of analysis tools to carry out sensitivity assessments and to examine the robustness of the design including manufacturing variability.
Simulating the Influence of Machining Processes on Part Quality
C. E. Fischer, Scientific Forming Technologies Corporation, Columbus, OH
Aerospace part performance is influenced by geometric tolerances, microstructure, residual stress, and surface finish, among other factors. These characteristics are developed through the entire processing sequence, from primary processing, through forming and machining.
Computer simulation has proven to be a valuable tool for understanding the role of manufacturing processes on part quality. This presentation will examine how recent advances in finite element modeling technology have enhanced machining process simulation. Simulation technology has enabled the coupling of machining process models with residual stress prediction, microstructure models, and the influence of forming and heat treatment processes.
Simulation results include bulk and surface residual stress, bulk and surface microstructure, and bulk distortion. An understanding of these values support the selection of manufacturing process parameters to improve part quality while reducing production cost.
Fatigue Variability in through-Transus Processed Ti-6Al-2Sn-4Zr-6Mo at Elevated Temperature
A. Hutson1, W. J. Porter1, J. M. Larsen2, (1)University of Dayton Research Institute, Dayton, OH, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH
Fatigue behavior of structural metals is known to vary widely, even with focused loading and environmental conditions. The mechanisms that drive this variability are unknown for most alloys; however, it has been suggested that the worst case fatigue behavior may be dominated by crack growth, with little contribution from crack initiation to the total fatigue life. Often, this worst case is not seen in laboratory experiments, because too few experiments are performed to capture the “1 in 1,000” behavior. In the present study, fatigue and crack growth samples were taken from a section of through-transus processed Ti-6Al-2Sn-4Zr-6Mo for the purpose of evaluating variability in behavior. Twenty-five constant load amplitude fatigue experiments were conducted for each of three test conditions. Two sets of tests were conducted on low-stress ground specimens, one at 827 MPa and one at 860 MPa. The third set of tests was conducted on electro-polished specimens at 860 MPa. All tests were performed in lab air at 260°C using a stress ratio of 0.05 at a frequency of 30 Hz. Statistical analysis of the resulting data provided a means of estimating a value for the “1 in 1,000” fatigue life.
Fatigue crack growth experiments were also conducted, under similar laboratory conditions, to provide a basis for fatigue life prediction. Characterization of the microstructure and of the resulting fracture surfaces from S-N tests allowed estimates of the initial crack sizes for the predictions. A few fatigue experiments were conducted in which surface flaws with a ~ 0.010 mm and c ~ 0.020 mm were introduced, to validate the predictions. Life prediction analysis was conducted using a modified small plus large crack growth model. The results from the analysis were compared with the “1 in 1000” minimum fatigue lives from the statistical analysis. They were also compared with the minimum S-N fatigue lives and with the experimental fatigue lives from the micro-notched specimens. While the fatigue life variability was quite wide, exceeding a factor of ten in some cases, the minimum fatigue lives compared well with the crack growth predictions and with the fatigue lives obtained from the micro-notched samples.
Multiscale Modelling of Primary and Secondary Creep in Nickel Super-Alloy CMSX4
W. Vorster, F. P. E. Dunne, University of Oxford, Oxford, United Kingdom
This paper presents a multiscale, crystal plasticity, model that may be used to study the deformation behaviour of second-generation nickel super-alloy, CMSX4. CMSX4 is one of the nickel super-alloys used in gas turbines for non-stationary components in aero-engines, such as turbine blades. Accurate knowledge of this material’s deformation behaviour is crucial to increase engine efficiency and life of the component but, even more so, to avoid catastrophic failure of critical components.
Primary creep deformation of CMSX4 is, for the most part, governed by the gliding of dislocations through the super-alloy’s g-g’ microstructure. Under these creep conditions it is the g’ precipitate that acts as pinning mechanism and hence results in dislocation retardation and material strengthening during deformation. It has been shown that primary creep of such alloys is accurately modelled using an Orowan approximation for slip rate. However, as deformation progresses, dislocation pile-up become pronounced within the g channels, further increasing the material resistance to deformation by effectively increasing the activation volume needed to initiate slip. It is speculated that the pile-up of dislocation in the g channels may be accounted for by the evolution and saturation of geometrically necessary dislocations (GNDs). Such effects are difficult to account for without exact modelling of crystal morphology and volume fraction of precipitate within the material matrix subjected to thermal and mechanical loading environments.
Multiscale modelling is achieved by means of communicating data between a continuum finite element model (FEM) and one of a representative volume element (RVE) of the CMSX4 microstructure. The outcome of this study contributed to the understanding of the deformation processes involved in super-alloys that ultimately results in greater accuracy in the design of components manufactured from this material.
Microstructure-Sensitive Constitutive Relations for Prognosis and Location-Specific Design
C. Przybyla, D. McDowell, Georgia Institute of Technology, Atlanta, GA
Models for prognosis applications are desired that reflect underlying microstructure. Conventional macroscopic viscoplastic constitutive models for
Analysis and Simulation of Heat Treatment Processes for Fatigue and Fracture Optimization of Forged Aircraft Engine and Structural Parts
M. Riedler1, M. Stockinger1, M. Stoschka2, B. Oberwinkler2, W. Tan2, H. Leitner2, (1)Böhler Schmiedetechnik GmbH & Co KG, Kapfenberg, Austria, (2)University of Leoben, Leoben, Austria
The tendency of increasing operating temperatures in order to produce more efficient and green engines leads to development of new materials and processes. Furthermore, aerospace structural parts are optimized in respect of light weight in order to increase pay load and efficiency.
With the objective of optimizing forgings with respect to desired mechanical and micro structural properties, design and weight an application tailored forging and heat treatment process can be worked out, when the affecting mechanisms are clarified.
Therefore, in addition to engine and structural parts, special purpose tailored parts are designed for the analysis of fatigue and fracture properties depending on the forging process (hydraulic press, screw press and hammer; influences of process temperature, strain, strain rate), heat treatment process (influences of temperature and time on temperature, cooling medium, cooling rate) and technological influences from machining and surface treatment (surface layer, shot-peening, residual stresses and distortion).
In order to optimize the heat treatment processes defined process parameters have to be analyzed and optimized. For characterization of different types of heat treatment and quenching possibilities available at Böhler (air, pressed air, salt, polymer and water) special field tests with highly instrumented forged parts are performed. Additional quenching tests with specimens are done with special laboratory equipments. This allows the investigation and implementation of a wide variety of possible process matrix parameters in simulation tools like DeformTM (temperature dependent emissivity, convection and heat transfer coefficient).
Based on a deep knowledge of micro structure affecting fatigue and fracture and the possibility of creating and using finite element tools a tailored multidisciplinary forging, heat treatment and part optimization and a useful definition of the demanded specifications (micro structure, mechanical properties, static and cyclic properties) can be worked out together with the aerospace part designers in order to deliver economic and safe parts.
Probabilistic Fatigue Life Prediction of Turbine Engine Materials
S. K. Jha1, M. J. Caton2, J. M. Larsen2, (1)Universal Technology Corporation, Dayton, OH, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH
Physics-based probabilistic methods are essential in appreciably reducing the uncertainty in fatigue life prediction. Towards this objective, the role of competing mechanisms in producing dual-fatigue variability behavior in turbine engine materials is discussed. The competing modes could be related to randomly occurring microstructural configurations, differing in the degree of heterogeneous deformation accumulation in fatigue. The fatigue variability is described as a sequence of mechanisms, probabilistically originating from these configurations, in the order of decreasing heterogeneity level. These mechanisms separated into two primary contributions to the lifetime probability density: (i) the mean-lifetime response and (ii) the crack-growth-controlled, life-limiting behavior. A model incorporating this dual behavior was developed and provided reasonable predictions of the influence of material and extrinsic variables on the lifetime density and the probabilistic lifetime-limit.
Effect of a Graded Layer on the Dissipated Energy during Fatigue Crack Growth along Plastically-Mismatched Interfaces
C. Baudendistel, N. Klingbeil, Wright State University, Dayton, OH
The development of layered material systems for aerospace components (including laser-deposited materials, multi-layer damping treatments and a variety of protective coatings) requires methods for predicting interfacial fatigue crack growth under sustained mixed-mode loading. To this end, a dissipated energy theory of fatigue crack growth for homogeneous materials under mode I loading has recently been extended to a general bimaterial specimen configuration under sustained mixed-mode I/II loading. The dissipated energy theory allows the prediction of fatigue crack growth rates based on numerical results for the plastic dissipation per cycle in conjunction with a substantially reduced test matrix of cyclic constitutive and monotonic fracture properties, without the need for extensive crack growth testing. As such, it provides a method for rapid evaluation of prospective new material systems, as well as insight into the design of fatigue-resistant interfaces.
An inherent assumption of the authors' prior work is that a perfectly sharp interface exists between the top and bottom layers, when in reality a grading of mechanical properties can exist across the interface. As such, the current work extends the approach of the previous studies to incorporate a grading of yield strength between the two layers through parametric finite element modeling with ABAQUS. Results suggest that incorporation of a graded layer acts to increase the overall amount of plastic dissipation, which is dominated by the weaker (i.e., lower yield strength) material. However, this increase is bounded between the numerical results for a perfectly sharp interface (no graded layer) and those for a homogeneous specimen of the weaker material (no strength mismatch), and is small relative to the effect of applied mode-mix ratio. Overall, results suggest that while the presence of a graded layer can have a measurable effect on the plastic dissipation, the assumption of a perfect interface is reasonable for typical material systems.
Rotor TMF Testing – Current State of the Art
R. Murner, P. Wawrzonek, Test Devices, Hudson, MA
Higher gas turbine flow path temperatures have steadily increased the rim-to-bore gradients on both the rear stages of high pressure compressors and high pressure turbines. This has increased the likelihood of TMF related lifing issues with the disk live rims and with creep and stress rupture failures of disk blade attachment lugs. Lifing models enter a realm of high uncertainty when significant plasticity is present as a percentage of total cyclic strain and the result is more frequent and expensive inspection of service components in order to prevent potentially catastrophic liberation of parts. Other turbine hardware such as blade retention plates, rivets, dampers and even blade attachments cannot escape the effects of increased temperatures that border the creep regimes of the latest turbine superalloys.
For decades TMF testing of rotating structures has not been practical since the localized heating and cooling methods required were not available. Recent advances in focused heating methods have now made TMF a viable test option for material and engine development programs. Quartz lamps and lasers offer exceptional focused thermal flux combined with capabilities that lend themselves to digital programming and control. The prior issues of not being able to rapidly cycle heating and cooling on narrow annuli of disks no longer exist.
The objective of this briefing is to present the results of an aft stage compressor TMF test that was recently performed by Test Devices Incorporated. The test component was a fully bladed, retired F100 10th stage compressor disk. The briefing highlights the unique design features of the test rig, presents the test results and offers insight into the potential of the test method to investigate the issues related to hot section rotors.
Structural Analyses in Support of Alloy Development at Aleris
R. De Rijck1, M. Miermeister2, A. Norman1, W. Spanjer1, M. Lansbergen1, B. Neelis1, (1)Corus Research Development & Technology, IJmuiden, Netherlands, (2)Aleris Aluminum Koblenz GmbH, Koblenz, Germany
In the highly competitive field of aerospace materials development Aleris has taken the approach of using structural analyses to highlight new material developments and manufacturing process'. The conceptual design of aircraft structures shows the possibilities of new material applications in aircraft. The development of analyses tools by CRD&T alongside the development of future aluminum alloys by Aleris approaches a similar conceptual design philosophy as has been discussed in recent years. This approach allowed Aleris not only to look at the performance of alloys in current and future structures but also for a closer look at production advantages that could be gained by alloy improvements, e.g. welding, integrated parts. Composite materials found their way onto the aircraft structures, they can be carbon fibre reinforced plastic or a fibre metal laminate. The evaluation of alloys is not only looking at the behaviour of single alloy solutions, but also at the interaction between different material solutions. The conceptual approach is used for the fuselage structure, combining static analysis and damage tolerant analysis resulting in different concepts, e.g. riveted, bonded or welded. And thus taking into account at an early stage the production advantages that solutions can offer with an improvement in performance and/or cost. In competition with the composite solutions new AlLi alloys have been developed as a weight‑saving solution for metal design. The Aleris AlMgSc development provides similar results for fuselage applications with improved impact and fatigue crack growth rate performance. Application of AlMgSc in the upper fuselage requires a riveted or bonded stringer, application in the lower fuselage a welded structure. The task then is to answer the following questions. What is the most optimum combination of properties to achieve an improvement in performance and/or a reduction in cost? Answers to these questions will be addressed in the conceptual fuselage analyses.
Light Weight Modular Platforms for Machining and Other Shop Functions
P. W. Marino, Paul W. Marino Gages, Inc., Warren, MI
This light weight, modular platform brings new opportunities to the pre-prototype and prototype industries, providing highly accurate work and work surface. Holes, precisely located in a grid pattern, are used to fasten pieces for holding.
Wood, polystyrene, clay, urethane, aluminum and other typical materials used are machined while still on the armature structure. Weight limit is tested to 10,000 lbs; heavier load values are available upon request.
The platform’s modular construction allows for expansion in increments of 40mm in X, Y and Z directions.
Auto-Leveling Option
Auto-leveling is accomplished with linear actuators. Each actuator features 0-10” of movement up/down and an individual load capacity of 1½ tons, for a combined load of 12,000 lbs., a 24 volt motor, 110/230 AC power and is PLC controlled for height. Leveling feedback is via high gain electronic inclinometer. Auto-leveling is achieved by moving the armature to the approximate height and pushing the single push button on the hand box to initiate the leveling sequence this is accomplished in less than two minutes. Tests have provided 0.008” levelness repeatedly every ten feet. Actuators may be packaged inside or outside the frame. (Patent Pending).
Alternative Validation Technique for Accurate Modelling of Hydro, Pneumatic and Superplastic Forming Operations
F. Abu-Farha1, M. Nazzal2, O. Rawashdeh3, (1)Penn State University/Erie, Erie, PA, (2)German-Jordanian University, Amman, Jordan, (3)Oakland University, Rochester, MI
The increasing interest in lightweight metallic sheets has led to the growing activities on hydro/pneumatic forming operations; particularly at warm and elevated temperatures, provided the limited cold formability of most lightweight alloys. This is most prominent in the case of the superplastic forming (SPF) technique, which seems to go hand-in-glove with lightweight alloys. However, there is still a lack of accurate models that can describe the behaviour of the formed material, hence adequately predict/control the forming process; a fact that is hampering SPF’s use on a larger scale. One critical problem is the accustomed model validation process, which is predominantly based on a comparison of final thickness distribution in the formed part against FE predictions. While this is a good practice, it is not direct enough to provide an explicit feedback for fine tuning the constitutive model, simply because it is solely based on a post-forming result (rather than the process itself).
The need for a more direct verification approach provoked this effort, in which simple electrical contact sensors are planted across the surfaces of selected calibration forming dies. The constitutive model for each of the investigated materials is first fed into a FE package, which in turn is used to simulate the forming process corresponding to the die geometry. The contact sensors are then used to monitor the deformation of the sheet, and compare it to the FE predictions. It is shown how monitoring the progress of the forming process provides a significant in situ feedback on the accuracy of the FE generated pressure-time profiles, and hence the accuracy of the adopted material’s constitutive model. The effectiveness of this approach is demonstrate by the presented attempt to generate accurate constitutive/FE models for both the 5083 aluminium and the AZ31 magnesium alloys, at different sets of forming conditions.
Simulation of Interdiffusion Kinetics in Ni-Base Superalloy / NiAl-Coating Systems
A. Engström1, Q. Chen1, L. Höglund1, P. Mason2, (1)Thermo-Calc Software AB, Stockholm, Sweden, (2)Thermo-Calc Software Inc, McMurray, PA
This paper discusses modelling and simulation of interdiffusion in Ni-base superalloy / NiAl-cotaing diffusion couples, by means of a thermodynamic and kinetic modelling approach as taken in a commercial finite-difference code, DICTRA[1]. This code solves the multi-component diffusion equations, combining assessed thermodynamic and kinetic data in order to determine the full composition dependent interdiffusion matrix. In this work, the so-called homogenization approach to diffusion in multi-phase systems[2] have been used in order to simulate interdiffusion in complex Ni-base superalloy / NiAl-coating diffusion couples. The simulation results obtained are validated against experimental data, and the agreement is very satisfactory given the complexity of the problem.
References: 1. J.O. Andersson, T. Helander, L. Höglund, P.F. Shi, and B. Sundman, Calphad, 26 (2002), pp. 273-312. 2. H. Larsson and A. Engström, Acta Materialia, 54 (2006), pp. 2431-2439.
SERDP/ESTCP Surface Engineering Database – a New Tool for Engineering Decision-Making
K. O. Legg1, B. D. Sartwell2, (1)Rowan Technology Group, Libertyville, IL, (2)SERDP/ESTCP, Arlington, VA
Between OSHA and EPA regulations, and now the European REACH statute, the aerospace and defense industry is under continual pressure to replace materials such as Cd and chromates. However, it is difficult to find out what alternatives have already been authorized and successfully adopted, and to choose the best option for each application, because the necessary information is hard to locate. The DoD environmental research and development programs, SERDP and ESTCP, have established a new Surface Engineering Database under their ASETSDefense initiative (Advanced Surface Engineering Technologies for a Sustainable Defense) on its website at www.asetsdefense.org. The database pulls together all the detailed engineering data and significant background information, as well as information on what technologies and materials have been validated, authorized, flight tested and implemented.
This briefing will describe the database structure and contents, and will include a demonstration of its function.
First-Principles Studies on the Elastic Constants of Ni-X (X=alloying elements) Alloys
D. Kim, S. Shang, Y. Wang, Z. K. Liu, Pennsylvania State University, University Park, PA
The Ni-based superalloys are widely used for equipments operating at high temperatures. The prediction of their deformation behaviors will be very useful in understanding existing alloys and designing new alloys. In this study, the effects of alloying elements (Al, Co, Cr, Cu, Fe, Hf, Mo, Nb, Pt, Re, Ta, Ti, W, Y and Zr) on the elastic constants (cij’s) of Ni have been investigated using the first-principles calculations within the generalized gradient approximation. The supercells with 31 Ni atoms and one alloying atom were used. The calculated bulk modulus and shear modulus are compared with the available experimental data and analyzed based on the volume changes and electron density of the Ni-X dilute solutions. The addition of Y, Zr and Hf results in larger decrease of elastic moduli of Ni with respect to other alloying elements studied herein, which are traceable to the larger increase of volume. The solid solution strengthening on Ni caused by the addition of alloying elements is also studied. The melting temperatures of Ni-X dilute solutions obtained from the available thermodynamic databases have been compared to those obtained from the empirical relationship with the elastic constant c11.
Precipitation Simulation in Multi-Component Ni-Based Alloys
Q. Chen, X. Lu, H. Strandlund, A. Engström, Thermo-Calc Software AB, Stockholm, Sweden
In this presentation we simulate the concurrent process of nucleation, growth, and coarsening of gamma prime particles in several Ni-based alloys by using TC-PRISMA, a computational tool that is integrated with Thermo-Calc and DICTRA, and can use existing thermodynamic and kinetic databases directly. The multi-component Gibbs-Thomson effect and cross diffusion have been treated exactly in our approach. We have calculated the temporal evolutions of the number density, particle size, particle size distribution, and compositions in both matrix and precipitate phases, and compared the calculation results with experimental ones from the literature. A fair agreement has been found, but a few issues and challenges remain and will be discussed.
Role of Materials Manufacturers’ in future Aerospace Materials R&D efforts
L. Christodoulou, DARPA/DSO, Arlington, VA
Dr. Leo Christodoulou, Deputy Director of DARPA/DSO, will discuss the role of materials manufacturers’ in future aerospace materials R&D efforts, and will explain how companies can participate. This presentation will provide the information you need to take part in DARPA projects.
Integrated Computational Materials Engineering: Emerging Tools and Their Impact
T. M. Pollock, University of Michigan, Ann Arbor, MI
Computational tools have transformed many fields of engineering and their use has accelerated product design processes. However, a critical missing link in the integrated product development and manufacturing process is a full set of computational materials engineering tools. The fundamental technical challenge is that the structure and behavior of engineering materials involves a multitude of physical phenomena spanning many orders of magnitude in length and time. While a comprehensive set of tools for materials are far from fully developed, it will be shown that integration of emerging models and information can have a substantial impact on design and manufacturing and implementation of new high temperature materials and processes. Examples of the impact of materials modeling on metallic components in aerospace vehicles will be reviewed. The development of some new materials characterization tools that support model development will be presented. Finally, future challenges for integrated computational materials engineering will be reviewed.
Progress toward integration of AFRL programs across the various component directorates
B. Farmer, AFRL, Dayton, OH
After brief overviews of the Air Force Research Laboratory (AFRL) and the Materials and Manufacturing Directorate (RX), this presentation will describe the progress toward integration of AFRL programs across the various component directorates. The alphabet soup (FLTCs, Discovery, STTs, DCTs) used to describe relationships of programs with one another and to capabilities needed by the now and future Air Force will be decoded. Finally, the current focus areas, thrusts, and initiatives for the Materials and Manufacturing Directorate will be discussed in the context of the AFRL integration constructs.
Technical Innovation and Growth: How Boeing Hones Its Competitive Edge
D. Chong, The Boeing Company, Seattle, WA
Advanced Aerospace Engine Requirements and Materials Development
F. Preli, Pratt & Whitney, East Hartford, CT
Next generation engine design, such as advanced versions of the Pratt & Whitney PurePower™ PW1000G engine with Geared Turbofan™ technology and the F135 engine for the F-35 Joint Strike Fighter must balance the seemingly conflicting requirements of higher performance, reduced weight and lower cost. Instability in the price of fuel and the desire to reduce the environmental footprint of aircraft engine operation increases the need to reduce fuel burn. More efficient engines generally tax the temperature capability of materials systems and put pressure on the designers to reduce weight. State of the art turbine engines represent highly engineered complex systems. Several materials options are available to reduce the weight of the fan and compressor, such as Organic Matrix Composites and Advanced lightweight metallic materials, but cost limits their application. For the combustor and turbine, more capable nickel alloys and Ceramic Matrix Composites will be required to meet the weight and temperature requirements of future engines. Additional capability enhancements can be achieved through engineered material systems.
Assessing Health of Military Engines
N. H. W. Eklund, H. Qiu, W. Yan, X. Hu, General Electric Global Research, Niskayuna, NY
The path of a commercial aircraft engine through the flight envelope is generally quite predictable, and the bulk of operational time is at steady state; conversely, military engines are frequently used in dramatically different ways from flight to flight, with very little - if any - time spent at steady state. Thus, characterizing the health of military engines is much more difficult, and requires a very different approach than the one used for commercial engines. This paper describes an artificial intelligence approach for identifying semi-steady state points in a military engine, and for using the data collected at those points for characterizing engine health.
Worst-Case Prognosis of Advanced Turbine Engine Materials
J. M. Larsen1, S. K. Jha2, M. J. Caton1, A. Rosenberger1, R. John1, (1)Air Force Research Laboratory, Wright-Patterson AFB, OH, (2)Universal Technology Corporation, Dayton, OH
Material State Awareness through Virtual Sensing for Engine System Prognosis
D. A. Ress, J. J. Heyob, GDIT, Dayton, OH
This paper investigates how information gathered during routine system maintenance actions and residing in numerous disparate databases, could become, if appropriately fused, a virtual sensor providing otherwise unobtainable knowledge of the current state of the system. Understanding the past performance of turbine engine components is currently an exhaustive time-intensive manual task infrequently performed only on a few selected high-value components. The laborious nature of this current state of the art severely limits past performance metrics to very few applications beyond research. A large driver for the collection of engine data has been scheduled engine removal, disassembly and non-destructive component inspection to assure safety and reliability of the entire system. The frequency of these inspections is driven by conservative service within each component's safe life design limits. While this safety assurance process is both time-consuming and expensive, the current use of the information generated is only to determine a go/no-go status for each engine component. It is proposed that this data could have significant additional value for quantifying the remaining useful life of the components and in tailoring schedules for future maintenance actions based on a predicted condition. This paper will illustrate how these engine maintenance databases could provide a source of copious, low-cost, usage-relevant data for statistically validating and establishing confidence in the predictive models which are so critical to a prognosis-based system. This paper leverages a unique opportunity made possible by the Air Force for access to several government owned databases containing decades of turbine engine component inspection information. The evaluation of these databases will specifically consider and support material models currently under development in the DARPA Engine System Prognosis (ESP) program but will also identify opportunities for the larger vision of rapid analytical certification and engineering of future system designs, processes, and materials.
Enabling Sensing and Life Prediction Technologies for Prognosis
S. J. Hudak1, M. P. Enright1, H. Millwater2, R. C. McClung1, (1)Southwest Research Institute, San Antonio, TX, (2)University of Texas at San Antonio, San Antonio, TX
The development and implementation of Prognosis Systems has the potential to significantly enhance the reliability and readiness of high-value assets, while concurrently decreasing sustainment costs. This process includes the acquisition and fusion of on-line sensor information, combined with physics-based models for damage accumulation, and higher order reasoning for decision making. This paper will summarize and demonstrate several prognosis-enabling technologies. First, an advanced fracture mechanics model, which explicitly treats crack nucleation, small crack propagation, and large crack propagation, is described. The utility of this model is demonstrated for predicting fatigue life in the presence of high stress gradients associated with beneficial surface treatments, including shot peening and low-plasticity burnishing. The development and laboratory demonstration of a novel thin-film magnetostrictive sensor for detection and monitoring crack propagation is also summarized. Results from laboratory experiments that monitored the propagation of a surface crack in a Ti-6Al-4V specimen using the thin-film sensor are used to formulate a statistical model for sensor uncertainty. This sensor uncertainty model is also combined with probabilistic simulation to assess the potential benefits of embedded sensors for on-line detection and monitoring of defects, as compared to the more traditional depot inspections. The benefits of using Bayesian statistics to fuse continual sensor inputs with life prediction models for predicting the current state of fatigue damage in fracture-critical components is also demonstrated.
Application of Real Time Engine Health Performance Prognosis for Turboshaft Engines
T. Mooney, K. Wepfer, GE Aviation, Lynn, MA
An engine performance and health monitoring system has been developed for the T700 gas turbine engine for several Army and Navy applications. The T700 system uses sensed engine and aircraft parameters with robust performance algorithms derived from engine thermodynamic models to provide an accurate and fully automated assessment of engine performance health. An on-board system calculates engine power to its first limiting condition and determines engine power at its rating point without the need for special tests or flight conditions.
Engine power at its rating point is further processed post-flight in a ground station where, in combination with information from previous flights, it is used for short and long term engine performance prognosis. Engine performance trends are matched with deterioration models so that recommendations for engine maintenance and accompanying logistics can be made in proactive, cost effective manner. Prognosis algorithms in the ground station use this information to predict remaining time-on-wing.
This paper describes a cooperative program funded by DARPA, the US Army and US Navy to develop and demonstrate a system to determine engine performance health and provide useful prognosis based on that data. The system is being developed for the H60M and H-60R/S applications.
Structural Health Monitoring of Aircraft: An Aluminum Producer's Contribution
J. C. Ehrstrom1, G. Pouget2, L. Cervi2, M. Marquette3, (1)Alcan, Voreppe, France, (2)Alcan CRV, Voreppe, France, (3)Alcan PAT, Montreuil Juigné, France
Structural Health Monitoring (SHM) is perceived as a technology that will reduce the maintenance cost and that can offer weight saving options in future aircraft structures. Different technologies are proposed, including vibration based methods, acoustic emission, vacuum monitoring, fiber optics. These are currently being tested or even implemented in aircraft structures thereby preparing a real widespread use.
Ultrasonic Sensing for Structural State Awareness of Fastener Hole Fatigue Cracks
J. E. Michaels1, T. E. Michaels1, A. C. Cobb2, (1)Georgia Institute of Technology, Atlanta, GA, (2)Southwest Research Institute, San Antonio, TX
A robust ultrasonic method for in situ monitoring of fastener hole fatigue cracks was developed as part of the DARPA Structural Integrity Prognosis System (SIPS) program. Over the four years of the SIPS program, this ultrasonic method was applied to many coupon tests as well as three full scale fatigue tests. Both the ultrasonic method and the fatigue test results are summarized in this talk. The conclusion is that this method is viable for on-aircraft use, particularly when combined with a state estimation framework that merges ultrasonic measurement results with crack growth models.
Vibration and on-Line Oil Debris Sensor Fusion for Aircraft Engine Bearing Prognosis
N. H. W. Eklund1, H. Qiu1, E. Hindle2, M. Hirz2, G. Van Der Merwe2, (1)General Electric Global Research, Niskayuna, NY, (2)General Electric Aviation, Cincinnati, OH
This paper introduces a sensor fusion approach for rolling element bearing prognostics in an aircraft engine application. Bearings are a critical component of aircraft engines, so detecting a defect as early as possible and the ability to assess damage state in real time has a profound effect on both operational safety and mission success, particularly in single-engine aircraft. The bearing prognostics problem can be divided into three sub problems, a) defect detection – the rapid and robust detection of spall, b) defect assessment – the quantitative assessment of current spall length, and c) life prediction – the estimation of spall propagation rate under a future operational scenario. The accuracy of life prediction relies on accurate defect detection and assessment, and a good understand of fault propagation physics. This paper focuses on a sensor fusion technique for defect detection and assessment. Remaining useful life prediction is covered in a separate report.
Direct Sensing of the Composite Materials Elastic Modulus
B. B. Djordjevic, Materials and Sensors Technologies, Inc., Glen Burnie, MD
Advanced composite materials mechanical properties can degrade due to range of events including aging, fatigue, lightening strike, thermal overloads and others. In situ, direct sensing of the mechanical properties change enables designer to asses the severity of damage and actual condition of the composite material. New technology has been developed for a direct sensing of the mechanical modulus of the composite structure that enables on structure estimate of the actual materials modulus. The sensing methodology and measurement methods are based on laser ultrasonic transduction and ultrasonic guided weave propagation. The plate like geometry of many composite structures readily supports guided waves that are hard to induce using conventional transducers and are not commonly used for materials condition sensing. Overall, guided wave types are better suited for larger area testing requirements but are significantly less developed than conventional ultrasonic approach. Because guided waves propagate in fiber plane, they are directly affected by the in-plane elastic constants that represent the mechanical response of the composite structure. Combined with models and advanced signal processing, this methodology enables independent nondestructive characterization and sensing of the composite material integrity damage over large range of thicknesses, and for different fiber materials (graphite, fiberglass, Kevlar). Application of laser ultrasonic is critical to achieve signal fidelity and timing measurements’ exciding resolution of about 10-9 seconds. Such high resolution measurements are required to sense materials modulus changes and are not achievable via conventional ultrasonic sensing. The paper will present experimental and application data on a variety of materials and for broad rang of applications.
Advanced Nonlinear Vibration Analysis for Next-Generation Crack Propagation Algorithms
A. Saito1, M. Castanier1, B. Epureanu1, R. Morris2, (1)University of Michigan - Ann Arbor, Ann Arbor, MI, (2)United Technologies / Pratt & Whitney, East Hartford, CT
Cracking of metallic components in complex structural systems is an important structural health consideration for a wide variety of aerospace systems. In particular, predicting crack growth is of paramount importance. The growth is dependent on amplitude and frequency of the local stresses in the structure, which are determined by the dynamics of the structure. In turn, this dynamics is affected in a complex and nonlinear way by the crack. Although the crack propagation occurs at time scales considerably slower than the time scales of the dynamics of the structure, the crack size affects the amplitude of vibration, the level of stresses in the vicinity of the crack, and the frequency of vibration. Hence, the feedback mechanism between the crack propagation and the dynamics of the structure is essential for ensuring accurate predictions of the next-generation of crack propagation algorithms. Thus, an efficient and accurate analysis framework for such structures with a crack is highly desirable.
The focus of this presentation is a novel high-fidelity approach for modeling the nonlinear effects of a crack on the dynamics of complex structures. Special attention is paid to turbomachinery rotors with a cracked blade. A key challenge addressed is that a vibrating cracked structure features a non-smooth nonlinearity caused by repetitive opening and closing, or intermittent contacts of crack faces during vibration cycles. This nonlinearity dramatically reduces the accuracy of current linear-based techniques for predicting the structural dynamics. Also, this nonlinearity affects the dynamics of the overall structure and, more importantly, significantly influences the amplitude and frequency of the stresses in the vicinity of the crack.
This presentation discusses fundamental aspects of the nonlinear dynamics of cracked structures. Also, a novel methodology for accurately predicting with very high computational efficiency the dynamics of a cracked structure and the stresses in the vicinity of a crack is presented. This methodology is based on a novel combination of finite-elements, component-mode-synthesis, and harmonic-balance-based nonlinear forced-response predictions. The analysis is demonstrated for a turbomachinery rotor with a cracked blade, and the crack effects on the system-level response are discussed. Finally, a new resonant-frequency-approximation method for turbomachinery is presented.
Automated Fatigue Test Monitoring and Damage Evolution Tracking for Prognosis in Support of Condition Based Maintenance Decisions – Part I: Fatigue Tests
N. J. Goldfine1, D. Grundy1, D. Jablonski1, V. Zilberstein2, (1)Jentek Sensors, Inc., Waltham, MA, (2)JENTEK Sensors, Inc., Waltham, MA
As part of an ongoing U.S. Navy program to enable adaptive life management of dynamic rotorcraft components, the authors have enhanced previously developed mapping and tracking capability to apply it to continuous MWM-Array monitoring of fatigue-critical regions during fatigue tests. This presentation describes the fatigue specimen design, MWM-Array sensor, in-situ scanning apparatus, and test procedure. The tests were interrupted at preselected intervals, and acetate replicas were taken to document surface-connected cracks. Examples of photomicrographs from the replicas will be presented and discussed, together with MWM-Array generated B-scans and C‑scans that are discussed in more detail in the companion presentation “Automated Fatigue Test Monitoring and Damage Evolution Tracking for Prognosis in Support of Condition Based Maintenance Decisions – Part II: Prognosis”.
Automated Fatigue Test Monitoring and Damage Evolution Tracking for Prognosis in Support of Condition Based Maintenance Decisions – Part II: Prognosis
N. J. Goldfine1, S. Denenberg1, R. Lyons1, Y. Sheiretov1, A. Washabaugh1, V. Zilberstein2, (1)Jentek Sensors, Inc., Waltham, MA, (2)JENTEK Sensors, Inc., Waltham, MA
As part of an ongoing U.S. Navy program to enable adaptive life management of dynamic rotorcraft components, the authors have demonstrated a rapid, low cost method for generating signature libraries of early and later stage fatigue damage in titanium alloys. This presentation describes generation of signature libraries as well as a new approach to generating early damage POD (probability of detection) curves using only a relatively limited number of coupon tests, e.g., two or three tests, thereby reducing the costs relative to the currently required numerous “simulated” or real crack specimens. The fatigue damage detection and tracking is executed using time sequenced B-scans and C-scans generated with the MWM-Array, i.e., using flexible eddy current sensing methods. The goal is to use these signature libraries, along with results from field inspections and component tests, to reduce NDT implementation costs and enable prognosis of damage evolution for condition based maintenance decision support. This will require early damage detection capability sufficient for dynamic component life management.
Digtial Radiography for the Aerospace Industry
C. Strong, YXLON International Inc, Akron, OH
Film X-ray inspection has been a standard NDT process for the Aerospace Industry for decades. Weaknesses of film include the time and cost to process and the difficulty to store or transmit the final images. While Digital Radiography (DR) is less time-consuming and easier to distribute, the higher quality images traditionally provided by film far out-weighed the weaknesses.
Recent advances in Digital Radiography will not only meet film image quality, but can exceed these requirements. Key considerations such as Signal to Noise Ratio, Contrast Sensitivity and Spatial Resolution must be taken into account. ASTM E2597 establishes a quantitative method to qualify digital detectors.
This presentation will cover the latest DR technologies, the underlying technology, types of panels, integration speed, and appropriate applications. We will cover the new definitions for “bad pixels” that have recently been published, and explain how to compare between manufactures.
Controlling Material State Awareness with Low Plasticity Burnishing (LPB) to Improve Component Life, Damage Tolerance, Performance and Safety
N. Jayaraman, Lambda Technologies, Cincinnati, OH
The concept of gathering information about the current material state awareness to determine the remaining life of a component is gaining acceptance among the Department of Defense. Several efforts based on this idea are under way to support the Prognostics and Health Management (PHM) of turbine engines, with varying degrees of success. These include the determination of distribution of residual stresses in the component and the use of nondestructive testing methods to detect damage in the part as a function of life cycles. However, as the fleet ages, the increasing frequency of required inspections to determine the current material state could lead to prohibitive costs, and aircraft downtime. Developing new materials or modifying component designs to improve damage tolerance is generally extremely costly. Introduction of compressive residual stresses at critical regions of the part can completely mitigate corrosion, fretting, or other damage induced failures. This technology enables the conversion of Life Limited Components (LLC) to Safe Life Components (SLC) without changing either the material or the design.
Examples of successful applications of LPB to control the material state of aircraft structure, landing gear and engine components will be discussed. The quality assurance (QA) program associated with LPB by way of closed-loop monitoring and control at every moment of the treatment process will be discussed. The QA exceeds six sigma and leads to repeatable safe and stable material state in the component. The importance of rigorous quality assurance program and the need for closed loop process monitoring and control of the compressive residual stress technologies to achieve the designed residual stresses with specific examples from LPB treatment of aircraft structural and engine components will be highlighted.
Relaxation of Shot Peened and Laser Shock Peened Residual Stresses In a Nickel-Base Superalloy
D. J. Buchanan1, R. John2, M. Shepard3, (1)University of Dayton Research Institute, Dayton, OH, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH, (3)Air Force Research Laboratory, Wright Patterson AFB, OH
Shot peening (SP) is a commonly used surface treatment that imparts compressive residual stresses into the surface of components. The shallow depth of compressive residual stresses, and the extensive plastic deformation associated with shot peening, has been overcome by modern approaches such as laser shock peening (LSP). LSP surface treatment produces compressive residual stress magnitudes that are similar to SP, that extend 4-5 times deeper, and with less plastic deformation. Retention of compressive surface residual stresses is necessary to retard initiation and growth of fatigue cracks under elevated temperature loading conditions. This presentation compares the thermal relaxation behavior of SP and LSP residual stress profiles in a powder metal nickel-base superalloy (IN100) for a range of temperatures and exposure times. Results indicate that the LSP processing retains a higher percentage of the initial (as processed) residual stress profile over that of SP.
Limitations of Eddy Current Residual Stress Profiling In Surface-Treated Engine Alloys
P. B. Nagy1, B. Abu-Nabah2, W. Hassan3, M. P. Blodgett4, (1)University of Cincinniti, Cincinnati, OH, (2)GE Aviation, Cincinnati, OH, (3)Rolls-Royce Corporation, Indianapolis, IN, (4)US Air Force Research Laboratory, Wright-Patterson AFB, OH
Recent research results indicate that eddy current conductivity measurements can be exploited for nondestructive evaluation of subsurface residual stresses in surface-treated nickel-base superalloy components. According to this approach, first the depth dependent electric conductivity profile is calculated from the measured frequency-dependent apparent eddy current conductivity spectrum. Then, the residual stress depth profile is calculated from the conductivity profile based on the piezoresistivity coefficient of the material, which is determined separately from calibration measurements using known external applied stresses. This paper presents new results that indicate that in some popular nickel-base superalloys the relationship between the electric conductivity profile and the sought residual stress depth profile is more tenuous than previously thought. In particular, it is shown that in IN718 the relationship is very sensitive to the state of precipitation hardening and could render this technique unsuitable for eddy current residual stress profiling in components of 36 HRC or harder, i.e., in most critical engine applications.
Investigation of Microstructural Effects On Electrical Resistivity
T. A. Parthasarathy1, S. Boone1, P. Wang1, S. I. Rao1, P. B. Nagy2, M. P. Blodgett3, (1)UES, Inc., Dayton, OH, (2)University of Cincinniti, Cincinnati, OH, (3)US Air Force Research Laboratory, Wright-Patterson AFB, OH
A systematic investigation is being carried out to evaluate and model the effects of chemistry, heat treatment, and plastic deformation on the electrical resistivity of an IN718 alloy, to help calibrate an eddy current methodology of measuring resisdual stresses in turbine disk components. The alloy was procured in different heat treated conditions with different hardness levels to determine the effect of prior-heat treatments. Investigation showed that the eddy current spectra of the shot-peened alloy transitions gradually from a "normal" behavior to "abnormal" behavior as hardness increases. Microstructural differences accompany this transition. To better undersand the origins of this behavior, samples from selected heat treat conditions were uniformly deformed at room temperature to different levels of cold work. These samples were then annealed for 1hr at different temperatures representing service temperature range. The attendant changes in electrical resistivity and microstructures were followed. A predictive model for the effect of microstructure on electrical resisitvity was developed. The experimental results are analyzed using the model framework to separate the relative effects of each microstructural variable on the electrical resistivity. The experimental results will be fit to analytical models (to extract unknown variables in the model) for use in calibrating eddy current methods for measuring residual stress in shot-peened or LPB treated engine parts. The status of our understanding of the mechanisms will be presented in this talk.
Hole Cold Expansion Verification and Structural Health Monitoring by Optical Strain Measurement
L. Reid1, B. Ranson2, (1)Fatigue Technology,, Seattle, WA, (2)Direct Measurements Inc, Columbia, SC
Aircraft and other structures subjected to cyclic loading are prone to developing fatigue cracks, particularly at holes, that if not detected could lead to catastrophic failure. Holes are routinely cold expanded to induce a beneficial residual stress zone around the hole, shielding it from the effect of cyclic loading. Life enhancement and/or damage tolerance benefit from the process is not taken advantage of in determination of life improvement or inspection intervals because there has been no economical method or system to verify the process was correctly applied or that the residual stress state has not changed over time. A practical method of measuring and recording the residual stress state of materials, including cold expanded holes, has recently been developed by Direct Measurements Inc. (DMI). Using innovative optically read “gauges”, similar to a bar code strategically placed around holes or at critical regions, gauge reference lengths are measured before and after cold expansion, providing a relative measure of residual stress. This reading can then be used to determine any change in the residual stress state as a result of a crack growth after a period of cyclic loading. Furthermore, monitoring of the gauge readings could be used to establish a fatigue index of the aircraft which would then be used for future life extension determination as a measure of the structural health of the specific aircraft. It would be a critical tool for ongoing life management based on individual tail number tracking. This paper will describe the philosophy behind the gauges, their application and current results associated with the hole cold expansion process as a tool for verifying correct expansion. With correct process verification design and maintenance, engineers can pre-determine what level of sustainment inspection, if any, is required. Other potential applications for structural health monitoring will also be presented.
Elastic Modulus, Electrical Conductivity and Residual Stress Variation In LSHR Turbine Disk Material
R. Martin1, S. Sathish2, (1)UDRI, Dayton, OH, (2)University of Dayton Research Institute, Dayton, OH, OH
The currently used high temperature turbine engine disks consist of two separate sections welded together. The inner section has a fine grain microstructure while the outer section has large grain sizes. The two microstructures are designed to mitigate different types of accumulated damage in the disk. The outer section is exposed to higher temperatures compared to the inner section and experience creep damage over time. To mitigate the failure due to creep damage the large grain microstructure is created. Recently new engine turbine disks have been developed with out the need for welding two separate sections. The new disks have been developed to have fine grain microstructure in the inner section and very large grain microstructure in the outer section. Instead of welding structure, the new disks have a continuously graded microstructure. The defects and damage developed during service for the currently used disks are fairly well known. In the case of new disk material, defects and the damage accumulation processes need to be investigated to develop appropriate NDE tools. In this direction, this paper presents the results of the measurement of elastic modulus, electrical conductivity and residual stress performed using traditional NDE techniques. Local variation of the properties across the microsructurally graded LSHR material were measured using different methods. The elastic modulus variations were measured using focused acoustic beam. The eddy current technique was used to measure the local electrical conductivity variations. The residual stress measurements were performed using a dedicated x-ray residual stress analyzer. The results of the three physical properties are presented and the local variations are discussed along with the microstructure variations.
Review of Progress on the Science for Sustainment Residual Stress Characterization Program
D. S. Erdahl1, J. D. Hoeffel1, D. Daniels2, M. P. Blodgett3, (1)University of Dayton, Dayton, OH, (2)Rapiscan Systems, An OSI Company, Wright-Patterson AFB, OH, (3)US Air Force Research Laboratory, Wright-Patterson AFB, OH
Surface residual stresses are induced in critical aerospace system components, such as engine disks and landing gear, in order to prevent or delay fatigue crack initiation and growth. However, the potential for allowing increased service life of these components due to the residual stresses is not being realized due to an inability to determine how much stress remains in the component after some portion of the service life has been used. Research on nondestructively measuring residual stresses in some aerospace materials has recently focused on using two methods: a highly enhanced version of traditional eddy current nondestructive testing (EC NDT) and a specialized high-energy x-ray diffraction technique. Each method measures the residual stress as a function of depth beneath the surface of the component, thus overcoming the limits of other techniques that only make surface measurements. The EC NDT technique was found to be applicable to many nickel-based alloys, commonly used in high value fighter engine turbine disks. The high-energy x-ray diffraction system has shown promise to measure residual stress in titanium disks and certain nickel-based alloy disks, which can’t be measured by the EC NDT method.
Previous research has initiated the development of both methods, but significant research tasks remain to be answered before a complete technology transition program can be implemented. The current Science for Sustainment program is targeted at advancing both of these methods by systematically measuring the effects of cold work, heat treatments and residual stress in IN718 material, working to eliminate measurement issues identified with specific material conditions. A series of specimens has been created that, when fully characterized, will allow for separation of experimental variables and more accurate measurement of residual stress profiles in aerospace materials. The presentation will cover measurements made with high-energy x-ray diffraction equipment and eddy current conductivity measurements.
Statistically Representative Digital Microstructures for Modeling Microscale Fatigue Crack Growth and Coalescence in AA7075
A. D. Rollett1, S. D. Sintay2, J. Ledonne1, J. Brockenbrough3, J. Fridy3, (1)Carnegie Mellon Univ., Pittsburgh, PA, (2)Los Alamos National Laboratory, Los Alamos, NM, (3)Alcoa, Alcoa Center, PA
Aluminum Alloy AA7075 has a high volume fraction of Al-Cu-Fe constituent particles (1.5%-2.5%). Under fatigue loading these particles will crack and nucleate fatigue cracks into the surrounding aluminum matrix. For a given region of interest many (tens to hundreds) of micro-cracks may propagate simultaneously. These micro-cracks will interact through shielding and or coalescence, which can result in discontinuous growth rates and contribute to variability in component lifetime predictions. Digital microstructure reconstructions of the alloy are utilized to simulate the process of micro-crack growth and coalescence. The synthetic digital microstructures are matched to experimental measurements of distributions of grain size, shape and particle characteristics (especially spatial correlation). In the digital microstructure a 3D volume of grains (with assigned crystallographic orientations) and constituent particles are generated and then subsequently sliced. The resulting 2D field of particles embedded in a polycrystalline matrix is allowed to nucleate fatigue cracks. Linkup events and crack size statistics are tracked as a function of cyclic loading.
Modeling the Effect of Local Microstructure on Fatigue Crack Nucleation
A. M. Maniatty1, D. J. Littlewood2, (1)Rensselaer Polytechnic Institute, Troy, NY, (2)Sandia National Laboratories, Albuquerque, NM
The effect of local microstructure on fatigue crack nucleation is investigated in an aluminum alloy 7075 by modeling polycrystals in the vicinity of cracked second phase particles. The polycrystals are analyzed using detailed, 3D finite element models. A crystal plasticity formulation that captures the behavior of the precipitation strengthened alloy is developed and implemented into a parallel finite element framework. First, the model is applied to an idealized grain containing a cracked ellipsoidal particle, and results for differently oriented grains are investigated. Several different postulated crack nucleation metrics and non-local methods for computing them in the vicinity of the crack front are compared. The evolution of the crack nucleation metrics with cycles is also studied and discussed. Models of experimentally observed grain structures are then modeled, and the crack nucleation metrics are correlated with crack nucleation data. Finally, conclusions are drawn regarding appropriate crack nucleation metrics, non-local methods for computing them, and how they might be applied for predicting the effect of microstructure on fatigue life.
Probabilistic Microstructural Model to Predict Dual Fatigue Mechanisms in AA 7050-T7451
R. V. Pulikollu, G. Krishnan, R. G. Tryon, K. Line, VEXTEC, Brentwood, TN
Most current design analysis approaches assume material homogeneity and ignores the effects of microstructure on the reliability of aluminum components. VEXTEC has developed aluminum 7050-T7451 probabilistic microstructural model to predict dual crack initiation mechanisms, distribution of cracks and the fatigue life of varying component geometries. Crack coalescence and mission modeling capability is incorporated in the model.
Unified Low Cycle Fatigue Models for Gas Turbine Engine Rotor Alloys
D. Harmon, M. McClure, Pratt & Whitney, East Hartford, CT
For many years, Pratt & Whitney (P&W) has developed and leveraged advanced analytical methods to ensure the health and safety of gas turbine engines. In the last decade, working with the Defense Advanced Research Projects Agency (DARPA) and the United States Air Force (USAF), P&W has extended these capabilities to demonstrate the accuracy of fatigue life design systems using advanced material behavior models. These models result in reduced design system scatter. This approach has been shown to provide a more accurate assessment of remaining life capability for gas turbine engine rotor structures.
Competing Failure Modes In Aerospace Alloys And the Implications for Life Management Approaches
M. J. Caton1, J. M. Larsen1, S. K. Jha2, (1)Air Force Research Laboratory, Wright-Patterson AFB, OH, (2)Universal Technology Corporation, Dayton, OH
Recent fatigue studies of numerous aerospace alloys have revealed competing failure modes under relevant loading conditions contributing to dual-fatigue lifetime distributions. It has been observed that inherent fatigue life variability is often composed of a population of life-limited specimens that experience immediate crack initiation and a population of long-life specimens that demonstrate a significant crack initiation period. The life-limited population is well described by the variability in small and long crack growth rates. Alloys demonstrating this phenomenon include Ni-base superalloys, Ti alloys, Al alloys, and gamma-TiAl. Recognizing the competition of these distinctly different mechanisms enables reduced uncertainty in life prediction methods and has significant implications for damage prognosis and life-management practices for fracture critical components. The framework for applying probabilistic life prediction methods for aerospace structures will be presented.
Cumulative Damage Modeling for Single Crystal Nickel-Based Superalloy
J. Rigney, K. Wright, D. DeCesare, J. Laflen, M. Chati, GE Aircraft Engines, Evandale, OH
High- and low-pressure turbine airfoils operating in aircraft engines experience extreme loading histories that include a combination of very high temperatures and high thermal stresses. Numerous researchers in the past have attempted to develop life prediction methods to account for the combinations of mechanisms that eventually contribute to component cracking or rupture, including creep, fatigue, and environmental mechanisms. Due to shortcomings of these models, a new physics-based cumulative damage model (CDM) and mission interrogation procedure was developed to account for a broad range of complex stress conditions and mission strain-temperature histories that can be experienced in such components. The presentation will review the literature models evaluated, the development of the CDM, and the predictive capability of the new model and methods versus complex laboratory tests.
Simulating Crack Growth Under Combined HCF/LCF Loading
P. Wawrzynek1, B. Carter1, R. Pettit2, (1)Fracture Analysis Consultants, Inc., Ithaca, NY, (2)Pratt & Whitney, East Hartford, CT
Rotating aircraft engine components are subject to transient combine high cycle and low cycle fatigue loading (HCF/LCF) as resonances are crossed during throttle excursions. Current design practice is to assume a component's fatigue life has been expended once a crack is large enough to grow under such conditions. However, such an assumption may be unrealistically conservative in a prognosis framework were a high fidelity prediction of the actual useful life is required. This paper describes a simulation capability that has been developed to model fatigue crack growth under HCF/LCF conditions. It combines the FRANC3D/NG program to adaptively modify finite element meshes to simulate crack growth and the VICTER program to perform reduced order vibratory analyses of components with cracks.
Characterizing Uncertainty in Aircraft Bearing Spall Length Estimation
H. Qiu1, F. Gruber2, M. Hirz3, N. H. W. Eklund1, (1)General Electric Global Research, Niskayuna, NY, (2)GE Aviation, Evendale, OH, (3)General Electric Aviation, Cincinnati, OH
Noise, bias, and variation in use strongly affect the output of a aircraft bearing spall length estimation system. In turn, this uncertainty in the true spall length translates to uncertainty in the remaining useful life estimation of the bearing system. This paper describes a strategy for characterizing uncertainty in the spall length estimate, and how to translate that into an estimate of variation in remaining life.
Physics-Based Model for Gear Health Prognosis
R. V. Pulikollu, R. Mcdaniels, R. Holmes, R. G. Tryon, VEXTEC, Brentwood, TN
The Helicopter Integrated Diagnostic System has achieved a documented success rate of up to 70% in detecting faults. However, despite all the improvements in failure detection, the remaining 30% of faults are not diagnosed. VEXTEC has developed a physics-based model for detection of gear faults by modeling the effects of tooth bending, contact fatigue and lubrication on gear performance. The technology involves successful modeling of the gear material microstructure and the highly localized multi-axial stresses at tooth contact. The prognostic model is demonstrated through comparison of the modeling results with gear test data.
Crack Detection and Prognosis Using Non Contact Time of Arrival Sensors for Fan and Compressor Airfoils In Gas Turbine Engines
R. Morris1, J. W. Littles1, B. Hall1, W. D. Owen1, S. Tulpule2, (1)United Technologies / Pratt & Whitney, East Hartford, CT, (2)Pratt & Whitney, East Hartford, CT
For many years Pratt & Whitney (P&W) has developed and leveraged advanced analytical methods and instrumentation technologies to ensure the health and safety of gas turbine engines. In the last decade, working with the Defense Advanced Research Projects Agency (DARPA), the United States Air Force (USAF), United States Navy (USN) and academia, P&W has extended these capabilities to enable a structural prognosis and engine health management (SPHM) system for fielded systems. SPHM is an integrated family of technologies that will allow P&W and operators of P&W products to monitor the health and remaining capability of engines based on the actual and planned future usage of each engine.
One area of significant interest to P&W and P&W customers is in the prevention of high cycle fatigue related airfoil fractures in the fan and compression systems of aircraft gas turbines. Key to that system is the integration of advanced sensors with physics-based models that capture the airfoil material behavior and structural dynamics. Key building blocks of the integrated prognosis system have been successfully developed on part bench and component spin tests, with demonstration and validation of the integrated system on full-up engine tests under the DARPA Engine Systems Prognosis (ESP) program.
Crack Detection and Prognosis Using Time of Arrival Sensors for Gas Turbine Engine Disks
L. Gray1, J. Midgley1, S. Tulpule1, J. W. Littles1, D. Harmon1, G. C. Muschlitz2, (1)Pratt & Whitney, East Hartford, CT, (2)Navy, Patuxent River, MD
For many years, Pratt & Whitney (P&W) has developed and leveraged advanced analytical methods and instrumentation technologies to ensure the health and safety of gas turbine engines. In the last decade, working with the Defense Advanced Research Projects Agency (DARPA), the United States Air Force (USAF), United States Navy (USN), and academia, P&W has extended these capabilities to enable a structural prognosis and engine health management (SPHM) system for fielded systems. SPHM is an integrated family of technologies that will allow P&W and operators of P&W products to monitor the health and remaining capability of engines based on the actual and planned future usage of each engine.
The potential safety implications and cost of a fatigue crack in gas turbine engine disks have brought significant interest to expanding rotor life prediction and management capabilities. Blade tip time of arrival sensors in combination with physics-based modeling can be used to identify and monitor the growth of fatigue cracks in disk rim features. An integrated prognosis system incorporating these technologies has been demonstrated on component spin tests under the DARPA Engine Systems Prognosis (ESP) program.
Generic and Deployable Reasoning and Prognosis Technology
G. J. Kacprzynski, L. Tang, B. Walsh, A. Palladino, Impact Technologies, LLC, Rochester, NY
While the DARPA Structural Integrity Prognosis System (SIPS) and the Engine System Prognosis (ESP) programs focus on very different application domains, both programs have a common Reasoning and Prognosis element with the same objective; to provide the best possible decision support to maintainers and operators. Though SIPS addresses aging aircraft structures and ESP life limiting gas turbine engine components, there is the common challenge of fusing sparse and imperfect data with physics-of-failure models to arrive at the most accurate estimates of remaining useful life possible. Such capability is truly game changing in that it allows critical assets to be managed on the basis of actual failure risk rather than in costly scheduled intervals. This presentation will summarize the Reasoning and Prognosis methodologies “under the hood” for both programs and provide demonstrations of the software applications that now embody them.
Application of near Real Time LCF Prognosis for Turboshaft Engines
T. Mooney, K. Wepfer, GE Aviation, Lynn, MA
Current methods to determine low cycle fatigue (LCF) damage in gas turbine engines rely on algorithms to approximate LCF usage. Current algorithms are based on combinations of operating time and/or speed counts to estimate LCF usage. Variation inherent in these approximation methods forces conservatism in the establishment of safe part and engine life limits. This conservatism limits combat readiness, reduces time-on-wing and increases operating and support costs.
GE developed an approach to accurately determine LCF usage for each part by calculating the cyclical stresses on each part after each flight. The calculation is based on measured data recorded during each flight. The data is processed through an aero-thermal engine model to calculate the parameter suite needed for the stress calculations. Direct calculation of cyclical stresses provides a more accurate determination of LCF. Furthermore, flight-to-flight evaluation of LCF provides insight useful for part, module and engine prognosis for estimating remaining time-on-wing. The improved estimate of life usage enables optimal part life entitlement, improves asset utilization and reduces the risk of overflying cyclical limits.
This paper describes a cooperative program funded by DARPA and the US Navy to develop and demonstrate a ground based system for determining LCF damage after each mission. This system is being developed for the T700-GE-401C engine in the H60R/S helicopter.
Forecasting Future Damage Based on Nonparametric Probabilistic Treatment of Aircraft Engine Usage Data
S. J. Hudak. Jr., M. P. Enright, Southwest Research Institute, San Antonio, TX
The fatigue crack growth life of military aircraft gas turbine engine components is strongly dependent on the magnitude and sequence of the applied stress values. The stress values associated with composite usages, typically modeled as deterministic variables, are useful for design purposes when little or no operational information is available. However, they are often inadequate for fleet management purposes, since mission usage and mission mixes can change over the life of the aircraft engine. Data from engine flight data recorders can be directly applied to predict the crack growth life history of a specific component. However, it is unclear how these data can be applied to the prediction of future crack growth, because values from previous flights do not address changes in future usage. In addition, the engine flight recording devices currently used in the field do not have the capability to identify the mission type, which is essential for prediction of current and future usage. In this presentation, a conceptual framework is presented for probabilistic treatment of aircraft engine usage that consists of the following three stages: (1) identification, (2) characterization, and (3) prediction. In the identification stage, a recently developed technique known as PMI (probabilistic mission identification) is used to predict the most likely mission type of each flight. In the characterization stage, probability densities associated with each mission type are quantified using an adaptive kernel approach. In the final stage (prediction), future usage is simulated based on values obtained from the mission probability densities, previous stress values, and future mission mix values from fleet management projections. An example is presented that illustrates the approach for a number of actual flight histories. The results can be applied to quantitative risk predictions of gas turbine engine components for enhanced life management, including potential life extension and associated cost savings.
Precipitation of the Omega Phase in Beta Titanium Alloys
S. Nag1, A. Devaraj1, R. Williams2, S. Rajagopalan2, R. Banerjee1, H. L. Fraser3, (1)University of North Texas, Denton, TX, (2)The Ohio State University, Columbus, OH, (3)Center for Accelerated Maturation of Materials, Columbus, OH
The omega phase is commonly observed in many commercial beta or near-beta titanium alloys on quenching from the solutionizing temperature in the single beta phase field. These omega precipitates typically have an embrittling effect on the alloy and are therefore considered detrimental for its mechanical properties. However, since omega precipitates are highly refined (nanometer scale) and homogeneously distributed, they can potentially act as heterogeneous nucleation sites for the precipitation of the equilibrium alpha phase. This leads to a homogeneous distribution of refined alpha precipitates that can substantially strengthen the alloy. Therefore, the detailed investigation of omega precipitation in the beta matrix of titanium alloys is rather important. The present study focuses on omega precipitation within the beta matrix of simple binary titanium alloys, such as Ti-Mo, as well as commercial alloys, such as Ti-5553. Quenching from beta solutionizing temperatures results in the formation of athermal omega precipitates that typically inherit the composition of the parent beta matrix. These athermal omega precipitates are formed by a displacive mechanism that transforms the structure from bcc to hexagonal. On subsequent isothermal annealing, coarsening of the omega precipitates is accompanied by the diffusional partitioning of the alloying elements. Advanced characterization techniques such as 3D atom probe (3DAP) tomography and high-resolution scanning transmission electron microscopy (HRSTEM) will be employed for determining the true atomic scale structure and chemistry changes associated with the precipitation of omega as a function of heat-treatments in these alloys.
Effect of Boron on Thermomechanical Processing of Beta Titanium Alloys
B. Cherukuri1, R. Srinivasan1, S. Tamirisakandala2, S. Roy3, S. Suwas3, (1)Wright State University, Dayton, OH, (2)FMW Composites, Bridgeport, WV, (3)Indian Institute of Science, Bangalore, India
The addition of trace amounts (~0.1wt %) of boron has been shown to significantly reduce the as-cast grain size in several common alpha, alpha+beta and near-beta alloys. This presentation will include results of a study on the effect of boron on thermomechanical processing of two metastable beta titanium alloys: Beta21S (Ti-15Mo-2.6Nb-3Al-0.2Si) and Ti-5553 (Ti-5Al-5V-5Mo-3Cr) by conducting hot compression tests at different temperatures and strain rates. Though no significant differences were observed in flow behavior between the boron-containing and boron-free alloys below the beta transus, above the beta transus flow softening was observed in boron-containing alloys, while strain hardening was observed in the boron-free alloys. Differences in the recrystallization behavior between the boron-containing and boron-free alloys were also observed above the beta transus. The presence of hard TiB particles in the boron containing alloys resulted in the formation of voids during deformation. Since the flow stress of the metallic matrix varied significantly over the deformation conditions used in this study, the nature and location of the cracks depended on strain rate, temperature and the base alloy composition. Finite element simulations were conducted to model conditions that could lead to the formation of voids during deformation.
Smart Material - Strain Recovery of Solid, Forged Blocks of Nitinol
M. Fonte1, A. Saigal2, (1)Tufts University, Medford, MA, (2)Department of Mechanical Engineering, Tufts University, Medford, MA
As the shape memory material Nitinol (55% Nickel– 45% Titanium alloy) emerges to find more and more applications in aerospace, medical and commercial industries, understanding the effects of material processing becomes increasingly important. More so than other materials, properties and shape recovery characteristics of Nitinol are significantly affected by it’s texturing during fabrication processes and subsequent heat treatment operations. Published literature is almost exclusively related to processing and testing of thin wall, smaller diameter tubing and wire devices, usually exhibiting superelastic characteristics. The mechanism of deformation is well characterized in polycrystalline NiTi shape memory alloys subjected to monotonic tensile loading conditions. However, the characteristics of deformation in polycrystalline NiTi subjected to compression deviate from the well-documented monotonic tensile response and until recently, there has been rare attempt to understand the tension/compression asymmetry for textured and untextured polycrystalline NiTi. It is well understood that Nitinol wire products are pulled and bent in tension in order to prepare and set the material for shape recovery, whereas Nitinol tubing is drawn over an inner mandrel to expand the diameter circumferentially. In both instances the material is stretched between 2%-8% to prepare and set the material for shape recovery. The motivation for this research is to provide the first characterization of the shape recovery effects of “bulk” Nitinol material under compressive deformation versus the often practiced and well understood tensile loading of wire and thin wall tubing. Compressive martensite deformation of “bulk” Nitinol can be used in the fabrication of many large devices such as actuator, springs, torque tubes, shafts, dampeners and coupling stock. To our knowledge, this work is the first to quantify the shape recovery and superelastic characteristics of Nitinol “bulk” material.
Mechanical Properties of TiB Whisker-Reinforced Titanium by Spark Plasma Sintering
H. Izui, Nihon University, Chiba, Japan
TiB whisker reinforced β21S titanium matrix composites have been fabricated by spark plasma sintering (SPS). The microstructure and morphology of the in-situ TiB whiskers in the matrix was observed by scanning electron microscopy (SEM). Mechanical properties, such as elevated-temperature tensile strengths and Young's modulus, were investigated. When the composites (TiB/β21S) were sintered at 1000 ºC with a pressure of 60 MPa for 30 min, most of TiB2 was transformed into TiB whiskers in the matrix. The composites sintered at 900ºC with a pressure of 60 MPa for 30 min had the highest tensile strength at room temperature. The tensile strength of the composites sintered by SPS is higher than those produced by vacuum arc melting. The elastic modulus of the composites increased proportionally with the TiB volume fraction. The composites show the same or higher strength of β21S sintered by SPS at less than 600 ºC.
New Patented Technology for Highly Effective Processing of Ti Alloys
G. Ostrovsky, D. S. M. Gugel, SANOVA LLC, Long Island, City, NY
Advanced alloys are being developed and tested to offer superior functional characteristics of Aerospace components. Metals such as Ti, Al and Mg are evaluated and utilized. Specifically, Ti is light, non-corrosive and structurally strong. However, excessive wear, erosion and friction of Ti surfaces due to strong metal-to-metal contact, cold welding and low hardness prohibit wider use of Ti alloys for such components as gears, shafts, axles, bearings, etc. SANOVA has developed and patented new highly advanced method for thermo-chemical processing of metal surfaces - LINTERPROCESS™ (Liquid Internal Thermo-chemical Processing) - to dramatically improve their performance characteristics, such as hardness, strength, wear, erosion and corrosion resistance. The process employs rapid physical direct heating (inductive, resistive, etc.) of metal parts in contact with specially formulated cold liquid active medium (LAM). This simple, inexpensive, safe and highly effective process creates a superior diffusion protective surface layer on various metal parts and components, achieved with gradual enhancement of chemical composition, structure and properties of metal. LINTERPROCESS™ technology is unique and brings many important benefits as compared to traditional heat treatment technologies. Specifically, SANOVA’s work with various products made from titanium alloys consistently yielded diffusion surface layer hardness of HRC 70+, achieved in just minutes of processing! Such performance breakthroughs allow significantly broader and more effective use of Ti alloys in manufacturing of lightweight highly durable and cost-effective aerospace components. SANOVA’s new powerful treatment technology is highly effective, versatile and tightly controlled. It is equally efficient in treating the entire component, or just a portion of a component. A fullyfunctional production treatment equipment prototype, created by SANOVA, greatly simplifies customization of treatment protocols and serves as base for design of custom production equipment for effective processing of many production components. Further explanation of LINTERPROCESS™ technology and production equipment, as well as examples of treatment results, are presented in this article.
“Onion Band” Surface Effects on Friction Stir Welded Titanium Alloy 6Al-4V
D. G. Sanders, The Boeing Company, Seattle, WA
A development program was performed for friction stir welding (FSW) of titanium alloy 6Al-4V to make butt welds. It was found that the top and bottom surfaces of the FSW welds are profoundly influenced by the key process parameters, which are the spindle speed (rpm), feed rate (mm/sec), the pin tool material/geometry and the amount of heat removed from the process by water cooling the pin tool. The swirling patterned “onion band” marks on the top surface of the weld joint were investigated using metallography, SEM and other methods. The marks, which are caused by the rotating shoulder of the pin tool being pressed against the surface of the part under high temperature and pressure, were found to make very sharp and deep crack-like features. Testing has shown that the “onion bands” have a profound influence on the fatigue performance of the weld joint and that this condition is aggravated by the notch sensitivity of titanium.
Processing-Microstructure-Properties Relationships in Cast Alloy Ti-5Al-5Mo-5V-3Cr
E. Y. Chen1, L. W. Weihmuller2, D. R. Bice1, G. D. Hall2, W. A. Thomas2, (1)Transition45 Technologies, Inc., Orange, CA, (2)Bell Helicopter Textron, Hurst, TX
Alloy Ti-5Al-5Mo-5V-3Cr-0.5Fe (Ti-5553) is an emerging high-strength titanium alloy with improved static mechanical properties compared with the industry workhorse alloy Ti-6Al-4V. Previous studies have shown that this material also has comparable or better fatigue properties to 4340 steel and Ti-6Al-4V, respectively, thus could be a replacement candidate for these alloys to achieve weight savings and/or enhanced durability. The ability to cast complex net shapes from a high strength titanium as this also offers the potential to save both cost and weight over traditionally forged aerospace components. This presentation highlights the latest results obtained in a Navy program to understand the effect of processing on the microstructure-properties of cast Ti-5553. Mechanical properties covered here include tensile, toughness, and fatigue behavior for microstructures achieved under different thermo-mechanical processing conditions. The results achieved to date show outstanding strength and fatigue properties relative to both wrought and cast Ti-6Al-4V. These properties will be discussed in light of potential applicability to airframe structures that have requirements for such alloys for current and next generation commercial and military systems. This work was supported by the Naval Air Warfare Center.
Surface Conditioning of Aerospace Titanium Alloys
M. Jackson1, M. Thomas1, T. Lindley2, S. Turner3, (1)University of Sheffield, Sheffield, United Kingdom, (2)Imperial College London, London, United Kingdom, (3)University of Sheffield, Rotherham, United Kingdom
The majority of aerospace titanium alloy components will be high performance machined and/or peened using laser shock or mild steel shot. Such techniques impart a high degree of surface deformation at very high strain rates. Peening, for example, is an established technique designed to impart compressive residual stresses that provide enhanced damage tolerance. However, recent work at
The effect of shot peening and high performance machining on the surface microstructure and subsequent damage tolerance for a range of titanium alloys will be presented. The deformation mechanism with regard to alpha-beta morphology and texture has been investigated using scanning electron microscopy and electron backscatter diffraction. The effect of thermal cycling during service on the oxygen diffusion kinetics has also been determined and measured using secondary ion mass spectrometry.
Thermomechanical Processing of High Strength Titanum Alloys Used In Landing Gear Forgings
M. Jackson1, N. G. Jones2, D. Dye2, R. J. Dashwood3, (1)University of Sheffield, Sheffield, United Kingdom, (2)Imperial College London, London, United Kingdom, (3)University of Warwick, Coventry, United Kingdom
High strength titanium alloys have replaced steel as the material of choice for large components, such as the main truck beam on the latest generation of airframes. The production of these components is carried out by hot near net shape forging, during which process variable control is essential to achieve the desired microstructural condition and subsequent mechanical properties. The plastic flow behaviour during forging and microstructural development of the near β alloys Ti-5Al-5Mo-5V-3Cr and Ti-10V-2Fe-3Al employed in the 777 and 787 are compared. Results indicate that newer β alloy Ti-5Al-5Mo-5V-3Cr has a shallower β approach curve, and therefore, offers a more controllable microstructure than Ti-10V-2Fe-3Al. Whilst Ti-5Al-5Mo-5V-3Cr is almost insensitive to starting microstructure, alloy Ti-10V-2Fe-3Al on the other hand exhibits intense flow softening during forging for certain starting microstructures and is extremely sensitive to processing temperature. The paper underlines the advantages of employing alloy Ti-5Al-5Mo-5V-3Cr for larger landing gear forgings.
Processing of (α/β) and (α2/γ) Titanium Alloys to Tailor Their Microstructure for Performance
G. Welsch1, J. Hausmann2, K. Baumann2, S. Lenser2, K. Kelm2, L. Chernova2, K. Weber2, S. Reh2, W. Smarsly3, (1)Case Western Reserve University, Cleveland, OH, (2)Deutsches Zentrum für Luft- und Raumfahrt, Inst, Köln, Germany, (3)MTU Aero Engines, München, Germany
An objective of processing is to shape the microstructure of a structural material to enable its performance in a finished product, e.g., by providing high strength, stiffness, and reliability. Microstructures that exhibit these properties can be formed in (α/β) as well as in (α2/γ) titanium alloys through methods which effect high degrees of refinement in composition and microstructure. The refinements concern (1) alloy homogeneity and uniformity, (2) grain- and colony size, (3) volume fraction and distribution of phases, (4) lattice misfit at phase boundaries, (5) texture, (6) residual stress, and (7) crystal defects that comprise mobile dislocations. Processing strategies are proposed for exemplar (α/β)-Ti-6Al-4V and (α2/γ)-Ti-Al alloys.
Plastic Flow and Microstructure Evolution During Low Temperature Superplasticity of Ultrafine Ti-6Al-4V Sheet Material
S. L. Semiatin1, G. A. Sargent2, (1)Air Force Research Laboratory, Wright-Patterson AFB, OH, (2)UES, Inc., Dayton, OH
The low-temperature superplastic flow behavior of two lots of ultrafine Ti-6Al-4V sheet, was established by performing tension tests, in vacuum, at temperatures of 775 and 815°C and true strain rates of 10-4 and 10-3 s-1. The as-received microstructures of the two materials comprised either equiaxed or slightly-elongated alpha particles in a beta matrix. The material with equiaxed-alpha particles exhibited flow hardening which was correlated with concurrent (dynamic) coarsening. The rate of dynamic coarsening was rationalized in terms of static coarsening measurements and the enhancement of kinetics due to pipe diffusion. By contrast, the material with initially elongated alpha particles exhibited comparable flow hardening at the lower strain rate but a complex, near-steady state behavior at the higher strain rate. These latter observations were explained on the basis of evolution of alpha-particle shape and size during straining; relatively large or small amounts of alpha-particle spheroidization and coarsening occurred at the lower and higher strain rates, respectively.
Novel Heat-Treatments for the Production of Refined Microstructures In Alpha/Beta Titanium Alloys
P. C. Collins1, J. Orsborn2, H. L. Fraser3, (1)Quad City Manufacturing Lab, Rock Island, IL, (2)The Ohio State University, Columbus, OH, (3)Center for Accelerated Maturation of Materials, Columbus, OH
High strength α/β Ti alloys often involve sub-solvus thermo-mechanical processing to effect a duplex, equaixed alpha/transformed beta, microstructure. There are, however, significant advantages to be accrued from effecting such high strengths in alloys with a microstructure consisting either of Widmanstätten alpha plates in either the colony or basketweave forms. The coarseness of the microstructural features and the significant volume fraction of allotriomorphic alpha phase precipitated along prior beta grain boundaries limit the strength that can be achieved in these alloys with these microstructures when conventionally processed, i.e., solution heat-treatment in the beta phase field followed by cooling to room temperature followed by a sub-solvus annealing/aging treatment. This paper describes a new heat-treatment process that produces a refined distribution of Widmanstätten alpha plates with minimal grain boundary alpha phase which results in very high strengths (e.g., yield strengths ≈1200MPa) in alloys such as Ti-6-4 and Ti-6-2-2-2-2. The use of far from equilibrium processing routes will also be explored.
Aeronca's Capabilities in Honeycomb Brazing of Beta 21s & Ti-6Al-4V with TiCuNi Braze Alloy
J. C. Mishurda, Aeronca, Middletown, OH
A presentation of Aeronca's capabilities in brazing honeycomb panels made of Beta 21s or Ti-6Al-4V with TiCuNi braze alloy. Topics that will be covered include furnace capabilities; braze alloy phase equilibria, melting, and diffusion zone microstructure; typical braze furnace run; typical heat treatment furnace run; resulting heat treated microstructure; mechanical property data of brazed panels; and potential applications in exhaust systems.
Ageing Response of the Beta Titanium Alloy Ti-5553 with Added Carbon
N. Wain, X. Hao, R. Aswathanarayana Swamy, M. H. Loretto, X. Wu, University of Birmingham, Birmingham, United Kingdom
Beta titanium alloys are often used for structural components in the aerospace industry due to their high strength, obtained by ageing the metastable beta phase to precipitate fine, well-dispersed alpha particles. The recently-introduced alloy Ti‑5553 shows excellent tensile properties, along with a wider available processing window than previous beta alloys such as Ti‑10‑2‑3. However, the ideal combination of high strength and high toughness is still difficult to achieve due to the tendency of the alloy to form a brittle continuous alpha phase along grain and subgrain boundaries. This investigation shows the effects of changing different aspects of the ageing process on the resultant microstructure and properties of Ti‑5553 alloys, with particular emphasis on grain boundary alpha formation. The effect of added carbon, which is known to influence grain boundary precipitation in other beta titanium alloys, is also investigated. Results show that very small additions of carbon can strongly influence alpha precipitation and the consequent age hardening response. Aspects of the ageing process such as heating rate and the introduction of an intermediate dwell are also shown to be significant.
Optimization of Canless Extrusion Product Form Properties for Aerospace Applications of Blended Elemental Powder-Based Titanium Ti-6AL-4V Alloy
S. M. El-Soudani1, K. O. (. Yu2, F. Sun2, M. Campbell3, J. Phillips3, V. S. Moxson4, V. Duz4, T. Esposito3, (1)The Boeing Company, Huntington Beach, CA, (2)RTI International Metals Inc., Niles, OH, (3)Plymouth Engineered Shapes, Hopkinsville, KY, (4)ADMA Products, Twinsburg, OH
The feasibility of canless extrusion in ambient environment using blended-elemental hydrided titanium powder, ADMA-processed by phase-blending with master alloy powder for Ti-6AL-4V composition, then direct-consolidated by cold isostatic pressing (CIP), and vacuum sintering has been demonstrated. Extensive measurements of tensile properties of such blended-elemental ADMA powder-based extrusions conforming to Ti-6AL-4V composition processed both in the beta or alpha-beta ranges of extrusion temperatures showed equivalent or superior tensile properties as compared to identically processed wrought, ingot-based and extruded Ti-6AL-4V billet materials. Additionally, in the blended-elemental powder-based extrusions both nitrogen and carbon contents were within specification limits for Ti-6AL-4V alloy, while any excessive residual hydrogen was successfully vacuum-degassed after extrusion to within AMS specification limits for Ti-6AL-4V alloy. In such extruded billets with relatively high oxygen content (2700 to 2900 ppm) the high cycle fatigue S/N properties showed equivalence with ingot-based same-product-form behavior, but with a significant reduction in fracture toughness, ASTM-E399-KIC(KQ), and stress-corrosion resistance as measured by the NACE-KISCC test. Further optimization for fracture toughness, stress-corrosion resistance, and fatigue crack growth (da/dN) properties is continuing, and will build on the encouraging static and dynamic (S/N-fatigue) results, while seeking the best overall property balance for meeting Aerospace Material Specifications (AMS). This is to be achieved by monitoring and controlling oxygen uptake during pre-extrusion powder-consolidation processing steps. Reducing oxygen content to a maximum of 2000 ppm is recommended, and will be verified for final optimized powder-based titanium Ti-6AL-4V property balance for aerospace applications.
Superplastic Formability of TIMETAL® 54M Sheets
Y. Kosaka1, P. Gudipati2, J. Fanning3, (1)Timet, Henderson, NV, (2)TIMET, Henderson, NV, (3)TIMET-R&D, Henderson, NV
Ti-5Al-4V-0.6Mo-0.4Fe alloy (Ti-54M) is a new alloy developed at TIMET. The alloy exhibits superior machinability in most of machining conditions and strength comparable to that of Ti-6Al-4V. The alloy possesses relatively lower flow stress at elevated temperatures, which is believed to be one of contributors to its superior machinability. The alloy has commercially been produced with Electron Beam Single Melt process for automotive forgings applications. Evaluations of other product forms are currently in progress targeting various applications. Since the beta transus of Ti-54M is lower than Ti-6Al-4V, and the alloy contains iron, a fast diffuser, superplasticity at lower temperature than Ti-6Al-4V is expected. This paper will introduce and discuss superplastic forming capability of Ti-54M sheets produced in a laboratory scale. Effects of strain rate, temperature and microstructure will be discussed.
Induction Heating of Titanium and Aluminum Alloys
V. Rudnev, Inductoheat Inc., Madison Heights, MI
Presentation discusses different aspects of using induction for heating titanium alloys including
Ø Induction system for heating large diameter titanium and aluminum billets prior to metal forming.
Ø Specifics of induction slug pre-heating for semi-solid processing.
Ø Induction heating of selected areas of non-ferrous parts
Ø Numerical computer modeling of induction heating of non-ferrous parts. Demonstration of the results of computer modelling of different applications and machine operation will be provided here as well.
Selective Plating on Titanium Alloys
S. Clouser1, D. Radatz1, A. Zhecheva2, (1)SIFCO Applied Surface Concepts, Independence, OH, (2)SIFCO Applied Surface Concepts, Bromsgrove, United Kingdom
The application of a coating to the surface of titanium can improve tribological properties and increase titanium’s usefulness in aerospace applications. The inherent difficulty caused by the oxide film with plating a coating onto titanium alloys was overcome by the use of a selective electroplating process. The surface of titanium 6Al-4V was subjected to electrochemical treatments to increase surface area, remove the oxide film, and immediately apply an adherent metallic coating by brush plating. The anodic pretreatment microroughened the surface while the cathodic pretreatment reduced the oxide. A nickel strike electrolyte applied directly into the anode – cathode gap to displaced the pretreatment solution while the titanium surface was maintained under cathodic potential control to prevent titanium oxides from reforming. The thin nickel strike layer was used as the substrate to buildup duplex coatings. The adhesion of the coatings to titanium 6Al-4V was verified by passing bend, chisel, heat-quench, scribe, and tape tests. The non-hydrogen embrittlement nature of the process was demonstrated by static loading at 85% yield strength without fracture. The coatings can improve the wear, galling, conductivity, and lubricity of the Ti 6-4 surface and are useful in brazing, resizing and repair applications.
Processing and Properties of TIMETAL 54M
S. Nyakana1, Y. Kosaka2, J. Fanning3, (1)TIMET, Henderson, NV, (2)Timet, Henderson, NV, (3)TIMET-R&D, Henderson, NV
TIMETAL 54M (Ti-5Al-4V-0.6Mo-0.5Fe) is an alpha-beta titanium alloy that was developed to provide a producibility benefit over Ti-6Al-4V while offering similar tensile properties. TIMET has produced over 200MT of 54M product from Electron-Beam Single-Melt (EBSM) and VAR ingots. Studies on a variety of 54M products have confirmed a machinability benefit versus Ti-6Al-4V. 54M is already being used for automotive turbocharger applications and is being evaluated for airframe and aeroengine applications. Recent work includes statistical analysis of product tensile properties, additional mechanical properties testing, and additional component manufacturing trials.
Metal Additive Process Requirements for Aerospace Applications
M. E. Kinsella, H. Sizek, Air Force Research Laboratory, Wright-Patterson AFB, OH
Additive manufacturing processes are evolving out of their rapid prototyping predecessors and finding application in various industries. Metal additive processes are being developed to the point that they are capable of meeting quality and performance requirements, even for some aerospace applications. To get to that point requires that processes can demonstrate material quality, process repeatability, and robustness through appropriate testing and the use of process controls and capable non-destructive evaluation techniques. This presentation will summarize the status of metal additive processes and discuss some key considerations for implementing them to build aerospace components.
Advanced Powder-Based Aerospace Manufacturing Concepts: Building Specialized, Complex Component Geometries Utilizing Electron Beam Melting of Ti-6Al-4V
L. E. Murr, S. M. Gaytan, M. I. Lopez, E. Martinez, F. Medina, R. B. Wicker, University of Texas at El Paso, El Paso, TX
Additive layered manufacturing (ALM) has emerged over the past two decades as rapid prototyping, solid freeform fabrication and direct digital manufacturing mostly utilizing laser beams to fabricate complex, 3-dimensional (3D) components by successively stacking selectively melted powder layers one layer at a time. More recently, electron beam melting (EBM) systems have been developed for layer-based manufacturing.
In this study, Ti-6Al-4V powder (~30 mm mean diameter) was used to build a variety of fully dense prototypes as well as complex, structural-geometrical mesh prototypes and full density-to-graded density monolithic prototypes by EBM. The mesh arrays, in particular, can have stress-directed geometrical structures which, together with dimensional variations, can produce very strong, light-weight aeronautical or aerospace components and prototypes superior to metal foams. In addition, because of the electron beam rastering speeds and configurations, the microstructures and related mechanical properties of layered manufactured prototypes can be altered or graded. Optical metallography as well as scanning and transmission electron microscopy have been used to characterize variations in alpha (hcp) and alpha-prime (hcp) martensite phase microstructures, while both Vickers microindentation (HV) and Rockwell C-scale (HRC) hardnesses have been measured for these microstructures. Solid prototypes exhibit values of HRC 35 to 45 while fine mesh prototypes exhibit values of HV 480. In addition, build defects have been characterized in relation to the development of quality control and other certification issues for these unique prototypes using optical metallography and scanning electron microscopy.
Electron Beam Melting Manufacture of Ti-6Al-4V Flight Hardware
J. R. Wooten1, P. Yavari2, C. Uwate2, (1)CalRAM, Inc, Simi Valley, CA, (2)Northrop Grumman, El Segundo, CA
Layer building technologies offer the potential to reduce cost, shorten delivery time, minimize inventory and increase design flexibility for the manufacture of functional hardware. Although these technologies have been used for several years to produce visualization models and make prototype components, the use of these processes to produce hardware that meets design requirements is just beginning to be realized. The insertion of a new technology requires a significant commitment in terms of developing a materials database to generate design data as well as being able to guarantee the quality of the material is capable of meeting these requirements. The Northrop Grumman Corporation (NGC) and CalRAM, Inc. have been exploring the potential to insert electron beam melted (EBM) Ti-6Al-4V for components that have been previously fabricated by conventional fabrication processes. This paper will describe the EBM process, present the material performance, discuss design requirements for candidate parts and show the quality requirements that are needed to insert the EBM process for the production of flight hardware. A discussion of failure modes will be included. A case study will be presented for a component, the Warm Air Mixer, for the Navy Unmanned Combat Aerial Surveillance (UCAS) which has been manufactured from EBM Ti-6Al-4V.
Design, Fabrication, and Performance of Electron Beam Melted Titanium Lattice Block Structures
D. Cormier, O. L. A. Harrysson, O. Cansizoglu, H. West, North Carolina State University, Raleigh, NC
Some Mechanical Properties and Microstructure Observations for An as-Grown Two Phase Ti6Al4V Alloy Produced Via Electron Beam Melting Free Form Fabrication
D. Cormier, R. Benson, R. Sanwald, North Carolina State University, Raleigh, NC
Effect of Free-Edges on Melt Pool Geometry and Solidification Microstructure in Beam-Based Additive Manufacturing of Ti-6Al-4V
J. Davis, N. Klingbeil, Wright State University, Dayton, OH
Both laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components, and offer significant increases in efficiency and flexibility compared to conventional manufacturing methods. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. To this end, recent work has focused on the development of simulation-based process maps for solidification cooling rate and thermal gradient (the key parameters controlling microstructure) as a function of deposition process variables (beam power and velocity). Process map results have been further plotted on solidification maps to predict trends in grain size and morphology for Ti-6Al-4V. However, these results have been limited to semi-infinite geometries, where a steady-state melt pool exits away from free-edges. The extent to which transient changes in melt pool geometry near free-edges also affect solidification microstructure is still unclear, and is the focus of the current study. Much of the authors' prior work has been based on the steady-state Rosenthal solution for a moving point heat source. In the current study, the Rosenthal solution is modified to include the effects of free-edges. This is accomplished by superposition of two point heat sources symmetrically approaching one another, with the line of symmetry representing the free-edge. The result is an exact solution for the case of temperature-independent properties, which supplements nonlinear finite element modeling currently ongoing. Dimensionless results for melt pool geometry, solidification cooling rate and thermal gradient are determined numerically with MATLAB, and plotted as a function of distance from the free-edge. Results are further plotted on solidification maps to predict trends in grain size and morphology for Ti-6Al-4V. Results suggest that melt pool geometry is more sensitive to free-edges than solidification microstructure, which is an important result for process developers.
New Developments in 3D Laser Fabrication of Titanium Components
J. W. Sears, V. Kalanovic, South Dakota School of Mines & Technology, Rapid City, SD
Laser Additive Manufacturing (LAM) titanium powder consolidation has been practiced for a number of years. The LAM technology holds great promise for repair, direct fabrication and modification of Titanium Alloy components, This technology can also provide for surface modification through alloying and physical texturing. The LAM technology has been applied to the development of a number of aerospace applications through its ability to add almost any powder material to a surface of an existing sub-structure. However, this technology as been limit by the inability of systems to operate in a true 3-D environment. The limitations have been the result of the inability to easily translate from solid models and program the system to have coordinated motion with 6 degrees of freedom and program in parameter changes at selected points. This presentation describes a new technology that allows true three-dimensional fabrication to those applications where a high resolution and tolerances are important (e.g., knife edges, seal edges, optics fixtures). This new technology, MicroLam, an adaptation of the flexible robotic environment (FRE) to LAM, is being developed to fabricate bio-medical devices under an grant from the US Army Medical Command. The MicroLam employs a six axis coordinated motion system with a higher resolution (~100 microns) than previously possible for other LAM systems. The general areas where this and the current LAM technologies will be direct includes but is not limited to:repair of complex structures, fabrication of additive shapes on existing structures; seal edges, leading edges; wear resistant surfaces containing a variety of conventional carbides, silicides, borides and novel nano-particle reinforcements; build up of functional material on wrought and cast structures; and functionally gradient transition layers.
Formation Mechanisms in Deposited Materials
S. Al-Bermani, I. Todd, Advanced Manufacturing Research Center with Boeing, Sheffield, England
Metallic materials produced by additive layer manufacturing (ALM) exhibit microstructures markedly different to those of their wrought counterparts. This is due, in large measure, to their mechanism of formation, which may differ radically from those developed by conventional processing routes. The present paper concentrates on the microstructure of Ti-6Al-4V components, developed via electron beam melting (EBM) and compares and contrasts the structures with wrought plate and laser ALM manufactured materials. Whilst wrought and cast products transform from β → α + β structures; EBM material undergoes an initial diffusionless transformation from β → α’ (hcp martensite) before decomposition/tempering of α’ → α + β; Laser deposited Ti-6Al-4V also forms the martenistic structure on cooling, but does not decompose, because of differences in build environment. In EBM this decomposition arises due to the temperature of the powder bed, maintained in excess of 650°C. Build duration and temperature determine the extent of martensite decomposition to a basket weave α + β structure whilst powder bed systems operating at low build temperatures, produce fully martensitic structures due to the lack of thermal energy necessary to decompose the martensite.
The Role of Software in the Rp&m Process
K. lenaerts, Materialise, Leuven, Belgium
The demands towards the performance, reliability and repeatability of Additive Fabrication (AF) processes (a term combining Rapid Prototyping, Rapid Manufacturing, 3D Printing and so on) have increased substantially over the past few years. In order to keep up with these demands, more advanced software systems are needed to guide the design and manufacturing process. These include among others technological software solutions to automate the work preparation steps as much as possible and to facilitate communication, (semi-)automatic and interactive planning systems, and easy traceability and quality control methods. Furthermore, AF enables series manufacturing of personalized designs, which is only possible with optimized design automation solutions.
Machines and materials both have to be reliable and of high quality to meet the expectations. However, covering the entire process from customer order until physical part(s) delivered to the customer is something out of the scope of machines and materials. It is the task of software to control the AF process and to make it fully traceable.
Effect of Local Stress On Variant Selection During Transformations In Ti-64: A Phase Field Modeling Study
Y. Wang1, R. Shi2, N. Zhou2, (1)The Ohio State University, Columbus, OH, (2)Ohio State University, Columbus, OH
The effect of local stress in a polycrystalline aggregate on variant selection during a ® b transformation in Ti-64 was investigated using quantitative 3D phase field models. The stress field in a single b phase polycrystalline sample under an external load was first calculated using a phase field microelasticity model developed for elastically anisotropic and inhomogeneous media. The local stress field was then imported into a phase field model of a ® b transformation where the effects of stress and grain boundary on variant selection during nucleation and growth of a phase were captured. The spatial distribution of different variants of the a phase was found to correlate strongly with the stress distribution in the polycrystalline sample. Under certain circumstances, certain variants may percolate through the entire sample. The work is supported by ONR under D 3-D program.
Damage Accumulation and Variability In Fatigue Behavior of An &alpha + &beta Titanium Alloy
C. J. Szczepanski1, S. K. Jha1, J. M. Larsen2, J. W. Jones3, (1)Universal Technology Corporation, Dayton, OH, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH, (3)University of Michigan, Ann Arbor, MI
Commercial interest in very high cycle fatigue (VHCF) has been spurred by the safe-life extension of components in transportation and energy production systems. In the VHCF regime, cyclic plastic strains are very low, fatigue damage is very localized, and the propensity for significant damage accumulation is highly dependent on the characteristics of local microstructures. New techniques have been developed for characterizing VHCF behavior as well as new understanding of the role of microstructure-specific fatigue damage accumulation and short/small crack growth in fatigue. In this work, ultrasonic fatigue was used to characterize the VHCF behavior of Ti-6246 and three distinct categories of crack initiation sites are observed. Examination of the initiation sites indicates that crystallographic texture suitable for basal <a>-type slip is present within these critical microstructural locations. Insights into the process of fatigue crack initiation that consider the influence of textured regions in damage accumulation will be discussed.
The Application of Bayesian Neural Network Modeling and Critical Experimentation for the Prediction of Fracture Toughness Properties In Alpha/Beta Titanium Alloys
S. K. Koduri1, V. Dixit1, P. C. Collins2, H. L. Fraser3, (1)The Ohio State University, Columbus, OH, (2)Quad City Manufacturing Lab, Rock Island, IL, (3)Center for Accelerated Maturation of Materials, Columbus, OH
The development of computational tools that permit microstructurally-based predictions for tensile and fracture toughness properties of commercially important titanium alloys is a valuable step towards the accelerated maturation of materials. Modeling tools, such as Neural Network Models based on Bayesian statistics have been used to predict the toughness of Ti-6Al-4V at room temperature. The development of such rules-based models requires the population of extensive databases containing compositional and microstructural information. These databases have been used to train and test Neural Network models. These models have been successfully used to identify the influence of individual microstructural features on the mechanical properties, consequently guiding the efforts towards development of more robust phenomenological models. The influence of the individual microstructural features on toughness have been subsequently probed using a variety of characterization techniques, including orientation microscopy and transmission electron microscopy. These results will be discussed.
Microstructural Evolution and Properties of Timetal 5553
J. Foltz1, B. Welk1, P. C. Collins2, H. L. Fraser3, (1)The Ohio State University, Columbus, OH, (2)Quad City Manufacturing Lab, Rock Island, IL, (3)Center for Accelerated Maturation of Materials, Columbus, OH
During thermo-mechanical processing of metastable β Ti alloys such as Ti-5553, a variety of phase transformations can occur, including the precipitation of α-Ti, the ω-phase, the formation of silicides and, depending upon composition, the β-Ti may phase-separate into two β-Ti solid solutions. While the size and distribution of the phases resulting from these precipitation reactions can have a significant impact upon the properties, the influence of time and temperature upon the resulting microstructure is not well understood. Indeed, detailed TTT and CCT diagrams are not available for materials and design engineers. Hence, risk-free applications of these alloys in commercial systems remain limited. Using a suite of thermomechanical simulators, the microstructural evolution of Timetal 5553 has been studied, and the importance of the β-phase separation probed. This has led not only to a preliminary TTT diagram, but also to the development of databases relating microstructure and property in this important high-strength alloy.
FSW Applied on Mid Size Aircraft
L. Fortes, Embraer, Sao Jose dos Campos - São Paulo, Brazil
The continued expansion in air transport has placed an increasing demand on the aerospace industry to manufacture aircraft at lower cost, while ensuring the products are efficient to operate, friendly to the environment and ensure that the safety requirements are met. The primary objective for the aerospace industry is to offer products that not only meet the operating criteria in terms of loads and range but also significantly reduce the direct operating costs of the airlines. Airframe manufacturers therefore continually make effort to improve aerodynamic and structural efficiency, and reduce the cost of the product and maintenance throughout its life cycle. Then, in this context, FSW enters in scene as one of the attractive options to consider mainly for the goal of cost reduction on fuselage of a mid size aircraft.
To show availability of the FSW technology on the EMBRAER products a barrel was chosen contemplating skin and stringer lap joint and skin butt joint as part of the test matrix.
The barrel article tested is a cylinder fuselage section of a mid size aircraft including eight frames. It is basically composed of available fuselage section of a mid size aircraft, with new FSW lateral panels. Each lateral panel includes 10 stringers welded to the skin, one welded butt joint between two skin parts. The barrel ends were closed with dummy steel pressure bulkheads. The design of the barrel panels is mainly concentrated on the fatigue and damage tolerance aspects.
The barrel had lasted for 5 lives of a mid size aircraft pressure cycles, without any crack, showing excellent fatigue behavior. The test showed very good performance in residual strength and crack propagation as well. The analysis and test results revealed that significant cost savings and some weight savings are possible for the metallic structure of a pressurized fuselage using FSW technology.
FSW of Ti-6Al-4V
P. Edwards, Boeing Research & Technology, Seattle, WA
Friction Stir Welding of Ti-6Al-4V was performed on 5mm thickness sheet. A wide range of processing conditions, such as spindle speed and feed rate, were tested and an experimentally determined process window was established for this given material, thickness and tooling configuration. Temperature measurements were also taken in order to determine a relationship between process parameters and workpiece temperatures. Peak temperatures measured in the weld nugget approached 1000 C, and vary depending on the weld parameters used. The process window and temperature measurements were also compared to process models. It was found that simple models can be used to predict trends such as peak temperatures and acceptable welding conditions.
Evaluation of FSW Trials Using ATI 425 Titanium Alloy at Remmele Engineering
T. Morri, Remmele Engineering Inc., New Brighton, MN
Demand for titanium alloys in the current generation of fuel efficient, high performance aircraft is projected to exceed industry capacity sometime in the next decade. Development of materials efficient processes and products will be a key factor in insuring the future affordability and availability of strategic materials like titanium. Significant progress has been reported in the development of Friction Stir Welding of titanium alloys. FSW manufacture of near-to-net shape pre-forms has the potential to dramatically improve the ratio of purchased raw material stock to aircraft fly-away weight compared with conventional methods such as machine from plate stock, effectively increasing the net stock of industry mill capacity. This paper will report the results of FSW fabrication trials performed at Remmele Engineering in
Friction Stir Welding for Aerospace Applications
J. Bernath, T. Stotler, B. Thompson, EWI, Columbus, OH
Research and Development (R&D) of Friction Stir Welding (FSW) has expanded rapidly since the inception of the technology in 1991. As the technology has matured in recent years, FSW has been of increasing interest to not only those focused on R&D but also to the manufacturing community. The technology is being readily applied to aluminum production components and developed for titanium and super alloy applications. FSW is now being investigated for a wide range of aerospace applications in both the engine and airframe industry for reasons of cost and performance. Recent advancements in the FSW for joining of aluminum, titanium, and nickel based alloys will be discussed.
Processing and Properties of Tungsten Rhenium for Friction Stir Welding Application
T. Leonhardt1, R. Johnson2, (1)Rhenium Alloys Inc., Elyria, OH, (2)The Welding Institute Technology Centre (Yorkshire) Limited, Cambridge, England
Historically, tungsten-rhenium wire has been manufactured for the thermocouple industry, but recent demands for high-temperature structural components have promoted the use of tungsten 25% rhenium in larger diameters. It has been found that high strength, increased toughness, and low erosion are critical parameters for the tooling used in friction stir welding. The tungsten 25% rhenium alloy has a melting point of 3050°C, and a recrystallization temperature near 1900°C. The tensile properties at room temperature, 1371°C, and 1926°C, will be examined in different processing conditions. These properties will be compared to the performance of friction stir welding tools.
Development and Application of Online Weld Modeling Tool for Process Optimizations
Y. P. Yang, J. Xu, S. Khurana, Edison Welding Institute, Columbus, OH
With the development of weld modeling technology and high performance computation, a web-based analysis tool (http://eweldpredictor.ewi.org/) was developed to predict temperature, microstructure, hardness, residual stress and distortion for arc welding processes. This online tool provides an engineer with easy access to advanced modeling tools over the internet to quickly explore various welding scenarios for process optimizations. By providing welding parameters, defining a weld joint, giving geometry dimensions, and specifying a material, the simulation is conducted automatically at a remotely located super computer. After calculation, a PDF report documenting the analysis results is produced for review.
This paper reveals the underlying thermal, microstructure, and mechanical model implemented in the online modeling tool and discusses several applications of the online modeling tool. The first application is to understand the effect of heat input on the resulting microstructure, residual stresses and distortion for a U-groove Ti64 butt joint. Results show that a larger heat input is likely to result in higher heat build-up, larger residual stresses and larger distortion. The second application is to calculate the cooling rates for a narrow groove X-100 steel weld. The results show that increase of preheating temperature reduces the cooling rate so that the amount of martensite and hardness in the heat-affected zone are reduced. The third application is to minimize the welding-induced distortion of aluminum alloy 6061 lap-joint.
The new development of predicting microstructure, weld residual stress, and distortion for arc welding processes will provide benefit to welding-related industries. It will help design engineers to better design welded structures and help manufacturing engineers to optimize welding processes.
The Latest Advances in Welding and Joining for Aerospace
I. D. Harris, EWI, Columbus, OH
Welding and joining has a longstanding place in the Metallics M&P arena for a wide range of products and materials including predominantly stainless steels, aluminum alloys, nickel alloys and titanium alloys. These processes, such as GTAW, PAW, and EBW are well characterized and used daily, especially within the tier supplier base. Particular advancements, especially in Yb-Fiber lasers, and other proceses such as CSC/CMT GMAW, laser weld-bonding, and novel additive manufacturing processes such as very high power ultrasonic additive manufacturing (VHP UAM) or titanium and nickel alloys offer particular advantages to cut cost and increase performance in airframe, substructure and subsystem fabrication. These novel processes will be highlighted as they impact metallic and composite structure and composite to metallic joining technologies in transition to manufacturing. The TRL and MRL positions of these technologies will be discussed and application examples will be presented. Examples range from additive manufacturing using lasers and arc welding to cut buy to fly costs on titanium forgings, to upscaling UAM capabilities from 1.5 kW to 9 kW on a 5 axis CNC workstation to produce VHP UAM capabilities. Laser weld-bonding of aircraft structure to replace fasteners and promote laminar flow in skin structure for regional jet and bizjet applications will be highlighted, and examples given of structure fabricated to date.
Pulsed GMAW Welding of Titanium with a Novel Wire
S. Pike, TWI Ltd, Cambridge, United Kingdom
The use of titanium in aerospace structures has many, well documented benefits however, the welding of quality components can be expensive due to the difficulty in welding these alloys with many processes. Historically GTAW and electron beam welding have been most prevalent and GMAW is generally not accepted within aerospace Industry.
TWI carried out welding trials using a novel wire produced by Daido Steel called G-coat. The main objective of the project was to determine if the quality concerns previously associated with GMAW welding of titanium, such as weld spatter and porosity, could be overcome.
Pulse parameters were optimised using Ti6Al4V plate and once stable conditions were established, butt welds and fillet welds were produced in 7mm thickness material and butt welds also produced in 4mm material.
Welds were analysed visually and non-destructively in accordance with AWS D17.1. It was found that the 7mm butt welds met the Class A requirements of D17.1 including internal porosity, surface appearance and no spatter was evident.
Only limited information is available concerning the surface modification of the wire however, it is thought that the improved transfer is achieved by controlling the oxide layer on the surface of the wire. This results in the surface tension of the molten titanium being reduced, facilitating droplet detachment at lower pulse energy.
The use of the G-coat wire has been shown to have benefits for GTAW welding in processes such as manual edge build up, where small droplet deposition is required and also in the Air Liquide TOPTIG™ at high deposition rates.
In conclusion TWI have found that through the use of optimised pulse parameters and a novel wire, aerospace quality GMAW welds can be produced economically and to a high standard of quality. TWI is interested in further development of the process for industrial applications.
Opportunities and Challenges for Future Welded Aerostructures
V. R. Dave, Beyond6 Sigma, Santa Fe, NM
Despite significant advances in the welding of aerostructures over the past decade and the introduction of welding into production commercial airframes, significant challenges still remain in order to achieve the full potential that welding could offer. Some of the barriers to entry for welded aerostructures include quality control challenges both real and perceived, as well as the effective incorporation of welding into the design methodology of aerostructures, i.e. designing structures to be welded as opposed to considering welding as an afterthought. Additionally, there is an intrinsic conservatism and a 50-plus year history of not making extensive use of welding.
In this talk we first review the drivers which are increasingly pushing manufacturers to seriously consider welding for components that historically have not been welded. These drivers include improved material utilisation as well as the opportunity to significantly reduce structural weight. Then the key technical issues which must be addressed to significantly expand the applications of welded aerostructures are reviewed. Many of these issues centre on quality control and effective design for welding. Lastly specific examples are shown of successful implementations as well as some applications which are still under development. For example some of these case studies include friction welding of titanium and of high strength steels, gas metal arc welding of titanium, laser welding, and electron beam processing for both welding as well as additive manufacturing. The lessons that were learned during these development activities are generalised. A guiding framework is therefore developed that if followed could streamline the design, process development, and eventual widespread production implementation of welded aerostructures.
Advanced Manufacturing Processes for the Fabrication and Repair of Aerospace Components
N. Kapustka1, I. D. Harris2, J. Bernath2, (1)Edison Welding Institute, Columbus, OH, (2)EWI, Columbus, OH
The main drivers for development/implementation of advanced welding in aerospace applications are high material cost, long lead times on materials and components, and increasing performance requirements. Increasing performance requirements have resulted in the use of some difficult-to-weld nickel-based superalloys in gas turbine engine components. These materials can be susceptible to heat affected zone and fusion zone cracking during welding for maintenance, repair, and overhaul. Cracks adjacent to rivet holes are currently repaired by reaming the hole and either replacing the rivet, gas tungsten arc plug welding or friction stir plug welding. Rivet replacement is labor intensive and does not ensure elimination of cracks. Gas tungsten arc plug welding can result in relatively high distortion while application of friction plug welding is limited by fixture accessibility – these techniques are used for repairing miss-located holes in airframe structures as well. Other than repair techniques for nickel-based superalloys, fabrication and repair methods for Ti-6-4 structural components are also needed.
This paper addresses the above challenges and provides examples of advanced welding processes that have been implemented in fabrication and repair of aerospace components. Laser powder build-ups with Rene 142, resistance hole repair techniques, repair of structural components with reciprocating wire feed gas metal arc welding, and fabrication of airframe skins and structural components with hybrid laser welding and friction stir welding are discussed.
Nanotechnology Bird Eye of View on the Effect of the Flux on Soldering and Brazing
M. R. Reda, CanadElectrochim, Saskatoon, SK, Canada
In metallurgy, flux is a substance which facilitates soldering, brazing, and welding by chemically cleaning the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing or braze-welding ferrous metals. Different fluxes, mostly based on sodium chloride, potassium chloride, and a fluoride such as sodium fluoride, are used in foundries for removing impurities from molten nonferrous metals such as aluminum, or for adding desirable trace elements such as titanium.In soldering of metals, flux serves a threefold purpose: it removes oxidation from the surfaces to be soldered, it seals out air thus preventing further oxidation, and by facilitating amalgamation improves wetting characteristics of the liquid solder. Flux is corrosive, so the parts have to be cleaned with a damp sponge or other absorbent material after soldering to prevent damage. Brazing (sometimes known as silver soldering or hard soldering) requires a much higher temperature than soft soldering, sometimes over 850 °C. As well as removing existing oxides, rapid oxidation of the metal at the elevated temperatures has to be avoided. This means that fluxes need to be more aggressive and to provide a physical barrier. Traditionally borax was used for a flux for brazing, but there are now many different fluxes available, often using active chemicals such as fluorides as well as wetting agents. Many of these chemicals are toxic and due care should be taken during their use.It is clear that the flux is specific to the type of the substrate undergoing soldering,or brazing. The objective of this publication is to try to elucidate new mechanism for the action of the flux based on the fact that the type of flux is specific to the type of substrate. The new mechanism consider Nanotechnology as new frontier which can give better understanding of the actual phenomenon which is taking place.
Development of Linear Friction Welding for the Low Cost Manufacturing of High Performance Aerospace Components
M. J. Russell1, M. E. Nunn1, N. Edge2, A. Shilton2, (1)TWI Ltd, Cambridge, United Kingdom, (2)Thompson Friction Welding Ltd., West Midlands, United Kingdom
This presentation will describe recent progress on the development of Linear Friction Welding (LFW) technology and equipment for the production of high performance aerospace components. LFW is a fast and efficient solid-phase joining process, capable of producing high quality joints, with near parent properties, in a wide range of engineering materials.
This talk will focus on the use of LFW to produce near net shape parts for aerospace components, and the development of this application towards production. A large number of metallic aerospace parts are currently machined from solid block material, or from oversize forgings, resulting in relatively poor buy-to-fly ratios. The use of near net shape parts produced by LFW can provide significant savings, both in terms of material costs and production time. Build up of parts by LFW also provides the opportunity for selection of appropriate materials/alloys in different areas of a structure, which can provide both functional and economic benefits.
This presentation will summarise recent work at TWI on the LFW of a range of demonstration components in Ti-6Al-4V, which illustrate the potential for applying this technology to the manufacture of aerospace parts. An analysis of the material savings that can be achieved will be included to highlight the benefits of the approach.
Recent developments on LFW equipment will also be presented, including an overview of the capabilities of a new 100 Tonne LFW machine, recently produced by Thompson Friction Welding in