LMM4.1

Mechanical Properties of GLARE Fiber Metal Laminates
H. Phelps, D. D. Miller, Lockheed-Martin, Marietta, GA

Fiber metal laminates (FML) consist of alternating metallic and fiber reinforced polymer composite layers. FMLs are an extension of metal bonding technology that has been used in the aerospace industry for decades. The hybrid material has significantly improved damage tolerance and impact characteristics compared to metallic or composite materials. The most advanced form of FMLs, currently in production, consist of 2024 aluminum layers with S2 glass/epoxy composite layers and are referred to as "GLAss-REinforced" aluminum or GLARE. Most of the work done with FMLs has occurred in Europe. Recently, the USAF has sponsored programs to develop the analysis methods required to apply these materials to military aircraft. The “Advanced Hybrid Structures, Core Technology Development” (AHSCTD) contracts are developing analysis methods to predict the mechanical property behavior of these materials and validating those models with mechanical property testing. This presentation will cover the interim results of model development and testing performed by Lockheed Martin Aeronautics.

LMM4.2

Optimizing the Performance and Affordability of Advanced Hybrid Structures (AHS)
E. Forster, Air Force Research Laboratory, Wright-Patterson AFB, OH

This paper may be considered for a Keynote Introduction on the three planned sessions covering:  1) FML materials, microstructures, and properties, 2) design and analytical methods, and 3) ASIP, building blocks, and applications.

Air Force Research Laboratory, Air Vehicles Directorate envisions application of advanced hybrid materials to replace problematic monolithic metal in the current veteran aircraft fleet, but also leverage advanced hybrid structures to not only maximize traditional military aircraft performance parameters, but also minimize life cycle costs. The current state-of-the-art Fiber Metal Laminate (FML) material systems have shown improved fatigue resistance, excellent impact resistance and damage tolerance, as well as resistance to corrosion and lightning strike. Currently, GLARE (GLAss REinforced aluminum) is utilized on large acreage of the upper fuselage and leading edges of the horizontal and vertical tail of the A380 commercial aircraft.  Application of GLARE, or CentrAl (Center reinforced Aluminum) as replacement parts for veteran military aircraft enhances sustainment by reducing the frequency of inspection and increasing useful structural life.  Designs that reduce life-cycle costs and minimize structural weight are desirable for future military aircraft.

This paper will address the optimal performance and affordability of advanced hybrid structures.  Consideration of hybrid material properties will include a basic comparison to monolithic aluminum metal (elastic modulus and corresponding density), but also will investigate the performance of structural properties essential for part replacement.  Design of a replacement structure will meet form/fit/function, but also take advantage of higher dynamic stress levels due to the slow crack growth characteristic of the material and provide trade space opportunities between performance and sustainment.  The complexities involved in the design of such aircraft structures will require formal design optimization, likely crossing preliminary and detailed design.  Lastly, the advanced hybrid structure must address all technology challenges for the disciplined transition to a flight structure, managing risk and providing a life cycle cost benefit to the end-user.  As an overview on these topics, this paper will provide an introduction to these sessions of the Aeromat conference, specifically calling out other Keynote presenter accomplishments in each session topic area.

LMM2.6

Aerospace Applications of Aluminum-Lithium Alloy Thick Plate
K. M. B. Taminger¹, S. J. Hales², (1)NASA Langley Research Center, Hampton, VA, (2)NASA, Hampton, VA

Acceptance of aluminum-lithium (Al-Li) alloys for aerospace applications has become more widespread following the emergence of commercially-viable product in the 1990’s.  The structural weight reduction and stiffness enhancement afforded by these alloys has resulted in cost savings which outstrip the premiums associated with material production and certification.  Current generation Al-Li alloys are available in a variety of wrought forms including, but not limited to, sheet, plate, forgings and extrusions.  Examples of commercial alloy applications include 2098 & 2297 (Lockheed Martin), 2196 (Airbus) and 2099 (Boeing & Airbus).  Alloy development has become more refined, and processing technology has evolved, such that compositions tend to be tailored to specific product form.  During potential application, specific (density-compensated) property improvements are addressed, but the issues of commercial availability and certification often remain.  Therefore, the synergy between materials and structures engineers has become imperative during an era of budget constraints.  A relevant example is the desire to utilize Al-Li alloy plate up to 5 inches thick for cryogenic tank and dry bay structures on future launch vehicles.  The incumbent plate alloy is 2195, but alloy 2050 may prove to be a better choice for plate gages greater than 2 inches.  The metallurgical issues relating to alloy selection in this particular application will be outlined in this presentation.  The correlation of alloy composition/processing with microstructural characteristics and orientation-dependent mechanical properties will be discussed.

LMM4.4

Multifunctional, Lightweight, Low-Cost Composite Structures for Missile Applications
J. K. Roberts, A. T. Owens, K. A. Spencer, U.S. Army Aviation and Missile Research Development and Engineering Center, Huntsville, AL

Carbon fiber reinforced polymer composites are finding increasing application in Army aviation and missile systems due to their high specific strength and superior insensitive munitions performance as compared to conventional metallic structures. However, some functions inherent to metals are compromised when polymer composites are integrated.  The Aviation and Missile Research, Development and Engineering Center is conducting research to improve the thermal and electrical conductivity of polymer composite materials for missile applications.  Alternate materials and processes have been evaluated based on performance, cost and ease of processing.  The goal of the research is to provide options to missile designers for improved thermal and electrical conductivity along with a data set that can be used for material selection trade studies.

LMM4.5

New High Strength Al-Li Extruded and Forged Structural Elements
E. Colvin¹, L. Yocum², D. Bush³, R. J. Rioja⁴, (1)Alcoa Forgings and Extrusions, Lafayette, IN, (2)Alcoa Engineered Products, Lafayette, IN, (3)Alcoa Forged Products, Cleveland, OH, (4)Alcoa, Inc., Alcoa Center, PA

Alcoa Forgings and Extrusions has developed and is introducing a new Al-Li alloy, designated C99N, with strength, toughness, fatigue and corrosion combinations exceeding previously available Li-containing products.  The alloy is intended for high strength extrusion and forging applications to compete with advanced 7xxx alloys with improved resistance to SCC and exfoliation and significantly lower density and higher modulus of elasticity.  The new alloy can save weight and improve durability of structures such as compression-dominated stringers and web-rib forgings.  Alcoa is generating extrusion design allowables and has developed a set of preliminary forging properties.

LMM4.6

Multicontinuum Technology for Hybrid and Textile Composites
R. S. Fertig III¹, M. R. Garnich², J. A. Schultz², D. Robbins¹, (1)Firehole Technologies, Laramie, WY, (2)University of Wyoming, Laramie, WY

We report recent developments in multicontinuum theory (MCT) focused on multiscale material models that enable the simulation of progressive failure of structures composed of hybrid or textile reinforced composite materials. Recent accomplishments include: a) a demonstration that the constituent average stress states that are obtained using MCT provide superior correlation with initial failure events observed in a triaxial braid composite, and b) numerical demonstration that the MCT decomposition process can be pragmatically extended from a simple unidirectional fiber-reinforced composite material to a plain weave composite material. These results indicate the value and efficacy of extending MCT to more complex composite micro/meso-scale materials. Ongoing efforts are enabling general application of MCT for structural-level finite element progressive failure modeling that will allow the designer to more fully exploit the unique characteristics of complex composite materials.

Session 5: Characterization of Light Materials

LMM5.1

Cyclic Stress-Strain and Strain-Life Data for Aerospace Materials
A. Brown¹, A. C. Quilter², S. Walker², (1)IHS, Stockholm, Sweden, (2)IHS, London, United Kingdom

Local strain-based fatigue analysis has been in use since the 1970s, its applications being initially rooted  in the military aircraft and automotive industries of the US where much of the developmental work was based.  The technique tracks conditions of local stress and strain at a notch root and in order to estimate life two sets of data are required for each material - cyclic stress-strain data and strain-life data.  Most of the large number of data initially produced are held privately by industry, and relatively few data have entered the public domain.  The technique is now widely accepted throughout the aerospace industry, yet the extent of published data, whilst increasing, remains limited and much of the testing continues to be done on a private basis.  In many cases this can involve duplicating tests carried out by another company on the same material.

ESDU began work in 2006 on the collection and collation of raw cyclic stress-strain and strain-life data points for aerospace metallic materials.  Beside the data available in the literature and other readily-accessible sources, efforts were made to encourage organisations with their own data to contribute to a database from which they would then benefit.  Considerable support and enthusiasm were expressed for this project and generous donations of data were received from a number of companies.  The ESDU Data Item containing the data is nearing completion and will be issued shortly.

LMM5.2

Fatigue Crack Propagation in a New Generation Al-Cu-Li Alloy
S. RICHARD, C. SARRAZIN-BAUDOUX, J. PETIT, P. VILLECHAISE, Laboratoire de Mécanique et de Physique des Matériaux, ENSMA, Chasseneuil du Poitou, France

In view of reducing the fuel consumption, low-density third generation aluminum‑lithium alloys are good candidates for substituting to conventional aluminum alloys widely used in the aeronautical industry. However, for in-service application, a better knowledge of their damage tolerance properties is required. To contribute in answering this question, a study of fatigue crack growth behavior of a 2050 new aluminium-lithium alloy in T8 temper was undertaken. Fatigue crack propagation tests were performed at 35Hz on CT specimens W=50mm and 6mm thick. Constant amplitude loading tests were performed with a load ratio of 0.1 and 0.7. Crack closure was systematically evaluated by mean of a strain gauge stuck at the back face of the specimens. The stress intensity factor level for crack opening, K_op, was detected by mean of the compliance method. Both the mid DK regime and near-threshold domain were explored. The influence of microstructure associated to the T8 temper and of the specimen texture on fatigue crack growth at constant amplitude loading is discussed on the basis of EBSD identification of slip planes orientation along the crack path. The discussion is particularly focussed on the deviation in the crack path in ambient air from the reference propagation plane for stage II crack, which is normal to the loading axis. Reference tests run in high vacuum (P<3e^-4 Pa) clearly show the existence of a substantial influence of ambient air on the propagation crack path, and hence, on the propagation mechanisms. These results are discussed on the basis of an existing framework modelling. Variable amplitude loading tests in ambient air, consisting in blocks of 1000 constant amplitude loadings in similar condition as above plus a 70% overload, were also performed to evaluate the applicability of the PREFFAS model, for industrial application.

LMM5.3

Effect of Microstructure and Anodizing On the Fatigue Performance of a Large 2219 Aluminum Forging
W. Wentland, J. Y. Yung, J. York, Hamilton Sundstrand, Rockford, IL

Pressure testing of a thick section 2219 aluminum forging resulted in cracking at one of the internal bores.  An examination of the crack revealed that the part failed in fatigue.  Fatigue had occurred due to extensive attack at the surface from the anodizing treatment.  An investigation took place in order to improve the homogeneity and microstructure of the material in order to lessen the surface attack of the anodizing treatment.  This presentation will show the steps taken to improve the material microstructure and reduce the fatigue debit associated with the surface treatments.  Axial fatigue testing was carried out in order to validate the material properties in line with the new heat treatment steps.  Test data for the thick section forging will be shared.

Main Program

Materials for High Temperature Applications (including metals, refractories, metal-matrix composites, ceramics, ceramic matrix composites and high temperature coatings)

Session 1: Ceramic Matrix Composites and Ultrahigh Temperature Ceramics

HTA1.1

Elevated Temperature Time-Dependent Mechanical Properties of Ceramic Matrix Composites
G. Morscher, University of Akron, Akron, OH

Woven SiC fiber-reinforced, SiC matrix matrix composite are being pursued for hot section components of gas turbine engines. Considerable work has been done to determine and understand the time-temperature-stress-environment dependent properties of these composites. In this presentation, an overview of elevated temperature creep rupture properties will be presented for select SiC/SiC composites tested in air and in vacuum. The composites discussed will include those reinforced with polycrystalline SiC fiber-types and considered to be some of the most creep-resistant CMCs available. The physical mechanisms which lead to failure will be highlighted as well as initial attempts to model life. In addition, approaches to improve creep-rupture properties will be discussed. 

HTA1.2

CMC Combustor Demonstration in a Small Helicopter Engine
D. C. Jarmon¹, T. Bhatia¹, J. Shi¹, S. Kearney¹, A. Kojovic², A. Prociw², J. Hu², (1)United Technologies Research Center, E. Hartford, CT, (2)Pratt & Whitney Canada, Mississauga, ON, Canada

Silicon-based ceramics are attractive materials for use in gas turbine engine hot sections due to their high temperature mechanical and physical properties as well as lower density than metals.   Ceramic matrix composite (CMC) hot section components offers the potential elimination of the film cooling to provide reduced emissions and increased durability.  The high temperature capability of a CMC combustor is expected to increase the life of the combustor while enabling the elimination of film cooling and a reduction of combustor cooling.  In addition, the profile of the combustion gas entering the turbine is predicted to improve which will increase the life of turbine components.  Further improvements in the CO, NOx and smoke emissions are projected.

UTRC and P&W Canada partnered to demonstrate an advanced combustor configuration that was enabled by high temperature CMC materials, in a PW200 series combustor.  The PW200 series have reverse flow combustors and the program presented significant challenges in design and fabrication.  The advanced CMC configuration was successfully tested in a PW206 combustor rig.  At full power, a 40-50% reduction in pattern factor relative to the bill-of-material metal combustor was measured.  The combustor exit plane temperatures were generally better mixed due to the combined effects of (1) eliminating the cold film layers near the combustor walls and (2) the increase in fuel injector count enabled by the increase in dilution air.  The CMC combustor was also successfully tested in an engine configuration.  Post test gas path surfaces of the EBC coated CMC combustor components were in good condition.

HTA1.3

Cohesive Zone Finite Element Modeling of Delamination Initiation and Propagation in Ceramic Matrix Composites
R. S. Kumar, G. S. Welsh, P. F. Croteau, United Technologies Research Center, East Hartford, CT

Delaminations may initiate and propagate in two-dimensional ceramic matrix composites (CMC) when they are subjected to multiaxial stress states. Such stress states may arise as a result of the applied loading and/or due to complex features within the CMC components such as matrix-rich regions, ply curvature, and notches. An effective way to model delaminations is to use a cohesive zone methodology. In this methodology potential interfaces where delaminations may occur are modeled explicitly using either cohesive finite elements or contact-based cohesive surfaces. The initiation and propagation of delamination is controlled by the traction-separation constitutive response of the cohesive zone that characterizes the interface fracture behavior.

In this work the cohesive zone approach is used to study the initiation and propagation of delamination in various test coupons and sub-elements made from a 2D woven CMC. The results from the finite element simulations are compared with the experimental results where available. A parametric study is conducted to understand the effect of variation in cohesive material properties on the delamination initiation and growth and the overall response of the sub-elements.

HTA1.4

Foreign Object Damage in SiC/SiC and Oxide/Oxide Ceramic Matrix Composites
D. Faucett, D. J. Alexander, S. R. Choi, NAVAIR, Patuxent River, MD

Foreign object damage (FOD) of two different ceramic matrix composites (CMCs), MI SiC/SiC and oxide/oxide (N720/A), was assessed via impact testing at ambient temperature using impact velocities ranging from 100 to 400 m/s by 1.59-mm diameter steel ball projectiles.  Two different support systems of targets, full support and partial support, were employed for each of the CMCs.  The extent of impact damage as well as post-impact strength degradation of both CMCs increased with increasing impact velocity, and were greater in partial support then in full support, attributed to the additional backside tensile stress field in partial support.  The degree of relative post-impact strength degradation of the oxide/oxide composite was similar to that of the MI SiC/SiC composite.  Both of the CMCs were able to survive high energy (~1.3J) impacts without complete structural failure, which is in a notable contrast with gas-turbine monolithic silicon nitrides.  Impact damage morphology and response to static indentation by projectiles were also determined and will be discussed in terms of impact modeling.

HTA1.5

Carbon/Carbon Composites and the Design and Process Effect On the Mechanical Properties
L. O. Vatamanu, NanoVAT Inc. and ITT Technical Institute, Lakewood, OH

The influience of the design preform have been investigated. The fibers/matrix compatibility, the infiltation proces of the woven preform, the type of carbon architecture preform, and the carbonization and graphitization process have been analyzed. The morphology of the C/C/C and the mechanical properties and the coating process with SiC are presented in this this research paper.

HTA1.6

Thermomechanical Properties of Heat Treated ZrB2-SiC Composites with WC Additions
E. W. Neuman, G. E. Hilmas, W. G. Fahrenholtz, Missouri University of Science and Technology, Rolla, MO

Mechanical properties of hot pressed, heat treated zirconium diboride – silicon carbide (ZrB₂-SiC) composites were tested at room temperature and at elevated temperatures.ZrB₂-SiC composites, containing 20-30 vol% SiC as a dispersed particulate phase and up to 4mol%WC additions, were hotpressed to near full density at 1900°C under an applied pressure of 32MPa in a flowing argon atmosphere.  The hotpressed billets were machined to ASTM standard test bars with the tensile surface polished to 1um. The test bars were heat treated at temperatures up to 1800°C for times up to 24 hours in an argon atmosphere. Young’s modulus, Vickers’ hardness, fracture toughness (chevron notch), and four-point bend strength were measured for the heat treated samples. Four-point bend tests, and fracture toughness from room temperature to 1800°C were performed in an air atmosphere. The influence of microstructure on the mechanical properties will be discussed.

Session 2: Advances in High Temperature Alloys For Aerospace Applications

HTA2.1

Effect of Thermo-Mechanical Processes On ATI718 Plus Contoured Rings
O. Covarrubias, Frisa Aerospace SA de CV, Santa Catarina, Mexico

ATI 718plus® is a nickel-base superalloy designed to promote excellent resistance and thermal stability at elevated temperatures. Beside these properties, this material presents superior formability during forging operations, making ATI 718plus® a suitable material for the manufacture of non-rotating and rotating jet engine components.
Ring rolling process for the production of seamless rings is the natural option for the manufacture of superior aerospace components, increasing material resistance and reducing input weight. Use of contoured shapes on such components simplifies and improves manufacturing processes, reducing machining touch time and, in some cases, eliminating welding operations.
Present document summarizes main results when several contoured rings are produced by ring-rolling processes, considering parameters as temperature and deformation ratios. Effect of solution and hardening precipitation heat treatments on ATI 718plus® microstructure and mechanical properties are also reported. These results include tensile testing at room temperature and elevated temperature, hardness and stress-rupture testing. Microstructural evaluations were performed by optical microscopy and electronic microscopy.

HTA2.2

Microstructural and Environmental Effects On the Mechanical Behaviour of Allvac® 718Plus®
S. M. Oppenheimer¹, R. Kearsey², J. Tsang², P. Au², E. T. McDevitt¹, (1)ATI Allvac, Monroe, USA, NC, (2)National Research Council of Canada, Institute for Aerospace Research, Ottawa, ON, Canada

Four microstructural variants of 718Plus^® are produced via modified heat treatments to elucidate the effects of grain size, precipitate size, morphology, and phase fraction (δ and γ'), on the mechanical properties of low cycle fatigue (LCF) life, fatigue crack growth rate (FCGR) properties, and creep-fatigue crack growth rate (CFCGR) behaviour at both 650ºC and 704ºC under 100s dwell and no dwell conditions. Similar testing is also performed on Waspaloy in two comparative microstructural conditions. FCGR results show that at both test temperatures, all microstructural conditions of 718Plus^® and Waspaloy exhibit identical behavior in the steady state regime, except that 718Plus^® exhibits a much higher threshold stress intensity (ΔK_TH). However, the CFCGR results show that Waspaloy displays better steady state crack growth resistance under dwell conditions, with an optimized precipitate microstructure of 718Plus^® showing considerable improvement. Environmental effects are also investigated by performing FCGR and CFCGR tests in both air and high vacuum conditions. LCF test results, with and without 100s dwell, demonstrate that all four microstructural conditions of 718Plus^® have superior life compared to Waspaloy under all test temperatures and total strain ranges investigated.

HTA2.3

Direct Metal Laser Sintering (DMLS) of Heat Resistant Nickel Alloys
T. Syvänen, EOS Electro Optical Systems Finland Oy, Turku, Finland

Direct Metal Laser Sintering (DMLS) is an additive laser melting technology that can be used for manufacturing functional metal components and tools in various alloys including light metal alloys, high grade steels, stainless steels and super alloys – both nickel and cobalt chrome based.
This presentation will review the latest results of the materials development work done with EOSINT M270 laser sintering machine. The main topic of the presentation will be in heat resistant nickel alloys but a short status update will be given also on other available DMLS-materials.
Several DMLS-processed nickel alloys have been investigated and characterized in the recent years. EOS NickelAlloy IN718 (UNS N07718) and IN625 (UNS N06625) have been the first ones developed and optimised for the DMLS-process. Material characterization and testing has proven that properties of these laser processed alloys are close to the wrought specifications of similar alloys. The microstructure quality, soundness and special characteristic of the laser processed alloys will be discussed.
These current generation DMLS-materials, EOS NickelAlloy IN625 and IN718, will show the potential and the viability of the technology in aerospace applications in the near future. It is possible that modern nickel superalloys, which have even higher temperature resistance and other improved characteristics, will open even more possibilities for this technology in the coming years.

HTA2.4

Improved Superalloy Grinding Performance with Novel CBN Crystals
S. Kompella, K. Zhang, G. Ruland, Diamond Innovations, Columbus, OH

The retention of key mechanical properties by nickel-based superalloys at high operating temperatures makes them suitable for use in aircraft engines, petrochemical industries, and premium automotive exhaust applications. However, superalloys are difficult to grind materials: prone to thermal damage with associated high tool wear. In addition, the adherence of grinding debris to the wheel necessitates frequent process interruptions to re-profile the wheels with a diamond dressing roll. Ensuring adequate thermal management during grinding by way of a sharp, thermally conductive abrasive is important. Cubic boron nitride (CBN), with its high hardness and thermal conductivity, coupled with a vitrified bond system, is ideally suited for superalloy grinding. Even so, the high specific energy in superalloy grinding can cause dulling of the CBN crystals with potential detrimental effects on workpiece microstructure and properties.

Superalloy grinding efficiencies can be improved by maintaining CBN crystal sharpness or by reducing the grinding cycle time while ensuring negligible thermal damage in the part. In this paper, in creep-feed grinding of Inconel-718, we compare the wheel wear and workpiece attributes when using currently available CBN crystals against two newly developed CBN crystals. The new CBN crystals enable a reduction in wheel dressing frequency by over 60% compared to that with standard CBN at the same material removal rates (Q’). The specific energy with the new CBN crystals is also lower by about 20%. Finally, the new CBN crystals also lend themselves to grinding at 33% higher Q’ without inducing workpiece damage; the higher Q’, though, is accompanied by a higher wheel wear than at standard Q’. We compare the physical properties and shape characteristics of the new CBN crystals with standard crystals and speculate on possible mechanisms that enable both the slower grinding wheel wear and the improved cutting efficiency.

EMP3.2

Additive Manufacturing of Gamma Titanium Aluminide Parts
M. Svensson¹, U. Ackelid¹, S. Sabbadini², O. Tassa³, (1)Arcam AB, Mölndal, Sweden, (2)Avio S.p.A, Rivalta Torino, Italy, (3)Centro Sviluppo Materiali S.p.A, Roma, Italy

Electron Beam Melting (EBM) has become an established manufacturing technology for fully dense metal parts with excellent material properties. The parts are built in a vacuum chamber by additive consolidation of thin layers of metal powder. EBM opens up new degrees of freedom in design of complex 3D geometries, e.g. fine network structures, internal cavities and channels. With its production like environment it delivers full traceability from ingot to the final part and do comply with the industrial driven standards for both medical and aerospace applications. The process is particularly attractive for:
i)                    reactive metals, e.g. titanium alloys, which are safely processed without risk of contamination
ii)                  expensive materials, because the powder waste is negligible
iii)                materials which are difficult to fabricate or shape into full density with conventional methods, e.g. hard or brittle materials.
The EBM technology will be described in detail, with focus on mechanical and chemical properties at elevated temperatures for heat treated gamma titanium aluminide. This intermetallic compound has a strong potential for aerospace applications due to its low density and high strength at high temperatures, but its use has previously been hampered by the available fabrication methods.

HTA2.6

High Thermal Conductive Tool Steels for Part Quality Improvement in Permanent Mold and Die Castings of Light Alloys
A. Hamasaiid¹, B. Casas¹, S. Molas², D. Casellas², I. Valls¹, (1)ROVALMA, S.A., Terrassa, Spain, (2)CTM- Technological Centre, Manresa, Spain

This work deals with a series (HTCS^(R)) of  new tool steels,  recently developed and patented by Rovalma, S. A. Company, for the application in permanent mold and die casting of light alloys. HTCS^(R) posses a high thermal conductivity (58-62 W/mK), which is at least two times larger than this of conventional H11 and H13 tools steels, and remarkable mechanical properties. The high die thermal conductivity enhances the effective thermal conductivity and the thermal conductance at the casting-die interface. Hence the heat transfer is higher during solidification of the casting in a HTCS die. Higher heat transfer rate results in finer microstructure of solidified castings and superior part properties such as tensile strength and percentage elongation. Higher heat transfer improves also the die liftime as the extraction of heat from the casting is faster, the  die surface temperature is lower and the die cooling system is more efficient during the first stage of contact between molten alloy and die surfaces. A large experimental investigations are currently carried out,  using alternately H11 and HTCS ^(R) for the die material, on gravity and high pressure die casting of Al-Si alloys. The obtained microstructure, mechanical properties of the castings along with the heat transfer during thier solidification are closely studied for the two cases .

Session 3: Advances in High Temperature Alloys II

HTA3.1

Advanced Gamma-Titanium Aluminide with Improved Ductility and Tensile Strength
L. O. Vatamanu¹, A. Sherman², (1)NanoVAT Inc. and ITT Technical Institute, Lakewood, OH, (2)Powdermet Inc., Euclid, OH

This reseach paper demonstrated an innovative manufacturing technique to produce a strengthened niobium, vanadium alloyed gamma-titanium aluminide with impoved room temperatue ductility and fracture oxidation resistance. Controlled nanoengineered microencapsulated composite structures by powder metallurgy processing route have been investigated.  FBCVD coating and HIP processes allowed major improvement for these intermetalllic microstructures for high temperature application in aerospace industry as turbine engines, airframe structures and thermal protection systems.  Effect of variables as deposition cycles, precursors feeding  rate, carrier gas and helium feed rate, weight of the CVD Bed,  particle size, deposition temperature, coating thickness on Nb and V coatings have been studyed. Have been analyzed also the morphology, density, surface area, particle size and microstructure of the TiAl/Nb composite components and the mechanical properties. The project demostrated that the proposed approach is a technically and economically feasable route to improve the gamma Ti-Al.

HTA3.2

Metal Matrix Composites Applied by Selective Brush Plating
S. Clouser, H. Xiao, SIFCO Applied Surface Concepts, Independence, OH

Metal matrix composites were deposited onto the surface of steel and titanium alloys by selective brush plating.  The adhesion of the composites to the substrates was measured using standard tests.  The use of a brush plated nickel interlayer between the substrate and composite coating was found to have a substantial effect on adhesion.  The composites examined include chromium carbide in a cobalt metal matrix also applied by brush plating.  The concentration of carbide in the matrix was varied between 10% and 50% by weight by controlling the deposition conditions.  The particle distribution uniformity throughout the composite was examined by optical cross-section.  The effect of the brush plated Co-Cr₃C₂ composite on the surface properties of wear and high temperature oxidation resistance was measured using Taber wear tests and baking up to 800°C in air.  The stability of the Co-Cr₃C₂ composite was examined through hardness measurement after exposure to a series of temperatures up 800°C.

HTA3.3

Novel Processing Approaches for Advanced Thermal / Environmental Barrier Coatings
D. D. Hass, S. Eustis, Directed Vapor Technologies International, Charlottesville, VA

Lightweight silicon-based ceramics are leading candidates to replace heavier nickel-based superalloys for use on hot section components in next generation gas turbine engines having increased specific power.  However, exposures of these materials to the high temperatures, pressures and velocities of water vapor containing combustion environments alter the effectiveness of thermally grown silica scales in protecting the ceramic components from oxidation and component recession during service. To limit this drawback, environmental barrier coatings (EBCs) are required that protect the underlying ceramic substrate from environmental attack. Such coatings require good stability in the presence of water vapor, a mechanism for limiting the transport of oxygen and water vapor to the ceramic substrate, good chemical compatibility at the interface of unlike materials, high temperature phase stability to limit volume changes resulting from phase transformations in the coating materials and the ability to provide thermal and erosion protection. The ongoing drive to promote higher temperature protection and prime reliant performance of these systems has led to interest in advanced thermal/environmental barrier coating (T/EBC) systems having enhanced performance over current state-of-the-art T/EBC systems (based on silicon / mullite + barium strontium aluminosilicate (BSAS) / BSAS). In this work, novel coating synthesis techniques that enable the deposition of multilayered T/EBC’s anticipated to have higher temperature capability and improved durability over of current systems have been investigated. The effect of processing variables on the microstructure of T/EBC layers will be discussed, along with the effect of coating composition, microstructure and architecture on the performance of T/EBC systems in high temperature, water vapor containing environments.

HTA3.5

Developments in the Manufacturing of Reaction Cured Glass Coatings for the Orion Backshell Thermal Protection System
C. M. Larson, S. H. Wallace, C. C. Kammerer, United Space Alliance, LLC, Cape Canaveral, FL

The Reaction Cured Glass (RCG) coating that is used on Space Shuttle High Temperature Re-useable Surface Insulation (HRSI) tile is comprised primarily of borosilicate glass frit, which provides an impermeable barrier to hot gas flow during earth re-entry. United Space Alliance, LLC (USA) has developed a process to produce borosilicate glass frit for this coating, and is currently exploring ways to improve the technology. The manufacturing process outlined in U.S. Patent 4,093,771, Reaction Cured Glass and Glass Coatings allows for considerable variation in coating appearance and properties. The current study aims to more tightly control the coating properties through manipulation of the manufacturing process. Several test coatings have been fabricated using experimental frit material, and preliminary results have indicated strong relationships between process parameters and coating properties. A summary of these results, along with a prospectus of future work, will be discussed.

HTA3.6

Comparative High Temperature Oxidation Behaviour of Ni-20Cr Coating Deposited by High-Velocity-Oxy-Fuel and Detonation Gun Spray Techniques
G. kaushal¹, H. S. Saheet², S. Prakash³, (1)RIMT-Institute of Engineering & Technology, Mandi Gobindgarh, India, (2)Indian Institute of Technology Ropar, Roopnagar, India, (3)Indian Institute of Technology, Roorkee, India, Roorkee, India

In this study, High velocity oxy fuel (HVOF) spray and Detonation gun (D-Gun) spray techniques were used to deposit Ni-20Cr coatings on a commonly used boiler steel ASTM SA213-T-22. The specimens with and without coatings were subjected to cyclic oxidation testing at an elevated temperature of 900°C to ascertain their oxidation behaviours. Mass change data  was recorded to formulate the kinetics of oxidation for the specimens. The exposed specimens were characterized by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The uncoated sample suffered intensive spallation and mass gain. It was observed that the oxidation rate was appreciably reduced in terms of mass gain after the application of the both thermal sprayed Ni-20 Cr coatings .The HVOF spray Ni-20Crcoating showed a better oxidation resistance in comparison with the D-gun spray Ni-20Cr coating.

Model Development and Implementation for Materials, Process and Residual Stress

Session 1: Advances in Materials Modeling

MDE1.1

Fast-Acting Property Models for the Transient Constitutive Properties of Superalloys
R. Dutton¹, R. Goetz², T. A. Parthasarathy³, S. L. Semiatin¹, (1)Air Force Research Laboratory, Wright-Patterson AFB, OH, (2)Rolls-Royce Corporation, Indianapolis, OH, (3)UES, Inc., Dayton, OH

Current alloy design or improvement efforts are typically based on the designer’s need for uniform increases in one or more mechanical properties, even though these properties may not be needed everywhere throughout a disk. Designers are now considering the use of dual microstructure turbine disks to obtain optimum local properties while minimizing component weight.  State-of-the-art dual microstructure disks utilize sophisticated tooling and furnace temperature profiles to tailor the mechanical properties of the rim and bore of the disk.  The build-up of residual stresses during heat treatment and subsequent relaxation following heat treatment are difficult to assess using intuition, engineering judgment, or empirical methods. Subtle changes in processing conditions and component geometry can significantly affect the magnitude and pattern of residual stresses.  The rapid cooling required to control microstructure evolution generates large temperature gradients and hence thermal stresses leading to the development of residual stresses which in turn can lead to in-process cracking, distortion during machining  and/or a reduced service life. While on-cooling tensile tests attempt to capture this microstructural effect it is unlikely that the resulting data fully covers the range of thermal history present within and between components, particularly given the highly non-linear nature of precipitation and its influence on flow stress.  Consequently, the further development of location-specific property technologies will require fast-acting validated modeling tools which can accurately and relatively easily provide constitutive properties for standard industry modeling packages such as DEFORM. To that end, we present results from the development of fast-acting property models to predict transient constitutive properties during quenching operations.

MDE1.2

Recent Advances in Modeling Methodologies towards Achieving Integrated Computational Materials Engineering
R. Shankar, A. Bandar, W. T. Wu, Scientific Forming Technologies Corporation, Columbus, OH

Integrating process simulations with location specific microstructure modeling to predict part performance is a key component of Integrated Computational Materials engineering (ICME). This presentation focuses on the recent developments in modeling methodologies specifically addressing topics related to microstructure modeling, property response and process optimization. Improving computational efficiency will play a significant role in achieving ICME and this presentation will highlight some of the key needs in this area.

MDE1.4

Corrosion: Acquisition and Sustainment Life Cycle Management During the Development of Aircraft Programs
D. Ellicks, W. Barfield, Air Force Corrosion Prevention and Control Office (AFCPCO), Robins AFB, GA

Corrosion is a significant cost, readiness, and safety driver for the U.S. Air Force (USAF) and for the U.S. Department of Defense as a whole. The Air Force spent $5.4 billion on corrosion-related actions as determined in the 2009 Cost of Corrosion Report which is about one-third of its total aircraft and missile maintenance costs.  Corrosion is one key area that is often forgotten during acquisition and sustainment life cycle management during the development of aircraft and support equipment programs.  In fact too often, corrosion is an afterthought until problems start to arise in aircraft availability (Ao).   This paradigm does not support the Systems Lifecycle Integrity Management (SLIM). 

Air Force Policy Directive 63-1 “Acquisition and Sustainment Life Cycle Management” points out that “all programs shall consider corrosion implications.”    Even Congress understands the importance of corrosion mitigation with various publications such as DoDI 5000.67 “Prevention and Mitigation of Corrosion on DoD Military Equipment and Infrastructure.”  It is vital for corrosion to be included in SLIM during the planning stages of  SLIM Policies & Guidance and Acquisition Guidance & Templates stages as outlined in SLIM Timeline Long Term for FY 2010 and FY 2011.

 It is for these reasons that engineering must engage corrosion prevention and control during the acquisition phases.  Corrosion mitigation and repair results in increased cost and significant reduction of Ao.  Results have shown that programs who address corrosion initially have huge savings in life cycle and mission readiness.

MDE1.3

Advanced Metallic Rib Solutions for Composite Wing Box: Joint Study by Aleris and Bombardier
R. De Rijck¹, B. mulvihill², L. Marcel¹, G. Moore², M. Miermeister³, (1)Corus Research Development & Technology, IJmuiden, Netherlands, (2)Bombardier Aerospace - Shorts, Belfast, Northern Ireland, (3)Aleris Aluminum Koblenz GmbH, Koblenz, Germany

In the frame of customer (Bombardier) supplier (Aleris) cooperation a support project was initiated. Within the cooperation Aleris performed an optimisation study into a structural metallic rib component in a composite wing torque box. A topological optimisation, using the Altair Optistruct Software, has been identified to serve as a tool to show a potential weight saving based on both the topology and sizing of the rib. Parallel to study performed by Aleris/CRD&T Bombardier used their own methods to reach a solution for an optimised wing rib. Both solutions take into account any manufacturing preferences on minimum gauge, machining tolerances etc. The objectives of the project are to achieve a low weight and low cost solution for a metallic rib in a composite torque box. The stepped approach to achieve the objective is built-up of several phases. Phase 1 is using the topology software in combination with the boundary conditions, e.g. respective load cases etc. to asses the most optimum geometry (closed web, truss or combination) Second Phase will then focus on the influence of different materials on the solution. Starting with the baseline material being 7475-T7351 and two alloys suggested for by Aleris 7081-T7651 and a corrosion resistant alloy 5059-H136. 7081-T7651 offers improved static and fatigue properties over the baseline material and 5059-H136 offers low cost and low density benefits. The result of the activities is an optimised I-beam truss design for a metallic rib, each design fulfils the design criteria for limit stress, machining tolerances etc. The low weight solution is based on 7081-T7651, 7475-T7351 is a second solution with the 5059-H136 being the last in line. All three designs provide a weight saving over the traditional closed web solution.

Session 2: Application Of Modeling and Simulation To Residual Stresses I

MDE2.1

Modeling of Part Distortion in Components Machined From Plates and Forgings
A. Rakshit, T. Marusich, S. Usui, C. Arthur, 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 that takes into account the pre-machined bulk stress state and machining-induced stresses for monolithic parts. Sources of stresses include heat treatment, quenching, forging, cold working and machining operations. A customized solid model representation of the initial workpiece geometry is developed, and bulk stresses are mapped onto the solid model. Computer numerical control (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. Challenges and approaches for accurate and timely simulation are discussed.

MDE2.2

Distortion Modeling of Airframe Components
J. B. Castle, The Boeing Company, Saint Louis, MO

Structural airframe design is driving to maximize structural unitization.  This enables appreciable cost, weight savings, and improved buy-to-fly in large structural components.  However, as parts become larger and more unitized the demands imposed on the design and manufacturing process increases.  While it may be feasible to compensate for distortion during assembly of many small parts, large unitized structure lacks the degrees of freedom to compensate and is less forgiving of distortion.  Distortion can be caused by material bulk stresses resulting from processing operations and/or by local near-surface machining induced stresses.  Typically additional machining operations and setups are added in a time-consuming and costly approach to minimize the effects of part distortion.  There is a need to understand the effects of materials processing and machining on distortion and to predict, minimize, and control these distortions.  This presentation will review progress that has been made on the machining modeling side to relate material and machining process to distortion in airframe parts. 

MDE2.3

Computational Design Tool for Residual Stress Surface Treatments
M. R. Hill¹, A. T. DeWald², (1)University of California, Davis, CA, (2)Hill Engineering, LLC, McClellan, CA

The field of residual stress engineering is rapidly evolving, due in large part to investment by DoD aircraft programs under USAF, NAVAIR, and Army Aviation sponsorship. The current state of the art for implementing residual stress surface treatments focuses on a set of empirical steps and process trials that have significant cost and duration. Software design tools represent a clear path towards reducing empirical efforts, potentially saving upfront costs and reducing the threshold for use of residual stress. The presentation provides an overview of a new methodology for surface treatment engineering and a summary of recent validation experiments focused on the use of laser shock peening on turbine engine airfoils. A computational model will be described that provides an efficient means for predicting the full-field residual stress distribution in surface treated, geometrically complex parts. The model enables trades among residual stress treatment processes, including the effects of process parameters and treated area. Ultimately, the model provides a tool that can enable broader adoption of residual stress treatments by reducing risk, cost, and time to market currently associated with their use.

MDE2.4

Advanced Software for Integrated Probabilistic Damage Tolerance Analysis Including Residual Stress Effects
R. C. McClung¹, M. P. Enright¹, Y. D. Lee¹, W. Liang¹, S. H. K. Fitch², (1)Southwest Research Institute, San Antonio, TX, (2)Mustard Seed Software, Charlottesville, VA

New analysis methods and software tools are being developed for improved accuracy and efficiency in performing damage tolerance analyses of critical aerospace components.  This presentation provides an overview of recent advances that automate and streamline the process of fracture mechanics (FM) model development and life analysis, including direct integration of finite element (FE) models that simulate the manufacturing process and the service usage.  Stress analysis results from the FE models are directly incorporated into the life analysis through a powerful graphical user interface.  Residual stresses can be included in this analysis, including bulk residual stresses arising from forging and heat treating as well as localized residual stresses from peening or other surface engineering processes.  The effect of these residual stresses on fatigue crack growth life and component reliability can be automatically computed using algorithms that include advanced weight function stress intensity factor solutions to accommodate arbitrary stress gradients accurately.  A novel scheme has been developed that automatically determines (without user input) the orientation, size, and stress input for a FM model that will produce accurate life results, given only a 2D model of the crack plane and an initial crack location, and taking into account the actual component boundaries and stress fields.  This capability is then exercised to construct life contours that visualize the fatigue life response over an entire component.  The life calculation capabilities are combined with probabilistic descriptions of key input variables and tailored probabilistic methods to calculate the probability of fracture of the component.  Long-range goals include performing this reliability calculation in a similar automated fashion with minimal user intervention, as well as optimizing the manufacturing and inspection plans through the integrated software system in order to maximize the reliability.

MDE2.5

The Prediction of Fatigue Crack Propagation in a Friction Stir Welded Specimen Containing a Residual Stress Distribution
S. W. Smith¹, J. A. Newman¹, B. R. Seshadri², W. M. Johnston³, (1)NASA Langley Research Center, Hampton, VA, (2)National Institute of Aerospace, Hampton, VA, (3)Lockheed Martin, Hampton, VA

An on-line compliance-based method for the measurement of the component of residual stress normal to a growing fatigue crack has been evaluated.  Results from this crack-compliance method for specimens containing a friction stir weld are presented, and found to be in excellent agreement with residual stress data obtained using the cut-compliance method.  Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress contribution, can be used to determine the local crack-tip stress-intensity factor.  Finite element and J-integral analyses have been developed to predict weld-induced residual stress using thermal expansion/contraction and an equivalent ΔT for the welding process.  An equivalent ΔT was established and applied to an analysis for all specimen geometries investigated to yield predicted residual stress distributions in very good agreement with experimental results obtained using the crack and cut-compliance methods.  Results from 3D finite element analyses for the propagation of a crack in components containing friction stir welds will be presented and compared to experimental observations.

Variability of Bulk Residual Stress Predictions as a Result of Critical Heat Treatment Parameters and Control
M. G. Glavicic, Rolls-Royce Corporation, Indianapolis, IN

Bulk residual stresses that develop during the final cooling of a forging pre-determines whether a component will be distortion free during machining or be inherently problematic to machine.  A review of development efforts aimed at the sources of bulk residual stresses have identified several critical parameters which control the variability in the final bulk residual stresses.  The sensitivity of these parameters on final residual stresses will be presented. 

Session 3: Application Of Modeling and Simulation To Residual Stresses II

MDE3.1

Toward Understanding the Impact of Bulk Residual Stress On the Life, Weight and Cost of Primary Aircraft Structure
D. L. Ball¹, B. K. Tom¹, R. J. Bucci², M. A. James², (1)Lockheed Martin Aeronautics Company, Fort Worth, TX, (2)Alcoa, Inc., Alcoa Center, PA

A variety of advanced material / structural concepts are being developed by, or with the support of airframe manufacturers who are in pursuit of enhanced performance at reduced cost.  One of the more promising concepts, and one that has already been adopted for a number of high profile applications, is the unitization / integration of multiple, machined and subsequently assembled parts, into a single monolithic component.  When this is done with large monolithic forgings, the presence of bulk residual stresses must be addressed during design.

This presentation will describe methods for the explicit inclusion of bulk residual stresses in design analysis (specifically in fatigue life analysis).  The life versus weight optimization that this inclusion enables will be described for several aircraft bulkheads.  Finally, current results from ongoing weight and cost impact studies will be presented.

MDE3.2

An Integrated R&D Roadmap for Residual Stress Management in Large Structural Forgings
M. A. James¹, J. D. Watton¹, R. J. Bucci¹, D. L. Ball², J. B. Castle³, (1)Alcoa, Inc., Alcoa Center, PA, (2)Lockheed Martin Aeronautics Company, Fort Worth, TX, (3)The Boeing Company, Saint Louis, MO

For more than a decade, the authors’ companies have been advancing their respective visions for residual stress and machining distortion management in large, three-dimensional components.  During that time, substantial progress has been made towards solving a myriad of complex technical challenges.  Recently, under the Metals  Affordability Initiative, the Air Force provided opportunity for stakeholder companies to join forces in an integrated planning effort to outline a technology roadmap.  The process affirmed that more than ever, knowledge of residual stress influences on design/manufacturing processes is essential to both assure conservatism and maximize performance.  Furthermore, expanded supply chain integration is necessary to realize the full range of end-product benefits.  This presentation summarizes the ongoing effort to develop the roadmap and execute the vision.

MDE3.3

Computational Modeling and Optimization of Residual Stress for Large Structural Forgings
J. D. Watton, Alcoa, Inc., Alcoa Center, PA

In line with Alcoa's goal of manufacturing forgings with consistently low residual stress Alcoa has developed in-house and integrated commercial finite-element tools to model first the heat treatment quench induced residual stress and second the practice of cold work stress relief of large aluminum (alloys 7050 and 7085) aerospace forgings. We will highlight the state-of-the-art tools with examples of how they have been used to improve and optimize quench and cold work stress relief practice. In addition, Alcoa's modeling tools are used to give guidance on the bulk residual stress contribution to machining distortion. We will also acknowledge our validation work that compares measured and modeled residual stress components. Finally, we discuss the limitations of the computational modeling tools and our future direction.

Session 4: Application Of Modeling and Simulation To Residual Stresses III

MDE4.1

Residual Stress Relaxation under Uniform and Gradient Applied Stresses
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.

MDE4.2

Engineering Measurement of Bulk Residual Stress Distributions in Thick-Section Components
M. R. Hill¹, A. T. DeWald², (1)University of California, Davis, CA, (2)Hill Engineering, LLC, McClellan, CA

Prediction of the fatigue and fracture performance of large, monolithic components depends on knowledge of the bulk residual stresses that they contain. The contour method is a new way to measure bulk residual stress fields that provides data useful for forecasting fatigue and fracture performance, and it can be applied to thick-section parts. Relying on simple assumptions and straightforward experimental procedures, the method provides the two-dimensional spatial distribution of residual stress normal to a plane of interest within the component. When the method is applied at sections with high failure risk, the measured residual stress field may be used directly with standard methods for predicting fatigue crack initiation and growth. The presentation provides a summary of the experimental details of the contour method and examples of its application. The paper further demonstrates the use of residual stress measurement data for correlating the fatigue and fracture performance of residual stress bearing test articles.

MDE4.3

Application of Peening Surface Residual Stresses for Durability and Damage Tolerance Improvements in Wing Attachment Lugs
R. J. Weiss¹, J. Bunch², (1)Boeing, Auburn, WA, (2)Boeing, Seattle, WA

Engineered residual stresses have long been utilized to enhance the fatigue properties of metallic components.  The Boeing Company has conducted an investigation  to establish a calculable life benefit of engineered residual stresses for applications to titanium structural components.  Both glass bead peening and laser shock peening were selected for this investigation.  Recent work has focused on both optimizing laser shock peening for complex titanium hardware as well as performing sub-component testing to define the fatigue improvements available from both peening methods.
      A scale-up method based on the ASIP building block approach was used in the laser shock peening optimization work.  Residual stresses were measured on small test blocks, representative geometry blocks, sub-component test articles, and full-scale test articles.  The criteria for selection, residual stress data, as well as the chosen laser shock peening parameters will be discussed.  Both laser shock peening as well as glass bead peening were applied to sub-component test articles and cycled through a typical wing up-bending flight spectrum.  Durability and damage tolerance benefits from both laser shock and glass bead peening have been calculated and will be discussed.

Superplastic Forming (SPF), Superplasticity in Advanced Materials and SPF/Diffusion Bonding

Session 1: Superplastic Forming Materials & Processes I

SSF1.1

Superplastic Forming and Superplastic Forming and Diffusion Bonding of Fine Grain Titanium 6Al-4V for Producing Aerospace Hardware
L. D. Hefti, The Boeing Company, Seattle, WA

In the past, if you wanted a fine grain alpha-beta titanium material capable of Superplastic Forming (SPF) at temperatures lower than about 900°C, you were limited to the SP700 alloy that had been developed by NKK Corporation, now JFE Steel Corporation, in Japan.  The most widely used standard grain titanium alloy is 6Al-4V, which has a grain size of about 8 µm, and this material is typically formed at around 900°C.  Verknaya Salda Metallurgical Production Association (VSMPO) in Russia has developed a fine grain version of the 6Al-4V alloy, with a grain size of about 1 µm, which is able to be superplastically formed at around 775°C.   Since this material diffusion bonds to itself as well as standard grain size alpha-beta titanium alloys at this temperature, Superplastically Formed and Diffusion Bonded (SPF/DB) hardware can be produced.  There are several advantages to using this lower forming temperature including a smaller amount of alpha case is developed on parts so there is less to remove, longer press platen and heater life, and less oxidation of the tool surface.  In order to take advantage of these improvements, this material is currently being used in the production of SPF and SPF/DB aerospace components.

SSF1.2

Effects of Interfacial Friction Distribution On the Superplastic Forming of AA5083
M. I. Albakri¹, F. Jarrar², M. Nazzal³, M. K. Khraisheh¹, (1)Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates, (2)University of Jordan, Amman, Jordan, (3)German-Jordanian University, Amman, Jordan

This paper studies the effects of the interfacial friction distribution on the integrity of superplastic formed parts. For that purpose, the deformation of an AA5083 superplastic aluminum alloy into a long rectangular box is investigated. The die surface is divided into five regions for local application of constant friction coefficients. The commercial finite element code (Abaqus) is used to carry out the forming simulations and calculate the thickness distribution, forming time and forming pressure profile for different combinations of friction coefficients. It was found that the friction distribution at the die-sheet interface strongly affects the metal flow during the forming process. This is a key factor that can be controlled and optimized so as to enhance parts integrity and prevent localized thinning.

SSF1.3

Where,When and How to Utilize Superplastic Materials and Superplastic Forming Technology for Optimum Results
A. J. Barnes, H. Raman, Superform USA, Riverside, CA

Although superplasticity in metals has engaged the interest of scientists, metallurgists and engineers for more than forty years it is only in the last ten years that it’s full potential has begun to be realized. 

This presentation examines the key factors that are needed for potential applications to succeed. These include: market and service conditions,material selection, part design and accurate process simulation. Integration of SPF’s forming capabilities into achieving optimal design, in terms of: functionality, part count, weight, integrity, durability and overall manufacturing costs are also examined and illustrated by ‘successful’ application examples.

Session 2: Superplastic Forming Materials & Processes II

SSF2.1

Utilizing Centrifugal Cast Mandrels for DB and Hot Sizing Applications
G. E. Gapinski, MetalTek International, Waukesha, WI

Abstract:

Manufactures have reported increased tool life and improved dimensional stability with centrifugal cast mandrals. This paper will review the alloy selection options available with centrifugal cast mandrals and discuss how machining and heat treating practice have been found to influence dimensional stability.

SSF2.2

Advanced Fabrication of Titanium Alloys
J. Monsees, Hi-Tech, El Cajon, CA

This title has been submitted as a placeholder by John Fanning based on a verbal discussion with the author. Title is tentative and abstract is tbd.

SSF2.3

The Benefits of Selective Gauge Reduction Prior to Superplastic Forming
J. B. Brewer, R. Hedrick III, Ducommun AeroStructures Incorporated, Parsons, KS

Ducommun AeroStructures has refined a process in which selectively reducing the gauge thickness of titanium, prior to superplastic forming (SPF), can aid in a more consistent product. This gauge reduction is utilized to control thinning and to provide a more uniform thickness product. Other benefits of selectively reducing the thickness prior to SPF are blank size reduction and tooling size reduction. When forming over a mandrel style die, the distance between the seal and the mandrel may be substantial to allow for acceptable thinning. With selective gauge reduction prior to SPF, this distance can be reduced. This process forces the reduced section to elongate at a faster rate which allows the thicker material to stay more uniform through the final forming process. By creating specific gauge reduced patterns, this process can yield more and/or less thinning where required. This provides a more consistent product for the customer. As indicated previously, this process will allow for the tooling to be created with a smaller footprint. This equates to less tooling material required to produce the same product, which in turn equates to a more affordable process.

Session 3: Superplastic Forming Materials & Processes III

SSF3.1

SPF Characteristics of Fine Grain TIMETAL^®54M Sheets
P. Gudipati, D. Y. Kosaka, TIMET, 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. In the previous conference (AeroMat 2009), SPF (Superplastic Forming) properties of Ti-54M sheets were presented. A total elongation exceeding 500% was observed at temperatures between 1400ºF (760°C) and 1600ºF (871°C) at a strain rate of 10^-3/S. Steady stress-strain curves in tensile tests, indicating the occurrence of grain boundary sliding, were observed at temperatures between 1400ºF (760ºC) and 1550ºF (843ºC) at a strain rate of 5x10^-4/S. It is well understood that primary alpha grain size is the most influential factors that enable SPF behavior at lower temperatures and higher strain rates. An attempt was made to produce ultra-fine grain (UFG) Ti-54M sheets in a laboratory scale. SPF properties of the sheets were evaluated in accordance with ASTM 2448-06. The sheets exhibited SPF behavior at the temperatures as low as 1300°F (704°C) at a strain rate of 5x10^-4/S. This paper will discuss SPF capability of fine grain Ti-54M sheets compared with regular grain Ti-54M and Ti-64. The effects of strain rate, temperature and microstructure on flow behaviors and m-values, as well as micro structural development during SPF tensile tests will be presented and discussed.

SSF3.2

Superplastic Forming Technologies and Implementation at Boeing Over the Past 25 Years
D. G. Sanders, L. D. Hefti, The Boeing Company, Seattle, WA

This paper examines the strategy devised for implementing superplastic forming (SPF) at Boeing from its early history to the present day.  Titanium and aluminum part fabrication is discussed, along with examples of how built up assemblies have been converted to monolithic designs.  The most recently developed technology that combines SPF with friction stir welding of titanium for tailor shaped blanks is presented. 

SSF3.3

Finite Element Simulations of a Hybrid Forming Process: Combined Deep Drawing and Superplastic Forming
M. A. Nazzal¹, F. Abu-Farha², (1)German Jordanian University, Amman, Jordan, (2)Penn State University/Erie, Erie, PA

It is well established that superplastic forming is limited to low volume production, due to the low deformation rates associated with superplastic deformation. In this work, finite element simulations of a hybrid forming technology that combines superplastic forming with deep drawing are presented. This hybrid process aims at obtaining complex light weight structures without sacrificing the production rate. A two dimensional finite element model is used to simulate the process. The forming process consists of two steps. In the first step, the sheet is drawn into the die, to a preselected level, using a mechanical punch. Thereafter, pressurized gas is applied at a controlled rate in order to force the sheet to acquire the intricate die details. Different aspects of this hybrid process are studied in this paper like the forming time, final thickness distribution and wrinkling possibilities. The ratio between the deformation caused by the first step and that caused by the second step will be varied to investigate its influence on the forming process. The overall objective is to construct deformation maps that describe the optimum forming scheme which guarantees the shortest forming time and best component integrity.

Session 4: Superplastic Forming Materials & Processes IV

SSF4.1

Effects of Hydrostatic Pressure On Superplastic Deformation Stability
M. A. Nazzal¹, F. Jarrar², F. Abu-Farha³, (1)German Jordanian University, Amman, Jordan, (2)University of Jordan, Amman, Jordan, (3)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 stability analyses are carried out to study the effects of hydrostatic pressure on the superplastic deformation process. The finite element analysis is based on a three dimensional model, that utilizes 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. The effect of hydrostatic pressure on the limiting strains is emphasized through an analytical stability model. Cavitation evolution paths are generated for uniaxial and biaxial loading conditions.   

SSF4.2

On the Formability of 5083 Aluminium Alloy Sheets at Elevated Temperatures by Pneumatic Stretching
F. Abu-Farha¹, L. Hector², M. Nazzal³, (1)Penn State University/Erie, Erie, PA, (2)General Motors R&D Center, Warren, MI, (3)German-Jordanian University, Amman, Jordan

With the ever-growing interest in lightweight alloy sheets for potential applications in the transportation sector, the need for accurate forming limit diagrams (FLD’s) at higher-than-ambient temperatures is becoming a necessity, since these materials are typically formed at elevated temperatures. Unhappily, mechanical stretching tests, such as the ones according to the Marciniak and Nakazima methods, are generally limited to warm forming temperatures (~350 ºC). Pneumatic stretching, on the other hand, has the advantage of being applicable to much higher temperatures, in addition to eliminating possible friction influences. In this work, the latter approach is utilised to construct the forming limit curves for the AA5083 alloy at temperatures as high as 550 ºC. Such formability maps will be instrumental in understanding the material behaviour, and hence optimising actual superplastic and quick plastic forming practices.

Titanium Alloys and Processing Technologies

Session 1: Titanium Metallurgy I

TAL1.1

Titanium Alloy Development Needs for Commercial Airframes: An Update
J. D. Cotton, R. R. Boyer, G. R. Weber, K. T. Slattery, The Boeing Company, Seattle, WA

There is increasing pressure on the aircraft industry to reduce both manufacturing and operating costs. The former occurs in the form of pressure to reduce component and material costs; the latter in the form of reduced maintenance costs and aircraft weight. Weight and cost are thus interrelated, and sometimes at odds, in the design process.

Titanium is historically utilized in airframes to solve specific problems related to high temperatures, specific strength or corrosion. For graphite-reinforced composite airframe structures, the natural compatibility of titanium has lead to an increase in the fraction of titanium alloys on the airframe, but with concordant increases in build costs. Titanium is galvanically compatible with the graphite in the graphite-reinforced composite, and the coefficient of thermal expansion of titanium is closer to graphite than to aluminum or steel. This has lead to an evolution in the needs of the airframe industry with respect to titanium alloy properties and utilization.

This paper will provide an overview of cost reduction opportunities, typical airframe applications and design drivers for titanium alloys. The purpose of this paper is to relate these needs to the titanium industry so that better alloy development solutions and improved processing methods can be conceived and offered.

TAL1.2

The Development of An Advanced Titanium Metal Matrix Composite Material for Aerospace Applications
J. R. Silk¹, J. Panter², S. Gourdet³, (1)Aerospace Metal Composites Ltd., Farnborough, United Kingdom, (2)Eurocopter, Marignane Cedex, France, (3)EADS France, Suresnes Cedex, France

This presentation will summarise the mechanical properties and microstructure of a Ti-3Al-2.5V alloy reinforced with 10% titanium boride particulate. The increased availability of titanium alloy powders in combination with recent developments in the Powder Metallurgy manufacturing process have led to the production of a stiff, fatigue resistant and ductile material that shows significant property benefits over conventional titanium alloys, such as Ti-10V-2Fe-3Al. The likely influence of the titanium boride particulate on density and wear characteristics will also be discussed. Secondary processing routes such as extrusion and forging will be reviewed to demonstrate the potential opportunity for cost-effective manufacturing of final components through near-net-shape processing.

TAL1.3

On the Emergence of An Integrated Titanium Processing Facility
P. C. Collins¹, J. W. Sears², (1)Quad City Manufacturing Lab, Rock Island, IL, (2)South Dakota School of Mines & Technology, Rapid City, SD

The Quad City Manufacturing Lab, a 501(c)3 organization, has as a mandate not only for the development and maturation of state-of-the-art manufacturing technologies but also their transition to regional partners, specifically Rock Island Arsenal (RIA). Importantly, the activities of QCML under this program are well aligned with those identified as critical for not only RIA but the larger DoD community. In the main, these efforts are focused on the improvement of legacy systems or development and production of new systems that exploit the advantages afforded by advanced materials. Many of these efforts focus on advantages offered by the attractive combination of high-strength and reduced weight offered by, specifically, titanium alloys and advanced composites. While QCML is focused on the provision of a manufacturing readiness that will allow RIA and the greater region to produce advanced materials that achieve/surpass the required design properties, an equally important element of the project is the development of methods that reduce costs – often seen as the primary challenge when considering a broader use of titanium in many economic sectors. Thus, QCML will continue to pursue two primary activities, namely the development of novel materials and processes for the manufacture of superior lightweight equipment and the demonstration (via prototyping) of the state-of-the-art manufacturing technologies. The near-term programs focus on the development and transfer of technologies for near-net shape manufacturing, including, specifically, additive powder based approaches, HIP consolidation, and spark plasma sintering. The progress associated with the start-up of this new organization will be discussed. The equipment capabilities will be presented, and opportunities for public-private partnerships will be given.

TAL1.4

Mechanical, Physical and Microstructure Characterization of the Effects of Sn Addition On Ti-24Nb-4Zr-(0.75-0.81)Sn Cast Alloys
P. S. Nnamchi, I. Todd, W. M. Rainforth, University of sheffield,United kingdom, Sheffield, United Kingdom

The authors investigated the effects of Sn additions on the microstructure, physical and mechanical properties of Ti-24Nb-4Zr-(0.75-0.81) Sn (wt.%) alloys. The result reveals that the stability of the alloys was improved by Sn addition, which had close correlation with the compositional specific electrons per atom ratios (e/a), and the room temperature mechanical behaviors could not show a trend with Sn constituents in all the alloys, before the anneal treatment. The high strength and toughness exhibited by Ti-24Nb-4Zr-8Sn and Ti-24Nb-4Zr-8.1Sn alloys means that they can be useful for Engineering applications, where strength to weight ratio is essential. Keywords: Titanium alloy; mechanical strength; physical properties; electrons per atom ratios (e/a); phase stability.

TAL1.5

Influence of Casting Defects On Fatigue Strength of An Investment Cast TA6V Alloy
Y. NADOT¹, G. LEOPOLD¹, J. Mendez¹, T. billaudeau², (1)Institut PPRIME, ENSMA-CNRS-UP, UPR 3346, Futuroscope, France, (2)AIRBUS FRANCE, toulouse cedex 9, France

Cast components are well known for having complex geometries. These components can be manufactured by an investment casting process in one operation while keeping good static and fatigue properties but defects or microstructural inhomogeneities can reduce fatigue strength. This paper deals with the influence of casting defects on the fatigue behaviour. These defects can be internal defects like ceramic inclusions. Internal shrinkages or porosities are reduced thanks to Hot Isostatic Pressure (HIP). Casting defects can also be at the surface of components like pin holes or HIP-Sinks. It is necessary to study the influence of these defects on fatigue strength in order to assess defect size allowable in the component. In order to analyze casting defects harmfulness, fatigue tests are performed on artificial defects and natural defects. Artificial defects are spherical and introduced at the surface of fatigue test specimens. Fatigue tests are performed under a tension-tension loading (R=0.1). Thanks to their reproducibility, artificial defects allow understanding fatigue mechanisms from defects. It is important to understand the number of cycles required to initiate and to propagate the critical crack in order to assess the fatigue life using relevant modelling. In order to characterize fatigue lifetime, fracture surfaces are observed and length of the critical defect is monitored on each sample. This experimental study puts in relief the main parameters influencing fatigue strength of a cast Ti-6Al-4V alloy. All of these experimental results can be used to evaluate fatigue strength of a material containing defects thanks to a multiaxial fatigue criterion.

Baseline Characterization of Ti-6242 Sheet for Low-Temperature SPF Applications
E. Crist, RTI International Metals, NIles, OH

“Ti-6Al-2Sn-4Zr-2Mo Sheet is widely used in aerospace structures requiring creep resistance at elevated temperatures. Many components are manufactured using superplastic forming (SPF) at temperatures as high as 1700F (927C). In recent years, significant effort has been devoted to developing Ti-6Al-4V sheet with “low-temperature” SPF capability in the 1400-1500F range, and for which the benefits have been described in recent conferences. Engine components and heat shields (currently manufactured from Ti-6Al-4V sheet) requiring increased elevated temperature resistance are being converted to Ti-6242. Consequently, airframe manufacturers and tier 1 suppliers have expressed an interest in Ti-6242 sheet exhibiting “low-temperature” SPF behavior at 1550F or lower. As with Ti-6Al-4V, lowering the SPF temperature will provide for improved die life, less alpha case, the need for chemical milling, and thus reducing associated environmental concerns. The purpose of this present work is to define baseline data for 1550F-1700F SPF behavior of Ti-6242 sheet produced per AMS 4919, and to identify opportunities for future investigation.”

Session 2: ATI 425 Developments

TAL2.1

Characterization of the Mechanical Properties of ATI 425® Alloy According to the Guidelines of the Metallic Materials Properties Development & Standardization Handbook
E. T. McDevitt¹, D. J. Bryan¹, J. V. Mantione¹, L. J. Ruiz-Aparicio², T. D. Bayha¹, (1)Allegheny Technologies Incorporated (ATI), Monroe, NC, (2)Allegheny Technologies Incorporated (ATI), Natrona Heights, PA

ATI 425^® Alloy is an alpha-beta titanium alloy with good ductility and strengths comparable to Ti-6Al-4V alloy.  The higher ductility of ATI 425^® alloy permits continuous cold-rolling into coil sheet products and provides better formability during component manufacturing.  The combination of strength and ductility of the alloy has generated interest within the airframe community.  However, one barrier to insertion in aerospace applications has been the lack of detailed characterization of the mechanical properties of the alloy as required by the Metallic Materials Properties Development & Standardization (MMPDS) Handbook.  This presentation will describe the testing program that was executed to achieve inclusion in the MMPDS handbook.  The mechanical properties, including “A” and “B” basis minimums, for ATI 425^® alloy cold-rolled coil sheet and hot-rolled plate products, produced according to AMS 6946, will be presented.  The development of an AMS specification for hot-rolled bar and shape products will also be discussed.

TAL2.2

Development of ATI 425 Alloy Titanium Sheet Products
L. J. Ruiz-Aparicio, Allegheny Technologies Incorporated (ATI), Monroe, NC

Cold-formable ATI 425 Alloy sheet is an innovative alpha/beta titanium alloy with strength comparable to Ti 6/4 but with hot- and cold-ductility superior to current alternatives for aerospace and defense applications.  The alloy's combination of mechanical properties allows it to be considered for a wide variety of applications where design challenges include weight reduction or for an alternative to steel, aluminum, composites, CP titanium or other titanium alloys.

The major focus of this talk will be on the mechanical properties of this alloy, with special attention to its enhanced super-plastic formability, open-hole fatigue behavior and friction stir welding capabilities.  The presentation will also describe the advantages ATI 425 Alloy possesses in continuous coil, strip and cut-to-length sheet for aerospace and defense applications.

TAL2.3

Laser Welding ATI 425® Alloy
P. Edwards¹, T. Morton², G. L. Ramsey², (1)Boeing Research & Technology, Seattle, WA, (2)The Boeing Company, Seattle, WA

Laser Beam Welding of ATI 425® Alloy was performed on 2.5 mm thick butt joints.  This new alloy could be used in place of standard Ti-6Al-4V for a variety of lower-cost structural solutions.  Demonstration of its fusion weldability with laser welding is of particular interest because it is a near-net- shape process, capable of high welding speeds, which will further enable lower cost manufacturing options.  It was found that ATI 425® Alloy could be successfully welded using a fiber laser at speeds over 3 m/min.  Microstructural, microhardness and tensile property evaluations were performed on the resulting welds.  It was found that there was a 15% hardness increase in the weld and the strength of the joints was within 2% of base metal properties.

TAL2.4

ATI 425® Alloy Plate Products for Aerospace and Defense Applications
J. V. Mantione¹, T. Hackett², T. D. Bayha¹, (1)Allegheny Technologies Incorporated (ATI), Monroe, NC, (2)Allegheny Technologies Incorporated (ATI), Monaca, PA

ATI 425^® alloy is a recently developed alpha-beta titanium alloy with strength comparable to Ti-6Al-4V but with improved ductility and formability.

Due to the unique combination of properties, ATI 425^® alloy is an attractive candidate for replacement of Ti 6Al-4V (AMS 4911) for certain structural applications as well as a potential upgrade from alloys such as Ti 3Al-2.5V (AMS 4989) and Ti CP-4 (AMS 4901). 

 The improved workability of ATI 425^® alloy allows this alloy to be hot rolled and warm or cold formed into larger section parts with fewer joints thereby reducing the costs of large components. 

This presentation will focus on potential applications of ATI 425^® alloy plate for aerospace and defense structures requiring cold formability, strength, toughness and/or ballistic resistance.

TAL2.5

ATI 425® Alloy Long Products Development
D. J. Bryan, P. C. Markle, R. T. Grzeskiewicz, ATI Allvac, Monroe, NC

ATI 425^® Alloy, nominal composition Ti-4.0Al-2.5V-1.5Fe-0.25O, is a new alpha-beta (α/β) Ti alloy of significant commercial interest as a viable replacement for Ti-6Al-4V, CP-Ti, and other alloys in a variety of low- to moderate-strength aerospace applications.  ATI 425® Alloy offers Ti-6Al-4V alloy-like properties with significant improvements in formability.  The advantages in formability, combined with the depth and breadth of manufacturing capabilities within ATI, have led to some unique product and property combinations not accessible by conventional α/β Ti alloys.  This talk focuses on the development of ATI 425® Alloy long products.

 A major focus of the development effort was on hot-rolled bar and rod with AMS 4928 equivalent properties.  Subsequently, a design of experiments was employed for the optimization of STA heat treatments targeting AMS 4965 equivalent properties.  The improved formability of the alloy was tested during the development of hot-rolled shapes and cold-drawn bar.  Lastly, the smallest end of the size spectrum was explored in the development of hot-rolled and cold-drawn wire.  The culmination of the development efforts is a product family with a useful and unique set of properties amongst the α/β Ti alloys.

TAL2.6

Structural Titanium Biomedical Alloys for Aerospace Applications
E. Keys¹, D. J. Bryan², J. V. Mantione¹, H. Freese², (1)Allegheny Technologies Incorporated (ATI), Monroe, NC, (2)ATI Allvac, Monroe, NC

Historically, there has been a transfer of technology and commercial metallic alloys developed for aerospace and industrial applications into the manufacture of implantable medical and surgical devices. Examples include: stainless steels (ATI 316L), cobalt base alloys (ATI 35N alloy, ATI L-605 alloy) and titanium alloys (ATI Ti-CP-2, Ti-6Al-4V ELI, ATI Ti-6Al-4V, ATI Ti-3Al-2.5V). There has not, however, been significant cross-pollination of metallic alloys developed for biocompatibility and other specialized requirements of the medical industries into industrial and aerospace applications. This talk will present an overview of the mechanical properties of selected titanium alloys designed specifically for structural orthopedic implant applications with a comparison with more traditional aerospace titanium alloys. These structural biomedical titanium alloys include an alpha+beta alloy (ATI Ti-6Al-7Nb alloy) and several metastable beta alloys (Stryker TMZF® [Ti-12Mo-6Zr-2Fe] alloy, ATI Ti-15Mo alloy, ATI TiOsteum® [Ti-35Nb-7Zr-5Ta] alloy).

Session 3: High Strength Titanium Alloys

TAL3.1

Prediction of the Influence of Microstructure On Fatigue Life and Yield Strength in Ti-5Al-5Mo-5V-3Cr-0.5Fe
J. Foltz¹, B. Welk², P. C. Collins³, J. Williams¹, H. L. Fraser², (1)The Ohio State University, Columbus, OH, (2)Center for Accelerated Maturation of Materials, Columbus, OH, (3)Quad City Manufacturing Lab, Rock Island, IL

Beta-solutionized and aged conditions of metastable β-Ti alloys, such as Ti-5Al-5Mo-5V-3Cr-0.5Fe (Timetal 555), can result in a rich variety of microstructures that affect mechanical properties and fractographic features.  In Timetal 555 there is limited data relating the size and distribution of microstructural features to properties such as yield strength and fatigue life. Using neural networks, databases have been developed to quantify the microstructrual dependencies of yield strength in sub-scale tensile tests and fatigue life in four-point bend tests. These interpolative models can be used as predictive tools to investigate microstructrual dependencies using virtual experiments. The fractographic implications of several of these features will also be discussed.

TAL3.2

Ti-5553 Wrought Processing and Heat Treatment Optimization
N. Sonnentag, Ladish Forging, Cudahy, WI

The Ti-5Al-5V-5Mo-3Cr alloy offers a potential solution to thermomechanical processing challenges commonly associated with many commercially available beta and near-beta titanium alloys. Wrought process and heat treatment capabilities of the Ti-5553 alloy were investigated.  Forge processes and heat treatment conditions producing either high strength and moderate tensile ductility or moderate strength and high fracture toughness were identified and further refined. Those processes yielding an optimal balance of strength, ductility, and fracture toughness were selected for use on full-scale wrought thick-section Ti-5553 alloy components.  Beta and alpha-beta forging combined with standard or slow-cooling heat treatment of thick-section components will be reviewed and resulting mechanical properties will be presented.

TAL3.3

Properties and Processing of a New Beta-Rich Alpha Beta Alloy for High Strength Applications
J. Fanning, TIMET, Henderson, NV

Properties and Processing of a New Near-Beta Titanium Alloy for High Strength Applications
J. Fanning, Timet, Henderson, NV

The high specific strength of near-beta titanium alloys is very useful for structural airframe applications. Near-beta alloys have been extensively used in such applications for about the past 20 years, including TIMETAL 10-2-3 for the C-17, 777 and A380. On the 787, TIMETAL 555 was extensively utilized in lieu of TIMETAL 10-2-3 due to the deeper hardenability and improved mechanical property combinations.   More recently, TIMET has performed an investigation of new titanium alloys (with Mo, V, Cr, Fe and Al) to identify and characterize new allow compositions that offer advantages with regards to mechanical properties, cost or processing. The down-selected composition (weight percent) is nominally Ti-5.5Al-5Mo-5V-2.4Cr-0.7Fe and has been named TIMETAL 18.

TAL3.4

Influence of Carbon Additions On the Properties of Ti-5Al-5Mo-5V-3Cr-0.5Fe
J. Foltz¹, B. Welk², H. L. Fraser², J. Williams¹, (1)The Ohio State University, Columbus, OH, (2)Center for Accelerated Maturation of Materials, Columbus, OH

Microstructural features in metastable β-Ti alloys, such as continuous layers of grain boundary alpha (GBA) in Ti-5Al-5Mo-5V-3Cr-0.5Fe (Timetal 555), are known to affect mechanical properties. Several methods to control the amount of GBA are available, including carbon additions as shown recently by Wu and Loretto. Other methods of managing GBA include using metastable transition precipitates to nucleate α more rapidly, and hot working the material to recrystallize both alpha and beta phases. Each of these methods to reduce GBA affects properties such as fracture behavior and fatigue life differently. In carbon-free Timetal 555, high strength conditions commonly exhibit ductile intergranular fracture in four-point bending fatigue, as well as short lifetimes when tested with the maximum cyclic stress near the yield stress. This talk focuses on the differences in four-point bending fatigue lifetime and fracture behavior between two of methods of controlling GBA: Timetal 555 containing carbon provided by Wu and Loretto, and carbon-free material provided by Boeing.

TAL3.5

Mechanical Properties and Microstructural Evaluation of High Strength Titanium Alloy Upset Forgings
S. Nyakana¹, J. Fanning², (1)TIMET, Henderson, NV, (2)TIMET-R&D, Henderson, NV

TIMET has manufactured upset forgings from a variety of titanium alloys including Ti-6Al-4V, 54M, 54M+, Ti550, and Ti5553. Room and elevated temperature tensile tests, fracture toughness, low cycle fatigue (LCF), and high cycle fatigue (HCF) properties were evaluated for pancakes of all alloys and heat treatment conditions. Fatigue crack growth rate, precision modulus, and other tests were also performed on selected forgings. Summaries of mechanical properties and microstructural observations will be presented.

TAL3.6

Evaluation of Newly Developed Ti-555 High Strength Titanium Fasteners
L. Zeng, Alcoa Fastening Systems, Carson, CA

Titanium alloy 555 (Ti-5Al-5Mo-5V-3Cr-0.5Fe), emerging high strength alloy, is capable of very favorable combination of strength, strength-weight ratio, ductility and toughness that expanded use of titanium in many applications. In the past few years, Alcoa Fastening System (AFS) has successfully launched a series of high-strength titanium fasteners using Ti555 in many aerospace fastener applications, from threaded pins to panel fasteners and blind bolts applications.  For close tolerance threaded pins, Ti555 Aero-Lite fasteners can offer more robust properties with higher strength, ductility and toughness than traditional Ti-6Al-4V pins. It can achieve 180 ksi tensile strength and 108 ksi double shear strength up to 0.5 inch diameter. The newly developed Panel (Mark IV) fastener with high strength Ti555 studs achieved 180 ksi tensile strength and 40% weight reduction when compared to similar A-286 studs.  A new high strength Blind Bolt system using Ti-555 as corebolt is in a late stage of development.  It is configured to generate high joint preloads, high shear strength up to 105 ksi, and large blind side foot prints of 1.5 x the nominal shank diameters.  This paper summarizes the mechanical properties and microstructures and discusses a few aerospace fasteners products developed using Titanium alloy 555 material.

Session 4: Titanium Processing I

Induction Heating of Titanium Alloys for Extrusion
D. Li, RTI International Metals, Inc., Niles, OH

Induction heating technology is commonly used for heating titanium billets prior to extrusion.  An induction heating simulation program using finite element method has been developed that is capable of simulating electromagnetic field and thermal effects.   The electromagnetic field, eddy current distribution, and temperature profile of billets of various dimensions and alloys have been computed and studied.  This model has been calibrated based on temperature measurement, and is able to accurately predict the billet temperature profile.  As a result, it provides an effective tool to control induction heating in order to achieve the desired billet temperature profile for extrusion.

TAL4.1

TIMETAL 54M: A New Alpha-Beta Titanium Alloy with Improved Machinability
J. Fanning¹, D. Y. Kosaka², S. Nyakana², (1)TIMET-R&D, Henderson, NV, (2)TIMET, Henderson, NV

TIMETAL 54M (Ti-5Al-4V-0.5Fe-0.8Mo) is an alpha-beta alloy with superior machinability and similar mechanical properties compared to Ti-6Al-4V, the most widely used alpha-beta alloy. TIMETAL 54M is expected to provide a substantial cost savings over Ti-6Al-4V parts that require extensive machining operations. This presentation will discuss processing experiences from ingot melting to billet forging, along with heat treatments to achieve optimal tensile, fracture, and fatigue properties. In addition, results from studies on drilling and milling machinability of TIMETAL 54M will be provided.

TAL4.2

Laser Assisted Machining of Titanium Alloy
Y. Shin, C. Dandekar, Purdue University, W. Lafayette, IN

Titanium alloy (Ti-6Al-4V) is one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance, but it also presents problems wherein it is an extremely difficult material to machine. The cost associated with titanium machining is also high due to lower cutting speeds (<60m/min) and shorter tool life.  Laser-assisted machining (LAM) and consequently hybrid machining is utilized to improve the tool life and the material removal rate.  The effectiveness of the two processes is studied by varying the tool material and material removal temperature while measuring the cutting forces, specific cutting energy, surface roughness, microstructure and tool wear. Laser-assisted machining improved the machinability of titanium from low (60m/min) to medium-high (107m/min) cutting speeds; while hybrid machining improved the machinability from low to high (150-200m/min) cutting speeds. The optimum material removal temperature was established as 250°C. 2-3 fold tool life improvement over conventional machining is achieved for hybrid machining up to cutting speeds of 200 m/min with a TiAlN coated carbide cutting tool. Tool wear predictions based on 3-D FEM simulation show good agreement with experimental tool wear measurements. Post machining microstructure and micro-hardness profiles showed no change from pre-machining conditions. An economic analysis, based on estimated tooling and labor costs, shows that LAM and the hybrid machining process with a TiAlN coated tool can yield an overall cost savings of ~30% and ~40% respectively.

TAL4.3

New Advances in the Machining of Hard Metals Using Physics-Based Modeling
L. Zamorano, T. Marusich, K. Marusich, C. Arthur, Third Wave Systems, Minneapolis, MN

The machining of hard metals has historically been understood to be challenging and costly due to its material properties, including titanium’s low thermal conductivity and high hardness, and nickel’s rapid work-hardening and high strength at elevated temperatures; as well as limited industry understanding of the physics behind chip formation and material removal.  The achievement of meaningful cycle time reductions while maintaining part quality depends on a capability to model the physics of hard metal machining operations.   With the help of a validated toolpath analysis model that can predict forces at each cutter location, cycle times and scrap can be reduced, and machine breakdown can be avoided, all through off-line analysis.  Productivity and process efficiency can be improved through simulation, drastically reducing testing setup and machining time. 

Physics-based modeling technology has been identified as a cost-effective solution for identifying optimum cutting speeds, enabling researchers and manufacturers to increase material removal rates, reduce machining costs, and enhance industry expertise in hard metal machining best practices.  This paper presents new advances to physics-based modeling that have been validated using experimental tests and comparisons with finite element milling simulations, used to compare different process parameters and resulting material removal rates, and successfully advance hard metal machining processes.

TAL4.4

Advanced Thermal Management Tooling System for Milling of Titanium Structures
P. D. Prichard, T. O. Muller, T. J. Long, Kennametal Inc., Latrobe, PA

The projected growth in titanium usage for commercial and military aircraft has elevated the importance of manufacturing strategies to improve machining productivity.  The high temperature strength, inherent chemical reactivity and limited thermal conductivity of titanium are the major factors contributing to poor machinability and excessive tool wear.  FEA metalcutting simulations indicate that tool surface temperatures are in excess of 1000°C at contact stresses of 3 GPa.  The metal cutting tool industry has improved tool performance by engineering the insert geometry, substrate materials, and coatings.  In addition, performance has been improved by directing metalworking coolant into the cutting zone with external nozzles to reduce tool temperatures and evacuate metal chips. Recently, an indexable milling tool system has been developed with internal coolant capability to directly apply metalworking coolants from beneath the tool/chip interface by incorporating coolant channels through the inserts.  The internally cooled tooling systems increase metal removal rates by at least 50%, while improving tool life up to 400% compared with the most advanced tooling today.  FEA metalcutting simulations indicate a significant reduction in tooling temperatures as a major factor in tool life extension.  The impact temperature reduction on fatigue of WC-Co tools and tool life extension will be discussed.  In addition, the implications for specific applications in machining titanium with these commercial tooling systems will be discussed.

TAL4.5

Titanium Forging – Finite Element Modeling of Ti64 Thermomechanical Processing
N. Rizzi, J. Tschofen, Manoir Aerospace, Bologne, France

Titanium alloys are used in both engines and airframes in the aerospace industry. The new aircrafts use more titanium fraction compared to the previous generations. Properties of titanium alloys (tensile, ductility, fatigue, fracture toughness compromise) are related to microstructure achieved through thermomechanical processing. Process development of forged parts has to be cost effective and in shorter lead time. Thus process modeling is today commonly used in engineering department in order to define material flow and processing windows (temperature, deformation, ...) to produce reliable forgings. The presentation will show the basis of modeling and the effect several thermomechanical treatments on Ti64 (Ti-6Al-4V) on tensile properties and microstructures.

TAL4.6

“A Contribution to Anisotropic Deformation Behavior of Alpha+Beta Titanium Alloys Inherent in the Crystallography of the Burgers Orientation Relationship”
T. F. Broderick¹, P. Shade¹, M. A. Groeber², G. B. Viswanathan³, H. L. Fraser⁴, (1)UTC, Beavercreek, OH, (2)The Materials and Manufacturing Directorate, Wright-Patterson AFB, OH, (3)Universal Energy Systems, Dayton, OH, (4)Center for Accelerated Maturation of Materials, Columbus, OH

Abstract: A new source of anisotropic deformation behavior for alpha and beta titanium aligned according to the Burgers orientation relationship has been understood from the perspective of 2-fold maximum common crystal symmetry. Overlays of stereographic projections viewed along {011} || (0001) and rotated so that <111> || <2-1-10>, establishing a Burgers orientation relationship, revealed the maximum common crystal symmetry between bcc-β and hcp-α phases in the composite α/β material was only 2-fold. This new observation had implications for necessary anisotropy of deformation behavior between and within a-basal, a-prism, a-pyramidal and c+a pyramidal slip systems. Consideration for requirements of 2-fold crystal symmetry, e.g. testing of slip systems at loading orientations within 180° of each other and relative orientation with respect to the {011} || (0001) mirror planes, showed that 3, 6, 6 and 12 unique responses were required when testing hcp-α slip systems at orientations of constant maximum Schmid factor. Calculation showed this contribution to anisotropic deformation behavior resulted from geometrical hardening, i.e. large changes in Schmid factor on mating bcc-β slip systems when testing hcp-α slip systems at orientations of constant maximum Schmid factor. Comparison is made between these calculated results and those obtained during testing of single variant, single colony alpha+beta titanium materials at maximum Schmid factor on hcp-α slip systems.

Session 5: Titanium Processing II

TAL5.1

The Effect of Heat Treatment On Beta Grain Growth and Alpha-Phase Variant Selection in a Ti-6Al-4V Ingot
G. A. Sargent¹, T. T. Gorman², A. Salem³, A. L. Pilchak³, M. G. Glavicic⁴, S. L. Semiatin⁵, (1)UES, Inc., Dayton, OH, (2)University of Dayton, Dayton, OH, (3)Universal Technology Corporation, Wright-Patterson AFB, OH, (4)Rolls-Royce Corporation, Indianapolis, IN, (5)Air Force Research Laboratory, Wright-Patterson AFB, OH

Beta grain growth behavior and the evolution of transformed alpha-phase variants during beta annealing and subsequent slow cool-down of a Ti-6Al-4V ingot were determined using an electron- backscatter-diffraction (EBSD) technique.  To this end the prior beta grains were deduced from room temperature alpha-phase data.   The area fraction and location of individual alpha variants with respect to the beta grain boundaries were determined in both the as-cast and heat treated conditions.   It was found that while repeated beta annealing and cooling had minor effect on the prior beta grain boundaries, it had a pronounced effect on the area fraction and the location of the alpha variants within each beta grain

TAL5.2

On Powder Consolidation Methods for Compositionally and Microstructurally Graded Components
P. C. Collins¹, B. Welk², H. L. Fraser³, J. W. Sears⁴, (1)Quad City Manufacturing Lab, Rock Island, IL, (2)The Ohio State University, Columbus, OH, (3)Center for Accelerated Maturation of Materials, Columbus, OH, (4)South Dakota School of Mines & Technology, Rapid City, SD

There exist many different routes to producing compositionally and microstructurally graded components. Many of these processing routes exploit the unique advantages of processing with powder materials. Specifically, the liquid-based additive manufacturing approaches (e.g., laser-based and electron-beam based) allow for a high degree of spatial control of the designed compositional variation where the local composition may be described as relatively homogeneous. Conversely, spark plasma sintering and HIP consolidation may be used when liquid-based processing would be detrimental to the microstructure. These methods will be discussed, with the advantages and limitations presented. They have been used to produce a range of Ti-based compositionally and microstructurally graded systems, including simple binary systems and more complex alloy variations. The effect of composition on the resulting microstructure will be presented, and the effect on local properties will be assessed.

TAL5.3

Rapid Consolidation of Ti-6Al-4V Powders by Thermal Transformation-Mismatch Plasticity
M. R. Matsen¹, D. C. Dunand², B. Ye², (1)The Boeing Company, Seattle, WA, (2)Northwestern University, Evanston, IL

The densification kinetics of Ti-6Al-4V powders with spherical or angular shapes are compared in uniaxial die pressing experiments between isothermal conditions (at 1020 °C, in the beta-field, where deformation occurs by creep) and during thermal cycling (860-1020 °C, within the range of the alpha-beta phase transformation of the alloy, where transformation-mismatch superplasticity is activated). Densification kinetics are markedly faster under thermal cycling than under isothermal conditions, as expected from the higher deformation rate achieved under transformation-mismatch plasticity conditions as compared to creep conditions. The densification curves are successfully modeled for both creep and superplastic deformation mechanisms using (i) simple closed-form solutions and (ii) the finite-element method. Densification kinetics, under isothermal and thermal cycling conditions, of Ti-6Al-4V powders containing 5-20 vol.% ceramic particles are also presented.

Session 6: Titanium Processing II - Continued

TAL6.2

Properties of Conventionally Alloyed and Powder Alloyed Nano-Crystalline Titanium Consolidated Via Spark Plasma Sintering
R. Gansert¹, C. Melnyk², S. Schroeder², D. Grant², (1)AMTS Incorporated, Simi Valley, CA, (2)California Nanotechnologies, Inc., Cerritos, CA

Nano, near-nano, and multi-modal grained materials show great potential for application in many commercial industries. The Hall-Petch relationship cites the strengthening of materials by reducing the average crystallite size. A study is proposed to investigate the increase in mechanical properties provided by nano, near-nano as well as multi-modal grained powders used in powder metallurgical applications. Consolidations of processed materials will be produced using Spark Plasma Sintering (SPS). Nano-crystalline titanium, and titanium alloy powders and will be processed via cryogenic milling. The mechanical properties of the nano, near-nano and multi-modal crystalline materials will be compared to conventional materials of the same composition. Initial testing of titanium based materials indicates an increase in strength and hardness by 2 to 3 times from the use of nano and near nano crystalline structures. Cryo milled powders and the consolidated forms of these powders will be examined using microstructural analysis and mechanical testing.

TAL6.3

Mechanical and Fatigue Properties of Ti-6Al-4V and TiB/Ti-6Al-4V Prepared by Spark Plasma Sintering
H. Izui¹, A. Ohta², H. Egawa², D. Nakano³, (1)Nihon University, Chiba, Japan, (2)Graduate School of Science and Technology, Nihon University, Chiba, Japan, (3)Nihon University,, Chiba, Japan

Titanium alloy parts for aerospace seek to meet strong demand for low costs.  Powder metallurgy is expected to be low-cost processing technology of titanium alloy.  An innovative powder densification technology known as SPS has been developed in recent years.  The SPS process is a synthesis and processing technique which makes it possible to at low sintering temperature and in a short sintering duration.  This study focuses on the mechanical and fatigue properties of Ti-6Al-4V and TiB/Ti-6Al-4V composites (TMC) prepared by spark plasma sintering (SPS) in vacuum.  The microstructure, mechanical properties and fretting fatigue strength of the sintered Ti-6Al-4V and TMC were investigated.