MDI3.2

Material Properties For Process Simulation
N. Saunders, Z. Guo, J. P. Schillé, A. P. Miodownik, Sente Software Ltd., Guildford, United Kingdom

Process simulation requires reliable data for a wide variety of material properties, ranging from thermal conductivity to flow stress curves.  Traditionally such data are gathered from experimentation, which has significant disadvantages in that not all of the required data is readily available and, in particular, measurement of high temperature properties is expensive.  Therefore, it is highly desirable to develop computer models that can calculate all relevant material properties required by process simulation.
This presentation will describe the development of computer models that can provide many of the properties required by process simulation for multi-component commercial alloys.  These models are integrated into the computer software package JMatPro, which can then be used to export datafiles directly to FE/FD based packages used for casting, forging and deformation simulation.  The properties that are calculated are wide ranging, including Thermophysical and physical properties (from room temperature to the liquid state), such as density, thermal expansion coefficient, thermal conductivity, Young's/shear/bulk moduli, Poisson's ratio, viscosity, specific heat and enthalpy. Temperature and strain rate dependent mechanical properties up to the liquid state, including high temperature flow stress-strain curves.  Physical and mechanical properties as a function of time, temperature and cooling rate including user-defined cooling profiles.  The calculations are based on sound physical principles rather than purely statistical methods, thus many of the shortcomings of methods such as regression analysis have been avoided.  Examples of calculated properties will be provided for steels, titanium and nickel-based superalloys, with extensive comparison made to experiment. 

MDI3.3

Rolling Modeling for Development of Fine Grain Titanium Sheet at RMI
E. Crist, D. Li, R. Porter, J. W. Bennett, P. A. Russo, RMI Titanium Company, Niles, OH

Fine-grain Ti-6Al-4V sheet has several advantages compared to conventional sheet when used to produce super-plastically formed parts. These advantages include lower forming temperatures due to finer grains, less surface oxidation and subsequently less yield loss. Computer modeling has been utilized to assist in the development of fine grain Ti-6Al-4V sheet by optimizing rolling parameters and pass schedules. These modeling studies together with production trials have allowed fine-grain Ti-6Al-4V sheet to be successfully produced.

MDI3.4

The Use of Computational Modeling in Aerospace Alloy Production Environments
M. E. Epler¹, V. Mendoza², A. Patel¹, G. Maurer¹, (1)Carpenter Technologies, Reading, PA, (2)Carpenter Technology Corporation, Reading, PA

Commercially available computation modeling packages present great opportunities for advancement in alloy and process development programs.  These packages allow for timely and cost effective analysis of a wide range of processing and metallurgical variables when performing research and development.  Modeling can be used to solve problems in current products and processes or be applied to the design and implementation phases of new products and processes.

This presentation will discuss some of the uses of modeling in aerospace alloy production and R&D environments where a great number of different processing routes exist.  Solidification modeling may be used to determine optimum casting parameters to increase yields and improve cleanliness during primary melt processing.  VAR and ESR modeling packages can be used to minimize segregation during secondary melting.    Thermo-mechanical modeling may be used to optimize heating times and cooling rates and to develop deformation strategies to ensure uniform macrostructures and to avoid centerline and surface cracking.  All of the process models help the process engineer design processes within the design capability of the equipment.

The long tedious trial-and-error method to process scale-up is becoming obsolete.  Modeling can give insight into material behavior during processing that may not be available otherwise, especially in full-scale, large-section size products.  This ability shortens the time for alloy development and scale-up from small laboratory-based heats to full-scale production without many costly trials.  Some current limitations of modeling software will be discussed and speculation on opportunities for advancement will be made.

MDI3.5

Considering Criteria for Ductile Fracture (Damage) in Designing near Net-shape Forging for Aerospace Applications
V. Saraf, T. Furman, R. Ramanathan, M. Ricker, Ladish Co., Inc., Cudahy, WI

Stringent property requirements from the parts for aerospace applications have led to development and modification of advance Ti and Ni-based alloys. With new alloys come the challenges of optimum processing so as to meet the final requirements in terms of mechanical strength among other properties. Economics of producing such alloys at mills have made these alloys very expensive. Effect of all these factors on the design is to produce near-net shape where material loss in machining from forging to final assembly shape is minimal.

In the near-net shape forging, if the processing variables are not chosen correctly, a ductile fracture may occur on the surface because of strain and thermal gradient. Damage criteria that helps in determining the amount of work exceeding the ductile limit of the material resulting in ductile fracture is very important to include in FEM analysis of such forging processes during the design stage. Commonly used damage criteria and their applications are studied to predict the surface damage from the forging process. This helps the design engineer in designing the near-net shape without compromising on the part and process quality.

Results predicted using damage criteria are compared with the actual production.

MDI3.6

Use of Numerical Modeling to Enhance Understanding of Radial Forging of Nickel-Base Superalloys
C. M. O'Brien, R. S. Minisandram, J. M. Hyzak, ATI Allvac, Monroe, NC

Conversion of ingot to fine-grained billet is a complex process for superalloys.  The thermo-mechanical processing is effected by a range of parameters including heating temperature, transfer time to the forging die, overall forging reductions along with incremental forging reductions per pass.  The effects of each individual processing parameter along with their interactions cannot be practically determined experimentally. Numerical modeling analysis, however, provides the opportunity to determine these effects analytically.  Modeling results for the conversion of Alloy 718 billet will be reviewed.  Thermal and strain distributions from the model are useful in predicting coarse surface structure.

Session 4: Additive Manufacturing Process Modeling and Simulation

MDI4.1

Suggestions on Metal Deposition Process Simulation From a Practitioners Perspective
B. H. Walker, R. M. Walker, Keystone Synergistic Enterprises, Inc., Port St. Lucie, FL

Process simulation tools for modeling of the various metal deposition processes are under development at several universities and small companies. Most of these models have placed emphasis on simulation of the melt pool to model the complex interactions associated with the powder or wire feeding into the melt pool as well as its key characteristics; e.g., size or shape as a function of heating source power, etc. From this practitioners perspective there are other high value process simulation opportunities; therefore, this presentation will suggest several, perhaps less exciting but very important, areas for modeling of electron beam and laser metal deposition processes for direct and additive manufacturing of components

MDI4.2

Design and Optimization of Structures Using Additive Manufacturing Processes
R. Kapania, S. B. Mulani, J. Li, Virginia Polytechnic Institute and State University, Blacksburg, VA

We have all heard the stories of how during World War II, Rosie the Riveter saved the world by pumping tens, if not hundreds, of millions of rivets to build thousands of fighters.  Rosie can finally retire now. Ongoing revolution in information management, materials science, computational science and manufacturing technology has made it now possible to fabricate new generation of, mostly custom-built, structures that will have a low part count, built-in multi-functionality, and an ability to tailor the structure according to the design requirements. Termed Unitized Structures, these structures are formed by adding or building up material as opposed to Subtractive (i.e. taking the material away as in machining) or Formative (casting) methods of manufacturing.  Built using a family of processes that go under such names as Rapid Manufacturing, Rapid Prototyping, Solid Freeform Fabrication, Additive Manufacturing technologies, etc. these structures would be built by Debbie the Digital Fabricator by the click of the computer mouse as opposed to pumping of the rivet gun. To that end, for nearly two years, under a grant from NASA Langley Research Center (Karen Taminger, grant monitor), administered by the National Institute of Aerospace (Dr. David Peake a TM), we have been developing a computer environment that will help NASA optimally design unitized structures built using such approaches as the Electronic Beam Free Form Fabrication, EBF³, and will make use of the design flexibility (efficient use of geometry) made possible by these new manufacturing technologies.   The environment, EBF3PanelOpt, involves an integration of continuous mesh generation, optimization, NURBS to represent curvilinear stiffeners, and commercial finite element software.  The talk will describe the progress made to date, the challenges faced and our vision of future research in this area.

MDI4.3

Finite Element Models for the Electron Beam Freeform
U. Chandra, G. Barot, Modern Computational Technologies, Inc., Cincinnati, OH

This presentation will discuss the ongoing effort in the development of finite element models for computer simulation of the electron beam freeform fabrication (EBF³) process under a NASA funded Small Business Innovation Research (SBIR) program.  Although the present effort deals primary with on-ground fabrication it further serves as a starting point for eventual development of the methodology for in space fabrication.  The presentation will include highlights from Phase I as well as Phase II of the effort. 

 Phase I of the program dealt primarily with the thermal and mechanical models of the process.  Multi-layered deposits of stainless steel 304 were investigated using a commercial code, ABAQUS.  Several issues of practical significance were addressed; e.g., thermal management during fabrication, inter-layer fusion, reheating of the previously deposited material, residual stresses/distortions and an often used method of estimating solidification morphology.  A parametric study was also performed.  Current efforts in Phase II of the program include further refinements in the thermo-mechanical model, development of microstructure models, study of the role of convection in the melt pool, and experimental validation using geometries of moderately complex shapes.

MDI4.4

Modeling of Distortion and Residual Stress Control in Unitized 2219 Aluminum Stiffened Structure Produced by Electron Beam Free Form Fabrication
S. Y. Lin¹, E. K. Hoffman², M. Domack³, (1)Lockheed Martin, Hampton, VA, (2)NASA Langley Research Center, Hampton, VA, (3)NASA Langley Research Center, Houston, VA

The electron beam freeform fabrication (EBF³) layer-additive manufacturing process has been developed to directly fabricate airframe structural metallic parts from CAD.  The EBF³ process was used to build a unitized stiffened structure by direct deposition of a blade stiffener onto base skin material.  Advantages of fabricating stiffened structure by the EBF³ process include fabrication of complex geometry stiffeners, reduced material waste compared with integrally machined concepts, and reduced part count compared with built-up concepts like riveting or welding.

 

All thermo-mechanical manufacturing processes create residual stresses in the component.  Compressive residual stresses in the surface of a part can improve the mechanical properties such as fatigue life and corrosion resistance.  However, the presence of residual stresses may be detrimental to the integrity of the part under service conditions.  For these reasons, understanding the source of such stresses, their control, and relief are critical to the application of the manufacturing process.

 

The residual stress distribution in the unitized EBF³ structure depends upon parameters such as heat input, travel speed, wirefeed speed, baseplate and deposit thickness, part geometry, and process schedule.  Additional parameters used to control distortion and residual stress include external constraint (clamping), preheat, post-heat, active cooling, machined lands, and insulation.  To identify the relative significance of each process parameter on residual stress distribution and to arrive at some optimal combination of parameters, a finite element analysis model was developed and used to guide the design of experiments.  Experimental studies coupled with surface profile and residual stress measurements were used to validate the finite element model.  To date, one set of deposition parameters (beam power, translation speed, and wire feed rate) was selected and used for all cases evaluated.  Salient features of the model are presented for various process parameter cases and selected experimental trials are presented to verify the model.

MDI4.5

Modeling Net-Shape Spray Forming of Ni Superalloys
J. Mi, P. S. Grant, University of Oxford, Oxford, United Kingdom

A multiphysics numerical model has been developed at Department of Materials, University of Oxford to simulate the net-shape spray forming process. The model consisted of four sub-models: (1) a droplet deposition model simulating droplet deposition, splashing and re-deposition behavior and the resulting preform dynamic shape; (2) a preform heat flow model simulating the preform internal heat flow and solidification behavior; (3) a porosity model simulating the porosity distribution inside the spray formed preform; (4) a thermal stress model simulating the thermal stress evolution during spray forming and the subsequent cooling stage. The model has been validated against experiments of the spray forming of profiled IN718 Ni superalloy rings. The modelled preform shape, surface temperature, microporosity distribution and thermal stresses showed good agreement with experimental measurements. The model has been proven as a powerful tool for the optimisation of the net-shape spray forming process.

MDI4.6

Multiscale Modeling of Transport Phenomena and Microstructure Evolution during Laser Deposition
J. W. Newkirk¹, Z. Fan², F. Liou², (1)University of Missouri-Rolla, Rolla, MO, (2)Missouri University of Science & Technology, Rolla, MO

A multiscale model for the laser deposition process has been developed. The multi-scale model consists of two parts at different levels: a macroscopic model to model mass, heat and momentum transfer, and a microscopic model to model the evolution of solidification and solid phase transformation microstructures during laser deposition. These two models are fully coupled. At the macroscopic scale, a comprehensive mathematical model and the associated numerical technique have been developed to simulate the coupled, interactive transport phenomena between the laser, the powder, and the substrate during the laser deposition process. The simulation involves laser material interaction, free surface evolution, droplet formation, transfer and impingement onto the substrate, and melt-pool dynamics. Transient temperature and velocity distributions of the falling particles, shape of the falling particles and melt pool, and heat transfer and fluid flow in the melt pool are all calculated in a single, unified model, using the continuum formulation and the volume of fluid technique. At the microscopic scale, a stochastic microstructure model is developed to simulate dendritic grain structures and morphological evolution in solidification. The model is based on the cellular automata approach, which takes into account the heterogeneous nucleation both within the melt pool and at the substrate/melt interface, the growth kinetics, and preferential growth directions of dendrites. Both diffusion and convection effects are included, for which the input parameters are from the macroscopic model. This model enables prediction and visualization of grain structures during and after the deposition process. In the model, solid phase transformation is also modeled with application to Ti-6Al-4V.  The coupling between macroscopic and microscopic simulations is performed using different time steps and mesh sizes, with those for microscopic simulation much finer. Adaptive time steps are adopted for both macroscopic and microscopic simulations.

MDI4.7

Integrated Computational Materials Design
C. J. Kuehmann¹, G. B. Olson², (1)QuesTek Innovations LLC, Evanston, IL, (2)Northwestern University, Evanston, IL

QuesTek Innovations has applied computational modeling and simulation to the design and development of high-performance steels, high-strength aluminum alloys, high-temperature nickel superalloys and amorphous metals using Materials by Design^® technology. For high-performance alloys, numerical implementation of materials science, applied mechanics and quantum physics principles provides a hierarchy of computational models defining subsystem design parameters that are integrated through multicomponent computational thermodynamics and kinetics. The approach integrates these design oriented process/structure and structure/property relations to determine optimal microstructures, meeting specified material property goals. The process then finds available processing paths to access the desired dynamic multilevel structures. A serial sequence of design-prototype-evaluate refines a design through subsequent iterations, providing a solution in less time and lower cost than traditional empirical methods that employ the parallel evaluation of a large matrix of material candidates. Examples of Materials by Design in steels, aluminum and nickel alloys will be discussed.

Session 5: Application of Modeling and Simulation to Component Design and Performance Assessment

MDI5.1

Materials Modeling and Simulation—A Game Changing Technology for Propulsion Materials Development
D. D. Whitis¹, R. Schafrik², (1)GE Aviation, Evendale, OH, (2)GE Aircraft Engines, Cincinnati, OH

The “jet age” is about 60 years old, and arguably materials development has played a major role in making jet engines practical and pervasive. The demands of these aeronautical applications spurred great advancements in titanium and superalloy materials and processing, and the drive for lighter weight solutions served as a compelling forcing function for a variety of composites technology. The path to success, however, was often tortuous, long, and expensive. Large national efforts and huge investments in industry were required to achieve success. Today, the situation has changed. The expectation is that new M&P will be developed faster with no unpleasant surprises. This challenge can only be met by aiding our materials development decisions with computational tools. These tools encapsulated our knowledge of materials science and engineering and leverage the impressive computing infrastructure. The best models are derived from basic knowledge, but data-driven models can also provide useful assistance. This presentation will summarize a few examples of applying models to provide critical insight into a variety of typical issues that arise when advancing the state of art in materials technology.

MDI5.2

Proabilistic Property Prediction of Ultra High Strength Corrosion-Resistant Steel
J. W. Jung, B. Tufts, QuesTek Innovations LLC, Evanston, IL

As the first prospective application of the Accelerated Insertion of Materials (AIM) technology, QuesTek Innovations achieved the validation and adoption of Ferrium S53 in landing gear. The goal was to produce a mechanistic-based method for estimating property variation with calibration by minimal data sets. The Metallic Materials Properties Development and Standardization handbook ultimately requires 100 measurements of yield and ultimate tensile strength from 10 heats of material to establish A-basis minimum design properties. The AIM procedure estimates these from science-based modeling using only an S-basis data set of 30 measurements collected from 3 heats. The reduced technical risk enabled by the AIM methodology accelerates technology insertion through substantial reduction of certification investment risk.

MDI5.3

Development and Application of Computer Simulations of NDE for Flaw Detection
R. B. Thompson, J. Gray, T. Gray, M. Garton, N. Nakagawa, L. Brasche, Iowa State University, Ames, IA

An important part of component design, optimization and lifting is the determination of what flaws might be expected to be produced by manufacturing and/or service and whether these flaws might be detectable by NDE techniques.  Work on the development of computer tools to predict the detectability of flaw started at the Center for Nondestructive Evaluation in the late 1980’s under the support of NIST and has continued since then with important developments made possible through support from industrial sponsors, the Federal Aviation Administration, the National Aeronautics and Space Administration, and the Air Force Research Laboratories.  This paper will summarize the current capabilities of those tools, XRSIM, UTSIM, and ECSIM, including their general framework, state of development, and advances in progress.  Illustrations of recent applications will be presented followed by a discussion of lessons learned, leading to an indication of steps that should be taken by potential users to assure a successful application.

MDI5.4

Recent Advances in Model-Assisted Probability of Detection
R. B. Thompson, L. H. Brasche, Iowa State University, Ames, IA

Probability of Detection (POD) is the metric whereby the efficacy of an inspection is judged in probabilistic life management.  Traditionally, this is determined empirically by first measuring the flaw response as a function of flaw size for a set of samples and conditions believed to be representative of the inspection situation of interest.  The data is then analyzed by what is known as the â versus a technique.  In the simplest implementation, a linear regression of log flaw response (â) versus log flaw size (a) is conducted.  The regression line and the standard deviation of the data about this line, along with the inspection threshold, then determine the POD.  This well accepted procedure suffers from the significant time and cost associated with the POD determination, which should be repeated for each change in the inspection problem.  To overcome this limitation, there is significant interest in the use of models, derived from either careful laboratory experiments or physics-based computations, to generalize the results of one POD determination to another, related physical situation.  The Model-Assisted POD (MAPOD) Working Group, led by the Center of NDE at Iowa State University, has been formed under the joint support of the Air Force, Federal Aviation Administration and National Aeronautics and Space Administration to explore this possibility.  This paper will review recent progress of the MAPOD Working Group, including past demonstrations that have occurred, future demonstrations that are in the planning process, and protocols that are currently being developed.

MDI5.5

Recent NDE Modeling Developments for Metallic Aerospace Components
J. C. Malas¹, M. P. Blodgett², (1)AFRL Materials and Manufacturing Directorate, Wright-Patterson AFB, OH, (2)US Air Force Research Laboratory, Wright-Patterson AFB, OH

Abstract to come.

MDI5.6

Models for the Interaction of Ultrasound with Microstructure
R. B. Thompson, F. J. Margetan, Iowa State University, Ames, IA

The interaction of ultrasound with microstructure is important in many material problems.  Attenuation and backscattering reduce the detectability of flaws, particularly in materials with coarse grains or complex microstructures such as titanium alloys.  In addition, the value of these wave propagation properties provide information about the microstructure that can be used in materials characterization studies, e.g. the nondestructive determination of grain size.  This paper will summarize the current status of models for ultrasonic velocity, attenuation and backscattering that take into account two major sets of factors, those of the measurement system (frequency, transducer diameter and focusing, etc.) and those of the material (a property known as the backscattering coefficient).  Also included will be a discussion of the relationship of the backscattering coefficient to the microstructure (grain size and shape in the simplest case).  Applications of these models to predict signal-to-noise ratios in flaw detection experiments, to predict flaw response distributions in assessment of probability of detection, to use that information to design optimal inspections, and to characterize microstructures will be reviewed.

Session 6: Application of Modeling and Simulation to Component Design

MDI6.1

Key Accomplishments of the P&W DARPA AIM Program and Implications for Transformation of the Materials Discipline
J. Schirra, Pratt & Whitney, East Hartford, CT

Materials and Processes Engineering;Pratt & Whitney. There is a well documented need to better align the materials development and insertion cycle with new product development and delivery. To address this DARPA developed the Acceleration of Insertion Materials Initiative and funded a P&W Program focused on rotor materials. This talk will highlight key accomplishments of the P&W team including integration of the materials discipline into the analytical design process, development of advanced data/model fusion techniques, material behavior modeling, etc. These accomplishments will highlight the fundamental changes in the materials discipline that will need to occur to accommodate the transformation envisioned as part of the AIM Initiative.

MDI6.2

Development of an Accelerated Insertion of Materials (AIM) System for an Aluminum Extrusion
D. R. Forrest¹, D. Backman², M. J. Hayden³, J. A. Christodoulou⁴, (1)Naval Surface Warfare Center, West Bethesda, MD, (2)Worchester Polytechnic Institute, Worchester, MA, (3)The Naval Surface Warfare Center, Carderock Division, West Bethesda, MD, (4)Office of Naval Research, Arlington, VA

Accelerated Insertion of Materials (AIM) is a methodology that was recently developed for streamlining the difficult task of optimizing and qualifying new materials for service in critical applications.  Computer models, developed from both commercial software and custom-written packages, can calculate the evolution of microstructure and properties of materials during the fabrication of components.  These calculations can reduce the amount of mechanical testing required by narrowing the test matrix:  only the most promising and relevant combinations of composition and processing conditions need be explored.  The challenge is to integrate these disparate computer models in a way that is useful to the materials design and optimization process.

As an entry point for implementing a fully-capable package, we have developed a simplified AIM system for AA6082 extrusions.  Using DEFORM 3D, the system calculates the thermomechanical history of the material during the extrusion of sidewall panels for a Littoral Combatant Ship.  Then the precipitate distribution is derived from thermodynamic and kinetic data using Thermo-Calc and PrecipiCalc.  Finally, strength and hardness are estimated from the microstructural constituents.  The software package iSight provides a framework to integrate these models and an environment for materials design.

MDI6.3

Accelerating the Development of the Next Generation of High Temperature Metals
S. M. Russ, C. Woodward, D. M. Dimiduk, J. Simmons, M. Uchic, AFRL/MLLMD, Wright-Patterson AFB, OH

The USAF depends upon the timely development and transition of structural materials to deliver technically advanced systems.  However, conventional materials development is a time consuming and evolutionary process.  Even when known materials systems are modified slightly, certification for use on aerospace platforms can take a decade or longer. New materials require an even longer development and certification process.  Thus, a challenge for the aerospace industry is to shorten the materials development and maturation time, and as a result accelerate transition of new, more capable alloys.

 This presentation will attempt to describe the puzzle commonly referred to as multi-scale modeling of materials and will outline a template for realizing aspects of accelerating the exploration and development of materials.  It will highlight progress on certain technologies and describe challenges being worked within the Metals Branch of the Materials and Manufacturing Directorate, Air Force Research Laboratory.  Lastly, it will challenge industry to begin (or continue) to use these methods as they develop the next generation of high temperature metals required for future USAF capabilities.

MDI6.4

EPICUR - Development of TiMMC Components
P. Gomez, Centre d'Essais Aéronautique de Toulouse (CEAT), Balma Cedex, France

The aerospace industry has severe technical and economical requirements needed to continuously improve performance. Therefore the industrials are always looking for lighter weight and, for aeroengines, higher thrust and better efficiency.
Metal matrix composites (MMCs) are a possible attractive issue to this fact because of their specific mechanical properties in comparison with the monolithic alloys currently used. MMCs allow imagining breakthrough technologies.
The blings - bladed rings - constitute one of these possible breakthrough technologies. The blings are MMC rings which could replace the compressor and turbine disks in turbojet engines. This design would lead to an important weight reduction of the engine rotating parts and would increase its compactness.
The EPICUR program is targeting the development of a Titanium matrix composite TiMMC obtained by the Snecma’s EGV coating process; the setting-up of a sizing procedure; the production of real scale bling (i.e. 400 mm diameter), and the spinning test of the parts.
Snecma has already produced a TiMMC composed of a Ti6242 titanium alloy matrix  reinforced with the SCS-6 silicon carbide fibre. Several blings scale ½ (i.e. 200 mm diameter) have been compacted by Hot Isostatic Pressure HIP among which one is stemming from the EGV process.
ONERA has performed two kinds of calculations to satisfy the requirements of the bling sizing. The first one attempts to predict the static speed burst. This finite element (FE) analysis is based on anisotropic non linear constitutive equations (plasticity coupled to damage) using a stiffer behavior in the reinforced direction and poor mechanical properties in the transverse ones. The second calculation evaluates the lifetime of the blings from the post-processing of the results obtained by the FE calculation. ONERA’s fatigue damage model is stress based and is able to take into account the load multiaxiality and the material anisotropy.

MDI6.5

Physics of Failure Models for Electronic Systems Sustainment
K. Line¹, G. Krishnan¹, M. Oja¹, W. Li¹, R. Tryon², (1)VEXTEC, Brentwood, TN, (2)VEXTEC Corporation, Brentwood, TN

Electronic prognostics is a growing field important to both military and commercial applications. When implemented, this capability will greatly enhance the maintenance management of platforms. Electronic prognostics require extensive use of physics of failure models to predict the remaining useful life of complex electronic failure modes. VEXTEC has developed a material-based physics of failure analysis tool for use in a variety of programs with aerospace OEMs. These techniques are far more accurate and versatile than traditional fatigue life analysis by using the grain and material properties for damage prediction. By modeling the stresses induced on interconnects by thermal and vibration forces, current damage estimates and remaining useful life can be calculated. The data required to drive these models uses measurands commonly available from electronic systems such as board temperature and loads induced by flight or operational conditions. The electronic circuit accelerated life test programs have shown excellent correlation between the predictions from material based physics of failure models and induced circuit board failures. VEXTEC’s probabilistic roll-up models of electronic component circuits and interconnects predict overall system reliability to provide the operator with useful information for managing vehicle maintenance.

MDI6.6

Software for Managing Large Multiphase Material Data Sets
D. Boyce, Cornell University, Ithaca, NY

As experimental and simulation capabilities have continually increased, the need has developed to manage the resulting large data sets. Techniques such as serial sectioning lead to data sets on the order of gigabytes. Likewise, large finite element simulations can involve millions of elements and also produce gigabytes of output. Developed for the U.S. Navy, the Materials Atlas is a database and storage system for managing large data sets arising from various sources. Specifically, the project targets titanium and stainless steel data. Data sets are stored using a model based on HDF5, a scientific data format developed at the National Center for Supercomputing Applications. Information about the data, including material chemistry, crystal structure and phase definition, is stored separately in a relational database. Ultimately, data sets can be accessed and viewed according to data source (experiment, simulation, etc.), material or material phases, or other meta-data. The author will discuss the schema design, the software implementation and user experience.

MDI6.7

Modeling the Impact of Life Cycle Cost and Performance When Implementing New Materials
K. O. Legg¹, B. Tufts², D. Tibbitts³, (1)Rowan Technology Group, Libertyville, LA, (2)QuesTek Innovations LLC, Evanston, IL, (3)General Atomics, Kaysville, UT

Hill AFB is in the process of qualifying for flight a new ultra-high strength corrosion-resistant landing gear steel, designated Ferrium® S53.  The steel has essentially the same mechanical properties as standard 300M landing gear steel, yet has significantly higher resistance to general corrosion, impact damage, stress corrosion cracking, hydrogen embrittlement and grind burns.  Thus the condemnation rate at overhaul due to any of these causes is expected to be significantly lower, as is the probability of service failure.  Lower condemnation and service failure rates represent major potential cost savings.  On the other hand the steel is more expensive than 300M.  The question is which components can be cost-effectively replaced with Ferrium S53 items, and whether the replacement should be made at overhaul, at condemnation, or (for any component that presents a safety-of-flight risk) across-the-board.  Evaluations made for various types of landing gear components will be presented to illustrate the most important cost and performance issues that need to be taken into account in this type of analysis.  The analysis is based on the C-MAT life-cycle cost analysis decision tool that was designed specifically for analyzing materials and technology replacements.  This decision tool takes into account all the costs of changing technologies, qualifying the alternatives and using them in production, balanced against the savings that may result from lower production cost, smaller inventories, faster turnaround on overhaul, longer overhaul cycles and lower condemnation or failure rates.Work funded by DoD Environmental Security Technology Certification Program.

Nondestructive Evaluation/Health Monitoring/Prognostics

Session 1: High Temperature Health Monitoring

NDE1.1

Novel Thin Film Sensor Technology for Turbine Engine Hot Section Components
J. D. Wrbanek, G. C. Fralick, National Aeronautics and Space Administration, Cleveland, OH

Degradation and damage that develops over time in hot section components can lead to catastrophic failure of the turbine section of aircraft engines. A range of thin film sensor technologies has been demonstrated enabling on-component measurement of multiple parameters either individually or in sensor arrays including temperature, strain, heat flux, and flow. Conductive ceramics are beginning to be investigated as new materials for use as thin film sensors in the hot section, leveraging expertise in thin films and high temperature materials. The current challenges are to develop new sensor and insulation materials capable of withstanding the extreme hot section environment, and to develop techniques for applying sensors onto complex high temperature structures for aging studies of hot propulsion materials. The technology research and development ongoing at NASA Glenn Research Center for applications to future aircraft, launch vehicles, space vehicles, and ground systems is outlined.

NDE1.2

Strain Induced Diffusivity Effects in Indium-Tin-Oxide Strain Gages
O. J. Gregory, X. Chen, C. Cummiskey, University of Rhode Island, Kingston, RI

Ceramic strain gages based on reactively sputtered indium tin oxide (ITO) are being developed to measure both static and dynamic strain of rotating components in the hot sections of gas turbine engines. Such strain measurements are necessary to validate structural models and monitor the performance of newly developed materials.  ITO strain gages exhibit excellent oxidation resistance and high temperature electrical stability.  They can survive tens of hours of strain testing at temperatures as high as 1550^oC in air. However, due to the limitations associated with the alumina constant strain beams used to evaluate the piezoresistive response of these ceramic gages at elevated temperatures, little or no work has been done to determine the response of these gages at strain levels beyond 400 με.  With specially prepared ceramic substrates (laminates based on scandium doped zirconia) capable of being strained in excess of 1000 με without fracture, the piezoresistive response of the ITO strain gages can now be evaluated at strain levels approaching 1000 με. Therefore, the effect of strain on gage factor was systematically studied from room temperature to 1000^oC, and the range of conditions expanded over which the difference in piezoresistive response (between tension and compression) could be studied. The results indicated that gage factor was somewhat dependent on strain at these higher strain levels, regardless of being loaded in tension or compression.  However, when the ITO strain gages were sputter-coated with approximately 2 μm of alumina and tested in tension, the gage factor became independent of strain. As might be expected, this effect was not observed when the same alumina coatings were applied to ITO strain gages and subsequently tested in compression.

NDE1.3

Direct Write Sensors for Turbine Engine Applications
J. Brogan, C. Gouldstone, R. Greenlaw, MesoScribe Technologies, Inc., Stony Brook, NY

New approaches to traditional sensor fabrication and methodology have been developed allowing sensors to be deposited directly onto conformal components.  The Company’s Direct Write MesoPlasma™ process enables structural health sensing capabilities for gas turbine engines and aerospace structures operating in harsh environments.  Thermocouple and strain sensors are embedded within protective coatings and allow for both wire connections and wireless interrogation. 
Recent activity has focused on increasing sensor durability at high temperatures.  Thermocouple sensors were deposited onto coupons and engine components and subjected to a number of thermal exposure tests using oxy-acetylene burner rigs, lasers, and high pressure combustion test rigs.  In addition, advances in high temperature strain measurement capability will be reported for both static and dynamic strain applications.

NDE1.4

Autonomous High-Temperature Bearing Sensors for Prognostics
R. Draney, S. Marble, Sentient Corporation, Idaho Falls, ID

Accurate estimates of component health are required for successful Condition Based Maintenance (CBM).  A sensor used to provide diagnostic indication for bearings is presented.  The sensor is designed to operate in a high temperature environment while providing both temperature and vibration data wirelessly.  Size, power, temperature, and communication requirements are discussed.  Promising solutions are outlined.

NDE1.5

High Temperature Fiber Optic Sensing Technologies for Structural Health Monitoring
R. J. Black, D. B. Moslehi, K. Chau, G. Chen, L. Oblea, K. Sourichanh, Intelligent Fiber Optic Systems Corporation, Santa Clara, CA

Light-weight fiber optic sensors have the potential for noise-free measurement to high temperatures with electromagnetic interference immunity, electrical passivity and thus safety in explosive environments, and remote access. Fiber optic grating sensors are also multiplexable and precise, but standard gratings are subject to high-temperature degradation. Methods to alleviate this problem include annealing, chemical composition grating techniques and electric arc writing. This paper will discuss recent developments in special fiber grating using these techniques to extend the maximum temperature at which accurate strain sensing is achievable to fill needs for users of high-temperature health monitoring for aerospace applications.

NDE1.6

Advances in Thin Film Technology for High Temperature Condition Based Maintenance Sensor Applications
M. Pereira da Cunha, R. Lad, T. Moonlight, G. Bernhardt, D. Frankel, University of Maine, Orono, ME

Session 2: Residual Stress Measurement and Eddy Current Methods

NDE2.1

Recent Improvements in High-Frequency Eddy Current Conductivity Spectroscopy for Residual Stress Profiling in Surface-Treated Nickel-Base Superalloys
B. Abu-Nabah¹, P. B. Nagy², (1)University of Cincinnati, Cincinnati, OH, (2)University of Cincinniti, Cincinnati, OH

Due to its frequency-dependent penetration depth, eddy current measurements are capable of mapping near-surface residual stress profiles based on the so-called piezoresistivity effect, i.e., the stress-dependence of electric conductivity.  To capture the peak compressive residual stress in moderately shot-peened (Almen 4-8A) nickel-base super alloys, the eddy current inspection frequency has to go as high as 50-80 MHz.  Recently, we have reported the development of a new high-frequency eddy current conductivity measuring system that offers an extended inspection frequency range up to 80 MHz with a single coil.  Unfortunately, spurious self- and stray-capacitance effects render the complex coil impedance variation with lift-off to be more nonlinear, which makes it difficult to achieve accurate apparent eddy current conductivity (AECC) measurements with the standard four-point linear interpolation method beyond 25 MHz.  In other words, the coil becomes excessively sensitive to lift-off uncertainties.  In this presentation, we will report improvements in the coil design that reduce its sensitivity to lift-off variations.  The new design uses a reduced coil size even though that also reduces its absolute impedance and its relative sensitivity to conductivity variations, but it is still sufficient for residual stress assessment.  In addition, we will demonstrate the benefits of implementing a quadratic interpolation scheme together with the reduced lift-off sensitivity of the smaller probe coil to minimize, and, in some cases, eliminate the coil sensitivity to lift-off uncertainties.  These, modifications allow us to do much more robust measurements up to as high as 80 MHz with the required high accuracy.

NDE2.2

Advances in Swept High Frequency Eddy Current Residual Stress Characterization
C. Lo, Y. Shen, S. J. Lee, A. M. Frishman, N. Nakagawa, Iowa State University, Ames, IA

This paper reports on the recent progress in a swept high frequency eddy current (SHFEC) technique for nondestructive characterization of residual stresses in engine materials with specific application to shot-peened components. The methodology determines conductivity depth profile by model-based SHFEC data inversion, which can then be converted into residual stress profile using a material-based model that includes the piezoresistivity (PR) and other possible non-PR effects. Recent upgrades to the detection coil and measurement system has extended the frequency upper bound to 80 MHz.  An improved algorithm based on perturbation with respect to small conductivity deviations and small skin depth (compared to coil outer radius) has been derived to replace Cheng-Dodd-Deeds forward model calculations, and is expected to reduce the computation time of SHFEC data inversion significantly. Microstructural characterizations on peened Inconel 718 samples show experimental evidences of shot-induced changes in texture. These have been incorporated into a theory of anisotropic piezoresistivity effect, which is being developed to reconcile the non-trivial relationship between conductivity and residual stress. 

 This work was performed at the Center for NDE at Iowa State University with funding from the Air Force Research Laboratory through S&K Technologies, Inc. on delivery order number 5007-IOWA-001 of the prime contract F09650-00-D-0018.

NDE2.3

Resonant Frequency Eddy Current Liftoff Measurements for Evaluating Conductivity in Materials
R. T. Ko¹, S. Sathish², T. R. Boehnlein¹, M. P. Blodgett³, (1)University of Dayton Research Institute, Dayton, OH, (2)University of Dayton Research Institute, Dayton, OH, OH, (3)US Air Force Research Laboratory, Wright-Patterson AFB, OH

An eddy current liftoff signal which arises from a small variation of distance between a probe and a material is often considered an undesirable test variable. Rotating the liftoff signal in the impedance plane or finding a position where the liftoff signal has the least impact on the desired signal is a routine step in an eddy current inspection. In this study, the material dependency of the liftoff signal using resonant frequency eddy current is evaluated. This is to examine the feasibility of using the liftoff signal in monitoring a small change of conductivity in materials at high frequencies beyond 12 MHz. Experimental results were obtained from materials of various conductivities as well as shot peened specimens with different peening intensities and residual stresses. Preliminary results indicated that the liftoff measurement using resonant frequency eddy current could be a potential tool for evaluating small changes of conductivity in materials.

NDE2.4

Characterization of Cold Work in Shot Peened Nickel-Base Superalloy by Nanoindentation
S. I. Rokhlin¹, L. Yang¹, E. Kahana¹, L. Wang¹, X. Bin¹, P. B. Nagy², M. P. Blodgett³, (1)The Ohio State University, Columbus, OH, (2)University of Cincinniti, Cincinnati, OH, (3)US Air Force Research Laboratory, Wright-Patterson AFB, OH

Nondestructive evaluation of residual stresses and of residual stress relief in service conditions has great significance for reliability of turbine engine components.  It is important to achieve better fundamental understanding of relations between nondestructive signature and material properties such as hardness, plasticity, cold-work and residual stress. In this work a nanoindentation technique is explored to determine the micromechanical properties and their relation to different levels of cold work in Ni based superalloys. It is shown that cold work has strong effect on hardness and yield stress. Significant size effect has been observed in indentation responses. Nanoindentation measurements were performed on the shot peened Ni based superalloy sample. For this, the sample was cross-sectioned and hardness was measured as function of depth from the sample surface. Reasonable correlation has been observed between dependences on depth of hardness and of cold work and residual stresses measured by X-ray diffraction. Also the cold work induced by spherical indentation, which produce roughness comparable to that from shot peening, has been investigated. The nanoindentation results are compared with non contact measurements of electrical conductivity.

Residual Stress Profiling in DP718 Ni-Base Super Alloy Using Eddy Current Measurements
W. Hassan¹, D. Ryan², B. Abu-Nabah³, P. B. Nagy⁴, (1)Rolls-Royce Corporation, Indianapolis, IN, (2)Honeywell Engines, Phoenix, AZ, (3)University of Cincinnati, Cincinnati, OH, (4)University of Cincinniti, Cincinnati, OH

Near surface residual stresses directly influence the fatigue life of critical engine rotating components. Depending on sign and magnitude a near surface residual stress gradient can either inhibit or accelerate fatigue initiation and crack propagation. Shot peening is a common surface treatment that can enhance machining residual stresses by increasing the magnitude and depth of compression. Shot peening is intended to create a uniform, consistent, and reliable sub-surface compressive residual stress layer. Recently, it has been demonstrated that, in contrast with most other materials, shot-peened nickel-base super alloys exhibit an apparent increase in eddy current conductivity at increasing inspection frequencies, which can be exploited for nondestructive residual stress assessment of subsurface residual stresses. Honeywell Aerospace is particularly interested in DP718 Ni-base superalloy as it is the main Ni alloy used in the manufacturing of critical rotating components in its engines.   We will present the results of the process used to build sets of flat and curved samples with graduated residual stress profiles. The process, which utilizes design of experiment (DOE) approach, targets producing samples with four different stress profiles namely, as shot peened,  25% reduction in peak stress from the as shot peened case, 50% reduction in peak stress from the as shot peened case, and finally 75% reduction in peak stress from the as shot peened case. Thermal relaxation of the stress profiles is used to achieve these different levels. The model that relates the temperature and time parameters to the peak compressive stress level will also be presented and discussed. X-ray diffraction measurements will be used to quantify the generated profiles and the results will be compared to the residual stress profiles obtained using eddy current measurements at high frequencies (up to 80 MHz).

NDE2.6

Model-Assisted Characterization of a Pulsed Eddy Current Instrument
N. Nakagawa, S. J. Lee, C. Lee, C. Lo, Iowa State University, Ames, IA

Eddy current (EC) NDE modeling can be useful in improving and optimizing performance of EC instrumentation.  However, to apply any model-predicted signals to a given instrument, one must understand the relationship, or the system transfer function, that relates instrument output signals to predicted signals.  This paper reports on a system transfer function determination for a proprietary pulsed eddy current (PEC) instrument, based on the analytical Cheng-Dodd-Deeds model.  Specifically, measured PEC waveforms taken with generalized half-space samples are compared with model-predicted waveforms in frequency domain, leading to the determination of the PEC instrument transfer function.  We present studies of half-space and layered samples in various material combinations, so that we not only determine the transfer function but also validate it among the variety of the sample configurations.  We plan to present PEC waveforms for defect specimens as well, namely both instrument and converted waveforms.

 This work was performed at the Center for NDE at Iowa State University with funding from the Air Force Research Laboratory through S&K Technologies, Inc. on delivery order number 5007-IOWA-001 of the prime contract F09650-00-D-0018.

Session 3: Health Monitoring

NDE3.1

Ultrasonic Plate Waves for Fatigue Crack Detection in Multi-Layered Metallic Structures
E. A. Lindgren¹, K. V. Jata², B. Scholes², J. Knopp², J. C. Aldrin³, (1)US Air Force Research Laboratory, Wright-Patterson AFB, OH, (2)AFRL/MLLP, Metals, Ceramics and NDE Divison, Wright-Patterson AFB, OH, (3)Computational Tools, Gurnee, IL

A representative area of concern for fatigue crack detection in aircraft is multi-layered metallic structures.  Ultrasonic plate waves are currently being investigated by multiple initiatives to detect these types of flaws with a minimal number of sensors to enable Structural Health Monitoring (SHM).  Previous work has focused on structures with one or two layers, coupled with modeling of the wave propagation within these representative samples.  However, it is common for multi-layered structures to have more than two layers in many areas of interest.  Therefore, this study investigates ultrasonic wave propagation and fatigue crack detection in a multi-layered sample consisting of 2 to 4 total layers with fatigue cracks located in only one layer.  The samples contain fastener holes configured as would be expected to be found on typical aircraft structure.  The fatigue cracks were grown using cyclic fatigue loading after the fastener holes were placed in the samples.

Preliminary measurements show that fatigue cracks can be detected by the guided ultrasonic waves, but that the sensitivity to crack size is dependent on the boundary conditions of each layer.  The boundary conditions are changed by applying various loads on the surface of each layer by tightening and loosening the fasteners that hold the sample together.  This variation depicts representative conditions found on aircraft.  The experimental results are supplemented by modeling of guided wave propagation within the structure using Finite Element Methods.  The primary parameter studied in the modeling effort is the effect of the changes in the boundary condition on the mode and amplitude of the guided wave.  The results of this investigation establish some recommendations for the use of guided waves in multi-layered structures, plus challenges that exist for their use in SHM applications and potential strategies to address these challenges.

NDE3.2

Active Health Monitoring of a Composite Plate Structure using MsS-generated guided-wave Technology
S. Y. Kim, G. M. Light, Southwest Research Institute, San Antonio, TX

A magnetrostrictive sensor (MsS) guided-wave technology was developed for generating and receiving guided wave in a plate-like structure. The MsS probe consists of a thin ferromagnetic strip (approximately 0.12mm thick) and a flat excitation circuit pattern (approximately 0.15mm thick) that are permanently bonded to the surface of a structure being monitored. One 200-mm-long MsS probe can monitor an area approximately 300mm by 3700mm (1-by-12-feet).  The probe generates a guided wave that can propagate long distances and that fills the entire cross sectional area of the material. The large area monitoring with the guided wave is a fast and cost-effective method compared to scanning over the entire area under test using point probes. As an example of its applicability for composite aircraft structure, notch defect growth in IM7-6K plain weave carbon fabric was monitored with Lamb wave.  The results obtained will be presented.

NDE3.3

Structural Health Monitoring Methods using Nuclear Quadrupole Resonance (NQR)
N. Tralshawala¹, T. Batzinger¹, S. Nath¹, M. Gigliotti¹, H. Robert², (1)GE Global Research Center, Niskayuna, NY, (2)Quantum Magnetics, San Diego, CA

The measurement of component strain has been typically accomplished using strain gauges attached to the surface of the component.  Recently, GE has been investigating the use of crystalline solids embedded in coatings such as paint or embedded through the volume of the component as part of the matrix material (i.e. embedded in the epoxy resin of composite materials) .  To measure strain experienced by the component, NQR or nuclear quadrupole resonance techniques relying on the interaction between the nuclear quadrupole moment and a locally applied electric field (lattice field) gradient can be used for strain measurement.  Some crystalline solids such as 14N, 35Cl, 37Cl, 63Cu and 65Cu have quadrupolar nuclei.   Since the NQR frequency is directly related to lattice field, any perturbation that changes the local field properties, such as strain or temperature change will result in a NQR frequency shift. Detection of this shift enables ability to monitor strain in various structures and has the added advantage that the frequency shifts are independent of direction. This is especially important since in many applications where printed strain gauges or FBGs are employed, the strains normal to the fiber or coil direction cannot be detected. Applications such as bond integrity and structural damage detection are thus especially suited to NQR strain gauging. We will present data from some preliminary experiments conducted so far and exploration of applications in structural health monitoring.

NDE3.4

Lateral Heat Flow Infrared Thermography for Thickness Independent Determination of Thermal Diffusivity in Carbon Fiber Reinforced Polymer Composites
N. Tralshawala, D. R. Howard, B. Knight, Y. Plotnikov, A. May, H. I. Ringermacher, GE Global Research Center, Niskayuna, NY

Infrared thermography is one of the non-destructive evaluation techniques for non-contact quantification of porosity, voids, and delaminations in thin-walled carbon fiber reinforced polymer composite aircraft structures. Determining porosity using thermography is based on the calculation of thermal diffusivity, which in turn requires thickness information. Recently GE has been experimenting with the use of lateral heat flow to determine thermal diffusivity and porosity, without thickness information. We have developed appropriate theoretical models and a new data analysis framework to experimentally determine all three components of thermal diffusivity from these temperature measurements. The analysis did not require any curve fitting to the temperature profile and was based on the creation of thermal time-of-flight (tof) images from the stripe edge. Experimental validation was done using anisotropic carbon fiber reinforced polymer (CFRP) composites. We found that in the CFRP samples used, the in-plane component of diffusivity is ~ 4-5 times larger than the through-thickness component. The data indicate that the in-plane component of diffusivity is as sensitive to porosity as the through-thickness component. We thus have a method to quantify porosity where two-sided access to structure is not needed.

Surface-Wave Sensing of Cracks in Complex Geometry Aerospace Structures
S. Kuhr¹, J. K. Na¹, J. L. Blackshire², S. A. Martin³, (1)University of Dayton Research Institute, Wight Patterson AFB, OH, (2)US Air Force Research Laboratory, Wright-Patterson AFB, OH, (3)NDE Computational Consultants, Dublin, OH

The use of guided elastic waves as an effective structural health monitoring sensing method has been proven in recent years in a number of important applications. Much of this work has focused on the development of innovative global sensing methods where elastic waves are used to detect damage over extended ranges from 10’s of centimeters to meter distances. In many aerospace applications, the location of the anticipated damage is deterministic and localized in nature. This is particularly true for fatigue cracks which typically initiate and grow in joints, fastener, and high-stress structural locations. When this is the case, a global integrated sensing method is not required, and a local, targeted sensing method is the preferred choice. In this research effort, the development of a surface-wave sensor is described for the detection of fatigue cracks in complex-geometry aerospace structures. The use of surface-wave sensors provide an effective way of detecting cracks based on pulse-echo and pitch-catch methods, where the blocking or reflection of elastic wave energy by the crack provides a simple means for detecting the crack.

NDE2.5

Replacing Magnetic Particle and Liquid Penetrant Inspections With High Resolution MWM-Array Eddy Current Imaging
V. Zilberstein¹, D. J. Cammett², N. J. Goldfine², A. Washabaugh², M. Windoloski², (1)JENTEK Sensors, Inc., Waltham, MA, (2)Jentek Sensors, Inc., Waltham, MA

Abstract

This paper describes advances in the implementation of high resolution imaging with MWM-Array eddy current sensors as a direct replacement for Magnetic Particle Inspection (MPI) and Liquid Penetrant Inspection (LPI) for critical components.  Demonstrated results are provided for engine components, landing gear components, tubing and piping. In one example, for engine disk slot inspection, the MWM-Array eddy current method has demonstrated improved performance in comparison with LPI and conventional eddy-current testing (ET).  Over 3000 slots in titanium alloy engine disks have been inspected with zero false indications. Several cracks have been detected, all of which were missed by conventional ET and LPI, and all verified destructively or by other means.  A comparison is also provided between MPI results and MWM-Array imaging for a steel component, illustrating clear advantages not only in performance but also in ease-of-use and digital data storage.  Also, the MWM-Array can provide reliable inspection of surfaces typically not accessible for MPI or LPI inspection, such as high length-to-diameter ratio holes and tubing inside diameter surfaces. This paper also describes MWM-Array technology and results of specific examples for titanium, and aluminum alloys as well as steel surfaces and components.

Session 4: Property and Damage Characterization

NDE4.1

Materials Prognosis for Solder Interconnect Fatigue Reliability
R. G. Tryon, G. Krishnan, VEXTEC, Brentwood, TN

VEXTEC developed a probabilistic, material microstructural-based fatigue simulation approach for metallic life prediction. This methodology uses virtual testing to address real world variation in loading as well as the microscopic substructure of metals by modeling grain size, grain orientation, micro-applied stress and micro-yield strength as random variables. The fatigue simulation process is segregated into three phases: crack initiation, short crack growth and long crack growth. Global loading conditions, from finite element analyses, are translated to the local material microstructural level using 3-D Voronoi modeling. Although this technology was originally developed for lifing large structural aerospace components, it is now being used to predict fatigue response of electronic device interconnects. Electronic systems, such as circuit boards, are complex multilayered devices consisting of different materials with inherent variability. The electronics industry has extensively researched the root causes of lead solder failure. Thermal cycling causes global stresses across the devices which are translated to the stresses at the local solder material microstructure. Thermal cycling causes intermetallic shifting of the material microstructure that connects the metal to the board substrate. All of this, results in energy build up within solder material grains, which ultimately results in the initiation of a crack within the solder joint which grows to failure over time. Given the microstructural characteristics of lead-free solder, comparisons between these two types of materials can be made using this virtual simulation approach. Years of component or device fatigue testing can now evaluated based on near real time results from thousands or millions of virtual simulations.

NDE4.2

Materials Defect Chracterization Using Mesoscopic Laser Ultrasonic Methods
O. O. Balogun¹, R. D. Huber¹, D. J. Chinn¹, J. B. Spicer², (1)University of California, Livermore, CA, (2)The Johns Hopkins University, Whiting School of Engineering, Baltimore, MD

Microstructural variations in materials lead to measurable changes in ultrasonic wave velocity and attenuation.  Consequently, ultrasound is sensitive to the presence of microstructural defects including dislocation networks, microcracks and voids and can be used to assess the damage state in a material. Furthermore, it is known that effects associated with material microstructures can lead to the nonlinear elastic behavior leading to harmonic generation of ultrasound. These effects are explored in this work for characterization of microscale defects and mesoscale structure in metals and metal alloys. To perform this type of characterization, a laser-based ultrasonic system has been used in which ultrasonic wave generation is achieved using a 900 picosecond pulse duration Nd:YAG laser and ultrasonic wave amplitudes are measured using a path-stabilized Michelson interferometer. Micron scale spatial resolution is achieved with this system by monitoring the variation in the amplitude and attenuation of ultrasound at frequencies up  to 1 GHz.  Experimental results obtained in commercially pure polycrystalline materials without engineered defects indicate that ultrasonic properties over mesoscale dimensions are strongly influenced by local variation in material microstructure.

NDE4.3

Nondestructive Testing Methods for the Determination of Materials Properties
N. Tralshawala¹, H. Sun¹, W. Faidi¹, Y. Plotnikov¹, W. McKnight², (1)GE Global Research Center, Niskayuna, NY, (2)GE Aviation, Cincinnati, OH

The measurement of variations in the materials property (MP) with depth of various surface treated metals and alloys is typically accomplished by destructive methods such as sectioning and/or hole drilling of the surface and then using x-ray diffraction to estimate MP variations as a function of depth. The relationship between the residual stress and electrical conductivity or thermoelectric properties has been investigated to develop nondestructive techniques for this task.

This work describes results obtained from multi-frequency eddy current and thermo-EMF measurements of MP. Small (1.5-3 mm) flexible spiral printed coils were used for the eddy current method. Detailed electromagnetic simulations were carried out to model the coil impedance changes as a function of frequency and material conductivity. Experimentally obtained appeared eddy current conductivity profiles will be presented. Simulations were also performed to optimize parameters for the non-contact thermoelectric system, where thermoelectric currents are detected using the magnetic fields they generate. Surface profiles of the magnetic field were obtained for a given thermoelectric potential difference. Criteria for the magnetic sensor selection will be discussed. Initial data for the proof-of-concept will be shown.

NDE4.4

Comparison Between Imaging Ductile Damage in High Strength Steels Using First-Generation, Synchrotron-Based and Table-Top X-Ray Tomography Systems
R. K. Everett, A. B. Geltmacher, K. E. Simmonds, A. C. Lewis, Naval Research Laboratory, Washington, DC

Advances in x-ray imaging, automation, and computer processing speeds have allowed the development of x-ray tomography systems which can comfortably sit on a laboratory workbench.  These devices can potentially replace the synchrotron sources and supercomputers required only a few short years ago.  In this talk we revisit the tomographic imaging issues associated with ductile damage in HY-100 steel sectioned from interrupted notched tensile test specimens.  Higher x-ray energies and better voxel resolutions are achievable with the table-top unit.   A comparison of tomograms showing void growth and coalescence (number, spatial arrangement, linking) will be presented and consequences for finite element modeling will be discussed.

Plenary Program

Session: Plenary

PL1.2

Evolution of Engines
J. Williams, The Ohio State University, Columbus, OH

Abstract to come.

PL1.3

Evolution of Materials
C. H. Ward, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH

Abstract to come.

PL1.4

Evolution of Design
P. Chivers, Airbus UK, Filton, United Kingdom

Abstract to come.

PL1.5

Evolution of Manufacturing
P. Nuyen, Boeing Commercial Airplanes, Seattle, WA

Abstract to come.

PL1.6

Evolution of Certification
D. Swartz, Federal Aviation Administration, Anchorage, AK

Abstract to come.

Superplasticity and Superplastic Forming

Session 1: SPF Aerospace Applications

SSF1.1

Innovations in the Superplastic Forming and Diffusion Bonding Process
L. D. Hefti, The Boeing Company, Seattle, WA

The Superplastically Formed and Diffusion Bonded (SPF/DB) titanium structure in production today for Boeing products, not including engines, are all diffusion bonded using matched metal tooling and are all fabricated using the common 6Al-4V alloy.  The matched metal tooling concept presents a challenge in obtaining high quality bonds over large areas due to tolerance build-up in the tools and the titanium sheets.  Boeing Commercial Airplanes is currently advancing the state of the SPF/DB process in several ways.  One of these advances is using stop-off between the sheets and diffusion bonding the pack first and then superplastically forming the stiffening features.  This generates a component that is very well bonded in the required locations.  However, this process also has its challenges.  One of these involves how to apply the stop-off material in the proper location using the most cost effective process.  Historically, silk screening has been used to define the required pattern for the stop-off material.  This process requires several pieces of equipment including a wash booth since the screen needs to be cleaned after each part.  A paper maskant and laser scribing process has been developed for defining the stop-off pattern.   Also, because diffusion bonding is performed first, when the component is superplastically formed, there is a tendency to form creases on the surface of the part.  Methods have been developed to eliminate these surface creases on the unformed surface.  Another advance in the SPF/DB process is in the titanium alloys being used for products.  A fine grain 6Al-4V material has been developed that bonds and forms at 1450 °F.  This use of this material will minimize wear on the tools and presses as well as significantly reducing the amount of alpha case on the part surface.

 

SSF1.2

Finite Element Simulation on Superplastic Blow Forming of Ti-6Al-4V Tank and its Verification
J. H. Yoon, H. S. Lee, Y. M. Yi, Korea Aerospace Research Institute, Daejeon, South Korea

In the current study, Ti-6Al-4V tank has been superplastically blow formed from initially diffusion bonded envelope, rather than using two separated blank, and the performance was experimentally verified throughout pressure loading test. A finite element analysis has been carried out in order to establish blow forming process and to obtain the optimal pressure profile. When using initially diffusion bonded envelope, the forming process was divided into three steps; initial opening, free bulging to reduce the diameter of the envelope, and then final sizing. The thickness distribution of the formed tank and deformed shape showed a reasonable agreement with the simulation. In addition, it is construed that the performance of the tank is satisfactory with the design requirement throughout pressure loading test. In the future, more precise control of the diffusion bonding condition should be followed to enhance the reliability of bonded area.

SSF1.3

Superplastic Forming:  Applications and Opportunities in the Aerospace Industry
A. J. Barnes, Superform USA, Riverside, CA

Abstract to come.

SSF1.4

A Historical Perspective of Superplastic Forming Evolution in Aerospace
D. G. Sanders, The Boeing Company, Seattle, WA

Abstract to come.

SSF1.5

Tensile Behavior Simulation of Friction Stir Welded and Superplastically Formed - Friction Stir Welded Titanium Alloy
P. Edwards¹, D. G. Sanders¹, M. Ramulu², (1)The Boeing Company, Seattle, WA, (2)University of Washington, Seattle, WA

A research project was undertaken to evaluate the performance of as Friction Stir Welded (FSW) and Superplastically Formed Friction Stir Welded (SPF-FSW) Titanium joints [1].  This paper presents numerical models which were developed to simulate mechanical response of as FSW and SPF-FSW joints.  The simulation results were then compared to experimentally determined behavior to assess the validity of the modeling approach.  It was found that the proposed numerical modeling method can adequately simulate the behavior of a FSW joint.  However, there were several difficulties associated with the simulation of a FSW-SPF joint.

Session 2: Advances in SPF Aluminum

SSF2.1

Development of a Multi-Stage Forming Process Integrating Hot Drawing with Superplastic Forming
P. A. Friedman, S. G. Luckey, Y. Luo, Ford Motor Company, Dearborn, MI

Superplastic forming (SPF) is a manufacturing process that has the potential to facilitate increased use of aluminum and magnesium in automobile body structures.  Despite considerable advantages with regards to formability and tooling costs, the process has been mostly limited to low volume production due to relatively long cycle times and higher costs associated with fine-grain sheet materials.  This paper focuses on the development of a novel process that integrates hot drawing with SPF to expand the forming limits of difficult to form materials as well as improve production efficiency by enabling significantly faster forming times.  A commercially-available explicit finite element analysis (FEA) code was adopted to establish feasibility of the new forming process and to develop a prototype die with a deep-draw geometry.  The predictive accuracy of the FEA tools was established in terms of thickness distribution and material draw-in by correlating simulation results with experiment.  Forming trials verified that this novel technology can deliver a superior thickness profile and significantly decrease forming time as compared to conventional SPF.  Furthermore, it has been demonstrated that this technology enables the forming of conventionally-processed aluminum and magnesium sheet into deep-draw panels that cannot otherwise be formed by conventional stamping or SPF processes.

SSF2.2

Design and Experimental Validation of a Two Stage Superplastic Gas Forming Die 
S. G. Luckey¹, P. A. Friedman¹, K. J. Weinmann², (1)Ford Motor Company, Dearborn, MI, (2)University of California - Berkely, Berkeley, CA

The conventional superplastic forming (SPF) of complex and deep geometries can result in excessive thinning and necking.  To address these issues, a two stage SPF process has been developed and demonstrated in forming trials using a superplastic aluminum sheet alloy.  This process preforms the blank with gas pressure to create length of line, while preserving metal thickness in certain regions to improve the thickness profile of the final part.  In this paper, a preform has been designed to improve the forming of a complex component by providing a superior thickness profile and enabling a faster forming cycle as compared to a conventional single stage forming cycle.  Finite element analysis was essential to the development of the preform since the preforming surface was not intuitive and could cause wrinkling in the final part. 

SSF2.3

Controlled Biaxial Testing of AZ31 Magnesium Alloy at Elevated Temperatures
M. K. Khraisheh¹, F. Abu-Farha², (1)Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates, (2)Penn State University/Erie, Erie, PA

Abstract to come.

SSF2.4

Improved Lubricant Formulation for Elevated Temperature Aluminum Forming Processes
M. D. Hanna¹, P. E. Krajewski², J. G. Schroth², (1)GM Reserach and Development Center, Warren, MI, (2)GM Research and Development Center, Warren, MI

Development of lubricants for elevated temperature metal forming processes such as Quick Plastic Forming (QPF), Superplastic Forming (SPF), or warm forming requires the following features; low coefficient of friction, good adhesion to the blank, uniform application pattern, low cost and ease of removal after forming.  This study focuses on the tribological performance and evaluation of alternative solid lubricants using flat-on-flat testing tribo-tester to simulate sheet forming at high temperature applications. Improved lubricant formulations containing boron nitride lubricant with graphite additions were found to enhance lubricity while maintaining good adherence to the surface of the aluminum blank temperatures.

SSF2.5

Use of In-situ Reinforcements During Hot Blow Forming
M. D. Hanna¹, P. E. Krajewski², (1)GM Reserach and Development Center, Warren, MI, (2)GM Research and Development Center, Warren, MI

Hot blow forming enables complex shapes to be formed which provide part consolidation and reduce the number of dies required to make a given component.  The excessive thinning during forming often necessitates the use of reinforcements in service which are welded or bonded to the blow formed part.  The present work investigates a number of methods for forming these reinforcements in-situ during forming of the main component.  which can provide a perfectly matched reinforcement for the panel.  A number of methods are discussed including bonding reinforcements prior to forming, locating the reinforcement in the die prior to introducing the large blank, or multiple sheet forming.  Issues with implementing these approaches are discussed and opportunities for further developed are provided.

SSF2.6

Microstructural Evolution During Tensile deformation of Near-Nano Cryomilled Al-6.5%Mg Alloy
Y. Xun, F. Mohamed, University of California, Irvine, Irvine, CA

Tensile tests were performed on a cryomilled Al-6.5%Mg with an average grain size of 300 nm at temperatures of 473, 573 and 673 K and strain rates of 10^-2, 10^-3 and 10^-4 s^-1. The microstructures associated with deformation were characterized by means of transmission electron microscopy (TEM). Experimental data show that ductility increases with increasing strain rate and decreasing temperatures. A considerable strain hardening behavior was observed in the sample tested at 473 K and 10^-2 s^-1. Three types of deformation microstructures were identified: fine equaxid, coarse equiaxid and elongated band-like structures. The dislocation density was found to decrease with deformation. Consideration of these observations leads to the conclusion that grain boundary sliding rather than conventional dislocation slip serves as the major deformation mechanism. The observed mechanical behavior can be explained in terms of the effects of the complex microstructures developed and the accommodation process for grain boundary sliding.

Session 3: Superplasticity Theory and Metallurgy

SSF3.1

To Be Determined Aluminum SPF Topic
A. Ghosh, University of Michigan, Ann Arbor, MI

Abstract to come.

SSF3.2

ASTM E2448 – A Unified Test for Determining SPF Properties
P. N. Comley, The Boeing Company, Seattle, WA

Abstract
The determination of the superplastic properties of a material, just like any mechanical property, is highly dependent on the test method, coupon geometry and analysis of the raw data from the test. Thus the published properties of a material from one source will differ from that of another source unless a common test method is employed.  The ASTM E2448 Standard Test Method for Determining the Superplastic Properties of Metallic Sheet Materials has been written to provide a common platform for testing, evaluating and publishing superplastic properties to a uniform format, useful for both academia and industry. The Boeing Company is now using ASTM 2448 to quantify the superplastic properties of fine grain Ti-6Al-4V alloy, and is specifying it to qualify production material to the Boeing Material Standard BMS7-385.
The standard includes specimen geometry and testing conditions, the test machine requirements, and how to analyze the data, including the basic stress v. strain curve and determination of ‘m’ value.

SSF3.3

Investigation of Post-Superplastic Forming Properties Under Different Loading Paths
M. K. Khraisheh¹, F. Abu-Farha², (1)Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates, (2)Penn State University/Erie, Erie, PA

Abstract to come.

SSF3.4

Correlation of Alpha Case and Fatigue Results in Titanium after Simulated SPF Exposure
F. S. Pitt¹, M. Ramulu², (1)The Boeing Company, Seattle, WA, (2)University of Washington, Seattle, WA

Abstract to come.

SSF3.5

Interaction of Magnesium Sheet with Steel Tool during High Temperature Forming
M. D. Hanna¹, N. Mahayotsanun², J. T. Carter¹, R. Verma³, (1)GM Reserach and Development Center, Warren, MI, (2)Northwestern University, Evanston, IL, (3)General Motors, Warren, MI

An investigation was undertaken to understand the interaction between a steel tool and AZ31 magnesium alloy sheet during high-temperature forming.  A new flat-on-flat tribo-testing method involving reciprocating sliding of steel specimens against magnesium alloy sheet at elevated temperature was used to determine the effects of temperature, load and lubricant thickness on the steel tool/magnesium sheet interaction.  The coefficient of friction increased with increasing test temperature but was reduced substantially by the use of a solid lubricant.  The tribological behavior of the magnesium alloy is compared with that of aluminum alloy AA 5083.

Titanium Alloy Technology

Session 1: Alloy Development

TAL1.1

The Titanium Alloy Development Challenge
J. D. Cotton, The Boeing Company, Seattle, WA

The aerospace industry has long been viewed as the recipient of the

latest materials technologies, where any weight reduction is considered

justification for development. But in fact, the present aerospace

industry is quite risk-adverse and cost-sensitive. Improved performance,

in terms of improved properties or reduced density, is only useful if

the cost of the improvement is exceeded by weight or life improvements.

Thus, goals for new titanium-based materials must include (in addition

to improved performance): robust property suites with a low sensitivity

to chemistry and process variability, simple processing requirements,

affordable constituents, and low-cost approaches to shape, fabricate and

machine. For large airframe components, the ability to produce single

components of large dimension and heavy section thickness is helpful.

Therefore, the challenge is developing and maintaining processes that

result in titanium alloys that are consistent and affordable, not just

strong and light. This paper will elaborate and extend this challenge to

titanium researchers and suppliers.

TAL1.2

Assessment of Advanced Titanium Alloys for Affordability
J. Meudt, Ladish Co., Inc., Cudahy, WI

The concern with cost in the aerospace industry is increasing and there is a need to reduce these costs creating affordable applications.  There are new titanium alloys being designed to reduce the overall processing costs and to improve performance such as strength, stiffness, or microstructure over traditional titanium, steel, and aluminum alloys.  Three of these new titanium alloys; Timetal54M, Ti6-4 modified with boron, and Ti5553, have been evaluated and the forging, casting, and machineability results will be presented.

TAL1.3

ATI Allvac Development of Ti-5-5-5-3 for Aerospace Structural Applications
J. V. Mantione, T. D. Bayha, Allegheny Technologies Incorporated (ATI), Monroe, NC

Titanium alloy 5-5-5-3 (Ti-5Al-5V-5Mo-3Cr) is a near beta titanium alloy intended for fatigue and fracture toughness limited aircraft structural applications requiring superior tensile strength when compared to beta processed alpha/beta titanium alloys.  Its ability to be forged into complex shapes and heat treated to above 180 ksi ultimate tensile strength makes it a promising titanium alloy material for landing gear applications over traditional Ti alloys such as Ti-10-2-3.  Additionally, the inherent corrosion resistance of titanium alloys relative to steels reduces operation and sustainment costs for the airline industry.  Reducing the bulk weight of the major structural components while simultaneously increasing system operating efficiency is currently a key challenge for the aircraft design community.  The mechanical properties of alloy Ti-5-5-5-3 are developed by sub-transus solution heat treat or supra-transus beta anneal and appropriate ageing to control grain size and precipitation in the wrought microstructure.  Based on a history of successfully casting highly alloyed titanium ingots with precise chemistry, ATI Allvac has leveraged extensive experience with Cold Hearth Plasma Melting for the production of Ti-5-5-5-3 ingot.  An added benefit for flight critical hardware is the extremely low melt-related defect rate historically demonstrated by Cold Hearth Plasma Melted titanium ingots in jet engine rotating components.

TAL1.4

Effect of Thermomechanical Processing on Properties of TIMETAL 555
V. Venkatesh¹, J. Fanning², (1)TIMET-R&D,, Henderson, NV, (2)TIMET-R&D, Henderson, NV

TIMETAL 555 (Ti-5Al-5Mo-5B-3Cr), a near beta titanium alloy, is capable of attaining a good combination of strength, ductility and toughness, for use in structural airframe parts. In order to achieve optimal mechanical properties, good control of thermomechanical processing parameters is required. This study summarizes the effect of processing conditions, such as temperature, strain and strain rate, on flow localization, damage and microstructural evolution. In addition, the effects of solution treatment temperatures, cooling rates and aging conditions on tensile and fracture properties will also be discussed.

TAL1.5

High Strength, Lightweight Cast Titanium Alloys for Airframe Structures
E. Y. Chen¹, L. W. Weihmuller², D. R. Bice¹, W. A. Thomas², G. D. Hall², (1)Transition45 Technologies, Inc., Orange, CA, (2)Bell Helicopter Textron, Hurst, TX

It is well established that military aircraft systems would benefit greatly from the development and application of high strength, lightweight titanium alloys with improved durability and damage tolerance.  Naval aircraft have requirements for such alloys for current and next generation airframes, particularly if they can be used in the cast form for affordability.  For certain classes of airframe components, it well established that the potential cost savings can be significant if they were converted from a machined forging to a machined Ti-6Al-4V investment casting.  The primary purpose of applying a higher strength-low weight titanium alloy versus Ti-6Al-4V would be to allow direct conversion of these forged components to titanium castings without sacrificing strength or increasing weight.  This potential weight saving is especially advantageous for rotorcraft.  This study evaluates the high strength, lightweight titanium alloys Ti-6Al-2Sn-2Zr-2Mo-2Cr (Ti-6-22-22) and Ti-5Al-5Mo-5V-3Cr-0.5Fe (Ti-5553) as castings.  The castability of these alloys as compared to Ti-6Al-4V will be investigated, as well as their microstructure-properties including tensile and fatigue behavior.  A comparison of the mechanical properties of these cast alloys versus those of their wrought counterparts will also be made and these results will be discussed in light of potential applicability to naval airframe structures.

TAL1.6

Recent Progress in the Development of New Titanium Alloys
Y. Kosaka, S. P. Fox, Timet, Henderson, NV

There has been a notable progress in the development of new titanium alloys for non-aerospace applications in recent years particularly in US and Japan. Since the process steps required for the qualification of new alloys in non-aerospace applications is not as stringent as that for aerospace applications normally, the introduction of new alloys in non-aerospace applications is relatively easier and faster. This paper will review the recent progress in the development and the application of new titanium alloys primarily in automotive applications and introduce the characteristics and production experiences of the alloys. The alloys include TIMETAL 54M (Ti-5Al-4V-0.7Mo-0.5Fe) and TIMETAL Exhaust XT (Ti-0.25Fe-0.4Si). The advantages of new alloys over existing alloys and the potential for aerospace applications will be discussed.

Session 2: Titanium General

TAL2.1

Laser Clad Repair of Dissimilar Titanium Alloys
K. Shanker¹, B. Junkin¹, J. Cuddy², (1)Standard Aero Ltd., Winnipeg, MB, Canada, (2)Standard Aero Ltd, Winnipeg, MB, Canada

Cladding of titanium alloys using a laser as a heat source has been successfully used for a number of years. Much of this usage involves powder feed-stock and, in general, of a composition very similar to the base alloy being clad. While powders in a wide range of compositions are available, the large surface area of the powders and the cladding operation itself makes it difficult to ensure a low oxygen content in the cladding. Even small concentrations of oxygen can cause a significant decrease in the ductility of the cladding. Therefore, inert gas enclosures surrounding the cladding area are usually necessary, which is difficult when cladding large or complex shaped parts. The work presented in this paper investigates the use of Ti-6Al-4V wires as feed-stock; high purity Ti-6Al-4V wire in different diameters are readily available, making them ideal filler materials.  The effect of laser cladding of two different titanium alloys (Ti-17 and Ti-5553) subject to different pre- and post- heat treatments will be presented, with particular emphasis on their tensile and impact properties. Both of these alloys are, like Ti-6Al-4V, mixed (a+b) phase alloys, but have compositions and b-phase contents that differ. Dense, crack- and pore- free claddings in excess of 3mm thickness x 25mm width are consistently obtained with wire feed-stock. The mechanical properties of the cladded material combination will be measured by tensile, bend and impact testing of test samples that are a composite of the base alloy and the clad layer, to simulate the mechanical properties of locally clad repaired parts. The bond tensile properties of cladded alloys will be measured using Ti-17 and 5553 laser welded together with Ti-6Al-4V wire, with the weld being transverse to the direction of testing. Welded and clad Ti-6Al-4V base alloys will be used for comparison.

TAL2.2

Comparative Fatigue Study of Titanium Alloys including ATI 425(tm), Ti325 and Ti64
M. E. Martinez, J. Hebda, R. A. Graham, ATI Wah Chang, Albany, OR

It can be a challenge to compare data found in the literature on titanium alloy properties.  The effect of processing history can make separating property differences due to a material composition from those due to processing a complex task.  To assist in comparing the fatigue properties of Allegheny Technologies ATI 425™ alloy (4Al-2.5V-0.2Fe-0.2O) to Ti 6Al-4V Super ELI and Ti 3Al-2.5V alloys, a study was undertaken whereby the materials were processed similarly from billet to sheet.  The temperatures for hot work and annealing were adjusted for each alloy’s beta transition temperature, but the reduction schedule and other process steps were identical for each alloy.  Fatigue testing was performed on unnotched tensile coupons in the transverse direction with an R-ratio of 0.1.  Stress versus cycles to failure (S-N) curves were developed for three anneal cycles for ATI 425™ alloy, as well as the Ti6-4 and Ti325 alloys.

TAL2.3

Identifying Microstructural Units in Titanium Using Heat Tinting
M. Harper, Y. Kosaka, S. P. Fox, Timet, Henderson, NV

Heat tinting is a seldom-used metallographic technique whose usefulness may prove valuable when characterizing titanium alloys. Like other sample preparation techniques, heat tinting makes use of the differences in phase composition and crystal structure to gather information about microstructural features. Using a low temperature heat treatment to build an oxide film on a well-polished surface is the essence of this simple technique. The rate of film growth has been shown to vary with the crystallographic orientation of the underlying alpha and beta phases as well. Good color contrast is achieved when a heat tinted sample is viewed using polarized light. While the technique cannot reveal detailed orientation information, the result is a view of the effective structural unit size and shape of the material. These colorful results are compared to those of other characterization techniques to show that features such as texture bands may be seen without employing costly texture analysis. It is believed that the use of heat tinting as a quick and easy tool will provide supplemental information to typical microstructure characterization. In addition, the texture structure may be useful in further understanding the relationships of processing, microstructures, and properties.

TAL2.4

Ballistic Performance of Thin Titanium Plates
M. S. Burkins, U.S. Army Research Laboratory, APG, MD

In the United States, titanium armor is procured to the requirements of the MIL-DTL-46077F armor specification.  However, this specification does not cover thicknesses below 6.35mm.  The Army Research Laboratory (ARL) conducted an initial assessment to determine if the specification can be modified to include thicknesses as low as 3mm.  Plates in thicknesses from 3mm to 6.35mm were obtained and testing was conducted with fragment simulating projectiles (FSPs) and with bullets in order to look at target failure modes and to assess the best ballistic test projectile to use for the modified specification.  Some additional testing was performed with commercially pure titanium (CP Ti) and with a high-strength beta alloy (Ti-10V-2Fe-3Al) for comparison.

TAL2.5

Near-Net Extrusion: An Ideal Manufacturing Process for High - Strength Titanium Aerospace Components
J. Phillips, T. Esposito, Plymouth Engineered Shapes, Hopkinsville, KY

The prime aerospace companies and their subcontractors, as well as several aerospace service centers are currently using titanium extrusions in commercial and military aircraft and assemblies. Some proven applications for titanium extrusions include floor beams, seat tracks, engine pylons, pylon attach beams, chords, stiffeners, stringers, spars, longerons, belly fairings, flap and slat tracks, hinges, mounting brackets, jet engine rings and related components and space vehicle components. The total cost savings benefits of selecting the near-net extrusion process can be substantial.

Extrusion provides advantages not offered by alternative methods such as forging or machining from bar or plate stock. Economic advantages include minimal tooling costs, reduced material usage, lower parts count resulting from the ability to extrude complex shapes over length in a single operation and less downstream machining and finishing. The quality benefits of extrusion include improved surface quality and superior flatness and straightness, which is especially critical for long-length structural operations. Specifying titanium near-net extrusions for high-strength structural parts and high temperature engine components can deliver significant cost and quality benefits to aerospace manufacturers.

Session 3: Powder Metallurgy

TAL3.1

Effect of Electron Beam Freeform Fabrication (EBF3) Processing Parameters on Composition and Geometry of Ti-6-4
C. L. Lach¹, K. M. B. Taminger¹, A. Schuszler II¹, S. N. Sankaran², (1)NASA Langley Research Center, Hampton, VA, (2)Lockheed Martin, Hampton, VA

The Electron Beam Freeform Fabrication (EBF³) process developed at NASA Langley Research Center was evaluated using a design of experiments approach to determine the effect of processing parameters on the composition and geometry of Ti-6-4 deposits.  The effects of three processing parameters: beam power, translation speed, and wire feed rate, were investigated by varying one while keeping the remaining parameters constant.    A three-factorial, three-level, fully balanced mutually orthogonal array (L27) design of experiments approach was used to examine the effects of low, medium, and high settings for the processing parameters on the chemistry, geometry, and quality of the resulting deposits.  Single bead high deposits were fabricated and evaluated for 27 experimental conditions.  Loss of aluminum in Ti-6-4 was observed in EBF³ processing due to selective vaporization of the aluminum from the sustained molten pool in the vacuum environment; therefore, the chemistries of the deposits were measured and compared with the composition of the initial wire and base plate to determine if the loss of aluminum could be minimized through careful selection of processing parameters.  The influence of processing parameters and coupling between these parameters on bulk composition measured by Direct Current Plasma (DCP), local microchemistries determined by Wavelength Dispersive Spectrometry (WDS), and deposit geometry will also be discussed.

TAL3.2

Electron Beam Free Form Fabrication Processing Methods: State of The Technology
K. W. Lachenberg, S. D. Stecker, R. C. Salo, Sciaky, Inc., Chicago, IL

Abstract: Electron Beam Free Form Fabrication is a process that utilizes proven EB Welding Technology to create metallic parts using an additive layering method to produce near-net-shape preforms using high deposition rates.  This process is ideally suited to a wide range of aerospace materials including many reactive and refractory alloys.   

 

The aerospace industry has been challenged in procuring many structural components.  Lead times in the Ti industry, for example, have been driven by material availability and processing limitations that force customers to wait 12 to 24 months until completion.  Through the use of generic raw materials and simplified tooling, EBFFF promises great potential for significant reductions in lead times. High value low volume structural assemblies appear to be ideally suited to the EBFFF process. 

 

This presentation will focus on recent experience with the fabrication of Ti-6Al-4V aerospace components using Sciaky’s EBFFF equipment. Successes and challenges will be reviewed as they pertain to programming, distortion control, metallurgical tests and general process improvements in recent months.

TAL3.3

Mechanical Properties of TiB Whisker-Reinforced Titanium by Spark Plasma Sintering
H. Izui, Nihon University, Chiba, Japan

Discontinuously reinforced titanium composites containing titanium boride(TiB) whisker are emerging as possible candidate materilals for advanced aerospace applications.  Because all of the attractive reinforcements, such as SiC, Al₂O₃, Si₃O₄, and B₄C, lead to the formation of reaction products at the interfaces.  TiB as reinforcement for Ti is the most attractive because of the absence of an intermediate phase between Ti and TiB.  The TiB phase provides significant increase in strength and stiffness without increasing density.  The coefficient of thermal expansion of TiB is comparable to that of titanium, which eliminates residual stresses at the interfaces between Ti and TiB.

A TiB reinforced titanium matrix composite is produced by a cost-effective sintering process called Spark Plasma Sintering (SPS).  In the SPS, the pulsed DC current goes through the powder directly.  Compared to HIP or hot-pressing(HP) SPS can be consolidated lower temperature and shorter sintering duration.  The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) by exploiting the simultaneous TiB whisker formation and the densification occurring during the spark plasma sintering process.  The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at sintering temperature ranging from 800°C to 1000°C and at sintering duration from 10 min to 50 min.  The mechanical properties of TiB whisker-reinforced titanium composite were found to be influenced by the sintering conditions.  Tensile specimens of TiB/Ti composites were tested at room temperature, 200, 400, 600, and 800^oC.  Fatigue tests of the composites were carried out at room temperature and 600^oC.  The evolution of the composite microstructure, the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.

TAL3.4

Titanium Alloys Modified with Boron: A Current Update
S. Tamirisa¹, D. B. Miracle², R. Srinivasan³, V. Sinha², (1)FMW Composite Systems Inc., Bridgeport, WV, (2)Air Force Research Laboratory, Wright-Patterson AFB, OH, (3)Wright State University, Dayton, OH

Small additions of boron (£1 wt %) to titanium alloys provide important benefits. These boron additions result in dramatically finer grain sizes in the as-cast condition. In addition, grain growth is inhibited, even above the beta transus. Together, these features offer the potential to develop disruptive thermo-mechanical processing paths for titanium. The finer grain size improves hot workability, and inhibited grain growth above the beta transus may open up the processing window, enabling higher deformation rates and lower press forces. The boron is essentially insoluble in titanium and precipitates as fine (~1 mm diameter) TiB whiskers that increase the strength and stiffness by up to 30% while retaining acceptable tensile ductility, fracture toughness, and fatigue properties. A current overview of the progress achieved toward establishing thermo-mechanical processes and applications of boron-modified titanium alloys will be presented.

TAL3.5

Cost Effective Powder Metallurgy Approach for Producing Ti Alloys
F. Sun, D. K. O. (. Yu, RTI International Metals Inc., Niles, OH

A cost effective powder metallurgy approach has been employed for producing Ti-6Al-4V alloy. Pressed and sintered Ti-6Al-4V compacts were from two types of titanium powders. CP titanium powders from the Armstrong process were blended with Al-V master alloy, and then pressed and sintered at elevated temperatures. Prealloyed Ti-6Al-4V powder from the Armstrong process were directly pressed and sintered.  Pressed and sintered Ti-6Al-4V compacts were characterized in terms of chemistry, microstructure and properties. Effects of sintering and hot rolling on the microstructure and mechanical properties of Ti-6Al-4V alloy have been studied. Sintering and hot rolling processes was found to have significant influence on microstructure and mechanical properties.

Session 4: Titanium Modeling

TAL4.1

Grain Size Modeling of Investment Cast Ti-6Al-4V
D. S. Lee¹, S. J. Veeck¹, S. Cheong², (1)Howmet Research Corporation, Whitehall, MI, (2)Alcoa Technical Center, Pittsburgh, PA

Experimental evaluations were conducted to examine the grain growth of the beta phase in investment cast Ti-6Al-4V as a function of time and temperature.  These data were then used as input to the subsequent development of a model that would allow the prediction of grain size in titanium castings, based on the  thermal history of the casting during solidification. Using Procast to model thermal history, validation of the grain growth model was conducted using an investment cast step block.  Prior studies have shown a relationship between the beta grain size in titanium and the tensile properties of the casting.  The availability of a model to predict grain size will enhance the prediction of tensile properties in titanium casitngs during the early stages of design.

TAL4.2

Static and Dynamic Coarsening and Plastic Flow of Ti-6Al-4V
G. A. Sargent¹, D. Li², S. L. Semiatin³, (1)University of Dayton, Dayton, OH, (2)RMI Titanium Company, Niles, OH, (3)Air Force Research Laboratory, Wright-Patterson AFB, OH

Ultrafine microstructure Ti-6Al-4V material was obtained in both sheet and billet form via severe plastic deformation processes.  Static coarsening of the microstructure of both materials was measured at temperatures of 775 and 815^oC for annealing times up to 96 hours.  Hot compression and hot tension tests were conducted to establish the dynamic coarsening and its impact on the plastic flow response also at temperatures of 775 and 815^oC at strain rates of 10^-3 -10^-4. The influence of particle size, diffusivity, alpha/beta interface energy, and phase equilibria on static and dynamic coarsening was established.   The static and dynamic coarsening kinetics were interpreted in terms of models previously determined for the coarsening behavior at higher temperatures (900, 955^oC).   The flow-hardening behavior at 775 and 815^oC was discussed in relationship to the dynamic-coarsening rates. Detailed microstuctural characterization enabled the determination of the effect of particle size, shape, and stability on plastic flow at temperatures between 775 and 995^oC.

TAL4.3

Progress Towards the Development of a Creep-Resistant b-Titanium Alloy Based on Timetal-21S
B. Peterson, P. Collins, V. Levit, H. Fraser, The Ohio State University, Columbus, OH

The composition of the alloy Timetal 21S has been selected as a baseline for the development of a new high temperature beta titanium alloy. A combinatorial approach employing directed laser deposition of elemental powders has been used to produce a number of test coupons that represent a controlled variation of alloy composition. Subsequently, the creep properties are assessed using an Instron ETMT instrument operating in a constant load mode, and represented by their minimum creep rates (i.e., the tests are terminated as soon as minimum creep is achieved). The microstructures of the test coupons are characterized using rigorous stereological techniques. These data populate the databases used to train and test fuzzy logic based models for predicting the creep properties. In addition to the base elements (Ti, Mo, Nb, Al, and Si), neutral elements (Zr and Sn), beta-stabilizers (W), and dispersoid formers (B, C, Ge) are being tested as alloying additions. The most promising alloying additions have been identified. Based on the results of the coupled mechanical tests and computer models, a new group of alloys for application in high temperature thermal protection systems are being developed.

TAL4.4

Investigation of the Early Stages of  a Nucleation and Growth in b-Titanium Alloys
S. Nag¹, P. Collins², G. B. Viswanathan³, H. Fraser², R. Banerjee¹, (1)University of North Texas, Denton, TX, (2)The Ohio State University, Columbus, OH, (3)Universal Energy Systems, Dayton, OH

Titanium alloys containing substantial amounts of b-stabilizing alloying additions often retain a single metastable b phase on fast cooling from above the b-transus temperature. However, strictly speaking this single b phase often consists of nanometer-scale solid-state decomposition products such as b phase separation, the omega and alpha phases. Ageing of these alloys after quenching results in coarsening of these phases, possibly accompanied with additional phase transformations. By employing 3D atom probe tomography, carried out in a local electrode atom probe (LEAP) instrument, these early stages of decomposition of the b phase have been investigated in some complex commercial alloys such as Ti-5Al-5Mo-5V-3Cr-1Fe (TIMETAL-5553 or Ti-5553) and Ti-35Nb-7Zr-5Ta (TNZT). While the former alloy is of interest in the aerospace industry, the latter alloy is of interest for biomedical applications. The results of these studies coupled with relevant TEM investigations of the same materials will be presented.

TAL4.5

The Application of Bayesian Neural Network Modeling for the Prediction of Tensile, Toughness, and Fatigue Properties in a/b Ti Alloys
S. K. Koduri¹, B. Welk¹, P. C. Collins², G. B. Viswanathan¹, H. Fraser¹, (1)The Ohio State University, Columbus, OH, (2)Quad City Manufacturing Lab, Rock Island, IL

The development of a set of computational tools that permit microstructurally-based predictions for mechanical properties of commercially important titanium alloys, such as Ti-6Al-4V and Ti-6242, is a valuable step towards the accelerated maturation of materials. This paper will discuss the development of Neural Network Models based on Bayesian statistics to predict the yield strength, ultimate tensile strength and fatigue of Ti-6Al-4V at room temperature, as well as the fatigue in a/b processed Ti-6242. The development of such rules-based models requires the population of extensive databases.  For the case of Ti-6Al-4V, the database contains both compositional and microstructural information.  For the case of Ti-6242, the database contains both microstructural and experimental information (frequency, temperature, and stress). These databases have been used to train and test Neural Network models to predict the tensile and fatigue properties. In addition, these models have been successfully used to identify the influence of individual microstructural features on the mechanical properties, consequently guiding the efforts towards development of more robust phenomenological models.

TAL4.6

Quantification of High Temperature Strength and Flow Stress Curves in Titanium Alloys
N. Saunders, Z. Guo, J. -. P. Schillé, A. P. Miodownik, Sente Software Ltd., Guildford, United Kingdom

A key element in thermo-mechanical processing practice and simulation of metallic alloys is the high temperature mechanical behaviour, particularly with respect to flow stress as a function of temperature and strain rate.  It is therefore of substantial interest to develop physically based models that can both account for known experimental data and be applied to new and very different regimes with great confidence.

This paper describes the recent developments of JMatPro, a computer software for material property simulation, on calculating high temperature strength and flow stress curves of titanium alloys.  The first part of the paper provides a background to the related models for high temperature strength and flow stress curve modelling.  The high temperature strength is found to be not only a function of microstructural changes in the material, but the result of a competition between two deformation modes, i.e. the normal tensile deformation and the deformation via a creep mode.  Extensive validation has been carried out during the model development and is shown in the second part of the paper.  Good agreement between calculated and experimental results has been achieved for a wide range of titanium alloys, including alpha, near-alpha, alpha+beta, and beta types.  A feature of the new program is that the models are based on sound physical principles rather than purely statistical methods.  Thus many of the shortcomings of methods such as regression analysis can be overcome.

Keywords:      Titanium alloys; JMatPro; High temperature strength; Property simulation.

TAL4.7

Predictability Of Fracture Toughness In Ti-6al-4v Alloy Rings For Aerospace Application : A Practical Experience
U. V. Gururaja, M. N. Rao, Mishra Dhatu Nigam Limited (MIDHANI), Hyderabad, India

The present ever increasing designer product performance demands shall be the driving force for continuous improvements in the product manufacturing techniques.  In spite of over four decades of research on workhorse alloy 6-4, it is often quite difficult to fully understand the role of microstructure and alloy chemistry on mechanical properties of Ti-64.

 

            In the current study, a number of production heats were analysed for variation in Fracture toughness values, keeping constant processing parameters.  The paper brings out the Fracture toughness prediction band in the form of NAF (Net Alpha Formers) and NBF (Net Beta Formers) for a given chemistry and process route.  The observed effect of primary alpha with respect to NAF and NBF on Fracture toughness values will also be presented.

Session 5: Armstrong Powder Technologies: An Update

TAL5.1

The Armstrong Titanium Production Process
T. Lyssenko, International Titanium Powder LLC, Lockport, IL

In aerospace applications, as with other markets, titanium cost and availability is a major factor in system design.  Traditional Titanium production methodologies have never been able to achieve a stable price points which allow full utilization of the metal's superior properties.  The development of the "Armstrong" Production Process with its direct production to titanium/titanium alloyed powders has brought forth an entirely new understanding of the use and applications of this family of critical materials.  The presentation will provide an overview and present status of the low-cost Armstrong Titanium Production Process.

TAL5.2

Melt Processing of Armstrong Titanium and Titanium Alloy Powders
K. O. (. Yu¹, F. R. Dax², T. Lyssenko³, S. Luckowski⁴, (1)RTI International Metals Inc., Niles, OH, (2)Concurrent Technologies Corporation, Pittsburgh, PA, (3)International Titanium Powder LLC, Lockport, IL, (4)US Army, ARDEC, Picatinny Arsenal, NJ

Ti-6Al-4V 0.5" plates were rolled from 2.75" x 8" x 30" slabs made by PAM single melting of Armstrong powders. Armstrong powders were mixed with Al-V master alloy powders to form the Ti-6Al-4V chemistry. The mixture of these powders were then pressed to 2 lb weight compacts which were used as the input material for PAM processing. Rolled plates were heat treated and evaluated for microstructure, mechanical properties, weldability and ballistic property.

Powders produced by ITP's Armstrong Process can be used as a sponge replacement for the conventional melt processing as well as input material for the powder metallurgy non-melt processing.  This presentation provides a summary of the process and results conducted at RTI and Concurrent Technologies Corporation (CTC) and funded by the US Army in using ITP powder in manufacturing plate from cast slabs produced from plasma melting of the powder.

TAL5.3

Press and Sinter Processing of Armstrong Titanium Powders
T. Zwitter¹, P. Nash², (1)Webster-Hoff Corporation, Glendale Heights, IL, (2)Illinois Institute of Technology, Chicago, IL

The Powder Metallurgy Industry is a well developed world wide commercial industry, annually producing 50,000 tons of cost effective press and sinter components from iron, steel, stainless steel, bronze, copper, and other metal powders. The technology for press and sinter of Titanium and Titanium alloy powders is not yet commercially developed. With the availability of lower cost Titanium Powders from the Armstrong Process, Webster-Hoff has been working with Illinois Institute of Technology to develop a commercially viable process for low cost press and sinter Titanium alloy components for a wide variety of applications. This paper will report on the progress to date of these process development endeavors.

TAL5.4

Non-Melt Consolidation Techniques of Armstrong Titanium and Pre-Alloyed Titanium Powders for Production of “Low Cost” Plate, Sheet, and Bar Components
C. Yu¹, C. R. Scorey¹, W. H. Peter², J. E. McKernan¹, C. A. Blue², (1)AMETEK, Inc., Wallingford, CT, (2)Oak Ridge National Laboratory, Oak Ridge, TN

Ti-6Al-4V and CP Ti powders have been consolidated into sheet, plate and bar shapes using the near net shape powder metallurgical processes of cold roll compaction and CIP.  Mechanical properties and microstructures developed in roll compacted sheet after processing to full density through cold rolling and sintering steps are discussed.  Shapes formed in CIP have been taken to full density with a single PIF (pneumatic isostatic forging) step.  Microstructures obtained following PIF and after subsequent heat treatment are presented.

TAL5.5

Joining Evaluations of “Low-Cost”, Armstrong Ti-6Al-4V Plate
N. B. Dahotre, University of Tennessee, Knoxville, TN

Abstract to come.

TAL5.6

Powder Morphology Modification and Consolidation Techniques of Armstrong Titanium Powder
W. H. Peter¹, C. A. Blue¹, J. O. Kiggans, Jr.¹, D. C. Harper¹, D. Kogut², W. Ernst², L. Jacobsen², C. R. Scorey³, C. Yu³, J. E. McKernan³, (1)Oak Ridge National Laboratory, Oak Ridge, TN, (2)International Titanium Powder LLC, Lockport, IL, (3)AMETEK, Inc., Wallingford, CT

Powder handling practices and room temperature consolidation techniques have been of interest with Armstrong process powders due to the sponge-like morphology and low initial tap densities.   Cost effective methods to increase the apparent densities of the powders are required to improve volumetric processing considerations and efficiencies in the shipping and handling of powders.  However, the pickup of oxygen and other interstitials must be minimized.  Powder attrition techniques, such as ball and jet milling, and the resulting chemistries and morphologies will be reviewed.  Recent studies investigating the cold consolidation of these powders, including cold hydraulic pressing and roll compaction followed by cold rolling, will also be discussed. Lastly, unique rapid thermal processing technologies will be examined that can be used to modify the initial powder morphology of the Armstrong powder.

Welding and Joining Technologies

Session 1: Welding and Joining 1

WDJ1.1

Implementation of a Bellville Spring Stack Opposed Shoulder and Retractable Tool Pin Design in the FSW of Closed Contours
D. H. Lammlein¹, T. J. Lienert², M. Bement², D. DeLapp³, G. Cook³, A. Strauss³, T. Bloodworth³, P. Fleming³, T. Prater³, M. Wilkes³, (1)Welding Automation Laboratory Vanderbilt University, Nashville, TN, (2)Los Alamos National Laboratory, Los Alamos, NM, (3)Vanderbilt Univertsity, Nashville, TN

Demonstration has shown that the Friction Stir Welding of closed contours can be accomplished via the gradual insertion and retraction of a tool pin relative to its shoulder during the weld traverse.  In this work, a novel method of pin retraction and shoulder force control is implemented.  In this method, a Bellville disc spring stack is used to maintain shoulder pressure on the workpiece throughout the welding process.  This process involves simultaneous movement in the traverse and plunge axes; the automated axes of a vertical mill are used to accomplish this.  A four axis dynamometer is integrated into this setup for the purposes of mechanistic analysis and design optimization.  A Matlab Simulink model is used to analyze the effect that the cyclic forces common to FSW have on the displacements of and forces in various tool apparatus components and in the workpiece.  The tool apparatus design allows for adjustability based on those analyses as well as adjustability to various FSW process parameters via the insertion or removal of springs, the movement of a plate backing the spring stack, and by the swapping of the tool pins.   

WDJ1.2

Automatic Wear Detection in Friction Stir Welding
P. A. Fleming¹, D. M. Wilkes¹, T. J. Lienert², M. Bement², G. E. Cook¹, A. M. Strauss³, D. DeLapp¹, T. Bloodworth¹, T. Prater⁴, D. Lammlein¹, (1)Welding Automation Laboratory Vanderbilt University, Nashville, TN, (2)Los Alamos National Laboratory, Los Alamos, NM, (3)Vanderbilt University, Nashville, TN, (4)Vanderbilt University, Clarksville, TN

Friction Stir Welding (FSW) is a relatively new and effective joining technique which is becoming used more and more in a number of industries including: aerospace, automotive, locomotive and maritime. This is largely due to the advantages FSW has over other techniques including high weld quality, low power and heat and no fumes or spatter. There are several disadvantages to the process however, including the reliance of correct weld parameter selections and pin tool design, as well as the condition of said tool. If the tool was to wear unknown to the operator, the system might produce bad welds, even if the weld parameters are correct. In this paper we investigate techniques based on acoustic emissions, thermography and force detection in order to automatically detect tool wear. The tool selected is of a material chosen to wear at a rate faster than a normal tool would.

WDJ1.3

Welding of Titanium and Aluminum with High Power Fiber Laser
S. Mueller, E. Stiles, Fraunhofer USA, Plymouth, MI

Laser welding is increasingly being looked at by the aerospace industry as a process for joining titanium and aluminum alloy structural components, due to the reduced material usage vs. riveting, or machining to shape from larger pieces. With the recent development of high power fiber lasers, laser welding can be now considered for generation of narrow welds with low heat input and high weld speeds, due to the available high beam quality. This paper describes potential applications of the fiber laser for welding of typical aerospace materials Ti6Al4V and Al 6013. Also the results of a study of laser welding process parameters and their effect on porosity formation during welding of Ti6Al4V are presented.

WDJ1.4

Friction Stir Welding of Aluminum, Titanium, and Aluminum Metal Matrix Composities using a Diamond Coated Molybdenum Tool
T. Prater¹, T. Bloodworth¹, P. Fleming¹, D. Lammlein¹, A. Strauss¹, G. Cook¹, T. J. Lienert², M. Bement², (1)Vanderbilt Univertsity, Nashville, TN, (2)Los Alamos National Laboratory, Los Alamos, NM

Diamond coating of tools is used for a wide range of manufacturing applications.  In this investigation, we will examine changes to Friction Stir Welding (FSW) samples when a diamond coated molybdenum (Mo) tool is used to perform welds on Al alloys and Al metal matrix composites (Al-MMCs). The tool has a pin and shoulder of Mo which is coated with nanodiamonds using a chemical vapor deposition (CVD) process.  The use of the diamond tool may reduce the axial force encountered during the weld, thus opening up possibilities for high-speed welding and robotic applications. Additionally, a diamond-coated FSW tool will not wear and may prove advantageous from a thermal conductivity or surface morphology standpoint.  A metallurgical analysis of the welds will be conducted as well as mechanical tests to compare the weld integrity of the diamond/Mo tool with that of control samples welded at identical parameters.

WDJ1.5

Room Temperature Hermetic Sealing Using Composite Reactive Preforms
S. Xun, D. Van Heerden, T. Weihs, Reactive NanoTechnologies, Inc, Hunt Valley, MD

This paper describes a process which uses a composite reactive preform to hermetically seal cavities for microelectronic, optoelectronic and other applications.  The composite preform consists of a multilayered reactive foil embedded in a solder preform. The reactive foil consists of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing, such as Al and Ni.  When the reaction is activated in the foil using a small electrical or thermal stimulus, the heat generated melts the adjoining solder layers and permanently joins the package lid to the base forming a hermetic seal. The seal is achieved without exposing the components to high reflow temperatures.

The composite preforms are fabricated by uniaxial pressing of solder and reactive foil preforms. This process creates a fully dense, robust, composite preform which can readily be tailored to a wide variety of existing cavity or package designs.   We show that by using these composite preforms to seal packages helium leak rates of less than 1 x 10^-10 atm-cc/sec can be achieved.  This process provides an attractive alternative to more expensive sealing methods such as laser welding and eliminates the need for costly fabrication equipment.

Session 2: Welding and Joining 2

WDJ2.1

Residual Stress and Microstructural Effects on FCGR in Friction Stir Welded 2050 Plate
A. Reynolds¹, G. Pouget¹, J. C. Ehrstrom², M. J. Philbrook³, (1)University of South Carolina, Columbia, SC, (2)Alcan, Voreppe, France, (3)Alcan Aerospace, Ravenswood, WV

Friction stir welding (FSW) is emerging as a promising choice for joining high strength aluminum alloys. In this work, results of a study conducted on fatigue crack propagation in friction stir welded AA2050 and the effects of FSW induced residual stresses are presented. Longitudinal residual stress profiles across butt welded 2050 plates were determined using the cut compliance technique and fatigue crack growth testing was conducted on compact tension specimens machined from the friction stir welds. Tests were performed with the crack propagating nominally perpendicular to the weld and with a constant, applied, cyclic, stress intensity factor. Different cases were investigated, included different specimen configurations and material tempers, but in all cases residual stresses were found to have a major effect on the fatigue crack propagation. It was shown that compressive residual stresses are present in the vicinity of the weld and that these residual stresses lead to a decrease in the fatigue crack growth rate as the crack approaches the weld. Once in the weld nugget, the crack propagation rate increases again. The principal variations of fatigue crack growth rates in the different zones of the weld can be linked to the presence of residual stresses; however, microstructural effects were also noted.  Prediction of fatigue crack growth rates was attempted using both the residual stress intensity from the cut compliance testing and the measured ΔK_eff.  

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WDJ2.2

An Investigation Into Submerged Friction Stir Welding
T. Bloodworth¹, P. A. Fleming¹, T. J. Lienert², M. Bement², G. E. Cook¹, A. M. Strauss³, D. M. Wilkes¹, D. DeLapp¹, T. Prater⁴, D. Lammlein¹, (1)Welding Automation Laboratory Vanderbilt University, Nashville, TN, (2)Los Alamos National Laboratory, Los Alamos, NM, (3)Vanderbilt University, Nashville, TN, (4)Vanderbilt University, Clarksville, TN

Friction Stir Welding (FSW) is a relatively new welding method which is finding application in a number of industries including marine, aerospace, and transportation.  Submerged friction stir welding involves under water. Submerged FSW offers potential for use as a welding method for under-water construction and for lower heat input with smaller recrystallized grain size. In our research, we compare FSW welds run submerged in water to welds of equivalent weld parameters run in the traditional fashion in air.  The phenomena of hydrogen generation due to submerged FSW of aluminum is also discussed.

WDJ2.3

Fault Detection And In-Process Control Of Friction Stir Welding
P. A. Fleming¹, D. M. Wilkes¹, G. R. Shearer², T. J. Lienert³, M. Bement³, G. E. Cook¹, A. M. Strauss², D. DeLapp¹, T. Bloodworth¹, D. Lammlein¹, T. Prater⁴, (1)Welding Automation Laboratory Vanderbilt University, Nashville, TN, (2)Vanderbilt University, Nashville, TN, (3)Los Alamos National Laboratory, Los Alamos, NM, (4)Vanderbilt University, Clarksville, TN

Friction Stir Welding (FSW) is a relatively new welding method which is finding application in a number of industries including marine, aerospace and transportation.  It offers a number of advantages over fusion welding methods, but also presents new challenges.  Defects can occur during FSW when incorrect weld parameters are chosen, or when joint misalignment is present.  In this work, we present results of our recent work on automatic detection of defects using non-destructive sensing (force signals, acoustic emissions) as well as on closed loop motor control for correction of these errors.  This work is aimed at establishing a more robust FSW process which can automatically adjusted to provide reliably good welds.

WDJ2.4

Modeling the Bonding of Ceramics to Ni Base Alloy
Z. Hu¹, J. W. Brooks¹, H. S. Ubhi¹, I. C. Wallis¹, A. Wisbey², (1)QinetiQ Ltd., Farnborough, United Kingdom, (2)Serco Technical Services, Warrington, United Kingdom

Increasing temperature requirements in various applications are determining the need to include some ceramic based materials into structures. A major difficulty with these components can be interfacing them with conventional metallic parts. In the work presented here the brazing of Al₂O₃ and SiC monolithic ceramics to a nickel base alloy (Nimonic 90) has been investigated. As part of these investigations the bonds have been modelled to identify potential routes to minimise residual stresses and so optimise the brazing cycle. A Ag-Cu-Ti braze alloy has been found to be particularly successful in producing metallurgical joints between the ceramic and metal components. As part of the process modelling the high temperature deformation behaviour of this braze alloy has been determined to allow time dependent plastic deformation effects to be included in the calculation of bond stresses. A variety of bond geometries have been considered, from simple butt joints, to more complex tube – flange geometries. This work has indicated the importance of careful joint design on the minimisation of the residual stresses, including the potential application of soft compliant layers. Preliminary validation work on the predicted strains at the bond interfaces, carried out using electron-back scattered electron diffraction analysis, is presented.

WDJ2.5

Application of Laser Spot Welding on LY12 Aluminum Alloy
Z. Gao, J. Huang, Y. Wu, Shanghai Jiaotong University, Shanghai, China

Rivet joint technology has now been applied in the automotive industry and aerospace for many years. Laser welding has developed to an advanced level of maturity. Laser spot welding taking place rivet joint have some potential advantages include time saving, reduction cost, material usage and weight and so on. Commercially available LY12 aluminum alloy is selected as the workpiece which typical used in aircraft structures, rivetes, hardware, truck wheels, screw machine products and other miscellaneous structural applications, 2mm and 1.2mm two kind of different thickness materials are welded by special pulse controlled laser spot lap joint welding. The energy, time of pulse, that is on-time and defocus are varied in order to obtain a good weld profile, decrease porosity and cracking. The causes of porosity and cracking in the weld and HAZ are described. Macrograph and microstructure of weld are analyzed at different welding process parameters by optical microscopy and SEM, and inclusions and precipitates among the weld are observed by SEM with an EDAX analysis. Meanwhile mechanical properties such as, hardness test and shear strength are tested. Furthermore, shear strength of rivet joint and laser spot welding are compared.