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6 PROCESSING OF DUCTILE ORDERED ALLOYS INTRODUCTION Recent breakthroughs in the development of ductile ordered alloys have resulted in research focused on the development of a variety of ordered alloys including aluminides (Liu and Koch 1982) and (FeNi)â¢j-V type materials (Liu 1973 and 1979). This work has focused primarily on mechanical property behavior as a function of composition and heat treatment. As these materials mature, consideration must be given to the manufacturing technology required for the fabrication of useful hardware. At the present time, consideration of processing techniques is generally limited to the generation of small lots of material for characterization purposes. In the future, attention should be given to the production and subsequent processing of commercial lots of material. The processing technology is extremely important because most of the cost associated with incorporating a new material system into either military or commercial systems is related to process optimization and finalization (Stephens and Tien 1983). In anticipation of this need to consider production requirements, current methods used for the manufacture of material for characterization purposes were reviewed. CURRENT PRODUCTION METHODS The literature on the various production processes employed for the preparation of ordered alloys for alloy development and characterization studies was surveyed. This review revealed that: 1. A wide variety of methods have been employed for the wide range of compositions under investigation. To date, there has been no focus on any particular method for fabricating any particular class of ordered material. 87
2. The methods can be classified into three generic types as shown in Figure 30, which represents a flow diagram or process routing for the preparation of ordered material. Starting with the initial melting operation, the three generic types include casting, deformation processing, and powder metallurgy. 3. In all cases, the amounts of material made were relatively small (generally less than 50 pounds) and did not represent production type quantities. 4. With the exception of the casting approach, some type of subsequent secondary processing such as machining, forming or forging, or joining (welding, brazing, diffusion bonding) would be required for the fabrication of useful hardware. With these general points in mind, a brief description of the routing steps is presented below. Melting Each of the three process routings begins with the preparation of alloy ingot or melt stock. In general, either vacuum induction or arc melting MELT1NG CAST1NG DEFORMAT1ON PROCESS1NG POWDER ATOM1ZAT1ON POWDER CONSOL1DAT1ON FIGURE 30 Current process routing for the production of ordered alloys.
89 under some type of protective atmosphere was used to produce the initial ingot material. Vacuum melting was used for such materials as Cu3Au (Rear and Wilsdorf 1962, Chien and Starke 1975), Cu2NiZn (Van der Wegen et al. 1982), and Ni3Al (Thornton et al. 1970, Davies and Stoloff 1965). Arc melting was used for a wide variety of materials including Niâ¢jAl (Guard and Westbrook 1959), FeCoV/Fe3Al (Stoloff and Davies 1964a), Mgâ¢jCd (Stoloff and Davies 1964b), AgMg (Westbrook and Wood 1962-63), Ni3Ge/Fe3Ge (Suzuki et al. 1980), Ni-Ni^Mo (Nesbit and Laughlin 1980), and beta brass (Shea and Stoloff 1974). High-purity elemental constituents were used as the starting stock and, in general, argon gas was used as the protective atmosphere for the arc melting operations. A variety of crucibles, including ceramic and graphite containers, was used to produce round ingot shapes or buttons. In general, less than 50 pounds, and in most cases less than 10 pounds, of alloy was produced. There appear to have been few problems with off-chemistry compositions, and good yields generally were achieved. In summary, little difficulty has been encountered during the melting of small quantities of ordered alloy compositions. Casting Subsequent preparation of cast specimens for mechanical property evaluations has been directed towards obtaining either an equiaxed microstructure, as in studies involving ordered intermetallic phases in superalloys (Copley and Rear 1967), or single crystals in the Ni3(Al,Nb) (Ezz et al. 1982) and Niâ¢j(Al.W) (Kuramoto and Pope 1978) systems. In all cases, vacuum casting was employed and equiaxed microstructures were obtained through conventional solidification techniques in which heat is extracted from the molten metal by radiation through the mold material. The single-crystal castings also were produced in vacuum, and the mold containing the molten metal was withdrawn through a thermal gradient at a controlled rate to achieve directional solidification. Orientation control was achieved by using either a single-crystal seed or a grain selector configuration to obtain the desired orientation. It is recognized that the development of casting techniques was not a major thrust in these investigations. It can therefore be concluded that the casting approach represents a potential method for manufacturing components from ordered alloys. Deformation Processing Deformation processing of ordered alloys involves a variety of operations performed subsequent to the preparation of the melt stock material. The primary purpose is to obtain a homogeneous composition and a uniform microstructure. Vacuum-melted ingots have been subjected to hot (Kear and Wilsdorf 1962, Davies and Stoloff 1965) and cold (Van der Wegen et al. 1982) rolling, and arc-melted ingots have been subjected to hot (Stoloff and Davies 1964a, 1964b) and cold (Nesbit and Laughlin 1980) rolling, hot extrusion (Westbrook and Wood 1962-63), and upset forging (Shea and Stoloff 1974). The rolling operations resulted in sheet or plate of varying thickness, the hot extrusion operations generally resulted in cylindrical bar stock, and the upset forging operations resulted in pancake type configurations. These operations were conducted on alloys canned or clad
90 with various materials in order to aid heat retention during processing, avoid surface cracking during processing, and protect the various alloys from environmental degradation during heating to the working temperature. It must be emphasized that the deformation processing operations cited here were performed for the purpose of supplying small laboratory lots of material. They were not conducted as part of a systematic program to select optimum process routings that achieve maximum material yield or optimum mechanical properties. The various process variables, including cladding material, reduction ratio (for extrusion), reduction per pass (for the rolling operations), and working temperature, were selected on the basis of previous experience with similar types of material. The overall results of these studies were quite encouraging, however, in that the workability potential of a wide variety of compositions by a wide variety of processing methods has been demonstrated. These results suggest that plate or bar stock material can be produced by normal deformation processing methods. Powder Metallurgy Processing PM processing of ordered alloys also is under investigation because it can offer a number of important advantages. In addition to the savings resulting from increased materials utilization compared to conventional ingot metallurgy, PM allows the formulation of structures with nonequilibrium phases, an extension of the range of solid solubility, a refinement of resultant grain size, and a suppression of grain boundary segregation. As a result of these advantages, PH processing of ordered alloys has received considerable attention. PM processing involves two basic steps: powder atomization and powder consolidation. A number of atomization approaches have been employed for the production of ordered alloys. These approaches feature a range of cooling rates between 1000°C/sec and l,000,000°C/sec. The lower cooling rates generally are associated with the rotating electrode process (REP) and higher rates with inert gas (argon) atomized powder. REP has been used for the preparation of titanium aluminide powders (Sastry and Lipsitt 1977, Mendiratta and Lipsitt 1980) while argon atomization has been used for the preparation of iron aluminide powders (Vedula 1983). The higher rates are generally associated with rapid solidification rate (RSR) processing, which is achieved by centrifugal atomization in combination with forced convective cooling, and with melt-spun ribbons. The RSR process has been used for the preparation of various materials including iron aluminides (Chatterjee and Mendiratta 1982), and melt spinning has been used for the preparation of various materials including Ll£ compounds of the type Ni-Al-X(X=Cr, Mn, Fe, Co, or Si) (Inoue et al. 1983). Each of the processes offers advantages associated with either process economics, production scale-up capability, or the ability to achieve extremely high cooling rates. At this point, no preferred atomization process has evolved for the preparation of ordered alloy powders. Characterization of powders made from a wide variety of alloys and processes is under way. As is the case for deformation processing of ordered alloys, no systematic investigation has yet been conducted relating powder processing parameters to overall process economics or mechanical property performance.
91 Subsequent to atomization, the powders must be consolidated for further evaluations. Although a number of consolidation approaches are available, most of the work done to date on ordered alloy powders involves either vacuum hot pressing or hot extrusion. Vacuum hot pressing can be used to form a net shape or near net shape, but hot extrusion must be followed by subsequent fabrication to form a useful component. Again, no systematic investigations of the hot pressing or hot extrusion operations have been conducted to optimize process economics or mechanical property performance. Characterizations thus far of the melt-spun ribbons have been limited to the ribbons themselves, but studies involving pulverized ribbons subjected to subsequent PM consolidation processes are in progress (Ray et al. 1983). Although the results of PM studies conducted to date on ordered alloys are of a preliminary nature, they do suggest that this type of processing approach can be applied to this class of materials. PRODUCTION SCALE-UP CONSIDERATIONS In order to address the issues that must be considered when scaling-up for large-scale production of a new material, a specific processing approach must be selected. On the basis of the studies conducted to date on ordered alloys, some potential has been demonstrated for processing a wide variety of compositions by a wide variety of processing methods. Although no single processing approach has evolved for any particular composition, an assessment can be made regarding what is currently known about the manufacture of these materials. In general, three major issues must be addressed: scale-up to larger, production size quantities; process optimization to reach a compromise between process economics and mechanical property performance; and secondary fabrication approaches necessary to manufacture production hardware. These issues are discussed below for each of the steps shown in Figure 30. Melting The major issue regarding melting of ordered alloys is related to the maximum size production heat that can be produced with the desired chemistry. Ingots of melt-stock material of specialty alloys such as ordered alloys are qualified on the basis of their chemistry specifications, which control not only the major element additions but also the tramp or impurity levels. The specific major element chemistry ranges for ordered alloys will be established as more knowledge is obtained regarding the effects of off-chemistry. Because on-line chemical analysis is now routinely performed during vacuum-induction melting, off-chemistry with regard to the major element additions is not anticipated to be a problem. This may not be the case, however, for other kinds of melting operations, and certain of the ordered alloy systems may present particular chemistry problems. For example, the properties of some alloys change greatly with small changes in stoichiometry. This may make the control of composition more difficult than in ordinary alloys. Impurity levels also may present a problem, particularly if high superheat or pour temperatures are required. Higher temperature melting operations usually are associated with a greater degree of crucible/metal reactivity and can result in degradation of the ceramic filters currently used to remove nonmetallic inclusions.
92 Scale-up to production size heats of ductile ordered alloys also may require secondary processing steps for macrostructural and microstructural control. In many instances, primary ingots cannot be directly hot worked because of coarse and nonuniform grain sizes, shrinkage pipes, and relatively high degrees of macrosegregation and microsegregation, which represent problems particularly in alloys featuring complex chemistries. Vacuum arc remelting has overcome many of these problems and, in addition to developing more uniform composition, properties and structure, offers the capability to improved purity. A recent innovation in remelting, termed the VADER process (Boesch et al. 1982), offers significant advantages compared to vacuum arc remelting including a decrease in energy consumption for comparable melt rates and significantly finer and more uniform grain sizes to enhance subsequent deformation processing. Although these secondary melting operations have not yet been applied to the ductile ordered alloy class of materials they do represent potential methods for improving the quality of primary ingots. Process yield is also an important consideration. For example, a process yield of 90 percent or greater usually is obtained when producing superalloys, and any melting process that results in yields of less than 90 percent would have limited applicability. Casting The manufacture of castings of new materials such as the ordered alloys requires extensive process optimization to ensure high yields. Important considerations are the specific gating/risering systems to be employed for the specific configurations, the mold systems that must be used, the number of individual castings that can be made per mold, and the specific casting procedure that must be used. So far, none of these considerations has been addressed with regard to cast ordered alloys. Casting yield is a direct function of the types of defects encountered during the production operation. In general, the quality requirements increase with the complexity of the casting operation, being more stringent with single-crystal castings than with equiaxed castings. Equiaxed castings are evaluated in terms of x-ray (for internal porosity and inclusions), Zyglo penetrant inspection (for surface-connected porosity and surface inclusions), dimensional tolerance (including core shift for the production of castings with internal cooling passages), and mechanical properties of specimens machined from actual components. Columnar-grain and single-crystal castings also undergo this type of inspection and an additional step involving etching to check for the presence of off-axis grains (for columnar-grained castings) and surface equiaxed grains (for single-crystal castings). Single-crystal castings also undergo inspection for orientation determination. Significant costs are associated with this quality assurance activity and, when combined with the cost of the casting processes themselves, account for approximately 90 percent of the component costs. This means that since materials constitute less than 10 percent of the final cost, the use of smaller quantities of critical or strategic materials in some of the new ordered alloys cannot be expected to result in dramatically reduced costs.
93 Deformation Processing The production scale-up considerations related to deformation processing concern economics, capital equipment needs, and mechanical property requirements. Process economics generally are controlled by process yields. Most material losses during processing occur due to the rejection of material that contains edge or surface defects. Losses also are encountered in the extrusion operation due to the need to crop off nose and tail sections to remove undeformed or nonuniformly deformed material in these locations. In general, material yields in excess of 90 percent are usually required in order to achieve attractive process economics. Another concern regarding process economics is the degree of control required to accomplish the desired deformation. This is usually referred to as the processing "window" and includes the specific tolerances that must be maintained in terms of process temperature, amount of reduction, and time required. All of these parameters influence the uniformity of the deformation response throughout the material. Process costs escalate as the "window" narrows, and no data on the size of this "window" for the newly developed ordered alloys are yet available. Capital equipment needs relate to the size of the equipment needed to accomplish the desired deformation. As size requirements increase, the number of vendors able to accomplish the work with the desired quality decreases. A potential problem area here may be the long lead times associated with scheduling the work. This situation is already prevalent in the aircraft industry where lead times of more than one year are not uncommon. The scale-up problem associated with mechanical property performance is related to achieving the desired property levels in large section size. Extrusion barstock and plate specifications call for minimum mechanical property requirements to be met as a function of various specimen orientations. In scale-up operations, there usually is a decrease in mechanical property performance due to section size effects. This is related in part to the significantly slower cooling rates obtainable in large section sizes that have an adverse effect on the morphology of the various strengthening phases in the microstructure. Increasing the cooling rate from the heat treatment temperature by the use of various quenching media (hot salt, for example) can up-grade the mechanical property response, but care must be taken so that quench cracks are not developed. This problem may not arise with the scale-up of single-phase ordered alloys but may be present in ordered alloys featuring a second phase. Powder Metallurgy Processing In discussing the scale-up of PM processing, both powder atomization and powder consolidation must be considered. These two areas will be discussed separately below. Both the production capability and the quality of the resulting powder are important considerations. Production size capability is intimately associated with economics, and a relatively large-scale production
capability now exists for the slower-cooling-rate powders produced by REP and inert gas atomization. In fact, inert gas atomization is currently in use for the production of large quantities of nickel-base superalloy powders used for disk applications in the aircraft industry. The atomization costs for these powders generally are less than $2 per pound. Atomization costs for the REP powder are approximately $6 per pound. With regard to the faster-cooling-rate powders and ribbons produced by the RSR and melt-spinning processes, large-scale production quantities of these materials are not yet available. Efforts are in progress, however, to scale-up facilities to produce larger quantities of these materials. No cost projections are yet available. At the current time, then, large scale-up PM processing of ordered alloys would be limited to the PREP and inert gas atomization processing. Powder quality concerns are related primarily to the presence of defects in the powders and their effects on low cycle fatigue, fracture toughness, and fatigue crack growth. The evolution of damage-tolerant designs and retirement-for-cause concepts in the aircraft industry has placed stringent requirements on powder quality. As a result of these requirements, powder producers now have strict control of powder chemistry, both major elements and tramp or impurity levels. Powder lots also are inspected by water elutriation and metallographic techniques to determine the presence of extraneous particles such as ceramic particles from mold/metal reaction, reactive defects such as parts of 0-ring seals, and cross alloy contamination resulting from the atomization of various alloy compositions. Currently, efforts are being made to minimize the use of ceramics during the atomization of high-temperature powders. Since the presence of ceramic particles in ordered alloys are also expected to be very deleterious, similar quality control procedures will be required for their powder production. The vacuum hot pressing and hot extrusion consolidation approaches for the ordered alloys involve scale-up considerations similar to those discussed previously for deformation processing (i.e., process economics, capital equipment needs, and mechanical property requirements). An additional requirement, however, is the need to maintain powder purity during any consolidation operation. This is related to the possible contaminant pick-up during powder transfer and handling and subsequent loading into vacuum hot pressing or hot extrusion cans. In certain instances all-inert powder handling is thus specified for critical rotating components. Secondary Fabrication With the exception of cast-to-size components, some type of secondary processing will be required for the fabrication of useful hardware from ordered alloy material. These secondary processing procedures could include machining, forging or forming, and some type of bonding fabrication operation such as welding, brazing, or diffusion bonding. To date, systematic studies of these techniques involving process optimization and definition have not been done on the ordered alloys. Some preliminary work has been conducted on welding of nickel aluminides (private communication
95 with S. A. David, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1983) and (Ni,Fe)3(V,Ti) long-range-ordered material (Braski 1983). The effects of electron beam welding parameters (for the aluminides) and gas tungsten arc (GTA) welding parameters (for the long-range-ordered material) on weld quality were characterized. For both types of materials, conditions were identified that resulted in crack-free welds. In more general terms, the incorporation of joining fabrication operations in the overall processing sequence for ordered alloys also will have to address section size effects on joint quality and mechanical property response as well as the effects of phase transformations in those systems featuring multiphase microstructures. Until such studies have been conducted, no realistic assessment can be made as to whether the ordered alloys as a class of materials would present any more difficulties than do the currently used materials. SUMMARY-PROCESSING A wide range of processing methods have been employed for the preparation of material for the initial characterization of ordered alloys, including such primary processing techniques as alloy melting, casting, deformation processing, and PM methods. These efforts have demonstrated that considerable flexibility exists for the manufacture of ordered alloys in bar and sheet form as well as in simple cast configurations. There have been no systematic studies of these approaches with regard to achieving an optimized process in terms of economics and mechanical property performance. In addition, except with casting, the primary processing must be followed by some type of secondary operation in order to fabricate useful hardware. Up to now only limited efforts have been directed towards evaluation of these secondary operations. Once specific alloy compositions evolve from the current work in progress on ordered alloys and possible defense applications can be identified, studies can be directed toward process optimization and scale-up. Until these studies are conducted, a realistic assessment cannot be made of the difficulty of fabricating components from ordered alloys relative to current bill-of-materials. REFERENCES Boesch, W. J., J. K. Tien, and T. E. Howson. 1982. Metals Progress 122(5):49-56. Braski, D. N., and S. A. David. 1983. Met. Trans A 14A:1785-91. Chatterjee, D. K., and M. G. Mendiratta. 1982. J. of Metals 33(12):5. Chien, K. H., and E. A. Starke. 1975. Acta Met. 23:1173-84. Copley, S. M., and B. H. Kear. 1967. Trans Met. Soc. AIME 239:984-92. Davies, R. G., and N. S. Stoloff. 1965. Trans. Met. Soc. AIME 233:714-19.
96 Ezz, S. S., D. P. Pope, and V. Paidar. 1982. Acta Met. 30:921-26. Guard, R. W., and J. H. Westbrook. 1959. Trans Met Soc. AIME 215:807-14. Inoue, A., H. Tomioko, and I. Masumoto. 1983. Met. Trans. A 14A:1367. Kear, B. H., and H. G. F. Wilsdorf. 1962. Trans TMS-AIME 224:382 Kuramoto, E., and D. P. Pope. 1978. Acta Met. 26:207-10. Liu, C. T. 1973. Met Trans 4:1743. Liu, C. T. 1979. J. Nuc. Mat. 85-86:907. Liu, C. T., and C. C. Koch. 1982. Development of Ductile Polycrystalline Niâ¢jAl for High Temperature Applications. In Proceedings of the Conference on Trends in Critical Materials Requirements for Steels of the Future. Nashville, Tennessee: Vanderbilt University. Mendiratta, M. G., and H. A. Lipsitt. 1980. J. Mat. Sci. 15:2985-90. Nesbit, L. A., and D. E. Laughlin. 1980. Acta Met. 28:989-98. Ray, R., P. Viswanathan, and S. Isserow. 1983. J. of Metals 35(6):30-5. Sastry, S. M. L., and H. A. Lipsitt. 1977. Met. Trans. A 8A:299-308. Shea, M. M., and N. S. Stoloff. 1974. Met. Trans. 5:755-762. Stephens, J. R., and J. K. Tien. 1983. Considerations of Technology Transfer Barriers in the Modification of Strategic Superalloys for Aircraft Turbine Engines. NASA TM 83395. Washington, D.C.: National Aeronautics and Space Administration. Stoloff, N. S., and R. G. Davies. 1964a. Acta Met. 12:473-85. Stoloff, N. S., and R. G. Davies. 1964b. Trans ASM 57:247-60. Suzuki, T., Y. Oya, and D. M. Wee. 1980. Acta Met. 28:301-10. Thornton, P. H., R. G. Davies, and T. L. Johnston. 1970. Met. Trans. 1:207-18. Van der Wegen, G. J. L., P. M. Bronsveld, and J. Th. M. De Hosson. 1982. Acta Met 30:1537-47. Vedula, K. 1983. Effect of Ternary Additions on High Temperature Properties of Iron Aluminides. Paper presented at the AIME Fall meeting. New York: American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Westbrook, J. H., and D. L. Wood. 1962-63. J. Inst. Met. 91:174-82.
97 APPENDIX BIOGRAPHICAL SKETCHES OF COMMITTEE MEMBERS MARTIN J. BLACKBURN received his B.A. (1958) and Ph.D. (1962) from the University of Cambridge. Upon graduation he joined the Boeing Company and worked for ten years in the Scientific Research Laboratory. After a year (1972-3) as Visiting Scientist at the Aerospace Research Laboratories, Wright-Patterson Air Force Base, he joined Pratt and Whitney Aircraft. There he is currently Manager of Structural Metals and Process Development. During his career he has worked on a wide variety of materials including extensive development activities in the field of ordered alloys. He published widely in earlier years and holds a number of patents including two for ordered alloys based on the titanium aluminides. THOMAS F. KEARNS received his B.S. in Metallurgical Engineering from Columbia University in 1940. He is currently a member of the Research Staff at the Institute for Defense Analyses, where he is involved in advisory studies and analyses for the Department of Defense and Defense Advanced Research Projects Agency in the area of materials and structures research and development. From 1941 to 1980 Mr. Kearns was a Materials Engineer with the Department of the Navy. His major activities with the Navy were in the area of engineering control of materials in Naval aircraft and equipment and in planning and sponsorship of research and development in materials, structures, and aerodynamics related to Naval aircraft. He also served as National Liaison Officer for Materials with the Organization for Economic Cooperation and Development, Chairman, Structures and Materials Panel, AGARD/NATO, and was a member of the Advisory Technical Awareness Council of the ASM. He is a Fellow of the American Society for Metals and a recipient of the ASM Burgess Award and the Navy Superior Civilian Service Award. CHARLES S. KORTOVICH joined TRW in 1964 and has been closely involved with research in the area of high temperature superalloys, including isothermal forging dies, computerization studies in investment castings, trace element effects, hot isostatic pressing of castings, and the development of superalloys through PM techniques for blade/vane and disk applications. He is currently responsible for evaluation and monitoring of strategic elements, physical metallurgy (alloy development, powder metallurgy, and coating development), and fracture mechanics and mechanical property behavior evaluation of high temperature materials. Dr. Kortovich received his Ph.D. from Case Western Reserve University in 1973. He is a member of the American Society for Metals and the American Institute of Mining, Metallurgical, and Petroleum Engineers, of which he is currently a member of the Gas Turbine Panel of the High Temperature Alloys Committee. He holds several patents in the area of processing high temperature materials for gas turbine applications. DONALD E. MIKKOLA has served on the faculty of the Michigan Technological university for twenty years and is currently Professor of Metallurgical Engineering. His research is concerned with structure-property relations in materials as studied with x-ray diffraction and electron microscopy, with current emphasis on ordered alloys, high strain rate deformation, and
98 comminution. He received his Ph.D. from Northwestern University in 1964. He is a member of the Engineering Accreditation Commission of the Accreditation Board for Engineering and Technology. DAVID P. POPE received his B.S. degree from the University of Wisconsin in 1961 and his M.S. and Ph.D. degrees from the California Institute of Technology in 1962 and 1967, respectively. Dr. Pope has been a member of the faculty of the University of Pennsylvania since 1968 and is now Professor of Materials Science and Engineering and Associate Dean for Undergraduate Education in the School of Engineering and Applied Science. He is a member of the American Institute of Mining, Metallurgical, and Petroleum Engineers and the American Society for Metals. His recent publications have been in the fields of deformation behavior of ordered alloys and on composition-mechanical behavior relationships in steels. NEIL E. PATON received his B.S. and M.S. degrees in Mechanical Engineering from the University of Auckland, New Zealand in 1961/1962 and his Ph.D. in Materials Sciences from M.I.T. in 1969. He is currently the Director of Materials Engineering and Technology at the Rocketdyne Division of Rockwell International. Dr. Paton has been engaged in the study of physical metallurgy and deformation of metals for the past 20 years and has authored or co-authored over 55 technical papers and given more than 60 technical presentations based on his research. He is also the holder of 10 patents. Dr. Paton was awarded a Titanium Metal Corporation of America Fellowship in 1965 and the Rockwell International Engineer of the Year Award in 1976. He is a member of The Metallurgical Society/American Institute of Mining, Metallurgical, and Petroleum Engineers and is currently Chairman of the Titanium Metallurgy Committee of IMS. He has served on several National Academy of Sciences committees and was Chairman of the 1983 Gordon Conference on Physical Metallurgy. DAVID I. ROBERTS is currently Manager of Materials Engineering and Testing at GA Technologies (formerly General Atomics) in San Diego, California. He is responsible for programs to select and qualify materials for gas cooled reactors, for fusion reactor development programs, and for nuclear space power and related advanced energy generation system development. Mr. Roberts received his HIM degree from the University of London in 1960. He is a registered Professional Engineer in the state of California and a member of the American Society for Metals, the American Society of Mechanical Engineers, the National Association of Corrosion Engineers, and the Institute of Met. (United Kingdom). MICHAEL J. STALLONE received his BME degree from Polytechnic Institute of Brooklyn in 1953 and completed the General Electric's Advanced Engineering Program in 1956. At General Electric Company he conducted analytical and experimental studies in low cycle fatigue, bucket creep, and life prediction methods. He has held a series of managerial positions responsible for providing advanced analytical methods in various aspects of structural and vibration analysis. In his present position as Manager of Applied Stress and Dynamics, he is responsible for advanced analysis and methods development for blade aeromechanics, rotor and structural vibration, and life design of engine blading and structures. In 1968 he was awarded the
99 General Electric Company Perry T. Edbert Memorial Award for Outstanding Technical Contribution. He is a member of the American Institute of Aeronautics and Astronautics and the American Society of Mechanical Engineers. NORMAN S. STOLOFF received his Ph.D. in Metallurgy in 1961 from Columbia University. He is currently Professor of Materials Engineering at Rensselaer Polytechnic Institute. Dr. Stoloff's research interests include fatigue of composite materials, microstructure and properties of nickel-base superalloys, and deformation and fracture of intermetallic compounds. He is a member of and has been active on various technical committees of the American Institute of Mining, Metallurgical, and Petroleum Engineers, the American Society for Metals, and the American Society for Testing and Materials. He is co-author and co-editor of a monograph and a conference proceedings dealing with ordered alloys and is author or co-author of over 100 technical papers.
