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Session Chairpersons: Prof. Leon L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; Prof. Carl C. Koch, Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695
8:30 am INVITED
PROCESSING OF CONTINUOUSLY REINFORCED Ti-ALLOY MMCS BY PHYSICAL VAPOR DEPOSITION: P. R. Subramanian, S. Krishnamurthy, and S. Keller, UES, Inc., Materials and Processes Division, 4401 Dayton-Xenia Rd., Dayton, OH 45432-1894
Fiber-reinforced titanium aluminide composites are of particular interest as candidate materials for aerospace structural applications at moderately high temperatures. Conventional techniques for fabrication of these composites pose many technical challenges, and serve as one of the barriers to the practical use of these composite systems. The present work deals with a novel vapor synthesis route, the matrix-coated fiber process, for producing Ti-alloy metal matrix composites (MMCs). In this process, the matrix alloy is directly deposited on continuous SiC fibers by hollow-cathode magnetron sputtering. The matrix-coated fibers are then consolidated to produce unidirectionally reinforced MMC panels. Details of the processing technique will be presented, along with results on microstructural evolution. Results from room-temperature mechanical evaluation of the MMC specimens will also be presented. This research is funded by the U.S. Air Force as a Small Business Innovative Research Program under Contract No. F33615-94-C-5214 . Program Monitor: Dr. Stephen W. Schwenker, USAF Wright Laboratory, Materials Directorate (WL/MLLM), Wright-Patterson AFB, OH 45433-7817.
COMBUSTION CHEMICAL VAPOR DEPOSITION (CCVD) OF LaPO4 MONAZITE ON ALUMINA FIBERS FOR CERAMIC MATRIX COMPOSITES: T.J. Hwang, M.R. Hendrick, H. Shao, H.G. Hornis, A.T. Hunt, Micro Coating Technologies, 430 Tenth Street, Suite N-108, Atlanta, GA 30318
It has been demonstrated that monazite compounds can serve as an oxidation protection and crack deflecting interface coatings to improve the strength and toughness in oxide-oxide ceramic matrix composite. In this study, lanthanum phosphate LaPO4 (monatize) was coated on alumina fibers (Nextel 610) using the combustion chemical vapor deposition (CCVDSM) method in the open atmosphere. This study has shown that the CCVD is feasible for applying a dense LaPO4 coating while moving the fiber tows through the deposition zone. A systematic stoichiometry study showed that monazite was the predominate phase in the film. Deposition temperatures were controlled to prevent degradation of fibers while maintaining an optimal deposition rate and coating quality. Several interlayer materials were investigated to minimize the reaction and recrystallization of the A12O3 fibers. Since a vacuum chamber is not required for the CCVD process, large scale, continuous coating of fibers is possible.
DENSE TITANIUM MATRIX COMPOSITE MONOTAPE FROM E-BEAM METAL COATED FIBERS: Herve Deve, Metal Matrix Composites Program, 3M Center, Bldg 60-1N-01, St Paul, MN 55144-1000
The high temperature specific strength and stiffness of titanium matrix composites (TMC's) make them very attractive for the next generation of jet engine components. Significant efforts are now underway at 3M to reduce the cost of TMC's; bring them to a production status; and offer the customer a TMC precursor that will be easy to integrate into titanium components. The recent advances in the production of metal coated fibers by electron beam evaporation have allowed the development of continuous dense monotape. Dense TMC monotape will facilitate the fabrication of complex curved parts such as rings. A dense monotape is a single composite ply made by roll-bonding cylindrical metal coated fibers. Continuous roll-bonding allows the low-cost fabrication of TMC tape that do not contain organic binders. Monotapes have been produced that are typically 200 =B5m thick by 10 mm wide and greater than 30 meter long. The flexible composite tape can be easily laid-up on flat or curved parts. Final bonding of the component requires a HIP or diffusion bonding cycle without the complex removal of organic binders. TMC rings with a nearly perfect fiber distribution were fabricated to illustrate the simplicity of use of TMC monotapes.
REACTIVE SPRAY ATOMIZATION AND DEPOSITION OF ALUMINUM ALLOYS: MODELING DISPERSOID VOLUME FRACTION AND SIZE DISTRIBUTION: J.-P. Delplanque, E.J. Lavernia, R.H. Rangel, Department of Mechanical and Aerospace Engineering, Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, California 92697-2575
Reactive spray atomization and deposition combines atomization, chemical reaction and consolidation into a single step. It offers a unique opportunity for in-situ, continuous control over alloy composition and chemical reaction between atomized droplets and reactive atomization gas. During reactive spray deposition a molten alloy is atomized by using a reactive gas mixture. The atomized droplets are subsequently deposited on a substrate. Chemical reactions occur between the matrix material and the reactive gas during both atomization and deposition. By carefully selecting alloying additive and reactive gas combinations on the basis of containing in-situ dispersoids such as carbides, nitrides, and oxides, leading to grain refinement. The volume frac tion and the size distribution of the dispersoids is critical to the grain refinement mechanisms. The primary goal of the present work is to define a model to estimate these characteristics. The materials considered are aluminum alloys while target dispersoids are primarily oxides. These may be obtained by the reaction of oxygen containing atomization gas mixtures with molten alloy droplets or with minor alloy additives which exhibit a high affinity for oxygen. Droplet position and velocity histories are obtained from the numerical solution of the one-dimensional equation of motion. The energy equation inside the droplet is solved numerically using finite-differences to predict the spatially resolved temperature field. The solid/liquid interface progression rate is estimated using a power law. The effect of the dispersiods on the achievable undercooling is included. This model is then used to determine the parameters controlling the volume fraction and the size distribution of the dispersiods.
10:15 am BREAK
10:25 am INVITED
PLASMA SPRAYED MULTI-LAYERED AND FUNCTIONALLY GRADED MATERIALS: H. Herman, Department of Materials Science and Engineering, State University of New York, Stony Brook, NY 11794
Multi-layered (MLM) and functionally graded (FGM) composites display discrete or continuously varying compositions of metals, ceramics and polymers and/or microstructures over definable geometrical orientations and distances. Plasma spray offers a flexible and economic means for producing non-uniform composites and is used to apply layered and graded deposits to enhance the survivability of thick ceramic coatings (e.g., TBCs). These "graded coatings" are primarily applied to reduce CTE mismatch-related failure. The versatility of plasma spray allows the processing of a wide range of high performance materials, including most metals and refractory ceramics, under a controlled atmosphere if desired. Using plasma spray, it is possible to deposit multiple constituents simultaneously, thus providing a unique means of producing FGMs. Plasma spray MLM/FGM production will be discussed and the characteristics and properties of two FGM systems, Ni-Al2O3 and NiCrAlY-ZrO2, will be presented. This research is supported by NIST-Caterpillar Advanced Technology Program and the INEL University Research Consortium.
SPRAY FORMING OF TiB2 REINFORCED GAMMA TITANIUM ALUMINIDE ALLOYS: B. Li, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA 92697-2575
Gamma titanium aluminide composite with a nominal composition of Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2 was spray formed using a skull melting technique. Microstructure characteristics of as-received and spray formed Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2, along with the oversprayed powders, were examined by optical microscope and SEM, and rationalized on the basis of numerical analysis.
11:20 am INVITED
SOL-GEL SYNTHESIS OF CERAMIC MATRIX COMPOSITES: E.D. Rodeghiero, E.P. Giannelis, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853
Sol-gel techniques provided new and powerful means by which to synthesize oxide-based ceramic matrix composites. The advantages of sol-gel approaches relative to conventional powder processing are numerous. First, sol-gel synthesis can achieve extremely fine (nanoscale) microstructures with high degrees of dispersion between the matrix and reinforcement phases. In addition, the chemical compositions of the various phases can be precisely controlled. Furthermore, gel-derived composites are also highly uniform, as a result of eliminating powder mixing and segregation problems. Finally, sol-gel synthesis can reduce consolidation temperatures significantly, leading to more efficient, economical processing. This talk will present the results of our work in synthesizing both Ni/-Al2O3 metal-ceramic composites and SiC(whisker)/-Al2O3 ceramic-ceramic composites. The unique physical and mechanical properties of these composites in their various forms will be discussed, as well as their potential applications.
NANOCOMPOSITE MATERIALS VIA CHEMICAL ROUTES: Kenneth E. Gonsalves, X. Chen, Department of Chemistry & Institute of Materials Science, University of Connecticut, Storrs, CT 06269
The formation of an AlN/Polyimide (PI) nanocomposite was achieved by the rapid solidification of the precursor suspension, followed by compression molding. Such an approach for nanocomposites exhibits improved homogeneity with ultrafine fillers and allows a tailorable composition and property at the nanoscale level. AlN/PI nanocomposites with an increased ceramic loading up to 50% by volume were attained and their thermal and mechanical properties, along with the compositional effects, were investigated.
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