FGM Fabrication by Combustion Synthesis
- PDF / 206,205 Bytes
- 2 Pages / 576 x 777.6 pts Page_size
- 56 Downloads / 261 Views
52
process, it looks much like a Fourth-ofJuly sparkler that burns in a steady fashion from one end to the other. The high temperature in the combustion wave itself is beneficial, not only because it makes it possible to synthesize refractory materials, but also because it generates a liquid intermediate phase (which might be a
molten reactant or the molten, refractory product material before it has crystallized).23 This brief appearance of a liquid phase gives rise to a sample whose yield strength is much less than that of either the starting powder mixture or the final product material. That is, the timely application of a mechanical load to the sample during the combustion synthesis process can and, in some cases, does result in a low-porosity FGM that consists only of the target materials. The principal mechanical-load-delivery systems that have been used in this regard include hot pressing,4'5 hydrostatic pressing," 3 and spring-pressurization methods. is In addition, the speed of the combustion wave (up to 0.3 m/s) and the rapid rate at which the sample cools immediately following the passage of the combustion wave (>500 Ks) combine to inhibit the longrange phase migration and subsequent segregation of material that may arise in other FGM fabrication processes. The FGM material combinations (as prepared by combustion synthesis) that
Table I. Material Combinations in FGMs Prepared by Combustion Synthesis. Materials
TiC/Ni TiC/Ni3AI Cr3C2/Ni TiB2/Ni TiB2/Cu ZrO2/TiAI (Ti-Si-O)/Ti (TiB2-Zr02)/Cu (MoSi2-SiC)TiAI TiB2/TiAI3/AI ),-SiCHAUO,-TiCi/AI
Density-Increase Method Hydrostatic pressing Hot pressing Hydrostatic pressing Hydrostatic pressing Hydrostatic pressing Spring-pressurization Hydrostatic pressing Hot pressing Hydrostatic pressing Hydrostatic Dressina
Reference 6,8,9,10 4,5 20 7 12,13 14,15 19 18 18 11,17 16 18
Table II. FGM/Combustion Synthesis Research Groups. Principal Researcher S. Bhaduri M. Koizumi A.G. Merzhanov Y. Miyamoto J.J. Moore Z.A. Munir N. Sata G.C. Stangle R.Z. Yuan
Research Organization University of Idaho, U.S. Ryukoku University, Japan Institute for Structural Macrokinetics, Russia Institute of Scientific and Industrial Research, Osaka University, Japan Colorado School of Mines, U.S. University of California at Davis, U.S. Government Industrial Research Institute, Tohoku, Japan Alfred University, U.S. Wuhan University of Technology, P.R. China
MRS BULLETIN/JANUARY 1995
FGM Fabricator! by Combustion Synthesis
have been reported in the literature are listed in Table I. Each material contains a refractory ceramic compound and either a metallic or an intermetallic phase. As such, they would be expected to be particularly useful in severe environments, where extreme mechanical or thermomechanical loads are anticipated. Further, it is true in some of these cases that these composite materials—either as FGMs or as the more simple, homogeneous (i.e., spatially uniform) composites—could not be prepared by any other method. This feature is a particularly attractive aspect of the combu
Data Loading...
