|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1995 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1994 : ¥1,900,000 (Direct Cost : ¥1,900,000)
SELF-PROPAGATING HIGH TEMPERATURE SYN-THESIS (SHS) process in which at least one of the reactants is a solid, so-called combustion synthesis, has been gradually received attention from materials scientists. The products of these "solid flames" are technologically important materials such as structural ceramics with high melting temperature, intermetallics and the composites. Solid combustion reaction are generally accompanied by the release of a large amount of heat. In reactions that are sufficiently exothermic, the heat liberated is adequate to sustain the reactions by the rapid propagation of the combustion front without further addition of energy. The process are characterized by a high generated temperature (e.g., 2000 to 4000K), a fast-moving combustion wave front (e.g., 0.1 to 25 cm/sec), and extremely high heating (e.g., 10^4 to 10^6 K/sec) and cooling rates. The advantages of SHS process include high purity of products, low energy and short-time requirements, and relative simp
licity of the process. SHS products are generally powdery or porous. But the highly dense form can be also fabricated using a combination technique of this process and an external pressure such as hot press, hot isostatic press (HIP), pseudo-HIP (P-HIP), explosive consolidation, and high-velocity forging. The objective of this research is to fabricate ceramics/metal composite, for example, TiC/Ti-Al by a combination technique of SHS for short time process and pseudo isostatic compaction through a sand medium for densification. A SHS heat generated by a Ti-C reaction is very large and the adiabatic combustion temperature reaches to 3210K.But a Ti-Al reaction is weak exothermic and is not easy to initiate without pre-heating the reactant. The reaction maximum temperature was contolled so that the Ti-Al alloy could be molten because a liquid phase is very important to make the composite dense well. The reason why Ti-Al alloy was chosen as a SHS sub-product was that the alloy is hard, light, and has received attention as structural materials in space materials.
A pseudo isostatic compaction (PIC) was applied for densification of the hot and partially molten samples after the SHS.The PIC using sand as the pressure transmitting medium has been developed for the densification of the ceramics/metal composite. This technique should be similar to that developed by Merzharnov et al. An ignition method may be different from Russian SHS researchers. In our PIC apparatus, a sheet of carbon ribbon as the heat device only for ignition is embedded with a sample in commercial casting sand, which is inserted in a pressure vessel. The compaction was performed by quickly pressing the sand containing the sample just after the SHS reaction. A static pressing of PHIP using sand as the pressure transmitting medium is known to cause pseudo isostatic pressing. Herein, the sand-pressing by high speed auto-pressing machine was applied dynamically to perform the PIC after SHS.