A Consideration on TiC-Core/(Ti,Mo)C-Rim Structure of TiC-Mo2C-Ni Cermet in Relation to Hypothesis "Exhaustion of Diffusion-Contributable Atomic Vacancies in Core/Rim Structure" (特集 硬質材料) A Consideration on TiC-Core/(Ti, Mo)C-Rim Structure of TiC-Mo_2C-Ni Cermet in Relation to Hypothesis "Exhaustion of Diffusion-Contributable Atomic Vacancies in Core/Rim Structure"
TiC-core/(Ti, Mo)C-rim structure in TiC-Mo<SUB>2</SUB>C-Ni cermet where the equilibrium phase of carbide is only (Ti, Mo)C is known to be not generated by solid-diffusion process, but by solution-reprecipitation process in the case of usual sintering temperatures (1528-1723 K). On the other hand, in our recent study on the microstructure of Fe-66.7at%Si peritectoid alloy where the equilibrium phase is FeSi<SUB>2</SUB>, it was found that FeSi-core in FeSi-core/FeSi<SUB>2</SUB>-rim structure hardly disappeared by solid-diffusion process in the compact inside, but relatively easily disappeared and/or shrunk near the compact surface to the depth of FeSi-core size (about 15μm) by heating at high temperature. The phenomenon in the compact inside could be explained by our newly proposed hypothesis "Exhaustion of diffusion-contributable atomic vacancies in core/rim structure".<BR>In this study, it was investigated in relation to the above hypothesis whether TiC-core in the compact inside disappears or not due to solid-diffusion process by heating at 2073-2473 K which are extremely higher than the usual sintering temperature. As the result, it was judged that TiC-core in the compact inside really disappeared by solid-diffusion process at 2273-2473 K, differing from FeSi-core in the compact inside. Based on these results on Fe-66.7 at%Si alloy and the cermet, it was generally concluded that our new hypothesis can be applied to the alloy where the rim phase is a stoichiometric compound unable to dissolve the core elements and also the diffusion from the core to the rim is not thermodynamically allowed like in Fe-66.7 at% Si alloy, but not to the alloy where the rim is a solid solution able to dissolve the core elements and thus the diffusion from the core to the rim is thermodynamically allowed like in the cermet.
粉体および粉末冶金 51(5), 374-384, 2004-05-15