ヘプタン添加Ti–Alメカニカルアロイング材の組織形成過程と結晶粒微細化

抄録

Microstructure formation process during heating of n-heptane added mechanically alloyed (MA) Ti–Al compacts, as well as the effects of aluminum content and heating rate on the grain refinement of the MA compacts whose compositions were Ti–33~53 mol%Al were investigated. Aluminum supersaturated α nanocrystals were formed in Ti-rich Ti–Al powders, while the mixture of an amorphous phase and aluminum supersaturated α nanocrystals was formed in the MA powders with the aluminum contents more than 49 mol%. TEM/EDS examination of Ti–41, 46 and 51 mol%Al MA powders revealed that the α phase in the MA powders underwent a massive transformation to a non-equilibrium γ phase at the heating between 873 K and 973 K. In the case of Ti–51 mol%Al MA powder, crystallization of the amorphous phase to an α phase took place prior to the massive transformation. In the case of Ti–46 mol%Al MA powder, higher heating rate yielded finer grain size due to the finer dispersion of Ti₂AlC particles. Increase in aluminum content resulted in the finer grain microstructure because of the increase in Ti₂AlC particles in the vacuum hot pressed compacts sintered at 1173 K for 3.6 ks. Thus, grain refinement in the Ti–Al MA compacts can be accomplished by controlling the heating rate and the aluminum content.