TiAl 금속간화합물의 기계적 특성에 미치는 Mo첨가의 영향

Abstract

The effects of Mo addition on the crystallographic factors and chemistry of y phase, the as-cast and heat-treated microstructures, and the mechanical properties of Ti-48at%Al intermetallic compound have been investigated. The Mo addition has been found to have an effect on stablizing fine β particles in the heat-treated structure. The Mo addition also tends to enhance work hardening rate by stabilizing the lamellar structure in the heat-treated condition. These results lead to the fact that the compressive yield stress increases from 349㎫ to 617㎫ as Mo content increases from 0 to 3at.%Mo in Ti-48at.%Al. The Mo additon increases c/a ratio as well as Al and Mo contents of γ phase. However although the increment of Al content and c/a ratio in γ phase is relatively small, a significant decrease in ductility is observed. The fracture tensile strain has been calculated using Chan`s model and the deterioration in ductility with Mo addition is predicted primarily to be due to the high intrinsic yield stress in Mo-added alloys. We also suggest the modified Ashby`s work hardening theory considering the effect of volume fraction of second phase in α (lamellar)-γ two-phase structure. Using this model, the dependence of work hardening rate on the lamellar volume fraction has been calculated. The result shows that the separate lamellar volume fraction contributes additionally to the enhancement of the work hardening rate in α (lamellar)-γ two-phase structure.