On the high temperature deformation of a directionally solidified γ-TiAl alloy

The gamma-TiAl alloy with a nominal composition of Ti-47Al-2Nb-2Cr-0.2C directionally solidified by electromagnetic cold crucible was isothermally compressed at different temperatures and strain rates. Experimental results revealed that the peak stress decreased with the increased deformation temperature or decreased strain rate. Subgrains were formed in the interior of the lamellae during thermo-compression and the dislocation walls served as the subgrain boundaries. The dynamic recrystallization grain (DRX) size was larger and a single DRX grain grew at the expense of many lamellae. Slip bands formed during thermo-compression process were in a single direction at a small strain, while the increase in the strain led to the intersections of slip bands in two directions. Kink bands were developed as the strain reached or exceed a critical value, acting as the preferred nucleation sites for recrystallization grains. Moreover, the model for the nucleation of recrystallization grains was given.