Transition behaviors of γ-β0/β in V-, Cr-, Mn-doped TiAl alloys

The behavior of gamma-beta/beta (0) phase transition in TiAl alloy doped with beta stabilizers (V, Cr, Mn) are studied by using the first principles method. It is found that alloying addition as well as anharmonic lattice vibration and disordered atomic occupation contributes to enhance the stability of cubic structure and accordingly introduce the disordered beta phase into the high-temperature microstructure. The formation of low-temperature beta (0) phase originates from not only the stabilization of cubic structure but also the destabilization of tetragonal structure. In particular, the latter is the main reason for the premature precipitation of the hard-brittle beta (0) phase in the room-temperature microstructure at low nominal doping concentrations. We also find a special doping region in which the gamma and the beta phases are stable, while the beta (0) phase is unstable. The existence of this region provides an opportunity for the regulation of the contents of beta and beta (0) phases.