A first-principles study of displacive β to ω transition in Ti-V alloys

The ground state properties of β and ω phases in Ti-(0-30 at%)V alloys were calculated, and subsequently thermodynamics and energy barriers of the displacive β to ω transition were investigated by first-principles. The results show that the lattice parameters of β and ω phases decreases with increasing V content in Ti-V alloys. The principal lattice strains for the β to ω transition are highly compositional dependent, and the volume variation decreases with increasing V content. The mechanical stability of the ω phase increases initially at the V content around 10 at% and then decreases with increasing V content. Based on the quasiharmonic Debye model, a metastable diffusionless phase diagram has been established, showing that the ω phase is thermodynamically more stable than the β phase at room temperature, anticipating a spontaneous transition from β to ω phases in Ti-V alloys. The calculations of energy pathways indicate that there is an energy barrier during the displacive β to ω transition in Ti-V alloys at temperatures from 100 to 500 K, but not at 0 K.