Martensitic transformation from β′ to α′ and α" phases in Ti-V alloys: A first-principles study

The ground state properties of the alpha ' and alpha '' martensitic phases and energetic pathways of the beta -> alpha '/alpha '' martensitic transformations in Ti-(0-30 at.%) V alloys were investigated by first-principles method in combination with virtual crystal approximation. The results show that lattice parameters with c/a of the alpha ' phase and lattice parameters with b/a, c/a of the alpha '' phase are significantly sensitive to composition, and the atomic shuffle y of the alpha '' phase decreases from that of the alpha ' phase toward that of the beta phase with increasing V content in Ti-V alloys. The compositional alpha '/alpha '' phase boundary is about 10 at.% V, from the viewpoints of energetics and mechanical stability of these phases. The principal lattice strains of the beta -> alpha ' transformation are insensitive to the V content, while those of the beta -> alpha '' transformation change significantly with increasing V content. The volume variation for beta -> alpha ' increases, whereas that for beta -> alpha '' decreases with increasing V content in Ti-V alloys. The energetic pathway results show that the relative stability of the alpha ' and alpha '' phases decrease with increasing V content and temperature and that there is no energy barriers during the beta -> alpha '/alpha '' martensitic transformations at temperatures from 0 to 400 K.