Ab initio modeling of TWIP and TRIP effects in β‑Ti alloys

Abstract: Transformations in bcc-β, hcp-α, and the ω phases of Ti alloys are studied using density functional theory for pure Ti and Ti alloyed with Al, Si, V, Cr, Fe, Cu, Nb, Mo, and Sn. The β-stabilization caused by alloying Si, Fe, Cr, and Mo was observed, but the most stable phase appears between the β and the α phases, corresponding to the martensitic α′′ phase. Next, the {112}⟨111¯⟩ bcc twins are separated by a positive barrier, which further increases by alloying w.r.t. pure Ti. The {332}⟨113¯⟩ twinning yields negative barriers for all species but Mo and Fe. This is because the transition state is structurally similar to the α phase, which is preferred over the β phase for the majority of alloying elements. Lastly, the impact of alloying on twin boundary energies is discussed. These results may serve as design guidelines for novel Ti-based alloys with specific application areas.