Ab initio modeling of TWIP and TRIP effects in $\beta$-Ti alloys

Abstract

Transformations in bcc-$\beta$, hcp-$\alpha$, and the $\omega$ 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 $\beta$-stabilization caused by alloying Si, Fe, Cr, and Mo was observed, but the most stable phase appears between the $\beta$ and the $\alpha$ phases, corresponding to the martensitic ${\alpha }^{\prime \prime }$ phase. Next, the $\{112\}⟨11\bar{1}⟩$ bcc twins are separated by a positive barrier, which further increases by alloying w.r.t. pure Ti. The $\{332\}⟨11\bar{3}⟩$ twinning yields negative barriers for all species but Mo and Fe. This is because the transition state is structurally similar to the $\alpha$ phase, which is preferred over the $\beta$ 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.

26 pages, 8 figures. J. Mater. Res. (2025)