Stability of the B2 phase in refractory high entropy alloys containing aluminum

We study the phase stability of the B2 phase in a two-phase Al0.5NbTa0.8Ti1.5V0.2Zr refractory high entropy alloy. We find that the ordered phase of this alloy primarily contains Zr, Al, and Ti, where Zr and Al occupy opposite sublattices. Although the site occupancy of Ti is not conclusive from the experiments, first-principles calculations confirm the preference of Ti atoms to occupy the Zr sublattice. We also find the B2 phase composed of Al, Zr, and Ti is unstable and that it transforms into Zr5Al4 Omega, L10, or an ordered hexagonal phase depending on strain and the presence of antisite defects.