Phase stability and elastic constants in Ti-Ta random alloys from first-principles calculations

The relative phase stability of the α, ω and β phases of Ti_1-xTa_x(0 < × ≤ 0. 4) random alloys as well as the single crystal elastic constants of the β phase for 0. 25 ≤ × ≤ 0. 4 have been investigated using the first-principles exact muffin-tin Orbitals method in combination with the coherent potential approximation. The calculated results suggest that Ta addition stabilizes the β phase over the α and ω phases. The predicted critical Ta concentration above which a single β phase is obtained agrees well with the experimental data. With increasing x, the C₁₁, C₁₂, and C₄₄ elastic constants increase. The tetragonal shear modulus C′ is also found to increase with x, reproducing well the experimental trends of the martensitic transformation start temperature M_s of Ti-Ta random alloys.