First-principles study to explore the possibility of inducing martensitic transformation in ordered B2 TiRu phase by alloying with Pd

Abstract

Density functional theory (DFT) based on the first-principles technique, CASTEP, was used to explore the possibility of inducing martensitic transformation (MT) in a stable B2 TiRu alloy by systematic introduction of palladium (Pd) on the ruthenium (Ru) site. The structural, mechanical and electronic properties of pure, as well as, Pd-doped TiRu were calculated. The elastic constants obtained show that the addition of Pd seems to induce MT in the ordered TiRu, as shown by mechanical instability (C΄= C₁₁-C₁₂ < 0) of the B2 phase against shear deformation at 0 K. This is an indication that B2 is likely to transform to low symmetry phases such as L1₀/B19/B19’. Moreover, the calculated total density of states (T-DOS) also indicated that the addition of Pd shifted the Fermi level (E_F) from the centre of the pseudogap of the ordered pure TiRu towards the right (anti-bonding region), rendering the resulting B2 ternary phase unstable at certain Pd compositions higher than 10 atomic percent (at.%). The predicted induced martensitic transformation is one of the key characteristics of shape memory behaviour in B2 Ti-based alloys such as NiTi, TiPd and TiPt. Further work on the possible low temperature phases resulting from B2 Ti-Ru-Pd ternary alloys is underway.