Ab initio studies of TiPd-M (M= Os, Ru, Co) high temperature shape memory alloys*

The TiPd alloy has a potential for high temperature shape memory applications due to its martensitic transformation capability from B2 to B19 at 823 K. Previous studies indicated that B2 TiPd is unstable displaying a negative C at room temperature. In order to improve its properties, the effects of partial substitution of Pd with either Os, Ru or Co were investigated using density functional theory. The calculations are carried out within PBE-GGA for the exchange correlation functional. It was found that the heats of formation decrease with an increase in Os and Ru concentration and increases with Co addition. The ductility of TiPd-M (M= Os, Ru and Co) is predicted using Pugh‘s ratio, Poisson‘s ratio and Cauchy pressure. It was found that the structures showed positive C above 18.75 at. % Os, 20 at. % Ru and 31 at. % Co, displaying condition of stability. The calculated moduli confirm that alloying with Os effectively increases hardness and ductility better compared to Ru and Co. Partial substitution of Pd with Os and Ru was found more effective as a strengthening elements and may enhance the martensitic transformation temperature of B2 TiPd alloy.