Microstructures and thermal behaviour of Ti31.75V18.25Pt50 and Ti25V25Pt50 potential shape memory alloys

Abstract

The binary Ti50Pt50 alloy exhibits high transformation temperatures (1050°C) and has gained a great deal of attention due to its potential for high temperature applications in the automotive and aerospace industries. However, this binary system has negligible shape memory effect. Shape memory effect is the property of a material to recover to its initial shape following heating while retaining residual deformations throughout an inelastic loading/unloading cycle. Improved shape memory properties could be achieved by ternary alloying Ti50Pt50. A study reported on partial substitution of Ti with 6.25 and 12.5 at. % V in the equi-atomic TiPt resulted in increased austenite and martensitic transformation temperature. This study is a follow-up to investigate the impact of higher V contents (18.25 and 25 at. %) on microstructures and the thermal behaviour of the alloys. Samples were prepared by arc melting of blended powders, and characterised for microstructures, thermal behaviour and hardness. The as-cast microstructure of Ti31.75V18.25Pt50 revealed a matrix of a single phase (Ti, V) Pt and second phases comprising TiO and (Ti2O) + Pt, while that of Ti25V25Pt50 showed a matrix of (Ti,V) Pt with TiO and Ti2O. Solution heat-treated Ti31.75V18.25Pt50 showed a matrix of the single phase (Ti, V) Pt with second phases of (Ti, V) Pt, while Ti25V25Pt50 showed a matrix of (Ti, V) Pt with second phases of (Ti, V) Pt, TiO, TiO2 and Ti2O. Increasing vanadium from 18.25 to 25 at. % led to a decrease in transformation temperature in both the as-cast and solution heat-treated conditions. The transformation temperature increased after solution heat treatment. The enthalpy change during transformation ( H) decreased with higher vanadium content. Hardness values increased with vanadium content increase in both as-cast and heat-treated conditions.