Effects of ageing on microstructure, martensitic transformation and shape memory performance of a Ni-rich Ti_49.5Ni_34.5Cu_11.5Pd_4.5 alloy

The ageing effects on the microstructure, martensitic transformation and shape memory performance of a Ni-rich Ti_49.5Ni_34.5Cu_11.5Pd_4.5 alloy as a function of temperature were investigated. The formation of (Ni,Cu)₂Ti-type precipitated phases arises from the ageing treatment. When ageing at 500 °C, the fine precipitated phases are diffusely distributed, which improves the shape memory performance efficiently. With the tensile deformation of 5%, the 500 °C aged specimen shows a 25% larger strain recovery rate (a maximum value of 96.8%) than that of the specimen under solution treatment. And after 100 thermal cycles, the transformation temperature variation is lesser than 0.2 °C in the specimen aged at 500 °C. There presents excellent thermal cycling stability while keeping near-zero thermal hysteresis.