Martensitic transformation of Ni50Ti45Ta5 shape memory alloy

Ni50Ti45Ta5 alloy is similar to equiatomic NiTi alloy with near equal transformation temperatures and having B2 ↔ B19′ one stage transformation. The main lattice twin is 〈0 1 1〉 type II twin. The lattice parameter of B2 austenite is a = 0.3025 nm, and the lattice parameters of B19′ martensite is a = 0.290 nm, b = 0.412 nm, c = 0.473 nm and β = 98.2°. The transformation temperature depression of Ni50Ti45Ta5 alloy is larger than that of NiTi alloy under the same number of thermal cycles due to the presence of more particles. The martensite stabilization occurs due to the deformation. It is closely related to the variation of the elastic energy and the irreversible energy during deformation. The Ni50Ti45Ta5 alloy has a higher martensite stabilization than NiTi alloy under the same degree of deformation due to the presence of a soft β-Ta phase.