Martensitic transformation of Ni50Ti45Ta5 shape memory alloy

Abstract Ni 50 Ti 45 Ta 5 alloy is similar to equiatomic NiTi alloy with near equal transformation temperatures and having B 2 ↔  B 19′ one stage transformation. The main lattice twin is 〈0 1 1〉 type II twin. The lattice parameter of B 2 austenite is a  = 0.3025 nm, and the lattice parameters of B 19′ martensite is a  = 0.290 nm, b  = 0.412 nm, c  = 0.473 nm and β  = 98.2°. The transformation temperature depression of Ni 50 Ti 45 Ta 5 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 Ni 50 Ti 45 Ta 5 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.