Microstructure, martensitic transformation and superelasticity of Ti 49.6Ni 45.1Cu 5Cr 0.3 shape memory alloy

Abstract

The aim of this study is to investigate the microstructure, martensitic transformation behavior, shape memory effect and superelastic property of Ti 49.6Ni 45.1Cu 5Cr 0.3 alloy, with Cu and Cr substituting for Ni. After annealing, the alloy showed single step A–M/M–A transformations within the whole annealing temperature range of 623 K to 1273 K even in the presence and Ti 2(Ni, Cu) precipitates. With the increase of the annealing temperature, the transformation temperatures exhibited three stages: increasing from 623 K to 873 K, decreasing from 873 K to 1023 K and unchanging from 1023 K to 1273 K. Meanwhile, the critical stress for stress induced martensitic (SIM) transformation decreased to a minimum value and increased after that, exhibiting a V shape curve. The alloy annealed at 623, 773 and 923 K exhibited shape recovery ratio more than 90% when the deformation strain was below 20%.