Progress in Ti-based shape memory alloys

In recent years, Ti based shape memory alloys have become one of the research hotspots in the field of smart metal materials. These alloys, on one hand, can be used as the replacement of the biomedical NiTi shape memory alloys to avoid the cytotoxicity and allergenicity caused by Ni ion release. On the other hand, they can have high martensitic transformation temperature and thus can be used as high temperature shape memory alloys in the fields of aviation, aerospace and energy industries. Ti based shape memory alloys mainly include Ti-Nb, Ti-Ta and Ti-Zr alloys. Ti-Nb based shape memory alloys have a very broad phase transformation temperature ranging from 180 to 561 K and their maximum shape memory effect and superelasticity are about 4.0% and 5.0%, respectively. The binary Ti-Ta and Ti-Zr alloys are typical high temperature shape memory alloys with martensite transformation temperatures above 373 K. The effects of the addition of alloying elements and thermo-mechanical treatment on phase transformation, microstructures, mechanical properties, shape memory effect, superelasticity and biocompatibility of Ti-Nb, Ti-Ta and Ti-Zr alloys were reviewed. Some aspects of future research on Ti based shape memory alloys were suggested.