Microstructure evolution and strain recovery characteristic of proton-irradiated Ti-rich NiTi thin films

The effect of 120 ​keV proton irradiation with different fluences on the phase constitution, microstructure, and shape recovery characteristics of Ni-51.4 ​at.%Ti shape memory alloy thin films was systematically investigated. The results showed that the proton irradiation induced the formation of a multiple-layer structure at the surface of NiTi thin film. Meanwhile, the hybrid defects such as vacancies, dislocations, and nano-scale precipitates were observed in the irradiation layer. The transition temperature and shape recovery strain decreased gradually with the increasing irradiation fluence, which can be attributed to the formation of the multilayer structure and the generation of irradiation-induced defects.