Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

Ni–48.5at%Ti thin films were irradiated in the austenite phase by different energy-level protons at a dose rate of 1.85 × 1012 p/(cm2·s), and the total dose was 2.0 × 10¹⁶ p/cm². The microstructures of the thin films before and after irradiation were evaluated by transmission electron microscopy (TEM) and grazing-incidence X-ray diffraction (GIXRD), which showed that the volume fraction of Ti₃Ni₄ phase elevated with proton energy level. The influence of proton irradiation on the transformation behavior of the TiNi thin films was investigated by differential scanning calorimetry (DSC). Compared with the unirradiation film, the reverse transformation start temperatures (A_s) decreased by about 3°C after 120 keV proton-irradiation. The proton irradiation also had a significant effect on the mechanical properties of the TiNi thin films. After 120 keV energy proton-irradiation, the fracture strength increased by 8.44%, and the critical stress increased by 21.1%. In addition, the nanoindenter measurement image showed that the hardness of the thin films increased with the increase of proton-irradiation energy. This may be due to the defects caused by irradiation, which strengthen the matrix.