Influence of aging temperature on phase transformation and mechanical behavior of NiTi thin films deposited by magnetron sputtering technique

In this study, NiTi thin films were deposited on the glass and NaCl substrates by means of magnetron sputtering method. The influence of aging temperature, over the range 300-500 oC, on phase transformation and mechanical properties of the sputtered NiTi thin films were studied by differential scanning calorimetry (DSC) and nano-indentation assay, respectively. The DSC curves showed that the aged specimens at 350, 400, and 500°C underwent two steps transformation during cooling process while a three steps transformation has been observed for the film aged at 450°C. This behavior clearly demonstrated the heterogeneity in chemical composition and microstructure of the sputtered thin film, which consequently resulted in the martensitic transformation of R and remained B2 to B19' within two steps. According to nano-indentation analysis results, a peak point at aging temperature of 450°C is reached. The temperature hysteresis of all aged films was about 1°C, which can be considered as a positive sign for sensor application.