Effects of thermal aging on phase transformation and microstructural characteristics of NiTi shape memory alloy

In this study, the effects of aging temperature and time on microstructure and phase transformation behaviors of the NiTi shape memory alloy were investigated with the effects of precipitates. NiTi SMA was synthesized using powder metallurgy process followed by the solution annealing at 850 °C for 1 h. The thermal aging process has been executed on NiTi alloy in the temperature range of 450 °C–750 °C for 1 h, 3 h and 5 h respectively. It was found that the enhancement of transformation temperatures due to the formation of secondary phases during the transformation of cubic to monoclinic. The lenticular structured Ni ₄ Ti ₃ precipitate was mainly influenced the phase transformation by changing the Ni composition in the NiTi matrix. The significant changes were observed in the austenite and martensite finish temperatures with increasing the aging temperature and time. This study suggests that the NiTi SMA can be implemented in biomedical applications when heat treated at 650 °C for 5 h. (paper)