Effect of aging on shape memory behavior of Ti-51.3 at pct Ni thin films

Thin films of Ti-51.3 at. pct Ni were prepared by sputtering. The sputter-deposited thin films were solution treated at 973 K for 1 hour and then aged at various temperatures between 573 and 773 K for 3 different times of 1, 10, and 100 hours. After the heat treatment, the shape memory behavior was examined with a thermomechanical tester. The aging effects on the shape memory characteristics, such as the critical stress for inducing slip deformation, the maximum recoverable strain, and the R phase and martensitic transformation temperatures, were discussed based on transmission electron microscopic (TEM) observation of the microstructure in the age-treated thin films. In all the age-treated thin films, the presence of Ti3Ni4 precipitates was confirmed. When the precipitate diameter was less than 100 nm, the shape memory characteristics were very sensitive to the microstructure. The aging effects on the shape memory characteristics of the Ni-rich Ti-Ni thin films were found to be almost consistent with those reported in bulk specimens, and, thus, the shape memory behavior of the sputter-deposited thin films of Ni-rich Ti-Ni can be controlled in the same manner as that of bulk specimens.