Mechanical properties of Ti–Ni shape memory thin films formed by sputtering

The stress–strain curves of Ti–48.3, 50.0, 51.5at.%Ni thin films were measured. The results showed that sputter-deposited thin films possess sufficient ductility and strength for practical use. Particularly it was noted that a Ti–48.3at.%Ni thin film annealed at 773 K for 300 s shows a large elongation of 20% contrary to bulk specimens. However, the ductility of Ti–48.3at.%Ni thin films was found to be very sensitive to annealing conditions. Ti–48.3at.%Ni thin films annealed at 873 K for 3.6 ks do not show any ductility. The difference in the ductility of the Ti–48.3at.%Ni thin films can be explained by grain-boundary precipitates of Ti2Ni.