Shape memory behavior of sputter-deposited Ti-Ni-Pd thin films

Characteristics of Ti-Ni-Pd high temperature shape memory alloy thin films with various Pd contents between 2.3 at% and 35.3 at% were investigated. The thin films were made by the r.f. magnetron sputter-deposition method followed by heat-treatments at 743 K or 973 K for 3.6 ks. Transformation behavior and shape memory characteristics were evaluated by constant stress tests during thermal cycles. It was found that the transformation start temperature M, of Ti-Ni-Pd thin films heat-treated at 973 K was higher than that of the films heat-treated at 743 K. The highest M. was around 560 K in the 52.0Ti-12.7Ni-35.3Pd(at%) thin film heat-treated at 973 K. The critical stress for slip or, and maximum shape recovery strain epsilon(A)(MAX) of the film heat-treated at 743 K are larger than those of the film heat-treated at 973 K. The maximum shape recovery strain of 5.6% was achieved in the 51.2Ti-39.7Ni-9.1 Pd(at%) thin film heat-treated at 743 K.