Shape memory characteristics of sputter-deposited Ti-Ni-base thin films

Ti-Ni-Cu and Ti-Ni-Pd ternary shape memory alloy thin films were made by sputtering. They showed smaller temperature hysteresis and higher transformation temperatures, respectively, than those of Ti-Ni binary thin films; these characteristics are effective to achieve a high response actuator characteristic. The transformation temperatures and shape memory behavior were characterized by DSC measurement and thermal cycling tests under a variety of constant stresses, respectively. The Ti-Ni-Pd thin film showed a single stage transformation both upon cooling and heating similarly to a Ti-Ni binary alloy thin film which was also made in the present report; the transformation occurred between the parent B2 phase and martensite M(monoclinic)-phase. Correspondingly, they showed a single stage deformation both upon cooling and heating. The Ti-Ni-Cu thin film showed a two-stage transformation and hence a two-stage deformation; the first stage corresponds to the transformation between B2 and O(Orthorhombic)-phase and the second stage between the O- and M-phases. The first stage transformation was accompanied by a small temperature hysteresis. All these thin films showed perfect shape memory effect.