Recent developments in sputter-deposited Ti-Ni-base shape memory alloy thin films

Abstract

Since 1992 the present authors have been successful in making Ti-Ni shape memory alloy thin films, which can show perfect shape memory effect and superelasticity equivalent to those of bulk materials, by utilizing a r.f. sputtering method. In the present paper, some of their recent results were reviewed. The alloys investigated are Ti-Ni, Ti-Ni-Cu and Ti-Ni-Pd, the alloy content ranging from 45.4 to 51.9 at%Ni for Ti-Ni, from 0 to 18.0 at%Cu for Ti-Ni-Cu and from 0 to 21.8 at%Pd for Ti-Ni-Pd. The Ti-Ni films were used for investigating the effects of Ni-content and heat-treatment condition on the transformation and deformation behavior, the effect of cyclic deformation on the stability of shape memory behavior, the effect of nonequilibrium state created during crystallization process on the transformation behavior, etc. The Ti-Ni-Cu films were made in order to decrease the transformation hysteresis, while the Ti-Ni-Pd films were made in order to increase the transformation temperatures: both are effective to increase the response speed in actuation.