RECENT DEVELOPMENTS IN SPUTTER-DEPOSITED TI-NI-BASE SHAPE-MEMORY ALLOY THIN-FILMS

Since 1992 the present authors have been successful in making Ti-Ni sh ape memory alloy thin films, which can show perfect shape memory effec t and superelasticity equivalent to those of bulk materials, by utiliz ing a r.f. sputtering method. In the present paper, some of their rece nt 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 deforma tion behavior, the effect of cyclic deformation on the stability of sh ape memory behavior, the effect of nonequilibrium state created during crystallization process on the transformation behavior, etc. The Ti-N i-Cu films were made in order to decrease the transformation hysteresi s, while the Ti-Ni-Pd films were made in order to increase the transfo rmation temperatures: both are effective to increase the response spee d in actuation.