Shape Memory Behavior of Ti-Ni-X (X=Pd, Cu) Ternary Alloy Thin Films Prepared by Triple-Source DC Magnetron Sputtering

摘要

We have deposited the Ti-Ni-X films having various compositions while keeping the Ti content to be ～50at% by means of triple-source dc magnetron sputtering. All of the annealed films showed thermoelastic martensitic transformation. M_s temperature of the Ti-Ni-Pd films increased with increasing Pd content, and the highest M_s temperature of ～180°C was attained for the Ti-23%Ni-27%Pd film. On the other hand, M_s temperature of Ti-Ni-Cu films slightly increases as Cu content increases. The transformation hysteresis is decreased rapidly down to 15～20°C by adding Pd or Cu more than 10at%. Both ternary alloy films showed shape memory behavior during thermal cycling tests under various constant stresses. The critical stress against plastic deformation, σ_c, of the Ti-Ni-Cu films is higher than that of the Ti-Ni-Pd films. The recoverable strain of these ternary alloy films is found to be ～2%. Actuation response by Joule's heat induced shape memory effect of Ti-Ni shape memory alloy films was slightly improved by the addition of Pd or Cu into the alloy.