Effects of Ti content on microstructure and shape memory behavior of TixNi(84.5−x)Cu15.5 (x = 44.6–55.4) thin films

Abstract

Ti–Ni–Cu films with Cu and Ti contents of 15.5 and 44.6–55.4at.%, respectively, were prepared by sputtering and their structure and shape memory behavior after annealing for 1h at 773, 873 and 973K were investigated. The Cu content of the B2 phase was constant for the Ti-rich films, but decreased with decreasing Ti content for the (Ni,Cu)-rich films. The (Ni,Cu)-rich films annealed at 773K were supersaturated with Ni. The grain size of the Ti-rich films was smaller than that of the (Ni,Cu)-rich films. These differences corresponded to the difference in the shape memory behavior. The martensitic transformation start temperature was almost constant for the Ti-rich films annealed at 873 and 973K, but decreased with decreasing Ti content for the (Ni,Cu)-rich films. The critical stress for slip was larger for the Ti-rich films than for the (Ni,Cu)-rich films. The maximum recoverable strain was smaller for the Ti-rich films than for the (Ni,Cu)-rich films. The relationship between the structure and shape memory behavior is discussed.