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 44.6–55.4 at.%, respectively, were prepared by sputtering and their structure and shape memory behavior after annealing for 1 h at 773, 873 and 973 K 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 773 K 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 973 K, 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.