Substrate-induced stress and transformation characteristics of a deposited Ti–Ni–Cu thin film

Abstract

This article presents the investigation results on the transformation characteristics of a sputter-deposited Ti–Ni–Cu shape memory alloy thin film and its relation to the substrate-induced stress. Experimental results show that, with the substrate attachment, the transformation interval increases while the transformation hysteresis decreases in comparison with those of the same thin film in the free-standing condition. By assuming a stress distribution through the film thickness, a layer-by-layer transformation sequence in the substrate-attached film is proposed and the transformation interval and hysteresis are analysed. The analysis results show qualitative agreement with the experimental observations, suggesting that the approach taken is plausible. This approach may also be used to examine the transformation characteristics of other thin films having thermally induced phase transformations.