Composition–Structure–Property Relations in Au35–68Cu49–15Al16–17 Shape Memory Thin Films

Abstract

The phase transformation behaviour, structure and mechanical properties of Au 35-68 Cu 49-15 Al 16-17 thin film shape memory alloys (SMA) have been investigated, with emphasis on the effects of Au content. The results revealed the underlying composition-structure-property relations. The thermal transformation hysteresis (DT) is wide (*55 K) for thin films with Au \50 at.%, while it is narrow (*15 K) for thin films with Au [50 at.%. This behaviour is correlated with the change in lattice constant of b-(Au-Cu-Al) (a b), suggesting a structural origin on the DT behaviour. The mechanical properties, such as hardness and elastic modulus, varied in the range of 2-4 and 70-120 GPa, respectively. The optimum Au composition range for tuning the functional property is between 43 and 55 at.% Au, where the least amount of non-transforming phases form and DT can be tailored between 55 K (43 at.% Au) and 17 K (55 at.% Au). This is important for the development and practical application of Au-Cu-Al based thin film SMA.