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

Abstract

The phase transformation behaviour, structure and mechanical properties of Au35–68Cu49–15Al16–17 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 (ΔT) is wide (~55 K) for thin films with Au 50 at.%. This behaviour is correlated with the change in lattice constant of β-(Au–Cu–Al) (a β ), suggesting a structural origin on the ΔT 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 ΔT 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.