Effect of Al and Cu contents on mechanical properties of Au-Cu-Al shape memory alloys

Abstract

In order to develop high performance biomedical shape memory alloy having both good biocompatibility and high X-ray radiography resolution, effects of Al and Cu contents on the martensitic transformation, microstructure and mechanical properties of AuCuAl ternary alloys were studied. Differential scanning calorimetry revealed that the martensitic transformation start temperature decreased with a rate of -7 K/mol%Al in the Au-30 mol%Cu-Al alloys. Besides, the Ms increased with a rate of 18 ∼53 K/mol%Cu in the Au-Cu-15∼20 mol%Al alloys in the Cu-poor side of stoichiometry, while the Ms was almost constant in Cu-rich side. By taking into account of the estimated defect structures, the number of Au-Al atomic bonds is important for the stabilization of the parent β phase. Corresponding microstructural change due to the martensitic transformation was confirmed by optical microscopy. Vickers hardness of the Au-30 mol% Cu-Al alloys decreased with increasing Al content, and a minimum was reached at 20∼25 mol%Al and then the Vickers hardness increased at 25 mol%Al. The alloys at a limited composition range around Au-30∼31 mol%Cu-14∼15 mol%Al possessed both high strength and ductility in addition to pseudoelasticity, while the other alloys exhibited poor ductility.