Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

Abstract

This study investigated the selective leaching, chemical compositions, and electrochemical properties of Cu–XAl–4Ni (X = 12.5, 13.0, and 13.5) shape memory alloys (SMAs). The selective leaching results showed that the Cu–XAl–4Ni SMAs released approximately 200 ppb of Cu ions, 200 ppb of Al ions, and 600 ppb of Ni ions after immersion in Ringer’s solution for 90 days. The low concentrations of Cu and Al ions stem from the oxidation of Cu and Al atoms near the surface of the Cu–XAl–4Ni SMAs to form Cu₂O and Al₂O₃ films. The selective leaching properties of the Cu–XAl–4Ni SMAs were inferior to that of the TiNi SMA, which possessed a highly passive TiO₂ film on the surface, but were much better than those of the TiNiCu and TiNiFe SMAs, whose TiO₂ films were deteriorated by the formation of NiO, Cu₂O, and Fe₂O₃ oxides. Cu–XAl–4Ni SMAs are potential candidates to serve as biomaterials, owing to their acceptable surface and selective leaching properties, high martensitic transformation temperatures, low cost, good machinability, and excellent electric and thermal conductivities.