Effect of ternary element addition on the corrosion behaviour of Ni T i shape memory alloys

The goal of this study is to compare the corrosion behaviour of selected ternary nickel titanium (NiTi)‐based alloys (Ni45Ti50Cu5, Ni47Ti50Fe3 and Ni39Ti50Pd11) with a binary, pseudoelastic Ni50.7Ti49.3 alloy. We examine the influence of the ternary elements on the corrosion behaviour using standard electrochemical techniques. All measurements were done in a physiological solution (0.9% NaCl) simulating a body temperature of 37 ± 1 °C. The influence of Cu and Pd addition on the surface oxide film was characterised by X‐ray photoelectron spectroscopy (XPS). The results revealed that, the localised corrosion resistance of these ternary alloys is lower than the binary NiTi alloy. By comparing the different NiTi‐based alloys, the following relation has been proposed for their localised corrosion resistances: NiTiCu < NiTiFe < NiTiPd < NiTi. Depth profiling by XPS showed that the surface oxide film on all the investigated NiTi‐based alloys is mainly of TiO2, however, the NiTiPd and NiTiCu alloys showed metallic ternary element distributed within TiO2 layer.