Phase Transformation and Corrosion Properties of Surface Oxidized NiTi Shape Memory Alloy

Abstract

Oxide film was obtained on a NiTi shape memory alloy by a chemical method. The influences of surface oxidation on the phase transformations and corrosion resistance were assessed. Light blue oxide film formed on the alloy was mainly composed of TiO₂. Differential scanning calorimetry(DSC) measurement displayed that the phase transformations was not affected by surface oxidation. Electrochemical tests indicated that the oxidized NiTi alloy showed better corrosion resistance than the non-oxidized one in the simulated body fluid. Scanning Electron Microscopy (SEM) revealed that lower pitting corrosion occurred for the oxidized NiTi alloy compared with the non-oxidized. The oxidized samples did not show any surface alterations except very small and homogeneously distributed pits were observed.