Surface characterization of Ni-Ti alloy modified by isothermal oxidation

In order to improve the corrosion resistance of Ni-Ti alloys, mechanically polished Ni-Ti alloys discs were subjected to isothermal oxidation (TO) treatment in N₂-20vol.%O₂ at temperatures ranging from 300 to 800°C. TO-treated surfaces were then analyzed by Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray spectroscopy (EDX), and X-ray electron spectroscopy (XPS). Electrochemical corrosion tests and wear tests were carried out. Ni-Ti alloys exhibited different oxidation behavior depending on the treatment temperatures. An almost Ni free layer was observed on the surface layer of the specimens treated at temperatures 500°C and above. TO-treated specimens showed a higher corrosion resistance compared to that of the untreated sample, and a higher wear resistance. Consequently, TO-treatment produced an almost nickel free smooth protective oxide layer, which might contribute to good biocompatibility.