Surface oxidation of NiTi shape memory alloy in a boiling aqueous solution containing hydrogen peroxide

Oxidation behavior and surface characterizations of NiTi shape memory alloy (SMA) treated with a boiling H2O2 aqueous solution were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. It is found that the low-temperature oxidation of NiTi SMA in H2O2 solution resulted in the formation of a titania scale enriched with Ti–OH groups. The titania scale is mainly composed of rutile and anatase, and is relatively depleted in Ni, which can improve the biocompatibility of NiTi SMA. Depth profiles of O, Ni and Ti show the titania scale possesses a smooth graded interface structure to NiTi substrate, which is in favor of high bonding strength of the titania scale with NiTi substrate. A different oxidation mechanism for NiTi SMA in H2O2 solution from that for NiTi SMA at high temperature air environment was proposed based on the experimental results.