The corrosion resistance behavior of Al2O3 coating prepared on NiTi alloy by micro-arc oxidation

Al2O3 coating was prepared on biomedical NiTi alloy by micro-arc oxidation in an aluminate solution using pulsed bipolar power supply to improve the corrosion resistance. The microstructure and composition were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), and thin-film X-ray diffraction (TF-XRD), respectively. The corrosion resistance in 0.9% NaCl solution was evaluated by open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The results show that the well-adhered coating with thickness of 4 μm consists of only Al2O3 crystalline phase. The concentration of Ni on the surface is 3.33 at.%, which is greatly lower than that of NiTi substrate. The results of EIS study and potentiodynamic polarization test indicate that the corrosion resistance of the coated sample is increased by about 40 times higher than that of uncoated sample.