Structure and properties of TiO 2 coatings on biomedical NiTi alloy by microarc oxidation

Abstract

A porous TiO₂ coating was prepared on NiTi alloys by microarc oxidation (MAO) in a titania sol containing solution at constant current density. The surface of the TiO₂ coating displays a rough and porous structure. The roughness and thickness of the MAO coating depend on the applied voltage for MAO treatment. X-ray photoelectron spectroscopy (XPS) analysis reveals that the elements of the coatings mainly contain Ti, O, P and Ni elements, and the Ni content is significantly lower in the coating than in the NiTi substrate. Thin film X-ray diffraction shows that the MAO coating is composed of amorphous titanium oxide. The coatings are tightly adhesive to the substrates. Potentiodynamic polarisation curves indicate that the corrosion resistance of the MAO coating is better than that of uncoated NiTi. The MAO coating prepared on the NiTi has been soaked in a simulated body fluid (SBF) to investigate the biomimetic deposition of apatite on the surface of the MAO coating. It is found that the MAO coating shows an excellent apatite forming ability after soaking in a SBF for 14 days.