Preparation and properties of titanium oxide film on NiTi alloy by micro-arc oxidation

► Titanium oxide coatings were produced on the NiTi alloy by micro-arc oxidation. ► The coatings were tightly adhesive to the substrates. ► The corrosion resistance of NiTi alloy was significantly improved by micro-arc oxidation. Titanium oxide ceramic coatings were prepared by micro-arc oxidation (MAO) in galvanostatic regime on biomedical NiTi alloy in H3PO4 electrolyte using DC power supply. The surface of the coating exhibited a typical MAO porous and rough structure. The XPS analysis indicated that the coatings were mainly consisted of O, Ti, P, and a little amount of Ni, and the concentration of Ni was greatly reduced compared to that of the NiTi substrate. The TF-XRD analysis revealed that MAO coating was composed of amorphous titanium oxide. The coatings were tightly adhesive to the substrates with the bonding strength more than 45MPa, which was suitable for medical applications. The curves of potentiodynamic porlarization indicated that the corrosion resistance of NiTi alloy was significantly improved due to titanium oxide formation on NiTi alloy by MAO.