Structure, corrosion resistance and apatite-forming ability of NiTi alloy treated by micro-arc oxidation in concentrated H2SO4

► TiO2 coatings are fabricated on the NiTi alloys by MAO in concentrated H2SO4. ► The coatings have a porous structure and tightly adhesive to the substrates. ► The corrosion resistance of NiTi alloys has been significantly improved by MAO. ► The TiO2 coatings could induce the apatite formation and have good bioactivity.