Effect of heat treatment atmosphere on the structure and apatite-inducing ability of Ca, P, Si and Na incorporated microarc oxidation coating on titanium

Amorphous microarc oxidation (MAO) coating containing Ca, P, Si and Na elements on Ti substrate has been heat treated in different atmospheres (air or argon) to adjust the phase composition, surface structure and bioactivity. After heat treatment in air at 800 °C for 1 h, the coating consists of anatase, rutile and CaTi₄(PO₄)₆, with almost unchanged microporous surface structure. As for the one treated in argon at 800 °C for 1 h, anatase and rutile are formed on the coating, and the coating surface is covered by flower-like rutile particles. The formation of rutile particles could be attributed to the prior growth of the oxidized β-Ti along the discharge channel caused by the diffusion of incorporated elements. Thanks to the crystallization of TiO₂ and the rise of surface roughness, which provides good sites for apatite nucleation, the MAO coated Ti after heat treatment in argon at 800 °C exhibits good apatite-inducing ability.