The action of anodic TiO2 coating against thermal oxidation of pure titanium

This study aims to produce a micro-arc oxidation (MAO) layer of TiO₂ on commercially pure titanium (CP-Ti) and analyze the influence of heat treatment temperatures in the air to promote thermal oxidation and in a vacuum to prevent oxidation. The results showed that the MAO coating is amorphous and constituted by TiO₂ as anatase and rutile. The increase in heat treatment temperature (600–1200 °C) promoted the formation of rutile, an increase in surface roughness, but decreased the contact angle and pore size. In the condition subjected to heat treatment in vacuum, there is also a decrease in the thickness of the layer due to atomic diffusion (13 →  ~ 0 μm). On the other hand, the heat treatment out of vacuum oxidized the CP-Ti MAO surfaces, increasing the oxide thickness as the temperature increased (9 → 325 μm). The increased hardness of CP-Ti at the metal/oxide interface was high due to the incorporation of oxygen in solid solution, which acts as a hardening agent. The MAO coating acts as an effective protective layer of the metal substrate against thermal oxidation.