Effect of different surface oxidation treatments on structural, mechanical and tribological properties of ultrafine-grained titanium

Four different surface oxidation treatments, so-called, anodizing oxidation (AO), micro-arc oxidation (MAO), plasma oxidation (PO) and thermal oxidation (TO), were applied to ultrafine-grained (UFG) pure titanium produced by equal-channel angular extrusion/pressing (ECAE/P). Before and after all treatments, mechanical, structural and tribological properties were investigated. The strength of pure titanium increased substantially after ECAE process. TiO2 phases included the anatase and/or the rutile formed on the surface of UFG Ti depending on oxidation treatments. High strength of UFG Ti was deteriorated by TO and PO treatments because of the recrystallization occurred at high-temperature, while applications of MAO and AO did not cause a significant decrease in its strength due to the prevention of recrystallization of UFG Ti. All oxidation treatments brought about a remarkable increase in wear resistance of UFG Ti because of the formation of adhered and hard TiO2 film developed on the surface. It was concluded that the AO and MAO treatments could be applied to the UFG Ti without any deteriorations in bulk mechanical and wear properties to obtain biocompatible pure titanium with high strength and excellent wear resistance.