Microstructure and elevated temperature tribological behavior of TiO2/Al2O3 composite ceramic coating formed by microarc oxidation of Ti6Al4V alloy

Microarc oxidation (MAO) treatment of Ti6Al4V alloys in silicate electrolyte with Al2O3 microparticles resulted in a composite ceramic coating containing Al2O3. The microstructure, phase composition and high temperature tribological behavior of the composite coating were analyzed by SEM, EDS, XRD and ball-on-disc abrasive tests. The results revealed that the MAO coating formed in the absence of Al2O3 microparticles was porous, and mainly composed of rutile-TiO2, anatase-TiO2 and Al2TiO5 phase. In the composite ceramic coating, the surface porosity decreased significantly, and α-Al2O3 and more Al2TiO5 phase were identified. Compared to the MAO coating without Al2O3, the composite ceramic coating exhibited better wear resistance at 300 °C, as demonstrated by the lower friction coefficient, lower wear rate and mild wear spots. The enhancement of wear resistance at high temperature is attributed to the denser surface structure and higher fraction of Al2TiO5 phase.