Growing characters and tribological properties of microarc oxidation composite coating containing Cr2O3 microparticles on Ti6Al4V alloy

The microarc oxidation (MAO) composite coating containing Cr2O3 microparticles on Ti6Al4V alloy was prepared by co-deposition in the electrolyte with Cr2O3 microparticles addition. The growing characters of the composite coating and deposition styles of Cr2O3 microparticles were studied by SEM, XRD and EDS. The tribological behaviors of the composite coating formed at different oxidation time were evaluated using abrasive tests. The results show that the thickness of the composite coating is linearly increased in 30 min; afterwards the growth rate e the composite coating decreases evidently, and large lumps of Cr2O3 agglomerate appear on the film surface in the later stage. The composite coating is mainly composed of rutile-TiO2, anatase-TiO2 and Cr2O3 phase. The anatase-TiO2 decreases gradually, the content of rutile-TiO2 increases firstly and then becomes stable, but the diffraction peak of Cr2O3 phase strengthens continuously with the increasing of oxidation time. Besides, the wear-resistance of the composite coating is improved firstly and then reduced with the increasing of oxidation time. The composite coating formed at 20 min exhibits good antifriction property, whose friction coefficient is 0.05 similar to 0.2. In the process of MAO, Cr2O3 microparticles may be adsorbed directly on the surface of the molten oxidation coating, or may be caught and locked into the irregular pores of oxidation coating. In additon, some Cr2O3 particles may be wrapped by molten products generated in the microarc discharge channel, and solidified together into the oxidation coating.