Effects of Graphite on Microstructure and Corrosion Resistance of Microarc Oxidation Coatings on Surface of TA7 Titanium Alloy

In order to improve the anti-corrosion and anti-wear properties of TA7 titanium alloy, microarc oxidation (MAO) coatings were prepared on the surface of the alloy. The effects of graphite particles on the microstructure and corrosion resistance of the MAO coating were investigated. The results show that the addition of graphite particles into basic electrolyte increased the coating thickness, and decreased the surface roughness and micro-hardness. With the increase of graphite concentration, the MAO coating increased in thickness and decreased in micro-hardness, but remained the same in surface roughness. The phases of the MAO coating were high-temperature stable rutile phase and anatase phase. MAO treatment made the free corrosion potential increase and made the corrosion current density decrease for TA7 titanium alloy. The addition of graphite particles further increased the corrosion potential and decreased the corrosion current density, resulting in the significant increase of corrosion resistance of the MAO coating.