Effects of high temperature oxidation on composition and structure of microarc ceramic coating on Ti alloy

Due to the poor high temperature resistance of Ti alloy, ceramic coatings with the main crystalline of Al₂TiO₅ were prepared on TC4 alloy in NaAlO₂ solution by pulsed bi-polar microarc oxidation technique. And the effects of high temperature oxidation at 1000°C on composition, structure and the weight gains of ceramic coatings were investigated. The results showed that the oxidation process of the ceramic coatings included the decomposition of Al₂TiO₅, the oxidation of the substrate and the changes of the coating morphology. After high oxidation, the main crystalline of the coating became α-Al₂O₃ and rutile TiO₂ from Al₂TiO₅, and the surface morphology of the coatings changed greatly. Because of the different heal expansion coefficients between the substrate and the coating and the oxidation of the substrate in itself, the coatings cracked and separated from the substrate during the cooling process. Compared with the substrate, the ceramic coatings greatly decreased the weight gains of the TC4 alloy under the high temperature oxidation of 1000°C. Therefore, the ceramic coatings may be used as a kind of isothermal oxidation resistance coating in practice.