Effect of Cathodic Voltage on Phase Composition, Microstructure, and Elevated-Temperature Oxidation Resistance of Micro-Arc Oxidation Ceramic Coatings on Ti65 Alloy

This study investigates the effect of cathodic voltage on the thickness, morphology, composition, phase structure, adhesion, and elevated-temperature oxidation resistance of the micro-arc oxidation (MAO) ceramic coatings on Ti65 alloy. Coatings were fabricated via MAO under cathodic voltages of 50 V, 100 V, 150 V, and 200 V. Results indicate that the coatings primarily consist of rutile TiO2 (R-TiO2), anatase TiO2 (A-TiO2), and amorphous SiO2. The thickness of the MAO coatings increased with rising cathodic voltage, while the surface porosity and average pore size of the coatings were first decreased and then increased with the increase in cathodic voltage. Excellent coating adhesion to the substrate was confirmed by 50 thermal shock cycles between 700 °C and room temperature. Cyclic oxidation tests at 750 °C for 100 h demonstrated that all MAO coatings significantly enhanced elevated-temperature oxidation resistance compared to the bare Ti65 substrate. Notably, the coating produced at 100 V exhibited the lowest oxidation weight gain (0.50 mg/cm2), amounting to only one-third of the substrate’s gain. The effect of the cathodic voltage on the high-temperature oxidation performance of the MAO coatings was systematically analyzed.