Cyclic oxidation behaviour of the Al₂TiO₅/TiO₂/ZrO₂ composite coating on Ti-6Al-4V

Al₂TiO₅/TiO₂/ZrO₂ plasma electrolytic oxidation coating deposited on the surface of Ti-6Al-4V alloy was prepared in NaAlO₂-NaH₂PO₂-NaOH electrolytes system, which was doped with ZrO₂ micro-particles by a kind of pulsed bipolar plasma electrolytic oxidation. The microstructure, surface morphology and phase composition of the Al₂TiO₅/TiO₂/ZrO₂ coatings were studied by SEM and XRD, respectively. Its cyclic oxidation behaviour was studied over the temperature of 1000°C for 100 hours in dry air. After high-temperature oxidation, the original crater eruption topography of plasma electrolytic oxidation coating has disappeared and it obviously took a decreasing tendency of both pore numbers and their diameters. The scales of original plasma electrolytic oxidation coating consisted mostly of Al₂TiO₅, R-TiO₂ and α-Al₂O₃intermixed with small amounts of ZrO₂ particles. They were transferred into R-TiO₂, α-Al₂O₃ and ZrO₂ with small amounts of Al₂TiO₅ after high-temperature oxidation procedure. The weight gains of plasma electrolytic oxidation composite coating increased linearly with the extended oxidation cycles.