Isothermal oxidation property of the Al₂TiO₅/ TiO₂/ZrO₂ composite coating on TC₄ alloy prepared by micro-arc oxidation

The isothermal oxidation behaviours of Al₂TiO₅/TiO₂/ZrO₂ composite coating on titanium alloy (TC₄) deposited by micro-arc oxidation technique were studied at different temperature points of 1073, 1173 and 1273 K in dry air. The surface morphology and phase composition of all coated samples were investigated before and after oxidation by SEM and XRD, respectively. The weight gaining curves of the coated samples were plotted and the high temperature oxidation rates were evaluated, showing that the oxidation kinetics followed the parabolic rate law. And with increasing oxidation temperature, their oxidation rates also increased. The original phases of Al₂TiO₅/TiO₂/ZrO₂ coating on TC₄ alloy consisted mostly of Al₂TiO₅ and R-TiO₂ intermixed with small amounts of ZrO₂ and the phased changed into mainly of R-TiO₂, Al₂O₃ and little Al₂TiO₅ when after 1273 K oxidation for 1 h, whose average parabolic rate constant was 6.43 × 10-13 g2 cm-4 s-1, greatly lower than that of blank samples, 6.01 × 10-12 g2 cm-4 s-1, indicative of a good oxidation resistance for the Al₂TiO₅/TiO₂/ZrO₂ composite coating on TC₄ surface.