Preparation of PEO ceramic coating on Ti alloy and its high temperature oxidation resistance

Ceramic coatings were prepared in Na₂SiO₃–Na₂CO₃–NaOH system by pulsed bi-polar plasma electrolytic oxidation on Ti–6Al–4V alloy. The phase composition, structure and the elemental distribution of the coatings were studied by XRD, SEM and energy dispersive spectroscopy, respectively. The thermal shock resistance of the coated samples at 850 °C was evaluated by the thermal shock tests. The high temperature oxidation resistance of the coating samples at 500 °C was investigated. The results showed that the coating was mainly composed of rutile- and anatase TiO₂, Increasing the concentration of Na₂SiO₃, TiO₂ content decreased gradually while the thickness of the coating increased. There were a large amount of micro pores and sintered particles on the surface of the coatings. Increasing concentration of Na₂SiO₃, the sintered particles on the surface turned large, and the Si content increased while the Ti content decreased gradually. When the concentration of Na₂SiO₃ was 15 g/L, the thermal shock resistance of the coatings was better than that of the coatings that prepared under other Na₂SiO₃ concentrations. The coating samples prepared under the optimized technique process based on the thermal shock tests improved the high temperature oxidation resistance at 500 °C greatly, whether considering the isothermal oxidation or the cyclic oxidation.