Preparation and structure of ceramic coatings containing zirconium oxide on Ti alloy by plasma electrolytic oxidation

The aim of this work was to prepare ceramic coatings containing ZrO2 phase on Ti alloy and study their structure and corrosion resistance. Compound ceramic coatings were prepared on Ti-6Al-4V alloy by pulsed single-polar plasma electrolytic oxidation (PEO) in K2ZrF6 electrolyte. The phase composition, morphology of the coatings and the element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of the coated samples was examined through the potentiodynamic anodic curves in 3.5% NaCl solution. The coatings prepared for short PEO time was composed of m-ZrO2, t-ZrO2 and ZrTiO4 and a little ZrP2O7; while increasing PEO time, the content of ZrP2O7 was increased and became the main crystalline. The Ti content in the coating near the substrate was decreased sharply while the content of Zr was increased greatly. The thickness of the coating was increased with the PEO time, but the coatings turned rougher and more porous. The prepared coated samples had better corrosion resistance than the substrate. Among the coated samples, the coated sample prepared for 40 min had the best corrosion resistance.