High temperature oxidation behavior of TiO2 + ZrO2 composite ceramic coatings prepared by microarc oxidation on Ti6Al4V alloy

• TiO2 + ZrO2 composite ceramic coatings were prepared by microarc oxidation on Ti6Al4V alloy.
• A double-layer structure forms at 500 °C and 600 °C, while a multilayer structure forms at 700 °C and 800 °C.
• TiN is found in the multilayer structure in coated samples oxidized at 700 °C and 800 °C.
• The presence of multilayer structure can provide an efficient diffusion barrier, which restrains the growth of TiO2 and TiN.

Microarc oxidation (MAO) was used to prepare TiO2 + ZrO2 composite coatings on Ti6Al4V alloy in Zr-containing electrolytes. The high temperature oxidation resistance and oxidation mechanism of MAO coatings were investigated and discussed. The composite ceramic coatings exhibit a porous structure with small pores (0.4–1 μm in diameter) on the inner wall of larger pores, and consist of m-ZrO2 and ZrTiO4. In the case of static oxidation at different temperatures, the high temperature oxidation resistance of Ti6Al4V is improved 2–10 times after MAO treatment. The coated samples oxidized at different temperatures present various oxidation behaviors. A porous TiO2 layer forms after exposing oxidation at 500 °C for 300 h, while a continuous TiO2 layer forms after oxidation at 600 °C for 75 h. However, when the coated samples oxidized at 700 °C and 800 °C, a multilayer structure of MAO coating/transitional layer/TiO2 layer/TiN layer forms on Ti6Al4V with the combined effect of interface migration of MAO coating and air diffusion inward, and the diffusion of substrate elements outward. Especially, it is found that a TiN layer with preferential growth towards (111) lattice planes forms in the multilayer structure in coated samples, which is much different from the oxidation behavior of Ti6Al4V at 700 °C and 800 °C. The presence of multilayer structure can provide an efficient diffusion barrier, which restrains the growth of TiO2 and TiN.