Phase composition, morphology and element contents of micro-arc oxidation ceramic coatings on Ti-6Al-4V alloy under different calcination conditions

Compound ceramic coatings with the main crystalline of Al_2TiO_5（in the as-prepared coating without treatment） were prepared in situ on the surface Ti-6Al-4V alloy by means of pulsed bipolar micro-arc oxidation in Na AlO_2 solution. For the purpose of studying the antioxidation properties of the samples, the coated samples treated in argon and the as-coated samples were calcined in air at 1000 °C. And the related characteristics were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and X-ray fluorescence（XRF） spectroscopy, respectively. The results show that, when it was calcined in air for 1 h, Al_2TiO_5in the as-prepared coating decomposed and transformed into α-Al_2O_3 and rutile TiO_2.However, after almost 4 h in argon, Al_2TiO_5in the asprepared coating decomposed and the final coating surface contents are completely α-Al_2O_3, and those of the middle interface are mainly Al_2O_3 and Ti_2O_3. The morphologies of the coatings after calcination in argon and air are different.High-temperature oxidation occurred violently in the alloy substrate without coatings. Furthermore, the weight gain curves of the as-prepared samples and the coated samples treated in argon both show a parabolic shape.