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 Al₂TiO₅ (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 NaAlO₂ solution. For the purpose of studying the anti-oxidation 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, Al₂TiO₅ in the as-prepared coating decomposed and transformed into α-Al₂O₃ and rutile TiO₂. However, after almost 4 h in argon, Al₂TiO₅ in the as-prepared coating decomposed and the final coating surface contents are completely α-Al₂O₃, and those of the middle interface are mainly Al₂O₃ and Ti₂O₃. 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.