Influences of calcinations ambience on phase composition of ceramic coatings on Ti-6A1-4V alloy by micro-plasma oxidation

Compound ceramic coatings with the main crystalline of Al₂TiO₅ (as-coated samples) were prepared on Ti-6A1-4V alloy by pulsed bi-polar Micro-arc oxidation (MAO) in NaAlO₂ solution system. The coated samples were calcined in argon and air under 1000°C respectively. XRD, SEM and XRF were used to investigate the phase composition, morphology and element content of the ceramic coatings. The results show that Al₂TiO₅ decomposed and transformed into corundum and rutile TiO₂ during the high temperature calcination. Al₂TiO₅ decomposed very quickly in air and the proportion of α-Al₂O₃ to TiO₂ was 44:55 after a complete decomposition. On the contrary, the Al₂TiO₅ decomposed very slowly in argon into α-Al₂O₃ on the coating surface. The content of Al₂O₃ was decreased from outside to inside and meantime Ti₂O₃ formed in the coating. The morphology of the ceramic coatings after the calcination was also different. The coatings calcined in argon were fined; grains and pores were smaller than that in air. The content of Ti, Al, P and O in the coating only changed a little before and after calcinations.