Effect of oxidation time on microarc oxidation ceramic coatings on Ti6Al4V alloy

Ceramic oxide coatings were formed on the Ti6Al4V alloy surface by microarc oxidation (MAO) in the Na2SiO3-KOH-(NaPO3)6 solution using an AC power supply. SEM, EPMA and XRD were employed to characterize the microstructure, the elements distribution across the coating and the phase composition. The results show that with the increase of oxidation time, the current density declines gradually and the thickness of ceramic coatings increases with constant electrical parameters (U+=500 V, U-=100 V and f=600 Hz). Relatively dense and uniform coatings consist of three layers: transitional, dense and loose layers, which are mainly made of anatase TiO2 are rutile TiO2. As the treatment time prolonged, the relative contents of anatase TiO2 and rutile TiO2 are changed, that is, the content of rutile TiO2 is increased while the content of anatase TiO2 is reduced. A double-stage phase formation mechanism of ceramic coatings was also proposed.