Effect of discharge pulsating on microarc oxidation coatings formed on Ti6Al4V alloy

Ceramic coatings were formed on a Ti6Al4V alloy in a Na2SiO3-KOH-(NaPO3)6 aqueous solution, using the pulsating microarc oxidation method. A constant voltage (500 V) was applied to reveal the effect of the positive-pulse duty cycle on the growth rate, microstructure and phase composition of the coating. To obtain the optimum process, a constant current density (60 mA cm−2) combined with a stepped adjusting of the positive-pulse duty cycle was also proposed. The coatings are mainly composed of anatase and rutile (TiO2). As the duty cycle increases, rutile increases and becomes the predominant phase. The coating formed at a duty cycle of 8% indicates an optimum combination of structure and thickness. When applying a constant current density, the growth rate of coatings is significantly increased compared with the application of a constant voltage. Further, using the stepped adjusting of the duty cycle, the microstructure of the coatings is improved obviously.