Influence of Electrolytes on the Microstructure of Microarc Oxidation Coatings on Ti-6Al-4V Alloy

Dense ceramic oxide coatings of about 50 μm may be prepared on Ti-6Al-4V alloy surface by alternating-currentmicroarc oxidation in aluminate and silicate solutions, respectively. Their phase constituent and microstructure werecharacterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that theelectrolytic ions have incorporated into the interior of the coatings. The coating formed in aluminate solution iscomposed of the rutile TiO2 and TiAl2O5 phases rather than the rutile, anatase and amorphous SiO2 phases for thecoating formed in silicate solution. However, TiAl2O5 content in the outer layer of the two coatings is much higherthan in the inner layer. It is suggested that all these oxides may result from a rapid solidification of the moltencoating in the microarc discharge zone.