Effects of processing parameters on microstructures of TiO2 coatings formed on titanium by plasma electrolytic oxidation

Abstract

Titanium oxide (TiO2) coatings were formed on titanium substrates in a sodium silicate (Na2SiO3) aqueous solution, using plasma electrolytic oxidation method. The effects of duty ratio, frequency, and positive/negative pulse proportion on the microstructure and phase compositions of the coatings were investigated. The coatings were mainly composed of anatase TiO2 plus a little amount of rutile TiO2. The coatings obtained at the frequency range 900–2700 Hz, under a duty ratio of 20%, and a positive/negative pulse proportion of 3, showed the best quality in terms of density and adhesion. The effect of positive/negative pulse proportion was relatively small. However, continuous coating could not be obtained using the positive/negative pulse proportion of 1. Compared with that of bare titanium, the property of resistance to corrosion was obviously improved for the titanium with TiO2 coating. The corrosion potential rose about 0.13 V and the corrosion current density decreased about one order of magnitude.