Fabrication and Wear Resistance of TiO2/Al2O3 Coatings by Micro-arc Oxidation

TiO2/Al2O3 composite coatings were prepared on the surface of Ti-6Al-4V alloy by micro-arc oxidation in the Na2SiO3-(NaPO3)6-NaAlO2 solution. The growth process reveals that O2- reacts rapidly with Ti4+ (from substrate) along the reaction channels to form TiO2, and because of the addition of AlO2−, Al2O3 and Al2TiO5 are simultaneously formed. Al2TiO5 is immediately decomposed into rutile TiO2 and α-Al2O3 owing to the high thermal energy caused by discharge. Finally the prepared composite phase coatings are mainly composed of anatase TiO2, rutile TiO2 and α-Al2O3 via XRD analysis. Furthermore, the microhardness HV increases and maintains at about 11 000 MPa, and the wear resistance of the TiO2/Al2O3 composite coatings is enhanced by about 9.5 times than higher that of Ti-6Al-4V alloy owing to the existence of ceramic layer.