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

Abstract TiO 2 /Al 2 O 3 composite coatings were prepared on the surface of Ti-6Al-4V alloy by micro-arc oxidation in the Na 2 SiO 3 -(NaPO 3 ) 6 -NaAlO 2 solution. The growth process reveals that O 2- reacts rapidly with Ti 4+ (from substrate) along the reaction channels to form TiO 2 , and because of the addition of AlO 2 − , Al 2 O 3 and Al 2 TiO 5 are simultaneously formed. Al 2 TiO 5 is immediately decomposed into rutile TiO 2 and α-Al 2 O 3 owing to the high thermal energy caused by discharge. Finally the prepared composite phase coatings are mainly composed of anatase TiO 2 , rutile TiO 2 and α-Al 2 O 3 via XRD analysis. Furthermore, the microhardness HV increases and maintains at about 11 000 MPa, and the wear resistance of the TiO 2 /Al 2 O 3 composite coatings is enhanced by about 9.5 times than higher that of Ti-6Al-4V alloy owing to the existence of ceramic layer.