Structure and properties characterization of ceramic coatings produced on Ti-6Al-4V alloy by microarc oxidation in aluminate solution

Microstructure and phase composition of the ceramic coatings formed on Ti-6Al-4V alloy by alternating-current microarc oxidation in aluminate solution were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Distributions of nanohardness, H, and elastic modulus, E, along the coating thickness were determined using a nanoindentation method, After microarc oxidation treatment, the microstructure in the Ti-6Al-4V substrate near the coating/metal interface has not been changed; meanwhile, the titanium substrate has hardly absorbed oxygen atoms. The oxide coating is mainly composed of TiO2 rutile and TiAl2O5 compounds. The rutile fraction in the inner layer coating is much higher than in the outer layer. On the contrary, the TiAl2O5 phase has a higher fraction in the outer layer. On the other hand, the nanoindentation test shows from the coating surface to the interior of the coating that the H and E gradually increase. The maximum H and E in the coating can reach 13 and 230 GPa, respectively. The changes of TiO2 and TiAl2O5 contents along the coating thickness determine the H and E profiles in the coating. (C) 2002 Elsevier Science B.V. All rights reserved.