Influence of alumina and zirconia incorporations on the structure and wear resistance of titania-based MAO coatings

In the present work, the influence of alumina (Al2O3) and zirconia (ZrO2) incorporation on the structural properties and wear resistance of titania (TiO2) based micro-arc oxidation (MAO) coatings fabricated on Ti6Al4V alloy was studied. For this purpose MAO was employed in a silicate-based electrolyte with and without additions of Al2O3 and ZrO2 particles. The structural properties were determined via X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy analysis and an energy dispersive spectrometer (EDS) equipped scanning electron microscope (SEM). Furthermore, thermochemical simulations were made by using FactSage 7.3. Mechanical properties of the MAO coatings were determined by hardness measurements and dry sliding reciprocating wear tests. Structural examinations revealed that the MAO coatings fabricated in Al2O3 and ZrO2 added electrolytes comprised of these oxides and their complex forms (Al2TiO5 and ZrTiO4, respectively) along with TiO2 and amorphous silica (SiO2). Although incorporations of Al2O3 and ZrO2 did not remarkably improve the hardness of the MAO coatings, the highest wear resistance was obtained from the one formed in the ZrO2 added electrolyte. On the other hand, the MAO coating fabricated in the Al2O3 added electrolyte exhibited lower wear resistance than that of fabricated in the particle-free silicate-based electrolyte.