Composition and mechanical properties of hard ceramic coating containing α-Al₂O₃ produced by microarc oxidation on Ti-6Al-4V alloy

Ceramic coatings with 1100- 1600 HK_{50 g} hardness were deposited on Ti-6Al-4V alloy substrates using a microarc oxidation (MAO) technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The influences of electrolyte concentration, deposition time and the cathodic to anodic current ratio Ic/Ia on phase composition and mechanical properties of the coatings have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis methods (EPMA), as well as microhardness measurement, direct pull-off and impact tests. The results show α-Al₂O₃ phase, which greatly improved the hardness of the coatings, can be obtained at high concentration of NaAlO₂ and its relative content increases with decreasing Ic/Ia ratio. The direct pull-off test and impact test results indicate that the films have the excellent adhesion with the substrate.