Influence of Voltage on the Microstructure and Tribocorrosion Properties of Porous Coatings Produced by Micro-Arc Oxidation

Micro-arc oxidation (MAO) coatings were produced on commercially pure titanium Grade 2 using a composite electrolyte containing sodium phosphate (Na3PO4) and sodium silicate (Na2SiO3), while varying the applied voltage. The surface morphology, phase composition, and structural features of the coatings were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coatings exhibited a characteristic crater-like microporous surface morphology associated with the micro-arc discharge process. XRD analysis confirmed the formation of mixed TiO2 phases in the anatase and rutile modifications, with higher voltages promoting the growth of the thermodynamically stable rutile phase. Corrosion and tribological properties were evaluated in a 3.5 wt.% NaCl solution using potentiodynamic polarization and a ball-on-disc test configuration, respectively. The results revealed a substantial improvement in both corrosion resistance and wear performance compared with bare titanium. The coating formed at 300 V demonstrated the highest wear resistance due to its denser microstructure, whereas the coating produced at 350 V exhibited the lowest friction coefficient and the greatest corrosion resistance, attributed to the increased rutile content. Overall, MAO coatings fabricated in the phosphate–silicate electrolyte effectively enhance the combined operational properties of titanium and can be recommended for applications requiring improved wear and corrosion resistance.