Effect of Bulk Phase Composition on the Growth of PEO Coatings on the Biomedical Ti-6Al-4V Alloy.

This study investigated the effects of plasma electrolytic oxidation (PEO) treatment in a Ca- and P-rich electrolyte on the surface of the Ti-6Al-4V alloy with distinct α/β phase proportions previously induced by heat treatments. The results revealed that the α/β phase proportions were successfully altered by the heat treatment temperatures, forming α phase plates surrounded by β phase precipitates. PEO-treated samples exhibited a thick and microsized porous TiO coating in the anatase and rutile crystalline forms. The oxide layer was depleted by Al and V atoms, while Ca and P were gradually enriched along the coatings. Chemical analysis also indicated the absorption of water and organic molecules into the outer layer. PEO-treated samples had microscale roughness and thickness, hydrophilic behavior, and surface energy mainly formed by the dispersive component. The bulk's elastic modulus decreased with β phase precipitation, while the alloying elements directly influenced the Vickers microhardness. The corrosion tests indicated a stable and protective layer in the PEO-treated samples, showing better corrosion resistance than untreated ones. Overall, the findings indicated that the α and β phase proportion significantly impacts the mechanical properties, while the PEO treatment acts in the corrosion protection and surface aspects, suggesting that combining both approaches could be a powerful tool in biomedical applications.