Bioactive coatings on Ti6Al4V alloy formed by plasma electrolytic oxidation

• Hydroxyapatite and TiO2 bioceramic phases were directly formed on Ti6Al4V in a single step.
• The wear and friction properties of the coatings in SBF were greater than those of uncoated Ti6Al4V alloy.
• The corrosion resistance of the coatings in SBF was improved compared to that of uncoated Ti6Al4V.
• After immersion in SBF, secondary apatite was formed on the PEO surface.

In this study, coatings, consisting of hydroxyapatite and titanium oxide bioceramic phases, were produced on Ti6Al4V alloy by plasma electrolytic oxidation for different times in a solution containing calcium acetate and β-calcium glycerophosphate. The phases of anatase, rutile, TCP (Ca3(PO4)2), perovskite-CaTiO3 and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) were detected in the PEO coatings. The crystallinity of these phases was enhanced with increasing treatment time. The friction and wear resistance properties of the PEO coatings in simulated body fluid (SBF) were substantially improved compared to Ti6Al4V alloy. The corrosion resistance of the PEO samples in SBF was determined by an electrochemical method, and found to be significantly improved compared to Ti6Al4V alloy due to the existence of titanium oxide and the calcium phosphate-based phases. The amount of apatite induced at the PEO surface increased with increasing immersion time in SBF at 36.5 °C. According to the SEM images and FTIR results, after soaking in SBF for 14 days, the amount of secondary apatite formed in the coating electrolytically oxidized for 90 min was maximized due to high surface area and high amount of TiO2 and HAp in the coating structure.