Anodic films obtained on Ti6Al4V in aluminate solutions by spark anodizing: Effect of OH− and WO4− 2 additions on the tribological properties

Spark anodizing of Ti6Al4V alloy has been performed in alkaline electrolytes containing aluminate to form wear-resistant coatings. Coatings obtained under potentiostatic conditions exhibit a better wear resistance, with a wear rate approx. 10 times lower than galvanostatic coatings, due to the formation of coatings with low porosity since potentiostatic mode controls the size of the micro-discharges. The coatings consist mainly of γ - Al2O3, whilst Al2TiO5 is present in minor proportions. For some coatings, the formation of Al6KO9.5 is observed due to the incorporation of potassium into the coating. EDS analysis shows that aluminum is the main constituent of the coatings, being mainly incorporated from the anodizing solution and homogeneously distributed into the coating. A decrease in pore density between 15 and 30% and roughness reduction of 10 to 60% was obtained with KOH and Na2WO4 additions, improving the coating wear resistance in pin-on-disc wear tests, especially by Na2WO4 addition.