Control of the physical properties of anodic coatings obtained by plasma electrolytic oxidation on Ti6Al4V alloy

Spark anodizing on Ti6Al4V has been performed in three alkaline solutions using different electrical parameters in order to study the coating formation. The surface features show a dependence on the shape and distribution of the electric microdischarges. In addition, the surface features and the chemical composition of the coatings are dependent on the anodizing solution employed. The tribological properties of the coatings formed are correlated with the morphology and the internal structure of the coatings. The variation of the internal structure of the coatings was evidenced by EIS analysis. Results indicate that it is possible to control the physical properties of the anodic film by an adequate selection of the process parameters. A porous structure is obtained using a solution mainly composed of hypophosphite, which exhibits a good tribological performance. Low porosity and compact structure can be obtained in the anodic film by using an anodizing solution composed of hypophosphite and metasilicate; furthermore, these coatings exhibit a good corrosion protection. Highly porous structure is achieved by using an anodizing solution composed of hypophosphite and sulfate. The best wear resistances were observed in coatings formed at potentiostatic mode, as demonstrated by the results of ball-on-disc wear tests.