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

• Published in: Surface & coatings technology Vol. 310; pp. 180 - 189
• Main Authors: Quintero, D., Gómez, M.A, Castaño, J.G, Tsuji, E., Aoki, Y., Echeverría, F., Habazaki, H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25-01-2017
• Subjects: Aluminate solution; Anodic coating; PEO; Titanium alloys; Wear; Titanium alloys; Anodic coating; PEO; Aluminate solution; Wear
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2016.12.063

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.
••Additives improve the tribological behavior as well as reduce roughness and thickness of coatings.••Potentiostatic mode allows controlling the size of micro-discharges, changing coating morphology.••Tribological properties are correlated with the surface morphology and the internal structure.••Thin coatings were obtained under potentiostatic conditions with good tribological performance.