Compositions and tribological properties of PEO coatings on Ti6Al4V alloy

Hard oxide coatings were deposited on Ti6Al4V alloy using plasma electrolytic oxidation process from mixed aluminate/phosphate electrolytes. The influence of aluminate/phosphate proportion on the phase compositions, mechanical and tribological properties was systematically investigated. The results showed that plasma electrolytic oxidation (PEO) coatings with high compactness and hardness were formed in high aluminate/phosphate ratio electrolyte and the wear resistance and load bearing capacity were greatly improved due to the presence of hard γ- and α-Al2O3 phases. Low aluminate/phosphate ratio electrolyte led to thin and loose coatings without α-Al2O3 phase. It was shown that a thicker coating could provide only a limited improvement in wear resistance unless it is hard and free of porosity.