Ceramic coating on Ti-6Al-4V by plasma electrolytic oxidation in molten salt: Development and characterization

Abstract

The plasma electrolytic oxidation (PEO) method is one of the most promising methods for the formation of oxide coatings on metallic substrates. This process is usually conducted in an aqueous solution electrolyte; however, it has several disadvantages, such as heating-up of the system and the formation of the undesired chemical components. This study addresses these disadvantages by conducting the process in a molten salt electrolyte. The surface morphology, phase composition, hydrophobicity, and the effects of process current frequency were examined. Thin titanium oxide, rutile and anatase, coating of 2–2.5 μm was formed on the treated Ti-6Al-4V alloys. The potentiodynamic polarization test evaluated the highest polarization polarization resistance for the alloy obtained using current frequency of 150 Hz which was 364×10 4 Ω·cm 2 in comparison with the pristine alloy which was 6.93×10 4 Ω·cm 2 . Electrochemical impedance spectroscopy revealed the same behavior. Morphology evaluation revealed that the structure of this coating contained uniform sub-micron porosity and its surface exhibited the highest hydrophobicity. • TiO 2 coating was developed by plasma electrolytic oxidation in nitrate salt. • Effect of PEO current frequency on structure and performance was examined. • The highest PEO coating properties were obtained using current frequency of 150 Hz. • The highest contact angle was obtained on the most compact titanium oxide coating. • The highest corrosion resistance was obtained on the most uniform coating.