Evaluation of Corrosion Resistance of Coatings Formed by Plasma Electrolytic Oxidation Method in Different Electrolytes on Titanium Substrate in Ringer's Solution

In the present study, the effect of different concentrations of calcium acetate (10 and 20 g/l) and potassium hydroxide (1 and 3 g/l) salts in electrolyte of the plasma electrolytic oxidation process on corrosion resistance of coatings formed on pure titanium has been investigated. After observation the surface structure of the coatings, it was found that the lowest porosity (about 4.86%) was related to the coating formed in the electrolyte containing 20 g/l calcium acetate and 1 g/l potassium hydroxide. This coating also showed the highest contact angle with water droplets (67.89 degrees) or in other words, the lowest wettability. The results of evaluation of corrosion behavior of coatings using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests after 48 hours of immersion in Ringer's solution indicated that the mentioned coating had the lowest corrosion current density (3.06 × 10-8 Ω/cm2 ) and the highest corrosion resistance (448272 Ω cm2 ) among all coatings. The high resistance of this coating against corrosion was due to low porosity percentage and thus reducing the penetration of corrosive ions into the substrate and also low wettability.