Evaluating the Properties of Protective Coating Prepared on Titanium Using Plasma Electrolytic Oxidation in Potassium Phosphate Electrolyte

Titanium oxide coatings were prepared on commercially pure titanium substrates using plasma electrolytic oxidation process under current density of 0.15 A/cm2 in electrolyte containing 5-15 g/L potassium phosphate for period of 120-600 s. The effects of oxidation time and electrolyte concentration on surface morphology, thickness, roughness, relative porosity, pores size distribution, microstructure and corrosion behavior were evaluated. Investigation of voltage-time variations showed that increasing the electrolyte concentration up to 15 g/l caused an acceleration of microdischarge events and reduced the breakdown voltage from 593 V to 516 V. Morphological observations revealed that the pores were located at long distances and protuberances around the pores were more prominent. By increasing the oxidation time to 600 s, the thickness and roughness of the coatings increased, and due to the presence of 11% porosity of the coating surface, the total number of pores with diameters greater than 1 μm to 18% of the total surface pores reached. Investigation of the corrosion behavior revealed that the thickness of 8.2 ± 0.3 μm and low porosity, increased the corrosion resistance of the sample coated in the concentration of 15 g/L of potassium phosphate up to 1670 kΩ.cm2.