An investigation on the Effect of Direct and Unipolar Pulse Currents on Surface Characteristics and Corrosion Behavior of Titanium Oxide Nanocrystalline Coating Produced by Plasma Electrolytic Oxidation Process

In this paper Titanium Dioxide was produced on the surface of commercial pure Titanium in Sodium carbonate an electrolyte with constant current density of 825 mA/cm2 by Plasma Electrolytic Oxidation process under applying unipolar Pulse and direct current. To evaluate phase composition, surface morphology and corrosion behavior, respectively The X-ray diffraction, microscopic investigation and potentiodynamic polarization test was conducted by X-ray diffractometer, scanning electron microscope, field emission scanning electron microscope, potentiostat and galvanostat respectively in 3.5 %wt sodium chloride solution. Chemical analysis conducted on sample showed that resulted coatings under unipolar Pulse current have Anataze and Rutile phase and under direct current have uniform Rutile phase. Microscopic results showed that created coating under unipolar Pulse current have a Pancake grain structure and coating produced by direct current have a volcanic structure. The estimated size of crystalline for this two coating also was 29 and 49 nm, respectively. Investigation of corrosion behavior of coated samples confirms that obtained coating with unipolar Pulse current have better corrosion resistance than coating with direct current, also electrochemical impedance spectroscopy results were supported by polarization test result shows that corrosion resistance of coating produced by unipolar Pulse current was 6times higher than direct current.