Comparing Morphology and Corrosion Behavior of Nanostructured Coatings Obtained via Plasma Electrolytic Oxidation with Direct and Pulse Currents on Commercial Titanium Substrate

Abstract

In this study, the effect of frequency, duty cycle, and type of current (direct or alternating) on the morphology and corrosion behavior of ceramic coatings formed via plasma electrolytic oxidation on a commercial titanium substrate was studied. The surface morphology and chemical composition of the coatings were analyzed via scanning electron microscopy and X-ray diffraction. The corrosion behavior of the coatings was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in aqueous 3.5% NaCl solution. A chemical analysis revealed that all coatings had a rutile phase. Since the coating obtained under AC condition had a small amount of anatase phase; the results indicated that the corrosion rate of the coated samples was notably reduced compared to that of the bare metal. Furthermore, an increase in the applied current frequency resulted in reduction of the current density and an increase in the corrosion potential. In addition, the electrochemical impedance spectroscopy showed that at a higher frequency, coatings exhibited the best corrosion resistance that was about 200 times higher than that of the uncoated sample.