Plasma electrolytic oxidation coating produced on 39NiCrMo3 steel

In this work, PEO process was applied for the first time on a 39NiCrMo3 steel using different solutions as electrolytes. Alkaline solutions containing mainly silicates and aluminates were used as electrolyte. The corrosion resistance of the PEO coated samples was studied with potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in chloride and sulphate environment, using the untreated sample as comparison. EIS data were fitted using the software Z-view with an appropriate equivalent circuit. The morphology and chemical composition of the obtained coatings were studied using a scanning electron microscope, equipped with EDS, and with X-ray Photoelectron Spectroscopy (XPS). The phase composition was studied with X-ray diffraction (XRD). The corrosion properties of the PEO coated steels were improved if compared with the uncoated samples, especially using aluminates in the electrolyte.