Composition, microstructure and corrosion resistance of coating formed on Ck45 steel by plasma electrolytic oxidation method

Plasma electrolytic oxidation (PEO) is the new, environmentally and cost-effective method for coating. This method vastly has been studied for coating Aluminum, Titanium and Magnesium and their alloys and recently for steel. In present study, Ck45 steel samples were coated by PEO method in order to improve corrosion resistance. During this process specimens were immerged in Carbonate solution contains Sodium dehydrogen phosphate (NaH2PO4) and Sodium Carbonate (Na2CO3) with PH equaled 8.3. Composition and microstructure of the coating were investigated by X-Ray pattern (XRD) and scanning electron microscopy (SEM). The electrochemical corrosion behavior of coated and uncoated species was verified in 3.5% NaCl solution by potentiodynamic polarization technique. The result of XRD and SEM test showed that nanocrystale particles of Fe3O4 were successfully formed on the surface of samples while the average size of particles and phase were less than 800nm. Grain size was estimated about less than 80 nm. Corrosion test exhibited the remarkable improvement (about three times) in corrosion resistance of coated samples (16023Ω) compared with those without coating (5200.4 Ω).