Influence of ZrO2 Incorporation into Coating on Electrochemical Response of Low-Carbon Steel Processed By Plasma Electrolytic Oxidation

Abstract

The carbon steel is one of the most widely used metals material in engineering with good properties, such as high strength, high toughness, good mechanical properties and low cost. The surface treatment of the steel is essential, however, before use it in industry due to the low corrosion resistivity of steel substrate, which is a problem to use in high humid environment. Meantime it is important to improve the wear resistance and the interfacial adhesion of the coating. Since the thick alumina coating is one of most effective anti-corrosion layer which has high corrosion resistance relatively with the metals, the alumina coating on the steel substrate is good way to improve corrosion resistance. Among the ceramic coating technique for fabrication the alumina layer, such as chemical vapor deposition, magnetron sputter and ionization-assisted beam, plasma electrolytic oxidation (PEO) has been investigation as a new electrochemical surface treatment.PEO process is a unique process that utilized electrochemical reactions to form an oxide layer on a metal surface. The PEO process has been reported to attractive combination of wear resistance and corrosion resistance as well as enhancing thermal property of coating layer. However this advanced coating technique has been performed only if material was valve metals, such as Mg, Al, Ti, Nb and etc. and only a few papers of PEO processed steel have been published. Although several researchers performed PEO process on the steel substrate, the specimen was pretreated by plasma spray, laser re-melting or chemical vapor deposition, therefore it was not convenience to widely use in engineering due to the very high cost and thermal shock to the substrate.The structure and morphology of coating layer formed by PEO process, on the other hand, is influenced on experiment conditions which are composition and concentration of electrolyte, current density and condition of substrate, in particular, composition of electrolyte effect on forming oxide layer. Recently, the incorporation of second oxide nanoparticles into the oxide layer generated by the PEO process in order to improve functionality has received considerable attention. Our previous work has demonstrated that incorporated ZrO2 nanoparticles into oxide layer may enhance the resistance against pitting corrosion.In this study, we conducted PEO process on A36 carbon steel without any pretreatment and successfully formed an incorporated alumina layer with 200-400 nm size of ZrO2 nanoparticles on the carbon steel and prepared comparison specimen which is unincorporated alumina coating with any others during PEO process. The microstructure and phase of coating layers were investigated and corrosion behavior was evaluated by electrochemical impedance spectroscopy.