Enhancement of corrosion protection of micro‐arc oxidation by applying nanostructured TiO2 thin film via the “sol‐gel” method

Abstract

PurposeUniform nanostructured TiO2 thin film has been applied as an over coat on micro‐arc oxidized substrate, using the sol‐gel method. The anticorrosion performance of the coating have been evaluated using electrochemical techniques. Owing to increasing application of light alloys in industry, the purpose of this paper is to report effort to increase the corrosion and wear resistance properties of these alloys by applying a TiO2 nanostructured coating using the sol‐gel method on the micro‐arc oxidation (MAO) surface. This approach will decrease the time for the MAO process, especially for achieving good mechanical properties, and will minimize energy consumption as well as achieving better results from the obtained coatings.Design/methodology/approachSol‐gel coatings were deposited (on titanium substrates) by spin coating techniques. The morphologies and nanostructures of thin films were analyzed using scanning electron microscope, atomic force microscopy and grazing incidence X‐ray diffraction (XRD). The anticorrosion performance of the coating has been evaluated by using electrochemical techniques. Tafel polarization measurements provide an explanation for the increased resistance of nanostructured TiO2 coated specimen against corrosion. Effective sol‐gel coating parameters were optimized with respect to this enhancement. Electrochemical impedance spectroscopy measurements showed the role of barrier layer on corrosion resistance of MAO and nanostructured TiO2 coating.FindingsThe results showed that icorr is decreased from 0.258 to 0.169 (μA/cm2). An optimized TiO2 nanostructured coating with thickness of 74 nm will shift the open circuit potential (OCP) about 165 mV and will improve the corrosion prevention properties of coated samples. Corrosion resistance by these duplex coatings can be improved by a factor of more than three times, compared to that of the uncoated substrate. Increasing the coating thickness to more than 74 nm will decrease the physical and corrosion properties of coated samples. It can be concluded that samples with the optimized coating showed higher values of charge transfer resistance, due to the presence of a newly formed layer that accounted for the greater corrosion protection.Practical implicationsThe results obtained in this research into nanostructured coating can be used wherever good corrosion and wear resistances are required.Originality/valueThe speed of treatment by this technique makes this method very suitable for industrial surface treatment of different components.