Preparation of Coating on the Titanium Surface by Micro-Arc Oxidation to Improve Corrosion Resistance

In this paper, two kinds of micro-arc oxidation (MAO) coatings on TA2 with different thickness were prepared by controlled oxidation time and then were characterized for their composition, crystalline structure, and surface morphology. The effect of MAO treatment on electrochemical corrosion behaviors of TA2 in 3.5% NaCl solution were studied by the electrochemical measurements including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The results indicate that the electrochemical behavior of MAO coating is related to the coating structure. OCP can be used to evaluate the porosity of MAO coating. More positive OCP indicates coating with lower porosity and larger resistance obtained from EIS. The MAO treatment can significantly enhance the corrosion resistance of TA2, but the thickness increase of MAO coating could not further improve the corrosion resistance. In addition, because of the increase in effective surface area, the MAO treatment may enhance the cathode action of TA2 when the galvanic cell is composed of TA2 and other more negative metal, which in turn promotes the corrosion of negative metal.