Electrochemical characteristics of iridium coating by double glow plasma discharge process on titanium alloy substrates

Iridium coating was fabricated by a double glow plasma discharge process on titanium alloy substrates. The electrochemical behaviours of the coating and the substrate were studied and compared. The coating exhibited a preferred (220) orientation. The coating was rough and many defects were present in the coating; the electrochemical activity of the coating was strong. The corrosion potential of the coating was more positive than that of the substrate, and corrosion current density of the coating was higher than that of the substrate. Although the polarisation resistance of the coating was less than that of the substrate due to the defects in the coating and the performance of the oxide film formed, such as conductive Ir oxides film and non-conductive ceramic oxide film on the substrate surface, the coating with a high corrosion potential and high width of the capacitive loop had significant benefit for anti-corrosive properties of titanium alloy substrate.