Alleviating detrimental effects of defects on corrosion performance of TiN coating by post-deposition treatment using polymethyl methacrylate

Coating defects provide an access channel for corrosive medium to penetrate and reach underlying metal substrate, therefore promoting localised corrosion. In this paper, a polymethyl methacrylate (PMMA) sealing technique was developed and applied to a TiN coating deposited by plasma assisted electron beam evaporation method. The as deposited and PMMA treated coating specimens were subjected to potentiodynamic polarisation measurements in 3.5% NaCl aqueous solution. The coating degradation with immersion time was evaluated at open circuit potential using electrochemical impedance technique. The test results indicate that PMMA post-deposition treatment successfully seals the pores, and therefore significantly improves the corrosion resistance of the coating. Additionally no obvious degradation has been observed for the PMMA treated samples during the long time exposure to the NaCl solution.