Porosity evaluation of protective coatings onto steel, through electrochemical techniques

Various electrochemical techniques, usually used to characterise the corrosion resistance of coated steel, are compared in order to evaluate the porosity of various protective coatings (Al, Ti, TiN or CrN). The porosity significantly influences the corrosion behaviour of the coated steel, tested in saline environment, and some gaps are evident in the porosity values determined from these techniques. These heterogeneous data are interpreted in terms of intrinsic behaviour of each coating and of galvanic effects between the relevant coating and the substrate. The advantages and drawbacks of each electrochemical technique are underlined in correlation with the type of tested coating.