Polarisation behaviour and corrosion initiation mechanisms of Mo coated with amorphous hydrogenated silicon alloy thin ceramic films

AbstractAmorphous hydrogenated silicon, silicon nitride, and silicon–carbon films on molybdenum substrates were anodically and cathodically polarised in NaCl and Na2SO4 solutions at 30°C. The silicon films showed signs of extensive deterioration, whereas the silicon nitride and silicon–carbon films were inert, but led to pitting of the Mo substrate predominantly at pre-existing coating breaches. Analysis of the corrosion morphology, and comparisons of actual polarisation diagrams to those generated by electrochemical polarisation models indicated that submicron cracks accounted for most of the breaches, while larger breaches, such as those caused by coating spallation were less frequent. To a lesser degree, pits also initiated from regions lacking pre-existing breaches during the later stages of anodic polarisation.