THERMODIFFUSION SURFACE ALLOYING AS AN EFFECTIVE METHOD OF CORROSION PROTECTION IN AGGRESSIVE ENVIRONMENTS

Chromium coatings on St45 steel produced by electroplating and thermodiffusion alloying are compared using the available cyclic polarization observations in sulfate and sulfate–chloride electrolytes. Chloride addition accelerates corrosion of the electroplated coating by a factor of 2–5, whereas the reported increase for the diffusion-alloyed layer is 15–20%. These observations are discussed alongside published studies of coating defects, diffusion-layer formation and localized corrosion. The protective effect is associated with the continuity of the surface barrier; specific phase composition and chloride adsorption mechanisms require independent structural evidence.