CORROSION STUDIES WITH HARD COATING SUBSTRATE SYSTEMS

After reviewing the fundamentals of corrosion, the various electrochemical and technical corrosion tests will be discussed with special emphasis on their problems and evidence. In addition to the corrosion behavior of the coating material, the effect of the substrate is also important. The experimental potential-current density curves reflect the electrochemical properties of the coating and the influence of the underlying substrate when micropores, pinholes and other defects are present. Examples are given for nitride hard coating-substrate and hard coating-interlayer-substrate systems. The interlayers can act as barrier layers improving corrosion resistance, The nitride hard coatings are deposited by various physical vapor deposition methods and the interlayers by electrochemical or physical vapor deposition.