Corrosion behaviour of TiN and CrN coatings produced by cathodic ARC PVD process on mild steel substrate

Abstract

Hard coatings are often used for their mechanical properties such as wear and friction resistance. Corrosion behaviour may also be an important criterion for industrial applications of such coatings. There is abundant literature on both mechanical and corrosion properties of titanium nitride coatings, however there is much less published data on the properties of CrN coatings. In the present paper, the protective behaviour of TiN and CrN coatings on mild steel immersed in 3%NaCl solution was investigated. Various electrochemical techniques were used to characterise the behaviour of the coatings and the galvanic corrosion of the uncoated metals and coatings was thoroughly studied. The overall corrosion behaviour of the coated steel depends not only on the intrinsic electrochemical properties of the coatings, but also on surface defects such as roughness, droplets deposited during the PVD process, and pinholes, cracks, and scratches. In saline solution, the TiN coating has a poor protective effect compared to CrN. Nevertheless, galvanic corrosion between coatings and substrate is deleterious for the substrate. In both cases, the porosity strongly influences the electrochemical behaviour of the coated specimens.