Tribological and corrosion behavior of CrN coatings: Roles of substrate and deposition defects

In this paper tribological and corrosion behavior of CrN coatings obtained through magnetron sputtering (MS) and cathodic arc evaporation (CAE) deposition techniques were studied. The effect of interfaces and defects like droplets or porosities detected with scanning electron microscope analysis, both on coating surface and cross sections, was stressed and interpreted in terms of different behavior during the electrochemical polarization tests carried out in NaCl solution or wear tests executed using a pin-on-disk tribometer. Nanoindentation measurements and scratch tests were also executed to characterize the coatings. The effect of different substrate hardness obtained changing the chemical composition of the steel bulk material was also considered, and its effect on the wear mechanisms of damaging was investigated. Regardless of the presence and distribution of the defects and the number of layers, a value of high hardness for the substrate is crucial for the long term pin-on-disk test because it can prevent the delamination of the coating. A different type of defect corresponds to a different corrosion current but, regardless of the deposition technique, the presence of a double layer ensures a better resistance to corrosion and excludes a preferential path for the localized corrosion in small areas of the steel substrate.