Multi-technique study of corrosion resistant CrN/Cr/CrN and CrN : C coatings

The three-layer CrN/Cr/CrN coatings were deposited on three types of steel substrates by means of PVD. The second series of these coatings was implanted with nanoclusters of carbon by using a pulsed microplasma cluster source. The physical and chemical properties of the coatings were investigated by using a multi-technique approach. The chemical composition of the samples was studied by XPS combined with cyclic Ar ion sputtering. Multi-point AES measurements and Auger chemical imaging were used to characterize the oblique cross-section of the coatings. Surface investigations revealed that CrN layers were characterized by the ratio of Cr : N = 1 with a low concentration of oxynitride compounds and that the nanoclusters of carbon were localized in the topmost sublayer of the coatings. XRD measurements were performed to study the residual stresses present in the CrN multiple-layers and in the coatings doped with carbon nanoclusters. It was found that the compressive residual stresses are present in the external layer of all multiple-layer coatings, independently from the type of substrate. The corrosion tests have been carried out by the techniques of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in electrochemical cell with NaCl solution. Obtained experimental results demonstrated that the corrosion process begins at the surface defects of the coatings and propagates towards the substrate.