Analytical studies of corrosion and wear resistant CrN/NbN superlattice PVD coatings.

CrN/NbN nano-scale multilayered coatings have found use in a number of commercial applications where both wear and corrosion resistance are important factors that are required. CrN/NbN nano-scale multilayered coatings have been successfully deposited at temperatures as low as 250°C on 304 stainless steel substrates. This has been achieved by the combined cathodic arc/unbalanced magnetron PVD technique (Arc Bond Sputter) with a coating thickness of 3.0 pm at bias voltages Ubeta of -75 and -95 Volts. The coatings exhibited a preferred {111} texture, good adhesion properties and plastic hardness of 38 to 69 GPa. The microstructural and surface morphology properties of these coatings in the as deposited and corroded conditions have been investigated. The corrosion resistance of the coatings was determined using potentiodynamic polarisation measurement in a 3%NaCl solution open to air at room temperature. The low temperature CrN/NbN coatings deposited onto stainless steel exhibited superior corrosion resistance properties than that for stainless steel. Both crevice and pitting corrosion had occurred at selective growth defect sites, beneath which, an under-dense (porous) coating microstructure was present. These under-dense coating regions provide solution pathways through the coating to the substrate. Wherever feasible comparisons were made with CrN/NbN superlattice coatings deposited at higher temperatures (400°C).