Corrosion resistance of CrN/NbN superlattice coatings grown by various physical vapour deposition techniques

The corrosion and tribological performance of CrN/NbN superlattice coatings deposited by the techniques of unbalanced magnetron (UBM) sputtering, steered cathodic arc evaporation, and the combined steered cathodic arc and UBM sputtering, i.e. arc-bond sputtering (ABS), have been studied. In corrosion tests, the coatings grown by the ABS technique were superior to those grown by either UBM sputtering or arc evaporation with clear passivation behaviour and low corrosion current densities of 10−8 A·cm−2. In tribological tests, the lowest coefficient of friction μ = 0.3 was shown by the arc evaporated coating whereas the CrN/NbN deposited by the ABS technique achieved the lowest dry sliding wear coefficient of Kc = 5.0 × 10−15 m3·N−1·m−1. The microstructure of the coatings was investigated by cross-sectional transmission electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy, and was related to the corrosion and the tribological behaviour.