Corrosion performance of CrN/NbN superlattice coatings deposited by the combined cathodic arc unbalanced magnetron technique

Potentiodynamic polarisation experiments have been used to evaluate the corrosion performance of novel CrN/NbN superlattice coatings in comparison with a commercial CrN coating and a 304L control specimen. In addition, electrochemical impedance has been used to determine the effective surface area of the coatings by capacitance measurements. Results indicate that the superlattice coatings have significantly improved barrier properties evidenced by increases in pitting potentials of up to 500 mV compared with 304L. Furthermore, the impedance evidence indicates that CrN has comparatively large pores while the superlattice coatings have extensive, but diffuse and fine-scale, surface porosity confirming that the corrosion performance improvement is most likely due to microstructural enhancements. (C) 1999 Elsevier Science Ltd. All rights reserved.