Chromium nitride/niobium nitride superlattice coatings deposited by combined cathodic-arc/unbalanced magnetron technique

CrN/NbN superlattice coatings have been developed as an attempt to replace electroplated chromium in some applications. The coatings have been deposited by a combined cathodic-arc/unbalanced magnetron technique in an industrial-size physical vapour deposition (PVD) coater. The investigations have been focused on the question of maximum hardness, adhesion and tribological performance of the coatings deposited at 400 degrees C as a function of the nitrogen content in the films. All CrN/NbN superlattice coatings produced exhibit a single-phase face-centred cubic structure and {200} preferred orientation. The superlattice period of the coatings varies in the range Delta = 3.4-7.4 nm depending on the N-2 flow rate. Under the sputtering conditions used, it was possible for stoichiometric CrN/NbN coatings to be deposited only in a narrow N-2 flow rate range of around 160 seem. Both stoichiometric and sub-stoichiometric coatings showed maximum hardness values of Hk = 3580 and Hk = 3600, respectively. CrN/NbN superlattice coatings outperformed electroplated chromium by factor of 13 in dry sliding conditions. However, both coatings show similar abrasive wear in the range of 0.63 mu m N-1. Stoichiometric CrN/NbN superlattice coatings possess high oxidation resistance in the range 820-850 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.