Dry Sliding Friction Study of ZrN/CrN Multi-Layer Coatings Characterized by Vibration and Acoustic Emission Signals

In this work, we studied single-layer ZrN and CrN coatings, as well as multi-layer ZrN/CrN coatings deposited by the vacuum-arc method on WC-8 wt.% Co substrates. The sliding friction parameters were preset to simulate different operating conditions for coatings, i.e., severe and zero wear regimes. During the tests, the friction coefficient, acoustic emission (AE) and vibration signals were recorded. After testing, the worn surfaces of the samples were studied using confocal laser scanning and scanning electron microscopy, elemental microanalysis and synchrotron XRD. Estimation of vibration accelerations and AE energy turned out to be very effective means of monitoring the wear of coatings, while median AE frequency turned out to be a less informative one. With the increase in the normal load applied on the samples after testing at zero wear regime, the coefficient of friction increased and wear transition to severe wear regime occurred but vibration acceleration decreased. The multi-layer ZrN/CrN coatings demonstrated much higher wear resistance as compared to those of single-layer ZrN and CrN.