Different tribological behavior of CrN and CrCuN coatings under glycerol lubrication

The study compares and deciphers the differences in tribological performance of CrN coatings after incorporation of Cu moiety, i.e. CrCuN coatings, prepared using DC magnetron sputtered physical vapor deposition (PVD), under glycerol lubrication conditions. The structures, compositions and mechanical properties of the coatings were investigated by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), atomic force microscopy (AFM), and nano-indentation. CrCuN coatings present superior mechanical characteristics than CrN coatings. Reduced COF and wear rate values were observed more for the CrCuN coating than the CrN coating. The reason why glycerol exhibits better friction-reducing and wear protection performance in CrCuN coatings than CrN coatings is explained using X-ray photoelectron spectroscopy (XPS). Glycerol molecules were found to be easily degraded on the surface of the CrCuN coating during the sliding process to form a tribofilm which can greatly reduce the friction and wear.