Nanostructured self-lubricating CrN-Ag films deposited by PVD arc discharge and magnetron sputtering

CrN-Ag nanostructured coatings are deposited onto low-alloy steel substrates by means of Physical Vapour Deposition (PVD) reactive magnetron sputtering and PVD reactive arc discharge evaporation. The two different kinds of film have been characterized morphologically, chemically and tribologically. Depending on the used technique, as-deposited film shows different morphology, but in both cases, Ag nano-clusters are present on the surface. The annealing leads to coarsening of superficial Ag clusters and segregation out of the CrN matrix, depending on the temperature. After 600 °C annealing the surface is covered by an almost continuous layer of Ag, no matter which deposition technique is used. Tribological tests at different temperatures show that the lowest coefficient of friction appears at 600 °C for both coatings. The analysis of the wear tracks reveals that such a low friction is related to continuous Ag segregation out-of-CrN matrix, which enables self-lubrication. ► CrN-Ag coatings deposited by PVD magnetron sputtering and PVD arc discharge. ► Thermal annealing leads to coarsening of superficial Ag clusters and segregation on coating surface. ► The lowest coefficient of friction appears at 600 °C for both coatings.