High-temperature tribological behavior of Cr′N-Ag self-lubricating coatings

The verification of the high-temperature lubrication concept of CrN coatings containing Ag is discussed. As-deposited coatings show a phase-separated structure consisting of CrN and Ag grains with domain sizes of 15-25nm. The friction coefficient against alumina at room temperature increases slightly from 0.4 to 0.5 with higher Ag contents, which is related to the lower hardness of these coatings. Ag agglomerates form on the coatings surface during annealing at 600°C, and decrease the friction coefficient to 0.2 at the beginning of the test. The value increases to 0.40-0.44 with increasing sliding distance, which is attributed to fast out-diffusion of Ag, and, in turn, a quick consumption of the lubricating phase. Alloying CrN coatings with Ag thereby offers a high potential to enhance the tribiological behavior in a wide temperature range and under varying environmental conditions, provided that the supply of the sliding contact with the Ag lubricant is controlled thoroughly.