Tribological and mechanical properties of Cr2N–11Ag-coatings deposited on Cr–V ledeburitic steel

• Cr2N–11Ag film grows in columnar manner, with presence of individual Ag grains.
• Addition of 11 wt% Ag accelerates the growth rate of Cr2N-film.
• Addition of 11 wt% Ag slightly improves some mechanical properties of Cr2N.
• Good adhesion of Cr2N–11Ag film on tool steel substrate was achieved.
• Addition of 11 wt% Ag improves tribological properties at elevated temperatures.

4.7 μm Thick Cr2N–Ag nanocomposite coatings, containing 11 wt% Ag solid lubricant, were deposited on substrate made of Cr–V ledeburitic tool steel by reactive magnetron sputtering. The nanohardness of the Cr2N–11Ag film was 17.86±0.79 GPa and the Young modulus was 280±7 GPa, e.g. they were not influenced negatively by elevated silver content. The Cr2N–11Ag film exhibited good adhesion on the substrate – the critical loads, related to the first indications of side flaking of the films, established by a scratch-testing method, ranged between 34 and 40 N. Tribological testing using a ball-on-disc apparatus has been realized at ambient and elevated temperatures: 300, 400 and 500 °C. Wear tracks after ball-on-disc testing were analysed by scanning electron microscopy and microanalysis. The self-lubricant effect is dependant on transport of lubricious Ag within the Cr2N matrix to the free surface of coatings. The experiments have shown the strong dependence of tribological properties on the temperature. At ambient temperature, the friction coefficient μ against alumina was 0.70 and it was reduced to 0.34 (e.g. by 52%) when tested at temperature of 500 °C. The friction coefficient of Cr2N–11Ag film against 100Cr6 at ambient temperature was 0.57.