Influence of silver content on structure, mechanical and tribological properties of WCN-Ag films

In recent years, the preparation of thin films with excellent tribological properties over a wide temperature range has attracted the attention of the researchers. It is reported that an effective way is the fabrication of films consisting of different lubricant phases, which exhibit self-lubricating characteristics at different temperatures. On this basis, WCN-Ag films with various silver contents ranging from 0 to 8.3 at.% were deposited by a multi-target magnetron sputtering system. The composition, structure, mechanical and tribological properties were characterized using XPS, XRD, HRTEM, nano-indentation, ball-on-disk dry sliding wear tester, Bruker 3D Profiler, SEM and compared to WCN. It is found that the incorporation of silver does not change the cubic structure, WCN-Ag films consist of a mixture of WCN, W2N, Ag, amorphous C and CNx phases. Although the addition of Ag into WCN films reduces the hardness, Young's modulus and compressive stress, it improves the tribological properties obviously. A low friction coefficient (< 0.4) is observed in the temperature range of 25-600 °C for WCN-Ag film containing 6.6 at.% Ag. Overall, the results reveal that WCN-Ag films by adding some Ag content can exhibit self-lubricating characteristics in the temperature range of 25-600 °C.