Structure, mechanical property, and tribological behavior of c-NbN/CNx multilayers grown by magnetron sputtering

The cubic-NbN/CNx multilayers with different CNx layer thicknesses (lCNx) are deposited on Si(100) substrate by reactive magnetron sputtering in a mixture of Ar and N2 gas. The effects of lCNx on the structure, mechanical property and tribological behavior for NbN/CNx multilayers have been explored. When lCNx = 0.2 nm, the NbN/CNx multilayer has a strong NbN(200) texture and a rough interface caused by intermixing between CNx and NbN layers; while when lCNx ≥ 0.4 nm, the multilayer has a mixture texture of NbN(200) and (111) with a good modulation periodic structure. The stress for all multilayers is compressive ranging in between the stress for both NbN and CNx single layers, which tends to decrease after an initial ascent with increasing lCNx. This means that the CNx layer is beneficial to relaxing the compressive stress induced by NbN layer. In addition, as lCNx increases, both hardness (H) and elastic modulus (E) first increase, and then decrease after reaching a maximum value. However, the ratio of hardness to Youngʹs modulus, H/E, for the multilayers monotonically decreases with the increase of lCNx. The obvious enhancement in hardness for multilayers is observed, whose maximum value approaches 39.2 GPa when lCNx = 0.4 nm, 78% larger than that obtained by the rule of mixture value. The friction coefficient of NbN/CNx multilayers have a decrease trend with increasing the H/E ratio, but the poor wear resistance occurs as the H/E ratio is high, which can be attributed to the presence of a high stress.