Microstructure and properties of DLC/CNx films with different CNx sublayer thicknesses

The DLC/CNx multilayer films with different CNx sublayer thicknesses were deposited on Si wafer by using magnetron sputtering technique. The microstructure and properties of the films were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, scratch tests and a ball-on-disc tribometer. All the DLC/CNx films were amorphous and compact with low internal stresses and strong reinforcement effects. The content of sp(3) bonds in CNx sub-layer, the hardness and adhesion of the overall films decreased while the wear rate of the multilayer films increased with increasing the CNx sublayer thickness. The friction states of the multilayer films in vacuum and air were very stable. The friction coefficients of the DLC/CNx films were similar to 0.16 in vacuum and similar to 0.20 in air, and they were independent of CNx sublayer thickness. The multilayer film with CNx sublayer thickness of 0.5 nm was of a hardness of 36.9 GPa and interface adhesion of 27 N, which exhibited excellent tribological properties in vacuum and in air.