Synthesis, Characterization, and Wear Behavior of W-DLC Films Deposited on Si Substrates

Tungsten (W) reinforced diamond-like carbon (DLC) nanocomposite thin films were deposited on silicon substrates by magnetron sputtering in a CH4/Ar discharge. The W content of the films was varied by varying the W target power (20, 40, 60, 80, and 100 W). The evolution of the W-DLC nanocomposites was studied by high-resolution transmission electron microscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, 3D optical profilometry and Raman spectroscopy. Increasing the W target power resulted in an almost liner increase in the W content, reduced the hardness and the sp3/sp2 ratio in the films, while it increased the surface roughness and promoted formation of WC nanoparticles. Tribological properties were studied by conducting sliding reciprocating testing. Wear tracks were analyzed with Raman spectroscopy and 3D optical profilometry. Increasing the W content in the films (increasing target power) resulted in a reduction of both, the friction coefficient and wear rate. The film deposited at 80 W target power (~8 at. % W) exhibited the lowest friction coefficient (0.15) and wear rate (6x10-7 mm3N-1m-1). The observed low friction and wear rate were attributed to the particular nanocomposite structure of the films involving a fine distribution of WC nanoparticles surrounded by a sp2 dominant carbon network. The present W-DLC nanocomposite films offer a highly desirable combination of low friction and low wear rate.