Nanocomposite coatings made of crystalline hard phases in combination with an amorphous soft matrix represent a good solution for achieving a compromise between mechanical and tribological properties. In this work, nanocrystalline tungsten carbide (WC) was combined with amorphous carbon (a-C) in different proportions by magnetron sputtering technique at near room temperature. By controlling the power applied to WC and graphite targets it is possible to obtain nanocomposite coatings with variable hard/lubricant phase composition. The microstructure and chemical composition of the samples were studied by transmission electron microscopy (TEM), electron (ED) and X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The crystalline phases were identified as WC_1-x and W₂C by XRD dispersed in a disordered carbon matrix. The C1s photoelectron peak was used to estimate the distribution of carbon in WC and a-C phases inside the composite (C_wc/a-C) and this parameter was correlated with the tribological properties measured in a pin-on-disk tester in dry conditions. The friction coefficients decreased from 0.8 to 0.15 when diminishing the C_wc/a-C ratio from »1.7 to 0.7. The endurance of the coatings is increased following the same trend reaching optimum values of 1×10^-7 mm³/Nm. In view of the results, relationships among synthesis conditions, microstructure, chemical bonding and compositions and tribological performance of the WC/a-C nanocomposites were established.

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