Microstructure and mechanical properties of WC-C nanocomposite films

WC-C nanocomposite film was prepared by using a hybrid deposition system of r.f.-PACVD and DC magnetron sputtering. W concentration in the film was varied from 5.2 to 42 at.% by changing the CH₄ fraction of the mixture sputtering gas of Ar and CH₄. Hardness, residual compressive stress and electrical resistivity were characterized as a function of W concentration. Raman spectroscopy, XRD and high resolution TEM were employed to analyze the structural change in the film for various W concentrations. In the present W concentration range, the film was composed of nano-sized WC particles of diameter less than 5 nm and hydrogenated amorphous carbon matrix. Content of the WC particles increased with increasing W concentration. However, the mechanical properties of the film increased only when the W concentration was higher than 13 at.%. Structural analysis and electrical conductance measurements evidently showed that the increase in hardness and residual stress occured as the WC particles were in contact with each other in the amorphous carbon matrix.