engleski

STRUCTURE AND MECHANICAL PROPERTIES OF DISORDERED W-C ALLOYS

Tungsten-carbon thin films were deposited onto monocrystalline silicone substrates by reactive magnetron sputtering. The magnetron discharge operated in argon, with benzene as the carbon supplying admixture added at 1,25%-6,5% partial pressure, respectively. Deposition rate was 0,1-0,2 nm/s, and the film thickness was about 0,5 mm. The substrate temperature (r.t., 200°C, and 400°C) and potential bias with respect to plasma (float, -70V) were varied. A total carbon content (RBS), film structure (XRD, SAXS), unbound carbon configuration (Raman), and micromechanical properties (nanoindentation) of the prepared films were examined. Structure of the films is dominated by WC1-x nonstoichiometric carbide, imbedded with the unbound carbon (or hydrocarbon fragments). The effects of substrate temperature are markedly different in low- and high-carbon-content films: In the first group, the substrate temperature affects mostly WC1-x matrix structure, which changes from strongly disordered (111)-textured structure to small-grained microcrystalline (200)-textured structure with the temperature increase, while the overall amount and graphite (G)/disordered (D) forms ratio of the unbound carbon is largely unaffected. In high-carbon-content films the opposite occured: The structure is a strongly disordered (111)-textured WC1-x in all cases, while the amount of unbound carbon and G/D ratio generally increase with temperature. The micromechanical properties of the films are governed mostly by total content and configuration of the unbound carbon: the nanohardness decreases from 30-34 GPa for the films produced with the l,25-2,5% admixtured benzene, to 21-30 GPa for the films prepared with 5% benzene, being higher in samples prepared at elevated temperatures.

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