COMPARISON OF WCL6-CH4-H-2 AND WF6-CH4-H-2 SYSTEMS FOR GROWTH OF WC COATINGS

Thermodynamic equilibrium calculations were performed using SOLGASMIX- PV at varying partial pressures of WCl6-CH4-H-2 and WF6-CH4-H-2. Chemi cal vapour deposition (CVD) phase diagrams, which display equilibrium condensed phases, were then constructed from the results of these calc ulations. These results indicated that for the WF6 and WCl6 systems th e phase transformation from W to WC occurs at a lower partial pressure of CH4 with decreasing total pressure. However, the partial pressure of CH4 needed to produce WC is lower for WF6 than WCl6. Information fr om these CVD phase diagrams was used to determine process parameters f or the deposition of monolithic hexagonal WC. It was observed that coa tings grown at low temperatures contained phases other than those pred icted in the CVD phase diagrams. Experimental results on the developme nt of WC coatings based on CVD phase diagrams have been presented and discussed.