FLUX DEPENDENCE OF METAL SPUTTERING FROM METAL-CARBON COMPOSITE-MATERIALS IN THE HIGH-TEMPERATURE REGIME

A WC layer deposited on graphite has been bombarded with a 5 keV Ar+ ion beam at different fluxes at 1550-degrees-C, as well as at 6 X 10(13) Ar+ cm-2 s-1 at different temperatures. The thickness and the atomic composition of the carbide layer have been measured by means of the RBS technique at each stage of the Ar+ bombardments. It is found that the sputtering yield of W at 1550-degrees-C decreases down to zero at a critical value of 4.6 X 10(13) cm-2 s-1 with decreasing ion flux, and that the sputtering yield of W at 6 X 10(13) cm-2 s-1 also decreases down to zero at a critical temperature of 1600-degrees-C with increasing temperature. It is determined from the analysis of the latter data that the activation energy of the dissolution rate of carbon atoms at the surface is 2.0 eV, which is a key parameter for predicting the critical flux and temperature under different conditions.