B4C-SIC REACTION-SINTERED COATINGS ON GRAPHITE FOR PLASMA-FACING COMPONENTS

Boron carbide plus silicon carbide (B4C-SiC) reaction-sintered coating s for use on graphite plasma-facing components were developed. Such co atings are of interest in TEXTOR tokamak limiter-plasma interactions a s a means of reducing carbon erosion, of providing a preferred release of boron for oxygen gettering, and of investigating silicon's effect on radiative edge phenomena. Specimens evaluated had (a) either Ringsd orfwerke EK 98 graphite or Le Carbone Lorraine felt-type AEROLOR A05 C FC substrates; (b) multiphase coatings, comprised of B4C, SiC, and gra phite; (c) nominal coating compositions of 69 wt% B4C + 31 wt% SiC; an d (d) nominal coating thicknesses between 250 and 775 mu m. Coated cou pons were evaluated by high heat flux experiments in the JUDITH (elect ron beam) test facility at KFA. Simulated disruptions, with energy den sities up to 10 MJ m(-2), and normal operation simulations, with power densities up to 12 MW m(-2), were conducted. The coatings remained ad herent; at the highest levels tested, minor changes occurred, includin g localized remelting, modification of the crystallographic phases, oc casional microcracking, and erosion.