POTENTIAL OF NANOCRYSTALLINE LOW-Z MATERIALS FOR PLASMA-FACING, STRUCTURAL APPLICATIONS IN FUSION-REACTORS

Several types of silicon based nanocomposite ceramics have been produc ed by hot isostatic pressing (HIP) mixtures of ultrafine SIG, CSiC and SiSiC powders (particle size below 50 nm) with conventional carbon, b oron carbide or silicon carbide powders. Compared to pressureless sint ering grain growth was substantially reduced by this technique. Sample s have been characterized with respect to microstructure. Thermal cond uctivity measurements at room temperature indicate a reduction of ther mal conductivity compared to conventional materials. High heat flux ex periments in the electron beam test facility JUDITH (Juelich divertor test equipment in hot cells) with energy densities up to 11 MJ/m(2) ha ve been performed. Although the thermal conductivity is relatively low the materials prepared from SiSiC/C-mixtures show lower erosion rates compared to conventional composites. The negative effect of low therm al conductivity on thermal shock resistance seems to be overcompensate d by the microstructural improvements in the nanocomposite materials. A model, which calculates the erosion rates and takes account of micro structural features like chemical composition and grain size, is prese nted.