Damages on carbon composites induced by high heat fluxes in electron beam tests

Three carbon fiber reinforced carbons (CC's) have been tested in an electron beam device with respect to their cracking and erosion behaviour. The materials were one 2-directional resin-bonded CC and two 3-directional CC's which were pyrocarbon-bonded. The 2-directional material showed the highest erosion rate, whereas the erosion of the 3-directional qualities was significantly lower. The interpretation of the experimental results show that the mechanical integrity and the thermal conductivity, and thus also the erosion rate, is highly influenced by the fiber density, fiber orientation, and the properties of the matrix (or bonding). The material loss by thermal erosion is clearly correlated to the thermal conductivity in that way that an increase of the thermal conductivity causes a significant decrease of the erosion rate under constant loading conditions. To evolve the structure of the CC's ceramographic sections were etched in a rf-oxygenplasma. Poorly organized or even amorphous carbon is removed more rapidly than highly organized, crystalline material. Thus it is possible to discriminate structural components with different degree of organisation (or graphitisation) with high local resolution. (orig.)