G. Ziegler et al./Composites: Part 4 30(1999)411-417 Fig. 6. Polished cross-section of a Hi-Nicalon/SiCN composite, P5, Fig. 4. Stress-strain diagram of C/SiCN composites 000°C P Hi-Nicalon/SiCN P5, perpendicular P7, perpendicular parallel P5, parallel Fig. 7. Relative dimensional changes of a UD-C/SiCN composite parallel and perpendicular to the fiber orientation after various infiltration cycles Fig. 5. Stress-strain diagram of Hi-Nicalon/SICN composites. the individual prepreg-layers), the fibers are partially still present, showing sufficient pull-out behavior. Fig. 12 33. Oxidation behavior and siliconization demonstrates the enhanced oxidation resistance of the For further characterization, C/SICN composites as well as the individual components(matrix and fiber)[material 4 Conclusions P5] were tested with respect to oxidation stability by oxida- tion up to 1600C in flowing air(Fig 9). The matrix itself is It has been shown that C and SiC fiber-reinforced compo- very stable at least up to 1400.C, whereas the fiber is sites can be successfully prepared using the liquid infiltra- oxidized as low as 600C Fig. 10 shows a micrograph of tion/pyrolysis method. Prerequisites are suitable precursor the oxidized composite. Therefore, this matrix in combina- catalyst systems with respect to setting temperature, viScos- tion with an oxidation-stable(eventually oxidic)fiber may ity and ceramic yield. An important aspect is the matrix constitute an excellent oxidation-resistant material development, affecting the mechanical properties by indu- In order to improve the oxidation and wear resistance, cing residual stresses due to shrinkage of the matrix upon siliconization experiments were carried out with the C/ pyrolysis, and due to the marked anisotropy of the CTEs of SICN composites. Experiments with varying fiber contents fiber and matrix. Furthermore, the C fibers used are showed clearly that closed packed and regular arranged fib damaged, also high modulus/high tenacity fibers(which bundles within a Sicn matrix remain unchanged, whereas will be used in the future)should be less susceptible to randomly arranged fibers within such a matrix will be degradation Composites with favorable mechanical proper converted to SiC. It is therefore possible to prepare C/ ties were prepared with Hi-Nicalon reinforcements, but SiCN composites with siliconized areas by careful arrange should also be preparable from suitable and coated C fibe ment of the c fibers reinforcements. Coefficients of thermal expansion of Fig. 1l shows a fracture surface of such a siliconized samples prepared from UD-prepregs were found to be material, indicating that in closed packed regions(within anisotropic, but can be adjusted by varying the stacking3.3. Oxidation behavior and siliconization For further characterization, C/SiCN composites as well as the individual components (matrix and fiber) [material P5] were tested with respect to oxidation stability by oxida￾tion up to 16008C in flowing air (Fig. 9). The matrix itself is very stable at least up to 14008C, whereas the fiber is oxidized as low as 6008C. Fig. 10 shows a micrograph of the oxidized composite. Therefore, this matrix in combina￾tion with an oxidation-stable (eventually oxidic) fiber may constitute an excellent oxidation-resistant material. In order to improve the oxidation and wear resistance, siliconization experiments were carried out with the C/ SiCN composites. Experiments with varying fiber contents showed clearly that closed packed and regular arranged fiber bundles within a SiCN matrix remain unchanged, whereas randomly arranged fibers within such a matrix will be converted to SiC. It is therefore possible to prepare C/ SiCN composites with siliconized areas by careful arrange￾ment of the C fibers. Fig. 11 shows a fracture surface of such a siliconized material, indicating that in closed packed regions (within the individual prepreg-layers), the fibers are partially still present, showing sufficient pull-out behavior. Fig. 12 demonstrates the enhanced oxidation resistance of the material. 4. Conclusions It has been shown that C and SiC fiber-reinforced compo￾sites can be successfully prepared using the liquid infiltra￾tion/pyrolysis method. Prerequisites are suitable precursor/ catalyst systems with respect to setting temperature, viscos￾ity and ceramic yield. An important aspect is the matrix development, affecting the mechanical properties by indu￾cing residual stresses due to shrinkage of the matrix upon pyrolysis, and due to the marked anisotropy of the CTEs of fiber and matrix. Furthermore, the C fibers used are damaged, also high modulus/high tenacity fibers (which will be used in the future) should be less susceptible to degradation. Composites with favorable mechanical proper￾ties were prepared with Hi-Nicalon reinforcements, but should also be preparable from suitable and coated C fiber reinforcements. Coefficients of thermal expansion of samples prepared from UD-prepregs were found to be anisotropic, but can be adjusted by varying the stacking G. Ziegler et al. / Composites: Part A 30 (1999) 411–417 415 Fig. 5. Stress–strain diagram of Hi-Nicalon/SiCN composites. Fig. 4. Stress–strain diagram of C/SiCN composites. Fig. 6. Polished cross-section of a Hi-Nicalon/SiCN composite, P5, 10008C. Fig. 7. Relative dimensional changes of a UD-C/SiCN composite parallel and perpendicular to the fiber orientation after various infiltration cycles