Manufacture and thermomechanical characterization of wet filament wound C/C-SiC composites

The paper presents manufacture of C/C-SiC composite materials by wet filament winding of C fibers with a water-based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C-SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm³. Thermomechanical characterization via tensile testing at room temperature and at 1300°C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C-SiC material obtained by wet filament winding and LSI-processing has excellent high-temperature strength for high-temperature applications. Crack patterns during pyrolysis, microstructure after siliconization, and tensile strength strongly depend on the fiber/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory, can be applied for structural evaluation and prediction of mechanical performance of C/C-SiC structures.     

Properties of C/C-SiC composites produced via transfer moulding and inner siliconization

Short carbon fiber reinforced polymers (CFRP) are successfully prepared by transfer moulding technology. For this purpose, compounds on the basis of novolac/urotropin with different 6 mm chopped carbon fibers and silicon powder contents are produced utilizing a laboratory tempered sigma-blade kneader. These compounds are then shaped into 46 × 8 × 3 mm³ CFRP specimens using a transfer moulding machine. Depending on the material composition, the conversion to C/C-SiC composites is performed through liquid silicon infiltration (LSI) process or inner siliconization. First, the short fiber content is varied between 30 and 50 wt% and its influence on the process and properties of the composites is studied. Second, an investigation of the inner siliconization through the co-mixing of silicon powder (1-23 wt% in CFRPs) during the compound production as well as a comparison with the external silicon infiltration process are presented and discussed. According to the results, the best mechanical properties are achieved at a fiber content of 40 wt% in the case of the external silicon infiltration and at silicon content below 14 wt% for composites produced by the inner siliconization process.