Impact of ex-PAN carbon fibers thermal treatment on the mechanical behavior of C/SiC composites and on the fiber/matrix coupling

Ceramic matrix composites reinforced by external polymerization of acrylonitrile (ex-PAN) carbon fibers with pyrocarbon (PyC) interphase are attractive materials for thermomechanical applications. Nevertheless, C/SiC composites suffer from a low damage tolerance. A 1600°C thermal pretreatment of the carbon fibers led to an improvement of the mechanical properties of the composites. Even if this heat treatment was seen to modify the fiber microstructure and texture, the changes were not sufficient to explain the observed improvements. The consequences of the thermal treatment on carbon fibers were studied by high resolution transmission electron microscopy and physicochemical analyses. The fiber/matrix debonding was also apprehended by analyzing the interfacial regions of C/SiC composites. The key role of the fiber surface structure on the fiber/matrix (F/M) coupling was highlighted. The microstructural reorganization of the heat-treated fibers surfaces induces a high F/M bonding strength and leads to better damage tolerance for the C/SiC composites.