The pretreatment of carbon fibres for 3D C/SiC composites

A hybrid pretreatment of the carbon fibers, consistingf of coating the fibers with pyrolytic carbon by the CVD process and then heating at 1500degreesC in N-2, has been introduced. The results show that the residual tensile strength of heat-treated fibers is merely 37% of the initial strength, while the residual tensile strength of the hybrid-treated fibers increases to 50% - 80% of the initial strength. The influence of the coating thickness on the residual fiber strength has also been investigated. The flexural strength and fracture toughness of the composites reinforced by the hybrid-treated carbon fibers improved in contrast to the composites reinforced with heated fibers. SEM microstructure analysis indicated that the increase in the strength of the carbon fibers and the reinforced composite is due to the healing of natural defects and cracks on the surface of the carbon fibers and protecting the fibers from being eroded by impurities at elevated temperatures.