Effects of processing methods and parameters on the mechanical properties and microstructure of carbon/carbon composites

The influence of the fabrication parameters during carbonization and densification processes on the mechanical properties and the microstructure of carbon/carbon (C/C) composites were investigated. The C/C composites were made by using phenolic resin as precursor and two-dimensional carbon fabrics as reinforcements for the first carbonization. The effects of heating rate and heat-treatment temperature during the initial carbonization process on the properties of C/C composites are presented. Further densification treatment was completed by chemical vapour infiltration (CVI) and a liquid-resin impregnation process. The CVI route was found to be more efficient than the resin-impregnation process. The interlayer spacing of C/C composites did not change after resin re-impregnation for several times. However, the interlayer spacing of the C/C composites was reduced when the processing temperature in the CVI process was increased. Higher flexural strength and flexural modulus were obtained because the densities of the composites were enhanced either by the chemical vapour infiltration process or by the resin-impregnation route. The variation in thickness of the CVI deposited carbon within the preformed composite was studied and the morphology of the fracture surface of the C/C composites was also examined.