Structure and properties of unidirectionally reinforced PAN-resin based carbon-carbon composites

A study has been made of the structure and properties of in-house fabricated, unidirectionally reinforced polyacrylonitrile (PAN) fibre-phenolic plus furfuryl alcohol matrix carbon/carbon (C/C) composites comprising surface-treated (ST) as well as non-surface-treated (NST) carbon fibres. The composites are subjected to a final heat treatment of 1000 or 2000°C. Mechanical properties of the composites were found to be sensitive to the process parameters (particularly the final heat-treatment temperature) as well as fibre surface condition (ST or NST). For the composites comprising ST fibres, flexural strength and modulus of those heat treated at 2000°C were higher than those treated at 1000°C. For the composites comprising NST fibres, the results were the opposite. At the carbon fibre-reinforced plastic (CFRP) stage, strength and modulus of ST fibre composites were higher than those of NST composites by 400% and 100%, respectively, due to the stronger fibre-resin bonding in the ST composite. After the first carbonization treatment, the ST composites always possessed higher strength and modulus values than NST composites, whether the final heat treatment temperature was 1000 or 2000°C. In the ST series of composites, the improvement in strength and modulus became significant from the third densification cycle, while in the NST series, both second and third cycles were effective. Microstructure, particularly fibre-matrix interface morphology, has been studied using polarized light microscopy, scanning electron microscopy, and transmission electron microscopy, to help interpret the process-structure-property relationships.