Microstructural and compositional characterisation of the pyrocarbon interlayer in SiC coated low density carbon/carbon composites

SiC coated carbon bonded carbon fibre (CBCF) composites, a special class of carbon/carbon composites for thermal insulation, were investigated. Successful deposition of SiC requires the CBCF material to be first given a pyrocarbon coating. SiC coating on pyrocarbon coated CBCF was assessed using several analytical techniques. X-ray diffraction identified the coating as β SiC. The fibre orientation in two perpendicular planes was determined using X-ray microtomography, and it was found to be random in one plane whereas there was a preferred orientation in the other plane. A comparison was made between the uncoated and pyrocarbon coated substrates in terms of surface roughness, purity and crystallinity, using white light interferometry, neutron activation analysis/secondary ion mass spectrometry and transmission electron microscopy, respectively. The higher roughness, greater purity and increased levels of crystallinity of pyrocarbon coated CBCF are considered to be responsible for the successful deposition of a SiC coating on this material.