Interfacial microstructures of intrabundle in as-received carbon/carbon composites prepared by CVI

A detailed study of the interfacial microstructures of the intrabundles in as-received carbon/carbon composites prepared by CVI was performed by high-resolution electron microscopy. Two kinds of carbon fibers, high strength carbon fiber T300 and high modulus carbon fiber T-50, were chosen for comparison. It was found that the interface between the carbon fiber and carbon matrix is not simply a mechanical pinning structure formed by pyrolytic carbons directly contacting the rough carbon fiber surface. A transitional interfacial layer between the carbon fibers and the pyrolytic carbon matrix was observed which is referred to as induced microstructure. The graphitic degree and the crystallite size of the carbon fiber surface markedly affect the induced interfacial microstructures. The more regular and graphitic the carbon fiber surface, the more ordered and thicker the interface layer induced.