Effect of structure of pyrocarbon on the static and dynamic mechanical properties of carbon/carbon composites

Carbon/carbon composites with two types of pyrocarbon matrices were prepared by Chemical Vapor Infiltration using methane and hydrogen, with or without a small added amount of carbon dioxide, as source and carrier gases. The pyrocarbon structures were respectively the usual Rough Laminar structure and a complex hybrid structure featuring Rough Laminar and overgrowth cones. Their microstructures, static and dynamic bending performances were characterized. Experimental results indicate that the hybrid structure can effectively improve the flexural and damping properties of composites compared with the simple structure. By introducing carbon dioxide in the gas phase, defects were formed in the deposits and the resulting overgrowth cones led to a better interconnection of matrix deposited on adjacent fibers. They deteriorate the texture degree of pyrocarbon but effectively improve the matrix strength, and they not only make the flexural strength of composites increase by 27.3% compared with reference composites, but also result in storage modulus, loss modulus and internal friction of composites increase by 3.5%, 30.5% and 23.1%, respectively, at 25° C, 10 Hz and 0.025% strain. The defects make the internal friction of composites more sensitive to temperature and amplitude, but on the other hand make the storage modulus of composites less sensitive to temperature.