The beginnings of graphitic alignment in the matrix of carbon-carbon composites

Abstract

Carbon-Carbon composites (C-C) may prove to be critical materials for high temperature applications, as they retain their mechanical properties well above 2000°C1. The development of a graphitic structure in the matrix of C-C composites is crucial to the understanding of their mechanical properties. To date very few transmission electron microscope (TEM) studies of these materials have been performed: as a result production often occurs without a full understanding of structural changes which occur during manufacture. X-ray diffraction has indicated that the degree of matrix alignment is greater in C-C composites than in the matrix carbon alone given same thermal history, in addition, the matrix graphitisation can occur in an orientation close to that of the long axis of the carbon fibres. These phenomena are thought to be the result of; a) the fibre-matrix interface acting as a nucleation site for graphitic domains forming in the matrix, and/or b) the difference in the coefficients of thermal expansion of the matrix and the fibres being sufficient to cause stresses which encourage graphitisation.