A TEM study of microstructure of carbon fiber/polycarbosilane-derived SiC composites

The structures of two types of mesophase pitch-based carbon fibers (M30 and M70) reinforced SiC composites, prepared by the polycarbosilane impregnation-pyrolysis process, were investigated using transmission electron microscopy (TEM). It was found that M70 possessed a highly-ordered graphite structure despite occasional misorientation of some crystallites. However, the skin of M70 was less ordered than the interior of M70. The structure of M30 was uniform throughout, and was less ordered than that of M70. The fiber and matrix in M70/SiC bonded weakly, whereas the fiber and matrix in M30/SiC bonded tightly and locked together. This difference in the interface feature originates from the difference of the surface crystalline structures of M30 and M70, and is formed during the first impregnation-pyrolysis cycle of polycarbosilane.