Effect of heat treatment on the microstructure of C/C composites with different high textured pyrolytic carbon contents

C/C composites reinforced using carbon felt and 3 K carbon cloth laminated preforms were prepared by chemical vapor infiltration and samples taken from them were subsequently subjected to heat treatment at 2500℃. The microstructures of the C/C composites were characterized by X-ray diffraction, polarized light microscopy and Raman spectroscopy. Results showed that the matrix of composites reinforced with carbon felt contained only high textured (HT) pyrolytic carbon, while those reinforced with the 3 K carbon cloth had a banded texture composed of isotropic, HT and medium textured (MT) pyrolytic carbon when moving from fibers to matrix, and the content of HT pyrolytic carbon was less than 50%. Regardless of the preform, both the as-prepared and heat-treated composites had a similar degree of graphitization. The L_c value of the carbon felt-reinforced composites was higher than their counterparts both for the as-prepared and heat-treated samples. The L_a values of the carbon fibers, MT and HT pyrolytic carbon increased after the heat treatment, and the L_a value of the HT pyrolytic carbon had a much larger increase than that of the others.