Stress-induced preferential alignment of basal planes in phenolic-based carbon-carbon composite

Using scanning transmission electron microscopy/microdiffraction as well as high-resolution electron microscopy techniques, this study provides direct evidence of stress-induced preferential alignment of basal planes in the matrix of a PAN-phenolic-based carbon-carbon composite. The results indicate that this preferential alignment occurs mostly in the stressed matrix during heating, including among fibers and surrounding matrix micropores. The basal planes in the stressed regions are aligned parallel to either the fiber axis or the micropore wall. Microdiffraction shows that atomic ordering in these regions is two-dimensional (with turbostratic structure). It is suggested that a compressive stress during heating, which is induced either by matrix/fiber expansion or by volatilized gases entrapped in micropores, is critical in order for the basal planes to be preferentially aligned. This argument is supported by the results of Kamiya and Inagaki and of Kimura et al., but is not in agreement with the suggestion made by Hishiyama et al.