Influence of heat treatment temperature on microstructure and thermal expansion properties of 2D carbon/carbon composites

The influence of heat treatment from 1900 to 2650 C on microstructure and thermal expansion properties of thermal gradient chemical vapor infiltration (TCVI)-infiltrated 2D carbon/carbon composites was investigated. The structure evolution was characterized by polarized light microscopy, X-ray diffractometer, Raman spectroscopy and thermal expansion behavior was studied by thermal dilatometer. The results revealed that with the increasing heat treatment temperature, successive microstructural changes in carbon matrix and fibers occurred, and cracks and pores in the composites increased. These resulted in a 35.6% decrease of CTE in Z direction and a 13.9% decrease in XY direction in the composites heat-treated at 2650 C compared with as-deposited composites. The CTE mainly depended on the thermal expansion of matrix in Z direction while it relied on that of the fibers in XY direction.