Variation of thermal expansion of carbon/carbon composites from 850 to 2500°C

Thermal expansion behaviors of carbon/carbon composites consisting of carbon fiber felts with high textured pyrolytic carbon matrix were investigated in a temperature range of 850-2500 C. Coefficient of thermal expansion (CTE) of the composites without heat treatment decreased clearly in the two temperature ranges of 1300-1500 C and 2100-2500 C. Raman spectra and scanning electron microscope analyses of the composites heat treated at different temperatures showed that the reduction of structural defects in fibers, and the graphitization of carbon matrix were responsible for the decrease of CTE. Furthermore, fiber/matrix interfacial debonding and fiber pull-out during the CTE measurement occurred with the increase of heat treatment temperature up to 1500 C, while at higher heat treatment temperature, circumferential cracks and layer bridging in the matrix were observed.