Thermal expansion behaviors of unidirectional carbon/carbon composites from 800 to 2500 °c

Unidirectional carbon/carbon (C/C) composites were prepared by the isothermal chemical vapor infiltration (ICVI) process. Thermal expansion behaviors of the composites from 800 to 2500 °C were investigated along the longitudinal and vertical directions. Meanwhile, the thermal expansion curves of carbon fibers (CF) and pyrolytic carbon (PyC) from 800 to 2500 °C were investigated individually. It was shown that coefficients of thermal expansion (CTEs) of untreated unidirectional C/C composites measured in the longitudinal and vertical directions gently increased with the increase of temperature from 800 to 1200 °C. But in the temperature range of 1200-1600 C, longitudinal CTE of the untreated composites decreased sharply till reaching the lowest point at around 1600 °C, and increased linearly as the temperature increased. While vertical CTE of the untreated ones increased rapidly over 1200 C until arriving the peak value at around 1600 °C and fell rapidly in the temperature range of 1600-2500 °C. On the other hand, for treated (2500 C, 2 h) unidirectional C/C composites, CTEs in both directions increased slowly as the temperature increased from 800 to 2500 °C, which varied from 1.68 to 3.07×10^-6 K^-1 in the longitudinal direction and from 6.78 to 8.04×10^-6 K^-1 in the vertical direction.