Effect of 3D-Braided Structure on Thermal Expansion of PIP–C f /SiC Composites

3D3d, 3D4d, 3D5d-braided Cf/SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) with polycarbosilane as the matrix precursor. The coefficient of thermal expansion (CTE) of C f /SiC composites was measured in longitudinal and transversal directions in the temperature range from –150°C to 25°C. The longitudinal CTE varies in the range (0.09–0.68) × 10 –6 /°C, and the transversal CTE varies in the range (0.21–1.95) × 10 –6 /°C. Various CTEs of 3D-braided C f /SiC composites were mainly determined by different braided structures of carbon fibers. The longitudinal CTE is lower than transversal CTE for the negative axial expansion of carbon fibers at cryogenic temperature. Microcracks were examined to understand the effect of structure on the thermal expansion of composites.