Improved thermal conductivity and mechanical properties of SiC/SiC composites using pitch-based carbon fibers

Pitch-based carbon fibers were assembled in horizontal and thickness directions of SiC/SiC composites to form three-dimensional heat conduction networks. The effects of heat conduction networks on microstructures, mechanics, and thermal conductivities were investigated. The results revealed the benefit of introducing heat conduction networks in the densification of composites. The maximum bending strength and interlaminar shear strength of the modified composites reached 568.67 MPa and 68.48 MPa, respectively. These values were equivalent to 18.6% and 69.4% increase compared to those of composites without channels. However, channels in thickness direction destroyed the continuity of fibers and matrix, creating numerous defects. As the volume fraction of heat conduction channels rose, the pinning strengthening effect of channels and influence of defects competed with each other to result in first enhanced mechanical properties followed by a decline. The in-plane thermal conductivity was found anisotropic with a maximum value reaching 86.20 W/(m·K) after introducing pitch-based carbon unidirectional tapes. The thermal conductivity in thickness direction increased with volume fraction of pitch-based carbon fibers and reached 19.13 W/(m·K) at 3.87 vol% pitch-based carbon fibers in the thickness direction. This value was 90.75% higher than that of composites without channels.