Abstract:C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration (CVI), with C₃H₆ as carbon source, N₂ as carrier gas, and three-dimensional (3D) 12K PAN-based carbon fabric with high density of 0.94 g/cm³ as preform. Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment (HTT) at the break of CVI process. According to the load−displacement curves, C/C composites showed a pseudoplastic fracture after twice of HTT. After three times of HTT, load−displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa. Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope. Because the content of pyrocarbon and fibers has a different distribution in layers, the C/C composites show different fracture characteristics at various regions, which leads to good toughness and bending strength.

Key words: C/C composites; chemical vapor infiltration (CVI); high density preform; bending properties; fracture mechanism