Influence of matrix microstructures on mechanical behavior of C/C composites

C/C composites were fabricated by a rapid chemical liquid-vaporized infiltration (CLVI) process. The deposition temperatures were in the range of 1200-1250°C. The microstructures of pyrolytic carbon and the morphologies of fractured surfaces were observed by polarized light microscope (PLM) and scanning electron microscope (SEM). The influence of matrix microstructures on flexural strength and fracture mode of C/C composites was analyzed. The results show that rough laminar pyrocarbon constitutes the majority of the matrix deposited at 1200°C, which results in higher flexural strength and lower fracture toughness. While the matrix pyrocarbon deposited at 1250°C displays an alternative layered structure with different optical reflectance, which brings about lower flexural strength and higher fracture toughness. Different mechanical behaviors may be caused by dissimilar spreading resistance of cracks along the interfaces between pyrocarbon laminae with distinct microstructures, and the deflection of cracks along the interfaces between smooth laminar and rough laminar pyrocarbon. In addition, a schematic drawing of fracture profiles of 2D-C/C composites was suggested to explain the fracture mechanism.