Influence of carbon nanotube content on microstructures and mechanical properties of carbon/carbon composite

Carbon nanotubes (CNTs) with a uniform growing and extending morphology were in situ grown on carbon fibers in carbon felt and then chemical vapor infiltration (CVI) was used to densify the felt to get a CNT-reinforced carbon/carbon (C/C) composite. The influences of CNTs on microstructures and mechanical properties of C/C composite were investigated by varying CNT content. The results show that a layer of isotropic (ISO) pyrocarbon is deposited closely around carbon fibers after growing CNTs and this zone becomes extended with CNTs increase, while the d₀₀₂ value of pyrocarbon decreases for CNT-related composites remarkably. Compared with pure C/C composite, CNT-reinforced C/C composites have much higher mechanical strength and modulus. However, with CNTs increase, the ductility of the composite deteriorates gradually according to the decrease of ductility factor (F_D) value and the fracture mode changes from pseudo-plastic fracture to brittle fracture in spite of the sharp increase in both mechanical strength and modulus.