Microstructures and flexural properties of C/C composites doped with CNTs by electrophoretic deposition

Carbon nanotubes (CNTs) were deposited uniformly on 1 k carbon cloth by electrophoretic deposition (EPD). After that, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor depositon (CVD) to prepare two dimensional (2D) carbon/carbon (C/C) composites. Effects of EPD CNTs on CVD process, microstructure and flexural property of 2D C/C composites were investigated. Results show that EPD CNTs are dispersed in the plane parallel to carbon fiber surface with random orientations and a high distribution density, leading to the decrease of densification rate of EPD CNT-doped C/C composites and the formation of pyrocarbon with high L_c and small L_a values. EPD CNTs increase the flexural strength and modulus of C/C composites and the improvements can reach 31.4% and 13.9% when the loading of EPD CNTs is 0.74wt%, with corresponding flexural strength and modulus being 150.83 MPa and 23.44 GPa, respectively. Further increasing the dope of EPD CNTs can decrease the flexural property of C/C composites, resulting in their bulk density decrease. The introduction of EPD CNTs changes the fracture mode of C/C composites from brittle fracture to pesudo-plastic fracture, which is related to the change of pyrocarbon in microstructures and the resulted carbon fiber pullout.