Mechanical and ablation properties of CNFs-modified C/C composites

Carbon nano-materials can strengthen the mechanical properties of C/C composites, but it is difficult to be uniformly introduced into the interior of performs. In this paper, a new strategy of efficiently loading carbon nanofibers (CNFs) by air compression spraying method before preform preparation was proposed, and CNFs were successfully introduced into the interior of the preform, and the CNFs-modified 2.5D C/C composites were prepared with improved mechanical and ablation properties. Results show that the CNFs-modified layer around the fibers increased the interfacial shear strength of the fiber/matrix interface by 57.4%. Coupled with the mechanism of energy dissipation through the pull-out of CNFs, the flexural strength of the CNFs-modified C/C composites increased from 195 MPa to 243 MPa, an increase of 24.6%. CNFs provided a large number of nucleation sites for the deposition of pyrolytic carbon, enhanced the cohesion of the matrix, and promoted the release of thermal stress during the heat treatment at 2450 °C. As a result, the CNFs-modified C/C composites exhibited high thermal stability and the strength retention rate of up to 77%. In addition, CNFs reduced the interfacial thermal resistance between the fibers and the matrix, enhanced the thermal conductivity of the composites, and lowered the ablation temperature. The mass ablation rate and linear ablation rate of the CNFs-modified C/C composites are only 0.645 mg/s and 3.01 μm/s, which are reduced by 21.6% and 28.8% respectively, indicating excellent ablation resistance. This work provides theoretical guidance for the large-scale preparation of nano-material modified C/C composites in the future.