Study on the strengthening mechanism of carbon nanotube film interlayer assisted for brazing C/C composite and Nb

To address the issues of high brittleness and residual stress of the C/C composite and Nb brazed joints, carbon nanotube film (CNT_f) was prepared by vacuum filtration method and introduced as an interlayer to help optimize the microstructure and mechanical performance. The typical microstructures of the brazed joints with and without the CNT_f interlayer were put into comparison. Due to the reaction between the Ti27–Cu73 filler metal and the CNT_f interlayer, the gathered TiCu brittle compound formation was suppressed. As a result, a CNT_f reaction zone, which was composed of Cu(s, s) + TiCu₄+(Ti, Nb)C + TiC nanoparticles and TiCu₄ matrix, formed in the central brazing seam. Compared to the IMC zone in the directly brazed joint, the CNT_f reaction zone had better plasticity, and the thermal expansion coefficient decreased. According to the numerical calculation results, the strain energy in the C/C composite was reduced by 20 % after adding the CNT_f interlayer. The shear strengths tested at room temperature and 600 °C were enhanced by 103 % and 68 % respectively with the CNT_f interlayer addition. This CNT_f interlayer could also assist in the active brazing of other ceramics and metal alloys, addressing brittle compound generation, base metal excessive dissolution, and joint thermal mismatch issues.