Improving the Bonding Strength of Nb–C/C Composite Brazed Structures by Preoxidation

Preoxidation treatment is used to modify the surface of C/C composite. An annular column gap is formed encasing the carbon fiber, which promotes the infiltration of C/C composite by liquid brazing alloy during brazing. Based on the optimized preoxidation condition of 800 °C/5 min, the effects of brazing temperature (860–940 °C) and holding time (5–20 min) on the microstructure and mechanical properties of Nb and C/C joints brazed with an AgCuTi alloy are systematically investigated. The shear strength of the brazed structure at 880 °C for 10 min reaches a maximum of 57 MPa, which is increased by 28 MPa compared with that of the structure without preoxidation. The infiltration depth, reaction layer thickness, Ti–Cu compound amount, and brazing seam width are characterized to reveal the synergistic effect of preoxidation and brazing parameters on the bonding strength of structures. The selection of an appropriate brazing parameter is conducive to maximizing the positive effects of preoxidation.