Forming mechanism of C_f/SiC-Nb brazed joints reinforced by core-sheath structure

In order to address the issues of high residual stress and low strength in the brazed joints between ceramic-matrix composites and metals, a hollow-skeleton network-structured carbon sponge was used as an interlayer to relieve the joint stress and improve the mechanical properties of the joint. The melamine-formaldehyde foam was subjected to rapid high-temperature carbonization treatment in a vacuum environment to obtain a hollow carbon sponge with continuous skeletons and uniform pores. Subsequently, it was used as an interlayer to assist in the brazing process between C_f /SiC composites and Nb. The results show that under the brazing parameter of 850 ℃/10 min, the Ag-27Cu-3.5Ti filler metal fully filled the hollow space of the carbon sponge and reacted with the carbon sponge skeleton to form a core-sheath structure in which the filler metal alloy was coated with TiC. When using the thickness of the carbon sponge interlayer as 2.0 mm, the joint strength reached a maximum value of 112.6 MPa, which is 56% higher than that of the direct brazed joint without an interlayer. This is attributed to the multiple synergistic strengthening effects of the core-sheath structure on the joint.