Diffusion bonding of Ti‐coated C _f ‐SiC _f /SiBCN composites to Nb using Ag–Pd interlayer

Abstract The Ti‐coated C _f ‐SiC _f /SiBCN ceramic was diffusion‐bonded to Nb using an Ag–Pd interlayer. At a ceramic/Ag–Pd interface, it is found that Ti first reacted with C and Pd to form a TiC _x /Ti(Pd) double‐layer structure, and then Ti(Pd) completely converted into TiC _x with the increase of holding time or temperature. Meanwhile, the infiltration of Pd along TiC _x grain boundary reacted with Si to form brittle Pd ₂ Si compound. By contrary, only a simple NbPd ₃ layer was formed at the Nb/Ag–Pd interface during the whole process. A maximum shear strength of 16 ± 3 MPa is obtained for the joint prepared at 900°C for 30 min. The plastic deformation of the Ag–Pd interlayer and pullout of fibers inside ceramic contributed to the superior performance. Nevertheless, as the holding time and temperature reached 90 min and 950°C, the high chemical affinity of the Pd–Si system and enhanced atomic diffusion led to the massive formation of Pd ₂ Si, which increased the joint brittleness and degraded the ceramic performance.