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.