Brazing C/C composites to DD3 alloy with a novel Ag-Cr active braze

A novel Ag-Cr active braze is presented to successfully braze carbon/carbon (C/C) composites to a Ni-based single crystal alloy (DD3). The microstructural characteristics and mechanical properties of C/C-AgCr-DD3 joints are investigated. Results indicate that Cr23C6 and Ni2Cr layers can be found nearby C/C and DD3 substrates, respectively. And Cr particles are aggregated outside the Ni2Cr layer. Amazingly, only Ag matrix and Cr particles can be observed in the brazed seam without the formation of brittle compounds, avoiding damage to the joint plasticity. The thickness of Cr23C6 and Ni2Cr layers can be increased with increasing Cr content and brazing temperature. The excessive brazing temperature results in a sharp narrowing of the brazed seam. The nanoindentation test shows that the Cr23C6 phase exhibits the highest hardness (22.5 GPa) and elastic modulus (316 GPa) among joint phases. The maximum value (27 MPa) of the joint shear strength is obtained using Ag-10 wt% Cr braze at 1040 degrees C. This work can facilitate revealing effects of the interfacial microstructure on the performance of C/C-metal joints, further promoting their reliable utilization. Furthermore, this study provides a new braze design strategy to avoid the formation of brittle compounds in joints of C/C composites and Ni-based alloy.