A novel in-situ forming 3D core-sheath interlayer designed to strengthen Cf/C composite-Nb joints during brazing

A novel interlayer designed to strengthen dissimilar material joints during brazing is reported in the current study. A highly elastic hollow carbon sponge was used as a consumable precursor to form a three-dimensional (3D) “metallic core-ceramic sheath” structure during the brazing of carbon-fiber-reinforced carbon matrix (Cf/C) composite /Nb with an Ag-Cu-Ti brazing filler. The brazing filler demonstrated excellent wetting properties on the sponge while simultaneously causing an in-situ reaction, producing a 3D interconnected and fine-grained TiC network shell filled with brazing filler as core due to capillary infiltration. The interlayer was shown to reduce residual stresses, prevent the formation of thick layered CuTi compounds, decrease the mismatch between the co-efficient of thermal expansion, and provide plastic strain accommodation. TGA, Raman, XRD and SAED were used to confirm various phase formations, locations and concentrations, and elucidate on the mechanism of formation. TEM and SEM were used for confirming microstructural properties and fracture morphology. Shear testing was conducted to confirm mechanical property increase, which was shown to be 260% above the baseline. The material and associated mechanism shown here are effective for the transmission and dissipation of shear loads and residual stresses, making it extremely attractive for high performance dissimilar material brazing. •A novel hollow carbon sponge was made by rapidly carbonizing a MF resin foam.•The Ag-Cu-Ti filler wetted the inner volume of the sponge due to the capillary effect.•A thin, fine-grained TiC shell wrapped core-sheath sponge interlayer formed in-situ.•The interlayer increased the shear strength of the Cf/C composite-Nb joint by 260%.•The interlayer reduces residual stress and enhances deformation tolerance.