Heterogeneous interpenetrating strong-tough structure enabling high-strength C_f/C-Nb joints via cold spray-assisted brazing

Heterogeneous structural design is an effective strategy for achieving breakthroughs in the mechanical properties of dissimilar material joints. In this study, a cold spray-assisted brazing technique was proposed to significantly improve the strength of C_f/C-Nb brazed joints by fabricating a dense and uniform Ti-Co-TiC composite interlayer. Research indicates that TiC particles promoted the reconstruction of the brazing seam through heterogeneous nucleation and Zener pinning effects, effectively disrupting the continuous Ti₂Co brittle network and constructing a strong-tough interpenetrating structure composed of a ductile β-Ti(s, s) and hard phases. The semi-coherent interfaces (lattice misfit of 6%–8%) formed between TiC and the β-Ti(s, s)/α-Ti phases were accompanied by significant localized strain gradients, leading to the enrichment of geometrically necessary dislocations (GNDs) nearby. This contributed to the accommodation of interfacial strain distribution. The dispersed TiC particles induced crack path deflection and branching by altering the local stress field, increasing energy dissipation during propagation. Combined with the plastic blunting effect of the ductile β-Ti(s, s) phase, a cross-scale synergistic strengthening was achieved. The peak shear strength of the C_f/C-Nb joints using the cold-sprayed interlayer reached 50.1 MPa, compared to 5.6 MPa for conventional powder-brazed joints. This study demonstrates the significant potential of cold spray-assisted brazing in regulating the performance of joints with extreme thermal expansion mismatches, offering a new microstructural construction strategy for high-performance brazed joints.