Dual-layer BNi2/HEA brazing filler for high-performance SiC_f/SiC-DD3 joints via reaction pathway engineering

The joining of SiC_f/SiC ceramic matrix composites (CMCs) and nickel-based superalloys has long been challenged by non-equilibrium interfacial reactions, residual stress mismatches, and the uncontrolled formation of brittle intermetallic compounds. Traditional single-layer filler metals are generally ineffective in simultaneously regulating and mitigating these complex interfacial phenomena. Following a partitioned regulation strategy for controlling the reaction pathway, a (FeCoNiCrCu)₉₅ Zr₅ + BNi2 double-layer filler metal system was designed and fabricated in this study. The BNi2 layer preferentially melts and wets the interface of the DD3 single-crystal alloy, while simultaneously promoting interdiffusion with the high-entropy alloy solder via capillary penetration, leading to the formation of low-melting-point Zr₂Ni intermetallic compounds and a reduction in grain boundary energy. Differential scanning calorimetry (DSC) results show that the final melting temperature decreases from 1154.9 °C to 1105.6 °C, representing a reduction of 49.3 °C. In the double-layer filler metal system, (FeCoNiCrCu)₉₅Zr₅ undergoes a moderate interfacial reaction with the SiC_f/SiC composite. The interfacial reaction layer comprises Cr₂₃C₆, ZrC, and Cr₆Si₇Ni₁₆. In addition, a dual-FCC (face-centered cubic) phase structure of Ni(s,s)/Zr₆Si₇Ni₁₆ with high plasticity forms near the composite side, effectively reducing residual stress. This reaction pathway allocation strategy simultaneously inhibits excessive Ni diffusion and suppresses the formation of the brittle CrTi₄C₅ phase. Compared with the traditional BNi2 joint, the shear strength of the optimized joint is improved by 28 %, reaching 88 MPa. The results of this study lay a solid foundation for designing low-melting-point high-entropy filler metal systems and fabricating high-performance brazed joints.