In-Situ formation of boride Composite zones in Novel NiPd-Based amorphous brazed dissimilar superalloy Joints: Microstructural synergy and performance optimization

The in-situ formation of borides during brazing of superalloys is difficult to control and often leads to grain-boundary segregation, which compromises the strength–ductility balance of brazed joints. Existing Pd-containing powder fillers can reduce boride precipitation to some extent, yet their limited compositional uniformity and poor fluidity restrict precise regulation of boride morphology and distribution. In this study, a Ni-Pd based amorphous brazing filler metal (NP-ABFM) was designed to address this gap by combining Pd-assisted compositional optimization with the inherent advantages of amorphous fillers. The NP-ABFM was applied to brazing of Inconel 718 and Inconel 625 at relatively low temperatures. The results show that excessive grain-boundary boride formation in the diffusion-affected zone is effectively suppressed, while fine intragranular borides are promoted. Interdiffusion between the filler and base metals induces the in-situ formation of dispersed M₃B₄ in the isothermal solidification zone, contributing to a favorable balance between strength and ductility. At 1060 °C, the joint achieves a tensile shear strength of 537 MPa and an elongation of 37.5%, with fracture occurring in the base metal. Quantitative analysis reveals that dispersed M₃B₄ accounts for approximately 40% of the joint strengthening, providing guidance for the compositional design of amorphous fillers.