Ultrastrong and ductile superalloy joints bonded with a novel composite interlayer modified by high entropy alloy

Diffusion bonding (DB) with interlayers is sought-after for manufacturing high-performance turbine disks of powder metallurgy (PM) superalloys with precise and intricate inner cavity structures. Developing novel interlayer materials is challenging but crucial for enhancing bonding quality and joint properties. We designed a multi-interlayer composite bonding (MICB) method, employing sandwich-structured interlayers of “BNi2/high entropy alloy (HEA)/BNi2”, to join a PM superalloy FGH98. The MICB joint exhibited an ultrahigh shear strength of ∼1132 MPa and exceptional ductility, indicating a typical ductile fracture pattern with numerous dimples. Owing to the introduction of liquid BNi2 interlayer, initial bonding interfaces were eliminated and replaced by newborn grain boundaries (GBs), preventing brittle interfacial fracture. Due to the diffusion of Al/Ti/Ta from the base metals (BMs), massive ordered γ' nanoparticles also precipitated in the joint. Moreover, the addition of HEA foil reduced the stacking fault energy (SFE) of the joint and facilitated the formation of deformation twins (DTs). Thus, during the deformation process, the γ' nanoparticles, and multiple substructures like stacking faults (SFs), Lomer-Cottrell (L-C) locks, DTs, and 9R phases enhanced the work-hardening capability and strengthened the joint. Simultaneously, the multiplication and interaction of DTs induced a softening mechanism of dynamic recrystallization (DRX) during the entire deformation process and dominated when the plastic instability occurred, resulting in numerous adiabatic shear bands (ASBs) consisting of γ/γ' nano-bands, which indicates a significant improvement of the joint ductility.