Extraordinary strength-ductility synergy in superalloy joints via a high-entropy-alloy modified multi-interlayer composite bonding strategy

Diffusion bonding with innovative interlayers is critical for manufacturing high-precision aerospace turbine components requiring exceptional comprehensive performances, yet achieving simultaneous strength and ductility in superalloy bonding joints remains challenging. Developing high-performance interlayer material, introducing effective strengthening strategies, and elucidating deformation mechanisms in the superalloy joints can address this issue. This study introduces a multi-interlayer composite bonding technique using a “BNi2/high entropy alloy/BNi2” sandwich structured interlayer to join powder metallurgy superalloy FGH98. The liquid BNi2 interlayer eliminated interfacial defects, reducing the risk of a brittle fracture at the interface. The high entropy alloy interlayer of FeCoNiTiAl promoted atomic diffusion between the interlayer and base metals, facilitating the in situ formation of TiB₂ borides, M₃B₂ borides, γ' nanoparticles and comprising distinct zones with different deformation capabilities. This heterogeneous joint microstructure resulted in an extraordinary strength-ductility synergy through strain partitioning and load transfer. Among these zones, the strengthening effect in the Ti-boride zone (TBZ) with in situ TiB₂ borides was crucial, particularly at elevated temperatures. High work-hardening and deformation capabilities were attributed to TiB₂’s effectiveness in obstructing dislocation movement and generating stacking faults within the borides. As a result, an ultrahigh ultimate tensile strength of 1410 ± 10 MPa, a total elongation at fracture of 19 ± 0.5 % at room temperature, and a maximum tensile strength of 981 ± 20 MPa at 800 °C were achieved in the bonding joint.