A high-entropy gradient filler metal enables high-strength joints of Ti2AlNb and GH4169 alloys

Abstract

Vacuum brazing with an innovative filler alloy is critical for manufacturing high-precision aerospace components requiring exceptional comprehensive performance, yet achieving superior strength in Ti₂AlNb/GH4169 brazed joints remains challenging. This study proposes a (TiZrHf)₅₀(NiCu)₄₅Al₅/(TiZrHf)₃₀(NiCu)₆₅Al₅ high-entropy gradient filler metal (HGFM) to join the Ti₂AlNb alloy and the GH4169 superalloy, which relieved the stress concentration and elevated microstructure stability, achieving a maximum shear strength of 335 MPa. The lower thermodynamic inclination and high entropy characteristics synergistically contributed to the solid solution mainly composed of (Ni,Cr,Fe)_ss and (Ni,Cu,Fe,Cr)_ss phases, replacing the intermetallic compounds dominated by (Ti,Zr,Hf)(Ni,Cu)₃ and (Ti,Zr,Hf)₂(Ni,Cu) phases. The corresponding lattice misfits between (Ni,Cr,Fe)_ss and (Ni,Cu,Fe,Cr)_ss phases were 3.72%, 13.24% and 20.14%, which enabled coherent and semi-coherent relationships, facilitating the dynamic equilibrium of dislocation motion without termination. A higher activation energy at the interface (393 kJ mol⁻¹) indicated that slow atomic diffusion controlled the excessive reaction at the interface. The remarkable drop in elastic modulus discrepancies in the customized solid solution region enhanced the synergistic deformation capacities, which drove the fracture locations to transform to the Ti₂AlNb dissolved with Ni and Cu phases, exhibiting a more tortuous fracture path and higher fracture toughness. Molecular dynamics simulations indicated that the solid solution interface enhanced the peak tensile strength to 10.36 GPa, demonstrating favorable high-temperature stability. The current work offers a directly transferable approach for developing a tailored filler metal for other dissimilar metal systems.