Interfacial Strengthening and Stress Mitigation in GH4169/Ti60 Diffusion-Bonded Joints Driven by Cu Interlayer Thickness Design

Abstract Heterogeneous joining of GH4169 Ni-based superalloy and Ti60 titanium alloy combines their advantages, but brittle Ti-Ni phases and stress concentration lower joint strength. Here, pure Cu interlayers were used for diffusion bonding GH4169/Ti60 joints. The Cu foil thickness was varied to study microstructural evolution and reveal strengthening and fracture mechanisms. Direct TLP bonding produces a joint comprising diffusion layer I (GH4169 side), central brazing seam II, and diffusion layer III (Ti60 side), with typical microstructure GH4169/Cr ss +(Ni,Cr,Fe) ss /TiNi/Ti 2 Ni/α-Ti/Ti60; brittle TiNi compounds degrade performance. With Cu foil, the typical microstructure becomes Ti(Ni,Cu)/TiCu+TiAl/β-Ti+Ti 3 Sn/α-Ti+Ti 2 Cu/α-Ti/Ti60. Increasing Cu thickness coarsens zone II grains and reduces the high-angle grain boundary fraction from 92.5% to 46.1%. At 0.03mm Cu, the maximum KAM values in zones I, II, and III are 4.88°, 4.99°, and 4.97°, respectively, indicating relatively uniform stress. The (Ni,Cu) ss /Ti 3 Sn/Ti–Cu layered structure in zone II greatly relieves residual stress and gives a maximum joint strength of 190MPa. Fracture morphology and path indicate brittle fracture; cracks initiate between the (Cu,Ni) ss and TiCu phases and form small secondary cracks.