Improving the mechanical properties of laser-welded joints of GH4169/Nb521 dissimilar materials by using a wedge-shaped Ni interlayer

Aiming to solve the problem of cracking caused by the brittle intermetallic compounds (IMCs) in the weld zone during the laser welding of ‘Ni - based alloy/Nb - based alloy’, a wedge-shaped Ni interlayer was fabricated via Electro-Spark Deposition (ESD) for laser welding of GH4169/Nb521 joints. The effects of wedge slopes on the microstructure and properties of the joints were investigated. This design effectively suppressed the formation of brittle Ni-Nb IMCs in the fusion zone, expanded the load-bearing area, and redirected stresses at the weak interface—shifting the dominant stress state from normal stress to a combination of normal stress and shear stress. The room - temperature tensile strength of the joint with a wedge slope of 1:6 reaches 391 MPa, which is 80 % of that of the Nb521 base metal. The room-temperature tensile joint failures mainly occur in Nb-rich regions adjacent to the Nb521/Ni interface, where contains significant quantities of Ni₃Nb and Ni₆Nb₇ IMCs. At 950 °C, the joint strength reaches 216 MPa with failure in FZ - Ni transition layer interface. The microhardness increase in Nb521 base metal at high temperature alters the joint’s microhardness distribution, weakening the IMC layer’s impact on joint performance.