Rapid pulsed current activated transient liquid phase bonding achieves extremely high-strength Ni3Al-based single-crystal superalloy joints

Transient liquid phase (TLP) bonding is a promising technology for joining Ni₃Al-based single crystal superalloys. However, achieving complete isothermal solidification requires prolonged holding times due to the low diffusion coefficients of the melting point depressant (MPD) atoms. Herein, the spark plasma sintering (SPS) technique was employed to address this challenge, and the microstructure evolution, phase constitution, fracture behavior, and mechanical properties of joints were systematically investigated with BNi-2 as the filler metal at bonding temperatures of 1000–1150 °C for 30 min. The results revealed that the pulsed current enhanced the diffusion kinetics of MPD atoms, thereby suppressing the formation of CrB borides in the athermal solidification zone (ASZ) and Ni₂₃B₆ borides in the diffusion affected zone (DAZ), which consequently reduced the risk of brittle fracture. At 1100 °C, complete isothermal solidification was achieved in merely 30 min, yielding a joint tensile strength of 798 MPa and reducing the bonding time by 75% compared with conventional TLP bonding. Further increasing the temperature to 1150 °C attained a maximum tensile strength of 885 MPa. This work provides a novel strategy for achieving rapid TLP bonding of Ni₃Al-based single crystal superalloys.