Abstract: An extremely high-strength TiAl/Ni-based superalloy dissimilar joint was obtained using a designed Ni₂₅Zr₂₅Sn₂₀Cu₁₀Hf₁₀Cr₅Fe₅ multi-principal element interlayer via contact reaction brazing. It was found that a joint mainly composed of eutectic structure of (Ni)ss, (Ni, Cr, Fe)ss, and (Cr, Ni, Fe, Mo)ss, as well as micro-nano precipitates of (Ti)ss and (Hf, Zr)ss, could be achieved through the interaction between the interlayer and the base metals. The joint exhibited a shear strength of 498 MPa when brazed at 1190 °C for 10 min, while the fracture occurred within the TiAl base metal, and the retention rate of high-temperature (HT) strength (650 °C) was ∼100%. The strengthening mechanism of the brazed joint was systematically discussed by transmission electron microscopy (TEM). It was shown that high-density dislocations existed in each phase of the seam as well as twinning and stacking faults existed in the micro-nano precipitates, caused by a mass of solute atoms, greatly strengthened the joint. At HTs, the dislocation strengthening effect weakened due to grain recovery and recrystallization, but the joint could be additionally toughened by multi-cracking. Meanwhile, granular (Ti)ss dispersed through the seam and ductile reticular structure (Ni)ss toughened the joint via the mechanism of crack termination and bridging. The proposed method provides a new approach for high strength and heat resistance joining of TiAl/Ni-based superalloy in aeroengine components.

Key words: Multi-principal element interlayer, Mechanical properties, Strengthening mechanism, High-entropy effect, Dislocations strengthening