Tailoring interfacial reactive layer for high-strength maraging steel/high-entropy alloy dissimilar joints

• Ultra-high-strength (>1 GPa) maraging steel/high-entropy alloy dissimilar joints are fabricated using a Nb interlayer. • Superior strength is enabled by a continuous, nanocrystalline (∼20 nm) Fe 2 Nb layer at the steel/Nb interface. • A robust and intermetallic-free diffusion bond forms at the HEA/Nb interface. • Thickening and coarsening of the Fe 2 Nb layer causes strength degradation at high bonding temperatures. Joining ultra-high-strength maraging steels and high-entropy alloys (HEAs) is crucial for advanced applications. However, the formation of brittle intermetallics often limits interfacial performance. Here, we demonstrate a rapid hot-compression bonding strategy that uses a niobium (Nb) interlayer to control interfacial reactions and produce a high-strength joint between 18Ni350 maraging steel and AlNbTi 3 Zr 1.5 HEA. The effects of bonding temperatures on the interfacial microstructures, mechanical properties, and fracture mechanisms were systematically investigated. An exceptional joint tensile strength exceeding 1 GPa was achieved at an optimal bonding temperature of 850 °C. This is attributed to the formation of a continuous, ultra-thin nanocrystalline Fe 2 Nb reactive layer (RL) at the 18Ni350/Nb interface, coupled with a well-bonded, intermetallic-free HEA/Nb interface. However, increasing the temperature to 1000 °C thickens the Fe 2 Nb RL to over 300 nm and promotes grain coarsening, reducing the joint strength to 747 MPa. Correspondingly, the fracture mode transitions from a complex path involving both interfaces and the interlayer at low temperatures to preferential fracture along the thickened Fe 2 Nb RL at 1000 °C. These findings reveal the central role of intermetallic design in governing interfacial performance, demonstrating that controlling interfacial nanostructures is a critical strategy for fabricating high-strength dissimilar joints.