Connection reinforcement design of ODS-W/Cu joint: Transforming immiscible interface into dual reaction diffusion interface

The inherent metallurgical incompatibility between dissimilar metals such as tungsten (W) and copper (Cu) engenders weak chemical bonding, substantially constraining the attainment of high strength. This constitutes a critical limitation for nuclear fusion applications demanding robust interfacial integrity. To address these limitations, this study introduces a dual interface reinforcement strategy employing a CrCoNi medium entropy alloy (MEA) interlayer and achieving diffusion bonding of oxide diffusion-strengthened tungsten (ODS-W) and Cu through spark plasma sintering (SPS) technology. At the optimized bonding temperature of 1000 °C, the joint achieves a maximum tensile strength of 256.7 ± 8.2 MPa, corresponding to a 171 % enhancement over direct bonding (DB) joint (94.6 ± 5.1 MPa), accompanied by a fracture mode transition from brittle to ductile failure. Multi-scaled microstructure and interface element diffusion behavior analyses reveal that reactive diffusion at the W/MEA interface facilitates the formation of a solution-strengthened matrix associated with an amorphous diffusion layer. Whereas mutual diffusion at the Cu/MEA interface induces multiple phase structures, resulting concurrently in solid solution strengthening and precipitation strengthening, thereby reinforcing the interface bonding. This dual interface reinforcement methodology establishes an effective design strategy for enhancing mechanical properties in immiscible metal systems.