A CuZnMnNiSi alloy interlayer reinforced W alloy/304 stainless steel composite with excellent interfacial strength

Diffusion bonding was successfully applied to join 90 W-7Ni-3Cu (W alloy) with 304 stainless steel (304SS) using CuZnMnNiSi high-entropy alloy (HEA) foil as an interlayer, and the effect of bonding temperature on microstructure and strength of joints was investigated. The present study shows that a sound W alloy/CuZnMnNiSi/304SS joint with sufficient mutual diffusion across the interfaces is obtained at a relatively lower bonding temperature of 900 °C. It is revealed by SEM and HRTEM that the interlayer elements preferentially diffuse into the base materials due to their smaller atomic radius and high activity. At the W alloy/interlayer interface, the Zn and Mn elements in the interlayer diffuse into the (Ni, Cu)ss phase to form (Ni, Cu, Zn, Mn)ss solid solution, while the W phase/interlayer phase forms a semi-coherent bonding. At the interlayer/304SS interface, the Cu and Zn elements in the interlayer diffuse into the 304SS to produce a γ-(Fe, Cu, Zn)ss supersaturated solid solution layer, while the interlayer phase/γ-Fe phase also generate a semi-coherent bonding. In addition, Cu0.64Zn0.36 particles which are judged to be precipitated form the γ-(Fe, Cu, Zn)ss supersaturated solid solution during the cooling process are discovered in the diffusion layer. The joint bonded at 900 °C shows an excellent tensile strength of 403 MPa with good ductility. The tensile fracture occurs at the interface of 304SS/interlayer, showing a mixed fracture mode of intergranular fracture and plastic fracture.