Nb3Sn Wire Fabrication Using Rod-in-Tube Method With a Diffusion Couple of Nb and Sn Alloy With Co-Addition of Cu and Zn

Large-scale devices, such as the next generation high energy particle accelerator project, demand the enhancement of the J_c and cost performance of Nb₃Sn wires. The cost performance is closely related to the design and drawability of the wires. This study aims to increase the hardness of the soft Sn core of the wires through the precipitation of fine compound particles, improve the hardness balance between the constituent materials (Nb, Cu, and Sn), and investigate the feasibility of this method for practical wire drawing. First, we investigated the variations in microstructure and hardness when Cu and Zn were co-added to Sn. A total addition of 50% Cu–Zn to the Sn alloy can triple the hardness, leaving the alloy ductile enough to sustain the entire deformation process. Subsequently, we manufactured tube-type multifilamentary wires using subelements containing different types of Sn alloys, with and without an intermediate layer of Cu between Sn and Nb. In the absence of Cu, we observed the formation of a large area of Nb₆ Sn₅, which is responsible for the formation of a large coarse Nb₃Sn grain area. The presence of Cu suppresses the formation of the Nb₆Sn₅, demonstrating that controlling the Cu/Sn ratio at the subelement level is critical to suppressing the formation of coarse Nb₃Sn areas.