Fabrication of New Internal Tin Nb$_{3}$Sn Wire Using Sn-Zn Alloy as Sn Core

Abstract

We proposed a new configuration for the precursor of Zn-added internal tin (IT) Nb $_3$ Sn wires, where Zn is added to Sn core and Ti is doped to Cu matrix. The aim is to avoid a Sn-Ti compound layer forming at the Nb filament pack, when one dopes Ti to Sn cores, while maintaining Zn effects such as promotion of Nb $_3$ Sn layer formation: Sn-Ti compound layer could be often a factor to yield inhomogeneous Sn and Ti distribution in the Nb filament modules. We here studied the microstructure and the $J_\mathrm{c}$ characteristic of IT wires fabricated using Sn-Zn/Cu-Ti/Nb composite. Use of Sn-Zn core is also effective to increase the hardness of Sn cores about 2 times higher than that of pure Sn core. In Sn-Zn/Cu-Ti/Nb composite samples, the Sn-Ti compound layer was found to be significantly suppressed, compared with Sn-Ti/Cu-Zn/Nb composite samples, which resulted in better Sn and Ti distributions. Zn diffusion rate across the Cu matrix appears to be so fast that Zn can almost diffuse to the other barrier by the heat treatment at 550 $^{\circ }$ C. Therefore, it is expected to gain the similar effect of Zn addition even for the wires that are made using the Sn-Zn/Cu-Ti/Nb composite, to the Sn-Ti/Cu-Zn/Nb composite wires.