Fabrication and Superconducting Properties of the Bronze-Processed Multifilamentary Wire Using Cu–Sn–Zn Alloy Matrix

We developed several new Cu-Sn-Zn-(Ti) alloys, which are so-called “CSZ alloy,” for practical bronze-processed Nb₃Sn wires. Several CSZ alloys were fabricated via the Mizuta method. The Zn was uniformly dissolved in the α phase of the Cu-Sn alloy, and the Zn-Ti compounds were not found in the CSZ alloy. Various 19 Nb-filament CSZ Nb₃Sn precursor wires were fabricated using CSZ matrices with different Sn and Zn nominal compositions. We also found that the CSZ/Nb composites showed excellent workability at room temperature. In this paper, changes in microstructure and superconducting properties of Nb₃Sn wires with different CSZ matrices as a function of the heat treatment condition were investigated. We clearly observed that the amount of Zn in the matrix remained constant after the Nb₃Sn formation. Thicker Nb₃Sn layers were formed by the Zn addition. T_c transitions of about 18 K have been obtained. Finally, we have succeeded in fabricating multifilamentary wires using CSZ matrices through the restacking method. The number of Nb filaments is 7771 with a diameter of 3.4 μm. The effect of the Zn addition on microstructures and superconducting property of the CSZ wires are also reported.