Investigation of Nb₃Sn multi-filament wire using a zinc solid-solution bronze matrix

The degradation of transport current property due to the high mechanical strain on practical Nb₃Sn wire is a serious problem for applying future fusion magnets operated under higher electromagnetic force environments such as DEMO. We have attempted to improve the mechanical strength of Nb₃Sn bronze-processed wire by using a high-strength bronze matrix produced through a solid-solution strengthening process. In this study, we developed several Zn solid-solution Cu-Sn-(Ti) alloys with a high Sn content, from 10 to 13.5 mass% (Cu-Sn-Zn), in order to investigate the effect of adding Zn to the microstructure and the superconducting properties of bronze-processed Nb₃Sn wire. We observed clearly that the amount of Zn in the matrix remained constant after Nb₃Sn formation. Thicker Nb₃Sn layers were formed as the result of adding Zn. No degradation of transition temperature due to adding Zn was observed, and the temperature attained was approximately 17.5 K. Finally, we succeeded to fabricate multi-filament wires (Nb filament: 7771 with a diameter of 3.4 μm) using various Cu-Sn-Zn matrices through the Cu restacking method. (author)