Nb_3Sn multifilamentary superconductors fabricated through a diffusion reaction between Nb and As-Sn alloys

摘要

Ag-Sn alloy is very attractive for fabricating Nb_3Sn wires through diffusion reaction, because Ag-based alloy including a large amount of Sn is ductile. Therefore we investigated the Nb_3Sn formation through the diffusion reaction between Nb and Ag-Sn alloys. With using Ag-9 at% Sn fee phase, Ag-12 at% Sn C, phase, and Ag-24at% Sn e phase alloys, we fabricated single-core, 200-core, and 40000-core composite wires with Nb matrix and Ag-Sn alloy cores. With increase of Sn content in Ag-Sn alloys, the obtained superconducting properties of heat treated composite wires were improved. T_c and B_c2(4.2 K) for the Nb/Ag-Sn are similar to those for the Nb/Cu-Sn. However, the I_c values are relatively small, due to the formed very thin Nb_3Sn layers. Ag is apparently not so effective to increase the formation rate of Nb_3Sn layer as Cu. We obtained very interesting results by making the 200-core and 40000-core wires, which show the improved T_c and B_C2(4.2 K) by 0.5-1 K and 2-5 T, respectively. From 10 to 500 times larger I_c(4.2 K) were also obtained for the multifilamentary wires.