New Fabrication Process for ${\hbox{Nb}}_{3}{\hbox{Sn}}$ Conductors Through Diffusion Reaction Between Nb and Ag-Sn Alloys

We investigated the superconducting properties of Nb ₃ Sn formed through the diffusion reaction between Nb and Ag-Sn alloys, including Ag-9at%Sn ductile fee phase and Ag-(12-16)at%Sn ductile zeta phase alloys, and Ag-24at%Sn brittle epsiv phase alloy. We fabricated single-core and multi-core composite wires by the rod-in tube and powder-in-tube processes. The composite wires were heat treated at 650-900degC to form Nb ₃ Sn filaments. With increase of Sn content in the Ag-Sn alloy cores, the superconducting properties of the Nb ₃ Sn composite wires were improved. T _c and Bc ₂ (4.2 K) values for the Nb/Ag-Sn wires are similar to those for the Nb/Cu-Sn. However the Ic values are relatively small, due to their very thin Nb ₃ Sn layers below 0.4 mum. Ag is apparently not effective to increase the formation rate of Nb ₃ Sn layer. By using the 200- and 40000-core wires, T _c and B _c2 (4.2 K) values were increased by 0.5-1 K and 2-5 T, respectively for these multifllamentary wires, while from 10 to 500 times larger Ic (4.2 K) were obtained for the wires. The typical values for Tc and Bc2 (4.2 K) are 16.5-17.7 K and 16-21 T, respectively. The addition of 5at%Cu to Ag-Sn alloys improves their superconducting properties.