Determination of α-(Cu, Sn) in bronze area in fabrication of Nb₃Sn superconductor

With the advancement in superconducting magnet technology, Nb₃Sn has emerged as the preferred choice for applications requiring high magnetic field. Moreover, Cu-Sn alloy is thought to be the primary material used to prepare Nb₃Sn superconductor. And Sn chemical potential (or Sn activity) could significantly affect the formation and the microstructure of Nb₃Sn superconductor. However, insufficient studies were conducted thus far on solid-state reactions and phase transformation in the bronze area, making it challenging to systematically analyze the influence of Sn activity on the preparation of Nb₃Sn. Therefore, in this work, Nb₃Sn superconductors and Cu-Sn alloys were simultaneously prepared by powder metallurgy method. In addition, the phase constitutes and microstructures in bronze area, as well as the superconducting properties of Nb₃Sn superconductors, were thoroughly investigated. The results indicated that α-(Cu, Sn) solid solution could be formed during heat treatment in both of the Nb-Sn-Cu and Cu-Sn samples. Furthermore, with the same composition ratio of Sn to Cu in the precursors, the α-(Cu, Sn) solid solution in Nb-Sn-Cu samples possessed a lower Sn content than that the Cu-Sn samples because part of Sn was consumed in the reaction with Nb. Additionally, among the Nb-Sn-Cu samples, the sample with the composition of Nb:Sn:Cu = 3:1:9.5 at% exhibited the thickest Nb₃Sn layer and the best superconducting performance due to the highest Sn activity in bronze area.