Development of the internal matrix reinforcement bronze processed Nb3Sn multicore wires using Cu-Sn-In ternary alloy matrix for fusion magnet application

Abstract

We approached the solid solution strength process for the high mechanical strength bronze processed Nb3Sn wires by the internal matrix reinforcement. Previously, we already reported the mechanical strength improvement of the Nb3Sn wire by the increasing of the amount of Zn element composition of the Cu-Sn-Zn ternary alloy matrix. However, there was also a trade-off relationship between the Sn and Zn compositions of the ternary matrix on the mechanical strength and superconducting properties. A Cu-Sn system ternary alloy containing Indium (In) element as a solute element (Cu-Sn-In), which is thought to be more effective solute element compared with Zn, was casted in order to improve mechanical strength beyond Cu-Sn-Zn ternary alloy matrix samples on the solid solution strength process. We fabricated various Cu-Sn-In-(Ti)/Nb precursor wires having 19 Nb multicores. The In element remained in the matrix after the Nb3Sn synthesis through the diffusion reaction, and then the Vickers hardness of the Cu-Sn-In matrices after the Nb3Sn synthesis heat treatment was higher than that of the conventional bronze and Cu-Sn-Zn matrices. We also confirmed that critical current density (Jc) property of the Nb3Sn wires using Cu-Sn-In-(Ti) was drastically increased at low and middle magnetic field below 15 T. These suggested that the In solute element in the matrix contributed the solid solution strengthening of the matrix after Nb3Sn synthesis and also improve Jc -B performance.