Development of bronze processed Nb3Sn wires using various Cu-Sn-In ternary alloy matrices

•A new ternary Cu-Sn-In alloy was developed for the internal reinforce strengthened Nb3Sn wire.•The solute Indium (In) remained in the matrix material after Nb3Sn synthesis heat treatment.•In element is a more suitable solute element than Zinc (Zn) on the ternary bronze alloy matrix for the internal reinforce strengthened Nb3Sn wire.•The Cu-Sn-In ternary bronze matrix will contribute to improve mechanical strength of bronze processed Nb3Sn wire. The degradation of transport current caused by high mechanical strain on practical Nb3Sn wire is a serious problem for future fusion magnets whose conductor is subjected to high electromagnetic forces. Therefore the increase of mechanical strength of Nb3Sn wire is an important research subject for fusion applications. We applied "internal matrix strengthening" using a solid solution strengthening mechanism to strengthen Nb3Sn wire and also fabricated bronze processed Nb3Sn wires using various ternary bronze alloys containing Indium (In) as the third solute element (Cu-Sn-In). Indium remained in the matrices of these wires after the Nb3Sn synthesis. The Vickers hardness of the Cu-Sn-In ternary matrices after the Nb3Sn synthesis was then higher than those of the conventional bronze and Cu-Sn-Zn ternary matrices. It is suggested that In acts more effectively as the third solute element for the solid solution strength process compared to Zn and that this may contribute to the further mechanical strengthening of Nb3Sn wire. In this study the effect of In as the solute element on microstructure and superconducting properties of bronze processed Nb3Sn wires using various Cu-Sn-In matrices was investigated.