Development of the bronze processed Nb3Sn multifilamentary wires using Cu-Sn-Zn ternary alloy matrix

The degradation of transport critical current density (Jc) property by the high mechanical strain on the practical Nb3Sn wire is serious problem for applying the future fusion magnet system. We developed the various solid solution strengthened ternary Cu-Sn-Zn bronze alloys for the development of the high strength Nb3Sn multifilamentary wires. The Zn element remained homogeneously into the bronze matrix after the Nb3Sn synthesis heat treatment, and it contributed to strengthening the bronze matrix. Mechanical strength of Nb3Sn wire was improved by the increase of the nominal Zn content of Cu-Sn-Zn ternary bronze alloy, and the tensile stress obtained to the maximum transport critical current (Ic) was enhanced from 80 MPa to 200 MPa. This value was comparable to the high-strengthened Nb3Sn wire using the CuNb reinforcement technique. The solid solution strengthening technique on the bronze alloy was a simpler method compared with the reinforcement techniques and became one of the attractive high strengthening processes in the bronze processed Nb3Sn wire.