Influence of Ge addition on phase formation and electromagnetic propertiesin internal tin processed Nb3Sn wires

In order to investigate the effect of Ge addition to the Cu matrix on the m icrostructure and the critical current density, four kinds of internal tin processed Nb3Sn strands with pure Cu and Cu - 0.2, 0.4, 0.6 wt % Ge alloys were drawn to 0.8 mm diameter. The microstructure and critical current of i nternal tin processed Nb3Sn wires that were heat treated at temperatures ra nging from 680 degreesC to 740 degreesC for 240 h were investigated. The Ge addition to the matrix did not make workability worse, A Ge rich layer in the Cu-Ge matrix suppressed the growth of the Nb3Sn layer and promoted grai n coarsening. The greater the Ge content in the matrix, the lower the net J (c) result after Nb3Sn reaction heat treatment. There was no significant va riation in J(c) observed with heat treatment temperature ranging from 680 d egreesC to 740 degreesC.