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

In order to investigate the effect of Ge addition to the Cu matrix on the microstructure 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 internal tin processed Nb₃Sn wires that were heat treated at temperatures ranging from 680°C to 740°C 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 grain coarsening. The greater the Ge content in the matrix, the fewer the net J_c result after Nb₃Sn reaction heat treatment. There was no significant variation in J_c observed with heat treatment temperature ranging from 680°C to 740°C