Critical current densities and magnetic hysteresis losses in submicron filament bronze-processed Nb3Sn wires

Submicron-filament bronze-processed multifilamentary Nb₃Sn wires with a Cu-5at.%Sn matrix and Nb or Nb alloy cores have been fabricated. The Nb alloy cores each contained 1-at.% Zr, Ti, Hf, or Ta. Among the peripheral-Cu-stabilizer-type wires, the Nb-1Ta core wire showed the highest non-Cu area critical current density, J _c of 3×10⁴ A/cm² at 12 T after all optimum heat treatment, in spite of its relatively low Sn concentration in the matrix. The deformation of Nb cores into ribbonlike shapes was apparently suppressed by the 1-at.% addition of Ti, Hf or Ta. The values of J_c per unit magnetic hysteresis loss for the Ti, Hf, and Ta alloyed Nb core wires have been evaluated to be higher than that for the pure Nb core wire. Central-Cu-stabilizer-type wires with the same alloy cores were also prepared. The Nb-1Ta core wire again showed the highest J_c´s. The J_c ´s for a Nb core wire increased further because of heat treating after Sn plating. It is shown that the hysteresis loss also decreases when the wire is heat treated after Sn plating, as a result of the increase in matrix resistivity. Thus, the bronze-process-based external Sn diffusion method using Nb alloy cores shows promise for the development of high-current-density and very-low-AC-loss Nb₃Sn wire