Strain characteristics of Nb₃Sn multifilamentary wires with CuNb reinforcing stabilizer

Bronze processed multifilamentary Nb₃Sn superconducting wires, with a CuNb reinforcing stabilizer instead of the conventional Cu stabilizer, were fabricated. The mechanical properties and the strain dependence of the critical current I_c were evaluated at 4.2 K and a magnetic field of 15 T. A remarkable increase in the yield stress (70%) and the plastic flow stress as compared to the values for the wire with Cu stabilizer was observed. The strain for the peak I_c was also increased by 0.2%. I_c on unloading was reversible within the strain range of 1.5%. The strain sensitivity of I_c in the CuNb/Nb₃Sn wire was almost the same as that of the Cu/Nb₃Sn wire. A decrease in the wire diameter from 0.8 to 0.5 mm resulted in a slight increase in the yield stress of the CuNb/Nb₃Sn wire, but no change in the strain dependence of I_c. An increase in the heat treatment temperature from 700 to 750°C resulted in a decrease in the flow stress of 15%, but no change in the strain dependence of I_c. A marked change in the morphology of the Nb filament in the CuNb reinforcing stabilizer was evidenced during heat treatment.