Superconducting and metallurgical properties of bronze processed Nb3Sn wires with Ni and Zn additions and comparison with Ta and Ti additions

Critical current density measurements up to 23 T of nineteen core Nb₃Sn wires with simultaneous addition of Ni to the core and Zn to the Cu-Sn bronze matrix have revealed a considerable increase of J_c at fields above 11 T. For a wire with the composition Nb-0.6 wt% Ni/Cu-10 wt% Sn-3 wt% Zn, reacted at 750°C for 64 h, J_c in the layer was determined to 1.3 × 10⁵A cm^?2 at 14 T and to 4 × 10⁴A cm^?2 at 19 T. Comparison with Ta and Ti core-alloyed Nb₃Sn wires, also performed in the present study, shows very similar results in J_c and J_c vs. ε up to the highest fields.Composition profiles for Sn and for Ni, Ta and Ti additives in the A15 layers were studied by Auger spectroscopy. For Sn a concentration gradient across the layer (from ≈ 25 at% to ≈ 22 at% Sn) was observed, with the highest Sn content occurring at the interface with the bronze. The presence of the additives in the layer was detected as well by Auger analysis as by X-ray diffractometry.