Abstract
Improvements of high-field properties of in situ Nb3Sn superconductors were studied by additions of 2%Zr, 2%Hf and 2%Ta to Cu-20 mass%Nb melts. The eutectic structures around Nb dendrites were observed in all as-cast materials, and some difficulties arose from the structures in drawing the ingots with Zr and Hf into wires. The critical current densities were measured up to 15 T after various heat treatments.
Additions of Zr and Hf affected a little Jc in the high magnetic field region and HC2* of in situ Cu-20%Nb–Sn superconductors. On the contrary, additions of Ta improved appreciably the high-field performance of in situ Cu-20%Nb–Sn superconductors in spite of the fact that Ta was not soluble in the Nb dendrites in the as-cast state. The highest Jc of (1–2)×108 A/m2 at 12 T and HC2* of 17.5 T were obtained on the in situ Cu-20%Nb–2Ta–Sn superconductors.
