Evaluations of Nb-25 wt%Ti alloy wires

An arc-melted Nb-25 wt%Ti alloy was fabricated into monocore wires with Cu matrix. The structure and superconducting properties of the wires were compared with those of Nb-46.5 wt%Ti and Nb-36 wt%Ti wires prepared by a similar process. The formation of a thick Cu-Ti-Nb compound layer is observed at the Cu/Nb-46.5Ti interface after heat treatment at above 600 degrees C. A thin compound layer is also formed at the Cu/Nb-36Ti interface after beat treatment. Meanwhile, no compound layer is observed at the Cu/Nb-25Ti interface. This is a major advantage of Nb-25Ti wile, which may save the wrapping of Nh foil around the cores to prevent the reaction with the Cu matrix, when they are fabricated into fine filaments. The T-c of Nb-25Ti wile is about 0.7 K higher than that of Nb-46.5Ti wire. The T-c and B-c2 Of Nb-25Ti wire are less sensitive to the reduction ill diameter and the heat treatment compared to the Nb-46.5Ti wire. The B-c2(4.2 K) of Nb-25Ti as wire seems to be high enough for AC applications. The addition of boron enhances the T-c and B-c2 of Nb-25Ti alloy.