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 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/spl deg/C. A thin compound layer is also formed at the Cu/Nb-36Ti interface after heat treatment. Meanwhile, no compound layer is observed at the Cu/Nb-25Ti interface. This is a major advantage of Nb-25Ti wire, which may save the wrapping of Nb foil around the cores to prevent the reaction with the Cu matrix, when they are fabricated into fine filaments. The T/sub c/ of Nb-25Ti wire is about 0.7 K higher than that of Nb-46.5Ti wire. The T/sub c/ and B/sub c2/ of Nb-25Ti wire are less sensitive to the reduction in diameter and the heat treatment compared to the Nb-46.5Ti wire. The B/sub c2/(4.2 K) of Nb-25Ti as wire seems to be high enough for AC applications. The addition of boron enhances the T/sub c/ and B/sub c2/ of Nb-25Ti alloy.