Superconductivity in filamentary CuNb composites produced by powder metallurgy

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Abstract
Composite wires with discontinuous Nb filaments embedded in a Cu matrix are produced by hot extrusion of a powder mixture and subsequent wire drawing. The specimens exhibit superconductivity with critical current densities in zero field up to 4×104 A/cm2 at 4.2 K (after a reduction of the cross‐section area of 5×104 by wire drawing). The origin of resistanceless currents in these materials with only 10 wt% Nb is due to superconducting bridges between the filaments which are formed by the proximity effect. The critical currents are drastically enhanced by a final heat treatment, by which additional Nb precipitates are produced in the Cu marix.