Superconducting properties and annealing behavior of filamentary Cu-based composites produced by powder metallurgy

Composite wires with discontinuous Nb filaments embedded in a Cu matrix are produced by hot extrusion of a powder mixture and subsequent wire drawing. Nb
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Sn layers on the surface of the Nb filaments are formed by a diffusion treatment after plating with Sn. The peculiarities of the powdermetallurgical preparation technique and the origin of resistanceless currents in these materials are discussed. For Cu-Nb composites, it is shown that the critical currents are drastically enhanced by a final heat treatment, by which additional Nb precipitates in the Cu matrix.