The effect of heat treatment on the superconducting properties of Cu-Nb composites

Microfilamentary composites of continuous Nb fibers in Cu matrices were tested for superconducting transport properties after heat treatments at 200–900 °C. The critical current density at applied magnetic field was reduced dramatically as the heat treatment temperature was increased. The scaling relations describing the critical current as a function of applied field shifted from conventional (1−h)2 scaling to higher-order relations as the heat treatment history was varied. Critical temperature transitions were abnormally broad in the fine-filament composites examined. The upper critical fields and transition temperatures approached bulk values after severe heat treatment.