INSITU MULTIFILAMENTARY SUPERCONDUCTING WIRES FABRICATED USING A CONTROLLED HIGH-TEMPERATURE GRADIENT

A 0.64-cm-diam. Cu-Nb composite rod was continuously melted at 1800°C, then resolidified in a controlled large temperature gradient (∼ 400°C/cm) to produce a microstructure of aligned [directionally solidified, (DS)] dendrites in a copper matrix. Primary dendrite arm sizes of ∼50, 20, and 10 μm were measured for growth rates of 5.6×10-4, 1.7×10-2, and 0.11 cm/sec, respectively. Higher growth rates produced an equiaxed structure typical of chill casting. After processing, the overall Jc of the DS wires and the effect of stress on Jc were comparable to those of chill-cast specimens. The atomic fraction of Nb converted to Nb3Sn increased with decreasing filament size, and Tc was approximately 17.6 K for the DS alloys.