The fabrication and thermomechanical processing of Ag/Bi-2223 jelly-roll wires

For this feasibility study, silver/superconductor jelly-roll samples with a superconductor composition of Bi_1.8Pb_0.4Sr ₂Ca₂Cu₃O_x (2223), were fabricated via a thick-film processing technique. It was found that the densification and alignment of 2223 grains along the Ag layers was crucial to achieving high critical current densities (J_c). The effects of cyclic mechanical working and heat treatment were investigated to develop a scheme to maximize J_c. The highest zero-field J₀ value of 2650 A cm ^-2 (I_c=43 A) was obtained in a jelly roll heat treated at 815 degrees C, where the majority of the mechanical deformation was performed prior to the first heat treatment. Magnetic-field-dependence measurements made in a 50 G field showed a 23% reduction in J_c when the field was applied parallel to the current flow, and a 30% reduction when the field was applied perpendicular to the current flow. This was superior to the best comparable powder-in-tube samples.