Improving Bi-2212 multi-filament wire quality and superconductivity by cryogenic drawing

Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212)/Ag round wires were fabricated by cryogenic drawing under liquid nitrogen temperature (77 K). The influences of cryogenic drawing on the metallic sheath mechanical properties, filament densification, filament size uniformity, and superconducting properties have been systematically studied. Significant improvement of both strength and plasticity of Ag sheath was achieved under low temperature. Higher wire uniformity and densification state have been obtained by applying cryogenic drawing under 77 K, leading to the critical current density promotion by nearly 40 %. It is believed that cryogenic drawing of Bi-2212 wire is a feasible and effective way to improve the wire quality due to the mechanical reinforcement of metal sheath. • Simultaneous improvement of strength as well as plasticity for silver was found under cryogenic temperature of 77 K. • Novel cryogenic drawing method and device of Bi-2212 superconducting wires had been designed, built, and tested. • Better wire quality in terms of density, uniformity, and critical current capacity had been improved by cryogenic drawing. • The improvement of wire machinability provides the possibility of fabricating wire with more complicated structure.