Fabrication and superconducting properties of ex-situ PIT processed A15 type tape conductors

We fabricated three kinds of A15-type superconducting tapes by applying ex situ Powder-In-Tube method. Nb₃Sn, Nb₃Al, or V₃Si superconducting powder was tightly packed into a stainless steel (SUS 316) tube or a Cu-10wt%Ni tube. These tubes were cold-rolled into tapes. All tapes showed substantial J_c values at 4.2 K without any heat treatment. The SUS 316 tube with superior mechanical hardness was effective for obtaining high density A15 cores and realizing high J_c values although T_c values were depressed by the lattice distortion. Annealing after cold rolling recovered T_c values and enhanced J_c values of all three kinds of tapes. J_c increased with increasing annealing temperature. More than two orders of magnitude higher J_c values were obtained for Nb₃Sn and V₃Si tapes after the annealing at 900°C, while the J_c enhancement of Nb₃Al tape was smaller than one order of magnitude. This difference of J_c enhancement can be explained by the difference of microstructural change by the annealing. The field dependence of J_c decreased with increasing annealing temperature, which can also be explained by the recovery of T_c.