High critical current density in low-cost iron-based superconducting round wires annealed at ambient pressure

Superconducting round wires with isotropic architecture are preferred in fabrications of cables and magnets. To diminish the obstacles to supercurrent, e.g., voids, cracks and bubbles, over-pressure heat treatment or hot isostatic pressing is indispensable in the final annealing process. Here, we fabricated a stainless steel/Cu/Ag sheathed Ba0.6K0.4Fe2As2 superconducting round wire without the aid of high-pressure sintering. It was found that high-strength outer sheaths and groove rolling synergistically enhance the core density to similar to 100%. Combined with the fiber and concentric texture of the superconducting core, the J c reaches 4.45 x 104 A cm-2 at 4.2 K and 10 T. Furthermore, the specially designed conductor architecture not only reduces material costs by lowering the proportion of Ag to similar to 3.1%, but also provides high mechanical and thermal stability. This straightforward and cost-effective process can be scaled up for the massive production of long wires for high-field applications.