High transport Jc performance by enhancing grain coupling in (Ba,K)Fe2As2 multi-filamentary wires

Iron-based superconductors (IBSs) show great promise as materials for high-field magnets. Developing multi-filamentary wires with a large critical current density (J(c)) and high mechanical strength is essential for high-field applications. In this work, multi-filamentary Cu/Ag composite sheathed (Ba,K)Fe2As2 (Ba-122) wires with various diameters were prepared using an ex-situ powder-in-tube (PIT) method and heat-treated by a hot isostatic pressing (HIP) process. Notably, the transport J(c) of these wires, prepared by groove rolling, generally increases as the diameter decreases from 2.0 to 1.0 mm and reaches a maximum J(c) of 3.3 x 10(4) A cm(-2) (4.2 K, 10 T) in wires with a diameter of 1.0 mm. Additionally, the n-value of the transport J(c) was greatly increased in the 1.0-mm-diameter wire. We systematically investigated the relationship between these improved transport properties and the evolution ofmass density, grain alignment, and element distribution in Ba-122 filaments of wires with different diameters. Our work proves that higher mass density and improved grain texture through the groove rolling process are beneficial for improving the transport J(c). Furthermore, our results show the possibility of cost-effective and scalable applications of (Ba,K)Fe2As2 multi-filamentary wires, which, due to their unique structure, are set to become the most promising competitors for high-field applications.