Enhancing Transport Performance in 7-filamentary Ba_0.6K_0.4Fe₂As₂ Wires and Tapes via Hot Isostatic Pressing

Iron-based superconductors (IBS) are considered as potential materials for manufacturing high-field magnets, for which developing multi-filamentary conductors with high performance and high strength is essential. Herein, 7-filamentary Cu/Ag composite sheathed Ba_0.6K_0.4Fe₂As₂ (Ba122) round wires and tapes were successfully prepared through the ex situ powder-in-tube (PIT) method and treated by hot isostatic pressing (HIP) process. Pure Ba122 phase with roughly homogeneous element distribution was obtained in the superconducting filaments. The wires and tapes show very small low-temperature normal-state resistivity of 0.12 μΩ cm and 0.17 μΩ cm respectively owing to the high electrical conductivity of copper and silver. The HIP process greatly enhances the mass density of the superconducting filaments and promotes the formation of well-grown plate-like Ba122 grains. Vickers hardness measurements on the cross sections of these filaments reveal a rather good uniformity of the mass density. The transport critical current density (J_c) in the 7-filamentary Ba122/Ag/Cu round wires and tapes reached 1.3 × 10⁴ A cm⁻² and 4.8 × 10⁴ A cm⁻² at 4.2 K in 10 T respectively. These results indicate that hot isostatic pressing is advantageous in developing high-performance multi-filamentary iron-based superconductors.