Transport critical current density of high-strength Sr1−xKxFe2As2/Ag/Monel composite conductors

Abstract

Iron-based superconductors are very promising candidates for high-field applications owning to their ultrahigh upper critical field (Hc2) and very small anisotropy. For practical application, wires and tapes with high mechanical strength are essential. In this work, using Monel alloy as an outer reinforcing sheath, 7-filament Sr1−xKxFe2As2/Ag/Monel composite tapes with various thicknesses were developed based on the powder-in-tube method. Through microhardness characterization, it is found that the transport critical current density (Jc) of the tapes has a heavy dependence on the mass density of the Sr-122 phase, which varies widely according to the cold-work parameters and heat treatment temperatures for the tapes. In large-scale applications, conductors are usually designed to work under compressive state for safety, and so the compressive strain dependence of transport Jc was investigated for our tapes, which shows almost no Jc degradation under a large compressive strain of 0.6%. The transport Jc for the rolled tapes can be further significantly enhanced to 3.6 × 104 A cm−2 (4.2 K, 10 T) by a hot-press process. These results suggest the great potential of Monel/Ag composite sheath for developing high-strength and high Jc performance iron-based superconducting wires and tapes for high-field applications.