Critical current density and microstructure of iron sheathed multifilamentary Sr1-xKxFe2As2/Ag composite conductors

TL;DR

This study investigates the microstructure and critical current density of multifilamentary Sr-122 superconductors with iron sheaths, revealing how filament size, deformation, and microhardness influence superconducting performance.

Contribution

It provides new insights into how filament number, size, and mechanical processing affect the critical current density in iron-sheathed Sr-122 superconducting conductors.

Findings

Higher filament density correlates with increased Jc.

Flat rolling significantly enhances Jc in fine-filament conductors.

Jc decreases with increasing filament number due to microstructural effects.

Abstract

Iron-based superconductors have been considered to be very promising in high-field applications, for which multifilamentary wire and tape conductors with high mechanical strength are essential. In this work, 7-,19- and 114-filament Sr0.6K0.4Fe2As2 (Sr-122) superconducting wires and tapes with silver as matrix and iron as outer reinforcing sheath were produced by the ex situ powder-in-tube method. The mass densities of Sr-122 phase in 7- and 19-filament conductors were investigated by microhardness characterization, which revealed a positive correlation between hardness and transport critical current density (Jc) in round wires and flat tapes with various thicknesses. For Sr-122/Ag/Fe 114-filament conductors, in which an average cross-sectional filament size smaller than 50 microns was achieved by drawing into round wires of 2.0 mm in diameter, the transport Jc can be significantly enhanced by flat rolling, as for the 7- and 19-filament conductors. The highest transport Jc of the 7-,19- and 114-filament Sr-122/Ag/Fe tapes reached 1.4x10^4, 8.4x10^3 and 6.3x10^3 A cm-2 (4.2 K, 10 T), respectively, showing a Jc degradation with the increase of filament number. This Jc degradation can be ascribed to the sausage effect for filaments in longitudinal direction and the grain refinement in these very fine filaments.