Selection of Fe as a barrier for manufacturing low-cost MgB2 multifilament wires – Advanced microscopy study between Fe and B reaction

Abstract

The high cost of using the niobium (Nb) barrier for manufacturing magnesium diboride (MgB2) mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niobium-titanium superconductors. The potential of replacing the Nb barrier with a low-cost iron (Fe) barrier for multifilament MgB2 superconducting wires is investigated in this manuscript. Therefore, MgB2 wires with Fe barrier sintered with different temperatures are studied (from 650 °C to 900 °C for 1 h) to investigate the non-superconducting reaction phase of Fe-B. Their superconducting performance including engineering critical current density (Je) and n-value are tested at 4.2 K in various external magnetic fields. The best sample sintered at 650 °C for 1 h has achieved a Je value of 3.64 × 104 A cm−2 and an n-value of 61 in 2 T magnetic field due to the reduced formation of Fe2B, better grain connectivity and homogenous microstructure. For microstructural analysis, the focused ion beam (FIB) is utilised for the first time to acquire three-dimensional microstructures and elemental mappings of the interface between the Fe barrier and MgB2 core of different wires. The results have shown that if the sintering temperature can be controlled properly, the Je and n-value of the wire are still acceptable for magnet applications. The formation of Fe2B is identified along the edge of MgB2, as the temperature increases, the content of Fe2B also increases which causes the degradation in the performance of wires.

Keywords

• Superconducting wires
• MgB2
• MRI magnet
• Engineering critical current density
• Fe2B