Improvement of current density by texture andI_canisotropy in thin filament MgB₂/Fe tapes

Abstract

Thin filament MgB 2 /Fe tapes have been made by the powder-in-tube technique using a precursor powder prepared by mechanical alloying and deformed by two-axial rolling. Increasing critical current density (J c ) in a parallel external magnetic field has been measured for a reduced filament thickness up to 18.5 µm; this could be effective for future practical fine-filamentary MgB 2 conductors. This increase in J c is attributed to an apparent improvement in texture introduced by rolling. Further increase in J c with reduction of filament size is limited due to chemical reaction at the filament/Fe interface during the final heat treatment at 600 • C for 3 h. On the other hand, improved texture leads to a strong critical current anisotropy, which increases with the reduced filament thickness and temperature. High I c anisotropy can lead to an apparent reduction of the total magnet current due to the effect of the radial field component, as in the case of high temperature superconducting coils.

Tailored Materials for High‐Performance MgB2 Wire

“…This is the first time that fibrous structure has been observed in in situ MgB 2 wires. For ex situ wires, specifically for cold‐drawn tapes, similar structure has been reported 25. However, owing to the texturing and the anisotropic nature of MgB 2, the critical current density showed an angular dependence with respect to the applied field direction.…”

Magnetic properties and critical currents of MgB2

“…Material inhomogeneities and (partial) texture [64,106,118,153,168,252,[432][433][434][435][436][437][438][439][440] complicate the situation, because they influence the critical current densities and their field dependence. Although difficult to model, they have to be taken into account.…”

Fine-filamentaryin situMgB2wires

“…Up to now, mainly wires with core sizes above 100 μm have been made and studied. The thinnest filaments with a thickness of 20 μm have been made by two-axial rolling into a sandwich-like structure using fine-grain extensively milled powder [4]. Recently, multi-core in situ wires with filament size ≈30 μm have been made by drawing [5] and by an ex situ approach using drawing and groove rolling deformations [6].…”