Microstructure and critical current density of MgB2 and (Ba(Sr), K) Fe2As2 wires and tapes

Hiroaki Kumakura, Shujun Ye, Zhaoshim Gao, Yunchao Zhang, Akiyoshi Matsumoto, Kazumasa Togano

Research output: Contribution to journalArticlepeer-review

Abstract

MgB2 is expected to operate in helium-free condition to replace the practical metal superconducting wires in liquid helium condition. But the critical current properties for MgB2 wires are lower for large-scale applications at present. Internal Mg diffusion(IMD) method is promising to fabricate high performance MgB2 wires. Recently, we fabricated highJ thin MgB2 wires hy applying 1MB method and using 4%C-coated high quality B powder. During the heat treatment most of the B layer was reacted with Mg to form MgB2. Highest of 1100 A/mm2 and 760 A/mm2 were obtained at (4.2 K, 10 T) and (20 K, 5 T), respectively for the wire fabricated with the C-coated B powder. Engineering J(J,) was higher than 100 A/mm2 at 4.2 K and 10 T. These values of J andJe are higher than those of well-known SiC-added wire. SiC addition brings about Mg2Si precipitates which act as barriers of superconducting currents and decrease L, while the wire fabricated with C-coated B powder contains no such precipitates. Among many iron arsenide superconductors, K-doped BaFe2As2(Ba-122) and SrFe2As2(Sr-122) are the most interesting superconductors for high field magnet applications due to their high Bc2 of over SOT and relatively small anisotropy. We fabricated Ba(Sr)-122 tapes by applying cx situ powder-in-tube (PIT) technique. We found that the uniaxial pressing brings about a dramatic improvement of transport J for cx situ PIT processed Ba(Sr)-122 tape when it is properly combined with flat rolling and heat treatment. The pressure was changed between 0.4 GPa to 4 GPa. The increase of uniaxial pressing from 0.4 GPa to 4 GPa significantly enhanced J values from 210 A/mm2 to 860 A/mm2 at 4.2 K and 10 T. Microstructure analysis with SEM indicates that the packing density of Ba-122 core pressed under 4 GPa is higher than that of the tape pressed under 0.4 GPa. This suggests that the packing density is one of the most important parameters that influenceJ of cx situ PIT processed Ba-122 superconducting tapes.

Original languageEnglish
Pages (from-to)287-294
Number of pages8
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Volume78
Issue number8
DOIs
Publication statusPublished - 2014 Aug 1
Externally publishedYes

Keywords

  • Critical current density
  • Difficsion roccss
  • Iron arsenide
  • Magnesium di-boride
  • Packing density
  • Powder-in-tube process

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys
  • Materials Chemistry

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