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Detrimental Effects Depending on the Sheath Materials in Ex Situ Processed Heat Treated \hbox {MgB}_{2} Wires and Tapes

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4 Author(s)
Hiroki Fujii ; National Institute of Materials Science, Ibaraki, Japan ; Kazumasa Togano ; Kiyoshi Ozawa ; Hiroaki Kumakura

We have fabricated ex situ processed MgB2 round wires and tapes sheathed with various metals using chemically treated powders. The critical current density (Jc) properties of the as-fabricated wires and tapes are not so different, that is, independent of the sheath materials. On the other hand, the transport Jc properties of the heat-treated wires and tapes strongly depend on the sheath materials. Heat treatment of those wires and tapes brings about the sintering of MgB2 and slight enhancement in magnetization hysteresis when using Ta sheath, compared with Fe sheath. In contrast, the transport Jc properties of the wires sheathed with Ta as barrier are drastically deteriorated by heat treatment, whereas Fe-sheathed tapes show drastic Jc enhancement. Microstructural observation reveals that many cracks are generated in the MgB2 core by heat treatment only for the heat treated wires sheathed with Ta as barrier. Such cracks act as obstacles for supercurrent flow.

Published in:

IEEE Transactions on Applied Superconductivity  (Volume:21 ,  Issue: 3 )