We fabricated
in situ powder-in-tube(PIT) MgB
2 wires using three kinds of Mg powders with particle size of ~45 μm, ~150 μm and 212~600 μm. Mg particles were elongated to filamentary structure in the wires during cold drawing process. Especially, long Mg filamentary structure was obtained for large Mg particle size of 212~600 μm. Critical current density,
Jc, increased with increasing Mg particle size for 1 mm diameter wires. This is due to the development of filamentary structure of high density MgB
2 superconducting layer along the wires. This MgB
2 structure is similar to that of the internal Mg diffusion(IMD) processed MgB
2 wires. However,
Jc of the wires fabricated with 212~600 μm Mg particle size decreased and the scattering of
Jc increased with decreasing wire diameter, while the
Jc of the wires with ~45 μm Mg particle was almost independent of the wire diameter. The cross sectional area reduction of the Mg particles during the wire drawing is smaller than that of the wire. When using large size Mg particle, the number of Mg filaments in the wire cross section is small. These two facts statistically lead to the larger scattering of Mg areal fraction in the wire cross section with proceeding of wire drawing process, resulting in smaller volume fraction of MgB
2 in the wire and lower
Jc with larger scattering along the wire. SiC nano powder addition is effective in increasing
Jc for all Mg particle sizes.
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