Fabrication and Properties of Powder-in-Tube Processed MgB2 Tapes and Wires

MgB₂ tapes were fabricated with MgB₂ powder and several sheath materials such as Cu, Cu-Ni, Fe, carbon steel (Fe-C) and stainless steel. High-density MgB₂ cores were obtained for these sheath materials. J _c of the as-cold rolled (non heat treated) tape significantly increased with increasing the cross sectional area reduction by the cold working. Hard sheath materials (Fe-C and stainless steel) are effective to enhance J _c values. These results can be explained by the densification of MgB₂ core. Non heat treated MgB₂/(stainless steel) and MgB₂/(Fe-C) tapes showed extrapolated J _c values of 300–450 kA/cm² at 4.2 K and zero field. MgB₂ tapes show anisotropy in J _c with respect to field orientation. This anisotropy can be explained by the MgB₂ grain orientation. Heat treatment after the cold rolling is effective to enhance J _c values. An order of magnitude higher J _c values were obtained for Fe-C and stainless steel sheathed tapes by the heat treatment. J _c values extrapolated to zero field of MgB₂/(SUS 316) and MgB₂/(Fe-C) tapes reached 1,000 kA/cm² at 4.2 K.