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. Jc 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 Jc 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 Jc values of 300–450 kA/cm2 at 4.2 K and zero field. MgB2 tapes show anisotropy in Jc 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 Jc values. An order of magnitude higher Jc values were obtained for Fe-C and stainless steel sheathed tapes by the heat treatment. Jc values extrapolated to zero field of MgB2/(SUS 316) and MgB2/(Fe-C) tapes reached 1,000 kA/cm2 at 4.2 K.