Development of powder-in-tube processed MgB2 tapes and wires

Recent development of MgB2 tapes and wires fabricated by a powder-in-tube method is reviewed. Two methods are now being applied to fabricate MgB2 tapes and wires for the powder-in-tube method. One is to use MgB2 compound powder and the other is to use Mg+B mixed powders with stoichiometric composition. Commercial MgB2 compound powder is used as a starting material for the first method. Stainless steel, Fe, Cu-Ni alloy and Cu tubes are used as sheath materials. J(c) of the as-cold rolled (un-sintered) tape increases with increasing the hardness of the sheath material. Un-sintered MgB2/ (stainless steel) tapes showed an extrapolated J(c) of similar to4.5 x 10(9) A/m(2) at 4.2 K and zero field. Annealing after the cold rolling is effective to enhance J(c) values. Extrapolated J(c) higher than 10(10) A/m(2) at 4.2 K and zero field was reported for MgB2/Fe tapes annealed at 1223 K after the cold rolling. Multifilamentary (7-core) MgB2 tapes and wires were successfully fabricated by using Cu-Ni tubes. These tapes and wires showed J(c) of similar to3 x 10(8) A/m(2) at 4.2 K and self-field. For the second method, heat treatment after the cold working is essential. Thus, we have to use sheath material that is not reactive with Mg and B. Ta and Fe tubes are used to fabricate MgB2 tapes. MgB2/Ta tapes heat-treated at 1473 K showed J(c) of similar to2 x 10(9) A/m(2) at 4.2 K and self-field. This J(c) is much higher than that of the conventionally heat-treated MgB2 bulk. More excellent J(c) values were reported for Fe-sheathed tapes. J(c) of 3 x 10(9) A/m(2) at 20 K and self-field was obtained for the MgB2/Fe tape heat-treated at 1173 K. However, the J(c) values of MgB2 tapes and wires have not reached the practical level yet. Further research and development are required to improve the current carrying properties.