The superconducting properties of MgB/sub 2//(stainless steel) tapes fabricated by the pit process

Abstract

We have investigated the superconducting properties of monofilament MgB/sub 2/ tapes and wires with a stainless steel (SUS316) sheath. MgB/sub 2/ powder was put into a SUS316 tube with a 6.5 mm diameter; the tube was cold-rolled into a wire with a 1.4 mm-1.0 mm diameter using groove-rolling and cassette roller dies and then cold-rolled into tapes. The stainless steel sheath is effective to increase the density of the MgB/sub 2/ core. The transport critical current density depends on the wire diameter and tape thickness. The J/sub C/ values increase with increasing the total cross-sectional area reduction of tapes. However, the J/sub C/ value of the tape with a thickness of less than 0.3 mm deteriorated because of cracks introduced by rolling. Post-annealing increased the J/sub C/ properties of these tapes. The low annealing temperature of /spl sim/600/spl deg/C was effective to increase the J/sub C/ values for MgB/sub 2//(stainless steel) tapes. This temperature was much lower than the optimum annealing temperature of MgB/sub 2/ tapes with other sheath materials, such as MgB/sub 2//Fe tapes. The post-annealing improved the linkage of grains and enhanced the J/sub C/ values.