Annealing effects in PIT-processed MgB2/SUS316 (stainless steel) composite wires

The MgB2/SUS316 (stainless steel) wires were fabricated by powder-in-tube (PIT) method using commercially available superconducting MgB2 powder at ambient pressure, and the annealing effects on Tc as well as Jc were investigated. The as-rolled MgB2/SUS316 wire showed a zero-resistance superconducting transition temperature (Tc) at 33.4 K and a critical current density of 2.22 kAcm-2 at 18.4 K. In order to check the annealing effect, the different pieces of the as-rolled wires were annealed at various annealing conditions under Ar atmosphere in vacuum (60 cm Hg) sealed silica-tube. As compared to the MgB2/Fe wires, the annealing temperature and duration were lower and much shorter respectively, for the MgB2/SUS316 (stainless steel) wires. On annealing at 873 K for ~ 1 s, we obtained the best sample with a of 12.1 kAcm-2 at 16.9 K with a maximum Tc of 36.1 K. Longer annealing time (~ 10 s) above 873 K reduced the Tc as well as the Jc, indicating a possible chemical reaction between the MgB2 cores and the sheath material.