Fabrications and properties of MgB₂/stainless-steel tapes by PIT process

We have successfully fabricated single-filament composite MgB₂/Stainless-Steel (SS) tapes using powder-in-tube processes such as swaging and cold rolling. The transport critical currents, that were measured by a standard dc four-probe method, I_c ∼ 316 A and ∼105 A were observed at T = 4.2 K with H = 0 G for as-rolled and sintered MgB₂/SS tapes, respectively. In addition, the isothermal magnetizations M(H) of sintered MgB₂/SS tapes and commercial MgB₂ powder were measured at temperatures T between 5 and 50 K in fields up to 6 T, employing a PPMS. The critical current density (J_c) values obtained from the M(H) data, using Bean model, were >5 × 10⁵ A/cm² and >5 × 10⁷ A/cm² at T = 10 K with H = 0 G for the sintered MgB₂/SS tapes and the commercial MgB₂ powder, respectively. On the other hand, we investigated the cross sections of both the sintered and the as-rolled tapes, using SEM and EPMA. No evidence of significant diffusion between MgB₂ and SS tube was found in the SEM/EPMA. However, traces of reaction can be seen in the interface region between MgB₂ core and SS tube for the sintered MgB₂/SS tapes, from the EPMA line profiles. In addition, impurity phases such as MgO or MgB₄, which can be generated inside the superconductor MgB₂ core during fabrication, were observed by XRD analyses.