Engineering critical current density improvement in Ag-Bi-2223 tapes

Ag alloy sheathed Bi-2223 multifilament tapes were produced by the powder-in-tube method. Engineering critical current density improvement has been achieved through both enhancement of critical current density by control of the thermal behavior of oxide powder and by an increase of the filling factor of the tapes. Phase evolution at initial sintering stage has been studied by a quench experiment in Ag-Bi-2223 tapes. The content, texture, and microstructure of various phases were determined by XRD and SEM. A novel process approach has been invented in which square wire was chosen rather than round wire as a preform prior to the flat rolling that achieved more homogenous filament distribution. Filament geometry and density were simulated by finite element modeling. The tapes with large filling factor up to 45% have been produced with a hard metal outer sheath, which facilitates the superconductor composite sustaining large proportional oxide ceramics in the composite during drawing and rolling process. By optimization of the thermal and mechanical process, a J_c of 12 kA/cm² has been achieved in a 0.18×3.1 mm² size tape which carried 67 A