The effect of mechanical deformation on silver-core interface and critical current density in Ag-Bi-2223 single- and multifilament tapes

Ag sheathed Bi-2223 tapes were prepared by the powder-in-tube method. A smooth Ag-oxide interface was obtained by decreasing the number of annealing steps, annealing temperature and time and wire size prior to flat rolling and by varying reduction per pass during flat rolling. For fabrication of multifilamentary tapes, the fill geometry and fill number are controlled to accord with deformation symmetry and homogeneity. The particle size of precursor powder was found to have more effect on 'sausaging' in multifilamentary tape than monofilamentary tape. The difference in the deformation resistance between Ag sheath and oxide core was considered to explain and predict the 'sausaging' effect. A higher degree of deformation is more beneficial for achieving higher J(c) in the tapes made by square rolled wire than the tapes made by the conventional drawing method. However, the square rolling method is not suitable for fabricating multifilamentary tape because strong inhomogeneity of deformation is introduced by this method. Tapes with a 0.07 mm thickness can be made using flat rolling without any 'sausaging' effect. In the case of square rolled wire, the J(c0) reaches 4.2 x 10(4) A cm(-2) with J(c)(1 T, H parallel to ab plane)/J(c0) of about 20% at 77 K for the pressed tapes while J(c0) values of 3.5 x 10(4) A cm(-2) and 2.5 x 10(4) A cm(-2) are achieved in rolled single- and 16-filament tapes respectively. More reproducible results with a J(c0) in the range of (3-3.3) x 10(4) A cm(-2) for pressed tapes and (2.65-2.8) x 10(4) A cm(-2) for rolled tapes are achieved by conventional drawing approach in 19-filament tapes. Also, high J(c)(1 T, H parallel to ab plane)/J(c0) values of 21 and 18% were obtained for pressed and rolled 19-filament tape, respectively.