Progress in critical current density of long Bi(2223) tapes deformed by periodic pressing

Abstract

Critical current densities of multifilamentary Ag-sheathed Bi( 2223) up to about 35 000 A cm −2 have been achieved at 77 K and self-field for lengths of several metres using a new route: periodic pressing. This corresponds to an increase by 30-40% compared with the values obtained for conventionally rolled tapes starting with the same powders. Several pressing steps have been introduced during the anneal instead of only the standard rolling step (based on previous studies performed on both mono-and multifilamentary tapes). In contrast to earlier attempts by pressing techniques, periodic pressing is a practical and scaleable process for the fabrication of long lengths of Bi( 2223) conductor as the standard intermediate rolling step. Engineering critical current densities of 8000 A cm −2 have successfully been obtained for tapes with high filling factor (40%). Because of the possibility of applying three or four pressing steps during the whole annealing period, the choice of the first annealing time becomes less stringent, which may constitute an advantage.

PHASE FORMATION AND TEXTURE DEVELOPMENT IN AG-SHEATHED Bi, Pb(2223) TAPES STUDIED BY DIFFERENT IN-SITU AND EX-SITU DIFFRACTION TECHNIQUES

“…Therefore, the large difference of critical current between pressed and rolled tapes does not seem to be due to the different texture induced by the different deformation processes. By measuring the standard rocking curve on the surface of peeled tapes and the anisotropy of transport critical current in magnetic field, Marti et al found that periodically pressed tapes exhibited the best critical current but the worst texture [5,8]. These results are not in contradiction with the present data.…”

“…Firstly, multifilamentary tapes at different thermo-mechanical treatment stages and produced using different mechanical deformation techniques were measured at room temperature, in order to understand the effect of the mechanical deformation on the structural and physical properties of the tapes. 37-filament tapes were produced by standard Wire-In-Tube technique starting from a nominal cation ratio Bi:Pb:Sr:Ca:Cu=2.8:0.4:2.0:2.2:3.0 and then either rolled or uniaxially pressed at each deformation step, as described in [8]. The samples were quenched in air as shown in Table 1.…”

“…The temperature was controlled by a Pt-PtRhlO% thermocouple in contact with the sample. The samples were heated (following the standard procedure as in [8]) up to 837°C and then held at the annealing temperature for 20 hours. As our main interest concerned the phenomena occurring into the precursor Bi,Pb(2212) phase prior to the transformation into the Bi,Pb(2223) phase, the whole phase transformation was not completed.…”

Achievement of practical level critical current densities in Ba1−xKxFe2As2/Ag tapes by conventional cold mechanical deformation

“…However, it should be emphasized that practical application of uniaxial pressing process to manufacture of long length wires require specialized machine for continuous pressing the tape. Fortunately, there have been successful attempts at production of long Ag/Bi-2223 wires by periodic pressing [43] and eccentric rolling [44], which might be also applied for the production of long length Ba122 wires with high transport J c .…”

Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides

“…However, it should be emphasized that practical applications of uniaxial pressing for the manufacture of long length tapes require specialized machines for continuous pressing of the tape. Fortunately, there have been successful attempts at producing long Bi-2223/Ag wires by periodic pressing [506] and eccentric rolling [507], which might be also applied for the production of long length Ba-122 wires with high transport J c . Ba(Sr)-122/Ag tape conductors show very small field dependence of J c with small J c anisotropy.…”