Pressed and cold rolled Ag-sheathed Bi(2223) tapes: A comparison

Abstract High critical current densities in monofilamentary Ag-sheathed tapes of Bi(2223) have been obtained on tapes produced by different deformation techniques. For cold rolled tapes of > 1 m in length, promising critical currents of j c (77 K, 0 T)=18500 A cm -2 have been measured. These tapes have a relatively weak dependence of j c vs. B their corresponding value j c (77 K, 1 T) being 3550 A cm -2 . The present results on cold rolled tapes are compared to those of typical short uniaxially pressed tapes of j c (77 K, 0 T)=26000 A cm -2 and j c (77 K, 1 T)=5200 A cm -2 . This comparison reveals both for 4.2 and 77 K a weaker field dependence of j c for the rolled tapes with respect to the pressed ones. At zero field, the rolled tapes exhibit lower j c values, but reach higher j c values at high fields, the crossover occuring at 3 T for 77 K and at 14 T for 4.2 K. The j c (4.2 K, 15 T) value for rolled Bi(2223) tapes is 4.7×10 4 A cm -2 . The rolled tapes also exhibit a stronger anisotropy at 4.2 K, where the ratio j c⊥ / j c‖ at 10 T is 2.2 compared to 1.5 for pressed tapes. Scanning electron microscopy and X-ray diffraction analysis are extensively used to investigate the microstructure of the Bi(2223) phase in the two samples.