PRESSED AND COLD-ROLLED AG-SHEATHED BI(2223) TAPES - A COMPARISON

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 occurring 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 4.7X10(4) A cm(-2). The rolled tapes also exhibit a stronger anisotropy at 4.2 K, where the ratio j(c) perpendicular to/j(c) parallel to 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.