Effect of intermediate rolling on the microstructure and Je performance of Ag-sheathed Bi-2223 tapes

The effect of intermediate rolling (IR) deformation on the microstructure and engineering critical current density, Je (77 K, 0 T), has been investigated on Ag-sheathed Bi-2223 multifilamentary tapes. The experiment results showed that intermediate rolling reduces porosity, breaks down large deleterious secondary phases, and improves the alignment of Bi-2223 grains. All these effects strengthen the grain connectivity and therefore enhance the Je value of the tape. Degradation in Je with a further increase in IR reduction is caused by the introduction of more cracks that cannot be completely healed in subsequent heat treatment. Je reaches a maximum value with an optimum IR reduction, which is determined by a competition between grain connectivity improvement and introduction of cracks. As a function of IR reduction, the degree of texturing in HTS oxide core also shows a similar peak value. XRD analysis demonstrates that the optimum IR reduction depends also on the volume fraction of Bi-2212 after the initial heat treatment.