MICROSTRUCTURAL EVOLUTION OF THE BSCCO-2223 DURING POWDER-IN-TUBE PROCESSING

This paper reports a study of the microstructural changes that occur when BSCCO powder is processed by the powder-in-tube method. In this study the initial powder consisted of the 2212 phase plus second phases containing Ca, Cu, Sr, and Pb. When the material was drawn, there was no alignment of the 2212 phase and the second phase particles remained large and blocky. Rolling induced a small amount of alignment into the 2212 phase so that its c-axis was perpendicular to the rolling direction. Rolling also caused the second phase particles to become flatter. When these rolled samples were annealed at 828 degrees C, the core sintered into a platelet structure, and there was an increase in the amount of aligned material, particularly after annealing treatments of 16 and 32 h. After 8 h at 828 degrees C, the 2212 variant of the superconducting phase began to transform to the 2223 variant. Pressing this structure improved the alignment, and annealing after pressing allowed further conversion of the 2212 phase to the 2223 phase and apparently removed the strains produced by the pressing. Repeated pressing improved the alignment and repeated annealing allowed more conversion of 2212 to 2223. Both the improved alignment, produced by pressing, and the transformation of 2212 to 2223, produced by the anneals, caused the superconducting properties of the material to improve.