Current transport and microstructural development in BSCCO tapes and joints fabricated by groove rolling

Abstract

The powder-in-tube technique, which includes wire drawing and rolling, has been widely used to fabricate superconducting tapes for possible electric power applications. In the present study the starting billet was reduced in size by groove rolling instead of by wire drawing. To optimize the deformation and thermomechanical treatment processes, BSCCO wires of various dimensions were fabricated. The wires were flat rolled to a final thickness of 250 μm. Short-length tapes were subjected to a series of thermal and deformation steps. Phase development and microstructural development during the process were monitored by XRD, SEM and TEM. Current transport properties of the tapes were determined in the temperature range of 20-77 K in self-field. Thermomechanical treatment resulted in tapes with average critical current densities of 18 000 A cm-2 at 77 K. High-resolution electron microscopy revealed better texturing and grain structure at the superconductor-silver interface. Superconducting lap- and butt-joints have been formed by a chemical etching technique. Detailed microstructural and current transport profiles of the joints have also been measured.