Influence of rolling pressure on microstructures and current path evolution in Ag-sheathed Bi2223 monocore tapes

The influence of rolling pressure on microstructures and current transports has been investigated on Ag-sheathed Bi2223 monocore tapes, fabricated by a rolling process while changing mechanical load (i.e., rolling pressure). In combination with metallurgical studies, analyses on trapped-magnetic fields in a remanent state by a scanning Hall sensor show the evolution in transport current paths in the superconductor core, and also reveal critical current distributions therein. Enhancement of transport critical current density J/sub c/ at 77 K and 0 T with an increase in rolling pressure P up to /spl sim/0.3 GPa is ascribed to the evolution in transport current paths due to strengthening grain connectivity. Degradation in J/sub c/ with a further increase in P exceeding 0.3 GPa is caused by the occurrence of a sausaging effect. An optimum value of P is determined by a competition between strengthening grain connectivity and the occurrence of the sausaging effect. Numerical calculations on magnetic profiles give a variation of current capacity along a width direction in the core, so the local J/sub c/ value at the edge is 4-5 times greater than the value at the center.