Microstructure and transport current path in Ag-sheathed (Bi,Pb) 2 Sr 2Ca 2Cu 3O x monofilamentary tapes rolled at different pressures

Abstract

Ag-sheathed (Bi,Pb) 2 Sr 2Ca 2Cu 3O x monofilamentary tapes have been fabricated by a rolling process including an intermediate sintering step while changing mechanical load. The influence of rolling pressure on microstructure and transport current paths has been investigated through a scanning Hall sensor together with conventional metallurgical studies. An increase in rolling pressure up to 0.27 GPa enhances the transport critical current density J c through an improvement of grain connectivity. A further increase in the pressure i.e. >0.3 GPa lowers the J c value significantly by occurrence of a sausaging effect. The optimum rolling pressure is determined by a competition between strengthening grain connectivity and occurrence of sausaging effect. Calculations by modeling current loops reveal a variation in local J c values along a width direction. The J c value at the edge is 4–5 times greater than the value at the center. This is consistent with recent strip-cutting experiments.