Microstructure and transport current path in Ag-sheathed (Bi,Pb)(2) Sr2Ca2Cu3Ox monofilamentary tapes rolled at different pressures

Ag-sheathed (Bi,Pb)(2)Sr2Ca2Cu3Ox monofilamentary tapes have been fabricate d by a rolling process including an intermediate sintering step while chang ing mechanical load. The influence of rolling pressure on microstructure an d transport current paths has been investigated through a scanning Hall sen sor together with conventional metallurgical studies. An increase in rollin g 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 comp etition between strengthening grain connectivity and occurrence of sausagin g effect. Calculations by modeling current loops reveal a variation in loca l J(c) values along a width direction. The J(c) value at the edge is 4-5 ti mes greater than the value at the center. This is consistent with recent st rip-cutting experiments. (C) 2000 Elsevier Science Ltd and Techna S.r.l. Al l rights reserved.