Effects of pressing on the current flow in a Ag/Bi-2223 tape

The effects of compressive deformation on the current flow in a Ag/Bi-2223 tape have been investigated by pressing tape annealed at 840 degrees C for 50 h with various pressures. It was observed that the critical current, I-c, was gradually decreased with pressure and reached zero at a pressure of 600 MPa. After further annealing the pressed tape at 840 degrees C for 50 h, I-c, for the pressure smaller than 100 MPa, decreased with pressure and reached zero at a pressure of 100-200 MPa whereas I-c for pressure larger than 200 MPa increased with pressure. Low I-c of the tape processed with lower pressure was explained by small cold deformation energy insufficient to heal the destroyed current path during pressing and the thermal stress arisen during heating. The resistance of Ag/Bi-2223 tape to thermal stress was markedly decreased at the presence of pre-existing cracks. It is considered that the formation of microcracks, the sausaging effect and the hardening of Bi-2223 core were closely related with the fact that the strain of Bi-2223 core with pressure revealed nearly linear increase to a pressure of 600 MPa and then increased fast from a pressure of 800 MPa. (C) 1998 Elsevier Science B.V.