Microstructure and electromagnetic properties of Bi-2223 Ag alloy sheathedtapes prepared by a controlled melting process

The Bi-2223 superconducting tapes with the sheath of Ag-Au-Al and Ag-Au-Mg alloys were fabricated by the controlled melting (CM) process. It was found that the CM process is effective for eliminating weak links and improving the transport properties of Bi-2223 Ag alloy sheathed tapes. In the CM proc ess, part of Bi-2223 is decomposed to Bi-2212 and nonsuperconducting phases because of a short time melting, and then can be recovered in the subseque nt press-sinter cycles. In the fully CM-processed tapes, finely dispersed B i-2212 and secondary phase particles in well-aligned Bi-2223 matrix can be observed. Meanwhile, the improved magnetic field dependence of magnetizatio n and transport critical current density has been achieved through the CM p rocess. The compressive stress in the Ag alloy/oxide interface induced by t he fast cooling is decreased due to the low thermal conductivity of Ag allo y sheath. There is no microcracking observed at the interface of the fast-c ooled sample. (C) 2000 Published by Elsevier Science B.V.