Solid-state joining of multifilamentary Bi-2223/Ag superconducting tapes

For practical application of Bi-2223/Ag superconducting tapes, development of effective joining technologies is required. The conventional method consists of first cold-pressing preassembled joints under 600-2400MPa and then annealing for 50-200 h: this normally leads to significant degradation of the base tape superconductivity. In this study, a one step solid-state joining method with and without powder interlayers was investigated. Compared with the conventional method, direct pressure during the solid-state joining was beneficial to metallurgical bonding, shortening of joining time and reducing degradation of the base tape. Three factors, including a high content of 2223 (Bi 2Sr2Ca2Cu3Oχ) phases, an adequate addition of Ag powders in the interlayer and a suitable retention of Ag sheath in the lapping-window, all could improve the microstructures and superconducting-bonding quality of the joints. The best joints, for which average critical current reached up to 85% of the base tape value, were obtained by solid-state joining with direct pressure, without added interlayer material and utilizing lapping-windows with an optimum amount of Ag sheath remaining at the faying surface.