The property of (Bi,Pb)-2223 Ag-AgCu sheathed superconductors with varioussheath assemblages

In this paper the Ag-AgCu3 (Ag-97%, Cu-3%) sheathed (Bi,Pb)-2223 supercondu ctors with the different sheath assemblages were manufactured and investiga ted with the help of I-c measurement, X-ray diffraction (XRD) and scanning electron microscope observation, thermal stability and bending and straight ening measurements. The sheath assemblages were designed to be four forms a ccording to the special assemblage of the two sheath materials in the inner and outer sheath of the multi-filament conductors, which include inner Ag (inner)-Ag (outer), Ag (inner)-AgCu3 (outer), AgCu3 (inner)-Ag (outer) and AgCu3 (inner)-AgCu3 (outer). Deformation observation for the four series of the samples indicates that there are different deformation degrees for the se samples. Using AgCu3 as the outer sheath can improve the homogeneous def ormation of the multi-filament tapes. Therefore, there needs different inte rmediate rolling reductions for the four series of the samples in order to achieve the best transport capacity. XRD measurements indicate that there a re different amounts of 2223 in the four series of the conductors. Samples using Ag as the inner sheath and AgCu3 as the outer sheath have the largest amount of 2223 and the lowest amounts of the secondary phases, whereas sam ples using AgCu3 as the inner sheath have the lowest amount of 2223 and the largest amounts of the secondary phases. The thermal stability experiment shows that the transport capacity of the samples using AgCu3 as the outer s heath can be stabilized until the fifth circle, whereas the I-c values can be stabilized only until the third circle for the samples using Ag as the o uter sheath. The best result is achieved for the samples using Ag as the in ner sheath and AgCu3 as the outer sheath. The bending experiment shows the samples using AgCu3 as the outer sheath have better transport property duri ng the bending treatment. The critical tensile stress of the samples using AgCu3 as the outer sheath is about one time larger than that of the standar d Ag sheathed samples. From the aspects of the deformation and mechanical s trength, samples using AgCu3 as the inner and outer sheath is a good choice . But considering the contamination of the sheath element on the ceramic co re during the heat treatment in the samples using AgCu3 as the inner sheath , samples using Ag as the inner sheath and AgCu3 as the outer sheath may be an ideal choice in manufacturing of the Ag-AgCu sheathed conductors. This design not only avoids the contamination of the sheath element on the ceram ic core but also is comparable in the deformation and mechanical strength a spects with that of the samples using AgCu3 as the inner and outer sheath. On the other hand, if adjusting the chemical composition of the ceramic cor e to fit the contamination of the sheath element, the choice using AgCu3 as the inner and outer sheath may also be a good choice. Using AgCu3 as the i nner sheath and Ag as the outer sheath is obviously unsuitable for manufact uring of the alloy sheathed conductors even compared with that of the stand ard Ag sheathed conductors. (C) 2001 Elsevier Science B.V. All rights reser ved.