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

Abstract

In this paper the Ag–AgCu3 (Ag-97%, Cu-3%) sheathed (Bi,Pb)-2223 superconductors with the different sheath assemblages were manufactured and investigated with the help of I c measurement, X-ray diffraction (XRD) and scanning electron microscope observation, thermal stability and bending and straightening measurements. The sheath assemblages were designed to be four forms according 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 these samples. Using AgCu3 as the outer sheath can improve the homogeneous deformation of the multi-filament tapes. Therefore, there needs different intermediate rolling reductions for the four series of the samples in order to achieve the best transport capacity. XRD measurements indicate that there are 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 samples 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 sheath 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 outer sheath. The best result is achieved for the samples using Ag as the inner sheath and AgCu3 as the outer sheath. The bending experiment shows the samples using AgCu3 as the outer sheath have better transport property during 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 standard Ag sheathed samples. From the aspects of the deformation and mechanical strength, samples using AgCu3 as the inner and outer sheath is a good choice. But considering the contamination of the sheath element on the ceramic core 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 ceramic core but also is comparable in the deformation and mechanical strength aspects 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 core 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 inner sheath and Ag as the outer sheath is obviously unsuitable for manufacturing of the alloy sheathed conductors even compared with that of the standard Ag sheathed conductors.