The mass density of superconducting (bismuth, lead)-strontium-calcium-copper-oxide (PBSCCO) cores of silver-sheathed tapes, subject to different states of cold working and thermal treatment, has been determined taking advantage of a modified hydrostatic weighing. It turned out that the densification was more effective the smaller the initial density of the parent material. A core density of about 5 g cm −3 was attained, but could not be exceeded, independent of the deformation method and core density prior to deformation. When starting with high initial densities, drawing even reduced the core density. The density drop increased with reduced diameter reduction per drawing step, whereas rolling improved the core density. Heat treatment (reacting from the 2212 to the 2223 phase) resulted in a small loss of relative density, which raised with increasing core thickness. Nevertheless there is a positive correlation between densities before and after heat treatment. It is therefore important to obtain optimum core densities during the final steps of cold working.

Abstrcrd -Progress has been made in the development of long 2223 phase multifilamentary wire tapes using the powder-intube technique. Ramless extrusion was successfully used to deform multifilamentary Precursor/&-composites of large diameter. After extrusion and wire drawing the mean variation coefficient of filament cross sections along the wire length was determined to be about 10%. Studies of 2223 phase formation in the wire cores have shown, that the conversion of the precursor to 2223 has been accelerated by annealing under reduced 0, pressure compared with air. Critical current densities of 12 Wcm' and about 5 Wcm' (77 K, 0 T) were achieved for the 19 filament wire tapes of 17 m and 100 m length, respectively. JE of tapes of 0.12 mm thickness has been suppressed around a strain value of 0.1 Yo. L INTRODUCTION2223 BiPbSrCaCuO sheathed tapes are the most promising candidate among high-T, superconductors for electric power applications, particularly for uses in electric power transmission cables and transformers. Remarkable progress has been made over the last two years in extending the current carrying capability to 66 kA/cmZ at 77 K for short 2223 samples [l]. The best values of the critical current density (J,) achieved on long-length wires amounts to 20.5kA/cm2 (77K, O T ) for a loom-long multifilamentary wire [2] and 13 kA/cm2 for 300 m long wires [3]. A further improvement of Jc to nearly lo5 Ncmz of long-length conductors is necessary before they can be successfully applied to electric power applications [4]. This requires an intensive study of correlations between parameters of technological processes, microstructure and the Jc of the wires. In this paper the preparation of 19-and 30-filament wires the deformation conditions on the uniformity of crosssectional areas of the multifilaments along the wire length and the critical current density is demonstrated. To eleminate reactions of the precursor with the Ag sheath during heat treatment and to decrease the number of distortions of the microstructure by large second phase particles the formation of the 2223 phase in a reduced 0 2 pressure atmosphere at various temperatures has been studied and the results are summarized in this paper. Furthermore, results of the mechanical performance of the 1 of lengths from 10 to 100 m is described. The influence of I i Manuscript received October 18,1994.This work was supported by th Bundesminister f i r Forschung und Technologie (coneact No: 13 N 5953 and 13 N 6009)wires as degradation of Jc attributed to strain or handling are reported here. IL EXPERIMENTAL METHODSMultifilamentary wires were produced by using the OPIT (oxid-powder-in-tube) process. The details of preparing were published previously [5]. The precursor powders having a stoichiometry of Bi1,8 P h , 4 Sr2 C a 2 ,~ Cu3 0, were prepared by the solid state reaction of reagent grade (3N) reactants. Powders were pressed into rods by cold isostatic pressing (CIP), the rods were put and sealed into Ag tubes and then deformed by swaging and drawing into wires...

Abstraceuperconducting Bi-(2223) multifilamentary tapes with AglWxY, alloy sheaths, with Y=Cu, Mn and Pd, were made by the oxide-powder-in-tube technique. All resistivities of the Ag alloy sheaths exceed that of the pure Ag sheath by at least a factor of 2. The maximam resistivity was achieved for AgwPdl with ~7~1 . 3 pQcm. Tapes sheathed by Ag90Cu10 exceed the critical current density, Jc, of pure Ag sheathed ones. Jc up to 26 W c m 2 were achieved by pressing AgWCulo Sheathed tapes during the thermo-mechanical-treatment, TMT. For thinner AgWCu,, sheathed tapes up to 31 kA/cm2 were obtained employing flat rolling during TMT. Measured lines of thin and thicker tapes with comparable Jc bicker tapes have a larger pinning strength and a better grain texture but thinner ones a better grain-to-grain connectivity.

Bi-2223 multifilamentary tapes with Ag and Ag alloy (AgMn, AgPdAu) sheaths have been fabricated using the OPIT technique. From thermal analysis and XRD investigations one can conclude that the formation rate and microstructure of the Bi-2223 phase is strongly influenced by the occurrence of a liquid phase during the precursor transformation. The parameters of the thermomechanical treatment were optimized such that values of (77 K, 0 T) could be achieved for tapes of a length up to 550 m, independent of the tape length. On Ag alloy sheathed tapes values of were measured. The value of the tensile strength, which can be applied to the tapes without degradation of was doubled by substitution of Ag alloys for pure Ag sheath material.

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