Processing, microstructure and critical current density of 2223 BPSCCO/Ag tapes

Abstract

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...

The effect of the configuration of the silver layer on texture growth and microstructure in silver-sheathed superconducting tape

“…Third, it can be explained that there exists an optimal P O2 for 2223 phase formation in Ag/Bi(2223) tape at a fixed temperature [18]. For example, the optimal P O2 is 6 × 10 3 Pa at T = 830 • C. Under such conditions, 2223 phase formation was higher than 80% after the tape had been sintered for 20 h, whereas tape sintered in air under identical conditions contained only 2% of that phase.…”

Study of BSCCO core density in multicore Ag sheathed tapes by microhardness profiles

“…The importance of density in the BSCCO core of Ag sheathed tapes has been reported several times in the literature [1][2][3][4][5]. It was shown by Yamada et al [1] and by Parrell et al [2] that high transport current densities (J c ) reflect core density prior to heat treatment.…”

“…Since the hardness, i.e. the resistance to indentation, can be easily measured, it has frequently been used as a measure of core density for tapes made by the oxygen powder-in-tube process (OPIT) [1][2][3][4][5][6]. Measurement of microhardness profiles (MHP) can be very useful for the study of core density under any deforming process [3].…”

The effects of hydrostatic pressure on the BSCCO compound for the OPIT procedure

“…The proper fraction of core to sleeve volume and small core cross sections reduce the magnetic self-field and lead to a higher overall fraction of better aligned and dense core material close to the silver/superconductor interface [2]. Hydrostatic extrusion allows one to control the fill factor over a much wider range than wire-drawing, which is a very important factor for applicable superconductors [5,[20][21][22][23][24][25].…”

“…One of the most important factors is the fill factor, namely the ratio of the ceramic core to the overall conductor cross section. The 'pre-drilled' method offers higher fill factors, which generally, for conventional methods of deformation (swaging, drawing), do not exceed 30% [5,[20][21][22][23][24][25]. However, this method has two disadvantages.…”