Study of microstructures of Ag-sheathed (BiPbSrCaCuO) multifilamentary tapes in various stages of processing
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Study of microstructures of Ag-sheathed (BiPbSrCaCuO) multifilamentary tapes in various stages of processing R. K. Wang and X. H. Wang General Institute of Non-Ferrous Metals, Beijing 100088, China
R. Bhasale, H. K. Liu, and S. X. Dou Centre for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522, Australia (Received 26 December 1996; accepted 25 April 1997)
Microstructures of 27-filament (Bi, Pb)2 Sr2 Ca2 Cu3 O101x (BPSCCO 2223) tape at various stages of repetitive rolling and sintering have been investigated using TEM and SEM. It was found that the dislocation density increases with increasing sintering time with the maximum dislocation density of 1012ycm2 achieved for tapes sintered for 220 h. The interface between Ag-sheath and oxide core was observed to be wavelike. Small irregular 2223 colonies and cracks in the oxide cores were often observed near the Ag-sheath/oxide core interface. Repetitively rolled and sintered specimen with a total sintering time of 220 h was observed to have optimum phase purity of 2223 phase. Prolonged sintering results in recrystallization of the 2223 grains, degrading the texture of the oxide core.
I. INTRODUCTION
High critical current densities (Jc ) of Ag-clad, Bibased superconducting tapes have been reported by a number of research groups.1–4 In order to improve the critical current density of Ag-sheathed superconducting tape, it is essential to understand the correlation of Jc with the microstructure of the tape. There have been numerous studies on the microstructures of single filament tapes using transmission electron microscope (TEM) techniques.5–10 The Ag-sheathed (Bi, Pb)2 Sr2 Ca2 Cu3 O101x (PBSCCO 2223) multifilamentary tapes have been reported to withstand higher bend strain and tensile strain than that of single filament tape.12,13 It is therefore evident that the multifilamentary tape is more suitable for practical applications, in particular, for cables, coils, and magnetic windings where a high flexibility is required. Recently, the Jc of multifilamentary tape has been significantly improved in comparison with that of single filament tape. Furthermore, the interface area of Agycore for multifilamentary tapes is substantially larger than single core tapes. It would therefore be interesting to investigate the microstructures of multifilamentary tape during the process of fabrication using TEM techniques. In the present paper, we report the results on the study of microstructures of a 27-multifilament Agsheathed PBSCCO 2223 tape at the various stages of processing. II. EXPERIMENTAL PROCEDURE
The Ag-sheathed BPSCCO 2223 multifilamentary tapes studied here were prepared by using the powderJ. Mater. Res., Vol. 13, No. 2, Feb 1998
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in-tube technique as described previously.11 The powder was prepared by codecomposition of metal nitrate solutions having the cation ratio Bi : Pb : Sr : Ca : Cu 1.8 : 0.35 : 1.91 : 2.05 : 3.06. The powde
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