Novel Processing of Hts Based Conductors
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NOVEL PROCESSING OF HTS BASED CONDUCTORS D. S. GINLEY*, E. L. VENTURINI*, J. F. KWAK*, R. J. BAUGHMAN*, R. J. BOURCIER*, M. A. MITCHELL*, B. MOROSIN*, J. W. HALLORAN**, M. J. NEAL**, and D. W. CAPONE*** *Sandia National Laboratories, Albuquerque, NM 87185 **CPS Superconductor, Milford, MA 01757 ***Supercon, Shrewsbury, MA 01545 Abstract Conductor development is one of the major long term goals in high temperature superconductor research. In this paper we report on two promising processing technologies that have been utilized to produce superconducting HTS conductors. First, melt spun YBa.Cu307 fibers rapid thermal processed for 1-8 sec at 950 to 1075°C have Ta's to 92 K, JC's to 1100 A/cm 2 and the orthorhombic twinned morphology typical for high quality YBa 2Cu3O 7 . A processing matrix of time, temperature and composition for these fibers shows that slightly CuO-rich starting compositions give the best results. Second, silver tube encapsulated wires of Bi .7Pb0 3Sr2Ca 2Cu3010 have been made by extrusion, wire drawing and cold rolling. The resulting tapes show orientation of the crystallites, zero resistance up to 100K and improved magnetic hysteresis above 50 K. The combination of mechanical reprocessing and extended thermal anneals near 850'C appears to significantly improve these materials. Introduction The development of high current conductors from high temperature superconductors that can operate in high magnetic fields remains the greatest challenge in HTS research. To accomplish this, three major obstacles will have to be overcome. First is the brittle ceramic nature of the materials, which will necessitate composite structures to ensure mechanical and electrical integrity. Second is the weak link nature of the ceramics whereby the grain boundaries act as Josephson type junctions, inherently limiting critical currents. Third is the weak flux pinning observed in these materials which could severly limit their applicability in high magnetic fields. All of these problems will necessitate the development of new processing technologies which optimize the materials properties for the various applications. Because of the differences in the materials properties in the Y-Ba-Cu-O, Bi-Sr-Ca-Cu-0 and TI-Ca-Ba-Cu-O systems, the processing technologies will probably be materials specific. This is especially true of the YBa 2Cu 30 7 material which has a phase change and oxygen equilibrium problems in the processing range of interest, but is the most highly pinned of the current superconductors with Tc > 77K.[1] In this paper we investigate two different processing techniques which seem particularly well suited to a particular materials system. Data will be presented for the rapid thermal processing [2-4] of melt spun YBa 2Cu30 7 (Y-123) fibers [5] and for the mechanical extrusion and cold rolling followed by extended thermal anneals for Ag sheathed wires in the Bi(Pb)-Sr-CaCu-0 system [6,7]. Rapid thermal processing (RTP) of melt spun (Y-123) fibers has yielded wires with T..0 of up to 92 K and J, to 1100 A/cm 2. We have
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