1997 TMS Annual Meeting: Monday Abstracts

HIGH TEMPERATURE SUPERCONDUCTORS: Session I: BSCCO Conductor Development

Session Chairpersons: Gye-Won Hong, Superconductivity Research Laboratory, KAERI, Taejeon, Korea; P. Haldar, Intermagnetics General Corp., Latham, NY

8:30 am INVITED

POWER APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTORS: P. Haldar, M.S. Walker, D.W. Hazelton, J.G. Hoehn, Jr., Intermagnetics General Corporation, Latham, NY 12208

Intermagnetics has concentrated on manufacturing long lengths of silver sheathed Bi-2223 and surface coated Bi-2212 HTS conductor. Development work has led to the successful manufacture of Bi-2223 multifilament conductor in lengths exceeding 1 km, with properties useful for most electric power applications. Surface coated, low cost, Bi-2212 conductor in lengths over 400 meters are now also being produced. Several lengths of high performance tapes have already been delivered to GE to wind the first HTS generator coil. The coils were successfully tested in a steady state, conduction cooled environment generating 40,000 amp-turns at 23.5 K. Novel and unique hybrid magnet designs are being designed and built with the availability of both Bi-2212 and Bi-2223 HTS conductors. The demonstration and test of a pre-prototype 1 MVA transformer utilizing HTS windings is planned in collaboration with ORNL, Waukesha Electric, and RG&E. The development of the largest HTS coils is continuing, for the construction of a 15 KV fault current limiter as part of the DOE-SPI program with Lockheed Martin, Southern California Edison, and LANL. Several high amp-turn coils have also been fabricated and delivered to the U.S. Navy to demonstrate a high horse power HTS homopolar motor. These demonstrations indicate the rapid progress being made to develop commercial applications of high-temperature superconductors.

8:50 am INVITED

CONTROLLED PRECIPITATION OF SECOND PHASES IN (Bi,Pb)2223 CERAMICS AND ITS INFLUENCE ON THE PINNING: P. Majewski, S. Kaesche, A. Sotelo, F. Aldlinger, Max-Planck-Institut für Metallforschung, Pulvermetallurgisches Laboratorium, Heisenbergstr. 5, D-70569 Stuttgart

Taking the temperature dependent Pb solubility of (Bi,Pb)2+xSr2Ca2Cu2O10+d [(Bi,Pb)2223] into account, it is possible to precipitate various second phases in single phase (Bi,Pb)2223 ceramics at temperatures below 840°C, i.e., Pb4Sr5CuO10, Ca2CuO3, CuO and Bi2Sr2CaCu2O8 (Bi2212). At 800°C, the kinetic of the formation is fast resulting in mm-sized second phase precipitates after about 6 h. The Jc of the samples increases with precipitation, indicating increased pinning properties of the ceramics. After a maximum increase of Jc at about 3 h, Jc decreases again.

9:10 am INVITED

EFFECT OF LEAD CONTENT ON PHASE EVOLUTION AND MICROSTRUCTURAL DEVELOPMENT IN Ag-CLAD Bi-2223 COMPOSITE CONDUCTORS: N.N. Merchant, V.A. Maroni, A.K. Fischer, S.E. Dorris, W. Zhong, N. Ashcom, Argonne National Laboratory, Argonne, IL 60439

Silver-sheathed monofilamentary Bi1.8PbxSr1.98Ca1.97Cu3.08Oy (Bi-2223) tapes prepared by a two powder process that used powder containing varying lead contents, x, from 0.2 to 0.5 were subjected to thermomechanical processing and then characterized by XRD, SEM and EDX. Texture was studied using image analysis software on scanned SEM images. It was found that tapes with low lead content (0.20 and 0.25) showed incomplete conversion to Bi-2223, had small grain size, and poor c-axis texture. Tapes having higher lead content (0.4 and 0.5) also showed incomplete conversion and the presence of lead-rich secondary phases. Tapes with lead contents of 0.30 and 0.35 showed complete conversion to Bi-2223, had the least amount of secondary phases, showed best c-axis texture, and had the highest Jc. The carbon content of the precursor powder also had a strong influence on secondary phase chemistry. Work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of a DOE program to develop electric power technology, under Contract W-31-109-Eng-38.

9:30 am INVITED

EFFECT OF PARTICLE SIZE REDUCTION ON THE MICROSTRUCTURE EVOLUTION AND CRITICAL CURRENT DENSITY OF Ag/Bi-2223 TAPES: Weon-Ju Kim, Jae-Keun You, Ho Jin Lee, Hee-Gyoun Lee, Gye-Won Hong, Superconductivity Research Laboratory, Korea Atomic Energy Research Institute, P.O. Box 105, Taejon 305-600, Korea

The effects of the particle size of precursor powder on the microstructure and Jc of Ag-sheathed Bi-2223 tapes were investigated. The calcined powder with overall composition of Bi1.89Pb0.41Sr2.01Ca2.23Oy was milled for various times using planetary ball mill. The transport property of the tapes was found to depend strongly on the particle size of the precursor powder. Enhanced reactivity of the milled powder facilitated the formation of 2223 phase and resulted in an increase of Jc. Excessive milling, however, led to the amorphisation of the powder and degraded the electrical property of the tapes.

9:50 am

EFFECTIVE FABRICATION PRACTICES FOR Ag-SHEATHED SUPERCONDUCTOR: D.-W. Yuan, M. J. Pollock, J. Kajuch, Concurrent Technologies Corporation, Johnstown, PA 15904

The powder-in-tube (PIT) process has been widely used to fabricate long lengths of superconducting wires and tapes. However, problems associated with irregularly shaped cross sections resulting from the metalworking process have been identified and need to be addressed. In this investigation, Ag-clad Bi2Sr2CaCu2O8 superconductors were formed by using different wire drawing and tape rolling practices. The effects of annealing and drawing direction on geometric characteristics of the round wires were determined. Also, the impact of reduction in thickness per pass and roll configuration on the properties of the tapes was investigated. The study shows that geometrical uniformity and core dimensional stability are strongly influenced by the rolling parameters chosen. A combination of small roll diameter and small reduction per pass reduces dimensional variations. This practice also leads to higher critical current densities at cryogenic temperatures in the resulting superconducting tapes. Recommendations for optimum fabrication schemes for wires and tapes are presented.

10:10 am BREAK

10:20 am

FABRICATION OF TUBULAR SUPERCONDUCTOR STRUCTURES: J.F. Bingert, T.G. Holesinger, B.L. Bingham, D.A. Korzekwa, MST-6, LosAlamos National Laboratory, Los Alamos, NM 87545

A tubular architecture provides many potential attributes when applied to bulk superconductor structures. These include enhanced structural stability compared to wires and tapes, and isotropic field dependence transverse to the conductorís long axis. At the same time, virtues associated with traditional OPIT processing may be preserved, such as a thin, dense HTSC layer with basal-plane texture. In this study, candidate deformation processing routes for tubular composite conductors were investigated in order to determine their potential to produce desired structures and properties. These processes included tube drawing, tube ironing, and hydrostatic extrusion. For tube drawing and ironing, an HTSC precursor form was isostatically pressed over a mandrel, while the hydrostatic extrusion billet was manually loaded with powder. The as-deformed and sintered tubes were characterized for geometric uniformity, density, texture, and transport properties. An analysis of the relative stress states encountered during tube processing compared with rolling will also be presented.

10:40 am INVITED

MECHANICAL DEFORMATION AND INHOMOGENEITY OF BiSrCaCuO/Ag COMPOSITES: Z. Han and T. Freltoft, NKT Research Center A/S, Sognevej 11, DK-2605, Brøndby, Denmark

The mechanical deformation of BiSrCaCuO/Ag composites is generally an inhomogeneous process. Inadequate control of the deformation process results in sausaging and cracking, degrading the superconducting properties of the composite and reducing its mechanical strength. In this paper, we will apply our model of "powder flow" to describe the mechanical deformation process of BiSrCaCuO/Ag composites wires and tapes. Furthermore, results from experiments using a new deformation method "semi-continuous pressing" will be presented. By this method, it is possible to produce superconducting tapes with better homogeneity than obtained by conventional rolling. The influence of mechanical deformation on the strength of the tape, especially the bending strength, will also be discussed.

11:00 am INVITED

HIGH TEMPERATURE SUPERCONDUCTOR DEVELOPMENT AT TOSHIBA: HIGH TENSILE STRENGTH AgMg(Ni) SHEATHED Bi-2223 CONDUCTOR AND COILS: Y. Yamada, K. Yamamoto, K. Tasaki, H. Onoda, O. Horigami, Toshiba R&D Center, 4-1, Ukishima-Cho, Kawasaki, 210 Japan; T. Koizumi, T. Hasegawa, Showa Electric Wire and Cable Co., Ltd., 2-1-1, Odaskae, Kawasaki 210, Japan; T. Kiyoshi, K. Inoue, National Research Institute for Metals, 1-2-1, Sengen, Tukuba, Ibaraki 305, Japan

Recent activity of high temperature superconductors and its application at Toshiba will be presented. We have been developing high tensile strength conductor using AgMg(Ni) sheath material. Short samples exhibited 200 MPa of 0.2% yield strength which was 4 times to 10 times higher than that of the conventional Ag-sheathed conductor and also higher than the Nb8Sn conductor. Recently the high tensile strength conductor 100 m long was successfully fabricated and wound for the energizing test at 21 Tesla back up filed. The coil was successfully excited without any degradation. We have been also studying the effect of sausaging on critical current density. The sausaging started to occur clearly when the Vickers hardness of the oxide core was higher than that of Ag sheath. This implies that the harder sheath materials such as AgMg sheath may suppress the sausaging and improve critical current density.

11:20 am

RECENT DEVELOPMENTS IN THE FABRICATION OF HIGH-Jc Ag-CLAD (Bi,Pb)2Sr2Ca2Cu3Oy CONDUCTORS: U. Balachandran, A.N. Iyer, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439; M. Lelovic, T. Deis, N.G. Eror, Dept. of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, PA 15261; P. Haldar, Intermagnetics General Corp., Latham, NY 12110

We have resolved the issue of current distribution inside Ag-clad (Bi,Pb)2Sr2Ca2Cu3Oy (Bi-2223) superconductor tapes by showing that the region of high critical current density (Jc) is next to the Ag sheath. In this talk, we report a Jc value >105 A/cm2 at 77 K in a self-field in Bi-2223 tapes made by the Ag-wire-in-tube method, in which a silver wire was introduced into the Ag tube. The Ag wire extended along the entire length of the tape. At 77 K and in self-field, a maximum Jc of 2 x 105 A/cm2 (critical current, Ic, = 22 A) was measured after three pressing cycles. Recently, we analyzed the transport current properties of Ag-clad Bi-2223 tapes as a function of cooling rate. A comparison between furnace-cooled and slow-cooled tapes showed that the slow-cooled tapes reached Ic values two or three times higher than those of the furnace-cooled tapes. Based on our observations, a cooling schedule that includes several intermediate cooling steps is suggested and will be discussed in this talk. Work at ANL and part of the work at IGC is supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of a DOE program to develop electric power technology, under Contract W-31-109-Eng-38.

11:40 am INVITED

DEVELOPMENT OF HTS-POWER TRANSMISSION CABLES AND RESISTIVE FAULT CURRENT LIMITERS: H.-W. Neumüller, Siemens AG, Corporate Research and Development, P.O. Box 3220, D-91050 Erlangen, FRG

Our long-term joint project covers both the development of HTS conductors and the realization of junction models demonstrating the feasibility of future prototypes. Multifilament 2223 BPSCCO tapes are reproducibly produced having jc-s up to 30 kA/cm2 for short samples and jc 20 kA/cm2 for lengths 110m. In a first step two layer 10 m cable dfunction model was machine wound, which showed a current capacity of 1100 A. No degradation was found under bending tests down to bending radii of 1 m. The switching elements for resistive fault current limiters consist of ceramic plates with meander shaped YBCO coatings. Two ways are investigated: both polycrystalline YSZ substrates coated by biaxially in plane oriented IBAD YSZ buffer layers (pc) and single crystal sapphire substrates (sc). 10x10 cm2 pc switching elements have been produced up to a switching power of 1500 VA (jc=60 kA/cm2). Improvements of the large scale IBAD-deposition raised jc above 105 A/cm2, small samples (1x1 cm2) attained jc=1 MA/cm2, 10x10 cm2 pc- or alternatively ø sc switching elements are the basis of the proposed 100 kVA function model.