Microstructure and superconducting properties of silver clad Bi-2223 tape produced by sequential pressing

107

The mechanical deformation of BiSrCaCuO/Ag composites made by the powder-in-tube method is a multi-step process. The main difficulty is that the mechanical properties of the ceramic powder are very different from those of the Ag sheath. A key parameter is the core density, which changes during mechanical deformation. In this review, basic concepts of the classical mechanical deformation theory are briefly discussed. Simple descriptions of deformation processes like pressing, rolling, drawing and extrusion are also presented. The term 'freedom parameter', f , is introduced to illustrate the influence of various constraint factors on the mass-flow behaviour. Simple pictures including mass redistribution and the powder-flow model are presented for interpreting the plastic deformation process of the composites. Experimental results are reviewed and our proposed pictures and models are applied for discussion.

Section: Intermediate Mechanical Deformation Between Annealing Of The...mentioning

confidence: 99%

The mechanical deformation of superconducting BiSrCaCuO/Ag composites

Han

Skov-Hansen

Freltoft

1997

107

“…In this paper we will demonstrate that with the new process called 'periodic pressing' (PP) we are able to achieve high j c values on long lengths of Bi(2223) multifilamentary tapes while retaining all the advantages of pressing. The idea is not new: Ashworth et al [10] and Tomsic [11] have already proposed a similar process, and recently Kopera et al [12] described a new technique which combines rolling and pressing. Nevertheless, for the moment their j c values do not correspond to those of optimized short-pressed samples.…”

Section: Introductionmentioning

confidence: 99%

Progress in critical current density of long Bi(2223) tapes deformed by periodic pressing

Marti¹,

Grasso

Huang

et al. 1998

Critical current densities of multifilamentary Ag-sheathed Bi( 2223) up to about 35 000 A cm −2 have been achieved at 77 K and self-field for lengths of several metres using a new route: periodic pressing. This corresponds to an increase by 30-40% compared with the values obtained for conventionally rolled tapes starting with the same powders. Several pressing steps have been introduced during the anneal instead of only the standard rolling step (based on previous studies performed on both mono-and multifilamentary tapes). In contrast to earlier attempts by pressing techniques, periodic pressing is a practical and scaleable process for the fabrication of long lengths of Bi( 2223) conductor as the standard intermediate rolling step. Engineering critical current densities of 8000 A cm −2 have successfully been obtained for tapes with high filling factor (40%). Because of the possibility of applying three or four pressing steps during the whole annealing period, the choice of the first annealing time becomes less stringent, which may constitute an advantage.

“…Clearly realistic development of process anneal and cooling procedures requires a detailed knowledge of the proprietary precursor formulation (figure 2(a)), while a knowledge of the initial compaction process seems to be of less importance (figure 2(b)). Further important issues for this processing route are the control of transverse micromodulations and microcracks by advanced 'sequential pressing' (Ashworth et al 1995), and oxygen partial pressure management during final annealing (Noji et al 1993). For commercial production the development of 'quality control procedures' is of major importance.…”

Section: Incremental Development Of 'Established' Processing Routesmentioning

confidence: 99%

Superconducting materials - the path to applications

Evetts¹

2000

As the application of high-temperature superconductivity gradually becomes a reality it is clear that painstaking incremental progress in the development of materials is the key to success. Superconducting materials can only be applied against an engineering specification that has to be determined for each particular application from the design requirements for economic viability and for operation and safety margins in service. As a consequence the type of research activity appropriate for the development and optimization of a conductor processing route varies depending on the maturity of the technology. In this overview the evolution of research activity will be followed from near market industry driven design and development of fully engineered conductors through to research on basic and enabling science for materials processing that is largely academic and curiosity driven. The most effective path to applications depends on a considered balance of research that is different for each conductor family depending on the state of maturity of the conductor processing route.