Superconductor technology: apparatus – material – process – High temperature – per se – Having tc greater than or equal to 150 k
Patent
1990-06-11
1992-03-31
Dean, W.
Superconductor technology: apparatus, material, process
High temperature , per se
Having tc greater than or equal to 150 k
505739, 505740, 29599, 428595, 428673, 428677, H01L 3924
Patent
active
051008670
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for manufacturing wires or strips from high-temperature superconductors, wherein a superconductive material is prepared from oxidic powders through mixing, compressing, sintering and grinding, as well as through thermal treatment, and is then given the desired cross-section through profiling. If need be, the thermal treatment can also include metallurgical melting steps. In addition, the invention relates to the encasing members that are particularly necessary for the extrusion process.
It is well known to manufacture wires or strips from classic superconductors, particularly such as NbSn alloys. Since the discovery of the new, high-temperature superconductive materials (HTSC) it has already been suggested to process them into wires or strips. For example, prior German Patent Application P 3 721 147.1 proposes first grinding a homogenous, superconductive material to render it finely grained, and then filling suitable encasing members, for example, tubing or pockets made of highly cold-forming metals, with the finely grained material, and then giving the filled encasing members the desired cross-section through cold deformation. Before the encasing member is filled, the process steps grinding, compressing, sintering and heat treatment, in particular, is supposed to be repeated as often as needed until the desired homogeneity and superconductivity of the material is achieved.
What has been problematical for the wires and strips manufactured from high-temperature superconductive materials up until now is the current carrying capacity. Generally, it does not yet meet actual requirements. Usually, the conductive materials available to date are prepared by deforming the powder at room temperature. By this means, one essentially only achieves a compacting of the powder.
The object of the invention is therefore to create a manufacturing process which will improve the current carrying capacity of the wires and/or strips that are produced.
The objective is solved according to the invention by combining the following process steps: produced; metallic encasing member with a degree of deformation of at least 90%; strip.
According to process step (a) of the invention, before extrusion, the blank can be subjected to an additional heat treatment The isostatic compressing can be carried out in a cold isostatic process (the so-called CIP process) or also in a hot isostatic process (the so-called HIP process). The extrusion can take place alternatively as a forward, reverse or also as an isostatic extrusion.
The method according to the invention can be carried out with high-temperature superconductive materials based on four-component systems, such as in particular yttrium-barium-copper-oxygen (Y-Ba-Cu-O) or lanthanum-strontium-copper-oxygen (La-Sr-Cu-O), or based on five-component systems, such as in particular bismuth-strontium-calcium-copper-oxygen (Bi-Sr-Ca-Cu-O) or thallium-barium-calcium-copper-oxygen (Tl-Ba-Ca-Cu-O). Practical analyses were performed on Y-Ba-Cu-O materials in particular.
It was discovered within the scope of the invention that one achieves an increase in the current carrying capacity particularly by applying the hot-forming process to high-temperature superconductive materials. This is due to the fact that one succeeds in selectively orientating the crystallites in the extrusion process. Particularly decisive in the case of Y-Ba-Cu-O materials is the existence of the tetragonal phase in the superconductive material with a deformation starting at temperatures of 700.degree. C. According to the publication, "X-Ray Studies of Helium-Quenched Ba.sub.2 YCu.sub.3 O.sub.7 -.sub.x " from ADVANCED CERAMIC MATERIALS, Vol. 2, No. 3B, Special Issue (1987), pp. 624-631, with O<X=.delta.<0.5, in the case of this material, the orthorhombic structure is transformed into the tetragonal structure at approximately 700.degree. C. During the extrusion process at the elevated temperature, there must not be a reaction with the encasing member. This is provided for in particular, by in
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Grosse Joachim
Gunzelmann Karl-Heinz
Herkert Werner
Muller Reiner
Tiefel Gunter
Dean W.
Siemens Aktiengesellschaft
Wyszomierski George
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