US20170072470A1 - Method for producing a monofilament for an Nb3Sn superconductor wire - Google Patents
Method for producing a monofilament for an Nb3Sn superconductor wire Download PDFInfo
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- US20170072470A1 US20170072470A1 US15/361,541 US201615361541A US2017072470A1 US 20170072470 A1 US20170072470 A1 US 20170072470A1 US 201615361541 A US201615361541 A US 201615361541A US 2017072470 A1 US2017072470 A1 US 2017072470A1
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
- 229910000657 niobium-tin Inorganic materials 0.000 title claims description 31
- 239000002887 superconductor Substances 0.000 title description 2
- 238000005253 cladding Methods 0.000 claims abstract description 54
- 239000000843 powder Substances 0.000 claims abstract description 46
- 229910052802 copper Inorganic materials 0.000 claims abstract description 20
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 11
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- 229910052718 tin Inorganic materials 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 35
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- 239000010955 niobium Substances 0.000 description 25
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 17
- 238000000137 annealing Methods 0.000 description 13
- 239000000203 mixture Substances 0.000 description 9
- 238000007792 addition Methods 0.000 description 5
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- 229910052719 titanium Inorganic materials 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000003780 insertion Methods 0.000 description 3
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- 229910052715 tantalum Inorganic materials 0.000 description 3
- 238000005491 wire drawing Methods 0.000 description 3
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 2
- 229910000967 As alloy Inorganic materials 0.000 description 1
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- 239000000654 additive Substances 0.000 description 1
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- 239000004020 conductor Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- KUNSUQLRTQLHQQ-UHFFFAOYSA-N copper tin Chemical compound [Cu].[Sn] KUNSUQLRTQLHQQ-UHFFFAOYSA-N 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
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- 239000011265 semifinished product Substances 0.000 description 1
- 229910000679 solder Inorganic materials 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Images
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- B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
- B22F5/12—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of wires
-
- B22F1/0003—
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/09—Mixtures of metallic powders
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
- B22F7/02—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers
- B22F7/04—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers with one or more layers not made from powder, e.g. made from solid metal
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C13/00—Alloys based on tin
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C30/00—Alloys containing less than 50% by weight of each constituent
- C22C30/02—Alloys containing less than 50% by weight of each constituent containing copper
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
- H01F41/048—Superconductive coils
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F6/00—Superconducting magnets; Superconducting coils
- H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
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- H01L39/12—
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- H01L39/2403—
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- H01L39/2409—
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0128—Manufacture or treatment of composite superconductor filaments
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0184—Manufacture or treatment of devices comprising intermetallic compounds of type A-15, e.g. Nb3Sn
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/80—Constructional details
- H10N60/85—Superconducting active materials
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/20—Refractory metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/30—Low melting point metals, i.e. Zn, Pb, Sn, Cd, In, Ga
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2303/00—Functional details of metal or compound in the powder or product
- B22F2303/01—Main component
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49014—Superconductor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12014—All metal or with adjacent metals having metal particles
- Y10T428/12028—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]
- Y10T428/12063—Nonparticulate metal component
- Y10T428/12069—Plural nonparticulate metal components
- Y10T428/12076—Next to each other
Definitions
- the invention concerns a method for the production of a monofilament for a superconducting wire, the monofilament comprising:
- Nb 3 Sn is a widely used superconducting material, in particular, for the production of superconducting magnet coils.
- Nb 3 Sn superconducting wires achieve technically relevant current densities in higher magnetic fields.
- the production and processing of Nb 3 Sn superconducting wires is difficult, since Nb 3 Sn is a relatively brittle material and can therefore not be plastically deformed (or only to a minimum extent).
- Nb 3 Sn wires are usually produced in accordance with the bronze route, the internal tin diffusion technology, or the powder-in-tube technology (PIT). In all three cases, the production is divided into semi-finished product manufacture on the one hand and reaction annealing on the other hand. Brittle Nb 3 Sn is generated only during reaction annealing. Deformation of the superconducting wire is normally not carried out after reaction annealing.
- a powder mixture containing Sn is disposed in an inner tube, which is normally made of copper, and the inner tube is, in turn, introduced into an outer tube, which is normally made of Nb.
- the outer tube is, in turn, arranged in a round conductive matrix tube (cladding tube), which is normally made of Cu. A plurality of these monofilaments can be bundled.
- This object is achieved by a method for producing a monofilament of the above-mentioned type, and having an inner tube made of Nb or an alloy containing Nb.
- the method comprises the steps of:
- the inner tube is produced from Nb or an alloy containing Nb, one obtains a finer and more homogeneous structure of Nb 3 Sn grains after reaction annealing, in particular, in the area of the previous boundary surface between the inner tube and the powder core compared with the use of an inner tube of copper. Cavities (e.g. gaps) in this area are also prevented or at least reduced after reaction annealing. Both result in a significant increase in the superconducting current carrying capacity of the finished superconducting wire. The inventors have observed an increase in the critical current density by a factor of 1.5 to 2.
- the reaction front of Nb 3 Sn that advances to the outside is moreover easier to control during reaction annealing.
- breakthroughs of the reaction front into the cladding tube (matrix) and consequently contamination of the cladding tube (which is made of Cu in most cases) can be easily prevented.
- the residual resistance of the cladding tube can be kept low (or the RRR value can be kept high).
- the powder core contained in the inner tube can be well compacted by the inner tube in a drawing process prior to insertion into the outer tube.
- the main part of the niobium required to form Nb 3 Sn can be provided by the outer tube such that the inner tube can be designed to have relatively thin walls.
- the inner tube typically has an Nb content of at least 80 weight %, preferably at least 90 weight %.
- the inner tube is moreover typically free of copper.
- the powder core typically contains a mixture of different powders of different compositions, inter alia Cu which is required to accelerate formation of Nb 3 Sn.
- Cu is preferably present in elementary form whereas Sn is generally present at least partially in the form of an alloy (preferably alloyed with Nb).
- the cladding tube has a hexagonal outer cross-section and a round inner cross-section.
- an outer tube having a round outer cross-section (and round inner cross-section) can be inserted, the outer cross-section of which does not have to be changed within the scope of bundling processes. It is, in particular, no longer necessary to impress a hexagonal outer cross-section onto the cladding tube in a drawing step of the monofilament, which would also result in an approximately hexagonal outer cross-section of the previously round outer tube (the inner cross-section would remain substantially round). For this reason, the outer tube can maintain a uniform wall thickness, in particular, also at the beginning of reaction annealing.
- Nb 3 Sn can then be uniformly formed from the inside into the outer tube without fear of premature breakthrough of Sn into the cladding tube at a thin point, and no unreacted corner areas remain.
- a particularly large portion of the cross-sectional area of the monofilament can correspondingly react to Nb 3 Sn which is then available for the superconducting current transport. Since the reacted volume of Nb 3 Sn can moreover transport a relatively high current density due to its fine structure, the advantages of the invention exponentiate in this embodiment to yield a particularly high current carrying capacity for each monofilament or for the overall superconducting wire.
- the cladding tube may also have a round outer cross-section. For subsequent bundling, it is then necessary to impress a hexagonal outer cross-section in a drawing step.
- the inner tube has a round inner cross-section and a round outer cross-section and the outer tube has a round inner cross-section and a round outer cross-section.
- the reaction of Sn with Nb to Nb 3 Sn may be performed particularly evenly, in particular with a (circular) round reaction front in the monofilament.
- the powder core has a content of 2 weight % to 12 weight % of Cu, preferably 3 to 9 weight % of Cu, wherein the powder core preferably contains elementary Cu powder.
- the Cu addition in the powder core has a catalytic effect for the formation of Nb 3 Sn and reduces the reaction temperature.
- a copper content in the powder core of up to 5 weight % is often already sufficient to achieve an efficient reaction. Due to the omission of an inner tube of copper, the overall copper content in the reaction area of the monofilament can be selected relatively freely, in particular, to be lower than if an inner tube of copper were used. Distribution of copper in the reaction area, in particular uniformly in the powder core, is moreover also improved.
- the powder core is compacted in the inner tube, in particular with a density of at least 40%, preferably at least 50% of the theoretical density.
- the compaction can, in particular, be realized by a drawing process of the filled inner tube prior to insertion into the outer tube.
- the (pre)compaction improves the overall plastic deformability of the finished conductor (precursor of the superconducting wire) prior to reaction annealing.
- the powder core contains NbSn 2 and/or Nb 6 Sn 5 and/or elementary Sn. These materials can be well used as tin sources within the scope of the present invention. In most cases, a combination of two or also of all three materials is used.
- the inner tube and/or the outer tube are produced from an alloy containing Nb and containing Ta and/or Ti, in particular, with a summed content of at least 0.5 weight % of Ta and/or Ti, and in particular, with a summed content of maximally 10 weight % of Ta and/or Ti.
- Small additions of tantalum and/or titanium have a positive influence on the forming kinetics and on the structure of Nb 3 Sn and increase the achievable critical current density.
- the overall additions of tantalum and titanium should preferably maximally amount to 10 weight % in order to avoid undesired phases. Hf or Zr could also be used as alloy additions.
- the inner tube and the outer tube are produced from different materials.
- the inner and outer cladding tubes can consequently be designed to have different properties.
- the inner tube may, in particular, be selected through suitable composition and/or structural adjustment such that the outer side of the inner tube is minimally deformed during filling in the powder core and during a drawing process in order to facilitate subsequent insertion into the outer tube.
- the outer tube can e.g. consist of NbTa7.5 and the inner tube of Nb.
- the materials of the inner tube and of the outer tube could alternatively also be selected to be the same.
- the cladding tube is made of Cu. Copper has high conductivity and can therefore protect the Nb 3 Sn filament as a parallel current path close to it in case of a quench (loss of superconductivity).
- step b) is preferably performed prior to step c).
- the undrawn inner tube preferably has thin walls, e.g. with a ratio between wall thickness and outer diameter of 1/25 to 1/60, thereby achieving particularly high compaction of the powder core in step a).
- the cladding tube already has a hexagonal outer cross-section prior to step b). For this reason, bundling of the monofilaments does not require drawing to obtain a hexagonal outer cross-section and the outer tube can remain round inside and outside. A large portion of the cross-section of each monofilament can be used for forming Nb 3 Sn having a very homogeneous and fine structure. This leads to particularly high superconducting current carrying capacities (see above).
- the present invention also concerns a method for producing a precursor of a superconducting wire, characterized by the following steps:
- step a′ the monofilament(s) already has/have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube prior to drawing, and the drawn monofilaments also have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube after drawing.
- the monofilaments are thus merely “radially compressed” during drawing in step a′). This is particularly simple and prevents an outer shape change of the cladding tube from also being impressed inside, e.g. on the outer tube.
- the invention also concerns a precursor of a superconducting wire, produced by an inventive method as described above.
- a superconducting wire having particularly high current carrying capacity can be produced from the precursor.
- the invention also concerns a method for producing a superconducting wire from an inventive precursor of a superconducting wire as described above, characterized by the following steps:
- step e′ temperature treatment is terminated in step e′) before a reaction front that advances to the outside has reached the boundary surface between the outer tube and the cladding tube.
- the cladding tubes then provide powerful current paths parallel to the Nb 3 Sn filaments to protect the superconducting wire from burning through. Since advance of the reaction front during temperature treatment is relatively uniform, it is easy to find a suitable point in time for cooling in order to terminate the reaction advance for different wire geometries by means of a few tests with different annealing periods.
- the reaction fronts can be easily recognized e.g. in cross-section via a scanning electron microscope.
- the invention also concerns a superconducting wire produced by an inventive method as described above.
- the superconducting wire has a particularly high current carrying capacity as already described above.
- FIG. 1 shows a schematic cross-sectional view of a first embodiment of an inventive monofilament with hexagonal cladding tube
- FIG. 2 shows a schematic cross-sectional view of a second embodiment of an inventive monofilament with round cladding tube
- FIG. 3 shows a schematic cross-sectional view of an embodiment of an inventive precursor of a superconducting wire
- FIG. 4 shows a schematic diagram of the production of an inventive monofilament
- FIG. 5 shows a schematic diagram of the production of an inventive superconducting wire
- FIG. 6 shows a schematic cross-sectional view of a section of an inventive superconducting wire in the area of a monofilament.
- FIG. 1 schematically shows a first embodiment of an inventive monofilament 1 in cross-section perpendicular to its longitudinal direction.
- the monofilament 1 has an inner tube 2 which consists of niobium in the illustrated embodiment.
- a powder core 3 of a mixture of, in the present case, NbSn 2 powder, Sn powder and Cu powder is disposed in the inner tube 2 .
- the content of Cu in the mixture is approximately 5 weight % and the content of Sn in the mixture is typically at least 50 weight %.
- the inner tube 2 is arranged in an outer tube 4 which consists of NbTa7.5 in the present case.
- the outer side of the inner tube 2 thereby directly abuts the inner wall of the outer tube 4 .
- the inner tube 2 and the outer tube 4 each have (circular) round inner and outer cross-sections.
- the outer tube 4 is, in turn, arranged in a cladding tube 5 which consists of elementary copper in the present case.
- the cladding tube 5 has a round inner cross-section in the illustrated embodiment such that the outer tube 4 abuts the cladding tube 5 over the whole surface.
- the outer cross-section of the cladding tube 5 is hexagonal (“hexagonal tube”), thereby increasing the area portion of the finished superconducting wire that can be utilized for Nb 3 Sn.
- the main source of Nb for the reaction heat treatment is the outer tube 4 .
- the inner tube 2 enables good compaction of the powder core 3 in a previous drawing step (see also FIG. 4 in this context) due to its comparatively thin wall.
- the ratio VD between the outer diameter D outertube outside of the outer tube 4 and the outer diameter D innertube outside of the inner tube 2 is approximately 1.65 in the embodiment shown.
- the ratio VW between the wall thickness W outertube of the outer tube 4 and the wall thickness W innertube of the inner tube 2 is moreover approximately 4.2.
- the inner tube 2 , the outer tube 4 and the cladding tube 5 are arranged concentrically. No solder is required for the monofilament 1 .
- FIG. 2 schematically shows a second embodiment of an inventive monofilament 1 in cross-section perpendicular to its longitudinal extension.
- the second embodiment of the monofilament 1 largely resembles the embodiment of FIG. 1 , in particular, with respect to the inner tube 2 , the powder core 3 and the outer tube 4 .
- the cladding tube 5 here is provided with a (circular) round outer cross-section. For this reason, the monofilament 1 is easy to manufacture.
- the cladding tube 5 is also produced of elementary copper and has a (circular) round inner cross-section.
- FIG. 3 shows a cross-section perpendicular to its longitudinal extension of an embodiment of an inventive precursor 10 of a superconducting wire.
- a plurality of drawn monofilaments 11 (in the present case seven as an example), which are each produced from one monofilament by means of a filament drawing process, are bundled in a wire cladding tube 12 (“casing tube”) in the precursor 10 , and are subsequently subjected to an extrusion and/or wire drawing process in order to reduce the cross-section.
- the wire cladding tube 12 is preferably produced of elementary copper. Cavities at the inner edge of the wire cladding tube 12 are prevented or filled by means of filling profiles 13 which are preferably produced of elementary copper.
- the monofilaments had a hexagonal outer cross-section (see FIG. 1 ) already prior to the filament drawing process such that the monofilaments were only radially compressed during the filament drawing process.
- the outer tubes 4 in the drawn monofilaments 11 correspondingly still have a round outer cross-section.
- the round outer cross-section of each outer tube 4 is maintained even after the extrusion and/or wire drawing process of the precursor 10 .
- the reaction front of Nb 3 Sn can uniformly and concentrically approach the outer edge of the outer tube 4 during reaction annealing. There are no particularly thin points where Sn could prematurely break through into the cladding tube 5 . Nor are there particularly thick points where residual Nb not utilized for the reaction to Nb 3 Sn protrudes.
- FIG. 4 shows a schematic diagram of the respective cross-sections of the specified components for producing an inventive monofilament 1 .
- the inner tube 2 is filled with the powder core 3 and subjected to a drawing step a).
- the cross-section of the comparatively thin-walled inner tube 2 is thereby reduced and the powder core 3 is compacted.
- the non-filled outer tube 4 is furthermore inserted into the cladding tube 5 (in the present case of hexagonal outer cross-section) in one step b).
- the steps a) and b) can thereby be performed in arbitrary order or also simultaneously.
- step c) the drawn and filled inner tube 2 is subsequently introduced into the outer tube 4 which is already arranged in the cladding tube 5 .
- the drawn and filled inner tube may also be initially inserted into the outer tube and the outer tube can subsequently be inserted into the cladding tube (not separately shown).
- FIG. 5 schematically illustrates the production process of a superconducting wire 20 from monofilaments 1 as produced e.g. in accordance with FIG. 4 .
- a monofilament 1 is transformed into a drawn monofilament 21 by drawing in step a′) (“filament drawing process”).
- the cross-sectional surface area is thereby reduced. If the monofilament 1 already has a hexagonal outer cross-section (as illustrated in FIG. 5 ), drawing merely effects radial compression. This is preferred since in this case, a round outer cross-section of the outer tube 4 can be easily obtained after drawing. If the monofilament 1 has a non-hexagonal outer cross-section (e.g. a round outer cross-section) a hexagonal outer cross-section is also impressed during drawing according to a′).
- a non-hexagonal outer cross-section e.g. a round outer cross-section
- a hexagonal outer cross-section is also impressed during drawing according to a′).
- a plurality of drawn monofilaments 21 are then bundled in a wire cladding tube 12 in step b′).
- the number of drawn monofilaments is thereby basically arbitrary.
- Seven drawn monofilaments 21 are bundled in the illustrated variant.
- the monofilaments in the core area can be replaced by hexagonal Cu elements.
- step c′ Extrusion and/or drawing is subsequently performed in step c′) (“wire drawing process”) which is again accompanied by a reduction in cross-section, thereby obtaining a precursor 10 of a superconductor.
- This precursor 10 already has the cross-sectional shape and cross-sectional size of the subsequent superconducting wire but can still be plastically deformed.
- the precursor 10 For finishing the superconducting wire, the precursor 10 must be shaped in step d′) so as to have the shape required for the superconducting wire as determined by the desired application.
- the application concerns a magnet coil 23 .
- the precursor 10 is correspondingly wound onto a carrier 22 .
- reaction annealing of the formed precursor is subsequently carried out in step e′).
- the magnet coil 23 is put into a furnace 24 that is heated to a temperature of maximally 700° C.
- Sn from the powder cores reacts with Nb of the inner and outer tubes in the monofilaments of the precursor to Nb 3 Sn at these temperatures.
- Temperature treatment is terminated before the reaction front reaches the outer edge of the outer tubes.
- the formed precursor has been transformed into a superconducting wire 20 by means of the temperature treatment, the Nb 3 Sn filaments of which can carry an electrical current (with corresponding cooling e.g. with liquid helium) practically without ohmic losses.
- the superconducting wire 20 should not be deformed again after temperature treatment in order to prevent breaking of the enclosed brittle Nb 3 Sn filaments.
- FIG. 6 is a schematic cross-section illustrating a section of the superconducting wire 20 in the area of a temperature-treated monofilament 61 .
- a reaction front 62 has radially advanced from the inside to the outside in a temperature-treated monofilament 61 and has generated a relatively homogeneous fine-grained area 63 of Nb 3 Sn.
- the reaction front 62 has not completely crossed the outer tube 4 but has left a circumferential border 64 of non-reacted material of the outer cladding tube 4 (in the present case of NbTa7.5, i.e. Nb with 7.5 weight % Ta).
- the border 64 has an approximately uniform thickness S over its entire circumference.
- the thickness S is adjusted by the temperature treatment program to be just sufficiently large in order to reliably prevent breakthrough of Sn into the matrix 65 (formed from previous cladding tubes) of copper, thereby maintaining the electrical conductivity of the matrix 65 at a high level. Due to the round outer cross-section of the outer tube 4 , a large portion of the cross-sectional area of the superconducting wire 20 can react to Nb 3 Sn. In particular, there are no remaining useless bulges of material of the outer tube 4 (as would be generated at the edges of an outer tube having an outer hexagonal cross-section).
- the round outer cross-section of the outer tube 4 can already be obtained prior to drawing of the monofilaments (see step a′) in FIG. 5 ) through a hexagonal outer cross-section of the cladding tubes.
- a residual core 66 resulting from the powder core with a reduced amount of Sn generally remains in the temperature-treated monofilament 61 .
- the temperature-treated monofilament 61 is substantially free of gaps and cavities
Abstract
A monofilament (1) for the production of a superconducting wire (20) has a powder core (3) that contains at least Sn and Cu, an inner tube (2), made of Nb or an alloy containing Nb, that encloses the powder core (3), and an outer tube (4) in which the inner tube (2) is arranged. The outer side of the inner tube (2) is in contact with the inner side of the outer tube (4) and the outer tube (4) is produced from Nb or from an alloy containing Nb. The outer tube is disposed in a cladding tube. The superconducting current carrying capacity of the superconducting wire is thereby improved.
Description
- This application is a continuation of Ser. No. 14/198,618 filed Mar. 6, 2014 and also claims Paris convention priority from
EP 13 159 230.5 filed on Mar. 14, 2013, the entire disclosures of which are hereby incorporated by reference. - The invention concerns a method for the production of a monofilament for a superconducting wire, the monofilament comprising:
-
- a powder core that contains at least Sn and Cu,
- an inner tube that encloses the powder core,
- an outer tube in which the inner tube is arranged, wherein the outer side of the inner tube is in contact with the inner side of the outer tube, and wherein the outer tube is made from Nb or an alloy containing Nb, and
- a cladding tube in which the outer tube is arranged.
- A monofilament of this type is disclosed by EP 0 169 596 A1.
- Nb3Sn is a widely used superconducting material, in particular, for the production of superconducting magnet coils. In comparison with other metallic low-temperature superconducting materials (such as NbTi), Nb3Sn superconducting wires achieve technically relevant current densities in higher magnetic fields. However, the production and processing of Nb3Sn superconducting wires is difficult, since Nb3Sn is a relatively brittle material and can therefore not be plastically deformed (or only to a minimum extent).
- Nb3Sn wires are usually produced in accordance with the bronze route, the internal tin diffusion technology, or the powder-in-tube technology (PIT). In all three cases, the production is divided into semi-finished product manufacture on the one hand and reaction annealing on the other hand. Brittle Nb3Sn is generated only during reaction annealing. Deformation of the superconducting wire is normally not carried out after reaction annealing.
- With respect to powder-in-tube technology, as disclosed e.g. by EP 0 169 596 A1, a powder mixture containing Sn is disposed in an inner tube, which is normally made of copper, and the inner tube is, in turn, introduced into an outer tube, which is normally made of Nb. The outer tube is, in turn, arranged in a round conductive matrix tube (cladding tube), which is normally made of Cu. A plurality of these monofilaments can be bundled. Due to reaction annealing, during which Sn from the powder mixture reacts with Nb from the outer tube to form Nb3Sn with the catalytic assistance of Cu from the inner tube or as an additive to the powder mixture, one obtains a superconducting wire with high superconducting current carrying capacity using that powder-in-tube technology.
- H. Veringa et al., Adv. Cryo. Eng. (Materials), 1984; 30, pages 813-821 disclose a superconducting wire, wherein NbSn2 powder with addition of Cu is introduced into an Nb tube, the Nb tube is introduced into a hexagonal copper tube, and several copper tubes filled in this fashion are arranged in a bundling tube of copper and are temperature-controlled after extrusion and drawing. A similar procedure is also disclosed by A.C.A. van Wees et al., IEEE Trans. Magn., MAG 19, 556 (1983), pages 5-8.
- It is the object of the present invention to further increase the superconducting current carrying capacity of the superconducting wire.
- This object is achieved by a method for producing a monofilament of the above-mentioned type, and having an inner tube made of Nb or an alloy containing Nb. The method comprises the steps of:
-
- a) filling the powder core into the inner tube;
- b) drawing, following step a), the inner tube, thereby compacting the powder core;
- c) inserting the outer tube into the cladding tube; and
- d) inserting, following step b), the drawn, filled inner tube into the outer tube, wherein step c) is performed prior to or after step d).
- Due to the fact that the inner tube is produced from Nb or an alloy containing Nb, one obtains a finer and more homogeneous structure of Nb3Sn grains after reaction annealing, in particular, in the area of the previous boundary surface between the inner tube and the powder core compared with the use of an inner tube of copper. Cavities (e.g. gaps) in this area are also prevented or at least reduced after reaction annealing. Both result in a significant increase in the superconducting current carrying capacity of the finished superconducting wire. The inventors have observed an increase in the critical current density by a factor of 1.5 to 2.
- The reaction front of Nb3Sn that advances to the outside is moreover easier to control during reaction annealing. In particular, breakthroughs of the reaction front into the cladding tube (matrix) and consequently contamination of the cladding tube (which is made of Cu in most cases) can be easily prevented. In correspondence therewith, the residual resistance of the cladding tube can be kept low (or the RRR value can be kept high).
- The use of an inner tube of Nb or an alloy containing Nb surprisingly did not entail noticeable problems with the deformation behavior, e.g. during drawing of the filled inner tube only, during drawing of the monofilament or during drawing of a precursor of a superconducting wire with several drawn monofilaments. In particular, there was no increase in filament breakage in the reacted superconducting wire.
- The powder core contained in the inner tube can be well compacted by the inner tube in a drawing process prior to insertion into the outer tube. The main part of the niobium required to form Nb3Sn can be provided by the outer tube such that the inner tube can be designed to have relatively thin walls.
- The inner tube typically has an Nb content of at least 80 weight %, preferably at least 90 weight %. The inner tube is moreover typically free of copper. The same applies to the outer tube. The powder core typically contains a mixture of different powders of different compositions, inter alia Cu which is required to accelerate formation of Nb3Sn. Cu is preferably present in elementary form whereas Sn is generally present at least partially in the form of an alloy (preferably alloyed with Nb).
- In one particularly advantageous embodiment of the inventive monofilament, the cladding tube has a hexagonal outer cross-section and a round inner cross-section. In this case, an outer tube having a round outer cross-section (and round inner cross-section) can be inserted, the outer cross-section of which does not have to be changed within the scope of bundling processes. It is, in particular, no longer necessary to impress a hexagonal outer cross-section onto the cladding tube in a drawing step of the monofilament, which would also result in an approximately hexagonal outer cross-section of the previously round outer tube (the inner cross-section would remain substantially round). For this reason, the outer tube can maintain a uniform wall thickness, in particular, also at the beginning of reaction annealing. Nb3Sn can then be uniformly formed from the inside into the outer tube without fear of premature breakthrough of Sn into the cladding tube at a thin point, and no unreacted corner areas remain. A particularly large portion of the cross-sectional area of the monofilament can correspondingly react to Nb3Sn which is then available for the superconducting current transport. Since the reacted volume of Nb3Sn can moreover transport a relatively high current density due to its fine structure, the advantages of the invention exponentiate in this embodiment to yield a particularly high current carrying capacity for each monofilament or for the overall superconducting wire. As an alternative to this embodiment, the cladding tube may also have a round outer cross-section. For subsequent bundling, it is then necessary to impress a hexagonal outer cross-section in a drawing step.
- In one preferred embodiment, the inner tube has a round inner cross-section and a round outer cross-section and the outer tube has a round inner cross-section and a round outer cross-section. In this case, the reaction of Sn with Nb to Nb3Sn may be performed particularly evenly, in particular with a (circular) round reaction front in the monofilament.
- In a preferred further development of this embodiment, the following applies:
-
1.2≦D outertube outside /D innertube outside≦2.0 - with Doutertube outside:outer diameter of the outer tube and Dinnertube outside:outer diameter of the inner tube.
- In another preferred
further development 4≦Woutertube/Winnertube≦50 with Woutertube:Wall thickness outer tube and Winnertube:Wall thickness inner tube. These ranges of diameter ratios and wall thickness ratios have turned out to be advantageous in practice. In particular, there was no increase in filament breakage in the reacted superconducting wire. - In another advantageous embodiment, the powder core has a content of 2 weight % to 12 weight % of Cu, preferably 3 to 9 weight % of Cu, wherein the powder core preferably contains elementary Cu powder. The Cu addition in the powder core has a catalytic effect for the formation of Nb3Sn and reduces the reaction temperature. In practice, a copper content in the powder core of up to 5 weight % is often already sufficient to achieve an efficient reaction. Due to the omission of an inner tube of copper, the overall copper content in the reaction area of the monofilament can be selected relatively freely, in particular, to be lower than if an inner tube of copper were used. Distribution of copper in the reaction area, in particular uniformly in the powder core, is moreover also improved.
- In another preferred embodiment, the powder core is compacted in the inner tube, in particular with a density of at least 40%, preferably at least 50% of the theoretical density. The compaction can, in particular, be realized by a drawing process of the filled inner tube prior to insertion into the outer tube. The (pre)compaction improves the overall plastic deformability of the finished conductor (precursor of the superconducting wire) prior to reaction annealing.
- In one preferred embodiment, the powder core contains NbSn2 and/or Nb6Sn5 and/or elementary Sn. These materials can be well used as tin sources within the scope of the present invention. In most cases, a combination of two or also of all three materials is used.
- In another advantageous embodiment, the inner tube and/or the outer tube are produced from an alloy containing Nb and containing Ta and/or Ti, in particular, with a summed content of at least 0.5 weight % of Ta and/or Ti, and in particular, with a summed content of maximally 10 weight % of Ta and/or Ti. Small additions of tantalum and/or titanium have a positive influence on the forming kinetics and on the structure of Nb3Sn and increase the achievable critical current density. In accordance with this embodiment, the overall additions of tantalum and titanium should preferably maximally amount to 10 weight % in order to avoid undesired phases. Hf or Zr could also be used as alloy additions.
- In another preferred embodiment, the inner tube and the outer tube are produced from different materials. The inner and outer cladding tubes can consequently be designed to have different properties. The inner tube may, in particular, be selected through suitable composition and/or structural adjustment such that the outer side of the inner tube is minimally deformed during filling in the powder core and during a drawing process in order to facilitate subsequent insertion into the outer tube. The outer tube can e.g. consist of NbTa7.5 and the inner tube of Nb. The materials of the inner tube and of the outer tube could alternatively also be selected to be the same.
- In another advantageous embodiment, the cladding tube is made of Cu. Copper has high conductivity and can therefore protect the Nb3Sn filament as a parallel current path close to it in case of a quench (loss of superconductivity).
- In accordance with the present invention, step b) is preferably performed prior to step c). The undrawn inner tube preferably has thin walls, e.g. with a ratio between wall thickness and outer diameter of 1/25 to 1/60, thereby achieving particularly high compaction of the powder core in step a).
- In one particularly advantageous variant of the inventive method for producing a monofilament, the cladding tube already has a hexagonal outer cross-section prior to step b). For this reason, bundling of the monofilaments does not require drawing to obtain a hexagonal outer cross-section and the outer tube can remain round inside and outside. A large portion of the cross-section of each monofilament can be used for forming Nb3Sn having a very homogeneous and fine structure. This leads to particularly high superconducting current carrying capacities (see above).
- The present invention also concerns a method for producing a precursor of a superconducting wire, characterized by the following steps:
-
- a′) drawn monofilaments having a hexagonal outer cross-section are produced by drawing one or more inventive monofilaments;
- b′) a plurality of drawn monofilaments are bundled in a wire cladding tube;
- c′) the wire cladding tube that contains the bundled and drawn monofilaments, is extruded and/or drawn, thereby obtaining the precursor of the superconducting wire. The contact between the inner tube and the outer tube can be improved by the drawing step according to a′) (in particular, any gaps can be closed) and further compaction can be achieved such that more monofilaments can be bundled in step b′). The size of the monofilaments and, if required, the shape of the monofilaments can be adjusted for step b′). The precursor of the superconducting wire is given the size and cross-sectional shape required for the application (e.g. a magnet coil to be wound) in step c′). The wire cladding tube is typically produced of Cu in order to ensure a low residual resistance.
- In one variant of the inventive method of producing a precursor of a superconducting wire, in step a′) the monofilament(s) already has/have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube prior to drawing, and the drawn monofilaments also have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube after drawing. The monofilaments are thus merely “radially compressed” during drawing in step a′). This is particularly simple and prevents an outer shape change of the cladding tube from also being impressed inside, e.g. on the outer tube.
- The invention also concerns a precursor of a superconducting wire, produced by an inventive method as described above. A superconducting wire having particularly high current carrying capacity can be produced from the precursor.
- The invention also concerns a method for producing a superconducting wire from an inventive precursor of a superconducting wire as described above, characterized by the following steps:
-
- d′) the precursor of the superconducting wire is mechanically deformed, in particular, wound to form a coil;
- e′) the deformed precursor of the superconducting wire is temperature-treated, in particular at a maximum temperature of 700° C. or less, wherein Nb from the inner tube and the outer tube reacts with Sn from the powder core to form Nb3Sn. The superconducting wire produced in this fashion can achieve a particularly high superconducting current carrying capacity. In step d′), the precursor is brought into a form desired for the required application (which cannot be changed again after reaction annealing in step e′)). Temperature treatment is subsequently performed in this form in accordance with step e′). Typical applications are magnet coils, in particular for spectroscopic NMR apparatus and imaging MRI apparatus.
- In one preferred variant of the inventive method of producing a superconducting wire, temperature treatment is terminated in step e′) before a reaction front that advances to the outside has reached the boundary surface between the outer tube and the cladding tube. This prevents introduction of impurities into the cladding tubes of the contained monofilaments such that the residual resistance of the cladding tubes can be kept low. In case of a quench, the cladding tubes then provide powerful current paths parallel to the Nb3Sn filaments to protect the superconducting wire from burning through. Since advance of the reaction front during temperature treatment is relatively uniform, it is easy to find a suitable point in time for cooling in order to terminate the reaction advance for different wire geometries by means of a few tests with different annealing periods. The reaction fronts can be easily recognized e.g. in cross-section via a scanning electron microscope.
- The invention also concerns a superconducting wire produced by an inventive method as described above. The superconducting wire has a particularly high current carrying capacity as already described above.
- Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below may be used in accordance with the invention either individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration, rather have exemplary character for describing the invention.
- The invention is illustrated in the drawing and is explained in more detail with reference to embodiments. In the drawing:
-
FIG. 1 shows a schematic cross-sectional view of a first embodiment of an inventive monofilament with hexagonal cladding tube; -
FIG. 2 shows a schematic cross-sectional view of a second embodiment of an inventive monofilament with round cladding tube; -
FIG. 3 shows a schematic cross-sectional view of an embodiment of an inventive precursor of a superconducting wire; -
FIG. 4 shows a schematic diagram of the production of an inventive monofilament; -
FIG. 5 shows a schematic diagram of the production of an inventive superconducting wire; and -
FIG. 6 shows a schematic cross-sectional view of a section of an inventive superconducting wire in the area of a monofilament. -
FIG. 1 schematically shows a first embodiment of aninventive monofilament 1 in cross-section perpendicular to its longitudinal direction. - The
monofilament 1 has aninner tube 2 which consists of niobium in the illustrated embodiment. Apowder core 3 of a mixture of, in the present case, NbSn2 powder, Sn powder and Cu powder is disposed in theinner tube 2. The content of Cu in the mixture is approximately 5 weight % and the content of Sn in the mixture is typically at least 50 weight %. - The
inner tube 2 is arranged in anouter tube 4 which consists of NbTa7.5 in the present case. The outer side of theinner tube 2 thereby directly abuts the inner wall of theouter tube 4. Theinner tube 2 and theouter tube 4 each have (circular) round inner and outer cross-sections. - The
outer tube 4 is, in turn, arranged in acladding tube 5 which consists of elementary copper in the present case. Thecladding tube 5 has a round inner cross-section in the illustrated embodiment such that theouter tube 4 abuts thecladding tube 5 over the whole surface. The outer cross-section of thecladding tube 5 is hexagonal (“hexagonal tube”), thereby increasing the area portion of the finished superconducting wire that can be utilized for Nb3Sn. - The main source of Nb for the reaction heat treatment is the
outer tube 4. Theinner tube 2 enables good compaction of thepowder core 3 in a previous drawing step (see alsoFIG. 4 in this context) due to its comparatively thin wall. By way of example, the ratio VD between the outer diameter Doutertube outside of theouter tube 4 and the outer diameter Dinnertube outside of theinner tube 2 is approximately 1.65 in the embodiment shown. The ratio VW between the wall thickness Woutertube of theouter tube 4 and the wall thickness Winnertube of theinner tube 2 is moreover approximately 4.2. Theinner tube 2, theouter tube 4 and thecladding tube 5 are arranged concentrically. No solder is required for themonofilament 1. -
FIG. 2 schematically shows a second embodiment of aninventive monofilament 1 in cross-section perpendicular to its longitudinal extension. - The second embodiment of the
monofilament 1 largely resembles the embodiment ofFIG. 1 , in particular, with respect to theinner tube 2, thepowder core 3 and theouter tube 4. - However, the
cladding tube 5 here is provided with a (circular) round outer cross-section. For this reason, themonofilament 1 is easy to manufacture. Thecladding tube 5 is also produced of elementary copper and has a (circular) round inner cross-section. -
FIG. 3 shows a cross-section perpendicular to its longitudinal extension of an embodiment of aninventive precursor 10 of a superconducting wire. - A plurality of drawn monofilaments 11 (in the present case seven as an example), which are each produced from one monofilament by means of a filament drawing process, are bundled in a wire cladding tube 12 (“casing tube”) in the
precursor 10, and are subsequently subjected to an extrusion and/or wire drawing process in order to reduce the cross-section. - The
wire cladding tube 12 is preferably produced of elementary copper. Cavities at the inner edge of thewire cladding tube 12 are prevented or filled by means of fillingprofiles 13 which are preferably produced of elementary copper. - In the present case, the monofilaments had a hexagonal outer cross-section (see
FIG. 1 ) already prior to the filament drawing process such that the monofilaments were only radially compressed during the filament drawing process. Theouter tubes 4 in the drawnmonofilaments 11 correspondingly still have a round outer cross-section. The round outer cross-section of eachouter tube 4 is maintained even after the extrusion and/or wire drawing process of theprecursor 10. For this reason, starting from thepowder core 3, the reaction front of Nb3Sn can uniformly and concentrically approach the outer edge of theouter tube 4 during reaction annealing. There are no particularly thin points where Sn could prematurely break through into thecladding tube 5. Nor are there particularly thick points where residual Nb not utilized for the reaction to Nb3Sn protrudes. -
FIG. 4 shows a schematic diagram of the respective cross-sections of the specified components for producing aninventive monofilament 1. - Within the scope of the production variant illustrated here, the
inner tube 2 is filled with thepowder core 3 and subjected to a drawing step a). The cross-section of the comparatively thin-walledinner tube 2 is thereby reduced and thepowder core 3 is compacted. The non-filledouter tube 4 is furthermore inserted into the cladding tube 5 (in the present case of hexagonal outer cross-section) in one step b). The steps a) and b) can thereby be performed in arbitrary order or also simultaneously. In step c), the drawn and filledinner tube 2 is subsequently introduced into theouter tube 4 which is already arranged in thecladding tube 5. - Alternatively, the drawn and filled inner tube may also be initially inserted into the outer tube and the outer tube can subsequently be inserted into the cladding tube (not separately shown).
-
FIG. 5 schematically illustrates the production process of asuperconducting wire 20 frommonofilaments 1 as produced e.g. in accordance withFIG. 4 . - A
monofilament 1 is transformed into a drawnmonofilament 21 by drawing in step a′) (“filament drawing process”). The cross-sectional surface area is thereby reduced. If themonofilament 1 already has a hexagonal outer cross-section (as illustrated inFIG. 5 ), drawing merely effects radial compression. This is preferred since in this case, a round outer cross-section of theouter tube 4 can be easily obtained after drawing. If themonofilament 1 has a non-hexagonal outer cross-section (e.g. a round outer cross-section) a hexagonal outer cross-section is also impressed during drawing according to a′). - A plurality of drawn
monofilaments 21 are then bundled in awire cladding tube 12 in step b′). The number of drawn monofilaments is thereby basically arbitrary. Seven drawnmonofilaments 21 are bundled in the illustrated variant. In the bundled configuration, the monofilaments in the core area can be replaced by hexagonal Cu elements. - Extrusion and/or drawing is subsequently performed in step c′) (“wire drawing process”) which is again accompanied by a reduction in cross-section, thereby obtaining a
precursor 10 of a superconductor. Thisprecursor 10 already has the cross-sectional shape and cross-sectional size of the subsequent superconducting wire but can still be plastically deformed. - For finishing the superconducting wire, the
precursor 10 must be shaped in step d′) so as to have the shape required for the superconducting wire as determined by the desired application. In the illustrated variant, the application concerns amagnet coil 23. Theprecursor 10 is correspondingly wound onto acarrier 22. - Temperature treatment (“reaction annealing”) of the formed precursor is subsequently carried out in step e′). Towards this end, the
magnet coil 23 is put into afurnace 24 that is heated to a temperature of maximally 700° C. Sn from the powder cores reacts with Nb of the inner and outer tubes in the monofilaments of the precursor to Nb3Sn at these temperatures. Temperature treatment is terminated before the reaction front reaches the outer edge of the outer tubes. The formed precursor has been transformed into asuperconducting wire 20 by means of the temperature treatment, the Nb3Sn filaments of which can carry an electrical current (with corresponding cooling e.g. with liquid helium) practically without ohmic losses. Thesuperconducting wire 20 should not be deformed again after temperature treatment in order to prevent breaking of the enclosed brittle Nb3Sn filaments. -
FIG. 6 is a schematic cross-section illustrating a section of thesuperconducting wire 20 in the area of a temperature-treatedmonofilament 61. - A
reaction front 62 has radially advanced from the inside to the outside in a temperature-treatedmonofilament 61 and has generated a relatively homogeneous fine-grainedarea 63 of Nb3Sn. Thereaction front 62, however, has not completely crossed theouter tube 4 but has left a circumferential border 64 of non-reacted material of the outer cladding tube 4 (in the present case of NbTa7.5, i.e. Nb with 7.5 weight % Ta). The border 64 has an approximately uniform thickness S over its entire circumference. The thickness S is adjusted by the temperature treatment program to be just sufficiently large in order to reliably prevent breakthrough of Sn into the matrix 65 (formed from previous cladding tubes) of copper, thereby maintaining the electrical conductivity of thematrix 65 at a high level. Due to the round outer cross-section of theouter tube 4, a large portion of the cross-sectional area of thesuperconducting wire 20 can react to Nb3Sn. In particular, there are no remaining useless bulges of material of the outer tube 4 (as would be generated at the edges of an outer tube having an outer hexagonal cross-section). - The round outer cross-section of the
outer tube 4 can already be obtained prior to drawing of the monofilaments (see step a′) inFIG. 5 ) through a hexagonal outer cross-section of the cladding tubes. - A
residual core 66 resulting from the powder core with a reduced amount of Sn generally remains in the temperature-treatedmonofilament 61. - The temperature-treated
monofilament 61 is substantially free of gaps and cavities - Literature
-
- A. C. A. van Wees et al., IEEE Trans. Magn.; MAG 19, 556 (1983), pages 5-8;
- H. Veringa et al., Adv. Cryo. Eng. (Materials), 1984, 30; 813-821;
- W. L. Neijmeijer, B. H. Kolster, Journal of Less-Common Metals, 160 (1990), 161-170;
-
EP 1 701 390 A2 - U.S. Pat. No. 3,926,683
- T. Wong, C. V. Renaud, IEEE Trans. Appl. Supercond., Vol. 11, No. 1, March 2001, 3584-3587;
- JP 2006 252949 A
- US 2009/0011941 A1
- EP 0 169 596 A1
- S. Murase et al., IEEE Trans. Magn., Vol. Mag-21, No. 2, March 1985, pages 316-319;
- DE 26 20 271 A1
- D. Rodrigues Jr. et al., Materials Research Vol. 3, No. 4, 2000, pages 99-103;
- JP 05 298 947 A
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Claims (16)
1. A method for producing a monofilament for a superconducting wire, the monofilament comprising:
a powder core that contains at least Sn and Cu;
an inner tube that encloses the powder core, the inner tube being made of Nb or of an alloy containing Nb;
an outer tube in which the inner tube is disposed, wherein an outer side of the inner tube is in contact with an inner side of the outer tube, the outer tube being made of Nb or of an alloy containing Nb; and
a cladding tube in which the outer tube is disposed, the inner tube having a round inner cross-section and a round outer cross-section and the outer tube having a round inner cross-section and a round outer cross-section, wherein 4≦Woutertube/Winnertube50 with Woutertube:wall thickness of the outer tube and Winnertube:wall thickness of the inner tube,
the method comprising the steps of:
a) filling the powder core into the inner tube;
b) drawing, following step a), the inner tube, thereby compacting the powder core;
c) inserting the outer tube into the cladding tube; and
d) inserting, following step b), the drawn, filled inner tube into the outer tube, wherein step c) is performed prior to or after step d).
2. The method of claim 1 , wherein the cladding tube has a hexagonal outer cross-section and a round inner cross-section.
3. The method of claim 1 , wherein
1.2≦Doutertube outside/Dinnertube outside≦2.0 with Doutertube outside:outer diameter of the outer tube and Dinnertube outside:outer diameter of the inner tube.
4. The method of claim 1 , wherein the powder core has a content of 2 weight % to 12 weight % of Cu, 3 to 9 weight % of Cu or the powder core contains elementary Cu powder.
5. The method of claim 1 , wherein the powder core is compacted in the inner tube or has a density of at least 40% or of at least 50% of a theoretical density.
6. The method of claim 1 , wherein the powder core contains NbSn2 and/or Nb6Sn5 and/or elementary Sn.
7. The method of claim 1 , wherein the inner tube and/or the outer tube are produced from an alloy containing Nb and containing Ta and/or Ti, have a summed content of at least 0.5 weight % of Ta and/or Ti or have with a summed content of maximally 10 weight % of Ta and/or Ti.
8. The method of claim 1 , wherein the inner tube and the outer tube are produced from different materials.
9. The method of claim 1 , wherein the cladding tube is made of Cu.
10. The method of claim 1 , wherein the cladding tube already has a hexagonal outer cross-section prior to step c).
11. A method for producing a precursor of a superconducting wire using the monofilament produced by the method of claim 1 , the method further comprising the steps of:
a′) drawing one or more of the monofilaments to produce monofilaments having a hexagonal outer cross-section;
b′) bundling a plurality of drawn monofilaments in a wire cladding tube; and
c′) extruding and/or drawing the wire cladding tube containing the bundled and drawn monofilaments, thereby obtaining the precursor of the superconducting wire.
12. The method of claim 11 , wherein, in step a′), the monofilaments already have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube prior to drawing, wherein the drawn monofilaments also have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube after drawing.
13. The precursor of a superconducting wire produced by the method of claim 11 .
14. A method for producing a superconducting wire using the precursor of claim 13 , the method comprising the steps of:
d′) mechanically deforming the precursor or winding the precursor to form a coil; and
e′) temperature-treating the deformed precursor or temperature-treating the deformed precursor at a maximum temperature of 700° C. or less, wherein Nb from the inner tube and the outer tube reacts with Sn from the powder core to form Nb3Sn.
15. The method of claim 14 , wherein temperature treatment is terminated in step e′) before a reaction front that advances to an outside has reached a boundary surface between the outer tube and the cladding tube.
16. The superconducting wire produced by the method of claim 14 .
Priority Applications (2)
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US15/361,541 US20170072470A1 (en) | 2013-03-14 | 2016-11-28 | Method for producing a monofilament for an Nb3Sn superconductor wire |
US16/571,216 US11491543B2 (en) | 2013-03-14 | 2019-09-16 | Method for producing an Nb3Sn superconductor wire |
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EP13159230.5 | 2013-03-14 | ||
EP13159230.5A EP2779258B1 (en) | 2013-03-14 | 2013-03-14 | Monofilament for producing an Nb3Sn superconducting wire |
US14/198,618 US20140287929A1 (en) | 2013-03-14 | 2014-03-06 | Monofilament for the production of an Nb3Sn superconductor wire |
US15/361,541 US20170072470A1 (en) | 2013-03-14 | 2016-11-28 | Method for producing a monofilament for an Nb3Sn superconductor wire |
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US14/198,618 Continuation US20140287929A1 (en) | 2013-03-14 | 2014-03-06 | Monofilament for the production of an Nb3Sn superconductor wire |
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US14/198,618 Continuation US20140287929A1 (en) | 2013-03-14 | 2014-03-06 | Monofilament for the production of an Nb3Sn superconductor wire |
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US14/198,618 Abandoned US20140287929A1 (en) | 2013-03-14 | 2014-03-06 | Monofilament for the production of an Nb3Sn superconductor wire |
US15/361,541 Abandoned US20170072470A1 (en) | 2013-03-14 | 2016-11-28 | Method for producing a monofilament for an Nb3Sn superconductor wire |
US16/571,216 Active 2035-10-01 US11491543B2 (en) | 2013-03-14 | 2019-09-16 | Method for producing an Nb3Sn superconductor wire |
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US11758827B2 (en) | 2018-10-26 | 2023-09-12 | Bruker Eas Gmbh | Monofilament for producing an Nb3Sn-containing superconductor wire, especially for internal oxidation |
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CN106170464B (en) | 2014-02-18 | 2020-07-28 | 俄亥俄州立大学 | Superconducting wire and method for producing same |
DE102015203305A1 (en) * | 2015-02-24 | 2016-08-25 | Bruker Eas Gmbh | Semi-finished wire with PIT elements for a Nb3Sn-containing superconducting wire and method for producing the semifinished wire |
DE102019204926A1 (en) | 2019-04-05 | 2020-10-08 | Bruker Eas Gmbh | Finished conductor arrangement for an Nb3Sn superconductor wire and method for producing a sub-element for an Nb3Sn superconductor wire |
DE102019209170A1 (en) | 2019-06-25 | 2020-12-31 | Bruker Eas Gmbh | Sub-element based on Nb-containing rod elements with a powder-filled core tube for an Nb3Sn-containing superconductor wire and associated manufacturing processes |
CN113373404B (en) * | 2021-06-10 | 2022-09-27 | 中国科学院近代物理研究所 | Copper-based thick-wall Nb 3 Sn film superconducting cavity and preparation method thereof |
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DE2331962A1 (en) * | 1973-06-22 | 1975-01-16 | Siemens Ag | METHOD FOR PRODUCING A SUPRAL CONDUCTOR WITH A SUPRAL CONDUCTING INTERMETALLIC JOINT FROM TWO ELEMENTS |
JPS5216997A (en) * | 1975-07-31 | 1977-02-08 | Toshiba Corp | Processing method of multi-superconductor |
NL8402034A (en) * | 1984-06-27 | 1986-01-16 | Lips United B V | METHOD FOR MANUFACTURING A SUPER CONDUCTOR IN THE FORM OF A MONO OR MULTI-FILAMENT WIRE, AND SO MANUFACTURED SUPER CONDUCTOR. |
US7585377B2 (en) * | 2004-02-19 | 2009-09-08 | Oxford Superconducting Technology | Critical current density in Nb3Sn superconducting wire |
DE102004035852B4 (en) * | 2004-07-23 | 2007-05-03 | European Advanced Superconductors Gmbh & Co. Kg | Superconductive conductor element with reinforcement |
JP4728024B2 (en) * | 2005-03-24 | 2011-07-20 | 株式会社神戸製鋼所 | Powder method Nb3Sn superconducting wire manufacturing method |
US7752734B2 (en) * | 2005-11-08 | 2010-07-13 | Supramagnetics, Inc. | Method for manufacturing superconductors |
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- 2014-03-06 US US14/198,618 patent/US20140287929A1/en not_active Abandoned
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US11758827B2 (en) | 2018-10-26 | 2023-09-12 | Bruker Eas Gmbh | Monofilament for producing an Nb3Sn-containing superconductor wire, especially for internal oxidation |
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US20140287929A1 (en) | 2014-09-25 |
US11491543B2 (en) | 2022-11-08 |
EP2779258A1 (en) | 2014-09-17 |
EP2779258B1 (en) | 2015-09-16 |
US20200108447A1 (en) | 2020-04-09 |
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