JPH06176639A - Manufacture of superconductive raw material and nb-al superconductive wire - Google Patents

Abstract

PURPOSE:To effectively provide a higher-order element wire with disconnection prevented, by using an Al core in which Nb is diffused. CONSTITUTION:A bundle 4 of a primary element wire, in which an Al core 41, in which Nb of 1-30 parts by weight is diffused without alloying in Al (alloy) of 100 parts by weight, is coated with an Nb layer 42, is wire-drawing-worked under the surrounding of an Nb layer 51 to provided a fine wire 5. A fine wire, formed in a previous process by using the fine wire 5 as a start element wire, is used as an element wire in the next process to be bundled to be subjected to wire drawing work under the surrounding of the Nb layer. This operation is repeated to form a raw material in which a primary element wire formed into multiple cores. The raw material is heated to 700-1600 deg.C to provide an Nb-Al superconductive wire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superconducting material capable of preventing wire breakage during wire drawing and enabling long thin wires,
And a Nb-Al superconducting wire made of such a material, which is excellent in superconducting properties such as critical current density.

[0002]

2. Description of the Related Art Conventionally, a bundle of primary wires made of an Al-based core made of Al or an Al alloy coated with an Nb layer is housed in an Nb tube and then drawn to form a secondary wire having a multi-core structure. The thin wire formed in the previous step is used as the next strand so that the bundle of the secondary strands is housed in the Nb tube and the third strand obtained by wire drawing is used as the next strand. There has been known a method of manufacturing a superconducting material in which a predetermined number of primary strands are multicore by repeating an operation of accommodating a bundle of strands in an Nb tube and performing a wire drawing process.
Nb-Al-based superconducting wire is obtained by forming a Nb ₃ Al superconducting phase by heat treatment such superconducting materials.

As the Al alloy, Al or Al-
(5,7,10) Mg alloy, Al-3Ag alloy, Al-2C
u alloy, Al-1Cu-1Ge alloy, Al-1.5Ag-1.
5Ge alloy or the like is used. However, there has been a problem that a wire disconnection problem frequently occurs during wire drawing, particularly during the wire drawing after the secondary strand.

[0004]

In view of the above, the present inventor has attempted to use a primary element wire having a core made of an Al-Nb alloy. However, it has been found that the workability is poor and a disconnection problem is more likely to occur. Therefore, the present invention is a method for producing a superconducting material capable of efficiently obtaining a higher-order element wire by repeating the multicore of the primary element wire without causing a wire break, and Nb- which has excellent superconducting characteristics such as critical current density. The subject is the development of Al-based superconducting wires.

[0005]

According to the present invention, a bundle of primary wires obtained by coating an Al-based core containing Nb in a dispersed state without alloying with Nb is drawn by wire-drawing under the surrounding of the Nb layer. A thin wire is used as a starting wire, and the thin wire formed in the previous step is used as a wire in the next step to repeat the operation of wire-drawing a bundle of wires under the surrounding of the Nb layer to obtain the primary wire. A method for producing a superconducting material, which comprises forming a multi-core material, and heat-treating the superconducting material to produce Nb ₃
Nb-A characterized by forming an Al-based superconducting phase
l-type superconducting wire is provided.

[0006]

By the above-mentioned method using an Al-based core in which Nb is dispersed and contained in Al or an Al alloy without alloying, the physical properties such as hardness of the core can be made close to that of Nb and the workability is enhanced. It is possible to prevent wire breakage during wire drawing and to efficiently make long thin wires.
In the obtained superconducting material, Nb dispersed in the Al-based core also contributes to the formation of the superconducting phase, and Kirkendall voids due to the difference in diffusion rate during the heat treatment and reaction diffusion inhibition due to the formation of different phases are less likely to occur. An Nb-Al based superconducting wire having excellent superconducting properties such as critical current density can be obtained.

[0007]

EXAMPLE A manufacturing method of the present invention is to draw a bundle of primary wires in which an Al-based core in which Nb is dispersed and contained without alloying with an Nb layer is drawn under the surrounding of the Nb layer to form a thin wire. , The thin wire formed in the previous step is used as the starting wire for the thin wire as a starting wire, and the operation of drawing a bundle of wire wires under the surrounding of the Nb layer is repeated by the method of using the thin wire It is intended to obtain a superconducting material having a predetermined number of multicores. An example of such a superconducting material is shown in FIG. 1 is a wire obtained by increasing the number of cores of a primary wire to a higher order, and 2 is N composed of a final envelope layer.
It is layer b.

The Al-based core used in the present invention is obtained by dispersing Nb in an appropriate form in Al or an Al alloy without alloying it. Dispersion of Nb is intended to improve the tensile strength or hardness of the Al-based core and to make the wire-drawing workability of the Nb layer surrounding the Al-based core, and by extension, the respective constituent layers of the object to be drawn, as uniform as possible. And 2 to 4 illustrate the Al-based core 3 used in the present invention. Fig. 2 shows Nb in powder form
31 is dispersed, and FIG. 3 is one in which short fiber Nb 32 is dispersed. In FIG. 4, long fiber Nb33 is dispersed.

The Al-based core can be formed by an appropriate compounding method such as a melting method or a powder metallurgy method. In that case, it is necessary to form a composite so as not to alloy at the interface between Al and dispersed Nb. The alloying of Al and dispersed Nb is
Although the strength is improved, the wire drawing workability is lowered and the wire is easily broken. At the time of forming the composite, it is preferable to disperse Nb as homogeneously as possible from the viewpoint of improving the strength.

Incidentally, the formation of the Al-based core by the melting method is performed by adding Nb for dispersion to molten Al or a molten Al alloy having a melting point of 900 ° C. to 800 ° C. to 850 ° C.
It can be carried out by a method of stirring and mixing for 0 minutes, and solidifying it by casting to form a core material. Further, the Al-based core is formed by the powder metallurgy method, for example, a mixed powder of Al or Al alloy and Nb is molded into a core material, and the core material is melted at a temperature of 900 ° C., especially 80 ° C.
It can be performed by a method such as heat treatment at 0 to 850 ° C.

Examples of the Al alloy include Al-Mg
Alloys, Al-Ag alloys, Al-Cu alloys, Al-Cu-Ge alloys, Al-Ag-Ge alloys and the like may be used as appropriate, but in the case of Al alloys, the obtained Nb-Al-based superconducting wire Contains a small amount of alloying components that do not contribute to the formation of the superconducting phase, which causes the deterioration of superconducting properties such as critical current density, the tendency to generate Kirkendall voids due to the difference in diffusion rate, and the reaction diffusion due to the formation of a different phase. In the present invention, Al is preferably used for forming the Al-based core because it is easily inhibited.

The amount of Nb dispersed in the Al-based core can be appropriately determined according to the desired physical properties such as strength. Generally, 1 to 100 parts by weight of Al or Al alloy
30 parts by weight, especially 3 to 15 parts by weight of Nb are used.
The form of Nb for dispersion is arbitrary, but a smaller size is preferable from the viewpoint of exerting a dimensional effect and improving the strength.
The Nb for dispersion may be coated with Al by an appropriate method such as a CVD method, a PVD method, a plating (electrolytic or electroless) method, and a thermal spraying method in order to enhance the affinity with the Al base material.

The starting strand in the present invention is formed by wire-drawing a bundle of primary strands 4 in which an Nb-dispersed Al-based core 41 is covered with an Nb layer 42 as shown in FIG. It is a thin wire 5. The starting strand 5 (secondary strand)
Can be obtained by, for example, a method in which a large number of primary wires 4 are housed in a Nb tube and wire drawing is performed. The primary strand 4, that is, the strand in which the Al-based core 41 is covered with the Nb layer 42 can be obtained by, for example, a method in which the Al-based core is loaded in the Nb tube and a wire drawing treatment is performed.

The wire drawing may be carried out by an appropriate method, but in general, the cold wire drawing method is preferable because it can prevent the formation of a substance such as NbAl ₃ or Nb ₂ Al which inhibits the workability and the superconducting property by heating. . Examples of the cold wire drawing method include a die method, a cold forging method such as a swaging method and a hosing method, and a method using them in combination.

In the wire drawing process, the wire is successively thinned through a plurality of dies, a cold forging machine, etc., and the area reduction rate per one process may be appropriately determined. Generally 5
The area reduction rate is -25%. Although the degree of thinning may be appropriately determined, it is generally set to 0.1 to 2 mm, which is used as a wire for the next wire drawing or as a superconducting material.
It is used to form b-Al superconducting wires.

FIG. 6 shows an example of the wire drawing process. According to this, the material 7 to be drawn is thinned through the dies 8, 81, 82, 83 while being supplied from the delivery roll 6, and is gradually thinned into fine wires 71, 72, 73, and the fine wire 73 is forged. The wire is cold forged through the machine 9 to form the wire 10 and is wound on the winding roll 11. The wound wire 10 is Nb-Al as a wire for the next wire drawing, or as a superconducting material when a predetermined number of primary wires have been multicore.
Used to form superconducting wires.

In the present invention, in accordance with the formation of the starting strands described above, it is necessary to use the thin wires formed in the previous step as the strands in the next step and surround the bundle of strands with the Nb layer to perform wire drawing. Repeated a number of times, as shown in FIG.
Higher order strand 1 having 2 in the Nb layer 13 in a multi-core state
4 is obtained to form a desired superconducting material in which a predetermined number of primary strands have a multicore structure.

In forming the higher-order strands of the third or higher order, the bundle of strands is surrounded by Nb foil instead of the Nb pipe, housed in the support pipe, and subjected to wire drawing to form a layer outside the formed strand. The support layer can be removed to obtain the next strand.
In this case, Nb occupies the outer layer of higher-order strands after the third
The layer can be thinned, the Nb layer portion that does not contribute to the formation of the superconducting phase can be eliminated, the superconducting phase occupies a large area, and an Nb-Al-based superconducting wire having excellent superconducting properties such as critical current density can be obtained.

In addition to the Nb foil described above, an Al-based foil can also be enclosed. In this case, the Al-based foil layer made of Al or its alloy also contributes to the formation of the superconducting phase, and the superconducting phase ratio in the cross-sectional area of the superconducting wire can be easily controlled. In addition, instead of the Nb foil or Al-based foil described above,
The area occupied by the superconducting phase can also be increased by filling the gap between the Nb tube and the element wire with a mixed powder of Nb powder and Al-based powder.

The support tube used in the foil enclosing method is
It is for efficiently performing wire drawing without damaging the wires or surrounding foil, and therefore it can withstand wire drawing of copper, copper alloys, etc., and dissolves or etches with a chemical such as nitric acid after wire drawing. What can be removed appropriately is used. The support pipe may be provided outside the Nb pipe for wire drawing for the purpose of preventing damage in the system using the Nb pipe.

In the present invention, the cross-sectional shape and diameter of the superconducting material, the number of cores, etc. can be arbitrarily determined, and therefore the number of times of repeating the above operation is also arbitrary. Generally, Nb
-From the viewpoint of prevention of deterioration of mechanical strength and stability due to lack of matrix portion that is not an Al-based superconducting phase, or AC loss, 1
The structure is such that about 0 to 300 strands are sequentially made multi-core, and the Al system / Nb area ratio in the cross section is 0.2 to 2
10% to 10,000 cores of 0% / 99.8-80% secondary strands,
It is a superconducting material having a diameter of 0.1 to 10 mm and an area ratio of the secondary strand portion / other portion of the cross-sectional area of about 1/20 to 20/1.

The Nb-Al-based superconducting wire can be obtained by processing the superconducting material into a desired cross-sectional shape such as a tape, if necessary, and then heat-treating it to generate an Nb ₃ Al-based superconducting phase. it can. The heating conditions are appropriately determined depending on the thickness of the secondary element wire and the thickness of the Nb layer in the superconducting material, but generally heating is performed in the temperature range of 700 to 1600 ° C. By the heat treatment, Nb ₃ Al superconducting phase is generated all or part of the adjacent portion of the Nb layer and an Al-based layer reacts, Nb-Al-based superconducting wire is formed.

The Nb ₃ Al type superconducting phase produced by the heat treatment is usually about 4 times as much as the contained Al component. Therefore, by adjusting the Al-based part in the cross-sectional area of the superconducting material,
The content ratio of the Nb ₃ Al-based superconducting phase in the obtained superconducting wire can be controlled. Incidentally, when the superconducting material occupies 2 to 20% of the Al-based portion in its cross-sectional area, a superconducting wire in which the Nb ₃ Al-based superconducting phase occupies the cross-sectional area in the range of 8 to 80% is obtained.

Example 1 100 parts by weight of Al was heated and melted at 820 ° C., Nb powder having an average particle size of 500 μm was added, and the mixture was stirred for 5 minutes to form a homogeneous dispersion, which was then poured into a Nb tube and allowed to cool. As a result, a primary wire was obtained in which an Al-based core having a diameter of 0.3 mm was covered with a Nb layer having a thickness of 0.15 mm.

Then, the above-mentioned 300 primary strands were
The filling rate in the Nb tube is 1 when it is housed in the Nb tube with a thickness of 1 mm and a wall thickness of 1 mm.
After cold forging treatment (diameter 8mm) so that it becomes 00%,
Wire drawing was performed through 16 dies with a surface reduction rate of 10% per die to obtain a secondary strand having a diameter of about 1.3 mm.

Next, using the thin wire formed in the previous step as the starting wire with the secondary wire as the starting wire, the operation according to the method for forming the secondary wire is repeated three times and the tertiary wire is used. The target superconducting material (fifth element wire) was obtained by making the primary wire multicore by sequentially connecting the wire, the fourth element wire, and the fifth element wire. Therefore, the number of passing through the die after forming the secondary strands was 48, and the diameter of the obtained superconducting material was about 1.3 mm. In the above, disconnection never occurred until the desired superconducting material was obtained.

Comparative Example 1 A superconducting material was obtained in the same manner as in Example 1 except that an Al core containing no Nb was used instead of the Al core. In this case,
The disconnection occurred 5 times when forming the tertiary element wire, 8 times when forming the quaternary element wire, and 5 times when obtaining the target superconducting material.

Comparative Example 2 A superconducting material was obtained according to Comparative Example 1 except that an Al-2Cu alloy core containing no Nb was used instead of the Al core. In this case, disconnection occurred once when forming the tertiary element wire, five times when forming the quaternary element wire, and three times when obtaining the target superconducting material.

[0029]

According to the present invention, since the Nb-dispersed Al-based core is used, it is possible to efficiently cut a long thin wire of a higher order wire by repeating the multi-core of the primary wire while preventing the wire breakage. Can be easily obtained. In addition, the Nb-Al superconducting wire, which has excellent workability and can suppress the breakage of the filament composed of primary strands when it is multicore, can form the superconducting filament continuously in the length direction with good uniformity and has an excellent critical current density, Obtainable.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view illustrating the structure of a superconducting material.

FIG. 2 is a perspective explanatory view illustrating the structure of an Al-based core.

FIG. 3 is a perspective explanatory view illustrating the structure of another Al-based core.

FIG. 4 is a perspective explanatory view illustrating the structure of yet another Al-based core.

FIG. 5 is an explanatory cross-sectional view illustrating the structure of a secondary wire.

FIG. 6 is an explanatory sectional view illustrating a wire drawing process.

FIG. 7 is an explanatory cross-sectional view of a high-order and multi-core strand.

[Explanation of symbols]

 1: Elementary wire in which the primary elemental wire is made higher in number of cores 2: Nb layer consisting of the final surrounding layer 3: Al-based core 31, 32, 33: Dispersed Nb 4: Primary elemental wire 41: Al-based core 42 : Nb layer 5: Starting wire 14: Higher-order multi-core wire

Claims (2)

[Claims] 1. A bundle of primary wires in which an Al-based core in which Nb is dispersed and contained without alloying is coated with an Nb layer is drawn into a thin wire by being surrounded by the Nb layer, and the thin wire is a starting element. The thin wire formed in the previous step is used as the wire for the wire in the next step, and the operation of drawing a bundle of wire wires under the surrounding of the Nb layer is repeated to form a material in which the primary wire has multiple cores. A method for manufacturing a superconducting material, which is characterized in that 2. A Nb—Al-based superconducting wire, characterized in that the superconducting material according to claim 1 is heat-treated to form an Nb ₃ Al-based superconducting phase.