JP5598825B2 - Nb3Al superconducting wire manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a _Nb 3 Al superconductive wire. More specifically, the present invention relates to a manufacturing method for manufacturing a Nb ₃ Al superconducting wire whose characteristics are improved for practical use by devising the structure of the Nb ₃ Al thin wire.

At present, Nb ₃ Al superconducting wires excellent in high magnetic field characteristics that are expected to be put into practical use are manufactured by a method called a rapid heating / quenching / transformation method (Patent Documents 1 and 2). The outline of the rapid heating / cooling / transformation method is as follows.

(1) A Nb sheet having a thickness of about several tens to several hundreds of μm and an Al sheet are wound into a jelly roll, and then extruded and drawn as necessary to produce a primary wire.

(2) A plurality of primary wires are bundled and incorporated into an Nb or Ta tube, and then subjected to extrusion and wire drawing in order to produce a secondary composite multicore wire.

(3) After heating the secondary composite multifilamentary wire to a temperature of 1900 ° C. or higher, it is immediately cooled rapidly, and Nb and Al constituting the diffusion pair in the form of a jelly roll are reacted with each other to react with Nb (Al) supersaturated solid solution. And a composite multi-core supersaturated solid solution wire having a number of Nb (Al) supersaturated solid solution fine wires therein is prepared.

(4) subjecting the additional heat treatment to the composite multifilamentary supersaturated solid solution wire, Nb (Al) a supersaturated solid solution thin line Nb 3 _Al superconducting thin line f-phase is transformed to produce a Nb 3 _Al superconductive wire of the composite multi-core structure.

For the Nb ₃ Al superconducting wire produced by such a rapid heating / quenching / transformation method, further improvement of characteristics is urgently required for practical use.

One is the improvement of critical distortion. At present, the limit strain leading to damage of the Nb ₃ Al superconducting wire is smaller than that of the practical Nb ₃ Sn superconducting wire. In general, the superconducting wire having an ultrafine multi-core structure tends to improve the limit strain as the diameter of the fine wire is smaller. As described above, the Nb ₃ Al superconducting wire has an ultrafine multi-core structure, but the diameter of the fine wire is around 100 μm, which is not necessarily a sufficiently small value from the viewpoint of limit strain.

Further, in the production of the Nb ₃ Al superconducting wire by the rapid thermal quenching / transformation method, the reduction of the fine wire diameter to 100 μm or less is caused by the fact that the hardness of Al is considerably lower than the hardness of Nb / Al composite. In addition to the processing limit of the body, it is extremely difficult for reasons such as causing a significant increase in the manufacturing process.

  Another is an improvement in the bondability between the stabilizer and the metal matrix. In the rapid heating / cooling / transformation method, as described above, since the heating temperature is a high temperature of 1900 ° C. or higher, the metal matrix of the secondary composite multi-core wire is limited to refractory metals such as Nb. A highly conductive material such as Cu used has a melting point as low as about 1000 ° C., and evaporates during the rapid heating and cooling process.

Therefore, many methods for forming a stabilizing material after rapid heating and quenching have been proposed in the past. However, any of these methods is a radical solution from the standpoint of improving the characteristics of the Nb ₃ Al superconducting wire. No.

For example, a method has been proposed in which a Cu sheet is mechanically attached around an Nb (Al) supersaturated solid solution composite multi-core wire after rapid heating and rapid cooling treatment using the ductility of Nb (Al) supersaturated solid solution (patent) Reference 3). However, with this method, it is difficult to obtain a sufficiently good interface mechanically and electrically between Cu and the surface of the Nb matrix of the Nb (Al) supersaturated solid solution composite multifilamentary wire, and Nb ₃ Since the cross-sectional area of the Al superconductor portion is limited, there is a problem that it is difficult to increase the current capacity.

In addition, an internal stabilization method has been proposed in which a stabilizing material such as Cu or Ag is disposed inside the Nb / Al composite multicore precursor wire instead of the outermost portion (Patent Document 4). However, with this method, it is extremely difficult to increase the stabilizing material ratio. This is because the Nb ₃ Al superconductor portion is reduced when the stabilizer is incorporated inside. When the stabilizing material ratio is 0.3 or more, it is theoretically difficult to produce an Nb ₃ Al superconducting wire having a high current capacity.

In addition, as a stabilization method, there is a method in which Cu is ion-plated on the surface of the Nb matrix of the Nb (Al) supersaturated solid solution composite multi-core wire to improve mechanical and electrical bonding between Nb and Cu. Proposed. However, with this method, the apparatus is complicated and expensive to manufacture, and, like the above method, the cross-sectional area of the Nb ₃ Al superconductor portion is limited, and it is difficult to increase the current capacity.

JP-A-6-283059 JP-A-10-144162 JP 2000-1113748 A JP 2000-243158 A

The present invention has been made in view of the circumstances as described above, solves problems such as critical strain and bondability between the stabilizing material and the metal matrix, and devise the structure of the Nb ₃ Al fine wire to put it into practical use. properties towards has an object to provide a method of producing an improved Nb 3 _Al superconducting wire.

The Nb ₃ Al superconducting wire manufacturing method of the present invention has a multi-core structure in which a number of fine wires of Nb (Al) supersaturated solid solution are arranged in a refractory metal matrix formed of a refractory metal having a melting point higher than 1900 ° C. After multiple bundles are bundled and placed in a metal tube, wire drawing is performed to the extent that the refractory matrix does not break, and the same refractory metal matrix is formed in each cell constituting the refractory metal matrix. After the first step of forming the matrix structure , heat treatment is performed to transform the Nb (Al) supersaturated solid solution into an Nb ₃ Al superconductor.
The manufacturing method of the Nb ₃ Al superconducting wire of the present invention is a multi-core structure in which a number of fine wires of Nb (Al) supersaturated solid solution are arranged in a refractory metal matrix formed from a refractory metal having a melting point higher than 1900 ° C. After multiple bundles are bundled and placed in a metal tube, wire drawing is performed to the extent that the refractory matrix does not break, and the same refractory metal matrix is formed in each cell constituting the refractory metal matrix. The first step of forming a matrix structure and the second step of bundling a plurality of wires having an overlapping matrix structure and placing them in a metal tube and then drawing them to form a multiple matrix structure were repeated one or more times. Thereafter, heat treatment is performed to transform the Nb (Al) supersaturated solid solution into an Nb ₃ Al superconductor.

In the method for producing a Nb ₃ Al superconducting wire of the present invention, it is preferable that the area reduction rate of wire drawing is 50% or more.
The method of manufacturing a _Nb 3 Al superconducting wire of the present invention, preferably, the heat treatment temperature or equal to 600 ° C. to 1000 ° C..
In the method for producing a Nb ₃ Al superconducting wire of the present invention , preferably, the refractory metal is Nb, Ta or an alloy thereof.
In the method for producing an Nb ₃ Al superconducting wire of the present invention, it is preferable that the metal tube used in the final wire drawing step is made of a highly conductive metal having conductivity at room temperature.
In the method for producing a Nb ₃ Al superconducting wire of the present invention, it is preferable that the portion forming the inner and outer layers of the refractory metal matrix is Ta or an alloy thereof.
In the method for producing a Nb ₃ Al superconducting wire of the present invention, preferably, the highly conductive metal is Cu, Ag, or an alloy thereof.
In the method for producing a Nb ₃ Al superconducting wire of the present invention, it is preferable to perform the wire drawing by dicing.

According to the present invention, there is provided an Nb ₃ Al superconducting wire having a new structure in which a refractory metal such as fine Ta is introduced into the superconducting thin wire. In this Nb ₃ Al superconducting wire, the strength of the superconducting thin wire is provided. Is greatly improved, the critical strain that causes damage to the Nb ₃ Al superconducting wire can be greatly improved.

Further, according to the present invention, it is possible to manufacture an Nb ₃ Al superconducting wire material whose critical strain is greatly improved without adding special equipment.

Furthermore, according to the present invention, each cell constituting the refractory metal matrix has an overlapping matrix structure in which the same refractory metal matrix is formed, and the Nb ₃ Al fine wire is located in the smallest cell. Nb 3 _Al superconducting wire having the outer periphery of the ₃ Al superconductive wire a new structure highly conductive metal layer is formed having a conductivity at room temperature is provided. In this Nb ₃ Al superconducting wire, since a good electrical and mechanical interface is formed between the highly conductive metal as the stabilizing material and the refractory metal matrix, the stabilization in the Nb ₃ Al superconducting wire Bondability between the material and the refractory metal matrix is improved.

Furthermore, according to the present invention, it is possible to manufacture an Nb ₃ Al superconducting wire in which the bonding property between the stabilizing material and the refractory metal matrix is improved.

Therefore, according to the present invention, Nb 3 _Al manufacturing method of a superconducting material properties for practical use has been improved is provided.

The cross section of the Nb 3 _Al superconductive wire showing an embodiment relating to the present invention is a schematic diagram schematically showing. Description of Nb 3 _Al manufacturing method of a superconducting material showing an embodiment relating to the present invention is a flow diagram illustrating. The cross section of the Nb 3 _Al superconductive wire showing one embodiment of the present invention is a schematic diagram schematically showing. It is a process diagram illustrating an outline of a manufacturing method of the Nb 3 _Al superconductive wire showing one embodiment of the present invention. It is the schematic which showed typically the structure of the rapid heating rapid cooling apparatus used in Example 1. FIG. a and b are cross-sectional images of the Nb ₃ Al superconducting wire obtained in Example 1, respectively. A bending jig is a diagram showing a state in which sandwich the Nb 3 _Al superconductive wire. a is a view showing a longitudinal cross-sectional image of a comparative wire when a strain of 0.52% is applied, and b is obtained in Example 1 when a strain of 0.83% is applied. nb 3 _Al is a diagram illustrating a diagram illustrating a longitudinal vertical sectional image of a superconducting material. The left figure is a diagram showing a cross-sectional image of the Nb ₃ Al superconducting wire C obtained in Example 2, and the right figure is a partially enlarged view thereof. a is the figure which showed the state when bending distortion was added to the Nb (Al) supersaturated solid solution composite multi-core wire B in Example 2, and b is the figure which showed the state of the comparison wire D. FIG. FIG. 5 is a diagram showing critical current density characteristics of Nb ₃ Al superconducting wire C and comparative wire D obtained in Example 2.

1 Nb ₃ Al superconducting wire 2 Good conductive metal _{3, 30} refractory metal 4 Nb ₃ Al fine wire 10 cell 20 smallest cell

An Nb ₃ Al superconducting wire showing an embodiment related to the present invention has a multi-core structure in which a large number of Nb ₃ Al fine wires are arranged in a metal matrix, and Nb ₃ Al fine wires are arranged in Nb ₃ Al fine wires. Nb ₃ Al having a structure in which melting points higher than both melting points and a fiber-like refractory metal that is extremely thin compared to the thickness of the Nb ₃ Al fine wire are dispersedly arranged in a state in which the longitudinal direction is aligned with the wire center direction. Superconducting wire.

Specifically, in the Nb ₃ Al superconducting wire, as shown in FIG. 1, the refractory metal fiber having a thickness of 100 nm to 1 μm in the transverse cross section is 100 nm to 100 nm in the radial direction in the Nb ₃ Al thin wire. They are distributed at intervals in the range of 20 μm, continuously in the circumferential direction, or at intervals in the range of 20 μm. Although the area of the refractory metal fiber is small in cross section, it exists in a layered manner and is distributed continuously or intermittently in the direction of the core of the Nb ₃ Al superconducting wire. That is, in the Nb ₃ Al superconducting wire, the Nb ₃ Al fine wire is effectively divided by the high melting point metal fiber, and the generation and progress of fine cracks that can occur in the Nb ₃ Al fine wire are suppressed, and the Nb ₃ Al super wire is suppressed. The critical strain that leads to damage to the conductive wire is greatly improved. In _Nb 3 Al superconducting wire shown in FIG. 1, _Nb 3 Al thin line is a nineteen, the number of _Nb 3 Al thin wire may be a dozen to several hundred or so.

An Nb ₃ Al superconducting wire showing an embodiment related to the present invention as illustrated in FIG. 1 may be manufactured by a method of manufacturing an Nb ₃ Al superconducting wire showing an embodiment related to the present invention. In addition, according to the method of manufacturing an Nb ₃ Al superconducting wire showing an embodiment related to the present invention, an Nb ₃ Al superconducting phase having a high stoichiometric composition can be obtained in addition to the improvement of the limit strain. An Nb ₃ Al superconducting wire having excellent superconducting properties is realized.

In a method of manufacturing an Nb ₃ Al superconducting wire showing an embodiment related to the present invention, a Nb sheet, an Al sheet, and a sheet of a refractory metal having a melting point higher than both melting points of Nb and Al are stacked and wound, After obtaining a wire, drawing a jelly roll composite material to obtain a primary wire, bundling a plurality of primary wires and placing them in a metal tube, the wire is drawn so that the refractory metal is dispersed in a fiber shape, Next, after heating to produce a Nb (Al) supersaturated solid solution, it is immediately cooled rapidly and heated again to transform the Nb (Al) supersaturated solid solution into a Nb ₃ Al superconductor.

Specifically, as shown in FIG. 2, a sheet of Nb, Al and a refractory metal is overlapped and wound to obtain a jelly roll composite, the jelly roll composite is drawn, and a plurality of the bundles are bundled. After being inserted into a metal tube constituting the metal matrix, arranged (stacking), and drawn, after heating to a temperature of 1900 ° C. or higher and lower than the melting point of the refractory metal, an Nb (Al) supersaturated solid solution was generated, Immediately cool down (rapid heat quenching treatment) and heat again to a temperature of 600 ° C. to 1000 ° C. to transform the Nb (Al) supersaturated solid solution into Nb ₃ Al superconductor (additional heat treatment).

Nb and Al may be pure Nb, pure Al, or an Nb alloy or Al alloy having a composition that does not impair the superconducting properties of the Nb ₃ Al superconductor formed by the rapid thermal quenching / transformation method. .

Refractory metals can be drawn, have melting points higher than the melting points of Nb and Al, and exist in the form of fibers in the Nb ₃ Al fine wire even at the heat treatment temperature when alloying Nb and Al. Various metals or alloys that can be used can be employed. Specifically, Ta or an alloy thereof is preferably exemplified, and Ta or an alloy thereof is a high melting point material and has low reactivity with Nb and Al. Therefore, even in the rapid thermal quenching process from a high temperature of 1900 ° C. or higher and lower than the melting point, the fiber shape can be maintained in the Nb ₃ Al fine wire, and the influence on the Nb / Al reaction is small.

  The Nb, Al, and refractory metal are used as a sheet having a predetermined size and thickness.

A composite after wire drawing made by bundling a plurality of primary wires made by drawing a jelly roll composite material, placing them in a metal tube, and drawing them so that the refractory metal is dispersed in a fiber shape. The volume ratio of Nb to Al (Nb / Al) in the multicore precursor wire can be exemplified as a preferable range of about 2.5 to 3.5. The ratio of the refractory metal is not strictly defined, but is preferably 40% or less by volume in the Nb ₃ Al fine wire. This is because the Nb ₃ Al superconductor portion in the Nb ₃ Al fine wire decreases as the volume fraction of the refractory metal increases, and the current-carrying current characteristics of the obtained Nb ₃ Al superconductive wire are suppressed from decreasing. Further, the shape and size of the refractory metal in the composite multicore precursor wire is not strictly defined as long as it is fiber-like, but the diameter or thickness is preferably from 100 nm to 1 μm. If the diameter or the thickness is less than 100 nm, will readily react with Nb or Al in rapid heating and quenching treatment, _Nb 3 Al thin wire is altered, it exceeds 1 [mu] m, _Nb 3 Al than in _Nb 3 Al thin line The conductor portion is significantly reduced, and in any case, the superconducting properties of the Nb ₃ Al superconducting wire may be deteriorated.

In the composite multi-core precursor wire, the fiber-like refractory metal is dispersed in the Nb ₃ Al fine wire at intervals in the range of 100 nm to 20 μm in the radial direction and continuously in the circumferential direction or in the range of 20 μm. It is preferable to disperse them at intervals. In order to obtain such a dispersive arrangement of fiber-like refractory metals, shapes such as the thickness of Nb, Al and refractory metal sheets used in the preparation of the jelly roll composite material in the previous process, and wire drawing Set conditions as appropriate. Interval of at least 100nm, along a distance which can be split _Nb 3 Al thin wires effectively, it is effective for suppressing the proportion of high-melting metal to the _Nb 3 Al thin line. On the other hand, it is considered difficult to manufacture the refractory metal at intervals exceeding 20 μm.

The metal matrix of the Nb ₃ Al superconducting wire is formed by a metal tube in which a plurality of primary wires are bundled and inserted and arranged inside, but the metal forming the metal tube has high electrical conductivity, A metal having conductivity at room temperature, which can stabilize the Nb ₃ Al superconducting wire, is applicable. Specifically, Nb, Ta, Cu, Ag, or an alloy thereof can be used. In the case of heating to a high temperature of 1900 ° C. or higher in the subsequent process, Nb, Ta or an alloy thereof is exemplified. On the other hand, the production of the Nb ₃ Al superconducting wire is carried out by, for example, performing a diffusion reaction at a temperature of 1000 ° C. or less as disclosed in Japanese Patent Laid-Open Nos. 9-204826 and 6-260040. Can also be performed. In this case, Cu, Ag or an alloy thereof having a melting point of about 1000 ° C. can be used for the metal tube. However, in the production of a Nb ₃ Al superconducting wire using a diffusion reaction, there is a difficulty that it is difficult to obtain an Nb ₃ Al phase having a high stoichiometric composition.

The metal matrix ratio is 0.5 to 0.5 with respect to the cross-sectional area of the Nb ₃ Al fine wire in the transverse cross section of the obtained Nb ₃ Al superconducting wire in any case where the rapid heating and quenching treatment is performed or the diffusion reaction is used. It is preferable to adjust the ratio to 2. If the metal matrix ratio is less than 0.5, wire drawing is difficult, and if it exceeds 2, the current density of the Nb ₃ Al superconducting wire decreases, which is not realistic.

The rapid heating and quenching treatment is performed by heating the composite multi-core precursor wire to a temperature of 1900 ° C. or higher and lower than the melting point of the refractory metal, and reacting Nb and Al to generate an Nb (Al) supersaturated solid solution. Immediately cooled quickly. After the rapid heating and quenching treatment, additional heat treatment is performed again at 600 ° C. to 1000 ° C. to transform the Nb (Al) solid solution into an Nb ₃ Al superconductor.

In the rapid thermal quenching process, the heating temperature is set to 1900 ° C. or higher and lower than the melting point of the refractory metal. If the ultimate temperature is lower than 1900 ° C., the Nb ₃ Al phase is directly generated, and the Nb (Al) solid solution Is not generated. The Nb ₃ Al phase produced directly at high temperature has a large crystal grain size, does not exhibit excellent superconducting properties, and is impractical. When the heating temperature is equal to or higher than the melting point of the refractory metal, the refractory metal is melted, and the dispersive arrangement of the fiber-like refractory metal as described above is not realized. The temperature range of the additional heat treatment is set to 600 ° C. to 1000 ° C. When the transformation is performed at a temperature lower than 600 ° C., it becomes difficult to order the Nb ₃ Al phase, and when the heat treatment is performed at a temperature exceeding 1000 ° C., an undesirable phase, for example, Nb _{2 This} is because the generation of Al phase is promoted and the characteristics deteriorate. Note that the above temperature range is not strictly limited, and a slight increase or decrease including an error is allowed.

After the additional heat treatment, an Nb ₃ Al superconducting wire with greatly improved critical strain is obtained, which represents an embodiment related to the present invention.

An Nb ₃ Al superconducting wire showing an embodiment of the present invention has a large number of Nb ₃ Al thin wires arranged in a refractory metal matrix formed of a refractory metal having a melting point higher than both melting points of Nb and Al. Each cell constituting the refractory metal matrix has a core structure and has an overlapping matrix structure in which the same refractory metal matrix is formed. Nb ₃ Al fine wires are located in the smallest cell, and Nb ₃ Al This is a Nb ₃ Al superconducting wire in which a highly conductive metal layer having conductivity at room temperature is formed on the outer periphery of the superconducting wire.

Specifically, in the Nb ₃ Al superconducting wire, as shown in FIG. 3, the region inside the layer of the highly conductive metal 2 is divided into a plurality of cells 10 via the refractory metal 3. The inside of the cell 10 is further divided into a large number of cells by the refractory metal 30 and has an overlapping cell structure as if the cell 20 exists in each cell 10. The Nb ₃ Al fine wire 4 is located in the smallest cell 20 or the smallest cell 20 is the Nb ₃ Al fine wire 4. There is no difficulty in setting the degree of overlap to double, triple, or quadruple. When the diameter of the Nb ₃ Al superconducting wire 1 is large, the degree of overlap is increased, and the Nb ₃ Al superconducting wire 1 can be thickened without increasing the thickness of one Nb ₃ Al thin wire 4 itself. Is possible.

Such _Nb 3 Al superconductive wire 1 in the _Nb 3 Al thin wires 4 diameter (maximum diameter) can be realized 20μm or less, and for example 10μm approximately, as having been significantly reduced as compared with the prior art. As the Nb ₃ Al thin wire 4, various types that function as an Nb ₃ Al superconducting wire can be adopted. Preferably, those having a composition in the range of about Nb-22 to 28 at% Al, more preferably those having a composition as close as possible to the composition of Nb-25 at% Al, which is a stoichiometric composition, are exemplified. Specifically, similar to the Nb ₃ Al superconducting wire showing one embodiment related to the present invention, the melting point is higher than both melting points of Nb and Al, and is extremely thin compared to the thickness of the Nb ₃ Al thin wire. Nb ₃ Al fine wires in which the refractory metal is distributed in a state where the longitudinal direction is aligned with the direction of the wire center are exemplified.

The refractory metal 3 plays a role of dividing the Nb ₃ Al thin wire 4 and can be drawn in consideration of the manufacturing process described later, and is given to the reaction of the Nb (Al) supersaturated solid solution in the rapid heating and rapid cooling process. A metal having a small influence is preferred. As such a metal, a refractory metal having a melting point higher than 1900 ° C. is exemplified, and specifically, Nb, Ta or an alloy thereof is exemplified. The refractory metal 3 that separates the cells 10 and the refractory metal 30 that separates the Nb ₃ Al fine wires 4 may be the same or different. The total volume ratio of the refractory metals _{3 and 30 to} the Nb ₃ Al fine wires 4 is exemplified by about 0.5 to 2.0. Although the volume ratio of the refractory metal is preferably 0.5 or more in terms of processing, when the volume ratio exceeds 2.0, the ratio of the Nb ₃ Al fine wires 4 decreases, and thus the current density decreases.

The highly conductive metal 2 functions as a stabilizing material in the Nb ₃ Al superconducting wire 1, and a metal having high electrical conductivity or an alloy thereof can be used. Specifically, Cu, Ag, or an alloy thereof having excellent conductivity is exemplified. The volume ratio of the highly conductive metal 2 in the Nb ₃ Al superconducting wire 1 can be set high. The volume ratio of the highly conductive metal 2 is not specifically limited because the required amount varies depending on the application, but the volume ratio with respect to the portion other than the highly conductive metal 2 may be 0.3 or more. For example, 0.5 or more, more preferably 0.7 or more is exemplified as a preferable value for wire drawing. For example, when it is used for an accelerator magnet, it may be 1.0 or more. The upper limit of the volume ratio of the good conductive metal 2 to the portion other than the good conductive metal 2 can be set as appropriate according to the specification of the current density required from the application equipment. As the volume ratio of the highly conductive metal 2 increases, the current capacity of the Nb ₃ Al superconducting wire 1 decreases accordingly. The upper limit is exemplified as a temporary guide.

Note that the cell 10 can have a diameter of about 20 μm to 200 μm, although it cannot be generally stated because it depends on the diameter and desired characteristics of the Nb ₃ Al superconducting wire 1 and manufacturing restrictions. The diameter of the smallest cell 20 can be 20 μm or less. Further, the cell 10 can be divided into, for example, about 19 to 130 sections by the refractory metal 3, and the smallest cell 20 can be divided into about 19 to 300 sections by the refractory metal 30. In this case, about 300 to 39000 Nb ₃ Al thin wires 4 are arranged in the Nb ₃ Al superconducting wire 1.

Further, in the Nb ₃ Al superconducting wire 1, the average thickness of the refractory metal 3 between the cells 10 and the average thickness of the refractory metal 30 between the smallest cells 20 are different, and the refractory metal 30 is higher than the refractory metal 3. The average thickness is thin. The thickness of the refractory metal 30 between the smallest cells 20 can be made very thin. By making the refractory metal 30 very thin and high in density, the magnetic flux involved in improving the critical current density. The effect as a pinning center is expected. The average thickness of such a refractory metal 30, particularly the average thickness as a partition of the smallest cell 20 in the case where it is formed by the Nb ₃ Al thin wire 4, is 2 μm or less.

Although the cell 10 and the smallest cell 20 are illustrated in a substantially circular shape in FIG. 3, in the actual Nb ₃ Al superconducting wire 1, the cross-sectional shape is not limited to a circular shape or a substantially circular shape. It may be a polygonal shape, a star shape, or a shape in which they are broken. On the other hand, the cross-sectional shape of the Nb ₃ Al superconducting wire 1 is preferably circular or substantially circular, but is not limited thereto.

Nb 3 _Al superconductive wire showing one embodiment of the present invention as described above is implemented, for example, as more than the critical temperature 17K.

The Nb ₃ Al superconducting wire showing one embodiment of the present invention can be manufactured by the method for manufacturing the Nb ₃ Al superconducting wire showing one embodiment of the present invention. In the method of manufacturing an Nb ₃ Al superconducting wire showing one embodiment of the present invention, a thin wire of Nb (Al) supersaturated solid solution in a refractory metal matrix formed from a refractory metal having a melting point higher than both melting points of Nb and Al. After bundled a plurality of multi-core structures arranged in a metal tube, wire drawing is performed to such an extent that the refractory matrix does not break, and the same is applied to each cell constituting the refractory metal matrix. A first step of forming an overlapping matrix structure in which a refractory metal matrix is formed; a first step of bundling a plurality of wires having the overlapping matrix structure and arranging them in a metal tube; The Nb (Al) supersaturated solid solution is transformed into a Nb ₃ Al superconductor by repeating the two steps one or more times or by heat treatment without performing the second step. In the method of manufacturing an Nb ₃ Al superconducting wire showing an embodiment of the present invention, the Nb (Al) supersaturated solid solution composite multi-core wire that is additionally heat-treated in the conventional method is bundled again and subjected to wire drawing.

  A multi-core structure in which a number of fine wires of Nb (Al) supersaturated solid solution are arranged in a refractory metal matrix as a starting material must be prepared using various methods such as the jelly roll method and the rod-in-tube method. Can do. Preferably, as shown in FIG. 4, a sheet of refractory metal that functions as a partition wall between thin wires is wound around the rolled up sheet of Nb and Al stacked around the core, After forming the jelly roll composite material, drawing the jelly roll composite material, inserting and arranging a plurality of wire materials after drawing into a refractory metal tube made of refractory metal, and drawing the wire 1900 An Nb (Al) supersaturated solid solution composite multifilamentary wire heated to a temperature not lower than the melting point of the high melting point metal and below the melting point of the refractory metal and immediately cooled can be used. Note that the jelly roll method is practically suitable because the size of the final diffusion pair of Nb and Al can be reduced to about 500 nm even if the degree of processing is relatively small.

  The metal forming the refractory metal tube is preferably Nb, Ta or an alloy thereof. In particular, Ta or an alloy thereof has low reactivity with the liquid metal Ga used as a refrigerant in the rapid heating and quenching process, and can suppress the formation of a compound phase that is not desirable for wire drawing. In this case, the inner part of the refractory metal matrix is formed from Ta or an alloy thereof.

  For the core, a high melting point metal or a wire such as Cu laid with a high melting point metal can be used. Further, if the jelly roll composite material is processed into a hexagonal cross section, it is effective to suppress the misalignment of the jelly roll composite material when stacking and wire drawing. If the deviation can be suppressed, the degree of processing for each jelly roll composite material inserted and arranged in the refractory metal tube can be made uniform, the risk of disconnection during wire drawing can be reduced, and the design shape can be maintained. In addition, even if the jelly roll composite material has a round cross-sectional shape, when it is stacked and drawn, the wire sticks closely during processing and approaches the hexagonal shape due to its natural arrangement. Is not essential.

As for the composition of the Nb (Al) supersaturated solid solution core, it is preferable that the solid solution amount of Al in Nb is in the range of about 22 to 28 at%, and the solid solution amount of Al can be 25 at% of the stoichiometric composition. It is more preferable to make them as close as possible. The number of cores and stacks of Nb (Al) supersaturated solid solution composite multifilamentary wire is based on the fact that the processing limit of Nb (Al) supersaturated solid solution in restacking is about 99.9% or less in terms of surface reduction. The diameter of the Nb ₃ Al fine wire contained in the final Nb ₃ Al superconducting wire can be appropriately set so as to be 20 μm or less.

  As the refractory metal as the refractory metal matrix, an appropriate metal can be selected in consideration of a rapid thermal quenching process in which the metal is heated to a temperature of 1900 ° C. or higher and lower than the melting point of the refractory metal. Preferably, Nb, Ta or an alloy thereof is exemplified.

A plurality of Nb (Al) supersaturated solid solution composite multi-core wires are bundled and inserted into a highly conductive metal tube having a predetermined inner / outer diameter, and subjected to wire drawing with a surface reduction ratio of 50% or more. As described above, Cu, Ag, or an alloy thereof is preferable as the highly conductive metal that forms the highly conductive metal tube. The highly conductive metal tube is applied as a metal tube used in the final wire drawing step among the metal tubes used for manufacturing the Nb ₃ Al superconducting wire. The wire inserted into the highly conductive metal tube can include not only the Nb (Al) supersaturated solid solution composite multi-core wire but also a highly conductive metal wire. By increasing the thickness of the good conductive metal and increasing the number of good conductive metal wires, the stabilizer ratio, that is, the volume ratio of the good conductive metal to the portion other than the good conductive metal can be easily increased. Can be made.

The wire drawing with a surface reduction ratio of 50% or more can further reduce the diameter of the Nb ₃ Al thin wire, and can improve the bondability between the inner wall of the highly conductive metal tube and the surface of the refractory matrix. The wire drawing method is not particularly limited, but deformation pressure can be applied isotropically to the surface of the wire, and the inner wall of the highly conductive metal tube can From the viewpoint that the bonding property with the surface of the melting point matrix can be effectively improved, it is preferable to carry out by die drawing (die wire drawing). Since die drawing is performed with a large drawing force, it is necessary to sufficiently remove foreign matters on the surface of the Nb (Al) supersaturated solid solution composite multicore wire so as not to hinder the drawing.

  The surface reduction rate of 50% or more is the processing rate added to the Nb (Al) supersaturated solid solution. Even if the surface reduction rate is 95% or more, excellent superconductivity without deteriorating the characteristics. Characteristics can be maintained.

The heat treatment can be carried out as an equivalent to the additional heat treatment that can be employed in the Nb ₃ Al superconducting wire showing one embodiment related to the present invention. Heat to 600 ° C. to 1000 ° C. to transform the Nb (Al) supersaturated solid solution into Nb ₃ Al superconductor. When transformation is performed at a temperature lower than 600 ° C., it becomes difficult to order the Nb ₃ Al phase. When the temperature exceeds 1000 ° C., Cu is melted, and formation of an undesirable phase such as an Nb ₂ Al phase is promoted to deteriorate the superconducting properties. Problems occur. On the other hand, the temperature range of the heat treatment is not strictly limited to the above range, and a slight increase or decrease including an error is allowed.

After the heat treatment, an Nb ₃ Al superconducting wire having good mechanical and electrical bondability between the highly conductive metal and the refractory metal matrix can be obtained.

In addition, according to the Nb ₃ Al superconducting wire which shows an embodiment of the present invention, a plurality of Nb (Al) supersaturated solid solution composite multi-core wires can be restacked for wire drawing, so that Nb ₃ The superconducting cross-sectional area in the Al superconducting wire can be increased arbitrarily and easily, and a large current capacity of the Nb ₃ Al superconducting wire can be achieved.

Furthermore, the Nb ₃ Al superconducting wire material in which the Nb ₃ Al fine wire diameter is reduced and the problem of magnetic instability is improved is obtained by the above restacking and wire drawing.

In addition, when the wire drawing is performed by die drawing, the dimensional accuracy can be improved, and almost all the problems that have been pointed out to the Nb ₃ Al superconducting wire can be solved.

Hereinafter, Examples, Nb 3 _Al superconducting wire and its manufacturing method of the present invention is described in more detail.

It was produced _Nb 3 Al superconducting wire according to the manufacturing method of the _Nb 3 Al superconducting wire shown in FIG. 2. A Nb sheet having a thickness of 90 μm and a predetermined width and length, an Al sheet having a thickness of 30 μm and a predetermined width and length, and a Ta sheet having a thickness of 90 μm and a predetermined width and length are stacked. A jelly roll laminated composite was produced by winding in a jelly roll shape around a 0.0 mm Nb core. At this time, the volume ratio (Nb / Al) between the Nb sheet and the Al sheet was set to 3. In order to increase the volume ratio of Nb and Al, six layers of Nb sheets and Al sheets were alternately stacked, one Ta sheet was stacked, and the total number of layers was set to seven.

  The produced jelly roll laminated composite is inserted and arranged in an Nb pipe having a predetermined length and inner and outer diameter, and this Nb pipe is inserted and arranged in a Cu pipe having a predetermined length and inner and outer diameter, and then extrusion processing. Die wire drawing etc. were given, Cu which was an outer skin was then removed, and a Ta / Nb / Al jelly roll single core wire was produced.

  Around one Nb dummy wire, 84 Ta / Nb / Al jelly roll single-core wires were bundled and inserted into an Nb tube having a predetermined length and inner and outer diameters. The Nb tube in which the Ta / Nb / Al jelly roll single core wire was inserted and arranged was inserted and arranged in a Cu—Ni tube having a predetermined length and inner and outer diameters, and a multi-core billet was produced.

  The produced multi-core billet was subjected to extrusion processing, die drawing, etc., and then Cu-Ni as the outer skin was removed, and a large number of Ta / Nb / Al fine wires were arranged in the Nb matrix as the metal matrix. A composite multi-core precursor wire having an outer diameter of 1 mm was produced.

  The composite multi-core precursor wire thus produced was continuously wound at a rate of about 0.3 m / s using the rapid heating and quenching apparatus shown in FIG. It was heated to a high temperature and immediately entered into a liquid metal Ga bath that also served as an electrode within 1 second, and then rapidly cooled. Nb and Al were reacted to form a Nb (Al) supersaturated solid solution. At this time, Ta, which is a refractory metal, remains in the fine wire without changing the fiber form.

The composite multi-core precursor wire having this Nb (Al) supersaturated solid solution is subjected to additional heat treatment at 800 ° C. for 10 hours to transform the Nb (Al) solid solution into Nb ₃ Al superconductor, and Nb ₃ An Al superconducting wire was obtained. Table 1 shows the main specifications of the Nb ₃ Al superconducting wire obtained. Further, the end faces of the Ta fibers are scattered as black dots in the thin lines in FIGS. 6 (a) and 6 (b).
With respect to the obtained Nb ₃ Al superconducting wire, a superconducting characteristic with a critical magnetic field of about 20 T was obtained.

The obtained Nb ₃ Al superconducting wire is sandwiched between jigs with curved gaps, bending strain is applied at room temperature, and the strain resistance characteristics of the Nb ₃ Al superconducting wire, that is, how much strain it can withstand is investigated. It was.

  The radius of curvature of the curved gap is 6 to 10 cm, and the bending strain is defined as follows.

Bending strain (%) = wire radius / (wire radius + curvature radius) × 100 (1)

FIG. 7 shows a state in which the Nb ₃ Al superconducting wire is sandwiched. In order to investigate the effect of the dispersed Ta fibers, a Nb ₃ Al superconducting wire containing no Ta fibers was prepared as a comparative wire. The comparative wire is manufactured in the same process as described above except that the Ta sheet is not included in the jelly roll single core wire. Table 2 shows the specifications of the comparative wire.

In the Nb ₃ Al superconducting wire obtained in Example 1 shown in FIG. 8B, a large number of streaks were confirmed in the direction of the wire core inside the Nb ₃ Al thin wire. This streak is an introduced Ta fiber. Further, as is clear from the comparison between FIGS. 8A and 8B, the comparative wire (FIG. 8A) clearly has cracks at a strain of 0.52%. In the Nb ₃ Al superconducting wire obtained in No. 1, no cracks were found inside although a strain of 0.83% was applied.

Nb 3 _Al thin wire inside by dispersing arranged Ta fibers, generation of Nb 3 _Al thin wires inside the crack is suppressed, the limit strain Nb 3 _Al superconductive wire is damaged is greatly improved.

  Nb (Al) supersaturated solid solution composite with specifications of wire diameter 0.8mm, fine wire diameter 63.2μm, number of fine wires 66, refractory metal matrix ((Nb (as partition walls) + Ta (as outer skin)) ratio 1.654 A multi-core wire A was prepared, and 54 wires A were bundled around one copper wire of the same size, and inserted into a copper pipe having an inner diameter of 6.9 mm and an outer diameter of 9 mm to form a composite. On the other hand, wire drawing was performed with a carbide die at a surface reduction rate of about 15% per reduction, and finally the outer diameter was 1 mm, the number of fine wires was 3564, the fine wire diameter was about 10 μm, and the refractory metal matrix ratio was 1. A Nb (Al) supersaturated solid solution composite multi-core wire B having a .654 and Cu ratio of 0.88 was obtained, and the Nb (Al) supersaturated solid solution was subjected to a surface reduction work of 95% or more by wire drawing.

Then held at 800 ° C. 10 hours, to transform the Nb (Al) supersaturated solid solution to obtain a _Nb 3 Al superconductive wire C.

As can be seen from FIG. 9, the Nb ₃ Al superconducting wire C has a cellular structure in which the outer skin is made of Cu and the inside is divided by Ta into a plurality of small regions. Moreover, it can be seen from the enlarged view of each cell that the Nb ₃ Al superconducting wire C has an overlapping cell structure subdivided with Nb. The size of the Nb ₃ Al fine wire forming the smallest cell is about 10 μm in diameter and is much smaller than 20 μm.

  In order to confirm the bondability between the Cu shell as a stabilizing material and the refractory metal matrix, the Nb (Al) supersaturated solid solution composite multi-core wire B is bent at 90 ° or more at room temperature, and the Cu shell is a refractory metal. It was investigated whether it peeled from a matrix. For comparison, a Cu clad wire (state before phase transformation) produced by the method disclosed in Japanese Patent Laid-Open No. 2000-113748 was prepared as a comparative wire D. The specifications of the comparative wire D are 0.8 mm in thickness, 1.8 mm in width, 75.5 μm in fine wire diameter, 132 fine wires, a matrix ratio of 0.8, and a Cu ratio of 0.39. As shown in FIGS. 10A and 10B, the comparative wire D is subjected to a bending strain of about 35%, Cu is broken, and Cu is peeled off from the matrix. On the other hand, Nb (Al) supersaturated solid solution composite multifilamentary wire B was confirmed to have improved bondability, with no Cu peeling or breakage, despite about 50% bending strain. Is done. The bending strain is defined by the above formula (1).

Next, to measure the critical current density characteristics per _Nb 3 Al phase of the resulting _Nb 3 Al superconducting wire C in Example 2. FIG. 11 shows the result. FIG. 11 also shows the critical current density characteristics of the comparative wire D after the phase transformation heat treatment. The Nb ₃ Al superconducting wire C obtained in Example 2 is excellent in critical current density characteristics. The critical current density of the _Nb 3 Al superconductive body per divided by the total area of the energizing current value _Nb 3 Al superconductor unit, 4.2 K temperature, in a magnetic field of 15T, 1000A / mm ² or more Met. From this, it was confirmed that excellent critical current density characteristics were maintained even by surface reduction of 95% or more Nb (Al) supersaturated solid solution.

The comparative wire D often induced magnetic instability under a magnetic field of 12 T or less. However, the Nb ₃ Al superconducting wire C obtained in Example 2 was excellent without causing magnetic instability. It was possible to measure. It was also confirmed that the magnetic instability was suppressed in the Nb ₃ Al superconducting wire C obtained in Example 2.

  When the Nb (Al) supersaturated solid solution composite multi-core wire B was produced, the Cu outer shell sometimes cracked when the wire diameter was 1.13 mm. The Cu ratio of the wire at this time is 0.193, and it is considered that cracking occurred on the surface during wire drawing because the Cu ratio was small. As a result of the subsequent trial production, it was found that good wire drawing can be performed when the ratio of a highly conductive metal such as Cu is 0.3 or more.

After sufficiently removing the impurity phase on the surface of the Nb (Al) supersaturated solid solution wire (wire diameter: 1.01 mm) in which the high melting point metal Ta produced in Example 1 remains in the form of fibers in the fine wire, this wire 36 is removed. A book is bundled around a single copper wire of the same size, and inserted into a Cu pipe having an inner diameter of 7.4 mm and an outer diameter of 9.3 mm to form a composite. Die drawing was performed at a surface reduction rate of about 15% per reduction. Finally, an Nb (Al) supersaturated solid solution composite multifilamentary wire having an outer diameter of 1.0 mm, a number of fine wires of 3024, a fine wire diameter of about 15 μm, a refractory metal matrix ratio of 0.8, and a Cu ratio of 0.9 was obtained. Then held at 800 ° C. 10 hours, _Nb 3 Al superconductive wire is obtained by transformation of Nb (Al) supersaturated solid solution.
With respect to the obtained Nb ₃ Al superconducting wire, a superconducting characteristic with a critical magnetic field of about 20 T was obtained.

Because the reliability of Nb ₃ Al superconducting wire can be increased, the reliability and safety of large magnets such as fusion experimental reactor magnets, NMR magnets, and high-energy particle accelerator magnets, where the wires are subjected to strong electromagnetic force Can be increased. In addition, a long-life magnet can be realized, and cost reduction is expected. Furthermore, cabling with a complicated shape is possible, and the application range is wide. For example, it is particularly suitable for a Rutherford type cable used for an accelerator magnet.

Claims (9)

After bundling a plurality of multi-core structures in which a number of fine wires of Nb (Al) supersaturated solid solution are arranged in a refractory metal matrix formed from a refractory metal having a melting point higher than 1900 ° C. After the first step, wire drawing is performed to the extent that the refractory matrix does not break, and an overlapping matrix structure in which the refractory metal matrix is also formed inside each cell arranged in the refractory metal matrix is heat treated. A method for producing a Nb ₃ Al superconducting wire, comprising transforming a Nb (Al) supersaturated solid solution into a Nb ₃ Al superconductor. After bundling a plurality of multi-core structures in which a number of fine wires of Nb (Al) supersaturated solid solution are arranged in a refractory metal matrix formed from a refractory metal having a melting point higher than 1900 ° C. A first step of performing wire drawing to such an extent that the refractory matrix does not break, and forming an overlapping matrix structure in which the refractory metal matrix is also formed inside each cell disposed in the refractory metal matrix;
After bundling a plurality of wires having an overlapping matrix structure and placing them in a metal tube, the second step of drawing is repeated one or more times, and then heat-treated to convert the Nb (Al) supersaturated solid solution to Nb ₃ Al A method for producing a Nb ₃ Al superconducting wire characterized by transforming into a conductor. The method of manufacturing a Nb 3 _Al superconducting wire according to claim 1 or 2, the manufacturing method of the Nb 3 _Al superconductive wire, which comprises a reduction process rate of wire drawing of 50% or more. The manufacturing method of claims 1 to 3 any one _Nb 3 Al superconducting wire according to method of manufacturing a _Nb 3 Al superconductive wire, characterized in that the heat treatment temperature and 600 ° C. to 1000 ° C.. The method of manufacturing a Nb 3 _Al superconducting wire according to claims 1 to 4 any one method of the refractory metal is, Nb, Ta or Nb 3 _Al superconducting wire, characterized in that the alloy . 6. The method of manufacturing an Nb ₃ Al superconducting wire according to claim 1, wherein the metal tube used in the final wire drawing step is made of a highly conductive metal having conductivity at room temperature. Nb 3 _Al manufacturing method of a superconducting wire, characterized by that. The method of manufacturing a Nb 3 _Al superconducting wire according to claims 1 to 6 any one, Nb 3 _Al superconductive that portion forming the inner and outer skin of the refractory metal matrix characterized in that it is a Ta or an alloy thereof A manufacturing method of a wire. The method of manufacturing a Nb 3 _Al superconducting wire according to claim 6, highly conductive metal is Cu, Ag or Nb 3 _Al manufacturing method of a superconducting material characterized by its alloys. The method of manufacturing a Nb 3 _Al superconducting wire according to any one of claims 1 to 8, a manufacturing method of Nb 3 _Al superconducting wire which is characterized in that the wire drawing by dies pulling.