JP3602151B2 - Method for producing Nb (3) Sn compound superconducting wire - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for producing a Nb ₃ Sn compound superconducting wire, and more particularly, the present invention relates to a method for producing a superconducting wire having an extremely small hysteresis loss while maintaining a very high critical current density of the Nb ₃ Sn compound superconducting wire. The present invention relates to a method for producing an obtained Nb ₃ Sn compound superconducting wire.
[0002]
[Prior art]
Nb ₃ Sn compound superconducting wires have excellent superconducting properties such as critical temperature, critical magnetic field, and critical current, and are therefore used, for example, as winding materials for electromagnets for generating high magnetic fields.
[0003]
In general, an Nb ₃ Sn compound superconducting wire is a composite of a large number of Nb ₃ Sn filaments and a bronze matrix present around the Nb ₃ Sn filament, and contacts the stabilized copper via Ta or a Ta-based alloy or Nb or Nb-based alloy. It has a cross section.
FIG. 11 shows an example of a cross-section of a conventional Nb ₃ Sn compound superconducting wire after heat treatment and cross-section reduction processing. In FIG. 11, reference numeral 3 denotes stabilized copper, 4 denotes a diffusion barrier made of Ta or a Ta-based alloy, or Nb or Nb-based alloy, 5 denotes an Nb ₃ Sn filament, and 6 denotes a bronze matrix. The outer shape may be circular or rectangular. Of course, the Nb ₃ Sn filament 5 is a superconducting phase.
[0004]
However, since the Nb ₃ Sn compound superconductor is an intermetallic compound and is mechanically fragile, it is difficult to form a composite wire by a plastic working method like an alloy superconductor. Therefore, in the production of the Nb ₃ Sn compound superconducting wire, as shown in FIG. 12, as shown in FIG. 12, a cross section of the wire after the cross-section reduction processing and before the heat treatment, a large number of Nb filaments 1 and a Cu—Sn alloy, so-called bronze matrix 6, the diffusion barrier 4 for preventing the diffusion of Sn, and the stabilized copper 3 are combined. These are processed into a composite to obtain a desired cross-sectional shape, and then heat-treated to reduce the Nb ₃ Sn compound. The method of producing (bronze method) was adopted. However, according to this method, since the Sn concentration in the bronze matrix is as high as about 13% in cold area reduction processing, the work hardening of the Cu-Sn bronze matrix is extremely large, and many softening heat treatments are required during the processing. and then, because of its softening heat treatment, many costs, and requires time and since the Sn concentration in the bronze is approximately 13% and the upper limit, it is difficult to get a lot of Sn amount, Nb ₃ produced for the The amount of the Sn compound was small, for example, the critical current was as low as 650 A / mm ^{2 at} 12 T. If the Sn concentration is 13% or more, a compound is generated in the bronze matrix, and the processing of the bronze matrix becomes extremely difficult.
[0005]
In order to solve such a drawback, as an example, the following method has been adopted as shown in FIG. A Cu / Nb composite pipe is made from an extruded composite billet composed of Cu and Nb. Sn is inserted into the vertical hole at the center, and the cross-section is reduced by swaging, rolling, drawing, or other methods to obtain a thin wire. A plurality of these are bundled, put into another Cu pipe, and subjected to drawing or the like to obtain a superconducting element wire. If Nb ₃ Sn heat treatment is performed on this, Sn is diffused to form an Nb ₃ Sn matrix, which can be used as an Nb ₃ Sn compound superconducting wire.
In this method, the amount of Sn can be increased because the amount of Sn is not limited to 13% or less unlike the bronze method. Therefore, the amount of the generated Nb ₃ Sn compound can be increased. An extremely high critical current density can be obtained as compared with the method.
[0006]
[Problems to be solved by the invention]
However, even as a high critical current density as described above (Jc) is obtained, during Sn of the central portion Aima' can not be placed Nb is, since the Nb filament spacing is small, adjacent Nb ₃ The connection of the Sn compound filaments was likely to occur, and an increase in hysteresis loss was observed. For example, in the case of a wire having a Jc of 950 A / mm ² at 12 T, the effective filament diameter was 15 to 20 μm with respect to hysteresis loss. A superconducting pulse coil using such a superconducting wire generates a large amount of heat and requires a powerful refrigerator.
[0007]
The present invention has been made to solve the above problems, and there is no connection between filaments of adjacent Nb ₃ Sn compounds while maintaining a very high critical current density of the Nb ₃ Sn compound superconducting wire. It is an object of the present invention to provide a method for producing an Nb ₃ Sn compound superconducting wire from which a superconducting wire having an extremely small hysteresis loss can be obtained.
[0008]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors were able to solve the above-mentioned conventional problems.
[0009]
That is, the present invention provides a single Nb or Nb-based alloy rod or a plurality of closely arranged Nb or Nb-based alloy rods, an Sn or Sn-based alloy rod disposed around the Nb or Nb-based alloy rod, and Nb ₃ is obtained by bundling a plurality of composite wires made of Cu or a Cu-based alloy disposed around and inserting them into a sheath material, reducing the cross section to obtain a wire, and heat-treating the wire. An object of the present invention is to provide a method for producing a Sn compound superconducting wire.
[0010]
The present invention also provides a first composite wire made of one Nb or Nb-based alloy rod or a plurality of closely arranged Nb or Nb-based alloy rods and Cu or a Cu-based alloy disposed around them. A single Sn or Sn-based alloy rod or a plurality of closely arranged Sn or Sn-based alloy rods and a second composite wire made of Cu or a Cu-based alloy disposed around these rods so as to be dispersed. A method for producing an Nb ₃ Sn compound superconducting wire, characterized in that after the wire is inserted into a sheath material, a wire is obtained by reducing the cross section and the wire is heat-treated.
[0011]
Further, the present invention provides a method for forming one Nb or Nb-based alloy rod or a plurality of Nb or Nb-based alloy rods closely arranged in a plurality of vertical holes provided in a copper or copper-based alloy rod, and one Sn or Sn-based alloy rods or a plurality of closely arranged Sn or Sn-based alloy rods are separately or integrally inserted, a cross-section is reduced to obtain a strand, and the strand is heat-treated. An object of the present invention is to provide a method for producing an Nb ₃ Sn compound superconducting wire.
[0012]
[Action]
In the present invention, the arrangement of Sn is not concentrated, but is distributed around each Nb, so that there is no dead zone in the arrangement of Nb rods (Nb filaments). improvements can, even if there is expansion of the filament due to Nb 3 _Sn compound produced, no longer connected the filaments of Nb 3 _Sn compound, as a result it is possible to reduce the hysteresis loss, high-performance superconducting wire is manufacturable.
[0013]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Embodiment 1 FIG.
FIG. 1 shows an embodiment in which an Sn bar is disposed around an Nb bar as a composite wire. In FIG. 1, 1 is an Nb bar, 2 is a Sn bar, and 3 is a Cu tube. A 1.5 mm thick Sn plate was spread on an Nb rod 1 having a diameter of 10 mm and inserted into a Cu tube 3 having a concave groove on the inner surface. This was subjected to a drawing process to produce 253 hexagonal rods (composite wire rods) having a distance to the opposite side of 3.0 mm and a length of 1.0 m. The cross-sectional shape when the hexagonal rods are bundled at this time is as shown in FIG. 1, and the Sn rods 2 flow into the concave grooves on the inner surface of the Cu tube 3 and are embedded.
Next, these 253 pieces were bundled, put into another circular Cu tube (sheath material), and subjected to drawing processing, thereby producing 55 hexagonal rods having a distance of 3.5 mm across sides and a length of 1.0 m. This was inserted into another circular Cu tube together with a Ta barrier, and a superconducting wire having an outer diameter of 0.95 mm was produced by drawing.
During the processing, the processing could be favorably advanced without performing the softening heat treatment.
[0014]
Both ends of a sample having a length of about 1.5 m cut out from the prepared strand were heated to perform Sn sealing treatment, and Nb ₃ Sn compound generation heat treatment was performed. The heat treatment was 675 ° C. × 100 hours. As a result of measuring the critical current of the Nb ₃ Sn compound superconducting wire thus obtained, the critical current density was as high as 1040 A / mm ² per non-copper at a temperature of about 4.2 ° K in a magnetic field of 12 T. Met. Further, as a result of scanning electron microscope observation, it was found that there was no connected portion between the generated Nb ₃ Sn compounds, and the hysteresis loss was extremely small. The measurement result of the effective filament diameter in a coil shape of the sample subjected to the same heat treatment was 5 μm, and it was found that the Nb ₃ Sn compound superconducting wire was excellent in both critical current density and hysteresis loss characteristics.
[0015]
The cross-sectional reduction processing is not particularly limited, and swaging, rolling, drawing, and other methods can be appropriately selected.
Furthermore, the above heat treatment was performed at 675 ° C. × 100 hours, but the present invention is not limited to this heat treatment condition. For example, the heat treatment can be performed at 500 to 900 ° C. × 1000 hours or less. Preferably, it is 600 to 750 ° C. × 300 hours or less.
[0016]
Embodiment 2. FIG.
An Nb rod with a diameter of 10 mm is put into a Cu tube with an outer diameter of 15.5 mm and an inner diameter of 10.5 mm and drawn, and 84 hexagonal rods (first composite wire) with a distance of 3.0 mm across sides and a length of 1.0 m are manufactured. did. Also, a Sn rod having a diameter of 10 mm is put into another Cu tube having an outer diameter of 15.5 mm and an inner diameter of 10.5 mm, and is subjected to a drawing process. Similarly, a hexagonal rod having a distance to opposite side of 3.0 mm and a length of 1.0 m (second composite wire rod) ) Were manufactured. The above total 253 pieces were bundled so as to be dispersed, placed in another circular Cu tube (sheath material), and subjected to a drawing process, thereby producing 55 hexagonal rods having a distance of 3.5 mm across sides and a length of 1.0 m. This was further inserted into a separately prepared circular Cu tube together with a Ta barrier and subjected to drawing to obtain a superconducting element wire having an outer diameter of 0.95 mm. FIG. 2 is an enlarged view of the cross-sectional shape of the strand. As can be seen from FIG. 2, the first composite wire and the second composite wire are evenly distributed.
During the processing, a softening heat treatment such as the bronze method was not required, and the processing could be favorably advanced.
A part of this element wire was cut off, and a heat treatment for forming an Nb ₃ Sn compound at 675 ° C. × 100 hours was applied. As a result of measuring the critical current of this coil-heat-treated sample at a temperature of 4.2 ° K in a magnetic field of 12 T, a high critical current density of 1010 A / mm ² was obtained.
As in Example 1, in the observation with a scanning electron microscope, no connection between the generated Nb ₃ Sn compounds was found. Regarding hysteresis loss, the effective filament diameter was about 5 μm, and both critical current density and hysteresis loss characteristics It has been proved that it has excellent performance.
[0017]
Embodiment 3 FIG.
In the above and the following examples, the case where each of the metals used is a pure metal such as Nb, Sn, Cu, Ta is described. However, in order to improve the critical current density or to improve the processability, another element is used. The same effect can be obtained even if it is added. For example, Nb-Ti (Ti 5% or less), Nb-Ta (Ta 7% or less), etc. as Nb-based alloys, Sn-Ti (Ti 5% or less), Sn-In (In 10% or less), Sn as Sn-based alloys -Ta (Ta 7% or less) or the like can be used.
[0018]
Embodiment 4. FIG.
Also, regardless of the finished wire diameter of the Nb ₃ Sn compound superconducting wire, the presence or absence of stabilizing copper, and the material of the diffusion barrier, Nb or an Nb-based alloy as described above, which constitutes the superconducting compound, Sn or the above. Similar effects can be obtained if the Sn-based alloy and Cu are configured as in the present invention.
[0019]
Embodiment 5 FIG.
Further, in the first and second embodiments, an example in which the first 253 pieces and the second 55 pieces are bundled and put in a Cu tube (sheath material) is described, but the focusing is performed only once or three times as necessary. The same effect can be obtained by performing the above. Furthermore, the above-mentioned number of convergence is not particularly limited, and the same effect can be obtained regardless of the number of convergence.
[0020]
Embodiment 6 FIG.
In the first embodiment, only one example of the arrangement of Sn or Sn-based alloy around one Nb or Nb-based alloy rod is described, and another arrangement may be adopted.
For example, not one Nb or Nb alloy rod but a plurality of closely arranged Nb or Nb alloy rods can be used. Similar effects can be obtained by disposing the Nb or Nb-based alloy rod 1 and the Sn or Sn-based alloy rod 2 in the circular Cu tube 3 as shown in FIG.
[0021]
Embodiment 7 FIG.
In the second embodiment, the case where the first and second composite wires are formed into a hexagon and converged is described, but another wire shape is also effective.
For example, the same effect can be obtained by arranging each of the first and second composite wires in the circular Cu tube 3 as shown in FIG.
Further, the Nb or Nb alloy rod and the Sn or Sn alloy rod included in the first and second composite wires may each be a plurality of closely arranged rods.
[0022]
Embodiment 8 FIG.
The same effect can be obtained even if the arrangement of the first and second composite wires in the second embodiment is changed to an arrangement in which the second composite wire is surrounded by the first composite wire as shown in FIG. can get.
[0023]
Embodiment 9 FIG. ~ 13.
As shown in FIG. 6, a plurality of circular vertical holes are made in a copper or copper-based alloy rod (sheath), for example, a circular rod, and an Nb rod 1 and a Sn rod 2 are respectively formed therein. The heat treatment and the cross-section reduction processing may be performed in the same manner as in the above embodiment. FIG. 6 shows a case where seven circular vertical holes having the same size are provided and the Nb bar 1 and the Sn bar 1 are arranged adjacent to each other. In addition, seven circular vertical holes having the same size are provided, and When a bar having Sn provided around the Nb bar is inserted therein (FIG. 7), 19 circular vertical holes of the same size are provided, and a bar having Sn provided around the Nb bar is inserted therein. (FIG. 8), when Nb rods 1 and Sn rods 1 are inserted adjacent to each other in 19 circular vertical holes of the same size (FIG. 9), the Nb rod 1 is inserted into the central large circular vertical hole. Is inserted, and the same effect can be obtained in each case where an Sn bar is inserted into a small circular vertical hole around the hole (FIG. 10).
In the above description, the vertical hole of the sheath material is circular, but the shape is not particularly limited and can be various shapes. Further, in the above description, the case where the number of the vertical holes is 7 or 19 is described, but the number is not particularly limited, and other numbers can be used as necessary.
[0024]
【The invention's effect】
As described above, according to the present invention, the arrangement of Sn is not concentrated, but is distributed around each Nb, so that the dead zone for Nb arrangement is eliminated and the interval between Nb filaments is lengthened. I was able to. Therefore, since the connection between the Nb ₃ Sn compound filaments does not occur, the effective filament diameter is reduced, and the hysteresis loss can be reduced while the critical current density is kept high. For example, the calorific value in the superconducting wire of the pulse coil can be suppressed. There are effects that can be. Also in the production of the superconducting wire, since it is made of a soft pure metal without using a hard bronze matrix or the like, there is an effect that the production is easy and inexpensive.
[Brief description of the drawings]
FIG. 1 is a partially enlarged cross-sectional view of a bundle of Nb ₃ Sn compound superconducting composite wires according to one embodiment of the present invention.
FIG. 2 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 3 is a partially enlarged cross-sectional view when the Nb ₃ Sn compound superconducting composite wires according to one embodiment of the present invention are bundled.
FIG. 4 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 5 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 6 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 7 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 8 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to one embodiment of the present invention.
FIG. 9 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an embodiment of the present invention.
FIG. 10 is a partially enlarged cross-sectional view of an Nb ₃ Sn compound superconducting element wire according to an example of the present invention.
FIG. 11 is a cross-sectional view of an Nb ₃ Sn compound superconducting wire manufactured by a conventional method.
FIG. 12 is a cross-sectional view of an Nb ₃ Sn compound superconducting element wire being processed in a conventional method.
FIG. 13 is a cross-sectional view of an Nb ₃ Sn compound superconducting element wire being processed in a conventional method.
[Explanation of symbols]
1 Nb or Nb alloy rod 2 Sn or Sn alloy rod 3 Cu tube 4 Diffusion barrier 5 Nb ₃ Sn filament 6 Bronze matrix

Claims (3)

One Nb or Nb-based alloy rod or a plurality of closely arranged Nb or Nb-based alloy rods, Sn or Sn-based alloy rod disposed around the Nb or Nb-based alloy rod, and Cu disposed around these or Cu-based composite wire made of an alloy, after insertion into the sheath material by bundling a plurality of, to obtain a wire with reduced cross processed, characterized by heat-treating the plain lines, the Nb 3 _Sn compound superconducting wire Production method. One Nb or Nb-based alloy rod or a plurality of closely arranged Nb or Nb-based alloy rods, and a first composite wire made of Cu or Cu-based alloy disposed around them, and one Sn or Sn A base alloy rod or a plurality of closely arranged Sn or Sn-based alloy rods and a second composite wire made of Cu or Cu-based alloy disposed around these are disposed so as to be dispersed and inserted into the sheath material. A method of producing a Nb ₃ Sn compound superconducting wire, characterized in that a wire is obtained by reducing the cross section and then the wire is heat-treated. One Nb or Nb-based alloy rod or a plurality of closely arranged Nb or Nb-based alloy rods and one Sn or Sn-based alloy rod in a plurality of vertical holes provided in a copper or copper-based alloy rod Nb ₃ Sn compound superconductivity, characterized in that a plurality of closely arranged Sn or Sn-based alloy rods are separately or integrally inserted, a cross-section is reduced to obtain a strand, and the strand is heat-treated. Wire manufacturing method.

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