JP2010015821A - Precursor for manufacturing nb3sn superconductive wire rod and method of manufacturing the same, and nb3sn superconductive wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inner Sn method Nb3Sn superconductive wire rod and a precursor and the like for it increasing a volume ratio of Nb core rods, preventing the occurrence of bridging between the Nb core rods, exhibiting high critical current density Jc characteristics, allowing superconductive connection between the superconducting wire rods if necessary, and applicable to an NMR magnet. <P>SOLUTION: The precursor is obtained by forming a composite tube, which is constructed by having a cylindrical diffusion barrier layer equipped with a stabilization copper layer on the outer circumference and inserting a composite wire rod group inside the cylindrical diffusion barrier layer, into a wire. The composite wire rod group includes a plurality of Nb element wire rods each of which is prepared by embedding Nb or Nb-base alloy cores in a Cu or Cu-base alloy matrix and has a hexagonal cross section, and a plurality of Sn core rods each of which is formed of Sn or Sn-base alloy and has a polygonal or circular cross section, and the Nb element wire rods are arranged to be brought into contact mutually while surrounding the Sn core rod. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a precursor (precursor for producing a superconducting wire) for producing an Nb ₃ Sn superconducting wire by an internal Sn method, a method for producing the precursor, and an Nb ₃ Sn superconducting wire produced by such a precursor. In particular, the present invention relates to a Nb ₃ Sn superconducting wire useful as a material for a superconducting magnet, a precursor thereof, and the like.

Among the fields where superconducting wires are put into practical use, there are superconducting magnets used in high-resolution nuclear magnetic resonance (NMR) analyzers, fusion devices, accelerators, and the like. As a superconducting wire used for the superconducting magnet, an Nb ₃ Sn wire has been put into practical use, and the bronze method is mainly employed for manufacturing this Nb ₃ Sn superconducting wire. In this bronze method, a composite wire is formed by embedding a core material made of a plurality of Nb or Nb base alloys in a Cu—Sn base alloy (bronze) matrix. The composite wire is subjected to diameter reduction processing such as extrusion or wire drawing, whereby the core material is reduced in diameter to form an Nb-based filament, and a plurality of composite wires made of the Nb-based filament and bronze are bundled to form a wire group. After the copper for stabilization (stabilized copper) is disposed on the outer periphery, the diameter is further reduced. Subsequently, the wire group after the diameter reduction is heat-treated (diffusion heat treatment) at about 600 ° C. or more and 800 ° C. or less, so that an Nb ₃ Sn compound phase (Nb ₃ Sn superconducting phase) is formed at the interface between the Nb-based filament and the bronze matrix. Is a method of generating

However, in this method, there is a limit to the Sn concentration that can be dissolved in bronze (15.8% by mass or less), the thickness of the produced Nb ₃ Sn compound phase is thin, and the crystallinity is deteriorated. There is a drawback that a high critical current density Jc cannot be obtained. Superconducting magnets (hereinafter sometimes referred to as “NMR magnets”) can make the NMR magnets more compact as the critical current density Jc of the wire is higher, and can reduce the cost of the magnets and shorten the delivery time. Moreover, since the area of the superconducting portion in the conductor can be reduced, the cost of the wire itself can be reduced.

In addition to the bronze method, an internal Sn method is also known as a method for producing the Nb ₃ Sn superconducting wire. In this internal Sn method, since there is no limit on the Sn concentration due to the solid solubility limit as in the bronze method, the Sn concentration can be set as high as possible, and a high-quality Nb ₃ Sn compound phase can be generated. It is said that it can be obtained. Moreover, in the superconducting wire by the above bronze method, the Cu-Sn alloy undergoes work hardening during cold working, and thus requires many annealings. However, the internal Sn method requires almost no annealing, and the delivery time can be shortened. Therefore, it is expected that a superconducting wire manufactured by the internal Sn method (hereinafter, also referred to as “internal Sn method Nb ₃ Sn superconducting wire”) is used for NMR magnets.

In the internal Sn method, as shown in FIG. 1 (schematic diagram of the basic structure of the precursor for producing the internal Sn method Nb ₃ Sn superconducting wire), Cu or a Cu-based alloy (hereinafter sometimes referred to as “Cu matrix”) 4, a core 3 made of Sn or an Sn-based alloy (hereinafter sometimes referred to as “Sn core”) 3 is embedded, and a plurality of Cu matrices 4 around the Sn core 3 are embedded. A core material (hereinafter sometimes referred to as “Nb core material”) 2 made of Nb or an Nb-based alloy is disposed so as not to contact each other to form a precursor (precursor for manufacturing a superconducting wire) 1, which is expanded. In this method, after the wire processing, Sn in the Sn core material 3 is diffused by heat treatment (diffusion heat treatment) and reacted with the Nb core material 2 to generate an Nb ₃ Sn compound phase in the wire material.

  Further, in the precursor as described above, as shown in FIG. 2, a diffusion barrier layer 6 is provided between the portion where the Nb core material 2 and the Sn core material 3 are disposed and the stabilizing copper layer 4a outside thereof. The arranged configuration (precursor 5) may be employed. The diffusion barrier layer 6 has a cylindrical shape (cylindrical barrier layer) and is composed of, for example, an Nb layer or a Ta layer (including each alloy layer), or two layers of an Nb layer and a Ta layer. In this case, Sn in the Sn core material 3 is prevented from diffusing to the outside, and the effect of increasing the purity of Sn in the superconducting wire is exhibited.

  1 and 2 show the configuration in which one Sn core material 3 is arranged, the configuration of the precursor (precursor for manufacturing a superconducting wire) is not limited to this, and a plurality of Sn core materials 3 are provided. Is also adopted (see FIGS. 3 to 5 below).

Various proposals have been made for the construction of precursors that exhibit good superconducting properties (particularly, high critical current density Jc) in producing Nb ₃ Sn superconducting wires by the internal Sn method. As such a technique, for example, Patent Document 1 discloses an Nb element wire in which a core material (Nb core material) made of a plurality of Nb or Nb base alloys is embedded in a Cu matrix, and a core material made of Sn or Sn base alloy ( The structure which disperses Sn by arrange | positioning combining (Sn core material) is proposed.

  FIG. 3 is a cross-sectional view schematically showing the configuration of the precursor proposed in the above technique, and the same reference numerals are assigned to the portions corresponding to FIGS. In this configuration, the Nb element wire 7 in which a plurality (19 in this figure) of the Nb core material 2 is embedded in the Cu matrix 4 has a circular cross section (cross section perpendicular to the axis) and a Sn shape. The core material 3 is also formed into a circular shape in cross section (cross section perpendicular to the axis), and by combining these, a precursor in which the Nb core material 2 and the Sn core material 3 are appropriately dispersed is obtained (precursor 11). .

  In the configuration of the precursor 11 shown in FIG. 3, a gap is formed between the Nb element wires 7 due to the circular cross-sectional shape of the Nb element wires 7. The superconducting wire precursor is formed into a wire by being subjected to diameter reduction processing such as extrusion and wire drawing after the composite material having the configuration shown in FIGS. 1 to 3 is formed. During processing, the internal temperature of the precursor may rise to 210 ° C. or higher, which is the melting point temperature of Sn, due to processing heat generation. In such a case, if a gap is formed between the Nb element wires 7 as shown in FIG. 3, the melted Sn core material 3 enters the gap, causing non-uniform deformation and workability. There is a problem of getting worse.

  As techniques for solving these problems, for example, techniques such as Patent Documents 2 and 3 have been proposed. FIG. 4 shows a configuration example of the precursor proposed in Patent Document 2. In this configuration, an Nb element wire 7 in which a plurality of cores (Nb cores) 2 made of Nb or an Nb-based alloy are embedded in a Cu matrix 4 has a cross-sectional shape of a hexagon, and the Cu matrix The Sn element wire 8 in which a core material (Sn core material) 3 made of Sn or an Sn-based alloy is embedded has a hexagonal cross section, and these are combined to constitute a wire group. In the configuration shown in FIG. 4, a plurality of Sn element wires 8 are gathered at the center, and Nb element wires 7 are bundled and arranged around the periphery (precursor 13).

  On the other hand, in the configuration example of the precursor proposed in Patent Document 3, as shown in FIG. 5, the periphery of the Sn element wire 8 having a hexagonal cross section as described above is formed around Nb having a hexagonal cross section. The element wire 7 is dispersed and arranged so as to surround it (precursor 14).

  In the precursor as shown in FIGS. 4 and 5, the Sn core material 3 is embedded in the Cu matrix 4, so that Sn can be prevented from being melted into the interface of the Nb element wire 7 and good. Workability will be demonstrated. The structure of the precursor shown in FIGS. 1 and 2 shows a state in which each core material (Nb core material and Sn core material) and the Cu matrix 4 are integrated after the diameter reduction processing.

  However, in the configuration shown in FIGS. 4 and 5, it is difficult to reduce the ratio of the Cu matrix 4 constituting the Sn element wire 8, and the Cu portion (so-called “Cu fillet portion”) per cross-sectional area increases. Inevitably, the area ratio of the Sn core material 3 is insufficient. As a result, the arrangement number of the Sn element wires 8 is inevitably increased, so that the volume ratio of the Nb core material 2 is relatively reduced, which is expected as compared with the precursor as shown in FIG. There is a problem that the critical current density Jc improvement effect cannot be exhibited.

In order to increase the cross-sectional area ratio of the Nb ₃ Sn compound layer and improve the critical current density Jc, if the Nb cross-sectional area ratio of the Nb element wire 7 is increased, the interval between the Nb core materials 2 becomes narrow. In the diffusion heat treatment, the Nb core materials 2 cause bridging, the effective filament diameter is increased, and the stability of the NMR magnet tends to be deteriorated. The effective filament diameter means an effective diameter when the filament swings as one body, and is an index of magnetic stability. It is judged that the smaller this value, the better the superconducting characteristics. Will be. Further, in the technique shown in Patent Document 3, a configuration in which Cu is finned in the cross section of the Nb element wire is proposed in order to reduce the effective filament, but in such a configuration, the cross section of the Nb core material 2 is proposed. The ratio decreases, which is disadvantageous for the critical current density Jc.

By the way, superconducting magnets used in NMR analyzers and the like are required to have a very stable magnetic field change rate (attenuation rate) of 0.01 ppm / hr or less, so that the superconducting current is permanently looped. It needs to be operated in a “permanent current mode” that continues to flow. In an actual magnet, a plurality of superconducting coils are connected and used, but in order to realize the permanent current mode, the superconducting state is maintained even in the portion where the superconducting wires are connected between the coils (this is referred to as “superconducting”). Connection). For this reason, the diffusion barrier layer made of Nb-based metal or Ta-based metal that becomes normal conducting is removed by an external magnetic field (about 0.5 T) at the position where the connection portion is disposed, and Nb ₃ is added after the diffusion heat treatment. It is necessary to expose and connect the Sn compound layer.

From such a viewpoint, the internal configuration as shown in FIGS. 3 to 5 does not consider application to the NMR magnet (that is, the “superconducting connection”). In application to the NMR magnet, it is necessary to remove the diffusion barrier layer and expose the Nb ₃ Sn compound phase after the heat treatment in order to achieve superconducting connection. However, in the internal configuration as shown in FIGS. When the diffusion barrier layer is removed, the Nb core material 2 is exposed, which is easily oxidized during the heat treatment, and hinders superconducting connection.
Japanese Patent Publication No. 4-23363 Japanese Patent Publication No.7-17992 JP 2006-4684 A

The present invention has been made under such circumstances, and the object thereof is to increase the volume ratio of the Nb core material, to prevent bridging of the Nb core materials, and to have a high critical current density Jc characteristic. An internal Sn method Nb ₃ Sn superconducting wire and a precursor therefor, and a useful method for producing such a precursor, which can be applied to an NMR magnet by enabling superconducting connection between superconducting wires if necessary It is to provide.

The precursor for producing a superconducting wire of the present invention that has achieved the above-mentioned object is,
Precursor used when manufacturing Nb ₃ Sn superconducting wire by the internal Sn method has a cylindrical diffusion barrier layer provided with a stabilized copper layer on the outer periphery, and a composite wire group is inserted into the cylindrical diffusion barrier layer A precursor obtained by converting the composite pipe made into a wire,
The composite wire rod group is
A plurality of Nb element wires in which a Nb or Nb-based alloy core is embedded in a Cu or Cu-based alloy matrix and the cross-sectional shape is a hexagon;
A plurality of Sn cores made of Sn or Sn-based alloy and having a polygonal or circular cross-sectional shape,
The Nb element wire has a gist in that it is arranged in contact with each other so as to surround the Sn core material.

  Preferred embodiments of the precursor for producing a superconducting wire of the present invention include: (a) the size of the cross section of the Sn core material is the same as or smaller than the size of the cross section of the Nb element wire; (B) The cylindrical diffusion barrier layer is a layer made of Nb or Nb-based alloy and / or a layer made of Ta or Ta-based alloy, and further between the cylindrical diffusion barrier layer and the composite wire rod group. Examples include a configuration in which a layer made of Cu or a Cu-based alloy is arranged.

A Nb ₃ Sn superconducting wire exhibiting desired superconducting properties (critical current density Jc, magnetic field attenuation factor) can be produced by diffusion heat treatment using the precursor for producing a superconducting wire as described above.

On the other hand, the production method of the present invention that has achieved the above object
A Nb or Nb-based alloy core is embedded in a Cu or Cu-based alloy matrix, and a plurality of Nb element wires each having a hexagonal cross-sectional shape and a Sn or Sn-based alloy, and a plurality of cross-sectional shapes that are polygonal or circular Of Sn core material,
The Nb element wires are arranged in contact with each other so as to surround the Sn core material to form a composite wire group,
The present invention is summarized in that the composite wire group is inserted into a cylindrical diffusion barrier layer provided with a stabilizing copper layer on the outer periphery to form a composite tube, and the composite tube is reduced in diameter to form a wire.

In producing the Nb ₃ Sn superconducting wire production precursor of the embodiment shown in (b) above, a Cu hollow billet comprising a Cu outer cylinder and a Cu inner cylinder is prepared, and the outer periphery of the Cu inner cylinder After forming the cylindrical diffusion barrier layer on the surface and inserting it into the Cu outer cylinder, hot-extrusion it, and then inserting the composite wire group into the Cu inner cylinder And a step of reducing the diameter of the composite tube to form a wire rod.

In the precursor for manufacturing a superconducting wire according to the present invention, a composite wire group as a constituent element of the precursor is composed of a plurality of Nb or Nb-based alloy cores embedded in a Cu or Cu-based alloy matrix and a cross-sectional shape of a hexagon. The volume ratio of the Nb metal core can be increased because the Nb element wire is made of Sn or Sn-based alloy and the plurality of Sn cores having a polygonal or circular cross section are arranged and configured appropriately. At the same time, an internal Sn method Nb ₃ Sn superconducting wire that can prevent bridging between Nb cores and exhibit high critical current density Jc characteristics has been realized.

  The structure of the precursor for manufacturing a superconducting wire according to the present invention (hereinafter sometimes simply referred to as “precursor”) will be described with reference to the drawings. FIG. 6 is a cross-sectional view schematically showing a basic configuration example of the precursor of the present invention. In the structure of the precursor of the present invention, the Nb element wire 7 in which one or more (seven in the figure) Nb core material 2 (Nb or Nb-based alloy core) is embedded in the Cu matrix 4 has a cross-sectional shape. Is formed in a hexagonal shape, and the plurality of Sn core materials 3 are formed in a polygonal shape or a circular shape in cross section (precursor 15). The Nb element wire 7 is arranged so as to be in contact with each other so as to surround the Sn core material 3, thereby forming a wire group (composite wire group) in the precursor.

  In order to configure the wire group as described above, the size of the cross section of the Sn core 3 is preferably smaller than the size of the cross section of the Nb element wire 7 (that is, surrounded by the Nb element wire 7). The Sn core material 3 and the Nb element wire 7 can have the same cross-sectional shape (that is, a hexagonal cross-sectional shape). Further, the cross-sectional shape of the Sn core material 3 can be a hexagonal shape or a polygonal shape such as an octagonal shape, but is preferably a circular shape in consideration of the workability of the material. In any case, the Sn core material 3 used in the present invention has no Cu matrix 4 formed on the surface.

  In the configuration of the precursor as shown in FIG. 3, both the Nb element wire 7 and the Sn core material 3 are formed to have a circular cross-sectional shape. When the diffusion barrier layer 6 and the stabilized copper 4a are disposed and subjected to diameter reduction processing such as extrusion or wire drawing, the Sn core material 3 is deformed before the Nb element wire 7 is deformed and the interface is brought into close contact. In some cases, it enters the interface between the Nb element wires 7 in a melted state due to processing heat generation.

  On the other hand, in the configuration of the precursor of the present invention, at least the Nb element wire 7 has a hexagonal cross-sectional shape, so that the Sn core is in a state where the adhesion of the Nb element wire is ensured during the diameter reduction processing. Since the material is processed, melted Sn does not enter the interface between the Nb element wires, and the workability can be significantly improved.

  In the precursor 15 of the present invention, since the Sn core material 3 is not formed with the Cu matrix 4 on the surface, compared with the configuration of the precursors 13 and 14 shown in FIGS. Since the Cu core portion can be reduced, a small Sn core material 3 is sufficient, and as a result, the volume ratio of the Nb core material 2 can be relatively increased, and a high critical current density Jc can be secured.

  Production of the precursor for producing a superconducting wire as described above is performed in the following procedure. First, the Nb core material 2 is inserted into a Cu matrisk tube, and subjected to diameter reduction processing such as extrusion or wire drawing to form a composite (Nb element wire 7) having a cross-sectional shape formed in a hexagonal shape. Cut to the right. On the other hand, a plurality of Sn cores 3 made of Sn or Sn-based alloy and having a polygonal or circular cross-sectional shape are formed by diameter reduction processing. The Nb element wire 7 is arranged in contact with each other so as to surround the Sn core material 3 to form a composite wire group, and a diffusion barrier layer (tubular diffusion barrier layer) 6 provided with a stabilizing copper layer 4a on the outer periphery. The composite wire group is inserted into a composite pipe, and the composite pipe is reduced in diameter to form a wire.

  The diffusion barrier layer 6 is a layer made of Nb or an Nb-based alloy and / or a layer made of Ta or a Ta-based alloy (a layer made of Nb or an Nb-based alloy or a layer made of Ta or a Ta-based alloy, as in the prior art. The layer 4b (FIG. 6) made of Cu or a Cu-based alloy is further arranged between the diffusion barrier layer 6 and the composite wire rod group. This is a preferable form for realizing the superconducting connection in the superconducting wire.

  When realizing the superconducting connection in the superconducting wire, it is necessary to remove the diffusion barrier layer 6 and the stabilized copper 4a before the heat treatment, but the conventional precursors 11, 13, and 3 shown in FIGS. In the configuration of 14, the internal Nb core material 2 is exposed before the heat treatment, and this is oxidized during the heat treatment, so that the superconducting connection cannot be realized. On the other hand, by adopting the configuration in which the layer 4b made of Cu or a Cu-based alloy is arranged as described above, superconducting connection is possible without incurring the above disadvantages.

  In producing a precursor capable of superconducting connection as described above, a Cu hollow billet comprising a Cu outer cylinder and a Cu inner cylinder is prepared, and the cylindrical diffusion barrier layer is formed on the outer peripheral surface of the Cu inner cylinder. Is inserted into the Cu outer cylinder, and after hot hollow extrusion, the composite wire group is inserted into the Cu inner cylinder to form a composite pipe. This can be realized by including a step of reducing the diameter to form a wire (see Example 1 described later).

In the precursor of the present invention, the Cu content in the portion inside the diffusion barrier layer 6 (that is, in the composite wire group) (when the layer 4b made of Cu or a Cu-based alloy is disposed inside the diffusion barrier layer 6) Is included) and the ratio of Sn content to the total amount of Sn content [Su content / (Cu + Sn content)] is preferably about 20 to 38%. When this ratio is less than 20%, the Sn content is insufficient, the crystallinity of the Nb ₃ Sn compound phase is deteriorated, and the superiority to the bronze superconducting wire is lost. On the other hand, when the ratio exceeds 38%, Sn in the liquid phase is easily generated in the process of Sn diffusing into Cu, and the diffusion rate of Cu into Sn is increased. Voids are likely to occur in the Cu matrix portion. The generation of such voids induces bridging of the Nb core materials 2 and causes the effective filament diameter to increase and the superconducting characteristics to become unstable.

Moreover, in the precursor 15 of this invention, it is preferable to control so that the Nb volume ratio in the Nb element wire 7 may be set to 50 to 70%. When this ratio is less than 50%, the volume ratio of the Nb ₃ Sn compound phase decreases, and the critical current density Jc decreases. However, when this ratio exceeds 70% and becomes excessive, the interval between the Nb core materials 2 is narrowed, and bridging between the Nb core materials 2 is likely to be induced.

  In the precursor of the present invention, the diameter of the Sn core material 3 is preferably set to 20 to 50 μm at the stage after the final wire drawing and before the diffusion heat treatment. The smaller the Sn core material 3 is, the more preferable it is that the Nb core material 2 is evenly arranged. However, the Sn core material 3 is said to improve the superconducting characteristics in a high magnetic field. From the viewpoint, a Ti element alloy of about 1 to 2% by mass is often added, and the size of the Ti—Sn compound formed when such an element is added is about 20 μm at maximum. The size of 3 is preferably larger than the size of this compound. However, if the diameter of the Sn core material 3 is larger than 50 μm, when Sn diffuses into Cu, large voids are likely to occur in the vicinity of the Sn core material 3, leading to a decrease in strength of the superconducting wire.

In the precursor 15 having the above-described configuration, the Nb ₃ Sn superconducting wire obtained by diffusion heat treatment exhibits a higher critical current density Jc characteristic than the bronze normal wire. This will contribute to cost reduction and delivery time reduction.

  The precursor of the present invention basically includes an Nb element wire 7 in which a core material (Nb core material 2) made of Nb or an Nb base alloy is embedded in a Cu or Cu base alloy matrix, and an Sn or Sn base alloy. The core material (Sn core material 3) is a constituent material. However, as a Cu-based alloy used as a material of a Cu matrix, an element such as Nb or Ni is contained in Cu (up to about 5% by mass). Things can be used. As the Nb-based alloy used as the Nb element wire 7, an alloy containing an additive element such as Ta, Zr, Hf or the like up to about 10% by mass can be used. Further, as the Sn-based alloy used as the Sn core material 3, use is made of Sn containing an additive element such as Ti, Ta, Zr, Hf or the like to such an extent that the workability is not hindered (5% by mass or less). Can do.

In the present invention, excellent superconducting properties (critical current density Jc) are exhibited by using the precursor 15 as described above and performing diffusion heat treatment (typically about 200 ° C. or more and less than about 800 ° C.) including bronzing heat treatment. Nb ₃ Sn superconducting wire can be obtained. Specifically, after performing a bronzing heat treatment (diffusion of Sn into Cu) in a temperature range of 180 to 600 ° C., heat treatment for generating Nb ₃ Sn for about 100 to 300 hours in a temperature range of 650 to 750 ° C. To do. As the bronzing heat treatment, (a) about 180 hours at 180 to 200 ° C., about 50 hours at about 340 ° C., about 50 to 100 hours at about 550 ° C., or (b) about 50 hours at 300 to 350 ° C. , A combination of multi-stage heat treatments such as 30 to 100 hours at 500 to 550 ° C.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Example 1]
According to the following procedure, the precursor whose cross-sectional shape was shown in FIG. 6 was produced. First, an Nb core having an outer diameter of 28 mm was inserted into a Cu pipe having an outer diameter of 32.8 mm and an inner diameter of 29 mm, and then reduced in diameter to obtain a Cu / Nb composite single core wire (outer diameter: 9.5 mm). After making and correcting, it was cut to a length of 0.70 m. Seven of these are bundled and inserted into a Cu pipe (outer diameter: 32.8 mm, inner diameter: 29.0 mm) and drawn, and a Cu / Nb composite multifilamentary wire having a hexagonal cross-sectional shape (hexagonal opposite side: 2.0 mm) ( Nb element wire) was prepared and corrected, and then cut to a length of 0.70 m. In addition, a Sn-2 mass% Ti rod (Sn core material) having a diameter of 1.9 mm was prepared, and after correction, it was cut into a length of 0.70 m. The volume ratio of the Nb core material 2 in the Nb element wire at this time is 65%.

  On the other hand, a Cu hollow billet comprising a Cu outer cylinder (outer diameter: 143 mm, inner diameter: 88.5 mm) and a Cu inner cylinder (outer diameter: 76 mm, inner diameter: 51 mm) was prepared. Then, an Nb sheet (thickness: 0.2 mm) is wound around the outer peripheral surface of the Cu inner cylinder of the Cu hollow billet, inserted into the Cu outer cylinder, covered, vacuumed, and then welded. did. The hollow billet thus obtained was hot hollow extruded to obtain a composite pipe (outer diameter: 45 mm, inner diameter: 38 mm).

  The Nb element wire: 210 and the Sn core material: 73 are combined so that the Nb element wire surrounds the Sn core material to form a composite wire group, and this composite wire group is formed in the composite pipe. And drawn to obtain a precursor having an outer diameter of 1.0 mm (see FIG. 6). The diameter of the Sn core material at this stage is 43 μm.

The obtained precursor (with an outer diameter of 1.0 mm) was subjected to heat treatment (diffusion heat treatment) of 210 ° C. × 50 hours + 350 ° C. × 100 hours + 670 ° C. × 100 hours to obtain an Nb ₃ Sn superconducting wire. The resulting Nb ₃ Sn superconducting wire, by the method described below, was determined in terms of critical current density Jc, an effective filament diameter and the magnetic field attenuation rate. In addition, the number of breaks during diameter reduction (or wire drawing) was also investigated.

[Measurement of critical current density Jc]
In liquid helium (temperature 4.2K), a sample (superconducting wire) is energized under an external magnetic field of 12T (Tesla), and the generated voltage is measured by the 4-terminal method. This value is an electric field of 0.1 μV / cm. The critical current density Jc was determined by measuring the current value (critical current Ic) at which the current occurred and dividing this current value by the cross-sectional area per non-Cu portion of the wire.

[Measurement method of effective filament diameter]
The magnetization curve with respect to the magnetic field fluctuation within 3T (Tesla) was measured, and the effective filament diameter _def was determined based on the following equation (1).
Effective filament diameter d _ef = (3π × ΔM) / (4 μ ₀ × Jc) (1)
Where ΔM: magnetization curve width (mT), μ ₀ : 4π × 10 ⁻⁷ (H / m), Jc: critical current density (A / mm ² ), respectively.

[Measurement of magnetic field decay rate]
A connection resistance evaluation circuit as shown in FIG. 8 was formed. In FIG. 8, 21 is a U-shaped sample for connection made by the manufactured Nb ₃ Sn superconducting wire, 22 is a permanent current switch, 23 is a power source, and 24 is a superconducting coil. After the heat treatment of the connection U-shaped sample 21, as shown in FIG. 7, the outer shell Cu of the end 17 of the connection U-shaped sample 21 is removed to expose the Nb ₃ Sn filament 20, and the superconducting intermediate 18 The superconducting wire magnet 16 (superconducting coil 24) and the superconducting wire 16 are connected at two locations (both ends of the connecting U-shaped sample 21) via (for example, a Pb-based alloy), and the connection location is 4.2K. A magnetic field of 0.5 T was applied to measure the attenuation rate of the magnetic field at the center of the coil 24. At this time, the attenuation rate (ppm / hr) was measured by a change in resonance frequency (corresponding to a magnetic field) with an NMR probe. In FIG. 7, reference numeral 19 denotes a Cu base container.

(Comparative Example 1)
According to the following procedure, a precursor whose cross-sectional shape was shown in FIG. 3 was prepared. First, an Nb core having an outer diameter of 28 mm was inserted into a Cu pipe having an outer diameter of 32.8 mm and an inner diameter of 29 mm, and then reduced in diameter to obtain a Cu / Nb composite single core wire (outer diameter: 9.5 mm). After making and correcting, it was cut to a length of 0.70 m. Seven of these are bundled and inserted into a Cu pipe (outer diameter: 32.8 mm, inner diameter: 29.0 mm) and drawn to produce a Cu / Nb composite multifilamentary wire (Nb element wire) with a diameter of 2.0 mm. Then, after correction, it was cut into a length of 0.70 m. Moreover, a Sn-2 mass% Ti rod (Sn core material) having a diameter of 2.0 mm was prepared, and after correction, it was cut into a length of 0.70 m. At this time, the volume ratio of the Nb core material 2 in the Nb element wire is 0.17%.

  An Nb sheet (thickness: 0.2 mm) was wound around the inner peripheral surface of a Cu pipe (outer diameter: 45 mm, inner diameter: 38 mm). The Nb element wire: 210 and the Sn core material: 73 are combined so that the Nb element wire surrounds the Sn core material to form a composite wire group, and this composite wire group is formed in the Cu pipe. And was drawn into a precursor having an outer diameter of 1.0 mm (see FIG. 3). The diameter of the Sn core material at this stage is 70 μm.

The obtained precursor (with an outer diameter of 1.0 mm) was subjected to heat treatment (diffusion heat treatment) of 210 ° C. × 50 hours + 350 ° C. × 100 hours + 670 ° C. × 100 hours to obtain an Nb ₃ Sn superconducting wire. For the obtained Nb ₃ Sn superconducting wire, the critical current density Jc, the magnetic field attenuation factor, and the effective filament diameter were measured in the same manner as in Example 1.

(Comparative Example 2)
According to the following procedure, the precursor whose cross-sectional shape was shown in FIG. 5 was prepared. First, an Nb core having an outer diameter of 28 mm is inserted into a Cu pipe having an outer diameter of 32.8 mm and an inner diameter of 29 mm, and then reduced in diameter to produce a Cu / Nb composite single core wire (outer diameter: 9.5 mm). Then, after correction, it was cut into a length of 0.70 m. Seven of these are bundled and inserted into a Cu pipe (outer diameter: 32.8 mm, inner diameter: 29.0 mm) and drawn to produce a Cu / Nb composite multifilamentary wire (Nb element wire) with a diameter of 2.0 mm. Then, after correction, it was cut into a length of 0.70 m. At this time, the volume ratio of the Nb core material 2 in the Nb element wire is 28%.

  On the other hand, in a Cu pipe (outer diameter: 23 mm, inner diameter: 21 mm), an Sn-2 mass% Ti rod (Sn core material) having a diameter of 20 mm is inserted and drawn, and a hexagonal cross section (hexagonal opposite side: 2.. 0 mm) Cu / Sn composite single core wire was prepared, and after correcting this, it was cut into a length of 0.70 m.

  An Nb sheet (thickness: 0.2 mm) was wound around the inner peripheral surface of a Cu pipe (outer diameter: 45 mm, inner diameter: 38 mm). The Nb element wire: 192 and the Cu / Sn composite single core wire: 91 are combined so that the Nb element wire surrounds the Sn core material to form a composite wire group, and this composite wire group, It was inserted into a Cu pipe and drawn to obtain a precursor for producing a superconducting wire having an outer diameter of 1.0 mm (see FIG. 5). The diameter of the Sn core material at this stage is 64 μm.

The obtained precursor (with an outer diameter of 1.0 mm) was subjected to heat treatment (diffusion heat treatment) of 210 ° C. × 50 hours + 350 ° C. × 100 hours + 670 ° C. × 100 hours to obtain an Nb ₃ Sn superconducting wire. For the obtained Nb ₃ Sn superconducting wire, the critical current density Jc, the magnetic field attenuation factor, and the effective filament diameter were measured in the same manner as in Example 1.

(Comparative Example 3)
A precursor by the bronze method was prepared according to the following procedure. An Nb rod having a diameter of 8.0 mm was inserted into a Cu-15 mass% Sn alloy having an outer diameter of 67 mm, the end was sealed by welding, and an extruded billet was produced. This extruded billet was drawn while appropriately annealing at 400 to 600 ° C. for 1 hour to obtain a Cu—Sn / Nb composite wire having a hexagonal cross section (hexagon opposite side: 2.5 mm). 433 Cu-Sn / Nb composite wires are bundled, and a Nb sheet having a thickness of 0.2 mm is wound twice around the outer periphery (diffusion barrier layer), and a Cu pipe having an outer diameter of 67 mm and an inner diameter of 59 mm around the periphery. (Stabilized copper) was placed. The composite wire thus obtained was sealed at the end by electron beam welding and extruded billet. This extruded billet was extruded and drawn into a wire having a wire diameter of 1.0 mm (precursor for producing a superconducting wire).

The obtained precursor (with an outer diameter of 1.0 mm) was subjected to a heat treatment (diffusion heat treatment) at 700 ° C. for 100 hours to obtain an Nb ₃ Sn superconducting wire. The resulting Nb ₃ Sn superconducting wire, the critical current density in the same manner as in Example 1 (Jc), the effective filament diameter, the magnetic field attenuation rate, and breakage number was measured.

The superconducting characteristics (magnetic field: 12T, temperature: critical current density Jc at 4.2K), effective filament diameter, and number of disconnections of the superconducting wires obtained in Example 1 and Comparative Examples 1 to 3 are as follows. These are shown collectively in Table 1 below. The critical current density Jc needs to be at least 800 A / mm ² (preferably 2000 A / mm ² or more), and the magnetic field attenuation factor needs to be 0.01 ppm / hr or less.

  As is clear from this result, in Example 1 that satisfies the requirements defined in the present invention, the magnetic field attenuation rate is extremely low, and the critical current density Jc is also good, and It can be seen that the effective filament diameter can be reduced without any disconnection during the wire drawing.

It is sectional drawing which showed typically the example of a basic composition of the precursor for superconducting wire manufacturing applied to the internal Sn method. It is sectional drawing which showed typically the other structural example of the precursor for superconducting wire manufacturing applied to the internal Sn method. It is sectional drawing which showed typically the example of a structure of the precursor for superconducting wire manufacturing in a prior art. It is sectional drawing which showed typically the example of another structure of the precursor for superconducting wire manufacturing in a prior art. It is sectional drawing which showed typically the example of another structure of the precursor for superconducting wire manufacturing in a prior art. It is sectional drawing which showed typically the example of a structure of the precursor for superconducting wire manufacture of this invention. It is a schematic sectional view showing a connection status between the Nb ₃ Sn superconducting wire and connection resistance evaluation superconducting magnet of a superconducting wire of the present invention. Connecting U-shaped samples using a Nb ₃ Sn superconducting wire of the present invention, a permanent current switch, which is a schematic illustration of a connection resistance evaluation circuit manufactured by connecting the superconducting coil.

Explanation of symbols

1, 5, 11, 13, 14, 15 Superconducting wire production precursor 2 Nb or Nb-based alloy core (Nb core material)
3 Sn or Sn-based alloy core (Sn core material)
4 Cu matrix 4a Stabilized copper layer 6 Diffusion barrier layer (tubular diffusion barrier layer)
7 Nb element wire 8 Sn element wire 16 Superconducting wire 17 of conductive coil 24 End 18 of connecting U-shaped sample 21 Superconducting intermediate inclusion 19 Cu-based container 20 Superconducting filament 21 U for connection made with Nb3Sn superconducting wire of the present invention Sample 22 Permanent current switch 23 Power supply 24 Superconducting coil

Claims (6)

Precursor used when manufacturing Nb ₃ Sn superconducting wire by the internal Sn method has a cylindrical diffusion barrier layer provided with a stabilized copper layer on the outer periphery, and a composite wire group is inserted into the cylindrical diffusion barrier layer A precursor obtained by converting the composite pipe made into a wire,
The composite wire rod group is
A plurality of Nb element wires in which a Nb or Nb-based alloy core is embedded in a Cu or Cu-based alloy matrix and the cross-sectional shape is a hexagon;
A plurality of Sn cores made of Sn or Sn-based alloy and having a polygonal or circular cross-sectional shape,
A precursor for producing a Nb ₃ Sn superconducting wire, wherein the Nb element wire is disposed so as to surround the Sn core material. 2. The precursor for producing an Nb ₃ Sn superconducting wire according to claim 1, wherein a size of a cross section of the Sn core material is the same as or smaller than a size of a cross section of the Nb element wire. The cylindrical diffusion barrier layer is a layer made of Nb or an Nb-based alloy and / or a layer made of Ta or a Ta-based alloy, and a Cu or Cu group is further interposed between the cylindrical diffusion barrier layer and the composite wire rod group. The precursor for producing a Nb ₃ Sn superconducting wire according to claim 1 or 2, wherein an alloy layer is disposed. Nb ₃ Sn superconducting wire a precursor for fabricating a superconducting wire according to any one of claims 1 to 3, is obtained by forming a Nb ₃ Sn superconducting phase by diffusion heat treatment. A plurality of Nb or Nb-based alloy cores embedded in a Cu or Cu-based alloy matrix and having a hexagonal cross-sectional shape when manufacturing a precursor used in manufacturing an Nb ₃ Sn superconducting wire by the internal Sn method Nb element wire and a plurality of Sn cores made of Sn or Sn-based alloy and having a polygonal or circular cross-sectional shape,
The Nb element wires are arranged in contact with each other so as to surround the Sn core material to form a composite wire group,
An Nb ₃ Sn superconducting wire, characterized in that the composite wire group is inserted into a cylindrical diffusion barrier layer provided with a stabilizing copper layer on the outer periphery to form a composite tube, and the composite tube is reduced in diameter to form a wire. A method for producing a precursor for production. In producing the precursor for producing the Nb ₃ Sn superconducting wire according to claim 3, a Cu hollow billet comprising a Cu outer tube and a Cu inner tube is prepared, and the tube is formed on the outer peripheral surface of the Cu inner tube. Forming a cylindrical diffusion barrier layer and then inserting it into the Cu outer cylinder, hot-extruding it, and then inserting the composite wire group into the Cu inner cylinder to form a composite pipe; and The manufacturing method according to claim 5, further comprising a step of reducing the diameter of the composite pipe to form a wire.