JP2014137917A - Nb3Sn SUPERCONDUCTOR PRECURSOR WIRE, Nb FILAMENT SINGLE WIRE, Nb3Sn SUPERCONDUCTOR WIRE AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a NbSn superconductor precursor wire by an internal tin method compositing a reinforcement member, good in workability and excellent in Jc property, and to provide a Nb filament single wire, a NbSn superconductor wire and a manufacturing method thereof.SOLUTION: A NbSn superconductor precursor wire has a plurality of Nb filament single wires containing Nb or a Nb alloy and a plurality of Sn single wires containing Sn or a Sn alloy, and the Nb filament single wire has a reinforcement member consisting of at least one kind of metal selected from a group consisting of Ta, a Ta alloy, W, a W alloy, Mo, a Mo alloy, V, a V alloy, Zr, a Zr alloy, Hf and a Hf alloy, or the Nb alloy containing at least one kind of metal selected from a group consisting of Ta, W, Mo, V, Zr and Hf at a center.

Description

The present invention relates to an Nb ₃ Sn superconducting precursor wire, an Nb filament strand, an Nb ₃ Sn superconducting wire and a method for producing the same, and in particular, has a high Jc (critical current density) and high strength applicable to a high magnetic field magnet. The present invention relates to an Nb ₃ Sn superconducting precursor wire, an Nb filament strand, an Nb ₃ Sn superconducting wire, and a method for manufacturing the same.

Conventionally, the bronze method has been widely used as a method for producing an Nb ₃ Sn superconducting wire. In the bronze method, the Nb ₃ Sn superconducting precursor wire having a structure in which a large number of Nb filaments are arranged inside a matrix made of Cu—Sn alloy is subjected to heat treatment to convert Sn in the Cu—Sn alloy into Nb filaments. This is a method of forming Nb ₃ Sn superconducting wire by diffusing to generate Nb ₃ Sn in the Nb filament portion. However, since the upper limit of the solid solubility limit of Sn in the Cu—Sn alloy is about 16% by mass, no more Nb ₃ Sn can be generated, and the critical current value (Ic) is also limited.

  In order to address the above problems, an internal tin method (internal diffusion method) has been developed that can supply Sn more than the bronze method, except that the Sn supply source is other than a Cu-Sn alloy.

In the internal tin method, a sub-element line having a structure in which a plurality of Nb filaments are arranged inside a Cu matrix (Cu matrix) and an Sn or Sn alloy layer is arranged as a Sn supply source at the center of the Cu matrix. A multi-core wire material produced by bundling a plurality of sub-element wires is subjected to heat treatment, whereby Sn is diffused from the Sn layer through the Cu matrix to generate Nb ₃ Sn in the Nb filament portion, and Nb ₃ This is a method of forming a Sn superconducting wire.

As another method of manufacturing an Nb ₃ Sn superconducting wire of the internal tin method, there are a plurality of wires each having a multi-core Nb filament arranged in a Cu matrix and a single-core Sn wire having Cu arranged on the outer periphery of Sn or the outer periphery. A method of producing a multi-core wire by combining this is also performed (Patent Document 1).

JP 2006-4684 A Japanese Patent Publication No. 1-8698 US Pat. No. 6,981,309 JP 2008-166173 A JP 2010-129453 A

J.A. Parrel et al., "High field Nb3Sn conductor development at Oxford Superconducting Technology" IEEE Trans. Appl. Supercond., 2006, vol. 13, issue 2, pp.3470-3473

Since the internal tin method can increase the composite ratio of Sn as compared with the bronze method, the Jc of the Nb ₃ Sn superconducting wire is, for example, a non-Cu Jc (non-copper critical current density) in a magnetic field of 12T. ) = 2900 A / mm ² is obtained (Non-Patent Document 1).

When a superconducting magnet is manufactured using such an internal tin method Nb ₃ Sn superconducting wire (internal tin method wire), the current flowing per unit cross-sectional area of the Nb ₃ Sn superconducting wire is J (A / mm ² ), where the magnitude of the magnetic field (magnetic flux density) in the winding portion is B (T) and the radius of the winding in the magnet is R (mm), σ in the direction of pulling the Nb ₃ Sn superconducting wire = Electromagnetic stress represented by BJR (electromagnetic force per unit cross-sectional area of the Nb ₃ Sn superconducting wire) σ is generated.

The internal tin normal wire is characterized by high Jc, and the magnetic field generated by the magnet using this can also be increased. Accordingly, the electromagnetic stress applied to the Nb ₃ Sn superconducting wire is increased as shown in the above equation.

In general, the Jc characteristic of Nb ₃ Sn superconducting wire is sensitive to strain, and it is known that Jc is lowered even when strain of about 1% is applied. For this reason, when producing a magnet with a high magnetic field, a composite wire having a structure in which a reinforcing member is combined in the wire has been used. As for the arrangement of the reinforcing members in the cross section of the wire rod, the superconducting filament near the center of the multi-core wire rod is replaced with a reinforcing member such as Ta as necessary in both the bronze wire rod and the internal tin wire rod. The structure has been used.

In the bronze method, a Cu—Sn alloy is used as a Sn supply source. Since the Cu—Sn alloy is hard, there is no great hardness difference with respect to the reinforcing members such as Nb filaments and Ta, and there is no large distribution of hardness in the cross section of the Nb ₃ Sn superconducting precursor wire. For this reason, it was possible to perform uniform processing during wire drawing.

  On the other hand, in the internal tin method, a very soft Sn material is incorporated alone inside the internal tin normal wire. Here, if a reinforcing Ta member is disposed at the center of the multi-core wire and Sn is disposed on the outer peripheral side of the multi-core wire as in the prior art, a large distribution of hardness can be obtained within the cross-section of the multi-core wire. There is a possibility that non-uniform deformation of the cross section or disconnection may occur during the wire drawing process.

In the method of replacing the central filament of the multi-core wire with the reinforcing member, the strength of the multi-core wire is improved by adding the reinforcing member, but the individual Nb ₃ Sn filament is not reinforced, so that distortion occurs. Cheap.

  That is, in a situation where tensile strain is applied in the longitudinal direction of the multi-core wire, an improvement in strength corresponding to the composite ratio of the reinforcing member is expected no matter where the reinforcing member is in the multi-core wire. The However, in reality, the strain applied to the multi-core wire is not only the tensile strain in the longitudinal direction of the multi-core wire, but for example, when a plurality of multi-core wires are twisted to form a conductor, the wires in the stranded wire cross each other. Local bending strain and lateral compression strain are generated. In such a case, even if the reinforcing member is arranged at the center of the multi-core wire, it is expected that the individual filaments are distorted and the wire properties are deteriorated.

In the bronze method, by heat treatment, Sn is supplied from the bronze portion to the Nb filament portion in the Nb ₃ Sn superconducting precursor wire to generate Nb ₃ Sn. At this time, it is often seen that Nb ₃ Sn is not generated and unreacted Nb remains in the central portion of the Nb ₃ Sn filament. This is thought to be due to the small amount of Sn incorporated in the bronze method. Naturally, the superconducting characteristics of Nb ₃ Sn cannot be obtained in the unreacted Nb portion. Further, it is known that Jc is lower than the outer peripheral side of Nb ₃ Sn because the Sn concentration is low in the portion of Nb ₃ Sn close to unreacted Nb.

  Therefore, in order to improve the critical current density (Jc), a method of incorporating 5 atomic% or less of Ti into the core of the Nb filament has been proposed (Patent Document 2). In addition, a method has also been proposed in which a hole is formed in the center of an Nb filament and an Nb—Ti alloy core is inserted (Patent Document 3). However, these methods have problems such as an increase in production cost and a possibility of disconnection during production.

  In order to solve this problem, a cylindrical layer made of an Nb-based alloy containing one or more elements selected from the group consisting of Ti, Ta, Zr and Hf around the core of the Nb filament, or the above-mentioned Nb group A method has been proposed in which a substantially cylindrical layer formed by combining a plurality of plate-like members made of an alloy is disposed, and a cylindrical layer made of Nb is disposed on the outer periphery thereof (Patent Document 4). However, this method has a complicated manufacturing process and low processability.

On the other hand, since the Nb ₃ Sn superconducting wire tends to deteriorate in characteristics with a slight strain as described above, the individual Nb ₃ Sn filaments are reinforced by having an unreacted Nb core, It has also been proposed to prevent deterioration of characteristics against strain by an unreacted Nb core (Patent Document 5).

Thus, it is preferable not unreacted Nb in the center of the Nb 3 _Sn filaments in terms of critical current density, unreacted Nb in the center of the Nb 3 _Sn filaments in terms of reinforcement for strain of the filaments is of the It was a contradictory event of being preferable.

The present invention has been made in order to solve the above-mentioned problems, and a Nb ₃ Sn superconducting wire used for manufacturing an Nb ₃ Sn superconducting wire by an internal tin method is combined with a reinforcing member, has good workability, and has excellent Jc characteristics. ₃ Sn superconductor precursor wire, and an object thereof is to provide a Nb filament strands, Nb 3 _Sn superconducting wire, and a method for producing the same.

A first aspect of the present invention is an Nb ₃ Sn superconducting precursor wire used when an Nb ₃ Sn superconducting wire is manufactured by an internal tin method in order to solve the above-described problem, and includes a plurality of Nb or Nb alloys. Nb filament strand and a plurality of Sn strands containing Sn or Sn alloy, the Nb filament strand includes a reinforcing member in the center, and the reinforcing member is Ta, Ta alloy, W, W alloy, Mo , Mo alloy, V, V alloy, Zr, Zr alloy, at least one metal selected from the group consisting of Hf and Hf alloys, or at least selected from the group consisting of Ta, W, Mo, V, Zr and Hf An Nb ₃ Sn superconducting precursor wire comprising an Nb alloy containing one kind of metal is provided.

  The Nb filament strand includes an Nb or Nb alloy layer provided around the reinforcing member, and a cross sectional area of the reinforcing member with respect to a sum of a cross sectional area of the Nb or Nb alloy layer and a cross sectional area of the reinforcing member. The ratio is preferably from 0.19 to 0.69.

The ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is preferably 0.04 or more and 0.30 or less. Furthermore, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is more preferably 0.06 or more. The ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is more preferably 0.19 or less.

  The second aspect of the present invention further includes an Nb or Nb alloy layer provided around the reinforcing member, and the reinforcing member includes Ta, Ta alloy, W, W alloy. At least one metal selected from the group consisting of Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy, or from the group consisting of Ta, W, Mo, V, Zr, and Hf An Nb filament strand made of an Nb alloy containing at least one selected metal is provided.

  In the Nb filament strand, the ratio of the cross-sectional area of the reinforcing member to the total of the cross-sectional area of the Nb or Nb alloy layer and the cross-sectional area of the reinforcing member is preferably 0.19 or more and 0.69 or less. Furthermore, the ratio of the cross-sectional area of the reinforcing member to the sum of the cross-sectional areas of the Nb or Nb alloy layer and the reinforcing member is more preferably 0.51 or less.

A third aspect of the present invention, by heat-treating the above-mentioned _Nb 3 Sn superconductor precursor wire, providing a _Nb 3 Sn superconducting wire in which the Nb filaments wire to diffuse the Sn and to generate _Nb 3 Sn.

According to a fourth aspect of the present invention, there is provided a step of preparing a plurality of Nb filament strands including Nb or Nb alloy and a plurality of Sn strands including Sn or Sn alloy, and a Ta at the center of the Nb filament strand. , Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and at least one metal selected from the group consisting of Hf alloy, or Ta, W, Mo, V , Zr, to provide a method of manufacturing a Nb 3 _Sn superconductor precursor wire, characterized in that it comprises the step of placing a reinforcing member made of Nb alloy containing at least one metal selected from the group consisting of Hf.

  The step of disposing the reinforcing member at the center of the Nb filament strand is made of Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy. A bar made of an Nb alloy containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf and containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf is placed in a pipe made of Nb or Nb alloy. A step of inserting may be included.

  The step of disposing the reinforcing member at the center of the Nb filament strand is made of Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy. Or Nb or Nb alloy around a metal rod made of Nb alloy containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf. A step of winding the sheet may be included.

According to a fifth aspect of the present invention, there is provided an Nb ₃ Sn superconducting wire comprising a step of generating Nb ₃ Sn by diffusing Sn in the Nb filament strand by heat-treating the Nb ₃ Sn superconducting precursor wire. A manufacturing method is provided.

According to the present invention, a Nb ₃ Sn superconducting precursor wire, an Nb filament element, which is used when an Nb ₃ Sn superconducting wire is manufactured by an internal tin method, composites a reinforcing member, has good workability, and has excellent Jc characteristics. A wire, a Nb ₃ Sn superconducting wire, and a method for manufacturing the same can be provided.

The Nb 3 _Sn superconducting precursor wire structure according to a first embodiment of the present invention is a cross-sectional view illustrating. It is a flowchart which shows an example of the manufacturing process of the subelement strand which concerns on the 1st Embodiment of this invention. It is a flowchart which shows an example of the manufacturing process of the Nb filament strand which concerns on the 1st Embodiment of this invention. It is a flowchart which shows an example of the manufacturing process of Sn strand which concerns on the 1st Embodiment of this invention. The structure of the Nb 3 _Sn superconductor precursor wire according to the second embodiment of the present invention is a cross-sectional view illustrating. It is sectional drawing which shows the structure of the Nb3Sn superconducting precursor wire which concerns on the _3rd Embodiment of this invention. It is a schematic diagram explaining the bending distortion which generate | occur | produces in a wire. It is a sectional view showing the structure of a Nb 3 _Sn superconductor precursor wire of a conventional (Comparative Example 1). It is a sectional view showing the structure of a Nb 3 _Sn superconductor precursor wire of a conventional (Comparative Example 2). It is a sectional view showing the structure of a Nb 3 _Sn superconductor precursor wire of a conventional (Comparative Example 3). It is a sectional view showing the structure of a Nb 3 _Sn superconductor precursor wire of a conventional (Comparative Example 4).

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing the structure of the Nb ₃ Sn superconducting precursor wire according to the first embodiment.

(Nb ₃ Sn superconducting precursor wire 1)
In the Nb ₃ Sn superconducting precursor wire 1, a plurality of Nb filament strands 11 are arranged around a Sn strand 15, and the periphery of the plurality of Nb filament strands 11 is sequentially covered with a diffusion barrier layer 18 and a Cu coating layer 19. Thus, the sub-element strand 20 is formed, and a plurality of sub-element strands 20 are arranged inside the stabilizing Cu layer 21.

(Sub-element strand 20)
The sub-element strand 20 includes an Sn strand 15, a plurality of Nb filament strands 11 provided around the Sn strand 15, and a diffusion barrier layer 18 provided around the plurality of Nb filament strands 11. A Cu coating layer 19 that covers the periphery of the diffusion barrier layer 18 is provided.

(Nb filament strand 11)
The Nb filament strand 11 is formed by coating a Cu coating layer 13 on the outer periphery of a layer (Nb or Nb alloy layer) 12 made of Nb or Nb alloy, and a reinforcing member 14 inside the Nb or Nb alloy layer 12. Is provided. More specifically, the Nb filament strand 11 includes a reinforcing member 14 provided as a core at the center, an Nb or Nb alloy layer 12 provided around the reinforcing member 14, and an outer periphery of the Nb or Nb alloy layer 12. A Cu coating layer 13 to be coated is provided. The Nb filament strand 11 has a hexagonal cross section, and is embedded in the stabilized Cu layer 21 after being drawn or reduced.

(Sn strand 15)
The Sn strand 15 includes an Sn filament 16 made of Sn or an Sn alloy, and a Cu coating layer 17 that covers the outer periphery of the Sn filament 16. Sn strand 15 has a cross-sectional area larger than that of Nb filament strand 11. Similar to the Nb filament strand 11, the Sn strand 15 has a hexagonal cross section and is embedded in the stabilization Cu layer 21 after wire drawing and area reduction.

(Diffusion barrier layer 18)
The diffusion barrier layer 18 is for preventing diffusion of Sn to the outside during the heat treatment of the Nb ₃ Sn superconducting precursor wire 1 and is made of Nb or Nb alloy, or Ta or Ta alloy.

(Cu coating layers 13, 17, 19 and stabilized Cu layer 21)
The Cu covering layers 13, 17, 19 and the stabilizing Cu layer 21 are mainly made of oxygen-free copper, and for example, those having a purity of 99.95% or more (JIS3510 C1020) can be used. If it is desired to further improve the conductivity, a material having a purity of 99.99% or more (JIS 3510 C1011) can be used. In addition, this invention is related to the internal tin method, and it is preferable that Sn contained in Cu coating layers 13, 17, and 19 is 0.01% or less. The reason is as follows. Bronze (Cu-Sn alloy) is used as a matrix material including Nb filaments in the production of the Nb ₃ Sn superconducting precursor wire by the conventional bronze method, but the bronze height is increased by work hardening in the wire drawing process It was possible to reduce the hardness by annealing and subsequently repeat the wire drawing process. However, in the internal tin method, a single Sn or Sn alloy is incorporated in the wire being drawn. When the wire is annealed in the middle of wire drawing, Sn diffuses into the surrounding Cu matrix to form a Cu—Sn alloy or Cu—Sn compound phase, and the workability deteriorates. Therefore, as described above, it is preferable that the Cu coating layers 13, 17, and 19 are mainly pure Cu, and it is more preferable that the Sn content is as small as possible.

(Nb ₃ Sn superconducting wire)
By heat treating the Nb ₃ Sn superconductor precursor wire 1, _Nb 3 Sn is generated by Sn is diffused into the Nb filament strands 11, _Nb 3 Sn superconducting wire according to the present embodiment is manufactured.

(Reinforcing member 14)
Hereinafter, the reinforcing member 14 disposed at the center of the Nb filament strand 11 will be described.

(1) the materials of the reinforcing member 14 of the reinforcing member 14, so provided in order to reinforce the _Nb 3 Sn _Nb 3 higher strength than Sn, and _Nb 3 Sn because they are located in the center of the Nb filaments wire 11 It is required to have a property that does not react and does not deteriorate the superconducting properties.
Therefore, the reinforcing member 14 is made of tantalum (Ta), tantalum alloy, tungsten (W), tungsten alloy, molybdenum (Mo), molybdenum alloy, vanadium (V), vanadium alloy, zirconium (Zr), zirconium alloy, hafnium (Hf ) And at least one metal selected from the group consisting of hafnium alloys.
The reinforcing member 14 includes at least one metal selected from the group consisting of tantalum (Ta), tungsten (W), molybdenum (Mo), vanadium (V), zirconium (Zr), and hafnium (Hf). It is preferably made of a niobium (Nb) alloy.

In particular, the material of the reinforcing member 14 is preferably Ta, Ta alloy, or Nb alloy that is also used as the diffusion barrier layer 18. This is because a large hardness distribution does not occur in the cross section of the wire, and it is possible to prevent disconnection, non-uniform processing, and the like from occurring when the Nb filament strand 11 and the sub-element strand 20 are drawn. Further, when the Nb ₃ Sn superconducting wire is used as a superconducting magnet, it is preferable to use a relatively high strength W, W alloy, Mo, Mo alloy, Hf, or Hf alloy as the material of the reinforcing member 14. This is because even if the magnetic field generated by the superconducting magnet increases, Nb ₃ Sn can be sufficiently reinforced. In addition, the material of the reinforcing member 14 can be appropriately selected from the above group in consideration of the availability of the material.

  The Ta alloy, Nb alloy, W alloy, Mo alloy, and Hf alloy preferably have a composition having an additive element of 5% by mass or more, for example.

(2) Ratio of the reinforcing member 14 to the Nb filament The inventors of the present invention have proposed that the Nb ₃ Sn superconducting wire produced by the internal tin method is subjected to heat treatment to generate Nb ₃ Sn in the Nb filament, The thickness of the reaction Nb was studied earnestly. For example, a general heat treatment (for example, 500 ° C. × 100 hours + 700 ° C. × 100 hours, etc.) for an Nb ₃ Sn superconducting precursor wire having an Nb filament outer diameter of 5 μm excluding the Cu coating layer from the Nb filament strand 11 ), Unreacted Nb having a diameter of about 1 μm remains in the center of the produced Nb ₃ Sn filament, and a layer of Nb ₃ Sn having a thickness of about 2 μm is formed around the unreacted Nb. It was. That is, it was found that in the internal tin method, Nb ₃ Sn is generated at a depth of at least about 2 μm from the outermost surface of the Nb filament.

It is desirable to reinforce Nb ₃ Sn by replacing a portion that can remain as unreacted Nb after the heat treatment with the reinforcing member 14. Therefore, in the Nb filament strand 11, it is desirable that the reinforcing member 14 be disposed at the center and on the inner side from the outer surface of the Nb or Nb alloy layer 12 to a depth of 2 μm.

Here, since the Nb ₃ Sn filament obtained by heat treatment reduces the AC loss and stabilizes the superconducting characteristics by reducing its size, it is desirable that the Nb ₃ Sn filament has an outer diameter of at least 30 μm or less. . Moreover, in order to avoid disconnection at the time of wire drawing, it is desirable that the Nb ₃ Sn filament has a diameter of 5 μm or more. That is, it is desirable that the Nb filament has an outer diameter of 5 μm or more and 30 μm or less.

When Nb ₃ Sn having a thickness of 2 μm is formed on the outermost surface of Nb or Nb alloy layer 12 having an outer diameter of 5 μm or more and 30 μm or less, the unreacted Nb remaining in the center is 1 μm or more and 26 μm or less. Therefore, the diameter of the reinforcing member 14 to be replaced with the unreacted Nb is preferably in the range of 1 μm to 26 μm. Therefore, the ratio of the diameter (outer diameter) of the reinforcing member 14 to the diameter (outer diameter) of the Nb ₃ Sn filament (Nb filament) is 0.2 or more and 0.87 or less, and the reinforcing member 14 has a cross-sectional area of the Nb filament. The ratio is 0.04 or more and 0.75 or less. Therefore, also in the Nb filament strand 11, the ratio of the reinforcing member 14 to the sectional area of the sectional area of the Nb filament (the sum of the sectional area of the Nb or Nb alloy layer 12 and the sectional area of the reinforcing member 14) is theoretically 0.04. Above 0.75 is preferable.

In the Nb ₃ Sn superconducting wire, in order to obtain a sufficient mechanical strength by combining the reinforcing member 14, the reinforcing member 14 has a ratio of 0.19 or more with respect to the cross-sectional area of the Nb ₃ Sn filament (Nb filament). It is desirable to combine. On the other hand, when a large amount of the reinforcing member 14 is inserted, the mechanical strength is greatly increased, but the critical current characteristic is lowered due to a trade-off relationship. Therefore, the cross-sectional area of the Nb filament (the cross-sectional area of the Nb or Nb alloy layer 12 and the reinforcing member 14). The cross-sectional area ratio of the reinforcing member 14 to the total cross-sectional area) is preferably 0.69 or less. Therefore, the cross-sectional area ratio of the reinforcing member to the cross-sectional area of the Nb filament is more preferably in the range of 0.19 to 0.69.

(3) Ratio of the reinforcing member 14 to the entire Nb ₃ Sn superconducting precursor wire 1 Generally, when a reinforcing member is combined in the cross section of the Nb ₃ Sn superconducting precursor wire, the cross-sectional area of the portion related to superconducting is reduced accordingly. This leads to a decrease in the critical current value. In the present embodiment, the reinforcement by the reinforcing member 14 is to replace a part of the Nb filament by the reinforcing member 14. When the ratio of the cross-sectional area of the reinforcing member 14 to the cross-sectional area of the Nb filament is small, an unreacted Nb region having a low Jc is replaced, so the influence on the superconducting characteristics of the Nb ₃ Sn superconducting wire is small. On the other hand, as the ratio of the cross-sectional area of the reinforcing member 14 to the cross-sectional area of the Nb filament increases, the Nb ₃ Sn region effective for superconducting characteristics is replaced, and the critical current characteristics of the Nb ₃ Sn superconducting wire are reduced. End up.

The present inventors have, it is possible to reduce the influence on the superconducting properties of the Nb 3 _Sn superconducting wire, and the results of investigation of the ratio of the reinforcing member 14 can be sufficiently reinforced Nb 3 _Sn, the cross-sectional area of the entire Nb 3 _Sn superconducting wire It has been found that the ratio of the cross-sectional area of the reinforcing member 14 to the above is preferably in the range of 0.04 to 0.30.

Therefore, the ratio of the cross-sectional area of the reinforcing member 14 to the entire cross-sectional area of the wire (Nb ₃ Sn superconducting precursor wire 1 or Nb ₃ Sn superconducting wire) is 0.04 or more as shown in the examples described later. It is desirable to set it to 0.30 or less. More preferably, the lower limit value is 0.06, and the upper limit value is 0.19.

(4) Ratio of the Nb filament strand 11 including the reinforcing member 14 to the total number of Nb filament strands 11 The reinforcing effect of the reinforcing member 14 disposed at the center of a certain filament is not limited to the filament but also to the filament. It also acts on other adjacent filaments. That is, in this embodiment, it is not necessary to arrange the reinforcing members 14 on all the Nb filament strands in the Nb ₃ Sn superconducting precursor wire 1. By adjusting the number of Nb filament strands 11 including the reinforcing member 14, it is possible to reinforce Nb ₃ Sn while reducing the influence on the superconducting characteristics of the wire. In this case, it is desirable that the Nb filament strands 11 including the reinforcing member 14 are evenly arranged in the cross section of the Nb ₃ Sn superconducting precursor wire 1 so that the characteristics of the wire are not biased.

(Method for producing Nb ₃ Sn superconducting wire)
Will now be described with reference to FIGS. 2-4 an example of a method for manufacturing a Nb 3 _Sn superconducting wire.

FIG. 2 is a flowchart showing an example of a manufacturing process of the sub-element wire 20 according to the embodiment of the present invention.
First, in step S21, the Nb filament strand 11 is manufactured.

  With reference to FIG. 3, an example of the manufacturing process of the Nb filament strand 11 of step S21 is demonstrated. First, a Cu pipe is prepared (step S211), an Nb pipe made of Nb or an Nb alloy is inserted into the Cu pipe (step S212), and a reinforcing member (for example, a Ta bar) is further inserted into the Nb pipe. Thus, an Nb composite material is produced (step S213). The Nb filament strand 11 is manufactured by repeatedly applying a surface reduction process (drawing) to the Nb composite material to form a hexagonal cross section (step S214). The above steps are repeated until the required number of Nb filament strands are manufactured.

  Further, in parallel with step S21, in step S22, the Sn strand 15 is manufactured by the Sn strand manufacturing process.

  With reference to FIG. 4, an example of the manufacturing process of the Sn strand 15 of step S22 is demonstrated. First, a Cu pipe is prepared (step S221), and an Sn rod made of Sn or an Sn alloy is inserted into the Cu pipe (step S222). Sn wires are manufactured (step S223). The above process is repeated until a required number of Sn strands are manufactured.

  After the necessary number of Nb filament strands 11 and Sn strands 14 are manufactured by the Nb filament strand manufacturing process (step S21) and the Sn strand manufacturing process (step S22), the process proceeds to step S23, and a new Cu pipe is added. In step S24, a barrier sheet is provided on the inner peripheral surface of the Cu pipe. The barrier sheet is a sheet material for forming the diffusion barrier layer 18 and is made of Nb or Nb alloy, or Ta or Ta alloy, like the diffusion barrier layer 18.

  Thereafter, in step S25, the Sn strand 15 is inserted into the Cu pipe provided with the barrier sheet, and a plurality of Nb filament strands 11 are inserted around the Sn strand 15 to produce a composite.

  The sub-element strand 20 is manufactured by performing surface-reducing processing on the manufactured composite in step S26.

The above-described manufacturing process of the sub-element strand 20 is repeated until the required number is manufactured, and then a plurality of sub-element strands 20 are inserted into the Cu pipe to form a multi-core billet. The Nb ₃ Sn superconducting precursor wire 1 is manufactured by repeating the surface-reducing process for the multi-core billet. Further, the Nb ₃ Sn superconducting precursor wire 1 is heat treated to produce an Nb ₃ Sn superconducting wire.

(Operation of the first embodiment)
Next, the operation of the present embodiment will be described.
In the present embodiment, in the Nb ₃ Sn superconducting wire that generates Nb ₃ Sn by the internal tin method, the reinforcing member 14 made of Ta or the like is formed at the center of the Nb filament strand 11 embedded in the Nb ₃ Sn superconducting precursor wire 1. Configured to arrange.

(1) By replacing the center of each Nb filament strand 11 with the reinforcing member 14, the strain applied to the Nb ₃ Sn superconducting wire is reinforced for each filament, and the deterioration of the superconducting characteristics due to the strain is reduced.

(2) Further, compared to the case where unreacted Nb is left at the center of each filament, the reinforcing member 14 is arranged in the Nb ₃ Sn region of low Jc that is in contact with the originally unreacted Nb. The decrease in Jc due to combining 14 with the wire is reduced.

  (3) Further, in the present embodiment, the reinforcing member 14 is disposed at the center of the Nb filament strand 11, and the Nb or Nb alloy layer 12 and the Cu coating 13 are sequentially disposed outside the reinforcing member 14, and the reinforcing member 14 and Nb or The Nb alloy layer 12 is in contact with soft Sn via Cu. For this reason, a large hardness distribution does not occur in the wire as in the case of replacing the filament at the center of the multi-core wire with a reinforcing member. Therefore, disconnection or non-uniform processing does not occur during the surface reduction processing, and the workability is good.

(Second Embodiment)
FIG. 5 is a cross-sectional view showing the structure of the Nb ₃ Sn superconducting precursor wire 5 according to the second embodiment of the present invention. In the Nb ₃ Sn superconducting precursor wire 5 according to the second embodiment, a plurality of Nb filament strands 11 are arranged in a Cu coating layer 19 to form a Nb filament composite wire (Nb subelement strand 22). A plurality of Nb sub-element strands 22 and a plurality of Sn strands 15 are arranged inside a stabilizing Cu layer 21 provided with a diffusion barrier layer 18 on the inner peripheral surface. The Nb ₃ Sn superconducting precursor wire 5 includes an Nb sub-element strand 22 and an Sn strand 15 formed in substantially the same size, and an Nb sub-element strand 22 around the Sn strand 15. Are adjacent to each other and the Sn strands 15 are not adjacent to each other.

The Nb ₃ Sn superconducting precursor wire 5 according to the second embodiment includes an Nb ₃ Sn superconducting precursor wire 1 according to the first embodiment and a plurality of Nb filament strands 11 and Nb subelement elements. The wire 22 is formed, and then the wire 22 is embedded in the stabilized Cu layer 21 together with the Sn wire 15 having substantially the same size as the Nb sub-element wire 22. The Nb ₃ Sn superconducting precursor wire 5 relates to an Nb ₃ Sn superconducting precursor wire having an arrangement known as a DT (Dispersed Tin) method, and Sn wires 15 are dispersedly arranged as the name implies. It has a structure.

The Nb ₃ Sn superconducting precursor wire 5 can be manufactured by the same process as in the first embodiment. For example, in the Nb ₃ Sn superconducting precursor wire 5, a plurality of Nb filament strands 11 are inserted into a Cu pipe, and the surface of the Nb subelement strands 22 is reduced to produce Nb subelement strands 22. The wire 22 and the plurality of Sn strands 15 can be inserted into a Cu pipe provided with a barrier sheet on the inner peripheral surface, and can be manufactured by reducing the surface.

(Effect of the second embodiment)
In the Nb ₃ Sn superconducting precursor wire 5 according to the second embodiment, the same effect as that of the first embodiment can be obtained by arranging the reinforcing member 14 at the center of the Nb filament strand 11. .

(Third embodiment)
FIG. 6 is a cross-sectional view showing the structure of the Nb ₃ Sn superconducting precursor wire 6 according to the third embodiment of the present invention. On the other hand, the Nb ₃ Sn superconducting precursor wire 6 shown in FIG. 6 has a plurality of Nb filament strands 11 and a plurality of Sn strands 15 in the stabilization Cu layer 21 provided with the diffusion barrier layer 18 on the inner peripheral surface. It has the structure which arranges. The Nb ₃ Sn superconducting precursor wire 6 includes an Nb filament strand 11 and an Sn strand 15 that are formed to have substantially the same size, and the Nb filament strand 11 is adjacent to the periphery of the Sn strand 15. It has the structure arrange | positioned so that Sn strand 15 may not adjoin.

The Nb ₃ Sn superconducting precursor wire 6 according to the _third embodiment is replaced with the Nb ₃ Sn superconducting precursor wire 5 according to the second embodiment and the Nb filament element wire 11 instead of the Nb sub-element wire 22. Is different in that

The Nb ₃ Sn superconducting precursor wire 6 can be manufactured by the same process as in the first embodiment. For example, in the Nb ₃ Sn superconducting precursor wire 5, a plurality of Nb filament strands 11 and a plurality of Sn strands 15 are inserted into a Cu pipe having a barrier sheet on the inner peripheral surface, and the surface is reduced. Can be manufactured.

(Effect of the third embodiment)
Also in the Nb ₃ Sn superconducting precursor wire 6, by arranging the reinforcing member 14 at the center of the Nb filament strand 11, the same effect as in the above embodiment can be obtained.

However, the present invention is not limited to the above embodiment of the manufacturing method of the Nb 3 _Sn superconducting wire and Nb 3 _Sn superconductor precursor wire.

  For example, the manufacturing process (steps S21 and S22) of the Nb filament strand and the Sn strand is parallel to the preparation of the Cu pipe for the sub-element strand (step S23) and the installation of the barrier sheet (step S24), or It may be inserted between the preparation of the Cu pipe and the installation of the barrier sheet, or between the installation of the barrier sheet and the insertion of the strand (step S25).

  In addition, in the manufacturing process of the Nb filament strand, instead of the Nb pipe, an Nb sheet made of Nb or Nb alloy is used, and the Nb sheet is wound around the reinforcing member and inserted into the Cu pipe. An Nb filament strand can also be manufactured.

  Examples of the present invention will be described below.

[Example 1]
The Nb ₃ Sn superconducting precursor wire of Example 1 will be described. The Nb ₃ Sn superconducting precursor wire of Example 1 has the cross-sectional structure shown in FIG.

<Nb filament strand>
A Cu pipe having an outer diameter of 32.2 mm and an inner diameter of 29 mm is prepared. An Nb-1 mass% Ta alloy pipe having an outer diameter of 28.6 mm and an inner diameter of 20.4 mm is inserted inside, and further, a Ta pipe with an outer diameter of 20 mm is inserted inside the pipe. A rod was inserted as a reinforcing member to prepare an Nb composite material. This Nb composite material is extruded using an extruder and processed to a wire diameter of 10 mm, and then repeatedly processed using a wire drawing machine to form a hexagonal shape with a distance between opposite sides of 2 mm. Nb filament A strand was prepared. By repeating these steps, 126 Nb filament strands whose center was reinforced with Ta were prepared.

<Sn strand>
A Cu pipe having an outer diameter of 34 mm and an inner diameter of 30.4 mm is prepared. After inserting an Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti with an outer diameter of 30 mm into this Cu pipe, the surface is reduced. Then, it was processed into a hexagonal shape with a distance between opposite sides of 12.4 mm to produce a Sn strand. One Sn strand was prepared.

<Sub-element wire>
A Cu pipe having an outer diameter of 33 mm and an inner diameter of 30 mm was prepared, and a Ta sheet having a thickness of 0.1 mm was wound around the inner peripheral surface for 5 turns. Inside this Ta sheet, Sn strands were arranged and 126 Nb strands were arranged around the Sn strands to produce a composite. This was subjected to surface reduction to obtain a sub-element strand having a distance between opposite sides of 3 mm.

<Nb ₃ Sn superconducting precursor wire>
Finally, 85 sub-element wires are inserted into a Cu pipe having an outer diameter of 38 mm and an inner diameter of 32 mm to produce a multi-core wire composite (multi-core billet). _{A 3} Sn superconducting precursor wire was prepared.

In this Nb ₃ Sn superconducting precursor wire, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the Nb filament portion of the Nb filament element wire is 0.50, and the Nb filament element including the reinforcing member with respect to the entire Nb filament element wire The ratio of the number of wires is 1, and the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.18.

[Example 2]
Next, the Nb ₃ Sn superconducting precursor wire of Example 2 will be described. The Nb ₃ Sn superconducting precursor wire of Example 2 has the cross-sectional structure shown in FIG.

<Nb filament strand>
The manufacturing method of the Nb filament strand is the same as that of Example 1. A Cu pipe having an outer diameter of 32.2 mm and an inner diameter of 29 mm is prepared. An Nb-1 mass% Ta alloy pipe having an outer diameter of 28.6 mm and an inner diameter of 20.4 mm is inserted inside, and further, a Ta pipe with an outer diameter of 20 mm is inserted inside the pipe. A rod was inserted as a reinforcing member to prepare an Nb composite material. The Nb composite material was subjected to surface reduction processing (drawing) and processed into a hexagonal shape with a distance between opposite sides of 3 mm to produce an Nb filament strand. In this way, 85 Nb filament strands whose center was reinforced with Ta were prepared.

<Nb subelement strand>
Then, 85 Nb filament strands are inserted into a Cu pipe having an outer diameter of 35 mm and an inner diameter of 32 mm, and this is reduced to a hexagonal shape with a distance between opposite sides of 2 mm, and an Nb filament composite wire (Nb subelement) Obtained).

<Sn strand>
The production method of the Sn strand is the same as that in the first embodiment. An Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 30 mm is inserted into a Cu pipe having an outer diameter of 34 mm and an inner diameter of 30.4 mm, and this is reduced to a distance between opposite sides of 2 mm. An Sn strand was fabricated by processing into a hexagonal shape. Thirty-seven Sn wires were prepared.

<Nb ₃ Sn superconducting precursor wire>
A Cu pipe having an outer diameter of 36 mm and an inner diameter of 30 mm is prepared, and a Ta sheet having a thickness of 0.1 mm is wound around the inner circumferential surface to form a diffusion barrier layer. Inside this, 126 Nb subelement strands and Sn are formed. 37 strands are arranged so that the Sn strands are not adjacent to each other, a multi-core wire composite (multi-core billet) is manufactured, and this is reduced in area to obtain a Nb ₃ Sn superconducting precursor wire having a wire diameter of 1 mm. Produced.

In this Nb ₃ Sn superconducting precursor wire, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the Nb filament portion of the Nb filament element wire is 0.50, and the Nb filament element including the reinforcing member with respect to the entire Nb filament element wire The ratio of the number of wires is 1, and the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.18.

[Example 3]
Next, the Nb ₃ Sn superconducting precursor wire of Example 3 will be described. The Nb ₃ Sn superconducting precursor wire of Example 3 has the cross-sectional structure shown in FIG. And 5 types of sample Nos. 3 to 7 having different cross-sectional areas of the Nb filament part were produced as follows.

<Nb filament strand>
The manufacturing method of the Nb filament strand is the same as that of Example 1.

  Sample No. 3) Prepare a Cu pipe with an outer diameter of 32 mm and an inner diameter of 21.2 mm, insert an Nb-1 mass% Ta alloy pipe with an outer diameter of 20.9 mm and an inner diameter of 9.2 mm inside, and A Nb composite material was prepared by inserting a Ta rod having a diameter of 9 mm.

  Sample No. 4) Prepare a Cu pipe with an outer diameter of 32 mm and an inner diameter of 22.2 mm, insert an Nb-1 mass% Ta alloy pipe with an outer diameter of 21.9 mm and an inner diameter of 11.2 mm inside, and further insert an outer diameter inside An Nb composite material was produced by inserting an 11 mm Ta rod.

  Sample No. 5) Prepare a Cu pipe with an outer diameter of 32 mm and an inner diameter of 27.1 mm, insert an Nb-1 mass% Ta alloy pipe with an outer diameter of 26.8 mm and an inner diameter of 19.2 mm inside, and further inside the outer diameter A 19 mm Ta rod was inserted to prepare an Nb composite material.

  Sample No. 6 is prepared with a Cu pipe having an outer diameter of 32 mm and an inner diameter of 29.3 mm, an Nb-1 mass% Ta alloy pipe having an outer diameter of 29 mm and an inner diameter of 23.2 mm is inserted inside, and an outer diameter of 23 mm is further inserted inside thereof. A Ta rod was inserted to prepare an Nb composite material.

  Sample No. 7 is prepared with a Cu pipe having an outer diameter of 32 mm and an inner diameter of 29.3 mm, an Nb-1 mass% Ta alloy pipe having an outer diameter of 29 mm and an inner diameter of 24.2 mm is inserted inside, and further an inner diameter of 24 mm is inserted therein. A Ta rod was inserted to prepare an Nb composite material.

  Sample No. The Nb composite material of 3 to 7 was subjected to surface reduction processing (drawing) and processed into a hexagonal shape with a distance between opposite sides of 1 mm to produce an Nb filament strand. In this way, the Nb filament strand whose center is reinforced with Ta is referred to as “No. 816 samples were prepared for each of 3 to 7 samples.

<Sn strand>
The production method of the Sn strand is the same as that in the first embodiment. An Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 25 mm is inserted into a Cu pipe having an outer diameter of 32 mm and an inner diameter of 25.3 mm, and the surface is reduced to a distance between opposite sides of 1 mm. An Sn strand was fabricated by processing into a hexagonal shape. This Sn strand is No. 265 samples were prepared for each of 3 to 7 samples.

<Nb ₃ Sn superconducting precursor wire>
No. For each of the samples 3 to 7, a 0.1 mm-thick Ta sheet is wound around the inner peripheral surface of a Cu pipe having an outer diameter of 43 mm and an inner diameter of 38 mm to form a diffusion barrier layer. A multi-core wire composite (multi-core billet) is prepared by arranging 265 Sn wires and 265 Sn wires so that the Sn wires are not adjacent to each other, and this is subjected to surface reduction processing to produce a Nb ₃ Sn superconducting precursor having a wire diameter of 1 mm. A body wire was prepared.

In this Nb ₃ Sn superconducting precursor wire, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the Nb filament strand is No. 1. For each of the samples 3 to 7, they are 0.19, 0.26, 0.51, 0.64, and 0.69, and the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is They are 0.04, 0.06, 0.19, 0.28, and 0.30, respectively.

  Next, a comparative example of the present invention will be described.

[Comparative Example 1]
FIG. 8 shows a cross-sectional structure of the Nb ₃ Sn superconducting precursor wire 8 of Comparative Example 1.

The Nb ₃ Sn superconducting precursor wire 8 of Comparative Example 1 is obtained by reinforcing a Nb ₃ Sn superconducting precursor wire by a conventional reinforcing method. In Example 1, a reinforcing member is provided inside the Nb filament strand 11a. The difference is that the sub-element strand 20a is produced without being arranged, and the sub-element strand 20a in the vicinity of the center of the Nb ₃ Sn superconducting precursor wire is replaced with a reinforcing member 14a.

The manufacturing method is as follows.
First, an Nb-1 mass% Ta alloy rod having an outer diameter of 28 mm is inserted inside a Cu pipe having an outer diameter of 36 mm and an inner diameter of 28.4 mm to produce an Nb composite material. Was processed into a hexagonal shape to prepare an Nb filament strand.

  In addition, an Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 30 mm is inserted into a Cu pipe having an outer diameter of 34 mm and an inner diameter of 30.4 mm, and this is reduced to reduce the distance between opposite sides. A Sn strand was fabricated by processing into a 15 mm hexagonal shape.

  Next, a diffusion barrier layer is provided on the inner circumferential surface of a Cu pipe having an outer diameter of 33 mm and an inner diameter of 30 mm by wrapping a Ta sheet having a thickness of 0.1 mm for five turns, and a single Sn wire is disposed therein. A composite was prepared by arranging 102 Nb filament strands having a distance between opposite sides of 2 mm around a Sn strand having a distance between opposite sides of 15 mm.

  Further, the Ta bar was processed into a hexagonal shape with a distance between opposite sides of 2 mm by a surface reduction process to produce a Ta reinforcing member.

Thereafter, a Cu pipe having an outer diameter of 38 mm and an inner diameter of 32 mm is prepared, 19 Ta reinforcing members are arranged at the center thereof, 66 composites are arranged around the Ta reinforcing member, and this is subjected to surface reduction processing to obtain a wire. An Nb ₃ Sn superconducting precursor wire having a diameter of 1 mm was produced.

In the Nb ₃ Sn superconducting precursor wire 8 of Comparative Example 1, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.15.

[Comparative Example 2]
FIG. 9 shows a cross-sectional structure of the Nb ₃ Sn superconducting precursor wire 9 of Comparative Example 2.

The Nb ₃ Sn superconducting precursor wire 9 of Comparative Example 2 is obtained by reinforcing a Nb ₃ Sn superconducting precursor wire by a conventional reinforcing method. In Example 2, a reinforcing member is provided inside the Nb filament strand 11a. The difference is that the Nb sub-element wire 22a is produced without being arranged, and the Nb sub-element wire 22a and the Sn wire 15 near the center of the Nb ₃ Sn superconducting precursor wire are replaced with a reinforcing member 14a.

  The manufacturing method is as follows. First, an Nb-1 mass% Ta alloy rod having an outer diameter of 28 mm is inserted inside a Cu pipe having an outer diameter of 36 mm and an inner diameter of 28.4 mm to produce an Nb composite material. Was processed into a hexagonal shape to prepare an Nb filament strand.

  Thereafter, 85 Nb filament strands were inserted into a Cu pipe having an outer diameter of 36 mm and an inner diameter of 32 mm, and the surface of the Nb filament strands was reduced to a hexagonal shape with a distance between opposite sides of 2 mm, thereby producing an Nb subelement strand.

  In addition, an Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 30 mm is inserted into a Cu pipe having an outer diameter of 34 mm and an inner diameter of 30.4 mm, and this is subjected to surface reduction to provide a distance between opposite sides of 2 mm. Was processed into a hexagonal shape to produce a Sn strand.

Thereafter, a Ta sheet having a thickness of 0.1 mm is wound around the inner surface of a Cu pipe having an outer diameter of 36 mm and an inner diameter of 30 mm to form a diffusion barrier layer, and a Ta reinforcing member having a distance between opposite sides of 2 mm is formed at the center of the inner portion. The core is arranged, and 84 hexagonal Nb composite wires with a distance between opposite sides of 2 mm and 42 Sn strands with a distance between opposite sides of 2 mm are arranged so that the Sn strands are not adjacent to each other to produce a multi-core wire composite. Then, this was subjected to surface reduction processing to produce a Nb ₃ Sn superconducting precursor wire having a wire diameter of 1 mm.

In the Nb ₃ Sn superconducting precursor wire 9 of Comparative Example 2, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.14.

[Comparative Example 3]
FIG. 10 shows a cross-sectional structure of the Nb ₃ Sn superconducting precursor wire 10 of Comparative Example 3.

The Nb ₃ Sn superconducting precursor wire 10 of Comparative Example 3 is obtained by reinforcing a Nb ₃ Sn superconducting precursor wire by a conventional reinforcing method. In Example 3, a reinforcing member is provided inside the Nb filament strand 11a. The difference is that the Nb filament strand 11a and the Sn strand 15 in the vicinity of the center of the Nb ₃ Sn superconducting precursor wire are replaced with a reinforcing member 14a without being arranged.

  The manufacturing method is as follows. First, an Nb-1 mass% Ta alloy rod having an outer diameter of 27 mm is inserted inside a Cu pipe having an outer diameter of 38 mm and an inner diameter of 27.4 mm to produce an Nb composite material. Was processed into a hexagonal shape to prepare an Nb filament strand.

  In addition, an Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 30 mm is inserted into a Cu pipe having an outer diameter of 36 mm and an inner diameter of 30.4 mm, and the surface is processed to reduce the distance between opposite sides. A Sn strand was fabricated by processing into a 1 mm hexagonal shape.

After that, 8 sheets of 0.1 mm thick Ta sheet is wound around the inner peripheral surface of a Cu pipe having an outer diameter of 43 mm and an inner diameter of 38 mm to form a diffusion barrier layer. 271 members are arranged, 540 Nb filament strands with a distance of 1 mm across the circumference and 270 Sn strands with a distance of 1 mm across the circumference are arranged so that the Sn strands are not adjacent to each other, and a multi-core wire composite Was manufactured, and an Nb ₃ Sn superconducting precursor wire having a wire diameter of 1 mm was manufactured by reducing the surface.
In the Nb ₃ Sn superconducting precursor wire 10 of Comparative Example 3, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.17.

[Comparative Example 4]
FIG. 11 shows a cross-sectional structure of the Nb ₃ Sn superconducting precursor wire 100 of Comparative Example 4.

The Nb ₃ Sn superconducting precursor wire 100 of Comparative Example 4 is obtained by reinforcing the Nb ₃ Sn superconducting precursor wire by a conventional reinforcing method. Comparative Examples 1 to 3 are different from the Nb filament element in the multicore wire. The difference is that the wire 11a and the Sn wire 15 are arranged, and the reinforcing wire 14 'in which the periphery of the reinforcing member 14a is covered with the covering Cu layer 13a is dispersedly arranged so as not to be adjacent to each other. The reinforcing member is dispersedly arranged in the same manner as in the first embodiment, but the reinforcing member is in contact with the Sn filament via the Cu member or Cu.

  The manufacturing method is as follows. First, an Nb-1 mass% Ta alloy rod having an outer diameter of 27 mm is inserted inside a Cu pipe having an outer diameter of 38 mm and an inner diameter of 27.4 mm to produce an Nb composite material. Was processed into a hexagonal shape to prepare an Nb filament strand. In addition, an Sn alloy material (Sn-2 mass% Ti) containing 2% by mass of Ti having an outer diameter of 30 mm is inserted into a Cu pipe having an outer diameter of 36 mm and an inner diameter of 30.4 mm, and the surface is processed to reduce the distance between opposite sides. A Sn strand was fabricated by processing into a 1 mm hexagonal shape. Furthermore, a Ta reinforcing member having an outer diameter of 30 mm was inserted into a Cu pipe having an outer diameter of 35 mm and an inner diameter of 30.4 mm, and this was reduced in surface and processed into a hexagonal shape with a distance between opposite sides of 1 mm to produce a reinforcing member.

Thereafter, a Ta sheet having a thickness of 0.1 mm is wound around the inner peripheral surface of a Cu pipe having an outer diameter of 43 mm and an inner diameter of 38 mm to form a diffusion barrier layer, and an Nb filament strand having a distance between opposite sides of 1 mm is formed inside the Ta barrier sheet. 558, Sn filament strands 265, and Ta reinforcing members 258 are arranged so that the Sn strands are not adjacent to each other and the reinforcing members are not connected to each other to produce a multi-core wire composite, This was surface-reduced to produce an Nb ₃ Sn superconducting precursor wire with a wire diameter of 1 mm.
In the Nb ₃ Sn superconducting precursor wire 100 of Comparative Example 4, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire is 0.16.

Table 1 shows the measurement results of the arrangement of the reinforcing members of each Nb ₃ Sn superconducting precursor wire, the ratio of the cross-sectional area of the reinforcing member, the drawing workability, and the critical current density Jc of the Nb ₃ Sn superconducting wire. Show.

The Nb ₃ Sn superconducting precursor wire samples of Examples 1 to 3 and Comparative Examples 1 to 4 drawn to a wire diameter of 1 mm were cross-sectional observed using a microscope, and the cross-sectional uniformity in wire drawing was evaluated. Samples Nos. 8 to 11 in Comparative Examples 1 to 4 have shapes of Nb filaments and Sn filaments adjacent to the reinforcing member arranged at the center of the multi-core wire, and are deformed into flat shapes along the outer periphery of the reinforcing member. Large and small filaments were mixed, and variation in filament cross-sectional area was observed. On the other hand, No. produced in Examples 1-3. In the samples 1 to 7, each Nb filament and Sn filament are regularly arranged in the same manner as the cross-sectional arrangement in which multi-core incorporation was originally performed, and the shape of each filament is not a shape that is deformed in one direction but a shape close to a circle. As shown, the sizes are uniform and the variation in the cross-sectional area of the filament is small. In the embodiment, by arranging the reinforcing member at the center of the Nb filament, the reinforcing member having a high strength and the low-strength Sn filament or the member such as Cu are arranged without being in direct contact, so that uniform workability can be obtained. It is a thing.

Next, in order to investigate the superconducting characteristics of each sample, a part of the Nb ₃ Sn superconducting precursor wire having a wire diameter of 1 mm in Examples 1 to 3 and Comparative Examples 1 to 4 prepared as described above was placed at 500 ° C. A measurement sample for measuring the critical current density Jc was prepared from the Nb ₃ Sn superconducting wire obtained by heat treatment under conditions of 100 hours + 700 ° C. × 100 hours. The prepared measurement sample was energized in liquid helium (temperature 4.2 K) with a 12 T magnetic field applied, and the critical current value was measured. Two measurement samples were prepared for each of the examples and comparative examples. One sample was measured without any distortion after heat treatment, and the other sample was measured with a curvature of 250 mm in diameter after heat treatment. . The bending strain ε is expressed as ε = d / D as described in FIG. 7 where d is the diameter of the wire and D is the diameter of the bending curvature, and a wire having a diameter of 1 mm is bent with a curvature of 250 mm. And a bending strain of about 0.4%.

The measured critical current value was divided by the cross-sectional area of the Nb filament strand excluding the Cu coating layer in the Nb ₃ Sn superconducting precursor wire to determine the critical current density Jc per Nb ₃ Sn filament cross-sectional area.

In Table 1, “each filament center”, “multi-core wire center”, and “dispersed arrangement” are respectively those when the reinforcing member (reinforcing wire) is arranged at the center of each Nb filament strand. The case where it arrange | positions in the center part and the case where it distributes and arrange | positions to the whole multi-core wire. The “Nb cross-sectional area ratio” is the ratio of the cross-sectional area of the Nb filament to the entire cross-sectional area of the wire (Nb ₃ Sn superconducting precursor wire). The “in-wire cross-sectional area ratio” is the ratio of the cross-sectional area of the reinforcing member in the entire cross section of the Nb ₃ Sn superconducting precursor wire. The “Nb cross-sectional area ratio” is the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the Nb filament (the total of the cross-sectional area of the Nb or Nb alloy layer and the cross-sectional area of the reinforcing member). Regarding “workability”, “○” indicates that breakage does not occur during machining and machining is easy, and “△” indicates that breakage occurs once or more during machining and machining is somewhat difficult. Show. As for “critical current density Jc”, the Jc value at a bending strain of 0.4% is Jc ₁ , the Jc value without a bending strain is Jc ₀ , and the characteristic ratio when there is no bending strain and when there is bending strain Jc ₁ / Jc ₀ was calculated as (Jc ratio).

When no strain was applied to the Nb ₃ Sn superconducting wire, no. The values of Jc ₀ of the samples 1 to 5 were about 2200 A / mm ² (12T). On the other hand, Jc ₀ of samples 8 to 11 of Comparative Examples 1 to 4 was approximately 2000 to 2100 A / mm ² (12T). In Samples 1 to 5 of Examples 1 to 3, the ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire Nb ₃ Sn superconducting precursor wire was approximately the same as that of Comparative Examples 1 to 3, respectively. It showed a higher value of Jc _0. In the Nb ₃ Sn superconducting wires of Comparative Examples 1 to 4 according to the prior art, since unreacted Nb remains at the center of the Nb ₃ Sn filament, the value does not become superconducting, and the value of Jc ₀ decreases. the Nb 3 _Sn superconducting wire of examples 1 to 3 for, considered showed high values of Jc ₀ to placing the reinforcing member in the central portion of the Nb 3 _Sn filaments comprising a portion which is not originally superconducting.

Moreover, the values of Jc ₀ of the samples 6 and 7 of Example 3 are 1970, 1010 A / mm ² (12T), respectively. The Jc characteristic was lower than 1-5. In Samples 6 and 7, since the ratio of the reinforcing members was increased to 0.64 and 0.69, respectively, the Nb or Nb alloy layer was reduced accordingly (the Nb cross-sectional area ratios in Table 1 were 0.16 and 0.13, respectively). ), Jc characteristics are reduced. From this result, it can be seen that the cross-sectional area ratio of the reinforcing member in the cross section of the Nb filament strand is more preferably 0.51 or less. In addition, as shown in Table 1, it can be seen that when the ratio of the cross-sectional area of the reinforcing member to the cross section of the entire Nb ₃ Sn superconducting precursor wire exceeds 0.19, the Jc characteristic is deteriorated. From this result, it can be seen that the cross-sectional area ratio of the reinforcing member to the entire cross section of the Nb ₃ Sn superconducting precursor wire is more preferably 0.19 or less.

On the other hand, in the sample to which 0.4% bending strain was applied, the Jc value was lower in both the examples and the comparative samples than when there was no strain. The Jc ratio (Jc ₁ / Jc ₀ ) was about 0.8 in Samples 1, 2, 4, 5, 6, and 7 of Examples 1 to 3. On the other hand, it is about 0.7 in the samples 8 to 10 of Comparative Examples 1 to 3, and the Nb ₃ Sn superconducting wire of the present invention has less characteristic deterioration in a state where bending strain is applied than the conventional Nb ₃ Sn superconducting wire. It was confirmed. However, in the sample 11 of Comparative Example 4, the Jc ratio (Jc ₁ / Jc ₀ ) is a value close to about 0.8, showing the bending strain characteristics equivalent to those of Examples 1 to 3, and the reinforcing member is dispersed. This is considered to be the effect of arrangement. However, in Comparative Example 4, Jc ₀ when there is no bending strain is lower than Jc _{0 of} Examples 1 to 3. This is considered to be because unreacted Nb remains in the Nb ₃ Sn superconducting wire as in Comparative Examples 1 to ₃ . Therefore, Examples 1 to 3 are effective for both improving the Jc value (Jc ₀ ) when there is no bending strain and reducing the decrease in the Jc value (Jc ₁ ) when bending strain is applied. Indicates that there is.

Considering the deterioration of the Jc characteristics due to bending strain, with reference to FIG. 7, when a Nb ₃ Sn superconducting wire having a diameter d is bent with a curvature diameter D, the wire is on the outer periphery side of the bending in the Nb ₃ Sn superconducting wire cross section. Elongation causes a tensile strain of ε = d / D, and conversely, a compressive strain of ε = −d / D occurs on the inner peripheral side of the bending. The center of the Nb ₃ Sn superconducting wire is a neutral position, and no distortion due to bending occurs. In Comparative Examples 8 to 10, the characteristic deterioration of Jc due to the bending strain of the Nb ₃ Sn superconducting wire is large because the combined reinforcing member is close to the neutral position of the strain, and thus plays a role as a reinforcing member for each filament. This is probably because it has not been fulfilled. On the other hand, in Examples 1 to 3, it is considered that the characteristic deterioration of Jc due to the bending strain of the Nb ₃ Sn superconducting wire is small because the individual filaments are reinforced.

Among the samples of Example 3, in Sample 3, Jc ₁ / Jc ₀ was 0.69, and the decrease in Jc characteristics due to bending strain was large. This is because, in the sample 3, the cross-sectional area ratio of the reinforcing member with respect to the entire cross section of the Nb ₃ Sn superconducting precursor wire is as small as 0.04. In sample 4, the cross-sectional area ratio was 0.06, and the value of Jc ₁ / Jc ₀ increased to nearly 0.8. From this result, it became clear that the cross-sectional area ratio of the reinforcing member to the entire cross section of the Nb ₃ Sn superconducting precursor wire is more preferably 0.06 or more.

Combined with the above results, the cross-sectional area ratio of the reinforcing member to the entire cross section of the Nb ₃ Sn superconducting precursor wire is 0.04 or more and 0.30 or less, preferably the lower limit is 0.06, and the upper limit The value is 0.19.

  Note that the present invention is not limited to the above-described embodiments and examples, and various modifications can be made within the scope of the gist of the present invention.

1, 5, 6, 8, 9, 10, 100 Nb ₃ Sn superconducting precursor wire 11, 11a Nb filament strand 12 Nb or Nb alloy layer 13 Cu coating layer 14, 14a Reinforcing member 15 Sn strand 16 Sn filament 17 Cu coating layer 18 Diffusion barrier layer 19 Cu coating layer 20, 20a Sub-element strand 21 Stabilized Cu layer 22, 22a Nb sub-element strand

Claims (13)

Nb ₃ Sn superconducting precursor wire used when producing an Nb ₃ Sn superconducting wire by an internal tin method, a plurality of Nb filament strands containing Nb or Nb alloy, and a plurality of Sn strands containing Sn or Sn alloy The Nb filament strand includes a reinforcing member at the center, and the reinforcing member includes Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf. Nb ₃ comprising an Nb alloy containing at least one metal selected from the group consisting of alloys or at least one metal selected from the group consisting of Ta, W, Mo, V, Zr and Hf Sn superconducting precursor wire. The Nb filament strand includes an Nb or Nb alloy layer provided around the reinforcing member, and a cross sectional area of the reinforcing member with respect to a sum of a cross sectional area of the Nb or Nb alloy layer and a cross sectional area of the reinforcing member. The Nb ₃ Sn superconducting precursor wire according to claim 1, wherein the ratio is 0.19 or more and 0.69 or less. _Nb 3 Sn superconductor precursor wire according to the _Nb 3 Sn claim 1 or 2 ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire superconductor precursor wire is 0.04 to 0.30. Nb 3 _Sn superconductor precursor wire according to the Nb 3 _Sn superconducting ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire precursor wire material is 0.06 or more claims 3. Nb 3 _Sn superconductor precursor wire according to the Nb 3 _Sn claim 3 or 4 ratio of the cross-sectional area of the reinforcing member to the cross-sectional area of the entire superconductor precursor wire is 0.19 or less.   A reinforcing member is provided at the center, and includes an Nb or Nb alloy layer provided around the reinforcing member. The reinforcing member includes Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Nb alloy containing at least one metal selected from the group consisting of Zr, Zr alloy, Hf, and Hf alloy, or at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, Hf Nb filament strand consisting of   The Nb filament strand according to claim 6, wherein the ratio of the cross-sectional area of the reinforcing member to the total cross-sectional area of the Nb or Nb alloy layer and the cross-sectional area of the reinforcing member is 0.19 or more and 0.69 or less.   The Nb filament strand according to claim 7, wherein the ratio of the cross-sectional area of the reinforcing member to the total cross-sectional area of the Nb or Nb alloy layer and the cross-sectional area of the reinforcing member is 0.51 or less. By heat treating the _Nb 3 Sn superconductor precursor wire according to claim 1, _Nb 3 Sn superconducting wire in which the Nb filaments wire to diffuse the Sn and to generate _Nb 3 Sn. Preparing a plurality of Nb filament strands including Nb or Nb alloy and a plurality of Sn strands including Sn or Sn alloy; and at the center of the Nb filament strand, Ta, Ta alloy, W, W alloy, At least one metal selected from the group consisting of Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy, or selected from the group consisting of Ta, W, Mo, V, Zr, Hf Nb 3 _Sn method of manufacturing a superconducting precursor wire material, characterized in that it comprises the step of placing a reinforcing member made of Nb alloy containing at least one metal. The step of disposing the reinforcing member at the center of the Nb filament strand is made of Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy. A bar made of an Nb alloy containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf and containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf is placed in a pipe made of Nb or Nb alloy. method for manufacturing a Nb 3 _Sn superconductor precursor wire of claim 10 further comprising inserting step. The step of disposing the reinforcing member at the center of the Nb filament strand is made of Ta, Ta alloy, W, W alloy, Mo, Mo alloy, V, V alloy, Zr, Zr alloy, Hf, and Hf alloy. Or Nb or Nb alloy around a metal rod made of Nb alloy containing at least one metal selected from the group consisting of Ta, W, Mo, V, Zr, and Hf. Nb 3 _Sn method of manufacturing a superconducting precursor wire material according to claim 10 further comprising the step of winding the sheet. By heat treating the _Nb 3 Sn superconductor precursor wire according to claim 1, _Nb 3 Sn method of manufacturing a superconducting wire comprising the Nb step of filament strands to diffuse the Sn to produce a _Nb 3 Sn.

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