JP2019053985A - Precursor used for manufacturing superconducting wire rod, manufacturing method of precursor and superconducting wire rod - Google Patents

Abstract

To provide a precursor used for manufacturing a superconducting wire rod capable of providing a superconducting wire rod high in critical current density.SOLUTION: There is provided a wire drawing processed article of a composite tube which is a precursor used for manufacturing NbSn superconducting wire rod by an inside tin diffusion method and has a composite wire group, a barrier layer surrounding the composite wire group and a copper layer coating an outer periphery surface of the barrier layer, in which the composite wire group has a plurality of tin wires having tin-made tin core material and a copper matrix surrounding the tin core material, and a plurality of niobium wires having a plurality of niobium-made niobium core materials and a copper matrix surrounding the niobium wires, a gravity center of a cross section area of a tin filament derived from the plurality of tin wires is positioned with an almost flat lattice shape in a cross section view, and average distance between a gravity center of a unit lattice forming the flat lattice and a gravity center of the cross section area of the tin filament at a lattice point of the unit lattice is 50 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a precursor used for manufacturing a superconducting wire, a method for manufacturing the precursor, and a superconducting wire.

A superconducting electromagnet is used to generate a strong magnetic field in a nuclear magnetic resonance apparatus (NMR apparatus), a magnetic resonance imaging apparatus (MRI apparatus), a nuclear fusion reactor, an accelerator, or the like. In recent years, superconducting electromagnets are required to have high performance and downsizing, and superconducting wires for superconducting electromagnets are also required to increase the critical magnetic field and critical current density in order to generate a strong magnetic field. Conventionally, Nb ₃ Sn superconducting wire has been used as a superconducting wire capable of generating a strong magnetic field.

As a manufacturing method of the Nb ₃ Sn superconducting wire, a bronze method and an internal tin diffusion method have been proposed (Patent Documents 1 and 2). Here, the internal tin diffusion method is a method in which a niobium core material and a precursor of a superconducting wire arranged so that the tin core material does not come into contact with each other in the copper matrix are subjected to heat treatment, and the tin diffused in the copper matrix is converted into niobium. and a method for producing a Nb 3 _Sn by reaction, it is known that as compared with the bronze process is advantageous in terms of cost of heat treatment on product efficiency and the wire of Nb 3 _Sn.

The Nb ₃ Sn superconducting wire of Patent Document 1 is manufactured by an internal tin diffusion method from a precursor combining a niobium wire in which a niobium core material is embedded in a copper matrix and a tin wire not having a copper matrix on the surface of tin. Is. Patent Document 1 states that the critical current density of the Nb ₃ Sn superconducting wire can be increased by reducing the volume of the copper matrix in the precursor.

The Nb ₃ Sn superconducting wire of Patent Document 2 is manufactured by an internal tin diffusion method from a precursor in which a copper matrix and a plurality of niobium core materials are arranged around a tin core material. In Patent Document 2, the niobium core material in the precursor has a wire diameter of 5 μm to 30 μm, and the average distance between the niobium core material and the tin core material present in the nearest vicinity of the tin core material is 100 μm or less. It is said that the critical current density of ₃ Sn superconducting wire can be increased.

Patent Document 1 and Patent Document 2 increase the critical current density of the Nb ₃ Sn superconducting wire by relatively increasing the volume ratio of niobium in the precursor. However, further contrivance is required to further increase the critical current density of the Nb ₃ Sn superconducting wire.

JP 2010-15821 A JP 2007-210402 A

  The present invention has been made based on the above circumstances, a precursor used for manufacturing a superconducting wire capable of obtaining a superconducting wire having a high critical current density, a method for manufacturing the precursor, and a critical current. An object is to provide a superconducting wire having a high density.

The inventors of the present invention manufactured an Nb ₃ Sn superconducting wire by an internal tin diffusion method, and as a result of observing the critical current density and internal structure of this superconducting wire, coarse Nb ₃ Sn crystal grains were formed in the superconducting wire. It has been found that the critical current density of the superconducting wire decreases. Therefore, the present inventors arranged coarse Nb ₃ Sn crystals in the superconducting wire manufactured from the precursor by arranging tin in the precursor used for manufacturing the superconducting wire so as to satisfy a predetermined condition. It discovered that the production | generation of a grain could be suppressed and completed this invention.

That is, the first invention made to solve the above problems is a composite wire group, a cylindrical barrier layer disposed so as to surround the composite wire group and preventing permeation of tin, and the cylindrical And a tubular copper layer covering the outer peripheral surface of the barrier layer of the composite pipe, and a precursor for use in the manufacture of a Nb ₃ Sn superconducting wire by an internal tin diffusion method. One or more tin cores made of tin or a tin alloy and a plurality of tin wires having a copper matrix surrounding the tin core, and adjacent to the tin wire, the wire group is made of niobium or niobium A plurality of niobium cores made of an alloy and a plurality of niobium wires having a copper matrix surrounding these niobium cores, and a cross section of a tin wire body derived from the plurality of tin wires in a cross-sectional view The center of gravity of the region is approximately The average distance between the center of gravity of the unit cell forming the plane lattice and the center of gravity of the cross-sectional area of the tin linear body at the lattice point of the unit cell is 30 μm or more and 50 μm or less. is there.

As a result of intensive studies, the present inventors have found that the diffusion distance of tin in the heat treatment of the precursor is about 50 μm, and coarse Nb ₃ Sn crystal grains are likely to be generated at a position far from the diffusion distance from tin. Have confirmed. Therefore, in the cross-sectional view, the precursor has the center of gravity of the cross-sectional area of the tin wire derived from a plurality of tin wires positioned in a substantially planar lattice shape, and the center of gravity of the unit lattice forming this planar lattice and the unit The average distance between the center of gravity of the cross-sectional area of the tin linear body at the lattice point of the lattice is 30 μm or more and 50 μm or less. Since the composite wire group of the composite tube has a structure in which a plurality of niobium wires are adjacent to each other around the tin wire, the precursor that is a drawn product of the composite tube is within a range of 50 μm or less from the tin wire. A niobium linear body derived from the niobium wire is positioned, and a sufficient amount of tin can be diffused in every corner of the niobium linear body in the heat treatment by the internal tin diffusion method. In other words, the precursor can prevent a short amount of tin diffusion at a position far away from the tin linear body and can suppress the formation of coarse Nb ₃ Sn crystal grains, so that a superconducting wire with a high critical current density can be obtained. Make it possible to get.

A second invention made to solve the above problems is a method for producing a precursor used for producing an Nb ₃ Sn superconducting wire by an internal tin diffusion method, and surrounds the composite wire group and the composite wire group. Preparing a composite pipe comprising a cylindrical barrier layer disposed so as to prevent permeation of tin and a cylindrical copper layer covering the outer peripheral surface of the cylindrical barrier layer, and the composite pipe A plurality of tin wires having a copper matrix surrounding the tin core and one or more tin cores made of tin or a tin alloy, and the tin A plurality of niobium cores made of niobium or niobium alloy adjacent to each other so as to surround the wire, and a plurality of niobium wires having a copper matrix surrounding these niobium cores, and after the wire drawing step In cross section view of composite pipe The center of gravity of the cross-sectional area of the tin wire derived from the plurality of tin wires is positioned in a substantially planar lattice shape, and the center of gravity of the unit lattice forming the planar lattice in the wire drawing step and the lattice of the unit lattice The composite pipe is drawn so that an average distance from the center of gravity of the cross-sectional area of the tin linear body at the point is 30 μm or more and 50 μm or less.

  Since the precursor manufactured by the precursor manufacturing method has the same structure as the precursor, the precursor manufacturing method makes it possible to obtain a superconducting wire having a high critical current density.

A third invention made to solve the above problems is an Nb ₃ Sn superconducting wire manufactured by an internal tin diffusion method, and has a plurality of holes along the longitudinal direction, and at least Nb ₃ Sn and copper Containing a composite linear body, a cylindrical barrier layer disposed so as to surround the composite linear body and preventing permeation of tin, and a cylindrical shape covering an outer peripheral surface of the cylindrical barrier layer And a center of gravity of the cross-sectional area of the plurality of vacancies is positioned in a substantially planar lattice shape in cross-sectional view, and the center of gravity of the unit lattice forming the planar lattice and the lattice point of the unit lattice are The average distance from the center of gravity of the cross-sectional area of the hole is 30 μm or more and 50 μm or less.

The superconducting wire is an Nb ₃ Sn superconducting wire manufactured by an internal tin diffusion method. Since tin disposed in the precursor diffuses by heat treatment by an internal tin diffusion method, voids are formed at the positions where tin was present. The superconducting wire has the center of gravity of a cross-sectional area of a plurality of cavities derived from tin positioned in a substantially planar lattice shape in a cross-sectional view, and is located at the center of gravity of the unit lattice forming this planar lattice and the lattice point of the unit lattice The average distance between the center of gravity of the cross-sectional area of the pores is 30 μm or more and 50 μm or less, and a sufficient amount of tin is diffused in every corner of the composite linear body in the heat treatment by the internal tin diffusion method. In other words, the superconducting wire prevents the insufficient amount of tin diffusion at a position far from the tin and suppresses the formation of coarse Nb ₃ Sn crystal grains, and thus exhibits a high critical current density.

  The present invention provides a precursor used in the production of a superconducting wire capable of obtaining a superconducting wire having a high critical current density, a method for producing the precursor, and a superconducting wire having a high critical current density.

It is a cross-sectional view which shows typically the precursor of one Embodiment of this invention. It is a cross-sectional view which shows typically the superconducting wire manufactured from the precursor of FIG.

  Embodiments of a precursor, a precursor manufacturing method, and a superconducting wire according to the present invention will be described in detail below with reference to the drawings.

A precursor 1 in FIG. 1 is a superconducting wire precursor before heat treatment used for manufacturing an Nb ₃ Sn superconducting wire by an internal tin diffusion method, and a cross-sectional area is formed in a substantially circular shape in a cross-sectional view. The precursor 1 is disposed so as to surround the composite wire group, a cylindrical barrier layer that prevents the permeation of tin, and a cylindrical shape that covers the outer peripheral surface of the cylindrical barrier layer. A wire-drawn product of a composite pipe comprising a copper layer. Here, the drawn product of the composite pipe refers to a molded product in which the composite pipe is radially reduced by drawing, and the change in the arrangement structure other than the reduced diameter is small before and after the drawing. Means.

[Composite pipe]
The composite tube before wire drawing is formed in a cylindrical body in which a cross-sectional area is formed in a substantially circular shape in a cross-sectional view, and a barrier layer is arranged in a cylindrical shape on the inner peripheral surface of a cylindrical copper layer. It has a structure in which a composite wire group is inserted inside. As the material of the barrier layer, for example, niobium or titanium is adopted, but niobium is preferable from the viewpoint that Nb ₃ Sn can be generated also on the inner peripheral surface of the barrier layer.

<Composite wire group>
The composite wire group includes a tin core made of tin or a tin alloy and a plurality of tin wires having a copper matrix surrounding the tin core, adjacent to each other so as to surround the tin wire, and a plurality of niobium or niobium alloy And a plurality of niobium wires having a copper matrix surrounding these niobium core materials. In the cross sectional view, the tin wire and the niobium wire are each formed in a substantially regular hexagonal shape in cross-sectional area, and are spatially combined with substantially no gap. Specifically, three niobium wires and tin wires are alternately adjacent to six surfaces of one niobium wire, and one niobium wire is adjacent to each of six surfaces of one tin wire. Niobium wire is combined, and the copper matrix of the niobium wire and the copper matrix of the tin wire are in contact with each other.

  The tin wire in the composite wire group is regularly positioned by the combination of the tin wire and the niobium wire as described above. Specifically, the center of gravity of the cross-sectional area of the plurality of tin wires is positioned in a substantially planar lattice shape (substantially triangular lattice shape) in a cross sectional view of the composite pipe. Further, in the cross sectional view of the composite pipe, the center of gravity of the cross-sectional area of the tin wire and the center of gravity of the cross-sectional area of the tin core substantially coincide.

[Precursor production method]
The manufacturing method of the precursor 1 has a preparation process for preparing a composite pipe and a wire drawing process for drawing the composite pipe.

<Preparation process>
The preparation step is a step of preparing the above-described composite pipe. In the preparation step, a composite wire group, a cylindrical barrier layer disposed so as to surround the composite wire group and preventing permeation of tin, and this A composite pipe provided with a cylindrical copper layer covering the outer peripheral surface of the cylindrical barrier layer is prepared.

  As described above, the prepared composite wire group of composite pipes includes one or more tin cores made of tin or a tin alloy, and a plurality of tin wires having a copper matrix surrounding the tin core, and a tin wire. A plurality of niobium cores made of niobium or a niobium alloy and a plurality of niobium wires having a copper matrix surrounding these niobium cores are provided so as to surround them.

<Wire drawing process>
The wire drawing step is a step of drawing the composite tube prepared in the preparation step to obtain the precursor 1, and in the wire drawing step, the composite tube is radially reduced by wire drawing. As this wire drawing, a known processing procedure using a die can be adopted.

  The composite pipe after the wire drawing (precursor 1) has a smaller change in the arrangement structure other than the reduced diameter as compared with the composite pipe before the wire drawing. Therefore, the precursor 1 is a niobium wire 2 derived from a plurality of niobium wires and a tin wire 3 derived from a plurality of tin wires other than the reduced diameters of the original plurality of niobium wires and the plurality of tin wires. Maintain the arrangement structure. That is, in the cross-sectional view of the composite pipe after the wire drawing step, the center of gravity of the cross-sectional area of the tin wire 3 derived from the plurality of tin wires corresponds to the arrangement of the plurality of tin wires in a substantially planar lattice shape ( It is located in a substantially triangular lattice shape.

  In the wire drawing step, the arrangement structure of the tin linear bodies 3 derived from the plurality of tin wire rods is adjusted by reducing the diameter. Specifically, in the wire drawing step, the average distance W between the center of gravity of the unit cell forming the plane lattice and the center of gravity of the cross-sectional area of the tin linear body 3 at the lattice point of this unit cell is the tin in the heat treatment. The composite tube is drawn so as to be adjusted to a value suitable for diffusion of Here, the average distance W indicates a value obtained by obtaining the distance from each lattice point to the center of gravity for any five unit lattices and averaging them.

  In the case of the above-described precursor 1, the shape of the cross-sectional area of the tin linear body 3 approximates a regular hexagon, and the shape of the unit cell approximates a regular triangle. As a method for extracting the lattice, for example, a known method such as shape matching using a microphotograph image can be employed.

The lower limit of the average distance W is preferably 30 μm, more preferably 33 μm, and even more preferably 35 μm. On the other hand, the upper limit of the average distance W is preferably 50 μm, more preferably 47 μm, and even more preferably 45 μm. If the average distance W is less than the lower limit, the drawing process itself may be difficult or the drawing process cost may increase. On the other hand, when the average distance W exceeds the upper limit, the amount of tin diffusion from the tin linear body 3 to the center of gravity of the unit cell forming the planar lattice becomes insufficient, and coarse Nb ₃ Sn at the center of gravity of the unit cell. The production of crystal grains may not be suppressed.

[precursor]
Since the precursor 1 is a drawn product of the composite pipe described above, it inherits the arrangement structure other than the reduced diameter of the composite pipe before drawing. Specifically, the precursor 1 includes a plurality of niobium linear bodies 2 derived from a plurality of niobium wires, and a plurality of tin linear bodies 3 derived from a plurality of tin wires, and one tin wire. 6 niobium linear bodies 2 are adjacent to the body 3. The precursor 1 is disposed so as to surround the plurality of niobium linear bodies 2 and the plurality of tin linear bodies 3, and has a cylindrical barrier layer 4 that prevents permeation of tin, and the cylindrical barrier layer. 4 and a cylindrical copper layer 5 covering the outer peripheral surface of 4. In FIG. 1, the precursor 1 is represented as having a gap on the inner peripheral surface side of the cylindrical barrier layer 4, but FIG. 1 is a schematic diagram for facilitating understanding of the structure of the precursor 1. This gap is actually a cross-sectional view, and this gap is actually closed by wire drawing when the precursor 1 is manufactured.

<Niobium linear body>
The niobium wire 2 is derived from the niobium wire before drawing, and is formed of a plurality of niobium cores 2b made of niobium or niobium alloy surrounded by the copper matrix 2a and the copper matrix 2a. The plurality of niobium cores 2b only have to be arranged in a state of being separated from each other by the copper matrix 2a, and the number and arrangement are not particularly limited.

<Tin linear body>
The tin wire 3 is derived from a tin wire before wire drawing, and is formed of a tin core 3b made of tin or tin alloy surrounded by the copper matrix 3a and the copper matrix 3a. In addition, one tin linear body 3 is not limited to the one having one tin core 3b, and one tin linear body 3 may have a plurality of tin cores 3b.

  The niobium linear body 2 and the tin linear body 3 are formed in a substantially regular hexagonal shape in cross-sectional area in a cross-sectional view, and are combined with no space in a space. In addition, as shown in FIG. 1, three niobium linear bodies 2 and three tin linear bodies 3 are alternately adjacent to six surfaces of one niobium linear body 2, and six surfaces of one tin linear body 3. Each niobium wire 2 is adjacent to each other, and the copper matrix 2a of the niobium wire 2 and the copper matrix 3a of the tin wire 3 are in contact with or joined to each other.

  The tin linear body 3 is regularly positioned by the combination of the niobium linear body 2 and the tin linear body 3 as described above. Specifically, in the cross-sectional view of the precursor 1, the centers of gravity of the cross-sectional areas of the plurality of tin linear bodies 3 are positioned in a substantially planar lattice shape (substantially triangular lattice shape). Further, in the cross-sectional view of the precursor 1, the center of gravity of the cross-sectional area of the tin linear body 3 and the center of gravity of the cross-sectional area of the tin core 3b substantially coincide.

The average distance W between the center of gravity of the unit cell forming this plane lattice and the center of gravity of the cross-sectional area of the tin linear body 3 at the lattice point of this unit cell is adjusted to a value suitable for tin diffusion in heat treatment. ing. That is, the lower limit of the average distance W is preferably 30 μm, more preferably 33 μm, and even more preferably 35 μm. On the other hand, the upper limit of the average distance W is preferably 50 μm, more preferably 47 μm, and even more preferably 45 μm. If the average distance W is less than the lower limit, the drawing process may be difficult and the drawing process cost may increase. On the other hand, when the average distance W exceeds the upper limit, the amount of tin diffusion from the tin linear body 3 to the center of gravity of the unit cell forming the planar lattice becomes insufficient, and coarse Nb ₃ Sn at the center of gravity of the unit cell. The production of crystal grains may not be suppressed.

<Barrier layer>
The barrier layer 4 is a layer that prevents the tin diffused from the tin linear body 3 from being transmitted to the outside in the heat treatment by the internal tin diffusion method, and includes a plurality of niobium linear bodies 2 and a plurality of tin linear bodies 3. Is formed in a cylindrical shape so as to surround. As the material of the barrier layer 4, for example, niobium or titanium is adopted, but niobium is preferable from the viewpoint that Nb ₃ Sn can be generated also on the inner peripheral surface of the barrier layer 4.

<Copper layer>
The copper layer 5 is a stabilizing material that protects the precursor 1 and is formed in a cylindrical shape so as to cover the outer peripheral surface of the cylindrical barrier layer.

[Superconducting wire]
The superconducting wire 11 in FIG. 2 is a wire-drawn product of the above-described composite tube, that is, an Nb ₃ Sn superconducting wire manufactured from the precursor 1 by the internal tin diffusion method, and the cross-sectional area is formed in a substantially circular shape in a cross-sectional view. Has been. Since the superconducting wire 11 is manufactured from the above-mentioned composite pipe drawn product, it inherits the arrangement structure other than the diameter reduction of the composite pipe before drawing. Specifically, the superconducting wire 11 includes a composite linear body derived from the composite wire group, a cylindrical barrier layer 14 disposed so as to surround the composite linear body, and preventing permeation of tin, And a cylindrical copper layer 15 covering the outer peripheral surface of the cylindrical barrier layer 14. In FIG. 2, the superconducting wire 11 is expressed as having a gap on the inner peripheral surface side of the cylindrical barrier layer 14, but FIG. 2 is a schematic diagram for facilitating understanding of the structure of the superconducting wire 11. In fact, this gap is closed.

Since the superconducting wire 11 is obtained by performing heat treatment by the internal tin diffusion method on the precursor 1 described above, tin contained in the tin wire 3 of the precursor 1 diffuses and is contained in the niobium wire 2. Niobium reacts with tin to become Nb ₃ Sn.

<Composite linear body>
The superconducting wire 11 has a plurality of holes X along the longitudinal direction and includes a composite linear body containing at least Nb ₃ Sn and copper. The composite linear body is formed by a plurality of niobium linear bodies 12 derived from a plurality of niobium linear bodies 2 and a plurality of tin linear bodies 13 derived from a plurality of tin linear bodies 3. Six niobium linear bodies 12 are adjacent to the linear body 13. However, since the plurality of niobium linear bodies 12 and the plurality of tin linear bodies 13 are integrally fused by heat treatment by the internal tin diffusion method, the composite linear bodies are the niobium linear bodies 12 and the tin. It is difficult to identify the boundary of the linear body 13 and to clearly distinguish Nb ₃ Sn and copper.

<Hole>
The hole X is a hole derived from the tin linear body 3. As described above, most of the tin diffuses from the tin linear body 3 of the precursor 1 by the heat treatment by the internal tin diffusion method. For this reason, void X is formed in the tin wire 13 due to the arrangement of the tin core 3b of the tin wire 3 in FIG. However, as described above, the niobium linear body 12 and the tin linear body 13 are all united, so in fact, as shown in FIG. 2, the composite linear body has a plurality of voids along the longitudinal direction. Observed to have hole X.

  When a part of tin contained in the tin core 3b of the precursor 1 remains without being diffused, a tin adhesion layer is formed on the inner peripheral surface of the hole X as shown in FIG.

  The holes X are regularly arranged due to the arrangement of the niobium linear body 2 and the tin linear body 3 of the precursor 1. Specifically, in the cross-sectional view of the superconducting wire 11, the center of gravity of the cross-sectional area of the plurality of holes X is positioned in a substantially planar lattice shape (substantially triangular lattice shape).

The average distance W between the center of gravity of the unit cell forming this plane lattice and the center of gravity of the cross-sectional area of the hole X at the lattice point of this unit cell is adjusted to a value suitable for tin diffusion in heat treatment It is. That is, the lower limit of the average distance W is preferably 30 μm, more preferably 33 μm, and even more preferably 35 μm. On the other hand, the upper limit of the average distance W is preferably 50 μm, more preferably 47 μm, and even more preferably 45 μm. If the average distance W is less than the lower limit, the drawing process may be difficult and the drawing process cost may increase. On the other hand, if the average distance W exceeds the upper limit, the amount of tin diffusion from the tin linear body 3 of the precursor 1 before the heat treatment to the center of gravity of the unit cell forming the planar lattice becomes insufficient, and the center of gravity of the unit cell There is a possibility that the formation of coarse Nb ₃ Sn crystal grains is not suppressed.

(advantage)
In the cross-sectional view, the precursor 1 has the center of gravity of the cross-sectional area of the tin wire 3 derived from a plurality of tin wire rods positioned in a substantially planar lattice shape, and the center of gravity of the unit lattice forming this planar lattice and the unit Since the average distance from the center of gravity of the cross-sectional area of the tin linear body 3 at the lattice point of the grid is 50 μm or less, the niobium linear body derived from the niobium wire within the range of 50 μm or less from the tin linear body 3 2 is positioned, and a sufficient amount of tin can be diffused in every corner of the niobium linear body 2 in the heat treatment by the internal tin diffusion method. In other words, the precursor 1 prevents the insufficient amount of tin diffusion at a position far from the tin linear body 3 and promotes the generation of fine and equiaxed grains of Nb ₃ Sn serving as a magnetic flux pinning site. In addition, since generation of coarse Nb ₃ Sn crystal grains having a small magnetic flux pinning force can be suppressed, a superconducting wire having a high critical current density can be obtained.

  In addition, since the precursor manufactured by the precursor manufacturing method has the same structure as that of the precursor 1, the precursor manufacturing method makes it possible to obtain a superconducting wire having a high critical current density.

Further, the superconducting wire 11 has the center of gravity of the cross-sectional area of the plurality of holes X positioned in a substantially planar lattice shape in a cross sectional view, and the center of gravity of the unit lattice forming this planar lattice and the lattice point of the unit lattice Since the average distance from the center of gravity of the cross-sectional area of a certain hole X is 50 μm or less, a sufficient amount of tin is diffused in every corner of the composite linear body in the heat treatment by the internal tin diffusion method. That is, the superconducting wire 11 prevents a shortage of tin diffusion at a position far away from tin and suppresses generation of coarse Nb ₃ Sn crystal grains, and thus exhibits a high critical current density.

[Other Embodiments]
The precursor used for the production of the superconducting wire of the present invention, the method for producing the precursor, and the superconducting wire are not limited to the above embodiment.

  In the above-described embodiment, the precursor has been described as including a niobium linear body and a tin linear body having a substantially regular hexagonal cross-sectional area in a cross-sectional view, but the niobium linear body and the tin linear body The shape of the cross-sectional area in the cross-sectional view is not limited to a substantially regular hexagon, and may be, for example, a substantially regular triangle or a substantially square. Further, the superconducting wire may be derived from the structure of the precursor in which the center of gravity of the cross-sectional area of the plurality of holes X is positioned in a substantially regular hexagonal lattice shape or a substantially square lattice shape in a cross sectional view. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Preparation of composite pipe]
First, a niobium core material (outer diameter: 99 mm) was inserted into a copper pipe (outer diameter: 114 mm, inner diameter: 100 mm), and a niobium single core wire having a regular hexagonal cross section was produced by wire drawing. The length between opposite sides of the regular hexagon of the cross section of the niobium single core wire was 3.8 mm. The manufactured niobium single core wire is cut into a large number, 583 niobium single core wires are combined and inserted into a copper pipe (outer diameter: 114 mm, inner diameter: 102 mm), and a niobium wire having a regular hexagonal cross section is drawn by wire drawing. Produced. The length between opposite sides of the regular hexagon in the cross section of the niobium wire was 2.8 mm.

  Next, a core material made of tin-titanium alloy (titanium content: 2 mass%, outer shape: 17.5 mm) is inserted into a copper pipe (outer diameter: 20.4 mm, inner diameter: 18.0 mm), and then drawn. A tin wire with a regular hexagonal cross section was produced by processing. The length between opposite sides of the regular hexagon in the cross section of the tin wire was 2.8 mm.

  The obtained niobium wire and tin wire were cut in large numbers, and 84 niobium wires and 37 tin wires were combined so as to have a substantially circular cross section to form a composite wire group. In this combination, the niobium wire was adjacent to all six surfaces of the tin wire, and three tin wires and niobium wires were alternately adjacent to the six surfaces of the niobium wire.

  A sheet of niobium (thickness: 0.2 mm) is inserted by one turn along the inner peripheral surface of the copper pipe (outer diameter: 43.2 mm, inner diameter: 37.2 mm), and more than the sheet material in the copper pipe. A composite wire group was inserted on the inner side to form a composite pipe.

[Precursor and superconducting wire]
The obtained composite pipe was integrated by wire drawing, and wire drawing was further performed to produce two types of precursors. Table 1 shows the wire diameters of the manufactured precursors. Moreover, when the manufactured precursor was cut and the cross section was observed with a microscope, it was confirmed that the center of gravity of the cross-sectional area of the tin wire derived from a plurality of tin wires was positioned in a substantially triangular lattice shape. . Therefore, in this cross section, the average distance W between the center of gravity of the unit cell forming the plane lattice and the center of gravity of the cross section of the cross section of the tin linear body at the lattice point of the unit cell was measured. This average distance is shown in Table 1.

  In addition, multistage heat treatment by an internal tin diffusion method was performed on the obtained two types of precursors to produce a superconducting wire. For these superconducting wires, under the conditions of a temperature of 4.2K and an external magnetic field of 16T, the total cross-sectional critical current density and the non-copper critical current density in the non-copper part excluding the area of the copper cross-sectional area from the total cross-sectional area And measured. These measurement results are also shown in Table 1.

As shown in Table 1, no. No. 1 has a critical current density of 1025 (A / mm ² ). 2 had a non-copper critical current density of 760 (A / mm ² ). From these results, no. 1 is No. Compared to 2, it was confirmed that the critical current density of the non-copper portion was improved by about 35%.

No. 1 and no. No. 2 was cut and the cross section was observed with a microscope. In No. 1, the crystal structure of Nb ₃ Sn is equiaxed, whereas In No. 2, it was confirmed that the crystal structure of Nb ₃ Sn near the center of the triangular lattice, which is a unit lattice, includes coarse crystal grains.

  The present invention provides a precursor used in the production of a superconducting wire capable of obtaining a superconducting wire having a high critical current density, a method for producing the precursor, and a superconducting wire having a high critical current density.

DESCRIPTION OF SYMBOLS 1 Precursor 2 Niobium linear body 2a Copper matrix 2b Niobium core 3 Tin linear body 3a Copper matrix 3b Tin core 4 Barrier layer 5 Copper layer 11 Superconducting wire 12 Niobium linear body 13 Tin linear body 14 Barrier layer 15 Copper layer X Hole

Claims (3)

A composite wire group, a cylindrical barrier layer disposed so as to surround the composite wire group and preventing permeation of tin, and a cylindrical copper layer covering the outer peripheral surface of the cylindrical barrier layer A wire-drawn product of a composite pipe, which is a precursor used for manufacturing an Nb ₃ Sn superconducting wire by an internal tin diffusion method,
The composite wire rod group is
One or more tin cores made of tin or tin alloy and a plurality of tin wires having a copper matrix surrounding the tin core;
A plurality of niobium cores made of niobium or niobium alloy adjacent to each other so as to surround the tin wire, and a plurality of niobium wires having a copper matrix surrounding these niobium cores;
In the cross-sectional view, the center of gravity of the cross-sectional area of the tin wire derived from the plurality of tin wires is positioned in a substantially planar lattice shape, and the center of gravity of the unit lattice forming this planar lattice and the lattice point of this unit lattice The precursor whose average distance between the gravity center of the cross-sectional area | region of the said tin linear body in said is 30 micrometers or more and 50 micrometers or less. A method for producing a precursor used for producing a Nb ₃ Sn superconducting wire by an internal tin diffusion method,
A composite wire group, a cylindrical barrier layer disposed so as to surround the composite wire group and preventing permeation of tin, and a cylindrical copper layer covering the outer peripheral surface of the cylindrical barrier layer Preparing a composite tube;
Drawing the composite pipe,
The composite wire rod group is
One or more tin cores made of tin or tin alloy and a plurality of tin wires having a copper matrix surrounding the tin core;
A plurality of niobium cores made of niobium or niobium alloy adjacent to each other so as to surround the tin wire, and a plurality of niobium wires having a copper matrix surrounding these niobium cores;
In the cross-sectional view of the composite pipe after the wire drawing step, the center of gravity of the cross-sectional area of the tin linear body derived from the plurality of tin wire rods is located in a substantially planar lattice shape,
In the wire drawing step, an average distance between the center of gravity of the unit lattice forming the planar lattice and the center of gravity of the cross-sectional area of the tin linear body at the lattice point of the unit lattice is 30 μm or more and 50 μm or less. A method for producing a precursor for drawing the composite pipe. A Nb ₃ Sn superconducting wire manufactured by an internal tin diffusion method,
A composite linear body having a plurality of holes along the longitudinal direction and containing at least Nb ₃ Sn and copper;
A cylindrical barrier layer disposed so as to surround the composite linear body and preventing permeation of tin; and
A cylindrical copper layer covering the outer peripheral surface of the cylindrical barrier layer,
In cross-sectional view, the center of gravity of the cross-sectional area of the plurality of holes is located in a substantially planar lattice shape, and the cross-section of the hole at the lattice point of the unit lattice and the unit lattice forming the planar lattice A superconducting wire having an average distance between the center of gravity of the region and 30 μm or more and 50 μm or less.

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