阅读说明：本技术 用于超导线材的制造的前驱体、前驱体的制造方法和超导线材 (Precursor for manufacturing superconducting wire, method for manufacturing precursor, and superconducting wire ) 是由 川岛慎也 川原田乔生 于 2019-10-25 设计创作，主要内容包括：本发明的前驱体是具备复合线材群和阻挡层和保护层的复合管的拉丝加工品,上述复合线材群具备：多个锡线材,其具有一个或多个锡芯材和包围该锡芯材的铜基；多个铌线材,其具有多个铌芯材和包围这些铌芯材的铜基,并以包围上述锡线材的方式配设,并且上述复合线材群含有钛,其含量为0.38质量％以上且0.55质量％以下,在横剖视下,来自上述多个锡线材的锡线状体的截面区域的重心以大致平面点陈状定位,形成该平面点阵的单位点阵的重心与处于该单位点阵的阵点的上述锡线状体的截面区域的重心之间的平均距离为30μm以上且50μm以下。(The precursor of the present invention is a drawn wire product of a composite tube having a composite wire group, a barrier layer, and a protective layer, the composite wire group including: a plurality of tin wires having one or more tin core materials and a copper base surrounding the tin core materials; and a plurality of niobium wires each having a plurality of niobium core materials and a copper base surrounding the niobium core materials and arranged so as to surround the tin wire, wherein the composite wire group contains titanium in an amount of 0.38 mass% or more and 0.55 mass% or less, and wherein, in a transverse cross-sectional view, the centers of gravity of cross-sectional areas of the tin wires from the plurality of tin wires are positioned in a substantially planar lattice form, and the average distance between the center of gravity of a unit lattice forming the planar lattice and the center of gravity of a cross-sectional area of the tin wire at a lattice point of the unit lattice is 30 μm or more and 50 μm or less.)

1. A precursor, a drawn wire product of a composite tube, is Nb based on an internal tin method₃A precursor for use in the production of a Sn superconducting wire, said drawn wire product of a composite tube comprising: a composite wire group; a cylindrical barrier layer arranged so as to surround the composite wire group and preventing tin from penetrating therethrough; a cylindrical protective layer covering an outer peripheral surface of the cylindrical barrier layer,

the composite wire rod group comprises:

a plurality of tin wires each having one or more tin core materials made of tin or a tin alloy and a copper base surrounding the tin core material;

a plurality of niobium wires which are provided so as to surround the tin wire, each niobium wire having a plurality of niobium core materials made of niobium or a niobium alloy and a copper base surrounding the niobium core materials,

the composite wire rod group contains titanium, the titanium content is 0.38-0.55 mass%,

in a transverse section, the centers of gravity of cross-sectional areas of the tin wire bodies from the plurality of tin wire rods are positioned in a substantially planar lattice shape, and the average distance between the center of gravity of a unit lattice forming the planar lattice and the center of gravity of the cross-sectional area of the tin wire body at the lattice point of the unit lattice is 30 μm or more and 50 μm or less.

2. A method for preparing a precursor, which is Nb based on an internal tin method₃A method for producing a precursor for use in the production of a Sn superconducting wire, comprising:

a step of preparing a composite pipe, the composite pipe comprising: a composite wire group; a cylindrical barrier layer arranged so as to surround the composite wire group and preventing tin from penetrating therethrough; a cylindrical protective layer covering an outer peripheral surface of the cylindrical barrier layer;

the step of drawing the composite pipe,

the composite wire rod group comprises:

a plurality of tin wires each having one or more tin core materials made of tin or a tin alloy and a copper base surrounding the tin core material;

a plurality of niobium wires each having a plurality of niobium core materials made of niobium or a niobium alloy and a copper base surrounding the niobium core materials and arranged so as to surround the tin wire, wherein,

the composite wire rod group contains titanium, the content of titanium is more than 0.38 mass% and less than 0.55 mass%,

in a cross-sectional view of the composite tube after the drawing step, the centers of gravity of cross-sectional areas of the tin wire bodies from the plurality of tin wire rods are positioned in a substantially planar lattice shape,

in the drawing step, the composite tube is drawn so that an average distance between a center of gravity of a unit lattice forming the planar lattice and a center of gravity of a cross-sectional area of the tin wire-like body at the lattice of the unit lattice is 30 μm or more and 50 μm or less.

3. A superconducting wire rod is provided with:

has a plurality of voids extending in the longitudinal direction and contains at least Nb₃A composite linear body of Sn and copper;

a cylindrical barrier layer disposed so as to surround the composite linear body and preventing tin from penetrating therethrough;

a cylindrical protective layer covering the outer peripheral surface of the cylindrical barrier layer,

the center of gravity of the cross-sectional area of the plurality of holes is positioned in a substantially planar lattice shape in a transverse section, and the average distance between the center of gravity of a unit lattice forming the planar lattice and the center of gravity of the cross-sectional area of the holes at the lattice points of the unit lattice is 30 μm or more and 50 μm or less,

the composite filament contains titanium, and the titanium content is 0.38 mass% or more and 0.55 mass% or less.

Technical Field

The present invention relates to a precursor for use in the production of a superconducting wire, a method for producing the precursor, and a superconducting wire.

Background

Nuclear magnetic resonance apparatuses (NMR apparatuses), magnetic resonance imaging apparatuses (MRI apparatuses), fusion reactors, accelerators, and the like use superconducting magnets for generating a strong magnetic field. In recent years, high performance and miniaturization of superconducting magnets have been required, and superconducting wires for superconducting magnets are also required to have a large critical magnetic field and a large critical current density in order to generate a strong magnetic field. Conventionally, Nb has been used as a superconducting wire material capable of generating a strong magnetic field₃An Sn superconducting wire.

As Nb₃Bronze method and internal tin method have been proposed as methods for producing Sn superconducting wire. Here, the internal tin method is a method of subjecting a precursor of a superconducting wire material in which a niobium core material and a tin core material are arranged in a copper base so as not to contact each other to heat treatment, and reacting tin diffused in the copper base with niobium to produce Nb₃Sn method, compared with bronze method, from Nb₃The Sn production efficiency and the cost for the heat treatment of the wire rod are advantageous.

As a precursor used in the internal tin method, a precursor in which a niobium wire material in which a niobium core material is embedded in a copper base and a tin wire material in which the surface of tin is not copper base are combined has been proposed (see jp 2010-15821 a). In this conventional precursor, Nb can be increased by reducing the volume of the copper base in the precursor₃Critical current density of the Sn superconducting wire.

In addition, a precursor in which a copper-based and a plurality of niobium core materials are arranged around a tin core material has been proposed (jp 2007-a 214002). In this conventional precursor, the wire diameter of the niobium core material in the precursor is set to 5 to 30 μm so as to be nearest to the niobium core materialThe average distance between the niobium core material and the tin core material of the tin core material is less than or equal to 100 [ mu ] m, thereby increasing Nb₃Critical current density of the Sn superconducting wire.

In these conventional precursors, Nb content is increased by relatively increasing the volume ratio of niobium in the precursor₃The critical current density of Sn superconducting wire, particularly under high magnetic field, is required to be further increased.

Prior art documents

Patent document

Patent document 1: japanese patent application laid-open No. 2010-15821

Patent document 2: japanese laid-open patent publication No. 2007 and 214002

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a precursor for use in manufacturing a superconducting wire rod that can obtain a superconducting wire rod having a high critical current density, a method for manufacturing the precursor, and a superconducting wire rod having a high critical current density.

The first invention made to solve the above problems is a drawn wire product of a composite pipe, which is Nb based on the internal tin method₃A precursor for use in the production of a Sn superconducting wire, said drawn wire product of a composite tube comprising: a composite wire group; a cylindrical barrier layer arranged so as to surround the composite wire group and preventing tin from penetrating therethrough; a cylindrical protective layer covering an outer peripheral surface of the cylindrical barrier layer, wherein the composite wire group includes: a plurality of tin wires each having one or more tin core materials made of tin or a tin alloy and a copper base surrounding the tin core material; a plurality of niobium wire rods arranged so as to surround the tin wire rods, the composite wire rod group containing titanium in an amount of 0.38 mass% or more and 0.55 mass% or less, the composite wire rod group having a plurality of niobium core materials made of niobium or niobium alloy and a copper base surrounding the niobium core materials, wherein the center of gravity of a cross-sectional area of a tin wire rod from the plurality of tin wire rods is positioned in a substantially planar lattice shape in a transverse cross-sectional view, and the center of gravity of a unit lattice of the planar lattice and the cross-sectional area of the tin wire rod at a lattice point of the unit lattice are formedThe average distance between the centers of gravity of (a) is 30 to 50 μm.

The present inventors have conducted extensive studies and, as a result, have confirmed that the diffusion distance of tin in the heat treatment of the precursor is about 50 μm, and coarse Nb is formed at a position farther than the diffusion distance from tin₃The Sn crystal grains tend to lower the critical current density of the superconducting wire. Therefore, in the precursor, the center of gravity of the cross-sectional area of the tin wire from the plurality of tin wires is positioned in a substantially planar lattice shape in a transverse section, and the 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 wire at the lattice point of the unit lattice is within the above range. Since the composite wire material group of the composite tube has a structure in which a plurality of niobium wire materials are adjacent to each other around the tin wire material, the niobium wire material from the niobium wire material is positioned in a range from the tin wire material to the upper limit or less as the precursor of the drawn wire product of the composite tube, and a sufficient amount of tin can be diffused to each corner of the niobium wire material in the heat treatment by the internal tin method. In other words, the precursor can prevent the insufficiency of the amount of tin diffusion at a position distant from the tin linear body, and promote Nb as a fine equiaxial crystal of a magnetic flux pinning point₃The generation of Sn crystal grains, and the suppression of coarse Nb with small magnetic flux pinning force₃Since Sn is formed as crystal grains, a superconducting wire having a high critical current density can be obtained. In addition, since the composite wire material group contains titanium and the content thereof is within the above range in the precursor, Nb of the obtained superconducting wire material can be suppressed₃The critical current density is increased particularly in a high magnetic field while the amount of Sn produced is reduced.

The second invention made to solve the above problems is Nb based on internal tin method₃A method for producing a precursor for use in the production of a Sn superconducting wire, comprising: a step of preparing a composite pipe, the composite pipe comprising: a composite wire group; and a cylindrical barrier layer arranged so as to surround the composite wire group and preventing the penetration of tin; and a cylindrical protective layer covering an outer peripheral surface of the cylindrical barrier layer; and a step of drawing the composite pipe, wherein the composite wire rod group includes: having tin or tin alloyOne or more tin core materials made of gold and a plurality of tin wire materials made of copper and surrounding the tin core materials; and a plurality of niobium wires arranged so as to surround the tin wire, wherein the composite wire group contains titanium in an amount of 0.38 mass% or more and 0.55 mass% or less, the composite tube after the wire drawing step has a center of gravity of a cross-sectional area of the tin wire from the plurality of tin wires positioned in a substantially planar cross-sectional shape in a horizontal direction, and the composite tube is drawn in the wire drawing step so that an average distance between the center of gravity of a unit lattice forming the planar lattice and the center of gravity of a cross-sectional area of the tin wire at a lattice point of the unit lattice is 30 μm or more and 50 μm or less.

Since the precursor produced by the precursor production method has the same structure as the precursor of the first invention, a superconducting wire having a high critical current density can be obtained by the precursor production method.

A third aspect of the present invention for solving the above problems is a superconducting wire material including: has a plurality of voids extending in the longitudinal direction and contains at least Nb₃A composite linear body of Sn and copper; a cylindrical barrier layer disposed so as to surround the composite linear body and preventing the penetration of tin; and a cylindrical protective layer covering an outer peripheral surface of the cylindrical barrier layer, wherein, in a transverse cross-sectional view, a center of gravity of a cross-sectional area of the plurality of holes is positioned in a substantially planar lattice shape, an average distance between a center of gravity of a unit lattice forming the planar lattice and a center of gravity of a cross-sectional area of the holes at the lattice point of the unit lattice is 30 μm or more and 50 μm or less, and the composite filament contains titanium in an amount of 0.38 mass% or more and 0.55 mass% or less.

This superconducting wire can be easily produced by the internal tin method using the precursor of the first invention. In the superconducting wire, the centers of gravity of cross-sectional areas of a plurality of voids derived from tin are positioned substantially in a planar lattice shape in a transverse section, and the center of gravity of a unit lattice forming the planar lattice and the centers of voids at lattice points of the unit lattice are positionedSince the average distance between the centers of gravity of the cross-sectional areas is within the above range, a sufficient amount of tin can be diffused to each corner in the composite linear body by the heat treatment based on the internal tin method in manufacturing. In other words, the superconducting wire material can prevent the insufficient diffusion amount of tin at the position far from the tin, and suppress the coarse Nb₃Sn crystal grains are generated, and thus, a high critical current density is exhibited. In addition, in the superconducting wire, since the composite filament contains titanium and the content thereof is within the above range, Nb is present in the superconducting wire₃The amount of Sn is large, and the critical current density is high particularly in a high magnetic field.

As described above, the present invention can provide a precursor for use in the production of a superconducting wire material that can provide a superconducting wire material having a high critical current density, a method for producing the precursor, and a superconducting wire material having a high critical current density.

Drawings

Fig. 1 is a cross-sectional view schematically showing a precursor according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view schematically showing a superconducting wire manufactured from the precursor of fig. 1.

Detailed Description

Hereinafter, embodiments of the precursor, the method for producing the precursor, and the superconducting wire rod according to the present invention will be described in detail with reference to the drawings.

Precursor 1 of FIG. 1 is Nb by internal tin method₃A superconducting wire precursor before heat treatment used for manufacturing an Sn superconducting wire has a substantially circular cross-sectional area in a cross-sectional view. This precursor 1 is a drawn wire product provided with a composite tube: a composite wire group; a cylindrical barrier layer arranged so as to surround the composite wire group and preventing tin from penetrating therethrough; a cylindrical protective layer covering the outer peripheral surface of the cylindrical barrier layer. Here, the term "drawn product of a composite pipe" means a molded product in which the diameter of the composite pipe is reduced in the radial direction by drawing, and means that the change in the arrangement structure other than the diameter reduction is small before and after the drawing.

[ Compound pipe ]

The composite pipe is processed before the wire drawing,the cross-sectional shape of the cross-sectional area is substantially circular, and the composite wire group is inserted inside a cylindrical body in which a barrier layer is cylindrically disposed on the inner circumferential surface of a cylindrical protective layer. Further, as the material of the barrier layer, for example, niobium or titanium can be used, but Nb can be formed from the inner peripheral surface of the barrier layer₃From the viewpoint of Sn, niobium is preferred.

< composite wire group >

The composite wire rod group is provided with: a plurality of tin wires each including a tin core material made of tin or a tin alloy and a copper base surrounding the tin core material; and a plurality of niobium wire rods each having a plurality of niobium core materials made of niobium or a niobium alloy and a copper base surrounding the niobium core materials, and arranged so as to surround the tin wire rods. The tin wire and the niobium wire are combined with each other in a substantially regular hexagonal shape in a cross section and with substantially no space in space. Specifically, 3 niobium wires and 3 tin wires were alternately adjacent to 6 surfaces of 1 niobium wire, and 1 niobium wire was adjacent to 6 surfaces of 1 tin wire, respectively, and the tin wire and the niobium wire were combined so that the copper base of the niobium wire and the copper base of the tin wire were in contact with each other.

The tin wire rods in the composite wire rod group are regularly positioned through the combination of the tin wire rods and the niobium wire rods. Specifically, in a cross-sectional view of the composite tube, the centers of gravity of the cross-sectional areas of the plurality of tin wires are positioned in a substantially planar lattice shape (a nearly triangular lattice shape). In the transverse section of the composite tube, the center of gravity of the cross-sectional area of the tin wire rod substantially coincides with the center of gravity of the cross-sectional area of the tin core material.

The composite wire rod group contains titanium (Ti). The titanium may be homogeneously contained in the tin wire and the niobium wire, but it is preferable to contain a tin core material. In other words, the tin core material is preferably made of an alloy of tin and titanium. By including titanium in the tin core material, the diffusion of tin can be promoted, and the critical current density can be increased.

The lower limit of the content of titanium in the entire composite wire rod group is 0.38 mass%, and more preferably 0.4 mass%. On the other hand, the upper limit of the content of titanium is 0.55% by mass, and more preferably 0.5% by mass. If the content of titanium is less than the lower limit, the result isThe effect of improving the critical current density of the obtained superconducting wire material derived from titanium may not be sufficiently obtained. On the other hand, if the content of titanium is higher than the upper limit, Nb is added₃The generation of Sn is inhibited, and the superconducting properties of the obtained superconducting wire may be degraded.

When the titanium is contained in the composite wire rod group by using the tin core material made of an alloy of tin and titanium, the titanium content of the tin core material made of the alloy can be determined so that the content of titanium with respect to the entire composite wire rod group becomes a desired value. Specifically, the titanium content of the tin core material made of the alloy is estimated to be 1 mass% or more and 2 mass% or less.

[ method for producing precursor ]

The precursor of the present invention is used for Nb based on internal tin method₃Production of precursor 1 for use in production of Sn superconducting wire. The method for producing a precursor includes a preparation step of preparing a composite tube and a drawing step of drawing the composite tube.

< preparation Process >

A preparation step of preparing the composite pipe, wherein the preparation step prepares a composite pipe comprising: a composite wire group; a cylindrical barrier layer arranged so as to surround the composite wire group and preventing tin from penetrating therethrough; a cylindrical protective layer covering the outer peripheral surface of the cylindrical barrier layer.

The prepared composite wire rod group of the composite pipe includes, as described above: a plurality of tin wires having one or more tin core materials made of tin or a tin alloy and a copper base surrounding the tin core materials; and a plurality of niobium wire rods each having a plurality of niobium core materials made of niobium or a niobium alloy and a copper base surrounding the niobium core materials, and arranged so as to surround the tin wire rods.

The composite wire rod group contains titanium in an amount of 0.38 mass% or more and 0.55 mass% or less as described above.

< wire drawing Process >

The drawing step is a step of drawing the composite tube prepared in the preparation step to obtain the precursor 1, and in the drawing step, the composite tube is reduced in diameter in the radial direction by drawing. As this drawing process, a known process using a die can be employed.

The composite tube after drawing (this precursor 1) has a smaller change in the arrangement structure other than the diameter reduction as compared with the composite tube before drawing. Therefore, the precursor 1 maintains the original arrangement structure of the plurality of niobium wires and the plurality of tin wires other than the diameter reduction in the niobium wire 2 and the tin wire 3. In other words, in a cross-sectional view of the composite tube after the drawing step, the centers of gravity of the cross-sectional areas of the tin wire bodies 3 from the plurality of tin wire rods are positioned in a substantially planar lattice shape (a nearly triangular lattice shape) in accordance with the arrangement of the plurality of tin wire rods.

In the drawing step, the arrangement structure of the tin wire members 3 from the plurality of tin wire members is adjusted by reducing the diameter. Specifically, in the drawing step, the composite tube is drawn by adjusting the average distance W 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 wire 3 at the lattice point of the unit lattice to a value suitable for tin diffusion during heat treatment. Here, the average distance W is a value obtained by obtaining distances from each lattice point to the center of gravity in an arbitrary 5 unit lattices and averaging the distances.

In the case of the precursor 1, the cross-sectional area of the tin wire-like body 3 is approximately regular hexagonal in shape and the unit lattice is approximately regular triangular in shape, and therefore, a known method such as shape matching using a microphotograph image can be used as a method for extracting the cross-sectional area of the tin wire-like body 3 and the unit lattice.

The lower limit of the average distance W is 30 μm, preferably 33 μm, and more preferably 35 μm. On the other hand, the upper limit of the average distance W is 50 μm, more preferably 47 μm, and still more preferably 45 μm. If the average distance W is less than the lower limit, the wire drawing process itself may be difficult, and the cost of the wire drawing process may increase. Conversely, if the average distance W is greater than the upper limit, the distance from the tin linear body 3 to the tin forming the center of gravity of the unit lattice of the planar latticeIs insufficient and large Nb at the center of gravity of the unit lattice₃The generation of Sn crystal grains may not be suppressed.

[ precursor ]

This precursor 1 is a drawn product of the composite tube described above, and therefore, it follows the arrangement structure of the composite tube before drawing except for the diameter reduction. Specifically, the precursor 1 includes a plurality of niobium wire-shaped bodies 2 derived from a plurality of niobium wires and a plurality of tin wire-shaped bodies 3 derived from a plurality of tin wires, and has a structure in which 6 niobium wire-shaped bodies 2 are adjacent to 1 tin wire-shaped body 3. Further, the precursor 1 includes: a cylindrical barrier layer 4 which is disposed so as to surround the plurality of niobium wire-shaped bodies 2 and the plurality of tin wire-shaped bodies 3 and prevents tin from penetrating therethrough; a cylindrical protective layer 5 covering the outer peripheral surface of the cylindrical barrier layer 4. Although the precursor 1 is shown in fig. 1 as having a gap on the inner peripheral surface side of the cylindrical barrier layer 4, fig. 1 is a schematic cross-sectional view for facilitating understanding of the structure of the precursor 1, and the gap is closed by actually performing a drawing process at the time of manufacturing the precursor 1.

< niobium filament >

The niobium wire body 2 is formed from a niobium wire material before wire drawing, and includes a copper base 2a and a plurality of niobium cores 2b made of niobium or a niobium alloy surrounded by the copper base 2 a. The plurality of niobium core bodies 2b may be arranged in a state of being separated by the copper base body 2a, and the number and arrangement are not particularly limited.

< solder line >

The tin wire 3 is a tin wire material before wire drawing, and is formed of a copper base 3a and a tin core 3b made of tin or a tin alloy surrounded by the copper base 3 a. Note that 1 tin wire 3 is not limited to having 1 tin core 3b, and 1 tin wire 3 may have a plurality of tin cores 3 b.

The niobium wire-like body 2 and the tin wire-like body 3 are combined with each other substantially without a space, in a cross-sectional view, so that the cross-sectional area is formed into a nearly regular hexagon. As shown in fig. 1, 3 niobium wire-shaped bodies 2 and 3 tin wire-shaped bodies 3 are alternately adjacent to 6 surfaces of 1 niobium wire-shaped body 2, 1 niobium wire-shaped body 2 is adjacent to 6 surfaces of 1 tin wire-shaped body 3, and copper bases 2a of the niobium wire-shaped bodies 2 and copper bases 3a of the tin wire-shaped bodies 3 are in contact with or joined to each other.

The tin wire-shaped bodies 3 are regularly positioned by the combination of the niobium wire-shaped bodies 2 and the tin wire-shaped bodies 3. Specifically, in a cross-sectional view of the precursor 1, the centers of gravity of the cross-sectional areas of the plurality of tin wire members 3 are positioned in a substantially planar lattice shape (a nearly triangular lattice shape). In a cross-sectional view of the precursor 1, the center of gravity of the cross-sectional area of the tin wire 3 substantially coincides with the center of gravity of the cross-sectional area of the tin core 3 b.

The average distance W 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 wire 3 at the lattice point of the unit lattice is adjusted to a value suitable for tin diffusion during heat treatment. That is, the lower limit of the average distance W is 30 μm, more preferably 33 μm, and still more preferably 35 μm. On the other hand, the upper limit of the average distance W is 50 μm, more preferably 47 μm, and still more preferably 45 μm. If the average distance W is less than the lower limit, the wire drawing process may be difficult and the cost of the wire drawing process may increase. Conversely, if the average distance W is greater than the upper limit, the amount of tin diffusion from the tin linear body 3 to the center of gravity of the unit lattice forming the planar lattice may be insufficient, and coarse Nb at the center of gravity of the unit lattice may be present₃The generation of Sn crystal grains may not be suppressed.

< Barrier layer >

The barrier layer 4 is a layer for preventing tin diffused from the tin wire-shaped bodies 3 from penetrating to the outside in the heat treatment by the internal tin method, and is formed in a cylindrical shape so as to surround the plurality of niobium wire-shaped bodies 2 and the plurality of tin wire-shaped bodies 3. As the material of the barrier layer 4, for example, niobium or titanium can be used, but Nb can be formed from the inner peripheral surface of the barrier layer 4₃From the viewpoint of Sn, niobium is preferable.

< protective layer >

The protective layer 5 is a stabilizing material made of copper for protecting the precursor 1, and is formed in a cylindrical shape so as to cover the outer peripheral surface of the cylindrical barrier layer 4.

[ superconducting wire rod ]

The superconducting wire 10 of FIG. 2 is Nb₃Sn superconducting wire rod in cross sectionThe cross-sectional area is formed substantially circular. The superconducting wire 10 can be produced from the precursor 1, which is a drawn product of the composite tube, by an internal tin method. In this case, the superconducting wire 10 has a configuration other than the diameter reduction of the clad pipe before drawing. Specifically, the superconducting wire 10 includes: a composite linear body 11 from the composite wire group; a cylindrical barrier layer 14 disposed so as to surround the composite linear body 11 and preventing the penetration of tin; a cylindrical protective layer 15 covering the outer peripheral surface of the cylindrical barrier layer 14. In fig. 2, the superconducting wire 10 is shown with a gap on the inner circumferential surface side of the cylindrical barrier layer 14, but fig. 2 is a schematic cross-sectional view for facilitating understanding of the structure of the superconducting wire 10, and the gap is actually closed. Hereinafter, the case of manufacturing by the internal tin method using the precursor 1 will be described as an example, but the superconducting wire 10 may be manufactured by another method.

In addition, when the above-described heat treatment by the internal tin method is performed on the precursor 1, the tin contained in the tin wire 3 of the precursor 1 diffuses, and the niobium contained in the niobium wire 2 reacts with the tin to become Nb₃Sn. In other words, the composite linear body 11 of the superconducting wire 10 contains Nb₃Sn。

< composite linear body >

The superconducting wire 10 includes: has a plurality of voids X in the longitudinal direction and contains at least Nb₃A composite linear body 11 of Sn and copper. The composite linear body 11 is formed of a plurality of niobium linear bodies 12 derived from the plurality of niobium linear bodies 2 and a plurality of tin linear bodies 13 derived from the plurality of tin linear bodies 3, and 6 niobium linear bodies 12 are adjacent to 1 tin linear body 13. However, the plurality of niobium wire-shaped bodies 12 and the plurality of tin wire-shaped bodies 13 are integrally fused together, the boundaries of the niobium wire-shaped bodies 12 and the tin wire-shaped bodies 13 of the composite wire-shaped body 11 are difficult to distinguish, and Nb is used as the boundary between the niobium wire-shaped bodies 12 and the tin wire-shaped bodies 13₃Sn and copper are difficult to clearly distinguish.

The composite linear body 11 contains titanium. As described above, in the precursor 1, titanium may be contained in the tin core material in the composite wire rod group of the composite tube before drawing, but even when titanium is contained in the tin core material as described above, the precursor is applied1, titanium is still diffused together with tin and introduced into Nb₃Sn. In this manner, Nb is also introduced into the composite linear body 11₃Sn contains titanium, and the critical current density in a high magnetic field can be increased by increasing the upper critical magnetic field. The "high magnetic field" means a magnetic field of, for example, 15T (tesla) or more.

The lower limit of the titanium content in the composite linear body 11 is 0.38 mass%, and more preferably 0.4 mass%. On the other hand, the upper limit of the content of titanium is 0.55% by mass, and more preferably 0.5% by mass. If the content of titanium is less than the lower limit, the effect of increasing the critical current density of titanium from the superconducting wire 10 may not be sufficiently obtained. On the other hand, if the content of titanium is higher than the upper limit, Nb is added₃The generation of Sn is inhibited, and the superconducting properties of the superconducting wire 10 may be degraded.

< void >

The void X is a void of the tin wire 3 from the precursor 1. As described above, in the heat treatment by the internal tin method, most of tin diffuses from the tin linear body 3 of the precursor 1. Therefore, the voids X are formed in the tin linear body 13 based on the arrangement of the tin core body 3b of the tin linear body 3 of fig. 1. However, since the niobium wire-like bodies 12 and the tin wire-like bodies 13 are integrated as described above, it can be seen that the composite wire-like body 11 actually has a plurality of voids X along the longitudinal direction as shown in fig. 2.

When a part of tin contained in the tin core body 3b of the precursor 1 remains without being diffused, as shown in fig. 2, a tin adhesion layer 13a is formed on the inner peripheral surface of the void X.

The holes X are regularly arranged based on the arrangement of the niobium wire-like body 2 and the tin wire-like body 3 of the precursor 1. Specifically, in a cross-sectional view of the superconducting wire 10, the centers of gravity of the cross-sectional areas of the plurality of voids X are positioned in a substantially planar lattice shape (a nearly triangular lattice shape).

The average distance W 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 hole X in the lattice of the unit lattice is adjusted to a value suitable for tin diffusion during heat treatment. That is, the lower limit of the average distance W is preferablyIt is preferably 30 μm, more preferably 33 μm, and still 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 still more preferably 45 μm. If the average distance W is less than the lower limit, the precursor 1 itself for producing the superconducting wire 10 may be difficult to wire-drawing during production, and the cost of wire-drawing may increase. Conversely, if the average distance W is greater than the upper limit, the amount of tin diffusion from the tin wire 3 of the precursor 1 before heat treatment to the center of gravity of the unit lattice forming the planar lattice is insufficient, and the superconducting wire 10 may have coarse Nb at the center of gravity of the unit lattice₃Crystal grains of Sn.

< advantage >

The precursor 1 is configured such that, in a transverse section, the centers of gravity of cross-sectional areas of the tin wire bodies 3 from the plurality of tin wire rods are positioned in a substantially planar lattice shape, and the average distance between the center of gravity of a unit lattice forming the planar lattice and the center of gravity of the cross-sectional area of the tin wire body 3 at the lattice point of the unit lattice is 30 μm or more and 50 μm or less. Since the composite wire material group of the composite tube has a structure in which a plurality of niobium wire materials are adjacent to each other around the tin wire material, the niobium wire material 2 derived from the niobium wire material is positioned in the range of 50 μm or less from the tin wire material 3 in the precursor 1 as a drawn product of the composite tube, and a sufficient amount of tin can be diffused to each corner of the niobium wire material 2 in the heat treatment by the internal tin method. In other words, the precursor 1 can prevent the diffusion amount of tin from being insufficient at a position distant from the tin linear body 3, and promote Nb as a fine isometric crystal of a magnetic flux pinning point₃The generation of Sn crystal grains, and the suppression of coarse Nb with small magnetic flux pinning force₃Since Sn crystal grains are generated, superconducting wire 10 having a high critical current density can be obtained. In addition, since the precursor 1 contains titanium in the composite wire material group and the content thereof is within the above range, Nb of the obtained superconducting wire material can be suppressed₃The critical current density is increased particularly under a high magnetic field while the amount of Sn produced is reduced.

In addition, in the superconducting wire 10, the center of gravity of the cross-sectional area of the plurality of voids X from tin is formed in a substantially planar lattice shape in a cross-sectional viewSince the 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 hole X at the lattice of the unit lattice is 30 μm or more and 50 μm or less, a sufficient amount of tin can be diffused to each corner in the composite linear body 11 by the heat treatment by the internal tin method at the time of manufacturing. In other words, in the superconducting wire 10, since the insufficient diffusion amount of tin at the position away from tin is prevented, the coarse Nb is suppressed₃Sn is generated as crystal grains, and thus exhibits a high critical current density. In addition, in this superconducting wire 10, since the composite linear body 11 contains titanium in an amount of 0.38 mass% or more and 0.55 mass% or less, Nb is used₃The amount of Sn is large, and the critical current density is high particularly in a high magnetic field.

[ other embodiments ]

The precursor used for producing the superconducting wire rod of the present invention, the method for producing the precursor, and the superconducting wire rod are not limited to the above embodiments.

In the above embodiment, the case where the precursor includes the niobium filament and the tin filament having the cross-sectional areas in the substantially regular hexagonal shapes in the cross-sectional view was described, but the cross-sectional areas in the cross-sectional views of the niobium filament and the tin filament are not limited to the substantially regular hexagonal shapes, and may be, for example, substantially regular triangular shapes or substantially square shapes. In addition, based on the structure of the precursor, the superconducting wire may be positioned such that the center of gravity of the cross-sectional area of the plurality of holes is substantially in a regular hexagonal lattice shape or a substantially square lattice shape in a cross-sectional view.

[ examples ] A method for producing a compound

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[ example 1]

< preparation of composite pipe >

First, a niobium core material was inserted into a copper pipe, and a niobium single core wire having a cross section of a regular hexagon was manufactured by wire drawing. The length between opposite sides of the regular hexagon of the cross section of the niobium single core wire is 3.8 mm. The produced niobium single core wire was cut into a plurality of pieces, 583 niobium single core wires were combined and inserted into a copper pipe, and a niobium wire rod having a cross section of a regular hexagon was produced by wire drawing. The length between opposite sides of the regular hexagon of the cross section of the niobium wire rod is 3.5 mm.

Subsequently, a core material (titanium content: 1.8 mass%) made of a tin-titanium alloy was inserted into the copper pipe, and a tin wire rod having a cross section of a regular hexagon was produced by wire drawing. The length between opposite sides of the regular hexagon of the cross section of the tin wire rod is 3.5 mm. The titanium content of the core material made of a tin-titanium alloy was such that the titanium content in the composite linear body of the superconducting wire rod produced was 0.55 mass%.

The obtained niobium wires and tin wires were cut into a large number of pieces, 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, all 6 surfaces of the tin wire rod were adjacent to the niobium wire rod, and 3 surfaces of the niobium wire rod were alternately adjacent to each of the tin wire rod and the niobium wire rod.

A coil of niobium sheet was inserted along the inner circumferential surface of the copper pipe, and a group of composite wires was inserted into the copper pipe further inside the sheet to form a composite pipe.

< precursor and superconducting wire >

The obtained composite tube is integrated by drawing and then drawn to produce a precursor. The cross-sectional shape and size of the drawn precursor are determined by the composition of the composite tube. In example 1, since the composite tube was configured as described above, after the wire drawing process, the centers of gravity of the cross-sectional areas of the tin wire bodies from the plurality of tin wire rods were positioned in a substantially triangular lattice shape. In the cross section, the average distance W between the center of gravity of the unit lattice forming the planar lattice and the center of gravity of the cross section of the cross-sectional area of the tin wire body at the lattice point of the unit lattice was 48 μm, and the wire diameter of the precursor to be produced was 0.6 mm. The centers of gravity of the cross-sectional areas of the tin wires from the plurality of tin wires were positioned in a substantially triangular lattice shape, and this was confirmed by cutting the produced precursor and observing the cross-section with a microscope.

The obtained precursor was subjected to a multistage heat treatment by the internal tin method to produce a superconducting wire rod of example 1. For this superconducting wire, the critical current density of the non-copper portion of the area of the cross-sectional area excluding copper from the total cross-sectional area was measured under the conditions of the temperature of 4.2K and the external magnetic field of 16T. The measurement results are shown in table 1.

[ example 2]

As the core material made of a tin-titanium alloy, a material having a titanium content of 1.5 mass% was used. The titanium content of the core material made of a tin-titanium alloy was such that the titanium content in the composite filament of the produced superconducting wire rod became 0.44 mass%.

The length between opposite sides of the cross-section of the regular hexagon of the niobium wire and the tin wire was 2.3mm, the average distance W between the centers of gravity after the drawing of the composite tube was 32 μm, and the wire diameter of the precursor was 0.8 mm.

Except for the above, the superconducting wire rod of example 2 was produced in the same manner as in example 1. The measurement results of the critical current density of the non-copper portion of example 2 are shown in table 1.

[ example 3]

As the core material made of a tin-titanium alloy, a material having a titanium content of 1.2 mass% was used. The titanium content of the core material made of a tin-titanium alloy was such that the titanium content in the composite filament of the produced superconducting wire rod became 0.38 mass%.

Except for the above, the superconducting wire rod of example 3 was produced in the same manner as in example 2. The measurement results of the critical current density of the non-copper portion of example 3 are shown in table 1.

Comparative example 1

A superconducting wire rod of comparative example 1 was produced in the same manner as in example 1, except that the average distance W between the centers of gravity after drawing of the composite tube was 60 μm, and the wire diameter of the precursor produced was 0.8 mm. The results of measuring the critical current density of the non-copper portion of comparative example 1 are shown in table 1.

[ TABLE 1]

As shown in Table 1, the critical current densities of the non-copper portions in examples 1 to 3Is 1000A/mm²The above is larger than that of comparative example 1.

In addition, when the superconducting wires of examples 1 to 3 and comparative example 1 were cut and the cross section was observed with a microscope, Nb in examples 1 to 3₃The crystal structure of Sn was equiaxed, whereas in comparative example 1, Nb was confirmed near the center of the triangular lattice as the unit lattice₃The crystal structure of Sn contains coarse crystal grains.

From the above results, it can be said that the critical current density of the superconducting wire rod is improved by positioning the centers of gravity of the cross-sectional areas of the plurality of holes derived from tin in a substantially planar lattice shape in a cross-sectional view, setting the 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 holes at the lattice point of the unit lattice to be 30 μm or more and 50 μm or less, and by including Ti in the composite linear body in an amount of 0.38 mass% or more and 0.55 mass% or less.

[ industrial applicability ]

The present invention can provide a precursor for use in the production of a superconducting wire material that can provide a superconducting wire material having a high critical current density, a method for producing the precursor, and a superconducting wire material having a high critical current density.

Description of the symbols

1 precursor

2 niobium wire

2a copper base

2b niobium core

3 tin linear body

3a copper base

3b tin core

4 barrier layer

5 protective layer

10 superconducting wire

11 composite linear body

12 niobium wire

13 tin linear body

13a tin adhesion layer

14 barrier layer

15 protective layer

X hole