Precursor for nb3sn superconducting wire and nb3sn superconducting wire

Abstract

To provide a precursor for a Nb3Sn superconducting wire rod and the Nb3Sn superconducting wire rod for manufacturing the superconducting wire rod having excellent strength and maintaining high critical-current density even if it is twisted.SOLUTION: A precursor for an Nb3Sn superconducting wire includes a tubular stabilized copper layer, a tubular first 1Sn diffusion barrier layer provided inside the copper layer, and a superconducting element group precursor housed inside the barrier layer, wherein the superconducting element group precursor includes a plurality of Sn-based reinforcement element wires and a plurality of Nb-based superconducting element wire precursors, the reinforcement element wires include a first stabilized matrix of Cu or a Cu-based alloy, a plurality of Sn-based filaments of Sn or a Sn-based alloy embedded in the first stabilized matrix, and a plurality of reinforcement multifilamentary wires composed of a plurality of reinforcement filaments made of a metal or an alloy, and the wire precursor includes a second stabilized matrix of Cu or a Cu-based alloy and a Nb-based superconducting filament precursor of Nb or a Nb-based alloy embedded in the second stabilized matrix.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a precursor for a Nb3Sn superconducting wire and a Nb3Sn superconducting wire. [Background technology]

[0002] A commonly used method for manufacturing Nb3Sn superconducting wire is the bronze method, in which a wire having a structure in which multiple Nb filaments are embedded in a Cu-Sn-based alloy (bronze) matrix is ​​heat-treated, and the Sn in the bronze matrix is ​​diffused into the Nb filaments to produce the superconducting phase Nb3Sn.

[0003] However, in the bronze process, there is an upper limit to the Sn concentration that can be dissolved in bronze (solid solubility limit), which limits the area of ​​Nb3Sn that can be produced, and as a result, there is a limit to the improvement in the critical current density Jc of the superconducting wire.

[0004] In addition to the bronze process, there is also a method called the internal tin process (internal diffusion process) for manufacturing Nb3Sn superconducting wire. In the internal tin process, a wire having a structure in which Nb-based alloy filaments and Sn-based alloy filaments are embedded in a Cu-based alloy matrix is ​​heat-treated, causing the Sn in the Sn-based alloy filaments to diffuse into the Nb-based alloy filaments, producing Nb3Sn at the interface between the Nb-based alloy filaments and the Cu-based alloy matrix.

[0005] The internal tin process is not affected by the solid solubility limit of Sn in Cu-Sn-based alloys, which is a problem with the bronze process, so the area where Nb3Sn is generated can be increased, resulting in a high critical current density Jc. Furthermore, the internal tin process can increase the Sn concentration compared to the bronze process, allowing for the generation of high-quality Nb3Sn.

[0006] Nb3Sn superconducting wires manufactured by the internal tin method are often used not as a single wire but as a stranded wire made by twisting together multiple wires.

[0007] As mentioned above, in the internal tin method, the critical current density Jc is improved by increasing the amount of Sn to increase the area where Nb3Sn is generated. Therefore, in order to maximize the amount of Sn in the wire, it is necessary to minimize the amount of Cu around the Sn-based alloy filament.

[0008] For example, Patent Document 1 describes a method for suppressing deterioration of wire drawing processability due to an increase in the Sn content, in which a precursor for superconducting wire has an Nb element in which Nb is embedded in a Cu matrix and an Sn element in which Sn filaments are embedded in Cu, and multiple Sn filaments are arranged in the Sn element.

[0009] However, the superconducting wire precursor described in Patent Document 1 has a problem in that weak Sn filaments are arranged in a cluster within the Sn element, resulting in a large difference in strength between the Sn and Nb elements, which causes the element arrangement to become disorganized during twisting. Disorganized element arrangement results in uneven distances between the Sn and Nb elements, which necessitates an extended Nb3Sn production heat treatment time to diffuse Sn throughout the wire. As a result, the Nb3Sn crystal grains become coarse, resulting in a decrease in the critical current density (Jc).

[0010] Furthermore, when Nb3Sn wire is subjected to Nb3Sn generation heat treatment using the internal tin method, Sn diffusion causes cavities to form in the areas that were previously Sn filaments. In the precursor for superconducting wire described in Patent Document 1, cavities form in the Sn elements. This results in a problem of a decrease in the strength of the wire and an accelerated decrease in the critical current density (Jc) due to electromagnetic stress. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-32930 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present disclosure is to provide a precursor for Nb3Sn superconducting wire and an Nb3Sn superconducting wire for producing superconducting wire that has good strength and can maintain a high critical current density Jc even after twisting processing. [Means for solving the problem]

[0013] [1] A precursor for an Nb3Sn superconducting wire, comprising: a cylindrical stabilizing copper layer provided on the outer periphery; a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer; and a superconducting element group precursor housed inside the first Sn diffusion barrier layer, wherein the superconducting element group precursor comprises a plurality of Sn-based reinforced element wires and a plurality of Nb-based superconducting element wire precursors, wherein the plurality of Sn-based reinforced element wires comprise: a first stabilizing matrix made of Cu or a Cu-based alloy; a plurality of Sn-based filaments embedded in the first stabilizing matrix and made of Sn or a Sn-based alloy; and a plurality of reinforced multifilamentary wires embedded in the first stabilizing matrix and composed of a plurality of reinforced filaments made of a metal or an alloy, and the plurality of Nb-based superconducting element wire precursors comprise: a second stabilizing matrix made of Cu or a Cu-based alloy; and one or more Nb-based superconducting filament precursors embedded in the second stabilizing matrix and made of Nb or a Nb-based alloy. [2] The precursor for a Nb3Sn superconducting wire according to [1] above, wherein in a cross section perpendicular to the axial direction of the precursor for a Nb3Sn superconducting wire, in each of the plurality of Sn-based reinforced element wires, a reinforcement multi-core wire assembly in which the plurality of reinforcement multi-core wires are assembled is arranged in the center, and a Sn-based filament assembly in which the plurality of Sn-based filaments are assembled is arranged on the periphery. [3] The precursor for a Nb3Sn superconducting wire according to [1] or [2] above, wherein the Sn-based reinforcing element wire further comprises a second Sn diffusion barrier layer made of Ta or Nb metal or an alloy containing at least one of Ta and Nb, which is provided between the reinforcing multi-core wire assembly and the Sn-based filament assembly in a cross section perpendicular to the axial direction of the precursor for a Nb3Sn superconducting wire. [4] The precursor for a Nb3Sn superconducting wire according to any one of [1] to [3] above, wherein the reinforcing filaments are made of a metal selected from Nb, Ta, Ti, V, W, Mo, Fe, and Hf, or an alloy containing at least one element selected from Nb, Ta, Ti, V, W, Mo, Fe, and Hf. [5] A Nb3Sn superconducting wire comprising: a cylindrical stabilizing copper layer provided on the outer periphery; a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer; and a group of superconducting elements housed inside the first Sn diffusion barrier layer, wherein the group of superconducting elements comprises a plurality of strengthening element wires and a plurality of Nb-based superconducting element wires, wherein the plurality of strengthening element wires comprise a first stabilizing matrix made of Cu or a Cu-based alloy and a plurality of strengthening multi-core wires composed of a plurality of strengthening filaments made of a metal or an alloy embedded in the first stabilizing matrix, and the plurality of Nb-based superconducting element wires comprise a second stabilizing matrix made of Cu or a Cu-based alloy and one or more superconducting filaments embedded in the second stabilizing matrix and having a compound superconducting phase made of Nb3Sn. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a precursor for Nb3Sn superconducting wire and an Nb3Sn superconducting wire for producing superconducting wire that has good strength and can maintain a high critical current density Jc even after twisting processing. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a precursor for a Nb3Sn superconducting wire according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. [Figure 3] FIG. 3 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the Nb3Sn superconducting wire precursor of the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. [Figure 5] FIG. 5 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the Nb3Sn superconducting wire precursor of the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. [Figure 7] FIG. 7 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the Nb3Sn superconducting wire precursor of the first embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. [Figure 9] FIG. 9 is a cross-sectional view showing an example of the precursor for a Nb3Sn superconducting wire according to the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a precursor for a Nb3Sn superconducting wire according to the third embodiment. [Figure 12] FIG. 12 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a detailed description will be given based on an embodiment.

[0017] As a result of extensive research into precursors for Nb3Sn superconducting wires and Nb3Sn superconducting wires, the inventors have discovered that the strength of Sn-based reinforced element wires is improved by providing a reinforced multi-core wire consisting of multiple reinforcing filaments, thereby reducing the difference in strength between the Sn-based reinforced element wires and Nb-based superconducting element wire precursors or Nb-based superconducting element wires, and preventing the Sn-based reinforced element wires from deforming significantly during twisting, causing the arrangement of the elements to become distorted, thereby enabling a high critical current density Jc to be maintained even after twisting, and have completed the present disclosure based on this finding.

[0018] An NbSn superconducting wire precursor according to an embodiment includes a cylindrical stabilizing copper layer provided on the outer periphery, a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer, and a superconducting element group precursor housed inside the first Sn diffusion barrier layer. The superconducting element group precursor includes a plurality of Sn-based strengthening element wires and a plurality of Nb-based superconducting element wire precursors. The plurality of Sn-based strengthening element wires include a first stabilizing matrix made of Cu or a Cu-based alloy, a plurality of Sn-based filaments embedded in the first stabilizing matrix and made of Sn or a Sn-based alloy, and a plurality of reinforcement multifilamentary wires embedded in the first stabilizing matrix and made of a plurality of reinforcement filaments made of a metal or alloy. The plurality of Nb-based superconducting element wire precursors include a second stabilizing matrix made of Cu or a Cu-based alloy, and one or more Nb-based superconducting filament precursors embedded in the second stabilizing matrix and made of Nb or a Nb-based alloy.

[0019] The Nb3Sn superconducting wire of the embodiment includes a cylindrical stabilizing copper layer provided on the outer periphery, a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer, and a superconducting element group housed inside the first Sn diffusion barrier layer. The superconducting element group includes a plurality of strengthening element wires and a plurality of Nb-based superconducting element wires. The plurality of strengthening element wires include a first stabilizing matrix made of Cu or a Cu-based alloy and a plurality of strengthening multifilamentary wires embedded in the first stabilizing matrix and composed of a plurality of strengthening filaments made of a metal or alloy. The plurality of Nb-based superconducting element wires include a second stabilizing matrix made of Cu or a Cu-based alloy and one or more superconducting filaments embedded in the second stabilizing matrix and having a compound superconducting phase made of Nb3Sn.

[0020] (First embodiment) Fig. 1 is a cross-sectional view showing an example of an Nb3Sn superconducting wire precursor according to the first embodiment. The cross-sectional view of the Nb3Sn superconducting wire precursor 1 is a cross section perpendicular to the axial direction (longitudinal direction) of the Nb3Sn superconducting wire precursor 1. As shown in Fig. 1, the Nb3Sn superconducting wire precursor 1 according to the first embodiment includes a cylindrical stabilizing copper layer 10, a cylindrical first Sn diffusion barrier layer 20, and a superconducting element group precursor 30.

[0021] The stabilizing copper layer 10 constituting the Nb3Sn superconducting wire precursor 1 has a cylindrical shape and is provided on the outer periphery of the Nb3Sn superconducting wire precursor 1 to coat the first Sn diffusion barrier layer 20 from the outside. The stabilizing copper layer 10 is made of Cu or a Cu alloy.

[0022] The first Sn diffusion barrier layer 20 constituting the NbSn superconducting wire precursor 1 is cylindrical and provided inside the stabilizing copper layer 10. The first Sn diffusion barrier layer 20 is preferably made of a metal such as Ta or Nb, or an alloy containing at least one of Ta and Nb.

[0023] The first Sn diffusion barrier layer 20 prevents Sn in the Sn-based filaments 42 from diffusing into the stabilizing copper layer 10 and causing the stabilizing copper layer 10 to bronze during heat treatment to produce a compound superconducting phase 73 made of Nb3Sn, as described below, thereby preventing a decrease in superconducting properties such as the residual resistivity ratio, and retaining inside the first Sn diffusion barrier layer 20 the amount of Sn required to react with the Nb-based superconducting filament precursor 53 to produce Nb3Sn.

[0024] The superconducting element group precursor 30 constituting the NbSn superconducting wire precursor 1 is housed inside the first Sn diffusion barrier layer 20. The superconducting element group precursor 30 includes a plurality of Sn-based strengthened element wires 40 and a plurality of Nb-based superconducting element wire precursors 50.

[0025] Each of the plurality of Sn-based reinforcing element wires 40 includes a first stabilizing matrix 41, a plurality of Sn-based filaments 42, and a plurality of reinforcing multifilamentary wires 44. The first stabilizing matrix 41 is made of Cu or a Cu-based alloy.

[0026] The Sn-based filaments 42 are made of Sn or an Sn-based alloy and are embedded in the first stabilizing matrix 41. By performing a heat treatment to generate a compound superconducting phase 73 (described later), the Sn in the Sn-based filaments 42 reacts with the Nb-based superconducting filament precursors 53 in the Nb-based superconducting element wire precursor 50 to form the compound superconducting phase 73 made of Nb3Sn. When the Nb3Sn superconducting wire precursor 1 is heat-treated in this manner, Sn diffuses from the Sn-based filaments 42, so that the Sn-based filaments 42 no longer exist as filaments, and a void V is formed in a part of the reinforcing element wire 40a in the Nb3Sn superconducting wire 2 (described later and shown in FIG. 2).

[0027] The reinforcement multifilamentary wire 44 is composed of a plurality of reinforcement filaments 43 made of a metal or alloy and is embedded in the first stabilizing matrix 41. The reinforcement filaments 43 are preferably made of a metal selected from Nb, Ta, Ti, V, W, Mo, Fe, and Hf, or an alloy containing at least one of Nb, Ta, Ti, V, W, Mo, Fe, and Hf. The reinforcement multifilamentary wire 44 has a strength greater than that of the Sn-based filaments 42. Therefore, the strength of the Sn-based reinforcement element wire 40 including the reinforcement multifilamentary wire 44 is greater than that of a Sn-based element wire not including the reinforcement multifilamentary wire 44.

[0028] Each of the plurality of Nb-based superconducting element wire precursors 50 includes a second stabilizing matrix 51 and one or more Nb-based superconducting filament precursors 53. The second stabilizing matrix 51 is made of Cu or a Cu-based alloy. The Nb-based superconducting filament precursors 53 are made of Nb or an Nb-based alloy and are embedded in the second stabilizing matrix 51.

[0029] 1 shows an example in which each of the plurality of Nb-based superconducting element wire precursors 50 includes only a plurality of Nb-based superconducting filament precursors 53. However, each of the plurality of Nb-based superconducting element wire precursors 50 may include only a single Nb-based superconducting filament precursor 53, or may include a mixture of a single Nb-based superconducting filament precursor 53 and a plurality of Nb-based superconducting filament precursors 53.

[0030] By carrying out a heat treatment to generate the compound superconducting phase 73 described later, all or part of the Nb-based superconducting filament precursor 53 reacts with Sn diffused from the Sn-based filament 42 to form a filament-shaped compound superconducting phase 73 made of NbSn.

[0031] In this way, the NbSn superconducting wire precursor 1 includes the Sn-based reinforced element wire 40 and the multiple reinforcement multi-core wires 44, which reduces the difference in strength between the Sn-based reinforced element wire 40 and the Nb-based superconducting element wire precursor 50, preventing the Sn-based reinforced element wire 40 from deforming significantly during stranding, thereby preventing the arrangement of the elements from becoming distorted. As a result, a high critical current density Jc can be maintained even after stranding.

[0032] Next, a description will be given of an Nb3Sn superconducting wire 2 obtained by subjecting the Nb3Sn superconducting wire precursor 1 to heat treatment for producing a compound superconducting phase 73 made of Nb3Sn. Fig. 2 is a cross-sectional view showing an example of an Nb3Sn superconducting wire 2 obtained by heating the Nb3Sn superconducting wire precursor 1 of Fig. 1.

[0033] As shown in FIG. 2, the Nb 3 Sn superconducting wire 2, which is a product of heating the Nb 3 Sn superconducting wire precursor 1, includes a cylindrical stabilizing copper layer 10, a cylindrical first Sn diffusion barrier layer 20, and a group of superconducting elements 60.

[0034] The stabilizing copper layer 10 and the first Sn diffusion barrier layer 20 of the Nb3Sn superconducting wire 2 have the same configuration as the stabilizing copper layer 10 and the first Sn diffusion barrier layer 20 of the precursor 1 for a Nb3Sn superconducting wire.

[0035] The superconducting element group 60 is housed inside the first Sn diffusion barrier layer 20. The superconducting element group 60 includes a plurality of strengthening element wires 40a and a plurality of Nb-based superconducting element wires 70.

[0036] Each of the plurality of reinforcing element wires 40a includes a first stabilizing matrix 41 and a plurality of reinforcing multifilamentary wires 44. The first stabilizing matrix 41 and the plurality of reinforcing multifilamentary wires 44 of the Nb3Sn superconducting wire 2 have the same configuration as the first stabilizing matrix 41 and the plurality of reinforcing multifilamentary wires 44 of the Nb3Sn superconducting wire precursor 1.

[0037] Furthermore, a cavity V is formed in each of the plurality of strengthening element wires 40a. When the Nb3Sn superconducting wire precursor 1 is subjected to heat treatment, Sn in the Sn-based filaments 42 provided in the Sn-based strengthening element wires 40 of the Nb3Sn superconducting wire precursor 1 is diffused, thereby forming the cavity V. The position of the cavity V in the strengthening element wire 40a corresponds to the position of the Sn-based filaments 42 in the Sn-based strengthening element wire 40.

[0038] Each of the plurality of Nb-based superconducting element wires 70 includes a second stabilizing matrix 51 and one or more superconducting filaments 80. The second stabilizing matrix 51 of the Nb3Sn superconducting wire 2 has the same configuration as the second stabilizing matrix 51 of the Nb3Sn superconducting wire precursor 1. The superconducting filaments 80 are embedded in the second stabilizing matrix 51. Each of the plurality of superconducting filaments 80 has a compound superconducting phase 73 made of Nb3Sn.

[0039] 2 shows an example in which each of the plurality of Nb-based superconducting element wires 70 includes only a plurality of superconducting filaments 80. However, each of the plurality of Nb-based superconducting element wires 70 may include only a single superconducting filament 80, or may include a mixture of a single superconducting filament 80 and a plurality of superconducting filaments 80.

[0040] 2 and the following figures show Nb-based superconducting element wires 70, 70a, 70b, and 70c manufactured by the internal tin method. In the internal tin method, when a NbSn superconducting wire precursor 1 is subjected to heat treatment to produce a compound superconducting phase 73 made of NbSn, Sn diffused from the Sn-based filaments 42 in the NbSn superconducting wire precursor 1 reacts with Nb on the surface of the Nb-based superconducting filament precursor 53, thereby producing NbSn filaments, which are the compound superconducting phase 73. Therefore, in the NbSn superconducting wire 2, there are no Sn-based filaments 42, and voids V are formed. The NbSn superconducting wire precursor 1 is heat-treated in an inert gas atmosphere, such as argon or nitrogen.

[0041] 2 and the following figures show examples in which the Nb-based superconducting element wires 70, 70a, 70b, and 70c have central portions of Nb-based superconducting filament precursors 53 remaining without reacting with Sn present in the superconducting filaments 80. However, depending on the amount of Sn contained in the Sn-based filaments 42 of the precursor 1 for NbSn superconducting wire and the diameter size of the Nb-based superconducting filament precursors 53, the Nb-based superconducting filament precursors 53 may not be present in the superconducting filaments 80, i.e., the superconducting filaments 80 may consist of a compound superconducting phase 73.

[0042] In this way, the NbSn superconducting wire 2 includes the strengthening element wire 40a and the multiple reinforcement multi-core wires 44, which reduces the difference in strength between the strengthening element wire 40a and the Nb-based superconducting element wire 70, thereby preventing the strengthening element wire 40a from deforming significantly during twisting, thereby preventing the arrangement of the elements from becoming disarrayed. As a result, a high critical current density Jc can be maintained even after twisting.

[0043] Since the heat treatment for producing Nb3Sn is usually carried out after the process of twisting the wires, even if some or all of the reinforcing filaments 43 react with Sn diffused from the Sn-based filaments 42 and Nb3Sn is formed in the reinforcing element wires 40a of the Nb3Sn superconducting wire 2, the effect of suppressing disorder in the arrangement of the elements during twisting can be maintained. Furthermore, the formation of Nb3Sn in the reinforcing element wires 40a increases the amount of Nb3Sn contained in the Nb3Sn superconducting wire 2, thereby further improving the critical current density Jc.

[0044] Furthermore, the strength of the reinforcing element wire 40a can be further improved by disposing the reinforcing multi-core wires 44 between the plurality of cavities V. Therefore, the Nb3Sn superconducting wire 2 can further reduce the deterioration of the critical current density Jc due to electromagnetic stress.

[0045] 3 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the NbSn superconducting wire precursor 1 of the first embodiment. FIG. 4 is a cross-sectional view showing an example of an NbSn superconducting wire obtained by heating the NbSn superconducting wire precursor of FIG.

[0046] 3, each of the plurality of Nb-based superconducting element wire precursors 50a includes a second stabilizing matrix 51, a plurality of Nb-based reinforcing filaments 52, and a plurality of Nb-based superconducting filament precursors 53. The plurality of Nb-based reinforcing filaments 52 and the plurality of Nb-based superconducting filament precursors 53 are both made of Nb or an Nb-based alloy and are embedded in the second stabilizing matrix 51.

[0047] The diameter of the Nb-based superconducting filament precursor 53 is larger than the diameter of the Nb-based reinforcing filament 52. For example, the diameter of the Nb-based reinforcing filament 52 is 0.04 μm or more and 0.30 μm or less, and the diameter of the Nb-based superconducting filament precursor 53 is 1 μm or more and 10 μm or less.

[0048] Furthermore, in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1, the ratio of the total area of ​​the plurality of Nb-based superconducting filaments 52 to the area of ​​the Nb-based reinforcing filament assembly 52a in which the plurality of Nb-based reinforcing filaments 52 are assembled is smaller than the ratio of the total area of ​​the plurality of Nb-based superconducting filaments 52 to the area of ​​the Nb-based superconducting filament assembly precursor 53a in which the plurality of Nb-based superconducting filament precursors 53 are assembled. For example, the ratio of the total area of ​​the plurality of Nb-based reinforcing filaments 52 to the area of ​​the Nb-based reinforcing filament assembly 52a is 0.1 or more and 0.5 or less, and the ratio of the total area of ​​the plurality of Nb-based superconducting filament precursors 53 to the area of ​​the Nb-based superconducting filament assembly precursor 53a is 0.6 or more and 0.9 or less. Here, the Nb-based reinforcing filament assembly 52a is defined as including a plurality of Nb-based reinforcing filaments 52, as well as a second stabilizing matrix 51 present between the plurality of Nb-based reinforcing filaments 52, but not including any second stabilizing matrix 51 that is not sandwiched between the plurality of Nb-based reinforcing filaments 52. Also, the Nb-based superconducting filament assembly precursor 53a is defined as including a plurality of Nb-based superconducting filament precursors 53, as well as a second stabilizing matrix 51 present between the plurality of Nb-based superconducting filament precursors 53, but not including any second stabilizing matrix 51 that is not sandwiched between the plurality of Nb-based superconducting filament precursors 53.

[0049] By providing the Nb-based superconducting element wire precursor 50a with the plurality of Nb-based reinforcing filaments 52 in this way, the Nb3Sn superconducting wire precursor 1 and the Nb3Sn superconducting wire 2 have high mechanical strength against axial tensile stress. This further suppresses a decrease in the critical current density Jc of the Nb3Sn superconducting wire 2 caused by axial tensile stress. Furthermore, when a radial compressive stress is applied to the Nb3Sn superconducting wire precursor 1 or the Nb3Sn superconducting wire 2, the second stabilizing matrix 51 in the portion where the Nb-based reinforcing filaments 52 are embedded, in other words, the second stabilizing matrix 51 of the Nb-based reinforcing filament assembly 52a, is preferentially deformed. This further reduces damage to the superconducting filaments during twisting and rolling, further suppressing a decrease in the critical current density Jc of the Nb3Sn superconducting wire 2. In this way, damage to the superconducting filament precursor due to twisting and rolling processes can be further suppressed, and the superconducting filaments are protected, so that even when twisted, the Nb3Sn superconducting wire 2 can fully exhibit a high critical current density Jc.

[0050] Furthermore, both the Nb-based reinforcing filament 52 and the Nb-based superconducting filament precursor 53 are made of Nb or an Nb-based alloy, which makes it possible to avoid deterioration in workability due to adjacent members with different mechanical properties.

[0051] 3, in a cross section perpendicular to the axial direction of the Nb3Sn superconducting wire precursor 1, in each of the plurality of Nb-based superconducting element wire precursors 50a, an Nb-based reinforcing filament assembly 52a, in which a plurality of Nb-based reinforcing filaments 52 are aggregated, is preferably arranged in the center, and an Nb-based superconducting filament assembly precursor 53a, in which a plurality of Nb-based superconducting filament precursors 53 are aggregated, is preferably arranged on the periphery. The Nb-based reinforcing filament assembly 52a is arranged in the center of the Nb-based superconducting element wire precursor 50a in the cross section of the Nb3Sn superconducting wire precursor 1. In addition, the annular Nb-based superconducting filament assembly precursor 53a, which is arranged around the entire outer periphery of the Nb-based superconducting element wire precursor 50a in the cross section of the Nb3Sn superconducting wire precursor 1, covers the periphery of the Nb-based reinforcing filament assembly 52a. With this configuration, when the Nb3Sn superconducting wire precursor 1 is subjected to heat treatment to generate the compound superconducting phase 73, the Sn diffused from the Sn-based filaments 42 reacts preferentially with the multiple Nb-based superconducting filament precursors 53 arranged on the outer periphery of the Nb-based superconducting element wire precursor 50a, making it easier to form a high-quality Nb3Sn compound superconducting phase 73.

[0052] Also, as shown in Figure 4, in the Nb3Sn superconducting wire 2 obtained by heating the Nb3Sn superconducting wire precursor 1 of Figure 3, the superconducting element group 60 housed inside the first Sn diffusion barrier layer 20 includes a plurality of strengthening element wires 40a and a plurality of Nb-based superconducting element wires 70a.

[0053] Each of the plurality of Nb-based superconducting element wires 70a includes a second stabilizing matrix 51, a plurality of Nb-based reinforcing filaments 52 made of Nb or an Nb-based alloy, and a plurality of superconducting filaments 80. Both the plurality of Nb-based reinforcing filaments 52 and the plurality of superconducting filaments 80 are embedded in the second stabilizing matrix 51.

[0054] Each of the plurality of superconducting filaments 80 has a compound superconducting phase 73 made of NbSn. The diameter of the superconducting filaments 80 is larger than the diameter of the Nb-based reinforced filaments 52. For example, the diameter of the Nb-based reinforced filaments 52 is not less than 0.04 μm and not more than 0.30 μm, and the diameter of the superconducting filaments 80 is not less than 1 μm and not more than 10 μm.

[0055] Furthermore, in a cross section perpendicular to the axial direction of the NbSn superconducting wire 2, the ratio of the total area of ​​the plurality of Nb-based reinforced filaments 52 to the area of ​​the Nb-based reinforced filament assembly 52a in which the plurality of Nb-based reinforced filaments 52 are assembled is smaller than the ratio of the total area of ​​the plurality of superconducting filaments 80 to the area of ​​the superconducting filament assembly 80a in which the plurality of superconducting filaments 80 are assembled. For example, the ratio of the total area of ​​the plurality of Nb-based reinforced filaments 52 to the area of ​​the Nb-based reinforced filament assembly 52a is 0.1 or more and 0.5 or less, and the ratio of the total area of ​​the plurality of superconducting filaments 80 to the area of ​​the superconducting filament assembly 80a is 0.6 or more and 0.9 or less. Here, the superconducting filament assembly 80a is defined as including the plurality of superconducting filaments 80 and second stabilizing matrices 51 present between the plurality of superconducting filaments 80, but excluding second stabilizing matrices 51 that are not sandwiched between the plurality of superconducting filaments 80.

[0056] Thus, the Nb3Sn superconducting wire 2 has high mechanical strength against axial tensile stress because the Nb-based superconducting element wire 70a includes multiple Nb-based reinforcing filaments 52. Furthermore, when radial compressive stress is applied to the Nb3Sn superconducting wire precursor 1 during stranding or rolling, the second stabilizing matrix 51 in the portion where the Nb-based reinforcing filaments 52 are embedded is preferentially deformed. Therefore, damage to the superconducting filaments 80 of the Nb3Sn superconducting wire 2 during stranding and rolling of the Nb3Sn superconducting wire precursor 1 is minimal, further suppressing a decrease in critical current density (Jc). Because the superconducting filaments 80 are protected in this way, the Nb3Sn superconducting wire 2 can fully exhibit a high critical current density (Jc) even when the Nb3Sn superconducting wire precursor 1 is subjected to stranding or rolling.

[0057] Moreover, both the Nb-based reinforcing filament 52 and the Nb-based superconducting filament precursor 53 are made of Nb or an Nb-based alloy, which further prevents deterioration in workability due to adjacent members with different mechanical properties.

[0058] 4, in each of the plurality of Nb-based superconducting element wires 70a, an Nb-based reinforcing filament assembly 52a, in which a plurality of Nb-based reinforcing filaments 52 are aggregated, is arranged in the center, and a superconducting filament assembly 80a, in which a plurality of superconducting filaments 80 are aggregated, is arranged on the periphery. In this case, the annular superconducting filament assembly 80a, which is arranged around the entire periphery of the Nb-based superconducting element wire 70a, surrounds the Nb-based reinforcing filament assembly 52a arranged in the center of the Nb-based superconducting element wire 70a. With this configuration, Sn diffused from the Sn-based filaments 42 in the Nb-based superconducting wire precursor 1 reacts preferentially with the plurality of Nb-based superconducting filament precursors 53, and therefore the Nb-based superconducting wire 2 has a high-quality Nb-based compound superconducting phase 73.

[0059] Fig. 5 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the NbSn superconducting wire precursor 1 of the first embodiment. Fig. 6 is a cross-sectional view showing an example of an NbSn superconducting wire obtained by heating the NbSn superconducting wire precursor of Fig. 5.

[0060] 5, the Nb-based superconducting element wire precursor 50b further includes a third Sn diffusion barrier layer 54 made of Ta or Nb or an alloy containing at least one of Ta and Nb, and disposed between the Nb-based reinforcing filament assembly 52a and the Nb-based superconducting filament assembly precursor 53a in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1. The third Sn diffusion barrier layer 54 completely covers the periphery of the Nb-based reinforcing filament assembly 52a. The third Sn diffusion barrier layer 54 is cylindrical and annular in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1.

[0061] Also, as shown in Figure 6, in the Nb3Sn superconducting wire 2 obtained by heating the Nb3Sn superconducting wire precursor 1 of Figure 5, the superconducting element group 60 housed inside the first Sn diffusion barrier layer 20 includes a plurality of strengthening element wires 40a and a plurality of Nb-based superconducting element wires 70b.

[0062] Each of the plurality of Nb-based superconducting element wires 70b includes a second stabilizing matrix 51, and a plurality of Nb-based reinforcing filaments 52, a plurality of superconducting filaments 80, and a third Sn diffusion barrier layer 54 embedded in the second stabilizing matrix 51.

[0063] 5 and 6, during the heat treatment for generating the compound superconducting phase 73, the third Sn diffusion barrier layer 54 prevents Sn in the Sn-based filaments 42 from diffusing into the Nb-based reinforcing filament assemblies 52a and reacting with the Nb-based reinforcing filaments 52 to form Nb3Sn. That is, even when the heat treatment is performed, the third Sn diffusion barrier layer 54 further suppresses the reaction of the Nb-based reinforcing filaments 52 to form a compound superconducting phase made of brittle Nb3Sn. Therefore, it is possible to further suppress a decrease in the mechanical strength of the Nb3Sn superconducting wire precursor 1 and the Nb3Sn superconducting wire 2 against axial tensile stress.

[0064] 7 is a cross-sectional view showing another example of an Nb-based superconducting element wire precursor constituting the Nb3Sn superconducting wire precursor 1 of the first embodiment. FIG. 8 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of FIG.

[0065] As shown in FIG. 7, a plurality of Nb-based superconducting element wire precursors 50c include a plurality of Nb-based strengthening sub-elements 55 and a plurality of Nb-based superconducting sub-element precursors 57.

[0066] Each of the multiple Nb-based reinforcing sub-elements 55 has a third stabilizing matrix 56 and multiple Nb-based reinforcing filaments 52. The third stabilizing matrix 56 is made of Cu or a Cu-based alloy. The multiple Nb-based reinforcing filaments 52 are made of Nb or an Nb-based alloy and are embedded in the third stabilizing matrix 56.

[0067] Each of the plurality of Nb-based superconducting subelement precursors 57 has a fourth stabilizing matrix 58 and a plurality of Nb-based superconducting filament precursors 53. The fourth stabilizing matrix 58 is made of Cu or a Cu-based alloy. The plurality of Nb-based superconducting filament precursors 53 are made of Nb or an Nb-based alloy and are embedded in the fourth stabilizing matrix 58.

[0068] A third stabilizing matrix 56 of the Nb-based reinforced subelement 55 is provided with a plurality of Nb-based reinforced filaments 52, but is not provided with Nb-based superconducting filament precursors 53. A fourth stabilizing matrix 58 of the Nb-based superconducting subelement precursor 57 is provided with a plurality of Nb-based superconducting filament precursors 53, but is not provided with Nb-based reinforced filaments 52. In other words, the Nb-based reinforced filaments 52 and the Nb-based superconducting filament precursors 53 are provided in different subelements (subelement precursors).

[0069] The diameter of the Nb-based superconducting filament precursors 53 embedded in the fourth stabilizing matrix 58 is larger than the diameter of the Nb-based reinforcing filaments 52 embedded in the third stabilizing matrix 56. For example, the diameter of the Nb-based reinforcing filaments 52 is 0.04 μm or more and 0.30 μm or less, and the diameter of the Nb-based superconducting filament precursors 53 is 1 μm or more and 10 μm or less.

[0070] Furthermore, in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1, the ratio of the total area of ​​the plurality of Nb-based superconducting filaments 52 to the area of ​​the Nb-based reinforcing filament assembly 52a in which the plurality of Nb-based reinforcing filaments 52 are assembled is smaller than the ratio of the total area of ​​the plurality of Nb-based superconducting filaments 52 to the area of ​​the Nb-based superconducting filament assembly precursor 53a in which the plurality of Nb-based superconducting filament precursors 53 are assembled. For example, the ratio of the total area of ​​the plurality of Nb-based reinforcing filaments 52 to the area of ​​the Nb-based reinforcing filament assembly 52a is 0.1 or more and 0.5 or less, and the ratio of the total area of ​​the plurality of Nb-based superconducting filament precursors 53 to the area of ​​the Nb-based superconducting filament assembly precursor 53a is 0.6 or more and 0.9 or less. Here, the Nb-based reinforcing filament assembly 52a is defined as including a plurality of Nb-based reinforcing filaments 52, a third stabilizing matrix 56 present between the plurality of Nb-based reinforcing filaments 52, and excluding any third stabilizing matrix 56 that is not sandwiched between the plurality of Nb-based reinforcing filaments 52. The Nb-based superconducting filament assembly precursor 53a is defined as including a plurality of Nb-based superconducting filament precursors 53, a fourth stabilizing matrix 58 present between the plurality of Nb-based superconducting filament precursors 53, and excluding any fourth stabilizing matrix 58 that is not sandwiched between the plurality of Nb-based superconducting filament precursors 53.

[0071] By providing the Nb-based superconducting element wire precursor 50c with multiple Nb-based reinforcing filaments 52, the NbSn superconducting wire precursor 1 and the NbSn superconducting wire 2 have even higher mechanical strength against axial tensile stress. Furthermore, when radial compressive stress is applied to the NbSn superconducting wire precursor 1 and the NbSn superconducting wire 2, the third stabilizing matrix 56 in which the Nb-based reinforcing filaments 52 are embedded—in other words, the third stabilizing matrix 56 of the Nb-based reinforcing filament assembly 52a—deforms preferentially. This reduces damage to the superconducting filaments during twisting and rolling, further suppressing a decrease in the critical current density (Jc) of the NbSn superconducting wire. Since damage to the superconducting filament precursor during twisting and rolling can be suppressed, the superconducting filaments are protected, allowing the NbSn superconducting wire to fully exhibit a high critical current density (Jc) even when twisted.

[0072] In addition, in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1, it is preferable that the plurality of Nb-based superconducting subelement precursors 57 and the plurality of Sn-based strengthened element wires 40 are arranged in the center of the superconducting element group precursor 30, and the plurality of Nb-based strengthened subelements 55 are arranged on the outer periphery of the superconducting element group precursor 30. In this case, the plurality of Nb-based strengthened subelements 55 arranged in an annular shape around the entire outer periphery of the superconducting element group precursor 30 cover the periphery of the plurality of Nb-based superconducting subelement precursors 57 and the plurality of Sn-based strengthened element wires 40 arranged in the center of the superconducting element group precursor 30. With this configuration, when the precursor 1 for Nb3Sn superconducting wire is subjected to heat treatment to produce a compound superconducting phase 73 consisting of Nb3Sn, Sn diffused from the Sn-based filaments 42 of the Sn-based strengthening element wire 40 reacts preferentially with the multiple Nb-based superconducting filament precursors 53, making it easier to form a high-quality Nb3Sn compound superconducting phase 73.

[0073] 8, in the Nb3Sn superconducting wire 2, which is a heated product of the Nb3Sn superconducting wire precursor 1 of FIG. 7, the superconducting element group 60 housed inside the first Sn diffusion barrier layer 20 includes a plurality of strengthening element wires 40a and a plurality of Nb-based superconducting element wires 70c. The plurality of Nb-based superconducting element wires 70c include a plurality of Nb-based strengthening sub-elements 55 and a plurality of superconducting sub-elements 77.

[0074] The Nb-based strengthening sub-element 55 of the Nb3Sn superconducting wire 2 has the same configuration as the Nb-based strengthening sub-element 55 of the precursor 1 for the Nb3Sn superconducting wire.

[0075] Each of the plurality of superconducting subelements 77 includes a fourth stabilizing matrix 58 and a plurality of superconducting filaments 80. The fourth stabilizing matrix 58 is made of Cu or a Cu-based alloy. The plurality of superconducting filaments 80 are embedded in the fourth stabilizing matrix 58.

[0076] Each of the plurality of superconducting filaments 80 has a compound superconducting phase 73 made of NbSn. The diameter of the superconducting filaments 80 is larger than the diameter of the Nb-based reinforcing filaments 52 embedded in the third stabilizing matrix 56. For example, the diameter of the Nb-based reinforcing filaments 52 is not less than 0.04 μm and not more than 0.30 μm, and the diameter of the superconducting filaments 80 is not less than 1 μm and not more than 10 μm.

[0077] Furthermore, in a cross section perpendicular to the axial direction of the NbSn superconducting wire 2, the ratio of the total area of ​​the plurality of Nb-based reinforced filaments 52 to the area of ​​the Nb-based reinforced filament assembly 52a in which the plurality of Nb-based reinforced filaments 52 are aggregated is smaller than the ratio of the total area of ​​the plurality of superconducting filaments 80 to the area of ​​the superconducting filament assembly 80a in which the plurality of superconducting filaments 80 are aggregated. For example, the ratio of the total area of ​​the plurality of Nb-based reinforced filaments 52 to the area of ​​the Nb-based reinforced filament assembly 52a is 0.1 or more and 0.5 or less, and the ratio of the total area of ​​the plurality of superconducting filaments 80 to the area of ​​the superconducting filament assembly 80a is 0.6 or more and 0.9 or less. Here, the superconducting filament assembly 80a is defined as including the plurality of superconducting filaments 80 and the fourth stabilizing matrix 58 present between the plurality of superconducting filaments 80, but excluding the fourth stabilizing matrix 58 that is not sandwiched between the plurality of superconducting filaments 80.

[0078] The third stabilizing matrix 56 of the Nb-based reinforced sub-element 55 is provided with a plurality of Nb-based reinforced filaments 52 but is not provided with a superconducting filament 80. The fourth stabilizing matrix 58 of the superconducting sub-element 77 is provided with a plurality of superconducting filaments 80 but is not provided with a Nb-based reinforced filament 52. In other words, the Nb-based reinforced filaments 52 and the superconducting filaments 80 are provided in different sub-elements.

[0079] Thus, the Nb3Sn superconducting wire 2 has even higher mechanical strength against axial tensile stress because the Nb-based superconducting element wire 70c includes multiple Nb-based reinforcing filaments 52. Furthermore, when radial compressive stress is applied to the Nb3Sn superconducting wire precursor 1 during stranding or rolling, the third stabilizing matrix 56 in which the Nb-based reinforcing filaments 52 are embedded is preferentially deformed. Therefore, damage to the superconducting filaments 80 of the Nb3Sn superconducting wire 2 during stranding and rolling of the Nb3Sn superconducting wire precursor 1 is reduced, further suppressing a decrease in the critical current density (Jc) of the Nb3Sn superconducting wire 2. Because the superconducting filaments 80 are protected in this way, the Nb3Sn superconducting wire 2 can fully exhibit a high critical current density (Jc) even when the Nb3Sn superconducting wire precursor 1 is subjected to stranding or rolling.

[0080] In addition, in a cross section perpendicular to the axial direction of the Nb3Sn superconducting wire 2, it is preferable that the multiple superconducting subelements 77 and the multiple strengthening element wires 40a are arranged in the center of the superconducting element group 60, and the multiple Nb-based strengthening subelements 55 are arranged on the outer periphery of the superconducting element group 60. In this case, the multiple Nb-based strengthening subelements 55 arranged in an annular shape around the entire outer periphery of the superconducting element group 60 cover the multiple superconducting subelements 77 and the multiple strengthening element wires 40a arranged in the center of the superconducting element group 60. With this configuration, Sn diffused from the Sn-based filaments 42 reacts preferentially with the multiple Nb-based superconducting filament precursors 53, and the Nb3Sn superconducting wire 2 has a higher quality Nb3Sn compound superconducting phase 73.

[0081] The above-described Nb3Sn superconducting wire 2 has good strength and can maintain a high critical current density Jc even after being twisted. Therefore, the Nb3Sn superconducting wire 2 is suitably used as a superconducting wire constituting a high-magnetic field superconducting magnet used in large accelerators, nuclear fusion reactors, analytical devices, etc.

[0082] According to the first embodiment described above, the Sn-based reinforced element wire is provided with a reinforced multi-core wire composed of multiple reinforced filaments, which improves the strength of the Sn-based reinforced element wire and prevents the Sn-based reinforced element wire from deforming significantly during twisting, thereby preventing the arrangement of the elements from becoming distorted, thereby maintaining a high critical current density Jc even after twisting.

[0083] (Second embodiment) Fig. 9 is a cross-sectional view showing an example of an Nb3Sn superconducting wire precursor of the second embodiment, and Fig. 10 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of Fig. 10.

[0084] In the following embodiments, the same components as those of the Nb3Sn superconducting wire precursor and Nb3Sn superconducting wire of the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted or simplified.

[0085] The second embodiment is basically the same as the first embodiment except for the arrangement of the plurality of reinforcing multifilamentary wires 44. Therefore, the different configuration will be mainly described here.

[0086] 9, a NbSn superconducting wire precursor 1a in the second embodiment includes a cylindrical stabilizing copper layer 10, a cylindrical first Sn diffusion barrier layer 20, and a superconducting element group precursor 30. The superconducting element group precursor 30 includes a plurality of Sn-based strengthening element wires 40 and a plurality of Nb-based superconducting element wire precursors 50.

[0087] In a cross section perpendicular to the axial direction of the Nb3Sn superconducting wire precursor 1a, in each of the plurality of Sn-based strengthening element wires 40, a strengthening multifilamentary wire assembly 44a, where a plurality of strengthening multifilamentary wires 44 are assembled, is arranged in the center, and an Sn-based filament assembly 42a, where a plurality of Sn-based filaments 42 are assembled, is arranged on the periphery. The strengthening multifilamentary wire assembly 44a is arranged in the center of the Sn-based strengthening element wire 40 in the cross section of the Nb3Sn superconducting wire precursor 1a. In addition, the annular Sn-based filament assembly 42a, which is arranged around the entire periphery of the Sn-based strengthening element wire 40 in the cross section of the Nb3Sn superconducting wire precursor 1a, covers the strengthening multifilamentary wire assembly 44a.

[0088] With this configuration, when the Nb3Sn superconducting wire precursor 1a is subjected to heat treatment to generate the compound superconducting phase 73, the Sn diffused from the Sn-based filaments 42 arranged on the outer periphery of the Sn-based strengthening element wire 40 reacts efficiently with the Nb-based superconducting filament precursor 53 of the Nb-based superconducting element wire precursor 50, making it easy to form a high-quality Nb3Sn compound superconducting phase 73.

[0089] 10, in a cross section of an Nb3Sn superconducting wire 2a obtained by subjecting an Nb3Sn superconducting wire precursor 1a to heat treatment to produce a compound superconducting phase 73, a reinforcement multifilamentary wire assembly 44a, in which a plurality of reinforcement multifilamentary wires 44 are aggregated, is disposed in the center of each of a plurality of reinforcement element wires 40a. An annular cavity assembly, in which a plurality of cavities V are aggregated, is formed around the entire outer periphery of the reinforcement element wire 40a and surrounds the reinforcement multifilamentary wire assembly 44a disposed in the center of the reinforcement element wire 40a.

[0090] As described above, when the Nb3Sn superconducting wire precursor 1a is subjected to heat treatment for producing the compound superconducting phase 73, Sn diffused from the Sn-based filaments 42 in the Nb3Sn superconducting wire precursor 1a reacts efficiently with the Nb-based superconducting filament precursor 53 of the Nb-based superconducting element wire precursor 50, facilitating the formation of a high-quality Nb3Sn compound superconducting phase 73. This further improves the critical current density Jc of the Nb3Sn superconducting wire 2a.

[0091] According to the second embodiment described above, by arranging a plurality of reinforcing multifilamentary wires in a predetermined arrangement, it is possible to further improve the critical current density Jc while maintaining good strength.

[0092] (Third embodiment) Fig. 11 is a cross-sectional view showing an example of an Nb3Sn superconducting wire precursor according to the third embodiment. Fig. 12 is a cross-sectional view showing an example of an Nb3Sn superconducting wire obtained by heating the Nb3Sn superconducting wire precursor of Fig. 11.

[0093] The third embodiment has basically the same configuration as the second embodiment except for the inclusion of a second Sn diffusion barrier layer 45. Therefore, the different configuration will be mainly described here.

[0094] 11, a NbSn superconducting wire precursor 1b in the third embodiment includes a cylindrical stabilizing copper layer 10, a cylindrical first Sn diffusion barrier layer 20, and a superconducting element group precursor 30. The superconducting element group precursor 30 includes a plurality of Sn-based strengthening element wires 40 and a plurality of Nb-based superconducting element wire precursors 50.

[0095] Each of the plurality of Sn-based reinforcement element wires 40 further includes a second Sn diffusion barrier layer 45, which is formed between the reinforcement multifilamentary wire assembly 44a and the Sn-based filament assembly 42a in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1b and is made of Ta or Nb or an alloy containing at least one of Ta and Nb. The second Sn diffusion barrier layer 45 completely covers the reinforcement multifilamentary wire assembly 44a. The second Sn diffusion barrier layer 45 is cylindrical and annular in a cross section perpendicular to the axial direction of the NbSn superconducting wire precursor 1b.

[0096] Furthermore, as shown in FIG. 12, in the Nb3Sn superconducting wire 2b obtained by subjecting the precursor 1b for the Nb3Sn superconducting wire to heat treatment to generate the compound superconducting phase 73, each of the multiple reinforcing element wires 40a further includes a second Sn diffusion barrier layer 45 provided between the reinforcing multi-core wire assembly 44a and the void assembly in the cross section of the Nb3Sn superconducting wire 2b.

[0097] With this configuration, during the heat treatment for generating the compound superconducting phase 73, the second Sn diffusion barrier layer 45 prevents Sn in the Sn-based filaments 42 from diffusing into the reinforcing multifilamentary wire assembly 44a and reacting with the reinforcing multifilamentary wires 44 to form Nb3Sn. That is, even when the heat treatment is performed, the second Sn diffusion barrier layer 45 further suppresses the reaction of the reinforcing multifilamentary wires 44 to form a compound superconducting phase made of brittle Nb3Sn. This further suppresses a decrease in the mechanical strength of the Nb3Sn superconducting wire precursor 1b and the Nb3Sn superconducting wire 2b against axial tensile stress.

[0098] According to the third embodiment described above, by providing the second Sn diffusion barrier layer, it is possible to maintain a high critical current density Jc even when twisting is performed, while further suppressing the decrease in mechanical strength against axial tensile stress.

[0099] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure. [Example]

[0100] Next, examples and comparative examples will be described, but the present disclosure is not limited to these examples.

[0101] Example 1 A precursor for a Nb3Sn superconducting wire as shown in FIG. 9 and a Nb3Sn superconducting wire as shown in FIG. 10 were produced.

[0102] First, a Sn-Ti alloy rod (diameter 24.2 mmφ) was inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ), and the resulting sample was drawn to form a Sn-based filament hexagonal wire with a face length of 2.82 mmH.

[0103] In addition, a Nb rod (pure Nb, diameter 103 mm) was inserted into a copper tube (oxygen-free copper, outer diameter 214 mmφ, inner diameter 103.7 mmφ), extruded, and then drawn and stripped to form a Nb-based reinforced filament primary hexagonal wire with a face length of 13.4 mmH.

[0104] Next, 109 of the above-mentioned Nb-based reinforced filament primary hexagonal wires were inserted into a copper tube (oxygen-free copper, outer diameter 214 mmφ, inner diameter 166 mmφ), and the tube was subjected to HIP (hot isostatic pressing), external cutting, and then extrusion processing.Furthermore, multiple wire drawing and peeling processing were performed to form a Nb-based reinforced filament secondary hexagonal wire with a face length of 2.82 mmH.

[0105] Next, 48 of the above-mentioned Sn-based filament hexagonal wires and 7 of the above-mentioned Nb-based reinforced filament secondary hexagonal wires were inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ) in an arrangement in which the Nb-based reinforced filament secondary hexagonal wires were gathered at the radial center, and the tube was subjected to HIP, external cutting, and then extrusion processing, and further wiredrawing processing multiple times to form an Sn-based reinforced element hexagonal wire with a face length of 2.24 mmH.

[0106] In addition, a sample was obtained by inserting an Nb rod (pure Nb, diameter 24.3 mm) into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ), and then drawing the obtained sample multiple times to form a hexagonal Nb-based superconducting filament precursor wire with a face length of 1.71 mmH.

[0107] Next, 151 of the above-mentioned Nb-based superconducting filament precursor hexagonal wires were inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ), and the tube was subjected to HIP, external cutting, extrusion processing, and further multiple wire drawing processing to form an Nb-based superconducting element precursor wire with a face length of 2.24 mmH.

[0108] Next, a 0.3 mm thick Nb sheet was wrapped around the inner circumference of a copper tube (oxygen-free copper, outer diameter 30 mmφ, inner diameter 20 mmφ), and then 19 of the above-mentioned Sn-based reinforced element hexagonal wires and 36 of the above-mentioned Nb-based superconducting element precursor wires were inserted inside it in an arrangement such that the Sn-based reinforced element hexagonal wires were not adjacent to each other.After CIP (cold isostatic pressing) and external cutting, a precursor for Nb3Sn superconducting wire with a diameter of 0.6 mmφ was formed by multiple wire drawing processes.

[0109] Next, the obtained Nb3Sn superconducting wire precursor was subjected to heat treatment in order to produce a compound superconducting phase consisting of Nb3Sn by heating at 210°C for 6 hours, then at 350°C for 18 hours, then at 480°C for 28 hours, then at 570°C for 180 hours, and finally at 665°C for 200 hours, thereby obtaining Nb3Sn superconducting wire.

[0110] The obtained Nb3Sn superconducting wire precursor and Nb3Sn superconducting wire had good strength. Furthermore, even when the Nb3Sn superconducting wire precursor and Nb3Sn superconducting wire were subjected to a twisting process, the obtained Nb3Sn superconducting wire was able to maintain a high critical current density Jc.

[0111] Example 2 A precursor for a Nb3Sn superconducting wire as shown in FIG. 11 and a Nb3Sn superconducting wire as shown in FIG. 12 were produced.

[0112] First, a Sn-Ti alloy rod (diameter 24.2 mm) was inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mm, inner diameter 24.5 mm), and the resulting sample was drawn to form a Sn-based filament wire with a diameter of 2.6 mm.

[0113] In addition, a Nb rod (pure Nb, diameter 103 mm) was inserted into a copper tube (oxygen-free copper, outer diameter 214 mmφ, inner diameter 103.7 mmφ), extruded, and then drawn and stripped to form a Nb-based reinforced filament primary hexagonal wire with a face length of 13.4 mmH.

[0114] Next, 109 of the above-mentioned Nb-based reinforced filament primary hexagonal wires were inserted into a copper tube (oxygen-free copper, outer diameter 214 mmφ, inner diameter 166 mmφ), and after HIP and external cutting, the tube was extruded, and then drawn and stripped multiple times to form an Nb-based reinforced filament secondary wire with a diameter of 2.6 mmφ.

[0115] Next, a 0.1 mm thick Nb sheet was wound six times around the outer periphery of the assembly of seven of the above-mentioned Nb-based reinforced filament secondary wires to form an Nb-based reinforced filament bundle.

[0116] Next, 48 of the above Sn-based filament wires and the above Nb-based reinforced filament bundle were inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ) so that the Nb-based reinforced filament bundle was positioned at the radial center, and after CIP and external cutting, the tube was extruded and further drawn multiple times to form a Sn-based reinforced element hexagonal wire with a face-to-face length of 2.24 mmH.

[0117] In addition, a sample was obtained by inserting an Nb rod (pure Nb, diameter 24.3 mm) into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ), and then drawing the obtained sample multiple times to form a hexagonal Nb-based superconducting filament precursor wire with a face length of 1.71 mmH.

[0118] Next, 151 of the above-mentioned Nb-based superconducting filament precursor hexagonal wires were inserted into a copper tube (oxygen-free copper, outer diameter 27.5 mmφ, inner diameter 24.5 mmφ), and the tube was subjected to HIP, external cutting, extrusion processing, and further multiple wire drawing processing to form an Nb-based superconducting element precursor wire with a face length of 2.24 mmH.

[0119] Next, a 0.3 mm thick Nb sheet was wrapped around the inner circumference of a copper tube (oxygen-free copper, outer diameter 30 mmφ, inner diameter 20 mmφ), and then 19 of the above-mentioned Sn-based reinforced element hexagonal wires and 36 of the above-mentioned Nb-based superconducting element precursor wires were inserted inside it in an arrangement such that the Sn-based reinforced element hexagonal wires were not adjacent to each other.After CIP (cold isostatic pressing) and external cutting, a precursor for Nb3Sn superconducting wire with a diameter of 0.6 mmφ was formed by multiple wire drawing processes.

[0120] Next, the obtained Nb3Sn superconducting wire precursor was subjected to heat treatment in order to produce a compound superconducting phase consisting of Nb3Sn by heating at 210°C for 6 hours, then at 350°C for 18 hours, then at 480°C for 28 hours, then at 570°C for 180 hours, and finally at 665°C for 200 hours, thereby obtaining Nb3Sn superconducting wire.

[0121] The obtained Nb3Sn superconducting wire precursor and Nb3Sn superconducting wire had good strength. Furthermore, even when the Nb3Sn superconducting wire precursor and Nb3Sn superconducting wire were subjected to a twisting process, the obtained Nb3Sn superconducting wire was able to maintain a high critical current density Jc. [Explanation of symbols]

[0122] 1, 1a, 1b Precursor for Nb3Sn superconducting wire 2, 2a, 2b Nb3Sn superconducting wire 10 Stabilized copper layer 20 First Sn diffusion barrier layer 30 Superconducting element group precursor 40 Sn-based reinforced element wire 40a reinforced element wire 41 First Stabilization Matrix 42 Sn-based filament 42a Sn-based filament aggregate 43 Reinforced Filament 44 Reinforced multi-core wire 44a Reinforced multifilamentary wire assembly 45 Second Sn diffusion barrier layer 50, 50a, 50b, 50c Nb-based superconducting element wire precursor 51 Second Stabilization Matrix 52 Nb-based reinforced filament 52a Nb-based reinforced filament assembly 53 Nb-based superconducting filament precursor 53a Nb-based superconducting filament assembly precursor 54 Third Sn diffusion barrier layer 55 Nb-based reinforced sub-element 56 Third Stabilization Matrix 57 Nb-based superconducting subelement precursor 58 Fourth Stabilization Matrix 60 Superconducting Elements 70, 70a, 70b, 70c Nb-based superconducting element wire 73 Compound superconducting phase 77 Superconducting Subelement 80 Superconducting filament 80a Superconducting filament assembly V cavity

Claims

1. a cylindrical stabilizing copper layer provided on the outer periphery; a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer; a superconducting element group precursor housed inside the first Sn diffusion barrier layer; Equipped with the superconducting element group precursor comprises a plurality of Sn-based strengthened element wires and a plurality of Nb-based superconducting element wire precursors, The plurality of Sn-based reinforcing element wires include a first stabilizing matrix made of Cu or a Cu-based alloy, a plurality of Sn-based filaments embedded in the first stabilizing matrix and made of Sn or a Sn-based alloy, and a plurality of reinforcing material multifilamentary wires embedded in the first stabilizing matrix and made of a plurality of reinforcing filaments made of a metal or an alloy, The plurality of Nb-based superconducting element wire precursors include a second stabilizing matrix made of Cu or a Cu-based alloy, and one or more Nb-based superconducting filament precursors made of Nb or an Nb-based alloy and embedded in the second stabilizing matrix. Nb ３ Precursor for Sn superconducting wire.

2. The Nb ３ 2. The Nb superconducting wire precursor according to claim 1, wherein in a cross section perpendicular to the axial direction of the Sn superconducting wire precursor, in each of the plurality of Sn-based reinforcing element wires, a reinforcing multifilamentary wire assembly in which the plurality of reinforcing multifilamentary wires are assembled is arranged in the center, and a Sn-based filament assembly in which the plurality of Sn-based filaments are assembled is arranged on the periphery. ３ Precursor for Sn superconducting wire.

3. The Sn-based reinforcing element wire is ３ 3. The Sn superconducting wire precursor according to claim 2, further comprising a second Sn diffusion barrier layer formed between the reinforcing material multifilamentary wire assembly and the Sn-based filament assembly in a cross section perpendicular to the axial direction of the Sn superconducting wire precursor, the second Sn diffusion barrier layer being made of Ta or Nb metal or an alloy containing at least one of Ta and Nb. ３ Precursor for Sn superconducting wire.

4. The Nb according to any one of claims 1 to 3, wherein the reinforcing filaments are made of a metal selected from Nb, Ta, Ti, V, W, Mo, Fe and Hf, or an alloy containing at least one element selected from Nb, Ta, Ti, V, W, Mo, Fe and Hf. ３ Precursor for Sn superconducting wire.

5. a cylindrical stabilizing copper layer provided on the outer periphery; a cylindrical first Sn diffusion barrier layer provided inside the stabilizing copper layer; a group of superconducting elements housed inside the first Sn diffusion barrier layer; Equipped with the superconducting element group includes a plurality of strengthening element wires and a plurality of Nb-based superconducting element wires, The plurality of reinforcing element wires include a first stabilizing matrix made of Cu or a Cu-based alloy, and a plurality of reinforcing multifilamentary wires embedded in the first stabilizing matrix and composed of a plurality of reinforcing filaments made of a metal or an alloy, The plurality of Nb-based superconducting element wires are embedded in a second stabilizing matrix made of Cu or a Cu-based alloy, and a Nb ３ and one or more superconducting filaments having a compound superconducting phase made of Sn. Nb ３ Sn superconducting wire.

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