Superconducting wire, method for manufacturing superconducting wire, and superconducting wire coil, magnetic resonance imaging apparatus, nuclear magnetic resonance apparatus and nuclear fusion reactor using superconducting wire

Abstract

To provide a superconducting wire having improved anti-fatigue characteristic.SOLUTION: A superconducting wire includes a substrate, a superconducting layer, and a stabilization layer, where the stabilization layer includes a rolled copper foil, and the rolled copper foil includes recrystallized grains.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a superconducting wire, a manufacturing method for the superconducting wire, a superconducting wire coil using the superconducting wire, a magnetic resonance imaging device, a nuclear magnetic resonance device, and a nuclear fusion reactor. In particular, the present invention relates to a superconducting wire that can be suitably used as a wire material for a high-temperature superconducting cable, a manufacturing method for the superconducting wire, and a superconducting wire coil using the superconducting wire, a magnetic resonance imaging device, a nuclear magnetic resonance device, and a nuclear fusion reactor. [Background technology]

[0002] A superconducting wire is an electric wire material that utilizes the superconducting phenomenon, in which electrical resistance becomes zero when cooled below a critical temperature, and when a current is passed through a superconducting wire coil made by winding a superconducting wire, a strong magnetic flux is generated in the axial direction of the coil, making it suitable for use in magnetic field generating devices. Typically, superconducting wires are used in magnetic resonance imaging (MRI) devices, nuclear magnetic resonance (NMR) devices, and nuclear fusion reactors.

[0003] Patent Document 1 (JP 2014-216412 A) describes a method for operating a high-temperature superconducting coil, which is characterized in that when using a high-temperature superconducting coil made of an oxide superconducting wire having an intermediate layer, an oxide superconducting layer, and a metal stabilizing layer on a substrate, and operating the high-temperature superconducting coil by setting the current flowing through the oxide superconducting layer, the method operates with a current flowing that is equal to or less than the maximum current that can be passed through the metal stabilizing layer without deteriorating the oxide superconducting layer during the normal conductive transition.

[0004] Patent Document 2 (JP 2008-060074 A) describes a composite superconducting wire having a thin-film superconducting wire including a substrate, a superconducting layer, and a stabilizing layer in this order, and a conductive tape material formed on the stabilizing layer via a lead-free solder containing at least Sn and Bi. It describes that the conductive tape is made of oxygen-free copper with a thickness of 100 μm.

[0005] Patent Document 3 (JP Patent Publication 2015-198009A) describes an oxide superconducting wire comprising an oxide superconducting laminate in which an intermediate layer and an oxide superconducting layer are formed on the main surface of a substrate, a protective layer formed on the outer periphery of the oxide superconducting laminate, and a stabilizing layer formed on the protective layer, the protective layer including a first protective layer made of Ag or an Ag alloy formed so as to cover at least the main surface of the oxide superconducting layer, and a second protective layer made of Ag or an Ag alloy formed so as to cover at least the back surface opposite to the main surface of the substrate, the stabilizing layer being provided so as to cover at least a part of the first protective layer and the second protective layer, and the peel strength between the substrate and the second protective layer being smaller than the peel strength between the oxide superconducting layer and the intermediate layer. It describes that an oxygen-free copper foil having a Sn plating layer of 2 to 4 μm on one side is used for the oxide superconducting conductor, and the stabilizing layer is formed by surrounding the oxide superconducting conductor while folding and forming into a C-shape using a heated and pressurized roll. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-216412 A [Patent Document 2] JP 2008-060074 A [Patent Document 3] JP 2015-198009 A Summary of the Invention [Problem to be solved by the invention]

[0007] Superconducting wires are usually used in a state where they are covered with insulating resin for protection. When a superconducting wire covered with insulating resin is used in a coil shape, compressive stress and tensile stress are repeatedly applied in the thickness direction of the stabilization layer of the superconducting wire when it is repeatedly exposed to low and normal temperatures due to the difference in thermal expansion between the insulating resin and the superconducting wire. As a result, the stabilization layer may become fatigued due to the stress and may be destroyed. Therefore, it is required to provide a copper foil with high fatigue resistance properties suitable for the stabilization layer of a superconducting wire.

[0008] The present invention has been completed in view of the above problems, and has an object to provide, in one embodiment, a superconducting wire with improved fatigue resistance and a manufacturing method thereof. In another embodiment, the present invention has an object to provide a superconducting wire coil, a magnetic resonance imaging device, a nuclear magnetic resonance device, and a nuclear fusion reactor using such a superconducting wire. [Means for solving the problem]

[0009] As a result of intensive research, the inventors have found that by using a rolled copper foil containing recrystallized grains as the stabilization layer of a superconducting wire, it is possible to suppress the growth of fine cracks caused by compressive stress and tensile stress that are repeatedly generated in the thickness direction of the stabilization layer, thereby solving the above-mentioned problems. The present invention has been completed based on the above findings, and is exemplified below.

[0010] [1] A superconducting wire comprising a substrate, a superconducting layer, and a stabilizing layer, the stabilizing layer including rolled copper foil, the rolled copper foil having recrystallized grains. [2] The superconducting wire according to [1], wherein in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the area ratio of recrystallized grains is 50% or more. [3] The superconducting wire according to [1], wherein the recrystallized grains include crystal grains having a Cube orientation. [4] The superconducting wire according to [3], wherein in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the area ratio of crystal grains having a Cube orientation is 30% or more. [5] A method for manufacturing a superconducting wire comprising providing a rolled copper foil having recrystallized grains on a laminate having a base material and a superconducting layer via a bonding layer. [6] A step of preparing a laminate including a base material and a superconducting layer, and a rolled copper foil having a bonding layer; A step of heating the rolled copper foil having the bonding layer to bond it to the laminate. Including, The method for producing a superconducting wire, wherein the rolled copper foil is turned into a rolled copper foil having recrystallized grains by the heating. [7] The method for manufacturing a superconducting wire according to [5], wherein the bonding layer comprises solder. [8] 1. A rolled copper foil, comprising recrystallized grains when heated at 220° C. for 30 seconds. [9] The rolled copper foil according to [8], wherein when heated at 220°C for 30 seconds, the area ratio of recrystallized grains is 50% or more in a cross section parallel to the length direction and parallel to the thickness direction of the rolled copper foil.

[10] The rolled copper foil according to [8], which contains crystal grains having a cube orientation when heated at 220°C for 30 seconds.

[11] The rolled copper foil according to

[10] , wherein when heated at 220°C for 30 seconds, the area ratio of crystal grains having a cube orientation in a cross section parallel to the length direction and parallel to the thickness direction is 30% or more.

[12] 1. A rolled copper foil, comprising recrystallized grains when heated at 200° C. for 8 seconds.

[13] The rolled copper foil according to

[12] , wherein when heated at 200°C for 8 seconds, the area ratio of recrystallized grains is 50% or more in a cross section parallel to the length direction and parallel to the thickness direction of the rolled copper foil.

[14] A rolled copper foil with a bonding layer, comprising a bonding layer and the rolled copper foil according to any one of [8] to

[13] .

[15] A step of preparing a laminate including the rolled copper foil according to any one of [8] to

[14] , a base material, and a superconducting layer; and A step of bonding the rolled copper foil and the laminate by heating via a bonding layer. A method for producing a superconducting wire comprising the steps of:

[16] A method for producing a superconducting wire coil using a superconducting wire produced by the method for producing a superconducting wire according to

[15] .

[17] A superconducting wire coil comprising the superconducting wire according to any one of [1] to [4].

[18] A magnetic resonance imaging device comprising the superconducting wire according to any one of [1] to [4].

[19] A nuclear magnetic resonance apparatus comprising the superconducting wire according to any one of [1] to [4].

[20] A nuclear fusion reactor comprising the superconducting wire according to any one of [1] to [4]. Effect of the Invention

[0011] According to one or more embodiments of the present invention, it is possible to provide a superconducting wire having improved fatigue resistance and a manufacturing method thereof. According to another embodiment of the present invention, it is possible to provide a superconducting wire coil, a magnetic resonance imaging device, a nuclear magnetic resonance device, and a nuclear fusion reactor using such a superconducting wire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Next, the embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] (1.Superconducting wire) In one or more embodiments of the present invention, the superconducting wire includes a substrate, a superconducting layer, and a stabilizing layer. The substrate is for forming the superconducting layer into a wire and is usually in the form of a long tape or pipe. The material of the substrate is not particularly limited, but is usually a metal. For example, nickel alloys such as Hastelloy (a trade name manufactured by Haynes Corporation, USA), Ni, Ag, clad materials, etc. can be used. The thickness of the substrate may be appropriately adjusted depending on the purpose, and may be in the range of 10 to 500 μm. In one or more embodiments of the invention, a superconducting wire includes a substrate, a superconducting layer, other protective structures, and stabilizing layers. In one or more embodiments of the present invention, the superconducting wire includes a substrate, an intermediate layer, a superconducting layer, an Ag layer, an electrolytic Cu plating layer, a bonding layer, and a rolled copper foil.

[0014] An intermediate layer may be provided as necessary. A known intermediate layer may be used. For example, the intermediate layer may have a diffusion prevention layer, a bed layer, an orientation layer, and / or a cap layer. The intermediate layer may also have an orientation layer and / or a cap layer.

[0015] The diffusion prevention layer may prevent or suppress the diffusion of constituent elements of the base material. The diffusion prevention layer may be made of silicon nitride (Si3N4), aluminum oxide (Al2O3), and / or GZO (Gd2Zr2O7), etc. The diffusion prevention layer may be formed by a film formation method such as sputtering. The diffusion prevention layer may have a thickness of 10 to 400 nm. The bed layer may have high heat resistance and may be used to reduce interfacial reactivity. The bed layer may be used to obtain orientation of a film formed thereon. The bed layer may be made of Y2O3, Er2O3, CeO2, Dy2O3, Er2O3, Eu2O3, Ho2O3, and / or La2O3, etc. The bed layer may be formed by a film formation method such as sputtering. The thickness of the bed layer may be, for example, 10 to 100 nm.

[0016] The alignment layer may be for controlling the crystal orientation of the cap layer thereon. The alignment layer may be formed of a biaxially oriented material. The alignment layer may be made of metal oxides such as Gd2Zr2O7, MgO, ZrO2-Y2O3 (YSZ), SrTiO3, CeO2, Y2O3, Al2O3, Gd2O3, Zr2O3, Ho2O3, and / or Nd2O3. When this oriented layer is deposited with good biaxial orientation using the IBAD (Ion-Beam-Assisted Deposition) method, the crystal orientation of the cap layer can be improved, which in turn improves the crystal orientation of the superconducting layer deposited on top of it, resulting in better superconducting properties.

[0017] The cap layer may be formed on the surface of the orientation layer. The cap layer may be made of a material that allows the crystal grains of the cap layer to self-align in the in-plane direction. The cap layer may be made of CeO2, Y2O3, Al2O3, Gd2O3, ZrO2, YSZ, Ho2O3, Nd2O3, and / or LaMnO3, etc. The CeO2 layer can be formed at a high deposition rate by PLD (pulsed laser deposition), sputtering, etc., and good crystal orientation can be obtained. The thickness of the cap layer may be in the range of 50 to 5000 nm.

[0018] The superconducting layer may be made of any superconducting material, and known materials can be used. For example, RE123 (REBa2Cu3O y , RE represents one or more rare earth elements selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.), Y123 (YBa2Cu3O 7-y ) or Gd123(GdBa2Cu3O 7-X ) are some examples.

[0019] A stabilization layer is formed directly on the superconducting layer or on another protective structure. The stabilization layer is for diverting the flowing current to stabilize the superconducting state even if the superconducting state becomes partially unstable and resistance occurs, and is usually composed of a layer and / or foil of Ag, Cu, or an Ag-Cu alloy. In this embodiment, the stabilization layer includes a rolled copper foil. The other protective structure may have a layer containing Ag, a layer mainly composed of Ag, a layer made of Ag, a layer containing Cu, a layer mainly composed of Cu, and / or a layer made of Cu. The other protective structure may be composed of a layer made of Ag and a layer made of Cu. The layer made of Ag may be formed by dry plating such as sputtering. The layer made of Cu may be formed by wet plating such as electrolytic Cu plating. Here, "B containing A as the main component" means that A has the highest concentration (mass %) of the elements constituting B. For example, "B containing A as the main component" may indicate that the concentration of A in B is 50 mass % or more.

[0020] (2. Rolled copper foil for stabilization layer) In one or more embodiments of the present invention, the material of the rolled copper foil is not particularly limited, but for example, tough pitch copper (TPC) specified in JIS-H3100-C1100 or oxygen-free copper (OFC) specified in JIS-H3100-C1020 is preferable. The oxygen concentration contained in the copper foil is usually 150 to 300 ppm by mass in the case of tough pitch copper, and usually 1 to 10 ppm by mass in the case of oxygen-free copper. Tough pitch copper with a higher oxygen concentration is preferable because it is more likely to have recrystallized grains as described later.

[0021] The rolled copper foil according to one or more embodiments of the present invention is made of industrially used copper and contains unavoidable impurities. Examples of unavoidable impurities include P, Fe, Zr, Mg, S, Ge, and Ti. In one embodiment, the rolled copper foil according to the present invention contains 99.9% by mass or more of Cu, with the remainder being unavoidable impurities. In another embodiment, the rolled copper foil may contain other minor components, such as one or more elements selected from the group consisting of Ag, Cr, Mg, Zr, P, and Sn. The minor components are preferably 0.5% by mass or less in total so as not to significantly change the properties of the rolled copper foil.

[0022] Furthermore, the thickness of rolled copper foil used in the stabilization layer of superconducting wires is generally about 40 μm to 500 μm, which is thicker than the thickness of about 4 μm to 35 μm for flexible printed circuit boards, which is the main application of rolled copper foil. However, depending on the quality and characteristics required of the superconducting wire, rolled copper foil with a thickness of less than 40 μm or more than 500 μm can also be used.

[0023] Also, a surface treatment layer can be provided on at least one surface of the rolled copper foil. The surface treatment layer may be a roughening treatment layer. The roughening treatment refers to a treatment in which, when a rolled copper foil is provided on a laminate having a base material and a superconducting layer via a bonding layer, a nodular electrodeposition is formed on the surface of the copper foil after degreasing in order to improve the peel strength between the laminate and the rolled copper foil. The roughening treatment can be performed, for example, by forming roughening particles with copper or a copper alloy. The roughening treatment may be fine. The roughening treatment layer may be a layer made of any one element selected from the group consisting of copper, nickel, cobalt, phosphorus, tungsten, arsenic, molybdenum, iron, chromium, and zinc, or an alloy containing at least one of them. In addition, after forming roughening particles with copper or a copper alloy, a roughening treatment can be performed in which secondary particles or tertiary particles are provided with nickel, cobalt, copper, zinc, or an alloy thereof.

[0024] The surface treatment layer may have one or more layers selected from the group consisting of a roughening treatment layer, a heat-resistant layer, a rust-preventive layer, a chromate treatment layer, and a coupling treatment layer. The surface treatment layer may have one or more layers selected from the group consisting of a heat-resistant layer, a rust-preventive layer, a chromate treatment layer, and a coupling treatment layer. The heat-resistant layer and the rust-preventive layer may be known. The heat-resistant layer and the rust-preventive layer may be a layer made of any single element selected from the group consisting of copper, nickel, cobalt, phosphorus, tungsten, arsenic, molybdenum, iron, chromium, and zinc, or an alloy containing one or more of them, or a layer containing an organic substance. The chromate treatment layer may be known. The chromate treatment layer may be a glossy chromate treatment layer. The coupling treatment layer may be known. The coupling treatment layer may be formed using a known coupling agent. The coupling agent may be a chromium-based coupling agent, a titanate-based coupling agent, a zirconate-based coupling agent, or a silane coupling agent. As a coupling agent, the coupling agent described in https: / / www.jstage.jst.go.jp / article / shikizai1937 / 59 / 3 / 59_176 / _pdf (Hiroshi Yoshioka, The Role of Coupling Agents in Composite Materials, Shikizai Kyokai Shogakukan vol. 59 no. 3, pp. 176-184, 1986) may be used. The coupling treatment layer may be one or more layers selected from the group consisting of a silane coupling treatment layer, an aluminate treatment layer, a titanate treatment layer, and a zirconate treatment layer. These layers can be provided using known methods. However, in one embodiment of the present invention, the rolled copper foil does not include a surface treatment layer in the sense that the manufacturing method is simple.

[0025] In one or more embodiments of the present invention, the rolled copper foil contains recrystallized grains. When a material is subjected to plastic processing, lattice defects such as dislocations are introduced inside, and internal energy resulting from these defects is accumulated. When a metal that has been subjected to plastic processing is held at high temperatures, crystal grains with a significantly low dislocation density are generated due to rearrangement of dislocations. This phenomenon is called recrystallization, and the crystal grains generated by this phenomenon are called recrystallized grains.

[0026] Although it is not intended to limit the present invention by theory, the principle of the improvement of fatigue resistance by the inclusion of recrystallized grains in rolled copper foil is presumed as follows. That is, rolled copper foil has a layered rolling texture parallel to the longitudinal direction in which crystal grains are stretched in the longitudinal direction. Therefore, when compressive stress or elongation stress is repeatedly applied to the rolled copper foil in the thickness direction, it is expected that microcracks will initially occur at the grain boundaries between the crystal grains stretched in the longitudinal direction. In addition, as a result of the repeated application of compressive stress or elongation stress to the rolled copper foil in the thickness direction, it is expected that the microcracks will gradually grow larger, causing fracture between the crystal grains, and the rolled copper foil will break in a direction parallel to the longitudinal direction.

[0027] Here, in the case of rolled copper foil having recrystallized grains, when compressive stress or elongation stress is repeatedly applied to the rolled copper foil in the thickness direction, small cracks are generated at the grain boundaries between the crystal grains stretched in the longitudinal direction in the early stage, but the existence of the recrystallized grains suppresses the progress of the cracks, and it is expected that fracture is less likely to occur between the crystal grains.

[0028] Therefore, in one or more embodiments, the present invention is a superconducting wire including a substrate, a superconducting layer, and a stabilizing layer, the stabilizing layer including rolled copper foil, and the rolled copper foil having recrystallized grains. Here, the presence of recrystallized grains can be confirmed by measuring a cross section parallel to the longitudinal direction and the thickness direction of the superconducting wire or rolled copper foil using an EBSD (Electron Back Scatter Diffraction) device. The recrystallized grains have any of the following orientations: Cube orientation, R orientation, BR orientation, RD rotated cube orientation, and Cu orientation (reference: Kaneko et al., Recrystallization Texture and Young's Modulus of Cu-3.8%Ni-0.9%Si Alloy Sheet, Journal of the Japan Institute of Metals, Vol. 77, No. 9, pp. 353-360, 2013). Each orientation is indicated by an index as follows: Cube direction:{001} <100> (The {001} plane is parallel to the rolling surface and in the rolling direction (RD) <100> (The grain orientation is parallel to the direction of the crystal grains.) R direction:{123} <634> BR direction:{362} <853> RD Rotation Cube Orientation: {012} <100> Cu orientation:{121} <111>

[0029] In order to improve the effect of suppressing the progress of the cracks, in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the ratio of the area of ​​the recrystallized grains (i.e., the total ratio of the area of ​​the recrystallized grains in each of the above orientations) is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more. If the ratio of the area of ​​the recrystallized grains is 50% or more, the recrystallized grains are present in a region of more than half the area of ​​the cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, so that the possibility of the microcracks hitting the recrystallized grains is increased, and the progress of the cracks can be suppressed better. And, by further increasing the ratio of the area of ​​the recrystallized grains to 60% or more, 70% or more, 80% or more, or 90% or more, the possibility of the microcracks hitting the recrystallized grains can be further increased, and the progress of the cracks can be suppressed better. The upper limit of the proportion of the area of ​​recrystallized grains is not particularly limited, but can be, for example, 100% or less, or 99% or less.

[0030] In addition, when the recrystallized grains are crystal grains having a Cube orientation (hereinafter referred to as "Cube orientation crystal grains"), the strength of the crystal grain boundaries is strong and the crystal grain size is large, so that the propagation of cracks is further suppressed. Therefore, in one embodiment of the present invention, the recrystallized grains of the rolled copper foil include crystal grains having a Cube orientation.

[0031] In order to improve the effect of suppressing the progress of the cracks, in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the area ratio of the Cube orientation crystal grains is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more. If the area ratio of the Cube orientation crystal grains is 30% or more, the possibility that the microcracks will encounter crystal grains with strong grain boundary strength or large crystal grains increases, so the possibility of suppressing the progress of the microcracks increases, and the progress of the cracks can be suppressed better. By further increasing the area ratio of the Cube orientation crystal grains to 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 95% or more, the possibility that the microcracks will encounter crystal grains with strong grain boundary strength or large crystal grains can be increased, the possibility of suppressing the growth of the microcracks can be increased, and the growth of the cracks can be suppressed more effectively. The upper limit of the area ratio of the Cube orientation crystal grains is not particularly limited, but can be, for example, 100% or less, or 99% or less.

[0032] In addition, as described later, when manufacturing a superconducting wire, a method of heating and pressing is usually adopted, but even if a rolled copper foil does not originally have recrystallized grains, if it becomes recrystallized grains by the heating, the effect of suppressing the progress of the cracks can be obtained, and the problem of the present invention can be solved. Therefore, in another aspect, the present invention relates to a rolled copper foil characterized by containing recrystallized grains when heated at 220°C for 30 seconds. Alternatively, in another aspect, the present invention relates to a rolled copper foil characterized by containing recrystallized grains when heated at 200°C for 8 seconds. The condition of heating at 220°C for 30 seconds or at 200°C for 8 seconds is a simulation of a general condition for manufacturing a superconducting wire.

[0033] For the same reasons as above, when heated under the above conditions, in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the ratio of the area of ​​recrystallized grains (i.e., the total ratio of the area of ​​recrystallized grains in each of the above orientations) is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more. The upper limit of the ratio of the area of ​​recrystallized grains is not particularly limited, but can be, for example, 100% or less, or 99% or less.

[0034] In particular, when heated under the above conditions, the rolled copper foil preferably contains Cube orientation crystal grains. In a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, the area ratio of Cube orientation crystal grains is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more. The upper limit of the area ratio of Cube orientation crystal grains is not particularly limited, but can be, for example, 100% or less, or 99% or less.

[0035] Next, an example of a method for measuring the area ratio of recrystallized grains will be described. Cube orientation crystal grains will be described as an example of the measurement target. The area ratios of other recrystallized grains can also be measured in a similar manner by adjusting the settings of the analysis software to the crystal orientation to be measured.

[0036] Cube orientation {001} in a cross section parallel to the length direction of the superconducting wire of the rolled copper foil and parallel to the thickness direction <100> The area ratio of is measured by EBSD. Here, EBSD is a technique for analyzing crystal orientation using reflected electron Kikuchi diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam inside a SEM (Scanning Electron Microscope).

[0037] Electropolishing is carried out under the following electrolytic solution and test conditions. After removing about 1μm from the sample surface, a scanning is performed at a step size of about 0.5μm for an arbitrarily set observation range of about 100μm×40μm such that one side of the observation field is parallel to the rolling direction, and the crystal orientation distribution is measured.

[0038] Furthermore, due to manufacturing and handling of rolled copper foil (for example, cutting out samples for measurement, etc.), abnormal parts such as parts where oil pits extremely enter and foreign matter adhesion may occur in some parts. When measuring the area ratio of Cube-oriented crystal grains, the measurement location should be set avoiding the parts corresponding to the abnormal parts. The abnormal parts can be grasped by observing the sample before electropolishing with SEM (observation magnification: 100 times), etc.

[0039] <Composition of electrolytic solution (an example)> · Distilled water: 250ml · Phosphoric acid: 125ml · Urea: 2.5g · Ethanol primary grade: 125ml · 1-Propanol: 25ml <Electropolishing conditions> Applied voltage: 10V Electrolysis time: 10 seconds <Measurement conditions of EBSD, etc.> · SEM conditions Apparatus: Scanning electron microscope (JSM-IT500HR or equivalent apparatus) manufactured by JEOL Ltd. Type of electron gun: Field emission type electron gun (Schottky type) Emitter of electron gun: ZrO tungsten cathode Type of objective lens: Out-lens type Presence or absence of focus correction: Yes (Dynamic focus: 50) Beam conditions Acceleration voltage: 15kV Working distance: 15mm Irradiation current amount: 15nA SEM probe diameter: 0.5~2nm Observation magnification: About 500 times EBSD equipment conditions Detector: Slow scan CCD camera manufactured by TSL Solutions Co., Ltd. Data processing conditions Data collection software: OIM Data Collection by TSL Solutions Co., Ltd. Phase:Copper CCD camera pixel count: 1394 x 1040 pixels Binning: 8×8 Exposure time: 8 ms Gain: 0.9~0.95 Background processing: Yes Scanning method of measuring points: Hexagonal grid ·Hough Transform (1) Hough Type: Classic (2) Hough Resolution: Low (3) Classic Hough Convolution Mask: 9×9 Min Peak Magnitude: 5 Min Peak Distance: 23 Peak Symmetry: 0.75 Vertical Bias: 0 (4) General Parameters Binned Pattern Size: 120 Theta Step Size: 1° Rho Fraction: 90% Max Peak Count: 8 Min Peak Count: 3

[0040] Then, the crystal orientation density function is analyzed, and the area of crystal grains with orientations within 15° from the Cube orientation is divided by the measurement area to obtain the area ratio. For collecting the above measurement data, OIM Data Collection manufactured by TSL Solutions Co., Ltd. is used, and for data analysis, OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. is used. Note that the information obtained in the orientation analysis by EBSD includes the orientation information up to a depth of several tens of nanometers where the electron beam penetrates the sample. Since it is sufficiently small compared to the measured area, it is described as the area ratio. <Data Analysis Conditions of OIM Analysis V8> ·New Map Window Map Style Grayscale: <none>Select . Select Color Coded:Crystal Orientation. Boundaries Second Partition: <none>Select . Crystal Orientation window (displayed when you click Edit in Color Coded in the Map Style window) Representation:Select Euler Angles (Bunge). Enforce Orthotropic Sample Symmetry checkbox: Check the box. Add Crystal Orientation Range window (the screen that appears when you click Add in the Crystal Orientation window) Orientation tab Phase:Select Copper. Euler Angles(Bunge):(φ1,φ,φ2)=(0,0,0) hkl input value: 001 UVW input value: 100 Tolerance tab Minimum input value: 0 Maximum input value: 15 The total fraction value in the Crystal Orientation measurement results performed under the above settings is the area ratio of Cube orientation crystal grains. When measuring other crystal orientations, simply change the hkl input values ​​and uvw input values, etc., to match the crystal orientation in question in the Orientation tab.

[0041] (3. Rolled Copper Foil Manufacturing Example) The manufacturing method of the rolled copper foil is not limited as long as it has the above-mentioned characteristics related to recrystallized grains. As an example of the manufacturing method, first, raw materials such as copper are melted in a melting furnace to obtain a molten metal of a desired composition. Then, the molten metal is poured (cast) into a mold to produce an ingot. In order to prevent oxidation wear of copper, it is preferable to perform melting and casting in a vacuum or an inert gas atmosphere. Then, homogenization annealing, hot rolling, cold rolling, recrystallization annealing, final cold rolling, etc. are performed to finish the rolled copper foil having the desired thickness and desired properties. Cold rolling and recrystallization annealing may be repeated multiple times.

[0042] When rolled copper foil is heated under the conditions of 0.5 to 2 hours at 180°C to 250°C or 1 to 10 seconds at 300°C to 450°C, recrystallization occurs and the rolled copper foil comes to contain recrystallized grains.

[0043] On the other hand, as a method for generating recrystallized grains in the rolled copper foil during heat treatment in bonding with the bonding layer without performing the above heat treatment, it is possible to increase the degree of processing in the final cold rolling. By increasing the degree of processing in the final cold rolling, the dislocation density introduced into the rolled copper foil increases, and the accumulated strain energy that serves as the driving force for recrystallization can be increased, and the rolled copper foil can be made to have recrystallized grains even by heat treatment in bonding with the bonding layer, which is generally performed at a low temperature and for a short time. By setting the degree of processing in the final cold rolling to at least 90% or more, the cube orientation crystal grains grow significantly by the heat treatment. More preferably, the degree of processing in the final cold rolling is 93% or more. More preferably, the degree of processing in the final cold rolling is 95% or more. More preferably, the degree of processing in the final cold rolling is 98% or more. The degree of reduction is defined as follows: degree of reduction (%)={(thickness before final cold rolling (mm)−thickness after final cold rolling (mm)) / thickness before final cold rolling (mm)}×100.

[0044] In addition, the higher the oxygen concentration, the more likely it is that recrystallized grains will be formed with a small amount of heat. In the case of tough pitch copper, the oxygen concentration is 150 to 300 ppm by mass, and in the case of oxygen-free copper, the oxygen concentration is 1 to 10 ppm by mass. Therefore, rolled copper foil using tough pitch copper makes it easier to obtain copper foil that is more likely to have recrystallized grains with a small amount of heat.

[0045] Furthermore, if the concentration of the minor component in the rolled copper foil is too high, recrystallization becomes difficult, so the concentration of the minor component is preferably 0.5 mass % or less.

[0046] (4. Manufacturing method of superconducting wire) In another aspect, one or more embodiments of the present invention relate to a method for manufacturing a superconducting wire, in which a laminate having a base material and a superconducting layer is provided with a rolled copper foil having recrystallized grains via a bonding layer. As described above, by using the rolled copper foil having recrystallized grains as a stabilization layer, it is possible to suppress the growth of fine cracks caused by compressive stress and tensile stress repeatedly occurring in the thickness direction of the stabilization layer, and it is possible to provide a superconducting wire with improved fatigue resistance.

[0047] Furthermore, in order to provide a rolled copper foil having recrystallized grains to a laminate having a base material and a superconducting layer via a bonding layer, a method of heating and pressing is usually adopted. However, even in the case of rolled copper foil that does not originally have recrystallized grains, if it is heated to include recrystallized grains, the effect of suppressing the progression of the cracks can be obtained, thereby solving the problem of the present invention.

[0048] Therefore, in yet another aspect, one or more embodiments of the present invention relate to a method for producing a superconducting wire, the method including the steps of preparing a laminate including a base material and a superconducting layer, and a rolled copper foil having a bonding layer, and heating the rolled copper foil having the bonding layer to bond it to the laminate, the rolled copper foil being turned into a rolled copper foil having recrystallized grains by heating. As the bonding layer, a layer having solder can be used, or a layer mainly composed of copper can be used.

[0049] Known solders can be used. The solder may be In, In alloy, an alloy mainly composed of In, Sn, Sn alloy, Sn-Ag alloy, Sn-Bi alloy, Sn-Cu alloy, Sn-Zn alloy, an alloy mainly composed of Sn, Pb-Sn alloy solder, lead-free solder, eutectic solder, and / or low-temperature solder. These solders can be used alone or in combination of two or more. Among these, it is preferable to use a solder having a melting point of 300°C or less. This makes it possible to bond the laminate including the base material and the superconducting layer to the rolled copper foil having the bonding layer at a temperature of 300°C or less, so that the characteristics of the superconducting layer are less likely to deteriorate due to the heat of bonding. Here, "A alloy" means a metal including A and other elements. "AB alloy" means a metal including A and B.

[0050] The solder preferably has one or more selected from the group consisting of In, In alloys, and / or alloys mainly composed of In. Alternatively, the solder is preferably one or more selected from the group consisting of In, In alloys, and / or alloys mainly composed of In. Since the melting point of In is as low as 156.7°C, when In is used for the bonding layer, it is possible to bond a laminate including a base material and a superconducting layer to a rolled copper foil having a bonding layer at a temperature of 200°C or less, so it is expected that the characteristics of the superconducting layer will be even less likely to deteriorate due to the heat of bonding. In addition, since In maintains malleability and ductility even in an extremely low temperature environment of -150°C or less, it is expected that it will be less likely to be destroyed even in an extremely low temperature environment in which the superconducting wire is in a superconducting state. In alloys include In-Sn alloys (e.g., 52 mass% In-48 mass% Sn, etc.), Sn-Ag-In-Bi alloys (e.g., 88.0 to 93.0 mass% Sn-3.2 to 3.5 mass% Ag-2.7 to 8.0 mass% In-0.5 to 2.7 mass% Bi, etc.), Sn-In-Ag alloys (e.g., 85 mass% Sn-10 mass% In-5 mass% Ag, 77.2 mass% Sn-20 mass% In-2.8 mass% Ag, etc.), In-Bi- The alloy may be one or more selected from the group consisting of Sn alloys (e.g., 51% by mass In-32.5% by mass Bi-16.5% by mass Sn, 3% by mass In-42% by mass Bi-55% by mass Sn, etc.), In-Sn-Zn alloys (e.g., 52.2% by mass In-46% by mass Sn-1.8% by mass Zn, etc.), In-Ag alloys (e.g., 97% by mass In-3% by mass Ag, etc.), and Sn-Ag-Cu-In alloys.

[0051] The layer containing copper as a main component may be a known one. The layer containing copper as a main component may be a layer of sintered copper (sintered copper layer). Low-temperature sinterable copper powder may be used to form the sintered copper layer. The low-temperature sinterable copper powder may be copper powder that starts to sinter at 400°C or less. The low-temperature sinterable copper powder may be copper powder that starts to sinter at 300°C or less. The low-temperature sinterable copper powder may be copper powder that starts to sinter at 200°C or less. A known low-temperature sinterable copper powder may be used as the low-temperature sinterable copper powder. Examples of low-temperature sinterable copper powder include sintered copper fine powder (Type L) manufactured by JX Metals Corporation, fine copper powder UCP series (e.g. UCP-030N) manufactured by Sumitomo Metal Mining Co., Ltd., low-temperature sinterable copper powder (CH-0200L1, CH-0200DP) manufactured by Mitsui Mining & Smelting Co., Ltd., low-temperature sinterable copper fine particles MD-200S (powder) and MDP-200 (paste-like high-concentration dispersion) manufactured by Ishihara Sangyo Kaisha, Ltd., and polymer-protected copper powder described in https: / / main.spsj.or.jp / koho / 63t / 63t_1.pdf (Yonezawa et al., Non-oxidized copper fine particles that can be sintered at low temperatures down to 150°C, 63rd Polymer Symposium of the Society of Polymer Science, 2014).

[0052] In yet another aspect, one or more embodiments of the present invention relate to a method for producing a superconducting wire, the method including the steps of preparing a rolled copper foil and a laminate including a base material and a superconducting layer, and bonding the rolled copper foil and the laminate by heating via a bonding layer. The rolled copper foil is characterized in that it contains recrystallized grains when heated at 220° C. for 30 seconds or when heated at 200° C. for 8 seconds. The rolled copper foil may also be a rolled copper foil with a bonding layer, in which a bonding layer is previously provided.

[0053] (5. Uses of superconducting wire)

[0054] In yet another aspect, one or more embodiments of the present invention relate to a method for producing a superconducting wire coil using the superconducting wire of the present invention or the superconducting wire produced according to the production method of the present invention.

[0055] The superconducting wire according to one or more embodiments of the present invention, or the superconducting wire manufactured according to the manufacturing method according to one or more embodiments of the present invention, can be used in a magnetic resonance imaging device, a nuclear magnetic resonance device, and a nuclear fusion reactor as a superconducting wire coil wound around an insulating tape or the like. Therefore, one or more embodiments of the present invention, in another aspect, are a superconducting wire coil having the superconducting wire according to one or more embodiments of the present invention, or the superconducting wire manufactured according to the manufacturing method according to one or more embodiments of the present invention. Also, one or more embodiments of the present invention, in another aspect, are a magnetic resonance imaging device having the superconducting wire according to one or more embodiments of the present invention, or the superconducting wire manufactured according to the manufacturing method according to one or more embodiments of the present invention. Also, one or more embodiments of the present invention, in another aspect, are a nuclear magnetic resonance device having the superconducting wire according to one or more embodiments of the present invention, or the superconducting wire manufactured according to the manufacturing method according to one or more embodiments of the present invention. Also, one or more embodiments of the present invention, in another aspect, are a nuclear fusion reactor having the superconducting wire according to one or more embodiments of the present invention, or the superconducting wire manufactured according to the manufacturing method according to one or more embodiments of the present invention.

[0056] (Potential to contribute to SDGs) According to one or more embodiments of the present invention, it is possible to provide a superconducting wire with improved fatigue resistance, which may reduce failures of devices using the superconducting wire. Reducing device failures may extend the life of the devices, which may contribute to reducing devices that are discarded at the end of their life. Furthermore, reducing discarded devices may lead to a reduction in loss of metal raw materials, which are limited resources, caused by the discarding of devices. Therefore, one or more embodiments of the present invention may contribute to Goal 12 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."< / none> < / none>

Claims

1. A superconducting wire comprising a substrate, a superconducting layer, and a stabilizing layer, the stabilizing layer including rolled copper foil, the rolled copper foil having recrystallized grains.

2. 2. The superconducting wire according to claim 1, wherein a ratio of an area of ​​recrystallized grains in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction is 50% or more.

3. The superconducting wire of claim 1 , wherein the recrystallized grains include grains having a Cube orientation.

4. 4. The superconducting wire according to claim 3, wherein in a cross section of the rolled copper foil parallel to the length direction of the superconducting wire and parallel to the thickness direction, a ratio of an area of ​​crystal grains having a Cube orientation is 30% or more.

5. A method for manufacturing a superconducting wire comprising providing a rolled copper foil having recrystallized grains on a laminate having a base material and a superconducting layer via a bonding layer.

6. A step of preparing a laminate including a base material and a superconducting layer, and a rolled copper foil having a bonding layer; A step of heating the rolled copper foil having the bonding layer to bond it to the laminate. Including, The method for producing a superconducting wire, wherein the rolled copper foil is turned into a rolled copper foil having recrystallized grains by the heating.

7. The method for producing a superconducting wire according to claim 5 , wherein the bonding layer comprises solder.

8. 1. A rolled copper foil, comprising recrystallized grains when heated at 220° C. for 30 seconds.

9. 9. The rolled copper foil according to claim 8, wherein when heated at 220° C. for 30 seconds, the area ratio of recrystallized grains is 50% or more in a cross section parallel to the length direction and parallel to the thickness direction of the rolled copper foil.

10. The rolled copper foil according to claim 8, which contains crystal grains having Cube orientation when heated at 220°C for 30 seconds.

11. 11. The rolled copper foil according to claim 10, wherein when heated at 220° C. for 30 seconds, the area ratio of crystal grains having the Cube orientation in a cross section parallel to the length direction and parallel to the thickness direction is 30% or more.

12. 1. A rolled copper foil, comprising recrystallized grains when heated at 200° C. for 8 seconds.

13. 13. The rolled copper foil according to claim 12, wherein when heated at 200° C. for 8 seconds, the area ratio of recrystallized grains is 50% or more in a cross section parallel to the length direction and parallel to the thickness direction of the rolled copper foil.

14. A rolled copper foil with a bonding layer, comprising a bonding layer and the rolled copper foil according to any one of claims 8 to 13.

15. A step of preparing a laminate including the rolled copper foil according to any one of claims 8 to 13, a substrate, and a superconducting layer; and A step of bonding the rolled copper foil and the laminate by heating via a bonding layer. A method for producing a superconducting wire comprising the steps of:

16. A method for producing a superconducting wire coil by using a superconducting wire produced by the method for producing a superconducting wire according to claim 15.

17. A superconducting wire coil comprising the superconducting wire according to any one of claims 1 to 4.

18. A magnetic resonance imaging device comprising the superconducting wire according to any one of claims 1 to 4.

19. A nuclear magnetic resonance apparatus comprising the superconducting wire according to any one of claims 1 to 4.

20. A nuclear fusion reactor comprising the superconducting wire according to any one of claims 1 to 4.