Patent Application
20180122534
The present invention relates to a superconducting wire, and more particularly to a superconducting wire having a superconducting material layer formed on a substrate.
Superconducting wires having a superconducting material layer on a metal substrate have recently been developed. Among those, an oxide superconducting wire has drawn attention, which includes a superconducting material layer made of an oxide superconductor which is a high-temperature superconductor having a transition temperature equal to or higher than liquid nitrogen.
Such an oxide superconducting wire is generally manufactured by forming a superconducting material layer on a metal substrate and further forming a metal layer of silver (Ag) or copper (Cu) (for example, see WO2001/008234 (PTD 1) and Japanese Patent Laying Open No. 2012-84478 (PTD 2)).
Patent Document
When an oxide superconducting wire having a configuration described above is wound in the form of a coil and cooled to critical temperature, tensile stress acts on the superconducting material layer in the radial direction of the coil due to the difference in coefficient of thermal expansion between the metal layer and the superconducting material layer to cause local separation in the superconducting material layer. Thus, breakage or deformation easily occurs in part of the superconducting material layer, resulting in degradation of superconducting properties.
As measures against separation of a superconducting material layer, for example, the entire outer periphery of the superconducting wire may be covered with a thick metal tape. In the configuration above, however, the thickness of the metal tape increases the cross-sectional area of the entire superconducting wire and thus reduces the critical current density (Jc).
The present invention is made in order to solve the problem as described above, and an object of the present invention is to provide a superconducting wire in which separation of the superconducting wire can be suppressed without reducing the critical current density of the superconducting wire.
A superconducting wire according to an aspect of the present invention includes: a laminated structure including a substrate having a main surface and a superconducting material layer formed on the main surface; and a reinforcing layer disposed on both side surfaces of the laminated structure in a width direction of the substrate. The laminated structure has a bottom surface on which the substrate is positioned, and a top surface on an opposite side to the bottom surface. The reinforcing layer has an exposed surface on at least one side of the bottom surface and the top surface of the laminated structure. In a cross section in the width direction of the substrate, a ratio of a total width of the reinforcing layer to a width of the laminated structure is 1% or more and 15% or less.
According to the above, separation of the superconducting wire can be suppressed without reducing the critical current density of the superconducting wire.
First of all, embodiments of the present invention will be described one by one.
(1) A superconducting wire 10 (see
In this manner, the tensile stress acting on laminated structure 20 can be distributed to reinforcing layer 12 disposed on both side surfaces of laminated structure 20, thereby improving tensile strength of superconducting wire 10. Accordingly, when superconducting wire 10 is wound in the form of a coil and cooled to extremely low temperature equal to or lower than the critical temperature, occurrence of local separation in laminated structure 20 can be suppressed. This eliminates the need for a thick metal tape covering the outer peripheral surface of laminated structure 20, thereby suppressing increase in cross section of the superconducting wire for improvement of tensile strength. As a result, occurrence of separation in the superconducting wire can be suppressed without reducing the critical current density.
In a cross section in the width direction of substrate 1, the ratio of the total width of reinforcing layer 12 to the width of laminated structure 20 is 1% or more and 15% or less, preferably 3% or more and 15% or less, more preferably 5% or more and 12% or less.
(2) A superconducting wire 10A (see
In this manner, since bonding member 28 functions as reinforcing layer 12, occurrence of separation in the superconducting wire can be suppressed even in a configuration in which coating layer 9 is disposed on one side of the top surface and the bottom surface of laminated structure 20.
(3) In a superconducting wire 10B (see
In this manner, since metal member 30 functions as reinforcing layer 12, occurrence of separation in superconducting wire 10B can be suppressed even in a configuration in which thin-film coating layer 34 is disposed.
(4) In superconducting wire 10B according to (3) above, preferably, reinforcing layer 12 further includes a bonding layer 32 that bonds metal member 30 extending along the direction in which laminated structure 20 extends to both side surfaces of laminated structure 20.
In this manner, since metal member 30 and bonding layer 32 function as reinforcing layer 12, occurrence of separation in superconducting wire 10B can be suppressed.
(5) In superconducting wire 10B according to (3) or (4) above, preferably, coating layer 34 is formed of a foil or a plating layer of a metal material provided so as to cover the outer peripheral surface of laminated structure 20 and metal member 30.
In this manner, since coating layer 34 can be formed as a thin film, occurrence of separation in superconducting wire 10B can be suppressed without reducing the critical current density.
(6) In a superconducting wire 10C (see
In this manner, since metal layer 38 functions as reinforcing layer 12, occurrence of separation in superconducting wire 10C can be suppressed.
(7) Superconducting wire 10C according to (6) above preferably further includes a coating layer 36 covering top surface 20A and bottom surface 20B of laminated structure 20. Metal layer 38 is formed integrally with coating layer 36.
In this manner, since metal layer 38 and coating layer 36 function as reinforcing layer 12, occurrence of separation in superconducting wire 10C can be suppressed.
(8) In superconducting wire 10C according to (7) above, preferably, metal layer 38 and coating layer 36 are formed of a plating layer.
In this manner, since coating layer 36 can be formed as a thin film while metal layer 38 has a thickness required as reinforcing layer 12, occurrence of separation in superconducting wire 10C can be suppressed without reducing the critical current density.
(9) A superconducting wire 10D (see
In this manner, since coating layer 42 positioned on both side surfaces of laminated structure 20 functions as reinforcing layer 12, occurrence of separation in superconducting wire 10D can be suppressed.
(10) In superconducting wire 10D according to (9) above, preferably, coating layer 42 is formed of a solder layer.
In this manner, since coating layer 42 positioned on the top surface and the bottom surface of laminated structure 20 can be formed as a thin film while coating layer 42 positioned on both side surfaces of laminated structure 20 has a thickness required as reinforcing layer 12, occurrence of separation in superconducting wire 10D can be suppressed without reducing the critical current density.
Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings below, the same or corresponding parts will be denoted by the same reference signs and a description thereof will not be repeated.
In a first embodiment, a basic configuration of a superconducting wire 10 according to an embodiment of the present invention will be described, and thereafter in second to fourth embodiments, a specific configuration of superconducting wire 10 and a method of manufacturing the same will be described.
(Basic Configuration of Superconducting Wire)
As shown in
Substrate 1 has a first main surface and a second main surface. The second main surface is positioned on the opposite side to the first main surface. It is preferable that substrate 1 is made of, for example, metal and formed in an elongated shape (tape-like shape) rectangular in cross section. In order to be wound into a coil, substrate 1 is preferably elongated, for example, to about 2 km.
It is further preferable that a textured metal substrate is used as substrate 1. The textured metal substrate means a substrate in which the crystal orientation is aligned with respect to two axis directions in a plane of the substrate surface. As a textured metal substrate, for example, an alloy made of two or more metals selected from nickel (Ni), copper (Cu), chromium (Cr), manganese (Mn), cobalt (Co), iron (Fe), palladium (Pd), silver (Ag), and gold (Au) is preferably used. These metals may be laminated on another metal or alloy, and, for example, an alloy such as SUS which is high-strength material can also be used. The material of substrate 1 is not limited to the above and, for example, a material other than metal may be used.
The length in the width direction of superconducting wire 10 is, for example, about 4 mm to 10 mm. In order to increase the density of current flowing through superconducting wire 10, a smaller cross-sectional area of substrate 1 is preferable. It is noted that if the thickness of substrate 1 (the top-bottom direction in
Intermediate layer 3 is formed on the first main surface of substrate 1. Superconducting material layer 5 is formed on the main surface (the upper main surface in
Intermediate layer 3 may be formed with a plurality of layers. When intermediate layer 3 is formed with a plurality of layers, the layers included in intermediate layer 3 may be formed of materials different from each other or partially the same material.
Superconducting material layer 5 is a thin-film layer to allow superconducting current to flow therethrough in superconducting wire 10. The superconducting material is preferably, but not limited to, for example, RE-123-based oxide superconductor. The RE-123-based oxide superconductor means a superconductor represented as REBa2Cu3O (y is 6 to 8, more preferably 6.8 to 7, RE means yttrium or a rare-earth element such as Gd, Sm, Ho). In order to improve the value of superconducting current flowing through superconducting material layer 5, the thickness of superconducting material layer 5 is preferably 0.5 μm to 10 μm.
Protection layer 7 is formed on the main surface (the upper main surface in
Laminated structure 20 is formed with substrate 1, intermediate layer 3, superconducting material layer 5, and protection layer 7 as described above. Laminated structure 20 has a bottom surface 20B on which substrate 1 is positioned and a top surface 20A on the opposite side to bottom surface 20B. Coating layer 9 is formed on top surface 20A of this laminated structure 20. Coating layer 9 may be formed on bottom surface 20B of laminated structure 20 in place of top surface 20A or in addition to top surface 20A. In a cross section in the width direction of substrate 1, it is preferable that width W2 of coating layer 9 is equal to width W1 of laminated structure 20 or wider than width W1 of laminated structure 20 (W2≥W1).
Coating layer 9 is formed of a foil or a plating layer of a metal material with good conductivity. Coating layer 9 functions together with protection layer 7 as a bypass through which current of superconducting material layer 5 is commutated when superconducting material layer 5 changes from a superconducting state to a normal conducting state. The material that forms coating layer 9 is preferably, for example, copper or copper alloy, or solder. The thickness of coating layer 9 is preferably about 20 μm to 100 μm in terms of reducing the cross-sectional area of superconducting wire 10 while physically protecting protection layer 7 and superconducting material layer 5.
Reinforcing layer 12 is disposed on both side surfaces of laminated structure 20 in the width direction of substrate 1. Reinforcing layer 12 is made of a metal material with good conductivity. The material that forms reinforcing layer 12 is preferably, for example, copper or copper alloy, nickel or nickel alloy, or solder.
In superconducting wire 10 shown in
Reinforcing layer 12 has an exposed surface on at least one side of top surface 20A and bottom surface 20B of laminated structure 20. In superconducting wire 10 shown in
In a cross section in the width direction of substrate 1, the ratio of the total width W3 of reinforcing layer 12 to width W1 of laminated structure 20 (W3×2/W1) is preferably 1% or more and 15% or less. The ratio can be more preferably 3% or more and 15% or less, further preferably 5% or more and 12% or less.
In this way, in superconducting wire 10 according to the present embodiment, reinforcing layer 12 is disposed on both side surfaces of laminated structure 20. Thus, when superconducting wire 10 is wound in the form of a coil and cooled to extremely low temperature equal to or lower than the critical temperature, occurrence of local separation in laminated structure 20 can be suppressed without reducing the critical current density (Jc) of superconducting wire 10.
In the following, referring to Example shown in
As shown in
In Comparative Example 1, laminated structure 20 has a structure similar to laminated structure 20 in Example. The outer peripheral surface of laminated structure 20 is covered with metal tapes 23, 25. Metal tape 23 is disposed on each of the top surface side and the bottom surface side of laminated structure 20. Width W2 of metal tape 23 is larger than width W1 of laminated structure 20, and both end portions of metal tape 23 protrude from both side surfaces of laminated structure 20. Metal tape 25 is disposed between the protruding portions of metal tape 23. Metal tape 23 has a width of 4.4 mm (W2=4.4 mm) and a thickness of 200 μm (L3=200 μm).
That is, metal tape 25 in Comparative Example 1 has the same shape as reinforcing layer 12 in Example. On the other hand, in Comparative Example 1, metal tape 23 is disposed on each of the top surface and the bottom surface of laminated structure 20 whereby the thickness of the superconducting wire is increased compared with Example.
For each of Example and Comparative Examples 1 and 2, the tensile strength and the critical current density of the superconducting wire were evaluated by simulation. The simulation result of each superconducting wire is shown in Table 1.
As shown in
When tensile stress F1 acts on laminated structure 20, tensile stress F2 also acts on reinforcing layer 12 disposed on both side surfaces of laminated structure 20. Reinforcing layer 12 is made of a metal material and therefore has a tensile strength higher than the tensile strength of laminated structure 20. For example, when reinforcing layer 12 is made of copper, reinforcing layer 12 has a tensile strength of about 220 MPa.
In Example, the tensile strength of the superconducting wire was calculated by summing the tensile strength of laminated structure 20 and the tensile strength of reinforcing layer 12 by the area ratio between laminated structure 20 and reinforcing layer 12 in the main surface of the superconducting wire. Similarly, the tensile strength of the superconducting wire according to Comparative Example 1 was calculated by summing the tensile strength of laminated structure 20 and the tensile strength of metal tape 25 by the area ratio between laminated structure 20 and metal tape 25 in the main surface of the superconducting wire. When metal tape 25 is made of copper, metal tape 25 has a tensile stress of about 220 MPa.
Furthermore, the critical current density of each superconducting wire was calculated by setting critical current Ic flowing through laminated structure 20 to 200A and dividing the set critical current Ic by the cross-sectional area of each superconducting wire.
Referring to Table 1, Example has a high tensile strength when compared with Comparative Example 2 that does not have reinforcing layer 12. This is because in Example, reinforcing layer 12 having a tensile strength higher than laminated structure 20 is disposed on both side surfaces of laminated structure 20 whereby reinforcing layer 12 takes charge of most of the tensile stress exerted on laminated structure 20 and consequently, tensile stress can be distributed to reinforcing layer 12. Also in Comparative Example 1, the tensile stress exerted on laminated structure 20 is distributed to metal tape 25 disposed on the side surfaces of laminated structure 20 in the same manner as in Example and, therefore, the tensile strength equivalent to Example is achieved.
On the other hand, the critical current density of the superconducting wire is highest in Comparative Example 2 and is lower in the order of Example and Comparative Example 1. In Example, the thickness of the metal layer provided on the top surface and bottom surface sides of laminated structure 20 is thin compared with Comparative Example 1, so that the thickness of the superconducting wire is reduced. Therefore, Example achieves a critical current density higher than Comparative Example 1 while ensuring a tensile strength equivalent to that of Comparative Example 1.
The cross-sectional area of the superconducting wire is smaller in Example than in Comparative Example 1. Thus, when the superconducting wire is wound to form a coil, the diameter of the coil is smaller in Example than in Comparative Example 1 even with equal turns. If the diameter of the coil is the same, there are more turns of the superconducting wire in Example than in Comparative Example 1.
As described above, in superconducting wire 10 according to the present embodiment, when the superconducting wire is wound in the form of a coil and cooled to very low temperature equal to or lower than the critical temperature, occurrence of separation in laminated structure 20 can be suppressed without reducing the critical current density.
In superconducting wire 10 according to the present embodiment, it is preferable that the ratio of the total width W3 of reinforcing layer 12 to width W1 of laminated structure 20 (W3×2/W1) is 1% or more and 15% or less in a cross section in the width direction of substrate 1. The ratio can be more preferably 3% or more and 15% or less, further preferably 5% or more and 12% or less.
In the second to fifth embodiments, a specific configuration for implementing superconducting wire 10 according to the first embodiment (see
(Configuration of Superconducting Wire)
As shown in
Laminated structure 20 and coating layer 9 are bonded together by a conductive bonding member 28. As the material of bonding member 28, for example, solder is used. As shown in
In superconducting wire 10A, bonding member 28 positioned on the side surfaces of laminated structure 20 forms reinforcing layer 12 in superconducting wire 10 shown in
With the configuration described above, in the second embodiment, when superconducting wire 10A wound in the form of a coil is cooled to very low temperature, tensile stress acting on laminated structure 20 can be distributed to bonding member 28 positioned on both side surfaces of laminated structure 20. Thus, occurrence of separation in laminated structure 20 can be suppressed. Since the thin-film coating layer 9 is disposed only on top surface 20A of laminated structure 20, increase in cross-section of the superconducting wire for improvement of tensile strength can be suppressed. As a result, occurrence of separation in superconducting wire 10A can be suppressed without reducing the critical current density.
(Method of Manufacturing Superconducting Wire)
In the laminated structure forming step (S10), first of all, a substrate preparation step (S11) is performed. Specifically, referring to
Next, an intermediate layer forming step (S12 in
Next, a superconducting material layer forming step (S13 in
Next, a protection layer forming step (S14 in
Next, a coating layer laminating step (S20 in
Next, coating layer 9 is laminated on one of top surface 20A and bottom surface 20B of laminated structure 20 using bonding member 28 such as solder. Coating layer 9 can be laminated by any method. Bonding member 28 may be melted by heating and, if necessary, pressed. For example, when coating layer 9 is laminated on top surface 20A of laminated structure 20, first, a mask layer is formed to cover bottom surface 20B of laminated structure 20. The mask layer can be formed by any method and can be applied, for example, by a coater or spraying. Next, laminated structure 20 and coating layer 9 are passed through a solder bath. Subsequently, the mask layer is removed from bottom surface 20B, and laminated structure 20 and coating layer 9 are integrally passed through between a pair of heating and pressing rollers.
Alternatively, first, bonding member 28 is formed on the main surface of coating layer 9 on the side opposed to top surface 20A of laminated structure 20. Subsequently, laminated structure 20, bonding member 28, and coating layer 9 are integrally passed through between a pair of heating and pressing rollers.
In both of the two methods above, since coating layer 9 protrudes from both side surfaces of laminated structure 20, the space between coating layer 9 and both side surfaces of laminated structure 20 is filled with solder. Reinforcing layer 12 (
(Modification to Second Embodiment)
Superconducting wire 10A# according to the present modification can be manufactured by laminating coating layer 9 on bottom surface 20B of laminated structure 20 in the coating layer laminating step (S20 in
(Configuration of Superconducting Wire)
As shown in
The prism-shaped metal member 30 is bonded to both side surfaces of laminated structure 20, for example, through a conductive bonding material such as a solder bonding material or a conductive adhesive. Bonding layer 32 is formed between metal member 30 and both side surfaces of laminated structure 20.
Coating layer 34 is provided so as to cover top surface 20A and bottom surface 20B of laminated structure 20 and also cover the outer peripheral surface of metal member 30. Coating layer 34 is formed of a foil or a plating layer made of a metal material. The thickness of coating layer 34 is about 20 μm to 100μ. The metal material that forms coating layer 34 is preferably, for example, copper or copper alloy.
In superconducting wire 10B, coating layer 34 positioned on the outer peripheral surface of metal member 30, bonding layer 32, and metal member 30 forms reinforcing layer 12 in superconducting wire 10 shown in
With the configuration described above, in the third embodiment, when superconducting wire 10B wound in the form of a coil is cooled to very low temperature, tensile stress acting on laminated structure 20 can be mainly distributed to metal member 30 positioned on both side surfaces of laminated structure 20. Thus, occurrence of separation in laminated structure 20 can be reduced. Accordingly, the thickness of coating layer 34 can be reduced, so that increase in cross section of the superconducting wire for improvement of tensile strength can be suppressed. As a result, occurrence of separation in superconducting wire 10B can be suppressed without reducing critical current density Jc.
(Method of Manufacturing Superconducting Wire)
First of all, the laminated structure forming step (S10) shown in
Finally, the coating layer plating step (S40) is performed. Specifically, coating layer 34 formed of a metal layer (plating layer) is formed on the outer peripheral surface of laminated structure 20 and metal member 30. As the step of forming coating layer 34, a step of integrally covering the outer peripheral surface of laminated structure 20 and metal member 30 with a foil made of a metal material may be performed in place of the above plating step.
(Modification to Third Embodiment)
As shown in
(Configuration of Superconducting Wire)
As shown in
Coating layer 36 is provided so as to cover top surface 20A and bottom surface 20B of laminated structure 20 and also cover the side surfaces of laminated structure 20. Coating layer 36 is formed of a plating layer made of a metal material. The thickness of coating layer 36 is about 20 μm to 100μ. The metal material that forms coating layer 36 is preferably, for example, copper or copper alloy.
Metal layer 38 is disposed on both side surfaces of laminated structure 20. Metal layer 38 has an extension portion extending above part of bottom surface 20B and top surface 20A of laminated structure 20. That is, metal layer 38 is formed integrally with coating layer 36 that covers top surface 20A and bottom surface 20B of laminated structure 20. Metal layer 38 is formed of a plating layer made of a metal material. The material that forms metal layer 38 is preferably, for example, copper or copper alloy.
In superconducting wire 10C, coating layer 36 and metal layer 38 positioned on the side surfaces of laminated structure 20 form reinforcing layer 12 in superconducting wire 10 shown in
With the configuration described above, in the fourth embodiment, when superconducting wire 10C wound in the form of a coil is cooled to very low temperature, tensile stress acting on laminated structure 20 can be distributed to metal layer 38 and coating layer 36 positioned on both side surfaces of laminated structure 20. Thus, occurrence of separation in laminated structure 20 can be suppressed. Furthermore, thin-film coating layer 36 is disposed on the top surface side and the bottom surface side of laminated structure 20, whereby increase in cross section of the superconducting wire for improvement of tensile strength can be suppressed. As a result, occurrence of separation in superconducting wire 10C can be suppressed without reducing the critical current density.
(Method of Manufacturing Superconducting Wire)
First of all, the laminated structure forming step (S10) shown in
Next, the metal layer plating step (S60) is performed. Specifically, first, as shown in
Subsequently, a plating layer (metal layer 38) is formed so as to cover coating layer 36 having mask layer 40 formed thereon. The plating layer has an extension portion extending onto part of top surface 20A and bottom surface 20B of laminated structure 20. It is noted that the plating layer may not be formed on the top surface side and the bottom surface side of laminated structure 20 as long as it is formed on both side surface sides of laminated structure 20. The plating layer may be formed by any method, for example, formed by electroplating. Subsequently, mask layer 40 is removed. Mask layer 40 can be removed by any method, for example, can be removed by etching. Thus, metal layer 38 formed of a plating layer can be formed on both side surfaces of laminated structure 20.
In the flowchart in
As shown in
Coating layer 42 is provided so as to cover the outer peripheral surface of laminated structure 20. Coating layer 42 is formed of a solder layer. In a cross section in the width direction of substrate 1, the thickness of coating layer 42 positioned on both side surfaces of laminated structure 20 is thicker than the thickness of coating layer 42 positioned on the top surface side and the bottom surface side of laminated structure 20.
In superconducting wire 10D, reinforcing layer 12 is formed with coating layer 42 positioned on both side surfaces of laminated structure 20. In other words, reinforcing layer 12 is formed integrally with coating layer 42.
With the configuration described above, in the fifth embodiment, when superconducting wire 10D wound in the form of a coil is cooled to very low temperature, tensile stress acting on laminated structure 20 can be distributed to coating layer 42 (solder layer) positioned on both side surfaces of laminated structure 20. Thus, occurrence of separation in laminated structure 20 can be suppressed. Furthermore, thin-film coating layer 36 is disposed on the top surface side and the bottom surface side of laminated structure 20, whereby increase in cross section of the superconducting wire for improvement of tensile strength can be increased. As a result, occurrence of separation in superconducting wire 10D can be suppressed without reducing the critical current density.
(Method of Manufacturing Superconducting Wire)
First of all, the laminated structure forming step (S10) shown in
It is understood that the embodiments and examples disclosed herein is illustrative in all respects and not limitative. The scope of the present invention is shown not by the foregoing embodiments and examples but by the clams, and it is intended that all equivalents to the claims and modifications within the scope of the claims are embraced.
1 substrate, 3 intermediate layer, 5 superconducting material layer, 7 protection layer, 9, 34, 36 coating layer, 10, 10A to 10D superconducting wire, 12 reinforcing layer, 20 laminated structure, 30 metal member, 32 bonding layer, 38 metal layer, 40 mask layer, 100 solder bath, 110 solder liquid, 112, 114 roll, 116, 118 ringer roll
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-100166 | May 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/055343 | 2/24/2016 | WO | 00 |
