Oxide superconductor wire, superconductor coil, and superconductor

Abstract

This oxide superconducting wire includes a tape-shaped metal substrate comprising a nickel alloy, an intermediate layer laminated on the metal substrate, and an oxide superconducting layer laminated on the intermediate layer, wherein the average KAM value of the metal substrate in a cross section along the longitudinal direction and the thickness direction of the metal substrate is within the range of 0.5-1.8°.

Description

Oxide superconducting wire, superconducting coil and superconducting conductor

[0001] The present invention relates to an oxide superconducting wire, a superconducting coil, and a superconducting conductor. This application claims priority to Japanese Patent Application No. 2024-056081, filed on March 29, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses an oxide superconducting wire comprising a tape-shaped metal substrate, an intermediate layer laminated on the metal substrate, and an oxide superconducting layer laminated on the intermediate layer.

[0003] Japanese Patent Application Publication No. 2020-166983

[0004] In the past, there was a problem that when excessive tensile stress was applied to an oxide superconducting wire in the longitudinal direction, the properties of the oxide superconducting wire were degraded. In general, an oxide superconducting layer has higher rigidity than a metal substrate and is less susceptible to elongation deformation. Therefore, when excessive tensile stress was applied to an oxide superconducting wire in the longitudinal direction, the oxide superconducting layer could not withstand the elongation deformation of the metal substrate, resulting in degradation of the oxide superconducting layer and a degradation of the superconducting properties of the oxide superconducting layer.

[0005] The present invention has been made in consideration of the above circumstances, and has as its object to provide an oxide superconducting wire, a superconducting coil and a superconducting conductor whose superconducting properties are unlikely to deteriorate even when a tensile stress is applied.

[0006] In order to solve the above problem, the oxide superconducting wire according to aspect 1 of the present invention comprises a tape-shaped metal substrate made of a nickel alloy, an intermediate layer laminated on the metal substrate, and an oxide superconducting layer laminated on the intermediate layer, and the average KAM value of the metal substrate in a cross section along the longitudinal direction and thickness direction of the metal substrate is within the range of 0.5 to 1.8°.

[0007] According to aspect 1 of the present invention, it is possible to realize an oxide superconducting wire whose superconducting properties are unlikely to deteriorate even when a tensile stress is applied.

[0008] In addition, in a second aspect of the present invention, in the oxide superconducting wire of the first aspect, the standard deviation of the average KAM value is within a range of 0.4 to 0.9°.

[0009] In addition, in a third aspect of the present invention, in the oxide superconducting wire of the first or second aspect, the relative standard deviation of the average KAM value is within a range of 0.5 to 0.8.

[0010] A superconducting coil according to a fourth aspect of the present invention is formed by winding the oxide superconducting wire according to any one of the first to third aspects.

[0011] In addition, a superconducting conductor according to aspect 5 of the present invention is formed by assembling a plurality of oxide superconducting wires according to any one of aspects 1 to 3.

[0012] According to the above aspects of the present invention, it is possible to provide an oxide superconducting wire, a superconducting coil, and a superconducting conductor whose superconducting properties are unlikely to deteriorate even when a tensile stress is applied.

[0013] Fig. 1 is a cross-sectional view showing an oxide superconducting wire according to an embodiment of the present invention. Fig. 2 is a diagram showing a measurement surface of a metal substrate for a KAM value. Fig. 3 is a perspective view of a superconducting coil using the oxide superconducting wire of Fig. 1. Fig. 4 is a diagram showing a superconducting conductor using the oxide superconducting wire of Fig. 1. Fig. 5 is a diagram showing another example of a superconducting conductor using the oxide superconducting wire of Fig. 1. Fig. 6 is a diagram showing another example of a superconducting conductor using the oxide superconducting wire of Fig. 1.

[0014] An oxide superconducting wire according to an embodiment of the present invention will now be described with reference to the drawings. As shown in Fig. 1, an oxide superconducting wire 10 according to this embodiment includes a metal substrate 11, an intermediate layer 12, an oxide superconducting layer 13, a protective layer 14, and a stabilizing layer 16. Hereinafter, the metal substrate 11, the intermediate layer 12, the oxide superconducting layer 13, and the protective layer 14 may be collectively referred to as a "superconducting laminate 15."

[0015] Each of the metal substrate 11, intermediate layer 12, oxide superconducting layer 13, and protective layer 14 is formed in a tape shape. The metal substrate 11, intermediate layer 12, oxide superconducting layer 13, and protective layer 14 are laminated in this order in the thickness direction of the metal substrate 11 (thickness direction of the oxide superconducting wire 10). The stabilization layer 16 covers the outer periphery of the superconducting laminate 15. The oxide superconducting wire 10 is tape-shaped.

[0016] (Directional Definition) In this embodiment, the positional relationship of each component will be described using an XYZ Cartesian coordinate system. The Z-axis direction (not shown in FIG. 1 ) is the direction along the longitudinal direction of the oxide superconducting wire 10. The Y-axis direction is perpendicular to the Z-axis direction and parallel to the thickness direction of the oxide superconducting wire 10. The Y-axis direction is also the direction in which the layers 11 to 14 of the superconducting laminate 15 are stacked. The X-axis direction is perpendicular to both the Z-axis direction and the Y-axis direction and parallel to the width direction of the oxide superconducting wire 10. In this specification, the X-axis direction may be referred to as the width direction X, the Y-axis direction as the thickness direction Y, and the Z-axis direction as the longitudinal direction Z. Furthermore, the direction from the metal substrate 11 toward the oxide superconducting layer 13 along the thickness direction Y is referred to as the +Y direction or upward. The direction opposite to the +Y direction is referred to as the -Y direction or downward. One direction along the width direction X is referred to as the +X direction or right side, and the direction opposite to the +X direction is referred to as the −X direction or left side.

[0017] A specific example of the metal constituting the metal substrate 11 is a nickel alloy such as Hastelloy (registered trademark). The thickness of the metal substrate 11 may be adjusted appropriately depending on the purpose, and is within the range of 10 to 1000 μm, for example.

[0018] The intermediate layer 12 is laminated on the metal substrate 11 (on the upper surface of the metal substrate 11). The configuration of the intermediate layer 12 is not limited to the example shown in FIG. 1 . For example, the intermediate layer 12 may have a multilayer structure. In this case, the intermediate layer 12 may have, in order from the metal substrate 11 toward the oxide superconducting layer 13, a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, and the like. These layers are not necessarily provided one by one; some layers may be omitted, or two or more layers of the same type may be repeatedly laminated. The intermediate layer 12 may be a metal oxide. By forming the oxide superconducting layer 13 on the upper surface of the intermediate layer 12 with excellent orientation, an oxide superconducting layer with excellent orientation can be easily obtained.

[0019] The oxide superconducting layer 13 is laminated on the intermediate layer 12 (on the upper surface of the intermediate layer 12). The oxide superconducting layer 13 is made of an oxide superconductor. Examples of the oxide superconductor that constitutes the oxide superconducting layer 13 include oxide superconductors represented by the general formula RE１ Ba ２ Cu ３ O ｙ Examples of the RE-Ba-Cu-O-based oxide superconductor (REBCO-based oxide superconductor) include RE123 (RE123). The rare earth element RE can be one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In the general formula of RE123, y is 7-x (oxygen deficiency amount x: approximately 0 to 1). The ratio of RE:Ba:Cu is not limited to 1:2:3 and may be non-stoichiometric. The thickness of the oxide superconducting layer 13 is, for example, within the range of 0.5 to 5 μm. The oxide superconducting layer 13 can be formed by a PLD (pulsed laser ablation) film formation method or the like.

[0020] Artificial pins made of a different material may be introduced as artificial crystal defects into the oxide superconducting layer 13. Examples of the different material used to introduce artificial pins into the oxide superconducting layer 13 include BaSnO ３ (BSO), BaZrO ３ (BZO), BaHfO ３ (BHO), BaTiO ３ (BTO), SnO ２ , TiO ２ , ZrO ２ , LaMnO ３ , ZnO, and the like.

[0021] The protective layer 14 is laminated on the oxide superconducting layer 13 (on the upper surface of the oxide superconducting layer 13). The protective layer 14 has functions such as bypassing overcurrent that occurs in the event of an accident and suppressing chemical reactions that occur between the oxide superconducting layer 13 and a layer provided on the protective layer 14. Examples of materials for the protective layer 14 include silver (Ag), copper (Cu), gold (Au), gold-silver alloys, other silver alloys, copper alloys, and gold alloys. The thickness of the protective layer 14 is, for example, within a range of 1 to 30 μm. The protective layer 14 may be composed of two or more types of metals or two or more metal layers. The protective layer 14 can be formed by vapor deposition, sputtering, or the like.

[0022] The stabilization layer 16 is formed around the entire periphery of the superconductor laminate 15. In other words, the stabilization layer 16 covers the top surface, bottom surface, and both side surfaces of the superconductor laminate 15. In this embodiment, the "top surface of the superconductor laminate 15" corresponds to the top surface of the protective layer 14, the "bottom surface of the superconductor laminate 15" corresponds to the bottom surface of the metal substrate 11, and the "side surface of the superconductor laminate 15" corresponds to the side surfaces of each of the layers 11 to 14. The stabilization layer 16 has functions such as bypassing overcurrents that occur in the event of an accident and mechanically reinforcing the oxide superconductor layer 13 and the protective layer 14. The stabilization layer 16 is made of, for example, a copper (Cu) plating layer. The thickness of the stabilization layer 16 is not particularly limited, but is, for example, in the range of 1 to 300 μm.

[0023] In general, the oxide superconducting layer 13 has higher rigidity than a metal substrate and is less susceptible to elongation deformation. Therefore, when excessive tensile stress is applied to the oxide superconducting wire 10 along the longitudinal direction, the oxide superconducting layer 13 cannot withstand the elongation deformation of the metal substrate 11, and the oxide superconducting layer 13 deteriorates, which may result in a decrease in the superconducting properties of the oxide superconducting layer 13. This deterioration of the oxide superconducting layer 13 may be caused by, for example, cracks or peeling of the oxide superconducting layer 13. Furthermore, while it is possible to improve the strength of the oxide superconducting wire 10 by increasing the thickness of the metal substrate 11 on which the oxide superconducting layer 13 is provided, this may increase the cross-sectional area of ​​the oxide superconducting wire 10, which may result in a decrease in current density.

[0024] As a result of extensive research by the present inventors into this problem, it has been found that the degradation of superconducting properties when tensile stress is applied can be suppressed by setting the KAM value (Kernel Average Misorientation value), which is a parameter of the structure of the metal substrate 11, within an appropriate range. Below, an appropriate value for the KAM value of the metal substrate 11 will be described using specific examples. Note that the present invention is not limited to the following examples.

[0025] Oxide superconducting wires of Examples 1 to 10 and Comparative Examples 1 to 3 were fabricated. These oxide superconducting wires differ from one another in the average KAM value of the metal substrate. The conditions other than the KAM value are common to the fabricated oxide superconducting wires, as listed below. The KAM value of the metal substrate 11 can be adjusted by adjusting the conditions (rolling ratio, rolling temperature, crystal grain size of the substrate before rolling, etc.) when rolling the metal substrate, and the conditions (temperature, time, etc.) when forming the intermediate layer and oxide superconducting layer. Generally, the higher the rolling ratio when rolling the metal substrate, the higher the KAM value, and the lower the rolling ratio, the lower the KAM value. Furthermore, the higher the temperature the substrate experiences, the lower the KAM value, and the lower the temperature, the higher the KAM value. Material of metal substrate 11: Hastelloy; Thickness of metal substrate 11: 50 μm; Width of metal substrate 11: 4 mm; Material of oxide superconducting layer 13: EuBa ２ Cu ３ O ｙ +BHO Thickness of oxide superconducting layer 13: 2 μm Method of forming oxide superconducting layer 13: PLD deposition Material of protective layer 14: Ag Thickness of protective layer 14: 2 μm Method of forming protective layer 14: sputtering deposition Material of stabilizing layer 16: Cu Thickness of stabilizing layer 16: 5 μm Method of forming stabilizing layer 16: plating deposition Note that a commonly used material was adopted as the intermediate layer 12.

[0026] Table 1 summarizes the results of measuring the average KAM value of the metal substrate, the standard deviation of the KAM value, the relative standard deviation of the KAM value, and Ic / Ic0 for each of the oxide superconducting wires of Examples 1 to 10 and Comparative Examples 1 to 3.

[0027]

[0028] <KAM Value> The average KAM value of the metal substrate in the produced oxide superconducting wire was measured using a reflection EBSD (electron backscatter diffraction) method with an FE-SEM. The KAM value of the metal substrate was measured on a measurement surface M (see Figure 2) that was revealed by mechanically polishing and Ar ion milling a cross section of the metal substrate along the longitudinal and thickness directions.

[0029] The sample observation conditions in the EBSD method were as follows: Acceleration voltage: 15 kV, Probe current: 15 nA, Sample tilt angle: 70°, Number of sample observation points: 1 arbitrary point, Interval: 0.15 μm / step. The sample observation range was 45 × 45 μm. The electron beam was scanned in 0.15 μm increments within the 45 × 45 μm field of view to obtain information on the crystal orientation within the two-dimensional plane. In the obtained data, the average value of the angle of deviation of the crystal orientation between one point of interest (F1) and all points (F2) adjacent to F1 was taken as the KAM value. The KAM value of the entire field of view was measured while moving the position of F1, and the average of the measured KAM values ​​was taken as the average KAM value for each sample. Note that if the misorientation between F1 and F2 was 5° or more, it was considered that a grain boundary was included between F1 and F2, and the KAM value was excluded from the calculation of the average KAM value. In other words, the average KAM value can be said to be a value that quantifies the degree of crystal distortion (the angle of deviation of crystal orientation) between F1 and F2 within the same crystal. In measuring the KAM value this time, the measurement interval is set so that the resolution is about 1 / 5 or less of the grain size of one crystal grain (average grain size). However, the measurement interval may be changed appropriately depending on the grain size, etc. The average grain size is, for example, the average grain size measured by the reflection EBSD method.

[0030] For each sample, the standard deviation, which indicates the variation from the average KAM value, and the relative standard deviation, which is the standard deviation divided by the average value, were calculated. The relative standard deviation allows the variation between the average KAM value data for each sample to be evaluated relatively.

[0031] <Decrease in Critical Current Value After Tensile Test (Ic / Ic0)> For the oxide superconducting wires of each Example and Comparative Example, the critical current value (Ic0) was measured when the oxide superconducting wire was in its natural length in an initial state, and then a tensile load of 550 MPa was applied in the longitudinal direction. The critical current value (Ic) after the tensile test was measured, and the decrease in critical current value after the tensile test (Ic / Ic0) was calculated.

[0032] <Judgment> If the value of Ic / Ic0 is 0.99 or more, it is judged that "the oxide superconducting layer has not deteriorated" and the judgment is "pass," whereas if it is less than 0.99, it is judged that "the oxide superconducting layer has deteriorated" and the judgment is "fail." In addition, considering that the measurement accuracy of the critical current value is about 1%, an Ic / Ic0 value of 0.99 or more is judged as pass.

[0033] In Examples 1 to 10, where the average KAM value was 0.5 to 1.8°, the Ic / Ic0 was 0.99 or higher, and the oxide superconducting layer did not deteriorate due to tensile stress, maintaining its superconducting properties. In contrast, in Comparative Examples 1 and 2, where the average KAM value was 0.3 to 0.4°, the Ic / Ic0 was less than 0.99, suggesting that the oxide superconducting layer deteriorated due to tensile stress. In Comparative Example 3, although the process conditions were adjusted to achieve an average KAM value of 1.9°, the crystal growth of the oxide superconducting layer did not proceed properly, and the initial critical current value of the sample was lower than that of the other samples. Adjusting the process conditions to increase the crystallinity of the oxide superconducting layer failed to increase the average KAM value, making it impossible to achieve both adjustment of the average KAM value and good crystallinity of the superconducting layer. For this reason, Comparative Example 3, where the average KAM value was 1.9°, was judged to be unsuccessful.

[0034] It can be seen that in samples with an average KAM value of 1.8° or less, the rate of decrease in the critical current value after the tensile test decreases as the average KAM value increases. Therefore, in oxide superconducting wires whose critical current value in the initial state is within an appropriate range, it is thought that the larger the average KAM value, the less likely the oxide superconducting layer will deteriorate due to tensile stress.

[0035] It is believed that changes in the average KAM value, i.e., changes in the degree of strain in one crystal of the metal substrate, affect the tensile properties of the metal substrate and the tensile stability of the intermediate layer and oxide superconducting layer formed on the metal substrate. Therefore, it has been discovered that the average KAM value can be used as an indicator of the tensile stability of an oxide superconducting wire. In particular, tensile stress may act in the longitudinal direction of an oxide superconducting wire during processing into a coil or superconducting conductor or during use. Therefore, by using the average KAM value measured at a cross section along the longitudinal direction of the metal substrate, which corresponds to this tensile direction, as an indicator, the characteristics of the oxide superconducting wire with respect to tensile stress can be more accurately evaluated.

[0036] Here, when focusing on the standard deviation of the KAM values ​​of each sample, the standard deviation increases as the average KAM value increases. Furthermore, in Examples 1 to 10, the standard deviation is in the range of 0.4 to 0.9°. Therefore, as in Comparative Examples 1 and 2, when the variation in strain within a single crystal is excessively small, the rate of decrease in the critical current value after tensile testing increases. Next, when focusing on the relative standard deviation of the KAM values ​​of each sample, when the average KAM value is in the range of 0.5 to 1.8°, the relative standard deviation is in the range of 0.5 to 0.8. Furthermore, when the average KAM value is in the range of 0.5 to 1.8°, the larger the average KAM value, the smaller the relative standard deviation. Therefore, in Examples 1 to 10, it is considered that as the average KAM value increases, the variation in the individual KAM values ​​becomes relatively smaller.

[0037] As described above, the oxide superconducting wire 10 of this embodiment comprises a tape-shaped metal substrate 11 made of a nickel alloy, an intermediate layer 12 laminated on the metal substrate 11, and an oxide superconducting layer 13 laminated on the intermediate layer 12, and the average KAM value of the metal substrate 11 in a cross section along the longitudinal direction and thickness direction of the metal substrate 11 is in the range of 0.5 to 1.8°.

[0038] According to this configuration, when a tensile stress is applied in the longitudinal direction, the oxide superconducting layer 13 is less likely to deteriorate, which would lead to a decrease in the superconducting properties. Therefore, an oxide superconducting wire whose superconducting properties are less likely to deteriorate even when a tensile stress is applied in the longitudinal direction can be realized. Furthermore, the average KAM value of the metal substrate 11 makes it possible to quantitatively measure minute changes in the tensile properties of the metal substrate 11 and minute changes in the tensile stability of the intermediate layer 12 and the oxide superconducting layer 13 formed on the metal substrate 11.

[0039] Furthermore, when the average KAM value is within the range of 0.5 to 1.8°, the standard deviation of the average KAM value is within the range of 0.4 to 0.9°. Furthermore, when the average KAM value is within the range of 0.5 to 1.8°, the relative standard deviation of the average KAM value is within the range of 0.5 to 0.8. When the standard deviation or relative standard deviation of the average KAM value is within the above range, the superconducting properties are less likely to deteriorate after a tensile test.

[0040] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0041] For example, the oxide superconducting wire 10 does not need to include the protective layer 14 or the stabilizing layer 16 .

[0042] Furthermore, as shown in FIG. 3 , a pancake-shaped multilayer wound coil (superconducting coil 100) may be formed by winding and stacking a tape-shaped oxide superconducting wire 10 many times in the thickness direction. For example, the superconducting coil 100 includes a laminate in which oxide superconducting wire 10 and metal tapes are alternately stacked, and an impregnated resin layer. The impregnated resin layer impregnates the laminate and covers the outer surface of the laminate. Examples of resins that constitute the impregnated resin layer include epoxy resin and phenolic resin. The superconducting coil 100 can be manufactured, for example, by co-winding the oxide superconducting wire 10 coated with a resin (e.g., epoxy resin) and the metal tape to form a coil, and then curing the resin by heating or the like. The superconducting coil 100 may also be manufactured by co-winding the oxide superconducting wire 10 and the metal tape to form a coil, impregnating the coil with the resin under reduced pressure, and then curing the resin by heating or the like. Such a superconducting coil 100 can be used in a superconducting magnet, a superconducting motor, or the like.

[0043] 4A to 4C, superconducting conductors 101, 102, and 103 may be formed by assembling a plurality of tape-shaped oxide superconducting wires 10. Although a current of several tens to several hundreds of amperes can be passed through a single oxide superconducting wire 10, a larger current can be passed by bundling a plurality of oxide superconducting wires 10 to form superconducting conductors 101, 102, and 103. Furthermore, the superconducting conductors 101, 102, and 103 can be easily wound.

[0044] As shown in Fig. 4A, one example of a superconducting conductor is a spiral-type superconducting conductor 101 in which N tape-shaped oxide superconducting wires 10-1 to 10-n are wound spirally around the outer periphery of a core material C, and a coating J is further provided on the outer periphery of the core material C. As shown in Fig. 4B, another example of a superconducting conductor is a laminated-type superconducting conductor 102 in which a plurality of oxide superconducting wires 10 are stacked and the outer periphery of the stack is coated with a stabilizing material S. As shown in Fig. 4C, another example of a superconducting conductor is a ROEBEL-type superconducting conductor 103 in which a plurality of oxide superconducting wires 10 bundled with a bundling portion B are patterned into a serpentine shape and twisted together.

[0045] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention.

[0046] REFERENCE SIGNS LIST 10: oxide superconducting wire 11: metal substrate 12: intermediate layer 13: oxide superconducting layer 100: superconducting coil 101, 102, 103: superconducting conductor

Claims

1. An oxide superconducting wire comprising: a tape-shaped metal substrate made of a nickel alloy; an intermediate layer laminated on the metal substrate; and an oxide superconducting layer laminated on the intermediate layer, wherein the average KAM value of the metal substrate in a cross section along the longitudinal direction and thickness direction of the metal substrate is within the range of 0.5 to 1.8°.

2. The oxide superconducting wire according to claim 1, wherein the standard deviation of the average KAM value is within a range of 0.4 to 0.9°.

3. The oxide superconducting wire according to claim 1 or 2, wherein the relative standard deviation of the average KAM value is within a range of 0.5 to 0.

8.

4. A superconducting coil formed by winding the oxide superconducting wire according to any one of claims 1 to 3.

5. A superconducting conductor assembled using a plurality of the oxide superconducting wires according to any one of claims 1 to 3.

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