JP2008311222A - Superconductive wire and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconductive wire showing excellent critical current characteristics with surface characteristics of a base body improved, and its manufacturing method. <P>SOLUTION: The superconductive wire equipped with a base body 1 containing a metal substrate, and a superconductive layer formed on the base body, is manufactured by applying polish on a metal plate with a high rolling treatment process of rolling reduction with 90% or more and an oriented heat treatment process applied, and removing a protrusion part A formed on a grain boundary, as well as flattening a substance structuring the protrusion part deposited in a groove part B, and then forming a superconductive layer on a base body surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a superconducting wire and a method for manufacturing the same, and more particularly to a superconducting wire exhibiting excellent superconducting characteristics by removing protrusions at a grain boundary and filling a groove, and a method for manufacturing the same.

A high-temperature superconducting wire using a metal substrate generally forms a three-layer structure of CeO ₂ / YSZ / CeO ₂ from the lower layer side as an intermediate layer on a biaxially oriented polycrystalline metal substrate. A film having a superconducting layer formed thereon is known (for example, see Patent Documents 1 and 2). The superconducting layer is an oxide high temperature superconductor, and its composition is RE-Ba-Cu-O (RE: rare earth metal). On the superconducting layer, a metal such as silver is deposited as a stabilizing metal.

  However, in a superconducting wire using an oriented metal substrate, the critical current density of the superconducting layer is lower than the original critical current density obtained from the single crystal of the superconductor. It has become a problem from the viewpoint of cost reduction and cost reduction.

  In general, in the manufacture of high-temperature oxide superconducting wires, an oriented metal substrate is strongly rolled into a tape shape and subjected to orientation heat treatment to biaxially orient the crystal grains of the surface layer. This biaxially oriented substrate When the intermediate layer is epitaxially grown and the superconducting layer is further epitaxially grown on the intermediate layer, the critical current characteristic of the superconducting layer is determined by the biaxial orientation of each crystal grain in the superconducting layer (superconducting crystal axis a-axis and b-axis are in-plane, and the directions of the a-axis and b-axis are aligned for each crystal grain). It is known that the critical current characteristic is low when the orientation of crystal grains is greatly shifted (state where a large tilt grain boundary exists) and the orientation is low.

  The degree of orientation of a conventional oriented metal substrate is Δφ of about 7 ° to 10 ° when viewed from the half-value width of the X-ray pole figure. When an intermediate layer is formed on this, Δφ on the surface of the intermediate layer is about 6 °. Furthermore, when a superconducting layer is formed, Δφ is macroscopically aligned to about 6 °, but a large-angle grain boundary is generated in the superconducting layer in a part of the surface layer. The result was lower than the original characteristics.

  In order to improve the low critical current characteristics of such a superconducting layer, it is necessary to increase its crystal orientation. To that end, the surface characteristics of the oriented metal substrate, which is the original (template), are used for the superconducting layer orientation. It needs to be optimized.

In addition, there exist patent documents 3-9 as prior well-known literature regarding the surface of a superconducting wire, These are only described about the grinding | polishing method and surface roughness of a superconducting material.
Japanese Patent Application No. 2005-100635 Japanese Patent Application No. 11-3620 Japanese Patent Application No. 2005-56754 Japanese Patent Application No. 2005-5089 Japanese Patent Application No. 11-329118 Japanese Patent Application No. 10-269865 Japanese Patent Application No. 06-251649 Japanese Patent Application No. 06-114812 Japanese Patent Application No. 05-250931

  The present invention has been made under the circumstances as described above, and an object thereof is to provide a superconducting wire exhibiting excellent critical current characteristics by improving the surface characteristics of a substrate and a method for manufacturing the same.

  In order to solve the above problems, a first aspect of the present invention is a superconducting wire comprising a base including a metal substrate and a superconducting layer formed on the base, wherein the surface of the base is a crystal grain boundary. There is provided a superconducting wire having a groove portion, wherein the groove portion is filled with a deposit. Thus, the flatness of the substrate surface is improved by filling the grooves on the substrate surface with deposits.

  In such a superconducting wire according to the first aspect of the present invention, the surface of the base body is fully oriented in {100} <001> or the deviation angle of the crystal axis from <001> is 25 ° or less. Can be. Thus, by aligning the crystal orientation in the direction in which current flows (the rolling direction of the metal substrate), the current easily flows in the superconducting layer formed thereon. An intermediate layer can be formed on the surface of the substrate. Here, by forming the intermediate layer, diffusion of metal atoms from the metal substrate to the superconducting layer can be prevented. Further, the surface of the substrate may be made of one kind of metal selected from the group consisting of Ni, Fe, Cu, and Ag or an alloy containing the same. Since these metals are cubic crystals, the crystal axes are easily oriented.

  The difference between the surface roughness Ra1 in the crystal grains not including the groove on the surface of the substrate and the surface roughness Ra2 of the crystal grain boundary including the groove is preferably 50 nm or less. Thus, by reducing the difference between the crystal grains and the crystal grain boundaries, the roughness of the entire substrate surface is made uniform.

  According to a second aspect of the present invention, there is provided a rolling process step for subjecting a metal plate to a strong rolling process at a rolling reduction of 90% or more, and an orientation process for subjecting the metal plate subjected to the rolling process to an orientation heat treatment in a reducing atmosphere. A heat treatment step, and polishing the metal plate having projections and grooves on the crystal grain boundaries that have been subjected to the orientation heat treatment, removing the projections, and forming a substance constituting the removed projections A superconducting process comprising: a polishing / depositing step for depositing in a groove on the surface of the metal plate; and a superconducting layer forming step for forming a superconducting layer on the metal plate subjected to the polishing / deposition step. A method of manufacturing a wire is provided. Thus, the flatness of the substrate surface is improved by filling the grooves on the substrate surface by the deposition process.

  In this case, the polishing step can be performed by a polishing method using mechanical polishing, chemical mechanical polishing, or a combination thereof.

  According to a third aspect of the present invention, there is provided a rolling process for subjecting a metal plate to a strong rolling process at a reduction rate of 90% or more, and an orientation for subjecting the metal sheet subjected to the rolling process to an orientation heat treatment in a reducing atmosphere. A polishing process for polishing the metal plate having the grain boundary protrusions and grooves on the surface, and removing the protrusions, and performing a plating treatment in the grooves. And a superconducting layer forming step of forming a superconducting layer on the metal plate on which the plating process has been performed. As described above, the flatness of the body surface is improved by filling the grooves on the surface of the base body by the deposition process by plating.

  In this case, the polishing step can be performed by a polishing method using electrolytic polishing, chemical polishing, mechanical polishing, chemical mechanical polishing, or a combination thereof. For example, polishing can be performed by electropolishing, chemical polishing, or a combination thereof, or after polishing by mechanical polishing, chemical mechanical polishing, or a combination thereof, electrolytic polishing, chemical polishing, or a combination thereof Polishing can be performed. In addition, the plating process may be performed after depositing a substance constituting the protrusion removed by mechanical polishing or chemical mechanical polishing in the groove on the surface of the metal plate.

  In the above method for manufacturing a superconducting wire, an intermediate layer can be formed on the surface of the metal plate before forming the superconducting layer. Here, by forming the intermediate layer, diffusion of metal atoms from the metal substrate to the superconducting layer can be prevented. Further, the surface of the intermediate layer can be polished. Thus, by further polishing the surface of the intermediate layer, the surface of the intermediate layer can be further flattened, and the superconducting characteristics of the superconducting layer can be improved.

  According to the present invention, the surface of the substrate is polished and the inside of the groove is filled with a deposit, so that the flatness of the substrate surface is improved, and a superconducting layer is formed on the substrate, thereby forming a superconducting wire with excellent superconducting characteristics. Can be provided.

  Hereinafter, embodiments of the present invention will be described.

  A superconducting wire according to an embodiment of the present invention is formed by forming a superconducting layer on a biaxially oriented metal substrate, and in order to improve the superconducting characteristics, a so-called crystal grain boundary on the surface of the substrate including the metal substrate is called It was made paying attention to the projection part and groove part called a "groove".

  In the present embodiment, it is desirable that at least the surface of the metal substrate is nickel or an alloy thereof, iron or an alloy thereof, copper or an alloy thereof, silver or an alloy thereof. Examples of nickel or an alloy thereof include Ni-W alloys such as Ni-3 at% W, Ni-5 at% W, Ni-7 at% W, Ni-Co, Ni-Fe, Ni-Mn, Ni-Cr, Ni- V etc. can be mentioned. Examples of iron or an alloy thereof include Fe—Cr, Fe—Co, Fe—Mn, Fe—Cu, and Fe—Sn. Examples of copper or an alloy thereof include Cu—Cr, Cu—Mo, Cu—W, Cu—V, and Cu—Sn. Examples of silver or an alloy thereof include Ag-Mn, Ag-Mg, Ag-Mo, and Ag-Cr.

  The surface metal of these metal substrates has the advantage that the crystal system belongs to the face-centered cubic crystal system and is easy to perform strong rolling. By such a strong rolling process and heat treatment, the surface is biaxially oriented and can be suitably used as a base for forming a superconducting layer.

  Further, in order to increase the strength and heat resistance of the metal substrate, or to lower the magnetism of the metal substrate, a metal different from the surface layer can be used for the core portion of the substrate. Here, as a core material different from the surface layer, Ni-W alloy, Ni-Fe alloy, Ni-Mn alloy, Ni-Co alloy, Ni-Mg alloy, Ni-V alloy, Ni-Co, etc. heat resistance and high strength Any metal having low magnetic properties can be used. Since the metal as the core material has higher strength than the surface metal, it is possible to improve the strength, for example, with respect to substrates having the same thickness as compared with a substrate not combined with a substrate having the same thickness.

  In order to make the surface metal biaxially oriented, the metal substrate as described above is subjected to strong rolling at a processing rate of 90% or more, and then heat-treated at 500 ° C. or more in a reducing atmosphere. Here, a particularly desirable orientation heat treatment is performed by flowing a reducing gas in which about 3% to 7% of hydrogen is mixed with argon gas into a heat treatment furnace, and the heat treatment temperature is between 900 ° C. and 1200 ° C., and the substrate is exposed to that heat treatment temperature. The time is selected from the balance between the orientation rate, the degree of orientation, and the size of the surface crystal grain size, but is at least 10 minutes.

  The “working rate” at a working rate of 90% or more is a “rolling rate” in rolling, and is a value obtained by dividing the difference in thickness before and after rolling by the thickness before rolling and multiplying by 100. It is.

  By such a strong rolling process and orientation heat treatment, the surface of the metal substrate can be biaxially or almost biaxially oriented in {100} <001>. Thus, by aligning the crystal orientation in the direction in which the current flows (the rolling direction of the metal substrate), the current can easily flow through the superconducting layer formed thereon, and the critical current can be improved.

  However, when the two processes of the strong rolling process and the orientation heat treatment are performed in this manner, the so-called “groove” projections are formed on the surface of the metal substrate, as shown in FIG. A part A and a groove part B are generated. The depth of the groove B is considered to be deeper as the heat treatment temperature is higher and / or the heat treatment time is longer. The presence of such “grooves” causes cracks in the intermediate layer when the intermediate layer is formed on the surface of the metal substrate, or causes growth of giant crystal grains with low superconducting characteristics when the superconducting layer is formed. I will let you.

  In the present embodiment, such a problem is solved by polishing the surface of the metal substrate after the alignment heat treatment. That is, the surface of the oriented metal substrate 1 that is biaxially or substantially biaxially oriented is subjected to a polishing process such as mechanical polishing, chemical mechanical polishing, or a combination thereof. As a result, the protrusion A is removed as shown in FIG. 1B, and the groove B is filled with the deposit C as shown in FIG.

  Here, that the groove B is substantially filled with the deposit C means that the surface roughness Ra2 of the region 3 (10 μm square) including the groove of the groove shown in FIG. 2 to be described later is 50 nm or less. .

  In this case, the deposit filling the groove portion B is a polishing rod of the protruding portion A removed by polishing, but may include a part of the abrasive grains. Any deposit is firmly deposited in the groove B and is not detached from the groove B in the subsequent cleaning process.

  Deposits can be analyzed by ICP (Inductively Coupled Plasma) analysis, EDX (energy dispersive X-ray analysis), SEM (scanning electron microscope) & EPMA (X-ray microanalyzer), etc. It is.

  As a polishing method, electrolytic polishing, chemical polishing, or a combination thereof may be employed. However, the protrusion A can be removed by these polishing, but the groove B cannot be filled. . In this case, after the polishing treatment, it is necessary to fill the groove B separately by a surface treatment such as plating. In this case, the flatness can be further improved by performing electrolytic polishing or chemical polishing after performing mechanical polishing or chemical mechanical polishing, and then performing surface treatment such as plating. Electropolishing has the advantages of high processing speed and low processing cost.

  Here, regarding mechanical polishing, in mechanical polishing, the abrasive grains are preferably diamond grains or oxide grains, particularly aluminum oxide, cerium oxide, chromium oxide, zirconium oxide, iron oxide, etc., and the solution (polishing liquid) is water or Surfactants, oils, organic solvents and mixtures thereof, or solutions in which water is mixed with an acid such as formic acid, acetic acid or nitric acid, or an alkali such as sodium hydroxide in water, are especially soapy water. desirable.

  In chemical polishing, the polishing liquid is a chemical solution that chemically reacts with the substrate surface, such as nitric acid, sulfuric acid, formic acid, acetic acid, hydrochloric acid, hydrofluoric acid, chromic acid, hydrogen peroxide, oxalic acid, tetraphosphoric acid, glacial acetic acid, etc. Or a mixed solution thereof, and a solution obtained by further mixing an accelerator such as saturated alcohol or sulfonic acid with the mixed solution.

  In chemical mechanical polishing, the abrasive grains may be the above-mentioned mechanically polished grains, and a polishing solution (slurry) containing a chemical polishing solution is used there.

  In electrolytic polishing, a substrate is immersed in an electrolytic solution, and the substrate surface is polished by an electrolytic reaction by energizing the substrate as an anode. This electrolytic solution may be an acid or an alkali, and nitric acid, phosphoric acid, chromic acid, hydrogen peroxide, potassium hydroxide, potassium cyanide and the like are particularly desirable.

  By performing the above-described polishing treatment (in some cases, subsequent plating treatment), the flatness is greatly improved, and the crystal grains of the intermediate layer and the superconducting layer formed thereon are flattened. Thus, the degree of orientation is improved, and the characteristics of the superconducting wire can be remarkably enhanced.

  As shown in FIG. 2, the flatness of the substrate surface is determined by the surface roughness Ra1 of the region 4 (10 μm square) not including the groove in the crystal and the region 3 (10 μm) in which the groove of the groove having a length of 10 μm or more is filled. The difference from the surface roughness Ra2 of the four sides) is preferably 50 nm or less, more preferably 10 nm or less, thereby preventing the occurrence of cracks due to grain boundaries due to the formation of the intermediate layer or the superconducting layer, The crystal grain size of the superconducting layer can be further refined, and the superconducting characteristics are remarkably improved.

  In particular, cracks (cracks often found in the vicinity of crystal grain boundaries of the underlying oriented metal substrate) that occur in the intermediate layer can be eliminated, so that superconducting properties are maintained well even under conditions such as bending as a superconducting wire. It becomes possible.

  The surface roughness Ra is the arithmetic average roughness Ra in the “amplitude average parameter in the height direction” of the surface roughness parameter defined in JIS B 0601-2001.

  The state where the groove on the substrate surface is filled can be confirmed by SEM or a laser microscope.

  An intermediate layer can be formed on the metal substrate. By forming the intermediate layer, diffusion of metal atoms from the metal substrate to the superconducting layer can be prevented. It is desirable to polish the intermediate layer as well. It is possible to form an intermediate layer with good flatness by polishing the surface of the metal substrate, but the surface of the intermediate layer can be further flattened by further polishing the surface of the intermediate layer. The superconducting properties of can be improved.

  As the intermediate layer, an oxide, particularly an oxide of a metal constituting the surface of the metal substrate can be used.

EXAMPLES Examples of the present invention will be shown below, and the present invention will be specifically described.

Example 1
FIG. 3 is a cross-sectional configuration diagram of a superconducting wire using an oriented metal substrate according to an embodiment of the present invention. In FIG. 3, three intermediate layers 12 having a total thickness of 300 μm are formed on an oriented metal substrate 11 having a thickness of 100 μm. A superconducting layer 13 having a thickness of 1 μm and a thickness of about 5 μm are formed on the intermediate layer 12. A silver layer 14 is formed to constitute a superconducting wire.

  The superconducting wire shown in FIG. 3 is manufactured as follows. First, a commercially available round bar made of Ni-5 at% W having an outer diameter of 25 mm and a length of 1000 mm is rolled to a thickness of 0.1 mm so as to achieve a rolling rate of 95%, and the width is further increased. Slit to 10 mm.

  The tape wire was attached to a reel-to-reel type continuous alignment heat treatment apparatus (furnace length 2 m) for a length of 200 m, and subjected to alignment heat treatment at 1100 ° C. at a conveyance speed of 3 m / hour. At this time, the inside of the furnace was biaxially oriented by reducing heat treatment in an argon gas mixed gas atmosphere of 3% hydrogen.

  When the surface of the tape wire subjected to orientation heat treatment as described above was examined, the orientation rate of the (100) crystal axis P was 99% with an X-ray diffractometer, and the biaxial crystal orientation degree Δφ = 6. It was 7 °.

  Here, the orientation rate of crystal grains is the following formula when the intensity of the (111) axis and the (200) axis is P1 and P2, respectively, as a diffraction intensity ratio in so-called θ-2θ measurement with an X-ray diffractometer. P represented.

P = [P2 / (P1 + P2)] × 100 (%)
The case where P exceeds about 90% is called high orientation.

  Further, a projection called a groove is seen at the crystal grain boundary from the observation with a laser microscope, and the surface roughness Ra2 of 10 μm square including the groove is 270 nm by the atomic force microscope (AFM), and the groove is included. The 10 μm-square surface roughness Ra1 of the portion not present (inside the crystal grains) was 28 nm.

  The surface of the oriented metal substrate 11 thus obtained was mechanically polished using a continuous mechanical polishing apparatus shown in FIG.

  That is, the oriented metal substrate 11 from the supply drum 21 is polished in the polishing chamber 22. A support base 23 and a polishing head 24 are disposed in the polishing chamber 22, and polishing slurry is supplied to the polishing head 24 from a slurry supplier 25. The oriented metal substrate 11 is continuously polished while running between the support base 23 and the polishing head 24.

  The polished alignment metal substrate 11 exits the polishing chamber 22 and enters the cleaning chamber 26, is cleaned by the cleaning machine 27, and is then dried by the air knife 29 in the drying chamber 28. The dried oriented metal substrate 11 is wound around a winding drum 30.

  For polishing, two types of abrasives with different particle sizes were prepared. The abrasive is a slurry mainly composed of aluminum oxide fine particles (particle size of about 1 μm) and water (a mixture of abrasive particles), and similarly a slurry mainly composed of aluminum oxide fine particles (particle size of about 0.02 μm) and water. Met.

  The continuous mechanical polishing apparatus shown in FIG. 4 is capable of continuously transporting tape wires in a reel-to-reel manner, and has a mechanism capable of adjusting the tension in cooperation between the feed drum 21 and the take-up drum 30 during transport. I have. Two disk-shaped polishing heads 24 are set on the pass line of the oriented metal substrate 11 of this apparatus, and the polishing head 24 is rotated while being pressed against the oriented metal substrate 11 to flow the slurry. Was carried out to carry out continuous polishing. The polishing head 24 is a disk with diamond fine particles attached to its surface. In continuous polishing, a slurry having a larger particle diameter is applied to the front stage and a slurry having a smaller particle diameter is applied to the rear stage.

  A portion of the alignment metal substrate 11 polished as described above was taken out, and its surface roughness was measured with an AFM apparatus, and the degree of alignment was measured with an X-ray pole figure. In addition, when the surface of the alignment metal substrate 11 was observed by SEM, it was confirmed that the groove part was filled. This is because the polishing ridges of the protrusions scraped off by polishing are firmly accumulated in the grooves.

A seed layer made of CeO ₂ is formed on the surface of the alignment metal substrate 11 thus polished by heating the alignment substrate temperature at the evaporation site to about 800 ° C. using a continuous electron beam evaporation apparatus. The film was formed to a thickness of about 100 nm under the conditions of a rate of 1 nm / s and a degree of vacuum of about 1 × 10 ⁻² Pa. On this seed layer, a YSZ (yttria stabilized zirconia) film having a thickness of 100 nm is formed by sputtering at 700 ° C. under a vacuum degree of about 5 × 10 ⁻³ Pa. A CeO ₂ film was formed to a thickness of about 100 nm by a sputtering method to form an intermediate layer having a three-layer structure.

  Next, the substrate was heated to 850 ° C., and a YBCO superconductor was formed on the intermediate layer to a thickness of about 1 μm by metal organic vapor phase epitaxy (MOCVD method).

  Then, silver was deposited on the upper surface of the YBCO superconducting layer to a thickness of about 1 μm using a high frequency sputtering apparatus to form an electrode part.

  In order to measure the critical current by the four-terminal method on the silver surface of the superconducting wire thus obtained, the current lead wire and the voltage lead wire are soldered and energized while immersed in liquid nitrogen. Was measured.

In order to investigate the influence of superconducting properties due to groove grooves in the crystal grain boundaries on the substrate surface, the polishing head pressure and the particle diameter in the above polishing process are the same, the conveying speed is changed, and the groove groove portion is filled. Experiments were made so that there were multiple levels. In order to quantify how the groove of the groove is filled, the difference between Ra1 in the region 4 not including the groove and Ra2 in the region 3 including the groove in FIG. 2 is about 130 nm, about 100 nm, about 80 nm, about 60 nm, about 50 nm. A superconducting wire was manufactured in the same process as described above so that the thickness was about 20 nm, about 10 nm, and about 5 nm. The results are shown in Table 1 below.

  From Table 1 above, it can be seen that Δφ of each oriented metal substrate is substantially in the first half of the 6 ° range, and thus has almost the same crystal grain orientation. On the other hand, the superconducting characteristics in which the intermediate layer and the superconducting layer are formed improve the critical current characteristics as the surface roughness becomes finer. However, the Ra1 and the groove in the region 4 not including the grain boundary groove of the present example are reduced. When the difference in Ra2 of the region 3 is 50 nm or less, the critical current is 200 A or more, which is practically required, and preferably 10 nm or less, the critical current is 400 A or more, and the critical current characteristics are drastically improved. I understand.

Example 2
In this embodiment, an example using a clad-type oriented metal substrate is shown. Here, the clad type refers to a structure in which different metals are arranged at the center portion and the surface portion, and as shown in FIG. 5, the number of layers of two layers (a), three layers (b), and four layers (c). Here, the case of the three-layer sandwich structure shown in FIG. In this three-layer structure, it is desirable that the strength of the central portion is higher than that of the surface portion.

  First, a Ni-7 at% W round bar having an outer diameter of 24.8 mm and a length of 40 mm is inserted into a commercially available Ni-3 at% W pipe having an outer diameter of 40 mm / inner diameter of 25 mm and a length of 50 mm. A billet was assembled by electron beam welding a disk made of Ni-3 at% W (outer diameter: 40 mm) as a tube lid to both ends of the tube.

  The billet was extruded with an extruder and finished into a tape having a thickness of 0.1 mm, a width of 10 mm, and a length of 50 m by roll rolling and slitting. At this time, the thickness of the Ni alloy layer on the surface was about 10 μm. As a result, a processing rate of 90% or more was secured.

  A coil in which the tape wire was wound in a pancake shape was placed in a box-shaped heat treatment furnace, and kept at 1100 ° C. for 3 hours in a mixed gas atmosphere of argon gas and hydrogen to perform orientation heat treatment (batch orientation heat treatment). As a result, the outermost Ni-3 at% W layer was biaxially oriented.

  When the Ni-3 at% W layer was examined, it was found that P = 99%, and in the X-ray pole figure, the biaxial crystal orientation degree Δφ = 6.9 ° and including the grain boundary groove by the atomic force microscope (AFM). The 10 μm square surface roughness Ra2 was about 270 nm, and the 10 μm square surface roughness Ra1 not including the groove in the crystal grains was 32 nm.

  Further, when the tensile test was performed at room temperature, the 0.2% yield strength was 900 MPa. Therefore, a highly oriented and high strength metal substrate could be obtained.

  The surface of this oriented metal substrate was electropolished using a continuous electropolishing apparatus shown in FIG. That is, the oriented metal substrate 11 from the delivery drum 31 is electrolytically polished in the electrolytic solution tank 33 through the insulated reel 32. A negative electrode 34 is disposed in the electrolytic solution tank 33, and electropolishing is performed by energizing between the negative electrode 34 and the alignment metal substrate 11.

  After the electrolytic polishing, the oriented metal substrate 11 exits the electrolytic solution tank 33 and enters the water washing / drying chamber 35. After being washed and dried, the oriented metal substrate 11 is wound around the winding drum 36.

The electrolytic polishing conditions are shown in Table 2 below.

In the electrolytic polishing as described above, the protrusion A shown in FIG. 1 can be removed, but the groove B cannot be filled. Therefore, in order to fill the groove B, the surface was subjected to electrolytic nickel plating. The plating bath at this time may be a so-called Watt bath mainly composed of nickel sulfate, nickel chloride and boric acid, or may be other nickel plating baths. Here, a plating bath shown in Table 3 below was prepared. In this bath, pure nickel was used as an electrode for the anode, a polished alignment substrate was attached to the cathode, and the surface of the alignment substrate was plated with nickel. The energization current at this time was 0.3 A, and the plating time was 1 minute.

A seed layer composed of CeO ₂ is formed on the surface of the oriented metal substrate 11 by using a continuous electron beam deposition apparatus to heat the orientation substrate temperature of the deposition site to about 800 ° C., and the deposition rate is 1 nm / s, and the degree of vacuum is about The film was formed to a thickness of about 100 nm under the condition of 1 × 10 ⁻² Pa. On this seed layer, a YSZ (yttria stabilized zirconia) film having a thickness of 100 nm is formed by sputtering at 700 ° C. under a vacuum degree of about 5 × 10 ⁻³ Pa. A CeO ₂ film was formed to a thickness of about 100 nm by a sputtering method to form an intermediate layer having a three-layer structure.

  Next, the substrate was heated to 850 ° C., and a YBCO superconductor was formed on the intermediate layer to a thickness of about 1 μm by metal organic vapor phase epitaxy (MOCVD method).

  Then, silver was vapor-deposited on the upper surface of the YBCO superconducting layer to a thickness of about 1 μm using a high frequency sputtering apparatus to form an electrode part.

  In order to measure the critical current by the four-terminal method on the silver surface of the superconducting wire thus obtained, the current lead wire and the voltage lead wire are soldered and energized while immersed in liquid nitrogen. Was measured.

In order to investigate the influence of superconducting properties due to groove grooves in the crystal grain boundaries on the substrate surface, the polishing head pressure and the particle diameter in the above polishing process are the same, the conveying speed is changed, and the groove groove portion is filled. Experiments were made so that there were multiple levels. In order to quantify how the groove of the groove is filled, the difference between Ra1 of the region 4 not including the groove and Ra2 of the region 3 including the groove in FIG. 2 is about 200 nm, about 100 nm, about 80 nm, about 60 nm, about 50 nm. A superconducting wire was manufactured in the same process as described above so that the thickness was about 20 nm, about 10 nm, and about 5 nm. The results are shown in Table 4 below.

  From Table 4 above, it can be seen that Δφ of each oriented metal substrate is almost in the first half of the 6 ° range, so that it has almost the same crystal grain orientation. On the other hand, the superconducting characteristics in which the intermediate layer and the superconducting layer are formed improve the critical current characteristics as the surface roughness becomes finer. However, the Ra1 and the groove in the region 4 not including the grain boundary groove of the present example are reduced. When the difference in Ra2 of the region 3 is 50 nm or less, the critical current is 200 A or more, which is practically required, and preferably 10 nm or less, the critical current is 400 A or more, and the critical current characteristics are drastically improved. I understand.

Example 3
Superconducting wires were manufactured in the same manner as in Example 1 except that Ra2 (average roughness of the region including the groove) was changed, and their critical currents were measured. The results are shown in Table 5 below.

  From Table 5 above, it can be seen that when Ra2 is 50 nm or less, the critical current becomes 200 A or more, which is practically required, and is improved. From this result, it can be said that Ra2 is 50 nm or less and the groove is substantially filled.

It is a figure for demonstrating the principle of this invention by grinding | polishing process. It is a figure explaining the difference of surface roughness Ra1 in the area | region 4 which shows the flatness of a substrate surface, and surface roughness Ra2 in the area | region 3. FIG. It is a section lineblock diagram of a superconducting wire using an orientation metal substrate concerning one example of the present invention. It is a figure which shows a continuous mechanical polishing apparatus. It is sectional drawing which shows the example using the clad type orientation metal substrate. It is a figure which shows a continuous electropolishing apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,11 ... Oriented metal substrate, A ... Protrusion part, B ... Groove part, C ... Deposit, 2 ... Grain boundary, 3 ... Area including groove, 4 ... Area not containing groove, 12 ... Intermediate layer, 13 ... Superconducting layer, 14 ... silver layer, 21 ... feed drum, 22 ... polishing chamber, 23 ... support base, 24 ... polishing head, 25 ... slurry feeder, 26 ... cleaning chamber, 27 ... washing machine, 28 ... drying chamber, 2 DESCRIPTION OF SYMBOLS ... Air knife, 30 ... Winding drum, 31 ... Sending drum, 32 ... Reel, 33 ... Electrolyte tank, 34 ... Negative electrode, 35 ... Washing / drying chamber, 36 ... Winding drum.

Claims (11)

  A superconducting wire comprising a base including a metal substrate and a superconducting layer formed on the base, wherein the surface of the base has a groove of a crystal grain boundary, and the groove is filled with a deposit. Superconducting wire characterized by   2. The superconducting wire according to claim 1, wherein the surface of the substrate is {100} <001> fully oriented or oriented so that a deviation angle of crystal axis from <001> is 25 ° or less.   The superconducting wire according to claim 1 or 2, further comprising an intermediate layer on a surface of the substrate.   The superconducting wire according to any one of claims 1 to 3, wherein the surface of the substrate is made of one kind of metal selected from the group consisting of Ni, Fe, Cu, and Ag or an alloy containing the same. .   The difference between the surface roughness Ra1 of the region in the crystal grains not including the groove on the surface of the substrate and the surface roughness Ra2 of the crystal grain boundary including the groove is 50 nm or less. The superconducting wire in any one of -4. A rolling process for subjecting a metal sheet to a strong rolling process with a rolling reduction of 90% or more;
An orientation heat treatment step of subjecting the metal plate subjected to the rolling process to an orientation heat treatment in a reducing atmosphere;
The orientation heat treatment is performed, the metal plate having projections and grooves on the crystal grain boundaries is polished, the projections are removed, and a substance constituting the removed projections is removed from the metal plate. Polishing / deposition process to deposit in the groove on the surface,
And a superconducting layer forming step of forming a superconducting layer on the metal plate that has been subjected to the polishing / deposition step.   The method of manufacturing a superconducting wire according to claim 6, wherein the polishing step is performed by a polishing method using mechanical polishing, chemical mechanical polishing, or a combination thereof. A rolling process for subjecting a metal sheet to a strong rolling process with a rolling reduction of 90% or more;
An orientation heat treatment step of subjecting the metal plate subjected to the rolling process to an orientation heat treatment in a reducing atmosphere;
Polishing the metal plate having the crystal grain boundary protrusions and grooves on the surface subjected to the orientation heat treatment, and removing the protrusions;
A deposition step of performing a plating process to deposit deposits in the groove;
And a superconducting layer forming step of forming a superconducting layer on the metal plate subjected to the plating treatment.   The method of manufacturing a superconducting wire according to claim 8, wherein the polishing step is performed by a polishing method using electrolytic polishing, chemical polishing, mechanical polishing, chemical mechanical polishing, or a combination thereof.   The method for manufacturing a superconducting wire according to any one of claims 6 to 9, further comprising a step of forming an intermediate layer on the surface of the metal plate before forming the superconducting layer.   The method of manufacturing a superconducting wire according to claim 10, further comprising a step of polishing a surface of the intermediate layer.

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