JP2013235796A - Rolled copper foil for forming superconducting film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolled copper foil for forming a superconducting material, with which characteristics of a superconducting film formed on a surface thereof is improved.SOLUTION: In a rolled copper foil for forming a superconducting film, a film of a superconducting material is formed on a surface of the rolled copper foil. When a peak intensity in each of regions where 0°≤β<90°, 90°≤β<180, 180°≤β<270° and 270°≤β<360° are satisfied respectively is plotted relative to α on the (111) normal pole figure (where, α represents an axis which is perpendicular to the rotation axis of a goniometer for diffraction defined in the Schultz method, and β represents a rotation axis in parallel with the ND direction of a sample), the average half-width of each peak is 7.5 or less.

Description

  The present invention relates to a rolled copper foil for forming a superconducting film in which a film of a superconducting material is directly or indirectly formed on its surface.

With the development of high-temperature superconducting materials, it has been studied to form a superconducting material on a substrate and process it into a wire or the like (Patent Document 1). Here, in order to obtain an excellent high-temperature superconducting wire, it is necessary to form a highly conductive superconducting film. In the technique described in Patent Document 1, a substrate (for example, Cu foil) in which metal atoms are biaxially oriented is used. The intermediate layer (for example, Ni film) is epitaxially grown on the substrate, and the superconducting film is epitaxially grown on the intermediate layer.
In addition, it is recommended to use a copper foil that is cold rolled at a high workability of 95% or more, subjected to orientation heat treatment at 200 ° C. or higher and below the melting point of copper, and has a cubic texture as the orientation substrate. Has been. Furthermore, a technique for clad bonding the orientation substrate to a support such as stainless steel has been developed (Patent Document 2).

JP 2006-127847 A JP 2008-266686A

However, the investigation of the surface properties of the copper foil for forming a superconducting film directly or indirectly on its surface is not yet sufficient, and the characteristics of the superconducting film (critical current density, etc.) are not sufficiently improved. There is a problem.
The present invention has been made to solve the above-described problems, and improves the surface properties of the copper foil while improving the degree of orientation of the copper foil in the cubic direction, and the characteristics of the superconducting film formed on the surface. An object of the present invention is to provide a rolled copper foil for forming a superconducting film that is improved and has excellent adhesion to a support.

As a result of various studies, the inventors have plotted the intensity of the four peaks corresponding to the cube orientation in the (111) positive electrode dot diagram of the copper foil, and when the half-value width of each peak is reduced, The present inventors have found that the degree of orientation in the cubic direction is improved and the characteristics of the superconducting film formed on the surface of the copper foil are improved.
In order to achieve the above object, a rolled copper foil for forming a superconducting film according to the present invention is a rolled copper foil for forming a superconducting film on its surface, and is a (111) positive electrode dot diagram. , 0 ° ≦ β <90 °, 90 ° ≦ β <180, 180 ° ≦ β <270 °, 270 ° ≦ β <360 °, and the peak intensity in each region is α (where α is defined by the Schulz method) When plotted against an axis perpendicular to the rotation axis of the diffraction goniometer, β: a rotation axis parallel to the ND direction of the sample, the average value of the half width of each peak is 7.5 or less.

It is preferable that recrystallization annealing is performed at 200 to 1000 ° C. for 1 minute or longer to temper the recrystallization structure.
The recrystallization annealing is performed in two stages of primary annealing and subsequent secondary annealing. After the primary annealing, 20 to 80% of the surface is recrystallized, and the secondary annealing is performed at 200 to 1000 ° C. for 1 minute or more. It is preferable.
The primary annealing is preferably performed at 150 to 250 ° C.
After the ingot is hot-rolled, it is manufactured by repeating cold rolling and annealing, and finally performing the final cold rolling, and the total workability of the final cold rolling process is 95.0 to 99.5%. It is preferable.
After the ingot is hot-rolled, cold rolling and annealing are repeated, and finally the final cold-rolling is performed. In the final cold-rolling process, on the surface of the copper foil one stage before the final pass The 60 ° gloss G60 _RD measured according to JIS-Z8741 in the rolling parallel direction is preferably more than 200.

  According to the present invention, the surface property of the copper foil is improved while improving the degree of orientation of the copper foil in the cubic orientation, the characteristics of the superconducting film formed on the surface are improved, and the adhesion to the support is improved. An excellent rolled copper foil for forming a superconducting film can be obtained.

It is a figure which shows the superconducting material formed by forming the superconducting film on the surface of the orientation board for superconducting film formation formed by laminating | stacking the rolled copper foil for superconducting film formation on a support body, and the orientation plate for superconducting film formation. 3 is a diagram showing a (111) positive electrode diagram of Example 1. FIG. FIG. 4 is a diagram showing a state in which a half width of a peak represents a deviation of crystal orientation from an ND direction with an axis of intersection X between a surface A including an ND direction and an X-ray incident direction and a sample surface B as an axis. It is a figure which shows the example of the chart which plotted the intensity | strength of the said peak with respect to (alpha) about Example 1. FIG. It is the figure which showed the half-value width (half-value full width, FWHM) of the peak of FIG.

  Hereinafter, the rolled copper foil for superconducting film formation which concerns on embodiment of this invention is demonstrated. In the present invention, “%” means “% by mass” unless otherwise specified.

FIG. 1 shows a superconducting film forming orientation plate 10 formed by laminating a rolled copper foil 4 for forming a superconducting film according to an embodiment of the present invention on a support 2, and a surface of the superconducting film forming orientation plate 10 (superconducting film formation). A superconducting material 100 formed by forming a superconducting film 8 on the rolled copper foil 4 side) is shown.
The support 2 is for ensuring the strength of the superconducting film-forming alignment plate 10 and is preferably a nonmagnetic metal material (for example, stainless steel or nickel alloy).
The rolled copper foil 4 is subjected to recrystallization annealing, and the cube orientation develops at that time. Preferred conditions for recrystallization annealing will be described later. The recrystallization annealing of the copper foil 4 may be performed before the copper foil 4 is laminated on the support 2 or after the copper foil 4 is laminated on the support 2.
As a method of laminating the rolled copper foil 4 on the support 2, both surfaces are cleaned by dry etching, then both are laminated with no pressure or pressure, and the surfaces are joined by atomic force on the surface. "Activated bonding" can be used (see Patent Document 2).

The superconducting substance constituting the superconducting film 8 is a substance that has an electric resistance of 0 when the substance is cooled below a specific temperature (critical temperature). In particular, a high temperature superconducting material having a critical temperature not lower than the boiling point of liquid nitrogen (−196 ° C.) is preferable from a practical viewpoint. Examples of the high-temperature superconducting material include, but are not limited to, an yttrium-based superconductor (YBCO, Y123), a rare earth element-based oxide superconductor (R123), and a copper oxide high-temperature superconductor.
In the example of FIG. 1, a barrier layer 6 made of a Ni plating layer or the like is formed on the surface of the rolled copper foil 4 for forming a superconducting film. This is because when the superconducting film 8 is directly formed on the surface of the rolled copper foil 4 for forming a superconducting film, components (oxides, etc.) of the superconducting film 8 are diffused to the copper foil 4 side during the film formation to form copper oxide. This is because the copper foil 4 is easily oxidized by the high temperature during film formation. Therefore, it is preferable to form the barrier layer 6 on the surface of the rolled copper foil 4 for forming a superconducting film. As the barrier layer 6, nickel or a nickel alloy is preferably used.
In the example of FIG. 1, the rolled copper foil 4 for forming a superconducting film is formed on one side of the support 2, but the rolled copper foil 4 for forming a superconducting film may be formed on both sides of the supporting body 2. .

Next, the rule and composition of the rolled copper foil of the present invention will be described.
(1) Orientation degree of copper foil in cube orientation Copper foil used as a substrate of a superconductive film is required to develop a cube orientation after recrystallization annealing. As an index for evaluating the cube orientation, the rolled copper foil for forming a superconducting film according to an embodiment of the present invention has a 0111 ≦ β <90 °, 90 ° ≦ β <180, 180 ° ≦ 180 (111) positive electrode diagram. A peak in each region of β <270 °, 270 ° ≦ β <360 ° (this peak (maximum value) is a peak corresponding to the cube orientation) is α (where α is a diffraction goniometer defined in the Schulz method) When plotted against an axis perpendicular to the rotation axis, β: a rotation axis parallel to the ND direction of the sample), the average value of the half width of each peak is 7.5 or less. The average half width is preferably 7 or less, more preferably 6.5 or less, and even more preferably 6 or less.
FIG. 2 shows a (111) positive electrode dot diagram of Example 1 described later. The positive electrode dot diagram is based on X-ray diffraction (X-ray diffractometer), and is used for measurement of a plate-shaped sample. In addition, RD in FIG. 2 indicates the rolling direction of the sample, and TD indicates the horizontal direction of the sample (direction perpendicular to the rolling direction and the normal to the rolling surface). The diffraction goniometer is a measuring device that adjusts so that Bragg reflection occurs only from the (111) plane. The diffraction goniometer is fixed after the diffraction goniometer is adjusted to an angle at which Bragg reflection occurs from the (111) plane. Next, the X-ray diffraction intensity of the (111) plane is measured while rotating the sample about the α axis perpendicular to the rotation axis of the diffraction goniometer and the β axis parallel to the ND direction of the sample. The X-ray diffraction method (Schulz method) is described in, for example, literature (Eiichi Furubayashi, “Materials series that draws out the functionality of metals”, Uchida Otsukurakusha, published in December 2002).
In FIG. 2, there are four texture peaks, which are present in the four regions described above.

Here, as shown in FIG. 3, α corresponds to rotation about the incident direction of the X-ray with respect to the sample. The half width of the peak represents the distribution of deviation in crystal orientation from the ND direction. The smaller this distribution, the smaller the variation in orientation from crystal to crystal, and the degree of orientation of the copper foil in the cube (Cube) orientation ( (Accumulation degree) becomes high.
FIG. 4 is a diagram showing a chart in which the peak intensity is plotted with respect to α in Example 1 to be described later. FIG. 5 is an example showing the half width of the peak in FIG. 4 (where 0 ° ≦ β <90 °). The full width at half maximum (full width at half maximum) is represented by the symbol FWHM.

As a method for controlling the above average value of the half width to 7.5 or less, the recrystallization annealing condition is preferably set to 200 to 1000 ° C. for 1 minute or more, more preferably 5 minutes or more. If the recrystallization annealing condition is less than 200 ° C. or less than 1 minute, a sufficient orientation structure may not be obtained. On the other hand, when the recrystallization annealing temperature exceeds 1000 ° C., the crystal grain boundaries are recessed in a groove shape, which is not suitable for superconducting film formation. The upper limit of the recrystallization annealing time varies depending on the recrystallization annealing temperature, and can be arbitrarily selected within a range in which the crystal grain boundaries do not dent in a groove shape, but is typically within 10 hours, more typically within 2 hours. .
Recrystallization annealing is performed in two stages of primary annealing and subsequent secondary annealing, and is controlled so that 20 to 80% of the copper foil surface is recrystallized after the primary annealing, and the secondary annealing is performed at 200 to 1000 ° C. for 1 minute or more. By doing so, the average value of the half width can be controlled to be smaller. When the recrystallization rate is less than 20%, the effect of performing annealing in two stages is not exhibited. On the other hand, when the recrystallization rate exceeds 80%, the processing strain that becomes the driving force of the recrystallization texture is excessively removed, so that the cube orientation is not sufficiently developed after the secondary annealing.
The primary annealing is preferably performed at 150 to 250 ° C. When the temperature of primary annealing is less than 150 ° C., the recrystallization rate may be less than 20%. On the other hand, when the primary annealing temperature exceeds 250 ° C., the recrystallization rate may exceed 80%. The primary annealing time can be arbitrarily selected within a range where the recrystallization ratio is 20 to 80%, but is typically 1 minute to 10 hours, more typically 5 minutes to 2 hours. If the time is too short, the recrystallization rate may vary in the material, and if the time is too long, the efficiency decreases.
When the secondary annealing temperature exceeds 1000 ° C., the crystal grain boundaries are recessed in a groove shape, which is not suitable for the superconducting film formation application. The upper limit of the secondary annealing time varies depending on the annealing temperature, and can be arbitrarily selected within a range in which the crystal grain boundaries do not dent in a groove shape, but is typically within 10 hours, more typically within 2 hours.

In addition, although 20 to 80% of the copper foil surface is recrystallized by the primary annealing, the primary annealing may be performed in a plurality of times. In this case, for example, the temperature may be raised stepwise by annealing multiple times.
Further, the surface of the copper foil is 100% recrystallized by the secondary annealing, and the cubic orientation grows, but this secondary annealing may be performed in a plurality of times.

(2) Composition As copper foil, tough pitch copper or oxygen-free copper having a purity of 99.9% by mass or more can be used, and a known copper alloy can be used depending on required strength and conductivity. . Oxygen-free copper is standardized by JIS-H3510 (alloy number C1011) and JIS-H3100 (alloy number C1020), and tough pitch copper is standardized by JIS-H3100 (alloy number C1100).
As a known copper alloy, for example, 0.001 to 0.3% by mass of tin-containing copper alloy (more preferably 0.001 to 0.02% by mass of tin-containing copper alloy); 0.01 to 0.05% Mass% silver-containing copper alloy; 0.005-0.02 mass% indium-containing copper alloy; 0.005-0.02 mass% chromium-containing copper alloy; 0.005-0.02 mass% titanium Copper alloy; copper alloy containing 0.05% by mass or less in total of one or more selected from the group consisting of tin, silver, indium, and chromium is mentioned. Among them, 0.02% by mass silver is excellent in conductivity. Additive copper is often used.

(3) Thickness of the copper foil The thickness of the copper foil is not particularly limited, but when the foil thickness is extremely thin, crystal grain growth during recrystallization is limited by the foil thickness, and is preferably 10 μm or more. The thickness of the copper foil is more preferably 15 μm or more, and further preferably 17 μm or more. On the other hand, even if the copper foil is excessively thick, there is no advantage in characteristics, and there are disadvantages in cost and handling. Therefore, the copper foil thickness is preferably 100 μm or less, more preferably 75 μm or less.

(4) Manufacturing method of copper foil Next, an example of the manufacturing method of the rolled copper foil of this invention is demonstrated. First, an ingot made of copper, necessary alloy elements, and inevitable impurities is hot-rolled, and then cold-rolling and annealing are repeated, and finally, it is finished to a predetermined thickness by final cold-rolling.
In the final cold rolling, the material is finished to a predetermined thickness by repeatedly passing (passing) the material through a rolling mill. By setting the total degree of work in the final cold rolling to 95.0% or more, the average value of the half width after the recrystallization annealing can be surely made 7.5 or less.
The total degree of work in the final cold rolling is preferably 99.5% or less, more preferably 99.0% or less, and still more preferably 98.0% or less. By reducing the total processing degree, the depth of the oil pit can be suppressed.

In the final cold rolling step, the rolling conditions can be controlled so that the 60 ° gloss G60 _RD measured in accordance with JIS-Z8741 in the rolling parallel direction exceeds 200 on the copper foil surface in the stage one pass before the final pass. preferable.
In this case, in the final cold rolling, the development of the shear band is suppressed in the pass before the final pass, that is, the material surface after rolling becomes smooth in the pass before the final pass. Further, in the final pass of the final cold rolling, rolling may be performed under the condition that the material surface after rolling becomes rough, and the finally obtained copper foil surface may be roughened.

Specifically, in the final cold rolling, rolling is performed using a roll having a relatively small roughness (surface roughness Ra is, for example, 0.05 μm or less) or the final cold rolling so that the surface of the copper foil is not too rough. What is necessary is just to enlarge and roll the 1 pass processing degree in rolling. However, in the final pass of the final cold rolling, rolling is performed using a roll having a relatively large roughness (surface roughness Ra is, for example, 0.06 μm or more), or rolling is performed using a highly viscous rolling oil. The obtained copper foil surface may be roughened to adjust the surface shape.
In the above, the method of rough finishing the copper foil surface only in the final 1 pass is exemplified, but in the final 2 passes, by using a rough roll or rolling with a high viscosity rolling oil as described above, It is also possible to finish the copper foil surface roughly. However, for ease of adjustment, it is preferable to adjust the rolling conditions for the final pass only. On the other hand, when the roughness of the roll is made rough before the final three passes of the final cold rolling, a shear deformation band develops, and the average value of the half width does not become 7.5 or less after the recrystallization annealing.

On the other hand, when the copper foil surface is roughened before the final pass of the final cold rolling and the surface of the copper foil is smoothed by the final pass of the final cold rolling, a shear band develops in the oil pit, It is not preferable because a deep oil pit with a shear band remains even after the final pass.
In all the passes of final cold rolling, if the copper foil surface is finished rough, deep oil pits are generated, and the average value of the half width is not 7.5 or less after recrystallization annealing.

After casting an ingot using tough pitch copper or oxygen-free copper added with the elements shown in Table 1 as a raw material, hot rolling to 800 mm in thickness to 10 mm, chamfering the surface oxide scale, The hot rolling and annealing were repeated, and finally the final cold rolling was performed to the thicknesses shown in Table 1. Further, after the final cold rolling, recrystallization annealing was performed under the conditions shown in Table 1.
In the column of composition in Table 1, for example, “0.02% Ag added TPC” means that 0.02 mass% Ag was added to tough pitch copper (TPC) of JIS-H3100 (Alloy No. C1100). “0.01% Ag 0.005% Sn-added OFC” was obtained by adding 0.01 mass% Ag and 0.005 mass% Sn to oxygen-free copper (OFC) of JIS-H3100 (Alloy No. C1020). Means that. However, oxygen free copper (OFC) standardized in JIS-H3510 (alloy number C1011) is used as oxygen free copper only in Example 6, and Examples 4, 5, 8, 9 and Comparative Examples 7 and 8 are oxygen free. As the copper, oxygen-free copper (OFC) standardized in JIS-H3100 (alloy number C1020) was used.

Various characteristics of each copper foil sample thus obtained were evaluated.
(1) Glossiness At a stage one pass before the final pass of the final cold rolling, the glossiness G60 _RD of the copper foil surface was measured according to JIS-Z8741 along the rolling parallel direction RD.
(2) Cubic texture The obtained copper foil was heated on the conditions shown in Table 1 in the nitrogen atmosphere which imitated joining heat processing with a support body. Thereafter, the (111) positive electrode diagram of the copper foil was measured using Schulz's diffraction method, and the half-value width of the diffraction peak derived from the cube orientation was determined. RINT2500 (manufactured by Rigaku Corporation) was used as the measurement apparatus, and Co was used as the X-ray source. In the measurement step, the α angle was 1 ° and the β angle was 2 °. Although the measurement may be performed in steps coarser than this, it is not preferable because the peak shape may not be measured accurately.

(3) Characteristics of superconducting film (critical current density Jc)
On the copper foil surface of the superconducting film-forming alignment plate obtained in (4) above, a 2 μm Ni plating layer is electroplated as a barrier layer. A superconducting film made of a film was formed. Then, the critical current density Jc was measured at a voltage reference of 1 μV / cm by a direct current four-terminal method in a self-magnetic field at 77K.
In addition, a case in which Jc is more than ^{100000A / cm 2 ◎, 10000A /} cm 2 Beyond ○ the case of 100000 A / cm ² or less, 100 more than the ^{A / cm 2 10000 A / cm} 2 or less of the case △ The case of 100 A / cm ² or less was expressed as x. If the evaluation is Δ to ◎, there is no practical problem.

  The obtained results are shown in Table 1.

In each example, the average value of the half width was 7.5 or less, and the characteristics (critical current density) of the superconducting film were improved. Moreover, in each Example, the total workability of the final cold rolling was adjusted to 95.0-99.5%. Further, except for Example 16, the 60 ° glossiness G60 _{RD in} the rolling parallel direction one pass before the final pass was 200 or more.
In particular, in Examples 17 to 20 in which recrystallization annealing is performed in two stages of primary annealing and subsequent secondary annealing and primary annealing is performed at 150 to 250 ° C., the characteristics of the superconducting film as compared with the other examples Improved further.
In the case of Example 16 where the glossiness G60 _RD is less than 200, the characteristics of the superconducting film are slightly inferior to those of the other examples, but there is no practical problem.

On the other hand, in the case of Comparative Example 1 in which the recrystallization annealing temperature is less than 200 ° C., the average value of the half width exceeds 7.5, and the characteristics (critical current density) of the superconducting film are lowered.
In the case of Comparative Examples 2 to 6 in which the total degree of work of the final cold rolling is less than 95.0%, the half width exceeds 7.5 regardless of the recrystallization annealing conditions, and the characteristics of the superconducting film (critical current density) ) Decreased. In particular, in the case of Comparative Examples 2 and 3 in which the total work degree of final cold rolling was less than 95.0% and the glossiness was less than 200, the average value of the half width was the largest value.

Claims (6)

A rolled copper foil for forming a superconducting film that forms a film of a superconducting material on its surface,
(111) In the positive pole figure, the peak intensity in each region of 0 ° ≦ β <90 °, 90 ° ≦ β <180, 180 ° ≦ β <270 °, 270 ° ≦ β <360 ° is expressed as α (however, , Α: axis perpendicular to the rotation axis of the diffraction goniometer specified in the Schulz method, β: rotation axis parallel to the ND direction of the sample), the average value of the half width of each peak is 7. The rolled copper foil for superconducting film formation which is 5 or less.   The rolled copper foil for forming a superconducting film according to claim 1, wherein the rolled copper foil is formed by recrystallization annealing at 200 to 1000 ° C. for 1 minute or longer and tempering the recrystallized structure.   The recrystallization annealing is performed in two stages of primary annealing and subsequent secondary annealing. After the primary annealing, 20 to 80% of the surface is recrystallized, and the secondary annealing is performed at 200 to 1000 ° C. for 1 minute or more. The rolled copper foil for forming a superconducting film according to claim 2.   The rolled copper foil for forming a superconducting film according to claim 3, wherein the primary annealing is performed at 150 to 250 ° C.   After the ingot is hot-rolled, it is manufactured by repeating cold rolling and annealing, and finally performing the final cold rolling, and the total workability of the final cold rolling process is 95.0 to 99.5%. The rolled copper foil for superconducting film formation in any one of Claims 1-4. After the ingot is hot-rolled, cold rolling and annealing are repeated, and finally the final cold-rolling is performed. In the final cold-rolling process, on the surface of the copper foil one stage before the final pass The rolled copper foil for forming a superconducting film according to any one of claims 1 to 5, wherein the 60 ° gloss G60 _RD measured according to JIS-Z8741 in the rolling parallel direction exceeds 200.