JP2013101832A - Substrate for epitaxial growth and method for manufacturing the same, and substrate for superconducting wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that, while a method using plating is known as a method for depositing Ni or an Ni alloy on a biaxially crystal oriented Cu layer, plating at a low current density (1-4 A/dm) is generally required in order to form an Ni layer having high crystal orientation, but time required for plating treatment at a low current density is prolonged, so that productivity is reduced, specifically overheat may be caused in a metal substrate as a laminate material when a long metal substrate is produced by a reel-to-reel method, and therefor, it is desired to establish a manufacturing condition capable of improving production efficiency by increasing current density while maintaining crystal orientation.SOLUTION: In order to solve the problem, a substrate for epitaxial growth of the present invention includes a biaxially crystal oriented Cu layer, and a protective layer provided on the Cu layer. The protective layer has a plating distortion ε of 15×10or less.

Description

  The present invention relates to an epitaxial growth substrate and a method for manufacturing the same. The present invention also relates to a substrate for a superconducting wire using an epitaxial growth substrate.

Conventionally, superconducting wires such as Y-based oxide superconducting wires have oxide layers such as cerium oxide (CeO ₂ ), zirconia-added yttrium oxide (YSZ), and yttrium oxide (Y ₂ O ₃ ) as intermediate layers on a metal substrate. Is grown epitaxially by sputtering or the like, and a superconducting compound layer (RE123 film, RE: Y, Gd, Ho, etc.) is further epitaxially grown thereon by laser ablation or the like.

  As a technique for obtaining a crystallographically oriented superconducting compound layer, an ion-assisted beam deposition method that allows the superconducting compound layer to inherit crystal orientation by forming an oriented intermediate layer on a non-oriented metal substrate such as Hastelloy. (IBAD method) and methods (RABiTS method and the like) for forming a film by taking over the crystal orientation with the intermediate layer and the superconducting compound layer by using a biaxial crystal-oriented metal substrate are known. The latter method is advantageous in consideration of future production efficiency such as film formation speed, but in order to improve the superconducting characteristics, it is necessary to highly orient the metal substrate in biaxial crystal orientation.

  As such a metal substrate (superconducting wire substrate), a substrate is known in which crystal-oriented copper is laminated on a stainless steel substrate, and nickel is further laminated thereon. For example, in (Patent Document 1), in an oriented substrate for forming an epitaxial film having an oriented metal layer such as a copper foil on at least one surface, a metal thin film such as nickel is formed on the surface of the oriented metal layer. An orientation improving layer having a thickness of 5000 nm is provided, and the difference between the orientation degree (Δφ and Δω) on the surface of the oriented metal layer and the orientation degree (Δφ and Δω) on the surface of the orientation improving layer is 0. An alignment substrate for forming an epitaxial film characterized by an angle of 0.1 to 3.0 ° is disclosed.

  In addition, as a method for manufacturing a biaxially crystallized metal substrate (Patent Document 2), there are a nonmagnetic metal plate made of stainless steel and the like, and a metal foil made of Cu or a Cu alloy cold-rolled at a high pressure rate. Are laminated by surface activation bonding, and after the lamination, the metal foil is biaxially crystallized by heat treatment, and then an epitaxially grown film of Ni or Ni alloy is provided on the metal foil side surface. A method for manufacturing a laminated substrate is disclosed.

JP 2009-46734 A JP 2010-118246 A

As a method for forming a Ni or Ni alloy film on a biaxially crystallized Cu layer, a plating method is known. In order to produce a Ni layer with high crystal orientation, it is generally necessary to perform plating at a low current density (1 to 4 A / dm ² ). In particular, when a long metal substrate is produced on a reel-to-reel basis, there is a problem that overheating of the metal substrate which is a laminated material may occur. Therefore, it has been desired to establish a production condition that can increase the current density and improve the production efficiency while maintaining the crystal orientation.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors pay attention to the strain generated in the plating film (protective layer) such as Ni provided on the Cu layer, and the value of this plating strain is a predetermined value. The inventors have found that high crystal orientation can be maintained when controlled to be within the range, and have completed the invention. That is, the gist of the present invention is as follows.

(1) An epitaxial growth substrate having a biaxial crystal-oriented Cu layer and a protective layer provided on the Cu layer, wherein the protective layer has a plating strain ε of 15 × 10 ⁻⁶ or less. Substrate.
(2) The epitaxial growth substrate according to (1), wherein the protective layer is made of Ni or a Ni alloy.
(3) The epitaxial growth substrate according to (1) or (2), wherein the thickness of the protective layer is 1 μm or more and 5 μm or less.
(4) A method for manufacturing a substrate for epitaxial growth, comprising a step of forming a protective layer by performing plating so that a plating strain ε is 15 × 10 ⁻⁶ or less on a biaxially crystallized Cu layer.
(5) The method for producing a substrate for epitaxial growth according to (4), wherein the plating is performed using a sulfamic acid bath.
(6) A superconducting wire substrate in which the epitaxial growth substrate according to any one of (1) to (3) is laminated on a nonmagnetic metal plate.

The substrate for epitaxial growth and the substrate for superconducting wire according to the present invention has a high crystal orientation retention and a high current because the plating strain ε of the protective layer provided on the crystal oriented Cu layer is defined as 15 × 10 ⁻⁶ or less. It is possible to increase the density and improve the production efficiency.

It is a graph which shows the relationship between the plating distortion (epsilon) of a protective layer in each Example, and biaxial crystal orientation degree (DELTA) phi.

Hereinafter, the present invention will be described in detail.
The substrate for epitaxial growth of the present invention has a Cu layer and a protective layer provided on the Cu layer, and the plating strain ε of the protective layer is 15 × 10 ⁻⁶ or less. Here, the plating strain represents the degree of strain (strain) generated in the plating film when a plating treatment is applied to a base such as a metal plate, and is a value defined by the following equation.
ε = ΔR / (R · K)
(Where, ΔR: resistance change due to expansion / contraction, R: original resistance value of strain gauge, K: gauge factor, ε: plating strain)

  The Cu layer must be highly biaxially crystallized in order to produce a superconducting wire by providing a protective layer thereon and further laminating an intermediate layer and a superconducting compound layer by epitaxial growth. Specifically, the crystal orientation of the Cu layer is expressed as follows: Δφ ≦ 5.5 °, with the half width (Δφ) of the φ scan peak (α = 35 °) in the (111) pole figure by X-ray diffraction as an index, Preferably, Δφ ≦ 5.2 °, more preferably Δφ ≦ 5 °.

  As such a Cu layer, a Cu foil is preferably used. The thickness of the Cu layer is usually preferably 7 μm or more and 50 μm or less in order to secure the strength of the Cu layer itself and improve the workability when processing the superconducting wire later.

  As a method for highly biaxial crystal orientation of the Cu layer, for example, a method of performing cold rolling at a high pressure ratio of 90% or higher, giving uniform strain to the entire Cu layer, and then recrystallizing by heat treatment is used. be able to. If the rolling reduction is less than 90%, sufficient biaxial crystal orientation may not be obtained by a heat treatment performed later. Such a high-pressure under-rolled Cu foil is generally available, for example, high-pressure under-rolled Cu foil (HA foil (trade name)) manufactured by JX Nippon Mining & Metals, Hitachi Cable ) Made of high pressure under rolled Cu foil (HX foil (trade name)) and the like.

  The heat treatment temperature needs to be 150 ° C. or higher in order to complete the recrystallization completely. If the heat treatment temperature is too high, the Cu layer tends to cause secondary recrystallization, and the crystal orientation deteriorates. More preferably, it is 600 to 900 degreeC. Moreover, although heat processing time changes with other conditions, it is appropriate to set it as about 1 to 10 minutes. As will be described later, such heat treatment is actually preferably performed after the Cu layer and the nonmagnetic metal plate are bonded together by a surface activated bonding method or the like in the process of manufacturing the substrate for a superconducting wire. .

  Moreover, in order to further improve the biaxial crystal orientation by heat treatment, the Cu layer may contain a trace amount of element of about 1% or less. Examples of such an additive element include one or more elements selected from Ag, Sn, Zn, Zr, O, N, and the like. These additive elements and Cu form a solid solution, but if the addition amount exceeds 1%, impurities such as oxides other than the solid solution increase, which may adversely affect the crystal orientation.

An epitaxial growth substrate of the present invention can be obtained by forming a protective layer by plating on the biaxially crystallized Cu layer. Such a protective layer is preferably made of Ni or Ni alloy. The protective layer containing Ni has better oxidation resistance than the Cu layer, and the presence of the protective layer makes it possible to form a Cu oxide film and form crystal orientation when an intermediate layer such as CeO ₂ is formed thereon. It is possible to prevent the characteristics from breaking. The element contained in the Ni alloy is preferably one that reduces magnetism, and examples thereof include elements such as Cu, Sn, W, and Cr. Further, impurities may be included as long as the crystal orientation is not adversely affected.

  If the thickness of the protective layer made of Ni or Ni alloy is too thin, Cu may diffuse when an intermediate layer or a superconducting compound layer is laminated thereon, and if it is too thick, the crystal orientation of the protective layer Is collapsed and the plating strain is increased, so that it is appropriately set in consideration of these. Specifically, it is preferably 1 μm or more and 5 μm or less.

The plating treatment can be performed by appropriately adopting conditions such that the plating strain ε of the protective layer is 15 × 10 ⁻⁶ or less. For example, when forming a Ni layer as a protective layer, it can carry out using the Watt bath and sulfamic acid bath conventionally known as a plating bath. In particular, the sulfamic acid bath is preferably used because it easily reduces the plating strain of the protective layer. The preferable range of the plating bath composition for setting the plating strain ε to 15 × 10 ⁻⁶ or less is as follows.

Watt bath nickel sulfate 200-300 g / l
Nickel chloride 30-60g / l
Boric acid 30-40g / l
pH 4-5
Bath temperature 40-60 ° C

Sulfamic acid bath nickel sulfamate 200-600 g / l
Nickel chloride 0-15g / l
Boric acid 30-40g / l
Additive appropriate amount pH 3.5-4.5
Bath temperature 40-70 ° C

The current density during the plating process is not particularly limited as long as the plating strain ε of the protective layer can be 15 × 10 ⁻⁶ or less, and is appropriately set in consideration of the balance with the time required for the plating process. Is done. Specifically, for example, when a plating film of 2 μm or more is formed as a protective layer, the time required for the plating process becomes long if the current density is low, and the line speed is slowed down in order to secure the time. In general, the current density is preferably set to 10 A / dm ² or more because the properties may be lowered or the control of the plating may be difficult. Further, when the current density is increased, the plating strain is increased accordingly. However, in order to suppress the plating strain ε of the protective layer to 15 × 10 ⁻⁶ or less, a suitable current density range varies depending on the type of the plating bath. It is preferably 25 A / dm ² or less for a watt bath and 35 A / dm ² or less for a sulfamic acid bath. Generally, when the current density exceeds 35 A / dm ² , good crystal orientation may not be obtained due to so-called plating burn.

  The formed protective layer may generate micropits on the surface depending on plating conditions and the like. In that case, if necessary, the surface can be smoothed by further averaging after the plating. It is preferable that the heat processing temperature in that case shall be 700-1000 degreeC, for example.

  The substrate for epitaxial growth having the Cu layer and the protective layer as described above can be further laminated with a nonmagnetic metal plate to obtain a substrate for a superconducting wire. When manufacturing this substrate for superconducting wires, in practice, the Cu layer rolled at a high pressure rate is first bonded to a nonmagnetic metal plate, followed by heat treatment to improve the biaxial crystal orientation of the Cu layer. Then, it is preferable to manufacture by forming a protective layer on the Cu layer by plating.

  Non-magnetic means a state that is 77K or higher and is not a ferromagnetic material, that is, a Curie point or a Neel point exists at 77K or lower and becomes a paramagnetic material or an antiferromagnetic material at a temperature of 77K or higher. As the non-magnetic metal plate, a nickel alloy or an austenitic stainless steel plate is preferably used because of its strength and role as a reinforcing material.

  In general, austenitic stainless steel is non-magnetic at room temperature, that is, the metal structure is 100% austenite (γ) phase, but the martensite (α ′) phase transformation point (Ms point) which is a ferromagnetic material is 77K. When positioned above, the α ′ phase, which is a ferromagnetic substance, may develop at the liquid nitrogen temperature. Therefore, as a substrate for a superconducting wire used at a liquid nitrogen temperature (77K), a substrate whose Ms point is designed to be 77K or less is preferably used.

  As the γ-based stainless steel plate to be used, SUS316, SUS316L, SUS310, and SUS305 have a stable γ phase designed with a Ms point sufficiently lower than 77K, and are generally popular and available at a relatively low price. Etc. is preferably used. The thickness of these metal plates is usually applicable if it is 20 μm or more, and considering the thinning and strength of the superconducting wire, it is preferably 50 μm or more and 100 μm or less, but is not limited to this range. Absent.

When the nonmagnetic metal plate and the Cu layer are laminated, a conventionally known method such as a surface activated bonding method can be used as appropriate. In the surface activated bonding method, the surfaces of the nonmagnetic metal plate and the Cu layer are subjected to a sputter etching process in an extremely low pressure inert gas atmosphere of about 10 to 1 × 10 ⁻² Pa, for example, and thereby the surface adsorption layer and The surface oxide film is removed and activated, and then the two activated surfaces are bonded together by cold pressure welding, for example, at a rolling reduction of 0.1 to 5%. The cold pressure welding is preferably performed under a high vacuum of 1 × 10 ⁻² Pa or less so that the activated surface is reoxidized and does not adversely affect the adhesion.

  Further, in order to maintain good crystal orientation of the intermediate layer and the superconducting compound layer that are further laminated by epitaxial growth on the protective layer, the Cu layer is bonded after joining the nonmagnetic metal plate and the Cu layer as necessary. You may perform the process for reducing the surface roughness Ra. Specifically, methods such as rolling with a rolling roll, buff polishing, electrolytic polishing, and electrolytic abrasive grain polishing can be used. By these methods, the surface roughness Ra is, for example, 40 nm or less, preferably 10 nm or less. Is desirable.

  Note that the biaxially crystallized Cu layer and the protective layer may be laminated only on one side of the nonmagnetic metal plate, or may be laminated on both sides of the metal plate.

A superconducting wire can be manufactured by sequentially laminating an intermediate layer and a superconducting compound layer on the protective layer of the superconducting wire substrate as described above according to a conventional method. Specifically, an intermediate layer such as CeO ₂ , YSZ, SrTiO ₃ , MgO, and Y ₂ O ₃ is epitaxially formed on the protective layer formed by plating using means such as a sputtering method, and further thereon. A superconducting wire can be obtained by forming a superconducting compound layer such as Y123 based on a laser ablation method or the like. If necessary, a protective film made of Ag, Cu or the like may be further provided on the superconducting compound layer.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example and a comparative example, this invention is not limited to these Examples.

(Examples 1-5 and Comparative Example 1)
First, using a standard test piece made of copper (manufactured by Yamamoto Metal Testing Co., Ltd., back side masked, with strain gauge) as the cathode, nickel plating was performed under the plating conditions shown in Table 1, and strain gauge precision The plating strain ε in the plating film was measured using a stress meter (B-72-SG, manufactured by Yamamoto Metal Testing Co., Ltd.). The nickel plating thickness was 2.5 μm, the plating bath temperature was 60 ° C. for the Watt bath, the sulfamic acid bath was 70 ° C., and the pH of the plating bath was set to pH 4 for both the Watt bath and the sulfamic acid bath. Moreover, the composition of the Watt bath and the sulfamic acid bath used in each Example and Comparative Example is as follows.

Watt bath nickel sulfate 300g / l
Nickel chloride 45g / l
Boric acid 30g / l

Sulfamic acid bath nickel sulfamate 450g / l
Nickel chloride 5g / l
Boric acid 30g / l
Additive (Pitless S) 5ml / l

  Next, except that the cathode standard test piece was changed to a laminate of SUS316L, which is a non-magnetic metal plate, and Cu foil cold-rolled at high pressure, nickel was deposited on the Cu foil under exactly the same conditions as above. Plating was applied. That is, masking was performed on the back surface of SUS316L where the size of the laminated material and the standard test piece were the same, and no Cu foil was provided. In addition, after laminating SUS316L and Cu foil, heat treatment was performed at 850 ° C. for 5 minutes, and the Cu foil was biaxially crystal-oriented. The biaxial crystal orientation degree Δφ of the Cu foil was 4.2 °.

  After nickel plating, the biaxial crystal orientation degree Δφ of each plating film (protective layer) was measured by X-ray diffraction in the same manner as the Cu layer. The results are shown in Table 1 and FIG.

As is clear from Table 1 and FIG. 1, by controlling the plating strain ε of the protective layer to 15 × 10 ⁻⁶ or less, Δφ of 6 ° or less was stably obtained. By keeping Δφ of the protective layer low, it is advantageous because a high critical current density can be expected when an intermediate layer and a superconducting compound layer are laminated thereon by epitaxial growth. In particular, when a sulfamic acid bath is employed as the plating bath (Examples 3 to 5), even if the current density is increased as compared with the watt bath, the plating strain is reduced, which is preferable from the viewpoint of production efficiency.

Claims (6)

An epitaxial growth substrate having a biaxial crystal-oriented Cu layer and a protective layer provided on the Cu layer, wherein the protective layer has a plating strain ε of 15 × 10 ⁻⁶ or less.   The epitaxial growth substrate according to claim 1, wherein the protective layer is made of Ni or a Ni alloy.   The substrate for epitaxial growth according to claim 1 or 2, wherein the thickness of the protective layer is 1 µm or more and 5 µm or less. A method for manufacturing an epitaxial growth substrate, comprising: forming a protective layer by performing plating so that a plating strain ε is 15 × 10 ⁻⁶ or less on a biaxially crystallized Cu layer.   The method for producing a substrate for epitaxial growth according to claim 4, wherein the plating is performed using a sulfamic acid bath.   A substrate for superconducting wires, wherein the epitaxial growth substrate according to any one of claims 1 to 3 is laminated on a nonmagnetic metal plate.

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