JP5624802B2 - Method for manufacturing substrate for oxide superconducting wire - Google Patents

Description

  The present invention relates to a method for producing a substrate for an oxide superconducting wire that is used when a superconducting layer is formed on a metal substrate to produce an oxide superconducting wire.

Conventionally, many attempts have been made to produce an oxide superconducting wire by forming a superconducting layer on a metal substrate. In particular, an oxide superconductor represented by the composition formula of REBa ₂ Cu ₃ O _7-d (RE = rare earth element, also referred to as 123-based or yttrium-based superconductor) is used to form a film on a tape-shaped metal substrate. An oxide superconducting wire having flexibility is one of the superconducting wires that are being actively researched and developed since high current characteristics can be obtained.

  In such an oxide superconducting wire, the superconducting characteristics greatly depend on the crystal orientation of the superconductor, particularly the biaxial orientation. Therefore, as disclosed in Patent Document 1, in order to obtain a superconducting layer having high biaxial orientation, it is necessary to improve the crystal orientation of the surface of the intermediate layer serving as a base.

  In addition, since the characteristics of oxide superconducting wires deteriorate due to diffusion of elements such as nickel contained in the metal substrate into the superconducting layer, an intermediate layer added with a characteristic to suppress diffusion is added to Patent Document 2. A method is disclosed in which a superconducting layer is formed and a superconducting layer is formed thereon to form a superconducting wire.

JP 2009-289666 A Japanese Patent Laid-Open No. 11-86647

  However, since oxide superconductivity forms a superconducting layer by performing a heating reaction in an oxygen atmosphere, even if the diffusion of elements contained in the metal substrate to the superconducting layer is prevented, Some nickel diffuses in the substrate and moves to the substrate surface, where it reacts with oxygen and is oxidized. When nickel is oxidized to become nickel oxide, irregularities are generated on the surface of the substrate, which causes the superconducting layer to be partially peeled off, resulting in a problem that the superconducting properties are deteriorated.

  The present invention has been made in view of the above circumstances, and provides a method for producing a good substrate for an oxide superconducting wire by preventing peeling caused by surface diffusion and surface oxidation of nickel contained in a substrate. The purpose is to provide.

That is, the present invention includes a step of forming a plating layer made of chromium or a chromium-based alloy on a substrate surface containing at least nickel, and an oxygen atmosphere of 1 atm with respect to the substrate on which the plating layer is formed. The plating layer has a thickness of 50 nm to 200 nm, the heat treatment temperature in the heat treatment step is 300 ° C. to 550 ° C., and the heat treatment time is 30 minutes to 50 minutes. It is the manufacturing method of the board | substrate for oxide superconducting wires characterized by the following.
In the present invention, when the thickness of the plating layer is less than 50 nm, there is a problem that diffusion of nickel contained in the substrate to the substrate surface and oxidation of the substrate surface cannot be prevented. When it is made thicker, there is a problem in that the oxide superconducting wire formed using the substrate has poor bending workability, and peeling occurs during processing.
Further, in the present invention, when the heat treatment is performed, if it is less than 300 ° C., there is a problem that chromium is not sufficiently oxidized and nickel oxide is difficult to be formed, and if it exceeds 550 ° C., not only chromium but also in the substrate. Oxidation of nickel contained also progresses, resulting in surface roughness, which may cause peeling between interlayers formed on the substrate or between the substrate and the interlayer, in order to obtain an oxide superconducting wire. .

At this time, it is preferable that the thickness of the plating layer is 100 nm and the heat treatment time is 50 minutes.

The present invention also includes a step of forming a plating layer made of chromium or a chromium-based alloy on the surface of a substrate containing at least nickel, and an oxygen atmosphere of 1 atm with respect to the substrate on which the plating layer is formed. The plating layer has a thickness of 100 nm to 200 nm, a heat treatment temperature in the heat treatment step is 500 ° C., and a heat treatment time is 50 minutes. It is a manufacturing method of the board | substrate for oxide superconducting wires.

  Furthermore, it is preferable to have the process of grind | polishing with respect to a base | substrate before the process of forming a plating layer. The smoothness of the intermediate layer formed on the substrate can be improved by setting the surface roughness Ra of the substrate surface to, for example, 10 nm or less by polishing.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the board | substrate for oxide superconducting wires which does not produce peeling between the film-forming film | membrane in the film-forming process or the heat processing after film-forming completion can be provided.

FIG. 1 is a cross-sectional view showing a superconducting thin film wire formed by forming an intermediate layer and a superconducting thin film on a substrate formed by the method for manufacturing a substrate for an oxide superconducting wire according to an embodiment of the present invention.

An embodiment of the present invention will be described. The manufacturing method of the substrate for oxide superconducting wire of the present invention is as follows:
(1) A step of forming a plating layer made of chromium or a chromium-based alloy on the surface of a substrate containing at least nickel (plating layer forming step);
(2) A heat treatment process (oxidation process) for performing heat treatment in an oxygen atmosphere on the substrate on which the plating layer is formed.
Have

FIG. 1 shows a bed layer on an oxide superconducting wire substrate (having a plated layer 2 formed on a substrate 1) formed by the method for manufacturing an oxide superconducting wire substrate according to an embodiment of the present invention. 3a is a cross-sectional view showing a superconducting thin film wire formed by forming an intermediate layer 3 composed of 3a, an alignment layer 3b, a cap layer 3c, and a superconducting layer 4. FIG.
Here, the material containing at least nickel as the substrate 1 is Hastelloy (trade name), Inconel (trade name), Haynes Alloy (trade name), MC Alloy (trade name), Monel (trade name), Yudimet (trade name). ), Nimonic (trade name), Rene (trade name), stainless steel, and Incoloy (trade name).

(1) Plating layer forming step According to the embodiment of the present invention, the plating layer 2 made of chromium or an alloy containing chromium as a main component may be formed on the surface of the base 1 containing at least nickel.
More preferably, as an embodiment of the present invention, as described below, it is preferable to have a step of polishing the surface of the substrate 1 before forming the plating layer 2.

(Polishing process)
Mirror polishing is performed on at least one surface of the surface of the substrate 1 containing at least nickel. As a polishing method, mechanical polishing, electrolytic polishing, chemical polishing, or a combination thereof can be employed.

In mechanical polishing, the abrasive grains are preferably diamond grains or oxide grains, especially aluminum oxide, cerium oxide, chromium oxide, zirconium oxide, iron oxide, etc., and their solutions (polishing liquid)
May be water, surfactants, oils, organic solvents, or a mixture thereof, or a solution 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.
Especially soapy water is 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 the electrolytic polishing, the substrate 1 is immersed in an electrolytic solution, and the surface of the substrate 1 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 the polishing process, the surface roughness Ra of the surface of the substrate 1 is set to 10 nm or less. If the surface roughness Ra of the surface of the substrate 1 exceeds 10 nm, the smoothness of the intermediate layer 3 is affected, which is not preferable. The surface roughness Ra of the surface of the substrate 1 is more preferably 5 nm or less, and further preferably 2 nm or less. 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.

(Plating process)
Next, a plating layer 2 made of chromium or a chromium alloy is applied to the surface (one side or both sides) of the substrate 1 by wet plating. The plating may be matte plating or gloss plating, and is not necessarily limited to wet plating, and dry plating can also be applied. Alternatively, for example, chromium may be deposited to a thickness of several nanometers by sputtering, and then, for example, a chromium alloy may be laminated to a thickness of several μm by wet plating. Alternatively, a plurality of layers can be formed by dry plating and wet plating, respectively.

  Here, as an alloy containing chromium as a main component, a Ni—Cr alloy such as Inconel (trade name) or a Co—Cr alloy such as stellite (trade name) (Stellite 6, 31, 21, etc.) can be used.

  The thickness of the plating layer 2 is preferably 50 nm to 200 nm, more preferably 70 nm to 100 nm so that surface diffusion and surface oxidation of nickel contained in the substrate 1 do not occur. When the thickness is less than 50 nm, the chromium oxide layer formed in the portion corresponding to the plating layer 2 is not sufficiently formed by the subsequent oxidation treatment process. Moreover, when it exceeds 200 nm, when it becomes an oxide superconducting wire, bending workability will worsen.

  In order to ensure the flatness of the surface, it is preferable that the conveyance speed of the substrate 1 in the plating step is 5 to 60 m / h. By carrying out at this conveyance speed, the surface roughness Ra of the plating layer 2 can be 10 nm or less.

(2) Oxidation treatment step Oxidation treatment is performed for the plating layer 2 formed on the substrate 1 to be a chromium oxide layer for preventing peeling caused by surface diffusion and surface oxidation of nickel contained in the substrate 1. I do.
This chromium oxide layer is considered to be a layer made only of chromium oxide (Cr ₂ O ₃ ). Alternatively, it may be present in the form of spinel type NiCr ₂ O ₄ or FeCr ₂ O ₄ . This formula is a composition as an ideal equilibrium state, and in actuality, the atomic ratio is not an integer ratio. In the case of NiCr ₂ O ₄ , the composition is, for example, Ni _1.2 Cr _1.8 O _3.9. Or (NiO) _1.2 (CrO _1.5 ) _1.8 .

Incidentally, the existence ratio of the ideal elements in NiCr ₂ O ₄ and FeCr ₂ O _4, in the case of _{NiCr 2 O 4, Ni (25.9wt} %, 14.3at%), Cr (45.9wt%, 28. 6 at%), O (28.2 wt%, 57.1 at%), and FeCr ₂ O ₄ , Fe (24.9 wt%, 14.3 at%), Cr (46.5 wt%, 28.6 at%), O (28.6 wt%, 57.1 at%).

Furthermore, these substances, small amounts of than Cr and Cr ₂ O _3, for example, other metals less than 30 wt% can be considered even if the solid solution. In the above case, the chromium oxide layer is represented by the formula Cr _w M ′ _x M “ _y ... O _z (w, x, y, and z are all positive numbers). Among them, the amount w (atomic%) of Cr is the maximum.

  The chromium oxide layer is preferably 10 to 300 nm. If the layer thickness is less than 10 nm, it is too thin to sufficiently exert the function of suppressing delamination. On the other hand, if it exceeds 300 nm, the chromium oxide layer itself may be cracked or peeled off.

  In order to form the chromium oxide layer as described above, it is preferable to use the following oxidation treatment conditions.

  The heat treatment temperature is desirably 300 ° C. or higher and lower than 550 ° C. When the temperature is lower than 300 ° C., the plating layer 2 is not sufficiently oxidized, and there is a problem that the chromium oxide layer does not sufficiently function to suppress delamination. When the surface of the layer becomes rough and becomes an oxide superconducting wire, it may cause deterioration of superconducting characteristics. The heat treatment time is desirably 10 minutes to 60 minutes. If it is less than 10 minutes, there is a problem that a sufficient film thickness of the chromium oxide layer cannot be ensured. If it exceeds 60 minutes, nickel contained in the substrate is also oxidized and may cause peeling.

  The heat treatment atmosphere may be an oxygen atmosphere or an atmosphere composed of oxygen and an inert gas, and the oxygen partial pressure at this time is preferably 0.2 atm or more and 1 atm or less. When the oxygen partial pressure is less than 0.2 atm, there is a problem that the amount of oxygen for oxidizing the chromium contained in the plating layer is insufficient, and the chromium oxide layer is difficult to be formed. Nickel contained in 1 is also oxidized and may cause peeling.

  Through the above steps, the oxide superconducting wire substrate of the present invention can be obtained. Moreover, an oxide superconducting wire can be obtained by performing the following steps using the obtained oxide superconducting wire substrate.

(Formation of intermediate layer)
An intermediate layer 3 for forming the superconducting layer 4 can be formed on the chromium oxide layer. In this case, the intermediate layer 3 can include Y ₂ O ₃ or Gd ₂ Zr ₂ O ₇ .

For example, a bed layer 3a made of Y ₂ O ₃ or Gd ₂ Zr ₂ O ₇ is formed by sputtering, and an alignment layer 3b made of MgO is formed on the bed layer 3a by IBAD, Furthermore, a cap layer 3c made of CeO ₂ may be formed on the alignment layer 3b by sputtering.

(Formation of superconducting layer)
A superconducting layer 4 is formed on the intermediate layer 3. At this time, the superconducting layer 4 may be any RE-based superconducting material. Here, RE is a rare earth element, and one or more kinds selected from Y, Nd, S m, E u, G d, D y, H o, E r, T m, Y b, and L u. It is a superconducting material consisting of elements. For example, a superconducting material made of YBCO may be formed by MOCVD.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited by the following Example.

One surface of a substrate made of tape-shaped Hastelloy C-276 was subjected to surface polishing by abrasive polishing. At this time, the surface roughness Ra of the substrate was 2 nm or less.
Next, a Cr film having a thickness of 10 nm to 250 nm was formed using a plating method to form a plating layer. The plating method used at this time was electrolytic plating, and a Sargent bath having 250 g / l chromic anhydride, 2.5 g / l sulfuric acid, a bath temperature of 50 to 55 ° C., and a current density of 15 to 60 A / dm ² was used. In addition, in order to raise the surface flatness of a plating layer, the conveyance speed of the wire was set to 60 m / h.
Thereafter, a heat treatment is performed for 20 minutes to 60 minutes in an oxygen atmosphere at 500 ° C. and 1 atm to form a chromium oxide layer made of Cr ₂ O ₃ having a thickness of 30 nm to 200 nm to obtain a substrate for an oxide superconducting wire. It was. At this time, the surface roughness Ra of the chromium oxide layer was 10 nm or less.

  As a comparative example, one surface of a base made of tape-shaped Hastelloy C-276 was subjected to surface polishing by abrasive polishing to obtain an oxide superconducting wire substrate. At this time, the surface roughness Ra of the substrate was 5 nm.

A 100 nm-thick bed layer made of Gd ₂ Zr ₂ O ₇ was formed on the oxide superconducting wire substrate obtained by the manufacturing methods of Examples and Comparative Examples using a sputtering apparatus. Then, on this bed layer, an alignment layer (IBAD-MgO layer) made of MgO was formed at a room temperature of 10 to 200 mm by an IBAD method. On the alignment layer, a cap layer made of CeO 2 was formed to a thickness of 200 nm at 650 ° C. by sputtering. On the cap layer, a superconducting layer made of YBCO was formed to a thickness of 1 μm at 845 ° C. by MOCVD to obtain an oxide superconducting wire. Further, although not shown in FIG. 1, an Ag protective layer was formed on the superconducting layer, and oxygen annealing was performed at 550 ° C. in an oxygen stream.

(Characteristic evaluation test)
Confirmation of delamination was performed by observing the surface of the obtained oxide superconducting wire by Auger electron spectroscopy. In addition, the observation of the surface of the obtained oxide superconducting wire includes a state in which bending strain is not applied to the obtained oxide superconducting wire, and a state in which bending strain is applied with the oxide superconducting wire wound around a coil. I went there.
Auger electron spectroscopy analysis was performed using a PHI-660 scanning Auger electron spectrometer manufactured by PHISICAL ELECTRONICS. The acceleration voltage of the electron gun was 10 kV, and the measurement was performed under the condition that the material current was 500 nA.
At this time, the state where there was no peeling or blistering was marked with ◯, the state where there was no flaking but there was blistering was marked with Δ, and the state where peeling was caused was marked with ×.

In addition, the conditions wound around a coil set the bending strain of a longitudinal direction to 1% in the formula regarding the bending strain shown by following formula (1).
ε = (t / D) × 100 (1)
Here, each symbol indicates the following.
ε (%): bending strain t (mm): oxide superconducting wire thickness D (mm): inner diameter of coil

  Moreover, the critical current Ic of the obtained oxide superconducting wire was measured. The critical current was measured using a four-terminal method in a state where 200 m of the oxide superconducting wire was immersed in liquid nitrogen. The measurement was performed at a pitch of 1 m, the voltage terminal was 1.2 m, and the electric field reference was 1 μV / cm.

  Table 1 shows the specifications and characteristics evaluation results of the examples and comparative examples.

  In Comparative Example 1, it can be seen that delamination occurs and Ic is low even in a normal wire state. On the other hand, about Examples 1-13, delamination has not arisen, Ic is also 100A or more, and in Examples 3-8 and 10-12 which are suitable conditions, an oxide superconducting wire of 200A or more is used. Current characteristics could be obtained.

  In Examples 1 to 8, when the thickness of the plating layer was changed to 10 to 250 nm, it was found that when the thickness was less than 50 nm, there was no delamination but slight swelling occurred. In the case of a plating layer thicker than 200 nm, a slight swelling occurred when bending strain was applied. For this reason, the thickness of the plating layer is preferably 50 nm or more and 200 nm or less.

  Further, in Examples 9 to 13, when the heat treatment temperature for performing the oxidation treatment was 250 ° C. to 600 ° C., when the temperature was less than 300 ° C., the chromium of the plating layer was insufficiently oxidized, and the film of the chromium oxide layer Since the thickness was reduced, there was no delamination, but blisters were formed. Moreover, when it exceeded 550 degreeC, since the base-material surface was roughened, it resulted in a blister being produced. This is presumably because nickel contained in the substrate diffused on the surface of the substrate and nickel oxide was formed between the chromium oxide layer and the substrate. Therefore, the heat treatment temperature for performing the oxidation treatment is preferably 300 ° C. or higher and 550 ° C. or lower.

1 Substrate 2 Plating layer 3 Intermediate layer 4 Superconducting layer

Claims (4)

Forming a plating layer made of chromium or a chromium-based alloy on a substrate surface containing at least nickel;
A heat treatment step of performing a heat treatment in an oxygen atmosphere of 1 atm on the substrate on which the plating layer is formed,
The plating layer has a thickness of 50 nm to 200 nm,
A method for manufacturing a substrate for an oxide superconducting wire, wherein a heat treatment temperature in the heat treatment step is 300 ° C. or higher and 550 ° C. or lower, and a heat treatment time is 30 minutes or longer and 50 minutes or shorter.   The method for manufacturing a substrate for an oxide superconducting wire according to claim 1, wherein the plating layer has a thickness of 100 nm and the heat treatment time is 50 minutes. Forming a plating layer made of chromium or a chromium-based alloy on a substrate surface containing at least nickel;
A heat treatment step of performing a heat treatment in an oxygen atmosphere of 1 atm on the substrate on which the plating layer is formed,
The plating layer has a thickness of 100 nm to 200 nm,
A method for manufacturing a substrate for an oxide superconducting wire, wherein a heat treatment temperature in the heat treatment step is 500 ° C. and a heat treatment time is 50 minutes.   The method for manufacturing a substrate for an oxide superconducting wire according to any one of claims 1 to 3, further comprising a step of polishing the substrate before the step of forming the plating layer.

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