JPH0421596A - Production of substrate for oxide superconductor - Google Patents

Abstract

PURPOSE:To form an oxide superconducting thin film in good crystalline orientation state by putting a noble metal material between two sheets of metal substrates consisting of a heat-resistant alloy having high strength and rolling the noble metal in the above-mentioned state to form a composite and then dividing the composite into two parts so as to leave the noble metal material on either one metal substrate and carrying out heat treatment of the noble metal material. CONSTITUTION:In the production of a substrate for oxide superconductor provided with a metal substrate part consisting of a heat resistant alloy having high strength such as hastelloy and covering layer formed on the upper face of the metal substrate part and consisting of a noble metal part having face-centered cubic structure and having an oxide superconducting thin film formed on the above-mentioned covering layer, the following method is selected: The noble metal material 3 is rolled in a state where the material 3 is put between two sheets of metal substrates 1 and 1' consisting of the heat-resistant alloy having high strength to form a composite. Then either one metal substrate 1' is peeled from the composite and then part of the noble metal material 3 is subjected to heat treatment and a crystal of the surface of noble metal material 3 is oriented along (100) face to form the aimed substrate consisting of the metal substrate part 1 and covering layer 3 of noble metal material.

Description

[Detailed Description of the Invention] "Field of Industrial Application" This invention is a base material for manufacturing oxide superconducting conductors, which are being developed for application as superconducting magnets, superconducting generators, superconducting energy storage, accelerator magnets, etc. Regarding.

"Prior art" Y-B a-Cu-0 system, B i-3r-Ca-Cu
BACKGROUND ART Elongated superconducting conductors have been developed using oxide superconductors typified by -0 series, TI-B a-Ca-Cu-0 series, and the like.

Considering the practical use of long superconducting conductors using this type of oxide superconductor, it is necessary to prepare a base material made of a material with excellent flexibility and good workability, such as metal tape. It is desirable to form an oxide superconducting thin film on this base material to produce an oxide superconducting conductor.

However, the metal substrates for oxide superconducting conductors that have been reported to date are limited to gold, platinum, silver, Hastelloy, etc., and it is difficult to form oxide superconducting thin films on substrates made of these metal materials. The obtained oxide superconducting conductor is an oxide superconducting conductor obtained by forming an oxide superconducting thin film on a substrate made of a single crystal such as strontium titanate (S rT io 3) or magnesia (MgO). In contrast, the current critical current density is two to three orders of magnitude lower.

The main cause of such a decrease in the critical current density of an oxide superconducting thin film formed on a metal base material is the problem of crystal orientation of the oxide superconductor.

That is, this type of oxide superconductor has electrical anisotropy that allows current to flow easily in a specific direction of the crystal and makes it difficult to flow a current in a specific direction.

Therefore, when attempting to manufacture a superconducting conductor using an oxide superconductor, controlling crystal orientation becomes an important issue.

In the crystal structure of an oxide superconductor having a perovskite structure as a basic structure, copper atoms and oxygen atoms are aligned and bonded in the a-axis direction and the b-axis direction of the crystal axis, and this bonding portion is It has a structure in which layers are stacked in the C-axis direction.

Therefore, this type of oxide superconductor has a high critical current density in the ab-axis direction of the crystal, so in order to increase the critical current density, the ab-axis of the crystal should be arranged parallel to the substrate surface. That is, it is preferable to form the oxide superconductor so that the C axis of the crystal axis is perpendicular to the surface of the substrate. Furthermore, since it is necessary to form an oxide superconducting thin film on the surface of a base material, the size of the crystal lattice on the surface of the base material used must be equal to the size of the crystal lattice in the ab-axis direction of the oxide superconductor. is desirable.

Examining the aforementioned single-crystal substrate from the above viewpoint, it is found that SrT i O3 is oriented in the (100) plane.
In the crystal of , a=3.91 people, (100)
In a plane-oriented MgO crystal, a=4.2
While there is one person, Y IB at CusO7-6
In the Y-based oxide superconductor with the composition, a=3.8
9 people, b=3.82 people, which is a value extremely close to the above value.

On the other hand, although the base material made of Ag has a face-centered cubic crystal structure with a = 4.09, there are many materials that have been conventionally used for manufacturing oxide superconducting conductors. It had a crystalline structure, and the orientation of the crystals was not aligned. Therefore, when an oxide superconducting thin film is fabricated on an Ag base material, it is difficult to align the oxide superconducting thin film with the C-axis due to the mismatch in the lattice constants between the surface of the base material and the ab axis of the oxide superconducting thin film. There was a difficult problem.

In addition, the base material made of Ag tends to soften due to heat treatment performed during or after the formation of the oxide superconductor, and it may not be strong enough to be applied to devices that are subjected to external forces caused by the electromagnetic force of superconducting magnets. There is a problem. Furthermore, if the strength of the base material itself is insufficient, there is a risk that the superconducting thin film on the base material will crack or the base material and the superconducting thin film may separate from each other due to the application of stress.

Based on the above background, the inventors of the present application have developed Ag on a high-strength metal base material as a base material for manufacturing oxide superconducting conductors.
We are conducting research and development on a technology that uses a base material with a coating layer formed on it.

Here, conventionally, in order to form an Ag coating layer on a metal base material part, the metal base material part and Ag tape are brought into close contact with each other by means such as explosive bonding, and then rolled into a composite body. That's what I do.

However, there is a large difference in mechanical strength between metal materials such as Hastelloy, which is widely used as a high-strength, heat-resistant metal material, and Ag, and the work hardening properties of the two are also significantly different. Alternatively, there were problems such as the metal base material being deformed into a wavy state or breaking, resulting in a low yield.

The present invention has been made to solve the above-mentioned problems, and it is possible to form an oxide superconducting thin film in a good crystal orientation state, and to efficiently produce a base material for producing an oxide superconducting conductor that has high mechanical strength and is resistant to stress. The purpose is to provide a method that can be manufactured well.

"Means for Solving the Problems" In order to solve the problems described above, the present invention provides a metal base made of a heat-resistant, high-strength alloy such as Hastelloy, and a crystalline surface formed on the upper surface of the metal base. A method for manufacturing an oxide superconducting conductor base material comprising a coating layer made of a precious metal material having a center-cubic structure, and an oxide superconducting thin film is formed on the coating layer, comprising: 2 made of a heat-resistant high strength alloy; A coating material made of a precious metal material is sandwiched between two metal substrates, and the metal substrate and coating material are pressed together to form a composite. The material is peeled off into two pieces at the boundary, and then heat treated to orient the crystals on the surface of the covering material made of a noble metal material along the (100) plane, thereby forming a base material consisting of a metal base material part and a covering layer. It is.

``Operation'' Since the rolling process is performed with the soft precious metal covering material sandwiched between the high-strength alloy metal base material from above and below, the rolling process is performed without causing any waving or wire breakage. A base material is used that is provided with a coating layer made of a noble metal having a lattice constant close to that of the oxide superconductor, and the crystals of this coating layer are oriented in the (100) plane direction. When a superconducting thin film is formed, the oxide superconducting thin film grows while matching the crystal structure of the surface of the coating layer. Therefore, a C-axis oriented oxide superconducting thin film is formed on the surface of the substrate.

Furthermore, since the noble metal coating layer is reinforced with a metal base portion having high strength, it is possible to obtain a structure that has superior mechanical strength and is resistant to external forces than a base material made of a noble metal alone.

The present invention will be explained in more detail below.

In order to form a base material and further manufacture an oxide superconductor by carrying out the method of the present invention, first, as shown in FIG. , 1 is prepared, and between this metal base material 1.1, A
A thin plate-shaped covering material 3 made of precious metals such as g, Au, Pt, or alloys thereof is sandwiched in between, and the whole is rolled in this state to form a tape-shaped composite with a three-layer structure as shown in Fig. 2. form 4. This composite body 4 has a tape-shaped metal base material 6 made of a heat-resistant high-strength alloy on both upper and lower surfaces of an Ag coating material 5.
The structure is made by crimping. The composite body 4 is therefore flexible and can be wound around a delivery drum 7 shown in FIG.

Next, the composite body 4 is peeled off into two pieces with the noble metal coating 5 as a boundary. Specifically, the peeling is performed as shown in FIG. 3. In FIG. 3, numeral 7 indicates a delivery drum formed by winding the composite material 4, 8 indicates a winding drum, and 9.9 indicates a roll. Here, the tip of the composite material 4 fed out from the delivery drum 7 is cut into two parts at the center in the thickness direction of the coating material 5, and the cut parts are passed between the rollers 9, 9, and wound. Attach it to the outer periphery of the take-up drum 8.8. From this state, by rotating the winding drum 8°8, the composite 4 is pulled out from the delivery drum 7 while the 2
The tape IO210 can be obtained by tearing it into books.

Note that the rolling process changes the crystal structure of the noble metal, resulting in elongated grains with crystal grains extending in the longitudinal direction, so that the silver easily tears in the longitudinal direction during the tearing process. Of course, in this case, it is assumed that the metal base material l made of Hastelloy and the coating material 5 made of silver are sufficiently firmly bonded. Note that by heating the composite 4 to a temperature of about 800°C for about 1 hour,
If the metal base material 1 and the coating material 5 are firmly bonded, and the silver coating material 5 is softened to cause stress concentration in the coating material 5, tearing becomes easy.

After tearing the composite 4 into two tape-like pieces, the tape l
In order to smooth the noble metal layer on the surface of O, polishing or light rolling is performed. To perform the rolling process, for example, as shown in FIG. 4, the tape IO is unwound from the winding drum 8, passed between rolls 11 and 11 to be rolled, and then wound onto the winding drum 12. Just do it.

Once the tape IO is rolled, it is preferably heated under an oxygen partial pressure of 1 atm or less at a temperature above 300°C and below 700°C, more preferably between 500 and 600°C.
C. for 100 hours or less, more preferably 1 to 6 hours, to orient the crystals on the surface of the noble metal layer.

Here, it is known that when a metal such as silver is subjected to strong plastic working such as hard rolling, it becomes a processed structure, that is, a texture with a preferential orientation, and crystals are aligned in a special orientation. Therefore, by forming the tape into a tape shape through the rolling process described above and developing a texture, and then applying heat treatment, the crystal orientation of the crystal grains can be preferentially aligned in a specific direction, and the orientation at this time is ( 100) direction, which contributes to the lattice constant and C-axis orientation of the oxide superconductor.

As a result of the above heat treatment, the crystals on the surface of the noble metal layer become (10
0) The planes are oriented to form the coating layer 15, and as a result, as shown in FIG. Material I7 is obtained.

Here, since the metal base member l is formed from a heat-resistant metal such as Hastelloy, it will not be damaged or deteriorated in strength by heat treatment.

The crystal structure of the coating layer 15 made of these noble metals is similar to that of the oxide superconductor, and the lattice constants are also similar. For example, Y IB at CLi2O, -6
In the crystal of the oxide superconductor with the composition, the crystal structure is based on perovskite, and a=3.89,
b=3.82. On the other hand, Ag, Au, and Pt all have face-centered cubic structures, with a=4.09 for Ag, a=4.08 for Au, and a=3.92 for Pt.

In order to manufacture an oxide superconducting conductor using the base material 17, an oxide superconductor is formed on the coating N15 of the base material 17 using a film forming method such as sputtering, molecular beam epitaxy, laser PVD, or CVD. Forms a thin film. The oxide superconducting thin film here is Y-Ba-Cu-0 based, Bi-
8r-Ca-Cu-0 system, Tl-Ba-Ca-Cu-0
It is an oxide typified by the

Specifically, for example, Y IB atc uso? -5, Bit S rt Cat Cus OX, or TltBatCax Cu30X.

When forming an oxide superconducting thin film on the base material 17, since the crystals on the surface of the base material are oriented in the (100) plane, the crystal orientation of the oxide superconducting thin film formed on the base material surface is also It will be in good condition. That is, a of the crystal of the oxide superconducting thin film
The -b plane is oriented parallel to the upper surface of the covering layer 15, and the crystal is oriented so that the C axis of the crystal is perpendicular to the surface of the covering layer 15.

Once the oxide superconducting thin film is formed on the base material I7, heat treatment may be performed to homogenize the oxide superconducting thin film by heating it to 500 to 800° C. for about 1 minute to several hours and then slowly cooling it. This heat treatment adjusts the crystal structure of the oxide superconducting thin film, improves superconducting properties, and yields an oxide superconducting conductor.

If an oxide superconducting thin film is further formed on the covering layer 15 in which the surface crystals are oriented as described above, the film can be formed without aligning the crystal axis of the oxide superconducting thin film with the crystal axis of the covering layer 15. An oxide superconducting thin film can be deposited on a Go board in an oriented state. Therefore, an excellent oxide superconductor having a high critical current density can be obtained.

In addition, the obtained oxide superconducting conductor has excellent heat resistance and is reinforced with a high-strength metal base material, so it is difficult to apply stress due to electromagnetic force when used as a superconducting magnet. Even if the superconducting thin film is used, there is little risk of cracks occurring in the superconducting thin film, and it is resistant to external forces.

By the way, when combining a metal base material made of a heat-resistant, high-strength metal and a coating material made of a noble metal, as shown in FIG. The base material may be formed by sandwiching the material by 3 degrees and rolling it.

If the composite is performed using two pieces of covering material 3° and 3° as in this example, when tearing in the later process, the covering material 3
°, 3° easily separates into two. Furthermore, in order to further facilitate the separation operation, a female molding agent may be applied to the interface between the coating materials 3' and 3'. This mold release agent can be removed by polishing or the like after tearing.

By manufacturing a base material using the metal base material 1.1 and the coating materials 3° and 3° shown in FIG. 6, a base material equivalent to the base material 17 of the previous example can be obtained.

"Example" A plate made of Ag with a thickness of 1 mm was sandwiched between two substrates made of Hastelloy C-276 with a thickness of 3 mm, and rolled to a total thickness of 0.35 a+. -1 width 5I
III11. A tape-shaped composite is formed with a metal base portion having a thickness of 0.3 tam and a coating layer having a thickness of 0.05 mm.
By heat treating at 600°C for 1 hour under an oxygen partial pressure of 5 to 1.0 atm, the Ag crystals on the surface of the coating layer are
0) Oriented along the plane.

FIG. 7 shows the results of an X-ray diffraction test of the coating layer of the base material produced as described above. As is clear from Figure 7, (2
A diffraction peak of the 00) plane was observed, indicating that the surface portion of the coating layer was crystal oriented.

Subsequently, Y was deposited on the coating layer using a laser evaporation device.

An oxide superconducting thin film having a composition of BatCuso t-6 could be formed.

Furthermore, as a result of measuring the tensile strength of the oxide superconducting conductor manufactured as described above, it showed an excellent value of 50 kg/mad''.
The tensile strength of the oxide superconducting conductor obtained by heat-treating the tape to crystallize it and forming a superconducting thin film thereon was 14 kg/11 m'.

From the above, it is clear that the oxide superconducting conductor manufactured using the base material of the present invention not only has an oxide superconducting thin film with good orientation, but also has high tensile strength compared to a tape material made only of Ag. Became. Therefore, the oxide superconducting conductor is suitable for use in superconducting magnets that are exposed to external forces such as electromagnetic force.

"Effects of the Invention" As explained above, according to the present invention, since a soft precious metal material is sandwiched between metal base materials made of a high-strength heat-resistant alloy and rolled, wavy parts and broken parts occur during rolling. This eliminates the problem and improves the yield during rolling. Furthermore, 1
Since two base materials can be manufactured from a book composite, manufacturing efficiency is good and it is suitable for mass production.

In addition, by using a base material in which a coating layer made of a noble metal having a lattice constant close to that of an oxide superconductor and having a similar lattice constant to a crystal is formed on a metal substrate, crystals on the surface of the coating layer of this base material are used. is oriented in the direction of the (100) plane, so if an oxide superconducting thin film is formed on the coating layer using this base material, the oxide superconducting thin film will align with the crystal structure of the coating layer surface. grow up. Therefore, a C-axis oriented oxide superconducting thin film can be produced on the substrate, and an oxide superconducting conductor with good crystal orientation and high critical current characteristics can be obtained.

Furthermore, since the proportion of noble metal used can be lower than when the entire base material is made of expensive noble metals, the cost of the oxide superconducting conductor obtained by using the base material of the present invention can be reduced.

Furthermore, by forming a coating layer on a heat-resistant, high-strength metal base material and further forming an oxide superconducting thin film, the metal base material exhibits strength when stress is applied, and the superconducting thin film Since the generation of cracks is prevented, an oxide superconducting conductor that is resistant to external forces can be obtained.

[Brief explanation of the drawing]

Figures 1 to 5 are for explaining an example of the method of the present invention. Figure 1 is a cross-sectional view showing the coating layer sandwiched between metal base parts, and Figure 2 is a cross-sectional view of the composite material. 3 is a side view showing the state of tearing the composite material, FIG. 4 is a side view showing the state of rolling processing, FIG. 5 is a perspective view of the obtained base material, and FIG. 6 is the second embodiment of the present invention. FIG. 7 is a side view showing the laminated state of the metal base material and the coating material used in the examples, and a graph showing the results of an X-ray diffraction test of the coating layer on the top surface of the base material. 1.6...Metal base material, 3.3', 5...Coating material, composite, 5...Coating layer, 6-Metal base material portion, 7... Base material.

Claims (1)

[Scope of Claims] A metal base made of a heat-resistant, high-strength alloy such as Hastelloy, and a coating layer made of a precious metal material with a crystalline face-centered cubic structure formed on the upper surface of the metal base. Then,
A method for producing a base material for an oxide superconducting conductor, in which an oxide superconducting thin film is formed on the coating layer, the noble metal material being sandwiched between two metal base materials made of a heat-resistant high-strength alloy. The metal base material and the precious metal material are pressed together to form a composite by rolling in the state, and then this composite is peeled off so that the precious metal material remains on one of the metal bases, and then heat treatment is performed. Production of a base material for an oxide superconducting conductor, characterized in that crystals on the surface of the noble metal material are oriented along the (100) plane to form a base material consisting of a metal base portion and a coating layer of the noble metal material. Method.