JPS6121371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a superconducting wire based on compounds such as Nb ₃ Sn and V ₃ Ga. The present invention relates to a method of manufacturing a wire rod.

In general, compound-based superconducting wire is produced by manufacturing a wire containing multiple metals that become a compound with superconducting properties through a reaction, and then heat-treating the wire to cause a reaction between the metal materials to form a superconducting material. A method of forming is adopted. For example, superconducting materials
In the case of Nb ₃ Sn, inside bronze, which is a Cu-Sn alloy,
By manufacturing a composite wire containing Nb wire and heat-treating it, a reaction of 3Nb + Sn → Nb ₃ Sn occurs between the Nb wire and Sn in the bronze, resulting in continuous Nb ₃ Sn in the Cu base. (Bronze method), or a method in which Cu-Nb alloy wire is plated with Sn and then heat treated to carry out the reaction (in-situ method).
There is a method (powder method) in which the powder and Nb powder are mixed and sintered, then drawn into a wire, and then the wire surface is plated with Sn and heat treated to carry out the reaction (powder method). Of these, the powder method in particular disperses dull Nb in the form of fine powder in the Cu matrix, so the Nb
Although it has many advantages over other methods, such as the ability to arbitrarily select the amount of compounding, the process is relatively simple, and the electrical properties of the product are excellent, there are still many technical problems. Problems remain to be improved or resolved. That is, conventionally, from a Cu-Nb powder compact,
To manufacture Nb ₃ Sn reaction superconducting wire, first Nb
Nb obtained by hydrogenating powder in a hydrogen gas stream
The hydride powder is further pulverized using a disc mill or the like to have an average particle size of approximately 50 microns or less, which is then dehydrogenated and annealed by heating under vacuum to produce Nb powder with an oxygen content of 0.08% or less. , then obtained
After mixing Nb powder with Cu powder, it is pressure-formed into a billet shape using a rubber press or the like, extruded, and wire-drawn to form a wire rod.The surface of the wire rod is plated with Sn, and then diffusion annealed by heating to form Nb ₃ Sn. A commonly used method is to generate . However, such a series of steps is accompanied by various inconveniences as described below.

(1) When Nb hydride powder is dehydrogenated and annealed by vacuum heating, the generated Nb powder is sintered and becomes coarse, making it necessary to re-pulverize it.

(2) In order to avoid such sintering, the dehydrogenation reaction must be carried out at a relatively low temperature, and the reaction takes a long time.

(3) Since the surface of the dehydrogenated Nb powder is in an active state, it is re-oxidized and the workability of the compact is reduced in subsequent steps.

(4) Since Nb powder is an extremely fine powder, the particles have a strong tendency to form aggregates, and therefore Cu
- In order to obtain a uniform mixture of Nb powder, it is necessary to further perform wet mixing using a ball mill or special mixing, but surface oxidation of the powder occurs during the mixing process of pure Nb and pure Cu powder, which can result in the above (3) ) A similar problem arises as mentioned above.

Such a problem becomes a serious hindrance in the subsequent wire drawing, compositing, or reaction process between the two metals, resulting in a loss of electrical and mechanical properties of the obtained wire.

Furthermore, when a composite wire made of two reacting metal materials is heat-treated to generate a superconducting phase, Kirkendal voids are created in the wire due to changes in the atomic arrangement caused by the reaction. In addition, after the superconducting wire is manufactured by the heat treatment, the superconducting compound generated in the wire is removed by rolling,
Since it is not suitable for processing such as wire drawing, it is currently used as a superconducting wire in a state containing pores without undergoing such processing after heat treatment.
Such pores existing in the superconducting wire reduce the thermal conductivity of the superconducting wire, and when stress is applied to the wire, they become a starting point for destruction of the fragile compound layer, and in turn, the electrical resistance of the compound superconducting wire decreases. It is well known that this causes deterioration of characteristics. However, since superconducting compounds are brittle, as mentioned above, it is not possible to use conventional means for eliminating pores, such as rolling or wire drawing, after the compound has been formed. This is a serious problem, and therefore, the present applicant first solved the above-mentioned pores by holding the heat-treated superconducting wire in a high-temperature, high-pressure gas atmosphere sufficient to plastically deform the wire for a certain period of time. We proposed a method for producing dense superconducting wires by crushing and diffusion bonding the crushed portions.

In view of the above-mentioned current situation and problems, the present invention is directed to a superconducting wire obtained by forming a highly reactive composite wire from a metal molded body with good workability, and then heat-treating the wire. The purpose of this work was to apply an invention proposed by someone, refine it, and obtain a compound-based superconducting wire with excellent electrical and mechanical properties.

The method of the present invention is characterized by forming a wire containing two metals that become a compound having superconducting properties by reaction, and heat-treating the wire to carry out the reaction to obtain a superconducting wire. The hydride powder of one of the two metals and the copper powder are uniformly mixed, pressure-formed into a billet, and then the billet is heated under vacuum to form the hydride. The powder is dehydrogenated and annealed and sintered to form a sintered billet, and then the sintered billet is made into a wire rod and compounded with the other of the two metals to form a composite wire rod. The purpose is to form a composite wire and heat-treat the composite wire to cause a reaction between the two metals.

In addition, by holding the compound-based superconducting wire obtained by the method of the present invention for a certain period of time in a gas atmosphere at a high temperature and pressure sufficient to plastically deform the wire, the pores generated in the wire during the reaction can be removed. The manufacturing method for compound-based superconducting wire, which is characterized by crushing the material and diffusion bonding the crushed portion to form a dense wire, is the second method for producing a high-performance, high-quality superconducting wire. This is the method of the present invention.

Below, these methods of the present invention will be further explained in detail.

Typical examples of two metals that produce compounds with superconducting properties by reaction are Nb ₃ Sn by the reaction of Nb and Sn, and V ₃ Ga by the reaction of V and Ga.
Although the present invention is applicable to any of them, the case of Nb ₃ Sn will be explained below for convenience.

It is desirable that the Nb used in the method of the present invention be fine. When pure Nb powder is pulverized using a ball mill, etc., the surface area increases, and the amount of oxygen adsorbed on the surface of the Nb particles increases due to frictional heat. Oxidation occurs and the workability of Nb particles deteriorates. Therefore, in order to obtain Nb particles with low oxygen content and good workability, large-sized Nb particles are heated in a hydrogen gas stream to hydrogenate them to form brittle NbH powder, and then, for example, Grind using a suitable grinding means such as disk milk until the average particle size is about 50 microns or less. Conventionally, as mentioned above, this fine powder NbH
It has been common practice to heat-treat Nb in a vacuum to dehydrogenate it to form a fine powder of pure Nb, then mix it with copper powder and press-form it. However, in the method of the present invention, dehydrogenation finely powdered
The most important point is that after uniformly mixing NbH with copper powder, the mixture is press-molded and then dehydrogenated annealed.

The copper powder used in the method of the present invention is manufactured by the so-called electrolytic method, has a particle size of 250 mesh or less, and has an oxygen content of 0.3.
% by weight or less is suitable. Also, the blending ratio of NbH fine powder and copper powder is 10/90 to 40/ by weight.
A range of 60 is preferable; if the amount of NbH is less than that, the amount of superconducting compounds produced will decrease and the electrical properties of the product will be impaired, while if the amount of copper is too small, the brittle superconducting phase will increase. This is not preferable because the physical or mechanical properties of the wire deteriorate as a result of this, and it is not possible to expect much improvement in the electrical properties. Both powders combined at such a mixing ratio are uniformly mixed by commonly used powder mixing means, but the most suitable mixing method is wet mixing using a ball mill. . According to this method, uniform mixing of both powders can be achieved, and at the same time, the pulverization of the powder can be further promoted by the crushing action of the ball mill, which is more advantageous than other methods. As the solvent used in the wet mixing, a volatile organic solvent with a relatively low boiling point is suitable because it facilitates the drying operation of the powder after the mixing operation is completed. Needless to say, such a volatile organic solvent should be selected to be inert to both metal powders.
A typical example is acetone.

After drying and removing the solvent, the mixed powder uniformly mixed in the above manner is then pressed into a billet shape under a pressure of at least 1.000 atm, preferably at least 1.500 atm, using a press molding machine such as a rubber press. molded. The accompanying drawing is a photograph of a characteristic X-ray image of Nb taken by an electroprobe microanalyzer (EPMA) of a cross section of the billet obtained by the above-mentioned pressure molding, that is, the Nb-Cu molded body. Since the same photograph is an enlarged image with a magnification of 400 times, it can be seen how the NbH powder is finely divided and uniformly dispersed in the Cu substrate, confirming the particularly remarkable effect of the method of the present invention. Good morning.

The molded body thus obtained is then heated under vacuum to approx.
It is heated to a temperature of 750-1000℃ and dehydrogenated annealed.
In the method of the present invention, the step of vacuum annealing a molded body in which NbH powder and Cu powder are uniformly dispersed and mixed with each other is such that hydrogen in the generator state dehydrogenated from NbH reduces and desorbs the oxidized surface of the Cu powder. Acid,
It has the remarkable effect that it becomes a mixed molded body of essentially pure Nb powder and pure Cu powder, and furthermore, sintering is performed all at once. That is, according to the conventional method, NbH
In contrast to dehydrogenation annealing as a powder, mixing it with Cu powder, press forming and subjecting it to the sintering process, according to the method of the present invention, the compact is dehydrogenated and sintered. can be carried out in one step, which not only simplifies the process significantly, but also dehydrogenation annealing of powder as it is, which requires a long time at a relatively low temperature due to the need to avoid sintering, whereas the present invention Rather, this method has the advantage that the molded body is annealed and sintered at the same time, so that it can be treated at high temperatures for a short time. In addition, according to the conventional method, the powder that has undergone reoxidation in the powder mixing process is directly made into a compact, but in the case of the method of the present invention, dehydrogenation and deoxidation are performed in the state of the compact, so that the obtained product is The resulting billet has a significantly low oxygen content and hydrogen content, and is extremely excellent in workability and reactivity.

The sintered body thus obtained is then subjected to cold or hot isostatic extrusion by a conventional method and then drawn into a wire rod. In this case, if annealing and sintering have been sufficiently performed and the billet density has reached 80% or more of the true density, it can be made into wire as is, but in order to ensure smoother production into wire, It is preferable to densify the billet by subjecting it to a so-called hot isostatic pressing treatment (hereinafter referred to as HIP treatment) in advance to form a billet with substantially true density. HIP processing is a process in which the object to be processed is held in a gas atmosphere at a high temperature and high pressure sufficient to plastically deform it for a certain period of time, thereby crushing the pores contained in the object and causing the crushed portions to be diffusion bonded. It is well known as a technique for making tissues denser.
When subjecting the sintered body to the HIP process, the sintered body is vacuum sealed in a metal container and heated to about 500 to 850
℃ and a pressure of about 1,000 atmospheres or more for at least about 1 hour, it is possible to obtain a molded body whose density is approximately equal to the true density, and it is extremely easy to convert the obtained molded body, that is, a billet, into a wire rod. , the workability and spreadability of the Nb particles are also extremely good.

Composite formation with Sn (gallium in the case of vanadium), which is a metal that produces a compound with superconducting properties by reaction with Nb, is carried out before and after the above-mentioned wire production. That is, after drawing the Nb-Cu sintered billet, the outer peripheral surface of the obtained wire is plated with Sn, or the sintered billet before wire drawing is coated with Sn or an alloy containing Sn, such as a Cu-Sn alloy. (bronze) can be coated by lining or the like, and then drawn into a wire rod.

Furthermore, it is more preferable to perform the compositing at the same time as the above-mentioned densification of the sintered billet, that is, densification by HIP treatment. We have previously described a method for densifying a sintered billet by vacuum sealing it in a metal container and subjecting it to HIP treatment. It is possible to achieve high density and compounding at the same time. However, in this case, as the formation of Nb ₃ Sn progresses due to the reaction between Nb and Sn, Nb ₃ Sn becomes brittle and may hinder the subsequent wire drawing, so the HIP treatment temperature should be lowered appropriately. It is desirable to take measures to suppress the excessive progress of the above-mentioned reaction.

The composite wire rod is then heated to approximately 500°C by a conventional method.
When heat treated at the above temperature, a reaction of 3Nb+Sn→Nb ₃ Sn occurs between Nb and Sn, and a superconducting phase consisting of a Nb ₃ Sn structure is formed in the Cu matrix. The Nb-Cu wire rod by Nb has highly reactive ultrafine and high purity Nb uniformly dispersed.
A superconducting phase is formed efficiently and uniformly along the length of the wire, and the resulting wire exhibits excellent electrical properties.Also, since it is made of a Cu base that maintains sufficient plastic strength, it is physically stable as a wire. It has excellent properties and mechanical properties such as flexibility, elasticity, malleability, ductility, and tensile strength.

However, as mentioned above, it is unavoidable in this case that the two metals react during heat treatment and Kirkendall pores are generated in the wire. The thus obtained wire must be further subjected to HIP treatment to crush the Kirkendall pores, and the crushed portions must be diffusion bonded to make it denser. The higher the temperature of HIP treatment, the more plastic deformation can be achieved with lower gas pressure, and the faster diffusion bonding can be performed, so the treatment time will be shorter.
Needless to say, the temperature must be lower than the melting point of the materials Cu, Nb, V, etc. In addition, the higher the pressure, the more plastic deformation can occur at a lower temperature, but if it becomes too high, the processing equipment will be required to have high pressure resistance, and it will take a long time to increase the pressure, so the pressure should be kept as low as possible. Lower is better. If the substrate containing pores is Cu or a similar alloy, the temperature should be at least 550°C and below the melting point and the pressure at least 200 atm.
In the case of Nb ₃ Sn, considering that the heat treatment temperature for the reaction is usually 500℃ or higher, if the treatment temperature with high-temperature, high-pressure gas is also 500℃ or higher,
Since the reaction of the unreacted areas between Nb and Sn occurs in parallel with the vacancy annihilation process, the Nb ₃ Sn volume fraction within the superconducting wire increases, which is expected to contribute to improving the superconducting properties.

In addition, gases that form a high-temperature, high-pressure atmosphere include:
An inert gas that does not harm the superconducting wire, such as argon gas, is preferable, but if you want to form an insulating oxide film on the surface of the superconducting wire, it is also effective to add a small amount of oxygen to the inert gas. be.

Examples of the present invention will be described below.

Example Oxygen content of commercially available mesh size 60: 0.07% by weight
Below, Nb powder with a hydrogen content of 0.0002% by weight or less is used.
Hydrogenation was performed in a H ₂ gas stream to obtain NbH powder. This material was pulverized using a disk mill to obtain fine NbH powder with an average particle size of 50 μm or less. 30 parts by weight of this fine NbH powder and 70 parts by weight of electrolytic Cu powder having a particle size of 250 mesh and an oxygen content of 0.3% by weight or less were mixed, acetone was added, and wet mixing was performed in a ball mill. The mixing time was 3 hours. After drying this powder, it is molded using a rubber press at a pressure of 2,000 atmospheres.
A billet-shaped molded body of 30 mmφ×100 mmL was obtained. The density of the compact is 80% of the true density, and its cross section
The photograph of the characteristic X-ray image of Nb obtained by EPMA is attached as attached 1.
As shown in the figure. As is clear from Figure 1,
Nb particles were extremely fine and uniformly dispersed in the compact. After vacuum annealing this material at a temperature of 850°C for 15 hours under a vacuum degree of 2 × 10 ^-6 Torr,
Analysis revealed that the oxygen content was 0.007% by weight.
Below, high purity Nb− with a hydrogen content of 0.002% by weight or less
It was a Cu molded body.

This molded body was vacuum-sealed in a copper case to make a billet for extrusion, and after cold isostatic extrusion (extrusion ratio 10), wire drawing was performed, and Nb was produced without wire breakage.
The spreadability of the particles was also good. Figure 2 is a cross-sectional micrograph after extrusion, showing that the Nb particles are well elongated.

Separately, the billet after dehydrogenation annealing was vacuum sealed in a copper case and heated to a temperature of 800°C.
When HIP treatment was performed for 2.5 hours at ℃ and 1500 atm pressure, a billet with a density of 100% of the true density was obtained. After cold isostatic extrusion of this billet, 0.5
When the wire was drawn to a diameter of mm, the workability of the Nb particles was further improved and was extremely good.

Next, the above Nb-Cu wire was plated with Sn, and then this composite wire was heat-treated at a temperature of 550°C for 72 hours to generate a compound phase of Nb ₃ Sn around the Nb-Cu wire. When the cross section was observed under a microscope, many fine pores were observed within the matrix. When this pore-containing wire was subjected to HIP treatment for 2 hours in an Ar gas atmosphere at 700°C and 1000 atm, a dense superconducting wire in which the pores had completely disappeared was obtained.

As detailed above, according to the method of the present invention, a high-density molded body in which ultrafine Nb or V particles of high purity are uniformly dispersed in a Cu matrix can be easily obtained through a streamlined process. In addition to being able to
The molded product has excellent reactivity and processability, so it can be easily made into a wire rod, and when heat-treated after being composited with a metal that can produce a superconducting compound by reaction, Nb, V, etc. The high purity, fine dispersion, etc. of superconducting wires support the progress of the reaction, increasing the proportion of superconducting compounds produced, and producing superconducting wires with unprecedented electrical and mechanical properties. There is. In addition, if the Kagendahl pores generated in the wire are eliminated by HIP treatment and the wire is densified, it is possible to manufacture an excellent wire with further improved mechanical and electrical properties. If the temperature is matched to the heat treatment temperature for compound generation, compound generation will proceed due to the reaction of unreacted materials during heat treatment, which will have the effect of improving superconducting properties, etc., making compound-based superconducting wires more practical. It also greatly contributes to the spread of the technology.

[Brief explanation of the drawing]

Figure 1 is a photograph of a characteristic X-ray image of Nb taken by EPMA of a cross section of a compact obtained by the method of the present invention;
The figure is a cross-sectional micrograph of the molded product after extrusion processing.

Claims (1)

[Scope of Claims] 1. A method of forming a wire containing two metals that become a compound having superconducting properties by reaction, and heat-treating the wire to carry out the reaction to obtain a superconducting wire, comprising: A powder of a hydride of one of the metals and a copper powder are uniformly mixed, pressure-formed into a billet, and then the billet is heated under vacuum to dehydrogenate and anneale the hydride. The powder is sintered to form a sintered billet, and then the sintered billet is made into a wire rod and the above-mentioned 2.
A method for producing a compound-based superconducting wire, which comprises forming a composite wire by combining one of the seed metals with another metal, and heat-treating the composite wire to cause a reaction between the two metals. . 2. The compound-based superconductor according to claim 1, wherein the sintered billet is densified by enclosing and sealing it in a copper container and subjecting it to hot isostatic pressing treatment before forming the sintered billet into a wire rod. Method of manufacturing wire. 3. Forming the sintered billet into a wire and combining it with the other metal comprises drawing the sintered billet into a wire and then plating the other metal on its outer peripheral surface, as described in claim 1 or 2. A method for manufacturing compound-based superconducting wire. 4. Forming the sintered billet into a wire and combining it with the other metal comprises coating the outer periphery of the sintered billet with a metal material containing the other metal, and then drawing the wire. 2. A method for producing a compound-based superconducting wire according to item 2. 5. Converting the sintered billet into a wire and combining it with the other metal increases the density of the billet by enclosing the sintered billet in a container made of a metal material containing the other metal, sealing it, and subjecting it to hot isostatic pressing. 3. A method for producing a compound-based superconducting wire according to claim 1 or 2, which comprises performing compounding and compounding, and then drawing the wire. 6 A compound with superconducting properties is Nb ₃ Sn,
6. The method for producing a compound-based superconducting wire according to any one of claims 1 to 5, wherein the powder of one metal hydride mixed with the copper powder is a hydrided Nb powder. 7 A compound with superconducting properties is V ₃ Ga,
6. The method for producing a compound-based superconducting wire according to any one of claims 1 to 5, wherein the powder of one metal hydride mixed with the copper powder is a hydrogenated V powder. 8. The method for producing a compound-based superconducting wire according to any one of claims 1 to 7, wherein the hydride powder has an average particle size of at most about 50 microns. 9. The method for producing a compound-based superconducting wire according to any one of claims 1 to 8, which comprises mixing 10 to 40 parts by weight of hydride powder and 90 to 60 parts by weight of copper powder. 10. The method for manufacturing a compound-based superconducting wire according to any one of claims 1 to 9, wherein the hydride powder and the copper powder are mixed by wet mixing in a volatile organic solvent. . 11. The method for producing a compound-based superconducting wire according to claim 10, wherein the volatile organic solvent is acetone. 12. The method for producing a compound-based superconducting wire according to claim 10 or 11, wherein the wet mixing is performed using a ball mill. 13 In a method of forming a wire containing two metals that become a compound having superconducting properties by reaction, and heat-treating the wire to carry out the reaction to obtain a superconducting wire, one of the two metals The hydride powder and the copper powder are uniformly mixed and pressed into a billet shape, and then the billet is heated under vacuum to perform dehydrogenation annealing of the hydride and sintering of the powder. Then, the sintered billet is made into a wire rod and composited with the other metal of the two types of metals to form a composite wire rod, and the composite wire rod is heat-treated. A superconducting wire is produced by a reaction between the two metals, and then held in a gas atmosphere at a high temperature and pressure sufficient to plastically deform the wire for a certain period of time, thereby removing the pores generated in the wire during the reaction. A method for manufacturing a compound-based superconducting wire, which comprises crushing and diffusion bonding the crushed portion to obtain a dense wire. 14 The superconducting wire obtained by heat treatment is
30 in a gas atmosphere of 500℃ or higher and a pressure of 200atm or higher.
14. The method for producing a compound-based superconducting wire according to claim 13, wherein the compound-based superconducting wire is retained for at least 1 minute. 15 The sintered billet is densified by enclosing and sealing the sintered billet in a copper container and subjecting it to hot isostatic pressing prior to forming it into a wire rod, as described in claim 13 or 14. A method for manufacturing compound-based superconducting wire. 16 The sintered billet is formed into a wire rod and the composite material with the other metal is formed by drawing the sintered billet into a wire and then plating the other metal on its outer peripheral surface, according to claims 13 to 15. A method for producing a compound-based superconducting wire as described in any of the sections. 17 Claims 13 to 17, wherein forming the sintered billet into a wire and compounding it with the other metal comprises coating the outer periphery of the sintered billet with a metal material containing the other metal, and then drawing the sintered billet into a wire. A method for producing a compound-based superconducting wire according to any one of Item 15. 18 The sintered billet is made into a wire rod and composited with the other metal by enclosing the sintered billet in a container made of a metal material containing the other metal and subjecting it to hot isostatic pressing, which increases the height of the billet. A method for producing a compound-based superconducting wire according to any one of claims 13 to 15, which comprises performing densification and compositing, and then drawing the wire. 19 Claim 13, wherein the compound having superconducting properties is Nb ₃ Sn, and the powder of one metal hydride mixed with the copper powder is a hydrided Nb powder.
A method for producing a compound-based superconducting wire according to any one of items 1 to 18. 20. Any one of claims 13 to 18, wherein the compound having superconducting properties is V ₃ Ga, and the powder of one of the metal hydrides mixed with the copper powder is a hydrogenated V powder. A method for manufacturing compound-based superconducting wire. 21. The method for producing a compound-based superconducting wire according to any one of claims 13 to 20, wherein the hydride powder has an average particle size of at most about 50 microns. 22. A method for producing a compound-based superconducting wire according to any one of claims 13 to 21, which comprises mixing 10 to 40 parts by weight of hydrogenated powder and 90 to 60 parts by weight of copper powder. 23. The method for producing a compound-based superconducting wire according to any one of claims 13 to 22, wherein the hydride powder and the copper powder are mixed by wet mixing in a volatile organic solvent. 24. The method for producing a compound-based superconducting wire according to claim 23, wherein the volatile organic solvent is acetone. 25. The method for producing a compound-based superconducting wire according to claim 23 or 24, wherein the wet mixing is performed using a ball mill.