JPS6121372B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing a molded body, which is a material for manufacturing superconducting wires based on compounds such as Nb ₃ Sn and V ₃ Ga, and particularly relates to a method for manufacturing a molded body, which is a material for manufacturing superconducting wires based on compounds such as Nb 3 Sn and V 3 Ga, and in particular, superconducting wires having excellent electrical and mechanical properties. The present invention relates to a method for manufacturing a material metal molded body with good processing characteristics for manufacturing a wire rod.

In general, compound-based superconducting wires are 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 by adding Sn to a Cu-Nb alloy wire.
A method in which the reaction is carried out by plating and subsequent heat treatment (in-situ method), or
After mixing and sintering Cu powder and Nb powder, the wire is drawn, 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 pure Nb in the form of fine powder in the Cu matrix.
Although it has many advantages over other methods, such as the ability to mix any amount, the process is relatively simple, and the electrical properties of the product are excellent, there are still many technical problems. There are still problems that need to be improved or resolved. That is, conventionally, from 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 disk 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.

In view of the above-mentioned current situation and problems, the first object of the present invention is to provide a metal molded body with good workability and suitable for forming a composite wire with high reactivity. The ultimate goal was to obtain a compound-based superconducting wire with excellent properties.

The method of the present invention is characterized by wet mixing niobium or vanadium hydride powder having an average particle size of at most about 50 microns with copper powder to form a uniform powder mixture, and pressurizing the mixture. After shaping, the hydride is dehydrogenated annealed and the powder is sintered by heating under vacuum.

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 is fine. When pure Nb powder is pulverized using a ball mill, etc., the surface area increases, and due to frictional heat, adsorbed oxygen on the Nb particle surface increases. Oxidation occurs and the processability of Nb particles decreases. Therefore, in order to obtain fine Nb particles with low oxygen content and good workability, Nb particles with a large particle size are heated in a hydrogen gas stream to undergo hydrogenation to form brittle NbH powder, which is then processed into, for example, a disk. Grind using a suitable grinding means such as a mill until the average particle size is about 50 microns or less. Conventionally, as mentioned above, this fine powder NbH was dehydrogenated and annealed by heat treatment under vacuum to form a fine powder of pure Nb, which was then mixed with copper powder and subjected to pressure molding. However, in the method of the present invention, fine powder is produced without dehydrogenation.
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 suitably one produced by the so-called electrolytic method, with a particle size of 250 mesh or less and an oxygen content of 0.3% by weight or less. In addition, the blending ratio of fine NbH powder and copper powder is preferably in the range of 10/90 to 40/60 by weight; if the blending amount of NbH is less than that, the amount of superconducting compound produced will decrease and the electrical performance of the product will be affected. On the other hand, if the amount of copper is too low,
This is not preferable because the physical or mechanical performance of the wire deteriorates as the number of brittle superconducting phases increases, and it is not possible to expect much improvement in electrical properties. Both powders combined at such a blending ratio are uniformly mixed by commonly used powder mixing means;
Among these, 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. The solvent used in wet mixing is preferably a volatile organic solvent with a relatively low boiling point because it facilitates drying of the powder after the mixing operation is completed. It goes without saying that such a volatile organic solvent should be selected to be inert to both metal powders, and a typical example is acetone.

After drying and removing the solvent from the mixed powder uniformly mixed in the above manner, the mixture is then heated under a pressure of at least 1.000 atmospheres, preferably at least 1500 atmospheres, using a press molding machine such as a rubber press.
Pressure-formed into billet shape. The illustrations in the attached drawings are
The billet obtained by the above pressure forming, i.e.
Characteristics of Nb measured by electron probe microanalyzer (FPMA) on the cross section of Nb-Cu compact
This is a photograph of a line image. Since the same photo is an enlarged image with a magnification of 400 times, it can be seen how fine the NbH powder is and how uniformly it is dispersed in the Cu matrix.
It will be appreciated that the method of the present invention has a particularly remarkable effect.

The molded body thus obtained is then heated under vacuum to approx.
It is heated and annealed to a temperature of 750-1000℃. 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, which is dehydrogenated from NbH and is in a generator state, reduces and desorbs the oxidized surface of the Cu powder. It has a remarkable effect in that it is acidified, becomes a mixed molded body of substantially pure Nb and pure Cu powder, and is further sintered all at once. That is, according to the conventional method, NbH powder is dehydrogenated as it is, mixed with Cu powder, and then press-formed and subjected to a sintering process, whereas according to the method of the present invention, a compact is formed. Since dehydrogenation annealing and sintering can be performed on a product in one step, the process is not only significantly simplified, but also conventional dehydrogenation annealing of powder requires a long time at a relatively low temperature to avoid sintering. In contrast, in the method of the present invention,
Rather, it is advantageous in that the molded body is annealed and sintered at the same time, allowing for short-time processing at high temperatures. 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 has excellent 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 the annealing and sintering has been sufficiently performed and the billet density has reached 80% or more of the true density, it can be made into a wire as is, but in order to ensure smoother production into a wire, It is preferable to perform so-called hot isostatic pressing treatment (hereinafter referred to as HIP treatment) in advance to densify the billet to form a billet having substantially true density. HIP processing is a process in which the object to be processed is held in a high-temperature, high-pressure gas atmosphere that is sufficient to plastically deform it for a certain period of time, thereby compressing the pores contained in the object and diffusion bonding the pressed portion. It is well known as a technique for making the tissue denser. When subjecting the sintered body to the HIP process, the sintered body is vacuum sealed in a metal container and heated at approximately 500 to 850°C.
It is only necessary to maintain the pressure at about 1,500 atmospheres or more for at least about 2 hours, and 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 also become extremely good.

The Nb-Cu molded billet obtained by the method of the present invention is then composited with Sn (gallium in the case of vanadium), which is a metal that produces a compound having superconducting properties by reaction with Nb, and The material is made into wire rods. That is, after drawing a Nb-Cu sintered billet, Sn is added to the outer surface of the resulting wire.
or by lining the sintered billet before wire drawing with Sn or an alloy containing Sn, such as a Cu-Sn alloy (bronze),
After that, it is drawn into a wire rod.

The composite wire rod is then heated to approximately 500°C by a conventional method.
If heat treatment is performed at the above temperature, a reaction of 3Nb+Sn→Nb ₃ Sn will occur between Nb and Sn, and a superconducting phase consisting of a Nb ₃ Sn structure will be formed in the Cu matrix. The wire rod obtained from the Nb-Cu molded body has highly reactive ultrafine and high-purity Nb uniformly dispersed, so the superconducting phase is efficiently formed uniformly along the length of the wire rod. The obtained wire exhibits excellent electrical properties, and since it is made of Cu material that has sufficient plastic strength, it has excellent physical properties as a wire, such as flexibility, elasticity, malleability, ductility, and tensile strength. It has excellent mechanical properties.

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 0.002% by weight or less is heated _{with H2}
Hydrogenation was performed in a gas stream to obtain NbH powder. This material was pulverized with a disk mill to obtain fine NbH powder with an average particle size of about 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 mm x 100 mm L was obtained. The density of the compact is 80% of the true density, and its cross section
A photograph of the characteristic X-ray image of Nb obtained by EPMA is shown in the attached drawing. As is clear from the photograph, 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 of 2×10 ^-6 Torr, analysis revealed that the oxygen content was 0.07% by weight or less, and the hydrogen content was 0.002% by weight or less. High purity Nb-Cu
It was a 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.

Next, the above-mentioned Nb-Cu wire and bronze were composited, and a composite wire with a diameter of 0.5 mm having the Nb-Cu wire inside the bronze base was heat-treated at a temperature of 550°C for 72 hours. A superconducting wire with excellent electrical and mechanical properties was obtained by forming a Nb ₃ Sn compound phase around the wire.

As detailed above, according to the method of the present invention, a high-density molded body in which ultrafine particles of high purity Nb or V are uniformly dispersed in a Cu matrix can be easily produced through a streamlined process. In addition, the molded product has excellent reactivity and processability, so it can be easily made into a wire, and it can be heat-treated after being combined with a metal that can produce a superconducting compound by reaction. In this case, the high purity and fine dispersion of Nb, V, etc. facilitate the progress of the reaction, increasing the proportion of superconducting compounds produced and creating superconducting wires with unprecedented electrical and mechanical properties. It has many advantages and will greatly contribute to the practical application and popularization of compound-based superconducting wires.

[Brief explanation of the drawing]

The figure shows a cross section of a molded product obtained by the method of the present invention.
This is a photograph of a characteristic X-ray image of Nb obtained by EPNA.

Claims (1)

[Claims] 1 Wet-mix niobium or vanadium hydride powder and copper powder having an average particle size of at most about 50 microns to form a uniform powder mixture, press-form the mixture, and then A method for producing a molded body for a superconductor having good workability, characterized in that the hydride is dehydrogenated annealed and the powder is sintered by heating under vacuum. 2. The method for producing a molded body for a superconductor according to claim 1, which comprises mixing 10 to 40 parts by weight of hydride powder and 90 to 60% by weight of copper powder. 3. The method for producing a molded article for a superconductor according to claim 1 or 2, wherein the wet mixing is performed in a volatile organic solvent. 4. The method for producing a molded article for a superconductor according to claim 3, wherein the volatile organic solvent is acetone. 5. The method for producing a molded article for a superconductor according to any one of claims 1 to 4, wherein the wet mixing is performed using a hole mill. 6. The method for producing a molded body for a superconductor according to any one of claims 1 to 5, wherein the pressure molding is rubber press molding. 7. Any one of claims 1 to 6, wherein the densification of the sintered compact is achieved by enclosing and sealing the sintered compact in a metal container and subjecting it to hot isostatic pressing. A method for producing a molded article for a superconductor as described in .