JP4652938B2 - Powder method Nb3Sn superconducting wire manufacturing method - Google Patents

Description

The present invention relates to a method for producing a Nb ₃ Sn superconducting wire by a powder method, and particularly to a method for producing a powder method Nb ₃ Sn superconducting wire useful as a material for a superconducting magnet for generating a high magnetic field.

  Among the fields in which superconducting wire is put to practical use, superconducting magnets used in high-resolution nuclear magnetic resonance (NMR) analyzers have higher resolution as the generated magnetic field increases. There is a tendency.

As a superconducting wire used for the superconducting magnet for generating a high magnetic field, an Nb ₃ Sn wire has been put into practical use, and the bronze method is mainly employed for manufacturing this Nb ₃ Sn superconducting wire. In this bronze method, a plurality of Nb base materials are embedded in a Cu-Sn base alloy (bronze) matrix and drawn to form the Nb base material as a filament, and a plurality of these filaments are bundled to form a wire group. No, it is buried in copper for stabilization (stabilized copper) and drawn. In this method, the wire group is heat-treated (diffusion heat-treated) at 600 to 800 ° C. to generate an Nb ₃ Sn compound phase at the interface between the Nb-based filament and the matrix. However, in this method, there is a limit to the Sn concentration that can be dissolved in bronze (15.8% by mass or less), the thickness of the Nb ₃ Sn layer to be formed is thin, and the crystallinity is deteriorated. There is a disadvantage that the magnetic field characteristics are not good.

As a method for producing an Nb ₃ Sn superconducting wire, a tube method and an internal diffusion method are known in addition to the bronze method. Among these, in the tube method, a Sn core is arranged in an Nb tube, these are inserted into a Cu pipe and subjected to diameter reduction processing, and then Nb and Sn are diffused by heat treatment to generate Nb ₃ Sn. (For example, Patent Document 1). Further, in the internal diffusion method, Cu is used as a base material, and an Sn core is embedded in the center portion of the base material, and a plurality of Nb wires are arranged in the Cu base material around the Sn core and subjected to diameter reduction processing. In this method, Sn is diffused by heat treatment and reacted with Nb to generate Nb ₃ Sn (for example, Patent Document 2). In these methods, since there is no limit to the Sn concentration due to the solid solubility limit as in the bronze method, the Sn concentration can be set as high as possible, and the superconducting characteristics are improved.

On the other hand, a powder method is also known as a method for producing an Nb ₃ Sn superconducting wire. As this method, for example, in Patent Document 3, one or more metals (alloy elements) selected from the group consisting of Ti, Zr, Hf, V, and Ta and Sn are melt-diffusion-reacted at a high temperature, and their alloys or An intermetallic compound (hereinafter sometimes referred to as “Sn compound”) is pulverized to obtain an Sn compound raw material powder, and this powder is used as a core material (powder core part described later) in an Nb or Nb-based alloy sheath. A method of performing heat treatment (diffusion heat treatment) after filling and reducing the diameter is disclosed. This method shows that a superconducting wire excellent in high magnetic field characteristics can be obtained because it is thicker than the bronze method and can produce a good-quality Nb ₃ Sn layer. It is also shown that the amount of Sn in the raw material powder can be increased to 20 to 75 atomic%.

FIG. 1 is a cross-sectional view schematically showing a state in which an Nb ₃ Sn superconducting wire is manufactured by a powder method, in which 1 is a sheath (tubular body) made of Nb or an Nb-based alloy, and 2 is filled with raw material powder The powder core parts to be processed are shown respectively. In carrying out the powder method, a raw material powder containing at least Sn is filled in the powder core portion 2 of the sheath 1, extruded, and subjected to diameter reduction processing such as wire drawing, and then converted into a wire, and then applied to a magnet or the like. A Nb ₃ Sn superconducting phase is formed at the interface between the sheath and the raw material powder by performing heat treatment after winding.

  By the way, although it is said that the heat treatment temperature when forming the superconducting phase is preferably about 900 to 1000 ° C., the heat treatment temperature is increased to about 650 to 750 ° C. by adding Cu to the raw material powder. It is also known that it can be lowered. From this point of view, in the powder method, a trace amount of Cu powder is added to the raw material powder, and then heat treatment is performed to form an intermetallic compound. In the tube method, a thin layer of Cu is disposed inside the sheath. In addition, although what was single-core was typically shown in the said FIG. 1, it is common to use in the form of the multi-core material by which the several single core was arrange | positioned in Cu matrix practically. .

The superconducting wire as described above is densely wound mainly in a solenoid shape, and is used as a high-field superconducting magnet. The wire is generally wound after the wire is disposed on the outer periphery of the wire. In addition, the shape of the wire includes not only a round wire but also a flat wire. And since _Nb 3 Sn phase is very fragile, after the magnet windings are to perform heat treatment for _Nb 3 Sn Naru Aioi [wind and REACT (W & R) method.
JP, 52-16997, A Claims etc. Japanese Patent Laid-Open No. 49-114389 Patent Claims, etc. Japanese Patent Laid-Open No. 11-250749

  It is said that the heat treatment temperature (diffusion heat treatment temperature) when forming the superconducting phase is preferably a high temperature of about 900 to 1000 ° C. When the heat treatment is performed at such a high temperature, glass as an insulator is used. The fiber becomes brittle, and sufficient insulation cannot be secured after heat treatment. On the other hand, when the heat treatment temperature is suppressed to about 750 ° C., the diffusion of Sn from the Sn compound and the reaction with Nb become insufficient and the superconducting characteristics (for example, critical current density Jc) are lowered. There is.

  It is also known that the heat treatment temperature can be lowered to 750 ° C. or less by adding Cu to the raw material powder, but when such a configuration is adopted, it is first made of Ti, Zr, Hf, V and Ta. In addition to one or more metals selected from the group and Sn, an appropriate amount of each Cu powder is weighed, mixed, heat-treated, and then pulverized. However, when the powder method is carried out in such a procedure, a very hard Cu—Sn compound is also generated at the time of heat treatment, and the presence of such a Cu—Sn compound is an abnormality in the sheath during the diameter reduction processing. Deformation will occur, and in the worst case, breakage will be induced.

  By the way, in order to fill the raw material powder into the sheath material, it is generally performed by a uniaxial press. However, instead of such a treatment, a compacting treatment by isotropic pressure such as cold isostatic pressing (CIP) is performed. By applying, the filling rate of the raw material powder can be increased, and it is preferable for uniform processing. However, when the CIP method is applied to the above Sn compound powder, since the ductility of the compound powder itself is poor, non-uniform deformation occurs during the subsequent wire drawing, and the production of the superconducting wire itself is There is a problem that it becomes difficult.

The present invention has been made under these circumstances, and its purpose is to perform uniform processing without causing disconnection during production, and to exhibit excellent superconducting characteristics even when heat-treated at a relatively low temperature. An object of the present invention is to provide a useful method for producing a powder process Nb ₃ Sn superconducting wire that can be used.

The method of the present invention that has been able to achieve the above object is to fill a raw material powder containing at least Sn into a sheath made of Nb or Nb alloy, reduce the diameter of the raw material powder, and then heat-treat after forming a wire. A powder method Nb ₃ Sn superconducting wire manufacturing method for forming a superconducting phase at an interface between a sheath and a powder, wherein the raw material powder is at least one metal selected from the group consisting of Ti, Zr, Hf, V and Ta And Sn alloy powder or intermetallic compound powder, and further using Sn powder and Cu powder added and mixed.

  The Sn powder and Cu powder added to the raw material powder in the present invention are 15 to 90 parts by mass of Sn powder and 1 to 20 parts by mass of Cu powder with respect to 100 parts by mass of the alloy powder or intermetallic compound powder. It is preferable. Further, in carrying out the method of the present invention, it is preferable to perform a compacting treatment by isotropic pressure before filling the sheath material with the raw material powder.

In the present invention, the Sn compound powder formed by previously reacting (melting diffusion reaction) Sn with one or more metals (alloy elements) selected from the group consisting of Ti, Zr, Hf, V and Ta, By adopting a configuration using raw material powder in which Sn powder and Cu powder are added and mixed, the amount of Sn contributing to the Nb ₃ Sn phase generation reaction can be increased, and even when the generation heat treatment temperature is 750 ° C. or less. A uniform and sufficient amount of superconductor could be produced, and as a result, a Nb ₃ Sn superconducting wire exhibiting a high critical current density could be realized. Further, since the Cu powder is added after the Sn compound powder is generated in advance, the wire is formed without generating a highly hard Sn—Cu compound in the Sn compound generation reaction (melt diffusion reaction). Therefore, the occurrence of abnormal deformation and disconnection during wire processing can be reduced as much as possible.

The present inventors have studied from various angles in order to achieve the above object. As a result, when the Nb ₃ Sn superconducting wire is produced by the powder method, Sn or more is reacted in advance with one or more metals (alloy elements) selected from the group consisting of Ti, Zr, Hf, V and Ta (melt diffusion reaction). The present invention has been completed by finding that the above-mentioned object can be achieved brilliantly by adopting a configuration using raw material powder in which Sn powder and Cu powder are further added and mixed with the Sn compound powder thus pulverized.

The raw material powder used in the present invention contains one or more metals (alloy elements) selected from the group consisting of Ti, Zr, Hf, V, and Ta. These alloy elements are Nb ₃ Sn-generated. Sometimes it exhibits the effect of improving the superconducting properties by dissolving in a small amount in the reaction layer. Moreover, the high melting point Sn compound is formed, and the effect of preventing Sn from eluting by the processing heat at the time of extrusion is also exhibited. That is, since Sn has a low melting point, Sn is eluted by the processing heat at the time of extrusion as it is, but such inconvenience can be avoided by pre-alloying Sn. In order to exert such an effect, it is necessary to preliminarily form these alloy elements and Sn in the form of an alloy with Sn or an intermetallic compound by a melt diffusion reaction. From this point of view, the entire amount of Sn contained in the raw material powder has been subjected to the melt diffusion reaction. Further, Cu for lowering the heat treatment reaction temperature was also added and mixed during the melt diffusion reaction from the viewpoint of improving the grindability of the compound after the melt diffusion reaction.

  However, when such a configuration is adopted, a Sn—Cu compound that adversely affects workability as described above is formed. In addition, the adhesiveness and workability of the raw material powder are deteriorated, which hinders the application of a compacting treatment with an isotropic pressure such as CIP.

Therefore, the present inventors have studied to realize an Nb ₃ Sn superconducting wire that exhibits good superconducting characteristics while preventing such inconveniences. As a result, when the melt diffusion reaction is performed, the minimum amount necessary for alloying alloy elements such as Ti, Zr, Hf, V, Ta, etc., rather than reacting the entire amount of Sn as a raw material. It turned out that it would be good to react. It has also been found that Cu is not added during the melt diffusion reaction, but is added to and mixed with the raw material powder after the reaction to effectively exhibit the heat treatment temperature reduction effect due to the addition of Cu. Further, by adopting such a configuration, the amount of Sn powder to be mixed and added thereafter can be increased, and Nb ₃ Sn exhibiting a high critical current density even when the heat treatment temperature is 750 ° C. or lower. A superconducting wire was realized, and the superconducting characteristics could be further improved.

  According to the present invention, since the Cu powder is added after the Sn compound powder is generated in advance, a highly hard Sn—Cu compound is generated during the Sn compound generation reaction (melt diffusion reaction). Therefore, it is possible to reduce the occurrence of abnormal deformation and disconnection during wire processing.

  The compound powder is obtained by subjecting an alloy element such as Ti, Zr, Hf, V, and Ta to a melt diffusion reaction with Sn, and the mixing ratio of the alloy element and Sn is not particularly limited. From the viewpoint of superconducting properties, it is preferable that the alloying element: Sn = 4: 1 to 1: 2 (atomic ratio).

  In the present invention, the Sn compound as described above is produced and then pulverized to form an Sn compound powder, and a powder obtained by adding and mixing Sn powder and Cu powder is used as a raw material powder. When the Sn compound powder is 100 parts by mass, the Sn powder is preferably 15 to 90 parts by mass and the Cu powder is preferably 1 to 20 parts by mass.

When the mixing ratio of the Sn powder is less than 15 parts by mass, the effect of improving the superconducting characteristics due to the addition of Sn becomes difficult to be exhibited. When the mixing ratio exceeds 90 parts by mass, the content of the alloy element in the raw material powder is relatively small. Thus, Sn is eluted by processing heat during extrusion processing. Moreover, if the mixing ratio of Cu powder is less than 1 part by mass, the effect of reducing the heat treatment temperature (diffusion heat treatment temperature) due to the addition of Cu is not exhibited. If it exceeds 20 parts by mass, Cu diffuses to the Nb ₃ Sn phase during the diffusion heat treatment. Therefore, a good quality Nb ₃ Sn phase cannot be obtained, and as a result, the critical current density Jc is lowered.

  In the method of the present invention, when filling the raw material powder into the sheath material, it is also effective to adopt a cold isostatic pressing method (CIP method) or the like, and subjecting the raw material powder to an isotropic pressure treatment. By performing such treatment, the filling rate of the raw material powder into the sheath can be increased to 95% or more. In addition, since the raw material powder used in the present invention is obtained by adding and mixing Sn powder with Sn compound powder, Sn powder can be used as a deformation medium and can be uniformly processed compared to Sn compound powder alone. Become.

  When CIP is applied, CIP is performed after filling the rubber mold. However, the CIP molded body can be machined, and the billet assembly accuracy can be increased accordingly. In addition, as a condition for performing CIP, from the viewpoint of filling powder more densely, the pressure is preferably 10 MPa or more, and as a pressurizing pattern, pressurization may be performed by gradually increasing the pressure from a low pressure. Conceivable. In addition, when Sn powder is added and then heated at about 300 ° C., Sn is well adapted to improve workability.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not of a nature that limit the present invention, and any design changes may be made in accordance with the gist of the present invention. It is included in the technical scope. For example, in the following examples, the case of using as a single-core superconducting wire has been shown, but it is of course applicable to the case where it is used in the form of a multi-core superconducting wire in which a plurality of single cores are arranged in a Cu matrix. .

Example 1
In an Ar gas atmosphere, Ta and Sn powder having a particle size of 350 mesh or less were weighed with an electronic balance so that Ta: Sn = 6: 5 (atomic ratio), and these were mixed in a V blender for 30 minutes. . This mixed powder was subjected to a heat treatment at 950 ° C. for 10 hours in vacuum to produce a Ta—Sn compound. In Table 1, No. In the case of No. 1, 2% by mass of Cu powder was further added at the mixed powder stage.

  The obtained Ta—Sn compound was coarsely pulverized and then pulverized in an automatic mortar for 1 hour in an Ar atmosphere to a particle size of 75 μm or less. The powder obtained at this stage is referred to as “original Sn alloy or compound” (the “Sn compound”).

  To 100 parts by mass of this Ta—Sn compound powder, Sn powder and Cu powder in the amounts shown in Table 1 below were added in an Ar atmosphere and mixed for 1 hour in a V blender. These powders were sealed in a rubber mold, and then compressed with CIP at 200 MPa for 15 minutes to obtain a molded body of 32 mmφ × 181 mm.

  The obtained molded body was machined to 30 mmφ × 180 mm, and then inserted into an Nb-7.5 mass% Ta alloy sheath having an outer diameter of 50 mm and an inner diameter of 30 mm, and further outer diameter: 65 mm, inner diameter: It was inserted into an extruded billet made of 55 mm oxygen-free copper. The extruded billet was extruded with a hydrostatic pressure extrusion device, and then processed to a wire diameter of 0.2 mm by die drawing.

In order to produce Nb ₃ Sn, this wire was subjected to heat treatment at 700 ° C. for 100 hours in vacuum. With respect to the wire after the heat treatment, the critical current (Ic) is measured with an external magnetic field applied by a superconducting magnet, and the critical current density (Jc) is evaluated by dividing Ic by the area of the non-copper portion of the wire cross section. It was. Among the results, the critical current density (Jc) in a temperature of 4.2 K and a magnetic field of 20 T is also shown in Table 1 below.

As is clear from this result, it can be seen that the Nb ₃ Sn superconducting wire manufactured by the procedure of the present invention exhibits high-performance superconducting characteristics.

The Nb 3 _Sn wire material obtained by the powder method is a sectional view schematically showing.

Explanation of symbols

1 Sheath 2 Powder core

Claims (3)

Powder method Nb in which a raw material powder containing at least Sn is filled in a sheath made of Nb or an Nb alloy, and the superconducting layer is formed at the interface between the sheath and the powder by reducing the diameter of the powder and then heat-treating it. _A method for producing a ₃ Sn superconducting wire, wherein the raw material powder is one or more metals selected from the group consisting of Ti, Zr, Hf, V and Ta, Sn alloy powder or intermetallic compound powder, and Sn A method of producing a powder method Nb ₃ Sn superconducting wire characterized by using a powder and Cu powder added and mixed. The powder according to claim 1, wherein the Sn powder and Cu powder to be added are 15 to 90 parts by mass of Sn powder and 1 to 20 parts by mass of Cu powder with respect to 100 parts by mass of the alloy powder or intermetallic compound powder. Method for producing Nb ₃ Sn superconducting wire. The method for producing a powder method Nb ₃ Sn superconducting wire according to claim 1 or 2, wherein the raw powder is subjected to a compacting treatment with an isotropic pressure before filling the sheath.

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