JP2005093235A - Nb3Sn SUPERCONDUCTING WIRE MATERIAL, AND MANUFACTURING METHOD OF THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Nb<SB>3</SB>Sn superconducting wire material having sufficient strength, preventing cracks or wire breakages due to differences in deformation resistance of constituents, exhibiting superior superconducting characteristics as a material for superconducting magnet, and to provide a method useful for manufacturing the same. <P>SOLUTION: In the manufacturing method of the Nb<SB>3</SB>Sn superconducting wire material, forming a Nb<SB>3</SB>Sn layer on the inner surface of a tubular body by inserting (a) a rod-shaped member made of Sn or Sn alloy, or filling (b) alloy powder, intermetallic compound powder or mixed powder containing Sn as the main component, into the tubular body made of Nb or Nb alloy, and by applying a wire drawing work and heat treatment to a complex material formed by arranging one or a plurality of the tubular body in a stabilized copper mother material, a middle layer, composed of one or more than two kinds of metals selected from among a group of Ta, Ti, W, Mo, or alloy thereof is arranged at the outer periphery of the tubular body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a Nb ₃ Sn superconducting wire manufactured by a tube method or a powder method and a method for manufacturing the same, and is particularly used for a nuclear magnetic resonance (NMR) analyzer, an MRI diagnostic apparatus, a fusion reactor, an accelerator, and the like. The present invention relates to a Nb ₃ Sn superconducting wire useful as a constituent material of a superconducting magnet and a method for manufacturing such a superconducting wire.

A superconducting magnet that uses a permanent current phenomenon realized by a superconducting material, allows a large current to flow without consuming electric power, and generates a magnetic field by forming a superconducting wire into a coil shape, has been applied to the various applications described above. As a constituent material of the superconducting magnet as described above, a Nb ₃ Sn superconducting wire has been conventionally used as a representative material.

Various methods for producing the Nb ₃ Sn superconducting wire as described above have been proposed so far, and the most representative method is a so-called bronze method. In this bronze method, a plurality of Nb-based alloy core materials are embedded in a Cu—Sn-based alloy (bronze) matrix and wire-drawn to form the Nb-based alloy core material as a filament, and a plurality of filaments are bundled. A wire group is formed, and the wire group is embedded in copper for stabilization (stabilized copper) and drawn. And by the resulting wire is heat-treated (diffusion heat treatment) at 600 to 800 ° C., a method of generating a Nb ₃ Sn compound phase at the interface between the Nb-based alloy filaments and the matrix. However, in this method, there is a limit to the Sn concentration that can be dissolved in the bronze (Sn content is 15.8% by mass), and the thickness of the Nb ₃ Sn phase to be generated is higher than the current level and is higher. Realizing a magnetic field is a difficult situation.

As a method for producing the Nb ₃ Sn superconducting wire, a tube method and a powder method are known in addition to the bronze method. Of these, in the tube method, a rod-shaped member made of Sn or Sn-based alloy is inserted into a tubular body made of Nb or Nb-based alloy, and one or more of the tubular bodies are arranged in stabilized copper to form a composite member. And Nb ₃ Sn phase is formed on the inner surface of the tubular body (tube) by wire drawing and heat treatment.

In this tube method, since there is no restriction on the Sn amount, the Sn amount can be increased as much as possible, and the generated Nb ₃ Sn phase can also be made relatively thick, so that it can be expected that the superconducting characteristics can be further improved. Moreover, in the wire obtained by this method, the non-superconducting portion can be reduced as much as possible, and the area ratio of the superconducting portion can be increased, so that the current density per critical area (critical current density) is very high. There is usefulness that can be.

On the other hand, the powder method is known as a method capable of realizing a high critical current density. As one method in this powder method, an intermediate compound powder of Nb and Sn is filled as a core material (core powder) into a tubular body made of Nb or an Nb-based alloy, and this tubular body is placed in stabilized copper. A so-called ECN method is known in which a composite member is formed and subjected to wire drawing and heat treatment to generate an Nb ₃ Sn phase at the interface between the core and the tubular body (see, for example, Non-Patent Document 1).

In addition, as a new powder method, Ta-Sn alloy powder produced by melt-diffusion reaction of Ta and Sn at a high temperature and pulverizing it is used as a core material, and this is filled into a tube made of Nb or Nb-based alloy. There is also a method (melt diffusion method) in which the Nb ₃ Sn phase is formed by reacting Sn in the powder and Nb in the tubular body by arranging this in the stabilized copper and reducing the diameter, followed by heat treatment. Are known. In this method, it is shown that a superconducting wire excellent in high magnetic field characteristics can be obtained because there is no limitation on the amount of Sn and a Nb ₃ Sn phase thicker than the bronze method and the ECN method can be generated (for example, , See Patent Document 1).

As described above, in the tube method, the ECN method, and the melt diffusion method, a metal or alloy containing Sn or powder is inserted as the core material 2 into the tubular body 1 made of Nb or an Nb-based alloy as shown in FIG. Alternatively, while filling, the tubular body 1 is placed in the stabilized copper 3 and subjected to wire drawing and heat treatment, thereby ensuring the supply of Sn from the core material to the tubular body 1, and the inner surface of the tubular body 1. to a method to produce Nb ₃ Sn phase, thereby realizes a superconducting wire of a high magnetic field current density. The stabilizing copper 1 is arranged as a stabilizing material for the Nb ₃ Sn superconducting wire, and is made of oxygen-free copper, for example. As the material of the tubular body 1, an Nb-based alloy containing about 0.5 to 10% by mass of Ta, Ti, Hf, Zr, etc. is used in addition to pure Nb.
WLNeijmeijer et al., J. Less-common Metals, vol. 160 (1990) p. 161 Japanese Patent Application Laid-Open No. 11-250749

  The tube method, ECN method, and melt diffusion method achieve a higher critical current density than conventional bronze methods. However, the constituent material for carrying out these methods is Cu (stabilized copper). ), Nb or Nb-based alloy (tubular body), Sn or Sn-based alloy (rod-like member), and powder (core powder) containing Sn as a main component are used, and these materials have a difference in deformation resistance. It will be very big. Therefore, in the composite member composed of these materials, uniform processing is very difficult, and the tubular body may be broken during processing or the wire may be broken.

Even if the wire is obtained without breaking, the thickness of the tubular body may not be uniform and may be very thin, or a part of the tubular body may be cracked. In this state, Nb ₃ when Sn Aioi subjected to heat treatment for forming a thick Nb ₃ Sn phase than the thickness of the tubular body by diffusion of Sn in the core material will be produced, Sn stabilization therefrom It will diffuse directly into the copper and contaminate the stabilized copper. As a result, there is a problem that the thermal and electromagnetic stability of the wire is impaired.

Even when uniform processing is possible, if the Nb ₃ Sn phase generated by the heat treatment is too thick and exceeds the thickness of the tubular body, Sn may contaminate the stabilized copper. there were.

  In order to avoid such a situation, conventionally, a composite member is generally formed by increasing the thickness of the tubular body as much as possible. If such a configuration is adopted, contamination of the stabilized copper as described above can be avoided, but the ratio of the non-superconducting portion in the wire cross section increases and the critical current density of the wire is reduced. become. In addition, when powder is filled as a core material arranged inside the tubular body, a void may be formed in the powder-filled portion, which may reduce the strength of the wire.

The present invention has been made to solve such problems in the prior art, and its purpose is to prevent cracking and disconnection due to differences in the deformation resistance of the constituent materials, and to achieve good superconductivity as a superconducting magnet material. An object of the present invention is to provide a Nb ₃ Sn superconducting wire exhibiting properties and sufficient strength, and a useful method for producing such a superconducting wire.

The method of the present invention that has solved the above problems includes (a) inserting a rod-shaped member made of Sn or a Sn-based alloy, or (b) alloy powder containing Sn as a main component, intermetallic compound powder, or mixed A Nb ₃ Sn phase is formed on the inner surface of the tubular body by drawing and heat-treating a composite member in which powder is filled and one or more of the tubular bodies are arranged in a stabilized copper base material. In the method for producing a Nb ₃ Sn superconducting wire, an intermediate layer made of one or more metals or alloys selected from the group consisting of Ta, Ti, W, Mo and V is disposed on the outer periphery of the tubular body It has a gist in the point to do.

  In carrying out such a method, it is preferable that when the thickness of the intermediate layer before wire drawing is t and the thickness of the tubular body is T, these satisfy the following formula (1).

0.05 ≦ t / T ≦ 0.5 (1)
It is also useful to interpose a buffer layer made of a metal that enhances the adhesion between the stabilized copper base material and the intermediate layer. By adopting such a configuration, stabilization by the stabilized copper base material is possible. While improving an effect more, the effect by arrange | positioning an intermediate | middle layer can be made more reliable.

  The superconducting wire produced by the above method exhibits characteristics suitable for the purpose of the present invention.

The present invention is configured as described above, prevents cracking and disconnection due to the difference in deformation resistance of constituent materials, exhibits good superconducting characteristics as a superconducting magnet material, and has sufficient Nb strength. ₃ Sn superconducting wire was realized.

  The present inventors have studied from various angles in order to achieve the above object. As a result, if the intermediate layer made of one or more metals or alloys selected from the group consisting of Ta, Ti, W, Mo and V is arranged on the outer peripheral portion of the tubular body, the above object is achieved. Was successfully achieved and the present invention was completed. The configuration of the present invention will be described in more detail based on the drawings.

  FIG. 2 is a cross-sectional view showing a structural example of a composite member configured to carry out the present invention. The basic structure is similar to that of FIG. 1, and corresponding parts are denoted by the same reference numerals. It is. In the configuration of the present invention shown in FIG. 2, the intermediate layer 4 is formed on the outer peripheral portion of the tubular portion 1. The intermediate layer 4 is made of one or more metals or alloys selected from the group consisting of Ta, Ti, W, Mo and V.

  The intermediate layer 4 made of a metal has a mechanical strength superior to that of the tubular body 1 made of Nb or an Nb-based alloy, improves workability in the middle of wire drawing, and facilitates uniform processing. become. Further, even if the tubular body 1 is broken during the wire drawing process, the intermediate layer 4 is present on the outer periphery of the tubular body 1 so that further progress of destruction can be prevented. Moreover, by arranging this intermediate layer 4, the strength of the wire after the reaction can be increased.

  Of the components used as the intermediate layer 4, Ta is particularly preferable, and this Ta has a low resistance value itself and also exhibits a function as a stabilizing material. Moreover, since Ta does not react with the Sn component, even if all of the tubular body 1 reacts, contamination of the stabilized copper by Sn can be prevented.

  Further, since the intermediate layer 4 exhibits the above-described action, the total thickness of the intermediate layer 4 and the stabilized copper (stabilized copper base material) 3 is thinner than the thickness of the conventional stabilized copper 3 alone. Therefore, the proportion of the non-superconducting portion can be reduced accordingly. The intermediate layer 4 may be finally formed into a tubular shape, and for example, a thin sheet-like member may be rolled up (see the examples described later), or may be formed into a tubular shape by welding them.

  A superconducting wire exhibiting desired characteristics can be obtained by performing wire drawing and diffusion heat treatment on the composite member shown in FIG. 2, but the number of tubular bodies 1 in the composite member is not limited to one, For example, it can be configured with 7 or more cores. In such multi-core, (1) the composite member shown in FIG. 2 is drawn and then bundled and placed in the stabilized copper 3 (for example, copper tube), or (2) the intermediate layer is formed. 2 (ie, without forming the stabilized copper 3 shown in FIG. 2), the tubular body may be drawn, bundled and placed in the stabilized copper, and then further drawn and diffusion heat treated.

  In the wire (composite member) of the present invention, when the thickness of the intermediate layer 4 is t and the thickness of the tubular body 1 is T (both before wire drawing), these satisfy the above formula (1). Preferably there is. When t / T is less than 0.05, the contribution of the intermediate layer 4 to the strength of the entire wire is reduced, and the intended effect is not exhibited effectively. On the other hand, when t / T exceeds 0.5, the number of non-superconducting portions increases so that the critical current density in the superconducting wire is lowered.

By the way, among the metals constituting the intermediate layer 4, Ta, W and Mo are inferior in adhesion to the stabilized copper 3 than the tubular body 1 made of Nb or Nb-based alloy, and decrease the stabilizing effect by copper. There are things to do. As a means for avoiding such inconvenience, for example, as shown in FIG. 3 (the basic configuration is the same as in FIG. 2), a buffer made of a metal that enhances the adhesion between the stabilized copper 3 and the intermediate layer 4. It is also useful to intervene layer 5. The buffer layer 5 reacts with the stabilized copper and the intermediate layer 4 in the processing step or the heat treatment for forming the Nb ₃ Sn layer to improve the adhesion between them. As a result, the stabilizing effect by the stabilizing copper 3 can be further improved, and the effect by arranging the intermediate layer 4 can be made more reliable.

  Examples of the metal constituting the buffer layer 5 include Rh and Ni. In order to exert the above-described effect by the buffer layer 5, it is preferable that the thickness before wire drawing is 1 μm or more. However, if it is too thick, it takes a long time for coating, so it is preferable that the thickness be about 10 μm. .

  As a configuration in which such a buffer layer 5 is interposed between the stabilizing copper 3 and the intermediate layer 4, for example, in the case of a single core wire as shown in FIG. 3, the inner surface of the stabilizing copper 3 or the outer peripheral surface of the intermediate layer 4. In addition, the buffer layer 5 may be formed by electroplating or vapor deposition, but in the case of a multi-core wire, the buffer layer 5 may be formed on the inner surface of the stabilized copper 3.

In the configuration shown in FIG. 2, any of a rod-shaped member made of Sn or a Sn-based alloy, an alloy powder containing Sn as a main component, an intermetallic compound powder, or a mixed powder can be used as the core material. Of these, the Sn-based alloy used as the rod-shaped member is preferably a Sn-based alloy having a Sn content of 80% by mass or more. When the Sn content is less than 80% by mass, the crystallinity of Nb ₃ Sn produced due to the small amount of Sn is deteriorated and the critical current density (Jc) is lowered. Moreover, Ti, Ta, Hf, Zr etc. are mentioned as another component which may be contained in such Sn alloy.

On the other hand, as the powder (core powder) used as the core material, conventionally used Nb—Sn intermetallic compound powder (ECN method) and Ta—Sn alloy powder (melt diffusion method) can be used. Any form of alloy powder, intermetallic compound powder, or mixed powder can be used as long as it contains at least one metal selected from Ta, Nb, and Ti and Sn as components. Of the components contained in this powder, Sn, which is the main component, reacts with Nb or an Nb-based alloy (tubular body 1) arranged around it to form an Nb ₃ Sn phase, but Ta, Nb Components such as Ti and Ti promote the formation of the Nb ₃ Sn phase, or react themselves with Sn to produce a superconductor.

The content of the Sn component in the core powder is preferably about 10 to 98% by mass. When the Sn content is less than 10% by mass, the Nb ₃ Sn phase becomes thin, the superconducting properties deteriorate, and 98% by mass. If it exceeds N, the amount of additive elements is relatively small, and the characteristics of Nb ₃ Sn deteriorate. Moreover, it is also effective to contain about 0.5-20 mass% Cu component in this core powder as needed. This Cu component exhibits the effect of reducing the diffusion heat treatment temperature. That is, the optimum reaction temperature (diffusion heat treatment temperature) in the conventional powder method is 900 to 925 ° C., but if the heat treatment is performed at 900 ° C. or higher, the crystal grains of the Nb ₃ Sn phase become too large and the superconducting properties deteriorate. However, by including the Cu component in the core powder, the optimum heat treatment temperature can be lowered. As a result, the crystal grains are refined, and high characteristics in the Nb ₃ Sn superconducting wire can be realized.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and any design changes in accordance with the gist of the preceding and following descriptions are technical aspects of the present invention. It is included in the range.

  Ta powder: Sn powder = 6: 5 (molar ratio) mixed powder added with 2% by mass Cu powder was pulverized by heat treatment at 950 ° C. for 10 hours, and the same heat treatment and pulverization The prepared powder was prepared as a core powder.

  Each of the cylinders (tubular bodies) having an outer diameter shown in Table 1 below, made of an Nb-7.5 mass% Ta alloy having an inner diameter of 30 mm and a length of 100 mm, is filled with the core powder prepared above. A Ta sheet having a thickness of 0.2 mm was wound around the outer periphery thereof as shown in Table 1 below, and inserted into a copper billet having an inner diameter of 58 mm and an outer diameter of 65 mm. This billet was extruded and drawn with a hydrostatic pressure extrusion apparatus, and then processed into a hexagonal material having an opposite side length of 12 mm by drawing. 19 pieces of this hexagonal material were placed in a copper billet (stabilized copper) having an inner diameter of 61 mm and an outer diameter of 68 mm, extruded again with hydrostatic pressure, drawn to a diameter of 1 mm by surface reduction, and subsequently 750 Heat treatment (diffusion heat treatment) was performed at 100 ° C. for 100 hours to obtain a superconducting wire. Table 1 below also shows the thickness T of the tubular body, the thickness t of the Ta sheet (intermediate layer), and the ratio (t / T) thereof.

  For each superconducting wire obtained, the critical current density (Jc) obtained by dividing the critical current in the external magnetic field 17T by the cross section of the wire at a temperature of 4.2K, the seating residual resistance ratio (RRR) at 4.2K, and The 0.2% proof stress (YS) was measured. At this time, each characteristic of the superconducting wire (No. 8 in Table 1) produced in the same manner as described above was also investigated except that no intermediate layer was provided. The relationship between the measured characteristics and the ratio (t / T) is shown in FIGS.

From these results, it can be considered as follows. First, no. In the case of 1, the value of t / T is increased and the ratio of the non-superconducting portion is increased, so that the critical current density (Jc) is reduced to about 300 A / mm ² (FIG. 4). No. In 7,8, but critical current density (Jc) is also close to ^{500A / mm 2, 100A / mm} 2 and 200A / mm ² and less Some like, it can be seen the variation of the characteristics is large ( FIG. 4).

  No. 1 and 8, the critical current density (Jc) is relatively low, and the residual resistance value RRR is relatively low (FIGS. 4 and 5). Contamination was observed. In addition, No. with t / T being 0.014. No. 7 also has a frequency of No. 7. Although little improvement was observed compared to those of 1,7, contamination of stabilized copper by Sn was also observed.

  In contrast, no. In the case of 2-7, the seat residual resistance ratio RRR was all 300 or more (FIG. 5), and the contamination of the stabilized copper by Sn was not recognized, and it was confirmed that it was processed normally. . Moreover, 0.2% yield strength (YS) is over 200 MPa in all cases, and it can be seen that the mechanical properties of the wire itself are remarkably improved (FIG. 6).

  As is apparent from these results, an intermediate layer is provided on the outer peripheral portion of the tubular body, and the value of the ratio (t / T) between the thickness t of the intermediate layer and the thickness T of the stabilized copper (t / T) is appropriately controlled ( It can be seen that RRR and YS can be improved more reliably by setting the value of t / T to 0.1 or more. The critical current density (Jc) tends to decrease as t / T increases (FIG. 4), but the decrease rate is about 30% even when t / T is 0.5. 3 shows that it is suppressed to about 20%.

  Copper pipes having outer diameters shown in Table 2 below, outer diameters: 29.5 mm, inner diameters: 26 mm, and lengths: 100 mm in various cylinders (tubular bodies) made of Nb having an inner diameter of 30 mm and a length of 100 mm. And a Sn-0.2 mass% Ti rod having a diameter of 25.5 mm and a length of 100 mm is inserted inside, and a Ta sheet having a thickness of 0.2 mm is provided on the outer periphery of the tubular body as follows. The coil was wound a number of times as shown in Table 2, and inserted into a copper billet having an inner diameter of 58 mm and an outer diameter of 65 mm whose inner surface was coated with Rh having a thickness of 5 μm by electroplating. This billet was extruded and drawn with a hydrostatic pressure extrusion apparatus, and then processed into a hexagonal material having an opposite side length of 12 mm by drawing. 19 pieces of this hexagonal material were placed in a copper billet (stabilized copper) having an inner diameter of 61 mm and an outer diameter of 68 mm, extruded again, and processed to a wire diameter of 1 mm by wire drawing. This wire was heat-treated at 300 ° C. for 48 hours and 700 ° C. for 100 hours to obtain a superconducting wire. Table 2 below also shows the thickness T of the tubular body, the thickness t of the Ta sheet (intermediate layer), and the ratio (t / T) thereof.

  About each obtained superconducting wire, it carried out similarly to Example 1, and measured critical current density (Jc), seat residual resistance ratio (RRR), and 0.2% yield strength (YS). At this time, each characteristic of the superconducting wire (No. 16 in Table 2) produced in the same manner as described above was also investigated except that no intermediate layer was provided. The relationship between the measured characteristics and the ratio (t / T) is shown in FIGS.

  As is apparent from these results, it can be seen that the same effect as in Example 1 is exhibited even when the present invention is applied to the tube method.

It is schematic description which shows the structure of the conventional tube method and a powder method. It is a schematic explanatory drawing which shows one structural example for implementing this invention. It is a schematic explanatory drawing which shows the other structural example for implementing this invention. 4 is a graph showing the relationship between t / T and critical current density (Jc) in the superconducting wire obtained in Example 1. 4 is a graph showing a relationship between t / T and a seat residual resistance ratio (RRR) in the superconducting wire obtained in Example 1. It is a graph which shows the relationship between t / T and the critical current density 0.2% yield strength (YS) in the superconducting wire obtained in Example 1. It is a graph which shows the relationship between t / T and critical current density (Jc) in the superconducting wire obtained in Example 2. It is a graph which shows the relationship between t / T and seat residual resistance ratio (RRR) in the superconducting wire obtained in Example 2. It is a graph which shows the relationship between t / T and critical current density 0.2% yield strength (YS) in the superconducting wire obtained in Example 2.

Explanation of symbols

1 Tubular body 2 Core material 3 Stabilized copper 4 Intermediate layer 5 Buffer layer

Claims (4)

(A) A rod-shaped member made of Sn or an Sn-based alloy is inserted into a tubular body made of Nb or an Nb-based alloy, or (b) an alloy powder, intermetallic compound powder or mixed powder containing Sn as a main component. Nb ₃ which forms an Nb ₃ Sn phase on the inner surface of the tubular body by filling and heat-treating a composite member in which one or more of the tubular bodies are arranged in a stabilized copper base material In the method for producing a Sn superconducting wire, an intermediate layer made of one or more metals or alloys selected from the group consisting of Ta, Ti, W, Mo and V is disposed on the outer periphery of the tubular body. Nb ₃ Sn method of manufacturing a superconducting wire according to claim. The production method according to claim 1, wherein when the thickness of the intermediate layer before wire drawing is t and the thickness of the tubular body is T, these satisfy the following formula (1).
0.05 ≦ t / T ≦ 0.5 (1)   The manufacturing method of Claim 1 or 2 which interposes the buffer layer which consists of a metal which improves both adhesiveness between the said stabilization copper base material and an intermediate | middle layer. Nb ₃ Sn superconducting wire are those prepared by the method according to any of claims 1 to 3.

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