JP2009004128A - BRONZE-PROCESS Nb3Sn SUPERCONDUCTING WIRE, AND PRECURSOR THEREOF - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bronze-process Nb<SB>3</SB>Sn superconducting wire which will not cause superconducting characteristics to deteriorate; and to provide a precursor (precursor for manufacturing a superconductive wire) for providing such a superconducting wire. <P>SOLUTION: This precursor is provided with a superconducting matrix part, having a plurality of Nb or Nb base alloy filaments arranged inside a Cu-Sn base alloy, and has stabilized copper arranged in its outer periphery. In the precursor, a reinforcing layer formed of Ta or a Ta base alloy is interposed between the superconducting matrix part and the stabilized copper; and when it is assumed that the distance from the center of a cross section of the precursor to the outer surface thereof, the distance from the center of the cross section to the inner surface of the reinforcing layer, and the distance from the center of the cross section to the outer surface of the reinforcing layer are R, r1 and r2, respectively, relations (1): 0.4≤r1/R≤0.8, (2): 0.55≤r2/R≤0.95 and (3): 0.05≤(r2-r1)/R≤0.22 are satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention, Nb ₃ Sn superconducting wire precursor for producing bronze method (precursor for fabricating a superconducting wire), and relates to the bronze process Nb ₃ Sn superconducting wire produced by such precursors, in particular The present invention relates to a Nb ₃ Sn superconducting wire useful as a material for a superconducting magnet and a precursor thereof.

Magnets (superconducting magnets) that generate a strong magnetic field by flowing a large current through a coil wound with Nb ₃ Sn superconducting wire are magnetic energy storage and nuclear fusion as well as nuclear magnetic resonance (NMR) analyzers and physical property evaluation devices. The development is progressing with the aim of applying power to devices. In the case of such power application, since a superconducting current that can be flowed with only one superconducting wire is insufficient, it is general to use a plurality of superconducting wires as a bundle in a conductor.

For example, in the International Thermonuclear Experimental Reactor (ITER) toroidal coil and center solenoid coil, 1000 levels of Nb ₃ Sn precursor wires (Nb ₃ Sn wires) are bundled in a stainless steel jacket. It is used as a housed and twisted conductor (CIC conductor) and then subjected to a firing heat treatment. After this firing heat treatment, there is a gap of about 36% in volume fraction, and when a coil is formed and a current is passed through the conductor, a large electromagnetic force is applied to the strand, and Nb ₃ Sn The strands move within the region where the air gap exists due to the electromagnetic force, and are subjected to a large bending stress by coming into contact with the adjacent strands. As a result, bending strain is introduced into the Nb ₃ Sn phase in the superconducting wire, resulting in a problem that superconducting characteristics such as critical current density Jc and n value deteriorate. The “n value” is an index indicating the uniformity of the current flowing in the direction of the wire in the superconducting wire, that is, the uniformity of the superconducting filament in the longitudinal direction of the wire. The larger the n value, the higher the superconducting characteristics. (That is, the uniformity of current) is said to be excellent.

In order to solve these problems, attempts have been made to reduce the bending stress by reducing the void ratio inside the CIC conductor as much as possible, but this is not so effective, but rather the characteristics of the Nb ₃ Sn strand itself. Therefore, it is hoped to develop a precursor wire excellent in resistance so that deterioration of superconducting properties does not become a problem even when bending stress is applied to some extent. It is the reality.

As such a technique, for example, in Patent Document 1, Ta or Hastelloy (Mo-containing Ni alloy) having a high Young's modulus and 0.2% proof stress is embedded as a reinforcing material in an Nb ₃ Sn strand, and against tensile stress. It has been proposed to increase the strength of. However, such a configuration is such that the reinforcing material is disposed in a portion having a relatively small bending stress at the center of the strand cross section, and thus the reinforcing material functions effectively with respect to the tensile stress. large Nb ₃ Sn filaments of the outer surface near will receive a large bending strain, it can not be said to have a sufficient resistance to bending stress.

By the way, a bronze method is known as a typical method for producing an Nb ₃ Sn superconducting wire. In this bronze method, as shown in FIG. 1 (schematic diagram of a precursor for producing an Nb ₃ Sn superconducting wire), A primary stack material 3 is formed by embedding a core material 2 made of a plurality of (seven in the figure) Nb or Nb-based alloy (for example, Nb-Ta alloy) in a Cu-Sn base alloy matrix 1. The primary stack material 3 has a hexagonal cross section as shown in FIG.

  The primary stack material 3 is subjected to surface-reducing processing such as wire drawing and extrusion to reduce the diameter of the core material 2 to form a filament (hereinafter sometimes referred to as “Nb-based filament”). A plurality of primary stack materials 3 made of Nb-based filaments and bronze are bundled to form a wire group, which is inserted into a pipe-shaped Cu-Sn base alloy 5 wound with an Nb sheet or Ta sheet as a diffusion barrier layer 4. Alternatively, a secondary multi-core billet is assembled by directly winding an Nb sheet or a Ta sheet around a wire group in which a plurality of primary stack members 3 are bundled, and disposing stabilizing copper 6 on the outer periphery thereof.

  The secondary multi-core billet as described above is hydrostatically extruded and subsequently subjected to surface reduction by drawing or the like, and the precursor for manufacturing a superconducting wire held while maintaining the cross-sectional shape of FIG. It is processed into a precursor for manufacturing a superconducting wire with a rectangular wire having a rectangular cross section as shown (hereinafter sometimes simply referred to as “precursor”).

By performing diffusion heat treatment (Nb ₃ Sn generation heat treatment) for about 100 hours at a temperature near 600 to 700 ° C., the above precursor (wire material after wire drawing) is applied to the interface between the Nb-based filament and the bronze matrix. An Nb ₃ Sn compound layer (which may be referred to as a “superconducting filament” or “Nb ₃ Sn filament” by paying attention to the overall shape of this layer) is used as a superconducting wire.

In general, as shown in FIGS. 1 and 2, the cross-sectional configuration of the bronze Nb ₃ Sn superconducting precursor is a portion in which a plurality of Nb-based filaments are arranged in a Cu—Sn-based alloy matrix at the center of the cross section ( Hereinafter, this portion is referred to as a “superconducting matrix portion”, and five layers of Cu—Sn base alloy are provided on the outside thereof (this layer may be omitted: see FIG. 2), and further, the superconducting matrix portion is provided on the outside thereof. A diffusion barrier layer (4 in FIGS. 1 and 2) that functions to prevent Sn from diffusing into and contaminating stabilized copper (6 in FIGS. 1 and 2) is disposed and stabilized in the outermost layer. Copper is arranged.

In the precursor structure as described above, Nb is often used as the diffusion barrier layer 4 from the viewpoint that it does not react with the stabilized copper 6 and has a certain degree of workability. Ta may be used. Since the diffusion barrier layer 4 made of these materials is outside the superconducting matrix, it is in a position to receive a bending stress larger than that of the Nb ₃ Sn filament after the heat treatment for heat treatment, and the possibility of reducing the bending strain of the entire strand can be reduced. It is in a certain position. However, the Ta or Ta-based alloy layer constituting the conventional diffusion barrier layer is configured from the viewpoint that it is only necessary to prevent the diffusion of Sn to the extent that it does not break, and its thickness is as thin as about 10 μm. This is not enough to reduce bending distortion.

  In addition, as a constitution of the diffusion barrier layer, Nb, Ta, V, W or an alloy sheet thereof and a Cu or Cu-based alloy sheet are alternately stacked, extruded, drawn, and drawn to form a dispersed fibrous structure. There has also been proposed a technique that also has strength by changing to (for example, Patent Documents 2 and 3).

  In such a technique, the reinforcing material is disposed at a position where the bending stress outside the superconducting filament assembly portion is large. Therefore, it is considered effective to alleviate the bending stress if sound processing is possible. . However, in such a configuration, dissimilar metals are processed in a complicated manner, so that the balance of internal stress is lost during processing, resulting in uneven thickness in the cross section (or even in the vertical section). The reinforcing layer is formed, and the area of the superconducting filament assembly is also affected, resulting in a problem that the variation in superconducting characteristics increases. In the worst case, a disconnection may occur due to the effect of combining different kinds of metals.

  On the other hand, Patent Document 4 also proposes a technique for prescribing and specifying the ratio of the cross-sectional area of the Ta tube for the diffusion barrier Ta layer with respect to the total cross-sectional area of the billet with emphasis on the workability of Ta. When the cross-sectional area of the Ta tube is increased in this way, the ratio of the cross-sectional area of the diffusion barrier Ta layer to the total cross-sectional area of the wire when processed into the wire can be increased, and the relative area compared to the case where the cross-sectional area ratio is low It is considered that resistance to bending strain is improved.

However, simply increasing the cross-sectional area and thickness cannot effectively improve the resistance to bending strain, and in some cases the superconducting characteristics may deteriorate or the resistance may decrease. In this technique, it is assumed that a welded pipe obtained by rounding plate-like Ta into a cylindrical shape and welding and joining the edge portions is used. When bending stress is applied, stress is concentrated on the welded joint. There is a problem that the bending stress cannot be alleviated evenly in the circumferential direction, and a large bending stress is applied to the superconducting filament existing at a specific position, thereby degrading the superconducting characteristics.
JP-A-2-213008 JP-A-9-153310 JP 2001-229749 A Japanese Patent No. 3454550

The present invention has been made under such circumstances, and the purpose thereof is to effectively relieve bending stress in the bronze Nb ₃ Sn superconducting wire and to perform uniform processing even during processing. Is to provide a bronze Nb ₃ Sn superconducting wire that does not deteriorate the superconducting characteristics, and a precursor (precursor for producing a superconducting wire) for realizing such a superconducting wire.

The Nb ₃ Sn superconducting wire precursor of the present invention that has achieved the above object is a superconducting wire precursor used in the production of a bronze Nb ₃ Sn superconducting wire. A precursor having a superconducting matrix portion on which Nb or Nb-based alloy filaments are arranged, and a stabilizing copper on the outer periphery thereof,
A reinforcing layer made of Ta or a Ta-based alloy is interposed between the superconducting matrix portion and the stabilizing copper, and the distance from the center of the cross section to the outer surface is R, and the inner surface of the reinforcing layer is from the center of the cross section. And the distance from the center of the cross section to the outer surface of the reinforcing layer is r2, the following points (1) to (3) are satisfied.
0.4 ≦ r1 / R ≦ 0.8 (1)
0.55 ≦ r2 / R ≦ 0.95 (2)
0.05 ≦ (r2-r1) /R≦0.22 (3)

In the Nb ₃ Sn superconducting wire precursor of the present invention, the Ta-based alloy forming the reinforcing layer contains 0.5% by mass or more of one or more elements selected from the group consisting of Nb, V, W and Mo. What is contained in the following ratio (excluding 0%) is mentioned.

Further, as a preferred embodiment of the Nb ₃ Sn superconducting wire precursor of the present invention, (a) a layer made of Nb or an Nb-based alloy is formed on the inner surface side and / or outer surface side of the reinforcing layer. (B) The reinforcing layer is formed by winding or laminating a sheet-like member made of Ta or a Ta-based alloy, and (c) made of Ta or a Ta-based alloy. When forming a sheet-like member by winding and laminating, a configuration in which an Nb or Nb-based alloy layer sheet is interposed between the respective layers is exemplified.

Nb ₃ Sn superconducting wires exhibiting desired superconducting properties (critical current density Jc, n value and resistance) can be produced by diffusion heat treatment using the various superconducting wire production precursors as described above.

In the present invention, a Ta or Ta-based alloy layer having a thickness suitable for the cross section of the wire at an appropriate position in the cross section of the wire in the precursor formed when manufacturing the bronze Nb ₃ Sn superconducting wire By adopting the configuration of forming a superconducting wire, it was possible to obtain a superconducting wire having sufficient strength while maintaining good superconducting characteristics.

  In the technology proposed so far, V (melting point: 1902 ° C.), W (melting point: 3380 ° C.), Mo (so that the recrystallization is not caused and softened by the heat treatment for generating NbSn as the reinforcing material to be used. High melting point metals such as melting point: 2617 ° C., Ta (melting point: 2998 ° C.), Nb (melting point: 2467 ° C.) are used. However, among these metals, only Ta and Nb can satisfy the requirement of being able to withstand strong processing at room temperature, such as a precursor for producing a superconducting wire. Further, when comparing Ta with Nb, the Young's modulus at low temperature and the 0.2% proof stress are high, and only Ta can be expected to have a sufficient reinforcing effect in a small amount as a reinforcing material (reinforcing layer). In addition, as Ta (pure Ta) used as a reinforcing layer in the present invention, inevitable impurities such as hydrogen, nitrogen, carbon, and oxygen may be included at 200 ppm or less, respectively. Specifically, hydrogen: 10 ppm or less, nitrogen: 50 ppm or less, carbon: 50 ppm or less, and oxygen: 100 ppm or less are preferable.

  Further, even when using a Ta-based alloy containing alloy elements such as Nb, V, W, and Mo up to about 0.5% by mass in Ta as described above, the workability is not impaired as compared with Ta. The reinforcing effect can be improved. Furthermore, it is considered that by winding Ta or a Ta-based alloy as described above as a sheet-like member, it is possible to perform processing with a uniform stress distribution in the circumferential direction without the presence of a weld joint.

  The inventors of the present invention have studied the specific configuration on the premise that Ta or a Ta-based alloy having the above characteristics is used as a reinforcing material (reinforcing layer). And the idea that the bending stress can be effectively relieved by arranging Ta or a Ta-based alloy as described above not at the central portion of the wire precursor but at a position where the bending stress is relatively large in the cross section. was gotten.

Increasing the cross-sectional area ratio of Ta or a Ta-based alloy increases the effect of reducing the bending stress, but simply increasing the cross-sectional area ratio decreases the area ratio of the superconducting filament (Nb ₃ Sn filament), The critical current density Jc will decrease.

  Under such circumstances, the present inventors are able to reduce the bending stress effectively, suppress a decrease in the critical current density Jc, and achieve a uniform processing, thereby realizing a structure of the superconducting wire precursor. Further investigation was made.

As a result, when the distance from the center of the cross section to the outer surface is R, the distance from the center of the cross section to the inner surface of the reinforcing layer is r1, and the distance from the center of the cross section to the outer surface of the reinforcing layer is r2, the following (1 ) To (3), the inventors have found that the above object can be achieved brilliantly, thereby completing the present invention.
0.4 ≦ r1 / R ≦ 0.8 (1)
0.55 ≦ r2 / R ≦ 0.95 (2)
0.05 ≦ (r2-r1) /R≦0.22 (3)

  If the distance r1 from the center of the cross section to the inner surface of the reinforcing layer is smaller than 0.4 in the ratio (r1 / R) to the distance R, the bending stress cannot be relaxed, and if larger than 0.8, Since Ta is arranged in the outermost layer or a relatively very thin Cu layer (stabilized copper) is arranged, inconvenience in processing such as die seizure during cold working such as wire drawing. Will occur. In addition, the preferable minimum of (r1 / R) is 0.57, and a preferable upper limit is 0.72.

  When the distance r2 from the center of the cross section to the outer surface of the reinforcing layer is smaller than 0.55 in the ratio (r2 / R) to the distance R, the bending stress cannot be relaxed, and when larger than 0.95, Since Ta is arranged in the outermost layer or a relatively very thin Cu layer (stabilized copper) is arranged, inconvenience in processing such as die seizure during cold working such as wire drawing. Will occur. In addition, the preferable minimum of (r2 / R) is 0.60, and a preferable upper limit is 0.75.

  Moreover, if the thickness (r2-r1) of the reinforcing layer becomes too small in the ratio [(r2-r1) / R] to R, the cross-sectional area ratio of the reinforcing layer becomes small, and the bending stress relaxation effect can be exhibited. However, if it becomes too large, the critical current density Jc is significantly reduced. From such a viewpoint, (r2-r1) / R needs to be in the range of 0.05 to 0.22. In addition, the preferable minimum of (r2-r1) / R is 0.07, and a preferable upper limit is 0.14.

  In the precursor of the present invention, the distances r1, r2 from the center of the cross section and the thickness of the reinforcing layer (r2-r1) are defined in relation to R [the above formulas (1) to (3)], Although the effect of the invention is exhibited, the present invention can be applied not only to the round wire precursor shown in FIG. 1 but also to a rectangular wire precursor having a rectangular cross section. For example, in the case of a round wire precursor, the distance R can be taken as the radius of the wire cross section, and r1 and r2 can be taken as the distance (radial distance) from the wire center to the inner and outer surfaces of the reinforcing layer. it can. On the other hand, in the case of a rectangular wire, the final cross-sectional shape is designed to satisfy the above relationship in each of the long side direction (left-right direction in FIG. 2) and the short side direction (up-down direction in FIG. 2). Just do it.

In forming the precursor of the present invention, as a basic configuration, it is preferable to configure a secondary multi-core billet by bundling a plurality of hexagonal cross-section primary stack materials 3 shown in FIGS. With such a multi-core structure, the number of Nb filaments can be increased and the Nb filament diameter can be reduced. Since the thickness of the Nb ₃ Sn layer to be formed is as thin as about 2 μm, by reducing the diameter of the Nb ₃ Sn filament (for example, about 5 μm), unreacted Nb is eliminated and the critical current density of the overall (the critical current becomes the wire rod). Current density divided by the total cross-sectional area) can be increased.

  The precursor of the present invention is characterized in that a reinforcing layer made of Ta or a Ta-based alloy is arranged at a predetermined position satisfying the relationships of the above formulas (1) to (3). For placement, a cylindrical shape (which may be a square tube in the final shape) may be placed on the outer periphery of the superconducting matrix. There are difficulties in terms of sex. Moreover, even if it is a case where it forms by welding construction, a uniform process will become difficult by presence of a welding junction part.

  Therefore, as a specific configuration for arranging the reinforcing layer, by winding a sheet-like member made of Ta or a Ta-based alloy as described above (that is, by making the entire shape cylindrical), a sheet-like member is formed. It is preferable to form the member as a reinforcing layer formed of a single layer or a stacked layer. In such a configuration, the reinforcing layer can be easily formed without causing inconvenience due to workability and welded joints.

  In forming the reinforcing layer as described above, a layer made of Nb or an Nb-based alloy is disposed on at least one of the inner surface side and the outer surface side of the reinforcing layer (that is, the superconducting matrix side and the stabilized copper side of the reinforcing layer). This is also a preferred embodiment. By arranging such layers, they have intermediate mechanical properties (elongation, tensile strength, etc.) between Cu or Cu-Sn base alloy and Ta or Ta base alloy, so that Ta or Ta base alloy is directly Cu etc. Compared with the case where it contacts, the processing balance is improved, and the uniformity of the cross-sectional shape is further improved.

  In addition, when a reinforcing layer is wound as a sheet-like member to form a laminate, a (111) surface integration of Ta or Ta-based alloy is performed by winding a sheet made of Nb or Nb-based alloy between the layers. As compared with the case of a single layer of Ta or a Ta-based alloy, it is possible to maintain a higher workability and to improve the uniformity of the cross-sectional shape.

  Examples of Nb-based alloys that can be used in these configurations include Nb containing alloy elements such as Ta, V, W, and Mo in an amount of 0.5% by mass or less. In addition, these Nb-based alloys used as Nb-based filaments arranged in the superconducting matrix can also be used, but other than these, Nb groups containing up to about 0.5% by mass of Zr, Ti, Hf, etc. Alloys can also be used.

  Since the reinforcing layer as described above can basically prevent the diffusion of Sn in the superconducting matrix to the outside, it also functions as a diffusion barrier layer.

  In the superconducting wire precursor of the present invention, stabilized copper (6 in FIG. 1 or 2) is arranged in the outermost layer, but the area relative to other parts (non-copper part) of this stabilized copper. The ratio (copper ratio) is preferably about 0.2 to 2.0, and more preferably 0.3 to 1.5. When the copper ratio is less than 0.2, the function as a stabilized copper is lowered. When the copper ratio is larger than 2.0, the critical current density of the overall (current density obtained by dividing the critical current by the total cross-sectional area of the wire) is lowered. It will be.

  The Cu—Sn base alloy used in the precursor of the present invention preferably has a Sn content of about 14 to 17% by mass. By setting it as such content, the critical current density Jc can be further improved. If the Sn content is less than 14% by mass, the effect of increasing the Sn concentration cannot be exhibited. If the Sn content exceeds 17% by mass, a large amount of Cu—Sn-based compound is precipitated, and uniform processing of the wire becomes difficult. In addition, this Cu-Sn base alloy may contain about 0.1-1.5 mass% Ti.

The superconducting wire precursor configured as described above is subjected to diffusion heat treatment (for example, at about 600 to 700 ° C. for about 100 hours) to exhibit good superconducting properties (critical current density Jc and n value) An Nb ₃ Sn superconducting wire having a sufficient strength can be obtained.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

(Comparative Example 1)
Nineteen holes with a diameter of 8.0 mm are made in a Cu-Sn base alloy ingot with a composition of Cu-15 mass% Sn-0.3 mass% Ti with a diameter of 67 mm, and an Nb bar having the same size as the hole is inserted into the hole. Electron beam welding was then performed to produce an extruded billet for the primary stack material. The billet was hot-extruded and reduced in diameter while being annealed in the middle to form a primary stack material having a hexagonal cross-section with an opposite side distance of 2.0 m.

  433 of the above-mentioned primary stack materials are bundled, and an Nb sheet having a thickness of 0.2 mm is wound around the outer periphery 6 times (diffusion barrier layer), and these are integrated and inserted into a pure Cu pipe having an outer diameter of 67 mm and an inner diameter of 47 mm. Electron beam welding was performed to produce an extruded billet for the secondary stack material. This billet was hot-extruded and reduced in diameter while being annealed in the middle to be processed into a round wire precursor having a diameter of 0.80 mm. At this time, R = 0.400 mm, r1 = 0.260 mm, r2 = 0.274 mm, r1 / R = 0.650, r2 / R = 0.585, (r2-r1) /R=0.035 It is. The copper ratio of this precursor is 1.0 (the same applies to Examples 2 and 3 and Comparative Examples 1 and 2).

The obtained precursor was subjected to diffusion heat treatment at 650 ° C. for 100 hours to obtain a Nb ₃ Sn superconducting wire. The obtained superconducting wire was placed in a liquid helium at 4.2 K temperature in an external magnetic field 12T (Tesla). FIG. 3 (FIG. 3 (a) shows before bending stress application, and FIG. 3 (b) shows after bending stress application. ], A bending stress is applied to the Nb ₃ Sn superconducting wire, and the generated voltage is measured by the four-terminal method in that state, and a critical current Ic (between voltage terminals) on the basis of 10 μV / cm (reference voltage) is measured. The current value when a voltage of 10 μV per 1 cm was generated was measured. In FIG. 3, the radius of curvature of the tip of the punch to which bending stress is applied is 20 mm, and it is between voltage terminals (indicated by “●” in the figure) attached to the Nb ₃ Sn superconducting wire (Nb ₃ Sn wire). The distance is 30 mm.

The critical current Ic is expressed as (Ic / Ic ₀ ) by normalizing the critical current at a bending stress of 0 with Ic ₀ , and the relationship between (Ic / Ic ₀ ) and the bending stress applying force (bending applying force) is shown in FIG. 4 (value in the figure where “◯” mark is Comparative Example 1).

As is clear from this result, the critical current Ic when the bending applied force is 400 N is reduced to about half compared to when the bending applied force is 0 (Ic / Ic ₀ = 0.5). On the other hand, it can be seen that the critical current is greatly reduced.

Moreover, about the obtained superconducting wire, while measuring critical current density Jc by each of the following method, n value was measured. In Comparative Example 1, the n value was obtained based on the critical current Ic when (Ic / Ic ₀ ) was 0.95. Moreover, r1, r2, R, etc. which are prescribed | regulated by this invention are typically shown in FIG.

[Measurement of critical current density Jc]
The critical current (Ic) determined above was divided by the cross-sectional area of the non-copper portion in the cross section of the wire to determine the critical current density Jc (nonCu-Jc) of the non-copper portion.

[Measurement of n value]
In the (Ic−Vc) curve obtained by the same measurement as that for obtaining the critical current Ic, data between 10 μV and 100 μV was displayed in logarithm and obtained as the slope. The relationship between the current and the voltage is empirically expressed by an approximate expression such as the following expression (4). The value of n (that is, the “n value”) is obtained based on this expression. .
V = Vc (I / Ic) ⁿ (4)
However, V and I are arbitrary voltages and currents lower than Vc and Ic, respectively.

(Example 1)
A primary stack material was produced in the same manner as in Comparative Example 1, and 403 primary stack materials were bundled, and a pure Ta sheet having a thickness of 0.2 mm was used 12 times instead of the Nb sheet used in Comparative Example 1. Winding (Ta reinforcing layer) and these were integrated and inserted into a pure Cu pipe having an outer diameter of 67 mm and an inner diameter of 47 mm, and electron beam welding was performed to produce an extruded billet for a secondary stack material. This billet was hot-extruded and reduced in diameter while being annealed in the middle to be processed into a round wire precursor having a diameter of 0.80 mm. At this time, R = 0.400 mm, r1 = 0.245 mm, r2 = 0.274 mm, r1 / R = 0.613, r2 / R = 0.585, (r2-r1) /R=0.0725 It is.

The obtained precursor was subjected to diffusion heat treatment at 650 ° C. for 100 hours to obtain a Nb ₃ Sn superconducting wire. The obtained superconducting wire, determine the critical current Ic in the same manner as in Comparative Example 1, the critical current Ic was normalized (Ic / Ic _0), investigated the relationship between the bending stress applied force (bending applied force). The results are also shown in FIG. 4 (“●” in the figure is the value in Example 1).

  As is apparent from this result, even when the bending force is 400 N, the critical current Ic maintains about 80% when the bending force is 0, and even when the bending force is 800 N, the critical current Ic is about 40%. It can be seen that That is, as compared with the case of Comparative Example 1, it can be seen that the decrease in the critical current Ic when subjected to bending stress can be remarkably suppressed.

Further the obtained superconducting wire, by the method indicated above, [Ic criteria for any of (Ic / Ic ₀₎ is 0.95] the critical current density Jc (nonCu-Jc) and were measured n values . As a result, the critical current density Jc was 805 A / mm ² and the n value was 29 (see Table 1 below). The current density Jc is a value after applying a bending stress.

(Comparative Example 2)
In the same manner as in Comparative Example 1, a plurality of round wire precursors having a constant r2 / R = 0.30 and different (r2-r1) / R were produced. Specifically, in the same manner as in Comparative Example 1, a primary stack material was produced, a plurality of primary stack materials were bundled, a pure Ta sheet having a thickness of 0.2 mm was wound around the outer periphery, and the primary stack was further formed on the outer side. A plurality of materials were arranged. At this time, instead of bundling a plurality of primary stack materials and winding a Ta sheet on the outside thereof, a material in which a Ta rod was arranged at the central portion of the wire cross section was also prepared. In addition, by adjusting the number of primary stack materials, the number of windings of pure Ta sheet, and the diameter of the Ta rod, when processed to a final diameter of 0.80 mm, r2 / R = 0.30 was made constant. .

  Each primary stack material bundled and integrated as described above was inserted into a pure Cu pipe having an outer diameter of 67 mm and an inner diameter of 47 mm in the same manner as in Comparative Example 1, and then subjected to electron beam welding to obtain a secondary stack material. An extruded billet was prepared. This billet is hot-extruded and reduced in diameter while annealing, and various round wire precursors having a diameter of 0.80 mm with a constant (r2-r1) / R of r2 / R = 0.30 and different (r2-r1) / R. Processed into body.

The obtained precursors were subjected to diffusion heat treatment at 650 ° C. for 100 hours to obtain Nb ₃ Sn superconducting wires. For the obtained superconducting wire, the critical current Ic was obtained in the same manner as in Comparative Example 1, and the bending stress application force (bending application) when the critical current Ic was normalized (Ic / Ic ₀ ) was 0.95. Force) and critical current density Jc (nonCu-Jc) were measured, and the influence of (r2-r1) / R on bending applied force and critical current density Jc was investigated. The results are shown in FIG.

As is clear from this result, a practical value where the bending force applied when (Ic / Ic ₀ ) is 0.95 is 100 N or more and the critical current density Jc is 700 A / mm ² or more is (r2− It can be seen that it cannot be obtained in the entire range of r1) / R.

(Example 2)
In the same manner as in Comparative Example 1, a plurality of round wire precursors having a constant r2 / R = 0.85 and different (r2-r1) / R were produced. Specifically, in the same manner as in Comparative Example 1, a primary stack material was produced, a plurality of primary stack materials were bundled, a pure Ta sheet having a thickness of 0.2 mm was wound around the outer periphery, and the number of primary stack materials When the number of windings of the pure Ta sheet was adjusted and processed to a final diameter of 0.80 mm, r2 / R = 0.685 was maintained constant.

  Each primary stack material bundled and integrated as described above was inserted into a pure Cu pipe having an outer diameter of 67 mm and an inner diameter of 47 mm in the same manner as in Comparative Example 1, and then subjected to electron beam welding to obtain a secondary stack material. An extruded billet was prepared. This billet is hot-extruded and reduced in diameter while being annealed to obtain various round wire precursors having a diameter of 0.80 mm with a constant (r2-r1) / R of r2 = 0.585. processed.

The obtained precursors were subjected to diffusion heat treatment at 650 ° C. for 100 hours to obtain Nb ₃ Sn superconducting wires. The obtained superconducting wire, determine the critical current Ic in the same manner as in Comparative Example 1, when the critical current Ic was normalized (Ic / Ic ₀₎ is 0.95, the bending stress applied force (bending applied Force) and critical current density Jc (nonCu-Jc) were measured, and the influence of (r2-r1) / R on bending applied force and critical current density Jc was investigated. The result is shown in FIG.

As is clear from this result, a practical value with a bending application force of 100 N or more and a critical current density Jc of 700 A / mm ² or more when (Ic / Ic ₀ ) is 0.95 is obtained. , (R2-r1) / R is in the range of 0.05 to 0.22 (provided that 0.4 ≦ r1 / R ≦ 0.8).

  In Example 2, a pure Ta sheet was used as a material (reinforcing material) to be wound around the outside of the primary stack material. However, alloy elements such as Nb, V, W, and Mo were added to this Ta at 0.5. Even when a Ta-based alloy sheet contained at a mass% or less was used, it was confirmed that the same reinforcing effect was exhibited without impairing workability.

(Example 3)
(a) A pure Ta sheet having a thickness of 0.2 mm was wound 16 times around the primary stack material so as to satisfy the common conditions of r2 / R = 0.585 and (r2-r1) /R=0.096. (B) Of the Ta sheet wound around the primary stack material in (a) above, a pure Nb sheet having a thickness of 0.2 mm instead of the two turns of the pure Ta sheet on the side in contact with the stabilized copper (C) three types of secondary stack materials, (c) a Ta sheet and a Nb sheet each having a thickness of 0.2 mm, and a total of 16 times. A billet was prepared (other basic procedures are the same as in Comparative Example 1).

The obtained precursors were subjected to diffusion heat treatment at 650 ° C. for 100 hours to obtain Nb ₃ Sn superconducting wires. For the obtained superconducting wire, the critical current Ic was obtained in the same manner as in Comparative Example 1, and the bending stress application force (bending application) when the critical current Ic was normalized (Ic / Ic ₀ ) was 0.95. Force) and critical current density Jc (nonCu-Jc). The n value was also measured in the same manner as described above.

As a result (see Table 1 below), each wire has a bending applied force of 100 N or more when (Ic / Ic ₀ ) is 0.95, a critical current density Jc of 700 A / mm ² or more, and an n value of Although a practical value of 20 or more is shown, it can be seen that the improvement of the n value is particularly remarkable in the wire partially replaced with the pure Nb sheet as compared with the wire wound only with the pure Ta sheet. Note that no dispersed fibrous structure was observed in the wire whose part was replaced with pure Nb.

  In Example 3, pure Nb was used as a material to replace a part of the pure Ta sheet, but alloy elements such as Ta, V, W, and Mo were contained in Nb at 0.5 mass% or less. Even when Nb alloy sheets are used, the effect of maintaining the same processing balance as that of pure Nb sheets and the effect of suppressing the (111) plane accumulation of Ta or Ta-based alloy layers are obtained, and the uniformity of the cross-sectional shape is improved. I was able to confirm.

Example 4
Billets of various secondary stack materials were prepared in the same manner as in Example 3 so as to satisfy the common conditions of r2 / R = 0.852 and (r2-r1) /R=0.150 (other basics The general procedure is the same as in Comparative Example 1).

Obtained subjected to diffusion heat treatment of 650 ° C. × 100 hours each precursor was Nb ₃ Sn superconducting wire. For the obtained superconducting wire, the critical current Ic was obtained in the same manner as in Comparative Example 1, and the bending stress application force (bending application) when the critical current Ic was normalized (Ic / Ic ₀ ) was 0.95. Force) and critical current density Jc (nonCu-Jc). The n value was also measured in the same manner as described above.

The Comparative Examples 1 and 2, characteristics of the resulting superconducting wire in Example _{1~4 [(Ic / Ic 0)} = bending applied force of 0.95 becomes that time, the critical current density Jc (nonCu-Jc) and n Value], and each condition [each value of r1 / R, r2 / R, (r2-r1) / R, and application form of the reinforcing material] when constituting the precursor are shown in Table 1 below.

As is clear from this result, in Examples 1 to 4 that satisfy the requirements defined in the present invention, the bending application force when (Ic / Ic ₀ ) is 0.95 becomes a large value and distortion occurs. It can be seen that the resistance to is improved. On the other hand, in Comparative Examples 1 and 2 that lack any of the requirements defined in the present invention, the characteristic deterioration due to the bending applied force is remarkable, and the characteristic deterioration with respect to the distortion appears remarkably.

It is sectional drawing which showed typically the example of a structure of the precursor for superconducting wire manufacturing applied to the bronze method. It is sectional drawing which showed typically the other structural example of the precursor for superconducting wire manufacturing applied to the bronze method. It is a schematic explanatory drawing which shows the structure of the jig | tool which applies a bending stress to a superconducting wire. For Example 1 and Comparative Example 1 obtained in the superconducting wire is a graph showing bending applied force and the relationship (Ic / Ic _0). It is a cross-sectional schematic diagram for demonstrating r1, r2 and R prescribed | regulated by this invention. In the superconducting wire obtained by the comparative example 2, it is a graph which shows the influence which (r2-r1) / R has on bending application force and critical current density Jc. For Nb ₃ Sn superconducting wire obtained in Example 2 is a graph showing the effect on (r2-r1) / R bending applied force and the critical current density Jc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cu-Sn base alloy matrix 2 Core material consisting of Nb or Nb base alloy 3 Primary stack material 4 Diffusion barrier layer 5 Cu-Sn base alloy 6 Stabilized copper

Claims (6)

A superconducting wire precursor used for preparing the bronze process Nb ₃ Sn superconducting wire, provided with a superconducting matrix portion which a plurality of Nb or Nb-based alloy filaments disposed in Cu-Sn-based alloy, stable on its outer circumference A precursor in which copper chloride is disposed,
A reinforcing layer made of Ta or a Ta-based alloy is interposed between the superconducting matrix portion and the stabilizing copper, and the distance from the center of the cross section to the outer surface is R, and the inner surface of the reinforcing layer is from the center of the cross section. The bronze Nb ₃ Sn superconducting wire characterized by satisfying the following relations (1) to (3) where r1 is the distance from the center of the cross section and r2 is the distance from the center of the cross section to the outer surface of the reinforcing layer: precursor.
0.4 ≦ r1 / R ≦ 0.8 (1)
0.55 ≦ r2 / R ≦ 0.95 (2)
0.05 ≦ (r2-r1) /R≦0.22 (3) The Ta-based alloy forming the reinforcing layer contains one or more elements selected from the group consisting of Nb, V, W and Mo in a proportion of 0.5% by mass or less (excluding 0%). The bronze process Nb ₃ Sn superconducting wire precursor according to claim 1. The bronze Nb ₃ Sn superconducting wire precursor according to claim 1 or 2, wherein a layer made of Nb or an Nb-based alloy is formed on the inner surface side and / or outer surface side of the reinforcing layer. The bronze Nb ₃ Sn superconductivity according to any one of claims 1 to 3, wherein the reinforcing layer is formed by winding a single layer or a laminated layer by winding a sheet-like member made of Ta or a Ta-based alloy. Wire precursor. The bronze Nb ₃ Sn superconductivity according to claim 4, wherein a sheet-like member made of Ta or a Ta-based alloy is wound and laminated to form a Nb or Nb-based alloy layer sheet interposed between the layers. Wire precursor. The bronze process Nb ₃ Sn superconducting wire precursor according to any one of claims 1 to 5, bronze process Nb ₃ Sn superconducting wire is obtained by forming a Nb ₃ Sn superconducting phase by diffusion heat treatment.

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