JP4699200B2 - Precursor for producing Nb3Sn superconducting wire and method for producing the same - Google Patents

Description

The present invention relates to a precursor (precursor for producing a superconducting wire) used when producing an Nb ₃ Sn superconducting wire by an internal diffusion method, and a method for producing such a precursor, and in particular, a superconducting magnet for generating a high magnetic field. The present invention relates to a technique for producing an internal diffusion method Nb ₃ Sn superconducting wire useful as a material for the above.

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

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 the Nb base material is reduced in diameter by drawing to form a filament. A plurality of filaments (Nb-based filaments) and a bronze composite material are bundled to form a wire group, and after copper for stabilization (stabilized copper) is disposed, wire drawing is performed. The wire group is heat-treated (diffusion heat treatment) at about 600 ° C. or higher and 800 ° C. or lower to form an Nb ₃ Sn compound layer 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 compound layer to be formed is thin, and the crystallinity is deteriorated. There is a disadvantage that the high magnetic field characteristics are not good.

In addition to the bronze method, an internal diffusion method is also known as a method for producing the Nb ₃ Sn superconducting wire. In this method, since there is no limit on the Sn concentration due to the solid solubility limit as in the bronze method, the Sn amount can be set as high as possible, and a high-quality Nb ₃ Sn layer can be generated. Therefore, a superconducting wire excellent in high magnetic field characteristics is obtained. It has been shown to be obtained.

In this internal diffusion method, as shown in FIG. 1 (schematic diagram of a precursor for producing a Nb ₃ Sn superconducting wire), a central portion of Cu or a Cu-based alloy (hereinafter sometimes referred to as “Cu base material”) 4 In addition, a core 3 (hereinafter also referred to as “Sn-based metal core”) 3 made of Sn or an Sn-based alloy is embedded in the Cu base material 4 around the Sn-based metal core 3 and a plurality of Nb or Nb Base alloy cores (hereinafter collectively referred to as “Nb base metal cores”) 2 are arranged so as not to contact each other to form a composite material, which is drawn to produce precursor 1 (manufacturing superconducting wire) This is a method in which Sn in the Sn-based metal core 3 is diffused by heat treatment (diffusion heat treatment) and then reacted with the Nb-based metal core 2 to form Nb ₃ Sn (for example, Patent Documents). 1).

  Further, in the precursor 1 as described above, as shown in FIG. 2, the portion where the Nb-based metal core 2 is disposed (hereinafter sometimes referred to as “Cu matrix portion”) and the stabilized copper on the outer periphery thereof are provided. A structure in which a diffusion barrier layer 6 is disposed between the layers 4a is also known. The diffusion barrier layer 6 is composed of, for example, an Nb layer or a Ta layer, or two layers of an Nb layer and a Ta layer, and Sn (Sn-based metal core 3) inside the Cu matrix portion diffuses to the outside during the diffusion heat treatment. The effect which raises the purity of Sn in a Cu mat risk part is exhibited.

  In order to manufacture the precursor for manufacturing a superconducting wire as described above, the following procedure is performed. First, an Nb-based metal core (Nb-based metal filament) is inserted into a Cu matrisk tube, subjected to extrusion, wire diameter reduction or the like to obtain a composite, and this is cut into an appropriate length. Then, after having a Cu outer cylinder, filling the composite in a billet with or without a diffusion barrier layer, placing a Cu matrix (Cu solid billet) in the center and extruding it, A Cu matrix at the center is mechanically drilled to form a pipe-shaped composite. Alternatively, as another method, a plurality of the composites are filled in a hollow billet (between the outer cylinder and the inner cylinder) which is composed of a Cu outer cylinder and a Cu inner cylinder and which has or does not have the diffusion barrier layer 6. The pipe is extruded to form a pipe-shaped composite.

  Then, the Sn-based metal core 3 is inserted into the central gap portion of the pipe-shaped composite produced by these methods and the diameter is reduced to produce the precursor as shown in FIGS.

  When manufacturing a superconducting wire by the internal diffusion method using the precursor as described above, the flat wire can be wound around the coil at a higher filling rate than the round wire, and in order to make the wire easier to wind. In general, the cross section is extruded and drawn to have a flat rectangular shape. When performing such processing, as shown in FIG. 3, the precursor 1 [FIG. 3 (a)] is pressed from one direction (vertical direction in FIG. 3) by a pair of rolls 10a and 10b. The cross section has a flat shape [FIG. 3 (b)]. As described above, in order to make the wire rod having a circular cross section into the final flat rectangular shape, the actual situation is that the flat angle is obtained after rolling with a roll in only one direction.

  However, in such a processing method, the Nb-based metal core 2 and the Sn-based metal core 3 are not necessarily made uniform, and the internal structure of the composite wire becomes distorted, and finally a superconducting wire is obtained. Sometimes, the critical current density Jc, the n value, the residual resistance value RRR, and the like may decrease. In particular, when the diffusion barrier layer 6 as described above is disposed, the diffusion barrier layer 6 may be damaged due to a difference in hardness from other portions.

  As a technique for making the precursor provided with the diffusion barrier layer into a flat rectangular shape, for example, a technique as disclosed in Patent Document 2 has been proposed. In this technology, from the viewpoint of preventing the diffusion barrier layer from being damaged when processing into a flat rectangular shape, the wire (precursor) is subjected to heat treatment at 300 to 550 ° C. for 20 to 100 hours before the roll processing to obtain a Cu matrix portion. By forming a Cu—Sn alloy, the hardness difference from the diffusion barrier layer is eliminated and the workability is improved.

However, such a technique has a problem that the heat treatment time for forming the Cu—Sn alloy becomes long and the productivity is inferior. Further, when heat treatment is performed at a temperature exceeding 500 ° C., Nb ₃ Sn is generated at the stage of the heat treatment, so that workability is deteriorated and normal rectangular shape machining cannot be performed.
Japanese Patent Laid-Open No. 49-114389 Patent Claims, etc. JP, 63-213213, A Claims etc.

  The present invention has been made under such circumstances, and its purpose is to produce uniform superconductors and produce good superconducting properties when producing a precursor for producing a superconducting wire having a flat cross section. It is an object of the present invention to provide a precursor for producing a superconducting wire capable of being subjected to internal oxidation, and a useful method therefor.

With the method for producing a precursor for producing a superconducting wire of the present invention that has achieved the above-mentioned object,
In producing a precursor for producing a superconducting wire used when producing a Nb ₃ Sn superconducting wire by an internal diffusion method,
Sn or Sn-based alloy core in the center, a Cu matrix portion in which a plurality of Nb or Nb-based alloy cores are arranged around the center, and a stabilizing copper layer on the outer periphery of the Cu matrix portion, and a cross-section is circular A composite material having a shape is formed and pressed from both the upper and lower sides and the left and right sides of the composite material, the rolling reduction R shown by the following formula (1) is set to -21 to -8%, and the cross-sectional shape is elliptical Alternatively, intermediate processing to form a flat shape to an intermediate processing wire,
The intermediate processed wire is drawn by a die to form a precursor having a flat rectangular shape.
R = (L ₁ −L ₀ ) / L ₀ (1)
However, L ₁ : Short side thickness after processing L ₀ : Short side thickness before processing, or wire diameter (diameter) in the case of a round wire

In the manufacturing method of the present invention, it is preferable that the short side thickness (L ₁ ) of the intermediate processed wire is set to be larger than the short side thickness of the flat rectangular precursor. In the manufacturing method of the present invention, the effect is effectively exhibited when a composite material in which a diffusion barrier layer made of Nb and / or Ta is interposed between the Cu matrix portion and the stabilizing Cu layer is used. .

In the precursor manufactured by the method of the present invention as described above, the aspect ratio (major axis / minor axis ratio in the cross section) of the Sn or Sn-based alloy core is R _c , and the Cu matrix part is arranged on the outermost peripheral side. When the aspect ratio of the Nb or Nb-based alloy core (major axis / minor axis ratio in the cross section) is R ₀ , it is preferable that these ratios (R _c / R ₀ ) satisfy 1.3 or less. In addition, by heat-treating such a precursor for producing a superconducting wire, an Nb ₃ Sn superconducting wire exhibiting desired characteristics can be obtained.

According to the method of the present invention, when the precursor for producing a superconducting wire is formed into a rectangular cross-sectional shape, the cross-sectional shape is substantially elliptical or flat by pressing from both the upper and lower sides and the left and right sides within a predetermined rolling reduction range. After intermediate processing to form a shape, it is shaped into a flat rectangular shape of the final shape, so it can be uniformly shaped without generating distorted parts inside the cross-sectional structure, and finally good superconductivity Nb 3 _Sn superconducting wire precursor for manufacturing capable of obtaining the wire could be realized.

  The present inventors have studied from various angles in order to achieve the above object. As a result, the wire (precursor) having a circular cross section is not formed into a flat rectangular shape by one strong processing, but is intermediated from a circular wire (round wire) to a final flat shape with a predetermined rolling reduction. As a result, the present invention has been completed by performing processing so as to obtain a perfect cross-sectional shape and then shaping it with a die so as to obtain a final shape, without causing any inconvenience as in the prior art.

  When performing the above-described intermediate processing, it is necessary to press from both the upper and lower sides and the left and right sides instead of processing in one direction. By processing in such a configuration, it is possible to perform uniform processing by preventing distortion deformation that escapes outwardly through the gap between the rolls that occurs when processing in one direction is performed. In particular, even when a hard diffusion barrier layer is provided, the spread in the lateral direction (left and right direction in FIGS. 2 and 3) is suppressed, and uniform processing can be realized. Further, according to the method of the present invention, since it can be processed in a short time without performing heat treatment, it is advantageous in terms of productivity.

  In the method of the present invention, the means for pressing from both the upper and lower sides and the left and right sides is not particularly limited. For example, the processing is performed using a two-way roll, or the cross-sectional shape is elliptical (intermediate shape). It is possible to process using an elliptical die. Such a state will be described with reference to the drawings.

  FIG. 4 is a diagram illustrating a state in which intermediate processing is performed using a two-way roll, in which 15a and 15b are a pair of rolls that press in the vertical direction, and 16a and 16b are a pair of rolls that press in the left-right direction. (The other parts correspond to FIGS. 1 and 2). In such a state, for example, rolling is performed while applying pressure from above and below, and processing is performed so as to reduce at least the thickness in the thickness direction (vertical direction in FIG. 4). At that time, the roll in the left-right direction does not necessarily have to be moved so that the distance between the rolls is shortened, and may be in a state of being fixed at a fixed position and restraining both ends in the left-right direction of the precursor 1. The same effect as pressing is exhibited by suppressing the spread to the. In addition, although the temperature at the time of processing by a two-way roll may be normal temperature, you may implement processing at 100-400 degreeC in order to make workability favorable.

  The state shown in FIG. 4 is shown when the precursor 1 is in a state close to the final cross-sectional shape, but the cross-sectional shape may be close to a circle (elliptical) or flat. In short, the processing may be performed at a predetermined rolling reduction (to be described later) so that the cross section becomes an intermediate shape between the wire having a circular shape and the flat rectangular shape of the final shape. In the method using the two-way roll, the strong processing to the final shape as it is cannot be performed, so after performing the intermediate processing as described above, a die whose cross-sectional shape becomes a rectangular shape [hereinafter referred to as “flat rectangular die”. Called: see FIG. 5C to be described later] to form a final rectangular wire.

  FIG. 5 is a diagram for explaining a state of intermediate processing using an elliptical die. The precursor 1 having a circular cross section [FIG. 5A] is first subjected to intermediate processing with an elliptical die 12 to have an elliptical cross section or a flat shape [FIG. 5B]. Then, it shape | molds using the die | dye 11 from which cross-sectional shape becomes a flat shape, and it shape | molds in the final flat wire shape [FIG.5 (c)].

  In any case, the processing rate during the intermediate processing needs to be set to be -21 to -8% in terms of the rolling reduction R shown in the equation (1). If this rolling reduction becomes a value larger than -8% (when the processing rate becomes small), the processing rate in drawing with a flat die up to the final shape after intermediate processing becomes too high, leading to non-uniform deformation. Become. Further, when the rolling reduction becomes a value smaller than -21% (when the processing rate increases), the processing rate in the intermediate processing increases, and thus non-uniform deformation occurs in the intermediate processing stage. In addition, the said rolling reduction should just be in said range in the stage of an intermediate process, and does not necessarily have to be in said rolling reduction range by one process. Therefore, it goes without saying that the rolling reduction after the plurality of times of processing may be within the above range.

The thickness on the short side when the rolling reduction is defined in the present invention is the thickness on the side where the length of the side becomes short (L ₁ or L ₀ ) in the cross-sectional shape shown in FIG. 4 and FIG. ) And the size of the side where the length of the side becomes longer is expressed as “long side length L ₂ ” (see FIG. 5). In short, in the intermediate processing, if the processing is performed such that the short side thickness (L ₁ or L ₀ ) of the intermediate processed wire becomes larger than the final flat rectangular thickness L ₃ [see FIG. 5 (c)]. good. In this stage of intermediate processing, although the long side length L ₂ increases basically, may be set so that almost no change, and 5 to 20% shorter in the range not impairing the processability May be. Incidentally, the short side thickness L ₀ before the processing, in the case of round wire is the same as the wire diameter (diameter).

After intermediate processing under the above conditions, a diffusion heat treatment (usually 650 to 750 ° C.) is performed using a precursor having a final cross-sectional shape formed by shaping with a die, thereby obtaining a superconducting wire exhibiting good characteristics. Although the it, as the configuration of the precursor at the stage of completion of the preform, arranged the aspect ratio of the Sn or Sn-based alloy cores (the major diameter / minor diameter ratio in the cross section) R _c, the outermost peripheral side of the Cu matrix portion When the aspect ratio (major axis / minor axis ratio in the cross section) of the Nb or Nb-based alloy core is R ₀ , these ratios (R _c / R ₀ ) satisfy 1.1 or more and 1.3 or less. It is preferable. Satisfying these requirements eliminates the difference in strain between the central portion of the wire and the outer peripheral portion as a result of the uniform processing being performed. However, even if the ratio (R _c / R ₀ ) is 1.3 or less, if the respective aspect ratios R _c and R ₀ are not within an appropriate range, the portion may have undergone extreme deformation. Will eventually lead to deterioration of the superconducting properties. And from this point of view, the aspect ratio _{R c} of the Sn or Sn-based alloy core is in the range of 1.05 to 1.4, and Cu aspect ratio of Nb or Nb-based alloy cores being disposed in the outermost peripheral side of the matrix portion R ₀ is preferably controlled to be in the range of 1.0 to 1.2.

  The precursor of the present invention has an Nb-based metal core 2 (Nb or Nb-based alloy core) and an Sn-based metal core 3 (Sn or Sn-based alloy core) in a Cu or Cu-based alloy as a basic configuration. Although it arrange | positions at intervals, as Cu alloy used by such a structure, what contains elements, such as Nb and Ni, can be used for Cu. Moreover, as a raw material used as the Sn-based metal core 3, a material containing elements such as Ti, Ta, Zr, Hf and the like that does not inhibit workability (about 5% by mass or less) can be used. As the Nb-based alloy core 2, Nb containing an additive element such as Ti, Ta, Hf, Zr or the like in an amount of about 10% by mass or less can be used.

  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.

Example 1
An Nb-7.5 mass% Ta alloy core having an outer diameter of 57 mm is inserted into a bit (tubular member) made of oxygen-free copper having an outer diameter of 68 mm and an inner diameter of 57 mm, extruded, and the opposite side length is 2 mm by wire drawing. A Cu / Nb composite wire having a hexagonal cross section was prepared.

  On the other hand, on the inner surface side of the Cu outer cylinder of a Cu solid billet composed of a Cu outer cylinder (outer diameter: 68 mm, inner diameter: 60 mm) and a Cu cylindrical member (outer diameter: 30 mm) disposed at the center thereof. , A barrier layer (thickness: 2 mm) made of Nb was pasted and arranged, and then 410 Cu / Nb composite wires were bundled and inserted around the Cu cylindrical member to form an extruded billet.

  After extruding this billet, a hole having a diameter of 10 mm was drilled in a central copper portion (Cu cylindrical member) by a drill, and a Sn rod having an outer diameter of 10 mm was inserted therein to produce a composite material (precursor). Then, the wire diameter was processed to 2.14 mm by die drawing.

Subsequently, this composite material was once subjected to intermediate processing using a two-way roll (processing temperature: 25 ° C.), and then finished to a final wire diameter using a flat rectangular die. In addition, the temperature at the time of these processes was normal temperature (25 degreeC). The obtained precursor was subjected to heat treatment (diffusion heat treatment) at 700 ° C. for 150 hours to obtain an Nb ₃ Sn superconducting wire. With respect to the obtained Nb ₃ Sn superconducting wire, the critical current (Ic) at a temperature of 4.2 K was measured by a four-terminal method with an external magnetic field 18T (Tesla) applied, and the area of the non-copper portion of the wire cross section was measured. The critical current density (Jc) was evaluated by removing Ic. The results, along with intermediate processing conditions (height, rolling reduction), final flat rectangular shape (height, width), aspect ratio (wire, central portion Rc, outer peripheral portion R ₀ ) and ratio (Rc / R ₀ ), Shown in Table 1 below.

  The aspect ratio of each part was measured by the following method.

[Aspect ratio measurement method]
Wire: A rectangular wire was measured by measuring a long side and a short side using a micrometer.
Center part (R _c ): The length in the major axis direction and the minor axis direction of the core part was measured and calculated from a cross-sectional photograph taken with an optical microscope.
Outer peripheral part (R ₀ ): Filaments at the outer peripheral part were arbitrarily selected from SEM photographs, and the lengths in the major axis direction and the minor axis direction were measured and calculated.

  As is apparent from this result, it is understood that good superconducting characteristics are obtained with the samples processed under the conditions specified in the present invention (Test Nos. 3 to 6). On the other hand, it can be seen that in the case where the rolling ratio of the intermediate processing is large (test Nos. 1 and 2), the aspect ratio Rc in the center portion is particularly large, resulting in distortion, and good superconducting characteristics cannot be obtained.

Example 2
In Table 1, the sample with a rolling reduction ratio of -6.5% (No. 7 in Table 1) was further rolled and processed to a height of 1.8 mm (final rolling reduction: 15.9). ). The obtained precursor was heat-treated under the same conditions as in Example 1 to obtain a Nb ₃ Sn superconducting wire, and the superconducting properties were measured by the same method. As a result, the critical current density (Jc) at a temperature of 4.2 K was 378 A / mm ² and a high critical current density (Jc) was obtained.

As is clear from this result, when the first rolling reduction is small, if the total rolling reduction is within the range defined by the present invention by continuing the rolling, the desired superconducting characteristics are obtained. It can be seen that At this time, it is effective to make the short side thickness L ₀ after the intermediate processing by rolling larger than the thickness of the final rectangular shape.

It is sectional drawing which showed typically the example of a structure of the precursor for superconducting wire manufacturing applied to the internal diffusion method. It is sectional drawing which showed typically the other structural example of the precursor for superconducting wire manufacturing applied to the internal diffusion method. It is a figure for demonstrating an example of the conventional processing method. It is a figure for demonstrating the example of the processing method of this invention. It is a figure for demonstrating the other example of the processing method of this invention.

Explanation of symbols

1 Precursor 2 Nb-based metal core 3 Sn-based metal core 4 Cu-based alloy (Cu base material)
4a Stabilized copper 6 Diffusion barrier layer

Claims (4)

In producing a precursor for producing a superconducting wire used when producing a Nb ₃ Sn superconducting wire by an internal diffusion method,
Sn or Sn-based alloy core in the center, a Cu matrix portion in which a plurality of Nb or Nb-based alloy cores are arranged around the center, and a stabilizing copper layer on the outer periphery of the Cu matrix portion, and a cross-section is circular A composite material having a shape is formed and pressed from both the upper and lower sides and the left and right sides of the composite material, the rolling reduction R shown by the following formula (1) is set to -21 to -8%, and the cross-sectional shape is elliptical Alternatively, intermediate processing to form a flat shape to an intermediate processing wire,
A method for producing a precursor for producing an internal diffusion method Nb ₃ Sn superconducting wire, characterized in that the intermediate processed wire is drawn with a die to form a precursor having a flat rectangular shape.
R = (L ₁ −L ₀ ) / L ₀ (1)
However, L ₁ : Short side thickness after processing L ₀ : Short side thickness before processing, or wire diameter (diameter) in the case of a round wire The short side thickness L ₁ of the preform wire is method of claim 1 set to be larger than the short side thickness of the precursor of the rectangular shape.   The manufacturing method of Claim 1 or 2 using the composite material which interposed the diffusion barrier layer which consists of Nb and / or Ta between the said Cu matrix part and the stabilization Cu layer. It is a precursor manufactured by the method according to any one of claims 1 to 3, wherein the aspect ratio (major axis / minor axis ratio in the cross section) of Sn or Sn-based alloy core is R _c , and the outermost periphery of the Cu matrix part When the aspect ratio (major axis / minor axis ratio in the cross section) of the Nb or Nb-based alloy core disposed on the side is R ₀ , these ratios (R _c / R ₀ ) satisfy 1.3 or less. A precursor for producing an internal diffusion method Nb ₃ Sn superconducting wire characterized by being.

Images