JP2004296124A - Manufacturing method of nb3sn superconductive wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a Nb<SB>3</SB>Sn superconductive wire rod capable of generating a magnetic field of 20 teslas or more at 4.2K, whereby the manufacturing cost of the wire rod is reduced. <P>SOLUTION: This manufacturing method of the Nb<SB>3</SB>Sn superconductive wire rod is provided with a process to manufacture a complex by alternately laminating a first base material comprising a mixture of Sn and M and a second base material comprising Nb or a Nb-based alloy, a process to machine the complex to the wire rod, and a process to heat-treat the wire rod. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００７６】
【表２】

【００７７】
【発明の効果】
以上説明したように、本発明の方法で作製された線材は、１ＧＨｚＮＭＲ分析装置に必要な２３．５テスラの磁界の発生を達成しうる可能性を示したので、従来法で作製された線材と比較して格段に高いＪｃ磁界特性が得られ、蛋白質の構造解析などに必要なＮＭＲ分析装置、クリーンなエネルギー源として期待される核融合、冷凍機直冷型超伝導マグネットなどの幅広い分野に応用することができる。
【００７８】
また、本発明によれば、ＴａとＳｎの合金あるいは金属間化合物を作製し、さらにこれをシース材に充填するため粉末に粉砕する工程を省略することができるので、線材作製コストが大幅に削減されるとともに、望ましい組成の芯材を容易に作製することができる。その結果、４．２Ｋで２３テスラ、２．１Ｋで２５テスラの磁界を発生しうる、インパクトの大きい超伝導線材を容易に提供することができる。なお、超伝導線材を磁界発生に実用する際には、Ｉ_ｃ を線材全断面積で除した臨界電流密度Ｊ_ｃ が１×１０^４ Ａ／ｃｍ^２ 以上あることが望ましい。
【００７９】
また、本発明によれば、Ｓｎ中にＭが分散した可塑性に優れたＳｎ−Ｍ合金とＮｂ又はＮｂ合金との複合体を線材に加工した後に反応熱処理するので、従来の粉末コア法よりも加工しやすく、また均一性に優れた線材を提供することができる。このように本発明方法により製造された線材は可塑性に富むものであるため、極細多芯線材の製造などが可能となり、工業的な利用価値が極めて高く、実用的である。
【００８０】
また、本発明の方法は、従来のブロンズ法において必要とされていた多くの中間焼鈍を省略することができるので、製造コストを大幅に低減することができる。
【００８１】
さらに、本発明によれば、少量のＣｕの添加によりＮｂ_３Ｓｎ層を生成する反応が促進されるので、最終熱処理温度を低下させ、製造コストを低く抑えることができる。
【００８２】
また、さらに本発明によれば、水素化物を出発物質として微細なＭ粒子をＳｎ中に均一に分散させることができるので、従来よりもさらに超伝導特性に優れた線材を提供できるとともに、実用上好ましい極細多芯形式の線材を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る超伝導線材の製造方法（ジェリーロール法）の概要を示すブロック工程図。
【図２】超伝導特性｛臨界電流Ｉｃ（左縦軸），線径１．３５ｍｍ臨界電流密度Ｊｃ（右縦軸）−磁界（横軸）特性｝を示す特性線図。
【図３】超伝導特性｛臨界電流Ｉｃ（左縦軸），線径１．３５ｍｍ臨界電流密度Ｊｃ（右縦軸）−磁界（横軸）特性｝を示す特性線図。
【図４】超伝導特性（臨界電流密度Ｊｃ−磁界特性）について本発明方法で作製した実施例サンプルと従来法で作製した比較例サンプルとを比べて示す特性線図。
【図５】本発明の他の実施形態に係る超伝導線材の製造方法の概要を示す工程図。
【図６】粉体原料の粒径分布を示す棒グラフ。
【図７】超伝導特性｛臨界電流Ｉｃ（左縦軸），臨界電流密度Ｊｃ（右縦軸）−磁界（横軸）特性｝を示す特性線図。
【図８】超伝導特性｛臨界電流Ｉｃ（左縦軸），臨界電流密度Ｊｃ（右縦軸）−磁界（横軸）特性｝を示す特性線図。
【図９】本発明方法を用いて製造された極細多芯線材の横断面を示す顕微鏡写真。
【符号の説明】
２…第１の基材（Ｓｎ−Ｍシート）
３…第２の基材（Ｎｂシート）
４…芯材（Ｎｂ棒）
５…複合体（Ｓｎ−Ｍ／Ｎｂ捲回体）
６…外筒（Ｎｂ−Ｔａチューブ）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an Nb for generating a high magnetic field which enables development of various new technologies such as an NMR analyzer, a fusion reactor, and a high-density energy storage. ₃ The present invention relates to a method for manufacturing a Sn superconducting wire.
[0002]
[Prior art]
As the superconducting wire, an Nb-Ti alloy wire is often used, and a large current can be supplied without power consumption to generate a high magnetic field. However, this alloy wire has a limit of a generated magnetic field at a liquid helium temperature (4.2 K) of about 9 Tesla (9 T). Therefore, it is necessary to use a compound superconducting wire in order to generate a high magnetic field of 10 T or more necessary for a nuclear fusion device, an NMR analyzer, and the like. Nb with A15 type crystal structure ₃ Sn compounds are known as one of the superconducting materials that meet such requirements. Its critical temperature T _c Is about 18K, upper critical magnetic field B _c2 (4.2K) is about 21T, which is almost twice as high as Nb-Ti about 9K and about 11.5 Tesla, respectively. Nb ₃ As a method for producing a Sn compound wire, for example, a bronze method described in Non-Patent Document 1 is used. The bronze method uses Nb as a core material, creates a composite in which this is wrapped in a Cu-Sn alloy matrix, plastically processes this, and performs diffusion heat treatment to form an Nb core at the interface between the Nb core and the matrix. ₃ This is a method for generating a Sn compound phase.
[0003]
Furthermore, in the bronze method, the present inventor added a small amount of Ti to the Cu-Sn alloy matrix to increase the upper critical magnetic field B. _c2 Was found to be improved and published in Non-Patent Document 2. The process was subsequently industrialized. Using this wire, a magnetic field of 18.8 Tesla at 4.2K and 21.6 Tesla at 1.6K was generated. In 2002, the world's best 920 MHz NMR analyzer useful for structural analysis of proteins and the like was completed. However, the properties of bronze normal wires have reached their limits, and the development of next-generation high-magnetic-field superconducting wires is expected.
[0004]
The inventor has made an alloy or an intermetallic compound of one or more metals selected from the group consisting of Ti, Zr, Hf, V and Ta and Sn and an intermetallic compound into a core material, and made Nb or an Nb alloy a sheath. After processing the composite obtained by filling the core material into a wire, the material is heat-treated to obtain Nb having excellent high magnetic field characteristics. ₃ Patent Document 1 proposes that an Sn wire can be manufactured. Further, the present inventor has applied for a related invention in the application specification (unpublished) of Japanese Patent Application No. 2001-275401. These are all based on the powder core method.
[0005]
[Non-patent document 1]
K. Tachikawa: Filamentary A15 Superconductors, Plenum Press (1980) p1
[0006]
[Non-patent document 2]
Hisashi Sekine, Yasuo Iijima, Kikuo Ito, Kyoji Tachikawa: Journal of the Japan Institute of Metals, Vol. 49, No. 10, (1985) p. 913
[0007]
[Patent Document 1]
JP-A-11-250749
[0008]
[Problems to be solved by the invention]
However, in the above-mentioned conventional method, the step of producing an alloy or an intermetallic compound of one or more metals selected from the group consisting of Ti, Zr, Hf, V and Ta and Sn and the alloy or intermetallic compound In order to fill the sheath material with the compound, a step of pulverizing the compound into powder is essential, but these steps are not always easy and have been a problem in industrialization.
[0009]
In addition, when a wire is manufactured by the conventional powder core method, so-called sausaging in which the wire is deformed in a wavy manner may occur, which makes it difficult to process a long wire having a uniform cross-sectional shape.
[0010]
An object of the present invention is to use Ta, which is most effective in improving high magnetic field characteristics, and to solve the above-mentioned problems in industrialization using a composite made of a plastic base material. Accordingly, Nb which can reduce the cost of wire production and easily produce a core material of a desired composition ₃ An object of the present invention is to provide a method for manufacturing a Sn superconducting wire.
[0011]
[Means for Solving the Problems]
Nb-Ti alloy wires and Nb produced by the bronze method are currently used as superconducting wires. ₃ There is Sn compound wire rod, Ti addition bronze method (Nb, Ti) ₃ A 920 MHz class NMR analyzer with the world's highest performance at 1.6K operation using a Sn wire has been developed. However, the performance of the bronze normal wire has reached its limit, and further improvement in the high magnetic field characteristics of the superconducting wire is expected. As a result of intensive research to meet such expectations, the present inventor has recently used a Ta-Sn powder core and an Nb (Nb-Ta) sheath as a next-generation superconducting wire (Nb, Ta). ₃ A Sn superconducting wire was developed.
[0012]
In this wire, the heat treatment causes Nb of the sheath to move to the core, thereby promoting the diffusion of Sn contained in the core to the sheath. ₃ An Sn layer is formed. This is because Sn is easier to form an intermetallic compound with Nb than Ta, and Ta and Nb are more likely to form a solid solution with each other, and Nb of the sheath forms a solid solution with the core material. This is based on a new finding discovered by the present inventor to promote the diffusion of. In the present invention, a Sn-Ta sheet having a high processability is newly prepared, and (Nb, Ta) ₃ The purpose was to produce a Sn superconducting wire and to study the effect of adding Cu to the substrate.
[0013]
According to the present invention, Ta is Nb ₃ Since the solid solution forms in the Sn layer, the high magnetic field characteristics are improved, and the Nb of the sheath diffuses into the core, so that voids do not occur in the core after the reaction. The generation of voids in the core degrades the mechanical properties of the wire.
[0014]
The present invention has been made based on the above findings, and has the following configuration.
(1) a step of alternately laminating a first substrate made of a mixture of Sn and M and a second substrate made of Nb or an Nb-based alloy to produce a composite; Nb, comprising: ₃ A method for producing a Sn superconducting wire.
[0015]
(2) M may be one or two or more metals selected from the group consisting of Ta, Ti, and Hf, and (3) one or two metals selected from the group consisting of Ta, Ti, and Hf. A metal hydride obtained by hydrogenating at least one kind of metal may be used. M is not limited to metal, but when a metal hydride such as Ta-H is used, the raw material powder is finely divided, and a practically useful multifilamentary wire can be easily produced.
[0016]
(4) The first base material contains 0.5 to 50 atomic% of M. When the content of M is less than 0.5 atomic%, the effect of improving the superconductivity is not recognized. On the other hand, if the M content exceeds 50 atomic%, the plasticity of the first base material is lost, which is not preferable.
[0017]
(5) It is desirable to melt the first base material in a temperature range from the melting point of Sn to 1200 ° C. before the composite manufacturing step. When the first base material is melted in such a temperature range, Sn and M are alloyed, and subsequent handling in processing is facilitated. If the melting temperature exceeds 1200 ° C., Sn evaporates and it becomes difficult to control the components.
[0018]
(6) The first substrate is made of an alloy having plasticity.
[0019]
(7) It is preferable that the first base material is further added with a third element to improve the composite workability with the second base material. Since Sn contained in the first base material is softer than Nb constituting the second base material, the hardness is adjusted by adding these third elements. As a result, the elongation of the first base material and the elongation of the second base material are uniform, and wire drawing with uniform elongation can be performed.
[0020]
(8) The third element is one or more elements selected from the group consisting of Bi, In, Sb, Mg, Ag, Zn, Al, Ge, Si, and Pb. Note that the addition amount of the third element is desirably 0.5 to 20 atomic%. If the addition amount is less than 0.5 atomic%, the hardness of Sn is insufficiently increased, and if the addition amount exceeds 20 atomic%, the Sn becomes too hard.
[0021]
(9) The first base material preferably further contains 0.5 to 30 atomic% of Cu. If the Cu content is less than 0.5 atomic%, the effect of lowering the heat treatment temperature cannot be obtained. On the other hand, if the addition amount exceeds 30 atomic%, the superconductivity is deteriorated.
[0022]
(10) The second substrate is an Nb alloy containing one or more metals selected from the group consisting of Ta, Ti, and Hf.
[0023]
(11) In the composite manufacturing step, a first base material and a second base material are used by using a core material having substantially the same composition as one of the first base material and the second base material. Are alternately overlapped and wound around the core material.
[0024]
(12) The first base material has a Sn content in the range of 20 to 80 atomic%. If the Sn content is less than 20 atomic%, Nb ₃ This is because the thickness of the Sn layer decreases. On the other hand, when the Sn content exceeds 80 atomic%, the effect of the M metal content is reduced, and the superconductivity is deteriorated.
[0025]
(13) The second substrate is made of an Nb alloy containing one or two elements selected from the group consisting of Ta, Ti, and Hf in an amount of 20 atomic% or less. This is because, if the addition amount of these elements exceeds 20 atomic%, the superconductivity is deteriorated.
[0026]
(14) The composite obtained by any of the methods (1) to (13) is filled in a Cu matrix, and the composite is processed into a wire and then heat-treated.
[0027]
In addition, during the step of processing the composite into a wire, it is desirable that the composite be subjected to intermediate annealing in a temperature range from the melting point of Sn to 650 ° C. or less. There is an advantage that the structure is homogenized by this annealing effect, which is advantageous in improving superconductivity.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
A composite obtained by alternately laminating a mixture of Ta and Sn (first substrate) and Nb or Nb alloy (second substrate) or the mixture is filled in an Nb or Nb alloy sheath material. After processing the composite obtained into a wire, heat treatment is performed to obtain Nb ₃ A Sn superconducting wire is manufactured. The Sn content in the mixture of Ta and Sn is desirably in the range of 20 to 80 atomic%, and Nb produced when the Sn content is less than 20 atomic% is formed. ₃ If the thickness of the Sn layer is reduced, and if it exceeds 80 atomic%, Nb ₃ The amount of Ta solid solution in the Sn layer decreases, and the effect of improving the high magnetic field characteristics decreases. The heat treatment temperature after processing is suitably in the range of 700 ° C. to 950 ° C., and is preferably performed in a vacuum or in an inert gas atmosphere.
[0029]
When a mixture of Ta and Sn (first base material) is melted at a temperature of not less than the melting point of Sn and not more than 1200 ° C., an alloy which is easy to process in which Sn is melted and Ta is dispersed in Sn is obtained. Alternatively, when a composite with an Nb alloy is produced and further processed into a wire, there is an advantage that handling becomes easy. Melting at a temperature exceeding 1200 ° C. is not preferable because the composition fluctuates due to evaporation of Sn. Also, the intermediate annealing may be performed during the wire rod processing step. ₃ Since the formation of the Sn layer causes inconvenience in the subsequent wire rod processing, the intermediate annealing is preferably performed at a temperature of 650 ° C. or less, preferably in a temperature range of 500 ° C. to 600 ° C.
[0030]
It is preferable that the first base material is further added with a third element to improve composite workability with the second base material. Since Sn contained in the first base material is softer than Nb constituting the second base material, Bi, In, Sb, Mg, Ag, Zn, Al, Ge, Si, The hardness is adjusted by adding Pb. As a result, the elongation of the first base material and the elongation of the second base material are uniform, and it is possible to perform wire drawing with uniform elongation. In this case, the addition amount of the third element is desirably 0.5 to 20 atomic%. If the addition amount is less than 0.5 atomic%, the hardness of Sn is insufficiently increased, and if the addition amount exceeds 20 atomic%, the Sn becomes too hard.
[0031]
Furthermore, when 0.5 to 30 atomic% of Cu is contained in the first base material, there is a remarkable effect in lowering the heat treatment temperature. Addition of less than 0.5 atomic% of Cu has no effect, while addition of 30 atomic% or more of Cu degrades high magnetic field characteristics. It is particularly preferable to add 3 to 15 atomic% of Cu, whereby the heat treatment temperature can be lowered to 800 ° C. or lower, which has a great advantage in industrial production.
[0032]
On the other hand, when the Nb alloy contains one or two metals selected from the group consisting of Ta, Ti, and Hf of 20 atomic% or less, there is a clear effect in improving the high magnetic field characteristics. If the content exceeds 20 atomic%, the superconductivity is deteriorated, and intermediate annealing is required for wire processing, which is not preferable. When a superconducting wire is put into practical use, it must be used in combination with a Cu matrix in order to maintain superconductivity stably even when there is a sudden magnetic field fluctuation. Therefore, after the composite of the core material and the sheath material according to the present invention is inserted into the Cu matrix, processing and heat treatment are performed, and the composite material is put to practical use.
[0033]
【Example】
Hereinafter, preferred embodiments of the present invention will be described.
[Example 1]
As Example 1, various wire rods were produced by a JR method using an Nb sheet or an improved JR method (MJR method) using an Nb mesh sheet. The manufacturing method will be described with reference to FIGS.
(Preparation of sample)
When the amount of Ta is 40 atom% or more, Ta-Sn is powdered, and the powder core method is applied to wire. In the present invention, it has been found that an Sn—Ta sheet having workability can be produced when the Ta amount is 30 atomic% or less. Therefore, the powders of Ta and Sn are mixed so that the Ta / Sn ratio becomes 3/7, 1/3, and then 1 × 10 ^-5 It was melted at 800 ° C. for 10 hours in a Torr vacuum. Further, 5% by mass of Cu was added to 3/7, 1/3 mixed powder, and the same treatment was performed.
[0034]
Thereafter, press working and flat roll rolling were carried out to form a sheet 2 having a thickness of 200 μm. As shown in FIG. 1, the Sn-Ta sheet 2 and the Nb sheet 3 having a thickness of 240 μm were superposed and wound around the Nb core material 4 to obtain a Sn-Ta / Nb wound body 5 (step S1). The Sn-Ta / Nb wound body 5 was inserted into an Nb-4 atom% Ta tube 6 having an outer diameter / inner diameter of 10/7 mmφ and incorporated (step S2).
[0035]
The composites 5 and 6 were formed into long articles having a circular or rectangular cross section by groove roll processing or flat roll processing (step S3). Further, this was finally processed into a round wire having a diameter of 1.35 to 1.90 mmφ by drawing (step S4).
[0036]
In addition, an Nb mesh sheet having a thickness of 340 μm was used in place of the Nb sheet 3, and an MJR method wire was separately produced by the same operation.
[0037]
The prepared sample is 1 × 10 ^-5 Heat treatment was performed at 775 ° C. to 925 ° C. × 80 hours in a vacuum of Torr to produce a superconducting wire. Critical temperature T of the last produced wire _c And the critical current I in a high magnetic field _c Was measured.
[0038]
(Evaluation)
In the present invention, a Sn-Ta sheet with excellent processability, in which Ta particles are uniformly distributed in Sn, could be produced.
[0039]
It has been found that when groove rolling is performed on the JR normal wire at first, a square residue remains in the internal structure, but a good structure can be obtained. In the case of the MJR method wire, it was found that a multi-core wire can be easily manufactured by using an Nb mesh sheet.
[0040]
Table 1 shows the conventional powder core method, the JR method of the present invention, the JR method (with Cu added), and the MJR method, respectively (Nb, Ta). ₃ Critical temperature T of Sn wire _c (K) shows the measurement results. In Table 1, On indicates the temperature at the start point of the superconducting transition, Off indicates the temperature at the end point of the superconducting transition, and Mid indicates the temperature at the midpoint of the superconducting transition. As is clear from Table 1, almost the same critical temperature T _c It turned out to show.
[0041]
FIG. 2 shows the magnetic field strength (T) on the horizontal axis and the critical current I on the left vertical axis. _c (A), the right vertical axis shows the critical current density J in a wire having a diameter of 1.35 mm. _c (A / cm ² FIG. 4 is a characteristic diagram showing the results of examining the superconducting characteristics in a high magnetic field of each sample manufactured by varying the composition, wire diameter, and heat treatment temperature by the JR method. In FIG. 2, a characteristic line A is a result of heat-treating a sample having a composition of Ta / Sn = 3/7 and a wire diameter of 1.35 mmφ at 900 ° C. for 80 hours, and a characteristic line B is Ta / Sn = 3/7. As a result of heat treatment of a sample having a composition and a wire diameter of 1.35 mmφ under a condition of 925 ° C. × 80 hours, a characteristic line C is a sample of Ta / Sn = 3/7 having a wire diameter of 1.90 mmφ and a temperature of 900 ° C. × 80 hours. As a result of heat treatment under the conditions, a characteristic line D shows a result of heat treatment of a sample having a Ta / Sn = 1/3 composition and a wire diameter of 1.90 mmφ at 900 ° C. for 80 hours. In the figures, data with an arrow above the plot symbol indicate data with a result higher than that value.
[0042]
As shown by the characteristic line A, when a sample having a wire diameter of 1.35 mmφ was subjected to an intermediate heat treatment at 900 ° C. for 80 hours, a sample having a diameter of 1.2 × 10 was obtained at 4.2 K and 23 Tesla. ⁴ A / cm ² Promising critical current density J _c was gotten. By the way, when a superconducting wire is put to practical use, 1.0 × 10 ⁴ A / cm ² J above _c Is required.
[0043]
A comparison between a wire having a heat treatment temperature of 900 ° C. (characteristic line A) and a wire having a heat treatment temperature of 925 ° C. (characteristic line B) shows that J is lower at 925 ° C. below 23 Tesla. _c Becomes (Nb, Ta) due to the high heat treatment temperature. ₃ This is probably because the Sn crystal grains became coarse and the pinning point of the magnetic flux decreased.
[0044]
Furthermore, when the characteristics of the wire (another sample different from the samples of the characteristic lines A to D produced by the method of the present invention) heat-treated at 900 ° C. were evaluated at 2.1 K in liquid helium under reduced pressure, 25 tesla was obtained. 1.0 × 10 at ultra high magnetic field ⁴ A / cm ² J _c showed that.
[0045]
Further, as shown in characteristic lines C and D, the critical current I of 200 A or more at 4.2 K and 23 Tesla is used. _c Was confirmed.
[0046]
FIG. 3 shows the magnetic field strength (T) on the horizontal axis and the critical current I on the left vertical axis. _c (A), the right vertical axis shows the critical current density J in a wire having a diameter of 1.35 mm. _c (A / cm ² FIG. 7 is a characteristic diagram showing the results of examining the superconducting characteristics of various Cu-added JR wire samples in a high magnetic field, respectively. In FIG. 3, a characteristic line E is a result obtained by heat-treating a 5% by mass Cu-added sample having a composition of Ta / Sn = 1/3 and having a wire diameter of 1.35 mmφ at 800 ° C. for 80 hours. As a result of heat treatment of a 5% by mass Cu-added sample having a Sn = 3/7 composition and a wire diameter of 1.35 mmφ under the condition of 800 ° C. × 80 hours, the characteristic line G is Ta / Sn = 1/3 composition and a wire diameter of 1. As a result of heat-treating a 35 mmφ 5 mass% Cu-added sample under the condition of 775 ° C. × 80 hours, the characteristic line H is a Ta / Sn = 1/3 composition and a 1.90 mm φ 5 mass% Cu-added sample at 800 ° C. The results of heat treatment under the conditions of × 80 hours are shown. In the figure, the plot symbols enclosed in parentheses indicate inaccurate data due to flux jumps (uncertain data), and those with an arrow above the plot symbols indicate results exceeding the values. Data shown.
[0047]
In FIG. 3, as shown by the characteristic line G, at 4.2 K and 22 Tesla, 1.3 × 10 ⁴ A / cm ² Of Jc was obtained. As shown by the characteristic line H, the critical current I of 200 A at 4.2 K and 22 Tesla was obtained. _c Was confirmed.
[0048]
By adding such a small amount of Cu, the heat treatment temperature can be lowered from 900 ° C. to 775 ° C., which proves to be advantageous for practical use. This is considered to be due to the fact that the melting point decreases due to the Nb-Sn-Cu ternary system, and diffusion proceeds rapidly even at a low temperature.
[0049]
Figure 4 shows the critical current density J _c -The magnetic field characteristic shows the result of comparing the example wire (not including Cu) and the comparative example wire. In the figure, the characteristic line M is (Nb, Ta) of the embodiment representative of the present invention. ₃ The result of the Sn wire (curve A in FIG. 2) is shown by the characteristic line N, which is a conventional bronze method (Nb, Ti) used in a 920 MHz class NMR analyzer. ₃ The results of the Sn wire (Comparative Example) are shown.
[0050]
As is clear from FIGS. 2 and 3, the wire manufactured according to the present invention has a sufficient performance of 20 Tesla or more at 4.2K, an NMR analyzer required for structural analysis of proteins, a clean energy source, and the like. It is expected to be applied in a wide range of fields such as nuclear fusion and refrigerator direct cooling type superconducting magnets.
[0051]
[Example 2]
As Example 2, various wires were produced using hydrides. The manufacturing method will be described with reference to FIGS.
[0052]
When Ta-Sn powder is used for the core and reacted with the Nb sheath, it is thick (Nb, Ta) ₃ An Sn layer was formed, and thus produced (Nb, Ta) ₃ Sn superconducting wire exhibits excellent high magnetic field characteristics. It is considered that if the Ta particles can be made fine and uniform in this production method, a practical ultrafine multifilamentary wire can be easily obtained. Therefore, in this example, a wire rod was prepared using a hydride Ta-H, which is easy to pulverize, as a starting material, and the structure and superconductivity were compared and studied.
[0053]
(Preparation of sample)
Next, a method for manufacturing a sample will be described with reference to FIGS.
First, a commercially available flake Ta-H is ground in a mortar for about 30 minutes (Step S21), and then ground in an Ar atmosphere using a planetary ball mill (hereinafter abbreviated as BM) for 30 minutes (Step S22). ) And Ta-H powder were produced. To this, Sn powder was prepared so that the Ta / Sn atomic ratio became 3/7 or 4/6, respectively.
[0054]
Next, melt-diffusion was performed at 925 ° C. for about 10 hours (step S23) to produce a Ta—Sn powder. It is considered that dehydrogenation was performed in the process of step S23. Further, a powder obtained by mixing 5 mass% of Cu powder with this Ta-H / Sn mixed powder, a powder obtained by mixing 7.5 mass% of Cu powder with the mixed powder, and a commercially available Ta powder instead of Ta-H are used. The powders used were similarly prepared (step S24).
[0055]
The particle size of each of the produced powders was measured by a particle size distribution analyzer. Thereafter, an Nb-4 at% Ta sheath (outside diameter 8.0 mm, inside diameter 5.0 mm) is filled with Ta-Sn powder to prepare a composite (step S25), and groove and flat rolls are processed (step S26). ), A tape having a thickness of 0.6 mm and a width of 4 mm was produced. 1 × 10 ^-5 Heat treatment was performed for 80 hours at each concentration in a Torr vacuum (Step S27) to obtain a superconducting tape sample. Observation of microstructure and critical temperature T _c Critical current I in a high magnetic field _c A measurement was made. Hereinafter, a sample prepared using Ta-H as a starting material is referred to as “TH”.
[0056]
(Evaluation)
Commercially available Ta powder (325 mesh or less) is coarse and varies in size, but powder produced by BM pulverization of Ta-H has a remarkably fine particle size and is confirmed by optical microscope observation to be uniform. Was done.
[0057]
FIG. 6 is a bar graph showing the particle size distribution of each powder raw material. In commercially available Ta powder, peaks of the particle size distribution are present at 2 to 3 μmφ and 20 to 30 μmφ, but in the case of BM-pulverized Ta-H powder, particles of 3 μmφ or more are not observed, and the particle size is reduced, and the distribution range is narrowed. found.
[0058]
The cross section of the sample of the superconducting tape using the commercially available Ta powder after the heat treatment at 900 ° C. × 80 hours and the cross section of the TH sample manufactured by using the method of the present invention were respectively observed with an optical microscope. As a result, it was confirmed that the structure of the sample using the commercially available Ta powder after the heat treatment had some coarse Ta particles remaining in the core, but the TH sample had a fine and uniform structure. This is presumed to be due to the use of Ta-H to finely powder the Ta powder. Also, after heat treatment, the TH sample is thick (Nb, Ta) as before. ₃ A Sn layer was created.
[0059]
Table 2 shows the critical temperature T of the BM sample with TH3 / 7, the sample without BM, and the sample with Cu added. _c (K) is shown. When the sample subjected to BM and the sample not subjected to BM were compared, the value almost did not change in the On / Off state. The sample to which Cu was added had a high critical temperature even when the heat treatment temperature was lowered.
[0060]
7 and 8 show the results of examining the characteristics of the critical current Ic (left vertical axis) -critical current density Jc (right vertical axis) -magnetic field (horizontal axis) of various samples under a temperature condition of 4.2K, respectively. . The characteristic line P in FIG. 7 shows the result of heat treatment of the Cu-free sample (TH3 / 7) having the composition of Ta-H / Sn = 3/7 under the condition of 880 ° C. × 80 hours, and the characteristic line Q shows the result of Ta-H / The characteristic line R shows the result of heat treatment of the Cu-free sample (TH3 / 7) having a composition of Sn = 3/7 under the condition of 900 ° C. × 80 hours (Cu-free sample having a composition of Ta-H / Sn = 3/7). TH3 / 7) was subjected to heat treatment at 925 ° C. for 80 hours. A characteristic line U in FIG. 8 shows a result of heat treatment of a 5% by mass Cu-added sample (TH3 / 7 + 5Cu) having a composition of Ta-H / Sn = 3/7 under the condition of 800 ° C. × 80 hours, and a characteristic line V shows Ta−H / Sn. The result of heat-treating a 7.5% by mass Cu-added sample (TH4 / 6 + 7.5Cu) having a composition of H / Sn = 4/6 under the condition of 775 ° C. × 80 hours, the characteristic line W is Ta−H / Sn = 4 / The results obtained by heat-treating a sample (TH4 / 6 + 7.5Cu (BM)) with 7.5% by mass of ball-milled 7.5 mass% Cu at 800 ° C. for 80 hours are shown.
[0061]
As shown in FIG. 8, in the sample (characteristic lines U, V, W) in which Cu was added to the core by several mass%, the critical current I was maintained even at the heat treatment of 775 ° C. to 800 ° C. _c , And it was confirmed that good characteristics were obtained.
[0062]
In the present embodiment, the T _c The value is the same as that of the sample using pure Ta of minus 325 mesh, and 1 × 10 at 4.2K and 22T. ⁴ / Cm ² J _c was gotten.
[0063]
As described above, in this embodiment, when a small amount of Cu is added to the Ta—Sn core, the heat treatment temperature decreases from 900 ° C. to 775 ° C. to 800 ° C., and becomes 1.5 × 10 at 4.2K and 21T. ⁴ A / cm ² Of Jc was obtained.
[0064]
Further, in this embodiment, fine Ta powder was successfully obtained by using Ta-H, and the thickness was as thick as the conventional one (Nb, Ta). ₃ It was found that an Sn layer was obtained.
[0065]
Furthermore, when an Sn-M alloy is produced using fine powder obtained by pulverizing a hydride of M metal, M is finely dispersed in Sn, so that there is a great merit in producing a practical wire rod.
[0066]
[Example 3]
As Example 3, a multi-core wire was manufactured by a method of winding a SnTaCu sheet around a plurality of Nb core materials. The manufacturing method is described below.
(Preparation of wire rod)
A Sn powder and a Ta powder are blended so that the Sn / Ta atomic ratio becomes 7/3, a 5 mass% Cu powder is added thereto, and heating is performed at 800 ° C. × 10 hours in a vacuum atmosphere using a quartz crucible. Was performed to melt the SnTaCu alloy. The particle sizes of the used Sn powder, Ta powder and Cu powder were all minus 325 mesh.
[0067]
The smelted SnTaCu alloy was formed into a plate by press working, and then processed into a sheet having a thickness of 100 μm by a flat roll. This sheet was wound six times around an Nb core material having a diameter of 1.2 mm to make seven, and these seven wound bodies were placed in an Nb-4 atom% Ta sheath tube having an outer diameter of 10 mm and an inner diameter of 7.3 mm. The complex was inserted and incorporated.
[0068]
This composite was formed into a long product having a predetermined length by groove roll processing, and finally a wire having a diameter of 1.4 mm was formed by wire drawing (drawing). In this example, the intermediate annealing was not performed during the groove roll and the wire drawing of the wire. The wire thus obtained was heat-treated at 800 ° C. for 80 hours.
[0069]
(Evaluation)
FIG. 9 is an enlarged micrograph showing a cross section of the multifilamentary wire of the present example. As a result of observing the cross section of the heat-treated wire by an optical microscope, it was found that thick Nb was formed around the seven Nb cores and inside the Nb-4 atom% Ta sheath tube. ₃ It was confirmed that the Sn layer was generated. When measured in the microscope field of view, the generated Nb ₃ The thickness of the Sn layer was about 30 to 50 μm.
[0070]
This wire is subjected to a critical current I in a vertical magnetic field of 4.2 K and 20 Tesla. _c Is 250 A when the critical current density J per unit cross-sectional area of the wire is measured. _c Is about 1.6 × 10 ⁴ A / cm ² Met.
[0071]
[Example 4]
As Example 4, a wire rod in which the first base material was an SnTiCu alloy was manufactured using the same sheet JR method as in Example 1. The manufacturing method is described below.
(Preparation of wire rod)
A Cu—Ti master alloy containing 25 atomic% of Ti was pulverized and mixed with a minus 325 mesh Sn powder to prepare a mixed powder having a composition of 90% by mass of Sn, 2% by mass of Ti, and 8% by mass of Cu.
[0072]
This mixed powder was placed in a quartz crucible and heated at 800 ° C. for 10 hours in a vacuum atmosphere to melt the SnTiCu alloy. This alloy was formed into a plate by pressing, and then processed into a sheet having a thickness of 100 μm by a flat roll. This SnTiCu alloy sheet was superimposed on a 100 μm thick Nb sheet, and wound 10 times around a 1.2 mm diameter Nb core material to form a roll. The wound body was inserted into an Nb-1.1 atom% Ti sheath tube having an outer diameter of 8 mm and an inner diameter of 5.5 mm to assemble into a composite.
[0073]
This composite was processed into a 1.5 × 1.5 mm square by a groove roll, and then rolled into a flat rectangular wire having a thickness of 0.8 mm and a width of 2.5 mm by flat roll processing. In this example, the intermediate annealing was not performed during the groove roll and the wire drawing of the wire. The wire thus obtained was heat-treated at 800 ° C. for 80 hours.
[0074]
(Evaluation)
This wire is subjected to a critical current I in a vertical magnetic field of 4.2 K and 20 Tesla. _c Is 345 A, and the critical current density J per unit sectional area of the wire is measured. _c Is about 1.7 × 10 ⁴ A / cm ² Met.
[0075]
[Table 1]

[0076]
[Table 2]

[0077]
【The invention's effect】
As described above, since the wire manufactured by the method of the present invention has a possibility of generating a magnetic field of 23.5 Tesla required for a 1 GHz NMR analyzer, the wire manufactured by the conventional method is different from the wire manufactured by the conventional method. Higher Jc magnetic field characteristics are obtained by comparison, and applied to a wide range of fields such as NMR analyzers required for protein structure analysis, nuclear fusion expected as a clean energy source, and refrigerator-cooled direct-cooled superconducting magnets can do.
[0078]
Further, according to the present invention, it is possible to omit the step of preparing an alloy or intermetallic compound of Ta and Sn and further pulverizing the alloy into a powder for filling the sheath material. At the same time, a core material having a desired composition can be easily produced. As a result, a high impact superconducting wire capable of generating a magnetic field of 23 Tesla at 4.2K and 25 Tesla at 2.1K can be easily provided. When a superconducting wire is used for generating a magnetic field, _c The critical current density J divided by the total cross-sectional area of the wire _c Is 1 × 10 ⁴ A / cm ² It is desirable that there be.
[0079]
Further, according to the present invention, a reaction heat treatment is performed after processing a composite of an Sn-M alloy having excellent plasticity in which M is dispersed in Sn and Nb or an Nb alloy into a wire rod, and thus, compared with the conventional powder core method. A wire rod that is easy to process and has excellent uniformity can be provided. Since the wire produced by the method of the present invention is rich in plasticity, it is possible to produce an ultrafine multifilamentary wire and the like, which has a very high industrial value and is practical.
[0080]
Further, the method of the present invention can omit many intermediate annealings required in the conventional bronze method, so that the manufacturing cost can be significantly reduced.
[0081]
Further, according to the present invention, Nb is added by adding a small amount of Cu. ₃ Since the reaction for forming the Sn layer is promoted, the final heat treatment temperature can be lowered, and the manufacturing cost can be kept low.
[0082]
Further, according to the present invention, fine M particles can be uniformly dispersed in Sn using a hydride as a starting material, so that a wire rod having more excellent superconductivity than before can be provided, and practically, A preferred ultrafine multifilamentary wire can be provided.
[Brief description of the drawings]
FIG. 1 is a block process diagram showing an outline of a method for manufacturing a superconducting wire (a jelly roll method) according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing superconductivity characteristics {critical current Ic (left vertical axis), wire diameter 1.35 mm critical current density Jc (right vertical axis) -magnetic field (horizontal axis) characteristics}.
FIG. 3 is a characteristic diagram showing superconducting characteristics {critical current Ic (left vertical axis), wire diameter of 1.35 mm critical current density Jc (right vertical axis) -magnetic field (horizontal axis) characteristics}.
FIG. 4 is a characteristic diagram showing a comparison between a sample of an example manufactured by the method of the present invention and a sample of a comparative example manufactured by a conventional method with respect to superconducting characteristics (critical current density Jc-magnetic field characteristics).
FIG. 5 is a process chart showing an outline of a method for manufacturing a superconducting wire according to another embodiment of the present invention.
FIG. 6 is a bar graph showing the particle size distribution of a powder raw material.
FIG. 7 is a characteristic diagram showing superconducting characteristics {critical current Ic (left vertical axis), critical current density Jc (right vertical axis) -magnetic field (horizontal axis) characteristics}.
FIG. 8 is a characteristic diagram showing superconducting characteristics {critical current Ic (left vertical axis), critical current density Jc (right vertical axis) -magnetic field (horizontal axis) characteristics}.
FIG. 9 is a micrograph showing a cross section of an ultrafine multifilamentary wire manufactured using the method of the present invention.
[Explanation of symbols]
2. 1st base material (Sn-M sheet)
3. Second substrate (Nb sheet)
4: Core material (Nb rod)
5. Composite (Sn-M / Nb wound body)
6. Outer cylinder (Nb-Ta tube)

Claims (14)

Producing a composite by alternately laminating a first substrate composed of a mixture of Sn and M and a second substrate composed of Nb or an Nb-based alloy;
Processing the composite into a wire;
Heat treating the wire,
A method for producing an Nb ₃ Sn superconducting wire, comprising: The method according to claim 1, wherein the M is one or more metals selected from the group consisting of Ta, Ti, and Hf. The method according to claim 1, wherein the M is a metal hydride obtained by hydrogenating one or more metals selected from the group consisting of Ta, Ti, and Hf. The method according to any one of claims 1 to 3, wherein the first substrate contains 0.5 to 50 atomic% of the M. The method according to any one of claims 1 to 4, wherein the first base material is melted in a temperature range from the melting point of Sn to 1200 ° C before the composite manufacturing step. The method according to claim 1, wherein the first substrate is made of a plastic alloy. 7. The first substrate according to claim 1, wherein a third element is further added to the first substrate to improve composite workability with the second substrate. The method of claim 1. 8. The method according to claim 7, wherein the third element is one or more elements selected from the group consisting of Bi, In, Sb, Mg, Ag, Zn, Al, Ge, Si, and Pb. The described method. 9. The method according to claim 1, wherein the first base material contains 0.5 to 30 atomic% of Cu. 10. The method according to claim 1, wherein the second substrate is an Nb alloy containing one or more metals selected from the group consisting of Ta, Ti, and Hf. The described method. In the composite manufacturing step, the first base material and the second base material are formed using a core material having substantially the same composition as one of the first base material and the second base material. The method according to any one of claims 1 to 10, wherein substrates are alternately overlapped and wound around the core material. The method according to claim 1, wherein the first substrate has a Sn content in a range of 20 to 80 atomic%. 13. The method according to claim 1, wherein the second base is made of an Nb alloy containing one or two elements selected from the group consisting of Ta, Ti, and Hf in an amount of 20 atomic% or less. Or the method of claim 1. 14. A method characterized by filling a composite obtained by the method according to any one of claims 1 to 13 into a Cu matrix, processing the composite into a wire, and then performing a heat treatment.

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