JP2004111237A - MgB2 SUPERCONDUCTIVE WIRE ROD AND ITS MANUFACTURING METHOD - Google Patents
MgB2 SUPERCONDUCTIVE WIRE ROD AND ITS MANUFACTURING METHOD Download PDFInfo
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Abstract
Description
【０００１】
【発明の属する技術分野】
この出願の発明は、ＭｇＢ２超伝導線材とその製造方法に関するものである。さらに詳しくは、この出願の発明は、臨界電流密度（Ｊｃ）の高いＭｇＢ２超伝導線材とその製造方法に関するものである。
【０００２】
【従来の技術とその課題】
従来、ＭｇＢ２超伝導線材は、シース材である金属管内にＭｇＢ２超伝導粉末を充填し、圧延加工することにより得られている。このＭｇＢ２超伝導線材の臨界電流密度（Ｊｃ）は４．２Ｋ、１０Ｔの磁場中で高々１００Ａ／ｃｍ２程度に過ぎない（たとえば、非特許文献１参照）。
【０００３】
この出願の発明は、臨界電流密度（Ｊｃ）の高いＭｇＢ２超伝導線材とこれを製造可能とする製造方法を提供することを解決すべき課題としている。
【０００４】
【非特許文献１】
熊倉、他３名（ＫＵＭＡＫＵＲＡ Ｈ．， ＭＡＴＳＵＭＯＴＯ Ａ．， ＦＵＪＩＩ Ｈ．， ＴＯＧＡＮＯ Ｋ．），「ステンレス鋼管と銅−ニッケル管を用いたパウダー・イン・プロセスによるＭｇＢ２テープ及び線材の高臨界電流密度（Ｈｉｇｈ ｔｒａｎｓｐｏｒｔ ｃｒｉｔｉｃａｌ ｃｕｒｒｅｎｔ ｄｅｎｓｉｔｙ ｏｂｔａｉｎｅｄ ｆｏｒ ｐｏｗｄｅｒ−ｉｎ−ｔｕｂｅ−ｐｒｏｃｅｓｓｅｄ ＭｇＢ２ ｔａｐｅｓ ａｎｄ ｗｉｒｅｓ ｕｓｉｎｇ ｓｔａｉｎｌｅｓｓ ｓｔｅｅｌ ａｎｄ Ｃｕ−Ｎｉ ｔｕｂｅｓ）」，アプライド・フィジックス・レターズ（Ａｐｐｌｉｅｄ Ｐｈｙｓｉｃｓ Ｌｅｔｔｅｒｓ），（米国），第７９巻，第１５号，２００１年１０月８日，ｐ．２４３５−２４３７
【０００５】
【課題を解決するための手段】
前述のＭｇＢ２超伝導線材の臨界電流密度（Ｊｃ）の原因を検討したところ、圧延加工時にＭｇＢ２超伝導粉末が硬化し、金属管との界面が凹凸となり、平滑性が失われているのがその原因ではないかと考えられた。
【０００６】
そこでこの出願の発明の発明者らは、圧延加工時にシース材である金属管からＭｇＢ２超伝導粉末に加わる圧縮力を緩和させ、ＭｇＢ２超伝導粉末が硬化するのを抑制し、金属管とＭｇＢ２超伝導粉末との界面を平滑に保つための方策を鋭意検討した。その結果、金属管にＭｇＢ２超伝導粉末だけでなく、金属粉末を添加、混合して充填することにより、添加金属が、圧延加工時の金属管からＭｇＢ２超伝導粉末に加わる圧縮力を吸収し、金属管とＭｇＢ２超伝導粉末との界面が平滑となり、Ｊｃが上昇することを見出し、この出願の発明を完成した。
【０００７】
すなわち、この出願の発明は、ＭｇＢ２超伝導粉末が金属管内に充填され、圧延加工されて作製されたＭｇＢ２超伝導線材において、ＭｇＢ２超伝導粉末とともに金属粉末が添加、混合され、圧延加工後の金属管とＭｇＢ２との界面が平滑であることを特徴とするＭｇＢ２超伝導線材（請求項１）を提供する。
【０００８】
またこの出願の発明は、請求項１に係る発明に関し、金属粉末は、ブリネル硬さが１５以上９０以下の金属の粉末であること（請求項２）、金属粉末は、銅、アルミニウム、インジウム又はこれらの混合物の粉末であること（請求項３）を一態様として提供する。
【０００９】
さらにこの出願の発明は、ＭｇＢ２超伝導粉末と金属粉末とを混合し、その混合粉末を金属管内に充填し、圧延加工してＭｇＢ２超伝導線材を作製することを特徴とするＭｇＢ２超伝導線材の製造方法（請求項４）を提供する。
【００１０】
そしてこの出願の発明は、請求項４に係る発明に関し、金属粉末は、ブリネル硬さが１５以上９０以下の金属の粉末であること（請求項５）、金属粉末は、銅、アルミニウム、インジウム又はこれらの混合物の粉末であること（請求項６）、圧延加工後、熱処理を行うこと（請求項７）をそれぞれ一態様として提供する。
【００１１】
以下、実施例を示しつつ、この出願の発明のＭｇＢ２超伝導線材とその製造方法についてさらに詳しく説明する。
【００１２】
【発明の実施の形態】
この出願の発明のＭｇＢ２超伝導線材は、前記のとおり、金属管内に充填するＭｇＢ２超伝導粉末に金属粉末が添加、混合され、圧延加工されて作製された線材であり、この線材において金属管とＭｇＢ２との界面は平滑となっている。このようなＭｇＢ２超伝導線材を製造する際には、ＭｇＢ２超伝導粉末と金属粉末とを混合し、その混合粉末を金属管内に充填し、圧延加工する。前述のとおり、金属粉末を添加、混合せず、ＭｇＢ２超伝導粉末のみを金属管に充填して圧延加工を行うと、ＭｇＢ２超伝導粉末は硬化して金属管とＭｇＢ２超伝導粉末との界面は凹凸になり、１００Ａ／ｃｍ２程度のＪｃしか得られない。しかしながら、この出願の発明のＭｇＢ２超伝導線材では、金属管とＭｇＢ２超伝導粉末との界面は平滑であり、Ｊｃは高まる。
【００１３】
ＭｇＢ２超伝導粉末に添加、混合する金属粉末は、ブリネル硬さが１５以上９０以下の金属の粉末であることが好ましい。ブリネル硬さが１５未満の軟らかい金属の粉末ではＭｇＢ２超伝導粉末の滑り加工に対する効果が得られない。ＭｇＢ２超伝導粉末は、金属管に充填後の加工により充填密度が上がり、大きな塊へと凝集しやすい。一旦固まった塊は加工時に塊として動くことになるため、ひび割れ、金属管との界面の破損などが生じる。金属粉末は、このようなＭｇＢ２超伝導粉末の大きな塊への凝集を防ぐとともに、万一塊が生じた場合、その塊を滑らせる（加工滑り）のための潤滑剤的な役割を果たすものと考えられる。したがって、ブリネル硬さが１５未満の軟らかい金属粉末では、粒界などに分散し、加工時のエネルギーを吸収することができないため、加工滑りに寄与することができない。ブリネル硬さが９０を超える硬すぎる金属の粉末は、展伸されにくいため、金属管とＭｇＢ２超伝導粉末との界面は平滑とならない。その結果、高いＪｃは得にくくなる。このような金属粉末としては、銅、アルミニウム、インジウム又はこれらの混合物の粉末が好ましく例示される。より高いＪｃを得るためには、後述する実施例に示すように、銅、アルミニウム又はこれらの混合物が金属粉末として好ましい。
【００１４】
以上のＭｇＢ２超伝導粉末に添加、混合する金属粉末の添加量は５−３０ｖｏｌ％が好ましく例示される。これは、界面の平滑性を得るために前述の加工滑りを起こさせることに基づく。５ｖｏｌ％未満では界面の平滑性は次第に得にくくなる。一方、３０ｖｏｌ％を超えると、ＭｇＢ２超伝導粉末に対する比率が多くなりすぎ、その結果、たとえ界面の平滑性は得られたとしても超伝導電流が流れにくくなり、その結果、臨界電流密度（Ｊｃ） が低下するおそれがある。
【００１５】
この出願の発明のＭｇＢ２超伝導線材の製造方法では、圧延加工後、熱処理を行うことができる。この圧延加工後の熱処理によりＪｃはより一層高くなる。熱処理条件はＭｇＢ２超伝導線材の超伝導特性を劣化させない限りにおいて特に制限はなく、たとえば３００℃で１時間を例示することができる。
【００１６】
【実施例】
ＭｇＢ２超伝導粉末は市販のものを使用した。このＭｇＢ２超伝導粉末にアルミニウム（Ａｌ）、銅（Ｃｕ）、インジウム（Ｉｎ）の粉末をそれぞれ１０ｖｏｌ％添加し、混合粉末を作製した。各混合粉末をステンレス（ＳＵＳ３１６）製で内径４ｍｍφ、外径８ｍｍφの金属管の内部に充填し、金属管の両端を混合粉末が出ないように圧着した。この混合粉末を充填した金属管を溝ロール圧延機により２ｍｍ×２ｍｍ角の角材に加工した。さらに、この角材を平ロール圧延機により厚さ０．５ｍｍのテープ状の線材にまで加工した。この線材を適当な長さに切断し、アルゴンガスを流通させた管状型の電気炉内で熱処理した。この熱処理は、試料の隣に熱電対を設置し、温度を計測しながら行い、３００℃で１時間とした。
【００１７】
以上のようにした作製した線材、非熱処理のもの、熱処理済みのものそれぞれを四端子抵抗法により４．２Ｋ、８Ｔの磁界下で臨界電流密度（Ｊｃ）を測定した。
【００１８】
図１は、それら線材のＪｃを添加、混合した金属種との関係でプロットした相関図である。この相関図には従来のＭｇＢ２超伝導線材のＪｃも合わせて示している。
【００１９】
非熱処理の線材では、Ａｌを添加、混合したＭｇＢ２超伝導線材が最大のＪｃを示し、４００Ａ／ｃｍ２となった。従来のＭｇＢ２超伝導線材のＪｃは２００Ａ／ｃｍ２程度であった。
【００２０】
また、従来のＭｇＢ２超伝導線材以外は、熱処理によりＪｃが大幅に上昇した。特に熱処理後のＣｕ添加線材では、無添加線材に比べ３倍程度も高いＪｃとなった。
【００２１】
Ｃｕ添加線材の熱処理前後のものと従来のＭｇＢ２超伝導線材（同じく熱処理前後のもの）についてその断面を光学顕微鏡により観察した。その断面像を示したのが図２である。
【００２２】
図２に確認されるように、従来のＭｇＢ２超伝導線材では、金属管とＭｇＢ２超伝導粉末との界面に大きな凹凸が発生していた。Ｃｕ添加線材の熱処理前後のものでは界面は平滑であった。従来のＭｇＢ２超伝導線材では、圧延加工時に加わる圧縮力によりＭｇＢ２超伝導粉末が硬化し、硬化したＭｇＢ２超伝導粉末が塊となり、圧延加工により金属管の内面を傷つけ、凹凸のある界面になったと考えられる。一方、Ｃｕ添加線材は、圧延加工時に加わる圧縮力を軟らかいＣｕ粉末が吸収し、ＭｇＢ２超伝導粉末の硬化を抑え、また、硬化してもＭｇＢ２超伝導粉末を滑りやすくして強加工によっても金属管の内面が傷つけられず、界面は平滑性を保ったと考えられる。
【００２３】
もちろん、この出願の発明は、以上の実施形態及び実施例によって限定されるものではない。ＭｇＢ２超伝導粉末に添加、混合する金属粉末の種類、添加量、さらに圧延加工後の熱処理条件などの細部については様々な態様が可能であることはいうまでもない。
【００２４】
【発明の効果】
以上詳しく説明した通り、この出願の発明によって、臨界電流密度（Ｊｃ）の高いＭｇＢ２超伝導線材が得られる。
【図面の簡単な説明】
【図１】実施例で作製した線材及び従来のＭｇＢ２超伝導線材のＪｃを添加、混合した金属種との関係でプロットした相関図である。
【図２】実施例で作製したＣｕ添加線材の熱処理前後のものと従来のＭｇＢ２超伝導線材（同じく熱処理前後のもの）についてその断面を光学顕微鏡により観察した断面像である。[0001]
TECHNICAL FIELD OF THE INVENTION
The invention of this application relates to a MgB 2 superconducting wire and a method for manufacturing the same. More specifically, the invention of this application relates to a MgB 2 superconducting wire having a high critical current density (Jc) and a method for producing the same.
[0002]
[Prior art and its problems]
Conventionally, a MgB 2 superconducting wire has been obtained by filling a MgB 2 superconducting powder in a metal tube serving as a sheath material and rolling it. The critical current density (Jc) of this MgB 2 superconducting wire is at most only about 100 A / cm 2 in a magnetic field of 4.2 K and 10 T (for example, see Non-Patent Document 1).
[0003]
An object of the invention of this application is to provide an MgB 2 superconducting wire having a high critical current density (Jc) and a manufacturing method capable of manufacturing the same.
[0004]
[Non-patent document 1]
Kumakura, three others (KUMAKURA H., MATSUMOTO A., FUJII H., TOGANO K.), "stainless steel and copper - high critical current density of the MgB 2 tapes and wires by a powder-in-process using a nickel tube (High transport critical current density obtained for powder-in-tube-processed MgB 2 tapes and wi res s ing s ti s p s s s s s s s s s s s s s s s s s s s s s s s s s s s s s. No. 15, October 8, 2001, p. 2435-2437
[0005]
[Means for Solving the Problems]
When the cause of the critical current density (Jc) of the MgB 2 superconducting wire was examined, the MgB 2 superconducting powder hardened during rolling, the interface with the metal tube became uneven, and the smoothness was lost. Was thought to be the cause.
[0006]
Therefore, the inventors of the invention of the present application relaxed the compressive force applied to the MgB 2 superconducting powder from the metal tube serving as the sheath material during rolling, suppressed the hardening of the MgB 2 superconducting powder, and We have studied diligently to keep the interface with the MgB 2 superconducting powder smooth. As a result, by adding, mixing and filling not only the MgB 2 superconducting powder but also the metal powder into the metal tube, the added metal absorbs the compressive force applied to the MgB 2 superconducting powder from the metal tube during rolling. Then, they found that the interface between the metal tube and the MgB 2 superconducting powder became smooth and Jc increased, and completed the invention of this application.
[0007]
That is, the invention of this application, MgB 2 superconducting powder filled in the metal tube, in MgB 2 superconducting wire produced is rolled, metal powders with MgB 2 superconducting powder is added, mixed, rolled An MgB 2 superconducting wire (claim 1), characterized in that the interface between the subsequent metal tube and MgB 2 is smooth.
[0008]
The invention of this application relates to the invention according to claim 1, wherein the metal powder is a metal powder having a Brinell hardness of 15 or more and 90 or less (claim 2), and the metal powder is copper, aluminum, indium or It is provided as an aspect that the powder is a mixture of these (claim 3).
[0009]
Furthermore the invention of this application, by mixing the MgB 2 superconductor powder and a metal powder, filling the mixed powder into a metal tube, MgB 2 than, characterized in that to produce the MgB 2 superconducting wire by rolling A method for manufacturing a conductive wire (claim 4) is provided.
[0010]
The invention of this application relates to the invention according to claim 4, wherein the metal powder is a metal powder having a Brinell hardness of 15 or more and 90 or less (claim 5), and the metal powder is copper, aluminum, indium or One aspect of the present invention is to provide powders of these mixtures (claim 6) and to perform heat treatment after rolling (claim 7).
[0011]
Hereinafter, the MgB 2 superconducting wire of the invention of the present application and a method for manufacturing the same will be described in more detail with reference to examples.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, the MgB 2 superconducting wire of the invention of this application is a wire made by adding, mixing and rolling metal powder to MgB 2 superconducting powder to be filled in a metal tube. The interface between the tube and MgB 2 is smooth. When manufacturing such an MgB 2 superconducting wire, the MgB 2 superconducting powder and the metal powder are mixed, the mixed powder is filled in a metal tube, and rolled. As described above, when the metal tube is filled with only the MgB 2 superconducting powder and rolled without adding and mixing the metal powder, the MgB 2 superconducting powder hardens and the metal tube and the MgB 2 superconducting powder are hardened. Is uneven, and only Jc of about 100 A / cm 2 can be obtained. However, in the MgB 2 superconducting wire of the invention of this application, the interface between the metal tube and the MgB 2 superconducting powder is smooth, and Jc increases.
[0013]
The metal powder to be added to and mixed with the MgB 2 superconducting powder is preferably a metal powder having a Brinell hardness of 15 or more and 90 or less. With a soft metal powder having a Brinell hardness of less than 15, the effect of the MgB 2 superconducting powder on the sliding process cannot be obtained. The MgB 2 superconducting powder has a higher filling density due to processing after filling into a metal tube, and tends to aggregate into a large lump. The lump that has hardened once moves as a lump during processing, so that cracks, breakage of the interface with the metal pipe, and the like occur. The metal powder serves to prevent the MgB 2 superconducting powder from agglomerating into a large lump and, if a lump occurs, to function as a lubricant for sliding the lump (working slip). it is conceivable that. Therefore, a soft metal powder having a Brinell hardness of less than 15 is dispersed in a grain boundary or the like and cannot absorb energy during processing, and cannot contribute to processing slip. Since a powder of a metal having a Brinell hardness exceeding 90 is too hard to spread, the interface between the metal tube and the MgB 2 superconducting powder is not smooth. As a result, it is difficult to obtain a high Jc. As such a metal powder, a powder of copper, aluminum, indium or a mixture thereof is preferably exemplified. In order to obtain a higher Jc, copper, aluminum or a mixture thereof is preferable as the metal powder, as shown in Examples described later.
[0014]
The amount of the metal powder to be added to and mixed with the above MgB 2 superconducting powder is preferably 5-30 vol%. This is based on causing the above-mentioned processing slip in order to obtain the smoothness of the interface. If it is less than 5 vol%, it becomes gradually difficult to obtain the smoothness of the interface. On the other hand, if it exceeds 30 vol%, the ratio to the MgB 2 superconducting powder becomes too large. As a result, even if the smoothness of the interface is obtained, the superconducting current becomes difficult to flow, and as a result, the critical current density (Jc ) May decrease.
[0015]
In the manufacturing method of the MgB 2 superconducting wire of the invention of this application, heat treatment can be performed after rolling. Jc is further increased by the heat treatment after the rolling. The heat treatment conditions are not particularly limited as long as the superconducting properties of the MgB 2 superconducting wire are not deteriorated, and for example, one hour at 300 ° C. can be exemplified.
[0016]
【Example】
Commercially available MgB 2 superconductive powder was used. Aluminum (Al), copper (Cu), and indium (In) powders were each added to the MgB 2 superconducting powder at 10 vol% to prepare a mixed powder. Each mixed powder was filled into a metal tube made of stainless steel (SUS316) having an inner diameter of 4 mmφ and an outer diameter of 8 mmφ, and both ends of the metal tube were pressed together so that the mixed powder did not come out. The metal tube filled with the mixed powder was processed into a 2 mm × 2 mm square bar by a groove roll mill. Further, this square material was processed into a tape-shaped wire having a thickness of 0.5 mm by a flat roll rolling mill. This wire was cut into a suitable length and heat-treated in a tubular electric furnace through which argon gas was passed. This heat treatment was performed by installing a thermocouple next to the sample and measuring the temperature, and was performed at 300 ° C. for 1 hour.
[0017]
The critical current density (Jc) of each of the thus prepared wires, non-heat-treated wires, and heat-treated wires was measured by a four-terminal resistance method under a magnetic field of 4.2 K and 8 T.
[0018]
FIG. 1 is a correlation diagram plotted in relation to the metal species to which Jc of these wires was added and mixed. The correlation diagram also shows Jc of the conventional MgB 2 superconducting wire.
[0019]
In the non-heat-treated wire, the MgB 2 superconducting wire to which Al was added and mixed showed the maximum Jc, which was 400 A / cm 2 . Jc of the conventional MgB 2 superconducting wire was about 200 A / cm 2 .
[0020]
Except for the conventional MgB 2 superconducting wire, the heat treatment significantly increased Jc. In particular, Jc of the Cu-added wire after the heat treatment was about three times higher than that of the non-added wire.
[0021]
The cross sections of the Cu-added wire before and after heat treatment and the conventional MgB 2 superconducting wire (also before and after heat treatment) were observed with an optical microscope. FIG. 2 shows a cross-sectional image thereof.
[0022]
As shown in FIG. 2, in the conventional MgB 2 superconducting wire, large irregularities occurred at the interface between the metal tube and the MgB 2 superconducting powder. The interface was smooth before and after the heat treatment of the Cu-added wire. In the conventional MgB 2 superconducting wire rod, the MgB 2 superconducting powder is hardened by the compressive force applied during rolling, and the hardened MgB 2 superconducting powder is agglomerated. It is thought that it became. On the other hand, Cu is added wire material, soft Cu powder compression force applied during rolling is absorbed by suppressing the curing of MgB 2 superconductor powder and by strong working and also slippery MgB 2 superconductor powder was cured Also, it is considered that the inner surface of the metal tube was not damaged, and the interface maintained smoothness.
[0023]
Of course, the invention of this application is not limited by the above embodiments and examples. It goes without saying that various aspects are possible for details such as the type and amount of metal powder to be added to and mixed with the MgB 2 superconducting powder and the heat treatment conditions after rolling.
[0024]
【The invention's effect】
As described in detail above, according to the invention of this application, a MgB 2 superconducting wire having a high critical current density (Jc) can be obtained.
[Brief description of the drawings]
FIG. 1 is a correlation diagram plotted in relation to a metal species to which Jc of an MgB 2 superconducting wire prepared in an example and a conventional MgB 2 superconducting wire is added and mixed.
FIG. 2 is a cross-sectional image obtained by observing a cross section of a Cu-added wire before and after heat treatment of a Cu-added wire produced in an example and a conventional MgB 2 superconducting wire (also before and after heat treatment) with an optical microscope.
Claims (7)
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2007049623A1 (en) * | 2005-10-24 | 2007-05-03 | National Institute For Materials Science | PROCESS FOR PRODUCING MgB2 SUPERCONDUCTING WIRE ROD |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007049623A1 (en) * | 2005-10-24 | 2007-05-03 | National Institute For Materials Science | PROCESS FOR PRODUCING MgB2 SUPERCONDUCTING WIRE ROD |
| US8173579B2 (en) | 2005-10-24 | 2012-05-08 | National Institute For Materials Science | Fabrication method of a MgB2 superconducting tape and wire |
| JP5229868B2 (en) * | 2005-10-24 | 2013-07-03 | 独立行政法人物質・材料研究機構 | Method for manufacturing MgB2 superconducting wire |
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