JP4142770B2

JP4142770B2 - NbTi superconducting multilayer rolled plate and method for producing the same

Info

Publication number: JP4142770B2
Application number: JP18211098A
Authority: JP
Inventors: 広明大塚; 郁夫伊藤; 光造長村; 敬人北井; 裕史鶴丸
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1997-08-18
Filing date: 1998-06-29
Publication date: 2008-09-03
Anticipated expiration: 2018-06-29
Also published as: JPH11126928A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＭＲＩ（磁気共鳴医療画像診断装置）、超電導リニアモーターカー等の強力な磁場を必要とする機器で使用されている超電導機器等に対し外部磁場を遮蔽したり、超電導機器が発する強磁場の漏洩範囲を抑制する磁気シールド材や、磁場を発生するマグネットとして利用されるＮｂＴｉ超電導多層板およびその製造方法に関するものである。
【０００２】
【従来の技術】
超電導材料と高導電性金属材料を交互に積層した構造を有する超電導板は、特開平２−９４４９８号公報に記載されているように、熱間加工及び冷間加工と熱処理の繰り返しによりＮｂＴｉ層中にＴｉの析出物（常電導物質）を分散させて量子化磁束のピン止め点とし、比較的高い臨界電流密度（Ｊｃ）を得るものである。量子化磁束のピン止め点をＴｉの析出物としてＮｂＴｉ層に析出させるためには最後に行う熱処理を数週間もの長時間行う必要があり、コスト上昇、製品工期の長期化という問題を有していた。また、Ｊｃ値は２Ｔの磁場下において約２４万Ａ／ｃｍ^２であり、磁気シールド材として厚さ１ｍｍ以下で１Ｔ以上の磁場（但し磁場の方向は多層板と平行）をシールドするためには、さらに高いＪｃが求められていた。
【０００３】
【発明が解決しようとする課題】
本発明が解決しようとする課題は以下の通りである。
（１）製造工期の短い超電導多層圧延板を提供すること
（２）Ｊｃ値の高い超電導多層圧延板を提供すること
（３）超電導層と常電導層の層厚のばらつきが小さく、大きなくびれも無い安定な電流を流せる超電導多層圧延板を提供すること
すなわち、長時間にわたる熱処理工程を必要としない製造工程で、２Ｔの磁場下におけるＪｃ値が２４万Ａ／ｃｍ^２より高い超電導多層圧延板を提供すること、これにより軽量で磁気シールド特性または磁場捕捉特性の優れた超電導多層圧延板を得ることを目的としている。
【０００４】
【課題を解決するための手段及び実施の形態】
請求項１に示す第１の発明は、図１に示すようにＮｂＴｉ合金層と常電導層が交互に２層以上積層した構造を有する複合層と、Ｎｉ及びＳｉを含むＣｕ合金からなる高導電性金属層とが交互に積層した構造を有し、最外層がＣｕ、ＣｕＮｉ合金、又はＡｌからなる高導電性金属である多層圧延板であって、常電導層の厚さが実質的に５ｎｍ以上、２００ｎｍ以下、ＮｂＴｉ合金層の厚さが実質的に５ｎｍ以上、５００ｎｍ以下であり、かつＮｉ及びＳｉを含むＣｕ合金からなる高導電性金属層の電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下であることを特徴とするＮｂＴｉ超電導多層圧延板である。
【０００５】
本発明のＮｂＴｉ超電導多層圧延板の複合層において、常電導の厚さを実質的に５ｎｍ以上、２００ｎｍ以下、ＮｂＴｉ層の厚さを実質的に５ｎｍ以上、５００ｎｍ以下とした理由を、以下に述べる。
金属、合金及び酸化物超電導体において量子化磁束の有効なピン止め点は量子化磁束の格子間隔に分散した超電導のコヒーレンス長の２倍程度の大きさの常電導物質である（ＮｂＴｉの場合５Ｔにおける量子化磁束の格子間隔は２２ｎｍ、コヒーレンス長の２倍は１１ｎｍ）といわれており（石田文彦他、Advances in Cryogenic Engineering (Materials), vol.36, P.287, Plenum Press New York,1990）、または、フレーク状（K. Matsumoto 他、IEEE Transactions on magnetics, Vol.27, No.2 March P.1125, 1991）で存在しているが、本発明者らは印加する磁場が多層圧延板に平行な場合、層形状の常電導相も量子化磁束のピン止めとして非常に有効であることを見いだした。
【０００６】
即ち、本発明の超電導多層圧延板の複合層において、常電導層の厚さを５ｎｍ以上としたのは、理想的なピン止め点の厚さはおよそ１１ｎｍとされているが、５ｎｍ程度でも十分ピン止め点としての効果があり高い磁場が得られるためであり、２００ｎｍ以下としたのはこれを超えるとピン止め効率が低下するためである。ＮｂＴｉ層の厚さを５ｎｍ以上としたのは、圧延法によりこれ以下の厚さとするのは実質的に困難であるためであり、５００ｎｍ以下としたのはこれを超えるとピン止め同士の間隔が大きくなり磁束捕捉の効率が悪くＪｃが低下するためである。特に、超電導層と常電導層の層厚の合計が実質的に１００ｎｍ以下となる場合にピン止め力は大きくなり、Ｊｃは飛躍的に上昇する。
【０００７】
なお、本発明において、実質的という意味は、本発明材料の断面構造写真に板厚方向に直線を引いて各層の厚さを調べたときに、各層の内の５０％以上が請求項で規定した範囲に入っていることを示す。高導電性金属とは、ＣｕＮｉ等の銅合金である。常電導相とは、使用時に常電導状態であるＮｂ、Ｔｉ、Ｔａ等のことである。
【０００８】
次に、本発明のＮｂＴｉ超電導多層圧延板の複合層において、高導電性金属層の電気伝導率がＩＡＣＳ３０％以上、硬度が１２０以上、２２０以下とした理由を、以下に述べる。
Ｊｃの高い超電導多層圧延板を製造するためには、超電導層と常電導層が設計通りまたは設計値に近い層厚になっていることが重要である。超電導層及び常電導層の層厚が１μｍ以下になるまで圧延を行う場合、超電導層と常電導層及び高導電性金属層の硬さが大きく異なると各層厚のばらつきが大きくなったりくびれが起こり超電導電流を阻害する原因となる。例えば、ＮｂＴｉの硬度と比較して純銅の硬度はかなり小さいことから純銅とＮｂＴｉを多層にした多層板の冷間圧延を行うと特にＮｂＴｉの層厚のばらつきが大きくなりＪｃが低下する。この問題を解決するために、本発明では、特に高導電性金属層の硬さを規定し、圧延性を層間で一様になるようにした。
【０００９】
なお、ＩＡＣＳとは、無酸素銅の電気伝導率を１００％としたときにどれだけの電気伝導率があるかを示す指標である。高導電性金属層のＩＡＣＳを３０％以上としたのは、３０％未満だと超電導層が局所的に常電導に転移した場合に材料に流れていた超電導電流を高導電金属層に流すのには不十分で、超電導層全体が一気に常電導に転移してしまう現象が起きやすくなるためである。高導電性金属層のビッカース硬度を１２０以上としたのは、ＮｂＴｉ層のビッカース硬度が１８０〜２２０であることから、硬度の差が１００を超えない値とした。硬度の差が１００を超えると圧延性が異なり超電導層の層厚のばらつきが大きくなり、くびれが多数発生するためである。高導電性金属層の硬度を２２０以下とした理由は、硬度が２２０を超えると高導電性金属層の圧延性が低下するためである。
【００１０】
請求項２に示した第２の発明は、請求項１記載のＮｂＴｉ超電導多層圧延板の製造方法を規定するものである。ＮｂＴｉ合金板と常電導板を交互に２層以上積層するように重ねた複合層と、前記高導電性金属層として、電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下のＮｉ及びＳｉを含むＣｕ合金からなる高導電性金属板をＣｕ、ＣｕＮｉ合金、又はＡｌからなる高導電性金属で作製した箱の中に交互に入れ、Ｃｕ、ＣｕＮｉ合金、又はＡｌからなる高導電性金属板で真空中で封止し、次に温度５００〜１０００℃で加熱した後に圧延し、冷間圧延を施して板状または、箔状とすることを特徴とする製造方法である。
【００１１】
電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下の合金の例としては、１〜５％のＮｉと０．１〜２％のＳｉを含む銅合金や、０．０５〜４％のＦｅと０．０１〜０．２のＰを含む銅合金などがある。ここで常電導板とはＮｂ、Ｔｉ、Ｔａ、及び電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下の銅合金等のことを示す。圧延の温度を５００℃以上としたのは、これ未満ではＮｂＴｉ層と高導電性金属層が接合しないためであり、１０００℃以下としたのは１０００℃超では高導電性金属層の融点に近く融解の危険が生じるためである。高導電性金属層の電気伝導率をＩＡＣＳ３０％以上としたのは、３０％未満だと超電導層が局所的に常電導に転移した場合に材料に流れていた超電導電流を高導電性金属層に流すのには不十分で、超電導層全体が一気に常電導に転移してしまう現象が起きやすくなるためである。ビッカース硬度を１２０以上としたのは、ＮｂＴｉ層のビッカース硬度が１８０〜２２０であることから、硬度の差が１００を超えない値とした。硬度の差が１００を超えると圧延性が異なり超電導層の層厚のばらつきが大きくなり、くびれが多数発生するためである。高導電性金属層の硬度を２２０以下とした理由は、硬度が２２０を超えると高導電性金属層の圧延性が低下するためである。
Ｔｉの析出物をピン止め点とする通常のＮｂＴｉ多層圧延板（特開平２−９４４９８号公報）では、熱間圧延後の工程において熱処理と冷間圧延を繰り返し行い、最後に長時間の熱処理を行うことが必要であるが、本発明の場合、常電導金属層がピン止めとなるため、熱間圧延で各層同士を接合した後は冷間圧延工程のみで材料を作製することができる。但し、機械的性質（例えば伸び）を改善するために軟化焼鈍を必要に応じて行うこともある。
【００１２】
請求項３に示した第３の発明は、請求項１記載のＮｂＴｉ超電導多層圧延板の製造方法を規定するものである。ＮｂＴｉ合金板と常電導板を交互に２層以上積層するように重ねた複合層と、電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下のＮｉ及びＳｉを含むＣｕ合金からなる高導電性金属層がＮｂを介して交互に２層以上積層した構造を有し、最外層が電気伝導率がＩＡＣＳ３０％以上、ビッカース硬度が１２０以上２２０以下のＣｕ、ＣｕＮｉ合金、又はＡｌからなる高導電性金属板であり、超高導電性金属を１０枚以上、１００枚以下重ねて真空中または不活性ガス雰囲気で５００〜７００℃で１０分〜５時間、１ＭＰａ〜４００ＭＰａの圧力をかけた後室温で冷間圧延を施して、板状または、箔状とすることを特徴とするＮｂＴｉ多層圧延板の製造方法である。
【００１３】
１０枚以上としたのは、１０枚未満だと重ね合わせて圧延した際、ＮｂＴｉ及び常電導層の厚さを薄くする効果が小さいためであり、１００枚以下としたのは、１００枚を超えると重ね合わせた後の材料の層厚が厚くなり、圧延に時間がかかり工期が長期化するためである。温度５００〜７００℃としたのは、５００未満では最外層の高導電性金属層が接合しないためであり、７００℃を超えるとＮｂＴｉ層中のＴｉの拡散が顕著となりＣｕ層と金属間化合物が形成され、後の圧延工程に悪影響を及ぼすためである。時間を１０分〜５時間としたのは、１０分未満では試料全体が加熱されるのに不十分であり、５時間を超えるとＴｉの拡散による悪影響が出始めるためである。圧力を１ＭＰａ以上４００ＭＰａ以下としたのは、硬度が１２０以上２００以下の高導電性金属とＮｂＴｉの両方に均一に充分に接合圧力を伝えるためで、１ＭＰａ未満では十分接合しないためであり、４００ＭＰａを超えるとＮｂＴｉや高導電性金属層に亀裂が入ったりするためである。
【００１４】
【実施例】
［実施例１］
本発明材として、以下を作製した。厚さ０．０１ｍｍのＮｂ板４１枚と厚さ０．０５ｍｍのＮｂ−４６．５質量％Ｔｉ板４０枚を交互に積層したトータル厚さ２．４１ｍｍのＮｂ／ＮｂＴｉ複合層を３０個用意した。これらＮｂ／ＮｂＴｉ複合層とＮｉを３．０％、Ｓｉを０．６％含み、残りＣｕと不可避不純物から成る厚さ１ｍｍのＣｕ合金板２９枚を交互にＣｕで作製した箱に積層充填し、内部を真空状態にして溶接密封し７００℃で圧下率８０％で熱間圧延を施して一体化させた。次にＣｕ合金板のビッカース硬度を１４０、ＩＡＣＳを５０％になるように５００℃で２時間の熱処理を施し、Ｃｕ合金板中にＮｉとＳｉの金属間化合物を析出させた。次に冷間圧延を行い、厚さ０．１ｍｍの超電導多層板を作製した。このときのＮｂＴｉ層の厚さ、即ちＮｂ層とＮｂ層の層間隔は設計値で４１．２ｎｍ、Ｎｂ層の厚さは設計値で８．２ｎｍである。
【００１５】
一方、比較材として、厚さ１ｍｍのＮｂＴｉ３０枚と厚さ１ｍｍのＣｕの板を０．１ｍｍのＮｂを介して交互にＣｕで作製した箱に積層充填し、内部を真空状態にして溶接密封し７００℃で圧下率５０％で熱間圧延を施して一体化させた後、冷間圧延と４００℃の熱処理を２回繰り返し、厚さ０．５ｍｍとし、最後に３７０℃で２００時間時効した材料を作製した。比較材の断面組織を電子顕微鏡で観察したところ、結晶粒界と結晶粒中にＴｉ析出物が存在していることが確認できた。
【００１６】
本発明材及び比較材の臨界電流密度Ｊｃを液体ヘリウムに浸漬した状態で、２Ｔの磁場下において測定した（磁場の方向は試料に対して平行）。試料は平行部長さ約３０ｍｍ、幅０．５ｍｍの板状試験片に１０ｍｍの間隔で電圧の検出端子を取り付け試料に電流を流し、電圧が１μＶに上昇したときの電流値を臨界電流とし、その値をＮｂＴｉの断面積で割った値を臨界電流密度とした。
【００１７】
その結果、２Ｔの磁場下に於けるＪｃ値は、本発明材が８１万Ａ／ｃｍ ^２、比較材が１９万Ａ／ｃｍ ^２となり、本発明材は、比較材に比べ４．２倍以上も大きい値となった。
本発明材は、比較材が必要とした３７０℃２００時間の時効工程を省くことができ、なおかつ、このように高Ｊｃ値が得られたものである。
【００１８】
尚、本発明材の製造工程の途中において、ＮｉとＳｉを含むＣｕ合金板を使用した多層板に５００℃で２時間熱処理を施した後のＮｂＴｉ層とＣｕ合金層のビッカース硬度を測定したところ、それぞれ１６０と１４０であった。両層の硬さがほぼ等しいので、均一に冷間圧延することができ、高Ｊｃ値が得られた。
【００１９】
［実施例２］
本発明材として、以下を作製した。厚さ１ｍｍのＮｂＴｉ板３０枚とＮｉ３．０％、Ｓｉ０．６％、Ｚｎ０．２％を含み残部は不可避不純物からなる厚さ１ｍｍのＣｕ合金の板を０．１ｍｍのＮｂを介して交互にＣｕで作製した箱に積層充填し、内部を真空状態にして溶接密封し８００℃で圧下率５０％の熱間圧延を施して一体化させた後、冷間圧延により厚さ０．１ｍｍの多層板を作製した。これを１０枚積層して銅の箔でくるみ、真空中で２５０ＭＰａの圧力をかけながら５５０℃で５時間加熱プレスし接合した。ここで３００層のＮｂＴｉ層をもつ多層板ができた。本多層板を室温で厚さ１４μｍまで圧延した。このときＮｂＴｉ層及びＣｕ合金層の厚さは１６ｎｍ、Ｎｂ層の厚さは２ｎｍであり、ＮｂＴｉ層同士の間隔は平均２０ｎｍであった。
一方、実施例１で示した比較材をさらに圧延して厚さ１４μｍとし、実施例２での比較材とした。
これらの臨界電流密度Ｊｃを液体ヘリウムに浸漬した状態で、１Ｔの磁場下において測定した（磁場の方向は試料に対して平行）。試料は平行部長さ約３０ｍｍ、幅０．５ｍｍの板状試験片に１０ｍｍの間隔で電圧の検出端子を取り付け試料に電流を流し、電圧が１μＶに上昇したときの電流値を臨界電流とし、その値をＮｂＴｉの断面積で割った値を臨界電流密度とした。
【００２０】
その結果、本発明材の１Ｔの磁場下に於けるＪｃ値は２９７万Ａ／ｃｍ^２と非常に高い値が得られた。実施例１に示した比較材を厚さ１４μｍまで圧延した材料の１Ｔに於けるＪｃ値は、４４万Ａ／ｃｍ ^２であったので、本発明材のＪｃ値は比較材の６．７倍以上という非常に大きな値を示した。
本発明材は、比較材が必要とした３７０℃２００時間の時効工程を省くことができ、なおかつ、このように高Ｊｃ値が得られたものである。
【００２１】
【発明の効果】
以上説明したように本発明により、製造工期が短く、超電導層と常電導層の層厚のばらつきが小さく、大きなくびれも無く、安定な電流を流せ、高いＪｃを有するＮｂＴｉ超電導多層圧延板が得られた。
【図面の簡単な説明】
【図１】本発明に係る超電導多層圧延板の断面模式図で、（ａ）は全体図、（ｂ）は（ａ）における複合層の断面図である。
【符号の説明】
１高導電性金属層（ＣｕＮｉ合金等）
２複合層
３常電導層（Ｎｂ、Ｔａ、Ｔｉ等）
４ＮｂＴｉ層[0001]
BACKGROUND OF THE INVENTION
The present invention shields an external magnetic field from a superconducting device used in a device that requires a strong magnetic field, such as an MRI (magnetic resonance medical image diagnostic apparatus), a superconducting linear motor car, or the like, or generates a strong force generated by the superconducting device. The present invention relates to a magnetic shield material that suppresses the leakage range of a magnetic field, an NbTi superconducting multilayer board that is used as a magnet that generates a magnetic field, and a manufacturing method thereof.
[0002]
[Prior art]
A superconducting plate having a structure in which a superconducting material and a highly conductive metal material are alternately laminated is formed in an NbTi layer by repeating hot working, cold working and heat treatment, as described in JP-A-2-94498. Ti precipitates (normal conducting material) are dispersed in the magnetic flux to serve as a pinning point for the quantized magnetic flux to obtain a relatively high critical current density (Jc). In order to deposit the pinning point of the quantized magnetic flux as a Ti precipitate on the NbTi layer, the last heat treatment needs to be performed for a long time of several weeks, which has the problems of cost increase and product construction period extension. It was. Also, Jc value was about 240,000 A / cm ² under a magnetic field of 2 T, 1 T or more magnetic field below 1mm thick as the magnetic shield material (although the direction of the magnetic field parallel to the multilayer plate) for shielding the Therefore, a higher Jc was required.
[0003]
[Problems to be solved by the invention]
The problems to be solved by the present invention are as follows.
(1) providing a short superconducting multilayer rolled plate of manufacturing period (2) to provide a high Jc value superconducting multilayer rolled plate (3) variations in the thickness of the superconducting layer and the normal conductive layer is small, a large constriction also no i.e. to provide a superconducting multilayer rolled sheet that can safely stable current, in the manufacturing process that does not require a heat treatment process over a long period of time, 2 T high superconducting multilayer rolled sheet than Jc value 240,000 a / cm ² under a magnetic field of It is an object of the present invention to provide a superconducting multilayer rolled sheet that is lightweight and has excellent magnetic shielding characteristics or magnetic field capturing characteristics.
[0004]
[Means for Solving the Problems and Embodiments]
The first invention described in claim 1 is a highly conductive material comprising a composite layer having a structure in which two or more NbTi alloy layers and normal conducting layers are alternately laminated as shown in FIG. 1, and a Cu alloy containing Ni and Si. A multilayer rolled plate having a structure in which conductive metal layers are alternately laminated, and the outermost layer is a highly conductive metal made of Cu, CuNi alloy, or Al, and the thickness of the normal conductive layer is substantially 5 nm. As described above, the electric conductivity of the highly conductive metal layer made of a Cu alloy containing Ni and Si is not less than 200 nm, the thickness of the NbTi alloy layer is substantially not less than 5 nm and not more than 500 nm, and the Vickers hardness is not less than IACS. It is a NbTi superconducting multilayer rolled plate characterized by being 120 or more and 220 or less.
[0005]
In the composite layer of the NbTi superconducting multilayer rolled plate of the present invention, the reason why the thickness of normal conduction is substantially 5 nm or more and 200 nm or less and the thickness of the NbTi layer is substantially 5 nm or more and 500 nm or less will be described below. .
In a metal, alloy, and oxide superconductor, the effective pinning point of the quantized magnetic flux is a normal conducting material having a size about twice the coherence length of the superconducting dispersed in the lattice spacing of the quantized magnetic flux (5 for NbTi). It is said that the lattice spacing of the quantized magnetic flux at T is 22 nm, and the coherence length is twice as long as 11 nm (Fumihiko Ishida et al., Advances in Cryogenic Engineering (Materials), vol. 36, P. 287, Plenum Press New York, 1990) ), or, flaky (K. Matsumoto another, IEEE Transactions on magnetics, Vol.27, No.2 March P.1125, although present in 1991), the present inventors have magnetic multilayer rolled sheet to be applied It was found that the layered normal conducting phase is very effective for pinning the quantized magnetic flux.
[0006]
That is, in the composite layer of the superconducting multilayer rolled plate of the present invention, the thickness of the normal conducting layer is set to 5 nm or more. The ideal pinning point thickness is about 11 nm, but about 5 nm is sufficient. This is because it has an effect as a pinning point and a high magnetic field is obtained, and the reason why it is set to 200 nm or less is that if it exceeds this, the pinning efficiency is lowered. The reason why the thickness of the NbTi layer is set to 5 nm or more is that it is substantially difficult to reduce the thickness to less than this by a rolling method. This is because it becomes larger and the efficiency of capturing the magnetic flux is poor and Jc is lowered. In particular, when the total thickness of the superconducting layer and the normal conducting layer is substantially 100 nm or less, the pinning force increases and Jc increases dramatically.
[0007]
Incidentally, specified in the present invention, means that substantially, when examining the thickness of each layer in the cross-sectional structure photograph of the present invention the material by pulling a line in the thickness direction, 50% or more of the respective layers in claim Indicates that it is within the specified range. The highly conductive metal is a copper alloy such as CuNi . The normal conducting phase refers to Nb, Ti, Ta, etc. that are in a normal conducting state at the time of use.
[0008]
Next, the reason why the electrical conductivity of the highly conductive metal layer in the composite layer of the NbTi superconducting multilayer rolled plate of the present invention is set to 30% or more for IACS and 120 to 220 for hardness is described below.
In order to manufacture a superconducting multilayer rolled sheet having a high Jc, it is important that the superconducting layer and the normal conducting layer have a thickness as designed or close to the designed value. When rolling until the layer thickness of the superconducting layer and the normal conducting layer is 1 μm or less, if the hardness of the superconducting layer, the normal conducting layer, and the highly conductive metal layer is greatly different, the variation in the thickness of each layer becomes large or constriction occurs. It becomes a cause of obstructing superconducting current. For example, since the hardness of pure copper is considerably smaller than the hardness of NbTi, when cold rolling is performed on a multilayer plate in which pure copper and NbTi are multilayered, the variation in the layer thickness of NbTi increases and Jc decreases. In order to solve this problem , in the present invention, the hardness of the highly conductive metal layer is specified, and the rollability is made uniform between the layers.
[0009]
Note that IACS is an index indicating how much electrical conductivity there is when the electrical conductivity of oxygen-free copper is 100%. The reason why the IACS of the highly conductive metal layer is set to 30% or more is that when the superconducting layer is less than 30%, the superconducting current flowing in the material when the superconducting layer is locally changed to normal conduction flows to the highly conductive metal layer. This is because the phenomenon that the entire superconducting layer is rapidly transformed into normal conduction is likely to occur. The reason why the Vickers hardness of the highly conductive metal layer was set to 120 or more was that the difference in hardness did not exceed 100 because the Vickers hardness of the NbTi layer was 180 to 220. This is because if the difference in hardness exceeds 100, the rollability is different and the variation in the thickness of the superconducting layer increases, resulting in a large number of constrictions. The reason why the hardness of the highly conductive metal layer is 220 or less is that when the hardness exceeds 220, the rollability of the highly conductive metal layer is lowered.
[0010]
The second invention shown in claim 2 prescribes the method for producing the NbTi superconducting multilayer rolled plate according to claim 1. A composite layer in which two or more layers of NbTi alloy plates and normal conductive plates are alternately stacked, and the highly conductive metal layer include Ni and Si having an electrical conductivity of IACS 30% or more and a Vickers hardness of 120 or more and 220 or less. the highly conductive metal plate made of Cu alloy containing Cu, CuNi alloy, or placed alternately in a box manufactured in highly conductive metal made of Al, Cu, CuNi alloy, or highly conductive metal plate made of Al And then, after heating at a temperature of 500 to 1000 ° C., rolling and cold rolling to form a plate or foil.
[0011]
Examples of alloys having an electrical conductivity of IACS 30% or more and Vickers hardness of 120 or more and 220 or less include copper alloys containing 1 to 5% Ni and 0.1 to 2% Si, and 0.05 to 4%. Examples include copper alloys containing Fe and 0.01 to 0.2 P. Here, the normal conductive plate indicates Nb, Ti, Ta, a copper alloy having an electrical conductivity of IACS 30% or more, and a Vickers hardness of 120 or more and 220 or less. The reason why the rolling temperature is set to 500 ° C. or higher is that the NbTi layer and the highly conductive metal layer are not bonded when the temperature is lower than this, and that the temperature is set to 1000 ° C. or lower is close to the melting point of the highly conductive metal layer when the temperature is higher than 1000 ° C. This is because there is a risk of melting. The reason why the electrical conductivity of the highly conductive metal layer is set to IACS 30% or more is that if it is less than 30%, the superconducting current flowing in the material when the superconducting layer locally transitions to normal conduction is changed to the highly conductive metal layer. This is because it is not sufficient to flow, and the phenomenon that the entire superconducting layer transitions to normal conduction at once is likely to occur. The reason why the Vickers hardness was set to 120 or more was that the difference in hardness did not exceed 100 because the Vickers hardness of the NbTi layer was 180 to 220. This is because if the difference in hardness exceeds 100, the rollability is different and the variation in the thickness of the superconducting layer increases, resulting in a large number of constrictions. The reason why the hardness of the highly conductive metal layer is 220 or less is that when the hardness exceeds 220, the rollability of the highly conductive metal layer is lowered.
In a normal NbTi multilayer rolled plate (JP-A-2-94498) having a Ti precipitate as a pinning point, heat treatment and cold rolling are repeated in the process after hot rolling, and finally a long time heat treatment is performed. Although it is necessary to perform, in the case of this invention, since a normal conducting metal layer becomes pinning, after joining each layer by hot rolling, a material can be produced only by a cold rolling process. However, in order to improve mechanical properties (for example, elongation), softening annealing may be performed as necessary.
[0012]
A third aspect of the present invention provides a method for manufacturing the NbTi superconducting multilayer rolled sheet according to the first aspect. A composite layer superimposed to laminate alternately two or more layers of NbTi alloy plate and normal-conducting plate, electric conductivity IACS30% or more, the Vickers hardness of the Cu alloy containing 120 to 220 or less Ni and Si high conductivity The conductive metal layer has a structure in which two or more layers are alternately laminated via Nb, and the outermost layer is made of Cu, CuNi alloy, or Al having an electrical conductivity of IACS 30% or more and a Vickers hardness of 120 to 220. 10 or more and 100 or less super high conductive metals are stacked, and after applying a pressure of 1 MPa to 400 MPa in vacuum or in an inert gas atmosphere at 500 to 700 ° C. for 10 minutes to 5 hours, room temperature The method for producing a NbTi multilayer rolled plate is characterized in that it is cold rolled to form a plate or foil.
[0013]
The reason why the number is 10 or more is that the effect of reducing the thickness of NbTi and the normal conducting layer is small when the number is less than 10 and rolled, and the number of 100 or less is more than 100. This is because the layer thickness of the material after being overlaid becomes thick, and it takes time to roll and the construction period is prolonged. The reason why the temperature is set to 500 to 700 ° C. is that when the temperature is less than 500, the outermost highly conductive metal layer is not bonded. When the temperature exceeds 700 ° C., the diffusion of Ti in the NbTi layer becomes remarkable, and the Cu layer and the intermetallic compound are formed. This is because it is formed and adversely affects the subsequent rolling process. The reason for setting the time to 10 minutes to 5 hours is that if the time is less than 10 minutes, the entire sample is insufficient to be heated, and if it exceeds 5 hours, adverse effects due to diffusion of Ti begin to appear. The reason why the pressure is set to 1 MPa or more and 400 MPa or less is to transmit the bonding pressure uniformly and sufficiently to both the highly conductive metal having a hardness of 120 or more and 200 or less and NbTi. If it exceeds, NbTi or the highly conductive metal layer will crack.
[0014]
【Example】
[Example 1]
The following were produced as the material of the present invention. 30 Nb / NbTi composite layers having a total thickness of 2.41 mm were prepared by alternately laminating 41 Nb plates having a thickness of 0.01 mm and 40 Nb-46.5 mass% Ti plates having a thickness of 0.05 mm. . These Nb / NbTi composite layers, Ni of 3.0%, Si of 0.6%, and 29 Cu alloy plates with a thickness of 1 mm consisting of the remaining Cu and inevitable impurities are alternately stacked and filled in a box made of Cu. The inside was vacuum-sealed and welded and sealed at 700 ° C. with a rolling reduction of 80% and integrated. Next, heat treatment was performed at 500 ° C. for 2 hours so that the Vickers hardness of the Cu alloy plate was 140 and IACS was 50%, and an intermetallic compound of Ni and Si was precipitated in the Cu alloy plate. Next, cold rolling was performed to produce a superconducting multilayer plate having a thickness of 0.1 mm. At this time, the thickness of the NbTi layer, that is, the distance between the Nb layer and the Nb layer is 41.2 nm as a design value, and the thickness of the Nb layer is 8.2 nm as a design value.
[0015]
On the other hand , as a comparative material, 30 NbTi plates with a thickness of 1 mm and Cu plates with a thickness of 1 mm are stacked and filled in a box made of Cu alternately with 0.1 mm of Nb, and the inside is vacuum-sealed and welded and sealed. A material that was integrated by hot rolling at 700 ° C. with a rolling reduction of 50%, then cold rolling and heat treatment at 400 ° C. were repeated twice to a thickness of 0.5 mm, and finally aged at 370 ° C. for 200 hours. Was made. When the cross-sectional structure of the comparative material was observed with an electron microscope, it was confirmed that Ti precipitates were present in the crystal grain boundaries and crystal grains.
[0016]
The critical current density Jc of the inventive material and the comparative material was measured under a magnetic field of 2 T in a state immersed in liquid helium (the direction of the magnetic field is parallel to the sample). A sample is a plate-shaped test piece having a parallel part length of about 30 mm and a width of 0.5 mm, and a voltage detection terminal is attached at an interval of 10 mm. A current flows through the sample, and the current value when the voltage rises to 1 μV is defined as a critical current. The value obtained by dividing the value by the cross-sectional area of NbTi was defined as the critical current density.
[0017]
As a result, the Jc value under a magnetic field of 2 T is 810,000 A / cm ^{2 for} the inventive material and 190,000 A / cm ² for the comparative material, which is 4.2 times that of the comparative material. The above was also a large value.
The material of the present invention can omit the aging process at 370 ° C. for 200 hours required for the comparative material, and has a high Jc value as described above.
[0018]
In the course of the production process of the material of the present invention , the Vickers hardness of the NbTi layer and the Cu alloy layer after the heat treatment at 500 ° C. for 2 hours on the multilayer plate using the Cu alloy plate containing Ni and Si was measured. , 160 and 140, respectively. Since the hardness of both layers was almost equal, it could be uniformly cold-rolled and a high Jc value was obtained.
[0019]
[Example 2]
The following were produced as the material of the present invention. 30 NbTi plates with a thickness of 1 mm and Ni alloy plates with Ni 3.0%, Si 0.6%, and Zn 0.2%, and the balance is made of unavoidable impurities. A box made of Cu is laminated and filled, and the inside is welded and sealed in a vacuum state. After being integrated by hot rolling at 800 ° C. with a reduction rate of 50%, a multilayer having a thickness of 0.1 mm is obtained by cold rolling. A plate was made. Ten sheets of these were laminated and wrapped with copper foil, and joined by press-pressing at 550 ° C. for 5 hours while applying a pressure of 250 MPa in a vacuum. Here, a multilayer board having 300 NbTi layers was obtained. The multilayer board was rolled to a thickness of 14 μm at room temperature. At this time, the thickness of the NbTi layer and the Cu alloy layer was 16 nm, the thickness of the Nb layer was 2 nm, and the interval between the NbTi layers was 20 nm on average.
On the other hand, the comparative material shown in Example 1 was further rolled to a thickness of 14 μm and used as the comparative material in Example 2.
These critical current densities Jc were measured in a magnetic field of 1 T while immersed in liquid helium (the direction of the magnetic field was parallel to the sample). A sample is a plate-shaped test piece having a parallel part length of about 30 mm and a width of 0.5 mm, and a voltage detection terminal is attached at an interval of 10 mm. A current flows through the sample, and the current value when the voltage rises to 1 μV is defined as a critical current. The value obtained by dividing the value by the cross-sectional area of NbTi was defined as the critical current density.
[0020]
As a result, the Jc value of the material of the present invention under a magnetic field of 1 T was as high as 2.97 million A / cm ² . Since the Jc value in 1T of the material obtained by rolling the comparative material shown in Example 1 to a thickness of 14 μm was 440,000 A / cm ² , the Jc value of the inventive material was 6.7 times that of the comparative material. It was a very large value.
The material of the present invention can omit the aging process at 370 ° C. for 200 hours required for the comparative material, and has a high Jc value as described above.
[0021]
【The invention's effect】
As described above, according to the present invention, an NbTi superconducting multilayer rolled sheet having a short manufacturing period, small variations in the layer thickness of the superconducting layer and the normal conducting layer, no large constriction, allowing a stable current to flow, and high Jc is obtained. It was.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a superconducting multilayer rolled plate according to the present invention, where (a) is an overall view and (b) is a cross-sectional view of a composite layer in (a).
[Explanation of symbols]
1 Highly conductive metal layer ( CuNi alloy, etc. )
2 Composite layer 3 Normal conducting layer ( Nb, Ta, Ti, etc. )
4 NbTi layer

Claims

It has a structure in which a composite layer having a structure in which two or more NbTi alloy layers and normal conducting layers are alternately stacked, and a highly conductive metal layer made of a Cu alloy containing Ni and Si , and the outermost layer is A multilayer rolled plate that is a highly conductive metal made of Cu, CuNi alloy, or Al , wherein the normal conductive layer has a thickness of substantially 5 nm or more and 200 nm or less, and the NbTi alloy layer has a thickness of substantially 5 nm or more. A NbTi superconducting multi-layer rolled sheet characterized by having an electric conductivity of a highly conductive metal layer made of a Cu alloy containing Ni and Si of not more than 500 nm and an IACS of 30% or more and a Vickers hardness of 120 or more and 220 or less.

A composite layer in which two or more layers of NbTi alloy plates and normal conductive plates are alternately stacked, and the highly conductive metal layer include Ni and Si having an electrical conductivity of IACS 30% or more and a Vickers hardness of 120 or more and 220 or less. the highly conductive metal plate made of Cu alloy containing Cu, CuNi alloy, or placed alternately in a box manufactured in highly conductive metal made of Al, Cu, CuNi alloy, or highly conductive metal plate made of Al The NbTi superconductivity according to claim 1, wherein the NbTi superconductor is sealed in a vacuum and then heated at a temperature of 500 to 1000 ° C, followed by hot rolling and cold rolling to form a plate or foil. A method for producing a multilayer rolled sheet.

A composite layer composed of two or more NbTi alloy plates and normal conductive plates stacked alternately, and a high conductivity made of a Cu alloy containing Ni and Si having an electrical conductivity of IACS 30% or more and a Vickers hardness of 120 to 220. has a structure in which sexual metal layer are laminated two or more layers alternately through Nb, outermost electrical conductivity IACS30% or more, Vickers hardness of 120 or more 220 or less of Cu, CuNi alloy, or high made of Al a conductive metal plate, a superconducting multilayer board 10 or more, stacked 100 sheets or less, 10 minutes to 5 hours at 500 to 700 ° C. in a vacuum or in an inert gas atmosphere, together with pressure of 1MPa~400MPa 2. The method for producing a NbTi multilayer rolled plate according to claim 1, wherein after cold forming, cold rolling is performed at room temperature to obtain a plate shape or a foil shape.