JP3757659B2

JP3757659B2 - Superconducting wire and method for manufacturing the same

Info

Publication number: JP3757659B2
Application number: JP02176699A
Authority: JP
Inventors: 高明笹岡
Original assignee: Hitachi Cable Ltd
Current assignee: Hitachi Cable Ltd
Priority date: 1999-01-29
Filing date: 1999-01-29
Publication date: 2006-03-22
Anticipated expiration: 2019-01-29
Also published as: JP2000222953A

Description

【０００１】
【発明の属する技術分野】
本発明は、超電導線材およびその製造方法に関し、特に超電導フィラメントが酸化物超電導材料からなり、金属被覆中で螺旋状の経路を有する超電導線材およびその製造方法に関する。
【０００２】
【従来の技術】
超電導体を複数に分割してフィラメントとし、それらを金属でマトリックス状に被覆した金属被覆超電導線材が知られている。高温で超電導特性を有する酸化物超電導線材も同様の構造が提案されており、銀または銀合金をマトリックスで被覆したいわゆる銀シース多芯超電導線材の開発が進められている。この場合、酸化物超電導体としては、たとえばＢｉ−２２１２，Ｂｉ−２２２３，Ｔｌ−１２２３，Ｔｌ−２２２３，Ｙ１２３，Ｎｄ−１２３，等の酸化物粉末を出発原料とし、銀または銀合金の被覆材と複合させ、さらに超電導化熱処理を施して、超電導線材が得られる。通常、このような複合化構造は、例えば図１１にその断面を示すように、超電導体を複数のフィラメント１の組織に分割し、これらを銀または銀合金２で被覆した断面円形すなわち丸線のマルチフィラメント超電導線材３とする方法が多く用いられている（例えば、特開平4-292809を参照）。また、このような断面円形の線材に圧延加工を施し、図１２に示すような断面が矩形状のテープ状酸化物超電導線材４とすることも多い。
【０００３】
酸化物超電導線材の場合、丸形状線材の７７Ｋにおける臨界電流密度をＪｃ₁、テープ状線材のそれをＪｃ₂とすると、Ｊｃ₁＜Ｊｃ₂となるのが普通である。つまり、酸化物超電導体の場合、個々の超電導フィラメントの断面形状を丸（フィラメントのアスペクト比が１）でなく、楕円またはテープ（フィラメントのアスペクト比１以上）にした方がＪｃを大きくすることができる。
【０００４】
ところで、線材の最終断面形状としては丸線の方がテープ状線材に比べ汎用性があり、しかも取り扱いが容易となるとの理由から、別の断面構造として、図１３に示すように、超電導フィラメント１がテープ状（アスペクト比１より大）で線材の断面は円形とした酸化物超電導線材５が提案されている（特開平9-223418号）。このような構造の超電導線材は、断面円形の線材に圧延加工を施して断面が矩形状のテープ状線材とし、そのテープ状線材の複数本を金属パイプないしビレット中に組込み、その後、縮径加工を行うことで長尺で丸形状の超電導線材を得ている。
【０００５】
また、超電導線材は交流損失低減対策や機械歪み耐性向上を目的として、線材の製作途中で線材をツイスト加工することにより、超電導フィラメントの経路を金属被覆中で長手方向に螺旋状に構成することがある。さらに、交流損失低減対策の他の手法として、超電導フィラメント間に電気的絶縁層を介在させることでフィラメント相互の電気的結合を抑制する、いわゆるバリアー層を形成する場合がある。このバリアー層の材料としては、通常ＢａＺｒＯ₃，ＳｒＺｒＯ₃，ＭｇＯ，ＭｎＯなどの酸化物材料がある。
【０００６】
こうした超電導線材においては、製造工程における減面加工時に超電導フィラメントが緻密化されることによって、高いＪｃ特性が得られている。横断面がテープ状の超電導フィラメントを有する超電導線材のＪｃが、横断面円形の超電導フィラメントを有する超電導線材のそれより高いのは、前者の場合、減面加工時の圧下力が超電導フィラメントの横断面内で均一にかかり緻密化も均一に行われるのに対し、後者の場合、超電導フィラメント横断面の中心部は外層部に比べて圧下力が小さくなって、十分に緻密化されないからである。つまり、後者の場合、各フィラメント横断面の超電導組織を均一に緻密化できないために、Ｊｃが制限されるのである。
【０００７】
ここで更に重要なのは、超電導フィラメントの長手方向での超電導組織の緻密度のばらつき、ムラの発生であり、これもＪｃを制限する原因となる。これは、線材の製造中における何らかの外乱や素材寸法のばらつき等に起因して、素材に許容される応力を超える局部的な応力が線材の塑性加工の際に素材に加わるためと考えられる。従って、高Ｊｃの超電導線材を安定的に歩留まり良く製造するためには、線材の長手方向において超電導フィラメントの超電導組織が均一かつ高い緻密度で形成されることが必要である。
【０００８】
そこで、本発明の目的は、上記の欠点を解消し、線材の長手方向において超電導フィラメントの超電導組織が均一かつ高い緻密度で形成でき、かつ、横断面が略円形の超電導線材においても横断面がテープ状の超電導線材と同等の臨界電流密度を達成できる超電導線材とその製造方法を提供することにある。
【０００９】
【課題を解決するための手段】
上記課題を解決するため、本発明では、横断面が略円形の外形を有する超電導線材であって、超電導線材は、その横断面が略半円形または中心角が略１２０度である扇形のセグメントの２本または３本が長手方向に所定のピッチで螺旋状に集合された集合体からなり、前記セグメントは酸化物超電導体からなる超電導フィラメントと当該超電導フィラメントを覆う金属被覆とからなる横断面が略円形の素線を螺旋状に撚り合せて縮径加工したものであり、前記超電導フィラメントは前記セグメント内でセグメントと異なる方向の螺旋状に所定のピッチで配置され、横断面のアスペクト比が１．５以上であることを特徴とする超電導線材を提供する。ここで、セグメントの各々の間に電気的絶縁層が設けられていることが好ましい。
【００１０】
さらにまた、本発明では、横断面が略半円形または中心角が略１２０度である扇形のセグメントの２本または３本が長手方向に所定ピッチで螺旋状に集合された集合体からなる超電導線材の製造方法であって、酸化物超電導材料からなる超電導フィラメントが金属で被覆され横断面が略円形の素線に所定のピッチＰ_０でツイスト加工を施し、そのツイスト加工された素線ｎ本（ｎ＝２、３）を所定のピッチで螺旋状に撚り合わせ、次いで当該撚線を所定の外径を有する横断面が略円形の線材に縮径加工して前記超電導フィラメントをアスペクト比が１．５以上の横断面にすることを特徴とする超電導線材の製造方法を提供する。ここで、素線外径をｄ_０、縮径加工前の撚線ピッチをＰ_１、縮径加工後の線材外径をｄ_Ｓとすると、
ｎ＝２の場合、Ｐ_１／ｄ_０＝３〜３０、ｄ_Ｓ＜１．２ｄ_０、
ｎ＝３の場合、Ｐ_１／ｄ_０＝８〜４０、ｄ_Ｓ＜１．７ｄ_０
であり、ピッチＰ_０とピッチＰ_１の螺旋の方向は反対とする。
【００１１】
なお、本発明において、横断面が略円形とは、円形のみならず、対称Ｎ角形（Ｎは６以上）を含む概念である。
【００１２】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態を説明する。
【００１３】
図３、図６、図７、図８及び図１０は、本発明に係る超電導線材の実施の態様を、酸化物超電導線材を例にとり、横断面図で示したものである。
【００１４】
図３に示す例は、アスペクト比が１．５以上で好ましくは２０以下である酸化物超電導フィラメント１を５５本と、酸化物超電導フィラメント１を覆う金属被覆２を有し、かつ横断面が略半円形であるセグメント８ａ，８ｂの２本を、長手方向に所定のピッチで螺旋状に集合した集合体９からなり、横断面が略円形の外形を有している酸化物超電導線材である。そして、各酸化物超電導フィラメント１は、各セグメント８ａ，８ｂ内において、セグメントの螺旋の方向と反対方向の螺旋状に、所定のピッチに配置されている。
【００１５】
図６は、他の例であって、アスペクト比が１．５以上で好ましくは２０以下である酸化物超電導フィラメント２１を５５本と、酸化物超電導フィラメント２１を覆う金属被覆２２を有し、かつ横断面において中心角が略１２０度であるセグメント３０ａ，３０ｂ，３０ｃの３本を、長手方向に所定のピッチで集合した集合体３１からなり、横断面が略円形の形状を有している。そして、この例においても、図３と同様に、各酸化物超電導フィラメント２１は、各セグメント３０ａ，３０ｂ，３０ｃ内において、セグメントの螺旋の方向と反対方向の螺旋状に、所定のピッチに配置されている。
【００１６】
図７は、さらに別の例であって、横断面において中心角が略１２０度であるセグメント３２ａ，３２ｂ，３２ｃのそれぞれに含まれる酸化物超電導フィラメント２１の本数を１９とし、これらセグメント３２ａ，３２ｂ，３２ｃを長手方向に所定のピッチで螺旋状に集合した集合体３３としたものであり、各セグメント３２ａ，３２ｂ，３２ｃの間には、電気的絶縁材料（例えば、ＢａＺｒＯ₃，ＳｒＺｒＯ₃，ＭｇＯ，ＭｎＯ等の酸化物）で構成されるバリアー層４４が設けられており、これにより各セグメントは電気的に絶縁されている。この例において、各フィラメント２１は、そのアスペクト比が１．５以上好ましくは２０以下であり、かつ、各セグメント３２ａ，３２ｂ，３２ｃ内において、セグメントの螺旋と反対方向の螺旋状に配置されている。
【００１７】
図８は、さらに別の例であって、横断面において中心角が略１２０度であるセグメント３４ａ，３４ｂ，３４ｃのそれぞれに含まれる酸化物超電導フィラメント４１の本数を５５とし、これらセグメント３４ａ，３４ｂ，３４ｃを長手方向に所定のピッチで螺旋状に集合した集合体４７としたものであり、各フィラメント４１の表面には、電気的絶縁材料（例えば、ＢａＺｒＯ₃，ＳｒＺｒＯ₃，ＭｇＯ，ＭｎＯ等の酸化物）で構成されるバリアー層４４が設けられており、これにより各フィラメントは電気的に絶縁されている。そして、各フィラメント４１は、そのアスペクト比が１．５以上好ましくは２０以下であり、かつ、各セグメント３４ａ，３４ｂ，３４ｃ内において、セグメントの螺旋と反対方向の螺旋状に配置されている。
【００１８】
図１０は、さらに別の例であって、ほぼ中心に金属芯材５３が配置された酸化物超電導フィラメント５１と、酸化物超電導フィラメント５１の１９本を覆う金属被覆（フィラメント被覆）５４と、その外側を覆うもう一つの金属被覆（セグメント被覆）５５からなる、横断面において中心角が１２０度であるセグメント３６ａ、３６ｂ、３６ｃを長手方向に所定のピッチ螺旋状に集合した集合体５７よりなる。金属芯材５３は、その硬さが金属被覆５４、５５よりも小さい、すなわち柔らかい材料が選ばれ、かつ金属被覆５４はその硬さが金属被覆５５よりも小さい、すなわち柔らかい材料が選ばれている。この例においても、金属芯材５３を含む酸化物超電導フィラメント５１の各々は、アスペクト比が１．５以上このましくは２０以下であり、かつセグメント３６ａ、３６ｂ、３６ｃ内において、セグメントの螺旋の方向と反対方向の螺旋状に配置されている。
【００１９】
以上の、本発明の実施の態様による酸化物超電導線材によれば、各超電導フィラメントはセグメント内においてセグメントの螺旋と異なる方向の螺旋状に所定のピッチで配置されるので、その製造工程において、撚線加工後の外観形状（撚線の最外径と撚線ピッチ）のばらつきが小さくなり、縮径加工時の素材の断線やキンク等の欠陥を減らすことができる。その結果、超電導線材の長手方向において超電導フィラメントの超電導組織が均一かつ高い緻密度で形成できる。
【００２０】
また、各超電導フィラメントが長手方向において線材の内層部側、外層部側に交互に配置されているので、線材の製造工程における縮径加工時の超電導フィラメントの圧下力、それに伴う超電導フィラメントの緻密化度が、各々の超電導フィラメント間で均一化される。しかも、超電導フィラメントは、アスペクト比が１．５以上である横断面が板状または楕円状に形成されるので、横断面が略円形の超電導線材においても横断面がテープ状の超電導線材と同等の臨界電流密度を達成できる。
【００２１】
特に、図１０の例では、各セグメントを構成する金属材料において、金属被覆（セグメント被覆）５５の硬さが、金属芯材５３および金属被覆（フィラメント被覆）５４の硬さよりも大きく選ばれているので、超電導フィラメントの界面における凹凸が減少して平滑化され、臨界電流密度Ｊｃの向上に寄与する。
【００２２】
次に、本発明に係る超電導線材の製造方法について、実施の態様を説明する。
【００２３】
図１は、本発明に係る製造方法の工程を示すフローチャートであり、金属被覆内部に１本の酸化物超電導体の芯を含む単フィラメントを作製する工程と、その単フィラメントの複数本を金属管内に複数本組み込んで多芯ビレット化し、それを静水圧押出しにより多芯フィラメント複合体を形成する工程と、その多芯フィラメント複合体を縮径加工し横断面が略円形の素線を作成する工程と、その素線に所定のピッチでツイスト加工する工程と、その素線を２本または３本撚り合わせる工程と、その撚線を更に縮径加工する工程を含む。
【００２４】
以下、仕様外径ｄｓ、仕様撚線ピッチＰｓの酸化物超電導線材を得ることを例に、各工程について詳細に説明する。
【００２５】
Ａ．単フィラメント作製
まず、１本の酸化物超電導フィラメントと金属被覆からなる単フィラメントを作製する。フィラメントを構成する物質は、公知の酸化物超電導材料、例えば、Ｂｉ−２２１２、Ｂｉ−２２２３、Ｔｌ−１２２３、Ｔｌ−２２２３、Ｙ−１２３、Ｎｂ-１２３からなる。一方、金属被覆は、特に限定するものではないが、芯となる酸化物超電導材料と反応して超電導特性を低下させない材料が好ましく、例えば、Ｂｉ−２２１２、Ｂｉ-２２２３の酸化物超電導材料のときは、銀または銀合金（Ａｇを主成分としてＡｕ、Ｐｄ、Ｔｉ、Ｍｇ、Ｎｉ、Ｓｂ、Ａｌ、Ｍｎより選ばれた少なくとも１種を添加したもの）であることが好ましい。本工程の一例として、超電導材料は超電導化熱処理を施していない粉末または一旦焼結後に粉砕した粉末（以下、前駆体粉末という）を所定の長さの金属管に充填し、次いで縮径加工することにより、横断面が略円形の単フィラメントを作製する。ここで、単フィラメントの最外層には金属被覆が設けられている（フィラメント被覆）。また、単フィラメントの中心には金属芯材を配置しても良く、この場合、金属芯材は、その硬さがフィラメント被覆よりも小さい、すなわち柔らかい材料に選ぶことが好ましい。これにより、後述の工程Ｌにおけるフィラメントの変形がスムースに起こる。さらに、交流損失低減効果を重視する場合は、フィラメント被覆の表面に金属または酸化物等であって後述する超電導化熱処理によって良導体とならない材料を、例えばペースト状にして２００μｍ以下の厚さで塗布してもよい。
【００２６】
Ｂ．多芯フィラメント複合体の作製
工程Ａで得た単フィラメントを複数本、所定の長さの別の金属管に組み込んで多芯ビレット化する。金属管は、その材料を特に限定するものではないが、好ましくは銀または銀合金（Ａｇを主成分としてＡｕ、Ｐｄ、Ｔｉ、Ｍｇ、Ｎｉ、Ｓｂ、Ａｌ、Ｍｎより選ばれた少なくとも１種を添加したもの）であり、その材料の硬さは、フィラメント被覆を構成する材料と同じとするか、より好ましくは、金属芯材およびフィラメント被覆を構成する材料の硬さより大きいものとする。多芯ビレット化に際し、中心に金属被覆と同様の材料からなり超電導材料を含まない金属芯材をさらに配置してもよい。この多芯ビレットは静水圧押出しにより、横断面が略円形の多心フィラメント複合体に成形される。これにより、金属管は多芯フィラメント複合体の最外層を構成する金属被覆となり、後工程の撚線加工、撚線の縮径加工を経てセグメント化されたときの金属被覆（セグメント被覆）となる。
【００２７】
Ｃ．縮径加工
次いで、工程Ｂの多芯フィラメント複合体を、押出し、スウェージャーまたは伸線により減面加工し、横断面が略円形で多芯フィラメントを有する素線を作製する。ここで、交流損失低減効果を重視する場合は、この素線の表面に、金属または酸化物等であって後述する超電導化熱処理によって良導体とならない材料を、例えばペースト状にして所定の厚さで塗布してもよい。この層は、線材化したときの各セグメント間の電気的接続を遮断するためのものである。なお、ここで塗布する材料は、塗布することによって潤滑性の向上するものが望ましいが、それに限定されるものではない。以下の工程での説明の便宜上、ここで得られた素線の外径をｄ₀、長さをＬ₀とする。
【００２８】
Ｄ．素線のツイストと撚線加工
工程Ｃで得られた素線にツイスト加工（ツイスト加工後のフィラメントの螺旋ピッチをＰ₀とする）を施し、次いで、図４に示すように、そのツイスト加工された素線の２本または３本を、素線のツイスト加工の方向と反対方向に所定のピッチＰ₁で螺旋状に撚り合わせる。図において、６１は素線、６２ａ，６２ｂ，６２ｃは撚線４６の進行方向を軸としてその周囲を公転する素線ボビンである。なお、ツイスト加工の直後に伸線または所定の熱処理のいずれか１つを施してから撚り合わせてもよい。
【００２９】
また、図５にあるように、別の態様として、素線ボビン６３ａ、６３ｂ、６３ｃを素線６１の送出し方向を軸にして回転させることによって素線をツイスト加工しつつ、素線ボビンを撚線４６の進行方向を軸としてその周囲に公転させることで、ツイスト加工と反対方向に撚り合わせを行うことも可能である。
【００３０】
素線の撚り合わせピッチは、素線が２本の場合、Ｐ₁／ｄ₀＝１．５〜３０、素線が３本の場合は、Ｐ₁／ｄ₀＝４〜４０を満足する範囲とする。通常の撚線で形状を維持するためには、Ｐ₁／ｄ₀の上限は約１００まで可能である。しかしながら、本発明では、撚線が次の縮径加工を経るので、Ｐ₁／ｄ₀が１００程度まで大きいと、縮径加工の際に素線がばらけてしまい、加工が困難になる。そこで、撚線に縮径加工を施すことができる上限として、Ｐ₁／ｄ₀は、素線が２本の場合３０、素線が３本の場合４０が選ばれる。一方、Ｐ₁／ｄ₀が小さすぎると、撚線加工時に素線が過度の加工歪を受け、金属被覆中のフィラメント組織に乱れや破壊が生じ、そのために最終的に得られた超電導線材において超電導特性の低下を招くおそれがある。しかしながら、撚線加工に先立って素線にツイスト加工を施すことにより、フィラメント組織の乱れや破壊がかなり防止されることがわかった。発明者らの実験の結果、撚線加工によって問題の生じないＰ₁／ｄ₀の下限が、素線が２本の場合１．５、素線が３本の場合４まで拡大できることがわかった。
【００３１】
図２および図９は撚線加工後の状態を示し、図２は２本の例を、図９は３本の例をそれぞれ示しており、６，５６はそれぞれ撚線である。図示のとおり、撚線加工後の外径をｄ₁とすると、ｄ₁は幾何学的に一義に決定し、２本の場合（図２）ではｄ₁＝２ｄ₀、３本の場合（図９）ではｄ₁＝２．３１ｄ₀である。また、素線のツイストピッチ（即ちフィラメントの螺旋ピッチ）Ｐ₀および素線の撚り合わせピッチＰ₁の回転方向は、いわゆるＳ巻またはＺ巻のいずれでもよいが、共に反対方向であるよう選択する。
【００３２】
このように素線のツイストピッチとＰ₀および素線の撚り合わせピッチＰ₁の回転方向を反対方向に選択すると、撚線加工後の外観形状（撚線の最外径ｄ₁と撚線ピッチＰ₁）のばらつきが小さくなり、次の縮径加工時の素材の断線やキンク等の欠陥を減らすことができる。このメカニズムは、次のように考えている。すなわち、素線のツイスト加工後は、被覆金属とその内部の各超電導フィラメントにせん断の残留応力が分布している。そして、その後の撚り合せ加工においては、その残留応力成分が開放されるような応力を受けて加工される。その結果、素材の力学的ポテンシャルエネルギーを大きくすることなく次の縮径加工を安定して行うことができるのである。
【００３３】
Ｅ．縮径加工
工程Ｄで得られた撚線に、ダイスを用いた伸線装置またはスウェージャー等公知の手段によって縮径加工を行なう。この縮径加工は１回でも複数回の繰り返しでもよいが、１回の縮径加工による外径の減少率は２〜２０％となるよう、ダイス口径を選定することが好ましい。縮径加工を複数回繰り返すときは、縮径加工の途中で、焼鈍処理や超電導化のための中間熱処理、あるいは前駆体粉末組織の脱ガス処理を施してもよい。中間熱処理を行なうときは、その後の縮径加工は、１回のパスによる外径の減少率は２〜５％とするのが好ましい。
【００３４】
縮径加工によって得られる複合線材の外径をｄとすると、素線が２本の場合ｄ＜１．３ｄ₀、素線が３本の場合ｄ＜１．８ｄ₀に達すると、外径が略円形に成形された線材が得られる。この際、縮径加工によって２本または３本の素線はつぶされて横断面が半円形または中心角が略１２０度の扇形に変形し、略半円形または中心角が略１２０度である扇形のセグメントを長手方向に所定のピッチで螺旋状に集合した集合体を構成する。さらに、各々の超電導フィラメントは、各々のセグメント内で所定のピッチで反対方向の螺旋状に配置されているので、結果として、各超電導フィラメントは２次螺旋状に集合している。
【００３５】
一方、金属被覆内の超電導フィラメントの横断面形状は、アスペクト比が高い（好ましくは１．５以上の）板状、楕円状に変形させられる。これは、本工程の減面加工によって、２本または３本の撚線の隣接素線同士と撚線外径ｄ₁の円筒内面で形成される空隙を埋めるように素線材料の一部が円周方向に展性変形するからである。
【００３６】
ところで、縮径加工時には、通常、潤滑材、例えば合成油、石油、モリブデン、２硫化モリブデン等が使用される。この潤滑材は、セグメント間の隙間に浸透し残留物となる。通常は、潤滑油を除去するために縮径加工後に拭き取り作業等の洗浄作業を行うが、本発明の実施の形態にかかる超電導線材の製造方法では、交流損失低減効果を重視する場合に限り、この残留潤滑材を残しておくことが好ましい。この残留潤滑材は、適切な材料を選択することによって、後述する超電導加熱処理を経ることによって、各セグメント間の電気的絶縁層を形成するよう変化するからである。したがって、縮径加工中では、潤滑材を豊富に使い、その後、セグメント間の潤滑材除去を目的とする洗浄作業をあえて行わないようにすることが好ましい。
【００３７】
今、撚線直後の空隙率ｖを、撚線外径ｄ₁に等しい円筒空間内での空隙（素線の占有しない体積）の割合と定義し、素線が２本の場合と３本の場合についてそれぞれ計算すると、素線が２本の場合、Ｐ₁／ｄ₀＝３〜３０の範囲でｖ＝０．４４〜０．５５、素線が３本の場合、Ｐ₁／ｄ₀＝８〜４０の範囲でｖ＝０．３８〜０．４３となる。この空隙率が略０％となった時点で、空隙のないセグメントの集合体となる。
【００３８】
一般に、縮径加工を施す毎に被加工材の撚線ピッチは長くなる。この繰り返しの縮径加工においても、加工前の撚線ピッチＰと外径ｄの比Ｐ／ｄが大きすぎると、縮径加工の際に素線がばらけてしまい、加工が困難になる。その限界値をＰ₂／ｄで表現すると、Ｐ／ｄ＜Ｐ₂／ｄであり、発明者の実験によれば、好ましくは、２本の素線の場合Ｐ₂／ｄ＝２０〜３０、３本の素線の場合Ｐ₂／ｄ＝３０〜６０である。
【００３９】
集合体が横断面で略円形になると、外径ｄと撚ピッチＰは縮径加工の前後で数値的に略次式が成立する。
【００４０】
Ｐ・ｄ²＝一定（１）
この（１）の関係式に基づいて、縮径加工を制御すれば、異なる仕様外径ｄｓ、撚線ピッチＰｓに応じた集合体が得られる。
【００４１】
一方、縮径加工後の集合体の総長については、長さＬ₀、外径ｄ₀の素線を撚り合わせ、次いで縮径加工すると、歩留まりを無視した場合、集合体外径がｄｓで長さｎ×Ｌｍａｘとなる。但し、ｎＬ₀ｄ₀ ²＝Ｌｍａｘｄｓ²である。
【００４２】
Ｆ．縮径加工途中のツイスト加工
工程Ｅの縮径加工において、外径ｄと撚線ピッチＰがＰ／ｄ＞Ｐ₂／ｄ、すなわち繰り返しの縮径加工が困難なとき、または、所定のピッチＰｓを縮径加工以外の方法でより短く調整しようとするときは、縮径加工の途中で撚線にツイスト加工を施し、Ｐ／ｄを小さくすることができる。この加工は、通常、撚線の撚りが締まる方向に回転する（ツイストする）ことで行なう。
【００４３】
ツイスト加工前の撚線のピッチＰ₂、ツイスト加工後のピッチをＰ₃、ツイスト加工時の撚線外径をｄとすると、ツイスト加工に必要な単位長さあたりの回転数ｄｎは、次式で与えられる。
【００４４】
ｄｎ＝１／Ｐ₃−１／Ｐ₂ （２）
このツイスト加工に先立ち、ツイストをやり易くするために、金属被覆に焼鈍処理を施してもよい。
【００４５】
ツイスト加工は、加工度が大きすぎると超電導フィラメントの組織に乱れが生じたり、破壊に至ることがある。これを防止するために、加工度は制約される。発明者の実験によれば、２本の素線の場合Ｐ₃／ｄ＞３であり、３本の場合Ｐ₃／ｄ＞５である。
【００４６】
Ｇ．超電導化熱処理
超電導化熱処理は、超電導フィラメントの超電導特性を発現させるために必要な処理である。この熱処理の条件は、一般に超電導材料の種類に依存するが、超電導フィラメントの厚さ（断面積）、アスペクト比、金属被覆マトリックスの組成によっても若干左右される。図４、図６および図８に示したように、本発明の酸化物超電導線材においては、超電導フィラメント自体は従来の線材（例えば図１２）の超電導フィラメントと同様、板状ないし断面楕円状に成形されているため、従来の線材における最適熱処理条件と略同様の熱処理を施せばよい。ここで、最適熱処理条件とは、臨界電流密度を最大にできかつ熱処理によって線材に膨れが生じたりしない条件である。
【００４８】
【実施例】
以下、本発明の実施例について詳細に説明する。
【００４９】
［実施例１］
組成としてＢｉ₂Ｓｒ₁Ｃａ₂Ｃｕ₂Ｏｘ（以下Ｂｉ−２２１２という）が得られるようにＢｉ₂Ｏ₃，ＳｒＣＯ₃，Ｃａ₂ＣＯ₃，ＣｕＯの各粉末を混合し、これを大気中で８２０℃、２０時間の熱処理を施した後、それを粉砕してＢｉ−２２１２相の前駆体粉末を用意した。外径１５mm、内径１３．５mm、長さ５００mmの銀合金パイプに前駆体粉末を充填した。この粉末と銀合金の複合体を、対辺寸法７．６４mmの６角棒形状にまで伸線加工し、素材Ａを得た。
【００５０】
この素材Ａの５５本を、外径７１．１mm、内径６４mm、長さ５００mmの銀合金パイプに組み込み、銀合金被覆酸化物ビレットＸ（外径７１．１mm、長さ５００mm、体積Ｖｘ＝２×１０⁶mm³）を得た。ビレットＸに、押出し加工、スウェージャー加工、伸線加工を施し、外径ｄ₀＝１．７mmの銀合金被覆酸化物の丸型素線（素材Ｂ）を得た。素材Ｂは、酸化物ビレットＸの体積Ｖｘの歩留まり約８０％で作製されるので、体積がＶｘ_B＝０．８Ｖｘとなっている。したがって、素材Ｂの長さはＬ₀＝Ｖｘ_B／（πｄ₀ ²／４）≒７０００００mm＝７００ｍである。また、素材Ｂの被覆材である銀合金の占有率は６６％であった。長さ約７００ｍの素線を２ロッド作製した（素材Ｂ）。この素線にＺ方向のツイスト加工を施し、表面のピッチがＰ₀＝７．５mmとなるようにした。
【００５１】
２ロッドのツイスト素線を用いて、図２に示すように、最外径約２ｄ₀＝３．４mmで２本束ね、Ｓ方向の撚線加工を施しピッチＰ₁＝１５mmの撚線を作製した。撚線の体積は２Ｖｘ_Bである。
【００５２】
上記の撚線に伸線加工を施すと、２本の丸型素線は徐々に潰され、最外径が約半分のｄｓ＝１．６mmまで縮径されると、図３に示すように、２個の半円形のセグメントが互いに合わさった丸型成形集合体（素材Ｃ）となった。この成形集合体は、体積を略維持したまま縮径加工されるので、外径ｄｓにおける線材単長Ｌｓは、Ｌｓ＝２Ｖｘ_BB／（πｄｓ²／４）＝１．６×１０⁶mm＝１５８０ｍである。図３に示すように、素材Ｃの超電導フィラメントの横断面は、多くがアスペクト比１．５から２０くらいの板型、または楕円型となっていることがわかる。また、素材Ｃの銀合金占有率は、素線（素材Ｂ）より若干大きくなり、６８％であった。
【００５３】
素材Ｃは、超電導フィラメントが銀合金で被覆されたセグメント撚線であって、さらに各セグメント内で超電導フィラメントがセグメントの螺旋の方向と反対方向の螺旋状に配置されている、２次螺旋配置構造である。
【００５４】
セグメント内のフィラメントの螺旋ピッチを１次ピッチＰｓ₁、セグメン撚線の螺旋のピッチをＰｓ₂とすると、両ピッチは縮径加工によって伸びるので、Ｐｓ₁＝Ｌｓ／Ｌ₀×Ｐ₀＝１７mm、Ｐｓ₂＝Ｌｓ／Ｌ₀×Ｐ₁＝３４mmであった。セグメント横断面における各超電導フィラメントの位置は、撚線長手方向の場所によって内層部と外層部で周期的に入れ替わるよう変化する。
【００５５】
撚線の縮径加工時には、横断面における外層部と内層部で加工変形度は異なり、外層部に行くほど加工度は大きい。この例では、超電導フィラメントは長手方向で内層部と外層部を周期的に延びるので、縮径加工による変形は、フィラメント長手方向全体として均一に起こるとみなすことができる。
【００５６】
素材Ｃを、１atm ，大気中で８８０℃、１０分間保持後、５℃／時間の冷却速度で８３０℃まで徐冷し、さらに１時間保持して炉冷した。この熱処理により、素材Ｃは超電導特性を有する超電導線材に変化した。この超電導線材の一部を長さ約５０mmに切断し、試料Ｃとした。試料Ｃを液体ヘリウム、外部磁場１０Ｔ中で、臨界電流密度Ｊｃを１μＶ／cmの定義で測定した。その結果、超電導フィラメントについてＪｃ＝２５００Ａ／mm²、線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃ＝８００Ａ／mm²であった。
【００５７】
一方、比較のため、素材Ｂをそのまま圧延し、テープ状の複合素材を得た。この複合素材に、上記と同様の超電導化熱処理を施し、テープ状超電導線材を得た。その一部を切り出し、比較材とした。比較材を試料Ｃと同様に、液体ヘリウム、外部磁場１０Ｔ中で、臨界電流密度Ｊｃを１μＶ／cmの定義で測定した。その結果、超電導フィラメントについてＪｃ＝１６００Ａ／mm²、線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃ＝６００Ａ／mm²であった。
【００５８】
試料Ｃと比較材から明らかなように、本発明による試料Ｃの丸型超電導線材は、従来のテープ状超電導線材よりも磁場中でのＪｃが大きく向上していることがわかった。
【００５９】
［実施例２］
実施例１で作製した丸型素線丸型素線（素材Ｂ、単長Ｌ₀＝７０５ｍ、外径１．７mm）に、ピッチＰ₀＝７．５mmにてＳ方向のツイスト加工を施し、その３本を束ねて図４に示すようにピッチＰ₁＝３６mmでＺ方向に撚り合わせた。撚線の最外径ｄ₁は約２．３ｄ₀＝３．３９mmであり、体積は３Ｖｘ_Bである。
【００６０】
上記の撚線に伸線加工を施すと、３本の丸型素線は徐々に潰され、最外径がｄｓ＝２．４mmまで縮径されると、図６に示すように、３個の中心角が略１２０度の扇形のセグメントが互いに合わさった丸型成形集合体（素材Ｅ）となった。この成形集合体は、体積を略維持したまま縮径加工されるので、外径ｄｓにおける線材単長ＬｓはＬｓ＝３Ｖｘ_BB／（πｄｓ²／４）＝１．０×１０⁶mm＝１０００ｍである。図６に示すように、素材Ｅの超電導フィラメントの横断面は、多くがアスペクト比２から２０くらいの板型、または楕円型となっていることがわかる。
【００６１】
素材Ｅは、実施例１と同様に、超電導フィラメントが銀合金で被覆されたセグメント撚線であって、さらに各セグメント内で超電導フィラメントがセグメントの螺旋の方向と反対方向の螺旋状に配置されている、２次螺旋配置構造である。
【００６２】
セグメント内のフィラメントの螺旋ピッチ（１次ピッチ）は、Ｐｓ₁＝Ｌｓ／Ｌ₀×Ｐ₀＝１０．６mm、セグメン撚線の螺旋のピッチ（２次ピッチ）Ｐｓ₂＝Ｌｓ／Ｌ₀×Ｐ₁＝５１mmであった。実施例１と同様にして、セグメント横断面における各超電導フィラメントの位置は、撚線長手方向の場所によって内層部と外層部で周期的に入れ替わるよう変化する。
【００６３】
この素材Ｅに超電導化熱処理を施し、超電導線材を得た。この超電導線材の一部を長さ約５０mmに切断し、試料Ｍとした。試料Ｍを実施例１と同様の測定方法で線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃを測定した。その結果、ｏｖｅｒａｌｌ−Ｊｃ＝７００Ａ／mm²であり、テープ状の線材のそれを超える値であった。
【００６４】
［実施例３］
実施例１で作製した丸型素線（素材Ｂ、単長Ｌ₀＝７０５ｍ、外径１．７mm）にピッチＰ₀＝７．５mmにてＺ方向のツイスト加工を施し、さらに、その表面に２硫化モリブデン粉末を含むペーストを約３０μｍの厚さに塗布した。この２硫化モリブデンを含む層を塗布により形成する目的は、第１には、その後の縮径加工の際の潤滑性を確保するためであり、第２には、素線間に電気的絶縁層（薄い膜）を設けるためである。
【００６５】
このような素線を３本を束ねて、図４に示すように、ピッチＰ₁＝３６mmでＳ方向に撚り合わせた。撚線の最外径ｄ₁は約２．３ｄ₀＝３．３９mmであり、体積は３Ｖｘ_Bである。
【００６６】
上記の撚線に伸線加工を施すと、３本の丸型素線は徐々に潰され、最外径がｄｓ＝２．４mmまで縮径されると、図７に示すように、３個の中心角が略１２０度の扇形のセグメントが互いに合わさり、かつセグメント間に２硫化モリブデンを主成分とするバリアー層が介在した丸型成形集合体（素材Ｆ）となった。セグメントは、このバリアー層によって、相互に電気的に絶縁されている。
【００６７】
先に説明したように、従来は潤滑材を十分に除去してから次の超電導化熱処理を行う。しかし、この例では、あえて２硫化モリブデンは残留させたまま超電導化熱処理を行った。この熱処理により、２硫化モリブデンは酸化モリブデンに変化し、電気的絶縁層、すなわちバリアー層としての機能が保証される。
【００６８】
この素材Ｆに超電導化熱処理を施し、超電導線材を得た。この超電導線材の一部を長さ約５０mmに切断し、試料Ｆとした。試料Ｆを実施例１と同様の測定方法で線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃを測定した。その結果、ｏｖｅｒａｌｌ−Ｊｃ＝７００Ａ／mm²であり、テープ状の線材のそれを超える値であった。また、超電導特性は、バリアー層を有しない試料Ｅと同等であることも確認した。
【００６９】
この例では、バリアー層を交流損失低減のために設けているが、その効果を確かめるために、実施例２で作製した試料Ｅ、従来のテープ状の線材、および試料Ｆの交流損失特性を比較した。評価は、各試料を液体窒素中のゼロ磁場下に置き、交流通電損失を測定する方法で行った。試料に、直流臨界電流値の半分の実効値電流を５０Ｈｚの交流で通電し、その時の損失電圧を測定した。結果は、電圧タップ１００mmで、従来のテープ状線材が１０μＶ、試料Ｅが１μＶ、試料Ｆが０．３μＶであった。試料Ｅ、試料Ｆでは、超電導フィラメントがインダクタンス的に等価に配置されているため、テープ状線材よりも交流損失が小さく、特に試料Ｆではセグメント間の電気的絶縁が確保されたことによって、さらに交流損失が小さくなったと考えられる。
【００７０】
［実施例４］
組成としてＢｉ_１．８Ｐｂ_０．３４Ｓｒ_１．９Ｃａ_２．２Ｃｕ_３．１Ｏ_ｘ（以下Ｂｉ−２２２３という）の前駆体粉末を用意した。外径１５mm、内径１３．５mm、長さ５００mmの銀合金パイプに前駆体粉末を充填した。この粉末と銀合金の複合体を、対辺寸法７．６４mmの６角棒形状にまで伸線加工し、素材Ｎを得た。
【００７１】
この素材Ｎの表面にペースト状のモリブデンを塗布し塗膜を形成した後、その５５本を、外径７１．１mm、内径６４mm、長さ５００mmの銀合金パイプに組み込み、銀合金被覆酸化物ビレットＹを得た。ビレットＹに、押出し加工、スウェージャー加工、伸線加工を施し、外径ｄ₀＝１．４mmの銀合金被覆酸化物の丸型素線（素材Ｐ）とし、さらに、長さあたり３３３回転（ピッチＰ₀＝３mm）のＳ方向のツイスト加工を施した。このツイスト加工した素材を３本用意し、最外径約２．３ｄ₀＝３．２mmで３本束ね、Ｚ方向の撚線加工を施しピッチＰ₁＝１２mmの撚線を作製した。
【００７２】
上記の撚線に伸線加工を施すと、３本の丸型素線は徐々に潰される。本実施例では、伸線のパスは、外径３．２mmから始まり、２．８mm、２．６mm、２．４５mmと順次伸線し、外径２．４５mmで、成形集合体に超電導化のための中間熱処理を施した。熱処理条件は、１atm 、空気中で８４０℃、５０時間とした。この第１回目の中間熱処理は、フィラメントの前駆体組織をＢｉ−２２２３相へ超電導化するためのものである。この熱処理によって、モリブデンの塗布膜は酸化モリブデンの電気的絶縁層に変化し、フィラメント間のバリアー層として機能する。
【００７３】
次いで、１回のパスの最外径ｄの減少率を４％とし、伸線加工を経て、最外径を２．３５mmとした後、第２回目の中間熱処理を施した。熱処理条件は、１atm 、空気中で８４５℃、５０時間とした。その後、それに伸線加工を施し、最外径を２．３mmの成形集合体（素材Ｑ）とした。この素材Ｑは、空隙率が略０％の３本撚りの丸型成形集合体で、最外径２．３mm、単長１１００ｍである。セグメント内における超電導フィラメントの螺旋ピッチ（１次ピッチ）Ｐｓ₁＝Ｌｓ／Ｌ₀×Ｐ₀＝１１００／１０００×３＝３．３mm、セグメントの螺旋のピッチ（２次ピッチ）Ｐｓ₂＝Ｌｓ／Ｌ₀×Ｐ₁＝１１００／１０００×１２＝１３．２mmであった。
【００７４】
次いで、素材Ｑに酸化物Ｂｉ−２２２３相生成のための最後の超電導化熱処理を施し、丸型超電導線材を得た。
【００７５】
一方、比較材として、素線（素材Ｐ）を用いて、圧延加工、中間熱処理、再圧延加工、第２回目の中間熱処理、再々圧延加工を施し、厚さ０．２mmのテープ状素材（素材Ｒ）とし、次いで最後の超電導加熱処理を施し、テープ状の超電導線材を得た。ここで、素材Ｑ，素材Ｒの中間熱処理と最終熱処理は、ともに同一のバッチで行なった。両線材の一部を長さ約２００mm切断し、それぞれ試料Ｑ、比較材Ｒとした。液体窒素中、外部磁場無しの状態で、線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃを１μＶ／cmの定義で測定した。試料Ｑでｏｖｅｒａｌｌ−Ｊｃ＝１００Ａ／mm²であり、比較材Ｒでｏｖｅｒａｌｌ−Ｊｃ＝１２０Ａ／mm²であった。酸化物バリアー層を含まないテープ状の線材に比べ若干低いＪｃ特性であった。
【００７６】
［実施例５］
組成としてＢｉ−２２１２が得られるようにＢｉ_２Ｏ_３、ＳｒＣＯ_３、Ｃａ_２Ｃｏ_３、ＣｕＯの各粉末を混合し、これを大気中で８２０℃、２０時間の熱処理を施した後、それを粉砕してＢｉ−２２１２相の前駆体粉末を用意した。外径１５mm、内径１４mm、長さ５００mmの純銀パイプと、外径３mm純銀丸棒を用意した。純銀丸棒を中心に配置して純銀パイプに前駆体粉末を充填した。この粉末と純銀の複合体を外径１２．３mmの丸棒に伸線加工し、素材Ｓを得た。
【００７７】
この素材Ｓの１９本を、外径７１．１mm、内径６４mm、長さ５００mmの銀合金パイプ（合金組成：Ａｇ−０．０５wt％Ｍｇ−０．０５wt％Ｎｉ）に組み込み、銀合金被覆酸化物ビレットＺを得た。ビレットＺに、押出し加工、スウェージャー加工、伸線加工を施し、外径ｄ₀＝１．７mmの銀合金被覆酸化物の丸型素線（素材Ｔ）を得た。素材Ｔを３本用意し、それにピッチＰ₀＝３mmのＳ方向のツイスト加工を施した。
【００７８】
ツイスト加工された３本のロッドを用いて、図４に示すように、最外径ｄ₁が約２．３ｄ₀＝３．２mmで３本束ね、Ｚ方向の撚線加工を施し、ピッチＰ₁＝１２mmの撚線を作製した。
【００７９】
上記の撚線に伸線加工を施すと、３本の丸型素線は徐々に潰され、最外径がｄｓ＝２．４mmまで縮径されると、図１０に示すように、３個の中心角が略１２０度の扇形のセグメントが互いに合わさった丸型成形集合体（素材Ｕ）となった。図１０に示すように、素材Ｕの超電導フィラメントの横断面は、中心に配置された純銀の金属芯材とともに多くがアスペクト比２から２０くらいの板型、または楕円型となっていることがわかる。また、フィラメントの経路は、セグメントの撚り方向と反対方向でかつセグメント内で螺旋状に延びる２次螺旋状である。
【００８０】
この素材Ｕに超電導化熱処理を施し、超電導線材を得た。この超電導線材の一部を切断し、試料Ｕとした。試料Ｕを実施例１と同様の測定方法で線材断面積で除した臨界電流密度ｏｖｅｒａｌｌ−Ｊｃを測定した。その結果、ｏｖｅｒａｌｌ−Ｊｃ＝１０００Ａ／mm²であった。
【００８１】
この実施例では、各フィラメントの中心に配置される金属芯材とフィラメント被覆には純銀が、セグメント被覆には銀合金（合金組成：Ａｇ−０．０５wt％Ｍｇ−０．０５wt％Ｎｉ）が使用されている。このため、セグメント被覆は、超電導化熱処理を経ることにより酸化分散型銀合金となり、その内側に使用されるフィラメント被覆および金属芯材よりも降伏応力、ビッカース硬さがともに大きな材料となる。したがって、縮径加工と同時に起こるフィラメントの円形断面から矩形または楕円形への変形挙動が安定して、線材長手方向のばらつきを抑制し、超電導特性の向上に寄与するものである。
【００８２】
本発明の超電導線材は、それ自体導体として、あるいはその複数本の集合化した導体として用いる場合の他、それらを他の部材と複合化した構成にしてもよい。その応用例としては、マグネット、コイル、ケーブル、ブスバー、電流リード、磁気シールド、永久電流スイッチ等の超電導デバイスがあげられる。さらに、前記の応用として使用する場合、その作製法はReact&Wind法あるいはWind&React法のいずれであってもよい。
【００８３】
また、セグメント間にバリアー層を有する超電導線材においては、そのまま３相一括の電力ケーブルとして使用することが可能である。
【００８４】
【発明の効果】
以上説明したように、本発明によれば、超電導フィラメントはセグメント内でセグメントの撚り合わせ方向と反対方向に螺旋状に配置されるので、線材の長手方向において超電導フィラメントの超電導組織が均一かつ高い緻密度で形成できる。その結果、横断面が略円形の超電導線材においても横断面がテープ状の超電導線材と同等の臨界電流密度を達成できる超電導線材が安定的に歩留まり良く得られるという効果があり、その工業的意義は極めて大きい。
【図面の簡単な説明】
【図１】本発明に係る超電導線材の製造方法の一例を示すフローチャートである。
【図２】本発明に係る超電導線材の製造工程における、撚線加工後の状態を示す説明図である。
【図３】図２の撚線より得られる超電導線材の一例を示す横断面図である。
【図４】撚線方法の一例を示す説明図である。
【図５】撚線方法の他の例を示す説明図である。
【図６】本発明に係る超電導線材の他の例を示す横断面図である。
【図７】本発明に係る超電導線材のさらに他の例を示す横断面図である。
【図８】本発明に係る超電導線材のさらに他の例を示す横断面図である。
【図９】本発明に係る超電導線材の製造工程における、撚線加工後の他の状態を示す説明図である。
【図１０】図９の撚線より得られるさらに別の超電導線材の例を示す横断面図である。
【図１１】従来の超電導線材の製造方法を示すフローチャートである。
【図１２】従来の超電導線材の例を示す横断面図である。
【図１３】従来の超電導線材の別の例を示す横断面図である。
【符号の説明】
１，２１，４１，５１超電導体フィラメント
２，２２，４２，５４金属被覆
６，５６撚線
８ａ，８ｂ，３０ａ，３０ｂ，３０ｃ，３２ａ，３２ｂ，３２ｃ，３４ａ，３４ｂ，３４ｃ，３６ａ，３６ｂ，３６ｃセグメント
９，３１，３３，４７，５７集合体
５３金属芯材
４４バリアー層[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a superconducting wire and a method for manufacturing the same, and in particular, a superconducting filament is provided.Made of oxide superconducting materialThe present invention relates to a superconducting wire having a spiral path in a metal coating and a method for manufacturing the same.
[0002]
[Prior art]
A metal-coated superconducting wire is known in which a superconductor is divided into a plurality of filaments and these are coated in a matrix with metal. A similar structure has been proposed for oxide superconducting wires having superconducting properties at high temperatures, and so-called silver-sheathed multi-core superconducting wires in which silver or a silver alloy is coated with a matrix are being developed. In this case, as the oxide superconductor, for example, an oxide powder such as Bi-2212, Bi-2223, Tl-1223, Tl-2223, Y123, Nd-123, etc. is used as a starting material, and a silver or silver alloy coating material And superconducting heat treatment is further performed to obtain a superconducting wire. In general, such a composite structure has a circular or round cross-section in which a superconductor is divided into a plurality of filaments 1 and coated with silver or a silver alloy 2 as shown in FIG. A method of using the multifilament superconducting wire 3 is often used (for example, see Japanese Patent Laid-Open No. 4-292809). In many cases, the wire having a circular cross section is rolled to obtain a tape-shaped oxide superconducting wire 4 having a rectangular cross section as shown in FIG.
[0003]
In the case of an oxide superconducting wire, the critical current density at 77 K of the round wire is expressed as Jc.₁Jc of tape-like wire₂Jc₁<Jc₂It is normal to become. That is, in the case of an oxide superconductor, Jc may be increased if the cross-sectional shape of each superconducting filament is not a circle (a filament aspect ratio of 1) but an ellipse or a tape (a filament aspect ratio of 1 or more). it can.
[0004]
By the way, as the final cross-sectional shape of the wire, the round wire is more versatile than the tape-like wire and is easy to handle. Therefore, as shown in FIG. However, an oxide superconducting wire 5 having a tape shape (greater than an aspect ratio of 1) and a circular cross section has been proposed (Japanese Patent Laid-Open No. 9-223418). The superconducting wire with such a structure is a tape-shaped wire having a rectangular cross section by rolling a wire having a circular cross section, and incorporating a plurality of the tape-shaped wires into a metal pipe or billet, and then reducing the diameter. By doing this, a long and round superconducting wire is obtained.
[0005]
In addition, the superconducting wire can be formed in a spiral shape in the longitudinal direction in the metal coating by twisting the wire during the production of the wire for the purpose of reducing AC loss and improving mechanical strain resistance. is there. Furthermore, as another technique for reducing AC loss, there is a case where a so-called barrier layer is formed in which an electrical insulating layer is interposed between superconducting filaments to suppress electrical coupling between filaments. As a material of this barrier layer, BaZrO is usually used._Three, SrZrO_ThreeThere are oxide materials such as MgO and MnO.
[0006]
In such a superconducting wire, a high Jc characteristic is obtained by densifying the superconducting filament during surface-reduction processing in the manufacturing process. The Jc of the superconducting wire having a superconducting filament with a tape-like cross section is higher than that of the superconducting wire having a superconducting filament with a circular cross section. In the latter case, the central portion of the cross section of the superconducting filament has a lower rolling force than the outer layer portion, and is not sufficiently densified. That is, in the latter case, Jc is limited because the superconducting structure of each filament cross section cannot be uniformly densified.
[0007]
What is more important here is the variation in the density of the superconducting structure in the longitudinal direction of the superconducting filament and the occurrence of unevenness, which also causes Jc to be restricted. This is presumably because local stress exceeding the stress allowed for the material is applied to the material during plastic processing of the wire due to some disturbance during manufacture of the wire, variation in material dimensions, and the like. Therefore, in order to produce a high Jc superconducting wire stably and with good yield, it is necessary that the superconducting structure of the superconducting filament be formed uniformly and with high density in the longitudinal direction of the wire.
[0008]
Accordingly, an object of the present invention is to eliminate the above-mentioned drawbacks, and to form a superconducting structure of a superconducting filament uniformly and with a high density in the longitudinal direction of the wire, and also in a superconducting wire having a substantially circular cross section, the cross section is An object of the present invention is to provide a superconducting wire that can achieve a critical current density equivalent to that of a tape-shaped superconducting wire and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
  In order to solve the above-described problems, the present invention is a superconducting wire having a substantially circular outer shape in cross section, and the superconducting wire has a semi-circular cross section or a fan-shaped segment whose central angle is approximately 120 degrees. 2 or 3ButHelical assembly at a predetermined pitch in the longitudinal directionWasConsisting of aggregates,SaidSegment isSuperconducting filament made of oxide superconductorMetal coating covering superconducting filamentThe superconducting filaments are arranged at a predetermined pitch in a spiral shape in a direction different from the segment in the segment. The aspect ratio of the surface is 1.5 or moreA superconducting wire is provided. Here, an electrical insulating layer is preferably provided between each of the segments.
[0010]
  Furthermore, in the present invention,A method for producing a superconducting wire consisting of an assembly in which two or three of fan-shaped segments having a substantially semicircular cross section or a central angle of approximately 120 degrees are spirally assembled at a predetermined pitch in the longitudinal direction,A superconducting filament made of an oxide superconducting material is coated with a metal, and a predetermined pitch P is formed on a strand having a substantially circular cross section.₀And twisting the n twisted strands (n = 2, 3) at a predetermined pitch in a spiral manner, and then the twisted wire has a substantially circular cross section with a predetermined outer diameter. A method for producing a superconducting wire is provided, wherein the superconducting filament is reduced in diameter to a cross section having an aspect ratio of 1.5 or more. Here, the outer diameter of the wire is d₀, P is the twisted wire pitch before diameter reduction₁The outer diameter of the wire after the diameter reduction processing is d_SThen,
When n = 2, P₁/ D₀= 3-30, d_S<1.2d₀,
When n = 3, P₁/ D₀= 8-40, d_S<1.7d₀
And pitch P₀And pitch P₁The spiral direction of is opposite.
[0011]
In the present invention, the term “substantially circular in cross section” is a concept including not only a circular shape but also a symmetric N-gon (N is 6 or more).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
3, FIG. 6, FIG. 7, FIG. 8 and FIG. 10 show embodiments of the superconducting wire according to the present invention in cross-sectional views, taking an oxide superconducting wire as an example.
[0014]
The example shown in FIG. 3 has 55 oxide superconducting filaments 1 having an aspect ratio of 1.5 or more, and preferably 20 or less, a metal coating 2 covering the oxide superconducting filaments 1, and a substantially cross-sectional view. The oxide superconducting wire is composed of an assembly 9 in which two semicircular segments 8a and 8b are spirally assembled at a predetermined pitch in the longitudinal direction, and has a substantially circular outer shape in cross section. The oxide superconducting filaments 1 are arranged in a predetermined pitch in the segments 8a and 8b in a spiral shape opposite to the spiral direction of the segments.
[0015]
FIG. 6 is another example, including 55 oxide superconducting filaments 21 having an aspect ratio of 1.5 or more, preferably 20 or less, and a metal coating 22 covering the oxide superconducting filaments 21; The cross section is formed of an assembly 31 in which three segments 30a, 30b, 30c having a central angle of about 120 degrees are gathered at a predetermined pitch in the longitudinal direction, and the cross section has a substantially circular shape. Also in this example, as in FIG. 3, each oxide superconducting filament 21 is arranged in a predetermined pitch in each segment 30a, 30b, 30c in a spiral shape opposite to the direction of the spiral of the segment. ing.
[0016]
FIG. 7 shows still another example, in which the number of oxide superconducting filaments 21 included in each of the segments 32a, 32b, and 32c having a central angle of approximately 120 degrees in the cross-section is 19, and the segments 32a and 32b. , 32c are formed into an assembly 33 that spirally gathers at a predetermined pitch in the longitudinal direction, and an electrically insulating material (for example, BaZrO) is interposed between the segments 32a, 32b, 32c._Three, SrZrO_Three, MgO, MnO, etc.) is provided, whereby each segment is electrically insulated. In this example, each filament 21 has an aspect ratio of 1.5 or more, preferably 20 or less, and is arranged in a spiral shape in a direction opposite to the spiral of the segment in each segment 32a, 32b, 32c. .
[0017]
FIG. 8 shows still another example, in which the number of oxide superconducting filaments 41 included in each of the segments 34a, 34b, and 34c having a central angle of approximately 120 degrees in the cross section is 55, and these segments 34a and 34b. , 34c are formed into an assembly 47 that spirally gathers at a predetermined pitch in the longitudinal direction, and the surface of each filament 41 has an electrically insulating material (for example, BaZrO_Three, SrZrO_Three, MgO, MnO, etc.) is provided, whereby each filament is electrically insulated. Each filament 41 has an aspect ratio of 1.5 or more, preferably 20 or less, and is arranged in a spiral shape in the opposite direction to the spiral of the segment in each segment 34a, 34b, 34c.
[0018]
  FIG. 10 shows still another example, in which an oxide superconducting filament 51 having a metal core 53 disposed substantially in the center, a metal coating (filament coating) 54 covering 19 of the oxide superconducting filaments 51, and It is composed of an assembly 57 that is composed of another metal coating (segment coating) 55 covering the outside, and is a set of segments 36a, 36b, and 36c having a central angle of 120 degrees in the cross section in a spiral shape with a predetermined pitch in the longitudinal direction. The metal core 53 is smaller in hardness than the metal coatings 54 and 55, that is, a soft material.ButAnd the metal coating 54 is less hard than the metal coating 55, ie a soft materialButHas been chosen. Also in this example, each of the oxide superconducting filaments 51 including the metal core material 53 has an aspect ratio of 1.5 or more.20In the segments 36a, 36b, and 36c, they are arranged in a spiral shape opposite to the direction of the spiral of the segment.
[0019]
According to the oxide superconducting wire according to the above-described embodiment of the present invention, each superconducting filament is arranged at a predetermined pitch in a spiral in a direction different from the spiral of the segment in the segment. Variations in the external shape (the outermost diameter of the stranded wire and the stranded wire pitch) after wire processing are reduced, and defects such as wire breakage and kinks during diameter reduction processing can be reduced. As a result, the superconducting structure of the superconducting filament can be formed uniformly and with high density in the longitudinal direction of the superconducting wire.
[0020]
In addition, each superconducting filament is alternately arranged in the longitudinal direction on the inner layer side and the outer layer side of the wire, so that the superconducting filament's rolling force during diameter reduction processing in the wire manufacturing process and the accompanying superconducting filament densification The degree is equalized between each superconducting filament. Moreover, since the superconducting filament has a cross section with an aspect ratio of 1.5 or more formed in a plate shape or an ellipse shape, a superconducting wire having a substantially circular cross section is equivalent to a superconducting wire having a cross section in a tape shape. A critical current density can be achieved.
[0021]
In particular, in the example of FIG. 10, in the metal material constituting each segment, the hardness of the metal coating (segment coating) 55 is selected to be greater than the hardness of the metal core material 53 and the metal coating (filament coating) 54. Therefore, the unevenness at the interface of the superconducting filament is reduced and smoothed, contributing to the improvement of the critical current density Jc.
[0022]
  Next, in the present inventionSuperconducting wireAbout the manufacturing method ofThe embodimentexplain.
[0023]
FIG. 1 is a flowchart showing the steps of a manufacturing method according to the present invention, in which a single filament including a single oxide superconductor core is formed inside a metal coating, and a plurality of single filaments are placed in a metal tube. A process of forming a multi-core billet by incorporating a plurality of cores into a multi-core billet, and isostatically extruding it, and a process of reducing the diameter of the multi-core filament composite to create a strand having a substantially circular cross section And a step of twisting the strands at a predetermined pitch, a step of twisting two or three strands, and a step of further reducing the diameter of the strands.
[0024]
Hereinafter, each process will be described in detail by taking an oxide superconducting wire having a specified outer diameter ds and a specified stranded wire pitch Ps as an example.
[0025]
A. Single filament production
  First, a single filament composed of one oxide superconducting filament and metal coating is prepared. The substance which comprises a filament consists of a well-known oxide superconductor material, for example, Bi-2212, Bi-2223, Tl-1223, Tl-2223, Y-123, and Nb-123. On the other hand, the metal coating is not particularly limited, but is preferably a material that does not deteriorate the superconducting properties by reacting with the core oxide superconducting material. For example, Bi-2212 and Bi-2223 oxide superconducting materials Is silver or silver alloy (AgIt is preferable that at least one selected from Au, Pd, Ti, Mg, Ni, Sb, Al, and Mn is added as a main component. As an example of this step, the superconducting material is filled with a powder that has not been subjected to superconducting heat treatment or powder that has been pulverized after sintering (hereinafter referred to as precursor powder) into a predetermined length of metal tube, and then reduced in diameter. Thus, a single filament having a substantially circular cross section is produced. Here, the outermost layer of the single filament is provided with a metal coating (filament coating). Further, a metal core material may be arranged at the center of the single filament. In this case, it is preferable to select a metal core material that is softer than the filament coating, that is, a soft material. Thereby, the deformation | transformation of the filament in the below-mentioned process L occurs smoothly. Furthermore, when importance is attached to the AC loss reduction effect, a material such as a metal or an oxide that does not become a good conductor by the superconducting heat treatment described later is applied to the surface of the filament coating in a paste form with a thickness of 200 μm or less. May be.
[0026]
B. Fabrication of multifilament composites
  Plural single filaments obtained in step A, another metal tube of a predetermined lengthIncorporatedMake multi-core billet. The material of the metal tube is not particularly limited, but preferably silver or a silver alloy (AgAnd the hardness of the material is the same as that of the material that constitutes the filament coating. In addition, at least one selected from Au, Pd, Ti, Mg, Ni, Sb, Al, and Mn is added. Or, more preferably, it is greater than the hardness of the material comprising the metal core and filament coating. When forming a multi-core billet, a metal core material made of the same material as the metal coating and not including a superconducting material may be further arranged at the center. This multi-core billet is formed into a multi-core filament composite having a substantially circular cross section by hydrostatic extrusion. As a result, the metal tube becomes a metal coating that constitutes the outermost layer of the multifilament filament composite, and becomes a metal coating (segment coating) when segmented through the stranded wire processing and the stranded wire diameter reduction processing in the subsequent process. .
[0027]
C. Diameter reduction processing
Next, the multicore filament composite of step B is extruded, surface-reduced by a swager or wire drawing, and a strand having a multicore filament having a substantially circular cross section is produced. Here, when importance is attached to the AC loss reduction effect, a material that is a metal or an oxide and does not become a good conductor by the superconducting heat treatment described later is applied to the surface of the element wire in a predetermined thickness, for example, in a paste form. It may be applied. This layer is for cutting off the electrical connection between the segments when the wire is formed. The material applied here is preferably a material whose lubricity is improved by application, but is not limited thereto. For convenience of explanation in the following steps, the outer diameter of the obtained wire is d₀, Length L₀And
[0028]
D. Wire twisting and twisting
Twisting the strands obtained in Step C (P₀Then, as shown in FIG. 4, two or three of the twisted strands are placed at a predetermined pitch P in a direction opposite to the twisting direction of the strands.₁Twist in a spiral. In the figure, 61 is a strand, and 62a, 62b, and 62c are strand bobbins that revolve around the traveling direction of the stranded wire 46 as an axis. In addition, you may twist after performing any one of a wire drawing or predetermined heat processing immediately after a twist process.
[0029]
  Also, as shown in FIG.AspectAs for wire bobbin 63a, 63b, 63c, the sending direction of strand 61 is changed.On the axisIt is also possible to twist the element bobbin in the opposite direction to the twisting process by rotating the element bobbin around the axis of the traveling direction of the twisted wire 46 while twisting the element wire by rotating.
[0030]
The twisting pitch of the strands is P when there are two strands.₁/ D₀= 1.5-30, if there are 3 strands, P₁/ D₀= 4 to 40 is satisfied. In order to maintain the shape with ordinary stranded wire, P₁/ D₀The upper limit of can be up to about 100. However, in the present invention, since the stranded wire undergoes the following diameter reduction processing, P₁/ D₀If it is large up to about 100, the strands are scattered during the diameter reduction processing, and the processing becomes difficult. Therefore, as an upper limit that can reduce the diameter of the stranded wire, P₁/ D₀Is selected when there are two strands and 40 when there are three strands. On the other hand, P₁/ D₀If the wire is too small, the strands are subjected to excessive processing strain during stranded wire processing, and the filament structure in the metal coating may be disturbed or broken, which may lead to deterioration of superconducting properties in the finally obtained superconducting wire. There is. However, it has been found that the twisting of the strands prior to the stranding can prevent the filament structure from being disturbed or broken considerably. As a result of experiments by the inventors, P does not cause a problem by twisting wire processing.₁/ D₀It has been found that the lower limit can be expanded to 1.5 when there are two strands and to 4 when there are three strands.
[0031]
2 and 9 show a state after twisted wire processing, FIG. 2 shows two examples, FIG. 9 shows three examples, and 6, 56 are stranded wires. As shown in the figure, the outer diameter after twisted wire processing is d₁Then d₁Is uniquely determined geometrically, and in the case of two (FIG. 2), d₁= 2d₀In the case of three (FIG. 9), d₁= 2.31d₀It is. Also, the twist pitch of the strands (ie, the helical pitch of the filament) P₀And strand twist pitch P₁The rotation direction may be so-called S winding or Z winding, but both are selected to be in opposite directions.
[0032]
Thus, the twisted pitch of the wire and P₀And strand twist pitch P₁If the rotation direction of the wire is selected in the opposite direction, the outer shape after twisting (the outermost diameter d of the twisted wire)₁And twisted wire pitch P₁) Can be reduced, and defects such as wire breakage and kinks in the next diameter reduction processing can be reduced. This mechanism is considered as follows. That is, after twisting of the strands, shear residual stress is distributed to the coated metal and each superconducting filament inside. Then, in the subsequent twisting process, the process is performed under such stress that the residual stress component is released. As a result, the next diameter reduction can be stably performed without increasing the mechanical potential energy of the material.
[0033]
E. Diameter reduction processing
The stranded wire obtained in step D is subjected to diameter reduction processing by a known means such as a wire drawing device using a die or a swager. The diameter reduction process may be repeated once or a plurality of times, but it is preferable to select the die diameter so that the reduction rate of the outer diameter by one diameter reduction process is 2 to 20%. When the diameter reduction process is repeated a plurality of times, an intermediate heat treatment for annealing or superconductivity or a degassing process of the precursor powder structure may be performed during the diameter reduction process. When the intermediate heat treatment is performed, it is preferable that the reduction rate of the outer diameter by one pass is 2 to 5% after that.
[0034]
When the outer diameter of the composite wire obtained by the diameter reduction processing is d, when there are two strands, d <1.3d₀D <1.8d for 3 wires₀Is reached, a wire rod having an outer diameter formed into a substantially circular shape is obtained. At this time, two or three strands are crushed by the diameter reduction process, and the cross section is transformed into a fan shape having a semicircular or central angle of approximately 120 degrees, and a fan shape having a substantially semicircular or central angle of approximately 120 degrees. An assembly is formed in which the segments are spirally assembled at a predetermined pitch in the longitudinal direction. Further, since each superconducting filament is arranged in a spiral in the opposite direction at a predetermined pitch in each segment, as a result, each superconducting filament is assembled in a secondary spiral.
[0035]
On the other hand, the cross-sectional shape of the superconducting filament in the metal coating is deformed into a plate shape or an ellipse shape having a high aspect ratio (preferably 1.5 or more). This is because the adjacent strands of two or three stranded wires and the stranded wire outer diameter d are reduced by the surface-reducing process in this step.₁This is because part of the wire material deforms malleably in the circumferential direction so as to fill the gap formed on the inner surface of the cylinder.
[0036]
By the way, at the time of diameter reduction processing, a lubricant such as synthetic oil, petroleum, molybdenum, molybdenum disulfide, or the like is usually used. This lubricant penetrates into the gaps between the segments and becomes a residue. Usually, a cleaning operation such as a wiping operation is performed after the diameter reduction processing in order to remove the lubricating oil, but in the method of manufacturing a superconducting wire according to the embodiment of the present invention, only when importance is attached to the AC loss reduction effect, It is preferable to leave this residual lubricant. This is because the residual lubricant is changed so as to form an electrically insulating layer between the segments by selecting a suitable material and performing a superconducting heat treatment described later. Therefore, it is preferable to use abundant lubricant during the diameter reduction process, and then do not dare to perform a cleaning operation for the purpose of removing the lubricant between the segments.
[0037]
Now, the porosity v immediately after the stranded wire is defined as the stranded wire outer diameter d.₁Is defined as a ratio of voids (volume not occupied by the strands) in a cylindrical space equal to, and calculation is performed for two strands and three strands.₁/ D₀= 3 to 30 and v = 0.44 to 0.55.₁/ D₀In the range of = 8 to 40, v = 0.38 to 0.43. When this porosity becomes approximately 0%, an aggregate of segments without voids is formed.
[0038]
In general, the stranded wire pitch of the workpiece becomes longer each time the diameter is reduced. Also in this repeated diameter reduction processing, if the ratio P / d of the twisted wire pitch P and the outer diameter d before processing is too large, the strands are scattered during the diameter reduction processing, and processing becomes difficult. The limit value is P₂In terms of / d, P / d <P₂/ D, and according to the inventor's experiment, preferably P in the case of two strands.₂/ D = 20-30, P for 3 wires₂/ D = 30-60.
[0039]
When the aggregate is substantially circular in cross section, the outer diameter d and the twist pitch P are numerically expressed by the following expression before and after the diameter reduction processing.
[0040]
P ・ d²= Constant (1)
If the diameter reduction processing is controlled based on the relational expression (1), aggregates corresponding to different specification outer diameters ds and stranded wire pitch Ps can be obtained.
[0041]
On the other hand, regarding the total length of the aggregate after the diameter reduction processing, the length L₀, Outer diameter d₀When the strands are twisted and then subjected to diameter reduction processing, when the yield is ignored, the outer diameter of the assembly is ds and the length is n × Lmax. However, nL₀d₀ ²= Lmaxds²It is.
[0042]
F. Twist processing during diameter reduction
In the diameter reduction processing in step E, the outer diameter d and the twisted wire pitch P are P / d> P₂/ D, that is, when it is difficult to repeatedly reduce the diameter or when the predetermined pitch Ps is to be adjusted to be shorter by a method other than the diameter reduction, twisting is applied to the stranded wire during the diameter reduction. , P / d can be reduced. This processing is usually performed by rotating (twisting) the twisted wire in a tightening direction.
[0043]
Pitch P of twisted wire before twist processing₂, P is the pitch after twisting_ThreeIf the outer diameter of the twisted wire during twisting is d, the number of rotations dn per unit length required for twisting is given by the following equation.
[0044]
dn = 1 / P_Three-1 / P₂      (2)
Prior to this twisting process, the metal coating may be annealed to facilitate the twisting.
[0045]
In twist processing, if the degree of processing is too large, the structure of the superconducting filament may be disturbed or broken. In order to prevent this, the degree of processing is limited. According to the inventor's experiment, in the case of two strands, P_Three/ D> 3 and P for 3_Three/ D> 5.
[0046]
G. Superconducting heat treatment
The superconducting heat treatment is a treatment necessary for expressing the superconducting properties of the superconducting filament. The conditions of this heat treatment generally depend on the type of superconducting material, but are slightly affected by the thickness (cross-sectional area) of the superconducting filament, the aspect ratio, and the composition of the metal coating matrix. As shown in FIG. 4, FIG. 6, and FIG. 8, in the oxide superconducting wire of the present invention, the superconducting filament itself is shaped like a plate or an ellipse in the same manner as the superconducting filament of the conventional wire (for example, FIG. 12). Therefore, it is only necessary to perform heat treatment substantially the same as the optimum heat treatment conditions for the conventional wire. Here, the optimum heat treatment condition is a condition in which the critical current density can be maximized and the wire does not swell due to the heat treatment.
[0048]
【Example】
Examples of the present invention will be described in detail below.
[0049]
[Example 1]
Bi as composition₂Sr₁Ca₂Cu₂Bi so that Ox (hereinafter referred to as Bi-2212) is obtained.₂O_Three, SrCO_Three, Ca₂CO_Three, CuO powders were mixed and subjected to heat treatment at 820 ° C. for 20 hours in the air, and then pulverized to prepare Bi-2212 phase precursor powders. Precursor powder was filled in a silver alloy pipe having an outer diameter of 15 mm, an inner diameter of 13.5 mm, and a length of 500 mm. This powder and silver alloy composite was drawn to a hexagonal bar shape with an opposite side dimension of 7.64 mm to obtain a material A.
[0050]
55 pieces of this material A were incorporated into a silver alloy pipe having an outer diameter of 71.1 mm, an inner diameter of 64 mm, and a length of 500 mm, and a silver alloy-coated oxide billet X (outer diameter of 71.1 mm, length of 500 mm, volume Vx = 2 × 10⁶mm^Three) The billet X is subjected to extrusion, swager, and wire drawing, and the outer diameter d₀= 1.7 mm round wire (material B) of silver alloy-coated oxide was obtained. Since the material B is produced with a yield of about 80% of the volume Vx of the oxide billet X, the volume is Vx._B= 0.8Vx. Therefore, the length of material B is L₀= Vx_B/ (Πd₀ ²/ 4) ≈700,000 mm = 700 m. Moreover, the occupation rate of the silver alloy which is the coating | covering material of the raw material B was 66%. Two rods having a length of about 700 m were prepared (material B). This strand is twisted in the Z direction so that the surface pitch is P₀= 7.5 mm.
[0051]
Using a 2-rod twisted strand, as shown in FIG.₀= 3.4mm, bundle 2 bundles, apply twisted wire in S direction and pitch P₁= 15 mm stranded wire was prepared. The volume of the stranded wire is 2Vx_BIt is.
[0052]
When the above-described stranded wire is drawn, the two round strands are gradually crushed, and when the outermost diameter is reduced to about half ds = 1.6 mm, as shown in FIG. A round molded assembly (material C) in which two semicircular segments were joined together was obtained. Since this molded assembly is reduced in diameter while maintaining the volume substantially, the single length Ls of the wire at the outer diameter ds is Ls = 2Vx._BB/ (Πds²/4)=1.6×10⁶mm = 1580 m. As shown in FIG. 3, it can be seen that the cross section of the superconducting filament of the material C is mostly a plate shape or an elliptical shape with an aspect ratio of about 1.5 to 20. In addition, the silver alloy occupation ratio of the material C was slightly larger than that of the strand (material B) and was 68%.
[0053]
Material C is a segment twisted wire in which superconducting filaments are coated with a silver alloy, and in each segment, superconducting filaments are arranged in a spiral shape in a direction opposite to the spiral direction of the segments. It is.
[0054]
The helical pitch of the filaments in the segment is the primary pitch Ps₁, Ps is the spiral pitch of the segmented stranded wire₂Then, since both pitches are elongated by diameter reduction processing, Ps₁= Ls / L₀× P₀= 17mm, Ps₂= Ls / L₀× P₁= 34 mm. The position of each superconducting filament in the segment cross-section changes so as to be periodically switched between the inner layer portion and the outer layer portion depending on the location in the longitudinal direction of the stranded wire.
[0055]
At the time of diameter reduction processing of the stranded wire, the degree of processing deformation differs between the outer layer portion and the inner layer portion in the cross section, and the degree of processing increases as the outer layer portion is reached. In this example, since the superconducting filaments periodically extend in the longitudinal direction through the inner layer portion and the outer layer portion, it can be considered that the deformation due to the diameter reduction processing occurs uniformly throughout the filament longitudinal direction.
[0056]
Material C was held at 880 ° C. for 10 minutes in the atmosphere at 1 atm, gradually cooled to 830 ° C. at a cooling rate of 5 ° C./hour, and further cooled for 1 hour. By this heat treatment, the material C was changed to a superconducting wire having superconducting properties. A part of this superconducting wire was cut to a length of about 50 mm to obtain a sample C. Sample C was measured in a liquid helium, external magnetic field of 10T, and the critical current density Jc was defined as 1 μV / cm. As a result, Jc = 2500A / mm for the superconducting filament.², Critical current density divided by wire cross-sectional area overall-Jc = 800 A / mm²Met.
[0057]
On the other hand, for comparison, the material B was rolled as it was to obtain a tape-shaped composite material. The composite material was subjected to the same superconducting heat treatment as described above to obtain a tape-shaped superconducting wire. A part thereof was cut out and used as a comparative material. As in the case of Sample C, the critical current density Jc was measured with the definition of 1 μV / cm in liquid helium and an external magnetic field of 10 T in the same manner as Sample C. As a result, Jc = 1600 A / mm for the superconducting filament², Critical current density divided by wire cross-sectional area overall-Jc = 600 A / mm²Met.
[0058]
As is apparent from Sample C and the comparative material, it was found that the round superconducting wire of Sample C according to the present invention has a significantly improved Jc in a magnetic field as compared with the conventional tape-shaped superconducting wire.
[0059]
[Example 2]
Round strand produced in Example 1 Round strand (material B, single length L₀= 705m, outer diameter 1.7mm), pitch P₀= 7.5 mm, twisting in the S direction is performed, and the three are bundled to form a pitch P as shown in FIG.₁= 36 mm and twisted in the Z direction. The outermost diameter d of the stranded wire₁Is about 2.3d₀= 3.39mm, volume is 3Vx_BIt is.
[0060]
When the above-described stranded wire is drawn, the three round strands are gradually crushed, and when the outermost diameter is reduced to ds = 2.4 mm, as shown in FIG. A round molded assembly (material E) in which fan-shaped segments having a central angle of approximately 120 degrees were combined with each other. Since this molded assembly is reduced in diameter while maintaining the volume substantially, the single wire length Ls at the outer diameter ds is Ls = 3Vx._BB/ (Πds²/4)=1.0×10⁶mm = 1000 m. As shown in FIG. 6, it can be seen that the cross section of the superconducting filament of the material E is mostly a plate shape or an elliptic shape with an aspect ratio of 2 to 20.
[0061]
The material E is a segment stranded wire in which superconducting filaments are coated with a silver alloy, as in Example 1, and the superconducting filaments are arranged in a spiral shape in the opposite direction to the spiral direction of the segments in each segment. The secondary spiral arrangement structure.
[0062]
The helical pitch (primary pitch) of the filaments in the segment is Ps₁= Ls / L₀× P₀= 10.6 mm, pitch of the spiral of the segment stranded wire (secondary pitch) Ps₂= Ls / L₀× P₁= 51 mm. In the same manner as in Example 1, the position of each superconducting filament in the segment cross-section changes so as to be periodically switched between the inner layer portion and the outer layer portion depending on the location in the longitudinal direction of the stranded wire.
[0063]
The material E was subjected to superconducting heat treatment to obtain a superconducting wire. A part of this superconducting wire was cut into a length of about 50 mm to obtain a sample M. The critical current density overall-Jc obtained by dividing the sample M by the wire cross-sectional area by the same measurement method as in Example 1 was measured. As a result, overall-Jc = 700 A / mm²It was a value exceeding that of the tape-shaped wire.
[0064]
[Example 3]
Round element wire (material B, single length L) produced in Example 1₀= 705m, outer diameter 1.7mm) pitch P₀A twist process in the Z direction was applied at 7.5 mm, and a paste containing molybdenum disulfide powder was applied to the surface to a thickness of about 30 μm. The purpose of forming the layer containing molybdenum disulfide by coating is firstly to ensure lubricity during subsequent diameter reduction processing, and secondly, an electrically insulating layer between the strands. This is for providing a (thin film).
[0065]
Bundling three such wires, as shown in FIG.₁= 36 mm and twisted in the S direction. The outermost diameter d of the stranded wire₁Is about 2.3d₀= 3.39mm, volume is 3Vx_BIt is.
[0066]
When the stranded wire is drawn, the three round strands are gradually crushed, and when the outermost diameter is reduced to ds = 2.4 mm, as shown in FIG. Sector-shaped segments having a central angle of approximately 120 degrees were combined with each other, and a round molded assembly (material F) in which a barrier layer mainly composed of molybdenum disulfide was interposed between the segments. The segments are electrically insulated from each other by this barrier layer.
[0067]
As described above, conventionally, after sufficiently removing the lubricant, the next superconducting heat treatment is performed. However, in this example, the superconducting heat treatment was performed while leaving molybdenum disulfide remaining. By this heat treatment, molybdenum disulfide is changed to molybdenum oxide, and the function as an electrically insulating layer, that is, a barrier layer is guaranteed.
[0068]
The material F was subjected to superconducting heat treatment to obtain a superconducting wire. A part of this superconducting wire was cut to a length of about 50 mm to obtain a sample F. The critical current density overall-Jc obtained by dividing the sample F by the wire cross-sectional area by the same measurement method as in Example 1 was measured. As a result, overall-Jc = 700 A / mm²It was a value exceeding that of the tape-shaped wire. It was also confirmed that the superconducting properties were equivalent to those of sample E having no barrier layer.
[0069]
In this example, a barrier layer is provided to reduce the AC loss, but in order to confirm the effect, the AC loss characteristics of the sample E prepared in Example 2, the conventional tape-shaped wire, and the sample F are compared. did. The evaluation was performed by a method in which each sample was placed in a zero magnetic field in liquid nitrogen and the AC current loss was measured. An effective current that is half of the DC critical current value was applied to the sample at an alternating current of 50 Hz, and the loss voltage at that time was measured. As a result, the voltage tap was 100 mm, the conventional tape-shaped wire was 10 μV, the sample E was 1 μV, and the sample F was 0.3 μV. In Sample E and Sample F, the superconducting filaments are arranged in an equivalent inductance, so that the AC loss is smaller than that of the tape-shaped wire. It is thought that the loss was reduced.
[0070]
[Example4]
  Bi as composition_1.8Pb_0.34Sr_1.9Ca_2.2Cu_3.1O_xA precursor powder (hereinafter referred to as Bi-2223) was prepared. Precursor powder was filled in a silver alloy pipe having an outer diameter of 15 mm, an inner diameter of 13.5 mm, and a length of 500 mm. This powder and silver alloy composite was drawn to a hexagonal bar shape with an opposite side dimension of 7.64 mm to obtain a material N.
[0071]
After applying paste-form molybdenum to the surface of this material N to form a coating film, 55 of them were incorporated into a silver alloy pipe having an outer diameter of 71.1 mm, an inner diameter of 64 mm and a length of 500 mm, and a silver alloy-coated oxide billet Y was obtained. The billet Y is subjected to extrusion, swager, and wire drawing, and the outer diameter d₀= 1.4 mm silver alloy coated oxide round wire (material P), and 333 rotations per length (pitch P)₀= 3 mm) was twisted in the S direction. Three twisted materials are prepared and the outermost diameter is about 2.3d.₀= 3.2mm, 3 bundles, Z direction twisted wire processing, pitch P₁= 12 mm stranded wire was prepared.
[0072]
When the stranded wire is subjected to wire drawing, the three round strands are gradually crushed. In this example, the wire drawing path starts from an outer diameter of 3.2 mm, and is successively drawn to 2.8 mm, 2.6 mm, and 2.45 mm, and the outer diameter is 2.45 mm. An intermediate heat treatment was applied. The heat treatment conditions were 1 atm and 840 ° C. in air for 50 hours. This first intermediate heat treatment is for superconducting the precursor structure of the filament into the Bi-2223 phase. By this heat treatment, the molybdenum coating film changes to an electrically insulating layer of molybdenum oxide and functions as a barrier layer between the filaments.
[0073]
Next, after the reduction rate of the outermost diameter d in one pass was set to 4% and the outermost diameter was set to 2.35 mm through wire drawing, the second intermediate heat treatment was performed. The heat treatment conditions were 1 atm and 845 ° C. in air for 50 hours. Thereafter, it was subjected to wire drawing to form a molded assembly (material Q) having an outermost diameter of 2.3 mm. This material Q is a three-stranded round molded assembly having a porosity of approximately 0%, and has an outermost diameter of 2.3 mm and a single length of 1100 m. Spiral pitch (primary pitch) Ps of superconducting filament in the segment₁= Ls / L₀× P₀= 1100/1000 × 3 = 3.3 mm, the pitch of the spiral of the segment (secondary pitch) Ps₂= Ls / L₀× P₁= 1100/1000 × 12 = 13.2 mm.
[0074]
Subsequently, the material Q was subjected to the final superconducting heat treatment for generating the oxide Bi-2223 phase, to obtain a round superconducting wire.
[0075]
On the other hand, as a comparative material, using a wire (material P), a rolling process, an intermediate heat treatment, a rerolling process, a second intermediate heat treatment, and a re-rolling process are performed, and a tape-shaped material (material) having a thickness of 0.2 mm R) and then the last superconducting heat treatment was performed to obtain a tape-shaped superconducting wire. Here, the intermediate heat treatment and the final heat treatment of the materials Q and R were both performed in the same batch. A part of both wires was cut to a length of about 200 mm, and used as sample Q and comparative material R, respectively. The critical current density overall-Jc divided by the cross-sectional area of the wire was measured in the definition of 1 μV / cm in liquid nitrogen without an external magnetic field. With sample Q, overall-Jc = 100 A / mm²In comparison material R, overall-Jc = 120 A / mm²Met. The Jc characteristic was slightly lower than that of a tape-shaped wire that did not contain an oxide barrier layer.
[0076]
[Example5]
  Bi so that Bi-2212 is obtained as a composition.₂O₃, SrCO₃, Ca₂Co₃, CuO powders were mixed and subjected to heat treatment at 820 ° C. for 20 hours in the air, and then pulverized to prepare Bi-2212 phase precursor powders. A pure silver pipe having an outer diameter of 15 mm, an inner diameter of 14 mm, and a length of 500 mm and a pure silver round bar with an outer diameter of 3 mm were prepared. Centering on a sterling silver round barPure silverThe pipe was filled with precursor powder. With this powderSterling silverThe composite was drawn into a round bar having an outer diameter of 12.3 mm, and a material S was obtained.
[0077]
19 pieces of this material S were incorporated into a silver alloy pipe (alloy composition: Ag-0.05 wt% Mg-0.05 wt% Ni) having an outer diameter of 71.1 mm, an inner diameter of 64 mm, and a length of 500 mm, and a silver alloy-coated oxide. Billet Z was obtained. The billet Z is subjected to extrusion, swager, and wire drawing, and the outer diameter d₀= 1.7 mm round element wire (material T) of silver alloy-coated oxide was obtained. Prepare 3 materials T and pitch P₀= Twisted in the S direction of 3 mm.
[0078]
Using the three twisted rods, as shown in FIG.₁Is about 2.3d₀= 3.2mm, 3 bundles, Z direction twisted wire processing, pitch P₁= 12 mm stranded wire was prepared.
[0079]
When the above-described stranded wire is drawn, the three round strands are gradually crushed, and when the outermost diameter is reduced to ds = 2.4 mm, as shown in FIG. A round molded assembly (material U) in which fan-shaped segments having a central angle of approximately 120 degrees were combined with each other. As shown in FIG. 10, it can be seen that the cross section of the superconducting filament of the material U is mostly a plate shape or an elliptical shape with an aspect ratio of about 2 to 20 together with a pure silver metal core disposed at the center. . The filament path has a secondary spiral shape extending in a spiral direction within the segment in a direction opposite to the twisting direction of the segment.
[0080]
This material U was subjected to superconducting heat treatment to obtain a superconducting wire. A part of this superconducting wire was cut to obtain a sample U. The critical current density overall-Jc obtained by dividing the sample U by the wire cross-sectional area by the same measurement method as in Example 1 was measured. As a result, overall-Jc = 1000 A / mm²Met.
[0081]
In this embodiment, pure silver is used for the metal core and filament coating disposed in the center of each filament, and a silver alloy (alloy composition: Ag-0.05 wt% Mg-0.05 wt% Ni) is used for the segment coating. Has been. For this reason, the segment coating becomes an oxide-dispersed silver alloy through a superconducting heat treatment, and is a material having a higher yield stress and Vickers hardness than the filament coating and the metal core used inside thereof. Therefore, the deformation behavior from the circular cross section of the filament, which occurs simultaneously with the diameter reduction processing, to the rectangle or the ellipse is stabilized, the variation in the longitudinal direction of the wire is suppressed, and the superconducting characteristics are improved.
[0082]
The superconducting wire of the present invention may be used as a conductor itself or as a plurality of aggregated conductors, or may be configured to be combined with other members. Examples of such applications include superconducting devices such as magnets, coils, cables, bus bars, current leads, magnetic shields, and permanent current switches. Furthermore, when used as the above application, the production method may be either the React & Wind method or the Wind & React method.
[0083]
In addition, in a superconducting wire having a barrier layer between segments, it can be used as a three-phase power cable as it is.
[0084]
【The invention's effect】
As described above, according to the present invention, since the superconducting filaments are spirally arranged in the segment in the direction opposite to the twisting direction of the segments, the superconducting structure of the superconducting filaments is uniform and highly dense in the longitudinal direction of the wire. Can be formed in degrees. As a result, even in a superconducting wire having a substantially circular cross section, there is an effect that a superconducting wire capable of achieving a critical current density equivalent to that of a tape-shaped superconducting wire can be stably obtained with a high yield, and its industrial significance is Very big.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a method for producing a superconducting wire according to the present invention.
FIG. 2 is an explanatory view showing a state after twisted wire processing in the manufacturing process of the superconducting wire according to the present invention.
3 is a cross-sectional view showing an example of a superconducting wire obtained from the stranded wire in FIG. 2. FIG.
FIG. 4 is an explanatory view showing an example of a stranded wire method.
FIG. 5 is an explanatory view showing another example of a stranded wire method.
FIG. 6 is a cross-sectional view showing another example of the superconducting wire according to the present invention.
FIG. 7 is a transverse sectional view showing still another example of the superconducting wire according to the present invention.
FIG. 8 is a transverse sectional view showing still another example of the superconducting wire according to the present invention.
FIG. 9 is an explanatory view showing another state after the stranded wire processing in the manufacturing process of the superconducting wire according to the present invention.
10 is a transverse sectional view showing still another example of a superconducting wire obtained from the stranded wire in FIG. 9. FIG.
FIG. 11 is a flowchart showing a conventional method of manufacturing a superconducting wire.
FIG. 12 is a cross-sectional view showing an example of a conventional superconducting wire.
FIG. 13 is a cross-sectional view showing another example of a conventional superconducting wire.
[Explanation of symbols]
1, 21, 41, 51 Superconductor filament
2,22,42,54 Metal coating
6,56 stranded wire
8a, 8b, 30a, 30b, 30c, 32a, 32b, 32c, 34a, 34b, 34c, 36a, 36b, 36c segment
9, 31, 33, 47, 57 aggregate
53 Metal core
44 Barrier layer

Claims

A superconducting wire cross section has a substantially circular outer shape, the superconducting wire, given two or three fan-shaped segment which is a cross section substantially semicircular or central angle of approximately 120 degrees in the longitudinal direction The segments are spirally assembled at a pitch of, and the segment is formed by spirally twisting strands having a substantially circular cross section made of a superconducting filament made of an oxide superconducting material and a metal coating covering the superconducting filament. The superconducting filaments are arranged at a predetermined pitch in a spiral shape in a direction different from the segment in the segment, and the aspect ratio of the cross section is 1.5 or more. wire.

The superconducting wire according to claim 1, wherein an electrically insulating layer is provided between each of the segments.

The segment includes a metal core disposed in the center of the superconducting filament, a metal coating covering the periphery of the filament, and an outermost metal coating, and the hardness of the metal coating covering the metal core and the filament is the outermost layer. 2. The superconducting wire according to claim 1, wherein the superconducting wire is smaller than the hardness of the metal coating.

A method for producing a superconducting wire consisting of an assembly in which two or three of fan-shaped segments having a substantially semicircular cross section or a central angle of approximately 120 degrees are spirally assembled at a predetermined pitch in the longitudinal direction, A superconducting filament made of an oxide superconducting material is coated with a metal, and a strand having a substantially circular cross section is twisted at a predetermined pitch P ₀ , and n twisted strands (n = 2, 3) are applied. Twist spirally at a predetermined pitch, and then reduce the diameter of the stranded wire into a wire having a predetermined outer diameter and a substantially circular cross section so that the superconducting filament has a cross section with an aspect ratio of 1.5 or more. A method of manufacturing a superconducting wire characterized by the above. Here, if the outer diameter of the wire is d ₀ , the twisted wire pitch before the diameter reduction processing is P ₁ , and the outer diameter of the wire after the diameter reduction processing is d _S ,
In the case of n = 2, P ₁ / d ₀ = 3 to 30, d _S <1.2 d ₀ ,
When n = 3, P ₁ / d ₀ = 8 to 40, d _S <1.7 d ₀
And the spiral directions of pitch P ₀ and pitch P ₁ are opposite.

A method for producing a superconducting wire consisting of an assembly in which two or three of fan-shaped segments having a substantially semicircular cross section or a central angle of approximately 120 degrees are spirally assembled at a predetermined pitch in the longitudinal direction, A superconducting filament made of an oxide superconducting material is coated with a metal, and a strand having a substantially circular cross section is twisted at a predetermined pitch P ₀ , and then one of a wire drawing step and a heat treatment step is performed. After that, n strands (n = 2, 3) of the strands are spirally twisted at a predetermined pitch, and then the twisted wire is reduced to a wire having a predetermined outer diameter and a substantially circular cross section. A method for producing a superconducting wire, characterized in that the superconducting filament has a cross section with an aspect ratio of 1.5 or more. Here, if the outer diameter of the wire is d ₀ , the twisted wire pitch before the diameter reduction processing is P ₁ , and the outer diameter of the wire after the diameter reduction processing is d _S ,
For _{_{n = 2, P 1 / d}} 0 = 1.5~30, d S <1.3d 0,
For _{_{n = 3, P 1 / d}} 0 = 4~40, d S <1.8d 0
And the spiral directions of pitch P ₀ and pitch P ₁ are opposite.

A method for producing a superconducting wire consisting of an assembly in which two or three of fan-shaped segments having a substantially semicircular cross section or a central angle of approximately 120 degrees are spirally assembled at a predetermined pitch in the longitudinal direction, A superconducting filament made of an oxide superconducting material is coated with a metal, and a strand having a substantially circular cross section is twisted at a predetermined pitch P ₀ , and then n strands (n = 2, 3) are applied to each strand. Twisting spirally at a predetermined pitch while interposing a lubricant layer between the strands, and then reducing the diameter of the stranded wire into a wire having a predetermined outer diameter and having a substantially circular cross section, thereby forming the aspect of the superconducting filament. A method for producing a superconducting wire, characterized in that the cross section has a ratio of 1.5 or more. Here, if the outer diameter of the wire is d ₀ , the twisted wire pitch before the diameter reduction processing is P ₁ , and the outer diameter of the wire after the diameter reduction processing is d _S ,
For _{_{n = 2, P 1 / d}} 0 = 1.5~30, d S <1.3d 0,
For _{_{n = 3, P 1 / d}} 0 = 4~40, d S <1.8d 0
And the spiral directions of pitch P ₀ and pitch P ₁ are opposite.

7. The method of manufacturing a superconducting wire according to claim 6, wherein the lubricant layer is made of a material that exhibits electrical insulation by superconducting heat treatment.

The method for producing a superconducting wire according to any one of claims 4, 5 and 6, wherein the diameter reduction processing comprises a plurality of times of diameter reduction processing and intermediate heat treatment.