JP3835757B2

JP3835757B2 - Plasma facing material and manufacturing method thereof

Info

Publication number: JP3835757B2
Application number: JP2003070593A
Authority: JP
Inventors: 朋広瀧田; 則彦長谷川
Original assignee: ALMT Corp
Current assignee: ALMT Corp
Priority date: 2003-03-14
Filing date: 2003-03-14
Publication date: 2006-10-18
Anticipated expiration: 2023-03-14
Also published as: JP2004279194A

Description

【０００１】
【発明の属する技術分野】
本発明は、プラズマ対向材料、照射環境下での構造材料に関し、特に、核融合炉等の超高温プラズマ中で用いられる材料に関する。
【０００２】
【従来の技術】
従来、プラズマ対向材料としてＣ／Ｃ複合材やベリリウムなどの低Ｚ材料が使用されていた（例えば、特許文献１、参照）。
【０００３】
しかしながら、これらの低Ｚ材料、とくに炭素材料では熱負荷による壁材の蒸発や損耗が激しいことや中性子照射による熱伝導率の低下が大きいこと、トリチウム吸蔵が高い等の問題があった。
【０００４】
モリブデン（Ｍｏ）やタングステン（Ｗ）などの高Ｚ材料、とくにタングステンは高融点、耐照射損耗性、低蒸気圧、低熱膨張係数，低トリチウム吸蔵性、液体金属との共存性をはじめ多くの優れた特性を有することから、核融合炉の高熱流速機器や核破砕中性子源用固体ターゲット、照射環境下での構造材料として注目・検討されている。
【０００５】
また、特許文献２では、材料からのガス放出量が少なく、プラズマ照射損傷が小さいプラズマ対向材料として、化学気相析出法（ＣＶＤ）によって形成されたタングステンが提案されている。
【０００６】
【特許文献１】
特開平１０−２５１７３号公報
【０００７】
【特許文献２】
特開平７―２２８９７６号公報
【０００８】
【発明が解決しようとする課題】
しかしながら、タングステンは靭性に乏しく、とくに熱負荷を受けると再結晶・粒成長を起こして容易に脆化するという間題がある。たとえば、靭性（延性）の指標のひとつである延性脆性遷移温度（ＤＢＴＴ）は、再結晶した純Ｗ板材の場合は３００〜５００℃で、室温では延性を示さない。
【０００９】
特許文献２において提案されているＣＶＤ−タングステンのＤＢＴＴは大凡５００〜１０００℃で再結晶した純Ｗ板材よりもさらに高く極めて脆い。強度の必要な場所での使用や取扱いが難しく、靭性の改善が今後の必須の検討課題である。
【００１０】
再結晶による脆化は、（イ）再結晶温度をできるだけ高めるか、（ロ）再結晶組織を脆化しにくい組織にすることで解決できる。
【００１１】
上記（イ）において、再結晶温度を高めるためには熱的に安定な粒子を分散させ高温での粒界移動を抑制すればよい。しかしながら、熱負荷や熱衝撃の繰返しによって再結晶抑制剤としての添加元素が選択的に分解したり蒸発したりすることによって、プラズマ照射損失、組織の変質や再結晶化、並びに強度特性の低下等が懸念される。
【００１２】
したがって、再結晶抑制剤としての添加物の分解や蒸発を想定するとその量は極力少ないほど良く、合金中の存在量はｐｐｍオーダーが望ましい。また、一旦、再結晶し、等軸粒組織を形成した場合は、プラズマ照射損失の原因となる粒界割れや再結晶粒の脱落が生じやすいので、上記（イ）再結晶温度の向上だけでは、プラズマ対向材料としては有効でない。
【００１３】
上記（ロ）において、再結晶粒のアスペクト比（短軸径に対する長軸径の比）の大きい長大粒組織は、等軸粒組織に比べて粒界割れしにくく、亀裂が発生・伝播しにくい。そのため、結晶粒の長大化はＤＢＴＴの低減や靭性の向上が期待でき、プラズマ対向材料としては有効であると考えられる。
【００１４】
熱間圧延などの塑性加工の全圧延率（＝１００（焼結体の厚さ−圧延板の厚さ）／焼結体の厚さ）との組合せで、再結晶後に長大粒組織を形成できる添加物としてはＴｈＯ_２、Ｌａ_２Ｏ_３などの酸化物やＫのバブルなどがある。
【００１５】
ＴｈＯ_２は放射性物質であるため取扱の法規制や使用時の環境への飛散による汚染などの観点から使用困難になっている。一方、Ｌａ_２Ｏ_３などの希土類酸化物は通常１〜数％と％オーダーの添加量であり、分解・蒸発した場合に大きなプラズマ照射損失を起こすことが懸念される。Ｋのバブルの場合では、線材は次の通り製造され実用化されている。すなわち、原料のＷ粉末中に少量のＡｌ―Ｓｉ−Ｋを酸化物の状態で添加し、焼結過程でＫだけを残存させ、転打や線引きによって加工方向に平行にＫを再配列させる。そのあとに焼鈍して線材中にＫのバブルの列を形成させて、加工方向に対して垂直方向の再結晶および結晶粒の成長を抑制することによって得られる。
【００１６】
しかしながら、板材の場合は、塑性加工が非常に難しく全圧延率を大きくすることができないことなどのために実用化されていないのが現状である。
【００１７】
しかし、ｐｐｍオ―ダーの少量に制御して再結晶組織を長大粒組織にすることが線材で実用化されているので、板材を得ることができればプラズマ対抗材料として期待できると考えられる。
【００１８】
そこで、本発明の技術的課題は、このＫバブルを分散したタングステン板材によって脆さの改善並びに照射損傷の少ないプラズマ対向材料とその製造方法とを提供することにある。
【００１９】
【課題を解決するための手段】
前記課題を解決するために、本発明では、Ｋバブルが分散し再結晶組織が長大粒組織を形成するタングステンの板材を得ることがまず第一である。そのためには、熱間圧延条件を最適化する必要がある。
【００２０】
本発明者らは、Ｋドープタングステン焼結体の熱間圧延条件について鋭意検討した。その結果、熱間圧延は、焼結体を加熱し圧延したのち、加熱と圧延を繰り返し行い板材としていくが、その際の加熱温度や、あるいはさらに圧延途中の素材の再結晶処理を目的とした熱処理を付与することが重要であることが分かった。すなわち、一般的には加工繊維組織を発達させるために加熱温度を加工度を増すごとに徐々に下げていく。この場合、得られた圧延板を再結晶処理してアスペクト比の大きい長大粒組織を得るためには全圧延率の大きい圧延加工が必須となる。板材の塑性加工が非常に難しいタングステンにとっては、このような全圧延率の大きな圧延加工が必須になるのは有用な方法でなく、このことがこれまでＫドープタングステンの板材が得られなかった一つの理由であると考えた。
【００２１】
本発明では、加工温度をあまり下げないで高温に保ち圧延することで、ドープ剤や組織（結晶粒）を伸ばすだけでなく、圧延中に結晶粒を比較的大きくすることで、圧延板の再結晶処理後にアスペクト比の大きい長大粒組織が得られることを見出した。また、さらに、圧延途中に再結晶処理を目的とした熱処理を付加することによって、さらに大きな長大粒組織が得られることを見出した。
【００２２】
さらに、本発明者らは、この再結晶したＫドープタングステンの板材の低温靭性（延性）や照射損傷について鋭意検討した。その結果、アスペクト比が２以上にすることによって、低温靭性（延性）や照射損傷が大きく改善されることを見出し、本発明をなすに至ったものである。
【００２３】
すなわち、本発明によれば、カリウム（Ｋ）量が１０ｐｐｍ以上２００ｐｐｍ以下で残部が実質的にタングステンであるドープタングステン板材であって、最終圧延方向に平行な断面において、再結晶粒の短軸径に対する長軸径の比は少なくとも２以上で、かつ板厚方向に占める再結晶粒の数が厚み１ｍｍ当り１０から５０個であり、高靭性で照射損傷の少ないことを特徴とするプラズマ対向材料が得られる。
【００２４】
ここで、本発明において、Ｋ量を１０ｐｐｍ以上２００ｐｐｍ以下と限定したのは、１０ｐｐｍ未満だとアスペクト比２以上が得られず、２００ｐｐｍを超えると素材の塑性加工が困難で製造歩留まりが悪く生産性に欠けていためである。なお、生産性を考慮し安価で大量に大きな板材を得るために、Ｋ量は、望ましくは、５０〜１００ｐｐｍである。
【００２５】
ここで、本発明において、アスペクト比を２以上と限定したのは、２未満ではＤＢＴＴの低下や照射損傷の改善が見られないためである。
【００２６】
また、本発明によれば、延性−脆性遷移温度が２００℃以下で、再結晶粒のアスペクト比が２以上であることを特徴とするプラズマ対向材料が得られる。
【００２７】
また、本発明によれば、延性−脆性遷移温度が４５℃以下で、再結晶粒のアスペクト比が１０以上であることを特徴とするプラズマ対向材料が得られる。
【００２８】
また、本発明によれば、延性−脆性遷移温度が２５℃以下で、再結晶粒のアスペクト比が２０以上であることを特徴とするプラズマ対向材料が得られる。
【００２９】
また、本発明によれば、再結晶粒のアスペクト比の大きさを調整するための熱処理を施す前のドープ板材であって、その板材の再結晶温度は１２００〜１８００℃であることを特徴とするプラズマ対向材料が得られる。
【００３０】
また、本発明によれば、再結晶粒のアスベクト比の大きさを調整するために、塑性加工後の板材を予め１４００〜２０００℃の温度範囲で熱処理されていることを特徴とするプラズマ対向材料が得られる。
【００３１】
本発明の塑性加工後の板材の再結晶開始温度（１時間加熱評価）は１２００〜１８００℃であり、再結晶開始温度＋２００℃の温度の熱処理で十分再結晶化しアスペクト比が２以上の板材を得ることができるため、熱処理温度を１４００〜２０００℃と限定した。
【００３２】
また、本発明によれば、粉末冶金法で作製したＫドープタングステン焼結体を加熱温度１２００〜１７００℃の温度で熱間圧延し、さらに１４００〜２０００℃の温度範囲で熱処理することを特徴とするプラズマ対向材料の製造方法が得られる。
【００３３】
また、本発明によれば、前記いずれか一つに記載のプラズマ対向材料を製造する方法であって、粉末冶金法で作製したＫドープタングステン焼結体を加熱温度１２００〜１７００℃の温度で一次熱間圧延し、その後再結晶化を目的とした熱処理を施したあとに二次熱間圧延し、１４００〜２０００℃の温度範囲で熱処理することを特徴とするプラズマ対向材料の製造方法が得られる。
【００３４】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
【００３５】
（第１の実施の形態）
種々の量のカリウムを含んだドープタングステン粉末は常法で作製することができる。たとえば、所定量のＡｌ、Ｓｉ、Ｋの酸化物を三酸化タングステン粉末（ＷＯ_３）や青色酸化物（Ｗ_４Ｏ_１１）に硝酸塩などの形で溶液ドープし十分乾燥したのち水素還元することで得ることができる。代表的なドープ粉末の平均粒径は４μｍであるが、水素還元の温度や還元チャージ量、水素分圧を制御することで種々の粒径の粉末を得ることができる。
【００３６】
しかしながら、その粒径は本発明ではとくに制限は必要としない。ただし、成形性や取扱いを考慮すると１〜８μｍが望ましい。得られた粉末を冷間静水圧プレスにより成形（たとえば、２００ＭＰａの加圧力）したのち、水素気流中で焼結（たとえば、２０００℃で１０時間）を行い、厚さ５０ｍｍの焼結体を作製した。焼結体の結晶粒径は２０〜５００μｍであった。また、焼結体の密度は９５％であった。なお、焼結体の密度は９０％以上あればそのあとの塑性加工は問題なくできる。得られた焼結体を１２００〜１７００℃で熱間圧延し厚さ１ｍｍの板材とした。全圧延率は９８％である。板中のカリウム量は、５，１０，３０，５５，７２，１０３，２００，２２０ｐｐｍで、いずれの板材も理論密度比は９９％以上であった。比較のため、カリウム量５５ｐｐｍに相当する焼結体を通常行われる９００〜１５００℃の温度でも熱間圧延を行った。
【００３７】
得られた板材を２０００℃で再結晶処理したところ、通常行われる加熱温度での圧延ではアスペクト比１．８程度であったが、本発明の材料においてはアスペクト比２以上得られ、加熱温度を高くすることでアスペクト比を大きくできることを確認した。
【００３８】
ここで、アスペクト比は、以下のように測定した。すなわち、圧延方向に平行な断面の組織写真を５０〜１００倍の倍率で撮影し、その写真上に板厚方向に任意の線を引く。線上の結晶粒の長軸径（圧延方向の長さ）と短軸径（板厚方向の長さ）を測定し、アスペクト比（＝長軸径／短軸径）を算出する。なお、アスペクト比の測定は約３００ヶの結晶粒に対して行った。
【００３９】
さらに、本発明材料において圧延途中で再結晶化を目的とした熱処理を付加したところ、熱処理を付加した場合はアスペクト比４以上得られ、付加しない場合に比べて大きなアスペクト比が得られ、圧延途中で熱処理することによってアスペクト比を大きくすることが可能であることを確認した。
【００４０】
再結晶化を目的とした熱処理をしていない板材について、水素中１０００〜２０００℃の温度で１時間加熱し、光学顕微鏡による組織観察を行い詳細な再結晶開始温度を調べた。
【００４１】
その結果を下記表１に示す。本発明の材料の再結晶開始温度では１２００〜１８００℃であった。
【００４２】
比較例８（カリウム量２２０ｐｐｍ）では熱間圧延時の加工割れが多く重量歩留まりが悪く良好な板材が得られなかった。また、比較例７（カリウム量５ｐｐｍ）の純Ｗ板材は再結晶開始温度１１００℃であった。これらの板材を再結晶温度よりも少なくとも２００℃高い温度で熱処理することで十分再結晶化できることを確認した。最終圧延方向に平行な断面において、再結晶粒の短軸径および長軸径を測定し、再結晶粒のアスペクト比（＝長軸径／短軸径）と層数（板厚／短軸径）を求めた。その結果を下記表１中に示した。表１に示すように、再結晶温度が高いほど大きなアスペクト比を有する板材が得られた。
【００４３】
以上の板材を静的３点曲げ試験により延性−脆性遷移温度（ＤＢＴＴ）を調べた。曲げ試験は厚さ１ｍｍ、幅２ｍｍ、長さ２５ｍｍの試験片を板材から切出し、−１２０〜１０００℃の温度で負荷速度１ｍｍ／ｍｉｎで行った。室温以下の温度は液体窒素とイソペンタンあるいはアルコールで制御した。室温〜１００℃の温度は温水で、それ以上の温度は電気炉で温度制御した。なお、支点間距離は、１６ｍｍである。得られた荷重−変位曲線から降伏強度および最大強度を求めＤＢＴＴを算出した。
【００４４】
ここで、図１に示す降伏強度の温度曲線と最大強度の温度曲線の交点の温度をＤＢＴＴとした。その結果を下記表１中に示す。アスペクト比を２以上（Ｋ量を１０ｐｐｍ以上）にすることでＤＢＴＴを低減、すなわち脆さを改善することができた。特に、アスペクト比１０（Ｋ量５０ｐｐｍ）を超えると室温近傍でも延性が出現した。
【００４５】
【表１】

【００４６】
（第２の実施の形態）
第１の実施の形態と同様な板材において照射損耗の評価を行った。１５００ＭＷ／ｍ^２（７０ｋＶ、４Ａ），の電子ビームを２．０ｍｓｅｃ試料に照射し損耗量（損耗深さ）を調べた。その結果を下記表２に示す。本発明の材料は、比較例７（Ｋ量５ｐｐｍ、アスペクト比１．３）に比べて損耗深さが半分以下であった。
【００４７】
照射後の断面組織を光学顕微鏡で確認したところ比較例７の材料は粒界に細かい割れが多数存在していたが、本発明の材料の場合はほとんど見られなかった。したがって、本発明の実施の形態においては、アスペクト比を２以上にすることによって照射損傷を極めて少なくし、結晶粒の脱落の起因となる粒界割れをほとんど生じない材料を得ることができた。
【００４８】
【表２】

【００４９】
【発明の効果】
以上、説明したように、本発明によれば、ＤＢＴＴが低く照射損耗の少ないプラズマ対向材料を提供することができる。
【００５０】
また、本発明によれば、これまで実用化されていなかったＫバブルが分散した長大粒組織のドープタングステン板材を提供することができる。
【００５１】
また、本発明によれば、長大粒組織の材料は高温特性、特に、クリープ特性や耐衝撃性に優れているので、本発明のプラズマ対向材料のみならず、高温加熱炉の反射板や構成材料、高輝度電極、抵抗溶接電極などの高温耐垂下性や耐衝撃性が要求される用途にも展開可能である。
【図面の簡単な説明】
【図１】降伏強度、最大強度および曲げ角の温度依存性を模式的に示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma facing material and a structural material in an irradiation environment, and more particularly to a material used in an ultrahigh temperature plasma such as a fusion reactor.
[0002]
[Prior art]
Conventionally, a low Z material such as a C / C composite material or beryllium has been used as a plasma facing material (for example, see Patent Document 1).
[0003]
However, these low-Z materials, particularly carbon materials, have problems such as severe wall material evaporation and wear due to heat load, large decrease in thermal conductivity due to neutron irradiation, and high tritium occlusion.
[0004]
High Z materials such as Molybdenum (Mo) and Tungsten (W), especially Tungsten, has many excellent properties such as high melting point, radiation wear resistance, low vapor pressure, low thermal expansion coefficient, low tritium occlusion, and compatibility with liquid metals. Therefore, it has been attracting attention and examination as a high thermal flow rate device for nuclear fusion reactors, a solid target for a spallation neutron source, and a structural material under irradiation environment.
[0005]
Further, Patent Document 2 proposes tungsten formed by chemical vapor deposition (CVD) as a plasma facing material that emits less gas from the material and has less plasma damage.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-25173
[Patent Document 2]
JP-A-7-228976 [0008]
[Problems to be solved by the invention]
However, tungsten has poor toughness, and there is a problem that recrystallization and grain growth occur and it easily becomes brittle when subjected to a thermal load. For example, the ductile brittle transition temperature (DBTT), which is one of indices of toughness (ductility), is 300 to 500 ° C. in the case of a recrystallized pure W plate, and does not exhibit ductility at room temperature.
[0009]
The CVD-tungsten DBTT proposed in Patent Document 2 is much higher and more brittle than a pure W plate recrystallized at about 500 to 1000 ° C. It is difficult to use and handle in places where strength is required, and improvement of toughness is an indispensable study issue in the future.
[0010]
Embrittlement due to recrystallization can be solved by (i) increasing the recrystallization temperature as much as possible, or (b) making the recrystallized structure difficult to embrittle.
[0011]
In (a) above, in order to increase the recrystallization temperature, it is only necessary to disperse thermally stable particles and suppress the grain boundary movement at high temperature. However, the additional element as a recrystallization inhibitor is selectively decomposed or evaporated by repeated heat load and thermal shock, resulting in plasma irradiation loss, structural alteration and recrystallization, and deterioration of strength characteristics, etc. Is concerned.
[0012]
Therefore, assuming decomposition and evaporation of the additive as the recrystallization inhibitor, the amount is preferably as small as possible, and the abundance in the alloy is preferably in the order of ppm. In addition, once recrystallized and an equiaxed grain structure is formed, grain boundary cracking and loss of recrystallized grains are likely to cause plasma irradiation loss. It is not effective as a plasma facing material.
[0013]
In (b) above, a long and large grain structure with a large aspect ratio of the recrystallized grains (ratio of the major axis diameter to the minor axis diameter) is less susceptible to intergranular cracking than the equiaxed grain structure, and cracks are less likely to occur and propagate. . Therefore, an increase in crystal grain size can be expected to reduce DBTT and improve toughness, and is considered effective as a plasma facing material.
[0014]
In combination with the total rolling rate of plastic working such as hot rolling (= 100 (thickness of sintered body−thickness of rolled plate) / thickness of sintered body), a long and large grain structure can be formed after recrystallization. Additives include oxides such as ThO ₂ and La ₂ O ₃ and K bubbles.
[0015]
Since ThO ₂ is a radioactive substance, it is difficult to use it from the viewpoint of handling laws and regulations and contamination due to scattering to the environment during use. On the other hand, rare earth oxides such as La ₂ O ₃ are usually added in the order of 1 to several percent and in the order of%, and there is concern that a large plasma irradiation loss will occur when decomposed and evaporated. In the case of K bubble, the wire is manufactured and put into practical use as follows. That is, a small amount of Al—Si—K is added to the raw material W powder in an oxide state, leaving only K during the sintering process, and rearranging K parallel to the processing direction by rolling or drawing. Thereafter, annealing is performed to form a row of K bubbles in the wire, thereby suppressing recrystallization in the direction perpendicular to the processing direction and growth of crystal grains.
[0016]
However, in the case of a plate material, the present situation is that it is not put into practical use because plastic processing is very difficult and the total rolling ratio cannot be increased.
[0017]
However, since it has been put to practical use in wire rods, the recrystallized structure is made into a large grain structure by controlling it to a small amount of ppm order, so it can be expected that it can be expected as a plasma-resistant material if a plate material can be obtained.
[0018]
Therefore, a technical problem of the present invention is to provide a plasma facing material with improved brittleness and less irradiation damage by a tungsten plate material in which K bubbles are dispersed, and a manufacturing method thereof.
[0019]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, it is first of all to obtain a tungsten plate material in which K bubbles are dispersed and a recrystallized structure forms a long and large grain structure. For this purpose, it is necessary to optimize the hot rolling conditions.
[0020]
The present inventors diligently studied the hot rolling conditions of the K-doped tungsten sintered body. As a result, in hot rolling, the sintered body is heated and rolled, and then heating and rolling are repeated to obtain a plate material. The purpose of this is to reheat the heating temperature at that time or to further recrystallize the material during rolling. It has been found that applying heat treatment is important. That is, generally, in order to develop a processed fiber structure, the heating temperature is gradually lowered as the degree of processing increases. In this case, in order to recrystallize the obtained rolled sheet to obtain a long and large grain structure having a large aspect ratio, a rolling process having a large total rolling ratio is essential. For tungsten, which is extremely difficult to plastically process a plate material, it is not a useful method to perform a rolling process with such a large total rolling rate, and this has not been able to obtain a K-doped tungsten plate material until now. I thought it was one reason.
[0021]
In the present invention, the rolling plate is re-rolled not only by extending the dopant and the structure (crystal grains) by rolling while keeping the processing temperature at a high temperature without significantly reducing the processing temperature, but also by relatively increasing the crystal grains during rolling. It has been found that a long and large grain structure having a large aspect ratio can be obtained after crystallization. Furthermore, it has been found that a larger and larger grain structure can be obtained by applying a heat treatment for the purpose of recrystallization during rolling.
[0022]
Furthermore, the present inventors diligently studied the low-temperature toughness (ductility) and irradiation damage of the recrystallized K-doped tungsten plate. As a result, it has been found that when the aspect ratio is 2 or more, the low-temperature toughness (ductility) and irradiation damage are greatly improved, and the present invention has been made.
[0023]
That is, according to the present invention, a doped tungsten plate material having a potassium (K) content of 10 ppm or more and 200 ppm or less and the balance being substantially tungsten, the minor axis diameter of the recrystallized grains in a cross section parallel to the final rolling direction. A plasma facing material characterized in that the ratio of the major axis diameter to is at least 2 or more and the number of recrystallized grains in the thickness direction is 10 to 50 per 1 mm thickness, which is tough and has little irradiation damage. can get.
[0024]
Here, in the present invention, the amount of K is limited to 10 ppm or more and 200 ppm or less. If it is less than 10 ppm, an aspect ratio of 2 or more cannot be obtained, and if it exceeds 200 ppm, plastic processing of the material is difficult and production yield is poor and productivity is low. Because it lacks. In order to obtain a large plate at a low cost and in large quantities in consideration of productivity, the amount of K is desirably 50 to 100 ppm.
[0025]
Here, in the present invention, the aspect ratio is limited to 2 or more because when it is less than 2, the DBT T is not lowered and the irradiation damage is not improved.
[0026]
In addition, according to the present invention, there can be obtained a plasma facing material characterized in that the ductile-brittle transition temperature is 200 ° C. or lower and the recrystallized grain aspect ratio is 2 or higher.
[0027]
In addition, according to the present invention, there can be obtained a plasma facing material characterized by having a ductile-brittle transition temperature of 45 ° C. or lower and an aspect ratio of recrystallized grains of 10 or higher.
[0028]
In addition, according to the present invention, there can be obtained a plasma facing material characterized in that the ductile-brittle transition temperature is 25 ° C. or lower and the recrystallized grain aspect ratio is 20 or higher.
[0029]
Further, according to the present invention, a dope plate material before heat treatment for adjusting the aspect ratio of the recrystallized grains, wherein the recrystallization temperature of the plate material is 1200 to 1800 ° C. A plasma facing material is obtained.
[0030]
Further, according to the present invention, in order to adjust the magnitude of the recrystallized grain aspect ratio, the plate material after plastic working is heat-treated in the temperature range of 1400 to 2000 ° C. in advance. Is obtained.
[0031]
The recrystallization start temperature (evaluation by heating for 1 hour) of the plate material after plastic working of the present invention is 1200 to 1800 ° C., and is sufficiently recrystallized by heat treatment at a temperature of recrystallization start temperature + 200 ° C. Since it can obtain, heat processing temperature was limited with 1400-2000 degreeC.
[0032]
According to the present invention, the K-doped tungsten sintered body produced by powder metallurgy is hot-rolled at a heating temperature of 1200 to 1700 ° C, and further heat-treated at a temperature range of 1400 to 2000 ° C. A method of manufacturing a plasma facing material is obtained.
[0033]
In addition, according to the present invention, there is provided a method for producing the plasma facing material according to any one of the above, wherein a K-doped tungsten sintered body produced by a powder metallurgy method is first heated at a heating temperature of 1200 to 1700 ° C. A method for producing a plasma facing material is provided, which is hot-rolled and then subjected to a heat treatment for recrystallization, followed by a secondary hot-rolling and a heat treatment in a temperature range of 1400 to 2000 ° C. .
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0035]
(First embodiment)
Doped tungsten powders containing various amounts of potassium can be prepared by conventional methods. For example, a predetermined amount of oxides of Al, Si, and K may be solution-doped in the form of nitrate or the like in tungsten trioxide powder (WO ₃ ) or blue oxide (W ₄ O ₁₁ ), and after sufficient drying, hydrogen reduction Obtainable. The average particle size of a typical dope powder is 4 μm, but powders with various particle sizes can be obtained by controlling the hydrogen reduction temperature, the reduction charge amount, and the hydrogen partial pressure.
[0036]
However, the particle size is not particularly limited in the present invention. However, in consideration of moldability and handling, 1 to 8 μm is desirable. The obtained powder is molded by a cold isostatic press (for example, a pressure of 200 MPa) and then sintered in a hydrogen stream (for example, at 2000 ° C. for 10 hours) to produce a sintered body having a thickness of 50 mm. did. The crystal grain size of the sintered body was 20 to 500 μm. Further, the density of the sintered body was 95%. If the density of the sintered body is 90% or more, the subsequent plastic working can be performed without any problem. The obtained sintered body was hot-rolled at 1200 to 1700 ° C. to obtain a plate material having a thickness of 1 mm. The total rolling rate is 98%. Amount of potassium in the plate, in 5,10,30,55,72,103,200,220Ppm, any sheet even theoretical density ratio was 99% or more. For comparison, hot rolling was performed even at a temperature of 900 to 1500 ° C., in which a sintered body corresponding to a potassium amount of 55 ppm is usually performed.
[0037]
When the obtained plate material was recrystallized at 2000 ° C., the aspect ratio was about 1.8 in the rolling at the normal heating temperature, but the aspect ratio of 2 or more was obtained in the material of the present invention. It was confirmed that the aspect ratio can be increased by increasing the aspect ratio.
[0038]
Here, the aspect ratio was measured as follows. That is, a structure photograph of a cross section parallel to the rolling direction is taken at a magnification of 50 to 100 times, and an arbitrary line is drawn on the photograph in the thickness direction. The major axis diameter (length in the rolling direction) and minor axis diameter (length in the plate thickness direction) of the crystal grains on the line are measured, and the aspect ratio (= major axis diameter / minor axis diameter) is calculated. The aspect ratio was measured for about 300 crystal grains.
[0039]
Furthermore, when a heat treatment for recrystallization was added during rolling in the material of the present invention, an aspect ratio of 4 or more was obtained when the heat treatment was added, and a larger aspect ratio was obtained than when no heat treatment was added. It was confirmed that the aspect ratio could be increased by heat treatment with
[0040]
About the board | plate material which has not been heat-processed for the purpose of recrystallization, it heated at 1000-2000 degreeC in hydrogen for 1 hour, the structure observation with the optical microscope was performed, and the detailed recrystallization start temperature was investigated.
[0041]
The results are shown in Table 1 below. The recrystallization start temperature of the material of the present invention was 1200 to 1800 ° C.
[0042]
In Comparative Example 8 (potassium amount 220 ppm), there were many work cracks during hot rolling, the weight yield was poor, and a good plate material could not be obtained. The pure W plate material of Comparative Example 7 (potassium amount 5 ppm) had a recrystallization start temperature of 1100 ° C. It was confirmed that these plate materials could be sufficiently recrystallized by heat treatment at a temperature at least 200 ° C. higher than the recrystallization temperature. In the cross section parallel to the final rolling direction, the minor axis diameter and major axis diameter of the recrystallized grains are measured, the aspect ratio of the recrystallized grains (= major axis diameter / minor axis diameter) and the number of layers (plate thickness / minor axis diameter) ) The results are shown in Table 1 below. As shown in Table 1, a plate material having a larger aspect ratio was obtained as the recrystallization temperature was higher.
[0043]
The plate material was examined for ductile-brittle transition temperature (DBTT) by a static three-point bending test. A bending test was performed by cutting a test piece having a thickness of 1 mm, a width of 2 mm, and a length of 25 mm from a plate material at a temperature of −120 to 1000 ° C. and a load speed of 1 mm / min. The temperature below room temperature was controlled with liquid nitrogen and isopentane or alcohol. The temperature from room temperature to 100 ° C. was warm water, and the temperature above that was controlled by an electric furnace. In addition, the distance between fulcrums is 16 mm. The yield strength and the maximum strength were obtained from the obtained load-displacement curve, and DBTT was calculated.
[0044]
Here, the temperature at the intersection of the temperature curve of the yield strength and the temperature curve of the maximum strength shown in FIG. The results are shown in Table 1 below. By making the aspect ratio 2 or more (K content 10 ppm or more), DBTT was reduced, that is, brittleness was improved. In particular, when the aspect ratio exceeded 10 (K amount 50 ppm), ductility appeared even near room temperature.
[0045]
[Table 1]

[0046]
(Second Embodiment)
Irradiation wear was evaluated on the same plate material as in the first embodiment. The sample was irradiated with an electron beam of 1500 MW / m ² (70 kV, 4 A), and the amount of wear (wear depth) was examined. The results are shown in Table 2 below. The wear depth of the material of the present invention was less than half that of Comparative Example 7 (K amount 5 ppm, aspect ratio 1.3).
[0047]
When the cross-sectional structure after irradiation was confirmed with an optical microscope, the material of Comparative Example 7 had many fine cracks at the grain boundaries, but was hardly observed in the case of the material of the present invention. Therefore, in the embodiment of the present invention, by setting the aspect ratio to 2 or more, irradiation damage is extremely reduced, and a material that hardly causes grain boundary cracking that causes dropout of crystal grains can be obtained.
[0048]
[Table 2]

[0049]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a plasma facing material with low DBTT and low irradiation wear.
[0050]
Further, according to the present invention, it is possible to provide a doped tungsten plate material having a long and large grain structure in which K bubbles that have not been put into practical use are dispersed.
[0051]
In addition, according to the present invention, the material having a long and large grain structure is excellent in high temperature characteristics, in particular, creep characteristics and impact resistance. Therefore, not only the plasma facing material of the present invention but also a reflector or a constituent material of a high temperature heating furnace. It can also be applied to applications requiring high temperature drooping resistance and impact resistance such as high brightness electrodes and resistance welding electrodes.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing the temperature dependence of yield strength, maximum strength, and bending angle.

Claims

A doped tungsten plate material having a potassium (K) amount of 10 ppm to 200 ppm and the balance being substantially tungsten, and in a cross section parallel to the final rolling direction, the ratio of the major axis diameter to the minor axis diameter of the recrystallized grains is at least A plasma-facing material characterized in that the number of recrystallized grains occupying 2 or more and in the thickness direction is 10 to 50 per 1 mm of thickness , high toughness and little irradiation damage.

2. The plasma facing material according to claim 1, wherein the ductile-brittle transition temperature is 200 [deg.] C. or less and the aspect ratio of the recrystallized grains is 2 or more.

2. The plasma facing material according to claim 1, wherein the ductile-brittle transition temperature is 45 [deg.] C. or less, and the recrystallized grain aspect ratio is 10 or more.

2. The plasma facing material according to claim 1, wherein a ductile-brittle transition temperature is 25 [deg.] C. or less and an aspect ratio of recrystallized grains is 20 or more.

In the plasma-facing material according to any one of claims 1 to 4, a dope sheet before the heat treatment for adjusting the size of the recrystallized grains of an aspect ratio, recrystallization of the sheet material A plasma facing material characterized in that the temperature is 1200 to 1800 ° C.

In the plasma-facing material according to any one of claims 1 to 5, in order to adjust the size of the recrystallized grains of an aspect ratio, at a temperature range of pre-1400 to 2000 ° C. The sheet material after the plastic working A plasma facing material characterized by being heat-treated.

A method for producing a plasma facing material according to any one of claims 1 to 6 , wherein a K-doped tungsten sintered body produced by a powder metallurgy method is heated at a temperature of 1200 to 1700 ° C. A method for producing a plasma facing material, comprising hot rolling at a rolling rate of 90% or more and further heat-treating in a temperature range of 1400 to 2000 ° C.

A method for producing a plasma facing material according to any one of claims 1 to 6, wherein the K-doped tungsten sintered body produced by powder metallurgy is heated primarily at a temperature of 1200 to 1700 ° C. A method for producing a plasma facing material , comprising: hot rolling, followed by heat treatment for recrystallization, second hot rolling, and heat treatment in a temperature range of 1400 to 2000 ° C.