JP3853035B2

JP3853035B2 - Oxidation resistant C / C composite and method for producing the same

Info

Publication number: JP3853035B2
Application number: JP23027697A
Authority: JP
Inventors: 敏孝大橋; 義雄鈴木
Original assignee: Tokai Carbon Co Ltd
Current assignee: Tokai Carbon Co Ltd
Priority date: 1997-08-12
Filing date: 1997-08-12
Publication date: 2006-12-06
Anticipated expiration: 2017-08-12
Also published as: JPH1160357A

Description

【０００１】
【発明の属する技術分野】
本発明は、コンバージョン法によりＣ／Ｃ複合基材（炭素繊維強化炭素複合基材）の表層部に傾斜機能組織のＳｉＣ被覆層を安定強固に形成した、高い材質強度と優れた耐酸化性能を備えた、耐酸化性Ｃ／Ｃ複合材及びその製造方法に関する。
【０００２】
【従来の技術】
Ｃ／Ｃ複合材は、卓越した比強度、比弾性率を有するうえに１０００℃を越える高温域において優れた耐熱性および化学的安定性を備えているため、航空宇宙用をはじめ高温過酷な条件で使用される構造材料として有用されている。しかしながら、Ｃ／Ｃ複合材には大気中において５００℃付近から材質酸化を受けるという炭素材固有の欠点があり、これがＣ／Ｃ複合材の応用途を制限する最大の障害となっている。このため、Ｃ／Ｃ複合材の表面に酸化抵抗性の大きな被覆層を形成して耐酸化性を改善する試みが盛んに行われており、例えばＳｉＣ、Ｓｉ₃Ｎ₄、ＺｒＯ₂、Ａｌ₂Ｏ₃等の耐熱セラミックス系物質によって被覆処理する方法が数多く開発されている。このうち、ＳｉＣの被覆化が技術性及び経済性の面で優れており、最も好適な工業化手段として実用されている。
【０００３】
Ｃ／Ｃ複合材の表面にＳｉＣの被覆層を形成する代表的な方法として、気相反応により生成するＳｉＣを直接沈着させるＣＶＤ法（化学的気相蒸着法）と、Ｃ／Ｃ複合材の炭素を反応源に利用してＳｉＯガスと反応させることによりＳｉＣに転化させるコンバージョン法が知られている。しかしながら、これらの方法によって形成されるＳｉＣ被覆層にはそれぞれに長所と短所がある。すなわち前者のＣＶＤ法により形成されるＳｉＣ被覆層は、緻密性には優れているものの、基材との界面が明確に分離している関係で熱衝撃を与えると相互の熱膨張率の差によって層間剥離現象が起こり易い欠点がある。この層間剥離現象は、主にＣ／Ｃ複合基材とＳｉＣ被覆層との熱膨張係数の差が大きく、最大歪みが追随できないことに起因して発生するため、Ｃ／Ｃ複合基材面をＳｉＣの熱膨張率に近似するように改質すれば軽減化させることができる。このような観点から、Ｃ／Ｃ複合基材面に気相熱分解法により熱分解炭素層を形成し、次いでＣＶＤ又はＣＶＩ法でＳｉＣを被覆する方法（特開平２−111681号公報）が提案されているが、操作の煩雑性に見合う程の充分な高温酸化抵抗性は期待できない。
【０００４】
これに対し、後者のコンバージョン法は珪素源と炭素源を加熱反応させて生成するＳｉＯガスとＣ／Ｃ複合材を構成する炭素組織を反応させ、Ｃ／Ｃ複合材の表層部の表面から内部にかけて漸次ＳｉＣ化する機構に基づくものであるため、形成される炭化珪素層はＳｉＣ化の度合が材質内部に向うに従って漸次減少する連続的な傾斜機能組織を呈する。したがって、ＣＶＤ法により形成される炭化珪素層のような層間がなく、熱衝撃を受けても層間界面剥離を生じることがない利点がある。しかし、その反面、表層部における炭化珪素層の緻密度合が低下して、充分な耐酸化性を付与できない欠点がある。
【０００５】
このため、Ｃ／Ｃ複合基材の表面に予めコンバージョン法によりＳｉＣ層を形成し、これをベース被覆層としてその上に各種の被覆層を形成して耐酸化性能を向上させる試みが提案されている。例えば、本出願人はＣ／Ｃ複合基材の表面にＳｉＣ被覆層、ＳｉＯ₂微粒被覆層、ＳｉＯ₂ガラス被覆層またはＢ₂Ｏ₃ガラス被覆層もしくはＢ₂Ｏ₃・ＳｉＯ₂ガラス被覆層が３層状に積層被覆された構造の耐酸化性Ｃ／Ｃ材とその製造方法（特開平４−42883 号公報）を開発し、更に、特開平４−187583号公報、特開平４−243989号公報、特開平４−243990号公報、特開平４−43366 号公報、特開平５−70228 号公報、特開平５−229886号公報、特開平５−330961号公報、特開平６−48872 号公報、特開平６−144967号公報、特開平６−247782号公報などの改良技術を開発、提案している。
【０００６】
これらの多層被覆手段によればＣ／Ｃ複合材の耐酸化性能を効果的に向上させることが可能となるが、ベース被覆層を構成するコンバージョン法によるＳｉＣ化には、本質的にＣ／Ｃ複合基材そのものの材質強度を損ねる問題がある。すなわち、コンバージョン法による被覆過程においては、ＳｉＯガスはＣ／Ｃ基材の表面から組織内部まで浸透拡散しながらＣ／Ｃ基材組織をＳｉＣに転化していくが、Ｃ／Ｃ基材に存在する気孔や亀裂に沿ってＳｉＯガスは比較的深い基材組織にまで浸透拡散し易い。そのためＣ／Ｃ複合材の表面ばかりではなく、比較的深い内部組織までＳｉＣ化が進行して基材組織、とくにＳｉＣ化し易いマトリックス炭素部分及び炭素繊維／マトリックス炭素の界面部分等が優先的に珪化されて鋸状や島状にＳｉＣ化され易く、その結果、基材組織全体を脆弱化する現象が生じる。この傾向はＣ／Ｃ基材の形状が大型化したり、複雑化するとより一層著しくなる。
【０００７】
このように、Ｃ／Ｃ複合基材の表面にコンバージョン法によりＳｉＣ被覆層を形成する場合、生成するＳｉＣ被覆層を均一、緻密化して基材の内部組織がＳｉＣ化する現象を抑制することが材質強度を確保する上で必要である。かかる観点から、本出願人は炭素繊維をマトリックス樹脂とともに複合成形し硬化した炭素繊維複合樹脂成形体の外周面に、ポリイミド系樹脂フィルムを展着した状態で焼成炭化し、得られたＣ／Ｃ複合基材を珪素源と炭材の混合粉末を加熱反応させて生成するＳｉＯガスと非酸化性雰囲気中１６００〜２０００℃の温度域で接触させ、Ｃ／Ｃ複合基材の表面にコンバージョン法によるＳｉＣ被覆層を形成する方法（特開平８−169786号公報）やＣ／Ｃ複合基材の表層部に易黒鉛化性炭素の被膜層を形成したのちコンバージョン法によりＳｉＣ被覆層を形成する耐酸化性Ｃ／Ｃ複合材の製造方法（特願平８−346730号）を開発した。
【０００８】
これらの方法によれば、炭素繊維強化樹脂成形体の段階で外周面に介在するポリイミド系樹脂フィルムが炭化して生成した薄膜の緻密カーボン層、あるいは、Ｃ／Ｃ複合基材の表層部に石炭系ピッチや石油系ピッチ等が炭化して形成した易黒鉛化性炭素の被膜層によりＣ／Ｃ複合基材の表層部のみが緻密なＳｉＣ被膜層に転化されて、Ｃ／Ｃ複合基材の組織内部にＳｉＯガスが浸透拡散する現象を抑制することができ、材質強度の低下を抑止するとともに優れた耐酸化性能を付与することが可能となる。
【０００９】
【発明が解決しようとする課題】
しかしながら、Ｃ／Ｃ複合材の優れた材質特性を損なわずに高度の耐酸化性能を付与するために、本発明者等は更に研究を進めた結果、上記の特開平８−169786号公報及び特願平８−346730号の技術では、ＳｉＯガスが内部組織に拡散浸透するのを防止することが充分でなく、特に三次元炭素繊維プリフォームを用いたＣ／Ｃ複合材（３Ｄ−Ｃ／Ｃ複合材）の場合にはＺ軸方向の繊維の界面あるいは周辺に存在する空隙等が珪化反応によりＳｉＣ化され易く、内部組織の脆弱化を充分に抑止することが困難となる問題があることを解明した。
【００１０】
本発明者等は、ＳｉＯガスのＣ／Ｃ複合基材内部への局所的侵入の機構について更に研究を進めた結果、Ｃ／Ｃ複合基材の表面状態を緻密化するとともに表面を研磨して平滑化し、その上に炭素質粉末とガラス状炭素からなる複合構造の炭素質被膜を被着することにより緻密なＳｉＣ被膜が形成され、また内部組織のＳｉＣ化に伴う材質強度の低下を大幅に防止できることを見出した。
【００１１】
本発明は上記の知見に基づいて完成したもので、その目的は内部組織のＳｉＣ化による材質強度の低下を招くことなく、コンバージョン法によりＣ／Ｃ複合基材の表層部に緻密なＳｉＣ被覆層を安定強固に形成した材質強度及び耐酸化性に優れた耐酸化性Ｃ／Ｃ複合材及びその製造方法を提供することにある。
【００１２】
【課題を解決するための手段】
上記の目的を達成するための本発明による耐酸化性Ｃ／Ｃ複合材は、表面が研磨処理されたＣ／Ｃ複合基材に被着した炭素質粉末と熱硬化性樹脂の炭化物とからなる厚さ１〜３０μm の炭素質被膜を傾斜機能組織のＳｉＣ被膜に転化した被覆組織構造が形成されてなることを構成上の特徴とする。
【００１３】
また、本発明による耐酸化性Ｃ／Ｃ複合材の製造方法は、炭素繊維をマトリックス樹脂とともに複合成形し、硬化および焼成炭化したＣ／Ｃ複合基材の表面を研磨処理した後、炭素質粉末と熱硬化性樹脂液との混合物を被覆して非酸化性雰囲気中８００℃以上の温度で焼成炭化して厚さ１〜３０μm の炭素質被膜を被着し、次いで珪素源と炭素源の混合粉末を加熱反応させて生成するＳｉＯガスと非酸化性雰囲気中１６００〜２０００℃の温度域で接触させ、Ｃ／Ｃ複合基材の表面をコンバージョン法により傾斜機能組織のＳｉＣ被膜に転化することを構成上の特徴とする。
【００１４】
【発明の実施の形態】
Ｃ／Ｃ複合材の強化材となる炭素繊維には、ポリアクリロニトリル系、レーヨン系、ピッチ系など各種原料から製造された平織、朱子織、綾織などの織布を一次元または多次元方向に配向した繊維体、フェルト、トウ等が使用され、マトリックス樹脂としてはフェノール系、フラン系など高炭化性の液状熱硬化性樹脂、あるいはタールピッチのような熱可塑性物質が用いられる。炭素繊維は、浸漬、塗布などの手段によりマトリックス樹脂を充分に含浸したのち半硬化してプリプレグを形成し、ついで積層加圧して複合成形したのち加熱して樹脂成分を完全に硬化し、常法に従い非酸化性雰囲気下で１０００〜２０００℃の温度に加熱して焼成炭化することによりＣ／Ｃ複合基材が作製される。Ｃ／Ｃ複合基材の密度は高いことが好ましく、例えば嵩密度は１．６０g/cm³以上であることが望ましいが、所望の嵩密度より低い場合には必要に応じてマトリックス樹脂を含浸、硬化、焼成炭化してマトリックス炭素による緻密化処理を反復して、Ｃ／Ｃ複合基材表層部の組織の緻密化を図る。嵩密度が低く、１．６０g/cm³未満の場合には炭素質被膜では充填しきれないマクロポアーが残留するので、ＳｉＯガスの侵入がマクロポアーを介して起きる。また嵩密度が１．６０g/cm³以上ではマクロポアーは大きく減少するものの、ミクロポアーがあるので炭素質被膜による充填が必要となる。
【００１５】
このようにして得られたＣ／Ｃ複合基材の表層部には緻密な炭素層が形成される反面微細なクラック等が生じ易く、ＳｉＯガスの侵入を充分に阻止することが困難となる。また、緻密化処理を反復しても表層部のみが緻密化されて基材の内部組織の空隙、ポア、クラック等は残留したままとなる。したがって、このままの状態でコンバージョン法によりＳｉＣ化を図るとＣ／Ｃ複合基材の内部組織の空隙、ポア、クラック等の周辺部がＳｉＯガスにより局部的にＳｉＣに転化し、材質強度の低下を招くこととなる。そこで、本発明においてはＣ／Ｃ複合基材の表層部に形成した緻密層の一部を研磨処理により除去する。研磨処理は、例えば研磨紙やショットブラスト等により基材に損傷を与えないようにしながら表層部を除去し、平滑化する。研磨量はＣ／Ｃ複合基材の大きさ、構造、緻密層の厚さ等により異なるが、通常５０〜５００μm 程度行えばよく、また研磨処理による表面粗さはＲmax ５０μm 以下に平滑化することが望ましい。
【００１６】
本発明の耐酸化性Ｃ／Ｃ複合材は、このようにして表面が研磨処理されたＣ／Ｃ複合基材表面に炭素質被膜が被着され、この被着した炭素質被膜をコンバージョン法により傾斜機能組織のＳｉＣ被膜に転化した被覆組織構造が形成された点に特徴がある。
【００１７】
この炭素質被膜は炭素質粉末と熱硬化性樹脂の炭化物とから構成される。炭素質粉末には黒鉛粉末、コークス粉末、カーボンブラック等が用いられ、熱硬化性樹脂としてはフェノール系やフラン系等の高炭化率の熱硬化性樹脂が用いられる。炭素質被膜は、これらの炭素質粉末が熱硬化性樹脂の炭化物であるガラス状炭素中に分散した複合構造からなり、Ｃ／Ｃ複合基材の表層部に強固に被着している。
【００１８】
このように、炭素質粉末とガラス状炭素の複合構造から構成される炭素質被膜は、複合炭素による高強度と気体不透過性に優れ、また炭化時における収縮が小さいのでＣ／Ｃ複合基材の表層部に存在する微細クラックや空隙を目詰めするとともにＣ／Ｃ複合基材面に強固に被着するので、ＳｉＯガスの侵入が効果的に阻止される。この場合、Ｃ／Ｃ複合基材表面の平滑性が劣り凹凸が存在すると、被着された炭素質被膜の膜厚にばらつきが生じてクラックが発生し易くなるために研磨処理により平滑化処理される。被着する炭素質被膜の厚さは１〜３０μm の範囲に設定する。膜厚が１μm 未満であるとＳｉＯガスの侵入を阻止する効果が小さく、３０μm を越えると炭素質被膜にクラックが生じ易くＣ／Ｃ複合基材から剥離し易くなるためである。なお、膜厚のばらつきは±１０μm 以内に抑えることが望ましい。
【００１９】
本発明の耐酸化性Ｃ／Ｃ複合材は、Ｃ／Ｃ複合基材の表層部に被着した炭素質被膜を傾斜機能組織のＳｉＣ被膜に転化した被覆組織構造が形成されたものであり、炭素質被膜が転化したＳｉＣ被膜とＣ／Ｃ複合基材表層部の炭素分が転化したＳｉＣ層とがＣ／Ｃ複合基材の表層部において緻密強固に結合し、また連続した傾斜機能組織のＳｉＣ被膜として一体的に形成されている。この被覆組織構造によりＳｉＯガスはＣ／Ｃ複合基材内部への浸透、拡散が阻止されるので、Ｃ／Ｃ複合基材の内部組織のＳｉＣ化及びＳｉＣ化の不均一性を効果的に抑制することができ、材質強度の低下を防止することが可能となる。
【００２０】
更に、このＳｉＣ被膜をベース被覆層としてその上にＳｉＯ₂、Ａｌ₂Ｏ₃、Ｂ₂Ｏ₃、ＺｒＯ₂の単体または複合体からなるガラス質被膜を積層形成した場合には、ガラス質被膜によるガス遮断効果により耐酸化性能を一層向上することができる。
【００２１】
本発明の耐酸化性Ｃ／Ｃ複合材は下記の方法により製造することができる。先ず、上記の方法により作製されたＣ／Ｃ複合基材の表面を研磨処理して平滑化する。研磨処理は研磨紙による研磨やショットブラスト等の適宜な手段が用いられ、研磨する範囲はＣ／Ｃ複合基材表層部の緻密化度合や組織構造によるが概ね５０〜５００μm 程度研磨すればよい。この研磨処理により表面は平滑化されるので、炭素質被膜を強固に被着させることができ、表面粗さとしてＲmax ５０μm 以下に平滑化することが望ましい。
【００２２】
研磨処理されたＣ／Ｃ複合基材は、黒鉛粉末、コークス粉末、カーボンブラック等の炭素質粉末（望ましくは平均粒径５μm 以下）とフェノール系、フラン系等の熱硬化性樹脂液とを混合した混合液中に浸漬、あるいは混合液を塗布する等の方法により被覆して、非酸化性雰囲気中８００℃以上の温度、好ましくは８００〜２０００℃の温度範囲で熱処理して焼成炭化することにより、炭素質粉末とガラス状炭素との複合構造からなる炭素質被膜が形成され、Ｃ／Ｃ複合基材面に強固に被着される。なお、炭素質被膜は１〜３０μm の厚さに被着することが好ましく、必要に応じて被着処理は繰り返し行われる。炭素質被膜の膜厚が１μm 未満であると、次工程のコンバージョン法によりＳｉＣ被膜に転化する際に、Ｃ／Ｃ複合基材内部にＳｉＯガスの侵入を阻止する効果が小さく、一方３０μm を越えると炭素質被膜にクラックが生じ易く、Ｃ／Ｃ複合基材から剥離し易くなるためである。なお、膜厚のばらつきは±１０μm 以内に抑えることが望ましい。
【００２３】
炭素質被膜を被着したＣ／Ｃ複合基材は、次いでコンバージョン法により基材表面にＳｉＣ被膜が形成被覆される。ＳｉＯガスを発生させる珪素源としては、石英、珪石、珪砂等のＳｉＯ₂含有物質を粒径１０〜５００μm に粉砕したものが用いられ、また炭素源には粒径１０〜５００μm のコークス、ピッチ、黒鉛、カーボンブラック等の炭素質粉末が使用される。珪素源と炭素源との配合組成は、各材料粉末の表面積を考慮して決定されるが、通常、ＳｉＯ₂：Ｃの重量比率が１：１〜５：１の範囲になるように配合される。配合物はＶ型ブレンダーなどの混合装置で十分に混合し、均一な混合物としたのち、黒鉛のような高耐熱性材料で構成された反応容器に入れる。
【００２４】
上記の反応容器を密閉加熱炉内に設置し、Ｃ／Ｃ複合基材を反応容器内の珪素源と炭素源との混合粉末中に埋没するか反応容器の近傍にセットした状態で系内を還元または中性の非酸化性雰囲気に保持しながら１６００〜２０００℃の温度に加熱処理する。処理過程で、珪素源と炭素源の加熱還元反応により発生したＳｉＯガスは、Ｃ／Ｃ複合基材の表層面と接触しながらＳｉＣに転化するが、Ｃ／Ｃ複合基材の表層部に被着された均一、緻密で強固な炭素質被膜によりＳｉＯガスはＣ／Ｃ複合基材の表層部のみを傾斜機能組織のＳｉＣ被膜に転化して、内部に拡散浸透する現象が効果的に阻止される。
【００２５】
したがって、Ｃ／Ｃ複合基材の内部組織の空隙、ポア、クラック等の周辺部の炭素がＳｉＯガスにより局部的にＳｉＣに転化したり、Ｃ／Ｃ複合基材の内部組織における炭素繊維部とマトリックス炭素部との界面部がＳｉＯガスにより局部的にＳｉＣに転化する現象が抑制され、Ｃ／Ｃ複合基材の内部組織がＳｉＣ化される現象が阻止される。このようにして、Ｃ／Ｃ複合基材表層部の均一、緻密な炭素質被膜が転化したＳｉＣ層とＣ／Ｃ複合基材表層部が転化したＳｉＣ層とが緊密に連続した傾斜機能組織のＳｉＣ被膜が一体的に形成され、高度の耐酸化性が付与されるとともに、Ｃ／Ｃ複合基材の内部組織におけるＳｉＣ化ならびにＳｉＣ化の不均一性を低減することができ、材質強度の低下を抑制することが可能となる。
【００２６】
このようにして、表面を傾斜機能組織のＳｉＣ被膜に転化したＣ／Ｃ複合基材は、このＳｉＣ被膜をベース被覆層としてその上にＳｉＯ₂、Ａｌ₂Ｏ₃、Ｂ₂Ｏ₃、ＺｒＯ₂の単体または複合体からなるガラス質被膜を積層形成することにより更に高度の耐酸化性能を付与することができる。ガラス質被膜は、例えば、Ｓｉ、Ａｌ、Ｂ、Ｚｒの少なくとも一種を含有するＳｉ（ＯＣ₂Ｈ₅)₄、Ｂ（ＯＣ₄Ｈ₉)₃、Ｚｒ（ＯＣ₄Ｈ₉)₄等の金属アルコキシドにアルコールを加えて撹拌混合した溶液中に水を滴下して加水分解するアルコキシド法によりガラス前駆体溶液を作成し、ＳｉＣ被膜を被覆したＣ／Ｃ複合基材をガラス前駆体溶液中に浸漬あるいは溶液を塗布する等の方法により含浸し、乾燥したのち５００〜１０００℃の温度で加熱処理する方法により形成することができる。
【００２７】
【実施例】
以下、本発明の実施例を比較例と対比して具体的に説明する。
【００２８】
実施例１
ポリアクリロニトリル系の炭素繊維〔東レ（株）製T900〕を体積含有率６０％になるように三次元方向に織り込んだ三次元炭素繊維プリフォームを作成し、プリフォームにフェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕を真空下で含浸した。この樹脂含浸炭素繊維プリフォームを電気オーブンに入れて、１７０℃の温度で加熱硬化して炭素繊維樹脂複合体を作製した。この複合体を窒素ガス雰囲気に保持した焼成炉に入れ、２０℃／hrの昇温速度で１０００℃に加熱して焼成炭化した。更にフルフリルアルコール初期縮合物を含浸し、再び焼成炉に移して５０℃／hrの昇温速度で１０００℃まで加熱して緻密化処理した。この緻密化処理を５回繰り返して行い、又３回目の緻密化処理後に上下両面をサンドペーパーにより研磨して、表層部を各２００μm 削除した。次いで、焼成炉中で７０℃／hrの昇温速度で２０００℃に加熱して、縦横２５０mm、厚さ４mmのＣ／Ｃ複合基材を作製した。ただし引張試験片は、あらかじめ試験片形状に加工した。このＣ／Ｃ複合材の嵩密度をアルキメデス法により測定した。なお、以下の実施例、比較例においてもこのＣ／Ｃ複合基材の嵩密度をアルキメデス法により測定した。
【００２９】
黒鉛粉末（平均粒子径 0.3μm)とフェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕とを重量比で１：１の割合で混合し、三本ロールで充分に混練して黒鉛粉末とフェノール樹脂液との混合液を調製した。この混合液を上記Ｃ／Ｃ複合基材面に塗布して、電気オーブン中で１７０℃の温度で加熱硬化した後、窒素雰囲気中１００℃／hrの昇温速度で２０００℃の温度に加熱して焼成炭化し、Ｃ／Ｃ複合基材面に厚さ２０μm の炭素質被膜を被着した。
【００３０】
この炭素質被膜を被着したＣ／Ｃ複合基材を気孔率９０％、気孔径１０μm 、厚さ１０mmの黒鉛繊維フェルトで被包し、珪素源として平均粒子径２８０μm の石英粉末と、炭素源として平均粒子径９０μm のコークス粉末を３：１の重量比で混合した混合粉末を黒鉛繊維フェルトの上下に配置した状態で黒鉛容器に入れた。黒鉛容器を窒素ガス雰囲気に保持された加熱炉に移し５０℃／hrの昇温速度で１８５０℃の温度に加熱し、３０分間加熱反応させてコンバージョン法により、Ｃ／Ｃ複合基材の表面を傾斜機能組織のＳｉＣ被膜に転化した。
【００３１】
このようにして製造したＳｉＣ被膜を形成したＣ／Ｃ複合材について、次の方法により引張強度、ＳｉＣ被覆層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性の評価を行って、その結果を表１に示した。
▲１▼引張強度：
厚さ２mm、長さ１６０mmの試料より掴み部分を長さ４０mm、幅２５．４mmとし、ゲージ部を長さ４０mm、幅１２．７mmのダンベル形状に加工して、引張強度測定用試験片とした。この試験片にクロスヘッド速度１．３mm／min で引張荷重を加え、破壊荷重を測定した。
▲２▼ＳｉＣ被膜層の厚さ等：
ＳｉＣを被覆したＣ／Ｃ複合材の一部をダイヤモンドカッターで切断した断面をＳＥＭで観察して、ＳｉＣ被膜層の厚さ、ならびにＣ／Ｃ複合材の内部組織におけるＳｉＣ化された最大深さを測定した。
▲３▼耐酸化性試験：
ＳｉＣを被覆したＣ／Ｃ複合材を電気炉に入れて、大気雰囲気下に１４００℃の温度に３０分間保持した時の重量減少率を測定した。
【００３２】
実施例２
Ｓｉ (ＯＣ₂Ｈ₅)₄とエタノールをモル比１：１２の割合で配合し、７０℃の温度で還流撹拌したのち、Ｓｉ (ＯＣ₂Ｈ₅)₄１モルに対して２５モルの水と０．２モルのＮＨ₄ＯＨの混合液を撹拌しながら滴下し（ｐＨ１２．０）、引き続き撹拌を継続して約０．２μm のＳｉＯ₂球状微粒子が均一に分散するサスペンジョンを作成し、このサスペンジョン中に前記実施例１で作製した炭化珪素被覆Ｃ／Ｃ材を浸漬して、１５分間１６０Torrの圧力下に含浸処理を行った後、風乾した。次に、Ｓｉ (ＯＣ₂Ｈ₅)₄とエタノールをモル比１：４．５の割合で配合し、室温で還流撹拌したのち、Ｓｉ (ＯＣ₂Ｈ₅)₄１モルに対し２．５モルの水と０．０３モルのＨＣｌの混合液を撹拌しながら滴下して（ｐＨ 3.0）、ＳｉＯ₂ガラス前駆体溶液を調製した。このガラス前駆体溶液に、前記ＳｉＯ₂微粒子層を形成したＣ／Ｃ複合材を浸漬し、１６０Torrの圧力下に１５分間含浸処理したのち風乾し、その後５００℃の温度で１０分間加熱して、ＳｉＯ₂のガラス質被膜（厚さ 5μm ）を形成した。
【００３３】
このようにして製造した実施例１のＣ／Ｃ複合材のＳｉＣ被膜の上にＳｉＯ₂のガラス質被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性試験を行って、その結果を表１に併載した。
【００３４】
実施例３〜４
ポリアクリロニトリル系の平織炭素繊維布〔東レ（株）製T300〕にフェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕をエタノールに溶解した溶液（濃度30Wt％）を塗布し、４８時間風乾してプリプレグシートを作製した。このプリプレグシート１６枚を積層してモールドに入れ、圧力２０Kg／cm²、温度１５０℃の条件で熱圧プレスして成形した。この成形体を１７０℃に加熱して硬化したのち、窒素ガス雰囲気に保持した焼成炉に入れ、２０℃／hrの昇温速度で１０００℃に加熱して焼成炭化した。更にフルフリルアルコール初期縮合物を含浸し、再び焼成炉に移して５０℃／hrの昇温速度で１０００℃まで加熱して緻密化処理した。この緻密化処理を５回繰り返して行い、又３回目の緻密化処理後に上下両面をサンドペーパーにより研磨して、表層部を各２００μm 研削削除した。次いで、焼成炉中で７０℃／hrの昇温速度で２０００℃に加熱して、縦横２５０mm、厚さ４mmのＣ／Ｃ複合基材を作製した。
【００３５】
このＣ／Ｃ複合基材に、黒鉛粉末（平均粒子径０．３μm)とフェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕とを重量比で１：１の割合で混合し、三本ロールで充分に混練して調製した黒鉛粉末とフェノール樹脂液との混合液を異なる厚さに塗布した。次いで、電気オーブン中で１７０℃の温度で加熱硬化した後、窒素雰囲気中１００℃／hrの昇温速度で２０００℃の温度に加熱して焼成炭化し、Ｃ／Ｃ複合基材面に異なる膜厚で炭素質被膜を被着した。
【００３６】
この炭素質被膜を被着したＣ／Ｃ複合基材を、実施例１と同一の方法により基材の表面を傾斜機能組織のＳｉＣ被膜に転化した。得られたＳｉＣ被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性試験を行ってその結果を表１に併載した。
【００３７】
実施例５
緻密化処理を３回繰り返したほかは、全て実施例１と同一の方法によりＣ／Ｃ複合基材を作製し、その表面を傾斜機能組織のＳｉＣ被膜に転化した。得られたＳｉＣ被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性試験を行ってその結果を表１に併載した。
【００３８】
比較例１〜２
実施例１と同一の方法により作製した炭素繊維樹脂複合体を、実施例１と同一の条件で焼成炭化及び緻密化処理した。得られたＣ／Ｃ複合基材に実施例１と同一の方法で調製した黒鉛粉末とフェノール樹脂液との混合液を異なる膜厚で塗布し、実施例１と同一の方法で焼成炭化して厚さ０．５μm および４０μm の炭素質被膜を被着し、実施例１と同一の方法でコンバージョン法によりＣ／Ｃ複合基材の表面を傾斜機能組織のＳｉＣ被膜に転化した。このようにして製造したＳｉＣ被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定しまた耐酸化性試験を行って、その結果を表１に併載した。
【００３９】
比較例３
実施例１と同一の方法により作製した炭素繊維樹脂複合体を、実施例１と同一の条件で焼成炭化及び緻密化処理した。得られたＣ／Ｃ複合基材を研磨処理及び炭素質被膜を被着することなく、実施例１と同一の方法でコンバージョン法によりＣ／Ｃ複合基材の表面を傾斜機能組織のＳｉＣ被膜に転化した。このようにして製造したＳｉＣ被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定しまた耐酸化性試験を行って、その結果を表１に併載した。
【００４０】
比較例４
ポリアクリロニトリル系の炭素繊維〔東レ（株）製T900〕を体積含有率６０％になるように三次元方向に織り込んだ三次元炭素繊維プリフォームを作成し、プリフォームにフェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕を真空下で含浸した。この樹脂含浸炭素繊維プリフォームを電気オーブンに入れて、１７０℃の温度で加熱硬化して炭素繊維樹脂複合体を作製した。この複合体を窒素ガス雰囲気に保持した焼成炉に入れ、２０℃／hrの昇温速度で１０００℃に加熱して焼成炭化した。更にフルフリルアルコール初期縮合物を含浸し、再び焼成炉に移して５０℃／hrの昇温速度で１０００℃まで加熱して緻密化処理した。この緻密化処理を５回繰り返して行った後、焼成炉中で７０℃／hrの昇温速度で２０００℃に加熱して、縦横２５０mm、厚さ４mmのＣ／Ｃ複合基材を作製した。
【００４１】
このＣ／Ｃ複合基材を加圧容器に入れて、１０Torrの減圧下で脱気処理したのち、２２０℃の温度で加熱溶融した石炭ピッチ中に浸漬し、５Kg／cm²の圧力を加えて１０分間加圧含浸した。このようにして表層部に石炭ピッチを含浸したＣ／Ｃ複合基材を窒素ガス雰囲気に保持した焼成炉に移し、５０℃／hrの昇温速度で２０００℃まで加熱処理して易黒鉛化性炭素の被膜層を形成した。このＣ／Ｃ複合基材を実施例１と同一の方法でコンバージョン法によりＣ／Ｃ複合基材の表面を傾斜機能組織のＳｉＣ被膜に転化した。このようにして製造したＳｉＣ被膜を形成したＣ／Ｃ複合材について、実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性試験を行って、その結果を表１に併載した。
【００４２】
比較例５
緻密化処理を３回繰り返して行い、研磨処理をせずに、実施例３、４と同一の方法によりＣ／Ｃ複合基材を作製し、このＣ／Ｃ複合基材を研磨処理することなく、フェノール樹脂初期縮合物〔住友デュレズ（株）製 PR940〕のみを塗布した。次いで、電気オーブン中で１７０℃の温度で加熱硬化した後、窒素雰囲気中１００℃／hrの昇温速度で２０００℃の温度に加熱して焼成炭化し、Ｃ／Ｃ複合基材面に厚さ２５μm のガラス状カーボン被膜を被着した。このガラス状カーボン被膜を被着したＣ／Ｃ複合基材を、実施例１と同一の方法により基材の表面を傾斜機能組織のＳｉＣ被膜に転化し、得られたＳｉＣ被膜を形成したＣ／Ｃ複合材について実施例１と同一の方法により引張強度、ＳｉＣ被膜層の厚さ及び内部組織のＳｉＣ化された深さを測定し、また耐酸化性試験を行ってその結果を表１に併載した。
【００４３】
【表１】

【００４４】
表１の結果から、実施例の耐酸化性Ｃ／Ｃ複合材はＣ／Ｃ複合基材面に緻密、強固で均一なＳｉＣ被膜が形成されて、内部組織がＳｉＣ化される現象が効果的に抑制されるので、引張強度が高く、酸化消耗による重量減少率も少ないことが判る。また酸化試験後のＳｉＣ被膜も剥離等の異常が認められず、安定である。特に、実施例１、２から明らかなように三次元織の炭素繊維クロスを用いたＣ／Ｃ複合材（３Ｄ−Ｃ／Ｃ複合材）の場合にも引張強度が高く、更にＳｉＣ被膜層の上にＳｉＯ₂のガラス質被覆層を積層形成した実施例２では耐酸化性能が一層向上することが認められる。これに対して、炭素質被膜の膜厚が薄い比較例１ではＳｉＯガスの侵入が充分に抑止できないために耐酸化性や強度が劣り、また膜厚が厚い比較例２では炭素質被膜にクラックが発生するために耐酸化性や強度が劣る上にＳｉＣ被膜の剥離が生じている。炭素質被膜を被着しない比較例３では耐酸化性や強度が一層低位に有り、また石炭ピッチを炭化した易黒鉛化炭素の被膜層を被着した比較例４でも強度及び耐酸化性が低く、ガラス状カーボン被膜を形成被着した比較例５では被膜の収縮によりクラックが生じて、ＳｉＣ被膜の侵入防止効果が充分でなく、強度低下、耐酸化性低下となっている。
【００４５】
【発明の効果】
以上のとおり、本発明の耐酸化性Ｃ／Ｃ複合材によれば表面を研磨して平滑化したＣ／Ｃ複合基材に被着した炭素質粉末とガラス状炭素の複合構造からなる炭素質被膜を傾斜機能組織のＳｉＣ被膜に転化した被覆組織構造により、Ｃ／Ｃ複合基材の内部組織のＳｉＣ化が効果的に阻止されてＣ／Ｃ複合材の材質強度の低下が防止されるとともにＣ／Ｃ複合基材に緻密、強固で均一に形成されたＳｉＣ被膜層により優れた耐酸化性能を付与することが可能となる。更にガラス質被膜を積層形成することにより耐酸化性を一層向上することができる。また、本発明の耐酸化性Ｃ／Ｃ複合材の製造方法によれば、上記の材質強度が高く、耐酸化性に優れたＣ／Ｃ複合材を容易に製造することができる。したがって、本発明は材質強度ならびに耐酸化性能に優れた耐酸化性Ｃ／Ｃ複合材及びその製造方法として極めて有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention has a high material strength and excellent oxidation resistance performance, in which a SiC coating layer having a functionally graded structure is stably and firmly formed on a surface layer portion of a C / C composite substrate (carbon fiber reinforced carbon composite substrate) by a conversion method. The present invention relates to an oxidation-resistant C / C composite material and a method for producing the same.
[0002]
[Prior art]
C / C composites have excellent specific strength and specific modulus, and have excellent heat resistance and chemical stability at high temperatures exceeding 1000 ° C. It is useful as a structural material used in. However, the C / C composite material has a defect inherent to the carbon material that is subject to material oxidation from around 500 ° C. in the atmosphere, and this is the biggest obstacle that limits the application of the C / C composite material. For this reason, many attempts have been made to improve the oxidation resistance by forming a coating layer having a high oxidation resistance on the surface of the C / C composite material. For example, SiC, Si _Three N _Four , ZrO ₂ , Al ₂ O _Three Many methods have been developed for coating with a heat-resistant ceramic material such as the above. Among these, the coating of SiC is excellent in terms of technical properties and economy, and is practically used as the most suitable industrialization means.
[0003]
As a typical method of forming a SiC coating layer on the surface of a C / C composite material, a CVD method (chemical vapor deposition method) in which SiC generated by a gas phase reaction is directly deposited, and a C / C composite material A conversion method is known in which carbon is used as a reaction source to react with SiO gas to convert it into SiC. However, each of the SiC coating layers formed by these methods has advantages and disadvantages. That is, although the SiC coating layer formed by the former CVD method is excellent in denseness, if a thermal shock is applied in a relationship where the interface with the substrate is clearly separated, the difference in the coefficient of thermal expansion between the two There is a drawback that the delamination phenomenon tends to occur. This delamination phenomenon occurs mainly because the difference in thermal expansion coefficient between the C / C composite substrate and the SiC coating layer is large and the maximum strain cannot follow. It can be reduced if it is modified to approximate the thermal expansion coefficient of SiC. From such a viewpoint, a method of forming a pyrolytic carbon layer on the C / C composite substrate surface by vapor phase pyrolysis and then coating SiC by CVD or CVI (Japanese Patent Laid-Open No. 2-111681) is proposed. However, sufficient high-temperature oxidation resistance that meets the operational complexity cannot be expected.
[0004]
On the other hand, in the latter conversion method, the SiO gas generated by heating and reacting the silicon source and the carbon source reacts with the carbon structure constituting the C / C composite material, and the inside of the surface layer portion of the C / C composite material is reacted. Therefore, the formed silicon carbide layer exhibits a continuous functional gradient structure in which the degree of SiC conversion gradually decreases toward the inside of the material. Accordingly, there is no interlayer such as a silicon carbide layer formed by the CVD method, and there is an advantage that interlayer interface peeling does not occur even when subjected to thermal shock. However, on the other hand, there is a disadvantage that the density of the silicon carbide layer in the surface layer portion is lowered and sufficient oxidation resistance cannot be imparted.
[0005]
For this reason, there has been proposed an attempt to improve the oxidation resistance performance by forming a SiC layer on the surface of the C / C composite base material in advance by a conversion method and using this as a base coating layer to form various coating layers thereon. Yes. For example, the applicant of the present invention has a SiC coating layer, SiO on the surface of a C / C composite substrate. ₂ Fine grain coating layer, SiO ₂ Glass coating layer or B ₂ O _Three Glass coating layer or B ₂ O _Three ・ SiO ₂ An oxidation resistant C / C material having a structure in which a glass coating layer is laminated in three layers and a manufacturing method thereof (Japanese Patent Laid-Open No. 4-42883) have been developed. -243989, JP-A-4-243990, JP-A-4-43366, JP-A-5-70228, JP-A-5-229886, JP-A-5-330961, JP-A-6-48872 No. 6, JP-A-6-144967, JP-A-6-247782, etc. have been developed and proposed.
[0006]
Although these multilayer coating means can effectively improve the oxidation resistance performance of the C / C composite material, the conversion to SiC by the conversion method constituting the base coating layer is essentially a C / C. There is a problem that the material strength of the composite substrate itself is impaired. In other words, in the coating process using the conversion method, the SiO gas permeates and diffuses from the surface of the C / C base material to the inside of the tissue to convert the C / C base material structure to SiC, but exists in the C / C base material. The SiO gas easily permeates and diffuses into a relatively deep substrate structure along the pores and cracks. Therefore, not only the surface of the C / C composite material but also SiC formation progresses to a relatively deep internal structure, and the base material structure, particularly the matrix carbon portion that is easily converted to SiC and the carbon fiber / matrix carbon interface portion, etc. are preferentially silicified. As a result, SiC is easily formed into a saw shape or an island shape, and as a result, a phenomenon of weakening the entire base material structure occurs. This tendency becomes more prominent when the shape of the C / C base material becomes larger or complicated.
[0007]
Thus, when a SiC coating layer is formed on the surface of a C / C composite substrate by a conversion method, the generated SiC coating layer is made uniform and dense to suppress the phenomenon that the internal structure of the substrate becomes SiC. Necessary for securing material strength. From this point of view, the present applicant has calcined and carbonized a carbon fiber composite resin molded body obtained by composite molding and curing of carbon fiber with a matrix resin in a state where a polyimide resin film is spread on the outer peripheral surface. The composite substrate is brought into contact with SiO gas produced by heating and reacting a mixed powder of a silicon source and a carbonaceous material in a non-oxidizing atmosphere at a temperature range of 1600 to 2000 ° C., and the surface of the C / C composite substrate is converted by the conversion method. Oxidation resistance in which a SiC coating layer is formed by a conversion method after forming a coating layer of graphitizable carbon on the surface layer of a C / C composite substrate (Japanese Patent Laid-Open No. 8-169786) or a method of forming a SiC coating layer Has developed a method for producing a conductive C / C composite (Japanese Patent Application No. 8-346730).
[0008]
According to these methods, a thin carbon layer formed by carbonization of a polyimide resin film interposed on the outer peripheral surface at the stage of a carbon fiber reinforced resin molded body, or coal on the surface layer portion of a C / C composite substrate Only the surface layer portion of the C / C composite substrate is converted into a dense SiC coating layer by the graphitizable carbon coating layer formed by carbonization of the system pitch, petroleum pitch, etc., and the C / C composite substrate The phenomenon in which SiO gas permeates and diffuses inside the tissue can be suppressed, and it is possible to suppress a decrease in material strength and to provide excellent oxidation resistance.
[0009]
[Problems to be solved by the invention]
However, as a result of further research conducted by the present inventors in order to impart a high level of oxidation resistance without impairing the excellent material properties of the C / C composite material, the above-mentioned JP-A-8-169786 and the patent In the technique of No. 8-346730, it is not sufficient to prevent the SiO gas from diffusing and penetrating into the internal structure, and in particular, a C / C composite material using a three-dimensional carbon fiber preform (3D-C / C In the case of a composite material), there is a problem that voids or the like existing at the interface or the periphery of the fiber in the Z-axis direction are easily converted to SiC by the silicidation reaction, and it is difficult to sufficiently suppress the weakening of the internal structure. Elucidated.
[0010]
As a result of further research on the mechanism of local penetration of SiO gas into the C / C composite substrate, the present inventors have refined the surface state of the C / C composite substrate and polished the surface. A smooth SiC coating is formed by applying a carbonaceous coating with a composite structure consisting of carbonaceous powder and glassy carbon on top of it, and a dense SiC coating is formed. I found out that it can be prevented.
[0011]
The present invention has been completed on the basis of the above knowledge, and its purpose is to provide a dense SiC coating layer on the surface layer portion of the C / C composite base material by a conversion method without causing a decrease in material strength due to the formation of SiC in the internal structure. It is an object to provide an oxidation-resistant C / C composite material having excellent strength and oxidation resistance, and a method for producing the same.
[0012]
[Means for Solving the Problems]
The oxidation-resistant C / C composite material according to the present invention for achieving the above object comprises a carbonaceous powder deposited on a C / C composite substrate whose surface is polished and a carbide of a thermosetting resin. A structural feature is that a coating structure is formed by converting a carbonaceous film having a thickness of 1 to 30 μm into a SiC film having a functionally graded structure.
[0013]
Also, the method for producing an oxidation resistant C / C composite material according to the present invention comprises: carbon fiber is composite-molded with a matrix resin, and the surface of the cured and fired carbonized C / C composite substrate is polished, and then carbonaceous powder And a mixture of a thermosetting resin liquid, calcined at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere to deposit a carbonaceous film having a thickness of 1 to 30 μm, and then a mixture of a silicon source and a carbon source Contacting the SiO gas produced by heating the powder with SiO gas in a non-oxidizing atmosphere at a temperature range of 1600 to 2000 ° C., and converting the surface of the C / C composite base material into a SiC film having a functionally gradient structure by a conversion method. This is a structural feature.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Carbon fibers used as reinforcements for C / C composites are oriented in one-dimensional or multi-dimensional directions, such as plain weave, satin weave and twill weave manufactured from various materials such as polyacrylonitrile, rayon and pitch. A fibrous body, felt, tow, etc. are used, and as the matrix resin, a highly carbonized liquid thermosetting resin such as phenol or furan, or a thermoplastic material such as tar pitch is used. Carbon fiber is fully impregnated with matrix resin by means of dipping, coating, etc., then semi-cured to form a prepreg, then laminated and pressed to form a composite, and then heated to completely cure the resin component. Thus, a C / C composite substrate is produced by heating to carbonization at 1000 to 2000 ° C. in a non-oxidizing atmosphere. The density of the C / C composite substrate is preferably high. For example, the bulk density is 1.60 g / cm. ^Three Although it is desirable that the density be lower than the desired bulk density, the surface of the C / C composite base material is repeatedly impregnated with matrix resin, cured, calcined and carbonized as necessary, and repeatedly densified with matrix carbon. To improve the organization of the department. Low bulk density, 1.60 g / cm ^Three If it is less than that, macropores that cannot be filled with the carbonaceous film remain, so that the penetration of SiO gas occurs through the macropores. The bulk density is 1.60 g / cm ^Three Although the macropores are greatly reduced as described above, since there are micropores, filling with a carbonaceous film is necessary.
[0015]
On the surface layer portion of the C / C composite substrate thus obtained, a dense carbon layer is formed, but fine cracks and the like are likely to occur, and it is difficult to sufficiently prevent the invasion of SiO gas. Even if the densification treatment is repeated, only the surface layer portion is densified, and voids, pores, cracks, etc. in the internal structure of the substrate remain. Therefore, if SiC is converted by the conversion method in this state, the peripheral part of voids, pores, cracks, etc. in the internal structure of the C / C composite base material is locally converted to SiC by SiO gas, and the material strength is reduced. Will be invited. Therefore, in the present invention, a part of the dense layer formed on the surface layer portion of the C / C composite substrate is removed by polishing treatment. In the polishing treatment, for example, the surface layer portion is removed and smoothed without damaging the base material by polishing paper, shot blasting, or the like. The polishing amount varies depending on the size, structure, dense layer thickness, etc. of the C / C composite base material, but it is usually about 50 to 500 μm, and the surface roughness by polishing should be smoothed to Rmax 50 μm or less. Is desirable.
[0016]
In the oxidation-resistant C / C composite material of the present invention, a carbonaceous film is deposited on the surface of the C / C composite substrate whose surface has been polished in this way, and this deposited carbonaceous film is converted by a conversion method. It is characterized in that a coating structure converted into a SiC film having a functionally gradient structure is formed.
[0017]
This carbonaceous film is composed of carbonaceous powder and a carbide of a thermosetting resin. As the carbonaceous powder, graphite powder, coke powder, carbon black or the like is used, and as the thermosetting resin, a thermosetting resin having a high carbonization rate such as phenol or furan is used. The carbonaceous film has a composite structure in which these carbonaceous powders are dispersed in glassy carbon that is a carbide of a thermosetting resin, and is firmly attached to the surface layer portion of the C / C composite substrate.
[0018]
Thus, the carbonaceous film composed of a composite structure of carbonaceous powder and glassy carbon is excellent in high strength and gas impermeability due to the composite carbon, and since the shrinkage during carbonization is small, the C / C composite base material Since the fine cracks and voids existing in the surface layer portion are clogged and firmly adhered to the C / C composite substrate surface, the penetration of SiO gas is effectively prevented. In this case, if the surface of the C / C composite substrate is inferior in smoothness and unevenness is present, the film thickness of the deposited carbonaceous film varies, and cracks are likely to occur. The The thickness of the carbonaceous film to be deposited is set in the range of 1 to 30 μm. This is because if the film thickness is less than 1 μm, the effect of preventing the invasion of SiO gas is small, and if it exceeds 30 μm, the carbonaceous film is liable to crack and peel from the C / C composite substrate. In addition, it is desirable to suppress variations in film thickness within ± 10 μm.
[0019]
The oxidation-resistant C / C composite material of the present invention has a structure in which a coating structure is formed by converting a carbonaceous film deposited on the surface layer portion of a C / C composite substrate into a SiC film having a functionally graded structure. The SiC film in which the carbonaceous film is converted and the SiC layer in which the carbon content of the C / C composite substrate surface layer is converted are bonded tightly and firmly in the surface layer portion of the C / C composite substrate, and the continuous gradient functional structure It is integrally formed as a SiC film. This coating structure prevents SiO gas from penetrating and diffusing into the C / C composite substrate, effectively suppressing the non-uniformity of SiC and SiC in the internal structure of the C / C composite substrate. It is possible to prevent the material strength from being lowered.
[0020]
Further, this SiC coating is used as a base coating layer on which SiO 2 is coated. ₂ , Al ₂ O _Three , B ₂ O _Three , ZrO ₂ When a glassy film made of a simple substance or a composite is laminated and formed, the oxidation resistance can be further improved by the gas barrier effect of the glassy film.
[0021]
The oxidation resistant C / C composite of the present invention can be produced by the following method. First, the surface of the C / C composite substrate produced by the above method is polished and smoothed. For the polishing treatment, an appropriate means such as polishing with abrasive paper or shot blasting is used, and the polishing range may be approximately 50 to 500 μm depending on the degree of densification of the surface layer portion of the C / C composite base material and the structure. Since the surface is smoothed by this polishing treatment, the carbonaceous film can be firmly applied, and it is desirable to smooth the surface to Rmax 50 μm or less.
[0022]
The polished C / C composite base material is a mixture of graphite powder, coke powder, carbon black or other carbonaceous powder (preferably having an average particle size of 5 μm or less) and a phenolic or furanic thermosetting resin liquid. By immersing in the mixed liquid or coating by a method such as applying the mixed liquid, and heat-treating in a non-oxidizing atmosphere at a temperature of 800 ° C. or higher, preferably 800 to 2000 ° C. A carbonaceous film having a composite structure of carbonaceous powder and glassy carbon is formed, and is firmly attached to the C / C composite substrate surface. The carbonaceous film is preferably deposited to a thickness of 1 to 30 μm, and the deposition process is repeated as necessary. When the film thickness of the carbonaceous film is less than 1 μm, the effect of preventing the penetration of SiO gas into the C / C composite base material is small when it is converted into the SiC film by the conversion method in the next step, whereas it exceeds 30 μm. This is because cracks are likely to occur in the carbonaceous film, and it is easy to peel from the C / C composite substrate. In addition, it is desirable to suppress the variation in film thickness within ± 10 μm.
[0023]
Next, the C / C composite base material coated with the carbonaceous film is coated with a SiC film formed on the surface of the base material by a conversion method. Examples of the silicon source that generates SiO gas include SiO, quartz, silica, and silica sand. ₂ A material obtained by pulverizing the contained material to a particle size of 10 to 500 μm is used, and a carbonaceous powder such as coke, pitch, graphite, or carbon black having a particle size of 10 to 500 μm is used as the carbon source. The composition of the silicon source and the carbon source is determined in consideration of the surface area of each material powder. ₂ : C is blended so that the weight ratio of C is in the range of 1: 1 to 5: 1. The blend is thoroughly mixed with a mixing device such as a V-type blender to make a uniform mixture, and then put into a reaction vessel composed of a high heat resistant material such as graphite.
[0024]
The above reaction vessel is installed in a closed heating furnace, and the C / C composite substrate is buried in the mixed powder of the silicon source and carbon source in the reaction vessel or set in the vicinity of the reaction vessel. Heat treatment is performed at a temperature of 1600 to 2000 ° C. while maintaining a reducing or neutral non-oxidizing atmosphere. During the treatment process, the SiO gas generated by the heat reduction reaction of the silicon source and the carbon source is converted to SiC while in contact with the surface layer surface of the C / C composite substrate, but the surface layer portion of the C / C composite substrate is covered. The uniform, dense and strong carbonaceous coating is applied to effectively prevent the phenomenon of diffusion and penetration of SiO gas by converting only the surface layer portion of the C / C composite base material into a SiC coating having a functionally graded structure. The
[0025]
Therefore, carbon in the peripheral part such as voids, pores, cracks, etc. in the internal structure of the C / C composite base material is locally converted to SiC by SiO gas, or the carbon fiber part in the internal structure of the C / C composite base material The phenomenon that the interface portion with the matrix carbon portion is locally converted to SiC by the SiO gas is suppressed, and the phenomenon that the internal structure of the C / C composite substrate is converted to SiC is prevented. Thus, the gradient functional structure in which the SiC layer in which the uniform and dense carbonaceous film of the C / C composite substrate surface layer portion is converted and the SiC layer in which the C / C composite substrate surface layer portion is converted is closely connected is formed. The SiC film is formed integrally, providing high oxidation resistance, and reducing the non-uniformity of SiC conversion and SiC conversion in the internal structure of the C / C composite substrate, resulting in reduced material strength Can be suppressed.
[0026]
In this way, the C / C composite base material whose surface is converted to a SiC coating having a functionally graded structure is obtained by using the SiC coating as a base coating layer and a SiO coating thereon. ₂ , Al ₂ O _Three , B ₂ O _Three , ZrO ₂ A higher level of oxidation resistance can be imparted by laminating and forming a glassy film composed of a simple substance or a composite of the above. The glassy film is, for example, Si (OC containing at least one of Si, Al, B, and Zr. ₂ H _Five ) _Four , B (OC _Four H ₉ ) _Three , Zr (OC _Four H ₉ ) _Four A glass precursor solution is prepared by an alkoxide method in which alcohol is added to a metal alkoxide such as alcohol and mixed with stirring to hydrolyze it, and a C / C composite substrate coated with a SiC coating is prepared as a glass precursor solution. It can be formed by a method of impregnating by a method such as dipping or applying a solution therein and drying, followed by heat treatment at a temperature of 500 to 1000 ° C.
[0027]
【Example】
Examples of the present invention will be specifically described below in comparison with comparative examples.
[0028]
Example 1
A three-dimensional carbon fiber preform was prepared by weaving polyacrylonitrile-based carbon fiber [T900 manufactured by Toray Industries, Inc.] in a three-dimensional direction so that the volume content was 60%. Durez Co., Ltd. PR940] was impregnated under vacuum. This resin-impregnated carbon fiber preform was put in an electric oven and heat-cured at a temperature of 170 ° C. to prepare a carbon fiber resin composite. This composite was placed in a firing furnace maintained in a nitrogen gas atmosphere, and heated to 1000 ° C. at a rate of temperature increase of 20 ° C./hr for firing and carbonization. Further, it was impregnated with an initial condensate of furfuryl alcohol, transferred again to a baking furnace, and heated to 1000 ° C. at a temperature increase rate of 50 ° C./hr for densification treatment. This densification treatment was repeated 5 times, and after the third densification treatment, the upper and lower surfaces were polished with sandpaper to remove 200 μm of the surface layer portion. Subsequently, it heated at 2000 degreeC with the temperature increase rate of 70 degreeC / hr in the baking furnace, and produced the C / C composite base material of length and width 250mm and thickness 4mm. However, the tensile test piece was processed into a test piece shape in advance. The bulk density of the C / C composite material was measured by Archimedes method. In the following examples and comparative examples, the bulk density of the C / C composite substrate was also measured by the Archimedes method.
[0029]
Graphite powder (average particle size 0.3 μm) and phenol resin initial condensate (PR940 manufactured by Sumitomo Durez Co., Ltd.) are mixed at a weight ratio of 1: 1, and sufficiently mixed with three rolls to obtain graphite powder. A mixed solution with a phenol resin solution was prepared. This mixed solution is applied to the surface of the C / C composite substrate and cured by heating in an electric oven at a temperature of 170 ° C., and then heated to a temperature of 2000 ° C. at a temperature increase rate of 100 ° C./hr in a nitrogen atmosphere. The carbonized film having a thickness of 20 μm was deposited on the surface of the C / C composite substrate.
[0030]
The C / C composite substrate coated with this carbonaceous film is encapsulated with graphite fiber felt having a porosity of 90%, a pore diameter of 10 μm and a thickness of 10 mm, and a quartz powder having an average particle diameter of 280 μm as a silicon source, and a carbon source A mixed powder prepared by mixing coke powder having an average particle diameter of 90 μm at a weight ratio of 3: 1 was placed in a graphite container in a state of being placed above and below the graphite fiber felt. The graphite container is transferred to a heating furnace held in a nitrogen gas atmosphere, heated to a temperature of 1850 ° C. at a temperature rising rate of 50 ° C./hr, heated for 30 minutes, and the surface of the C / C composite substrate is formed by a conversion method. It was converted into a SiC film having a functionally gradient structure.
[0031]
With respect to the C / C composite material with the SiC film thus produced, the tensile strength, the thickness of the SiC coating layer, and the SiC depth of the internal structure were measured by the following methods. Evaluation was performed and the results are shown in Table 1.
(1) Tensile strength:
From the sample with a thickness of 2 mm and a length of 160 mm, the gripping part is 40 mm long and 25.4 mm wide, and the gauge part is processed into a dumbbell shape having a length of 40 mm and a width of 12.7 mm to obtain a test piece for measuring tensile strength. . A tensile load was applied to the test piece at a crosshead speed of 1.3 mm / min, and the breaking load was measured.
(2) SiC coating layer thickness, etc .:
A cross-section of a part of the C / C composite coated with SiC was cut with a diamond cutter, and the thickness of the SiC coating layer as well as the maximum SiC depth in the internal structure of the C / C composite were observed by SEM. Was measured.
(3) Oxidation resistance test:
The weight reduction rate was measured when the C / C composite material coated with SiC was put in an electric furnace and kept at a temperature of 1400 ° C. for 30 minutes in an air atmosphere.
[0032]
Example 2
Si (OC ₂ H _Five ) _Four And ethanol are mixed at a molar ratio of 1:12, stirred at reflux at a temperature of 70 ° C., and then Si (OC ₂ H _Five ) _Four 25 moles of water and 0.2 moles of NH per mole _Four The mixture of OH was added dropwise with stirring (pH 12.0), and stirring was continued to obtain about 0.2 μm SiO 2. ₂ A suspension in which spherical fine particles are uniformly dispersed is prepared, and the silicon carbide-coated C / C material prepared in Example 1 is immersed in the suspension and impregnated at a pressure of 160 Torr for 15 minutes, and then air-dried. did. Next, Si (OC ₂ H _Five ) _Four And ethanol are mixed at a molar ratio of 1: 4.5 and stirred at reflux at room temperature, and then Si (OC ₂ H _Five ) _Four A mixture of 2.5 mol of water and 0.03 mol of HCl is added dropwise with stirring (pH 3.0) to 1 mol of SiO 2. ₂ A glass precursor solution was prepared. In this glass precursor solution, the SiO ₂ The C / C composite material on which the fine particle layer is formed is immersed, impregnated for 15 minutes under a pressure of 160 Torr, then air-dried, and then heated at a temperature of 500 ° C. for 10 minutes to form SiO ₂ A glassy coating (thickness 5 μm) was formed.
[0033]
The SiO film on the SiC film of the C / C composite material of Example 1 manufactured in this way was used. ₂ The C / C composite material with the glassy coating was measured for the tensile strength, the thickness of the SiC coating layer, and the depth of SiC in the internal structure by the same method as in Example 1, and the oxidation resistance test The results are also shown in Table 1.
[0034]
Examples 3-4
A solution (concentration 30 Wt%) of a phenol resin initial condensate [PR940 made by Sumitomo Durez Co., Ltd.] dissolved in ethanol was applied to a polyacrylonitrile plain woven carbon fiber cloth [T300 made by Toray Industries, Inc.] and air-dried for 48 hours. Thus, a prepreg sheet was prepared. Sixteen prepreg sheets are stacked and placed in a mold, and the pressure is 20 kg / cm. ² Then, it was molded by hot-pressing at a temperature of 150 ° C. The molded body was cured by heating to 170 ° C., and then placed in a firing furnace maintained in a nitrogen gas atmosphere, and heated to 1000 ° C. at a rate of temperature increase of 20 ° C./hr for firing carbonization. Further, it was impregnated with an initial condensate of furfuryl alcohol, transferred again to a baking furnace, and heated to 1000 ° C. at a temperature increase rate of 50 ° C./hr for densification treatment. This densification treatment was repeated 5 times, and after the third densification treatment, the upper and lower surfaces were polished with sandpaper, and the surface layer portion was ground and removed by 200 μm. Subsequently, it heated at 2000 degreeC with the temperature increase rate of 70 degreeC / hr in the baking furnace, and produced the C / C composite base material of length and width 250mm and thickness 4mm.
[0035]
This C / C composite substrate was mixed with graphite powder (average particle size 0.3 μm) and phenol resin initial condensate (PR940 manufactured by Sumitomo Durez Co., Ltd.) at a weight ratio of 1: 1. Mixtures of graphite powder prepared by sufficiently kneading with a roll and a phenol resin liquid were applied to different thicknesses. Next, after heat-curing at a temperature of 170 ° C. in an electric oven, it is heated and calcined at a temperature of 2000 ° C. at a temperature increase rate of 100 ° C./hr in a nitrogen atmosphere, and a different film is formed on the C / C composite substrate surface. A carbonaceous film was applied in thickness.
[0036]
The C / C composite base material coated with the carbonaceous film was converted to a SiC film having a functionally graded surface by the same method as in Example 1. For the C / C composite material on which the obtained SiC film was formed, the tensile strength, the thickness of the SiC film layer, and the depth of the internal structure converted to SiC were measured by the same method as in Example 1, and the oxidation resistance The test was conducted and the results are shown in Table 1.
[0037]
Example 5
A C / C composite base material was produced by the same method as in Example 1 except that the densification treatment was repeated three times, and the surface thereof was converted into a SiC film having a functionally gradient structure. For the C / C composite material on which the obtained SiC film was formed, the tensile strength, the thickness of the SiC film layer, and the depth of the internal structure converted to SiC were measured by the same method as in Example 1, and the oxidation resistance The test was conducted and the results are shown in Table 1.
[0038]
Comparative Examples 1-2
The carbon fiber resin composite produced by the same method as in Example 1 was subjected to firing carbonization and densification treatment under the same conditions as in Example 1. A mixed liquid of graphite powder and phenol resin liquid prepared by the same method as in Example 1 was applied to the obtained C / C composite substrate with different film thicknesses, and calcined and carbonized by the same method as in Example 1. A carbonaceous film having a thickness of 0.5 μm and 40 μm was applied, and the surface of the C / C composite substrate was converted into a SiC film having a functionally graded structure by the conversion method in the same manner as in Example 1. For the C / C composite material with the SiC coating thus produced, the tensile strength, the thickness of the SiC coating layer, and the SiC depth of the internal structure were measured by the same method as in Example 1, and the acid resistance The test was performed and the results are shown in Table 1.
[0039]
Comparative Example 3
The carbon fiber resin composite produced by the same method as in Example 1 was subjected to firing carbonization and densification treatment under the same conditions as in Example 1. The surface of the C / C composite substrate was converted into a SiC film having a functionally graded structure by a conversion method in the same manner as in Example 1 without subjecting the obtained C / C composite substrate to a polishing treatment and a carbonaceous coating. Converted. For the C / C composite material with the SiC coating thus produced, the tensile strength, the thickness of the SiC coating layer, and the SiC depth of the internal structure were measured by the same method as in Example 1, and the acid resistance The test was performed and the results are shown in Table 1.
[0040]
Comparative Example 4
Created a three-dimensional carbon fiber preform in which polyacrylonitrile-based carbon fiber [T900 manufactured by Toray Industries, Inc.] was woven in a three-dimensional direction so as to have a volume content of 60%, and the phenol resin initial condensate [Sumitomo] Durez Co., Ltd. PR940] was impregnated under vacuum. This resin-impregnated carbon fiber preform was put in an electric oven and heat-cured at a temperature of 170 ° C. to prepare a carbon fiber resin composite. This composite was placed in a firing furnace maintained in a nitrogen gas atmosphere, and heated to 1000 ° C. at a rate of temperature increase of 20 ° C./hr for firing and carbonization. Further, it was impregnated with an initial condensate of furfuryl alcohol, transferred again to a baking furnace, and heated to 1000 ° C. at a temperature increase rate of 50 ° C./hr for densification treatment. This densification treatment was repeated 5 times, and then heated to 2000 ° C. at a temperature increase rate of 70 ° C./hr in a baking furnace to prepare a C / C composite substrate having a length and width of 250 mm and a thickness of 4 mm.
[0041]
This C / C composite substrate was put in a pressure vessel, degassed under a reduced pressure of 10 Torr, then immersed in a coal pitch heated and melted at a temperature of 220 ° C., and 5 kg / cm. ² And pressure impregnation for 10 minutes. In this way, the C / C composite base material impregnated with coal pitch in the surface layer portion is transferred to a firing furnace maintained in a nitrogen gas atmosphere, and heat-treated up to 2000 ° C. at a temperature rising rate of 50 ° C./hr to easily graphitize. A carbon coating layer was formed. The surface of the C / C composite substrate was converted into a SiC film having a functionally gradient structure by the conversion method in the same manner as in Example 1 for this C / C composite substrate. With respect to the C / C composite material with the SiC coating thus produced, the tensile strength, the thickness of the SiC coating layer, and the SiC depth of the internal structure were measured by the same method as in Example 1. An oxidation resistance test was conducted and the results are shown in Table 1.
[0042]
Comparative Example 5
The densification process was repeated three times, and without performing the polishing process, a C / C composite substrate was prepared by the same method as in Examples 3 and 4, and this C / C composite substrate was not polished. Only the phenol resin initial condensate [PR940, manufactured by Sumitomo Durez Co., Ltd.] was applied. Next, after heat-curing at a temperature of 170 ° C. in an electric oven, the carbon is fired and carbonized by heating at a temperature increase rate of 100 ° C./hr in a nitrogen atmosphere to a thickness of C / C composite substrate. A 25 μm glassy carbon coating was applied. The C / C composite base material coated with the glassy carbon film was converted into a SiC film having a functionally graded structure by converting the surface of the base material into a SiC film having the gradient functional structure by the same method as in Example 1. For the C composite material, the tensile strength, the thickness of the SiC coating layer, and the depth of the internal structure made of SiC were measured by the same method as in Example 1, and the oxidation resistance test was conducted. The results are also shown in Table 1. did.
[0043]
[Table 1]

[0044]
From the results in Table 1, the oxidation-resistant C / C composite material of the example is effective in forming a dense, strong and uniform SiC film on the surface of the C / C composite base material and converting the internal structure to SiC. Therefore, it can be seen that the tensile strength is high and the rate of weight reduction due to oxidation consumption is small. Also, the SiC film after the oxidation test is stable with no abnormality such as peeling. In particular, as is clear from Examples 1 and 2, the tensile strength is high even in the case of a C / C composite material (3D-C / C composite material) using a three-dimensional woven carbon fiber cloth. SiO on ₂ In Example 2 in which the glassy coating layers were laminated, it was observed that the oxidation resistance was further improved. On the other hand, in Comparative Example 1 in which the film thickness of the carbonaceous film is thin, since the penetration of SiO gas cannot be sufficiently suppressed, the oxidation resistance and strength are inferior. In Comparative Example 2 in which the film thickness is thick, the carbonaceous film is cracked. Therefore, the oxidation resistance and strength are inferior, and the SiC film is peeled off. In Comparative Example 3 in which no carbonaceous coating is applied, the oxidation resistance and strength are lower, and in Comparative Example 4 in which a coating layer of graphitizable carbon obtained by carbonizing coal pitch is applied, the strength and oxidation resistance are low. In Comparative Example 5 in which the glassy carbon film was formed and deposited, cracks were generated due to the shrinkage of the film, and the effect of preventing the SiC film from entering was insufficient, resulting in a decrease in strength and a decrease in oxidation resistance.
[0045]
【The invention's effect】
As described above, according to the oxidation-resistant C / C composite material of the present invention, the carbonaceous material composed of a composite structure of carbonaceous powder and glassy carbon deposited on a C / C composite substrate whose surface has been polished and smoothed. The coating structure converted from a functionally graded SiC coating effectively prevents the internal structure of the C / C composite base material from being converted to SiC and prevents the material strength of the C / C composite material from being lowered. Excellent oxidation resistance can be imparted to the C / C composite substrate by a dense, strong and uniformly formed SiC coating layer. Furthermore, oxidation resistance can be further improved by laminating and forming a glassy coating. Moreover, according to the manufacturing method of the oxidation resistant C / C composite material of the present invention, the C / C composite material having high material strength and excellent oxidation resistance can be easily manufactured. Therefore, the present invention is extremely useful as an oxidation resistant C / C composite material excellent in material strength and oxidation resistance and a method for producing the same.

Claims

The surface is composed of a carbonaceous powder and a carbide of a thermosetting resin deposited on a C / C composite base material having a surface layer polished by 50 to 500 μm by polishing and smoothed to a surface roughness R max of 50 μm or less. An oxidation-resistant C / C composite material, wherein a coating structure is formed by converting a carbonaceous film having a thickness of 1 to 30 µm into a SiC film having a functionally gradient structure.

The oxidation-resistant C / C composite material according to claim 1, wherein the C / C composite base material is densified with a matrix carbon to a bulk density of 1.60 g / cm ³ or more.

A SiC coating having a functionally graded structure is used as a base coating layer, and a glassy coating made of a simple substance or a composite of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and ZrO ₂ is laminated on the base coating layer. The oxidation-resistant C / C composite material according to claim 1 or 2.

After carbon fiber is composite-molded with a matrix resin, the surface layer of the cured and baked carbonized C / C composite base material is polished and smoothed to 50 to 500 μm and the surface roughness R max is smoothed to 50 μm or less. A mixture of powder and thermosetting resin liquid is coated, calcined and carbonized at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere, and a carbonaceous film having a thickness of 1 to 30 μm is applied. Contact with SiO gas produced by heating the mixed powder in a non-oxidizing atmosphere at a temperature range of 1600 to 2000 ° C., and converting the surface of the C / C composite base material into a SiC film having a functionally gradient structure by a conversion method. A method for producing an oxidation-resistant C / C composite material.

A bulk density of 1.60 g / cm ³ or more is obtained by repeatedly impregnating a matrix resin into a C / C composite base material obtained by composite molding of carbon fiber with a matrix resin, curing and firing carbonization, and then curing and firing carbonization multiple times. The method for producing an oxidation resistant C / C composite according to claim 4, wherein the oxidation resistant C / C composite is densified.

A SiC coating having a functionally graded structure formed on the surface of a C / C composite substrate is used as a base coating layer, and a single or composite of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and ZrO ₂ is formed on the base coating layer. The method for producing an oxidation-resistant C / C composite material according to claim 4 or 5, wherein a glassy coating layer comprising:

Glass obtained by hydrolyzing a metal alkoxide containing at least one of Si, Al, B, and Zr in the base coating layer using a SiC coating having a functionally graded structure formed on the surface of a C / C composite substrate as a base coating layer The oxidation resistance according to claim 6, wherein the precursor solution is impregnated and then heat treated to form a glassy coating layer composed of a simple substance or a composite of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and ZrO ₂ . A method for producing a C / C composite material.