JP3853058B2 - Oxidation resistant C / C composite and method for producing the same - Google Patents
Oxidation resistant C / C composite and method for producing the same Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、C/C複合基材の表層部をコンバージョン法により珪化して、基材表層部に耐熱衝撃性及び耐久性に優れ、高い材質強度を備えたSiC被覆層が安定強固に形成された耐酸化性C/C複合材(炭素繊維強化炭素複合材)及びその製造方法に関する。
【0002】
【従来の技術】
C/C複合材は、軽量、高強度であることに加えて、1000℃を越える高温域において優れた耐熱性及び化学的安定性を備えているので、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古くから行われており、例えば炭化珪素、窒化珪素、ジルコニヤ、アルミナ等の耐熱セラミックス系物質を被覆処理する方法が開発されている。このうち、炭化珪素の被覆処理が技術性およ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複合材の表面に炭化珪素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複合材の表層部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炭化珪素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が加えられると相互の熱膨張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の熱膨張係数に近似するように改質すれば軽減化することができる。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、ついでCVDまたは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十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SiC被覆層は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SiC被覆層のような層間がなく、熱衝撃を受けても層間界面剥離が生じ難い利点がある。その反面、表層部におけるSiC被覆層の緻密度合が低下して、十分な耐酸化性を付与できない欠点がある。更に、コンバージョン法はC/C複合材表層部の炭素組織の一部が珪化されてSiCに転化するため、材質強度が低下する難点もあり、特にC/C複合基材の内部組織が部分的に珪化された場合には強度低下が大きくなる。
【0005】
そのため、強度の低下を来さないと共に耐熱衝撃性に優れたSiC被覆C/C複合材として、C/C複合基材にSiC被膜を形成してなるSiC被覆C/C複合材において、該C/C複合基材の表層部に表面から内部方向へ雨垂れ状に突出した多数の突出部を有する少なくとも未反応のカーボン繊維を含むけい化層が存在することを特徴とするSiC被覆C/C複合材が提案(特開平4−149081号公報)されている。この特開平4−149081号公報のSiC被覆C/C複合材は、C/C複合基材の表面にCVD法により多孔性のSiC被膜を形成した後、その表層部にけい化処理を施し、更にCVD法によるSiC被膜を形成する方法によって製造される。したがって、上記したCVD法の欠点であるC/C複合基材とSiC被膜との界面分離の問題が解消されず、耐熱衝撃性の改善も充分なものではない。
【0006】
一方、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SiC被覆層の形成過程においては、SiOガスはC/C複合基材の表面から組織内部に浸透拡散しながら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などの空隙部に沿って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にまでSiC化が進行して、基材組織、特にSiC化され易いマトリックス炭素部分が優先的に珪化されて鋸状や島状にSiC生成物が形成され易く、その結果基材組織全体の脆弱化を招くこととなる。
【0007】
そこで、コンバージョン法によりSiC被覆層を形成する場合に、生成するSiC被覆層を均一、緻密化してC/C複合基材の内部組織が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との観点から、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て得られたC/C複合基材の表面にコンバージョン法によりSiC被覆層を形成する方法(特開平8−169786号公報)、あるいは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被覆層を形成する方法(特願平8−346730号)を開発した。
【0008】
これらの方法は、C/C複合基材の表層部に形成した緻密な炭素被覆層や易黒鉛化性炭素の被膜層が、C/C複合基材の内部組織にSiOガスが浸透拡散する現象を抑制するバリアとして機能することにより、材質強度の低下を抑止するものである。
【0009】
【発明が解決しようとする課題】
本発明者は、C/C複合基材の表層部をコンバージョン法により珪化してSiC被覆層を形成した耐酸化性C/C複合材について、SiC被覆層の耐久性や耐熱衝撃性の向上、あるいは材質強度の低下防止などを図るために、SiC被覆層の性状について更に研究を進めた結果、SiCの結晶性や純度、更にC/C複合基材表層部の空隙中に侵入したSiOガスにより局所的に形成されたSiC被覆層の最大膜厚などが関係することを確認した。
【0010】
本発明は、上記の知見に基づいて開発されたもので、その目的とする解決課題は、C/C複合基材の表層部に耐熱衝撃性及び耐久性に優れ、高い材質強度を備えたSiC被覆層が安定強固に形成された耐酸化性C/C複合材及びその製造方法を提供することにある。
【0011】
【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の耐酸化性C/C複合材は、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複合基材の表層部をコンバージョン法により珪化して形成されたSiC被覆層が、金属不純物含有量が50ppm以下、かつC/C複合基材表層部の局所的に珪化されたSiC被覆層の最大膜厚が、SiC被覆層の平均膜厚の1.01〜1.2倍であることを構成上の特徴とする。
【0012】
また、本発明の耐酸化性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、硬化および焼成炭化し、更に高純度化処理と黒鉛化処理を行って、嵩密度が1.55〜1.75 g/cm3、空隙の最大モード径が0.1〜10μm 、金属不純物含有量が20 ppm以下のC/C複合基材を作製し、該C/C複合基材を、金属不純物量が100 ppm以下、粒子径が300μm 以下の珪素源と、金属不純物量が10 ppm以下、粒子径が100μm 以下の炭素源と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てC/C複合基材の表層部をコンバージョン法により珪化して、SiC被覆層を形成することを構成上の特徴とする。
【0013】
【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繊維を二次元あるいは三次元方向に織り込まれた繊維体やフェルト、トウなどが用いられ、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、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充填したのち半硬化してプリプレグを形成し、次いでプリプレグを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、常法に従って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。なお、C/C複合基材は必要に応じて、更にマトリックス樹脂を含浸、硬化、焼成炭化の処理を繰り返し行って緻密化を図り、高純度化処理と黒鉛化処理を行って基材の高純度化を図る。
【0014】
このC/C複合基材の表層部をコンバージョン法によって珪化して、形成されたSiC被覆層に高い耐久性を保持させるためには、SiCの純度と結晶性の向上が重要となる。すなわち、SiC被覆層中に金属不純物が存在するとSiCの材質劣化が進行するため、例えば、鉄、ニッケル、硼素、カルシウムなどの金属不純物の含有量は50ppm 以下であることが必要である。
【0016】
本発明の耐酸化性C/C複合材は、SiC被覆層が上記の金属不純物含有量が50ppm以下の純度を備えるとともに、C/C複合基材表層部の局所的に珪化されたSiC被覆層の最大膜厚が、SiC被覆層の平均膜厚の1.01〜1.2倍であることが必要である。コンバージョン法によりC/C複合基材の表層部にSiC被覆層が形成されるプロセスは、SiOガスがC/C複合基材の表面から内部に浸透拡散しながら炭素繊維を珪化してSiCに転化していくものであり、このプロセスにおいてSiOガスの一部はC/C複合基材に存在する気孔や亀裂などの空隙部に沿って、基材の内部組織に浸透拡散される。したがって、C/C複合基材の内部に侵入したSiOガスは逐次炭素組織と反応してSiCに転化するとともに、空隙部に沿って鋸刃状のSiC層が生成されることになる。
【0017】
すなわち、C/C複合基材表層部に形成されたSiC被覆層は図1の模式図に示したように、C/C複合基材1の表層部に局所的に珪化された局所的珪化部3が形成されている。図1において、1はC/C複合基材、2はSiC被覆層、3は局所的珪化部、4は最大膜厚、5は平均膜厚である。このように、C/C複合材の内部組織が部分的にSiC化されると材質強度の低下はより著しくなる。そこで、本発明の耐酸化性C/C複合材は、C/C複合基材の空隙部に沿って浸透拡散したSiOガスによって、C/C複合基材の表層部が局所的に珪化されて形成したSiC被覆層の最大膜厚4が、SiC被覆層の平均膜厚5の1.01〜1.2倍に制御することによって、材質強度の低下を抑制するとともに、急熱、急冷時に発生する内部組織に作用する熱応力を緩和して耐熱衝撃性も高位に保持することが可能となる。
【0018】
この耐酸化性C/C複合材は、嵩密度が1.55〜1.75 g/cm3、空隙の最大モード径が0.1〜10μm 、金属不純物含有量が20 ppm以下のC/C複合基材を作製し、該C/C複合基材を、金属不純物量が100 ppm以下、粒子径が300μm 以下の珪素源と、金属不純物量が10 ppm以下、粒子径が100μm 以下の炭素源と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ることにより製造される。
【0019】
C/C複合基材は炭素繊維をマトリックス樹脂とともに複合成形し、硬化及び焼成炭化することにより作製されるが、C/C複合基材は必要に応じてマトリックス樹脂を含浸、硬化、焼成炭化する処理を繰り返し行って嵩密度が1.55〜1.75 g/cm3の範囲に調整制御する。嵩密度が1.55 g/cm3を下回ると内部組織に存在する空隙が多く、C/C複合基材の内部組織が珪化される割合が高くなり強度低下が大きくなるためである。しかしながら、1.75 g/cm3を超える嵩密度に緻密化しても強度低下の抑制効果は殆ど変わらない。
【0020】
C/C複合基材の緻密化により基材に存在する気孔や亀裂などの空隙の大きさを、最大モード径が0.1〜10μm の範囲に調整したものが用いられる。最大モード径が10μm を超える大きな空隙が存在するとSiOガスが基材組織内部に侵入し易くなり、C/C複合基材の表層部が局所的に珪化されて内部組織に生じるSiC化が著しくなるためである。なお、最大モード径が0.1μm 未満に空隙部を緻密化してもSiOガスの侵入防止効果の増大はあまり認められない。また、C/C複合基材は可及的に高純度のものが好ましく鉄、ニッケル、硼素、カルシウムなどの金属不純物含有量は20ppm 以下のものが用いられる。金属不純物含有量が20ppm を越えると成膜したSiC被覆層中にも不純物が移行し金属触媒的に働いて耐蝕性を低下させる。C/C複合基材の金属不純物含有量を減少させるためには、作製したC/C複合基材をフッ素、塩素などのハロゲン含有ガスにより高温加熱処理して、高純度化処理することにより行うことができる。
【0021】
このようにして作製した嵩密度が1.55〜1.75 g/cm3、空隙の最大モード径が0.1〜10μm 、金属不純物含有量が20 ppm以下のC/C複合基材を用いて、コンバージョン法により表層部を珪化してSiC被覆層を形成する。珪化反応するSiOガスを発生させる珪素源としては、金属不純物含有量100ppm 以下、粒子径300μm 以下の石英、珪石、珪砂などのSiO2 含有物質が用いられる。また、炭素源としては金属不純物含有量10ppm 以下、粒子径100μm 以下のコークス、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。
【0022】
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C/C基材の炭素組織を珪化してSiC被覆層が形成される。この珪化プロセスにおいて、嵩密度、空隙の最大モード径及び金属不純物含有量などの性状が特定範囲にあるC/C複合基材を用いることによりSiOガスがC/C複合基材の内部組織に浸透拡散する現象が抑制されるので、内部組織におけるSiC化を低減することができ、また金属不純物含有量の低減化を図ることができる。したがって、金属不純物含有量50ppm以下、表層部の局所的に珪化されたSiC被覆層の最大膜厚が平均膜厚の1.01〜1.2倍のSiC被覆層が形成された耐酸化性C/C複合材の製造が可能となる。
【0023】
【実施例】
以下、本発明の実施例を比較例と対比して説明する。
【0024】
実施例1〜5、比較例1〜5
ポリアクリロニトリル系の平織炭素繊維織布〔東邦レーヨン(株)製 W6101〕にフェノール樹脂初期縮合物〔住友デュレズ(株)製 PR940〕をマトリックス樹脂として炭素繊維の体積含有率が60%となるように塗布し、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20枚を積層してモールドに入れ、20kg/cm2の圧力を掛けながら温度170℃で3時間加熱加圧処理して複合化した。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℃まで加熱するという緻密化処理を所望の嵩密度が得られるまで複数回繰り返した。次いで、70℃/hr の昇温速度で2000℃まで加熱処理した後、電気炉中で塩素ガスを導入した雰囲気下で2000℃の温度に加熱して高純度化処理した。このようにして、嵩密度、空隙最大モード径、金属不純物含有量の異なるC/C複合基材(縦横250mm 、厚さ4mm)を作製した。
【0025】
この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、珪素源として金属不純物量及び粒子径が異なる石英粉末、炭素源として金属不純物量及び粒子径が異なるコークス粉末を用い、重量比で3:1の割合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 の昇温速度で所定温度に加熱してコンバージョン反応を生起させ、C/C複合基材の表層部にSiC被覆層を形成した。このようにしてSiC被覆層を形成した耐酸化性C/C複合材について、その製造条件を対比して表1に示した。
【0026】
【表1】
【0027】
このようにして形成されたSiC被覆層について、下記の方法により金属不純物含有量、膜厚などのSiC被覆層の性状を測定した。また、これらのSiC被覆層を形成した耐酸化性C/Cについて、次の方法により引張強度、耐酸化性試験、耐熱衝撃性試験を行って、その耐酸化性能を評価した。得られた結果を表2に示した。
【0028】
(1)SiC被覆層の性状
(1) 金属不純物含有量;
空気中800℃で灰化処理して得られた残留物をプラズマ発光分析により測定。
(3) 膜厚;
渦電流測定法によりSiCの膜厚を測定。
【0029】
(2)耐酸化性能の評価
▲1▼引張強度;
厚さ4mm、長さ160mmに切り出した試料より、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▼耐酸化性試験;
SiC被覆層を形成した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。
▲3▼耐熱衝撃性試験;
SiC被覆層を形成したC/C複合材を電気炉に入れて、大気雰囲気下に1550℃の温度に5分間保持した後、室温中に取り出し急冷する操作を5回繰り返して行い、その時の被覆層の剥離状況を観察した。
【0030】
【表2】
【0031】
表1、2の結果から、SiC被覆層の性状が本発明の特性要件を満たす実施例のC/C複合材は、比較例のC/C複合材に比べて引張強度が高く、高温の大気中においても酸化による重量減少率も少ないことが判る。また、大気雰囲気中における急速な加熱と冷却による熱ショックを与えた場合の耐熱衝撃性にも優れていることが認められる。このような優れた耐酸化性能を備えたC/C複合材は、嵩密度や空隙などの特性を制御したC/C複合基材を用いて、特定の条件下でコンバージョン反応を行って、SiC被覆層の性状を制御することにより製造することができる。
【0032】
【発明の効果】
以上のとおり、本発明によればコンバージョン法により珪化してC/C複合基材の表層部に形成したSiC被覆層の性状を特定することにより、耐熱衝撃性、耐久性及び材質強度に優れたSiC被覆層が安定強固に形成された耐酸化性C/C複合材とすることができる。また、この耐酸化性C/C複合材はC/C複合基材の作製条件ならびにコンバージョン法による珪化条件を特定することにより製造することが可能である。したがって、高温苛酷な雰囲気下で使用されるC/C複合材及びその製造方法として極めて有用である。
【図面の簡単な説明】
【図1】C/C複合基材表層部に形成されたSiC被覆層の模式図である。
【符号の説明】
1 C/C複合基材
2 SiC被覆層
3 局所的珪化部
4 最大膜厚
5 平均膜厚[0001]
BACKGROUND OF THE INVENTION
In the present invention, the surface layer portion of the C / C composite base material is silicified by a conversion method, and a SiC coating layer having excellent thermal shock resistance and durability and high material strength is stably and firmly formed on the base material surface layer portion. The present invention relates to an oxidation-resistant C / C composite material (carbon fiber reinforced carbon composite material) and a method for producing the same.
[0002]
[Prior art]
In addition to being lightweight and high-strength, C / C composites have excellent heat resistance and chemical stability at high temperatures exceeding 1000 ° C. It is useful as a structural material to be used. 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 to limiting the application. For this reason, attempts have been made for a long time to improve the oxidation resistance by forming a coating layer having high oxidation resistance on the surface of the C / C composite material. For example, heat resistance of silicon carbide, silicon nitride, zirconia, alumina, etc. Methods for coating ceramic materials have been developed. Among these, the silicon carbide coating treatment is excellent in terms of technology and economy, and is practically used as the most suitable industrialization means.
[0003]
As a typical method for forming a silicon carbide coating layer on the surface of a C / C composite material, a CVD method (chemical vapor deposition method) for directly depositing SiC generated by a gas phase reaction, and a C / C composite material There is known a conversion method in which carbon in the surface layer is converted into SiC by reacting with SiO gas using a reaction source. However, each silicon carbide coating layer 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 because the interface with the base material is clearly separated, 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, so the C / C composite substrate surface is made of SiC. It can be reduced if it is modified to approximate the thermal expansion coefficient. 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 (JP-A-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 SiC coating 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 SiC coating layer formed by the CVD method, and there is an advantage that interlayer interface peeling hardly occurs even when subjected to thermal shock. On the other hand, there is a drawback that the density of the SiC coating layer in the surface layer portion is lowered and sufficient oxidation resistance cannot be imparted. Furthermore, since the conversion method partly converts the carbon structure of the surface layer of the C / C composite material into silicified and converted to SiC, there is a problem that the material strength is lowered. In particular, the internal structure of the C / C composite base material is partially When it is silicified, the decrease in strength becomes large.
[0005]
Therefore, as a SiC-coated C / C composite material in which a SiC film is formed on a C / C composite substrate as a SiC-coated C / C composite material that does not cause a decrease in strength and has excellent thermal shock resistance, A SiC-coated C / C composite having a silicified layer containing at least unreacted carbon fibers having a number of protrusions protruding like raindrops from the surface toward the inside in the surface layer of the / C composite substrate A material has been proposed (Japanese Patent Laid-Open No. 4-149081). The SiC-coated C / C composite material disclosed in JP-A-4-149081 is formed by forming a porous SiC film on the surface of the C / C composite base material by a CVD method, and then subjecting the surface layer portion to a silicidation treatment. Furthermore, it manufactures by the method of forming the SiC film by CVD method. Therefore, the problem of interfacial separation between the C / C composite substrate and the SiC film, which is a drawback of the above-described CVD method, is not solved, and the thermal shock resistance is not sufficiently improved.
[0006]
On the other hand, conversion to SiC by the conversion method inherently has a problem that the material strength of the C / C composite substrate itself is impaired. That is, in the process of forming the SiC coating layer by the conversion method, the SiO gas permeates and diffuses from the surface of the C / C composite substrate to the inside of the tissue to convert the C / C substrate structure to SiC. The SiO gas easily permeates and diffuses into a relatively deep substrate structure along voids such as pores and cracks existing in the C substrate. Therefore, SiC progresses not only to the surface of the C / C composite material but also to a relatively deep internal structure, and the base material structure, particularly the matrix carbon portion that is easily converted to SiC, is preferentially silicified to have a saw-like or island-like shape. Therefore, the SiC product is easily formed, and as a result, the entire base material structure is weakened.
[0007]
Therefore, when forming the SiC coating layer by the conversion method, the SiC coating layer to be generated is made uniform and dense to suppress the phenomenon that the internal structure of the C / C composite substrate is converted to SiC in order to secure the material strength. From the viewpoint that it is necessary, the present applicant baked and carbonized the carbon fiber composite resin molded body obtained by composite molding and curing the carbon fiber together with the matrix resin on the outer peripheral surface of the polyimide resin film. A method of forming a SiC coating layer on the surface of the obtained C / C composite substrate by a conversion method (JP-A-8-169786), or a film of graphitizable carbon on the surface layer of the C / C composite substrate After forming the layer, a method of forming a SiC coating layer by a conversion method (Japanese Patent Application No. 8-346730) was developed.
[0008]
These methods are a phenomenon in which a dense carbon coating layer or a graphitizable carbon coating layer formed on the surface layer portion of the C / C composite substrate penetrates and diffuses SiO gas into the internal structure of the C / C composite substrate. By functioning as a barrier that suppresses the decrease in material strength, a decrease in material strength is suppressed.
[0009]
[Problems to be solved by the invention]
The inventor has improved the durability and thermal shock resistance of the SiC coating layer for the oxidation-resistant C / C composite material in which the surface layer portion of the C / C composite substrate is silicified by a conversion method to form the SiC coating layer. Or, as a result of further research on the properties of the SiC coating layer in order to prevent a decrease in material strength, etc., as a result of the crystallinity and purity of SiC and the SiO gas that has penetrated into the voids of the surface layer portion of the C / C composite substrate It was confirmed that the maximum film thickness of the locally formed SiC coating layer was related.
[0010]
The present invention has been developed on the basis of the above knowledge, and the object of the solution is to provide SiC having excellent thermal shock resistance and durability and high material strength in the surface layer portion of the C / C composite substrate. An object of the present invention is to provide an oxidation-resistant C / C composite material in which a coating layer is stably and firmly formed, and a method for producing the same.
[0011]
[Means for Solving the Problems]
The oxidation-resistant C / C composite material of the present invention for achieving the above object is obtained by silicidizing the surface layer portion of a C / C composite base material obtained by composite molding of carbon fiber together with a matrix resin and curing and firing carbonization by a conversion method. The SiC coating layer formed in this manner has a metal impurity content of 50 ppm or less, and the maximum film thickness of the locally silicided SiC coating layer in the surface layer portion of the C / C composite substrate is the average film thickness of the SiC coating layer. It is 1.01 to 1.2 times as large as the structural feature.
[0012]
In addition, the method for producing an oxidation resistant C / C composite material of the present invention is such that carbon fiber is composite-molded, cured and calcined with a matrix resin, further subjected to high-purification treatment and graphitization treatment, and the bulk density is 1. .55~1.75 g / cm 3, the maximum mode diameter voids 0.1 to 10 [mu] m, the metal impurity content is prepared following C / C composite base material 20 ppm, the C / C composite base material And non-SiO 2 gas produced by heat-reacting a mixed powder of a silicon source having a metal impurity amount of 100 ppm or less and a particle size of 300 μm or less and a carbon source having a metal impurity content of 10 ppm or less and a particle size of 100 μm or less. It is structurally characterized by forming a SiC coating layer by contacting the surface layer portion of the C / C composite base material by a conversion method in a temperature range of 1600 to 2000 ° C. in an oxidizing atmosphere.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Carbon fibers that serve as reinforcing materials for C / C composite materials include fibers, felts, tows, etc., which are woven from polyacrylonitrile-based, rayon-based, and pitch-based raw materials in two- or three-dimensional directions. As the matrix resin, a highly carbonized liquid thermosetting resin such as phenol and furan, and a thermoplastic material such as tar pitch are used. The carbon fiber is sufficiently filled with a matrix resin by means of dipping, coating, etc. and then semi-cured to form a prepreg, and then the prepreg is laminated and pressurized to form a composite, and then heated to completely cure the resin component, A C / C composite base material is produced by heating and carbonizing in a non-oxidizing atmosphere at a temperature of 1000 to 2000 ° C. according to a conventional method. If necessary, the C / C composite base material is further densified by repeatedly impregnating the matrix resin, curing, and calcining carbonization to achieve densification, and high purity treatment and graphitization treatment are performed to increase the base material. Purify.
[0014]
In order to silicify the surface layer portion of the C / C composite base material by the conversion method and keep the formed SiC coating layer with high durability, it is important to improve the purity and crystallinity of SiC. That is, if metal impurities are present in the SiC coating layer, the material deterioration of SiC proceeds. For example, the content of metal impurities such as iron, nickel, boron and calcium needs to be 50 ppm or less.
[0016]
The oxidation-resistant C / C composite material of the present invention has a SiC coating layer having a purity of the above metal impurity content of 50 ppm or less and a locally silicided SiC coating layer of the surface layer portion of the C / C composite substrate. The maximum film thickness must be 1.01 to 1.2 times the average film thickness of the SiC coating layer. The process in which the SiC coating layer is formed on the surface layer of the C / C composite substrate by the conversion method is the conversion of SiC into SiC by silicifying carbon fibers while the SiO gas penetrates and diffuses from the surface of the C / C composite substrate to the inside. In this process, part of the SiO gas is permeated and diffused into the internal structure of the substrate along voids such as pores and cracks existing in the C / C composite substrate. Accordingly, the SiO gas that has entered the inside of the C / C composite base material sequentially reacts with the carbon structure and is converted to SiC, and a saw-tooth SiC layer is generated along the gap.
[0017]
That is, the SiC coating layer formed on the surface layer portion of the C / C composite substrate is locally silicided on the surface layer portion of the C / C composite substrate 1 as shown in the schematic diagram of FIG. 3 is formed. In FIG. 1, 1 is a C / C composite substrate, 2 is a SiC coating layer, 3 is a local silicified portion, 4 is a maximum film thickness, and 5 is an average film thickness. As described above, when the internal structure of the C / C composite material is partially converted to SiC, the material strength is more significantly reduced. Therefore, in the oxidation resistant C / C composite material of the present invention, the surface layer portion of the C / C composite substrate is locally silicified by the SiO gas permeating and diffusing along the voids of the C / C composite substrate. The maximum film thickness 4 of the formed SiC coating layer is controlled to 1.01 to 1.2 times the
[0018]
This oxidation resistant C / C composite material has a bulk density of 1.55-1.75 g / cm 3 , a maximum mode diameter of voids of 0.1-10 μm, and a metal impurity content of 20 ppm or less. A composite substrate is prepared, and the C / C composite substrate is divided into a silicon source having a metal impurity amount of 100 ppm or less and a particle size of 300 μm or less, and a carbon source having a metal impurity amount of 10 ppm or less and a particle size of 100 μm or less. It is manufactured by contacting SiO powder produced by heating reaction with a
[0019]
The C / C composite base material is produced by composite molding of carbon fiber together with a matrix resin, and curing and firing carbonization, but the C / C composite base material is impregnated, cured, and firing carbonized as necessary. The treatment is repeated and the bulk density is adjusted and controlled in the range of 1.55 to 1.75 g / cm 3 . This is because when the bulk density is less than 1.55 g / cm 3 , there are many voids present in the internal structure, and the ratio of silicification of the internal structure of the C / C composite base material increases and the strength decreases greatly. However, even if the density is increased to a bulk density exceeding 1.75 g / cm 3 , the effect of suppressing the decrease in strength is hardly changed.
[0020]
A C / C composite base material having a maximum mode diameter adjusted to a range of 0.1 to 10 μm is used in which the size of voids such as pores and cracks existing in the base material is adjusted. When there is a large void having a maximum mode diameter exceeding 10 μm, the SiO gas easily penetrates into the base material structure, and the surface layer portion of the C / C composite base material is locally silicified, resulting in remarkable SiC formation in the internal structure. Because. Even if the voids are densified so that the maximum mode diameter is less than 0.1 μm, the increase in the effect of preventing the penetration of SiO gas is hardly observed. Further, the C / C composite substrate is preferably as high as possible, and those having a metal impurity content such as iron, nickel, boron, calcium and the like of 20 ppm or less are used. If the metal impurity content exceeds 20 ppm, the impurities migrate into the deposited SiC coating layer and work as a metal catalyst to lower the corrosion resistance. In order to reduce the metal impurity content of the C / C composite base material, the produced C / C composite base material is heated at a high temperature with a halogen-containing gas such as fluorine or chlorine, and is subjected to a high purity treatment. be able to.
[0021]
A C / C composite substrate having a bulk density of 1.55 to 1.75 g / cm 3 , a maximum void mode diameter of 0.1 to 10 μm, and a metal impurity content of 20 ppm or less was used. Then, the surface layer is silicified by a conversion method to form a SiC coating layer. As a silicon source for generating SiO gas that undergoes silicidation reaction, SiO 2 -containing substances such as quartz, silica, and silica having a metal impurity content of 100 ppm or less and a particle diameter of 300 μm or less are used. As the carbon source, carbonaceous powders such as coke, pitch, graphite, carbon black and the like having a metal impurity content of 10 ppm or less and a particle diameter of 100 μm or less are used. The composition of the silicon source and the carbon source is determined in consideration of the surface area of each material powder, but is usually formulated so that the weight ratio of SiO 2 : C is in the range of 1: 1 to 5: 1. The 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.
[0022]
The reaction vessel is placed in a closed heating furnace, and the system is reduced or neutral non-oxidized while the C / C composite substrate is buried in the mixed powder 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 the sexual atmosphere. The SiO gas generated by the heat reduction reaction between the silicon source and the carbon source during the treatment process silicifies the carbon structure of the C / C base material while contacting the surface of the C / C composite base material to form a SiC coating layer. Is done. In this silicidation process, SiO gas penetrates into the internal structure of the C / C composite substrate by using a C / C composite substrate with properties such as bulk density, maximum mode diameter of voids and metal impurity content in specific ranges. Since the phenomenon of diffusion is suppressed, the formation of SiC in the internal structure can be reduced, and the content of metal impurities can be reduced. Therefore, the oxidation resistance C in which the metal impurity content is 50 ppm or less and the SiC coating layer in which the maximum thickness of the locally silicided SiC coating layer in the surface layer portion is 1.01 to 1.2 times the average film thickness is formed. / C composite material can be manufactured.
[0023]
【Example】
Examples of the present invention will be described below in comparison with comparative examples.
[0024]
Examples 1-5, Comparative Examples 1-5
Polyacrylonitrile-based plain woven carbon fiber woven fabric (Toho Rayon Co., Ltd. W6101) and phenol resin initial condensate (Sumitomo Durez Co., Ltd. PR940) as matrix resin so that the volume content of carbon fiber is 60%. This was applied and air-dried for 48 hours to prepare a prepreg sheet. Twenty prepreg sheets were laminated and placed in a mold, and composited by heating and pressing at a temperature of 170 ° C. for 3 hours while applying a pressure of 20 kg / cm 2 . This composite was placed in a firing furnace maintained in a nitrogen gas atmosphere and carbonized by heating to 1000 ° C. at a rate of temperature increase of 20 ° C./hr. Further, the densification treatment of impregnating the furfuryl alcohol initial condensate and again transferring to a baking furnace and heating to 1000 ° C. at a temperature rising rate of 50 ° C./hr was repeated several times until the desired bulk density was obtained. Subsequently, after heat-processing to 2000 degreeC with the temperature increase rate of 70 degreeC / hr, it heated to the temperature of 2000 degreeC in the atmosphere which introduce | transduced the chlorine gas in the electric furnace, and high-purification processing was carried out. In this way, C / C composite base materials (longitudinal and transverse 250 mm, thickness 4 mm) having different bulk densities, maximum void mode diameters, and metal impurity contents were prepared.
[0025]
This C / C composite base material is encapsulated with graphite fiber felt having a porosity of 90%, a pore diameter of 10 μm and a thickness of 10 mm, quartz powder having a different metal impurity amount and particle diameter as a silicon source, a metal impurity amount as a carbon source, and Coke powders having different particle diameters were used, and mixed powders mixed at a weight ratio of 3: 1 were placed in a graphite container in a state where they were arranged above and below the graphite fiber felt. The graphite container is transferred to a heating furnace maintained in a nitrogen gas atmosphere and heated to a predetermined temperature at a heating rate of 50 ° C./hr to cause a conversion reaction, and an SiC coating layer is formed on the surface layer portion of the C / C composite substrate did. The oxidation-resistant C / C composite material with the SiC coating layer formed as described above is shown in Table 1 in comparison with the production conditions.
[0026]
[Table 1]
[0027]
For the SiC coating layer thus formed, the properties of the SiC coating layer such as the metal impurity content and film thickness were measured by the following methods. Moreover, about the oxidation resistance C / C which formed these SiC coating layers, the tensile strength, the oxidation resistance test, and the thermal shock resistance test were done with the following method, and the oxidation resistance performance was evaluated. The obtained results are shown in Table 2.
[0028]
(1) Properties of SiC coating layer
(1) Metal impurity content;
The residue obtained by ashing in air at 800 ° C. was measured by plasma emission analysis.
(3) Film thickness;
Measure SiC film thickness by eddy current measurement method.
[0029]
(2) Evaluation of oxidation resistance (1) Tensile strength;
A specimen cut into a thickness of 4 mm and a length of 160 mm is made into a dumbbell shape with a grip portion of 40 mm length and width of 25.4 mm, and a gauge portion of 40 mm length and width of 12.7 mm. It was. 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) Oxidation resistance test;
The weight reduction rate was measured when the C / C composite material on which the SiC coating layer was formed was put in an electric furnace and kept at a temperature of 1400 ° C. for 30 minutes in an air atmosphere.
(3) Thermal shock resistance test;
The C / C composite material on which the SiC coating layer is formed is placed in an electric furnace, kept at a temperature of 1550 ° C. for 5 minutes in an air atmosphere, then taken out to room temperature and rapidly cooled, and then the coating is repeated five times. The peeling state of the layer was observed.
[0030]
[Table 2]
[0031]
From the results of Tables 1 and 2, the C / C composite material of the example in which the properties of the SiC coating layer satisfy the characteristic requirements of the present invention has higher tensile strength than the C / C composite material of the comparative example, and the high-temperature atmosphere. It can be seen that the rate of weight loss due to oxidation is small. It is also recognized that the thermal shock resistance is excellent when a heat shock is applied by rapid heating and cooling in the air atmosphere. A C / C composite material having such excellent oxidation resistance performance is obtained by performing a conversion reaction under specific conditions using a C / C composite base material with controlled properties such as bulk density and voids, and SiC. It can manufacture by controlling the property of a coating layer.
[0032]
【The invention's effect】
As described above, according to the present invention, by specifying the properties of the SiC coating layer silicified by the conversion method and formed on the surface layer portion of the C / C composite substrate, the thermal shock resistance, durability, and material strength were excellent. It can be set as the oxidation-resistant C / C composite material in which the SiC coating layer was formed stably and firmly. Moreover, this oxidation resistant C / C composite material can be manufactured by specifying the preparation conditions of the C / C composite base material and the silicidation conditions by the conversion method. Therefore, the present invention is extremely useful as a C / C composite material used in a high-temperature severe atmosphere and a method for producing the same.
[Brief description of the drawings]
FIG. 1 is a schematic view of a SiC coating layer formed on a surface layer portion of a C / C composite substrate.
[Explanation of symbols]
1 C / C
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