JP3716913B2

JP3716913B2 - Brittle material composite structure and manufacturing method thereof

Info

Publication number: JP3716913B2
Application number: JP2001113794A
Authority: JP
Inventors: 純明渡; 広典鳩野; 正勝清原; 達郎横山; 朋和伊藤; 勝彦森; 篤史吉田
Original assignee: National Institute of Advanced Industrial Science and Technology AIST
Current assignee: National Institute of Advanced Industrial Science and Technology AIST
Priority date: 2001-04-12
Filing date: 2001-04-12
Publication date: 2005-11-16
Anticipated expiration: 2021-04-12
Also published as: JP2002309383A

Description

【０００１】
【発明の属する技術分野】
本発明は、脆性材料基材表面にセラミックスや半導体などの脆性材料からなる構造物を形成した複合構造物およびその作製方法に関する。
【０００２】
【従来の技術】
一般にセラミックス製品は、焼成温度が低い場合には内部、表面にポアが多数残存しており、従って硬度も低く、耐食性、耐摩耗性に劣る。また焼成温度が高い場合には収縮による緻密化が進むものの、内部、表面ポアを完全取り除くことは困難である。また添加物を加えて粒界へのガラス層偏析を生じさせ、緻密化を行うことも考えられるが、このガラス層の存在のため、耐食性、耐摩耗性に劣ってしまう。そこで、セラミックス製品の機械的、化学的特性を向上させるためセラミックス製品の表面をこれよりも緻密な別のセラミックス膜で被覆することが考えられる。
【０００３】
セラミックス材料表面へのセラミックス膜を被覆するには、セラミックス焼成体表面に別のセラミックスのスラリーを塗布して焼成させる手法や、溶射、ゾルゲル法、ＣＶＤ法などが行われている。
【０００４】
【発明が解決しようとする課題】
スラリー塗布焼成法は多孔材料であるセラミック濾過膜や燃料電池支持体上への厚膜の形成などに利用されており、材料の被覆箇所の選択性にも優れ、大面積被覆にも比較的容易に対応できる手法である。しかしながら、焼成工程を含むため、多孔材料では比較的適用しやすいものの、緻密質を望む場合は、熱膨張率の差などの要因により、被覆層にクラックが生じやすく、また基材が必要以上に粒成長を起こすといった問題がある。
【０００５】
溶射の場合は、比較的高速でセラミックスが被覆できるといった優位点があるが、密着性に劣り、被膜を緻密質にすることが困難である。
【０００６】
ゾルゲル法は、容易に大面積被覆が可能であり、形成温度も数百℃と比較的低いものの、やはり加熱は必要であり、また体積収縮を伴う形成反応であるため膜のクラック防止のためには厚膜を形成させることは困難である。
【０００７】
ＣＶＤは比較的密着力に優れた薄膜をセラミック基材上へ被覆することが可能であるが、反応を促進するために基材を数百℃以上に加熱する必要があり、従って数μｍ以上の厚膜形成の場合は膜の剥離やクラックの発生などの問題を抱えている。
【０００８】
更に最近では、金属やセラミックス等の超微粒子をガス攪拌にてエアロゾル化し、微小なノズルを通して加速せしめ、基材表面に超微粒子の圧粉体層を形成させ、これを加熱して焼成させることにより被膜を形成するというガスデポジション法（加集誠一郎：金属１９８９年１月号）や、微粒子を帯電させ電場勾配を用いて加速せしめ、この後はガスデポジション法と同様の基本原理で被膜形成を行う静電微粒子コーティング法（井川他：昭和５２年度精密機械学会秋季大会学術講演会前刷）も知られているが、何れも加熱プロセスを伴うため、前記したように膜の剥離やクラック発生の問題があり、また基材が脆性材料の場合には膜が剥離しやすい。
【０００９】
また、上記のガスデポジション法あるいは静電微粒子コーティング法を改良した先行技術として、特開平８−８１７７４号公報、特開平１０−２０２１７１号公報、特開平１１−２１６７７号公報、特開平１１−３３０５７７号公報或いは特開２０００−２１２７６６号公報に開示されるものが知られている。
しかしながら、これらの先行技術も脆性材料からなる基板への適用が示唆されておらず、仮に脆性材料からなる基板に形成しても、膜の密着性、耐食性、耐摩耗性も十分なものとは考えられない。
【００１０】
【課題を解決するための手段】
本発明は以下の知見に基づいてなされた。
即ち、延展性を持たない脆性材料（セラミックス）に機械的衝撃力を付加すると、結晶子同士の界面などの劈開面に沿って結晶格子のずれを生じたり、あるいは破砕される。そして、これらの現象が起こると、ずれ面や破面には、もともと内部に存在し別の原子と結合していた原子が剥き出しの状態となった新生面が形成される。この新生面の原子一層の部分は、もともと安定した原子結合状態から外力により強制的に不安定な表面状態に晒され、表面エネルギーが高い状態となる。この活性面が隣接した脆性材料表面や同じく隣接した脆性材料の新生面あるいは基板表面と接合して安定状態に移行する。外部からの連続した機械的衝撃力の付加は、この現象を継続的に発生させ、微粒子の変形、破砕などの繰り返しにより接合の進展、緻密化が行われ、脆性材料構造物が形成される。
【００１１】
そして、更に上記機械的衝撃を搬送ガスにて脆性材料を基材に衝突させるようにした本発明の一態様を以後、微粒子ビーム堆積法と称する。
この微粒子ビーム堆積法は、ガスデポジション法より発展してきた手法であり、金属などの基材上に脆性材料の多結晶構造物をダイレクトに形成させる方法である。この手法は、脆性材料の微粒子をガス中に分散させたエアロゾルを搬送し、高速で基材表面に噴射して衝突させ、微粒子を破砕・変形せしめ、基板との界面にアンカー層を形成して接合させるとともに、破砕した断片粒子同士を接合させることにより、基材との密着性が良好で強度の大きい構造物を得ることができる。
【００１２】
上記の知見から発展した本発明に係る脆性材料複合構造物は、脆性材料の微粒子をガス中に分散させたエアロゾルを脆性材料焼成体の表面に噴射して衝突させ、前記脆性材料焼成体の表面に脆性材料からなる多結晶構造物が形成された脆性材料複合構造物であって、前記脆性材料焼成体の平均結晶粒径ｄ１と前記多結晶構造物の平均結晶粒径ｄ２の間にはｄ１＞ｄ２の関係があり、前記多結晶構造物を構成する結晶の X 線回折において、前記脆性材料の JCPDS （ ASTM ）データを指標として、前記多結晶構造物中の脆性材料を構成する物質をあげた前記指標における主要な回折３ピークの強度を１００％として、前記多結晶構造物の最も主要なピークの積分強度をこれにそろえた場合に、他の２ピークの積分強度が前記指標の値と比較してそのずれが３０％以内であり、また前記多結晶構造物の結晶同士の界面にはガラス層からなる粒界層が実質的に存在しない構成とした。
【００１３】
また、本発明に係る脆性材料複合構造物の作製方法は、脆性材料微粒子に内部歪を印加する工程を行った後に、この内部歪が付与された脆性材料微粒子を、平均結晶粒径ｄ１の脆性材料焼成体の表面に高速で衝突させ、この衝撃によって前記脆性材料微粒子を変形または破砕し、この変形または破砕にて生じた活性な新生面を介して微粒子同士を再結合せしめることで、前記脆性材料焼成体の表面に、平均結晶粒径ｄ２が前記脆性材料焼成体の平均結晶粒径ｄ１より小さい多結晶脆性材料からなる構造物を形成させるようにした。
【００１４】
平均粒径の算定は各種存在しているが、本件では比較が要点となっているため、材料表面や切断面において直線で切り取られた粒子の線分の長さや、一定の長さの線分で切り取られる粒子数から粒径を見積もる方法であるインターセプト法などを利用する。
【００１５】
上記作製方法は常温環境下にて行うことができる。本件における常温とは、室温に対して著しく高温でない温度環境のことであり、脆性材料の焼成温度のような１０００℃を越える高温、ゾルゲル法などの結晶化に必要な数百℃に対して十分低い温度であり、実質的に１００℃以下を指す。
【００１６】
また、上記作製方法を実施するに当たり、脆性材料微粒子を搬送する途中で脆性材料微粒子に振動を与え、脆性材料微粒子の凝集を防止することができる。
【００１７】
ここで、本発明を理解する上で重要となる語句の解釈を以下に行う。
（多結晶）
本件では結晶子が接合・集積してなる構造体を指す。結晶子は実質的にそれひとつで結晶を構成しその径は通常５ｎｍ以上である。ただし、微粒子が破砕されずに構造物中に取り込まれるなどの場合がまれに生じるが、実質的には多結晶である。
（結晶配向性）
本件では多結晶である構造物中での結晶軸の配向具合を指し、配向性があるかないかは、一般には実質的に配向性のないと考えられる粉末X線回折などによって標準データとされたJCPDS（ASTM）データを指標として判断する。
構造物中の脆性材料結晶を構成する物質をあげたこの指標における主要な回折３ピークのピーク強度を１００％として、構造物の同物質測定データ中、最も主要なピークのピーク強度をこれに揃えた場合に、他の２ピークのピーク強度が指標の値と比較して３０％以内にそのずれが収まっている状態を、本件では実質的に配向性がないと称する。
（界面）
本件では結晶子同士の境界を構成する領域を指す。
（粒界層）
界面あるいは焼結体でいう粒界に位置するある厚み（通常数ｎｍ〜数μｍ）を持つ層で、通常結晶粒内の結晶構造とは異なるアモルファス構造をとり、また場合によっては不純物の偏析を伴う。
（内部歪）
微粒子に含まれる格子歪のことで、Ｘ線回折測定におけるHall法を用いて算出される値であり、微粒子を十分にアニールした標準物質を基準として、そのずれを百分率表示する。
【００１８】
【発明の実施の態様】
以下に本発明の実施の形態を説明する。
（実施例１）
図１は、本発明に係る脆性材料複合構造物を作製する装置を示す図であり、窒素を内蔵するガスボンベ１１は、ステンレス製の搬送管１２を介してエアロゾル発生器１３に連結され、さらに搬送管１２を通じて構造物形成室１４内に１０ｍｍ×０．４ｍｍの長方形の開口を持つノズル１５が配置される。ノズル１５の先方にはＸＹステージ１７に設置された平均結晶粒径５μｍの平板状酸化アルミニウム基材１６がノズル１５に対向して１０ｍｍの間隔をあけて配置される。構造物形成室１４は排気ポンプ１８に接続している。またエアロゾル発生器１３とノズル１５の間を結ぶ搬送管１２のちょうど中間位置に圧電素子を用いた微細振幅振動装置１９を設置している。
【００１９】
本発明にあっては原料微粒子として平均粒径０．４μｍの酸化アルミニウム微粒子で内部歪を有するものを用いるため、原料微粒子に内部歪を付与するための前処理装置として、図示しない遊星ミルを有している。
【００２０】
以上の構成からなる脆性材料複合構造物作製装置の作用を次に述べる。あらかじめ酸化アルミニウム微粒子に遊星ミル処理を施し、微粒子に内部歪を付与する。これをエアロゾル発生器１３内に設置した後、ガスボンベ１１を開き、窒素ガスを流量３リットル／分で搬送管１２を通じてエアロゾル発生器１３に導入し、酸化アルミニウム微粒子をガス中に分散させたエアロゾルを発生させる。このエアロゾルを搬送管１２を通じてさらに構造物形成室１４の方向へ搬送し、高速に加速しつつノズル１５より酸化アルミニウム基材１６に向けて噴射させる。このときの酸化アルミニウム微粒子の速度は亜音速から音速程度まで加速されている。十分に加速されて運動エネルギーを得たエアロゾル中の酸化アルミニウム微粒子は、酸化アルミニウム基材１６に衝突し、その衝撃のエネルギーにより細かく破砕されて、発生した微細断片粒子が酸化アルミニウム基材１６に接合し、さらに微細断片粒子同士が接合して緻密質の酸化アルミニウム構造物を形成する。酸化アルミニウム基材１６はＸＹステージ１７により揺動され、所定の面積を持つ酸化アルミニウム膜として表面上に形成されていく。この制御により、膜厚９μｍの酸化アルミニウム膜（構造物）が形成された。
【００２１】
以上の操作はいっさい非加熱の常温工程であった。また形成中は排気ポンプ１８を運転し、形成室１４内は圧力が１ｋＰａ以下の低真空状態に置かれている。また形成中は微細振幅振動装置１９を稼動させ、搬送管１２を振動させており、搬送管１２の内壁に微粒子が付着して堆積することを防ぐ。このため堆積した微粒子が離脱し凝集粒となってノズルから噴射されるという弊害がない。
【００２２】
即ち、基材が金属の場合に比べて、セラミックスのような脆性材料の場合は比較的構造物形成が行われ難く、密着性も低下する。形成中に超微粒子の凝集粒が混在していると、これが基材に衝突した際に金属材質に比較して、エッチング（膜の削れ）が起きやすく、厚膜化が難しいと言った欠点があった。
そして、微粒子の凝集粒が混在する原因の一つに、微粒子を含むエアロゾルを加速しつつ搬送する搬送管の壁面に付着した微粒子が、ある程度堆積した後に剥離して、これがノズルより噴射されるといったことが挙げられる。この搬送管には可撓性のプラスチックチューブなどが良く用いられていたが、これを本実施例ではステンレスなどの金属製に置き換え、このチューブに微細な振動を与えるバイブレータを設置することにより、搬送管壁面への粉体の付着を速やかに解消し、大きな凝集粒が形成されるのを未然に防ぐ構造をとった。これによりエッチングが発生する確率を減少させることが可能となった。このバイブレータには圧電素子を用いた超音波発振子などを用いることができる。
【００２３】
図２はこのとき得られた構造物の断面ＳＥＭ観察写真である。酸化アルミニウム基材上に、微細な結晶を持つ酸化アルミニウムが膜状に形成されていることが見て取れる。この酸化アルミニウム膜の結晶粒径（ｄ２）は酸化アルミニウム基材の結晶粒径（ｄ１）より小さく、微細断片粒子の接合より形成されているという特徴からほぼその結晶子径に等しく、その結晶子径はＸＲＤ（マックサイエンス社製ＭＸＰ−１８）におけるＳｃｈｅｒｒｅｒの方法によって、９．８ｎｍであることがわかった。これは、平均粒径０．４μｍである酸化アルミニウム微粒子の結晶子径２４ｎｍよりも小さい数字であり、酸化アルミニウム微粒子が一度破砕されていることが示唆されている。
この酸化アルミニウム膜の硬度（ビッカース）はＨｖ＝１０００を越えており、緻密質で、その密着強度は６５９ｋｇｆ／ｃｍ²と非常に大きな値を示した。
【００２４】
また実施例では、基材も微粒子も酸化アルミニウムを使用しているが、この手法は材質をこれに限定する必要はない。常温プロセスであるがため、熱膨張のミスマッチの心配がなく、様々な脆性材料同士を用いて複合構造物を形成することが可能である。
【００２５】
（参考例）
この参考例は結晶配向性について行ったものである。平均粒径０．４μｍの酸化アルミニウム微粒子を用いて本発明の微粒子ビーム堆積法によりステンレス基板上に厚さ２０μｍの酸化アルミニウム構造物を形成した。この構造物の結晶配向性をＸ線回折法（マックサイエンス社製ＭＸＰ−１８）により測定した。この結果を表１に示す。
【００２６】
表１では代表的な面形のピーク４点の積分強度計算結果を[ｈｋｌ]＝[１１３]を１００とした強度比で示す。左から原料微粒子を薄膜光学系で測定した結果、構造物を薄膜光学系で測定した結果、JCPDSカード７４−１０８１コランダム酸化アルミニウムデータ、原料微粒子を集中光学系で測定した結果を記載する。
【００２７】
原料微粒子の集中光学系と薄膜光学系の結果がほぼ等しい為、原料粉体の薄膜光学系の結果を無配向状態と基準し、このときの構造物の強度比のずれを百分率表示したものを表２に示す。[１１３]を基準として、他の３ピークのずれは１１％以内に収まっており、実質上構造物は結晶配向性がないと言える。
【００２８】
【表１】

【００２９】
【表２】

【００３０】
また、本発明者らは同じ粒径の脆性材料を用いた場合でも、形成される構造物の形成速度、達成膜厚に相違があり、これは粒子の内部歪に起因するとの結論を得た。
そこで、内部歪と同一の形成時間で達成された構造物の膜厚の関係について実験した結果を図３に示す。実験は、純度９９.６％の酸化アルミニウム微粒子に遊星ミルを用いて粉砕処理を行い、微粒子のキャラクタリゼーションを変化させた後、超微粒子ビーム堆積法によりアルミニウム基板上に構造物を形成した。微粒子の内部歪はＸ線回折により測定し、歪量は同微粒子に熱エージングを施して内部歪を除去したものを０％として基準にした。
また、図３中のポイントＡ，Ｂ，Ｃにおける微粒子のＳＥＭ写真（日立製インレンズＳＥＭＳ−５０００）を図４、図５及び図６に示す。
【００３１】
図３から１μｍの膜厚を得るには０.０１〜２.５０％の内部歪があれば十分であることが分るが、安定した膜厚を得るには０.１〜２.０％の内部歪が好ましい。クラックと内部歪との関係は、内部歪がない場合には図４に示すようにクラックは発生しないが、内部歪が一定値以上、本件の場合には２．０％以上となると完全にクラックが形成されてしまい、さらには脱落した断片が表面に付着して図６に示すような再凝集状態となってしまう。
【００３２】
このように微粒子に歪を与える粉砕処理は、微粒子にかかる粉砕のための衝撃を大きく与えることのできる粉砕手段を用いるのが好ましい。微粒子に比較的一様に大きな歪を付与することができるからである。このような粉砕手段としては、セラミックスの粉砕処理によく用いられるボールミルに比べて大きな重力加速度を与えることの出来る振動ミルやアトライタ、遊星ミルを用いるのが好ましく、とりわけボールミルに比べて格段に大きな重力加速度を与えることの出来る遊星ミルを用いることが最も好ましい。微粒子の状態に着目すれば、クラックは内部歪をキャンセルするものであるので、最も好ましいのは、クラックが生じる直前まで内部歪が高まっている微粒子ということになる。図５に示す状態は若干のクラックが生じているが、十分に内部歪が残されている。
【００３３】
【発明の効果】
以上に説明したように本発明に係る脆性材料複合構造物によれば、緻密で耐食性および耐磨耗性に優れた脆性材料からなる被膜を、セラミックス基材の表面に形成したため、従来であれば、表面のポア近傍に応力が集中し、ここが起点となって亀裂が進展し、基材の脆性破壊が生じていたが、本発明によれば有効に脆性破壊を防止できる。
【００３４】
また、導電性セラミックスを被覆層として適用すれば、被覆層は電極材や静電気防止材として利用できる。
【図面の簡単な説明】
【図１】本発明に係る脆性材料複合構造物を作製する装置の概略図
【図２】本発明に係る脆性材料複合構造物の断面ＳＥＭ観察写真
【図３】脆性材料微粒子の内部歪と膜厚との関係を示すグラフ
【図４】図３のポイントＡにおける微粒子のＳＥＭ写真
【図５】図３のポイントＢにおける微粒子のＳＥＭ写真
【図６】図３のポイントＣにおける微粒子のＳＥＭ写真[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite structure in which a structure made of a brittle material such as ceramic or semiconductor is formed on the surface of a brittle material substrate, and a method for manufacturing the same.
[0002]
[Prior art]
In general, when the firing temperature is low, ceramic products have many pores remaining inside and on the surface, and therefore the hardness is low, and the corrosion resistance and wear resistance are poor. When the firing temperature is high, densification due to shrinkage proceeds, but it is difficult to completely remove the interior and surface pores. It is also conceivable to add an additive to cause segregation of the glass layer to the grain boundary and to perform densification, but due to the presence of this glass layer, the corrosion resistance and wear resistance are poor. Therefore, in order to improve the mechanical and chemical characteristics of the ceramic product, it is conceivable to coat the surface of the ceramic product with another ceramic film denser than this.
[0003]
In order to cover the ceramic film on the surface of the ceramic material, a method of applying another ceramic slurry to the surface of the ceramic fired body and firing it, thermal spraying, a sol-gel method, a CVD method, or the like is performed.
[0004]
[Problems to be solved by the invention]
The slurry coating and firing method is used to form porous ceramic filter membranes and thick membranes on fuel cell supports, etc., and is excellent in selectivity of the material coating location and relatively easy for large area coating. It is a method that can cope with. However, since it includes a firing step, it is relatively easy to apply to porous materials, but when a dense material is desired, cracks are likely to occur in the coating layer due to factors such as differences in the thermal expansion coefficient, and the substrate is more than necessary. There is a problem of causing grain growth.
[0005]
In the case of thermal spraying, there is an advantage that ceramics can be coated at a relatively high speed, but the adhesion is poor and it is difficult to make the coating dense.
[0006]
The sol-gel method can easily cover a large area and has a relatively low formation temperature of several hundreds of degrees Celsius. However, heating is still necessary, and since it is a formation reaction that involves volume shrinkage, it prevents cracks in the film. It is difficult to form a thick film.
[0007]
CVD can coat a thin film having relatively good adhesion on a ceramic substrate, but it is necessary to heat the substrate to several hundred degrees C or more in order to promote the reaction, and therefore, several μm or more. In the case of thick film formation, there are problems such as film peeling and generation of cracks.
[0008]
More recently, ultrafine particles such as metals and ceramics are aerosolized by gas stirring and accelerated through a minute nozzle to form a green compact layer of ultrafine particles on the substrate surface, which is heated and fired. Gas deposition method (Seiichiro Kashu: Metal January 1989 issue) that forms a film, and fine particles are charged and accelerated using an electric field gradient, and then the film is formed on the same basic principle as the gas deposition method. Electrostatic fine particle coating method (Ikawa et al .: Preprint of the 1978 Fall Meeting of the Japan Society for Precision Mechanics) is also known, but since all involve heating processes, as described above, film peeling and cracking occur In addition, when the substrate is a brittle material, the film is easily peeled off.
[0009]
Further, as prior arts improved from the above-described gas deposition method or electrostatic fine particle coating method, JP-A-8-81774, JP-A-10-202171, JP-A-11-21677, JP-A-11-330577 are disclosed. And those disclosed in Japanese Patent Application Laid-Open No. 2000-212766.
However, these prior arts are not suggested to be applied to a substrate made of a brittle material, and even if formed on a substrate made of a brittle material, the adhesion, corrosion resistance, and wear resistance of the film are sufficient. Unthinkable.
[0010]
[Means for Solving the Problems]
The present invention has been made based on the following findings.
That is, when a mechanical impact force is applied to a brittle material (ceramics) that does not have spreadability, the crystal lattice shifts along the cleaved surface such as the interface between crystallites or is crushed. When these phenomena occur, a new surface is formed on the slipping surface or fracture surface, in which atoms originally present inside and bonded to other atoms are exposed. The part of the atomic layer on the new surface is exposed to an unstable surface state by an external force from a stable atomic bond state, and the surface energy is high. The active surface joins the adjacent brittle material surface, the newly formed brittle material surface, or the substrate surface, and shifts to a stable state. The addition of a continuous mechanical impact force from the outside continuously generates this phenomenon, and the joining is progressed and densified by repeated deformation and crushing of fine particles, thereby forming a brittle material structure.
[0011]
Further, an embodiment of the present invention in which the above-described mechanical impact is caused to cause the brittle material to collide with the substrate with the carrier gas is hereinafter referred to as a fine particle beam deposition method.
This fine particle beam deposition method is a method developed from the gas deposition method, and is a method of directly forming a polycrystalline structure of a brittle material on a substrate such as a metal. This method transports an aerosol in which fine particles of a brittle material are dispersed in a gas, injects and collides with the surface of the base material at a high speed, crushes and deforms the fine particles, and forms an anchor layer at the interface with the substrate. By joining together the crushed fragment particles, it is possible to obtain a structure having good adhesion to the substrate and high strength.
[0012]
The brittle material composite structure according to the present invention developed from the above-mentioned knowledge is obtained by injecting and colliding an aerosol in which fine particles of a brittle material are dispersed in a gas onto the surface of the brittle material fired body. A brittle material composite structure in which a polycrystalline structure made of a brittle material is formed, and d1 is between the average crystal grain size d1 of the fired brittle material and the average crystal grain size d2 of the polycrystalline structure. > D2, and in the X- ray diffraction of the crystals constituting the polycrystalline structure, the substances constituting the brittle material in the polycrystalline structure are listed using JCPDS ( ASTM ) data of the brittle material as an index. Further, when the intensity of the main three diffraction peaks in the index is 100% and the integrated intensity of the most main peak of the polycrystalline structure is aligned with this, the integrated intensity of the other two peaks is the value of the index. Compare that deviation Is within 30%, and the grain boundary layer composed of a glass layer does not substantially exist at the interface between the crystals of the polycrystalline structure.
[0013]
In addition, in the method for producing the brittle material composite structure according to the present invention, after the step of applying internal strain to the brittle material fine particles, the brittle material fine particles to which the internal strain is applied are made brittle with an average crystal grain size d1. The brittle material is made to collide with the surface of the material fired body at high speed, and the brittle material fine particles are deformed or crushed by the impact, and the fine particles are recombined with each other through an active new surface generated by the deformation or crushed A structure made of a polycrystalline brittle material having an average crystal grain size d2 smaller than the average crystal grain size d1 of the brittle material fired body was formed on the surface of the fired body.
[0014]
There are various methods for calculating the average particle diameter, but in this case, the comparison is the key point, so the length of the line segment of the particle cut in a straight line on the material surface or cut surface, or a line segment of a certain length. The intercept method, which is a method for estimating the particle size from the number of particles cut out in step 1, is used.
[0015]
The above production method can be performed in a room temperature environment. The normal temperature in this case is a temperature environment that is not extremely high with respect to the room temperature, and is sufficient for high temperatures exceeding 1000 ° C. such as the firing temperature of brittle materials, and for several hundred ° C. necessary for crystallization such as the sol-gel method. It is a low temperature and substantially refers to 100 ° C. or lower.
[0016]
Further, in carrying out the above manufacturing method, the brittle material fine particles can be vibrated in the course of transporting the brittle material fine particles to prevent aggregation of the brittle material fine particles.
[0017]
Here, the interpretation of the words that are important for understanding the present invention will be described below.
(Polycrystalline)
In this case, it refers to a structure in which crystallites are joined and integrated. The crystallite is essentially one crystal, and its diameter is usually 5 nm or more. However, the case where the fine particles are taken into the structure without being crushed rarely occurs, but is substantially polycrystalline.
(Crystal orientation)
In this case, it refers to the degree of orientation of crystal axes in a polycrystal structure, and whether or not there is orientation is standard data by powder X-ray diffraction, which is generally considered to have substantially no orientation. JCPDS (ASTM) data is used as an index.
The index of the 3 major diffraction peaks in this index, which is the material constituting the brittle material crystal in the structure, is taken as 100%, and the peak intensity of the most significant peak in the same substance measurement data of the structure is aligned with this. In this case, the state in which the deviation of the peak intensity of the other two peaks is within 30% of the index value is referred to as having substantially no orientation in this case.
(interface)
In this case, it refers to the region that forms the boundary between crystallites.
(Grain boundary layer)
It is a layer with a certain thickness (usually several nm to several μm) located at the grain boundary in the interface or sintered body. It usually has an amorphous structure different from the crystal structure in the crystal grain, and in some cases, segregates impurities. Accompany.
(Internal distortion)
The lattice strain contained in the fine particles is a value calculated by using the Hall method in the X-ray diffraction measurement, and the deviation is expressed as a percentage with reference to a standard material in which the fine particles are sufficiently annealed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below.
(Example 1)
FIG. 1 is a view showing an apparatus for producing a brittle material composite structure according to the present invention, in which a gas cylinder 11 containing nitrogen is connected to an aerosol generator 13 via a stainless steel transport pipe 12 and further transported. A nozzle 15 having a rectangular opening of 10 mm × 0.4 mm is arranged in the structure forming chamber 14 through the pipe 12. At the tip of the nozzle 15, a flat aluminum oxide substrate 16 having an average crystal grain size of 5 μm installed on the XY stage 17 is arranged facing the nozzle 15 with an interval of 10 mm. The structure forming chamber 14 is connected to an exhaust pump 18. Further, a fine amplitude vibration device 19 using a piezoelectric element is installed at an exactly middle position of the transport pipe 12 connecting the aerosol generator 13 and the nozzle 15.
[0019]
In the present invention, since the raw material fine particles are aluminum oxide fine particles having an average particle size of 0.4 μm and having internal strain, a planetary mill (not shown) is provided as a pretreatment device for applying internal strain to the raw material fine particles. are doing.
[0020]
The operation of the brittle material composite structure manufacturing apparatus having the above configuration will be described below. The aluminum oxide fine particles are previously subjected to planetary mill treatment to impart internal strain to the fine particles. After this is installed in the aerosol generator 13, the gas cylinder 11 is opened, nitrogen gas is introduced into the aerosol generator 13 through the transport pipe 12 at a flow rate of 3 liters / minute, and the aerosol in which the aluminum oxide fine particles are dispersed in the gas is introduced. generate. This aerosol is further transported in the direction of the structure formation chamber 14 through the transport pipe 12, and sprayed from the nozzle 15 toward the aluminum oxide substrate 16 while being accelerated at a high speed. At this time, the speed of the aluminum oxide fine particles is accelerated from the subsonic speed to the sound speed. The aluminum oxide fine particles in the aerosol that have been sufficiently accelerated to obtain kinetic energy collide with the aluminum oxide base material 16 and are finely crushed by the energy of the impact, and the generated fine fragment particles are joined to the aluminum oxide base material 16. Further, the fine fragment particles are joined together to form a dense aluminum oxide structure. The aluminum oxide substrate 16 is swung by the XY stage 17 and formed on the surface as an aluminum oxide film having a predetermined area. By this control, an aluminum oxide film (structure) having a thickness of 9 μm was formed.
[0021]
The above operation was a non-heated room temperature process. During the formation, the exhaust pump 18 is operated, and the formation chamber 14 is placed in a low vacuum state with a pressure of 1 kPa or less. Further, during the formation, the fine amplitude vibration device 19 is operated to vibrate the transport pipe 12, thereby preventing fine particles from adhering to the inner wall of the transport pipe 12 and accumulating. For this reason, there is no adverse effect that the accumulated fine particles are separated and become agglomerated particles and ejected from the nozzle.
[0022]
That is, compared with the case where the base material is a metal, in the case of a brittle material such as ceramics, formation of a structure is relatively difficult to perform, and adhesion is also reduced. If there is a mixture of ultrafine particles during the formation, there is a disadvantage that etching (film scraping) is more likely to occur when it collides with the base material and it is difficult to increase the film thickness. there were.
Then, one of the causes of the coagulation of fine particles is that the fine particles adhering to the wall surface of the conveying tube that conveys the aerosol containing fine particles are accelerated to some extent and then peeled off, and this is ejected from the nozzle. Can be mentioned. A flexible plastic tube or the like was often used for this transfer tube. In this embodiment, this tube is replaced with a metal such as stainless steel, and a vibrator that gives fine vibration to the tube is installed. A structure was adopted in which the adhesion of powder to the tube wall surface was quickly eliminated to prevent the formation of large aggregated particles. This makes it possible to reduce the probability that etching will occur. As this vibrator, an ultrasonic oscillator using a piezoelectric element can be used.
[0023]
FIG. 2 is a cross-sectional SEM observation photograph of the structure obtained at this time. It can be seen that aluminum oxide having fine crystals is formed in a film shape on the aluminum oxide substrate. The crystal grain size (d2) of the aluminum oxide film is smaller than the crystal grain size (d1) of the aluminum oxide base material, and is substantially equal to the crystallite size because of the feature that it is formed by joining fine fragment particles. The diameter was found to be 9.8 nm by Scherrer's method in XRD (MXP-18 manufactured by Mac Science). This is a number smaller than the crystallite diameter of 24 nm of the aluminum oxide fine particles having an average particle diameter of 0.4 μm, suggesting that the aluminum oxide fine particles have been crushed once.
The hardness (Vickers) of this aluminum oxide film exceeded Hv = 1000, it was dense, and its adhesion strength showed a very large value of 659 kgf / cm ² .
[0024]
In the embodiment, aluminum oxide is used for both the base material and the fine particles, but this method does not require the material to be limited to this. Although it is a room temperature process, there is no fear of thermal expansion mismatch, and a composite structure can be formed using various brittle materials.
[0025]
( Reference example )
This reference example was conducted for crystal orientation. An aluminum oxide structure having a thickness of 20 μm was formed on a stainless steel substrate by the fine particle beam deposition method of the present invention using aluminum oxide fine particles having an average particle diameter of 0.4 μm. The crystal orientation of this structure was measured by an X-ray diffraction method (MXP-18 manufactured by Mac Science). The results are shown in Table 1.
[0026]
Table 1 shows the integrated intensity calculation results of four peak points of a typical surface shape as an intensity ratio with [hkl] = [113] as 100. From the left, as a result of measuring raw material fine particles with a thin film optical system, as a result of measuring a structure with a thin film optical system, JCPDS card 74-1081 corundum aluminum oxide data, and a result of measuring raw material fine particles with a concentrated optical system are described.
[0027]
Since the results of the concentrated optical system of the raw material fine particles and the thin film optical system are almost the same, the result of the thin film optical system of the raw material powder is based on the non-oriented state, and the deviation of the strength ratio of the structure at this time is displayed as a percentage It shows in Table 2. On the basis of [113], the deviation of the other three peaks is within 11%, and it can be said that the structure has substantially no crystal orientation.
[0028]
[Table 1]

[0029]
[Table 2]

[0030]
In addition, the present inventors have concluded that even when brittle materials having the same particle size are used, there is a difference in the formation speed of the structure to be formed and the achieved film thickness, which is caused by the internal strain of the particles. .
Therefore, FIG. 3 shows the result of an experiment conducted on the relationship between the film thickness of the structure achieved in the same formation time as the internal strain. In the experiment, aluminum oxide fine particles having a purity of 99.6% were pulverized using a planetary mill to change the characterization of the fine particles, and then a structure was formed on the aluminum substrate by an ultrafine particle beam deposition method. The internal strain of the fine particles was measured by X-ray diffraction, and the amount of strain was determined based on 0% obtained by subjecting the fine particles to thermal aging to remove the internal strain.
Moreover, the SEM photograph (Hitachi in-lens SEM S-5000) of the microparticles | fine-particles in point A, B, C in FIG. 3 is shown in FIG.4, FIG.5 and FIG.6.
[0031]
It can be seen from FIG. 3 that 0.01 to 2.50% of internal strain is sufficient to obtain a film thickness of 1 μm, but 0.1 to 2.0% to obtain a stable film thickness. Is preferable. As shown in FIG. 4, when there is no internal strain, cracks do not occur when there is no internal strain. However, when the internal strain exceeds a certain value, in this case, 2.0% or more, it is completely cracked. Are formed, and the dropped fragments adhere to the surface, resulting in a re-aggregation state as shown in FIG.
[0032]
Thus, it is preferable to use a pulverizing means capable of giving a large impact for the pulverization applied to the fine particles in the pulverization treatment for distorting the fine particles. This is because a large strain can be imparted to the fine particles relatively uniformly. As such a pulverizing means, it is preferable to use a vibration mill, an attritor, or a planetary mill that can give a large acceleration of gravity compared to a ball mill often used for pulverizing ceramics. Most preferably, a planetary mill that can provide acceleration is used. Focusing on the state of the fine particles, since the crack cancels the internal strain, the most preferable is the fine particle whose internal strain is increased until just before the crack is generated. In the state shown in FIG. 5, some cracks are generated, but sufficient internal strain remains.
[0033]
【The invention's effect】
As described above, according to the brittle material composite structure according to the present invention, a coating made of a brittle material that is dense and excellent in corrosion resistance and wear resistance is formed on the surface of the ceramic substrate. Stress concentrates in the vicinity of the pores on the surface, cracks develop from this point, and brittle fracture of the base material has occurred, but according to the present invention, brittle fracture can be effectively prevented.
[0034]
If conductive ceramics are applied as a coating layer, the coating layer can be used as an electrode material or an antistatic material.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for producing a brittle material composite structure according to the present invention. FIG. 2 is a cross-sectional SEM observation photograph of the brittle material composite structure according to the present invention. FIG. 4 is a SEM photograph of fine particles at point A in FIG. 3. FIG. 5 is an SEM photograph of fine particles at point B in FIG. 3. FIG. 6 is an SEM photograph of fine particles at point C in FIG.

Claims

A brittle material composite structure in which an aerosol in which fine particles of a brittle material are dispersed in a gas is injected and collided with the surface of the brittle material fired body to form a polycrystalline structure made of the brittle material on the surface of the brittle material fired body be those, wherein between the average crystal grain diameter d2 of the average crystal grain size d1 of the brittle material fired body the polycrystalline structure is related to d1> d2, the crystals constituting the polycrystalline structure In X- ray diffraction, using the JCPDS ( ASTM ) data of the brittle material as an index, the intensity of the main three diffraction peaks in the index listing substances constituting the brittle material in the polycrystalline structure is defined as 100%. When the integrated intensity of the most major peak of the polycrystalline structure is aligned with this, the integrated intensity of the other two peaks is within 30% of the value of the index, and the polycrystalline structure Interface between crystal of objects There is substantially no grain boundary layer composed of a glass layer in the brittle material composite structure.

A method for producing a brittle material composite structure according to claim 1, wherein after the step of applying internal strain to the brittle material fine particles , the brittle material fine particles to which the internal strain is applied are average grain size. By colliding at high speed with the surface of the brittle material fired body of d1, deforming or crushing the brittle material fine particles by this impact, and recombining the fine particles with each other through an active new surface generated by the deformation or crushing A brittle material composite structure in which a structure made of a polycrystalline brittle material having an average crystal grain size d2 smaller than the average crystal grain size d1 of the brittle material fired body is formed on the surface of the brittle material fired body. Manufacturing method.

3. The method for producing a brittle material composite structure according to claim 2, wherein the structure is formed in a room temperature environment.

3. The method for producing a brittle material composite structure according to claim 2, wherein the brittle material fine particles are vibrated during conveyance of the brittle material fine particles to prevent aggregation of the brittle material fine particles.