JP4032178B2

JP4032178B2 - Method for manufacturing silicon nitride sprayed film

Info

Publication number: JP4032178B2
Application number: JP2002353601A
Authority: JP
Inventors: 昌宏福本; 基宏山田
Original assignee: Tosoh Corp
Current assignee: Tosoh Corp
Priority date: 2002-12-05
Filing date: 2002-12-05
Publication date: 2008-01-16
Anticipated expiration: 2022-12-05
Also published as: JP2004183072A

Description

【０００１】
【発明の属する技術分野】
本発明は、高温構造材料としてのガスタービン部品、切削工具、製鋼用機械部品などの被覆や熱処理装置のサセプタ−部材等の被覆に好適な窒化珪素溶射膜の製造方法に関わるものである。
【０００２】
【従来の技術】
窒化珪素は密度が耐熱合金の約４０％程度と軽量であり、また熱膨張係数が非酸化物セラミックスの中で最も小さいために優れた耐熱衝撃性を有している。窒化珪素はこの様に優れた物性を有するため、これまではその焼結体が自動車のエンジン部品や耐熱性絶縁部品に使われて来た。昨今、この様に優れた窒化珪素をより幅広く利用するために、金属や酸化物の基材の上に、窒化珪素の厚膜を形成する技術への要望が高まっている。
【０００３】
従来、窒化珪素膜の作製方法としては、ＣＶＤ法、ＰＶＤ法、スパッタリング法といった成膜方法が知られている。しかしこれらの方法は極めて薄い薄膜を作製する方法であるため、１μｍ以上、特に数ｍｍの厚膜の作製をすることは困難であった。
【０００４】
一方、厚膜を作製する方法として溶射法が知られている。溶射法は溶射原料を融解し、当該融解溶射原料を高速で基板にぶつけて堆積させる方法である。溶射法を用いれば一般に数μｍ〜数ｍｍの厚膜作製が可能である。しかし窒化物、炭化物等の非酸化物を溶射法で成膜しようとした場合、それらの分解温度が低いため、溶射原料が溶射時に分解し、成膜できないという問題があった。
【０００５】
そこで純粋な窒化物の膜ではなく、酸化物と窒化物（或いは炭化物）の混合物よりなる被膜を形成することが提案されている（例えば特許文献１参照）。しかし、このような方法では、被膜中の窒化物の割合が少ない、或いは混合する酸化物の影響により得られる膜の性能が十分でなかった。
【０００６】
また、窒化珪素に加える助剤として、酸化物ではなくニッケル等の金属を添加した混合溶射原料を溶射し、窒化珪素と金属の混合皮膜を形成する方法が提案されている。（例えば非特許文献１参照）。しかしこの様な珪素以外の金属を含む被膜は、それらの金属が不純物となるため、高純度が必要なプロセスには用いられないという問題があった。
【０００７】
窒化珪素の被膜を形成する方法として、溶射法によって酸化珪素または金属珪素の膜を形成させた後、窒素雰囲気中で加熱処理することによって窒化物に変換させる方法が提案されている（例えば特許文献２参照）。しかし、この方法では、窒化物膜の生成が最表面のみにしか形成されないため、やはりその被膜は窒化珪素としての性能を十分に発揮するものではなかった。
【０００８】
これまでプラズマ溶射法によって純粋な窒化珪素の膜を形成しようとする試みがなかったわけではない。（例えば非特許文献２参照）しかしこれまでにプラズマ溶射法で得られた膜は、窒素含有量が２重量％程度、即ち窒素の原子比で４原子％までの窒化珪素比率の低い膜しか得られていなかった。
【０００９】
【特許文献１】
特開平０６−０４９６１７号公報
【特許文献２】
特開平０６−２２８７２４号公報
【非特許文献１】
Ｌｕｇｓｃｈｅｒｄｅｒ，Ｅ．，Ｒ．Ｌｉｍｂａｃｈ，Ａ．ＬｉｄｅｎａｎｄＪ．Ｌｏｄｉｎ，ＨｉｇｈＴｅｍｐ．Ｍａｔｅｒ．ＰｏｗｅｒＥｎｇ．１９９０，Ｐｏｒｃ．Ｃｏｎｆ．，Ｖｏｌ．１，８７７−８８０（１９９０）
【非特許文献２】
Ｐｒｏｃｅｅｄｉｎｇｏｆｔｈｅ７ｔｈＮａｔｉｏｎａｌＴｈｅｒｍａｌＳｐｒａｙＣｏｎｆｅｒｅｎｃｅ２０−２４Ｊｕｎｅ１９９４，ＢｏｓｔｏｎＭａｓｓａｃｈｕｓｅｔｔｓ
【００１０】
【発明が解決しようとする課題】
従来、厚膜を得るために用いられる溶射法では、窒化珪素のみからなる、或いは窒化珪素の比率の高い厚膜を得ることは困難であったため、窒化珪素特有の高硬度、耐熱性、絶縁性、耐摩耗性、耐酸化性、不純物拡散防止性等を発揮し得る厚膜、或いはその様な厚膜を被覆した部材を得ることが出来なかった。本発明の目的は、珪素の反応性プラズマ溶射において新規な方法を提案することにより、窒化珪素のみからなる、或いは窒化珪素比率が高く、窒化珪素と珪素のみからなる緻密な溶射膜、及び溶射膜を被覆した部材を提供することにある。
【００１１】
【課題を解決するための手段】
本発明者らは、上述のような現状に鑑み、鋭意検討を行った結果、窒素を含む熱プラズマを用い、基材が熱プラズマ中に十分に接触する距離、即ち基材が熱プラズマの高輝な部分に触れる条件において、珪素の融点以上窒化珪素の分解温度以下でプラズマ溶射することにより、基材上に窒化珪素の含有率が高く、なおかつ緻密な溶射膜が得られることを見出した。また本発明の方法で得られた溶射膜において、窒化珪素粒子のすきまに残存した珪素は、窒素を含む熱プラズマの高輝な部分をさらに照射することによって窒化を進行させ、窒化珪素の比率の高い緻密な溶射膜とすることが出来ることを見出した。また、本発明の方法においては、プラズマガスとして必須である窒素に水素を添加することによって窒化が促進されることを見出した。さらに本発明の方法で得られた窒化珪素の溶射膜を基材上に被覆した部材は、硬度、絶縁性、耐熱性、耐摩耗性、耐酸化性、不純物拡散防止性等に優れ、特に基材がグラファイトの場合に、基材との密着性に優れた部材となることを見出し、本発明を完成するに至ったものである。
【００１２】
本発明の方法により得られる窒化珪素溶射膜について説明する。
【００１３】
本発明の方法により得られる窒化珪素溶射膜は溶射法によって成膜してなる厚膜であり、従来のスパッタやＣＶＤで得られる薄膜とは異なる物である。その膜厚は１μｍ以上３ｍｍ以下が好ましく、さらに１００μｍ以上１ｍｍ以下であることが好ましい。１μｍより薄い膜では耐摩耗性に問題があり、一方３ｍｍを超えてつけることは、本発明の膜を用いる技術領域では一般的に要求されない上に、経済的でない。
【００１４】
本発明の方法により得られる窒化珪素溶射膜は窒化珪素と珪素からなる膜であり、その窒化珪素の含有量は高いことが好ましい。理由としては、窒化珪素含有量が大きいほど耐熱性、耐摩耗性、耐酸化性及び不純物拡散防止の効果が高いため、それらの特性を必要とする応用分野、例えば熱処理装置のサセプタ−等に使用した際に高い性能が発揮されるからである。
【００１５】
窒素の含有量は、１０原子％以上５８原子％以下、好ましくは４０原子％以上５８原子％以下、特に好ましくは５０原子％以上５８原子％以下の範囲である。窒素の含有率が１０原子％に満たない場合、膜の表面に窒化珪素でなく珪素が存在し易くなるため、本発明の目的の性能を発揮する上で好ましくない。一方、窒化珪素の膜が純粋に窒化珪素のみで形成されていれば、窒素の含有率は５７．１原子％となる。（Ｓｉ_３Ｎ_４換算）本発明の方法により得られる窒化珪素膜では、膜中に若干の非化学量論的な組成の窒化物が含まれても良く、上限は５８原子％程度まで許容される。
【００１６】
ここで本発明の溶射膜は膜全体で上記の範囲の窒素含有量を満足するものであり、例えば非特許文献２の様に、表面分析等で確認できる最表面だけの窒化珪素比率が高く、膜全体の窒素含有量が１０原子％に満たないものとは異なるものである。
【００１７】
また本発明の方法により得られる溶射膜は、窒化珪素を主体とする膜であり、窒化珪素以外の成分は珪素からなる膜であり、イットリア、カルシア、アルミナ等の助剤として添加された酸化物セラミックに起因する異種成分を含まない膜である。但し、これらの元素が不純物レベルで存在し、本発明の方法により得られる窒化珪素被膜と同等の性能を有するものは、本発明から除外されるものではない。
【００１８】
さらに本発明の方法により得られる膜は空気中の酸化によって形成される酸化珪素を含むものを除外するものではなく、通常考えられる範囲で自然に生成する酸化珪素を含む膜も本発明の範囲である。
【００１９】
本発明の方法により得られる溶射膜の組織構造は特に限定されず、緻密な膜から多孔質の膜まであらゆるモロホロジーをとり得る。しかし本発明の目的、即ち耐熱性、耐摩耗性等の用途においては特に空孔を有しない緻密な膜であることが好ましい。特に後述する本発明の方法では、従来の酸化物或いは金属の焼結助剤を含んだ窒化珪素溶射膜に比べて緻密な膜が得られ易い。
【００２０】
さらに本発明の方法により得られる窒化珪素溶射膜を基材の上に形成した部材を提案するものである。基材は特に限定されず、ガラス、セラミックス、金属等が適用できるが、特にグラファイトを基材に用いた場合、グラファイトの熱膨張率が窒化珪素や珪素に近いため、特に密着性に優れた部材が得られるために好ましい。この様なグラファイト基材に本発明の溶射膜を形成した部材は、特に熱処理装置のサセプタ−部材等の用途で優れた性能を発揮する。
【００２１】
次に本発明の溶射膜の製造方法を説明する。
【００２２】
図１、図２に示す装置の一例により本発明の窒化珪素を主体とする溶射膜の製造方法を説明する。
【００２３】
本発明の方法は、熱プラズマを発生させる部位と基材を保持する部位を有する装置に基材を装着して成膜する。
【００２４】
本発明の溶射の条件における圧力は特に限定されず、加圧、常圧、減圧で行うことができる。常圧の場合は、大気圧で行えば良いが、減圧で行う場合には、例えば図１に示す溶射容器をロータリーポンプ１０７により０．５Ｔｏｒｒ以下まで真空引きをした後、熱プラズマ源の石英管１１３保護のためのアルゴン等のシースガス１０８および窒素とアルゴン等のプラズマガス１０９を導入して２０〜１５０Ｔｏｒｒの圧力として成膜することが例示できる。
【００２５】
図２に大気圧で溶射する装置の例を示す。大気圧で熱プラズマを発生させる部位と基材２５を保持する部位を有する装置において、プラズマガスライン２２より窒素と水素等のプラズマガスを導入し、カソード２０とアノード２１間に電圧をかける事により直流アークで熱プラズマ２８を発生させることが出来る。
【００２６】
本発明で用いる溶射膜を形成する基材は特に限定しないが、例えばステンレスや炭素鋼等の金属基材、グラファイト、石英、セラミックス等を基材１０１、２５として用いることが出来る。用いる基材は溶射膜との密着性を向上するために、表面をブラスト法等により粗くして用いることが好ましい。
【００２７】
次に本発明の溶射法は熱プラズマを利用するものである。熱プラズマの発生方法は限定しないが、例えば高周波、直流アーク、または交流アーク等によって生成することが可能である。図１には、高周波コイル１１０に高周波を印加して熱プラズマ１０４を発生させる方法を例示している。ここで言う熱プラズマとは、上述の手段による気体放電で生成され、少なくとも部分的に電離した数千〜数万度の高温となったガス気流のことをいう。
【００２８】
本発明の溶射では、基材表面の熱プラズマが照射された部位の温度が珪素の融点以上窒化珪素の分解温度以下でなくてはならない。珪素の融点は１４１０℃、窒化珪素の分解温度は１９００℃である。温度が珪素の融点に達していないと窒化珪素が生成し難く、窒化珪素の分解温度を超えると、生成した窒化珪素が失われてしまい、本発明の窒素含有率の範囲の膜は得られない。この様な基材表面温度とするためには溶射成膜前に基材を予備加熱し、予熱温度を６００℃以上、基材の融点以下としておくことが好ましい。本発明では、溶射膜が堆積する部分、すなわち基材の最表面の温度が上記範囲にあれば良く、基材全体が上記温度となっている必要はない。熱プラズマが照射された部位の温度が本発明の範囲に入っているかどうかは、成膜中或いは成膜直後に基板の近傍（例えば裏面）の温度を接触型の熱電対で実測し、想定される温度勾配から基材表面の温度を測定するか、成膜中に非接触型の放射温度計で基材表面温度を直接測定することができる。
【００２９】
次に本発明の方法は、窒素を含む熱プラズマの高輝な部分を基材に接触させながら溶射することを特徴とするものである。例えば図１の場合、熱プラズマ１０４の出口と基材１０１の距離（溶射距離）１０６を、基材ホルダー１０２の下部にあるスペーサ１０５によりあらかじめ調整し、本発明の方法の特徴である基材への熱プラズマの高輝な部分が接触する条件、即ち熱プラズマが十分に基材に触れる状態で溶射する。この様な状態を発現するためには溶射距離１０６を１０ｍｍ以上１００ｍｍ未満とすることが好ましく、特に２０ｍｍから５０ｍｍとすることが好ましい。本発明では、窒化珪素の分解を回避するため、温度は珪素の融点（１４１０℃）以上、窒化珪素の分解温度（１９００℃）以下とするが、この様な温度で窒化珪素が生成する様にするためには、熱プラズマの高輝な部分を基材に接触させて、基材の成膜部分を活性化することが必須である。熱プラズマの高輝な部分を十分に基材に触れさせることにより、珪素成分の窒化を進めることが出来、尚且つ緻密な膜を得ることが出来る。
【００３０】
図２に示した大気圧で熱プラズマを基材へ照射する場合も、熱プラズマの出口と基材２５の距離（溶射距離）２４を基材の移動によりあらかじめ調整し、本発明の方法の特徴である熱プラズマの高輝な部分が基材に接触する条件、即ち熱プラズマが十分に触れる状態で溶射すれば良い。この場合は、溶射距離２４を１０〜５０ｍｍ程度とすることが好ましく、特に２０ｍｍから４０ｍｍとすることが好ましい。溶射距離を短くすることにより、熱プラズマの高輝な部分を十分に基材に触れさせることが出来、珪素成分の窒化を進めることが出来、尚且つ緻密な膜が得られる。
【００３１】
本発明の溶射における基材の位置は、熱プラズマの高輝な部分が接触する位置であれば良い。基材は固定されていても良いが、基材１０１、２５を前後左右に移動させて、基材全体に熱プラズマを照射し、均一に加熱、成膜することが好ましい。
【００３２】
本発明の溶射法では珪素を窒化する必要があるため、熱プラズマ中には窒素を含むことが必須である。前記熱プラズマを形成するガスとしては窒素にアルゴンなどのプラズマの安定性を高めるガスを加えてもよいが、本発明ではさらに水素を添加すると、膜中の珪素表面の酸化膜が除去されて窒化し易くなるために特に好ましい。水素の添加量は特に限定されないが、窒素に対して容量比で０．０３倍から０．５倍、特に０．１倍から０．４倍の範囲で添加することが好ましい。
【００３３】
次に本発明の方法は、窒素を含む熱プラズマ中に原料珪素を投入することによって溶射膜を形成する。投入する珪素の形状としては、粉末、ペレット等が適用出来るが、特に粉末であることが好ましい。図１は、珪素を粉末の形で供給する方法を例示している。粉末供給器１１１にキャリアガス１１２を導入し、珪素粉末を供給し、窒素を含む熱プラズマ中に投入するが、珪素粉末の供給速度は均一であることが好ましい。
【００３４】
本発明で原料珪素に粉末珪素を用いる場合、粉末の粒径は小さい方が窒素を含む熱プラズマとの反応性が高い為に好ましい。一方、あまり粒径が小さいと流動性が悪くなり、一定速度での供給が困難となるため、原料珪素粉末の粒径としては平均粒径が１μｍ以上７０μｍ以下であることが好ましい。珪素粉末の平均粒径の測定方法は、一般的な粒度測定装置、例えば光透過型粒度分布測定装置等で測定することが出来る。
【００３５】
本発明では上述の溶射で得られた溶射膜に、引き続き窒素、或いは窒素と水素を含む熱プラズマを熱プラズマの高輝な部分が基材に接触する条件で照射することにより、膜中の残存珪素を溶融させながら窒化させ、特に窒化珪素含有率の高い溶射膜を得ることが出来る。この場合、熱プラズマの照射の目的が、膜中に残存した珪素の窒化であるため、熱プラズマ中に珪素原料を新たに添加しないで照射する。
【００３６】
本発明の方法により得られる溶射膜は、何層も繰り返し堆積することによって厚い膜を成膜することができるが、例えば基材に一層の溶射層を堆積し、次の層の溶射層を堆積する前に珪素を供給しない熱プラズマの照射工程を施し、各層の膜中窒化珪素の比率を増大しながら積層することができる。後は同様の操作を繰り返し、膜全体において窒化珪素の含有率の高い溶射膜を得ることが出来る。ここで、本発明の方法によって複数の溶射層を堆積した後に、珪素を供給しない熱プラズマで仕上げの照射工程を施しても良い。
【００３７】
【実施例】
本発明を実施例に基づき更に詳細に説明するが、本発明はこれらの実施例のみに限定されるものではない。
【００３８】
実施例１
図１に示す装置を用い、グラファイト基材上に窒化珪素溶射膜を成膜した。ブラスト処理し表面を粗面化した２０ｍｍ角のグラファイト基材１０１を、真空槽１０３内の基材ホルダー１０２に装着した。溶射距離１０６は６０ｍｍに予め調整した後、ロータリーポンプ１０７により０．５Ｔｏｒｒ以下まで真空引きした。次にシースガス１０８をアルゴン１０Ｌ／分、窒素３Ｌ／分、水素０．５Ｌ／分とし、プラズマガス１０９としてアルゴン６Ｌ／分を導入して６０Ｔｏｒｒの圧力とし、高周波コイル１１０に１０ｋＷの電力の高周波を印加して熱プラズマを発生させた。
この条件で、発生した熱プラズマの高輝な部分は、グラファイト基材に十分に接触していた。
次に先に装着したグラファイト基材１０１に熱プラスマを照射し、熱プラズマを前後左右に振幅させながら基材１０１を加熱し、溶射前の予熱温度を９００℃とした。
【００３９】
次に、粉末供給器１１１にテクノサーブ社製微粉末供給器を用い、アルゴンを１Ｌ／分の流量でキャリアガス１１２として導入し、平均粒径は３５μｍ珪素の原料粉末を約１ｇ／分で熱プラズマ中に供給した。上記条件で熱プラズマを移動させながら溶射を繰り返し、１０層の溶射層を堆積させた。成膜中のプラズマが照射された部分の温度は放射温度計で測定して１５００℃から１７００℃の範囲であった。
【００４０】
得られた溶射膜は厚み２ｍｍで、蛍光X線法により組成を分析したところ窒素が５１原子％含まれていた。Ｘ線回折により結晶構造を分析したところβ−Ｓｉ₃Ｎ₄と珪素のピーク強度が観察された。また溶射膜の断面のＳＥＭ観察を行った結果、膜組織は緻密であった。
【００４１】
実施例２
水素流量を１Ｌ／分とし、溶射成膜後に窒素および水素を含む熱プラズマを基材に４回照射を繰り返して窒化を進行させた他は実施例１と同様の条件で窒化珪素を主体とする溶射膜を形成した。成膜中のプラズマが照射された部分の温度は放射温度計で測定して１５５０℃から１７５０℃の範囲であった。
【００４２】
得られた溶射膜は厚み２．５ｍｍで、蛍光X線法により組成を分析したところ窒素が５６原子％でほとんど窒化珪素の膜が得られた。Ｘ線回折により結晶構造を分析したところβ−Ｓｉ₃Ｎ₄相のみが観察された。断面のＳＥＭ観察を行った結果、実施例１と同様に緻密に充填された膜となっていた。
【００４３】
実施例３
水素流量を０．４Ｌ／分とした他は実施例１と同様の条件で窒化珪素を主体とする溶射膜を形成した。成膜中のプラズマが照射された部分の温度は放射温度計で測定して１４５０℃から１６５０℃の範囲であった。
【００４４】
得られた溶射膜は厚み１．８ｍｍで、蛍光X線法により組成を分析したところ窒素が３９原子％含まれており、Ｘ線回折により結晶構造を分析したところ珪素のピークが主体でβ−Ｓｉ₃Ｎ₄相の窒化珪素のピークが半分弱の強度で見られた。断面のＳＥＭ観察を行った結果、緻密な膜となっていた。
【００４５】
実施例４
水素をプラズマガスに添加せず、高周波電力を１２ｋＷとした他は実施例１と同様の条件で溶射膜を形成した。成膜中のプラズマが照射された部分の温度は放射温度計で測定して１５００℃から１６００℃の範囲であった。
【００４６】
得られた溶射膜は厚み２．０ｍｍで、蛍光Ｘ線法により組成を分析したところ窒素が４９原子％含まれており、Ｘ線回折により組成を分析したところ珪素のピークが主体でβ−Ｓｉ₃Ｎ₄相の窒化珪素のピークが半分弱の強度で見られた。プラズマガスに水素は添加しなかったが、投入電力を大きくすることによって、窒化が促進される結果となった。断面のＳＥＭ観察を行った結果、緻密な膜となっていた。
【００４７】
比較例１
窒素をプラズマガスに添加しなかった他は実施例１と同様の条件で溶射膜を形成した。
【００４８】
得られた溶射膜は、厚み１．５ｍｍで、蛍光Ｘ線法により組成を分析したところ珪素のみで窒化珪素は含まれておらず、Ｘ線回折により組成を分析したところ珪素のピークのみしか見られなかった。
【００４９】
比較例２
窒化珪素微粒子にアルミナとイットリアの粉末を各々１５モル％添加してスプレードライ法で平均粒径４０μｍの顆粒を作製し、窒素と水素の混合ガスによる大気圧プラズマ法を用い、あらかじめブラストしたグラファイト基材上にアルミナとイットリアを添加した窒化珪素溶射膜を２ｍｍの膜厚で成膜した。溶射条件は、予熱温度２００℃、ガス流量として窒素４０ＳＬＭ、水素１０ＳＬＭで、溶射距離が１０ｃｍ、ＤＣ電力は３８ｋＷとした。
【００５０】
蛍光Ｘ線法により組成を分析したところ窒素が３５原子％含まれていた。Ｘ線回折により結晶構造を分析したところβ−Ｓｉ₃Ｎ₄と珪素、アルミナ、イットリアのピークが見られた。溶射膜の断面のＳＥＭ観察を行った結果、膜組織にはポアが多く見られ、気孔率は２０％程度であった。
【００５１】
実施例５
実施例１〜４、比較例１、２の溶射膜の硬度を加重１００ｇでビッカース硬度計を用いて測定した。硬度は実施例１から実施例４まで夫々１２５０Ｈｖ、１４００Ｈｖ、１０５０Ｈｖ、１２００Ｈｖであり、比較例１で８００Ｈｖ、比較例２で８５０Ｈｖであった。窒化珪素の含有率の高い本発明の実施例では高い硬度が得られ、特に窒化珪素の含有比率の高いものほど相対的に硬度が高くなった。また、比較例２の酸化物の添加による大気圧プラズマ溶射膜ではポアが多く、窒化珪素が含有しているにも拘わらず十分な硬度は得られなかった。
【００５２】
実施例６
実施例１〜４、比較例１の基材裏面と溶射膜表面間の導電性を評価した。実施例１から実施例４までは導電性が認められなかったが、比較例１ではグラファイトも珪素も導電性があるため、基材裏面から溶射膜表面に導電性が認められた。
【００５３】
実施例７
実施例１〜４、比較例１、２を温度６０℃の王水に浸漬した。１０時間後に基材裏面を確認したところ実施例１から実施例４までは溶射膜が残っていたが、比較例１、２は残存珪素、共存酸化物の部分が選択的に溶解し、表面が粗面化し、一部では剥離していた。本発明の溶射膜は耐酸化性に優れていることが認められた。
【００５４】
実施例８
実施例１〜４、比較例１、２の溶射膜を加重２００ｇの条件で＃４００番の研磨紙を用いた回転式の摺動試験機（６０ｒｐｍ）で耐摩耗性を評価した。実施例１から実施例４までは１０００回の摺動後も被膜が保たれたが、比較例１、２は被膜の一部が剥離して基材面が現れた。実施例で得られた溶射膜は高い耐摩耗性があることが確認された。
【００５５】
実施例９
実施例１〜４、比較例２の溶射膜を、鉄を１００ｐｐｍ、ナトリウムを１０ｐｐｍ含むグラファイト基材の上全面に成膜したのち、超純水で洗浄した。当該成膜基材の上にシリコンウエハを置いて、真空電気炉中に入れて１１００℃で１時間加熱した後、シリコンウエハの表面を硝フッ酸でエッチングし、当該エッチング液をＩＣＰで分析した。実施例１〜４では、不純物は検出限界以下であったが、比較例２ではアルミニウム、イットリア、鉄、ナトリウムが不純物として検出された。
【００５６】
【発明の効果】
本発明の窒化珪素溶射膜の製造方法は、以下に示す効果を有する。
１）本発明の方法により得られる溶射膜は、窒化珪素の比率が高く、窒化珪素と珪素のみからなる膜であるため、高硬度を有し、部材に被覆した場合、高い耐磨耗性及び耐酸化性を発揮できる。
２）本発明の方法により得られる溶射膜は緻密な膜構造をとることが出来るため、基材からの不純物拡散防止を目的とした被覆として応用できる。
３）本発明の方法により得られる溶射膜は窒化珪素の比率が高いため、絶縁部品としての応用に適する。
４）本発明の溶射膜の製造方法は、溶射法だけで窒化珪素を主体とする溶射膜が製造でき、製造工程が簡便である。
【図面の簡単な説明】
【図１】本発明における溶射膜を減圧で製造するための装置の一例を示す図である。
【図２】本発明における溶射膜を常圧で製造するための装置の一例を示す図である。
【符号の説明】
１０１：基材
１０２：基材ホルダー
１０３：真空槽
１０４：熱プラズマ
１０５：スペーサ
１０６：溶射距離
１０７：ロータリーポンプ
１０８：シースガス
１０９：プラズマガス
１１０：高周波コイル
１１１：粉末供給器
１１２：キャリアガス
１１３：熱プラズマ源の石英管
１１４：熱電対
２０：カソード
２１：アノード
２２：プラズマガスライン
２３：粉末供給ライン
２４：溶射距離
２５：基材
２６：溶射膜
２７：直流電源
２８：熱プラズマ
２９：熱電対[0001]
BACKGROUND OF THE INVENTION
The present invention, high-temperature structural material as a gas turbine component, a cutting tool, a susceptor coating and heat treatment apparatus, such as a steel-making machine parts - are those involved in the manufacturing method of the preferred silicon nitride sprayed film for coating such member.
[0002]
[Prior art]
Silicon nitride is light and has a density of about 40% of that of heat-resistant alloys, and has the lowest thermal expansion coefficient among non-oxide ceramics, and therefore has excellent thermal shock resistance. Since silicon nitride has such excellent physical properties, the sintered body has heretofore been used for automobile engine parts and heat-resistant insulating parts. Recently, in order to use such excellent silicon nitride more widely, there is an increasing demand for a technique for forming a thick silicon nitride film on a metal or oxide base material.
[0003]
Conventionally, as a method for forming a silicon nitride film, a film forming method such as a CVD method, a PVD method, or a sputtering method is known. However, since these methods are methods for producing an extremely thin thin film, it has been difficult to produce a thick film having a thickness of 1 μm or more, particularly several mm.
[0004]
On the other hand, a thermal spraying method is known as a method for producing a thick film. The thermal spraying method is a method in which a thermal spray raw material is melted and the molten thermal spray raw material is deposited on the substrate at high speed. If the thermal spraying method is used, it is generally possible to produce a thick film of several μm to several mm. However, when non-oxides such as nitrides and carbides are formed by thermal spraying, the decomposition temperature thereof is low, so that there is a problem that the thermal spray raw material is decomposed during thermal spraying and cannot be formed.
[0005]
Accordingly, it has been proposed to form a film made of a mixture of oxide and nitride (or carbide) instead of a pure nitride film (see, for example, Patent Document 1). However, in such a method, the performance of the film obtained due to the influence of the mixed oxide is low or the ratio of the nitride in the film is not sufficient.
[0006]
In addition, a method for forming a mixed film of silicon nitride and a metal by spraying a mixed spray material in which a metal such as nickel is added instead of an oxide as an auxiliary agent to be added to silicon nitride has been proposed. (For example, refer nonpatent literature 1). However, such a film containing a metal other than silicon has a problem that the metal is an impurity, and thus cannot be used in a process requiring high purity.
[0007]
As a method of forming a silicon nitride film, a method of forming a silicon oxide or metal silicon film by a thermal spraying method and then converting it to a nitride by heat treatment in a nitrogen atmosphere has been proposed (for example, Patent Documents). 2). However, in this method, since the nitride film is formed only on the outermost surface, the film does not sufficiently exhibit the performance as silicon nitride.
[0008]
Until now, there has been no attempt to form a pure silicon nitride film by plasma spraying. (For example, see Non-Patent Document 2) However, the films obtained by the plasma spraying method so far can only obtain a film having a low nitrogen content of about 2% by weight of nitrogen, that is, up to 4 atomic% of nitrogen. It was not done.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 06-049717 [Patent Document 2]
Japanese Patent Laid-Open No. 06-228724 [Non-Patent Document 1]
Lugscherder, E .; , R. Limbach, A.M. Liden and J.M. Rodin, High Temp. Mater. Power Eng. 1990, Porc. Conf. , Vol. 1,877-880 (1990)
[Non-Patent Document 2]
Proceeding of the 7th National Thermal Spray Conference 20-24 June 1994, Boston Massachusetts
[0010]
[Problems to be solved by the invention]
Conventionally, in the thermal spraying method used to obtain a thick film, it has been difficult to obtain a thick film made of only silicon nitride or having a high silicon nitride ratio. Further, it has been impossible to obtain a thick film that can exhibit wear resistance, oxidation resistance, impurity diffusion prevention properties, and the like, or a member coated with such a thick film. It is an object of the present invention to propose a novel method for reactive plasma spraying of silicon, and to form a dense sprayed film consisting only of silicon nitride or having a high silicon nitride ratio and consisting only of silicon nitride and silicon, and a sprayed film. It is providing the member which coat | covered.
[0011]
[Means for Solving the Problems]
As a result of intensive studies in view of the above situation, the present inventors have used a thermal plasma containing nitrogen, and the distance at which the base material is sufficiently in contact with the thermal plasma, that is, the high brightness of the thermal plasma. It has been found that by spraying plasma at a temperature higher than the melting point of silicon and not higher than the decomposition temperature of silicon nitride under a condition that touches such a portion, a dense sprayed film having a high silicon nitride content on the substrate can be obtained. Further, in the sprayed film obtained by the method of the present invention, the silicon remaining in the gaps of the silicon nitride particles is further irradiated with a bright portion of the thermal plasma containing nitrogen to advance nitriding, and the ratio of silicon nitride is high. It has been found that a dense sprayed film can be obtained. Moreover, in the method of this invention, it discovered that nitriding was accelerated | stimulated by adding hydrogen to nitrogen essential as plasma gas. Further, a member obtained by coating a substrate with a silicon nitride sprayed film obtained by the method of the present invention is excellent in hardness, insulation, heat resistance, wear resistance, oxidation resistance, impurity diffusion prevention, and the like. When the material is graphite, it has been found that the material has excellent adhesion to the substrate, and the present invention has been completed.
[0012]
The silicon nitride sprayed film obtained by the method of the present invention will be described.
[0013]
The silicon nitride sprayed film obtained by the method of the present invention is a thick film formed by a spraying method, and is different from a thin film obtained by conventional sputtering or CVD. The film thickness is preferably from 1 μm to 3 mm, more preferably from 100 μm to 1 mm. A film thinner than 1 μm has a problem in wear resistance, while a thickness exceeding 3 mm is not generally required and economical in the technical field using the film of the present invention.
[0014]
The silicon nitride sprayed film obtained by the method of the present invention is a film made of silicon nitride and silicon, and the silicon nitride content is preferably high. The reason is that the higher the silicon nitride content, the higher the effects of heat resistance, wear resistance, oxidation resistance and impurity diffusion prevention, so it is used for application fields that require these characteristics, such as susceptors for heat treatment equipment, etc. This is because high performance is exhibited when it is done.
[0015]
The nitrogen content is in the range of 10 atomic% to 58 atomic%, preferably 40 atomic% to 58 atomic%, particularly preferably 50 atomic% to 58 atomic%. When the nitrogen content is less than 10 atomic%, silicon tends to exist on the surface of the film instead of silicon nitride, which is not preferable for achieving the target performance of the present invention. On the other hand, if the silicon nitride film is formed purely of silicon nitride, the nitrogen content is 57.1 atomic%. (Si ₃ N ₄ conversion) In the silicon nitride film obtained by the method of the present invention, the film may contain some non-stoichiometric nitride, and the upper limit is allowed to about 58 atomic%. The
[0016]
Here, the sprayed film of the present invention satisfies the nitrogen content in the above-mentioned range in the entire film. For example, as in Non-Patent Document 2, the ratio of silicon nitride only on the outermost surface that can be confirmed by surface analysis or the like is high, This is different from the case where the nitrogen content of the entire film is less than 10 atomic%.
[0017]
Further, the sprayed film obtained by the method of the present invention is a film mainly composed of silicon nitride, and the components other than silicon nitride are films composed of silicon, and oxides added as auxiliary agents such as yttria, calcia, and alumina. It is a film that does not contain foreign components due to ceramics. However, it is not excluded from the present invention that these elements exist at the impurity level and have the same performance as the silicon nitride film obtained by the method of the present invention.
[0018]
Further, the film obtained by the method of the present invention does not exclude the film containing silicon oxide formed by oxidation in the air, and a film containing silicon oxide that is naturally generated within a range that is normally considered is also within the scope of the present invention. is there.
[0019]
The structure of the thermal sprayed film obtained by the method of the present invention is not particularly limited, and can take any morphology from a dense film to a porous film. However, for the purpose of the present invention, that is, for applications such as heat resistance and wear resistance, a dense film having no pores is particularly preferable. In particular, according to the method of the present invention described later, a dense film can be easily obtained as compared with a silicon nitride sprayed film containing a conventional oxide or metal sintering aid.
[0020]
Furthermore, the member which formed the silicon nitride sprayed film obtained by the method of this invention on the base material is proposed. The base material is not particularly limited, and glass, ceramics, metal, and the like can be applied. Particularly, when graphite is used as the base material, the thermal expansion coefficient of graphite is close to that of silicon nitride or silicon, so that the member has particularly excellent adhesion. Is preferable. A member in which the thermal spray film of the present invention is formed on such a graphite substrate exhibits excellent performance particularly in applications such as a susceptor member of a heat treatment apparatus.
[0021]
Next, the manufacturing method of the sprayed film of this invention is demonstrated.
[0022]
A method for producing a thermal sprayed film mainly composed of silicon nitride according to the present invention will be described with reference to an example of the apparatus shown in FIGS.
[0023]
In the method of the present invention, a substrate is attached to a device having a portion for generating thermal plasma and a portion for holding the substrate to form a film.
[0024]
The pressure in the thermal spraying conditions of the present invention is not particularly limited, and can be performed under pressure, normal pressure, or reduced pressure. In the case of normal pressure, it may be carried out at atmospheric pressure. However, in the case of reducing pressure, for example, the thermal spray source shown in FIG. 1 is evacuated to 0.5 Torr or less by the rotary pump 107 and then the quartz tube of the thermal plasma source is used. For example, a sheath gas 108 such as argon for protection 113 and a plasma gas 109 such as nitrogen and argon are introduced to form a film at a pressure of 20 to 150 Torr.
[0025]
FIG. 2 shows an example of an apparatus for spraying at atmospheric pressure. In an apparatus having a part for generating thermal plasma at atmospheric pressure and a part for holding the substrate 25, a plasma gas such as nitrogen and hydrogen is introduced from the plasma gas line 22 and a voltage is applied between the cathode 20 and the anode 21. The thermal plasma 28 can be generated by a DC arc.
[0026]
Although the base material which forms the sprayed film used by this invention is not specifically limited, For example, metal base materials, such as stainless steel and carbon steel, graphite, quartz, ceramics, etc. can be used as the base materials 101 and 25. In order to improve the adhesion to the sprayed film, the substrate used is preferably used with the surface roughened by a blast method or the like.
[0027]
Next, the thermal spraying method of the present invention uses thermal plasma. Although the generation method of thermal plasma is not limited, for example, it can be generated by high frequency, direct current arc, alternating current arc, or the like. FIG. 1 illustrates a method of generating a thermal plasma 104 by applying a high frequency to the high frequency coil 110. The term “thermal plasma” as used herein refers to a gas stream generated by gas discharge by the above-described means and at least partially ionized to a high temperature of several thousand to several tens of thousands of degrees.
[0028]
In the thermal spraying of the present invention, the temperature of the portion of the substrate surface irradiated with the thermal plasma must be not lower than the melting point of silicon and not higher than the decomposition temperature of silicon nitride. The melting point of silicon is 1410 ° C., and the decomposition temperature of silicon nitride is 1900 ° C. If the temperature does not reach the melting point of silicon, it is difficult to produce silicon nitride. If the temperature exceeds the decomposition temperature of silicon nitride, the produced silicon nitride is lost, and the film having the nitrogen content range of the present invention cannot be obtained. . In order to obtain such a substrate surface temperature, it is preferable that the substrate is preheated before thermal spray film formation, and the preheating temperature is set to 600 ° C. or more and the melting point of the substrate or less. In the present invention, the temperature of the portion where the sprayed film is deposited, that is, the temperature of the outermost surface of the base material may be in the above range, and the entire base material does not need to be at the above temperature. Whether or not the temperature of the part irradiated with the thermal plasma is within the range of the present invention is assumed by measuring the temperature in the vicinity of the substrate (for example, the back surface) with a contact-type thermocouple during or immediately after the film formation. The temperature of the substrate surface can be measured from the temperature gradient to be measured, or the substrate surface temperature can be directly measured with a non-contact type radiation thermometer during film formation.
[0029]
Next, the method of the present invention is characterized in that thermal spraying is performed while bringing a bright portion of thermal plasma containing nitrogen into contact with the substrate. For example, in the case of FIG. 1, the distance (spraying distance) 106 between the outlet of the thermal plasma 104 and the substrate 101 is adjusted in advance by the spacer 105 at the bottom of the substrate holder 102, and the substrate is a feature of the method of the present invention. The thermal spraying is performed under the condition that the bright part of the thermal plasma is in contact, that is, the thermal plasma is sufficiently in contact with the substrate. In order to develop such a state, it is preferable to set the spraying distance 106 to 10 mm or more and less than 100 mm, particularly 20 mm to 50 mm. In the present invention, in order to avoid decomposition of silicon nitride, the temperature is not lower than the melting point of silicon (1410 ° C.) and not higher than the decomposition temperature of silicon nitride (1900 ° C.). In order to achieve this, it is essential to activate the film-forming portion of the base material by bringing the bright portion of the thermal plasma into contact with the base material. By sufficiently bringing the bright part of the thermal plasma into contact with the substrate, the silicon component can be nitrided and a dense film can be obtained.
[0030]
Also in the case of irradiating the substrate with thermal plasma at atmospheric pressure shown in FIG. 2, the distance (spraying distance) 24 between the outlet of the thermal plasma and the substrate 25 (spraying distance) is adjusted in advance by moving the substrate, and the method of the present invention is characterized. The thermal spraying may be performed under the condition that the bright part of the thermal plasma is in contact with the substrate, that is, the thermal plasma is sufficiently in contact. In this case, the spraying distance 24 is preferably about 10 to 50 mm, particularly preferably 20 mm to 40 mm. By shortening the spraying distance, the bright part of the thermal plasma can be sufficiently brought into contact with the substrate, the nitridation of the silicon component can be advanced, and a dense film can be obtained.
[0031]
The position of the base material in the thermal spraying of the present invention may be a position where the bright part of the thermal plasma comes into contact. Although the base material may be fixed, it is preferable to move the base materials 101 and 25 back and forth and to the left and right, irradiate the whole base material with thermal plasma, and uniformly heat and form a film.
[0032]
Since it is necessary to nitride silicon in the thermal spraying method of the present invention, it is essential that the thermal plasma contains nitrogen. As the gas for forming the thermal plasma, a gas for improving the stability of the plasma such as argon may be added to nitrogen. However, in the present invention, when hydrogen is further added, the oxide film on the silicon surface in the film is removed and nitrided. It is particularly preferable because it is easy to do. The amount of hydrogen to be added is not particularly limited, but it is preferably added in a range of 0.03 to 0.5 times, particularly 0.1 to 0.4 times the volume ratio to nitrogen.
[0033]
Next, in the method of the present invention, a thermal spray film is formed by introducing raw silicon into a thermal plasma containing nitrogen. As the shape of silicon to be added, powder, pellets, and the like can be applied, but powder is particularly preferable. FIG. 1 illustrates a method of supplying silicon in powder form. The carrier gas 112 is introduced into the powder supplier 111, silicon powder is supplied, and the powder is supplied into a thermal plasma containing nitrogen. It is preferable that the supply rate of the silicon powder is uniform.
[0034]
In the present invention, when powder silicon is used as the raw material silicon, it is preferable that the particle diameter of the powder is smaller because the reactivity with the thermal plasma containing nitrogen is higher. On the other hand, if the particle size is too small, the fluidity is deteriorated and it is difficult to supply at a constant rate. Therefore, the average particle size of the raw material silicon powder is preferably 1 μm or more and 70 μm or less. The method for measuring the average particle size of the silicon powder can be measured with a general particle size measuring device such as a light transmission type particle size distribution measuring device.
[0035]
In the present invention, the thermal sprayed film obtained by the above-described thermal spraying is subsequently irradiated with thermal plasma containing nitrogen or nitrogen and hydrogen under the condition that the bright part of the thermal plasma is in contact with the base material, thereby remaining silicon in the film. It is possible to obtain a sprayed film having a particularly high silicon nitride content by nitriding while melting. In this case, since the purpose of the thermal plasma irradiation is nitridation of silicon remaining in the film, the thermal plasma is irradiated without newly adding a silicon raw material.
[0036]
The sprayed film obtained by the method of the present invention can be formed into a thick film by repeatedly depositing many layers. For example, one sprayed layer is deposited on a substrate, and the next sprayed layer is deposited. It is possible to stack the layers while increasing the ratio of silicon nitride in each layer by applying a thermal plasma irradiation process in which silicon is not supplied. Thereafter, the same operation is repeated to obtain a sprayed film having a high silicon nitride content in the entire film. Here, after depositing a plurality of sprayed layers by the method of the present invention, a finishing irradiation step may be performed by thermal plasma without supplying silicon.
[0037]
【Example】
The present invention will be described in more detail based on examples, but the present invention is not limited to only these examples.
[0038]
Example 1
A silicon nitride sprayed film was formed on a graphite substrate using the apparatus shown in FIG. A 20 mm square graphite base material 101 having a roughened surface by blasting was mounted on the base material holder 102 in the vacuum chamber 103. The spraying distance 106 was adjusted in advance to 60 mm and then evacuated to 0.5 Torr or less by the rotary pump 107. Next, the sheath gas 108 is argon 10 L / min, nitrogen 3 L / min, hydrogen 0.5 L / min, argon 6 L / min is introduced as the plasma gas 109 to a pressure of 60 Torr, and a high frequency of 10 kW power is applied to the high frequency coil 110. Applied to generate thermal plasma.
Under these conditions, the bright portion of the generated thermal plasma was in sufficient contact with the graphite substrate.
Next, the graphite substrate 101 previously mounted was irradiated with a thermal plasma, and the substrate 101 was heated while amplifying the thermal plasma back and forth and left and right, and the preheating temperature before spraying was set to 900 ° C.
[0039]
Next, a fine powder feeder manufactured by Technoserve Co., Ltd. was used as the powder feeder 111, and argon was introduced as a carrier gas 112 at a flow rate of 1 L / min. The raw material powder having an average particle size of 35 μm was heated at about 1 g / min. It was supplied into the plasma. Spraying was repeated while moving the thermal plasma under the above conditions, and 10 sprayed layers were deposited. The temperature of the portion irradiated with plasma during film formation was in the range of 1500 ° C. to 1700 ° C. as measured with a radiation thermometer.
[0040]
The obtained sprayed film had a thickness of 2 mm, and its composition was analyzed by the fluorescent X-ray method. As a result, it contained 51 atomic% of nitrogen. When the crystal structure was analyzed by X-ray diffraction, the peak intensities of β-Si ₃ N ₄ and silicon were observed. Further, as a result of SEM observation of the cross section of the sprayed film, the film structure was dense.
[0041]
Example 2
Mainly silicon nitride under the same conditions as in Example 1 except that the flow rate of hydrogen was 1 L / min and the thermal plasma containing nitrogen and hydrogen was repeatedly applied to the substrate four times after the thermal spray film formation to advance nitriding. A sprayed film was formed. The temperature of the portion irradiated with plasma during film formation was in the range of 1550 ° C. to 1750 ° C. as measured with a radiation thermometer.
[0042]
The obtained sprayed film had a thickness of 2.5 mm, and its composition was analyzed by the fluorescent X-ray method. As a result, a film of almost silicon nitride with a nitrogen content of 56 atomic% was obtained. When the crystal structure was analyzed by X-ray diffraction, only the β-Si ₃ N ₄ phase was observed. As a result of SEM observation of the cross section, it was a densely packed film as in Example 1.
[0043]
Example 3
A sprayed film mainly composed of silicon nitride was formed under the same conditions as in Example 1 except that the hydrogen flow rate was 0.4 L / min. The temperature of the portion irradiated with plasma during film formation was in the range of 1450 ° C. to 1650 ° C. as measured with a radiation thermometer.
[0044]
The obtained sprayed film had a thickness of 1.8 mm, and its composition was analyzed by X-ray fluorescence. As a result, it contained 39 atomic% of nitrogen, and its crystal structure was analyzed by X-ray diffraction. A peak of Si ₃ N ₄ phase silicon nitride was observed with an intensity of a little less than half. As a result of SEM observation of the cross section, it was a dense film.
[0045]
Example 4
A sprayed film was formed under the same conditions as in Example 1 except that hydrogen was not added to the plasma gas and the high-frequency power was 12 kW. The temperature of the portion irradiated with plasma during film formation was in the range of 1500 ° C. to 1600 ° C. as measured with a radiation thermometer.
[0046]
The obtained sprayed film had a thickness of 2.0 mm, and its composition was analyzed by fluorescent X-ray method. As a result, it contained 49 atomic% of nitrogen, and its composition was analyzed by X-ray diffraction. The peak of ₃ N ₄ phase silicon nitride was observed with an intensity of a little less than half. Hydrogen was not added to the plasma gas, but nitriding was promoted by increasing the input power. As a result of SEM observation of the cross section, it was a dense film.
[0047]
Comparative Example 1
A sprayed film was formed under the same conditions as in Example 1 except that nitrogen was not added to the plasma gas.
[0048]
The obtained sprayed film had a thickness of 1.5 mm, and its composition was analyzed by fluorescent X-ray method. It contained only silicon and did not contain silicon nitride. When the composition was analyzed by X-ray diffraction, only the silicon peak was observed. I couldn't.
[0049]
Comparative Example 2
Graphite base is prepared by adding 15 mol% each of alumina and yttria powders to silicon nitride fine particles and producing granules having an average particle size of 40 μm by spray drying, and using an atmospheric pressure plasma method using a mixed gas of nitrogen and hydrogen. A silicon nitride sprayed film to which alumina and yttria were added was formed to a thickness of 2 mm on the material. The spraying conditions were a preheating temperature of 200 ° C., a gas flow rate of nitrogen 40 SLM and hydrogen 10 SLM, a spraying distance of 10 cm, and a DC power of 38 kW.
[0050]
When the composition was analyzed by the fluorescent X-ray method, it contained 35 atomic% of nitrogen. When the crystal structure was analyzed by X-ray diffraction, peaks of β-Si ₃ N ₄ and silicon, alumina, and yttria were observed. As a result of SEM observation of the cross section of the sprayed film, many pores were observed in the film structure, and the porosity was about 20%.
[0051]
Example 5
The hardness of the sprayed films of Examples 1 to 4 and Comparative Examples 1 and 2 was measured using a Vickers hardness meter at a load of 100 g. The hardness was 1250Hv, 1400Hv, 1050Hv, 1200Hv from Example 1 to Example 4, 800Hv in Comparative Example 1, and 850Hv in Comparative Example 2, respectively. In the examples of the present invention having a high silicon nitride content, high hardness was obtained, and in particular, the higher the silicon nitride content, the higher the hardness. Further, the atmospheric pressure plasma sprayed film with the addition of the oxide of Comparative Example 2 had many pores, and although the silicon nitride contained, sufficient hardness could not be obtained.
[0052]
Example 6
The electrical conductivity between the base material back surface of Examples 1-4 and Comparative Example 1 and the sprayed film surface was evaluated. Although conductivity was not recognized from Example 1 to Example 4, in Comparative Example 1, since graphite and silicon were both conductive, conductivity was recognized from the back surface of the substrate to the sprayed film surface.
[0053]
Example 7
Examples 1 to 4 and Comparative Examples 1 and 2 were immersed in aqua regia at a temperature of 60 ° C. When the back surface of the substrate was confirmed after 10 hours, the sprayed film remained in Examples 1 to 4, but in Comparative Examples 1 and 2, the remaining silicon and coexisting oxide portions were selectively dissolved, and the surface was It was roughened and partly peeled off. It was confirmed that the thermal sprayed film of the present invention is excellent in oxidation resistance.
[0054]
Example 8
The abrasion resistance of the thermal sprayed films of Examples 1 to 4 and Comparative Examples 1 and 2 was evaluated with a rotary sliding tester (60 rpm) using # 400 abrasive paper under the condition of a weight of 200 g. In Example 1 to Example 4, the film was maintained even after 1000 times of sliding, but in Comparative Examples 1 and 2, a part of the film was peeled off and the substrate surface appeared. It was confirmed that the thermal sprayed film obtained in the examples has high wear resistance.
[0055]
Example 9
The sprayed films of Examples 1 to 4 and Comparative Example 2 were formed on the entire surface of a graphite substrate containing 100 ppm of iron and 10 ppm of sodium, and then washed with ultrapure water. A silicon wafer was placed on the film-forming substrate, placed in a vacuum electric furnace and heated at 1100 ° C. for 1 hour, and then the surface of the silicon wafer was etched with nitric hydrofluoric acid, and the etching solution was analyzed by ICP. . In Examples 1 to 4, impurities were below the detection limit, but in Comparative Example 2, aluminum, yttria, iron, and sodium were detected as impurities.
[0056]
【The invention's effect】
The method for producing a silicon nitride sprayed film of the present invention has the following effects.
1) The thermal spray film obtained by the method of the present invention has a high ratio of silicon nitride and is a film made of only silicon nitride and silicon. Therefore, the thermal spray film has high hardness and high wear resistance when coated on a member. Exhibits oxidation resistance.
2) Since the sprayed film obtained by the method of the present invention can have a dense film structure, it can be applied as a coating for the purpose of preventing impurity diffusion from the substrate.
3) Since the sprayed film obtained by the method of the present invention has a high silicon nitride ratio, it is suitable for application as an insulating component.
4) The manufacturing method of the sprayed film of the present invention can manufacture a sprayed film mainly composed of silicon nitride only by the spraying method, and the manufacturing process is simple.
[Brief description of the drawings]
FIG. 1 is a view showing an example of an apparatus for producing a sprayed coating under reduced pressure in the present invention.
FIG. 2 is a view showing an example of an apparatus for producing a sprayed film at normal pressure in the present invention.
[Explanation of symbols]
101: Substrate 102: Substrate holder 103: Vacuum chamber 104: Thermal plasma 105: Spacer 106: Thermal spray distance 107: Rotary pump 108: Sheath gas 109: Plasma gas 110: High-frequency coil 111: Powder feeder 112: Carrier gas 113: Quartz tube 114 of thermal plasma source: Thermocouple 20: Cathode 21: Anode 22: Plasma gas line 23: Powder supply line 24: Thermal spray distance 25: Base material 26: Thermal spray film 27: DC power supply 28: Thermal plasma 29: Thermocouple

Claims

In an apparatus having a part for generating a thermal plasma and a part for holding the base material, irradiation is performed while bringing a bright part of the thermal plasma containing nitrogen into contact with the base material, and silicon is introduced into the thermal plasma to thereby form the base material on the base material. A method for forming a silicon nitride sprayed film in which the temperature of the portion of the substrate surface irradiated with thermal plasma is not lower than the melting point of silicon and not higher than the decomposition temperature of silicon nitride. .

2. The manufacturing method according to claim 1 , wherein an apparatus having a part for generating thermal plasma by a high frequency or a direct current arc and a part for holding the substrate is used in a decompression vessel.

A thermal spray film obtained by the method of claim 1 or claim 2 is irradiated while contacting a bright portion of a thermal plasma containing nitrogen, and is nitrided while melting silicon in the thermal spray film. Item 3. The method for manufacturing a silicon nitride sprayed film according to item 1 or 2 .

The method for producing a silicon nitride sprayed film according to any one of claims 1 to 3 , wherein the thermal plasma contains nitrogen and hydrogen.