JP3554311B2 - Ni-based alloy member and method of manufacturing the same - Google Patents

Description

【００２５】
上記表１（ここで、Ｍは金属元素を示す。）に明らかなように、本発明において使用可能な金属硼化物としては、金属元素の種類に関係なく、硼化物であればすべての化合物が適用できる。この理由は、これらの金属硼化物をＮｉ基単結晶合金基材の表面に被覆した後、高温に加熱すると、硼素（Ｂ）が速やかに単結晶合金基材中に拡散して、変質層部分の強化作用に寄与することになる。
なお、硼素（Ｂ）の合金基材中への侵入によるこの変質層の強化メカニズムは、完全に解明したわけではないが、変質層中に生成した微細な再結晶の粒界にＢが拡散浸透して、粒界の結合力を向上させる結果と考えている。
【００２６】
上記反応において、硼化物を構成している金属もＢと一緒に拡散するので、好ましくは、Ｎｉ基単結晶合金の成分と同じ金属、例えば、Ｎｉ，Ｃｒ，Ｗ，Ｍｏ，Ｃｏ，Ａｌ，Ｔｉ，Ｎｂ，Ｔａ，およびＨｆなどの金属硼化物が、Ｎｉ基単結晶合金中に異種の金属成分が拡散して新しい未知の金属間化合物が生成しないようにするためにも好ましいことである。なお、Ｚｒの硼化物は、Ｚｒ金属自体が結晶粒界強化作用を発揮するため好都合である。
【００２７】
上掲の表１に示すように、金属硼化物の化学式は、Ｍ_{１ 〜 １１}Ｂ_{１ 〜 １２}の化合物が知られているが、本発明では、その他のすべての金属硼化物も使用が可能である。なお、市販の金属硼化物の場合、ＴｉＢ_１やＴｉ_２Ｂが混在したり、ＮｉＢ中にＮｉ_４Ｂ_３、Ｎｉ_２ＢときにはＮｉ_３Ｂも共存していることがあるが、これらの金属硼化物についても同様の効果が認められるので，金属（Ｍ）および硼素（Ｂ）の原子数はとくに限定されるものではない。
【００２８】
一方、非金属硼化物の例としては、Ｂ_４Ｃ，ＢＮなどが好適に用いられる。これらの硼化物は、単独での使用が可能であるが、金属硼化物と混合したり、Ｂ_４ＣとＢＮを混合しても、Ｎｉ基単結晶合金の熱疲労強度の低下を抑制する機能を発揮する。とくに、Ｂ_４Ｃの被覆層は、Ｎｉ基単結晶基材が高温に加熱されると、ＢとともにＣも基材内部に拡散すると共に、両者が共働して機材の再結晶に伴う微細な結晶粒界の強化に寄与する点で有効である。
また、本発明の硼化物被覆層は、Ｂを含まない多結晶Ｎｉ基合金やＢを含むもののその含有量が本発明の硼化物被覆層中のＢ含有量より少ない多結晶Ｎｉ基合金に対しても、多結晶粒界の強化作用を発揮するので、これらの合金に対しても有効である。
【００２９】
（３） 溶射法による硼化物被覆層（アンダーコート）の形成
Ｎｉ基単結晶合金基材表面に、金属硼化物および／または非金属硼化物からなる硼化物被覆層を形成する方法としては、代表的には溶射法を採用する。本発明の上述した作用効果を十分に発揮できるようにするためには、前記基材表面に、アンダーコートとしての硼化物被覆層を形成したとき、該硼化物被覆層（アンダーコート）から、Ｎｉ基単結晶合金基材の表面へのＢの良好な拡散移動と該アンダーコート溶射被覆層自体の溶射粒子の相互結合力、さらには後で述べるオーバーコートとして形成するＭＣｒＡｌＸ耐熱合金被覆層との良好な密着性を確保することが大切である。この目的を達成するための最大の課題は、アンダーコートの硼化物被覆層中に含まれる酸化物量の管理とその限界含有量を決定することである。例えば、アンダーコートを大気中で溶射法によって形成すると、溶射熱源中あるいは熱源近傍に多量の空気が混入して、溶射材料粒子を酸化するため、粒子の相互結合力や基材合金との付着力が低下する原因となるほか、これらの酸化物はＢの拡散を抑制するとともに、オーバーコートとの結合力の低下などを招き、大きな障害となる。
【００３０】
このため本発明では、アンダーコート中に含まれる酸化物量を、酸素量に換算して、１．５ｍａｓｓ％以下に管理することとした。すなわち、大気プラズマ溶射法，減圧プラズマ溶射法，爆発溶射法，高速フレーム溶射法などのいずれかの方法によって溶射する場合でも、酸素含有量は１．５ｍａｓｓ％以下に制御する。なお、溶射法の種類は、特に規制されるものではない。具体的には、高速フレーム溶射法，減圧プラズマ溶射法などの方法を採用することが好ましい。
【００３１】
（４） 蒸着法等による硼化物被覆層（アンダーコート）の形成
硼化物被覆層中に含まれる酸素量を１．５ｍａｓｓ％以下に抑制することができる方法であれば、溶射用でなくとも、例えば、ＰＶＤ法（物理的蒸着法）を採用しても、本発明の要請に応えられるアンダーコートを形成することができる。たとえば、図１は、電子ビームを熱源としたＰＶＤ装置（ＥＢ−ＰＶＤ）を用い、被覆材料１に電子銃２からビームを照射して材料の微細な蒸気（矢印）を蒸発させ、単結晶合金３に蒸着させる装置の図である。この装置は、真空容器４中に収納され、その容器には真空ポンプ５およびＡｒ，Ｈｅなどの不活性ガスの導入管６が配設されているので、容器中の雰囲気はある程度、自由に調整できるようになっており、実質的に空気（酸素）がなく、不活性ガス雰囲気中で蒸着できるので、形成される皮膜中には殆んど酸化物が含まれない。なお、この装置には、単結晶合金を加熱するためのヒータ７が配設されているととともに、単結晶合金と被覆材料とをそれぞれ電極とするための直流電源８が設けられているため、電圧を負荷することによって、蒸着前処理としての不活性ガスによる浄化処理や蒸着粒子をイオン化し、単結晶合金面へ衝突させることができるので、高い密着性も期待できる。
なお、蒸着法としては、上記の方法以外の方法として、レーザやジュール熱源を用いる蒸着法、高周波励起式のＥＰ−ＰＶＤ法、スパッタリング法なども使用でき、熱ＣＶＤ法、プラズマＣＶＤ法によっても上述したアンダーコートの形成は可能である。
【００３２】
上記アンダーコート（硼化物被覆層）の厚さは、０．１〜５０μｍ程度の範囲が好適である。その理由は硼化物の膜厚が０．１μｍより薄いと、粒界強化作用が十分でなく、一方、５０μｍより厚くしても、その粒界強化に格別良好な作用が認められず、また合金基材の内部へ侵入したＢが粒界強化以外に、他の合金成分と反応して、低融点共晶などを生成するので好ましくないからである。
【００３３】
（５） 耐熱合金被覆層（オーバーコート）の形成
本発明の他の実施形態としては、Ｎｉ基単結晶合金等の基材表面に、まず金属硼化物および／または非金属硼化物からなる硼化物被覆層をアンダーコートとして形成した後、その上に耐高温環境性を付与するための耐熱合金被覆層をオーバーコートを形成したものが考えられる。この実施形態は、前記硼化物被覆層（アンダーコート）中の硼化物の作用を十分に発揮させるとともに、高温環境から受ける各種の作用、例えば燃焼ガスによる酸化反応やＳ化合物による硫化腐食などの化学的損傷にも耐え得るようにするものである。
そこで、本発明では、前記硼化物被覆層（アンダーコート）の上に、耐高温環境性を示す耐熱合金被覆層をオーバーコートとして、大気プラズマ溶射法、減圧プラズマ溶射法、高速フレーム溶射法などの溶射法を用いて積層形成することにしたのである。
アンダーコートの上にオーバーコートを重ねて積層する理由は，硼化物被覆層であるアンダーコートだけでは、耐高温環境性が十分でないうえ、特に高温下においてはアンダーコートが、酸化現象によって消耗するので、膜厚０．１〜５０μｍ程度の膜厚では、アンダーコートの寿命が甚しく、短くなるおそれがあるためである。
【００３４】
本発明において、オーバーコートである耐熱合金被覆層に用いる耐熱合金としては、上述した「ＭＣｒＡｌＸ合金」を用いることが望ましい。その主要化学成分はＣｏ，Ｎｉ，Ｃｒ，ＦｅおよびＡｌのうちから選ばれる少なくとも２種を含む合金に対し、Ｙ，Ｈｆ，Ｔａ，Ｃｓ，Ｃｅ，Ｌａ，Ｔｈ，Ｗ，Ｓｉ，ＰｔおよびＭｎのうちから選ばれる少なくとも１種の元素を添加してなるものである。そして、かかるオーバーコートは、前記ＭＣｒＡｌＸ合金を各種の溶射法により、膜厚を５０〜５００μｍ程度の厚みに溶射して被覆形成する。
【００３５】
なお、上記ＭＣｒＡｌＸ合金からなる耐熱合金被覆層は、Ｎｉ基合金機材の表面に形成した硼化物被覆層と良好な密着性を示すとともに、高温ガスによる外部からの酸化反応や腐食反応に十分耐え得る役目を担うものであり、下記組成のものが好適に用いられる。
Ｍ成分として、Ｎｉ：０〜７５ｍａｓｓ％、Ｃｏ：０〜７０ｍａｓｓ％、Ｆｅ：０〜３０ｍａｓｓ％、
Ｃｒ：５〜７０ｍａｓｓ％、Ａｌ：１〜２９ｍａｓｓ％、
Ｘ成分として、Ｙ：０〜５ｍａｓｓ％、Ｈｆ：０〜１０ｍａｓｓ％、Ｔａ：１〜２０ｍａｓｓ％、Ｓｉ：０．１〜１４ｍａｓｓ％、Ｂ：０〜０．１ｍａｓｓ％、Ｃ：０〜０．２５ｍａｓｓ％、Ｍｎ：０〜１０ｍａｓｓ％、Ｚｒ：０〜３ｍａｓｓ％、Ｗ：０〜５．５ｍａｓｓ％、Ｐｔ：０〜２．０ｍａｓｓ％
【００３６】
ただし、ＭＣｒＡｌＸ合金からなる上記耐熱合金の溶射皮膜、すなわちオーバーコートの形成に当っては、このオーバーコート中に含まれる酸化物量の管理とその限界含有量を検討することが、アンダーコートの場合と同様に重要である。すなわち、前記ＭＣｒＡｌＸ合金を大気中で溶射すると、熱原中あるいは熱源近傍に多量の空気が混入して、溶射材料粒子を酸化させるため、粒子の相互結合力や合金基材との付着力を低下させる他、これらの酸化物が硼化物アンダーコート中のＢ原子の拡散を抑制し、さらには、皮膜表面においてＡｌ_２Ｏ_３やＣｒ_２Ｏ_３の如き均質な保護性酸化膜の均質かつ緻密な膜の生成を妨げるなど、大きな障害となるからである。
このため本発明では、オーバーコート中に含まれる耐熱合金（ＭＣｒＡｌＸ合金）中の酸化物量を、酸素量として１．５ｍａｓｓ％以下に管理することとした。すなわち、大気プラズマ溶射法、減圧プラズマ溶射法、爆発溶射法、高速フレーム溶射法などのいずれの方法を施工する場合でも、溶射雰囲気中の酸素含有量を１．５ｍａｓｓ％以下に制御することにしたのである。
【００３７】
（６） Ａｌ拡散層の形成
また、本発明において、上記硼化物アンダーコートや耐熱合金オーバーコートの表面には、さらに、ＣＶＤ法や粉末法などのアルミニウム拡散浸透処理法を適用してＡｌ拡散層を形成することが好ましい。
たとえば、ＣＶＤ法は、真空容器中に有機または無機アルミニウム化合物（主としてハロゲン化合物）ガスを導入し、これに熱や低温プラズマを照射して化学反応を促進させて、アルミニウム化合物からＡｌを遊離させる方法、あるいは、真空容器中にＨ_２ガスを導入して、その化学的還元力によって、Ａｌを遊離させた後（遊離したＡｌ粒子は１μｍ以下の微粒子）、これを硼化物アンダーコートや耐熱合金オーバーコートの表面に析出させると同時に内部へ拡散浸透させる方法である。また、前記粉末法は、Ａｌ粉またはＡｌ合金粉末とＮＨ_４Ｃｌ，ＮＨ_４Ｆなどのハロゲン化合物、Ａｌ_２Ｏ_３粉末などの混合物中に非処理部材を埋没させ、その後、ＡｒガスあるいはＨ_２ガスを流しつつ、８００〜１０００℃，１〜２０ｈ加熱することによって、表面にＡｌ濃度の高い拡散層を形成させる方法である。
【００３８】
（７） セラミックス被覆層（トップコート）の形成
さらに、本発明では、前記硼化物アンダーコート、耐熱合金オーバーコート、または前記Ａｌ拡散層の表面に、大気プラズマ溶射法、減圧プラズマ溶射法および蒸着法（ＥＢ−ＰＶＤ）などによって、必要に応じてさらに、酸化物含有ＺｒＯ_２系セラミックスからなるトップコート（膜厚：３０〜５００μｍ）を形成し、高温強度のさらになる改善を図ることが、より好ましい実施態様となる。
上記ＺｒＯ_２系セラミックスのトップコートは、Ｙ_２Ｏ_３，ＣｅＯ，ＣａＯ，Ｓｃ_２Ｏ_３，ＭｇＯ，Ｙｂ_２Ｏ_３およびＣｅＯ_２のうちから選ばれる１種以上の酸化物を含むＺｒＯ_２系セラミックスが用いられる。これをトップコートとして用いる理由は、主として燃料の燃焼炎から放出される高温の輻射熱を防ぐためである。なお、このトップコート中にＺｒＯ_２以外の酸化物を含有させる理由は、ＺｒＯ_２単独では、高温に加熱されたり、冷却された際、その結晶形が単斜晶⇔正方晶⇔立方晶に変化し、それに伴って大きな体積変化（４〜７％）を招いて自ら壊すため、かかる酸化物は５〜４０ｍａｓｓ％程度として、体積変化率を緩和させることが望ましい。
【００３９】
（８） 本発明に係るＮｉ基合金部材の被覆層断面構造
図２は、本発明に係るＮｉ基高温強度部材の断面構造例を示したものである。
▲１▼ 図２（ａ）は、Ｎｉ基単結晶合金基材の表面に、金属硼化物および／または非金属硼化物からなる硼化物被覆層（アンダーコートを形成した場合の断面である。ここで２１は合金基材、２２は溶射法、各種のＰＶＤ法、ＣＶＤ法によって形成された硼化物被覆層である。
▲２▼ 図２（ｂ）は、硼化物被覆層（アンダーコート）２２の上に、アルミニウム拡散浸透処理を施した場合の断面構造図である。このＡｌ拡散処理は高温処理（７００〜１０００℃）であるため、Ａｌの一部が硼化物被覆層であるアンダーコート中に拡散するとともに、基材中にＢとともに侵入したものになるが、ここではアンダーコート中への拡散現象のみを図示した。ここで、図中の２３は、Ａｌ拡散層（含浸層）を示し、２４はＡｌ濃度の高い層を示したものである。
従って、Ａｌ拡散層とは、実質に基材中に拡散浸透（含浸）した部分とその表面を被う被覆層（Ａｌ皮膜）とからなるものと言える。
▲３▼ 図２（ｃ）は、硼化物被覆層２２（アンダーコート）の上に、耐熱合金被覆層としてＭＣｒＡｌＸ合金によるオーバーコート２５を形成した場合の断面構造図である。このオーバーコート２５は、アンダーコートおよび基材の高温燃焼ガスによる酸化や腐食を防ぐとともに、硼化物アンダーコートとの優れた密着性を確保しつつ、アンダーコート中からＢが基材中へ拡散して変質層の生成に伴う基材の高温強度の低下を抑制する役目を果すものである。ここで２５は、耐高温環境性の耐熱合金被覆層としてのＭＣｒＡｌＸ合金の溶射被覆層を示すものである。
▲４▼ 図２（ｄ）は、（ｃ）に示した構造の複合皮膜に対して、Ａｌ拡散浸透処理を施したものの断面構造を示したものである。この例は、上述した耐熱合金被覆層２５のみでも、耐高温環境性を示しているが、Ｎｉ基単結晶合金製翼材が用いられている最近のガスタービンは、従来の多結晶合金製翼材よりも一段と高温になる。そこで、保護皮膜の耐高温環境性をより一層発揮させるために最外表層のＡｌ濃度を向上させたものである。
なお、Ａｌ拡散浸透処理は、既知の気相法（ＣＶＤ法）や粉末法（例えば、本発明者の一人が出願した特許第２９６０６６４号、特許第２９６０６６５号参照）に従うことが望ましい。
▲５▼ 図２（ｅ）は、ＭＣｒＡｌＸ合金による耐熱合金オーバーコートの上に、さらにＺｒＯ_２系のセラミックス被覆層２６を、トップコートとして設けたものの断面構造図である。ガスタービンなどでは、燃焼フレームを熱源とする強い輻射熱が発生するため、熱伝導率の低い、ＺｒＯ_２系セラミックス被覆層を最外層に設けて輻射熱障害を防止するものである。該ＺｒＯ_２系セラミックスとしては、Ｙ_２Ｏ_３，ＣｅＯ_２，ＣａＯ，Ｙｂ_２Ｏ_３，Ｓｃ_２Ｏ_３，ＭｇＯのなかから選ばれるいずれか少なくとも１種の酸化物を含むＺｒＯ_２系セラミックスが好適である。
【００４０】
【実施例】
＜実施例１＞
この実施例では、表２に示すような化学成分を有するＮｉ基単結晶合金（Ａ合金）Ｎｉ基一方向凝固合金（Ｂ合金）とともに、比較例としてＮｉ基多結晶合金（Ｃ合金）を用い、合金の塑性加工に伴う変質層の発生の有無を調査した。これらの供試材の熱処理条件を表２の下段にそれぞれ記載した。
また、表３には、実施例において供試した本発明に係る金属硼化物と非金属硼化物の種類とその組合せ、表４には、ＭＣｒＡｌＸ合金の化学成分、表５には、塑性加工後に実施した熱処理条件について示した。
【００４１】
【表２】

【００４２】
【表３】

【００４３】
【表４】

【００４４】
【表５】

【００４５】
（試験片の調整）
表２記載の単結晶合金（寸法：直径１０ｍｍ×長１０ｍｍ）に対し、室温で下記のような条件の塑性加工を施した。
（１） ブリネル硬度計の鋼球を９８０Ｎで押し付けた。
（２） 旋盤加工により、試験片の表面を約１ｍｍ切削
（３） ＪＩＳ Ｚ ０３１２に規定されている溶融アルミナグリット（１ｍｍ〜２ｍｍ）を用いて試験片に強く吹き付けたもの
加工後の試験片は、表５記載のＡとＣの条件で熱処理を施したのち冷却し、その断面を光学顕微鏡および走査型電子顕微鏡によって観察した。
表６は、顕鏡結果を要約したものである。塑性加工を与えない試験片（試験片Ｎｏ．１）は、変質層が全く認められなかった。これに対し、塑性加工を施した試験片（Ｎｏ．２〜７）は、熱処理条件の相違、塑性加工法の種類にかかわらず変質層が発生し、特に旋盤加工した試験片ではｍａｘ５０μｍに達する変質層が生成していた。この変質層は、粗大γ’析出相とγ相から構成されており、また、変質層と未変化部での境界では（健全部）高温強度因子のγ’相の分解らしい現象が認められ、高温強度の低下に結び付く要因の生成が確認された。
【００４６】
【表６】

【００４７】
（実施例２）
この実施例では単結晶合金と一方向凝固合金を用いて、塑性加工，熱処理，溶射皮膜などの影響を高温疲労試験によって調査した。
（１）疲労試験要領と試験片の調整
疲労試験には、最大負荷５ｔｏｎ，ストローク５０ｍｍ（伸び圧縮とも），振動数０．０１〜２０Ｈｚの性能を有する電気油圧サーボ弁式疲労試験装置を用い、試験片の加熱は、高周波誘導加熱方式を採用し、９５０℃大気中，応力比Ｒ＝−１，正弦応力波形，周波数１０Ｈｚの条件で実施した。
【００４８】
一方、疲労試験用材料としては、単結晶合金と一方向凝固合金の２種とし、また、塑性歪の付与方法には、次のような方法を採用した。
（ａ） 型鍛錬による圧縮歪の付与
図３（ａ）に示すような凸部付き丸棒を切り出した後、凸部に半径方向に換算して、室温で約８．３％に相当する圧縮歪を型鍛造（図３（ｂ））して与えた。その後、表５記載の熱処理を行った後、試験片の中心部から図３（ｃ）に示すように、平行部直径４ｍｍ，平行部長さ１０ｍｍの平滑棒疲労試験片に加工した。
（ｂ） 旋盤加工による歪の付与
供試材を旋盤によって半径を約１ｍｍ切削し、その後１３５３Ｋ×１００ｈの熱処理を施したものから、疲労試験片を切り出した。旋盤加工の条件は切り込む深さ０．２〜０．２５ｍｍ，送り量０．０５１〜０．２ｍｍの範囲に変化させた。
（２） 溶射皮膜の形成
疲労試験片の平行部全面にわたって、減圧プラズマ溶射法によって、表３に記載の硼化物または表４に記載のＭＣｒＡｌＸ合金を、硼化物アンダーコート，ＭＣｒＡｌＸ合金オーバーコートとして、それぞれを単独に１５０μｍ厚に施工したものである。
（３） 疲労試験結果
単結晶合金について実施した結果を表７に要約した。この結果は、単結晶合金のバージン材（塑性加工しない試験片Ｎｏ．１）の強度を１００として、他の試験片の平均強度比で比較したものである。この結果から明らかなように、塑性加工を与えない合金では、ＭＣｒＡｌＸ合金被覆層を成膜しても疲労強度上の変化は少なく、大気環境による酸化反応を幾分抑制している程度であった。
これに対し、試験片に予め型鍛錬（Ｎｏ．４）や旋盤加工を施したもの（Ｎｏ．８）では、熱処理によって再結晶化現象が発生するため、疲労強度は極端に低下し、単結晶合金として致命的な強度低下を示した。しかし、予め硼化物被覆層（アンダーコート）を施工しておくと、試験片Ｎｏ．５，９，１１に見られるように疲労強度の低下は非常に少なく、再結晶化に伴う強度低下をほぼ防ぐことが可能であった。この傾向はＭＣｒＡｌＸ合金の施工（試験片Ｎｏ．６，１０）においても認められるが、硼化物に比較すると強度低下率の軽減効果は少ない。ＭＣｒＡｌＸ合金皮膜は、耐高温環境性の効果によるものと考えられる。
また、硼化物アンダーコートの効果は、試験片Ｎｏ．１１，１２の結果から明らかなように２種類の金属硼化物を用いても、また、金属／非金属硼化物の混合物を使用しても、単結晶合金の疲労強度の低下を抑制する効果が認められることがわかった。
【００４９】
なお、試験片Ｎｏ．７，１２に見られるように、硼化物をアンダーコート／ＭＣｒＡｌＸ合金をオーバーコートとした試験片では、ほぼ疲労強度が回復しているので、硼化物の施工は、単結晶合金と直接接触させることが必要である。
【００５０】
【表７】

【００５１】
一方、一方向凝固合金について実施した結果を表８に示した。一方向凝固合金では塑性加工の影響を単結晶合金ほど強く受けないが、ここでも疲労強度は低下する。硼化物の溶射皮膜は、一方向凝固合金の再結晶化に伴う強度低下に対しても軽減効率が認められている（試験片Ｎｏ．５，７，９，１１，１２）。
【００５２】
【表８】

【００５３】
（実施例３）
この実施例では、単結晶合金製の疲労試験片について、実施例２で採用した塑性加工法として旋盤による切削加工、熱処理条件として表５中のＡ条件の熱処理を行った後、皮膜形成法として、減圧プラズマ溶射法，電子ビーム蒸着法によって、表３記載の硼化物のうち（Ａ）（Ｂ）（Ｆ）（Ｇ）を用いてアンダーコートを形成し、その上に、表４記載のＭＣｒＡｌＸ合金をオーバーコートとして、高速フレーム溶射法によって１５０μｍ厚に施工した。なお、硼化物アンダーコートの膜厚は、溶射法２０μｍ、電子ビーム蒸着法では２μｍである。
以上のような要領で成膜した試験片について実施例２記載の熱疲労試験条件によって試験した。
上記試験片による１２２３Ｋにおける疲労試験結果を表９に示した。この結果から明らかなように、さきに実施例２で得られた比較例の塑性加工を与えない例（試験片Ｎｏ．１）、また塑性加工を与えたものの、硼化物のアンダーコートを形成していない条件（Ｎｏ．２）の疲労強度試験結果を併記し、これらの測定値を基準として比較した。こられの結果を要約すると、Ｎｉ基単結晶合金に塑性加工を与えると、その疲労強度はバージン材（Ｎｏ．１）３２％程度に低下するが、蒸着法や溶射法によって硼化物アンダーコートを施工した後、ＭＣｒＡｌＸ合金オーバーコートを積層したもの（Ｎｏ．４〜７，９〜１１）の疲労強度は、バージン材の強度とほぼ同等にまで回復し、変質層の生成による強度低下を防止していることが認められる。また、硼化物としては、金属硼化物単独（Ｎｏ４，５，９，１０）、２種の金属硼化物の混合（Ｎｏ．６）また金属硼化物と非金属硼化物の混合物などのアンダーコートにおいても、ほぼ同等の強度低下防止の効果が認められた。さらに、アンダーコートの形成法として蒸着法と溶射法の差はほとんど認められず、両者とも硼化物アンダーコートの施工法として十分な性能を発揮している。
一方、塑性加工試験片の表面に、ＭＣｒＡｌＸ合金の溶射皮膜を直接施工したもの（Ｎｏ．３，８）では、耐高温環境性は発揮するものの、基材の疲労強度の低下の抑制には、硼化物アンダーコートほどの性能は認められなかった。
【００５４】
【表９】

【００５５】
（実施例４）
この実施例では、単結晶合金と一方向凝固合金の表面に形成した本発明に適合する被覆層についての耐熱衝撃性を調査した。
（１） 供試基材と試験片の形状寸法
供試基材として、表２記載の単結晶合金と一方向凝固合金を用い、これを直径１５ｍｍ×長さ５０ｍｍの丸棒試験片に仕上げた。
（２） 試験片に対する塑性加工の有無
前記丸棒試験片の加工に対し、実施例１記載の旋盤加工条件のものを製作した。
（３） 供試被覆層の種類と被覆層形成方法
試験片に対する硼化物アンダーコートの形成法として、溶射法（減圧プラズマ）ＥＢ−ＰＶＤ法およびスパッタリング法を用い、それぞれＮｉＢを溶射法では２０μｍ、ＰＶＤ法では３μｍ、スパッタリング法では１μｍの厚さに成膜した。その後、ＭＣｒＡｌＸ合金として、表４記載の合金を減圧プラズマ溶射法および高速フレーム溶射法によって、膜厚１５０μｍに施工したものを作製し、その後、さらに、前記オーバーコートの上に、トップコートとして、Ｙ_２Ｏ_３を８ｍａｓｓ％含むＺｒＯ_２セラミックスの被覆層を大気プラズマ溶射法で３００μｍ厚形成したものを熱衝撃試験片とした。
（４） 熱衝撃試験条件
９５０℃に維持した電気炉に試験片を１５ｍｉｎ静置して加熱し、その後２９８Ｋの水中に投入して冷却する操作を１サクルとし、これを１０サイクル繰返し、被覆層の外観変化と剥離の有無を調査した。
上記試験結果を表１０に要約した。この結果から明らかなように、一般に広く使用されているＭＣｒＡｌＸ合金の被覆層とＹ_２Ｏ_３・ＺｒＯ_２セラミックス被覆層の組合せによる熱遮蔽皮膜（試験片Ｎｏ．１，２）は、１０回の繰返しによる熱衝撃試験に耐え、トップコートの割れや剥離は認められなかった。本発明にかかる複合皮膜（Ｎｏ．３〜８）についてもトップコートのＹ_２Ｏ_３・ＺｒＯ_２には、割れや局部剥離の兆候は全く認められず健全な状態を維持し、現行の熱遮蔽皮膜として汎用されている皮膜に対して遜色のない熱衝撃抵抗を保有していることが認められた。当然のことながら硼化物アンダーコートとＭＣｒＡｌＸ合金のオーバーコートとの界面の接合力についても十分な性能を保持していることが見られ、剥離現象は確認されなかった。
【００５６】
【表１０】

【００５７】
【発明の効果】
以上説明したように、予め歪や塑性加工を受けた従来のＮｉ基単結晶合金およびＮｉ基一方向凝固合金基材は、これらが高温に加熱されると、表面に再結晶化を伴う変質層を生成し、これが起点となって僅かな負荷応力によっても容易に破壊されるようになり、この種合金が保有する優れた高温強度を発揮することができないという致命的な欠陥があった。
これに対し、本発明は、このような合金基材の表面に、溶射法、ＰＶＤ法、ＣＶＤ法などによって直接、硼化物アンダーコートを形成することにより、高温環境下において硼素を優先的に合金基材中に拡散させて、再結晶粒界の相互結合力を強化することにより、高温強度の低下を効果的に低減し、もって前記基材本来の強度を発揮させるようにしたものである。
【００５８】
そして、本発明の他の実施形態によれば、たとえば前記硼化物被覆層（アンダーコート）とＭＣｒＡｌＸ合金被覆層（オーバーコート）との積層、さらには、ＺｒＯ２系セラミックス被覆層（トップコート）の積層形成などによって、高温環境中における燃焼ガス成分に対する物理・化学的作用を向上させることができる。
【００５９】
これらの効果は、単結晶合金や一方向凝固合金製のガスタービン翼部材などのように、製造・組立工程はもとより、運転中または運転後の皮膜再処理工程などにおける歪の付与や塑性加工を伴う機会が多い高温強度部材に適用した場合に、上記危険因子を完全に払拭することができ有効である。
従って、本発明によれば、この種の合金製ガスタービン翼部材の品質および生産性の向上に資するとともにガスタービンの長期安定運転と発電単価の低減に大きく寄与することができる。
【図面の簡単な説明】
【図１】電子ビーム熱源を有するＰＶＤ装置の概要を示す略線図である。
【図２】本発明の硼化物被覆層を利用して単結晶合金または一方向凝固合金部材上に、耐高温用被覆層を構成した場合の積層構造の例を示す断面図である。
【図３】凸部付き丸棒素材に対する凸部の型鍛造による応力の負荷とその丸棒からの高温疲労強度試験片の採取要領を示す図である。
【図４】塑性加工部に生成する変質層の形状例を示す金属顕微鏡写真である。
【図５】疲労試験片の破断面の状況と変質層が、破壊の起点となっていることを示す金属顕微鏡写真である。
【符号の説明】
１ 被覆材料
２ 電子ビーム銃
３ 単結晶合金基材
４ 真空容器
５ 真空ポンプ
６ 不活性ガスの導入管
７ 基材加熱用ヒータ
８ 直流電源
２１ 基材
２２ 硼化物被覆層（アンダーコート）
２３ Ａｌ拡散層（低濃度）
２４ 耐熱合金被覆層（オーバーコート）
２５ Ａｌ拡散層（高濃度）
２６ セラミックス被覆層（トップコート）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-temperature strength member used for a high-temperature exposed portion of a gas turbine, a jet engine, or the like, and in particular, to the surface of a moving / static vane substrate made of a Ni-based single crystal alloy and a Ni-based unidirectionally solidified alloy, plastic working strain is applied. The present invention relates to a Ni-based alloy member provided with a film for preventing a decrease in high-temperature strength due to the above-mentioned factors, and a method for producing the same. In addition, the technology of the present invention is effective even when the B content is smaller than the B content in the surface film according to the present invention, even for a polycrystalline Ni-based alloy containing no B and a BNi-containing polycrystalline alloy. Can be expected.
[0002]
[Prior art]
In recent years, research has been conducted on gas turbines aimed at increasing the working gas temperature in order to improve thermal efficiency. At present, the turbine inlet temperature has already exceeded 1500 ° C. Is required.
The technology for raising the temperature of gas turbines involves the development of materials for turbine blade members that are directly exposed to high-temperature combustion gas (including the development of coatings for high-temperature oxidation resistance and thermal insulation) and the cooling of blades. It depends heavily on the development of technology and is still an important research topic.
In particular, turbine blades are subject to creep due to centrifugal force in the operating environment, thermal fatigue due to starting and stopping of the turbine, high cycle fatigue due to mechanical vibration, and impurities such as sea salt particles, sulfur, and vanadium contained in combustion gas. Because of the corrosive action of the wing, it has become a central subject of wing member research.
[0003]
An overview of the research and development status of Ni-based alloys as conventional turbine blade members is summarized as follows.
(1) A large amount of intermetallic compound [Ni₃(Al, Ti)] alloy strengthening by precipitation / dispersion,
(2) Development of an alloying method that takes into account the atomic arrangement of the crystal interface due to the solid solution strengthening of the mother phases γ and γ ′, and the delicate balance of the composition of both phases, and the development of an alloy using the results.
(3) Establishment of high quality alloy manufacturing method by removing the effects of trace impurities and gases by adopting vacuum melting technology,
(4) Development of high-performance blade materials by switching from forging to precision casting technology (expansion of flexibility in the field of cooling mechanisms),
(5) Commercialization of wing material from equiaxed to columnar wing material by development of directional solidification method of alloy,
(6) Development of single-crystal blade material that eliminates material strength deterioration caused by crystal grain boundaries in polycrystalline alloys,
{Circle around (7)} The chemical composition of the single-crystal blade material is mainly Ni: 55 to 70 mass%, Cr: 2 to 15 mass%, Co: 3 to 13 mass%, Mo: 0.4 to 8 mass%, W: 4.5 to 8 mass%, Ta: 2 to 12 mass%, Re: 3 to 6 mass%, Al: 3.4 to 6 mass%, Ti: 0.2 to 4.7 mass%, Hf: 0.04 to 0.2 mass %, C: 0.06 to 0.15 mass%, B: 0.001 to 0.02 mass%, Zr: 0.01 to 0.1 mass%, Hf: 0.8 to 1.5 mass%. It is a thing. However, since these alloys have relatively low Cr and Al contents that are effective for high-temperature oxidation resistance, a surface treatment film with high-temperature oxidation resistance and high-temperature corrosion resistance (hereinafter referred to as high-temperature environment resistance) is applied. By doing so, an excellent high-temperature strength is exhibited for the first time.
{Circle around (8)} For high-temperature exposed members such as gas turbines and jet engines, an alloy coating excellent in high-temperature oxidation resistance called “MCrAlX alloy” is applied. Here, M represents Ni, Co or Fe alone or an alloy composed of a plurality of these elements, and X represents an element such as Y, Hf, Sc, Ce, La, Th, and B.
Many such MCrAlX alloys having various chemical compositions according to the purpose of use have been proposed. Prior arts relating to these alloys are listed as follows.
JP-A-58-37145, JP-A-58-37146, JP-A-59-6352, JP-A-59-89745, JP-A-50-29436, JP-A-51-1979. No. 30530, JP-A-50-158531, JP-A-51-10131, JP-A-52-33842, JP-A-55-115941, JP-A-53-112234, JP-A-52-66836, JP-A-52-88226, JP-A-53-33931, JP-A-58-141355, JP-A-56-108850, and JP-A-54-16325. JP, JP-A-57-155338, JP-A-52-3522, JP-A-54-66342, JP-A-59-118847, and JP-A-56-62956. JP-A-51-33717; JP-A-54-65718; JP-A-56-93847; JP-A-51-94413; JP-A-56-119766; JP-A-161041, JP-A-55-113871, JP-A-53-85829, JP-A-57-185955, JP-A-52-117826, JP-A-60-141842, JP-A-57-177952 and JP-A-59-1654.
These alloys have been developed mainly as high temperature environment resistant coatings for polycrystalline alloy blade materials, but are also effective for single crystal alloys and directionally solidified alloys, and are widely used.
[0004]
On the other hand, among Ni-based alloys, particularly Ni-based single crystal alloys and Ni-based unidirectional solidified alloys are subjected to plastic working and impact, and furthermore, as turbine blades under fatigue or thermal fatigue damage under the operating environment of a real machine. When heated to a high temperature, there is a characteristic that a portion of the residual strain due to processing or impact is altered to form an altered layer (see FIG. 4). It is thought that this part of the altered layer is in an aggregate of fine crystals indistinguishable by observation with an optical microscope or in its preliminary state, but it is very fragile and easily cracks small by the application of slight stress. It was confirmed by experiments of the present inventors that a large number of them occurred and became a starting point of destruction (see FIG. 5).
With respect to such a decrease in high-temperature strength due to the deteriorated layer appearing on the surface of the base material, no technique has been studied so far by focusing on this and preventing it by surface coating. It is well known that the technique is directed solely to the improvement of high temperature environment resistance for corrosion damage caused by high temperature combustion gas.
[0005]
[Problems to be solved by the invention]
The present invention relates to a wing member made of a Ni-based alloy, in particular, a Ni-based single crystal alloy and a Ni-based one-way solidified alloy (hereinafter, simply referred to as a single crystal alloy, a one-way solidified alloy). An object of the present invention is to solve the problem by forming a thermal spray coating or a vapor deposition coating.
{Circle around (1)} The single-crystal alloy wing member and the unidirectionally solidified alloy wing member are subjected to slight machining distortion and blasting during the manufacturing process, the operation as a turbine blade, and the formation of a protective coating. When this is heated to a high temperature after being subjected to surface roughening or the like, an altered layer in which a large number of fine crystals are generated in the affected portion is generated. In this altered layer, a large number of fine cracks are generated by the application of a fragile and small stress, and the high-temperature strength is remarkably deteriorated starting from this.
{Circle around (2)} When only the conventional MCrAlX alloy thermal spray coating is formed on the surface of a single crystal alloy or unidirectionally solidified alloy wing member subjected to strain or mechanical processing, high temperature accompanying the formation of the altered layer is obtained. The strength cannot be prevented from decreasing.
(3) As a result, even with moving and stationary blade members made of single crystal alloys and unidirectional solidified alloys that have excellent high-temperature strength in terms of material engineering, the current technology fully demonstrates its superiority. It is in a situation that cannot be done.
[0006]
[Means for Solving the Problems]
The present invention is attributable to the above-mentioned problems of the Ni-based single crystal alloy and the Ni-based directionally solidified alloy of the high-temperature strength member, namely, the collapse of crystal control (recrystallization in a broad sense) induced by plastic working. The purpose of the present invention is to prevent a decrease in high-temperature strength by surface coating, and has been developed based on the following technical concept.
a. By forming a boride coating layer composed of a metal boride and / or a non-metal boride on the surface of a single crystal alloy or a directionally solidified alloy, when the substrate is heated, boron ( B) diffusing and infiltrating into the alloy substrate, thereby increasing the interconnectivity of the recrystallized grain boundaries so as to prevent a reduction in the high temperature strength of the alloy.
b. The metal (M) boride applied as an undercoat on the surface of a single crystal alloy or a directionally solidified alloy has a chemical formula of M_{1 ~ 11}, B_{11 ~ 12}B is preferentially diffused into the Ni-based alloy by using one or more metal borides represented by the following formula.
c. As a non-metallic boride to be applied as an undercoat on the surface of a single crystal alloy or a directionally solidified alloy, B₄Attempt to spread B and C by using C and / or BN.
d. First, a boride coating layer composed of a metal boride and / or a non-metal boride is formed as an undercoat on the surface of a single crystal alloy or a directionally solidified alloy, and then CO, Ni, Cr is formed as an overcoat thereon. And at least one element selected from the group consisting of Y, Hf, Ta, Cs, Ce, La, Th, W, Si, Pt and Mn to an alloy containing at least two selected from Al and Al. By laminating a heat-resistant alloy coating layer made of an alloy (hereinafter, simply referred to as “MCrAlX alloy”), a decrease in high-temperature strength due to a recrystallization phenomenon of the alloy is prevented, and the MCrAlX alloy film (overcoat) is formed. To improve the high temperature environment resistance.
e. The surface of the boride coating layer (undercoat) or the MCrAlX heat-resistant alloy coating layer (overcoat) is subjected to Al diffusion / penetration treatment by a CVD method or a powder method to further improve the high-temperature environment resistance of these coating layers. To be.
f. An overcoat made of a heat-resistant alloy is formed on an undercoat made of boride formed on the surface of the base material, and Y is further formed on the overcoat.₂O₃, CaO, MgO, CeO₂, Yb₂O₃, Sc₂O₃Containing at least one oxide such as₂Forming a top coat consisting of a base ceramic coating layer to maintain the high-temperature strength of the base material and to impart further high-temperature environmental resistance.
g. A method of forming a boride coating layer composed of a metal boride and / or a non-metal boride on the surface of a single crystal alloy or a directionally solidified alloy is performed by a thermal spraying method, an electron beam evaporation method, a sputtering method, a thermal CVD method, or Performed by a surface treatment method such as a plasma CVD method.
h. A metal boride and / or a non-metallic boron is formed as an undercoat on a surface of a single crystal alloy or a directionally solidified alloy by a surface treatment method such as a thermal spraying method, an electron beam evaporation method, a sputtering method, a thermal CVD method, or a plasma CVD method. After forming a boride coating layer made of a nitride, an MCrAlX heat-resistant alloy coating layer for imparting high-temperature environment resistance is formed thereon by thermal spraying as an overcoat.
i. A metal boride and / or a non-metallic boron is formed as an undercoat on a surface of a single crystal alloy or a directionally solidified alloy by a surface treatment method such as a thermal spraying method, an electron beam evaporation method, a sputtering method, a thermal CVD method, or a plasma spraying method. After forming a boride coating layer composed of a nitride, a heat-resistant alloy coating layer having high-temperature environment resistance is formed thereon by thermal spraying as an overcoat, and a top coat is formed thereon as a top coat.₂O₃, CaO, MgO, Yb₂O₃, Sc₂O₃And CeO₂Containing at least one oxide selected from the group consisting of₂Forming a ceramic coating layer made of a base ceramic by thermal spraying or electron beam evaporation.
[0008]
The present invention also provides a boride coating of a metal boride and / or a non-metal boride as an undercoat on the surface of a Ni-base alloy, particularly a base made of a Ni-base single crystal alloy or a base made of a Ni-based directionally solidified alloy. The present invention proposes a Ni-based alloy member characterized in that a layer is provided thereon and a high-temperature environment-resistant heat-resistant coating layer is provided thereon as an overcoat.
[0009]
The present invention also provides a boride coating of a metal boride and / or a non-metal boride as an undercoat on the surface of a Ni-base alloy, particularly a base made of a Ni-base single crystal alloy or a base made of a Ni-based directionally solidified alloy. Layer is provided thereon, and a heat-resistant alloy coating layer having a high-temperature environment resistance is provided thereon as an overcoat.₂O₃, CaO, MgO, Yb₂O₃, Sc₂O₃And CeO₂Containing at least one oxide selected from the group consisting of₂A Ni-based alloy member provided with a ceramic coating layer made of a base ceramic.
[0011]
In addition, the present invention provides a method of spraying, electron beam vapor deposition (EB-PVD), sputtering, heat treatment on a surface of a Ni-based alloy, particularly a substrate made of a Ni-based single crystal alloy or a substrate made of a Ni-based unidirectionally solidified alloy. A boride coating layer composed of a metal boride and / or a non-metal boride is formed by a surface treatment method such as a CVD method or a plasma CVD method, and then the surface of the boride coating layer is subjected to high temperature resistance by thermal spraying. A method for producing a Ni-based alloy member, comprising laminating an alloy coating layer.
[0012]
The present invention provides a thermal spraying method, an electron beam evaporation method (EB-PVD), a sputtering method, a thermal spraying method on a surface of a Ni-based alloy, particularly a substrate made of a Ni-based single crystal alloy or a Ni-based unidirectionally solidified alloy. A boride coating layer made of a metal boride and / or a non-metal boride is formed by a surface treatment method such as a CVD method or a plasma CVD method, and then the surface of the boride coating layer is subjected to high temperature resistance by thermal spraying. An environmental high temperature resistant alloy coating layer is formed by lamination, and then Y is coated on the heat resistant alloy coating layer.₂O₃, CaO, MgO, Yb₂O₃, Sc₂O₃And CeO₂Containing at least one oxide selected from the group consisting of₂The present invention proposes a method for manufacturing a Ni-based alloy member, characterized in that a ceramic coating layer made of a base ceramic is laminated by a thermal spraying method or an electron beam evaporation method.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, after the metallurgical characteristics of the Ni-based single crystal alloy base material and the Ni-based unidirectionally solidified alloy base material are clarified, the operation mechanism of the protective film according to the present invention applied as a countermeasure will be described.
(1) Metallurgical characteristics and practical problems of Ni-based single crystal alloys,
Originally, Ni-based single crystal alloys have been developed in order to solve the problems of many Ni-based polycrystalline alloys that have been widely used in the past. That is, in a polycrystalline alloy, impurity elements, various carbides, intermetallic compounds, and the like are liable to concentrate and precipitate at crystal grain boundaries under practical environmental conditions of a gas turbine. The bonding strength of the field is reduced and becomes the starting point for mechanical destruction.
[0014]
Further, at the grain boundaries, oxidizing substances such as sulfur, vanadium, chloride, and water vapor contained in the combustion gas can easily enter, which often causes grain boundary corrosion damage.
[0015]
In order to solve such problems caused by crystal grain boundaries, polycrystalline alloys in which grain boundary strengthening elements (for example, C, B, Zr, Hf, etc.) are added to alloys have been developed. However, since eutectic γ 'having a low melting point is easily generated in this alloy, the solution treatment temperature must be lowered, which is not preferable from the viewpoint of improving the high-temperature strength of the alloy.
[0016]
The Ni-based single crystal alloy has been developed with the aim of solving the metallurgical problems of the polycrystalline alloy as described above. That is, the Ni-based single crystal alloy has no crystal grain boundaries that cause destruction, and there is no concern about the precipitation of the eutectic γ ′ phase, so that there is an advantage that the alloy can be subjected to high-temperature solution treatment. In addition, when the solution temperature is increased, the fine γ 'phase is uniformly precipitated and dispersed, so that the high-temperature strength of the alloy can be significantly improved.
[0017]
However, on the other hand, it has become apparent that the Ni-based single crystal alloy has a new problem not found in the polycrystalline alloy. When a single crystal alloy is given a strain of about several percent (2% to 8%) in advance or subjected to mechanical plastic working, and then heat-treated or exposed to the operating environment of a gas turbine, The processed part and its heat-affected zone appeared as an altered layer, and it was found that countless fine crystals seemed to be generated therein (here, this phenomenon is called "recrystallization phenomenon", FIG. 4). reference). Such a recrystallized portion is very brittle and has poor high-temperature strength, so that the application of a slight stress causes a large number of cracks originating from the crystal grain boundaries, which significantly reduces the strength of the entire single crystal alloy. There were spots (see FIG. 5).
[0018]
Since such recrystallization is not generated during plastic working but occurs only after the single crystal alloy is heated, it is very difficult to take preventive measures beforehand. In addition, the temperature at which recrystallization appears is relatively low. For example, after applying a general-purpose MCrAlX alloy thermal spray coating to improve the high temperature environment resistance on a general polycrystalline alloy gas turbine moving blade, the following solution treatment is performed. In addition, it appears even after heat treatment such as aging treatment.
1273K-1573K 1-10h (Solution treatment)
973K ~ 1273K 1 ~ 30h (aging treatment)
[0019]
For this reason, in order to improve the high-temperature environment resistance, it is not possible to prevent a remarkable decrease in high-temperature strength due to the recrystallization phenomenon of the base material by simply applying the MCrAlX alloy. In addition, for the reasons described above, there is a limit to the method of adding an element to the base material itself.
[0020]
Environmental conditions that may cause strain or plastic deformation on the base material made of Ni-based single crystal alloy include, for example, in the case of wing materials, the manufacturing process, the operation process, the gas turbine assembly process, and the thermal spray pretreatment. Blast surface roughening process, collision process of spray particles, transport process during spray process, inspection process, collision of fine solid particles contained in combustion gas during operation of gas turbine, construction on single crystal alloy blade surface For example, a blasting process or a polishing process at the time of recoding the protective film thus obtained may be considered.
Therefore, it is difficult to predict the occurrence of the recrystallization phenomenon, and it is necessary to improve the high-temperature strength of the Ni-based single crystal alloy substrate by providing the substrate itself or a protective film.
Further, in the above example, during the operation of the gas turbine, it is often observed that cracks and burnout due to thermal fatigue occur locally on the surface of the Ni-based single crystal alloy blade material. In such a repair, the surface of the member is often ground by a grinder, and then a weld overlay is performed to restore the shape. However, an altered layer caused by plastic working is inevitably generated in such a processed portion.
In addition, the recrystallization phenomenon which appears in the above-mentioned Ni-based single crystal alloy and its influence are recognized to the same extent in the Ni-based unidirectionally solidified alloy, though the degree thereof is different. However, the following describes an example of a Ni-based single crystal alloy.
[0021]
(2) Elimination of the recrystallization problem of the Ni-based single crystal alloy according to the present invention
Up to now, a protective film for a high-temperature member such as a gas turbine or a jet engine generally has a member surface coated with an MCrAlX alloy. The protective coating of the MCrAlX alloy is applied by a thermal spraying method or a vapor deposition method, and its purpose is to protect the member from the corrosive action of a high-temperature combustion gas. However, this is not intended to solve the above-mentioned problem caused by the recrystallized portion of the alloy base material. However, the chemical composition of the known MCrAlX alloy cannot achieve the object of the present invention.
[0022]
The present invention differs from the conventional single layer coating of MCrAlX alloy in that metal borides and / or non-metal borides having a chemical composition as described in detail below are spray-coated, various vapor-deposition methods or CVD methods ( This is a technique based on forming one or more predetermined coating layers on the surface of the base material of the single crystal alloy member by a method such as a plasma-containing CVD method. Hereinafter, the undercoat, which is the basic structure of the present invention, that is, the metal boride and nonmetal boride coating layers will be described in detail.
[0023]
Metal borides usable in the present invention include the following types. However, the metal boride is not limited to this example.
[0024]
[Table 1]

[0025]
As is clear from the above Table 1 (where M represents a metal element), as the metal boride usable in the present invention, regardless of the type of the metal element, any compound can be used if it is a boride. Applicable. The reason for this is that when these metal borides are coated on the surface of the Ni-based single crystal alloy base material and then heated to a high temperature, boron (B) is rapidly diffused into the single crystal alloy base material and the altered layer portion is formed. Will contribute to the strengthening action.
Although the mechanism of strengthening the altered layer due to the penetration of boron (B) into the alloy base material has not been completely elucidated, B diffuses and penetrates into the fine recrystallized grain boundaries generated in the altered layer. It is believed that the result is that the bonding strength of the grain boundaries is improved.
[0026]
In the above reaction, the metal constituting the boride also diffuses together with B. Therefore, preferably, the same metal as the component of the Ni-based single crystal alloy, for example, Ni, Cr, W, Mo, Co, Al, Ti , Nb, Ta, and Hf are also preferred in order to prevent dissimilar metal components from diffusing into the Ni-based single crystal alloy to form new and unknown intermetallic compounds. The boride of Zr is advantageous because the Zr metal itself exerts a grain boundary strengthening action.
[0027]
As shown in Table 1 above, the chemical formula of the metal boride is M_{1 ~ 11}B_{1 ~ 12}However, in the present invention, all other metal borides can be used. In the case of a commercially available metal boride, TiB₁And Ti₂B is mixed or NiB₄B₃, Ni₂Ni at B₃B may coexist, but the same effect is observed with these metal borides, so that the number of atoms of the metal (M) and boron (B) is not particularly limited.
[0028]
On the other hand, as an example of a non-metal boride, B₄C and BN are preferably used. These borides can be used alone, but they can be mixed with metal borides,₄Even when C and BN are mixed, they exhibit a function of suppressing a decrease in the thermal fatigue strength of the Ni-based single crystal alloy. Especially B₄When the Ni-based single crystal base material is heated to a high temperature, C is diffused into the base material together with B, and both cooperate to form fine crystal grain boundaries accompanying recrystallization of the equipment. It is effective in contributing to reinforcement.
Further, the boride coating layer of the present invention is a polycrystalline Ni-based alloy containing no B or a polycrystalline Ni-based alloy containing B but containing less than the B content in the boride coating layer of the present invention. However, since it exerts the effect of strengthening the polycrystalline grain boundaries, it is also effective for these alloys.
[0029]
(3) Formation of boride coating layer (undercoat) by thermal spraying
As a method for forming a boride coating layer made of a metal boride and / or a non-metal boride on the surface of the Ni-based single crystal alloy substrate, a thermal spraying method is typically used. In order to sufficiently exhibit the above-mentioned effects of the present invention, when a boride coating layer as an undercoat is formed on the surface of the base material, Ni is removed from the boride coating layer (undercoat). Good diffusion and transfer of B to the surface of the base single crystal alloy substrate, the mutual bonding force of the sprayed particles of the undercoat sprayed coating layer itself, and the good compatibility with the MCrAlX heat-resistant alloy coating layer formed as an overcoat described later. It is important to ensure good adhesion. The greatest challenge for achieving this object is to control the amount of oxide contained in the boride coating of the undercoat and to determine its critical content. For example, when an undercoat is formed by spraying in air, a large amount of air is mixed into or near the heat source of the spray and oxidizes the sprayed material particles. In addition to these, these oxides suppress the diffusion of B and cause a decrease in the bonding force with the overcoat, which is a major obstacle.
[0030]
Therefore, in the present invention, the amount of oxide contained in the undercoat is controlled to 1.5 mass% or less in terms of the amount of oxygen. That is, the oxygen content is controlled to 1.5 mass% or less even when thermal spraying is performed by any method such as atmospheric plasma spraying, low pressure plasma spraying, explosive spraying, and high-speed flame spraying. The type of the thermal spraying method is not particularly limited. Specifically, it is preferable to adopt a method such as a high-speed flame spraying method or a low-pressure plasma spraying method.
[0031]
(4) Formation of boride coating layer (undercoat) by vapor deposition or the like
If it is a method that can suppress the amount of oxygen contained in the boride coating layer to 1.5 mass% or less, even if it is not for thermal spraying, for example, if a PVD method (physical vapor deposition method) is adopted, An undercoat meeting the requirements of the invention can be formed. For example, FIG. 1 shows that a coating material 1 is irradiated with a beam from an electron gun 2 to evaporate fine vapors (arrows) of the material by using a PVD apparatus (EB-PVD) using an electron beam as a heat source, and a single crystal alloy is formed. FIG. 3 is a diagram of an apparatus for vapor deposition on No. 3. This apparatus is housed in a vacuum vessel 4, in which a vacuum pump 5 and a pipe 6 for introducing an inert gas such as Ar or He are arranged, so that the atmosphere in the vessel can be freely adjusted to some extent. Since the film can be deposited in an inert gas atmosphere with substantially no air (oxygen), almost no oxide is contained in the formed film. In addition, this apparatus is provided with a heater 7 for heating the single crystal alloy and a DC power supply 8 for using the single crystal alloy and the coating material as electrodes, respectively. By applying a voltage, a purification treatment using an inert gas as a pre-deposition treatment and ionization of the deposited particles can be made to collide with the surface of the single crystal alloy, so that high adhesion can also be expected.
In addition, as a vapor deposition method, as a method other than the above method, a vapor deposition method using a laser or a Joule heat source, a high frequency excitation type EP-PVD method, a sputtering method, or the like can be used. The formation of an undercoat is possible.
[0032]
The thickness of the undercoat (boride coating layer) is preferably in the range of about 0.1 to 50 μm. The reason is that if the thickness of the boride is less than 0.1 μm, the effect of strengthening the grain boundary is not sufficient, while if the thickness is more than 50 μm, no particularly good effect on strengthening the grain boundary is recognized. This is because B, which has entered the inside of the base material, reacts with other alloy components in addition to strengthening the grain boundary to form a low melting point eutectic and the like, which is not preferable.
[0033]
(5) Formation of heat-resistant alloy coating layer (overcoat)
According to another embodiment of the present invention, a boride coating layer composed of a metal boride and / or a non-metal boride is first formed as an undercoat on a surface of a substrate such as a Ni-based single crystal alloy, and then formed thereon. It is conceivable that an overcoat is formed on a heat-resistant alloy coating layer for imparting high-temperature environment resistance. In this embodiment, the boride in the boride coating layer (undercoat) fully exerts its function, and various actions received from a high-temperature environment, such as chemical reaction such as oxidation reaction by combustion gas and sulfurization corrosion by S compound. It is intended to be able to withstand the damage.
Therefore, in the present invention, a heat-resistant alloy coating layer exhibiting high-temperature environment resistance is used as an overcoat on the boride coating layer (undercoat), and the air plasma spraying method, the reduced pressure plasma spraying method, the high-speed flame spraying method, and the like are used. It was decided to form a laminate using a thermal spraying method.
The reason for laminating the overcoat on top of the undercoat is that the undercoat, which is a boride coating layer alone, does not have sufficient resistance to high-temperature environments, and especially at high temperatures, the undercoat is consumed by oxidation. If the thickness is about 0.1 to 50 μm, the life of the undercoat may be extremely long and may be shortened.
[0034]
In the present invention, it is desirable to use the above-mentioned “MCrAlX alloy” as the heat-resistant alloy used for the heat-resistant alloy coating layer that is the overcoat. Its main chemical components are Y, Hf, Ta, Cs, Ce, La, Th, W, Si, Pt and Mn of an alloy containing at least two kinds selected from Co, Ni, Cr, Fe and Al. It is obtained by adding at least one element selected from the above. The overcoat is formed by spraying the MCrAlX alloy to a thickness of about 50 to 500 μm by various spraying methods.
[0035]
The heat-resistant alloy coating layer made of the MCrAlX alloy has good adhesion to the boride coating layer formed on the surface of the Ni-based alloy equipment, and can sufficiently withstand an external oxidation reaction or corrosion reaction by a high-temperature gas. It plays a role, and those having the following composition are preferably used.
As the M component, Ni: 0 to 75 mass%, Co: 0 to 70 mass%, Fe: 0 to 30 mass%,
Cr: 5 to 70 mass%, Al: 1 to 29 mass%,
As the X component, Y: 0 to 5 mass%, Hf: 0 to 10 mass%, Ta: 1 to 20 mass%, Si: 0.1 to 14 mass%, B: 0 to 0.1 mass%, C: 0 to 0.25 mass %, Mn: 0 to 10 mass%, Zr: 0 to 3 mass%, W: 0 to 5.5 mass%, Pt: 0 to 2.0 mass%
[0036]
However, when forming the thermal sprayed coating of the heat-resistant alloy made of the MCrAlX alloy, that is, in forming the overcoat, it is difficult to control the amount of the oxide contained in the overcoat and to examine the limit content thereof. Just as important. That is, when the MCrAlX alloy is sprayed in the atmosphere, a large amount of air is mixed in the heat source or in the vicinity of the heat source to oxidize the sprayed material particles, thereby lowering the mutual bonding force of the particles and the adhesion force to the alloy base material. In addition to these, these oxides suppress the diffusion of B atoms in the boride undercoat, and further, Al₂O₃And Cr₂O₃This is a major obstacle such as preventing the formation of a homogeneous and dense film of a uniform protective oxide film as described above.
Therefore, in the present invention, the amount of oxides in the heat-resistant alloy (MCrAlX alloy) contained in the overcoat is controlled to 1.5 mass% or less as the amount of oxygen. That is, the oxygen content in the spraying atmosphere is controlled to 1.5 mass% or less in any of the methods such as the atmospheric plasma spraying method, the reduced pressure plasma spraying method, the explosive spraying method, and the high-speed flame spraying method. It is.
[0037]
(6) Formation of Al diffusion layer
In the present invention, it is preferable to further form an Al diffusion layer on the surface of the boride undercoat or the heat-resistant alloy overcoat by applying an aluminum diffusion and infiltration treatment method such as a CVD method or a powder method.
For example, in the CVD method, an organic or inorganic aluminum compound (mainly a halogen compound) gas is introduced into a vacuum vessel, and a gas is irradiated with heat or low-temperature plasma to promote a chemical reaction to release Al from the aluminum compound. Or H in a vacuum vessel₂After introducing a gas to release Al by the chemical reducing power (the released Al particles are fine particles of 1 μm or less), this is deposited on the surface of a boride undercoat or a heat-resistant alloy overcoat, It is a method of diffusing and penetrating into Further, the powder method comprises the steps of forming an Al powder or an Al alloy powder and NH₄Cl, NH₄Halogen compounds such as F, Al₂O₃The non-processed member is buried in a mixture such as powder, and then Ar gas or H₂This is a method in which a diffusion layer having a high Al concentration is formed on the surface by heating at 800 to 1000 ° C. for 1 to 20 hours while flowing a gas.
[0038]
(7) Formation of ceramic coating layer (top coat)
Further, in the present invention, the surface of the boride undercoat, the heat-resistant alloy overcoat, or the surface of the Al diffusion layer is subjected to an atmospheric plasma spraying method, a low-pressure plasma spraying method, a vapor deposition method (EB-PVD) or the like, if necessary. Furthermore, oxide-containing ZrO₂A more preferred embodiment is to form a top coat (thickness: 30 to 500 μm) made of a system ceramic to further improve high-temperature strength.
The above ZrO₂The top coat of ceramics is Y₂O₃, CeO, CaO, Sc₂O₃, MgO, Yb₂O₃And CeO₂Containing at least one oxide selected from the group consisting of:₂System ceramics are used. The reason for using this as a top coat is mainly to prevent high-temperature radiant heat emitted from the combustion flame of the fuel. In addition, ZrO₂The reason for containing an oxide other than ZrO₂By itself, when heated or cooled to a high temperature, its crystal form changes to monoclinic {tetragonal} cubic, which causes a large volume change (4-7%) and breaks itself, It is desirable that the volume of such an oxide be reduced to about 5 to 40% by mass to reduce the volume change rate.
[0039]
(8) Cross-sectional structure of coating layer of Ni-based alloy member according to the present invention
FIG. 2 shows an example of a cross-sectional structure of the Ni-based high-temperature strength member according to the present invention.
{Circle around (1)} FIG. 2 (a) is a cross-section when a boride coating layer (undercoat) made of a metal boride and / or a non-metal boride is formed on the surface of a Ni-based single crystal alloy substrate. Numeral 21 is an alloy substrate, and 22 is a boride coating layer formed by a thermal spraying method, various PVD methods, and a CVD method.
{Circle around (2)} FIG. 2 (b) is a cross-sectional structure diagram in the case where an aluminum diffusion and penetration treatment is performed on the boride coating layer (undercoat) 22. Since this Al diffusion treatment is a high-temperature treatment (700 to 1000 ° C.), a part of Al diffuses into the undercoat which is a boride coating layer and penetrates with B into the base material. Here, only the diffusion phenomenon into the undercoat is illustrated. Here, 23 in the drawing indicates an Al diffusion layer (impregnated layer), and 24 indicates a layer having a high Al concentration.
Therefore, it can be said that the Al diffusion layer is composed of a portion substantially diffused and infiltrated (impregnated) into the base material and a coating layer (Al coating) covering the surface thereof.
{Circle around (3)} FIG. 2 (c) is a cross-sectional structure diagram when an overcoat 25 of an MCrAlX alloy is formed as a heat-resistant alloy coating layer on the boride coating layer 22 (undercoat). The overcoat 25 prevents oxidation and corrosion of the undercoat and the base material due to the high-temperature combustion gas, and at the same time, ensures excellent adhesion to the boride undercoat while diffusing B from the undercoat into the base material. It serves to suppress a decrease in the high-temperature strength of the substrate due to the formation of the altered layer. Here, reference numeral 25 denotes a sprayed coating layer of an MCrAlX alloy as a heat-resistant alloy coating layer having high temperature resistance.
{Circle around (4)} FIG. 2 (d) shows a cross-sectional structure of a composite film having the structure shown in FIG. In this example, the high-temperature environment resistance is exhibited only by the heat-resistant alloy coating layer 25 described above. However, a recent gas turbine using the Ni-based single crystal alloy blade material is different from the conventional polycrystalline alloy blade. It will be even hotter than the material. Therefore, the Al concentration in the outermost surface layer is improved in order to further exhibit the high temperature environment resistance of the protective film.
The Al diffusion and infiltration treatment is preferably performed according to a known gas phase method (CVD method) or a powder method (for example, see Japanese Patent No. 2960664 and Japanese Patent No. 2960665 filed by one of the present inventors).
{Circle around (5)} FIG. 2 (e) shows that a heat-resistant alloy overcoat of MCrAlX₂FIG. 2 is a cross-sectional structural view of a system in which a system ceramic coating layer 26 is provided as a top coat. In a gas turbine or the like, since strong radiant heat is generated using a combustion flame as a heat source, ZrO with low thermal conductivity is used.₂A system ceramic coating layer is provided on the outermost layer to prevent radiation heat damage. The ZrO₂Y-based ceramics₂O₃, CeO₂, CaO, Yb₂O₃, Sc₂O₃Containing at least one oxide selected from the group consisting of MgO, MgO₂Base ceramics are preferred.
[0040]
【Example】
<Example 1>
In this example, a Ni-based polycrystalline alloy (C alloy) was used as a comparative example together with a Ni-based single crystal alloy (A alloy) and a Ni-based unidirectional solidified alloy (B alloy) having the chemical components shown in Table 2. In addition, the existence of an altered layer due to the plastic working of the alloy was investigated. The heat treatment conditions of these test materials are shown in the lower part of Table 2, respectively.
Table 3 shows the types and combinations of the metal borides and non-metal borides according to the present invention tested in the examples, Table 4 shows the chemical components of the MCrAlX alloy, and Table 5 shows the results after the plastic working. The conditions of the heat treatment performed are shown.
[0041]
[Table 2]

[0042]
[Table 3]

[0043]
[Table 4]

[0044]
[Table 5]

[0045]
(Adjustment of test piece)
The single crystal alloy (dimensions: diameter 10 mm × length 10 mm) shown in Table 2 was subjected to plastic working at room temperature under the following conditions.
(1) A steel ball of a Brinell hardness tester was pressed at 980N.
(2) The surface of the test piece is cut about 1 mm by lathe processing
(3) A test piece was strongly sprayed using fused alumina grit (1 mm to 2 mm) specified in JIS Z 0312.
The processed test piece was subjected to a heat treatment under the conditions A and C shown in Table 5 and then cooled, and the cross section was observed with an optical microscope and a scanning electron microscope.
Table 6 summarizes the microscopy results. In the test piece not subjected to plastic working (test piece No. 1), no altered layer was observed at all. On the other hand, in the test pieces subjected to plastic working (Nos. 2 to 7), a deteriorated layer is generated regardless of the difference in the heat treatment conditions and the type of the plastic working method. A layer had formed. This altered layer is composed of a coarse γ 'precipitated phase and a γ phase, and at the boundary between the altered layer and the unchanged portion, a phenomenon that seems to be the decomposition of the γ' phase of the high-temperature strength factor (healthy portion) is recognized. The generation of a factor leading to a decrease in high-temperature strength was confirmed.
[0046]
[Table 6]

[0047]
(Example 2)
In this example, the effects of plastic working, heat treatment, thermal spray coating, etc. were investigated by a high temperature fatigue test using a single crystal alloy and a directionally solidified alloy.
(1) Fatigue test procedure and specimen adjustment
For the fatigue test, an electrohydraulic servovalve type fatigue test device having a maximum load of 5 tons, a stroke of 50 mm (both elongation and compression), and a frequency of 0.01 to 20 Hz was used. The test was performed under the conditions of 950 ° C. in the atmosphere, stress ratio R = −1, sinusoidal stress waveform, and frequency of 10 Hz.
[0048]
On the other hand, as a material for a fatigue test, two kinds of a single crystal alloy and a directionally solidified alloy were used, and the following method was applied as a method of imparting plastic strain.
(A) Applying compression strain by die forging
After cutting out a round bar with a convex portion as shown in FIG. 3 (a), the convex portion is converted into a radial direction, and a compression strain corresponding to about 8.3% at room temperature is subjected to die forging (FIG. 3 (b) ) And gave. Then, after performing the heat treatment described in Table 5, from the center of the test piece, as shown in FIG. 3C, the test piece was processed into a smooth bar fatigue test piece having a parallel portion diameter of 4 mm and a parallel portion length of 10 mm.
(B) Applying distortion by lathe processing
A fatigue test piece was cut out from a test material which was cut by a lathe to a radius of about 1 mm and then heat-treated at 1353 K × 100 h. The conditions of the lathe processing were changed to a range of a cutting depth of 0.2 to 0.25 mm and a feed amount of 0.051 to 0.2 mm.
(2) Formation of thermal spray coating
The boride shown in Table 3 or the MCrAlX alloy shown in Table 4 was individually applied as a boride undercoat and an MCrAlX alloy overcoat to a thickness of 150 μm over the entire parallel portion of the fatigue test piece by a reduced pressure plasma spraying method. It was constructed.
(3) Fatigue test results
Table 7 summarizes the results performed on the single crystal alloy. This result is a comparison of the average strength ratio of other test pieces, with the strength of a single crystal alloy virgin material (test piece No. 1 not subjected to plastic working) as 100. As is clear from these results, in the alloy not subjected to plastic working, the change in fatigue strength was small even when the MCrAlX alloy coating layer was formed, and the oxidation reaction due to the atmospheric environment was somewhat suppressed. .
On the other hand, when the test piece was previously subjected to die forging (No. 4) or lathing (No. 8), the recrystallization phenomenon occurred due to the heat treatment, so that the fatigue strength was extremely reduced and the single crystal was The alloy showed a fatal decrease in strength. However, if a boride coating layer (undercoat) is applied in advance, the test piece No. As seen in 5, 9, and 11, the decrease in fatigue strength was very small, and it was possible to substantially prevent the decrease in strength due to recrystallization. This tendency is also observed in the application of the MCrAlX alloy (test pieces Nos. 6 and 10), but the effect of reducing the strength reduction rate is smaller than that of boride. It is considered that the MCrAlX alloy film is due to the effect of high-temperature environment resistance.
Further, the effect of the boride undercoat was determined by the test piece no. As is clear from the results of 11 and 12, the effect of suppressing the decrease in the fatigue strength of the single crystal alloy can be obtained by using two types of metal borides or by using a mixture of metal / non-metal borides. It turned out to be acceptable.
[0049]
The test piece No. As can be seen in Figures 7 and 12, the specimens with boride undercoat / MCrAlX alloy overcoat have almost recovered fatigue strength, so the boride application should be in direct contact with the single crystal alloy. is necessary.
[0050]
[Table 7]

[0051]
On the other hand, Table 8 shows the results obtained for the directionally solidified alloy. Unidirectionally solidified alloys are not as strongly affected by plastic working as single crystal alloys, but here too, fatigue strength is reduced. The thermal spray coating of boride has been found to have a reduction efficiency even with respect to a decrease in strength due to recrystallization of the directionally solidified alloy (test pieces No. 5, 7, 9, 11, 12).
[0052]
[Table 8]

[0053]
(Example 3)
In this example, a fatigue test piece made of a single crystal alloy was subjected to cutting by a lathe as a plastic working method used in Example 2, heat treatment under the condition A in Table 5 as a heat treatment condition, and then a film forming method. An undercoat is formed by using the borides (A), (B), (F), and (G) of Table 3 by the low pressure plasma spraying method and the electron beam evaporation method, and the MCrAlX shown in Table 4 is formed thereon. The alloy was used as an overcoat to a thickness of 150 μm by a high-speed flame spraying method. The thickness of the boride undercoat is 20 μm by thermal spraying and 2 μm by electron beam evaporation.
The test pieces formed as described above were tested under the thermal fatigue test conditions described in Example 2.
Table 9 shows the results of a fatigue test at 1223 K using the test pieces. As is clear from the results, the example of the comparative example obtained in Example 2 which was not subjected to the plastic working (test piece No. 1), and the plastic working was applied, but the boride undercoat was formed. The results of the fatigue strength test under no condition (No. 2) were also described, and comparison was made based on these measured values. To summarize these results, when plastic working is applied to a Ni-based single crystal alloy, its fatigue strength is reduced to about 32% of a virgin material (No. 1), but the boride undercoat is formed by a vapor deposition method or a thermal spraying method. After the application, the fatigue strength of the laminate of the MCrAlX alloy overcoat (Nos. 4 to 7, 9 to 11) recovers to almost the same as the strength of the virgin material, and prevents the strength from being reduced due to the formation of the altered layer. Is recognized. As the boride, metal boride alone (Nos. 4, 5, 9, 10), a mixture of two kinds of metal borides (No. 6), and an undercoat such as a mixture of a metal boride and a non-metallic boride are used. In addition, almost the same effect of preventing a decrease in strength was observed. Further, almost no difference between the vapor deposition method and the thermal spraying method is recognized as a method for forming an undercoat, and both of them exhibit sufficient performance as a method for applying a boride undercoat.
On the other hand, when the sprayed coating of the MCrAlX alloy is directly applied to the surface of the plastically processed test piece (Nos. 3 and 8), although the high temperature environment resistance is exhibited, the reduction of the fatigue strength of the base material is suppressed. It did not perform as well as the boride undercoat.
[0054]
[Table 9]

[0055]
(Example 4)
In this example, the thermal shock resistance of a coating layer conforming to the present invention formed on the surface of a single crystal alloy and a directionally solidified alloy was investigated.
(1) Shape and dimensions of test substrate and test piece
As a test substrate, a single crystal alloy and a unidirectionally solidified alloy shown in Table 2 were used, which were finished into a round bar test piece having a diameter of 15 mm and a length of 50 mm.
(2) Whether or not plastic working is performed on the test piece
For the processing of the round bar test piece, a lathe processing condition described in Example 1 was manufactured.
(3) Type of coating layer to be tested and coating layer forming method
As a method of forming a boride undercoat on the test piece, a spraying method (reduced pressure plasma) EB-PVD method and a sputtering method are used. NiB is formed to a thickness of 20 μm by the spraying method, 3 μm by the PVD method, and 1 μm by the sputtering method. Filmed. Thereafter, as the MCrAlX alloy, an alloy described in Table 4 was applied to a film thickness of 150 μm by a low-pressure plasma spraying method and a high-speed flame spraying method, and then a top coat was formed on the overcoat as a top coat.₂O₃Containing 8 mass%₂A thermal shock test piece was formed by forming a ceramic coating layer having a thickness of 300 μm by the atmospheric plasma spraying method.
(4) Thermal shock test conditions
The test piece was placed in an electric furnace maintained at 950 ° C. for 15 minutes, heated, and then put into 298K water to cool it as one cycle. This operation was repeated 10 cycles, and the appearance change and the presence or absence of peeling of the coating layer were repeated. investigated.
The test results are summarized in Table 10. As is apparent from the results, the coating layer of the MCrAlX alloy, which is generally widely used, and Y₂O₃・ ZrO₂The heat-shielding films (test pieces Nos. 1 and 2) formed by the combination of the ceramic coating layers endured the thermal shock test by repeating 10 times, and no cracking or peeling of the top coat was observed. Regarding the composite coating (Nos. 3 to 8) according to the present invention, the top coat Y₂O₃・ ZrO₂Has no signs of cracking or local peeling, maintains a healthy state, and has a thermal shock resistance comparable to that of the currently widely used thermal shield coating. Was. As a matter of course, it was found that the bonding strength at the interface between the boride undercoat and the MCrAlX alloy overcoat also maintained sufficient performance, and no peeling phenomenon was observed.
[0056]
[Table 10]

[0057]
【The invention's effect】
As described above, the conventional Ni-based single crystal alloy and the Ni-based unidirectionally solidified alloy base material which have been subjected to strain or plastic working in advance, when heated to a high temperature, have a deteriorated layer accompanied by recrystallization on the surface. Which is a starting point and can be easily broken even by a slight load stress, and there is a fatal defect that the high-temperature strength possessed by this kind of alloy cannot be exhibited.
In contrast, the present invention forms a boride undercoat directly on the surface of such an alloy substrate by a thermal spraying method, a PVD method, a CVD method, etc., so that boron is preferentially alloyed in a high-temperature environment. By diffusing into the base material to reinforce the mutual bonding force of the recrystallized grain boundaries, the decrease in high-temperature strength is effectively reduced, and thereby the original strength of the base material is exhibited.
[0058]
According to another embodiment of the present invention, for example, the lamination of the boride coating layer (undercoat) and the MCrAlX alloy coating layer (overcoat), and the lamination of the ZrO2 ceramic coating layer (topcoat) By the formation or the like, the physical and chemical action on the combustion gas component in a high temperature environment can be improved.
[0059]
These effects can be achieved by applying strain and plastic working in the film reprocessing step during or after operation, as well as in the manufacturing and assembly process, such as gas turbine blade members made of single crystal alloys and directionally solidified alloys. When the present invention is applied to a high-temperature strength member having many opportunities to accompany it, the above-mentioned risk factors can be completely wiped off, which is effective.
Therefore, according to the present invention, it is possible to contribute to the improvement of the quality and productivity of this kind of alloy gas turbine blade member, and to contribute significantly to long-term stable operation of the gas turbine and reduction of the unit cost of power generation.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an outline of a PVD apparatus having an electron beam heat source.
FIG. 2 is a cross-sectional view showing an example of a laminated structure in which a high-temperature resistant coating layer is formed on a single crystal alloy or a directionally solidified alloy member using the boride coating layer of the present invention.
FIG. 3 is a diagram showing a load of stress by die forging of a convex portion on a round bar material having a convex portion and a procedure for collecting a high-temperature fatigue strength test specimen from the round bar.
FIG. 4 is a metallurgical microscope photograph showing an example of the shape of a deteriorated layer generated in a plastically worked portion.
FIG. 5 is a metal micrograph showing that the state of the fracture surface of the fatigue test piece and that the altered layer is the starting point of the fracture.
[Explanation of symbols]
1 Coating material
2 electron beam gun
3 Single crystal alloy substrate
4 Vacuum container
5 vacuum pump
6 Inert gas inlet pipe
7 Heater for substrate heating
8 DC power supply
21 Substrate
22 boride coating layer (undercoat)
23 Al diffusion layer (low concentration)
24 Heat-resistant alloy coating layer (overcoat)
25 Al diffusion layer (high concentration)
26 Ceramics coating layer (top coat)

Claims (9)

A metal boride and / or non-metal boride boride coating layer is provided as an undercoat on the surface of the Ni-base alloy base material, and a high-temperature environment-resistant heat-resistant alloy coating layer is provided thereon as an overcoat. A Ni-based alloy member characterized in that: A metal boride and / or non-metal boride boride coating layer is provided as an undercoat on the surface of the Ni-base alloy base material, and a high temperature environment heat resistant alloy coating layer is provided thereon as an overcoat. And a ZrO ₂ ceramic containing at least one oxide selected from the group consisting of Y ₂ O ₃ , CaO, MgO, Yb ₂ O ₃ , Sc ₂ O ₃ and CeO ₂ as a top coat. A Ni-based alloy member provided with a coating layer. The boride coating layer, B ₄ C and / or Ni-based alloy member according to claim 1 or 2, characterized in that non-metallic boride consisting of BN. The heat-resistant alloy coating layer is further provided with Y, Hf, Ta, Cs, Ce, La, Th, W, Si, Pt for an alloy containing at least two kinds selected from Co, Ni, Cr, Fe and Al. , Ni-base alloy member according to claim 1 or 2, characterized in that it is formed by spray coating alloy containing at least one element selected from among Ti and Mn. Ni-base alloy member according to claim 1 or 2 wherein the surface of the boride coating layer and / or a heat-resistant alloy coating layer, characterized in that the Al diffusion layer is provided. Metal borides and / or non-metal borides are applied to the surface of a Ni-based alloy substrate by a surface treatment method such as thermal spraying, electron beam evaporation (EB-PVD), sputtering, thermal CVD, or plasma CVD. A method for producing a Ni-based alloy member, comprising: forming a boride coating layer made of a boride; and forming a high temperature resistant alloy coating layer on the surface of the boride coating layer by thermal spraying. Metal borides and / or non-metal borides are applied to the surface of a Ni-base alloy substrate by a surface treatment method such as thermal spraying, electron beam evaporation (EB-PVD), sputtering, thermal CVD, or plasma CVD. to form a boride coating layer comprising fluoride, then the surface of the boride coating layer, high temperature resistant alloy coating layer was laminated me by the spraying method, on subsequent said refractory alloy coating layer, Y ₂ A ceramic coating layer made of a ZrO ₂ -based ceramic containing at least one oxide selected from O ₃ , CaO, MgO, Yb ₂ O ₃ , Sc ₂ O _3, CeO _2, etc., is sprayed or sprayed with an electron beam. A method for producing a Ni-based alloy member, comprising forming a laminate. 8. The method according to claim 6 , wherein an Al diffusion layer is formed on the surface of the boride coating layer and / or the heat-resistant alloy coating layer by an aluminum diffusion infiltration treatment method. The boride coating layer is made of a metal boride represented by metals M _{1 to 11} B _{1 to 12} or a non-metal boride made of B ₄ C and / or BN, and the heat-resistant alloy coating layer is made of Co, Ni , Cr, Fe and Al, the alloy containing at least two kinds selected from Y, Hf, Ta, Cs, Ce, La, Th, W, Si, Pt, Ti and Mn. It consists of an alloy to which one kind of element is added, and the ceramic coating layer contains at least one kind of oxide selected from Y ₂ O ₃ , CaO, MgO, Yb ₂ O ₃ , Sc ₂ O ₃ and CeO _2. The method for producing a Ni-based alloy member according to claim 6, wherein the method comprises a ZrO ₂ -based ceramic.

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