JP3735671B2 - Method for forming sprayed coating - Google Patents
Method for forming sprayed coating Download PDFInfo
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- JP3735671B2 JP3735671B2 JP2003167002A JP2003167002A JP3735671B2 JP 3735671 B2 JP3735671 B2 JP 3735671B2 JP 2003167002 A JP2003167002 A JP 2003167002A JP 2003167002 A JP2003167002 A JP 2003167002A JP 3735671 B2 JP3735671 B2 JP 3735671B2
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- thermal
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- ceramic
- thermal spray
- forming
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Links
- 238000000034 method Methods 0.000 title claims description 63
- 239000011248 coating agent Substances 0.000 title claims description 10
- 238000000576 coating method Methods 0.000 title claims description 10
- 239000000843 powder Substances 0.000 claims description 43
- 239000000463 material Substances 0.000 claims description 32
- 238000005507 spraying Methods 0.000 claims description 31
- 239000000919 ceramic Substances 0.000 claims description 30
- 239000002245 particle Substances 0.000 claims description 29
- 238000007751 thermal spraying Methods 0.000 claims description 25
- 239000013078 crystal Substances 0.000 claims description 24
- 239000000758 substrate Substances 0.000 claims description 15
- 239000007921 spray Substances 0.000 claims description 9
- 239000012720 thermal barrier coating Substances 0.000 claims description 9
- 239000006104 solid solution Substances 0.000 claims description 7
- 230000015572 biosynthetic process Effects 0.000 claims description 6
- 238000004880 explosion Methods 0.000 claims description 6
- 238000010285 flame spraying Methods 0.000 claims description 6
- 238000002485 combustion reaction Methods 0.000 claims description 3
- 239000008187 granular material Substances 0.000 claims description 3
- 229910052574 oxide ceramic Inorganic materials 0.000 claims description 3
- 239000011224 oxide ceramic Substances 0.000 claims description 3
- 239000010408 film Substances 0.000 description 30
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 13
- 238000007750 plasma spraying Methods 0.000 description 8
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 7
- 239000002131 composite material Substances 0.000 description 7
- 238000001816 cooling Methods 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000012071 phase Substances 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 5
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 4
- 229910010293 ceramic material Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- 150000004706 metal oxides Chemical class 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 3
- 238000005469 granulation Methods 0.000 description 3
- 230000003179 granulation Effects 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 229910001233 yttria-stabilized zirconia Inorganic materials 0.000 description 3
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- -1 alumina Chemical class 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000000395 magnesium oxide Substances 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 229910052575 non-oxide ceramic Inorganic materials 0.000 description 2
- 239000011225 non-oxide ceramic Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 229920002451 polyvinyl alcohol Polymers 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000001694 spray drying Methods 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 229910006404 SnO 2 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 239000005388 borosilicate glass Substances 0.000 description 1
- 229910002084 calcia-stabilized zirconia Inorganic materials 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- UFGZSIPAQKLCGR-UHFFFAOYSA-N chromium carbide Chemical compound [Cr]#C[Cr]C#[Cr] UFGZSIPAQKLCGR-UHFFFAOYSA-N 0.000 description 1
- 239000000567 combustion gas Substances 0.000 description 1
- 238000002050 diffraction method Methods 0.000 description 1
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000001451 molecular beam epitaxy Methods 0.000 description 1
- 229910052863 mullite Inorganic materials 0.000 description 1
- 239000000075 oxide glass Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000011164 primary particle Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 238000004781 supercooling Methods 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 229910003470 tongbaite Inorganic materials 0.000 description 1
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 description 1
- 229910052845 zircon Inorganic materials 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T50/00—Aeronautics or air transport
- Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
Landscapes
- Turbine Rotor Nozzle Sealing (AREA)
- Coating By Spraying Or Casting (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、低い熱伝導性を有する溶射皮膜の形成方法に関する。
【０００２】
【従来の技術】
ジェットエンジン等の金属部材を高温の燃焼ガスから保護するための遮熱コーティングを形成する方法として、カルシア安定化ジルコニア、イットリア安定化ジルコニア等の低熱伝導率のセラミックス原料を用いて溶射法によって皮膜を形成する方法が知られている（例えば、下記非特許文献１参照）。
【０００３】
この様な方法で形成されるセラミックス皮膜は、基本的に単一材料で構成されており、遮熱能力を高めるには、より低熱伝導の材料を使用する方法や皮膜を厚くする方法等が考えられる。
【０００４】
低熱伝導材料については、高温での安定性と基材との適合性を同時に満足する必要があり、多くの研究者により精力的に材料探索が進められているが、現在の材料より優れた性能を有する決め手となる材料は未だ開発されていない。
【０００５】
また、皮膜を厚くする方法に関しては、膜が厚くなるに従って基材との熱膨張率差により生じる残留応力が急激に増大し、剥離しやすくなるため、その厚さには自ずと限界がある。さらに、残留応力を低減するために、基材の金属からセラミックへと次第に組成を漸変させていく傾斜機能材料という概念が提案され、応力緩和に有効であることが示されている（例えば、下記非特許文献２参照）。しかしながら、この様な傾斜機能材料には、セラミックス相だけではなく、金属相が加えられており、その結果、熱伝導率が高くなって厚さの割には充分な遮熱効果が得られない。しかも、金属相の酸化が生じる等のため高温への適用には限界がある。
【０００６】
ところで、セラミックス材料では、主に結晶格子の振動（フォノン）により熱が伝わるため、薄膜や超格子構造を作ってフォノンの平均自由行程を短くすれば、熱伝導率が低くなることが知られている（例えば、下記非特許文献３参照）。このような構造を作る方法としては、モレキュラービームエピタキシー等の方法が知られているが、この方法は、膜生成速度が極めて遅く、遮熱コーティングのような充分な膜厚が必要な用途への適用は事実上不可能である。しかも、人工的に作られた準安定な構造のため、高温でその構造を保持し続けることはできないと考えられる。
【０００７】
【非特許文献１】
原田 良夫：「発電用高温ガスタービンにおける溶射の適用動向」，溶射技術，22(2), 20-29 (2002).
【０００８】
【非特許文献２】
大木 基史：「傾斜組成遮熱コーティング材の熱サイクル損傷特性」，溶射技術，22(2), 45-58 (2002).
【０００９】
【非特許文献３】
宇野良清，津屋 昇，森田 章，山下次郎 共訳：「第５版キッテル固体物理学入門上」，丸善，1978, pp.132-141
【００１０】
【発明が解決しようとする課題】
本発明は、上記した如き従来技術の現状に鑑みてなされたものであり、その主な目的は、遮熱コーティング等の用途に有用な低い熱伝導性を有する材料を十分に速い速度で形成できる方法を提供することである。
【００１１】
【課題を解決するための手段】
本発明者は、上記した目的を達成すべく鋭意研究を重ねてきた。その結果、互いに固溶しない２種類以上のセラミックス微細粉末の造粒物を原料として用い、溶射法によって基材上に皮膜を形成する方法によれば、非常に微細な結晶粒子が分散したセラミックス複合皮膜を十分に速い速度で形成することができ、得られる皮膜は遮熱コーティング等の用途に適した優れた遮熱性を有することを見出した。
【００１２】
即ち、本発明は、下記の溶射皮膜の形成方法を提供するものである。
１． 平均粒径が１μｍ以下で互いに固溶しない２種類以上のセラミックス微粉末を造粒して、平均粒径が１０〜１００μｍの顆粒状物からなる溶射材料を形成する工程と、該溶射材料を溶射法により基材上に溶射し、複数種の平均粒径が３００ｎｍ以下である微細結晶を内部に有する皮膜を形成する工程とを含む溶射皮膜の形成方法。
２． 上記セラミックス粉末の少なくとも一種類が酸化物セラミックスである溶射皮膜の形成方法。
３． 上記溶射法が、プラズマ溶射法、ガス燃焼フレーム溶射法、高速フレーム溶射法、爆発溶射法又は線爆溶射法である溶射皮膜の形成方法。
４． 上記溶射皮膜が、遮熱コーティングである溶射皮膜の形成方法。
５． 上記溶射皮膜を基材から分離する工程をさらに含む溶射皮膜の形成方法。
【００１３】
【発明の実施の形態】
本発明方法では、溶射材料としては、互いに固溶しない２種類以上のセラミックス微粉末の造粒物を用いる。
【００１４】
セラミックス微粉末としては、アルミナ，ジルコニア，チタニア，マグネシア，イットリアなどの単一金属酸化物、スピネル，ムライト，ジルコンなどの複金属酸化物、硼珪酸ガラス，石英ガラスなどの酸化物系ガラスを用いることができる。また、単一金属酸化物であって、溶射後、反応により、Al2TiO5、3Y2O3・5Al2O3等の複金属酸化物を生成する材料系も利用可能である。さらに、炭化クロム，炭化タングステン，硼化ジルコニウム，硼化チタンなどの非酸化物セラミックスも用いることができる。本発明では、この様なセラミックス微粉末から、互いに固溶しない２種類以上の材料を選択して用いる。互いに固溶しないセラミックス材料を用いることにより、溶射法によって、複数種の非常に微細な結晶粒子が分散した皮膜を形成することができる。
【００１５】
特に、セラミックス微粉末の内で、少なくとも一種が酸化物セラミックスである場合には、形成されるセラミックス複合材料が優れた遮熱性を有するものとなる。
【００１６】
尚、本発明では、原料として用いる互いに固溶しない２種類以上のセラミックス微粉末については、相互に完全に固溶しないことが必要ではなく、溶射後に形成される溶射皮膜において、複数種の微細結晶が形成されればよく、このような複数種の微細結晶が形成される範囲内であれば、各結晶中において他の元素が少量固溶しても良い。
【００１７】
本発明における好ましいセラミックス微粉末の組合せとして、例えば、Al2O3とZrO2の組合せ、Al2O3とSnO2の組合せ、ZrO2とMgOの組合せ、ZrO2とThO2の組合せなど、共晶系の酸化物の組合せを挙げることができる。
【００１８】
上記したセラミックス微粉末は、平均粒径が１μｍ程度以下であることが好ましい。この様な微粉末を用いることにより、溶射中に短時間で溶融して容易に均質な液相を形成できる。セラミックス微粉末は、必要に応じて、ジェットミル、ビーズミルなどを用いて粒径１μｍ程度以下となるように微粉砕すればよい。尚、本願明細書では、平均粒子径は、レーザービーム回折法によって求めた値である。
【００１９】
本発明では、互いに固溶しない２種類以上のセラミックス粉末を造粒して顆粒状粉末とし、これを溶射材料として用いることが必要である。造粒した顆粒状粉末を溶射材料とすることによって、溶射の際に造粒粉が全体として溶融液滴となり、液相の粘性が高い場合であっても均質な組成の液滴を形成することができる。
【００２０】
セラミックス微粉末を造粒して顆粒状粉末を作製する方法としては、例えば、スプレードライ法、転造造粒法、流動床造粒法等各種の公知方法を適用できる。顆粒状粉末の平均粒径は、１０〜１００μｍ程度であることが好ましい。この範囲の粒径の顆粒状粉末を用いることにより、取り扱いが容易となり、しかも均質な溶融液滴を形成できる。
【００２１】
造粒して得られる顆粒状粉末は、結合強度が低い場合には、必要に応じて熱処理を行って焼結させても良い。これにより、溶射時に、溶融液滴が形成される前に造粒粉が崩壊することを抑制できる。この場合、焼結条件としては、造粒粉内の一次粒子同士が軽く焼結し、造粒粉同士は結合しない程度の条件を選べばよい。具体的な焼結条件については、粉末の種類に依存するので一概に規定できないが、例えば、アルミナ微粉末とジルコニア微粉末からなる造粒粉では、例えば、1000〜1200℃程度で３０分程度加熱すればよい。
【００２２】
溶射方法としては、基材上に溶射皮膜を形成できる方法であれば良い。具体的な方法については、特に限定的ではないが、例えば、プラズマ溶射法、ガス燃焼フレーム溶射法、高速フレーム溶射法、爆発溶射法、線爆溶射法などの公知方法を適用できる。これらの溶射法では、顆粒状の原料を溶融状態となるまで加熱して均質な液相状態とし、これを被覆対象物に吹き付けてその表面で凝固、堆積させることによって皮膜を形成できるので、ＣＶＤ，ＰＶＤ等の蒸着法と比べて高速で皮膜を形成できる。
【００２３】
溶射時の雰囲気は、用いるセラミックス微粉末の種類、溶射方法、基材の種類などに応じて、不活性気体雰囲気（Ａｒ，Ｎ2等）、大気雰囲気などとすることができる。例えば、セラミックス微粉末として、非酸化物系セラミックスを用いる場合には、溶射中に酸化されることを防止するためには、不活性気体雰囲気中で溶射を行えばよい。
【００２４】
特に、溶射法としてはプラズマ溶射法が好ましい。プラズマ溶射法によれば、原料を直流アークプラズマジェット中に投入し、高温のプラズマの熱で瞬時に溶融することにより、短時間で顆粒状粉末全体を完全に溶融させて均質な溶融物を容易に形成できる。また、プラズマ溶射法では、溶融物を高速のガスジェットにより加速して被覆対象物に吹き付け、その表面で凝固・堆積させるので、非常に高速での成膜が可能である。
【００２５】
溶射法によって溶融液滴を基材に吹き付けることにより、基材に衝突した液滴は、扁平に潰れるとともに基材に熱を奪われて瞬時に凝固する。この際、過冷却が生じると共に冷却速度が非常に大きいために、多数の結晶の核が生成し、ほとんど粒成長することなく凝固が完了する。本発明では、溶射材料として互いに固溶しない２種類以上のセラミックス微粉末を用いているため、形成される皮膜は、複数種の非常に微細な結晶粒子が分散したセラミックス複合材料となる。
【００２６】
この際、非常に微細な結晶粒子が分散した溶射皮膜が形成されるように冷却速度を制御する。結晶粒子の粒径は、３００ｎｍ程度以下であることが好ましく、５０ｎｍ程度以下であることがより好ましく、１０ｎｍ程度以下であることが更に好ましい。
【００２７】
具体的な冷却速度については、材料組成や基材の種類によって異なるので、一概に規定できないが、冷却速度が速くなると微細結晶が析出することなくアモルファス相が形成され、冷却速度が遅くなると析出する結晶径が大きくなるので、目的とする大きさの微細結晶が形成されるように、材料組成などに応じて適切な冷却速度を決めればよい。この際、必要に応じて、水冷ジグの使用、圧縮空気吹き付け等により温度管理を行えばよい。
【００２８】
上記した方法によって形成される溶射皮膜は、非常に低い熱伝導性を有する材料となる。この理由については、以下のように考えることができる。
【００２９】
即ち、上記した方法で形成される溶射皮膜では、異種結晶粒界は、結晶の不整合が大きい場合には、フォノン（結晶格子の振動の量子）の散乱サイトとして働くと考えられる。
【００３０】
熱伝導率λは、下記式
λ=ρ・Ｃp・α
（ここで、ρ：密度，Ｃp：比熱，α：熱拡散率）で表され、
熱拡散率αは、下記式
α=ｖs・ｌp／３
（ここで、ｖs：音速，ｌp：フォノンの平均自由行程）で表される。従って、結晶径を十分小さくすれば、異種結晶粒界でフォノンが散乱され、平均自由行程を短くすることが可能となる。本発明方法によれば、２種類以上の非常に微細な結晶粒子が分散した皮膜が形成されるために熱拡散率が小さくなり、その結果、熱伝導率も低下するものと考えられる。
【００３１】
また、一般に、溶射皮膜の硬度及び耐摩耗性は、分散した粒子の径が小さい程向上すると考えられる。本発明方法によって形成されるセラミックス複合材料は、微細な結晶粒子が分散した構造であることによって、高強度で靭性にも優れた皮膜となる。
【００３２】
溶射皮膜の支持体となる基材（被溶射体）としては、溶射が可能である限り特に限定されない。この様な基材としては、公知の被溶射体である金属、セラミックスなどが例示される。また、冷却操作を必要とするが、プラスチック、布帛、紙などを支持体として使用することも可能である。
【００３３】
被溶射体の具体的形状については、特に限定されず、用途に応じて種々の形態とすることができる。例えば、高温で使用されるタービン用部品、ジェットエンジン用部品などの表面に遮熱コーティングとして形成することができる。
【００３４】
また、本発明による複合材料は、平板基材上に堆積された溶射層を基材から分離することにより、板状又はシート状材料として形成することもできる。或いは、所定形状の部品に対応する形状を有する型内にセラミックス材料を溶射した後、溶射層を型から分離することにより、所望の形態の部品を得ることもできる。
【００３５】
上記した各種基材に溶射皮膜を形成する際には、基材が金属材料である場合には、必要に応じて、基材表面にブラスト加工などの前処理を施すことができる。
【００３６】
更に、金属基材と溶射皮膜との密着性を向上させるために、セラミックスの溶射皮膜を形成する前に、金属を溶射材料として用いて基材上に金属の溶射皮膜を形成しても良い。
【００３７】
【発明の効果】
以上の通り、本発明では、溶射法を採用しているために、膜生成速度が非常に速く、厚膜を容易に形成でき、また、大面積の部材や複雑形状の部材にも適用可能である。しかも、得られる皮膜は遮熱性が良好であり、高強度で靭性にも優れた皮膜となる。
【００３８】
従って、本発明によれば、例えば、タービン用部品、ジェットエンジン用部品等の比較的大きな複雑な形状の部品に対しても優れた性能を有する遮熱コーティングを容易に形成できる。
【００３９】
【実施例】
以下、実施例を挙げて本発明を更に詳細に説明する。
【００４０】
実施例１
平均粒径０．１６μｍのアルミナ粉末と平均粒子径０．０４２μｍのジルコニア粉末を体積比で５０：５０になるように混合し、さらに結合材としてポリビニルアルコール（PVA）を加え、水を分散媒として、ボールミル混合により均質なスラリーを作製した。このスラリーからスプレードライ法により平均２次粒子径約３０μｍの球状の造粒粉を製造した。
【００４１】
この造粒粉を用いて、プラズマ溶射法により炭素鋼基材上にセラミックス皮膜を形成した。溶射条件は、下記表１に示す通りである。
【００４２】
【表１】
得られた皮膜を剥離し、粉末X線回折法により測定したところ、結晶相としてm-ZrO2, t'-ZrO2, γ-Al2O3が生成しており、その結晶子サイズはそれぞれ、約６ｎｍ、５ｎｍ、８ｎｍであった。この皮膜の厚さ方向の熱拡散率を、室温でレーザーフラッシュ法により測定した結果を下記表２に示す。
【００４４】
実施例２
平均粒径０．１６μｍのアルミナ粉末と平均粒子径０．０４０μｍの３ｍｏｌ％イットリア安定化ジルコニア粉末を用いて、実施例１と同様の方法でプラズマ溶射法により皮膜を作製した。
【００４５】
得られた皮膜は、結晶相としては、割合は異なるもののやはりm-ZrO2, t'-ZrO2, γ-Al2O3が生成しており、その結晶子サイズはそれぞれ、約６ｎｍ、６ｎｍｍ、８ｎｍであった。この皮膜の厚さ方向の熱拡散率を実施例１と同様にして測定した結果を下記表２に示す。
【００４６】
比較例１
市販のプラズマ溶射用のアルミナ粉末（平均粒径 19.7μｍ）と8wt%イットリア安定化ジルコニア粉末（325〜140メッシュ）を体積比で５０：５０になるように単純に混合し、この粉末をプラズマ溶射してセラミックス複合皮膜を形成した。 得られた皮膜は、t'-ZrO2の扁平に潰れた粒子と γ-Al2O3の扁平に潰れた粒子の積層からなっており、潰れた粒子の厚さは１〜３μｍであった。この皮膜の厚さ方向の熱拡散率を実施例１と同様にして測定した結果を下記表２に示す。
【００４７】
【００４８】
尚、比較例１の熱拡散率から熱伝導率を見積もると2 w/m・K程度である。この値はバルクのジルコニアセラミックスの熱伝導率とほぼ同じであり、熱伝導率が約30 w/m・Kのアルミナを50vol%も含んでいることを考えると、熱伝導を妨げるようにアルミナ−ジルコニア粒界が存在するため、非常に小さな値になっていると言える。実施例１及び２では、比較例１と比べて、熱拡散率がほぼ半分であることから、ナノサイズの粒子分散複合構造を形成することにより、極めて熱伝導の低い皮膜が形成されることが判る。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a thermal spray coating having low thermal conductivity.
[0002]
[Prior art]
As a method of forming a thermal barrier coating to protect metallic members such as jet engines from high-temperature combustion gases, a coating is formed by thermal spraying using a ceramic material with low thermal conductivity such as calcia stabilized zirconia and yttria stabilized zirconia. A forming method is known (for example, see Non-Patent Document 1 below).
[0003]
The ceramic film formed by such a method is basically composed of a single material. In order to increase the heat shielding ability, a method using a material with lower thermal conductivity, a method of increasing the film thickness, etc. are considered. It is done.
[0004]
For low thermal conductivity materials, it is necessary to satisfy both high-temperature stability and compatibility with the substrate at the same time, and many researchers are energetically searching for materials. No decisive material has been developed yet.
[0005]
Further, regarding the method of thickening the film, the residual stress generated by the difference in thermal expansion coefficient from the base material increases rapidly as the film becomes thicker, and the film tends to peel off. Furthermore, in order to reduce the residual stress, the concept of functionally graded material that gradually changes the composition from the base metal to the ceramic has been proposed and has been shown to be effective in stress relaxation (for example, Non-patent document 2 below). However, such a functionally gradient material includes not only a ceramic phase but also a metal phase. As a result, the thermal conductivity is high and a sufficient heat shielding effect cannot be obtained for the thickness. . In addition, there is a limit to application to high temperatures because of the oxidation of the metal phase.
[0006]
By the way, in ceramic materials, heat is transmitted mainly by crystal lattice vibrations (phonons), so it is known that if a thin film or superlattice structure is made to shorten the mean free path of phonons, the thermal conductivity will be lowered. (For example, see Non-Patent Document 3 below). As a method for producing such a structure, a method such as molecular beam epitaxy is known, but this method has a very slow film formation rate and is suitable for applications requiring a sufficient film thickness such as a thermal barrier coating. Application is virtually impossible. Moreover, because of the artificially produced metastable structure, it is considered that the structure cannot be maintained at a high temperature.
[0007]
[Non-Patent Document 1]
Yoshio Harada: “Application trends of thermal spraying in high-temperature gas turbines for power generation”, Thermal spraying technology, 22 (2), 20-29 (2002).
[0008]
[Non-Patent Document 2]
Motoshi Oki: “Thermal cycle damage characteristics of gradient composition thermal barrier coating material”, Thermal spraying technology, 22 (2), 45-58 (2002).
[0009]
[Non-Patent Document 3]
Ryoyo Uno, Noboru Tsuya, Akira Morita, Jiro Yamashita Co-translation: "Fifth Edition: Introduction to Kittel Solid Physics", Maruzen, 1978, pp.132-141
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the current state of the prior art as described above, and its main object is to form a material having low thermal conductivity useful for applications such as a thermal barrier coating at a sufficiently high speed. Is to provide a method.
[0011]
[Means for Solving the Problems]
The present inventor has intensively studied to achieve the above-described object. As a result, according to the method of forming a film on a substrate by a thermal spraying method using a granulated product of two or more kinds of ceramic fine powders that do not form a solid solution with each other, a ceramic composite in which very fine crystal particles are dispersed It was found that the film can be formed at a sufficiently high speed, and the obtained film has excellent heat shielding properties suitable for applications such as thermal barrier coating.
[0012]
That is, this invention provides the formation method of the following thermal spray coating.
1. A process of granulating two or more ceramic fine powders having an average particle size of 1 μm or less and not forming a solid solution with each other to form a thermal spray material composed of granules having an average particle size of 10 to 100 μm, and spraying the thermal spray material And a step of forming a coating having a plurality of fine crystals having an average particle size of 300 nm or less inside by thermal spraying on a substrate by a method.
2. A method for forming a sprayed coating, wherein at least one of the ceramic powders is an oxide ceramic.
3. A method for forming a sprayed coating, wherein the spraying method is a plasma spraying method, a gas combustion flame spraying method, a high-speed flame spraying method, an explosion spraying method, or a line explosion spraying method.
4). A method for forming a thermal spray coating, wherein the thermal spray coating is a thermal barrier coating.
5. A method for forming a thermal spray coating, further comprising a step of separating the thermal spray coating from a substrate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, as a thermal spray material, a granulated product of two or more kinds of ceramic fine powders that are not solid-solved with each other is used.
[0014]
As ceramic fine powder, single metal oxides such as alumina, zirconia, titania, magnesia and yttria, double metal oxides such as spinel, mullite and zircon, and oxide glasses such as borosilicate glass and quartz glass should be used. Can do. A material system that is a single metal oxide and generates a double metal oxide such as Al 2 TiO 5 , 3Y 2 O 3 .5Al 2 O 3 by reaction after spraying can also be used. Further, non-oxide ceramics such as chromium carbide, tungsten carbide, zirconium boride and titanium boride can also be used. In the present invention, two or more kinds of materials that do not form a solid solution with each other are selected and used from such ceramic fine powder. By using ceramic materials that do not form a solid solution with each other, a coating in which a plurality of very fine crystal particles are dispersed can be formed by a thermal spraying method.
[0015]
In particular, when at least one of the ceramic fine powders is an oxide ceramic, the formed ceramic composite material has excellent heat shielding properties.
[0016]
In the present invention, it is not necessary for two or more kinds of ceramic fine powders used as raw materials that are not solid-solved with each other to completely dissolve each other. As long as a plurality of types of fine crystals are formed, other elements may be dissolved in a small amount in each crystal.
[0017]
Preferred ceramic fine powder combinations in the present invention include, for example, a combination of Al 2 O 3 and ZrO 2, a combination of Al 2 O 3 and SnO 2, a combination of ZrO 2 and MgO, a combination of ZrO 2 and ThO 2 , etc. A combination of crystalline oxides can be given.
[0018]
The above ceramic fine powder preferably has an average particle size of about 1 μm or less. By using such fine powder, a homogeneous liquid phase can be easily formed by melting in a short time during thermal spraying. The ceramic fine powder may be finely pulverized to a particle size of about 1 μm or less using a jet mill, a bead mill, or the like, if necessary. In the present specification, the average particle diameter is a value obtained by a laser beam diffraction method.
[0019]
In the present invention, it is necessary to granulate two or more kinds of ceramic powders that do not form a solid solution with each other to form a granular powder, which is used as a thermal spray material. By using the granulated granular powder as the thermal spray material, the granulated powder becomes a molten droplet as a whole at the time of thermal spraying, and even if the viscosity of the liquid phase is high, a droplet with a uniform composition is formed. Can do.
[0020]
As a method of granulating ceramic fine powder to produce a granular powder, various known methods such as a spray drying method, a rolling granulation method, and a fluidized bed granulation method can be applied. The average particle size of the granular powder is preferably about 10 to 100 μm. By using a granular powder having a particle size in this range, handling becomes easy, and homogeneous molten droplets can be formed.
[0021]
If the granular powder obtained by granulation has a low bond strength, it may be sintered by heat treatment as necessary. Thereby, it can suppress that granulated powder collapse | disintegrates before a molten droplet is formed at the time of thermal spraying. In this case, as a sintering condition, a condition that the primary particles in the granulated powder are lightly sintered and the granulated powders are not bonded to each other may be selected. The specific sintering conditions depend on the type of powder and cannot be specified unconditionally. For example, in the case of granulated powder composed of alumina fine powder and zirconia fine powder, for example, heat at about 1000 to 1200 ° C. for about 30 minutes. do it.
[0022]
Any thermal spraying method may be used as long as it can form a thermal spray coating on the substrate. The specific method is not particularly limited, and for example, known methods such as a plasma spraying method, a gas combustion flame spraying method, a high-speed flame spraying method, an explosion spraying method, and a line explosion spraying method can be applied. In these thermal spraying methods, a granular raw material is heated to a molten state to form a homogeneous liquid phase, which is sprayed onto the object to be coated and solidified and deposited on its surface, so that a film can be formed. Compared to vapor deposition methods such as PVD, a film can be formed at a higher speed.
[0023]
The atmosphere at the time of thermal spraying can be an inert gas atmosphere (Ar, N 2, etc.), an air atmosphere, or the like depending on the type of ceramic fine powder to be used, the thermal spraying method, the type of substrate, and the like. For example, when non-oxide ceramics are used as the ceramic fine powder, thermal spraying may be performed in an inert gas atmosphere in order to prevent oxidation during thermal spraying.
[0024]
In particular, the plasma spraying method is preferable as the spraying method. According to the plasma spraying method, the raw material is put into a direct current arc plasma jet and melted instantly with the heat of high-temperature plasma, so that the entire granular powder can be completely melted in a short time and a homogeneous melt can be easily obtained. Can be formed. In the plasma spraying method, the melt is accelerated by a high-speed gas jet, sprayed onto the object to be coated, and solidified and deposited on the surface thereof, so that film formation at a very high speed is possible.
[0025]
By spraying molten droplets onto the substrate by a thermal spraying method, the droplets that have collided with the substrate are crushed flat and the substrate is deprived of heat and solidifies instantaneously. At this time, since supercooling occurs and the cooling rate is very high, a large number of crystal nuclei are generated, and solidification is completed with almost no grain growth. In the present invention, since two or more kinds of ceramic fine powders that do not form a solid solution with each other are used as the thermal spray material, the formed film is a ceramic composite material in which a plurality of kinds of very fine crystal particles are dispersed.
[0026]
At this time, the cooling rate is controlled so that a sprayed coating in which very fine crystal particles are dispersed is formed. The particle size of the crystal particles is preferably about 300 nm or less, more preferably about 50 nm or less, and still more preferably about 10 nm or less.
[0027]
Since the specific cooling rate varies depending on the material composition and the type of the substrate, it cannot be specified unconditionally, but when the cooling rate is increased, an amorphous phase is formed without precipitation of fine crystals, and is precipitated when the cooling rate is decreased. Since the crystal diameter is increased, an appropriate cooling rate may be determined according to the material composition or the like so that a fine crystal having a target size is formed. At this time, temperature control may be performed by using a water-cooled jig, blowing compressed air, or the like as necessary.
[0028]
The thermal spray coating formed by the above-described method becomes a material having very low thermal conductivity. The reason for this can be considered as follows.
[0029]
That is, in the thermal spray coating formed by the above-described method, it is considered that the dissimilar crystal grain boundary functions as a phonon (crystal lattice vibration quantum) scattering site when the crystal mismatch is large.
[0030]
The thermal conductivity λ is expressed by the following formula: λ = ρ · Cp · α
(Where, ρ: density, Cp: specific heat, α: thermal diffusivity)
The thermal diffusivity α is expressed by the following formula: α = v s · l p / 3
(Where v s is the speed of sound, and l p is the phonon mean free path). Therefore, if the crystal diameter is made sufficiently small, phonons are scattered at different crystal grain boundaries, and the mean free path can be shortened. According to the method of the present invention, a film in which two or more types of very fine crystal particles are dispersed is formed, so that the thermal diffusivity is decreased, and as a result, the thermal conductivity is also considered to be decreased.
[0031]
In general, it is considered that the hardness and abrasion resistance of the thermal spray coating are improved as the diameter of dispersed particles is smaller. Since the ceramic composite material formed by the method of the present invention has a structure in which fine crystal particles are dispersed, it becomes a film having high strength and excellent toughness.
[0032]
The base material (thermal sprayed body) that serves as a support for the thermal spray coating is not particularly limited as long as thermal spraying is possible. Examples of such a substrate include metals and ceramics which are known sprayed objects. Further, although a cooling operation is required, plastic, cloth, paper, or the like can be used as the support.
[0033]
The specific shape of the sprayed body is not particularly limited, and various forms can be used depending on the application. For example, it can be formed as a thermal barrier coating on the surfaces of turbine parts, jet engine parts and the like used at high temperatures.
[0034]
The composite material according to the present invention can also be formed as a plate-like or sheet-like material by separating the sprayed layer deposited on the flat substrate from the substrate. Alternatively, after spraying a ceramic material in a mold having a shape corresponding to a part having a predetermined shape, the part having a desired shape can be obtained by separating the sprayed layer from the mold.
[0035]
When forming the thermal spray coating on the various base materials described above, if the base material is a metal material, pretreatment such as blasting can be applied to the base material surface as necessary.
[0036]
Further, in order to improve the adhesion between the metal base material and the thermal spray coating, the metal thermal spray coating may be formed on the base material using metal as the thermal spray material before the ceramic thermal spray coating is formed.
[0037]
【The invention's effect】
As described above, in the present invention, since the thermal spraying method is adopted, the film formation speed is very fast, a thick film can be easily formed, and it can be applied to a member having a large area or a complicated shape. is there. In addition, the obtained film has good heat shielding properties, and becomes a film having high strength and excellent toughness.
[0038]
Therefore, according to the present invention, for example, a thermal barrier coating having excellent performance can be easily formed even on relatively large and complicated parts such as turbine parts and jet engine parts.
[0039]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0040]
Example 1
Alumina powder having an average particle diameter of 0.16 μm and zirconia powder having an average particle diameter of 0.042 μm are mixed at a volume ratio of 50:50, and polyvinyl alcohol (PVA) is added as a binder, and water is used as a dispersion medium. A homogeneous slurry was prepared by ball mill mixing. From this slurry, spherical granulated powder having an average secondary particle size of about 30 μm was produced by spray drying.
[0041]
Using this granulated powder, a ceramic film was formed on a carbon steel substrate by plasma spraying. The thermal spraying conditions are as shown in Table 1 below.
[0042]
[Table 1]
When the obtained film was peeled off and measured by powder X-ray diffraction, m-ZrO 2 , t'-ZrO 2 and γ-Al 2 O 3 were produced as crystal phases, and the crystallite size was , Approximately 6 nm, 5 nm, and 8 nm. The results of measuring the thermal diffusivity in the thickness direction of this film at room temperature by the laser flash method are shown in Table 2 below.
[0044]
Example 2
A coating was formed by plasma spraying in the same manner as in Example 1 using alumina powder having an average particle size of 0.16 μm and 3 mol% yttria-stabilized zirconia powder having an average particle size of 0.040 μm.
[0045]
The obtained film has m-ZrO 2 , t'-ZrO 2 , and γ-Al 2 O 3 , although the proportion of the crystal phase is different. The crystallite sizes are about 6 nm and 6 nm, respectively. , 8 nm. The results of measuring the thermal diffusivity in the thickness direction of this film in the same manner as in Example 1 are shown in Table 2 below.
[0046]
Comparative Example 1
Simply mix commercially available alumina powder for plasma spraying (average particle size 19.7μm) and 8wt% yttria-stabilized zirconia powder (325-140 mesh) at a volume ratio of 50:50, and this powder is plasma sprayed Thus, a ceramic composite film was formed. The obtained film was composed of a laminate of flattened particles of t'-ZrO 2 and flattened particles of γ-Al 2 O 3 , and the thickness of the crushed particles was 1 to 3 μm. . The results of measuring the thermal diffusivity in the thickness direction of this film in the same manner as in Example 1 are shown in Table 2 below.
[0047]
[0048]
The thermal conductivity estimated from the thermal diffusivity of Comparative Example 1 is about 2 w / m · K. This value is almost the same as the thermal conductivity of bulk zirconia ceramics, and considering that it contains 50 vol% of alumina with a thermal conductivity of about 30 w / m · K, the alumina- Since zirconia grain boundaries exist, it can be said that the value is very small. In Examples 1 and 2, since the thermal diffusivity is almost half compared to Comparative Example 1, a film with extremely low thermal conductivity may be formed by forming a nano-sized particle-dispersed composite structure. I understand.
Claims (5)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003167002A JP3735671B2 (en) | 2003-06-11 | 2003-06-11 | Method for forming sprayed coating |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003167002A JP3735671B2 (en) | 2003-06-11 | 2003-06-11 | Method for forming sprayed coating |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2005002410A JP2005002410A (en) | 2005-01-06 |
| JP3735671B2 true JP3735671B2 (en) | 2006-01-18 |
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| JP4550613B2 (en) * | 2005-02-21 | 2010-09-22 | 古河電気工業株式会社 | Anisotropic heat conduction material |
| JP4518410B2 (en) * | 2005-03-09 | 2010-08-04 | エボニック デグサ ゲーエムベーハー | Plasma sprayed aluminum oxide layer |
| JP2009120887A (en) * | 2007-11-13 | 2009-06-04 | National Institute Of Advanced Industrial & Technology | Method for producing functional ceramic and functional ceramic produced by the method |
| JP5638765B2 (en) * | 2009-03-25 | 2014-12-10 | ウチヤ・サーモスタット株式会社 | Method for producing deposited film containing nanoparticles |
| JP2011017078A (en) * | 2009-06-10 | 2011-01-27 | Denso Corp | Method for forming thermal splay coating |
| US20110297358A1 (en) * | 2010-06-07 | 2011-12-08 | The Boeing Company | Nano-coating thermal barrier and method for making the same |
| JP5396672B2 (en) | 2012-06-27 | 2014-01-22 | 日本イットリウム株式会社 | Thermal spray material and manufacturing method thereof |
| WO2019017890A1 (en) * | 2017-07-18 | 2019-01-24 | General Electric Company | Freestanding ceramic seal for a gas turbine |
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