JP4385123B2 - High heat resistant silicon nitride sintered body and method for producing the same - Google Patents
High heat resistant silicon nitride sintered body and method for producing the same Download PDFInfo
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims description 129
- 229910052581 Si3N4 Inorganic materials 0.000 title claims description 128
- 238000004519 manufacturing process Methods 0.000 title claims description 21
- 239000002245 particle Substances 0.000 claims description 52
- 239000013078 crystal Substances 0.000 claims description 49
- 238000005245 sintering Methods 0.000 claims description 36
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 23
- 239000002994 raw material Substances 0.000 claims description 18
- 239000000843 powder Substances 0.000 claims description 16
- 238000000465 moulding Methods 0.000 claims description 14
- 239000000203 mixture Substances 0.000 claims description 11
- 239000000377 silicon dioxide Substances 0.000 claims description 11
- 238000002844 melting Methods 0.000 claims description 9
- 230000008018 melting Effects 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 7
- 238000001125 extrusion Methods 0.000 claims description 5
- 238000002425 crystallisation Methods 0.000 claims description 3
- 230000008025 crystallization Effects 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 230000000052 comparative effect Effects 0.000 description 14
- 238000000034 method Methods 0.000 description 13
- 238000010304 firing Methods 0.000 description 10
- 238000012360 testing method Methods 0.000 description 9
- 239000007789 gas Substances 0.000 description 8
- 239000000919 ceramic Substances 0.000 description 7
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 238000005259 measurement Methods 0.000 description 5
- 238000002156 mixing Methods 0.000 description 5
- 239000012299 nitrogen atmosphere Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 239000011230 binding agent Substances 0.000 description 3
- 238000004132 cross linking Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 208000037584 hereditary sensory and autonomic neuropathy Diseases 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000000280 densification Methods 0.000 description 2
- 238000007731 hot pressing Methods 0.000 description 2
- 239000003960 organic solvent Substances 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 238000013001 point bending Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 229910052765 Lutetium Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- -1 as a sintering aid Substances 0.000 description 1
- 239000012752 auxiliary agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000007657 chevron notch test Methods 0.000 description 1
- 238000004581 coalescence Methods 0.000 description 1
- 230000021615 conjugation Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000007606 doctor blade method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- OHSVLFRHMCKCQY-UHFFFAOYSA-N lutetium atom Chemical compound [Lu] OHSVLFRHMCKCQY-UHFFFAOYSA-N 0.000 description 1
- 229910003443 lutetium oxide Inorganic materials 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 239000011268 mixed slurry Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052574 oxide ceramic Inorganic materials 0.000 description 1
- 239000011224 oxide ceramic Substances 0.000 description 1
- MPARYNQUYZOBJM-UHFFFAOYSA-N oxo(oxolutetiooxy)lutetium Chemical compound O=[Lu]O[Lu]=O MPARYNQUYZOBJM-UHFFFAOYSA-N 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 229910021426 porous silicon Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
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- 230000035939 shock Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Description
本発明は、高耐性を有する窒化ケイ素焼結体、特に、高温の環境下でも使用可能な優れた耐熱性、かつ、特定方向において、高強度と高靱性を持つ窒化ケイ素焼結体及びその製造方法に関するものであり、更に詳しくは、シリカとルテチアを焼結助剤とし、窒化ケイ素原料粉末よりも大きな短径を持つアスペクト比が２以上の単結晶β型窒化ケイ素柱状粒子を種結晶として含有し、残部が窒化ケイ素からなる混合物を、種結晶が特定の方向に配向した成形体とし、次いで、焼結することにより作製した高耐熱性窒化ケイ素焼結体及びその製造方法に関するものである。
本発明は、高耐熱性材料として注目されている窒化ケイ素セラミックスの技術分野において、従来、１５００℃の高温での高強度と高破壊エネルギーを両立できる焼結体は開発されていないことを踏まえ、１５００℃の高温において、強度が７００ＭＰａ以上、かつ破壊エネルギーが７００J/ m2以上の窒化ケイ素焼結体を製造し、提供することを可能とする、新しい高耐熱性窒化ケイ素焼結体及びその製造技術を提供するものとして有用である。
本発明は、窒化ケイ素焼結体が有している、高強度、高耐熱性、高耐腐食性、高耐熱衝撃性等の優れた特性を利用して、例えば、高温下で使用する機械部品の構造材料を必要としている分野等において、好適に使用できる部品等、例えば、高温ガスタービンの部品等を提供することを可能とするものであり、特に、１５００℃の高温度での、高強度と高破壊エネルギーを両立する新しい窒化ケイ素系セラミックス素材及びその製造方法を提供するものである。
The present invention relates to a silicon nitride sintered body having high resistance, in particular, excellent heat resistance that can be used even in a high temperature environment, and high strength and toughness in a specific direction, and production thereof. More specifically, it contains silica and lutetia as sintering aids, and contains single crystal β-type silicon nitride columnar particles having a larger minor diameter than the silicon nitride raw material powder with an aspect ratio of 2 or more as seed crystals. In addition, the present invention relates to a high heat-resistant silicon nitride sintered body produced by forming a mixture composed of silicon nitride in the remainder into a molded body in which a seed crystal is oriented in a specific direction, and then sintering it, and a method for producing the same.
In the technical field of silicon nitride ceramics, which has been attracting attention as a high heat-resistant material, the present invention has been based on the fact that a sintered body that can achieve both high strength and high fracture energy at a high temperature of 1500 ° C. has not been developed. New high heat-resistant silicon nitride sintered body capable of producing and providing a silicon nitride sintered body having a strength of 700 MPa or more and a fracture energy of 700 J / m 2 or more at a high temperature of 1500 ° C. and its production It is useful as providing technology.
The present invention utilizes the excellent characteristics such as high strength, high heat resistance, high corrosion resistance, high thermal shock resistance, etc. possessed by the silicon nitride sintered body, for example, mechanical parts used at high temperatures. This makes it possible to provide components that can be suitably used, such as components for high-temperature gas turbines, in particular in fields that require structural materials, particularly high strength at a high temperature of 1500 ° C. And a new silicon nitride ceramic material that achieves both high fracture energy and a method for producing the same.
窒化ケイ素は、酸化物セラミックスと比べて、共有結合性が強く、高温での安定性に優れているため、高温構造材料として有望である。この窒化ケイ素を、特に、高温ガスタービンの部品に使用する場合には、入口の温度を高く設定でき、熱効率の向上が期待されている。しかし、このような窒化ケイ素は、難焼結性であり、従来では、酸化物を焼結助剤として用いることが一般的である。このような焼結助剤を用いた場合、低融点の粒界相が残留することが多い。これらの粒界相の存在は、高温での強度特性の低下をもたらす要因となっている。 Silicon nitride is promising as a high-temperature structural material because it has strong covalent bonding and excellent stability at high temperatures as compared with oxide ceramics. In particular, when this silicon nitride is used for components of a high-temperature gas turbine, the inlet temperature can be set high, and improvement in thermal efficiency is expected. However, such silicon nitride is difficult to sinter, and conventionally, an oxide is generally used as a sintering aid. When such a sintering aid is used, a grain boundary phase having a low melting point often remains. The presence of these grain boundary phases is a factor that causes a decrease in strength characteristics at high temperatures.
また、セラミックスの中では、靱性の高い部類に属する窒化ケイ素セラミックスにおいてさえ、金属材料と比較すると、その破壊靱性は著しく低く、信頼性に欠けるため、利用面での制約となっている。耐熱性の向上のため、添加する焼結助剤量の低減化や粒界の結晶化処理等の検討が従来なされている。また、α-サイアロン、β型サイアロン等のサイアロン基焼結体にすることにより、粒界相を減少させ、特性を向上させる試みもなされている。最近では、ルテチアとシリカを焼結助剤として添加した窒化ケイ素焼結体において、優れた耐熱性が得られるという報告がある（特許文献１）。これは、Luを含有する粒界相は高温においても高粘度であり、かつ、高融点の結晶第二相を形成しやすいことによるものとされている。しかし、このような粒界相の改善のみによる耐熱性の改善には限界がある。 Among ceramics, even silicon nitride ceramics belonging to a class with high toughness are extremely low in fracture toughness and lack of reliability as compared with metal materials, which is a limitation in use. In order to improve heat resistance, studies have been made on reducing the amount of sintering aid to be added and crystallization treatment at grain boundaries. Attempts have also been made to reduce grain boundary phases and improve properties by using sialon-based sintered bodies such as α-sialon and β-sialon. Recently, there has been a report that excellent heat resistance can be obtained in a silicon nitride sintered body to which lutetia and silica are added as sintering aids (Patent Document 1). This is due to the fact that the grain boundary phase containing Lu is highly viscous even at high temperatures and easily forms a high melting point crystalline second phase. However, there is a limit to improving the heat resistance only by improving the grain boundary phase.
一方、窒化ケイ素セラミックスの強度と靱性を改善するために、現在まで、種々の方法が検討されてきた。これらの方法の中でも、特に、窒化ケイ素原料粉末中に、原料粉末よりも大きな短径を持つ単結晶β型窒化ケイ素柱状粒子を、種結晶として０．１〜１０体積％添加し、当該混合物をシート成形、押出し成形等の成形手法を用いて、添加した単結晶β型窒化ケイ素柱状粒子を特定方向に配向させた成形体を作製し、最後に成形体を焼結して得られる窒化ケイ素焼結体が注目されている(特許文献２)。この方法においては、相対密度が９９％以上に緻密化するとともに、種結晶の配向方向に平行な方向に応力を負荷した場合、強度が１１００ＭＰａ以上、かつ破壊靱性が１１ＭＰａ・ｍ1/2以上の窒化ケイ素焼結体を得ることができる。 On the other hand, various methods have been studied so far in order to improve the strength and toughness of silicon nitride ceramics. Among these methods, in particular, 0.1 to 10% by volume of single crystal β-type silicon nitride columnar particles having a larger short diameter than the raw material powder are added as seed crystals to the silicon nitride raw material powder, and the mixture is added. Using a molding method such as sheet molding or extrusion molding, a molded body in which the added single crystal β-type silicon nitride columnar particles are oriented in a specific direction is produced, and finally the sintered body is sintered to obtain silicon nitride Conjugation has attracted attention (Patent Document 2). In this method, when the relative density is densified to 99% or more and the stress is applied in a direction parallel to the orientation direction of the seed crystal, the strength is 1100 MPa or more and the fracture toughness is 11 MPa · m 1/2 or more. A silicon nitride sintered body can be obtained.
また、イッテルビア及び／又はルテチアを１〜２０重量％添加し、当該窒化ケイ素系原料粉末を成型して予備成型体を作製し、当該予備成型体にその一部を拘束した状態で塑性流動を伴う焼結・成型加工を施し、予備成型体の少なくとも一部分に塑性流動を生じさせて焼結成型体各部分の結晶粒の配向方向を、所定の方向に制御することにより、配向組織を有し、１３００℃で曲げ強度６００ＭＰａ以上の、高温強度に優れた窒化ケイ素焼結体も作製されている（特許文献３）。 Also, 1 to 20% by weight of ytterbia and / or lutetia is added, the silicon nitride raw material powder is molded to produce a preform, and plastic flow is accompanied with a part of the preform being restrained. Sintering / molding is performed, plastic flow is generated in at least a part of the preform, and the orientation direction of the crystal grains of each part of the sintered compact is controlled in a predetermined direction, thereby having an orientation structure. A silicon nitride sintered body excellent in high temperature strength having a bending strength of 600 MPa or more at 1300 ° C. has also been produced (Patent Document 3).
しかしながら、従来の上記のような検討にもかかわらず、窒化ケイ素系焼結体の耐熱性や信頼性は未だ十分とはいえない。特に、１５００℃の高温での高強度と高破壊エネルギーを両立できる焼結体は報告されていない。近年、火力発電所におけるガスタービンの高効率化のため、高温で用いられる部材に対してセラミックス化への要求が高くなっているが、高い強度レベルを高温まで維持する材料が望ましい。しかし、上述したように、高温での高強度と高破壊エネルギーの両立の困難さから、ガスタービン部材としての要求性能を満たす窒化ケイ素焼結体が見当らないのが実情である。 However, despite the conventional studies as described above, the heat resistance and reliability of the silicon nitride-based sintered body are still not sufficient. In particular, a sintered body that can achieve both high strength at a high temperature of 1500 ° C. and high fracture energy has not been reported. In recent years, in order to increase the efficiency of gas turbines in thermal power plants, there is a growing demand for ceramics for members used at high temperatures, but materials that maintain high strength levels up to high temperatures are desirable. However, as described above, the fact is that there is no silicon nitride sintered body that satisfies the required performance as a gas turbine member due to the difficulty in achieving both high strength and high fracture energy at high temperatures.
このような状況の中で、本発明者らは、上記従来技術に鑑みて、上記要求に沿う窒化ケイ素焼結体、特に、高温の環境下での使用においても耐えられる、高強度、高破壊エネルギーの窒化ケイ素焼結体を開発することを目標として鋭意研究を積み重ねた結果、高温において、強度が７００ＭＰａ以上、かつ、破壊エネルギーが、７００J/ m2以上の高強度と高靭性を両立する窒化ケイ素焼結体を製造することに成功し、本発明を完成するに至った。
本発明の目的は、１５００℃の高温において、強度が７００ＭＰａ以上、かつ、破壊エネルギーが７００J/m2以上の高強度と高靭性が得られる窒化ケイ素焼結体を提供することにある。
また、本発明の目的は、室温において、強度が７００ＭＰａ以上、かつ、破壊エネルギーが３００J/ m2以上の高強度と高靭性が得られる、窒化ケイ素焼結体を提供することにある。
また、本発明の目的は、窒化ケイ素系セラミックスの結晶粒の配向方向に対して高い強度と、破壊エネルギーを発現する窒化ケイ素焼結体及びその製造方法を提供することにある。
また、本発明の目的は、上記窒化ケイ素焼結体を、そのような優れた機械的特性を生かして、ガスタービン等の高温構造用部品へ適用することにある。
Under such circumstances, in view of the prior art, the present inventors have been able to withstand the use of a silicon nitride sintered body that meets the above-mentioned requirements, particularly in a high-temperature environment, with high strength and high fracture. As a result of intensive research aimed at developing a silicon nitride sintered body with high energy, nitriding that achieves both high strength and high toughness at a high temperature with a strength of 700 MPa or more and a fracture energy of 700 J / m 2 or more. The present inventors have succeeded in producing a silicon sintered body and have completed the present invention.
An object of the present invention is to provide a silicon nitride sintered body capable of obtaining high strength and high toughness with a strength of 700 MPa or more and a fracture energy of 700 J / m 2 or more at a high temperature of 1500 ° C.
Another object of the present invention is to provide a silicon nitride sintered body that can obtain high strength and high toughness with a strength of 700 MPa or more and a fracture energy of 300 J / m 2 or more at room temperature.
Another object of the present invention is to provide a silicon nitride sintered body that exhibits high strength and fracture energy with respect to the orientation direction of crystal grains of silicon nitride ceramics, and a method for producing the same.
Another object of the present invention is to apply the silicon nitride sintered body to a high-temperature structural component such as a gas turbine by taking advantage of such excellent mechanical properties.
上記課題を解決するための本発明は、以下の技術的手段から構成される。
（１）混合物中に、シリカを０．１〜５．０重量％、ルテチアを１．０〜２０．０重量％を焼結助剤として含有し、窒化ケイ素原料粉末よりも大きな短径を持つアスペクト比が少なくとも２の単結晶β型窒化ケイ素柱状粒子を種結晶として０．１〜１０体積％含有し、残部が窒化ケイ素からなる混合物を、単結晶β型窒化ケイ素柱状粒子が特定方向に配向した成形体とした後に焼結した焼結体であって、
焼結助剤が、粒界において高融点の結晶相を形成して粒界相は耐熱性が優れる結晶第二相からなる微構造を有し、かつ、微細な窒化ケイ素粒子中に高アスペクト比で粗大な窒化ケイ素柱状粒子が配向して分散した組織を有すること、
室温において、強度が少なくとも７００ＭＰａ、かつ、破壊エネルギーが少なくとも３００Ｊ／ｍ２、また、１５００℃の高温において、強度が少なくとも７００ＭＰａ、かつ、破壊エネルギーが少なくとも７００Ｊ／ｍ２であること、を特徴とする高強度・高靭性を有する窒化ケイ素焼結体。
（２）焼結助剤が、結晶化することによりＬｕ２ＳｉＯ５、Ｌｕ２Ｓｉ２Ｏ７、Ｌｕ４Ｓｉ２Ｏ７Ｎ２のうち１種以上を形成・含有することを特徴とする前記（１）に記載の窒化ケイ素焼結体。
（３）前記（１）に記載の窒化ケイ素焼結体からなることを特徴とする高温構造用部材。
（４）前記（１）に記載の高強度・高靭性を有する窒化ケイ素焼結体を製造する方法であって、
窒化ケイ素原料と、焼結助剤として、シリカを０．１〜５．０重量％、ルテチアを１．０〜２０．０重量％、種結晶として、窒化ケイ素原料粉末よりも大きな短径を持ち、アスペクト比が少なくとも２の単結晶β型窒化ケイ素柱状粒子を０．１〜１０体積％からなる混合物を、成形して、単結晶β型窒化ケイ素柱状粒子が特定方向に配向した成形体とした後、この成形体を焼結することを特徴とする、高強度・高靭性を有する窒化ケイ素焼結体の製造方法。
（５）焼結体の相対密度が９９％以上になる条件で焼結されることを特徴とする前記（４）に記載の窒化ケイ素焼結体の製造方法。
（６）成形体を、１７００〜２０００℃、１〜２００気圧の窒素中で焼結することを特徴とする前記（５）に記載の窒化ケイ素焼結体の製造方法。
（７）上記混合物を、シート成形、又は押出成形により成形して、単結晶β型窒化ケイ素柱状粒子が特定方向に配向した成形体とすることを特徴とする前記（４）に記載の窒化ケイ素焼結体の製造方法。
The present invention for solving the above-described problems comprises the following technical means.
(1) The mixture contains 0.1 to 5.0% by weight of silica and 1.0 to 20.0% by weight of lutetia as a sintering aid, and has a larger minor diameter than the silicon nitride raw material powder. A mixture of 0.1 to 10% by volume of single-crystal β-type silicon nitride columnar particles having an aspect ratio of at least 2 as a seed crystal and the balance of silicon nitride remaining in a single crystal β-type silicon nitride columnar particle is oriented in a specific direction. A sintered body sintered after being formed into a molded body,
The sintering aid forms a high-melting crystalline phase at the grain boundary, and the grain boundary phase has a microstructure composed of a crystalline second phase with excellent heat resistance, and has a high aspect ratio in fine silicon nitride particles. And having a structure in which coarse silicon nitride columnar particles are oriented and dispersed,
At room temperature, strength of at least 700MPa and also at least 300 J / m 2, is the fracture energy, at a high temperature of 1500 ° C., the strength of at least 700MPa and it breaking energy of at least 700 J / m 2, and wherein Silicon nitride sintered body with high strength and toughness.
( 2 ) The sintering aid is characterized by forming and containing one or more of Lu 2 SiO 5 , Lu 2 Si 2 O 7 and Lu 4 Si 2 O 7 N 2 by crystallization. The silicon nitride sintered body according to (1).
( 3 ) A high-temperature structural member comprising the silicon nitride sintered body according to ( 1) .
( 4 ) A method for producing a silicon nitride sintered body having high strength and high toughness as described in ( 1 ) above,
Silicon nitride raw material, as a sintering aid, 0.1 to 5.0% by weight of silica, 1.0 to 20.0% by weight of lutetia, and as a seed crystal, it has a larger minor diameter than silicon nitride raw material powder. Then, a mixture of 0.1 to 10% by volume of single-crystal β-type silicon nitride columnar particles having an aspect ratio of at least 2 is formed into a formed body in which single-crystal β-type silicon nitride columnar particles are oriented in a specific direction. Thereafter, this molded body is sintered, and a method for producing a silicon nitride sintered body having high strength and high toughness.
( 5 ) The method for producing a silicon nitride sintered body according to ( 4 ), wherein the sintered body is sintered under a condition that the relative density of the sintered body is 99% or more.
( 6 ) The method for producing a silicon nitride sintered body according to ( 5 ), wherein the compact is sintered in nitrogen at 1700 to 2000 ° C. and 1 to 200 atmospheres.
( 7 ) The silicon nitride according to ( 4 ), wherein the mixture is molded by sheet molding or extrusion molding to form a molded body in which single crystal β-type silicon nitride columnar particles are oriented in a specific direction. A method for producing a sintered body.
次に、本発明について更に詳細に説明する。
本発明は、高温において優れた特性を有する窒化ケイ素焼結体及びその焼結・成型加工方法を提供するものである。高温での環境下での使用においても耐えられる窒化ケイ素焼結体を提供するためには、耐熱性の高い焼結体を得ることができる焼結助剤の選択が重要である。そこで、本発明は、好適には、ルテチウム(Ｌu)の酸化物を選択し、また、適量のシリカを加えて、高融点の酸窒化物のみを粒界相とする焼結体を製造することにより耐熱性を付与する方法が採用される。これは、Luを含有する粒界相は、高温においても高粘度であり、かつ、高融点の結晶第二相を形成しやすいことから、耐熱性を得やすいとされているからである。
Next, the present invention will be described in more detail.
The present invention provides a silicon nitride sintered body having excellent characteristics at a high temperature and a sintering / molding method thereof. In order to provide a silicon nitride sintered body that can withstand use even under high-temperature environments, it is important to select a sintering aid that can obtain a sintered body having high heat resistance. Accordingly, the present invention preferably selects a lutetium (Lu) oxide, and adds a suitable amount of silica to produce a sintered body having only a high melting point oxynitride as a grain boundary phase. A method of imparting heat resistance is adopted. This is because the grain boundary phase containing Lu is highly viscous even at a high temperature and easily forms a crystalline second phase having a high melting point, so that heat resistance is easily obtained.
また、本発明では、高強度・高靱性を実現させる方法として、種結晶として、窒化ケイ素原料粉末よりも大きな短径を持ち、アスペクト比が２以上の単結晶β型窒化ケイ素柱状粒子を、０．１〜１０体積％混合し、当該混合物をシート成形、押出し成形等の成形手法を用いて、添加した単結晶β型窒化ケイ素柱状粒子を、特定方向に配向させた成形体を作製し、脱脂後、窒素雰囲気中で焼結を行い、焼結体中に、微細な窒化ケイ素粒子中に高アスペクト比で粗大な窒化ケイ素柱状粒子が配向して分散した組織を有する焼結体とする方法が採用される。このようにして得られた窒化ケイ素焼結体の、結晶粒の配向方向での優れた耐熱性は、高融点の粒界相の形成と柱状結晶粒の配向によって実現される。 In the present invention, as a method for realizing high strength and high toughness, single crystal β-type silicon nitride columnar particles having a larger minor diameter than the silicon nitride raw material powder and having an aspect ratio of 2 or more are used as seed crystals. .1-10% by volume, and using the molding method such as sheet molding, extrusion molding, etc., the mixture is made into a molded body in which the added single crystal β-type silicon nitride columnar particles are oriented in a specific direction, and degreased Thereafter, sintering is performed in a nitrogen atmosphere, and in the sintered body, a sintered body having a structure in which coarse silicon nitride columnar particles with a high aspect ratio are oriented and dispersed in fine silicon nitride particles is obtained. Adopted. The excellent heat resistance in the crystal grain orientation direction of the silicon nitride sintered body thus obtained is realized by the formation of a high melting point grain boundary phase and the orientation of columnar crystal grains.
更に詳しくは、適切な焼結助剤として、ルテチアとシリカ、及び種結晶を混合した窒化ケイ素系原料粉末から混合したスラリーを調製し、かつ、添加した種結晶を、シート成形、あるいは押出成形等の成形手法により配向させることにより、窒化ケイ素の種結晶粒子が一方向に配向して結合した成形体を作製する。得られた成形体を、脱脂後、窒素雰囲気中で、気孔率が１％以下になる焼成条件で焼結する。なお、窒化ケイ素焼結体中の柱状粒子は、短径０．５〜１０μｍ、アスペクト比２〜１００の大きさを持ち、気孔率は１％以下になるようにそれぞれ制御することが、高強度と高靭性を発現させるために必要である。本発明による焼結体では、粒界において高融点の結晶第二相が形成され、かつ、焼結体中に、微細な窒化ケイ素粒子中に高アスペクト比で粗大な窒化ケイ素柱状粒子が配向して分散した組織が形成されていることで、高温においても高強度と高靭性を実現できる。 More specifically, as a suitable sintering aid, a slurry is prepared by mixing from a silicon nitride-based raw material powder in which lutetia and silica and a seed crystal are mixed, and the added seed crystal is formed into a sheet or extruded. Thus, a molded body in which the seed crystal particles of silicon nitride are aligned and bonded in one direction is produced. The obtained molded body is degreased and then sintered in a nitrogen atmosphere under firing conditions where the porosity is 1% or less. The columnar particles in the silicon nitride sintered body have a minor axis of 0.5 to 10 μm, an aspect ratio of 2 to 100, and a porosity controlled to be 1% or less, respectively. And is necessary to develop high toughness. In the sintered body according to the present invention, a crystalline second phase having a high melting point is formed at the grain boundary, and coarse silicon nitride columnar particles with a high aspect ratio are oriented in fine silicon nitride particles in the sintered body. By forming a dispersed structure, high strength and toughness can be realized even at high temperatures.
本発明により高強度窒化ケイ素焼結体を作製するには、まず、窒化ケイ素原料粉末に、所定量の種結晶柱状粒子及び焼結助剤を添加する。窒化ケイ素原料は、α型、β型、あるいは非晶質の、いずれの結晶系のものを用いてもよい。種結晶は、短径０．５〜１０μｍ、アスペクト比２〜１００のものを用いる。焼結助剤としては、焼結後、粒界で高融点の結晶相として残留し、耐熱性の高い焼結体が得られる、ルテチウム酸化物が助剤として用いられる。焼結助剤は、焼結後、粒界において、Ｌｕ2ＳｉＯ5 、Ｌｕ2Ｓｉ2Ｏ7 、Ｌｕ4Ｓｉ2Ｏ7Ｎ２のうち１種以上を有する結晶を形成する。これらの焼結助剤の組み合わせ、添加量は、焼成温度、時間、あるいは焼成時の窒素ガス圧などの焼成条件により異なるが、それぞれの焼成条件において、（１）焼結体の気孔率１％以下である、また、（２）窒化ケイ素柱状粒子が一方向に配向した組織が得られる、ように、選択される。焼結助剤が少ない場合は、成型体の緻密化が実現できず、多孔質の窒化ケイ素となる。焼結助剤が多い場合は、粒界相が増加し、耐熱性が大幅に減少する。
混合物中には、焼結助剤として、シリカを、０．１〜５．０重量％、好ましくは、０．１〜２．０重量％、ルテチアを１．０〜２０．０重量％、好ましくは、２〜１０重量％含有することが必要であるが、これは、上記より少量では緻密化できない。また、上記より多量では高温での耐熱性が低下する理由による。
In order to produce a high-strength silicon nitride sintered body according to the present invention, first, a predetermined amount of seed crystal columnar particles and a sintering aid are added to the silicon nitride raw material powder. The silicon nitride raw material may be any crystal type, α-type, β-type, or amorphous. A seed crystal having a minor axis of 0.5 to 10 μm and an aspect ratio of 2 to 100 is used. As the sintering aid, lutetium oxide is used as the aid, which remains as a crystalline phase having a high melting point at the grain boundary after sintering, thereby obtaining a sintered body having high heat resistance. The sintering aid forms crystals having at least one of Lu 2 SiO 5 , Lu 2 Si 2 O 7 , and Lu 4 Si 2 O 7 N 2 at the grain boundary after sintering. The combination and addition amount of these sintering aids vary depending on firing conditions such as firing temperature, time, or nitrogen gas pressure during firing. Under each firing condition, (1) porosity of sintered body is 1% And (2) selected so that a structure in which the silicon nitride columnar particles are oriented in one direction is obtained. When the sintering aid is small, densification of the molded body cannot be realized, resulting in porous silicon nitride. When there are many sintering aids, the grain boundary phase increases and the heat resistance decreases significantly.
In the mixture, as a sintering aid, silica is 0.1 to 5.0% by weight, preferably 0.1 to 2.0% by weight, and lutetia is 1.0 to 20.0% by weight, preferably It is necessary to contain 2 to 10% by weight, but this cannot be densified with a smaller amount than the above. Further, if the amount is larger than the above, the heat resistance at high temperature is lowered.
また、これらの原料の混合に当たっては、粉体の混合、あるいは混練に用いられる通常の機械を使用することができる。この場合は、湿式、乾式のどちらでもよいが、望ましくは湿式において混合される。湿式混合においては、水、メタノール、エタノール、トルエン等の溶剤が用いられるが、窒化ケイ素の酸化を抑えるために有機溶媒を用いることが望ましい。有機溶媒を用いた場合は、カチオン性セルロース等の分散剤を用いることにより効果的に混合を行うことができる。 Moreover, in mixing these raw materials, a normal machine used for mixing or kneading powder can be used. In this case, either a wet method or a dry method may be used. In the wet mixing, a solvent such as water, methanol, ethanol, or toluene is used, but it is desirable to use an organic solvent in order to suppress oxidation of silicon nitride. When an organic solvent is used, mixing can be performed effectively by using a dispersant such as cationic cellulose.
次に、この様にして得られた混合粉末に、種結晶として単結晶β型窒化ケイ素柱状粒子を０．１〜１０体積％、望ましくは１〜５体積％添加する。添加量が０．１体積％以下では、結晶体中に十分な柱状粒子群を導入することができない。一方、１０体積％以上においては、添加した種結晶が焼結を阻害し、緻密な焼結体が得られないばかりでなく、ホットプレス等の加圧焼結により緻密体を作製しても、種結晶から成長した柱状粒子群が互いに合体し、潜在欠陥サイズを増大させるため高強度の焼結体を得ることはできない。従って、種結晶の添加量は０．１〜１０体積％である。また、種結晶の形状は短径については、用いた窒化ケイ素原料粉末の平均粒径より大きく、アスペクト比が２以上であることが望ましい。種結晶の短径が原料の平均粒径より小さいと焼成中に助剤中に溶解するため、種結晶としての役目を果たさない。一方、アスペクト比が２以下の場合は、シート成形等において、種結晶を十分に配向させることができず、無秩序に成長した柱状粒子間の合体が生じ、得られた焼結体の特性は低下する。 Next, 0.1 to 10% by volume, preferably 1 to 5% by volume of single crystal β-type silicon nitride columnar particles are added as seed crystals to the mixed powder thus obtained. When the addition amount is 0.1% by volume or less, sufficient columnar particle groups cannot be introduced into the crystal. On the other hand, at 10% by volume or more, not only does the added seed crystal inhibit sintering, but a dense sintered body cannot be obtained, and even if a dense body is produced by pressure sintering such as hot pressing, Since the columnar particle groups grown from the seed crystals are united with each other and the latent defect size is increased, a high-strength sintered body cannot be obtained. Therefore, the addition amount of the seed crystal is 0.1 to 10% by volume. Moreover, the shape of the seed crystal is preferably larger than the average particle diameter of the used silicon nitride raw material powder and has an aspect ratio of 2 or more with respect to the minor axis. If the minor axis of the seed crystal is smaller than the average particle diameter of the raw material, it dissolves in the auxiliary agent during firing, so that it does not serve as a seed crystal. On the other hand, when the aspect ratio is 2 or less, the seed crystals cannot be sufficiently oriented in sheet molding or the like, and coalescence between the randomly grown columnar particles occurs, and the properties of the obtained sintered body deteriorate. To do.
次に、上述のようにして得られた混合スラリーは、適量の有機バインダーを添加混合した後、種結晶を配向させるために、ドクターブレード法等によるシート成形、あるいは押出し成形を用いて生成形体に成形される。特に、シート成形を行った場合は、所定の厚みを得るために成形後に、加熱圧着あるいは室温での圧着が行なわれる。 Next, the mixed slurry obtained as described above is added to and mixed with an appropriate amount of an organic binder, and then, in order to orient the seed crystal, it is formed into a generated shape by using a sheet molding by a doctor blade method or the like, or an extrusion molding. Molded. In particular, when sheet forming is performed, heat pressing or pressure bonding at room temperature is performed after forming to obtain a predetermined thickness.
次に、前記成形体は、通常の焼成方法、すなわち、まず、３００〜１０００℃程度の温度で仮焼を行い、成形バインダーを加熱除去した後、１７００〜２０００℃の温度、１〜２００気圧の窒素中で焼成することにより緻密化される。この際、高強度・高靱性を発現するために、相対密度９９％以上に緻密化し、更に、種結晶からβ型窒化ケイ素柱状粒子を十分に発達させることが重要である。本発明の窒化ケイ素焼結体は、好適には、通常の常圧焼成、あるいはガス圧焼成において緻密化されることを特徴とするが、例えば、ホットプレス、ＨＩＰにより緻密化を行うこともできる。 Next, the molded body is subjected to a normal firing method, that is, first, calcined at a temperature of about 300 to 1000 ° C., and the molded binder is removed by heating, and then the temperature of 1700 to 2000 ° C. and 1 to 200 atm. Densification is achieved by firing in nitrogen. At this time, in order to develop high strength and high toughness, it is important to make the relative density 99% or higher and to sufficiently develop β-type silicon nitride columnar particles from the seed crystal. The silicon nitride sintered body of the present invention is preferably characterized in that it is densified by ordinary normal pressure firing or gas pressure firing, but can be densified by, for example, hot pressing or HIP. .
このようにして得られた、本発明の窒化ケイ素焼結体は、柱状粒子が一方向に配向し、かつ、その粒界相は耐熱性が優れる結晶第二相からなる微構造を有する。そのため、これら二つの要素の組み合わせの結果、粒子の配向方向に対して高い強度と破壊エネルギーを発現することだけではなく、１５００℃の高温でもその強度はほとんど低下せず、かつ、破壊エネルギーが飛躍的に増大することが判明した。本発明によれば、柱状粒子の配向方向に応力を負荷した場合、室温において強度が７００ＭＰａ以上、かつ、破壊エネルギーが３００J/ m2 以上、また、１５００℃の高温において、強度が７００ＭＰａ以上、かつ、破壊エネルギーが７００J/ m2以上の特性を持つ焼結体が得られ、高温構造用部品としての使用に好適である。 The silicon nitride sintered body of the present invention thus obtained has a microstructure in which columnar particles are oriented in one direction and the grain boundary phase is composed of a crystalline second phase having excellent heat resistance. Therefore, as a result of the combination of these two elements, not only high strength and breaking energy are expressed in the orientation direction of the particles, but also the strength hardly decreases even at a high temperature of 1500 ° C., and the breaking energy jumps. Was found to increase. According to the present invention, when stress is applied in the orientation direction of the columnar particles, the strength is 700 MPa or more at room temperature, the fracture energy is 300 J / m 2 or more, and the strength is 700 MPa or more at a high temperature of 1500 ° C. In addition, a sintered body having a characteristic with a fracture energy of 700 J / m 2 or more is obtained, which is suitable for use as a high-temperature structural component.
本発明により、（１）高強度と高破壊エネルギーを両立する窒化ケイ素焼結体を製造することができる、（２）室温において、強度が７００ＭＰａ以上、かつ破壊エネルギーが３００J/ m2 以上の高強度と高靭性を持つ窒化ケイ素焼結体が得られる、（３）１５００℃の高温において、強度が７００ＭＰａ以上、かつ破壊エネルギーが７００J/m2以上の高強度と高靭性を持つ窒化ケイ素焼結体が得られる、（４）窒化ケイ素セラミックスの結晶粒の配向方向に対して、高い強度と、破壊エネルギーを発現することができる、（５）この窒化ケイ素焼結体は、そのような優れた機械的特性を生かして、ガスタービン等の高温構造用部品への適用に好適である、という効果が奏される。 According to the present invention, (1) a silicon nitride sintered body having both high strength and high fracture energy can be produced. (2) At room temperature, the strength is 700 MPa or more and the fracture energy is 300 J / m 2 or more. A silicon nitride sintered body having strength and high toughness can be obtained. (3) Sintered silicon nitride having high strength and high toughness at a high temperature of 1500 ° C. with a strength of 700 MPa or more and a fracture energy of 700 J / m 2 or more. (4) It can exhibit high strength and fracture energy with respect to the orientation direction of the crystal grains of silicon nitride ceramics. (5) This silicon nitride sintered body has such excellent properties. By taking advantage of the mechanical characteristics, there is an effect that it is suitable for application to a high-temperature structural component such as a gas turbine.
次に、実施例に基づいて本発明を具体的に説明するが、本発明は、当該実施例によって何ら限定されるものではない。 Next, the present invention will be specifically described based on examples, but the present invention is not limited to the examples.
（１）焼結体の作製
α型窒化ケイ素粉末（宇部ＳＮ−Ｅ１０、α含有量９５ｗｔ％以上）に、３ｗｔ％のβ型窒化ケイ素柱状粒子（短径１μｍ、アスペクト比３０）を添加し、更に、焼結助剤として９ｗｔ％のルテチアと１ｗｔ％のシリカを添加し、トルエン／ブタノール混合液（４／１）をバインダーとともに混合してスラリーにした。このスラリーを用いて、シート成形により、厚さ１００μｍの緻密層用のテープを製造した。このテープ成型法の概略を図1に示す。
(1) Production of sintered body To α-type silicon nitride powder (Ube SN-E10, α content of 95 wt% or more), 3 wt% β-type silicon nitride columnar particles (short diameter 1 μm, aspect ratio 30) were added, Further, 9 wt% lutetia and 1 wt% silica were added as sintering aids, and a toluene / butanol mixed solution (4/1) was mixed with a binder to form a slurry. Using this slurry, a tape for a dense layer having a thickness of 100 μm was produced by sheet molding. An outline of this tape molding method is shown in FIG.
（２）積層体の作製と焼結
作製したテープを計１００枚積層し、圧着して、積層体を作製した。この成形体をＣＩＰ処理後、脱脂し、更に、窒素雰囲気１０気圧中で、１９５０℃、６時間焼結を行った。
(2) Production of laminate and sintering A total of 100 tapes produced by sintering were laminated and pressure-bonded to produce a laminate. This molded body was degreased after CIP treatment, and further sintered at 1950 ° C. for 6 hours in a nitrogen atmosphere of 10 atm.
（３）特性の評価
得られた窒化ケイ素焼結体の強度を、幅３ｍｍ、厚み２ｍｍ、長さ２０ｍｍの試験片で、スパン長さ１６ｍｍの３点曲げ試験により調べた。また、破壊エネルギーの測定のために、図２に示したような、シェブロン型ノッチを導入した試験片を用い評価した。この試験法は、試験片のノッチの形状により、き裂進展が、巨視的にみれば、モードＩのき裂に拘束されるため、き裂が途中で柱状粒子の配向方向に偏向することがなく、再現性のある正確な評価ができる特徴がある。曲げ試験片は、引張り応力方向がキャスティング方向に平行で、かつ、応力面が積層面になるように切り出し、０．１ｍｍ幅のノッチを導入し、スパンの長さを３０ｍｍとし、０．０１ｍｍ/分の変位速度で３点曲げ試験を行った。
(3) Evaluation of characteristics The strength of the obtained silicon nitride sintered body was examined by a 3-point bending test with a span length of 16 mm using a test piece having a width of 3 mm, a thickness of 2 mm, and a length of 20 mm. Further, for the measurement of fracture energy, evaluation was performed using a test piece having a chevron-type notch as shown in FIG. In this test method, crack growth is restrained by mode I cracks when viewed macroscopically due to the notch shape of the test piece, so that the cracks may be deflected in the direction of columnar particles in the middle. There is also a feature that enables accurate evaluation with reproducibility. The bending test piece was cut out so that the tensile stress direction was parallel to the casting direction and the stress surface was a laminated surface, a 0.1 mm wide notch was introduced, the span length was 30 mm, and 0.01 mm / A three-point bending test was performed at a displacement rate of minutes.
（４）焼結体の構造
得られた窒化ケイ素焼結体について、図１の観察方向（ａ）及び（ｂ）から観察した組織写真を、図３及び４に、示す。それによると、高アスペクト比の柱状粒子が成長しており、それらの粒子は、成型時のキャスティング方向に配向していた。
(4) Structure of sintered body FIGS. 3 and 4 show structural photographs of the obtained silicon nitride sintered body observed from the observation directions (a) and (b) of FIG. According to this, high-aspect-ratio columnar particles were grown, and these particles were oriented in the casting direction during molding.
比較例１
（１）焼結体の作製
実施例１と同じα型窒化ケイ素粉末に、焼結助剤として、９ｗｔ％のルテチアと１ｗｔ％のシリカを加え、実施例１と同様にテープを作製した。作製したテープを計１００枚積層し、圧着して、積層体を作製した。この成形体を、ＣＩＰ処理後、脱脂し、更に、窒素雰囲気１０気圧中で、１９５０℃、６時間焼結を行った。
Comparative Example 1
(1) Production of sintered body To the same α-type silicon nitride powder as in Example 1, 9 wt% lutezia and 1 wt% silica were added as a sintering aid, and a tape was produced in the same manner as in Example 1. A total of 100 produced tapes were laminated and pressure-bonded to produce a laminate. This molded body was degreased after CIP treatment, and further sintered at 1950 ° C. for 6 hours in a nitrogen atmosphere of 10 atm.
（２）焼結体の構造
図５に、得られた窒化ケイ素焼結体断面の研磨エッチング写真を示す。それによると、α型窒化ケイ素を原料とした場合には、粒子の配向は存在せず、従来の窒化ケイ素焼結体と同様であった。
(2) Structure of sintered body FIG. 5 shows a polishing etching photograph of a cross section of the obtained silicon nitride sintered body. According to this, when α-type silicon nitride was used as a raw material, there was no particle orientation, which was the same as that of a conventional silicon nitride sintered body.
〔実施例及び比較例の窒化ケイ素焼結体の特性データ〕
実施例１の窒化ケイ素焼結体と、比較例１の窒化ケイ素焼結体の、強度及び破壊エネルギーの平均値と標準偏差を表１に示す。一条件下での試験片本数は、強度測定が４本、破壊エネルギー測定が３本であり、実施例１では、配向方向に平行に応力を負荷した。表１の記載から明らかなように、室温では、実施例１の窒化ケイ素は、強度が７００ＭＰａ以上で、比較例１の窒化ケイ素の強度と同程度であるが、破壊エネルギーは約３００J/ m2 であり、比較例１の窒化ケイ素の約３倍程度と非常に大きくなっていた。また、１５００℃の高温では、比較例１の窒化ケイ素は強度が低下するのに対して、実施例１では強度の低下は見られず、また、破壊エネルギーは、比較例１の約４５０J/m2に対して、実施例１では約７８０J/ m2となり、比較例１のほぼ２倍と非常に大きくなっていた。これは、本発明により、高温で、高い強度と、高い靱性がともに発現していることを示すものである。
[Characteristic data of silicon nitride sintered bodies of Examples and Comparative Examples]
Table 1 shows the average values and standard deviations of strength and fracture energy of the silicon nitride sintered body of Example 1 and the silicon nitride sintered body of Comparative Example 1. The number of test specimens under one condition was four for strength measurement and three for measurement of fracture energy. In Example 1, stress was applied parallel to the orientation direction. As is apparent from the description in Table 1, at room temperature, the silicon nitride of Example 1 has a strength of 700 MPa or more, which is similar to the strength of silicon nitride of Comparative Example 1, but the fracture energy is about 300 J / m 2. And about 3 times as large as the silicon nitride of Comparative Example 1. Further, at a high temperature of 1500 ° C., the strength of the silicon nitride of Comparative Example 1 decreases, whereas the strength of Example 1 does not decrease, and the fracture energy is about 450 J / m of Comparative Example 1. On the other hand, in Example 1, it was about 780 J / m 2 , which was almost twice as large as that in Comparative Example 1. This indicates that the present invention exhibits both high strength and high toughness at high temperatures.
図６及び図７に、室温と１５００℃での破壊試験後の破断面の写真を示す。引き抜けた柱状粒子の突出と柱状粒子が引き抜けた孔が観察され、これらの柱状粒子の架橋及び引き抜き効果により、高強度と高靭性が発現した。特に、実施例１の窒化ケイ素では、配向している柱状粒子が粗大であるため、架橋及び引き抜け時に柱状粒子の破壊が起こらないため、大きな架橋及び引き抜き効果が発現し、高強度と高靭性が得られた。更に、柱状粒子が、配向した方向に直角に応力を負荷した場合でも、室温で５５６ＭＰａ（標準偏差６４ＭＰａ）、１５００℃の高温において４６３ＭＰａ（標準偏差２７ＭＰａ）の比較的優れた強度を示した。尚、表１は、実施例１と比較例１の窒化ケイ素焼結体の強度及び破壊エネルギー（ ）内は標準偏差を示す。 6 and 7 show photographs of the fracture surface after a destructive test at room temperature and 1500 ° C. The protruding columnar particles and the holes from which the columnar particles were pulled out were observed, and high strength and high toughness were expressed by the crosslinking and extraction effect of these columnar particles. In particular, in the silicon nitride of Example 1, since the oriented columnar particles are coarse, the columnar particles do not break at the time of crosslinking and pulling out, so that a large crosslinking and pulling effect is exhibited, and high strength and high toughness are exhibited. was gotten. Further, even when the columnar particles were stressed at right angles to the oriented direction, they exhibited a relatively excellent strength of 556 MPa (standard deviation of 64 MPa) at room temperature and 463 MPa (standard deviation of 27 MPa) at a high temperature of 1500 ° C. Table 1 shows the standard deviation in the strength and fracture energy () of the silicon nitride sintered bodies of Example 1 and Comparative Example 1 .
比較例２
実施例１と同じα型粉末に、焼結剤として、９ｗｔ％のイッテルビア（Ｙｂ２Ｏ３）と、１ｗｔ％のシリカ（Ｓｉ０２）を加え、種結晶として、３ｗｔ％のβ型窒化ケイ素柱状粒子を加え、実施例１と同様にテープを作製した。作製したテープを、計１００枚積層し、圧着して、積層体を作製した。この成形体を、ＣＩＰ処理後、脱脂し、更に、窒素雰囲気１０気圧中で、１９５０℃、６時間焼結を行った。
実施例１の窒化ケイ素焼結体と、比較例２の窒化ケイ素焼結体の、強度及び破壊エネルギーの平均値と標準偏差を表２に示す。
一条件下での試験本数は、強度測定が４本、破壊エネルギー測定が３本であり、実施例１及び比較例２では、配向方向に平行に応力を負荷した。表２より、比較例２の窒化ケイ素は、室温強度は実施例１の窒化ケイ素より優れるが、１５００℃においては、大きく強度低下していることが分かる。また、破壊エネルギーは、室温、１５００℃ともに実施例１に劣っていた。これは、本発明により、高温で、高い強度と、高い靭性がともに発現していることを示すものである。
Comparative Example 2
9 wt% ytterbia (Yb 2 O 3 ) and 1 wt% silica (SiO 2 ) are added to the same α-type powder as in Example 1 as a sintering agent, and 3 wt% β-type silicon nitride pillars are used as seed crystals. Particles were added, and a tape was produced in the same manner as in Example 1. A total of 100 of the produced tapes were laminated and pressure-bonded to produce a laminate. This molded body was degreased after CIP treatment, and further sintered at 1950 ° C. for 6 hours in a nitrogen atmosphere of 10 atm.
Table 2 shows the average values and standard deviations of strength and fracture energy of the silicon nitride sintered body of Example 1 and the silicon nitride sintered body of Comparative Example 2.
The number of tests under one condition is 4 for strength measurement and 3 for measurement of fracture energy. In Example 1 and Comparative Example 2, stress was applied in parallel to the orientation direction. From Table 2, it can be seen that the silicon nitride of Comparative Example 2 has a room temperature strength superior to that of Example 1, but the strength is greatly reduced at 1500 ° C. The breaking energy was inferior to that of Example 1 at both room temperature and 1500 ° C. This indicates that the present invention exhibits both high strength and high toughness at high temperatures.
以上詳述したように、本発明は、高耐熱性窒化ケイ素焼結体及びその製造方法に係るものであり、本発明により、特に、高温の環境下でも使用可能な優れた耐熱性、かつ、特定方向において高強度と高靭性を持つ窒化ケイ素焼結体及びその製造方法を提供できる。本発明の窒化ケイ素焼結体は、柱状粒子が一方向に配向し、かつ、その粒界相は耐熱性が優れる結晶第二相からなる微構造を有する。そのため、これら二つの要素の組み合わせの結果、粒子の配向方向に対して高い強度と破壊エネルギーを発現することだけではなく、１５００℃の高温でもその強度はほとんど低下せず、かつ、破壊エネルギーが飛躍的に増大する。本発明によれば、柱状粒子の配向方向に応力を負荷した場合、室温において強度が７００ＭＰａ以上、かつ、破壊エネルギーが３００J/ m2 以上、また、１５００℃の高温において、強度が７００ＭＰａ以上、かつ、破壊エネルギーが７００J/ m2以上の特性を持つ焼結体が得られ、この材料は、高温構造用部品、例えば、高温ガスタービン部品等としての使用に好適である。 As described above in detail, the present invention relates to a high heat-resistant silicon nitride sintered body and a method for producing the same, and according to the present invention, in particular, excellent heat resistance that can be used even in a high-temperature environment, and A silicon nitride sintered body having high strength and high toughness in a specific direction and a method for producing the same can be provided. In the silicon nitride sintered body of the present invention, the columnar particles are oriented in one direction, and the grain boundary phase has a microstructure composed of a crystalline second phase having excellent heat resistance. Therefore, as a result of the combination of these two elements, not only high strength and breaking energy are expressed in the orientation direction of the particles, but also the strength hardly decreases even at a high temperature of 1500 ° C., and the breaking energy jumps. Increase. According to the present invention, when stress is applied in the orientation direction of the columnar particles, the strength is 700 MPa or more at room temperature, the fracture energy is 300 J / m 2 or more, and the strength is 700 MPa or more at a high temperature of 1500 ° C. Thus, a sintered body having a characteristic of fracture energy of 700 J / m 2 or more is obtained, and this material is suitable for use as a high-temperature structural component such as a high-temperature gas turbine component.
Claims (7)
焼結助剤が、粒界において高融点の結晶相を形成して粒界相は耐熱性が優れる結晶第二相からなる微構造を有し、かつ、微細な窒化ケイ素粒子中に高アスペクト比で粗大な窒化ケイ素柱状粒子が配向して分散した組織を有すること、
室温において、強度が少なくとも７００ＭＰａ、かつ、破壊エネルギーが少なくとも３００Ｊ／ｍ２、また、１５００℃の高温において、強度が少なくとも７００ＭＰａ、かつ、破壊エネルギーが少なくとも７００Ｊ／ｍ２であること、を特徴とする高強度・高靭性を有する窒化ケイ素焼結体。 The mixture contains 0.1 to 5.0% by weight of silica and 1.0 to 20.0% by weight of lutetia as a sintering aid, and has an aspect ratio that has a larger minor diameter than the silicon nitride raw material powder. A compact comprising 0.1 to 10% by volume of at least two single crystal β-type silicon nitride columnar particles as seed crystals and the balance of silicon nitride being the balance, wherein the single crystal β-type silicon nitride columnar particles are oriented in a specific direction. A sintered body sintered after
The sintering aid forms a crystalline phase with a high melting point at the grain boundary, and the grain boundary phase has a microstructure consisting of a crystalline second phase with excellent heat resistance, and has a high aspect ratio in fine silicon nitride particles. And having a structure in which coarse silicon nitride columnar particles are oriented and dispersed,
At room temperature, strength of at least 700MPa and also at least 300 J / m 2, is the fracture energy, at a high temperature of 1500 ° C., the strength of at least 700MPa and it breaking energy of at least 700 J / m 2, and wherein Silicon nitride sintered body with high strength and toughness.
窒化ケイ素原料と、焼結助剤として、シリカを０．１〜５．０重量％、ルテチアを１．０〜２０．０重量％、種結晶として、窒化ケイ素原料粉末よりも大きな短径を持ち、アスペクト比が少なくとも２の単結晶β型窒化ケイ素柱状粒子を０．１〜１０体積％からなる混合物を、成形して、単結晶β型窒化ケイ素柱状粒子が特定方向に配向した成形体とした後、この成形体を焼結することを特徴とする、高強度・高靭性を有する窒化ケイ素焼結体の製造方法。 A method for producing a silicon nitride sintered body having high strength and toughness according to claim 1 ,
Silicon nitride raw material, as a sintering aid, 0.1 to 5.0% by weight of silica, 1.0 to 20.0% by weight of lutetia, and as a seed crystal, it has a larger minor diameter than silicon nitride raw material powder. Then, a mixture of 0.1 to 10% by volume of single-crystal β-type silicon nitride columnar particles having an aspect ratio of at least 2 is formed into a formed body in which single-crystal β-type silicon nitride columnar particles are oriented in a specific direction. Then, the method for producing a silicon nitride sintered body having high strength and high toughness, characterized in that the molded body is sintered.
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