JP3236733B2 - Silicon nitride sintered body - Google Patents
Silicon nitride sintered bodyInfo
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- JP3236733B2 JP3236733B2 JP11840994A JP11840994A JP3236733B2 JP 3236733 B2 JP3236733 B2 JP 3236733B2 JP 11840994 A JP11840994 A JP 11840994A JP 11840994 A JP11840994 A JP 11840994A JP 3236733 B2 JP3236733 B2 JP 3236733B2
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- Prior art keywords
- sintered body
- phase
- silicon nitride
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Description
【０００１】[0001]
【産業上の利用分野】本発明は、室温から高温までの強
度特性に優れるとともに耐クリープ性に優れ、特にピス
トン、シリンダー、バルブ、カムローラ、ロッカーアー
ム、ピストンリング、ピストンピンなどの自動車用部品
や、タービンロータ、タービンブレード、ノズル、コン
バスタ、スクロール、ノズルサポート、シールリング、
スプリングリング、ディフューザ、ダクトなどのガスタ
−ビンエンジン用部品等に好適に使用される窒化珪素質
焼結体に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent strength characteristics from room temperature to high temperature and also has excellent creep resistance. In particular, the present invention relates to automotive parts such as pistons, cylinders, valves, cam rollers, rocker arms, piston rings, piston pins and the like. , Turbine rotor, turbine blade, nozzle, combustor, scroll, nozzle support, seal ring,
The present invention relates to a silicon nitride sintered body suitably used for a gas turbine engine component such as a spring ring, a diffuser, and a duct.
【０００２】[0002]
【従来技術】従来から、窒化珪素質焼結体は、耐熱性、
耐熱衝撃性、および耐酸化特性に優れることからエンジ
ニアリングセラミックス、特にタ−ボロ−タ−等の熱機
関用として応用が進められている。この窒化珪素質焼結
体は、一般には窒化珪素に対してＹ2 Ｏ3 、Ａｌ2 Ｏ3
あるいはＭｇＯなどの焼結助剤を添加することにより高
密度で高強度の特性が得られている。このような窒化珪
素質焼結体に対しては、さらにその使用条件が高温化す
るに際して、高温における強度および耐酸化特性のさら
なる改善が求められている。かかる要求に対して、これ
まで焼結助剤の検討や焼成条件等を改善する等各種の改
良が試みられている。2. Description of the Related Art Conventionally, a silicon nitride sintered body has been known to have heat resistance,
Because of its excellent thermal shock resistance and oxidation resistance, it is being applied to engineering ceramics, especially for heat engines such as turbo rotators. This silicon nitride sintered body is generally made of Y 2 O 3 , Al 2 O 3
Alternatively, by adding a sintering aid such as MgO, high density and high strength characteristics are obtained. As such silicon nitride sintered bodies are required to be further improved in strength and oxidation resistance at high temperatures when their use conditions are further increased. In response to such demands, various improvements have been attempted, for example, by studying sintering aids and improving firing conditions.
【０００３】その中で、従来より焼結助剤として用いら
れてきたＡｌ2 Ｏ3 、ＭｇＯ等の酸化物が高温特性を劣
化させるという見地から、窒化珪素に対してＹ2 Ｏ3 等
の周期律表第３ａ族元素（ＲＥ）および酸化珪素からな
る単純な３元系（Ｓｉ3 Ｎ4−ＳｉＯ2 −ＲＥ2 Ｏ3 ）
の組成からなる焼結体において、その焼結体の粒界にＳ
ｉ−ＲＥ−Ｏ−ＮからなるＹＡＭ相、アパタイト相、シ
リコンオキシナイトライド相等の結晶相を析出させるこ
とにより粒界の高融点化および安定化を図ることが提案
されている。例えば、特開昭６３−１０００６７号で
は、Ｙ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕのうちの２種以上の希
土類元素を含む焼結体で、粒界にアパタイト構造の結晶
相が形成された窒化珪素質焼結体が提案されている。Among them, from the viewpoint that oxides such as Al 2 O 3 and MgO, which have been conventionally used as sintering aids, deteriorate the high-temperature characteristics, the period of silicon nitride, such as Y 2 O 3 Simple ternary system (Si 3 N 4 —SiO 2 —RE 2 O 3 ) composed of Group 3a element (RE) and silicon oxide
In the sintered body having the composition of
It has been proposed to increase the melting point and stabilize the grain boundaries by precipitating a crystal phase such as a YAM phase, an apatite phase, and a silicon oxynitride phase composed of i-RE-ON. For example, Japanese Patent Application Laid-Open No. 63-1000067 discloses a silicon nitride having a crystalline phase having an apatite structure at grain boundaries formed of a sintered body containing two or more rare earth elements of Y, Er, Tm, Yb, and Lu. Quality sintered bodies have been proposed.
【０００４】[0004]
【発明が解決しようとする問題点】従来より提案されて
いる各種の希土類元素を含む焼結体をガスタービンや自
動車部品に実際に使用した場合、高温状態で高負荷が付
与された状態で長時間曝される場合があるが、この時、
焼結体が徐々に変形する、いわゆるクリープが発生する
という問題もあった。このようなクリープ変形が生じる
ことは、仮に高強度であっても実用化を阻害する大きな
要因となっていた。Problems to be Solved by the Invention When a conventionally proposed sintered body containing various rare earth elements is actually used for a gas turbine or an automobile part, the sintered body may be long under a high temperature and a high load. You may be exposed for a time,
There is also a problem that the sintered body is gradually deformed, so-called creep occurs. The occurrence of such creep deformation has been a major factor impeding practical application even if the strength is high.
【０００５】また、特開昭６３−１０００６７号は、ア
パタイト相を５０％以上析出させ、高温強度を向上させ
ているが、アパタイト相が多いと耐酸化性が低下すると
いう問題があった。耐酸化性を向上させるためにはシリ
コンオキシナイトライド（Ｓｉ2 Ｎ2 Ｏ）を多く析出さ
せると耐酸化性は良好であるが、破壊靱性値が低下した
り、焼成中に焼結体の表面から数ｍｍの外周部でシリコ
ンオキシナイトライドが分解し表面の粗れ、色調差が生
じるなどの問題があった。In Japanese Patent Application Laid-Open No. 63-1000067, the apatite phase is precipitated in an amount of 50% or more to improve the high-temperature strength. However, when the apatite phase is large, the oxidation resistance is lowered. If silicon oxynitride (Si 2 N 2 O) is precipitated in a large amount to improve the oxidation resistance, the oxidation resistance is good, but the fracture toughness value decreases, and the surface of the sintered body during firing is reduced. There is a problem that silicon oxynitride is decomposed at the outer peripheral portion of a few mm to roughen the surface and a color tone difference occurs.
【０００６】よって、本発明は、室温から高温まで十分
な高温強度と高温耐酸化性を有するとともに１５００℃
での耐クリープ特性に優れ、さらには破壊靱性が高く、
焼結体外周において分解相などが生じない窒化珪素質焼
結体を提供することを目的とするものである。Accordingly, the present invention has sufficient high-temperature strength and high-temperature oxidation resistance from room temperature to high
Excellent creep resistance and high fracture toughness,
It is an object of the present invention to provide a silicon nitride-based sintered body in which a decomposition phase or the like does not occur on the outer periphery of the sintered body.
【０００７】[0007]
【問題点を解決するための手段】本発明者等は、上述し
たように焼結体の高温強度や耐酸化性、耐クリープ性を
左右する要因として、用いる周期律表第３ａ族元素酸化
物の種類とその粒界の結晶相の種類が重要であるという
知見を得、これに基づき検討を重ねた結果、周期律表第
３ａ族元素として、少なくともＬｕを選択すること、焼
結体中の不純物的酸素と周期律表第３ａ族元素との比率
が特定の範囲にあること、焼結体の粒界にダイシリケー
ト相およびモノシリケート相が存在することにより上記
目的が達成されることを見いだし本発明に至った。As described above, the present inventors have determined that the oxides of Group 3a element of the periodic table used as factors affecting the high-temperature strength, oxidation resistance and creep resistance of a sintered body. That the type of and the type of crystal phase at the grain boundary are important, and as a result of repeated investigations based on this finding, it was determined that at least Lu was selected as a Group 3a element of the periodic table, It has been found that the above-mentioned object is achieved by the fact that the ratio of impurity oxygen to the element of Group 3a of the periodic table is in a specific range, and the presence of a disilicate phase and a monosilicate phase at the grain boundaries of the sintered body. The present invention has been reached.
【０００８】即ち、本発明の窒化珪素質焼結体は、窒化
珪素を主体とし、少なくともＬｕを含む周期律表第３ａ
族元素および不純物的酸素を含む焼結体であって、前記
周期律表第３ａ族元素が酸化物換算で全量中１〜１０モ
ル％の割合で含有されるとともに、前記不純物的酸素の
ＳｉＯ2換算量の前記周期律表第３ａ族元素の酸化物換
算量（ＲＥ2Ｏ3）に対するモル比（ＳｉＯ2／ＲＥ
2Ｏ3）が１．６〜３．５であり、且つ該焼結体の粒界相
が結晶相としてダイシリケート相およびモノシリケート
相を含むことを特徴とするものである。That is, the silicon nitride sintered body of the present invention is mainly composed of silicon nitride and contains at least Lu.
A sintered body containing a Group 3 element and impurity oxygen, wherein the Group 3a element of the periodic table is contained in a proportion of 1 to 10 mol% of the total amount in terms of oxide, and the impurity oxygen SiO 2 The molar ratio (SiO 2 / RE) of the conversion amount to the oxide conversion amount (RE 2 O 3 ) of the Group 3a element of the periodic table.
2 O 3 ) is 1.6 to 3.5, and the grain boundary phase of the sintered body contains a disilicate phase and a monosilicate phase as crystal phases.
【０００９】以下、本発明を詳述する。本発明の窒化珪
素質焼結体は、窒化珪素を主成分とするもので、これに
添加成分として周期律表第３ａ族元素および不純物的酸
素を含む。ここで、不純物的酸素とは、焼結体中の全酸
素量から添加物として周期律表第３ａ族元素化合物中に
化学量論的に含まれる酸素量を差し引いた残りの酸素量
であり、そのほとんどは窒化珪素原料に含まれる酸素、
あるいは添加される酸化珪素として混入するものであ
り、これらは全てＳｉ−Ｏの化学結合を含む、例えばＳ
ｉＯ2 として存在すると考えられる。Hereinafter, the present invention will be described in detail. The silicon nitride-based sintered body of the present invention contains silicon nitride as a main component, and contains, as additional components, a Group 3a element of the periodic table and impurity oxygen. Here, the impurity oxygen is the remaining oxygen amount obtained by subtracting the oxygen amount stoichiometrically contained in the Group 3a element compound as an additive from the total oxygen amount in the sintered body, Most of the oxygen contained in the silicon nitride raw material,
Alternatively, these are mixed as silicon oxide to be added, all of which contain a chemical bond of Si—O, for example, S
It is considered to exist as iO 2 .
【００１０】本発明の窒化珪素質焼結体は、組織的に
は、窒化珪素結晶相を主相とするものであり、そのほと
んどは１〜３０μｍの平均粒径のβ−Ｓｉ3Ｎ4からな
る。また、その主相の粒界には少なくとも周期律表第３
ａ族元素、Ｓｉ（珪素）、Ｏ（酸素）からなるＲＥ2Ｓ
ｉ2Ｏ7で表されるダイシリケート相およびＲＥ2ＳｉＯ5
で表されるモノシリケート相を含むことが大きな特徴で
ある。なお、粒界相には、上記の結晶相以外に結晶化が
十分でない場合などにおいて窒素成分を含むオキシナイ
トライトガラスが存在することがある。このようなガラ
ス相が存在すると、高温での機械的特性を若干低下させ
る場合があるが、耐酸化性および破壊靱性に与える影響
は小さいため、Ｘ線回折などで前述した結晶相が明らか
に検出されるレベルであれば特に問題はない。The silicon nitride-based sintered body of the present invention is structurally mainly composed of a silicon nitride crystal phase, and most of the sintered body is composed of β-Si 3 N 4 having an average particle size of 1 to 30 μm. Become. In addition, at least grain boundaries of the periodic table
RE 2 S consisting of group a elements, Si (silicon) and O (oxygen)
Disilicate phase represented by i 2 O 7 and RE 2 SiO 5
It is a great feature that it contains a monosilicate phase represented by In the grain boundary phase, oxynitrite glass containing a nitrogen component may be present when crystallization is not sufficient other than the above-mentioned crystal phase. The presence of such a glass phase may slightly lower the mechanical properties at high temperatures, but has a small effect on oxidation resistance and fracture toughness. Therefore, the aforementioned crystal phase is clearly detected by X-ray diffraction or the like. There is no particular problem as long as it is at the required level.
【００１１】本発明における焼結体の具体的組成として
は、窒化珪素を７０モル％以上、特に８５〜９９モル
％、周期律表第３ａ族元素を酸化物換算で１〜１０モル
％、特に１〜７モル％、不純物的酸素がＳｉＯ2 換算で
１〜１５モル％、特に１〜１２モル％の比率で含有され
ることが望ましい。これは、窒化珪素量が７０モル％よ
り少ないと高温強度が発揮されず、周期律表第３ａ族元
素量が１モル％未満では緻密化が不十分であり、１０モ
ル％を越えると高温強度および高温耐クリープ性が劣化
する。また、不純物的酸素量が１モル％より少ないと粒
界に窒化珪素と周期律表第３ａ族元素酸化物との化合物
であるメリライトなどの高温耐酸化性の小さい化合物が
生成されやすくなるため好ましくなく、１５モル％を越
えると粒界相の体積分率が増加し高温特性が劣化するた
めである。The specific composition of the sintered body according to the present invention is as follows: silicon nitride is 70 mol% or more, particularly 85 to 99 mol%, and Group 3a element of the periodic table is 1 to 10 mol% in terms of oxide, especially 1 to 10 mol%. It is preferable that 1 to 7 mol% and impurity oxygen be contained in a ratio of 1 to 15 mol%, particularly 1 to 12 mol% in terms of SiO 2 . This is because when the amount of silicon nitride is less than 70 mol%, high-temperature strength is not exhibited, and when the amount of group 3a element in the periodic table is less than 1 mol%, densification is insufficient, and when it exceeds 10 mol%, high-temperature strength is not obtained. And the high temperature creep resistance deteriorates. Further, when the amount of impurity oxygen is less than 1 mol%, a compound having low high-temperature oxidation resistance such as melilite, which is a compound of silicon nitride and an oxide of an element of Group 3a of the periodic table, is likely to be formed at the grain boundary. On the other hand, if it exceeds 15 mol%, the volume fraction of the grain boundary phase increases and the high temperature characteristics deteriorate.
【００１２】本発明における組成上の大きな特徴は、周
期律表第３ａ族元素として少なくともＬｕ（ルテチウ
ム）を含む点にある。このＬｕは酸化物換算で全量中１
モル％以上存在することが望ましい。なお、本発明にお
いて、Ｌｕ以外の周期律表第３ａ族元素としては、Ｙ、
Ｙｂ、Ｅｒ、Ｄｙ、Ｈｏ、Ｔｂ、ＳｃおよびＴｍなどが
挙げられる。A major feature of the composition in the present invention is that it contains at least Lu (lutetium) as a Group 3a element of the periodic table. This Lu is 1% of the total amount in terms of oxide.
Desirably, it is present in an amount of at least mol%. In the present invention, as elements other than Lu, Group 3a elements of the periodic table, Y,
Yb, Er, Dy, Ho, Tb, Sc and Tm.
【００１３】さらに、本発明によれば、前記周期律表第
３ａ族元素の酸化物換算量（ＲＥ2Ｏ3）に対する不純物
的酸素のＳｉＯ2換算量のモル比（ＳｉＯ2／ＲＥ2Ｏ3）
が１．６〜３．５、特に１．６〜２．７であることが重
要である。これは、上記モル比が１．６より小さいと、
ＲＥ2Ｓｉ2Ｏ7相およびＲＥ2ＳｉＯ5相の析出が望め
ず、３．５より大きいとＳｉ2Ｎ2Ｏ相の析出が増加し、
表面に分解層が生成され特性の劣化を招くためである。Furthermore, according to the present invention, the molar ratio (SiO 2 / RE 2 O 3 ) of the amount of impurity oxygen in terms of SiO 2 with respect to the oxide amount (RE 2 O 3 ) of the group 3a element of the periodic table is described. )
Is from 1.6 to 3.5, especially from 1.6 to 2.7. This means that if the molar ratio is less than 1.6,
Precipitation of RE 2 Si 2 O 7 phase and RE 2 SiO 5 phase cannot be expected. If it is larger than 3.5, precipitation of Si 2 N 2 O phase increases,
This is because a decomposition layer is formed on the surface, which causes deterioration of characteristics.
【００１４】Ｓｉ2 Ｎ2 Ｏ相の結晶はＳｉ3 Ｎ4 結晶と
類似の特性を有するが、その量が多くなるとＳｉ3 Ｎ4
の針状化を阻害し、破壊靱性値を低下させる。また、非
酸化性雰囲気中での焼成時にＳｉＯガス分圧が低いと焼
結体外周部のＳｉ2 Ｎ2 Ｏ結晶が分解しやすくなり、表
層より数ｍｍ程度の部分に分解相が生成し色調差が生じ
る。従って、ＳｉＯガス分圧を高くすることによりＳｉ
2 Ｎ2 Ｏ結晶の分解を抑制し色調差を無くすことは可能
である。[0014] Si 2 N 2 O phase crystal has a characteristic similar to Si 3 N 4 crystal, Si 3 N 4 if its amount is increased
In the form of needles, thereby lowering the fracture toughness value. Also, when the partial pressure of SiO gas is low during firing in a non-oxidizing atmosphere, the Si 2 N 2 O crystals on the outer peripheral portion of the sintered body are easily decomposed, and a decomposition phase is generated in a portion of about several mm from the surface layer, resulting in color tone. There is a difference. Therefore, by increasing the partial pressure of SiO gas,
It is possible to suppress the decomposition of 2 N 2 O crystal and eliminate the color tone difference.
【００１５】なお、本発明の焼結体中には、上記組成以
外にＴｉＮ、ＴｉＣ，ＴａＣ、ＴａＮ、ＶＣ、ＮｂＣ、
ＷＣ、ＷＳｉ2 、Ｍｏ2 Ｃなどの周期律表４ａ、５ａ、
６ａ族金属やそれらの炭化物、窒化物、珪化物またはＳ
ｉＣなどが、分散粒子やウイスカーとして本発明の焼結
体中に独立した相として存在しても特性を劣化させるよ
うな影響が小さいことからこれらを周知技術に基づき、
適量添加して複合材料として特性の改善を行うことも当
然可能である。In the sintered body of the present invention, TiN, TiC, TaC, TaN, VC, NbC,
Periodic tables 4a, 5a such as WC, WSi 2 , Mo 2 C,
Group 6a metals and their carbides, nitrides, silicides or S
Even if iC or the like is present as an independent phase in the sintered body of the present invention as dispersed particles or whiskers, the effect of deteriorating the properties is small, and therefore, based on known techniques,
It is of course possible to improve the properties of the composite material by adding an appropriate amount.
【００１６】しかし、Ａｌ、Ｍｇ、Ｃａ、Ｆｅ等の金属
は低融点の酸化物を形成しこれにより粒界の結晶化が阻
害されるとともに高温強度を劣化させるため、酸化物換
算量で１重量％以下、特に０．５重量％以下、さらに望
ましくは０．１重量％以下に制御することがよい。However, metals such as Al, Mg, Ca, and Fe form oxides having a low melting point, thereby inhibiting crystallization of grain boundaries and deteriorating high-temperature strength. %, Particularly preferably 0.5% by weight or less, more preferably 0.1% by weight or less.
【００１７】次に、本発明の窒化珪素質焼結体の製造方
法について説明する。本発明によれば、出発原料として
窒化珪素粉末を主成分とし、添加成分として少なくとも
Ｌｕ2 Ｏ3 を含む周期律表第３ａ族元素酸化物粉末、あ
るいは場合により酸化珪素粉末を添加してなる。また添
加形態としてＬｕ2 Ｏ3 とＳｉＯ2 からなる化合物、ま
たは窒化珪素とＬｕ2 Ｏ3 とＳｉＯ2 の化合物粉末を用
いることもできる。用いられる窒化珪素粉末は、α型、
β型のいずれでも使用することができ、その粒子径は
０．４〜１．２μｍ、陽イオン不純物量は１重量％以
下、特に０．５重量％以下、不純物酸素量が０．５〜
２．０重量％が適当であり、直接窒化法、イミド分解法
などのいずれの製法によるものであっても構わない。Next, a method for producing the silicon nitride sintered body of the present invention will be described. According to the present invention, a powder of a Group 3a element of the periodic table containing a silicon nitride powder as a main component as a starting material and at least Lu 2 O 3 as an additional component, or a silicon oxide powder as the case may be. Further, as an addition form, a compound composed of Lu 2 O 3 and SiO 2 , or a compound powder of silicon nitride, Lu 2 O 3 and SiO 2 can be used. The silicon nitride powder used is α-type,
Any of the β-forms can be used, the particle size is 0.4 to 1.2 μm, the amount of cationic impurities is 1% by weight or less, particularly 0.5% by weight or less, and the amount of impurity oxygen is 0.5 to 5%.
2.0% by weight is appropriate, and any method such as a direct nitriding method or an imide decomposition method may be used.
【００１８】本発明によれば、これらの粉末を用いて、
前述したような組成を満足するように調合する。調合に
際して前述したＳｉＯ2 ／ＲＥ2 Ｏ3 比を制御する場
合、窒化珪素中に不可避的に含まれる酸素をＳｉＯ2 分
あるいは製造過程で吸着される酸素分等を考慮してＬｕ
2 Ｏ3 などの周期律表第３ａ族元素酸化物量を決定する
が、場合によってはＳｉＯ2 粉末を添加して調製すれば
よい。According to the present invention, using these powders,
It is prepared so as to satisfy the above-mentioned composition. When controlling SiO 2 / RE 2 O 3 ratio described above in the formulation, Lu considering the oxygen partial or the like to be adsorbed oxygen unavoidably contained in the silicon nitride in the SiO 2 minutes or manufacturing process
The amount of an oxide of an element of Group 3a of the periodic table such as 2 O 3 is determined. In some cases, it may be prepared by adding SiO 2 powder.
【００１９】上記の割合で各粉末を秤量後、振動ミル、
回転ミル、バレルミルなどで十分に混合した後、混合粉
末を所望の成形手段、例えば、金型プレス、鋳込み成
形、押し出し成形、射出成形、冷間静水圧プレス等によ
り任意の形状に成形する。After weighing each powder at the above ratios,
After sufficiently mixing with a rotary mill, a barrel mill, or the like, the mixed powder is formed into an arbitrary shape by a desired molding means, for example, a die press, a casting molding, an extrusion molding, an injection molding, a cold isostatic pressing, or the like.
【００２０】次に、この成形体を公知の焼成方法、例え
ば、ホットプレス法、常圧焼成法、窒素ガス加圧焼成法
などにより緻密化することができる。さらには、これら
の焼成後に熱間静水圧焼成（ＨＩＰ）法により処理する
ことにより緻密化を高めることができる。また、その他
の方法として上記成形体または焼結体をガラスシールし
てＨＩＰ法により焼成することもできる。具体的な焼成
条件は、窒化珪素が分解しない窒素圧下で１５００〜２
０００℃の温度で焼成する。なお、焼成温度が２０００
℃を越えると窒化珪素結晶が粒子成長を起こし強度劣化
を引き起こす。Next, the compact can be densified by a known firing method, for example, a hot pressing method, a normal pressure firing method, a nitrogen gas pressure firing method, or the like. Furthermore, densification can be improved by performing treatment by hot isostatic pressing (HIP) after the calcination. As another method, the above-mentioned molded body or sintered body can be glass-sealed and fired by the HIP method. Specific firing conditions are 1500-2 under nitrogen pressure under which silicon nitride does not decompose.
Fire at a temperature of 000 ° C. When the firing temperature is 2000
When the temperature exceeds ℃, the silicon nitride crystal causes grain growth and causes strength deterioration.
【００２１】さらに、上記の焼成後の冷却過程で徐冷す
るか、または焼結体を１０００〜１７００℃で熱処理す
ることにより粒界の結晶化を図り特性のさらなる改善を
行うことができる。Further, by gradually cooling in the cooling step after the above-mentioned sintering, or by subjecting the sintered body to a heat treatment at 1000 to 1700 ° C., the grain boundaries can be crystallized and the characteristics can be further improved.
【００２２】また、高い寸法精度が要求される場合に
は、窒化珪素粉末の一部をＳｉ粉末に置き換えて成形体
を作製し、これを窒素含有雰囲気中、８００〜１５００
℃で熱処理してＳｉ粉末を窒化処理してＳｉ3 Ｎ4 に変
換して成形体密度を高めた上で、前述した焼成条件で焼
成することにより、焼成時の収縮を小さくすることがで
きる。If high dimensional accuracy is required, a part of the silicon nitride powder is replaced with Si powder to produce a compact, which is then placed in a nitrogen-containing atmosphere at 800 to 1500.
After the heat treatment at a temperature of ° C., the Si powder is nitrided and converted into Si 3 N 4 to increase the density of the compact, and then fired under the above-described firing conditions, the shrinkage during firing can be reduced.
【００２３】[0023]
【作用】本発明によれば、窒化珪素質焼結体の粒界を構
成する周期律表第３ａ族元素として少なくともＬｕを選
択することにより、従来から用いられている他の周期律
表第３ａ族元素に比較して高温特性を改善することがで
きる。このような優れた作用が発揮されるメカニズム
は、Ｌｕはランタノイド系の中で最もイオン半径が小さ
く、他の元素との結合力が大きいため高温での機械的強
度や、クリープの主因である粒界のすべり現象が小さ
く、また酸素の拡散が小さいため、耐酸化性も他の周期
律表第３ａ族元素より優れると考えられる。According to the present invention, at least Lu is selected as an element belonging to Group 3a of the periodic table constituting the grain boundary of the silicon nitride based sintered body, thereby attaining the other elements of the conventional periodic table 3a. High-temperature characteristics can be improved as compared with group-group elements. The mechanism by which such excellent effects are exerted is that Lu has the smallest ionic radius in the lanthanoid system and has a large bonding force with other elements, so that mechanical strength at high temperatures and grain size, which is the main cause of creep, are high. Since the slip phenomenon of the field is small and the diffusion of oxygen is small, it is considered that the oxidation resistance is superior to other Group 3a elements of the periodic table.
【００２４】さらに、焼結体の耐酸化性を決定するの
は、焼結体の粒界相の粒界の特性によるものであり、本
発明によれば、ＲＥ2Ｓｉ2Ｏ7相およびＲＥ2ＳｉＯ5相
を析出させることにより、これらの結晶相が高温酸化性
雰囲気でも非常に安定であることから、優れた耐酸化性
が発揮される。Further, the oxidation resistance of the sintered body is determined by the characteristics of the grain boundary of the grain boundary phase of the sintered body. According to the present invention, the RE 2 Si 2 O 7 phase and the RE By precipitating the 2 SiO 5 phase, since these crystal phases are very stable even in a high-temperature oxidizing atmosphere, excellent oxidation resistance is exhibited.
【００２５】高温酸化性雰囲気中で安定な結晶相とし
て、Ｓｉ2 Ｎ2 Ｏ結晶があるが、Ｓｉ2 Ｎ2 Ｏ相の結晶
はその量が多くなるとＳｉ3 Ｎ4 の針状化を阻害するた
め、結果として焼結体の破壊靱性値を低下させてしまう
とともに、焼成時の雰囲気を高ＳｉＯガス雰囲気に制御
しなければ表層に分解相が生じる。これに対して、上記
ＲＥ2 Ｓｉ2 Ｏ7 相、ＲＥ2 ＳｉＯ5 相の結晶は、Ｓｉ
3 Ｎ4 の針状化を阻害することなく、また焼成時の雰囲
気の影響を受けず安定して生成されるために、高い耐酸
化性を維持しつつ破壊靱性を向上させるとともに焼結体
表面での分解をも抑制できる。As a crystal phase stable in a high-temperature oxidizing atmosphere, there is a Si 2 N 2 O crystal. However, the crystal of the Si 2 N 2 O phase inhibits the needle-like formation of Si 3 N 4 when its amount increases. Therefore, as a result, the fracture toughness value of the sintered body is reduced, and a decomposition phase is generated in the surface layer unless the atmosphere during firing is controlled to a high SiO gas atmosphere. In contrast, the crystals of the RE 2 Si 2 O 7 phase and the RE 2 SiO 5 phase
3 without inhibiting the needle of N 4, also in order to be stably generated without being affected by the atmosphere during sintering, the sintered body surface improves the fracture toughness while maintaining high oxidation resistance Decomposition can be suppressed.
【００２６】[0026]
【実施例】原料粉末として窒化珪素粉末（ＢＥＴ比表面
積９ｍ2 ／ｇ、α率９８％以上、酸素量１．１重量％、
Ａｌ、Ｍｇ、Ｃａ、Ｆｅなどの陽イオン金属不純物量３
０ｐｐｍ以下）と、純度が９９％以上または９６％Ｌｕ
2 Ｏ3 粉末と、純度９９％以上の周期律表第３ａ族酸化
物粉末および純度９９．９％以上の酸化珪素粉末を用い
て、Ｓｉ3 Ｎ4 、ＲＥ2 Ｏ3 、ＳｉＯ2 を適量調合し、
メタノールを溶媒として窒化珪素ボールを用いて１２０
時間回転ミルで混合粉砕し、スラリーを乾燥後、直径６
０ｍｍ、厚み２０ｍｍの形状に３ｔ／ｃｍ2 の圧力でラ
バープレス成形した。EXAMPLES Silicon nitride powder (BET specific surface area 9 m 2 / g, α rate 98% or more, oxygen content 1.1% by weight,
Amount of cationic metal impurities such as Al, Mg, Ca, Fe, etc. 3
0 ppm or less) and a purity of 99% or more or 96% Lu
A proper amount of Si 3 N 4 , RE 2 O 3 , SiO 2 is prepared by using 2 O 3 powder, an oxide powder of Group 3a of the periodic table having a purity of 99% or more, and a silicon oxide powder having a purity of 99.9% or more. And
Using a silicon nitride ball with methanol as a solvent, 120
After mixing and crushing with a rotary mill and drying the slurry,
Rubber press molding was performed at a pressure of 3 t / cm 2 into a shape having a thickness of 0 mm and a thickness of 20 mm.
【００２７】そして、かかる成形体を表１に示す各種の
焼成方法で焼成した。表中、ＧＰＳは、成形体を１６０
０〜１９５０℃、窒素分圧１〜１０気圧下で２０時間焼
成したものである。ホットプレスは１７００〜１９００
℃で３６．３ＭＰａの加圧下で１時間焼成した。ＨＩＰ
は、成形体をバイコールガラス中に埋め、バイコールガ
ラスが溶融する１７５０℃の温度でＡｒガスを２０００
ａｔｍ印加した状態で１時間焼成したものである。さら
に、ＧＰＳ＋ＨＩＰは、上記ＧＰＳ条件で焼成後、１７
００℃、窒素圧２０００ａｔｍで１時間熱間静水圧焼成
したものである。常圧焼成は、１６００〜１８５０℃、
窒素１気圧下で５０時間焼成したものである。なお、焼
成時の分解を抑制するために焼成時の入炉量は３００ｇ
／リットルと一定にした。The compact was fired by various firing methods shown in Table 1. In the table, GPS indicates that the molded product is 160
It is fired at 0 to 1950 ° C. under a nitrogen partial pressure of 1 to 10 atm for 20 hours. Hot press is 1700-1900
Calcination was performed at a temperature of 36.3 MPa for 1 hour. HIP
Is to bury the molded body in Vycor glass and apply Ar gas at a temperature of 1750 ° C. at which Vycor glass melts for 2000 times.
It was fired for one hour with atm applied. Further, after firing under the above GPS conditions, GPS + HIP
Hot isostatic firing at 00 ° C. under a nitrogen pressure of 2000 atm for 1 hour. Atmospheric firing is 1600-1850 ° C,
It is calcined under 1 atm of nitrogen for 50 hours. In order to suppress decomposition during firing, the furnace input during firing is 300 g.
/ Liter.
【００２８】さらに、表１中試料Ｎo.２５、２６は窒化
珪素粉末の一部（窒化珪素換算でＮo.２５は５１モル％
相当量、Ｎo.２６は７０モル％相当量）を珪素粉末に置
き換え、１２００℃、窒素圧１０気圧下で２時間、１３
００℃、窒素圧６気圧で２時間、１４００℃、窒素圧１
気圧で２時間のパターンで窒化処理した後、上記ＧＰＳ
の条件で焼成した。Further, in Table 1, Samples Nos. 25 and 26 are a part of silicon nitride powder (No. 25 is 51 mol% in terms of silicon nitride).
Equivalent to 70 mol% for No. 26) was replaced with silicon powder at 1200 ° C. under a nitrogen pressure of 10 atm for 2 hours.
1 hour at 1400 ° C, nitrogen pressure 1
After nitriding in a 2 hour pattern at atmospheric pressure, the above GPS
It baked on condition of.
【００２９】得られた焼結体に対してアルキメデス法に
よる比重から対理論密度比を算出するとともに、３×４
×４０ｍｍのテストピース形状に切断研磨し、ＪＩＳ−
Ｒ１６０１に基づき室温および１５００℃での４点曲げ
抗折強度試験を実施し、１０個の試験結果の平均値を、
耐酸化性特性として焼結体を１５００℃の大気中に１０
０時間保持した後の重量増加を測定し表２に示した。ま
た、Ｘ線回折測定により焼結体の粒界相の結晶を同定
し、主相および副相を決定した。なお、表１中の不純物
的酸素量は、焼結体を粉砕し化学分析によって酸素量を
求め、添加した周期律表第３ａ族元素酸化物中の酸素量
を除いた酸素量をＳｉＯ2 換算したものである。さらに
抗折試験片をＪＩＳＲ１６０１の４点曲げ試験と同様に
支持し、４００ＭＰａの負荷を印加し１５００℃で最高
１００時間保持し、破壊に至るまでの時間を測定した。With respect to the obtained sintered body, the ratio of the theoretical density to the theoretical density was calculated from the specific gravity according to the Archimedes method.
Cutting and polishing into a test piece shape of × 40 mm, JIS-
Based on R1601, a 4-point bending strength test was performed at room temperature and 1500 ° C., and the average value of 10 test results was
The sintered body was placed in an atmosphere of 1500 ° C.
The weight increase after holding for 0 hours was measured and the results are shown in Table 2. Further, the crystal of the grain boundary phase of the sintered body was identified by X-ray diffraction measurement, and the main phase and the subphase were determined. The amount of oxygen in Table 1 is obtained by pulverizing the sintered body to obtain the amount of oxygen by chemical analysis, and calculating the amount of oxygen excluding the amount of oxygen in the added Group 3a element oxide of the periodic table in terms of SiO 2. It was done. Further, the bending test piece was supported in the same manner as in the four-point bending test of JISR1601, a load of 400 MPa was applied, the test piece was held at 1500 ° C. for a maximum of 100 hours, and the time until breakage was measured.
【００３０】また、本発明の典型的な窒化珪素質焼結体
として表中の試料Ｎo.６について、そのＸ線回折測定に
おけるチャート図を図１に示した。FIG. 1 shows a chart of X-ray diffraction measurement of Sample No. 6 in the table as a typical silicon nitride sintered body of the present invention.
【００３１】[0031]
【表１】 [Table 1]
【００３２】[0032]
【表２】 [Table 2]
【００３３】表１、２の結果からも明らかなように、周
期律表第３ａ族元素としてＹ、Ｙｂ、Ｅｒなどを用いた
試料Ｎo.１、２、３とＬｕを用いた試料Ｎo.６、１６〜
２０とを比較すると、高温強度についてＬｕを含む方が
高く、耐クリープ性においては非常に優れた結果を示し
た。さらに、周期律表第３ａ族元素酸化物の量を変化さ
せた試料Ｎo.４〜９において、その量が１モル％より少
ない試料Ｎo.４では緻密化不足であり、１０モル％を越
える試料Ｎo.６では高温強度、耐クリープ特性が低下し
た。As is clear from the results of Tables 1 and 2, Samples Nos. 1, 2, and 3 using Y, Yb, Er, etc. as Group 3a elements of the periodic table and Sample No. 6 using Lu. , 16-
As compared with No. 20, the one containing Lu was higher in the high temperature strength, and showed a very excellent result in the creep resistance. Furthermore, in Samples Nos. 4 to 9 in which the amount of Group 3a element oxide in the periodic table was changed, Sample No. 4 in which the amount was less than 1 mol% was insufficiently densified, and Samples in which the amount exceeded 10 mol%. In No. 6, the high temperature strength and the creep resistance were reduced.
【００３４】ＳｉＯ2／ＲＥ2Ｏ3モル比を変化させた試
料Ｎo.１０〜１５において、ＳｉＯ2／ＲＥ2Ｏ3比が
１．６以上のとき、粒界にダイシリケート相およびモノ
シリケート相の結晶が析出し耐酸化性が向上することが
わかる。しかし、ダイシリケート相のみ、またはからな
る試料Ｎｏ．１３、１４は破壊靱性の低下が認められ、
さらに、ＳｉＯ2／ＲＥ2Ｏ3比が３．５を越える試料Ｎ
o.１５ではＳｉ2Ｎ2Ｏが析出しており、破壊靱性値が低
下し、また外周部に分解相が生じており、焼結体の内外
で色調差が見られた。In Sample Nos. 10 to 15 in which the molar ratio of SiO 2 / RE 2 O 3 was changed, when the SiO 2 / RE 2 O 3 ratio was 1.6 or more, the disilicate phase and the monosilicate phase It can be seen that the crystals precipitate and the oxidation resistance is improved. However, Sample No. consisting of only the disilicate phase or consisting of 13 and 14 show a decrease in fracture toughness,
Further, the sample N having an SiO 2 / RE 2 O 3 ratio of more than 3.5
In o.15, Si 2 N 2 O was precipitated, the fracture toughness value was reduced, and a decomposition phase was generated on the outer peripheral portion, and a difference in color tone was observed inside and outside the sintered body.
【００３５】なお、他の焼成方法を用いた試料Ｎo.２１
〜２４や、窒化珪素の一部を珪素に代えて窒化処理した
試料Ｎo.２５、２６においてもいずれも満足する特性が
得られた。Sample No. 21 using another firing method was used.
Satisfactory characteristics were also obtained in Sample Nos. 25 and 26, which were subjected to nitriding treatment in which the silicon nitride was replaced with silicon.
【００３６】[0036]
【発明の効果】以上詳述したように、本発明によれば、
高温特性とともに高温での耐クリープ特性、耐酸化性、
破壊靱性を向上することができ、且つ色調差の生じない
焼結体を得ることができる。これにより自動車部品やガ
スタービン用部品などに用いた場合においても高い信頼
性を付与することができる。As described in detail above, according to the present invention,
Creep resistance at high temperature, oxidation resistance,
It is possible to improve the fracture toughness and obtain a sintered body having no color difference. Thereby, high reliability can be imparted even when used for automobile parts, gas turbine parts, and the like.
【図１】本発明の窒化珪素質焼結体におけるＸ線回折測
定のチャート図である。FIG. 1 is a chart of an X-ray diffraction measurement of a silicon nitride based sintered body of the present invention.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭63−100067（ＪＰ，Ａ) 特開 平４−292466（ＪＰ，Ａ) 特開 昭64−56368（ＪＰ，Ａ) 特開 平５−163066（ＪＰ，Ａ) 特開 平４−6160（ＪＰ，Ａ) 特開 平６−234571（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C04B 35/584 - 35/596 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-100067 (JP, A) JP-A-4-292466 (JP, A) JP-A-64-56368 (JP, A) JP-A-5-56 163066 (JP, A) JP-A-4-6160 (JP, A) JP-A-6-234571 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) C04B 35/584-35 / 596
Claims (1)
む周期律表第３ａ族元素および不純物的酸素を含む焼結
体であって、前記周期律表第３ａ族元素が酸化物換算で
全量中１〜１０モル％の割合で含有されるとともに、前
記不純物的酸素のＳｉＯ2換算量の前記周期律表第３ａ
族元素の酸化物換算量（ＲＥ2Ｏ3）に対するモル比（Ｓ
ｉＯ2／ＲＥ2Ｏ3）が１．６〜３．５であり、且つ該焼
結体の粒界相が結晶相としてダイシリケート相およびモ
ノシリケート相を含むことを特徴とする窒化珪素質焼結
体。1. A sintered body mainly composed of silicon nitride, containing a Group 3a element of the Periodic Table containing at least Lu and impurity oxygen, wherein the Group 3a element of the Periodic Table is contained in a total amount in terms of oxide. 1 to 10 mol%, and the periodic table 3a in terms of the amount of the impurity oxygen in terms of SiO 2 .
Molar ratio (S) relative to the oxide equivalent of group element (RE 2 O 3 )
iO 2 / RE 2 O 3 ) is 1.6 to 3.5, and the grain boundary phase of the sintered body contains a disilicate phase and a monosilicate phase as crystal phases. Union.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11840994A JP3236733B2 (en) | 1994-05-31 | 1994-05-31 | Silicon nitride sintered body |
| DE19519864A DE19519864B4 (en) | 1994-05-31 | 1995-05-31 | Silicon nitride intermediate and process for its preparation |
| US08/853,410 US5804523A (en) | 1994-05-31 | 1997-05-09 | Sintered product of silicon nitride |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11840994A JP3236733B2 (en) | 1994-05-31 | 1994-05-31 | Silicon nitride sintered body |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07330434A JPH07330434A (en) | 1995-12-19 |
| JP3236733B2 true JP3236733B2 (en) | 2001-12-10 |
Family
ID=14735937
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP11840994A Expired - Fee Related JP3236733B2 (en) | 1994-05-31 | 1994-05-31 | Silicon nitride sintered body |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3236733B2 (en) |
-
1994
- 1994-05-31 JP JP11840994A patent/JP3236733B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07330434A (en) | 1995-12-19 |
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