JPH06287065A - Silicon nitride sintered compact and its production - Google Patents
Silicon nitride sintered compact and its productionInfo
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- JPH06287065A JPH06287065A JP5073287A JP7328793A JPH06287065A JP H06287065 A JPH06287065 A JP H06287065A JP 5073287 A JP5073287 A JP 5073287A JP 7328793 A JP7328793 A JP 7328793A JP H06287065 A JPH06287065 A JP H06287065A
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Abstract
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、特に、自動車用部品やガスタ−ビンエンジ
ン用部品等に使用される窒化珪素質焼結体の製造方法に
関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon nitride sintered body which is excellent in strength characteristics from room temperature to high temperature and is particularly used for automobile parts, gas turbine engine parts and the like.
【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, silicon nitride sintered bodies have
Due to its excellent thermal shock resistance and oxidation resistance, it is being applied to engineering ceramics, especially for heat engines such as turbo-borers. This silicon nitride sintered material is generally used for Y 2 O 3 , Al 2 O 3 and silicon nitride.
Alternatively, by adding a sintering aid such as MgO, high density and high strength characteristics are obtained. Further improvement in strength and oxidation resistance at high temperatures is demanded for such silicon nitride sintered bodies when the operating conditions thereof further increase. In order to meet such demands, various improvements have been attempted so far, such as examination of sintering aids and improvement of 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 等の低融点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Ｓｉ
−ＲＥ−Ｏ−ＮからなるＹＡＭ相、アパタイト相等の結
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。その中でもシリコンオ
キシナイトライド（Ｓｉ2 Ｎ2 Ｏ）相とダイシリケート
（ＲＥ2 Ｓｉ2Ｏ7 ）相は窒化珪素の酸化生成物のＳｉ
Ｏ2 と平衡に存在し、それらを粒界に析出させると焼結
体の耐酸化性が向上することが知られている。Among them, from the viewpoint that low melting point oxides such as Al 2 O 3 which have been conventionally used as a sintering aid deteriorate the high temperature characteristics, the cycle of Y 2 O 3 or the like with respect to silicon nitride is deteriorated. In a sintered body having a simple ternary system (Si 3 N 4 —SiO 2 —RE 2 O 3 ) composition consisting of a Group 3a element (RE) of the table and silicon oxide, the grain boundaries of the sintered body are Si
It has been proposed to increase the melting point and stabilize the grain boundaries by precipitating a crystal phase such as a YAM phase or an apatite phase composed of -RE-O-N. Among them, the silicon oxynitride (Si 2 N 2 O) phase and the disilicate (RE 2 Si 2 O 7 ) phase are Si oxides of silicon nitride.
It is known that they exist in equilibrium with O 2, and that their precipitation at grain boundaries improves the oxidation resistance of the sintered body.
【０００４】[0004]
【発明が解決しようとする問題点】しかしながら、粒界
をシリコンオキシナイトライド相とダイシリケート相に
結晶化することにより粒界が非晶質である場合に比較し
て高温特性は改善されるものの、所定の結晶相が析出す
ると同時に結晶化に寄与しなかった成分により低融点の
粒界相あるいはアモルファス相が形成されてしまうため
に結晶化による十分な効果が得られていないのが現状で
ある。そのために、かかる焼結体を実用化するには特性
的に未だ不十分でありさらなる強度の改善が要求されて
いる。However, by crystallizing the grain boundaries into the silicon oxynitride phase and the disilicate phase, the high temperature characteristics are improved as compared with the case where the grain boundaries are amorphous. At present, a sufficient effect due to crystallization cannot be obtained because a grain boundary phase or an amorphous phase with a low melting point is formed by a component that does not contribute to crystallization at the same time when a predetermined crystal phase is precipitated. . Therefore, the characteristics are still insufficient for practical use of such a sintered body, and further improvement in strength is required.
【０００５】よって、本発明は、低温から高温までの耐
酸化特性に優れ、室温から高温までの自動車部品やガス
タ−ビンエンジン用等で使用されるに十分な強度特性、
特に、室温から１４００℃の高温までの抗折強度に優れ
た窒化珪素質焼結体およびその製造方法を提供すること
を目的とするものである。Therefore, the present invention is excellent in oxidation resistance from low temperature to high temperature and has sufficient strength property to be used for automobile parts and gas turbine engine from room temperature to high temperature.
In particular, it is an object of the present invention to provide a silicon nitride sintered body excellent in bending strength from room temperature to a high temperature of 1400 ° C and a method for producing the same.
【０００６】[0006]
【問題点を解決するための手段】本発明者等は、焼結体
の強度特性および耐酸化特性を高めるためには、焼結体
の組成および窒化珪素相の粒界に存在する副相を制御す
ることが重要であるという見地に基づき検討を重ねた結
果、粒界にＳｉ2 Ｎ2 Ｏおよび／またはＲＥ2 Ｓｉ2 Ｏ
7 （ＲＥは周期律表第３ａ族元素）の結晶相を析出させ
る過程での条件を制御し、最終焼結体中の粒界に析出す
る結晶相の平均粒径を微細にすることにより低融点相或
いはアモルファス相の生成を抑制することができ、これ
により室温から高温まで優れた強度を有するとともに低
温から１４００℃まで優れた耐酸化性を有する焼結体が
得られることを知見した。The inventors of the present invention have found that the composition of the sintered body and the sub-phase existing at the grain boundary of the silicon nitride phase are required to improve the strength and oxidation resistance of the sintered body. As a result of repeated studies based on the viewpoint that it is important to control, Si 2 N 2 O and / or RE 2 Si 2 O are formed at grain boundaries.
7 (RE is a Group 3a element of the Periodic Table) The conditions in the process of precipitating the crystal phase are controlled, and the average grain size of the crystal phase precipitating at the grain boundaries in the final sintered body is made fine to reduce the It has been found that it is possible to suppress the formation of a melting point phase or an amorphous phase, whereby a sintered body having excellent strength from room temperature to high temperature and excellent oxidation resistance from low temperature to 1400 ° C can be obtained.
【０００７】即ち、本発明の窒化珪素質焼結体は、窒化
珪素を主相として、その粒界にＳｉ2 Ｎ2 Ｏおよび／ま
たはＲＥ2 Ｓｉ2 Ｏ7 （ＲＥは周期律表第３ａ族元素）
の結晶が主結晶相として析出してなる窒化珪素質焼結体
であって、前記粒界に析出した結晶が多結晶質であり、
且つ該結晶の平均粒径が０．３μｍ以下であることを特
徴とするものであり、さらに製法として、窒化珪素７０
〜９７モル％と、周期律表第３ａ族元素酸化物および酸
化珪素が合量で３〜３０モル％で、且つ前記酸化珪素の
前記周期律表第３ａ族元素酸化物に対するモル比率が
２．０以上の組成からなる成形体を非酸化性雰囲気中で
焼成した後、前記焼結体の粒界に生成しているガラスの
融点の絶対温度Ｔｍの０．５倍の温度から、ＲＥ2 Ｓｉ
2 Ｏ7 （ＲＥ：周期律表第３ａ族元素）結晶がｙ型から
β型へ転移する相転移温度Ｔｔとの間で一旦保持した
後、前記相転移温度Ｔｔから粒界相の融点温度の間で保
持することを特徴とするものである。That is, the silicon nitride-based sintered body of the present invention has silicon nitride as a main phase and has Si 2 N 2 O and / or RE 2 Si 2 O 7 (RE is a group 3a of the periodic table) at its grain boundaries. element)
Is a silicon nitride sintered body formed by precipitating crystals as a main crystal phase, and the crystals precipitated at the grain boundaries are polycrystalline,
In addition, the average grain size of the crystals is 0.3 μm or less.
.About.97 mol%, the total amount of the group 3a element oxide of the periodic table and silicon oxide is 3 to 30 mol%, and the molar ratio of the silicon oxide to the group 3a element oxide of the periodic table is 2. After firing a molded body having a composition of 0 or more in a non-oxidizing atmosphere, from the temperature 0.5 times the absolute temperature Tm of the melting point of the glass formed in the grain boundaries of the sintered body, RE 2 Si
2 O 7 (RE: Group 3a element of the periodic table) The crystal is held once between the phase transition temperature Tt at which the y-type transitions to the β-type transition, and then from the phase transition temperature Tt to the melting point temperature of the grain boundary phase. It is characterized by holding between.
【０００８】以下、本発明を詳述する。本発明の窒化珪
素質焼結体は、組成上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族元素および過剰
酸素を含む。ここで、過剰酸素とは、焼結体中の全酸素
量から焼結体中のＳｉ以外の周期律表第３ａ族元素が化
学量論的に酸化物を形成した場合にその元素に結合して
いる酸素を除く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、本発明では全てＳｉＯ2
として存在するものとして考慮する。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の
であって、そのほとんどがβ−Ｓｉ3 Ｎ4 からなり、お
よそ０．４〜２μｍの平均粒径（短径）でアスペクト比
１．５〜２０の粒子として存在する。また、その粒界に
は周期律表第３ａ族元素および過剰の酸素（酸化珪素と
して存在すると考えられるが）が少なくとも存在し、そ
の粒界中にはシリコンオキシナイトライド相（Ｓｉ2 Ｎ
2 Ｏ）および／またはダイシリケート相（ＲＥ2 Ｓｉ2
Ｏ7 ）の結晶相が多結晶質として存在するが、本発明に
よれば、その結晶相の平均粒径が０．３μｍ以下、特に
０．２μｍ以下であることが重要である。The present invention will be described in detail below. The silicon nitride-based sintered body of the present invention is composed of silicon nitride as a main component in terms of composition, and further contains a Group 3a element of the periodic table and excess oxygen as additional components. Here, excess oxygen means that when a group 3a element of the periodic table other than Si in the sintered body forms a stoichiometric oxide from the total amount of oxygen in the sintered body, it is bonded to the element. a remaining amount of oxygen except in that oxygen, most are those mixed as silicon oxide oxygen, or is added is included in the silicon nitride raw material, all in the present invention SiO 2
Consider as existing. The silicon nitride-based sintered body of the present invention systematically has a silicon nitride crystal phase as a main phase, and most of it is composed of β-Si 3 N 4 , and has an average grain size of about 0.4 to 2 μm. It exists as particles having a (short diameter) and an aspect ratio of 1.5 to 20. In addition, at least the element of Group 3a of the periodic table and excess oxygen (which is considered to exist as silicon oxide) are present in the grain boundary, and the silicon oxynitride phase (Si 2 N 2 ) is present in the grain boundary.
2 O) and / or disilicate phase (RE 2 Si 2
The crystal phase of O 7 ) exists as a polycrystal, but according to the present invention, it is important that the average grain size of the crystal phase is 0.3 μm or less, particularly 0.2 μm or less.
【０００９】この粒界相は焼結過程では窒化珪素粒子と
の反応によって低融点の液相として存在し焼結性を高め
るが、冷却後、粒界にガラス相として存在すると高温特
性を低下させてしまうと同時に耐酸化性までも劣化させ
てしまう。よって、後述する所定の冷却過程あるいは熱
処理によって平均粒径が０．３μｍ以下の微細な多結晶
相として析出させることにより高温強度および耐酸化性
を高めることができる。粒界の結晶相の平均粒径を上記
範囲に限定したのは、平均粒径が０．２μｍより大きく
なると、粒界に結晶化に寄与しなかった成分が増加し、
ガラス相やアモルファス相の生成が多くなり焼結体の高
温特性が劣化するためである。This grain boundary phase exists as a liquid phase having a low melting point in the sintering process as a liquid phase having a low melting point to enhance the sinterability, but after cooling, if it exists as a glass phase in the grain boundary, the high temperature characteristics are deteriorated. At the same time, it also deteriorates the oxidation resistance. Therefore, high temperature strength and oxidation resistance can be enhanced by precipitating a fine polycrystalline phase having an average grain size of 0.3 μm or less by a predetermined cooling process or heat treatment described later. The average grain size of the crystal phase of the grain boundary is limited to the above range, because when the average grain size is larger than 0.2 μm, the components that have not contributed to crystallization increase in the grain boundary,
This is because the glass phase and the amorphous phase are generated more and the high temperature characteristics of the sintered body deteriorate.
【００１０】なお、粒界に上記結晶相を析出させるため
には焼結体中の過剰酸素の酸化珪素（ＳｉＯ2 ）換算量
と、周期律表第３ａ族元素の酸化物（ＲＥ2 Ｏ3 ）換算
量とのＳｉＯ2 ／ＲＥ2 Ｏ3 で表されるモル比を２以
上、特に２〜２０に組成制御することが必要であり、こ
のモル比が２より小さいと粒界にＳｉ2 Ｎ2 ＯやＲＥ2
Ｓｉ2 Ｏ7 以外にＲＥ10Ｓｉ2 Ｏ23Ｎ4 やＲＥ10（Ｓｉ
Ｏ4 ）6 Ｎ2 等で記述されるアパタイト相やＲＥ4 Ｓｉ
2 Ｏ7 Ｎ2 で記述されるＹＡＭ相などの結晶相が主とし
て析出し高温における特性、特に耐酸化性が低下してし
まう。In order to precipitate the above crystal phase at the grain boundary, the amount of excess oxygen in the sintered body converted to silicon oxide (SiO 2 ) and the oxide of the Group 3a element of the periodic table (RE 2 O 3 ) It is necessary to control the composition so that the molar ratio represented by SiO 2 / RE 2 O 3 with the converted amount is 2 or more, particularly 2 to 20. If this molar ratio is less than 2 , Si 2 N will be present at the grain boundaries. 2 O and RE 2
In addition to Si 2 O 7 , RE 10 Si 2 O 23 N 4 and RE 10 (Si
O 4 ) 6 N 2 and other apatite phases and RE 4 Si
A crystal phase such as a YAM phase described by 2 O 7 N 2 is mainly precipitated, and the characteristics at high temperature, particularly the oxidation resistance is deteriorated.
【００１１】なお、本発明に用いられる周期律表第３ａ
族元素としては、Ｙやランタノイド元素が挙げられる
が、その中でも特にＹｂ、Ｅｒ、Ｄｙが望ましい。The periodic table No. 3a used in the present invention.
Examples of the group element include Y and lanthanoid elements, and among them, Yb, Er and Dy are particularly desirable.
【００１２】一方、周期律表４ａ、５ａ、６ａ族金属や
それらの酸化物、炭化物、窒化物、珪化物、またはＳｉ
Ｃなどは、分散粒子やウイスカーとして本発明の焼結体
中に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。On the other hand, metals of Group 4a, 5a and 6a of the Periodic Table, their oxides, carbides, nitrides, silicides, or Si.
C and the like have a small effect of deteriorating the characteristics even if they exist in the sintered body of the present invention as dispersed particles or whiskers, and therefore, based on a well-known technique, they are added in appropriate amounts to improve the characteristics as a composite material. Of course, it is possible to do.
【００１３】しかし、Ａｌ、Ｍｇ、Ｃａ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、これらの金属は
酸化物換算量で０．５重量％以下に制御することが望ま
しい。However, metals such as Al, Mg, and Ca form oxides having a low melting point, which hinders crystallization of grain boundaries and deteriorates high-temperature strength. It is desirable to control to 0.5% by weight or less.
【００１４】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、添加成分として周期律表第
３ａ族元素酸化物、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周期律表第３ａ族元素酸化物
と酸化珪素からなる化合物，または窒化珪素と周期律表
第３ａ族元素酸化物と酸化珪素の化合物粉末を用いるこ
ともできる。Next, a method for manufacturing the silicon nitride sintered body of the present invention will be described. According to the present invention, silicon nitride powder is used as a main component as a starting material, and a Group 3a element oxide of the periodic table, and in some cases, silicon oxide powder is added as an additive component. Further, as a form of addition, it is also possible to use a compound consisting of an oxide of a group 3a element of the periodic table and silicon oxide, or a compound powder of silicon nitride and an oxide of a group 3a element of the periodic table and silicon oxide.
【００１５】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が適当である。The silicon nitride powder used may be either α-type or β-type, and the particle size thereof is 0.4 to 0.4.
1.2 μm is suitable.
【００１６】本発明によれば、これらの粉末を用いて窒
化珪素が７０〜９７モル％、周期律表第３ａ族元素酸化
物（ＲＥ2 Ｏ3 ）、過剰酸素（ＳｉＯ2 換算量）の合計
が３〜３０モル％、特に５〜２０モル％で、ＳｉＯ2 ／
ＲＥ2 Ｏ3 で表されるモル比が２以上、特に２〜２０で
あることが重要である。ここでの過剰酸素とは、窒化珪
素粉末に含まれる不純物酸素をＳｉＯ2 換算した量と添
加したＳｉＯ2 粉末の合量である。According to the present invention, using these powders, the total amount of silicon nitride is 70 to 97 mol%, the oxide of the Group 3a group 3a element (RE 2 O 3 ) in the periodic table, and the excess oxygen (equivalent to SiO 2 ). Is 3 to 30 mol%, especially 5 to 20 mol%, and SiO 2 /
It is important that the molar ratio represented by RE 2 O 3 is 2 or more, particularly 2 to 20. The excess oxygen here is the total amount of the impurity oxygen contained in the silicon nitride powder converted to SiO 2 and the added SiO 2 powder.
【００１７】なお、上記添加成分の合量が３モル％より
少ないと焼結性が低下し、３０モル％を越えると粒界成
分量が増加し高温強度が低下する。また上記モル比率が
２より小さいとＲＥ−Ｓｉ−Ｏ−Ｎからなる微量のガラ
ス相が生成しやすく、シリコンオキシナイトライド（Ｓ
ｉ2 Ｎ2 Ｏ）相および／またはダイシリケート（ＲＥ2
Ｓｉ2 Ｏ7 ）相以外のアパタイト相やＹＡＭ相などの結
晶相が析出し高温における特性、特に耐酸化性が低下し
てしまうためである。If the total amount of the above-mentioned additional components is less than 3 mol%, the sinterability is lowered, and if it exceeds 30 mol%, the amount of grain boundary components is increased and the high temperature strength is lowered. Further, when the above molar ratio is less than 2, a trace amount of glass phase composed of RE-Si-O-N is likely to be generated, and silicon oxynitride (S
i 2 N 2 O) phase and / or disilicate (RE 2
This is because an apatite phase other than the Si 2 O 7 ) phase or a crystal phase such as a YAM phase is precipitated and the characteristics at high temperature, particularly the oxidation resistance is deteriorated.
【００１８】上記の割合で混合された混合粉末を所望の
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。The mixed powder mixed in the above proportions is molded into a desired shape by a desired molding means such as a die press, a cast molding, an extrusion molding, an injection molding and a cold isostatic pressing.
【００１９】次に、この成形体を公知の焼成法、例え
ば、ホットプレス法、常圧焼成法、窒素ガス加圧焼成
法、さらにはこれらの焼成後に熱間静水圧処理（ＨＩＰ
処理）、及びガラスシール後ＨＩＰ処理して対理論密度
比９５％以上の緻密な焼結体を得る。この時の温度は高
すぎると窒化珪素結晶が粒成長し強度が低下するため、
１６００〜２０００℃、特に１６５０〜１９００℃であ
ることが望ましい。Next, this molded body is subjected to a known firing method, for example, a hot pressing method, a normal pressure firing method, a nitrogen gas pressure firing method, or a hot isostatic treatment (HIP) after these firings.
Treatment) and glass sealing followed by HIP treatment to obtain a dense sintered body having a theoretical density ratio of 95% or more. If the temperature at this time is too high, the silicon nitride crystal grains grow and the strength decreases.
The temperature is preferably 1600 to 2000 ° C, particularly 1650 to 1900 ° C.
【００２０】次に、上記焼成工程における冷却過程、ま
たは冷却段階での一時保持、あるいは焼成工程終了後の
熱処理により粒界にＲＥ2 Ｓｉ2 Ｏ7 結晶を析出させ
る。この時、従来の熱処理方法では粒界中で粗大な結晶
に成長する。その場合、結晶に寄与しない不純物が粒界
に濃縮して低融点あるいはアモルファス相を形成して高
温強度の劣化を招いてしまう。Next, RE 2 Si 2 O 7 crystals are precipitated at the grain boundaries by a cooling process in the above firing process, a temporary holding in the cooling stage, or a heat treatment after the end of the firing process. At this time, according to the conventional heat treatment method, coarse crystals grow in the grain boundaries. In that case, impurities that do not contribute to the crystal are concentrated at the grain boundaries to form a low melting point or an amorphous phase, which causes deterioration of high temperature strength.
【００２１】そこで、本発明によれば、熱処理方法とし
て、まず焼結体の粒界に生成しているガラスの融点温度
の絶対温度（Ｔｍ）の０．５倍からｙ型ＲＥ2 Ｓｉ2 Ｏ
7 結晶からβ型ＲＥ2 Ｓｉ2 Ｏ7 結晶に転移する転移温
度Ｔｔとの間で一旦保持してガラス中に微細な結晶核あ
るいは微細な結晶化組織を形成させることができる。Therefore, according to the present invention, as a heat treatment method, first, y-type RE 2 Si 2 O is added from 0.5 times the absolute temperature (Tm) of the melting point temperature of the glass formed at the grain boundaries of the sintered body.
7 can be formed temporarily held to fine crystal nuclei or fine crystal tissues in the glass between the transition temperature Tt to metastasize to β-type RE 2 Si 2 O 7 crystals from the crystal.
【００２２】その後、前記相転移温度（Ｔｔ）から粒界
相の融点温度の間で保持して結晶核を成長させるか、あ
るいはｙ型ＲＥ2 Ｓｉ2 Ｏ7 からβ型ＲＥ2 Ｓｉ2 Ｏ7
へ相転移させる熱処理を施すことにより、高温でも安定
な結晶粒径が０．２μｍ以下の微細な多結晶相を粒界に
析出させることができ、粒界中に存在する不純物の濃縮
を抑制し、低融点相およびアモルファス相の形成を防止
することができる。After that, crystal nuclei are grown by maintaining the temperature between the phase transition temperature (Tt) and the melting point temperature of the grain boundary phase, or from y-type RE 2 Si 2 O 7 to β-type RE 2 Si 2 O 7.
By performing the heat treatment for the phase transition to a fine polycrystalline phase having a crystal grain size of 0.2 μm or less, which is stable even at high temperature, can be precipitated at the grain boundary, and the concentration of impurities existing in the grain boundary can be suppressed. It is possible to prevent formation of a low melting point phase and an amorphous phase.
【００２３】本発明者らの実験によれば、各種の窒化珪
素とＲＥ2 Ｓｉ2 Ｏ7 から構成されるガラスの融点温度
Ｔｍは約１６５０℃前後、ｙ型ＲＥ2 Ｓｉ2 Ｏ7 からβ
型ＲＥ2 Ｓｉ2 Ｏ7 への転移温度Ｔｔは１３００℃前後
の温度である。したがって、本発明によれば、熱処理温
度として一段目を７００〜１２５０℃の範囲に設定する
が、温度が低いと結晶核の発生に時間を要するから９０
０℃以上の方が望ましい。また、二段目の温度は１３０
０〜１６００℃の温度範囲に設定することにより上記の
微細な多結晶質粒界相を形成することができる。According to the experiments conducted by the present inventors, the melting point temperature Tm of glass composed of various silicon nitrides and RE 2 Si 2 O 7 is about 1650 ° C., and y-type RE 2 Si 2 O 7 has β
The transition temperature Tt to the type RE 2 Si 2 O 7 is around 1300 ° C. Therefore, according to the present invention, the first stage is set as the heat treatment temperature in the range of 700 to 1250 ° C. However, if the temperature is low, it takes time to generate crystal nuclei.
A temperature of 0 ° C or higher is desirable. The temperature of the second stage is 130
The fine polycrystalline grain boundary phase can be formed by setting the temperature in the range of 0 to 1600 ° C.
【００２４】[0024]
【作用】前述したＳｉＯ2 ／ＲＥ2 Ｏ3 モル比が２．０
以上の組成からなる窒化珪素質焼結体の粒界相結晶はＲ
Ｅ2 Ｓｉ2 Ｏ7 （ＲＥ：周期律表第３ａ族元素）とＳｉ
2 Ｎ2 Ｏで表される結晶が主なものである。これらの結
晶はガラスから析出する際に核形成速度と結晶成長速度
との比は極端に小さく、しかも不純物を殆ど固溶しない
特質を有する。そのために普通の熱処理では粒界相が粗
大な結晶に成長すると同時に、不純物が粒界に濃縮して
低融点相を形成したり、一部のガラス相を安定化させ、
アモルファス相として焼結体中に残存し、焼結体の高温
特性を低下させる。[Function] The above-mentioned SiO 2 / RE 2 O 3 molar ratio is 2.0.
The grain boundary phase crystal of the silicon nitride sintered body having the above composition is R
E 2 Si 2 O 7 (RE: Group 3a element of periodic table) and Si
The crystals represented by 2 N 2 O are the main ones. These crystals have the characteristic that the ratio of the nucleation rate to the crystal growth rate is extremely small when they are precipitated from glass, and further, they have the characteristics of hardly forming a solid solution with impurities. Therefore, in the ordinary heat treatment, the grain boundary phase grows into coarse crystals, and at the same time, impurities are concentrated in the grain boundaries to form a low melting point phase, and some glass phases are stabilized,
It remains in the sintered body as an amorphous phase and deteriorates the high temperature characteristics of the sintered body.
【００２５】Ａｌ、Ｃａ、Ｆｅなどの金属元素は窒化珪
素原料中に不可避的に存在し、焼結体中の窒化珪素結晶
粒子間の粒界３重点に存在し、窒化珪素結晶と粒界結晶
相との界面にアモルファス相として残存し、高温特性、
特にストレスラプチャー特性を劣化させてしまう。本発
明によれば、熱処理条件により微細な粒界相多結晶組織
を形成させることによりＡｌ、Ｃａ、Ｆｅ等の元素を微
細な結晶粒界に均一に分散させ、低融点相あるいはアモ
ルファス相の形成を抑制することができる。Metal elements such as Al, Ca and Fe inevitably exist in the silicon nitride raw material, and exist at the grain boundary triple points between the silicon nitride crystal grains in the sintered body, and the silicon nitride crystal and the grain boundary crystal are present. Remains as an amorphous phase at the interface with the phase, high temperature characteristics,
In particular, the stress rupture characteristics are deteriorated. According to the present invention, by forming a fine grain boundary phase polycrystalline structure by heat treatment conditions, elements such as Al, Ca and Fe are uniformly dispersed in the fine grain boundary, and a low melting point phase or an amorphous phase is formed. Can be suppressed.
【００２６】これにより、室温から高温における強度劣
化を小さくすることができるとともに室温から高温まで
の優れた耐酸化性を付与することができる。This makes it possible to reduce strength deterioration from room temperature to high temperature and to impart excellent oxidation resistance from room temperature to high temperature.
【００２７】[0027]
【実施例】原料粉末として窒化珪素粉末（ＢＥＴ比表面
積８ｍ2 ／ｇ、α率９８％、酸素量１．２重量％、金属
不純物量０．０３重量％）と、各種の周期律表第３ａ族
元素酸化物粉末および酸化珪素粉末を用いて、Ｓｉ3 Ｎ
4 、ＲＥ2 Ｏ3 、ＳｉＯ2の量が表１になるように調合
し、１ｔ／ｃｍ2 の圧力で金型成形した。EXAMPLE Silicon nitride powder (BET specific surface area 8 m 2 / g, α ratio 98%, oxygen amount 1.2% by weight, metal impurity amount 0.03% by weight) as raw material powder, and various periodic table 3a Group 3 element oxide powder and silicon oxide powder are used to produce Si 3 N
The amounts of 4 , RE 2 O 3 , and SiO 2 were compounded so as to be shown in Table 1, and a mold was formed at a pressure of 1 t / cm 2 .
【００２８】表中、試料Ｎo,１〜８の成形体を炭化珪素
の匣鉢内に入れて、組成変動を少なくするためには雰囲
気を制御し、１０気圧窒素ガス気流中で１８５０℃４時
間の条件で焼成した。さらに一部の試料は表１に示す条
件で冷却中に熱処理を実施した。その他に一部の試料に
ついては常圧にて窒素ガス気流中、表１に示す条件で熱
処理した。In the table, the molded bodies of samples No. 1 to 8 were placed in a silicon carbide container and the atmosphere was controlled in order to reduce the composition fluctuation, and the atmosphere was controlled at 1850 ° C. for 4 hours in a nitrogen gas stream of 10 atmospheres. Was fired under the conditions. Further, some of the samples were subjected to heat treatment during cooling under the conditions shown in Table 1. In addition, some of the samples were heat-treated under the conditions shown in Table 1 in a nitrogen gas stream at normal pressure.
【００２９】また、試料Ｎo,９〜１６の成形体について
は、シールＨＩＰ法にて焼結体を作製した。具体的に
は、まず、焼成に先立ち、成形体の対して焼成工程にお
いてシール材であるガラス等との反応を防止することを
目的としてＢＮ粉末等のガラスとの濡れ性の悪い粉末を
スラリー化して成形体表面に塗布するか、または上記ス
ラリーをスプレー塗布する。次にＢＮが塗布された成形
体をガラス製カプセルに封入し、ＨＩＰ法にて１７００
℃、１時間の条件で焼結体を作製した。一部の試料につ
いては常圧にて窒素ガス気流中で表１に示す条件で熱処
理を実施し焼結体を得た。As for the compacts of samples No. 9 to 16, sintered compacts were prepared by the seal HIP method. Specifically, first, prior to firing, a powder having poor wettability with glass such as BN powder is slurried into a slurry for the purpose of preventing the molded body from reacting with glass or the like as a sealing material in the firing step. To the surface of the molded article by spraying, or the above slurry is spray-coated. Next, the molded body coated with BN is encapsulated in a glass capsule, and the HIP method is applied to 1700.
A sintered body was produced under conditions of 1 ° C. and 1 hour. Some of the samples were heat-treated under the conditions shown in Table 1 in a nitrogen gas stream at normal pressure to obtain sintered bodies.
【００３０】得られた焼結体をＪＩＳ−Ｒ１６０１にて
指定されている形状まで研磨し試料を作製した。この試
料についてＪＩＳ−Ｒ１６０１に基づく室温および１４
００℃での４点曲げ抗折強度試験を実施した。また、試
料を９００℃空気中、または、１４００℃空気中に１０
０時間暴露し、重量増加量と試料の表面積から単位表面
積当たりの重量変化を求めた。また、Ｘ線回折測定によ
り焼結体中の粒界相の結晶を同定した。結果は表１に示
した。また、得られた焼結体のミクロ組織を透過電子顕
微鏡を用いて観察しその組織と析出している多結晶質の
結晶平均粒径を求めた。結果は表１および表２に示し
た。The obtained sintered body was ground to a shape specified in JIS-R1601 to prepare a sample. For this sample, room temperature and 14 according to JIS-R1601
A 4-point bending bending strength test at 00 ° C was performed. In addition, the sample was placed in 900 ° C air or 1400 ° C air for 10
After exposure for 0 hours, the weight change per unit surface area was determined from the weight increase amount and the surface area of the sample. In addition, the crystal of the grain boundary phase in the sintered body was identified by X-ray diffraction measurement. The results are shown in Table 1. Further, the microstructure of the obtained sintered body was observed using a transmission electron microscope, and the structure and the average crystal grain size of the precipitated polycrystal were determined. The results are shown in Tables 1 and 2.
【００３１】[0031]
【表１】 [Table 1]
【００３２】[0032]
【表２】 [Table 2]
【００３３】表１および表２の結果によると、ＳｉＯ2
／ＲＥ2 Ｏ3 が２より小さい試料Ｎo,１、Ｎo,２、Ｎo,
９の粒界は、主としてＹＡＭあるいはアパタイトからな
る結晶相の析出が認められ、強度はある程度高い値を示
したが、高温における耐酸化性に劣るものであった。Ｓ
ｉＯ2 ／ＲＥ2 Ｏ3 が２以上でも熱処理条件が適切でな
く、粒界相の結晶粒径が大きいＮo,１、Ｎo,３、Ｎo,
４、Ｎo,９の試料は、高温強度が劣化していた。According to the results of Table 1 and Table 2, SiO 2
/ RE 2 O 3 is less than 2 samples No, 1, No, 2, No,
At the grain boundaries of No. 9, precipitation of a crystal phase mainly composed of YAM or apatite was observed and the strength showed a high value to some extent, but the oxidation resistance at high temperature was poor. S
Even if iO 2 / RE 2 O 3 is 2 or more, the heat treatment conditions are not appropriate and the grain size of the grain boundary phase is large No, 1, No, 3, No,
The samples of Nos. 4 and 9 had deteriorated high-temperature strength.
【００３４】また、周期律表第３ａ族元素酸化物と酸化
珪素との合量が３モル％より小さい試料Ｎo,１５では緻
密化することができず、３０モル％を越える試料Ｎo,１
６では強度の劣化が認められた。Sample No, 15 containing less than 3 mol% of the oxide of group 3a element of the periodic table and silicon oxide could not be densified, and sample No, 1 exceeding 30 mol% was used.
In No. 6, deterioration of strength was recognized.
【００３５】これらの比較例に対して、その他の本発明
に基づく試料は、いずれも粒界に多結晶質の結晶が析出
しており、その結晶粒径が０．３μｍ以下のＲＥ2 Ｓｉ
2 Ｏ7 、あるいはＲＥ2 Ｓｉ2 Ｏ7 結晶とＳｉ2 Ｎ2 Ｏ
結晶の析出が認められ、いずれも室温から高温まで優れ
た抗折強度、耐酸化性を示した。In contrast to these comparative examples, the other samples according to the present invention all have polycrystalline crystals precipitated at grain boundaries, and the crystal grain size of RE 2 Si is 0.3 μm or less.
2 O 7 or RE 2 Si 2 O 7 crystal and Si 2 N 2 O
Precipitation of crystals was observed, and all exhibited excellent bending strength and oxidation resistance from room temperature to high temperature.
【００３６】[0036]
【発明の効果】以上詳述したように、本発明によれば、
所定の条件で熱処理して粒界相を特定の結晶粒径で析出
させることにより室温から高温における強度劣化が小さ
く、優れた耐酸化性を有する窒化珪素質焼結体を提供す
ることができる。As described in detail above, according to the present invention,
By subjecting the grain boundary phase to precipitation of a specific crystal grain size by heat treatment under predetermined conditions, it is possible to provide a silicon nitride-based sintered body having little strength deterioration from room temperature to high temperature and having excellent oxidation resistance.
Claims (3)
Ｎ2 Ｏおよび／またはＲＥ2 Ｓｉ2 Ｏ7 （ＲＥは周期律
表第３ａ族元素）結晶が主結晶相として析出してなる窒
化珪素質焼結体であって、前記粒界に析出した結晶が多
結晶質からなり、且つ該結晶の平均粒径が０．３μｍ以
下であることを特徴とする窒化珪素質焼結体。1. Si 2 is used as a main phase in a grain boundary of silicon nitride.
A silicon nitride sintered body in which N 2 O and / or RE 2 Si 2 O 7 (RE is an element of Group 3a of the periodic table) crystals are precipitated as a main crystal phase, and the crystals are precipitated at the grain boundaries. Is a polycrystal, and the average grain size of the crystal is 0.3 μm or less, a silicon nitride sintered body.
の酸化物換算量（ＲＥ2 Ｏ3 ）と過剰酸素の酸化珪素
（ＳｉＯ2 ）換算量のＳｉＯ2 ／ＲＥ2 Ｏ3 で表される
比率が２．０以上である請求項１記載の窒化珪素質焼結
体。2. A group 3a element (RE) of the periodic table in the sintered body.
2. The silicon nitride according to claim 1, wherein a ratio represented by SiO 2 / RE 2 O 3 in terms of oxide equivalent (RE 2 O 3 ) and excess oxygen in terms of silicon oxide (SiO 2 ) is 2.0 or more. Quality sintered body.
３ａ族元素酸化物および酸化珪素が合量で３〜３０モル
％で、且つ前記酸化珪素の前記周期律表第３ａ族元素酸
化物に対するモル比率が２．０以上の組成からなる成形
体を非酸化性雰囲気中で焼成した後、前記焼結体の粒界
に生成しているガラスの融点の絶対温度Ｔｍの０．５倍
の温度から、ＲＥ2 Ｓｉ2 Ｏ7 （ＲＥ：周期律表第３ａ
族元素）結晶がｙ型からβ型へ転移する相転移温度Ｔｔ
との間で一旦保持した後、前記相転移温度Ｔｔから粒界
相の融点温度の間で保持することを特徴とする窒化珪素
質焼結体の製法。3. A total of 3 to 30 mol% of silicon nitride, 70 to 97 mol%, and an oxide of group 3a of the periodic table, and silicon oxide, and the element of group 3a of the periodic table of silicon oxide. After firing a molded body having a composition in which the molar ratio to the oxide is 2.0 or more in a non-oxidizing atmosphere, the absolute temperature Tm of the melting point Tm of the glass formed at the grain boundaries of the sintered body is 0.5. From the double temperature, RE 2 Si 2 O 7 (RE: Periodic Table 3a
Group element) Phase transition temperature Tt at which the crystal transitions from y-type to β-type
And a melting point temperature of the grain boundary phase from the phase transition temperature Tt.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP05073287A JP3124863B2 (en) | 1993-03-31 | 1993-03-31 | Silicon nitride sintered body and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP05073287A JP3124863B2 (en) | 1993-03-31 | 1993-03-31 | Silicon nitride sintered body and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH06287065A true JPH06287065A (en) | 1994-10-11 |
| JP3124863B2 JP3124863B2 (en) | 2001-01-15 |
Family
ID=13513788
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP05073287A Expired - Fee Related JP3124863B2 (en) | 1993-03-31 | 1993-03-31 | Silicon nitride sintered body and method for producing the same |
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| Country | Link |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000327426A (en) * | 1999-05-21 | 2000-11-28 | Ngk Spark Plug Co Ltd | Heating resistor, heating resistor for ceramic heater and ceramic heater using the same |
| JP2007169118A (en) * | 2005-12-22 | 2007-07-05 | Kyocera Corp | Silicon nitride sintered compact, and member for semiconductor manufacturing unit and member for liquid crystal manufacturing unit using the same |
| JP2014129223A (en) * | 2012-11-30 | 2014-07-10 | Kyocera Corp | Ceramic sintered compact and abrasion-resistant component possessing the same |
-
1993
- 1993-03-31 JP JP05073287A patent/JP3124863B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000327426A (en) * | 1999-05-21 | 2000-11-28 | Ngk Spark Plug Co Ltd | Heating resistor, heating resistor for ceramic heater and ceramic heater using the same |
| JP2007169118A (en) * | 2005-12-22 | 2007-07-05 | Kyocera Corp | Silicon nitride sintered compact, and member for semiconductor manufacturing unit and member for liquid crystal manufacturing unit using the same |
| JP2014129223A (en) * | 2012-11-30 | 2014-07-10 | Kyocera Corp | Ceramic sintered compact and abrasion-resistant component possessing the same |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3124863B2 (en) | 2001-01-15 |
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