JP3567001B2 - Method for producing composite sintered body of silicon carbide and silicon nitride - Google Patents

Description

【００２２】
各種試料粉末を金型プレス（２００ｋｇ／ｃｍ^２ ）で予備成形した後、ＣＩＰで４トン／平方センチの等方圧を加え、３０×５０×６ｍｍの成形体を作製した。成形体を図１に示すように伴粉に埋め込むようにＢＮルツボに入れ、これをさらにカーボンルツボに入れて、窒素ガス中１０００気圧の雰囲気下、１８５０℃でＨＩＰ焼結を行い、炭化珪素と窒化珪素の複合焼結体を得た。
【００２３】
得られた焼結体の密度をアルキメデス法で測定した。ＪＩＳ Ｒ−１６０１に従って、焼結体を３×４×４０ｍｍの大きさに切断して試験片とし、スパン３０ｍｍ及びクロスヘッドスピード０．５ ｍｍ／分の条件で室温での３点曲げ強度試験を行った。結果はまとめて表２に示す。
【００２４】

【００２５】
表２に示すように、ホウ素及び炭素を添加しない比較例１と炭化珪素の含有率が１５重量％以下の比較例２〜６の３点曲げ強度がいずれも実施例１〜５より低かった。また、Ｙ_２ Ｏ_３ とＡｌ_２ Ｏ_３ を添加せず、ホウ素と炭素のみを焼結助剤として添加した比較例７では、ＨＩＰによる焼結ができなかった。
【００２６】
図２には、実施例２で得た焼結体の顕微鏡断面写真（日本電子（株）製顕微鏡、倍率×１００，０００）を示す。焼結体のＳｉ_３Ｎ_４粒子Ａ内及び粒界に微細なＳｉＣ粒子Ｂが分散し、かつＳｉＣ粒子Ｃ内に微細なＳｉ_３Ｎ_４粒子Ｄが分散していることがわかる。
【００２７】
【発明の効果】
以上詳述したように、本発明の方法によれば、炭化珪素と窒化珪素と特定の焼結助剤を用い、ＨＩＰにより焼結することによって、Ｓｉ_３ Ｎ_４ 粒子内及び粒界に微細なＳｉＣ粒子が分散し、かつＳｉＣ粒子内に微細なＳｉ_３ Ｎ_４ 粒子が分散したナノコンポジット構造を有する複合焼結体が得られる。このため、本発明の方法により得られた複合焼結体は優れた緻密性と高温強度を有する。このような特性を有する炭化珪素と窒化珪素の複合焼結体は、高温下で使用される摺動部材等に好適である。
【図面の簡単な説明】
【図１】本発明の炭化珪素と窒化珪素の複合焼結体の製造に用いるＨＩＰ焼結用ルツボを概略的に示す断面図である。
【図２】本発明における炭化珪素と窒化珪素の複合焼結体の組織の一例を示す模式図である。
【符号の説明】
１・・・カーボンルツボ
２・・・ＢＮルツボ
３・・・伴粉
４・・・成形体
Ａ・・・窒化珪素粒子
Ｂ・・・炭化珪素微細粒子
Ｃ・・・炭化珪素粒子
Ｄ・・・窒化珪素微細粒子[0001]
[Industrial applications]
The present invention relates to a method for producing a composite sintered body of silicon carbide and silicon nitride, and more particularly to a method for producing a composite sintered body fired by HIP and having high density and excellent strength.
[0002]
Problems to be solved by the prior art and the invention
Silicon nitride ceramic sintered bodies have high strength, high thermal shock resistance, and high wear resistance, and silicon carbide ceramic sintered bodies have high strength and high oxidation resistance. It is expected to be used as structural ceramics, which are used under severe conditions. In recent years, such a monolithic sintered body has been combined with a silicon nitride-silicon carbide composite sintered body at a micro level having both advantages and a silicon nitride-carbonized carbide having a nanocomposite structure in which fine silicon carbide is dispersed in grains of silicon nitride. Various attempts have been made to obtain a silicon composite sintered body.
[0003]
JP-A-58-91070 discloses that silicon carbide and silicon nitride formed by adding, mixing and sintering boron, carbon and an inorganic oxide as a sintering aid to a mixed powder of silicon carbide and silicon nitride. Are disclosed. This composite sintered body is manufactured by using fine silicon nitride-silicon carbide mixed powder and sintering by normal sintering or hot pressing at 1500 to 2300 ° C in the presence of a sintering aid. However, this prior art does not specifically describe a method of adding boron, carbon, and an inorganic oxide at the same time. Therefore, in a sintered body by this method, it is necessary to use a hot press as a sintering method. Therefore, there is a problem that it is not possible to cope with a component having a complicated shape.
[0004]
Japanese Patent Application Laid-Open No. 2-160669 discloses that silicon carbide having an average particle size of 1 μm or less is dispersed at a grain boundary from amorphous silicon nitride-silicon carbide composite powder obtained by a gas phase reaction method, and is several nanometers. Discloses a silicon nitride-silicon carbide composite sintered body having a fine structure in which fine particles of silicon carbide having a size of several hundred nanometers are dispersed in silicon nitride particles. However, the amorphous silicon nitride-silicon carbide composite powder has poor moldability because decomposition components are generated during sintering and liquid phase sintering does not easily proceed and is very bulky. Therefore, also in this case, it is necessary to substantially use a hot press as the sintering method.
[0005]
Therefore, an object of the present invention is to provide a method for producing a composite sintered body of silicon carbide and silicon nitride, which has high denseness and excellent high-temperature strength, fired by HIP capable of handling a complicated shape.
[0006]
[Means for Solving the Problems]
In light of the above objects, as a result of intensive studies, the present inventors have found that, if a specific additive is added to a mixed powder of silicon carbide and silicon nitride and HIP sintering is performed, silicon carbide and silicon nitride having high density and strength can be obtained. It was discovered that a composite sintered body of the formula (1) was obtained, and the present invention was completed.
[0007]
That is, the method for producing a composite sintered body of silicon carbide and silicon nitride according to the present invention comprises the steps of: (a) adding a sintering aid, boron and carbon to a mixed powder of silicon carbide and silicon nitride; using (a) aluminum oxide and / or aluminum nitride as the aid, and (b) periodic table group 3A elements and / or oxides of group 4A elements, is then burned (b) HIP, silicon carbide and silicon nitride the total of 100 weight% of the content of silicon carbide and 15 to 50 wt%, the total content of the sintering aid and 15% by weight or less, 0.3 to the total content of the boron and carbon The ratio of the total content of (a) the aluminum oxide and / or aluminum nitride to the (b) the total content of the oxides of the Group 3A element and / or the Group 4A element of the periodic table is 2: 1. to 1: characterized by a 15.
[0008]
Hereinafter, the present invention will be described in detail.
[1] Starting Material (1) Si ₃ N ₄ Powder The silicon nitride powder used in the present invention preferably has an average particle size of 0.01 to 1 μm, particularly 0.1 to 0.8 μm. The addition amount of the Si ₃ N ₄ powder is preferably 50 to 85% by weight, more preferably 70 to 80% by weight, with the total weight of silicon carbide and silicon nitride being 100% by weight. If the amount of the Si ₃ N ₄ powder exceeds 80% by weight (the ratio of the Si ₃ N ₄ powder to the silicon carbide is too high), the combined effect of the silicon carbide is lost, which is not preferable.
[0009]
(2) Silicon Carbide Powder The silicon carbide powder preferably has an average particle diameter of 0.01 to 1 μm, particularly 0.08 to 0.8 μm. A preferable addition amount of the silicon carbide powder is 15 to 50% by weight, and more preferably 20 to 30% by weight, where the total weight of silicon carbide and silicon nitride is 100% by weight. If the content of the silicon carbide powder exceeds 50% by weight, densification becomes difficult, which is not preferable.
[0010]
(3) Sintering aid powder The sintering aid powder comprises (a) any one of aluminum oxide and aluminum nitride and / or (b) an oxide of a Group 3A element or a Group 4A element of the periodic table.
[0011]
Of Al ₂ O ₃ and AlN, Al ₂ O ₃ is more preferable. The other oxide is at least one selected from the group 3A elements of the periodic table such as Y ₂ O ₃ , Yb ₂ O ₃ and Er ₂ O ₃ and the compounds of the group 4A elements of the periodic table such as ZrO ₂ and HfO _2. And preferably Y ₂ O ₃ . A preferred combination is any one of Al ₂ O ₃ and AlN and one kind of inorganic oxide, particularly preferably Al ₂ O ₃ and Y ₂ O ₃ . The total content of the sintering aid is 15% by weight or less , preferably 8% by weight or less, with the total weight of silicon carbide and silicon nitride being 100% by weight. If the sintering aid powder is more than 15% by weight, the high-temperature strength of the sintered body is low. When simultaneously adding either Al ₂ O ₃ or AlN and an oxide of a Group 3A element or a Group 4A element of the Periodic Table, the total content of Al ₂ O ₃ and AlN and the Group 3A or Group 4A element of the Periodic Table are added. Is 2: 1 to 1:15.
[0012]
(4) Boron Boron may be any fine powder, but is preferably an amorphous powder. The average particle size of the boron powder is preferably 1 μm or less, particularly preferably 0.8 μm or less.
[0013]
(5) Carbon The carbonaceous powder used in the present invention is not particularly limited as long as it is fine, but graphite powder or carbon black powder such as acetylene black and Ketjen black is preferable, and graphite is particularly preferable. The average particle size of the carbonaceous powder is preferably 5 μm or less, particularly preferably 1 μm or less. If the average particle size is larger than 5 μm, uniform dispersion becomes difficult.
[0014]
The total content of boron and carbon is set to 0.3 to 5% by weight , and preferably 1 to 3% by weight , with the total weight of silicon carbide and silicon nitride being 100% by weight. If the total content of boron and carbon is more than 5% by weight, the density of the sintered body decreases.
[0015]
[2] Production method of composite sintered body (1) Production of molded body First, each component is blended so as to have the above-mentioned blending ratio, and is sufficiently mixed by a ball mill, a kneader or the like. Mixing may be dry or wet. In the case of wet mixing, a dispersion medium such as water, ethanol, or butanol is added to the powder mixture. In the case of injection molding, an appropriate organic or inorganic binder is added. Examples of the organic binder include ethyl silicate, polyethylene glycol, polyvinyl alcohol (PVA), acrylic emulsion, and polyurethane emulsion. Also, an inorganic binder can be added.
[0016]
The molded article can be produced by a method such as die molding. However, in order to produce a molded article having a complicated shape, slip casting or injection molding is preferable.
[0017]
(2) Sintering In the present invention, the compact is sintered by HIP. Good sintered body density can be achieved by HIP sintering. The sintering temperature is 1700-2200 ° C, preferably 1750-2000 ° C. If the sintering temperature is lower than 1700 ° C., the strength and toughness of the sintered body are low. If the sintering temperature exceeds 2200 ° C., decomposition of Si ₃ N ₄ starts, which is not preferable. Sintering is performed in a non-oxidizing atmosphere, preferably in a nitrogen gas atmosphere. At this time, the atmospheric gas pressure is preferably about 1 to 2000 kgf / cm ^2, and the sintering time is preferably about 1 to 5 hours. The compact is preferably put into a crucible and sintered together with the accompanying powder, preferably BN accompanying powder. The crucible is preferably a BN crucible, such as a BN crucible or a carbon crucible, particularly preferably a composite crucible composed of a carbon crucible and a BN crucible provided therein.
[0018]
In the composite sintered body of silicon carbide and silicon nitride obtained by the above method, fine SiC particles are dispersed in Si ₃ N ₄ particles and grain boundaries, and fine Si ₃ N ₄ particles are dispersed in SiC particles. It has a so-called nanocomposite structure. SiC particles for _Si 3 _{N 4} coefficient of thermal expansion than the particle is large, it believed to _Si 3 _{N 4} particles compressive residual stress acts. Further, the fine SiC particles dispersed in the grain boundaries the _Si 3 _{N 4} is believed to act as a suppressing wedge grain boundary sliding the _Si 3 _{N 4.}
[0019]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.
[0020]
Examples 1 to 5 and Comparative Examples 1 to 6
Si ₃ N ₄ powder having an average particle size of 0.1 μm, SiC powder having an average particle size of 0.2 μm, Y ₂ O ₃ powder having an average particle size of 1.4 μm, and an average particle size of 0 μm. 0.8 μm Al ₂ O ₃ powder, B powder having an average particle diameter of 0.8 μm, and C powder having an average particle diameter of 1 μm were weighed at the ratios shown in Table 1, and were weighed together with 300 g of ethanol and 600 g of silicon nitride balls. The mixture was placed in a 2 liter monopot, mixed by a ball mill using ethanol as a solvent for 64 hours, and the solvent was removed by drying to obtain a sample powder.
[0021]

[0022]
After various sample powders were preformed by a die press (200 kg / cm ² ), an isotropic pressure of 4 ton / square centimeter was applied by CIP to produce a 30 × 50 × 6 mm molded body. As shown in FIG. 1, the compact was placed in a BN crucible so as to be embedded in the accompanying powder, and this was further placed in a carbon crucible, and subjected to HIP sintering at 1850 ° C. in a nitrogen gas atmosphere at 1000 atm. A composite sintered body of silicon nitride was obtained.
[0023]
The density of the obtained sintered body was measured by the Archimedes method. According to JIS R-1601, the sintered body was cut into a size of 3 × 4 × 40 mm to obtain a test piece, and a three-point bending strength test was performed at room temperature under the conditions of a span of 30 mm and a crosshead speed of 0.5 mm / min. went. The results are summarized in Table 2.
[0024]

[0025]
As shown in Table 2, the three-point bending strengths of Comparative Example 1 in which boron and carbon were not added and Comparative Examples 2 to 6 in which the content of silicon carbide was 15% by weight or less were lower than Examples 1 to 5. In Comparative Example 7 in which only boron and carbon were added as sintering aids without adding Y ₂ O ₃ and Al ₂ O ₃ , sintering by HIP was not possible.
[0026]
FIG. 2 shows a micrograph of a cross section of the sintered body obtained in Example 2 (a microscope manufactured by JEOL Ltd., magnification × 100,000). It can be seen that the fine SiC particles B are dispersed in the Si ₃ N ₄ particles A and the grain boundaries of the sintered body, and the fine Si ₃ N ₄ particles D are dispersed in the SiC particles C.
[0027]
【The invention's effect】
As described in detail above, according to the method of the present invention, silicon carbide, silicon nitride, and a specific sintering aid are used, and sintering is performed by HIP, so that fine particles are formed in Si ₃ N ₄ particles and at grain boundaries. A composite sintered body having a nanocomposite structure in which SiC particles are dispersed and fine Si ₃ N ₄ particles are dispersed in the SiC particles is obtained. Therefore, the composite sintered body obtained by the method of the present invention has excellent denseness and high-temperature strength. A composite sintered body of silicon carbide and silicon nitride having such characteristics is suitable for a sliding member or the like used at a high temperature.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a crucible for HIP sintering used for manufacturing a composite sintered body of silicon carbide and silicon nitride according to the present invention.
FIG. 2 is a schematic diagram showing an example of a structure of a composite sintered body of silicon carbide and silicon nitride according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Carbon crucible 2 ... BN crucible 3 ... Powder 4 ... Molded body A ... Silicon nitride particle B ... Silicon carbide fine particle C ... Silicon carbide particle D ... Silicon nitride fine particles

Claims (2)

(A) A sintering aid, boron and carbon are added to a mixed powder of silicon carbide and silicon nitride, wherein (a) aluminum oxide and / or aluminum nitride ; (B) A method for producing a composite sintered body of silicon carbide and silicon nitride which is subjected to HIP sintering using an oxide of a group 3A element and / or a group 4A element, wherein the total of silicon carbide and silicon nitride is 100 weight %, The content of the silicon carbide is 15 to 50 % by weight, the total content of the sintering aid is 15 % by weight or less, and the total content of boron and carbon is 0.3 to 5% by weight. (A) The ratio of the total content of aluminum oxide and / or aluminum nitride to the total content of the oxides of Group 3A element and / or Group 4A element of the Periodic Table (B) is 2: 1 to 1:15 . A method comprising: The method for producing a composite sintered body of silicon carbide and silicon nitride according to claim 1 , wherein the HIP sintering is performed at 1700 ° C. or more and an atmospheric gas pressure of 1 to 2000 kgf / cm ² .

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