JPS6323153B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a silicon nitride sintered body. Furthermore,
The present invention relates to a silicon nitride sintered body that has high strength at high temperatures and is obtained by normal pressure firing. Silicon nitride sintered bodies are a type of ceramics that have made remarkable progress in recent years, and are being considered for application to parts used under harsh conditions, such as gas turbine parts, jigs, and internal combustion engine parts. These applications generally require complex shapes, high strength at high temperatures, and stability in quality, especially strength, and so far no product has been found that satisfies all of these requirements. . First, since a complex shape is required, there is a limit to the application of the hot press manufacturing method, and an atmospheric pressure firing method must be adopted. However, when using the atmospheric pressure firing method, it is not possible to obtain sufficiently high strength using various conventional additives, and the strength also varies widely, making it difficult to achieve sufficient quality stability. The present inventors have discovered the present invention as a _result of various studies to eliminate the above-mentioned _drawbacks .
Spinel represented by at least one divalent metal selected from Sr and Fe, and B representing at least one trivalent metal selected from Al, Cr, and Fe.
The gist is a silicon nitride sintered body consisting of 0.5 to 5% by weight of titanium carbide, 0.5 to 5% by weight of titanium carbide, and the balance silicon nitride. Although it has not yet been fully elucidated why the above object is achieved by the structure of the present invention, according to the structure of the present invention, a sintered body having high strength at high temperatures can be obtained. The spinel used in the present invention has the general formula AB ₂ O ₄
(A is at least one divalent metal selected from Mg, Ca, Ba, Sr, and Fe; B is at least one trivalent metal selected from Al, Cr, and Fe) with a spinel structure. Among these inorganic oxides, MgAl ₂ O ₄ is most preferred from the viewpoint of high melting point, high temperature stability, reactivity with silicon nitride, etc. These spinels need to be present in the silicon nitride sintered body compositionally, but it is not necessarily necessary that they be added as spinels in advance during manufacturing, and they can be added as AO and B ₂ O ₃ . Of course, this is a good thing. Below, MgAl ₂ O ₄ is the most preferred spinel.
This will be explained using an example. MgAl ₂ O ₄ is added as a sintering aid, but the amount added should be small as long as it is effective as a sintering aid. That is, if the amount added is too large, the heat resistance of the silicon nitride sintered body becomes insufficient, the strength decreases significantly at high temperatures, and the coefficient of thermal expansion of the silicon nitride sintered body increases. I don't like it. Of course, if it is too small, the effect as a sintering aid will not be fully manifested, so there is a lower limit to the amount of addition, and as a result of the inventors' studies,
It has been found that it is necessary to include _MgAl2O4 in the range of 0.5 to 5% by weight, preferably 1 to 2% _by weight. Furthermore, the present inventors have found that the presence of titanium carbide in the bonded portion of a silicon nitride sintered body has a significant effect in improving the high temperature strength of the sintered body. That is, although spinel alone has the above-mentioned effects, it tends to react with silica on the surface of silicon nitride particles to form a glass phase, and depending on the application, it is unsatisfactory in terms of high-temperature strength. However, it has been discovered that the presence of titanium carbide dramatically improves the high-temperature strength. Although it has not yet been fully elucidated why titanium carbide has such an effect, the presence of titanium carbide in the binder phase makes it difficult to form the glass phase described above. Alternatively, the present inventors speculate that this is due to the rapid crystallization of the generated glass phase. The amount of titanium carbide present is 0.5 to 5% by weight,
Preferably 1-2% by weight is required. The reason for this is that if it is less than 0.5% by weight, or even 1.0% by weight, the high-temperature strength of the silicon nitride sintered body cannot be sufficiently improved, and if it is more than 5% by weight, or even 2% by weight, the This is because not only is no further effect of improving high-temperature strength seen, but on the contrary, it causes a decrease in high-temperature strength. Furthermore, in the present invention, since it is necessary to reduce the amount of spinel as much as possible, the particle size of the spinel is also preferably as small as possible, and the average particle size is preferably 1 μm or less. The reason is that above 1μ,
Even if the amount of spinel present is set to its upper limit, spinel may not be uniformly distributed in the silicon nitride sintered body, and therefore the strength of the silicon nitride sintered body may vary depending on the location. It is. Although the present invention is not limited to those obtained by a specific manufacturing method, a preferred method for manufacturing the silicon nitride sintered body of the present invention will be described below as an example. Silicon nitride powder with an average particle size of about 2μ,
0.5 to 5% by weight of spinel of 1μ or less, preferably 0.5μ or less, and 0.5 to 5% of titanium carbide powder slightly finer than this
% by weight in a conventional manner. Of course, spinel is made of aluminum hydroxide, aluminum chloride,
It is also possible to produce the powder by blending powders of alumina, magnesium hydroxide, magnesia, etc. with silicon nitride powder. Then, an appropriate amount of an organic binder is added to this mixed powder, and the mixture is molded using a mechanical press. For this molding, if the shape is complex, a slurry casting method in which the shape is poured into a plaster mold can be adopted. After the molded body thus obtained is sufficiently dried, it is usually dried under a non-oxidizing atmosphere (an inert atmosphere such as argon or a neutral atmosphere such as nitrogen).
Sintered at 1600-1800℃. In addition to the above-mentioned normal sintering method, a hot pressing method may also be employed when a simple shape and high strength are required. Example Silicon nitride powder (α phase 75%, average particle size 1.5μ, purity
99.5%) and each of the additives shown in Table 1 were blended in the proportions shown in Table 1 and mixed in a pot mill. This mixed powder was molded into 2000Kg/cm ² by hydraulic press molding method.
After molding, it was fired. The properties of the sintered bodies are also listed in Table 1. Table 2 shows the properties of sintered bodies obtained in almost the same manner except that the types and blending ratios of additives were changed, along with the types and blending ratios of additives (each with an average particle size of approximately 0.5μ). .

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Claims (1)

[Claims] 1 General formula AB ₂ O ₄ (where A is Mg, Ca, Ba,
Spinel represented by at least one divalent metal selected from Sr and Fe, and B representing at least one trivalent metal selected from Al, Cr, and Fe.
A silicon nitride sintered body consisting of 0.5 to 5% by weight of titanium carbide, 0.5 to 5% by weight of titanium carbide, and the balance silicon nitride. 2. The silicon nitride sintered body according to claim 1, wherein the spinel has a grain size of 1 μm or less. 3. The silicon nitride sintered body according to claim 1 or 2, wherein the spinel is MgAl ₂ O ₄ .