JPH0244784B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic sintered body containing silicon nitride as a main component and a method for manufacturing the same, and more specifically, the present invention relates to a ceramic sintered body containing silicon nitride as a main component and a method for manufacturing the same. The present invention relates to a ceramic sintered body whose mechanical strength decreases little even when exposed to an oxidizing atmosphere, and a method for producing the same. Ceramic sintered bodies have excellent thermal properties and high density, so they are attracting wide attention in various industrial fields as being at the forefront of various structural materials. There is a sintered body of silicon nitride. Conventionally, in the production of silicon nitride sintered bodies, reaction sintering methods, hot pressing methods, and ordinary sintering methods have generally been employed. Among these, the reactive sintering method is a method in which metal silicon (Si) powder is molded into the required shape in advance, and this is gradually heated in a nitrogen or ammonia gas atmosphere to sinter it at the same time as nitriding. . In addition, the hot press method adds sintering aids _{(e.g., Y 2 O 3 ,}
MgO, Al ₂ O ₃ ) is added, and this is heated at a high temperature of 1700 to 1800℃ in a specified mold (for example, a graphite mold) for 150°C.
This is a method of sintering by applying a pressure of ~500 Kg/cm ² . According to this method, it is possible to obtain a sintered body having high density, high mechanical strength, and excellent thermal properties such as thermal shock resistance and small decrease in mechanical strength under high-temperature oxidizing atmosphere. . However, on the other hand, this method has the disadvantage that it is difficult to obtain a sintered body with a complicated and large shape, and furthermore, it is inferior in mass productivity. On the other hand, in the normal sintering method, Si ₃ N ₄ powder and sintering aid are preformed with a binder such as paraffin, and this is heated and sintered as it is without hot pressing in a non-oxidizing atmosphere. It's a method. However, with this method, it is difficult to obtain a sintered body with high density and excellent mechanical strength and thermal shock resistance. Therefore, as a result of various studies regarding the above-mentioned ordinary sintering method, the present inventors found that ordinary sintering is capable of producing high-density sintered bodies with excellent mechanical strength and thermal shock resistance, comparable to the hot pressing method. (Japanese Patent Application Laid-open Nos. 113674-1982 and 116670-1987). However, the resistance of the silicon nitride sintered bodies obtained by these methods to a decrease in mechanical strength under a high-temperature oxidizing atmosphere was not necessarily satisfactory. The present inventors further conducted intensive research regarding the above points, and as a result, completed the present invention. The purpose of the present invention is to have high density, excellent thermal shock resistance,
Moreover, it provides a ceramic sintered body whose mechanical strength decreases little even when exposed to an oxidizing atmosphere for a long time in the temperature range of 800 to 1000°C, especially a ceramic sintered body whose main component is silicon nitride, and a method for manufacturing the same. It is to be. That is, the ceramic sintered body of the present invention contains 0.1 to 10% by weight of yttrium oxide (Y ₂ O ₃ ); 0.1 to 10% by weight of aluminum oxide (Al ₂ O ₃ ); 0.1 to 10% by weight of aluminum nitride (Al ₂ N). %; titanium boride (TiB ₂ ),
Vanadium boride (VB ₂ ), chromium boride (CrB), zirconium boride (ZrB ₂ ), niobium boride (NbB),
At least one boride selected from the group consisting of molybdenum boride (MoB ₂ ), hafnium boride (HfB ₂ ), tantalum boride (TaB ₂ ), and tungsten boride (WB) from 0.1 to 5% by weight; and the remainder consists of silicon nitride (Si ₃ N ₄ ). The ceramic sintered body of the present invention has Si ₃ N ₄ as a main component, and it is preferable that Si ₃ N ₄ is used in a blending ratio of 70% by weight or more. used
Although Si ₃ N ₄ may be either an α-phase type or a β-phase type, the α-phase type is preferably used. Both Y ₂ O ₃ and Al ₂ O ₃ function as sintering accelerators. These ingredients have a mixing ratio of 10
If it exceeds % by weight, the mechanical strength and thermal shock resistance of the obtained sintered body will decrease, which is not preferable. Generally, it is preferable that these components have a combined blending ratio of 3 to 15% by weight. AlN not only has the function of suppressing the evaporation of Si ₃ N ₄ , the main component, during the sintering process, but also reacts with other components to generate a liquid phase that contributes to sintering, thereby contributing to the overall sintering process. If the blending ratio exceeds 10% by weight, the mechanical strength and thermal shock resistance of the obtained sintered body will be reduced. Also, TiB ₂ , VB ₂ , CrB, ZrB ₂ , NbB,
Borides such as MoB ₂ , HfB ₂ , TaB ₂ , and WB not only promote the functions of the sintering accelerators such as Y ₂ O ₃ and Al ₂ O ₃ mentioned above, but also cause damage to the surface of the sintered body. In order to form a borosilicate-based glass protective coating with high oxidation resistance, the obtained sintered body was heated at 800 to 1000°C.
It has the function of preventing a decrease in mechanical strength in an oxidizing atmosphere. In particular, MoB ₂ , CrB, and TiB ₂ greatly contribute to this effect. However, if the blending ratio thereof exceeds 5% by weight, it is undesirable because the mechanical strength and thermal shock resistance of the sintered body are reduced. The method for producing a ceramic sintered body of the present invention includes yttrium oxide (Y ₂ O ₃ ) powder 0.1 to 10% by weight; aluminum oxide (Al ₂ O ₃ ) powder 0.1 to 10% by weight; aluminum nitride (AlN) powder 0.1 to 10% by weight. 10% by weight; titanium boride (TiB ₂ ), vanadium boride (VB ₂ ), chromium boride (CrB), zirconium boride (ZrB ₂ ),
Niobium boride (NbB), molybdenum boride ( _MoB2 ),
0.1 to 5% by weight of at least one boride powder selected from the group consisting of boride powders of hafnium boride (HfB ₂ ), tantalum boride (TaB ₂ ), and tungsten boride (WB); and the remainder The method is characterized in that a mixed powder made of silicon nitride (Si ₃ N ₄ ) powder is molded, and the molded body is sintered in a non-oxidizing atmosphere. In the method of the present invention, these components are mixed using a grinding mixer such as an ordinary ball mill.
- It can be carried out using a solvent such as butyl alcohol. A binder such as paraffin is added to the mixed powder thus prepared, and an appropriate pressure is applied to form a molded body into a predetermined shape. This molded body was heated to 1500 to 1900 in a non-oxidizing atmosphere.
It is sintered by heating at 1600 to 1800°C, preferably 1600 to 1800°C, to form a sintered body. Examples of the non-oxidizing atmosphere include nitrogen, argon, and the like. In an oxidizing atmosphere
This is not possible because Si ₃ N ₄ oxidizes to become SiO ₂ . Incidentally, during this sintering, sintering may be performed in a hot press state where a pressure of 50 to 500 kg/cm ² is applied, or in a pressurized state in a non-oxidizing gas atmosphere. Alternatively, even if sintering is performed in a pressurized atmosphere after sintering by the normal sintering method, the properties of the sintered body will not be impaired in any way. The present invention will be explained in more detail below with reference to Examples and Reference Examples. Examples and Reference Examples As shown in the table, each component was blended at a predetermined blending ratio (wt%), an appropriate amount of n-butyl alcohol was added thereto, and then milled using a rubber-lined ball mill for 24 hours.
A total of 22 types of mixed powders, 13 types as examples according to the present invention and 9 types as reference examples, were prepared by mixing at different times. In addition, Si ₃ N ₄ powder is
It is a powder with an average particle size of 1.2μ containing 85% α phase type Si ₃ N ₄ . In addition, the average particle size of _Y2O3 powder is _1.0μ , the average particle size of _{Al2O3 powder} is 0.5μ, the average particle size of AlN is 1.5μ, and the average particle size of various borides is 1.0μ. Ta. After further adding 7% by weight of paraffin to the obtained mixed powder, a plate-shaped body having a length of 60 mm, a width of 40 mm, and a thickness of 10 mm was molded at room temperature under a molding pressure of 700 Kg/cm ² . Each of the obtained molded bodies was first heat-treated at 700°C to thermally decompose and remove paraffin, and then sintered at 1750°C while passing nitrogen gas (3/min). For each sintered body obtained, the relative density, bending strength at room temperature, in air, at 800℃, 900℃, and 1000℃,
After 5000 hours of oxidation treatment, the bending strength and thermal shock resistance at room temperature were measured. The results are summarized in Examples 1 to 13 and Reference Examples 1 to 1.
9 in the table. Each measurement item followed the specifications below. Relative density: Shown as a relative ratio (%) to the theoretical density calculated from the composition ratio. Transverse bending strength: Based on 3-point bending strength test, specimen size 3 x 3 x 30 mm, crosshead speed
0.5mm/min, span 20mm, temperature room temperature. Measurements were performed on four specimens of each sample, and the average value is shown. Thermal shock resistance: A test piece with the same shape as the test piece for measuring bending strength is heated to a certain temperature, then placed in water to rapidly cool it, and the presence or absence of cracks in the test piece is observed using fluorescent flaw detection. It is expressed as the difference ΔT between the heating temperature and water temperature at the time of occurrence. As is clear from the table, the sintered bodies obtained by the method of the present invention (Examples 1 to 13) have a high relative density of 95% or more of the theoretical density, and also have a bending strength of 85 kg. /mm ² or more, and thermal shock resistance is also ΔT
It is approximately 700℃ or higher. Among other things, 800
It was found that even after oxidation treatment at ~1000°C for 5000 hours, the decrease in bending strength was small. As detailed above, the method of the present invention does not require hot pressing, so it is suitable for mass production, and has high density, excellent thermal shock resistance, and
Since it is possible to produce a sintered body with a small decrease in mechanical strength in an oxidizing atmosphere at 800 to 1000°C, its industrial usefulness is great.

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Claims (1)

[Claims] 1 Yttrium oxide 0.1-10% by weight; Aluminum oxide 0.1-10% by weight; Aluminum nitride 0.1-10% by weight
10% by weight; selected from the group consisting of borides of titanium boride, vanadium boride, chromium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, tantalum boride, and tungsten boride A ceramic sintered body comprising: 0.1 to 5% by weight of at least one boride; and the remainder being silicon nitride. 2 Yttrium oxide powder 0.1-10% by weight; aluminum oxide powder 0.1-10% by weight; aluminum nitride powder 0.1-10% by weight; titanium boride, vanadium boride, chromium boride, zirconium boride, niobium boride, boride A mixed powder consisting of 0.1 to 5% by weight of at least one boride powder selected from the group consisting of boride powders of molybdenum, hafnium boride, tantalum boride, and tungsten boride; and the balance consisting of silicon nitride powder. 1. A method for producing a ceramic sintered body, comprising: molding the molded body, and sintering the molded body in a non-oxidizing atmosphere.