JPH068219B2 - Silicon carbide based sintered body and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to tool parts such as wear-resistant tools or cutting tools, and structural parts such as engine parts or turbine parts used in automobiles, aircraft, ships, etc., Further, the present invention relates to a silicon carbide based sintered body which can be applied to various electronic parts by utilizing its excellent thermal conductivity, and a method for producing the same.

(Prior Art) Silicon carbide is a compound having a high covalent bond, so that the self-diffusion coefficient of constituent atoms is small, and the ratio of grain boundary energies is large compared to ionic crystals and metal crystals. It is a sintered material. Silicon carbide, which is a material that is difficult to sinter, includes B, C, B ₄ C, BN, B ₂ O ₃ , Al, and Al.
_{B 2, Al 2 O 3,} Al 4 C 3, AlN, Be, Be
Sinters having a dense columnar crystal structure have been produced by reaction sintering or liquid phase sintering with addition of O, Si, etc., and many of these sintered bodies and manufacturing methods thereof have been proposed.

These sintered bodies have problems of poor oxidation resistance and extremely low strength at room temperature. As a material that can solve these problems, a sintered body obtained by combining silicon carbide and an oxide of a rare earth element is disclosed in JP-A-57-160970. Also, this Japanese Patent Laid-Open No. 57-1609
The inventor of JP-A-70 discloses a sintered body obtained by combining sintering of silicon carbide, an oxide of a rare earth element and an oxide of another metal, which is capable of further promoting sintering and achieving high toughness. It is disclosed in Japanese Patent Publication No. 59-21579.

(Problems to be Solved by the Invention) The silicon carbide sintered body disclosed in JP-A-59-21579 is
Compared to other conventional silicon carbide sintered bodies, this is an excellent sintered body in which the bending strength at room temperature is somewhat improved and the strength is not significantly reduced at high temperatures. However, this silicon carbide sintered body is still low in strength at room temperature as compared with a silicon nitride sintered body, and therefore, for example, when grinding and processing the sintered body for use as a tool part or structural part, or Even when it is used at high temperature, it may be easily damaged when it is set at room temperature, and there is a problem that it is strongly restricted in shape for practical use.

The present invention has solved the above-mentioned problems, and more specifically, it does not cause segregation in a powdery structure, has high strength at room temperature, and has little strength reduction at high temperature, and has a low strength. And a method for manufacturing the same.

(Means for Solving the Problems) One of the inventors of the present invention investigated a silicon nitride-based sintered body and applied for several patents for the results. Based on the application contents of these series of patents, a study was conducted on a silicon carbide-based sintered body. As a result, a compound of rare earth elements was mainly added to a mixture containing silicon carbide and silicon nitride in an amount smaller than the amount of silicon carbide. When sintering is performed by adding a sintering aid, highly activated Si decomposed from silicon nitride reacts with C in the atmosphere or the surroundings to form new silicon carbide on the surface of the crystal grain of silicon carbide. It was possible to obtain the knowledge that it becomes a dense and high-strength sintered body as a mediating action of bonding. The present invention has been completed based on this finding.

That is, the silicon carbide-based sintered body of the present invention, Dy, Y, Er, Y
From 0.1% by weight to 20% by weight of a grain boundary phase composed of a complex oxynitride or a complex oxymuronium carbide containing at least one rare earth element in b and Ce and Mg, and the remaining silicon carbide It is characterized by becoming.

The silicon carbide based sintered body of the present invention is a sintered body composed of silicon carbide and a grain boundary phase, and the inner grain boundary phase is at least one of rare earth elements composed of Dy, Y, Er, Yb and Ce. And a complex oxynitride or a complex oxynitride carbide containing Mg. Specifically, at least one of the rare earth elements is M
_When expressed as ₁ , the grain boundary phase is composed of a composite compound represented by (M ₁ , Mg) (O, N) or (M ₁ , Mg) (O, N, C). For this grain boundary phase, it is preferable to select the ratio of the rare earth element and other elements depending on the application and shape.For example, when used at high temperature, in the composite compound in which the rare earth element is contained more than other elements. When used at low temperature, it is preferable to use a composite compound containing a rare earth element less than other elements.

The grain boundary phase in the sintered body of the present invention is required to be 0.1% by weight or more from the viewpoint of accelerating the sintering in the sintering process and the strength of the sintered body at room temperature, but conversely, it increases the sintering at high temperature. 20% by weight to reduce various properties such as body hardness and strength
The following is recommended. Among these grain boundary phases, especially dysprosium and M, which belong to heavy rare earth elements among rare earth elements,
At least one kind of complex oxynitride or complex oxynitride carbide with g and / or Si, specifically, (Dy, Mg) (O, N), (Dy, Mg) (O, N, C ), (Dy, Si) (O, N), (Dy, Si) (O, N, C), (Dy, Mg, Si) (O, N), (Dy, Mg, Si) (O, N) , C) in the case of a grain boundary phase consisting of at least one of the above, since it tends to have a dense sinterability with silicon carbide, increases the strength at room temperature, and causes little decrease in hardness and strength at high temperatures. It is preferable. Since these grain boundary phases are composite compounds containing nitrogen, they have remarkably excellent properties at high temperatures as compared with those of a grain boundary phase composed of a lower oxide.

Silicon carbide in the silicon carbide-based sintered body of the present invention, even if β-SiC consisting of cubic crystals and / or various α-SiC consisting of hexagonal crystals, there is no great difference in their characteristics, especially the average particle size of silicon carbide. Having a grain structure of 3 μm or less is preferable because it is dense and has high strength.

The silicon carbide-based sintered body of the present invention can be produced by various manufacturing methods, but particularly 80% by weight of a mixed powder having a weight ratio of silicon nitride powder to silicon carbide powder of 2:98 to 35:65. ˜99.9% by weight and at least one compound powder of rare earth element in the oxide powder, nitride powder or oxynitride powder of the remaining rare earth element and oxide powder of Mg, nitride powder, and / or After mixing with an oxynitride powder and molding, pressureless sintering or pressure sintering at a temperature of 1600 ° C. or higher in a non-oxidizing atmosphere to contain at least one of rare earth elements and Mg A preferable method is a method of producing a sintered body composed of 0.1 wt% to 20 wt% of a grain boundary phase composed of the complex oxynitride or complex oxynitride carbide and the balance silicon carbide.

Furthermore, the production method of the silicon carbide-based sintered body of the present invention will be specifically described. As a starting material, β-SiC is used.
Powder, α-SiC powder or at least one of amorphous silicon carbide powder can be selected.
-Si ₃ N ₄ powder, β-Si ₃ N ₄ powder, or amorphous silicon nitride powder, or a method of selecting at least one of them, or 8% by weight or less of carbon and / or graphite based on these silicon nitride powders. There is a way to replace it. In order to obtain a dense and high-strength sintered body, it is very preferable that the starting material contains silicon nitride that produces highly activated Si.

Of these, silicon carbide is amorphous silicon carbide and β-S.
By transforming iC into α-SiC, the sinterability is remarkably improved, and it is preferable to use amorphous silicon carbide powder and / or β-SiC powder as a starting material particularly at a sintering temperature of 1900 ° C. or lower. It is preferable to use α-SiC powder and / or β-SiC powder as a starting material from the viewpoint of suppressing grain growth and preventing the strength of the sintered body from decreasing at a sintering temperature of ℃ or higher. Further, silicon nitride is decomposed in the sintering process and most of it is converted into SiC, which has the function of fixing the SiC particles of the starting material to each other. For this reason, it is preferable to use silicon nitride powder or silicon nitride powder and carbon and / or graphite in an amount of 8% by weight or less based on the silicon nitride powder as the starting material. If the amount of silicon nitride powder used as a starting material is too large, it will not be completely decomposed in the sintering process, and silicon nitride will remain after sintering. Since it is difficult to form a lump, the compounding ratio of the silicon nitride powder and the silicon carbide powder is determined to be 2:98 to 35:65 by weight.

Among the starting materials, the compound powder of the rare earth element is selected from at least one of oxide powder, nitride powder or oxynitride powder, and other than Mg oxide powder, nitride powder, carbide powder or Si. There is a method of selecting at least one kind of the oxide powder and the mutual solid solution powder thereof, or a method of using it as a solid solution powder of a compound of a rare earth element and a compound of Mg. For these starting materials, it is better to use a powder that is as fine as possible because it has better sinterability and tends to be a dense sintered body. Particularly, silicon carbide powder and silicon nitride powder are hydrothermally oxidized, hydrothermally precipitated, and hydrous. Carbonization of fine powder obtained by using solution reaction such as hydrothermal method such as thermosynthesis method, hydrothermal decomposition method, hydrothermal crystallization method, hydrothermal hydrolysis method, alkoxide hydrolysis method or neutralization coprecipitation method It is preferable to use a powder of 1 μm or less which can be obtained by the treatment or nitriding treatment.

Mixing and pulverizing the starting raw material powder should be performed with a cemented carbide ball, a stainless steel ball or a ceramics ball in a container made of stainless steel, a container lined with cemented carbide, a container lined with urethane rubber or a plastic container. it can. In particular, in order to enhance the crushing effect and to refine the starting material powder, a method of mixing and crushing with a cemented carbide ball using a stainless steel container or a container lined with a cemented carbide, a method using a vibrating ball mill or A method in which an organic solvent such as acetone, hexane, benzene or alcohol is added and wet-mixing and pulverizing is preferable. Also,
If it is necessary to prevent the components from mixing into the mixed powder as impurities due to abrasion of the container or balls, etc., make a silicon carbide and / or silicon nitride based sintered body in a container lined with urethane rubber. A method of mixing and pulverizing the starting material powder with the balls is preferable.

The mixed powder is molded by filling the mixed and ground powder into a graphite mold and hot pressing (HP) in a non-oxidizing atmosphere, or by adding a molding aid such as paraffin or camphor to the mixed and ground powder. If necessary, after granulating into granules, filling in a mold and press-molding, or enclosing the mixed powder with latex rubber etc., and then applying external pressure by pressurizing with water. A method, or a method of adding a thermoplastic resin, a plasticizer, a lubricant and the like to the mixed powder and molding the mixture with an injection molding machine can be applied. A method of directly sintering the powder compact molded in this way, or a method of pre-sintering the powder compact at a temperature lower than the sintering temperature and then performing cutting, grinding, cutting, etc. There is a method of sintering in an oxidizing atmosphere.

The sintering temperature is 1700 ° C. or higher in the case of pressureless sintering (sintering in a pressure including a reduced pressure state of atmospheric pressure or less) and 1600 ° C. or higher in the case of pressure sintering. .
After sintering, hot isostatic pressing (HIP) treatment may be performed to obtain a more dense and high-strength sintered body.

(Function) In the silicon carbide-based sintered body of the present invention, a nitrogen-containing metal compound is uniformly dispersed in a sintered grain boundary of silicon carbide, and the metal compound acts to suppress grain growth of silicon carbide, A dense sintered body having a fine granular isotropic structure is formed. For this reason, the sintered body of the present invention has excellent hardness, strength and thermal conductivity from room temperature to high temperature, and particularly strength and fracture toughness value at room temperature considered to be weak points of conventional silicon carbide-based sintered bodies. Is significantly superior.

(Example) α-SiC, β-SiC, amorphous silicon carbide (A-SiC) α-Si ₃ N ₄ , β-Si having an average particle size of 1 μm or less.
₃ N ₄ and various powders were blended as shown in Table 1, and a ball made of a Si ₃ N ₄ -based sintered body and a hexane solvent were added to this blended powder, and the mixture was ground for 48 hours. The mixed powder thus obtained is subjected to a hot pressing (HP) in a non-oxidizing atmosphere, a method of sintering after holding for 2 hours in a gas pressure of a non-oxidizing atmosphere after press molding, or a non-oxidizing property. Sintering was performed by performing HIP treatment after sintering while maintaining the pressure in the atmosphere without pressure for 2 hours. The sintering conditions of each sample at this time are also shown in Table 1. Various characteristic values of each sintered body thus obtained were examined, and the results are shown in Table 2. In addition, the composition and structure of each sintered body were examined by metallographic microscope, scanning microscope, X
The results were examined by line diffraction and Raman microanalysis, and the results are shown in Table 3.

(Effects of the Invention) As a result, the silicon carbide-based sintered body of the present invention has thermal conductivity, hardness, and strength at high temperatures that are almost the same as or higher than those of conventional silicon carbide sintered bodies, and that at room temperature The fracture toughness value is as high as 50% to 70%, which is remarkably excellent.

From this, the silicon carbide-based sintered body of the present invention, from tool parts such as cutting tools or wear-resistant tools to structural parts such as engine parts or turbine parts and thermal conductivity, wear resistance, corrosion resistance and high strength. It is an industrially useful material that can be applied to electronic parts used, and can also be used for applications or shapes that cannot be used due to insufficient strength in conventional silicon carbide sintered bodies.

Claims (6)

[Claims] 1. A grain boundary phase composed of a complex oxynitride or a complex oxynitride carbide containing at least one rare earth element selected from Dy, Y, Er, Yb, and Ce, and Mg. A silicon carbide-based sintered body, characterized by being composed of weight% and the balance being silicon carbide. 2. The silicon carbide based sintering according to claim 1, wherein the grain boundary phase is a complex oxynitride or a complex oxynitride carbide containing dysprosium and Mg. body. 3. The silicon carbide has a granular structure having an average particle size of 3 μm or less.
Item 3. The silicon carbide-based sintered body according to Item 2. 4. A mixed powder having a weight ratio of silicon nitride powder to silicon carbide powder of 2:98 to 35:65, 80 wt% to 99.9 wt%, and the balance of Dy, Y, Er, Yb, Ce. After mixing and molding at least one compound powder of rare earth element and Mg oxide powder, nitride powder and / or oxynitride powder, pressureless sintering at a temperature of 1600 ° C or higher in a non-oxidizing atmosphere. Or by pressure sintering
At least one rare earth element and Mg in Dy, Y, Er, Yb, Ce
A silicon carbide-based sintered body characterized by being a sintered body consisting of 0.1 wt% to 20 wt% of a grain boundary phase composed of a composite oxynitride or a composite acid chamber carbide containing Manufacturing method. 5. The silicon carbide group according to claim 4, wherein the compound powder of the rare earth element is at least one of dysprosium oxide powder, cisprosium nitride powder and dysprosium oxynitride powder. Manufacturing method of sintered body. 6. The silicon nitride powder is formed by substituting 8% by weight or less of carbon and / or graphite with respect to the silicon nitride powder.
Item 6. A method for producing a silicon carbide-based sintered body according to Item 5.