JPH04321578A - Production of sintered material of ceramics having compounded coating layer - Google Patents

Abstract

PURPOSE:To form a dense compounded coating layer of a silicon nitride layer and a silicon carbide layer having excellent adhesiveness on a heat-resistant substrate such as sintered material of silicon nitride or sintered material of silicon carbide. CONSTITUTION:A compounded coating layer of a silicon nitride layer and a silicon carbide layer is formed on the surface of a sintered material of silicon nitride or sintered material of silicon carbide by chemical vapor-phase growth method. A hydrogen gas is circulated in a reaction furnace when a reaction gas to be sent to the reaction furnace in order to form each coating layer and the amount of the hydrogen gas introduced to the reaction furnace is set at least >=3.4 times as much as the volume of the reaction furnace at room temperature under atmospheric pressure.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for producing a composite coated ceramic sintered body in which a composite coat layer consisting of silicon nitride and silicon carbide is formed in a layered manner on a heat-resistant base material by chemical vapor deposition, such as CVD. .

0002

BACKGROUND OF THE INVENTION Silicon nitride and silicon carbide sintered bodies have high strength at high temperatures and excellent thermal shock resistance, and are therefore used as high-temperature structural materials for gas turbine parts and the like. In addition, silicon nitride and silicon carbide sintered bodies have excellent corrosion resistance and chemical resistance, so they are used for parts such as susceptors, furnace tubes, and jigs used in the manufacture of semiconductor parts. In order to improve the oxidation resistance of silicon nitride sintered bodies, a silicon nitride sintered body coated with silicon nitride, which has excellent oxidation resistance, was produced using the CVD method.
It is disclosed in Japanese Patent Application Laid-Open No. 60-161383. In addition, at high temperatures, a reaction occurs between the grain boundary phase components of the silicon nitride sintered body and the silicon nitride coating layer, making it difficult to obtain a sufficient effect. A silicon nitride sintered body coated with silicon carbide by the CVD method is disclosed in JP-A-61-87573 and JP-A-2-289476. However, when a silicon nitride sintered body is coated with silicon nitride by the CVD method, it is not possible to completely prevent the reaction between the silicon nitride coating layer and the grain boundary phase components of the silicon nitride sintered body.
When silicon carbide is coated by the method, the reaction can be prevented, but the difference in thermal expansion between the coating layer and the base material is large, making it difficult to obtain sufficient adhesion. Further, even when coated with either silicon nitride or silicon carbide, there is a problem in that the strength of the silicon nitride sintered body is reduced by the coating.

On the other hand, when silicon carbide sintered bodies are used for parts such as susceptors, furnace tubes, and jigs used in the manufacture of semiconductor parts, there is a problem that the sintered bodies have many pores and the semiconductors are contaminated by impurities remaining in the pores. Therefore, coating with high-purity silicon carbide is performed using the CVD method. In addition, strength has been improved by filling the pores of the sintered body with silicon carbide using the CVD method. However, as the thickness of the silicon carbide coating layer increases, grain growth becomes significant, making it difficult to obtain sufficient strength and corrosion resistance.

In order to solve these problems, Japanese Patent Publication No. 60-45154 discloses a silicon nitride sintered body and a silicon carbide sintered body in which a composite coating layer made of a laminate of silicon nitride and silicon carbide is formed by the CVD method. has been disclosed. By laminating silicon nitride and silicon carbide in this way, it is thought that it is possible to control the difference in thermal expansion with the base material, suppress the reaction with the base material, and increase the strength.

[0005]

[Problems to be Solved by the Invention] However, the conventional method of synthesizing a composite coating layer of silicon nitride and silicon carbide by the CVD method requires that the nitrogen source and carbon source of the raw material gas be alternately and instantaneously switched. Since the composite coating layer is synthesized by introducing it into the furnace, unnecessary gas remains in the reactor when the raw material gas is switched, and the composite coating layer formed on the base material tends to become porous due to this residual gas. . Therefore, there is a problem that the strength of the composite coating layer is low and that the base material cannot be sufficiently protected from external air such as high temperature air, combustion gas, and chemicals. The present invention has been made to solve these problems, and it provides a ceramic sintered body that forms a dense composite coating layer with good adhesion on a ceramic base material such as silicon nitride or silicon carbide sintered body. The purpose is to provide a manufacturing method for.

[0006]

[Means for Solving the Problems] A method for manufacturing a ceramic sintered body having a composite coating layer according to the first aspect of the present invention to solve the above-mentioned problems is a method for manufacturing a ceramic sintered body having a composite coating layer. A method of forming a layered composite coating layer of a silicon nitride layer and a silicon carbide layer on the surface of a base material by chemical vapor deposition, the method comprising: switching the reaction gas flowed into the reactor to form each coating layer; Hydrogen gas is passed through the reactor, and the amount of hydrogen gas introduced into the reactor is set to a volume that is at least 3.4 times the volume of the reactor at room temperature and atmospheric pressure. shall be. A method for manufacturing a ceramic sintered body having a composite coating layer according to a second invention is characterized in that the chemical vapor deposition method is a low pressure thermal CVD method. The method for producing a ceramic sintered body having a composite coating layer according to the third invention includes, as a raw material gas for forming the layered coating layer of silicon nitride by the chemical vapor deposition method,
It is characterized in that silicon tetrachloride and ammonia are used, and silicon tetrachloride and methane are used as source gases for forming a layered coating layer of silicon carbide. A method for producing a ceramic sintered body having a composite coating layer according to a fourth aspect of the present invention is characterized in that the thicknesses of the silicon nitride and silicon carbide coating layers are graded. A method for producing a ceramic sintered body having a composite coating layer according to a fifth aspect of the present invention is characterized in that the base material is a silicon nitride or silicon carbide sintered body.

[0007] As the base material in the present invention, a heat-resistant material such as a ceramic sintered body or carbon can be used. In particular, the silicon nitride and silicon carbide sintered body is a mixture of silicon nitride or silicon carbide raw materials and various additives. A sintered body obtained by normal pressure or pressure sintering, hot pressing, HIP, etc. can be used. Furthermore, the shape and dimensions of the sintered body are not particularly limited.

[0008] As the chemical vapor deposition (CVD) method, it is desirable to use a low pressure thermal CVD method. In this case, the composition of the raw material gas, reaction temperature, reaction pressure, etc. are appropriately controlled in order to form a dense silicon nitride or silicon carbide coating layer. When synthesizing a composite coating layer having a laminated structure of silicon nitride and silicon carbide, as raw material gases, a silicon source and a nitrogen source are used for synthesizing silicon nitride, and a silicon source and a carbon source are used for synthesizing silicon carbide. Particularly when applied to high-temperature structural materials, etc., easily available raw materials such as silicon tetrachloride (SiCl4), ammonia (NH3), and methane (CH3) are used.
When manufactured by the VD method, a composite coating layer with good crystallinity can be manufactured at high speed and at low cost. Furthermore, by increasing and decreasing the thickness of the laminated silicon nitride and silicon carbide in stages, or by making one thicker and the other thinner, the thermal expansion of the coating layer can be tilted and the overall thermal expansion can be controlled. It is possible to match the thermal expansion of the sintered body of the material. For example, when the silicon nitride layer is thick and the silicon carbide layer is thin, the thermal expansion can be made close to that of silicon nitride alone.

The reason why the amount of hydrogen gas introduced into the reactor is set to be at least 3.4 times the volume of the inside of the reactor at room temperature and atmospheric pressure is that the hydrogen gas is less than this volume value. This is because the layered coating layer becomes porous. In other words, by circulating a hydrogen gas volume that is 3.4 times or more the volume of the reactor inside the reactor, the raw material gas remaining when switching the reaction gas can be removed to the extent that it does not affect the formation of the coating layer. This is because the inside of the reactor is sufficiently cleaned before synthesizing each coating layer. Here, the volume of the reactor refers to the volume of the part into which the raw material gas is introduced, and in external heating type reactors, the volume of only the reaction tube part into which the raw material gas is introduced, excluding the heating part. Refers to volume.

0010

[Function] The method for producing a ceramic sintered body having a composite coating layer according to the present invention includes laminating a silicon nitride layer and a silicon carbide layer on the surface of a ceramic such as silicon nitride or silicon carbide by chemical vapor deposition (CVD). In forming the composite coating layer of the structure, after forming the first layer of silicon nitride or silicon carbide on the ceramic surface, hydrogen gas of at least 3.4 times the volume of the reactor is passed through the reactor to cause nitriding. A second layer of silicon or silicon carbide is formed. and,
Hydrogen gas is passed in the same manner before synthesizing the third and subsequent coating layers. This prevents the composite coating layer from becoming porous and allows the synthesis of a dense composite coating layer that can sufficiently protect the base material. Further, since the coating layer is dense, the thickness of each coating layer can be controlled by adjusting the synthesis time, and the thermal expansion of the coating layer can be controlled. Furthermore, when a silicon nitride sintered body is coated, the reaction between the grain boundary phase components of the silicon nitride sintered body and the coating layer can be sufficiently suppressed by the lamination of silicon nitride and silicon carbide. Moreover, since it has a laminated structure, growth of crystal grains in the coating layer can be suppressed, and a high-strength coating layer made of fine crystals can be formed.

[0011]

[Examples] Examples of the present invention will be described below. Examples 1 to 8 In Examples 1 to 8, a pressureless sintered silicon nitride sintered body is used as a base material, and Si3 is deposited on the surface of this base material using a low pressure thermal CVD device.
A layered coating of N4 and SiC was formed as follows. First, a base material was inserted into a reaction tube with a volume of 11,451 cm3, and while the base material was heated to a predetermined synthesis temperature, a mixed gas of SiCl4 and NH3 was flowed for a predetermined time.
A Si3N4 layer is formed on the surface of the substrate. Next, H2 gas was introduced into the reaction tube under the conditions shown in Table 1, and then Si
A mixed gas of Cl4 and CH4 is allowed to flow into the reaction tube for a predetermined period of time. Then, a SiC layer is formed. Furthermore, when forming a Si3 N4 layer on the SiC layer, after flowing H2 gas into the reaction tube again under the conditions shown in Table 1, a mixed gas of SiCl4 and NH3 is allowed to flow into the reaction tube for a predetermined period of time. In this way, Si3 N4 layers and SiC layers were alternately formed on the surface of the base material. Table 1 shows the number of layers in Examples 1 to 8.

0012

[Table 1]

The synthesis temperature of the Si3N4 layer and the SiC layer was 1 for Example 1 and Examples 3 to 8.
The temperature was 450°C, and for Example 2 it was 1430°C. In addition, the synthesis time of the Si3 N4 layer and the SiC layer is
In the case of Example 1 and Examples 3 to 8, Si3N
4 and the SiC layer, and in Example 2, the SiC layer was heated in order from the bottom layer to the top layer.
3 N4 layer 2 minutes, SiC layer 5 minutes, Si3 N4 layer 4
5 minutes for the SiC layer, and 5 minutes for the Si3 N4 layer.

Examples 9 and 10 In Examples 9 and 10, a pressureless sintered silicon carbide sintered body was used as a base material, and the surface of this base material was coated in the same manner as in Examples 1 to 8. S
A layered covering layer of an i3 N4 layer and a SiC layer was formed. In this case, the number of laminated coating layers and the conditions of H2 gas introduced into the reaction tube in Examples 9 and 10 were set as shown in Table 1. The synthesis temperature of the Si3N4 layer and the SiC layer was 1450 in both Examples 9 and 10.
℃, and the synthesis time of the Si3 N4 layer and the SiC layer was 5 minutes per layer in both Examples 9 and 10.

Comparative Examples 1 to 5 In Comparative Examples 1 to 5, a pressureless sintered silicon nitride sintered body was used as a base material, and Si3 was deposited on the surface of this base material using a low pressure thermal CVD device.
A layered coating of N4 and SiC was formed as follows. First, a base material was inserted into a reaction tube with a volume of 11,451 cm3, and while the base material was heated to a predetermined synthesis temperature, a mixed gas of SiCl4 and NH3 was flowed for a predetermined time.
Forming a Si3N4 layer on the substrate surface (Comparative Example 1)
. Next, a mixed gas of SiCl4 and CH4 is allowed to flow into the reaction tube for a predetermined period of time. Then, a SiC layer is formed (Comparative Example 2)
~ Comparative Example 5). Furthermore, when forming a Si3 N4 layer on the SiC layer, after flowing H2 gas into the reaction tube again under the conditions shown in Table 1, a mixed gas of SiCl4 and NH3 is allowed to flow into the reaction tube for a predetermined period of time. In this way, Si3 N4 layers and SiC layers are formed alternately on the surface of the base material. Table 1 shows Comparative Examples 1 to 5.
Indicates the number of layers. The synthesis temperature of the Si3N4 layer and the SiC layer was 1450°C in both Comparative Examples 1 to 5,
The synthesis time for the Si3N4 layer and the SiC layer was 5 minutes for each layer in Comparative Examples 1 to 5.

Comparative Example 6 In Comparative Example 6, a pressureless sintered silicon nitride sintered body was used as a base material, and no coating layer was formed on the surface of the base material.

Comparative Examples 7 to 9 In Comparative Examples 7 to 9, a pressureless sintered silicon carbide sintered body was used as a base material, and the surface of this base material was coated in the same manner as in Comparative Examples 1 to 5. A layered coating of Si3N4 and SiC was formed. In this case, the number of laminated layers and the conditions of introduced H2 gas in Comparative Examples 7 to 9 were set as shown in Table 1. S
The synthesis temperature of the i3 N4 layer and the SiC layer was that of Comparative Example 7.
~ Comparative Example 9 The temperature was 1450° C., and the synthesis time of the Si3 N4 layer and SiC layer was 5 minutes per layer in Comparative Examples 7 to 9.

Next, for Examples 1 to 10 and Comparative Examples 1 to 9, the overall thickness of the coating layer and the porosity of the coating layer were investigated, and furthermore, a room temperature four-point bending strength test and an oxidation resistance test were conducted. I conducted a test. The 4-point bending strength test is
The oxidation resistance test was conducted in accordance with the JIS R-1601 bending strength test method for fine ceramics, under atmospheric pressure,
JIS R-16 under conditions of 1300℃, 100 hours
The test was conducted in accordance with the 06 non-oxide fine ceramics oxidation resistance test method. In addition, the porosity was determined from the pore area ratio by image analysis. The results are shown in Table 2.

[0019]

[Table 2]

As shown in Table 2, Examples 1 to 10
In Comparative Examples 1 to 9, a coating layer having a thickness corresponding to the synthesis time of the Si3N4 layer or the SiC layer was formed. For example, according to Example 1, the laminated state of the coating layer is as follows:
Si3N4 with a layer thickness of 9 μm and SiC with a layer thickness of 4 μm were alternately laminated, and the total layer thickness of the coating layer was 35 μm. Also, according to Example 2, Si3 N4 and S
iC alternately layer thickness 5μm, 4μm, 3μm, 8μm, 1
The layers were laminated at a thickness of 0 μm, and the total layer thickness of the coating layer was 31 μm. Comparing the porosity of the coating layer, Examples 1 to 10
The porosity of the coating layer is small, whereas Comparative Examples 1 to 9 have no coating layer (Comparative Example 7) and those with a single coating layer (Comparative Examples 1 and 9). Except for 7), the porosity of the coating layer is as large as 10% or more. Moreover, Examples 1 to 10 showed excellent values in both room temperature four-point bending strength and oxidation resistance, and the appearance of the fractured surface was also good. On the other hand, in Comparative Examples 1 to 9, at least one of the four-point bending strength at room temperature and the oxidation resistance was small, and the appearance of the fractured surface was porous.

The fractured surfaces and polished surfaces of the coating layers having the Si3 N4 --SiC laminated structure obtained in Examples 1 to 10 are as shown in FIGS. 1 and 3, for example. As is clear from FIGS. 1 and 3, the coating layer is formed in a dense layered manner. On the other hand, the fractured surface of the coating layer and its polished surface in Comparative Examples 1 to 9 are as shown in FIGS. 2 and 4, for example. As is clear from FIGS. 2 and 4, the coating layer is porous.

[0022]

As explained above, according to the method of manufacturing a ceramic sintered body having a composite coating layer of the present invention, the volume of the reactor is at least 3.
By flowing four or more times the volume of H2 gas into the reaction chamber, a dense composite coating layer of silicon nitride and silicon carbide with good adhesion can be formed on the surface of the ceramic sintered body. Furthermore, by controlling the thickness of each coating layer, it is possible to form a composite coating layer on a ceramic substrate having any thermal expansion. For silicon nitride sintered bodies, this prevents the reaction between the coating layer and the grain boundary layer of the silicon nitride sintered bodies at high temperatures, resulting in a composite coated silicon nitride sintered body with good oxidation resistance and high strength. It will be done. Further, in the silicon carbide sintered body, a composite coated silicon carbide sintered body having high strength and excellent corrosion resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph showing a fractured surface of a coating layer according to Example 1 of the present invention.

FIG. 2 is an electron micrograph showing a fractured surface of a coating layer according to conventional comparative example 1.

FIG. 3 is an optical micrograph showing the polished surface of the coating layer according to Example 1 of the present invention.

FIG. 4 is an optical micrograph showing a polished surface of a coating layer according to conventional comparative example 1.

Claims (5)

[Claims] 1. A method for forming a composite coating layer of a silicon nitride layer and a silicon carbide layer on the surface of a base material such as ceramics by chemical vapor deposition, wherein a reactor is used to form each coating layer. When switching the reaction gas to be flowed into the reactor, hydrogen gas is passed through the reactor, and the amount of hydrogen gas introduced into the reactor is adjusted to a volume that is at least 3.4 times larger than the volume inside the reactor at room temperature and atmospheric pressure. A method for manufacturing a ceramic sintered body having a composite coating layer, characterized in that the amount of gas is set to a certain amount. 2. The method for producing a ceramic sintered body having a composite coating layer according to claim 1, wherein the chemical vapor deposition method is a low pressure thermal CVD method. 3. Silicon tetrachloride and ammonia are used as source gases for forming the layered coating layer of silicon nitride by the chemical vapor deposition method, and silicon tetrachloride and ammonia are used as source gases for forming the layered coating layer of silicon carbide. The method for producing a ceramic sintered body having a composite coating layer according to claim 1 or 2, characterized in that methane is used. 4. The method for producing a ceramic sintered body having a composite coating layer according to claim 1 or 2, wherein the thicknesses of each of the silicon nitride and silicon carbide coating layers are graded. 5. The method for producing a ceramic sintered body having a composite coating layer according to claim 1, wherein the base material is a silicon nitride or silicon carbide sintered body.