JPH0798684B2 - Method for manufacturing high density SiC sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a manufacturing method for obtaining a high-strength and high-density SiC sintered body.

(Prior art) HIP after primary firing of a compact made of B-C additive β-SiC
In the method of obtaining a high-density SiC sintered body by treatment, if the primary firing temperature is high, the SiC particles will take in pores at the end of firing and grow abnormally over several hundreds of microns, resulting in deterioration of properties and incorporation into abnormally grown particles. The pores
There is a problem that it is difficult to remove by HIP treatment and it is difficult to improve the density, and if the primary firing temperature is lowered to avoid this abnormal grain growth, the density does not rise sufficiently, open pores remain, and even after HIP treatment There was a problem that the density was not increased. That is, in order to increase the density by HIP treatment, it was necessary to strictly control the primary firing temperature range within a narrow width, eliminate open pores in the primary fired body, and allow the remaining closed pores to exist at the grain boundaries.

From the above viewpoints, conventionally, in B, C-added SiC, additive composition range B: 0.2 to 0.5 wt%, C: 0.5 to 8 wt%, primary firing conditions 1950 to 2150 ° C., HIP treatment conditions 1850 to 1980 ° C. A method for obtaining a SiC sintered body having a high density of 99.3% or more and a high strength of 70 kg / mm ² or more by strictly limiting the pressure to 100 atm or more is known in JP-A-60-255672. .

Further, by adding 0.05 to 5 wt% of α-SiC having a grain size more than twice that of β-SiC to B, C-added β-SiC, the abnormal grain growth is effectively suppressed, the additive composition and firing are performed. A method of obtaining a SiC sintered body having a composite structure with plate-like α-SiC and finer granular β-SiC particles within a relatively wide range of conditions and having pores at grain boundaries under normal pressure, JP-A-52-6716
Known from the publication.

(Problems to be solved by the invention) However, in the technique disclosed in Japanese Patent Laid-Open No. 60-255672, control is difficult because the composition range, primary firing conditions, and HIP treatment conditions are narrow, and particularly large-sized products, etc. In the case of industrial mass production, there were problems that it was difficult to obtain a homogenous sintered body and that the strength was not as high as 70 kg / mm ² despite the high density of 99.3% or more.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 52-6716, a wide range of various manufacturing conditions and a large aspect ratio α-like plate considered to be preferable for high strength and high toughness
It has a composite structure with SiC particles and finer β-SiC particles, but its density is lower than that of β-SiC powder used alone, and the demand for high density and high strength in recent years is high. However, it was not possible to obtain a high toughness sintered body. Further, this atmospheric pressure sintered body has a low density, and the existing pores are open pores, so that it was not suitable for densification by HIP treatment.

The object of the present invention is to solve the above-mentioned problems, to provide a wide control range of various manufacturing conditions, to easily and stably provide high density and high strength Si.
An object of the present invention is to provide a manufacturing method capable of obtaining a C sintered body.

(Means for Solving the Problem) The method for producing a high-density SiC sintered body of the present invention is a method for producing a high-density SiC sintered body by hot isostatic pressing after firing a compact made of SiC powder and a sintering aid. In the method of obtaining a body, SiC powder consisting of at least one of 3C, 2H polytype 95.0-99.9w
5% to 6%, 6H, 4H, 15R polytype, and an average particle size of less than twice that of 3C, 2H polytype SiC powder 5.0-0.1wt% and SiC mixed powder 90.0-9
9.8 wt%, boron or a compound containing boron is converted to boron 0.1 to 5.0 wt%, carbon or an organic compound that produces carbon is converted to carbon 0.1 to 5.0 wt% to prepare a mixed powder. , Then in vacuum or in inert atmosphere 1900 ~
1800 ~ 22 in an inert atmosphere after firing at a temperature of 2300 ℃
It is characterized by hot isostatic pressing at a temperature of 00 ° C and a pressure of 100 atm or more.

Further, in order to further densify the SiC sintered body produced by the above process, 0.1 to 5.
The feature is that 0 wt% is added.

(Operation) In the above-mentioned configuration, by using SiC powder with a limited composition and grain size, a plate-shaped α with a large aspect ratio can be obtained.
-SiC particles and a finer granular β-SiC has a composite structure, and there is no open pores, it is possible to obtain a relatively dense primary fired body having residual closed pores at the grain boundaries, HIP treatment maintains the above composite structure and
%, High density, high strength SiC sintered body can be easily and stably obtained. That is, according to the present invention, the conventional HIP
Obtained by HIP treatment a high-density SiC sinter having a composite structure of plate-like α-SiC particles with a large aspect ratio and finer granular β-SiC particles, which was considered impossible to densify by treatment It has become possible. Further, according to the production method of the present invention, which can express the synergistic effect of combining the use of SiC powder having a predetermined composition and particle size and HIP treatment, the composition range for obtaining the above-mentioned sintered body, the primary firing condition, the HIP treatment The conditions can be widened and the value is extremely high industrially.

Furthermore, when MgO is added to the compounded powder, the distribution and shape of the pores remaining in the primary sintered body are controlled, and it becomes possible to densify to almost the theoretical density (3.21 g / cm ³ ). MgO produces its effect by using a SiC powder with a limited composition and particle size in the configuration described above. MgO is a plate α-S
SiC of at least one of 6H, 4H, 15R polytypes evenly dispersed in the compact to promote iC particle growth.
The plate-shaped α-SiC particles formed by the particles serving as nuclei grow uniformly in the primary sintered body. As a result, the pores of the MgO-added primary sintered body are uniformly dispersed in the grain boundaries, and the shape of the pores surrounded by the plate-like particles becomes sharp. MgO acts to control the microstructure of the sintered body, but since it evaporates during firing, it hardly remains in the primary sintered body. The microstructure of this primary sintered body
It was found that the effect of densification of SiC by HIP treatment is improved and a high density SiC sintered body having almost the theoretical density can be obtained.

The SiC powder consisting of at least one of the 3C and 2H polytypes is a low temperature type powder that is synthesized substantially at a temperature of 2000 ° C. or lower, and a silica reduction carbonization method or the like is known as a manufacturing method. The SiC powder consisting of at least one of the 6H, 4H, and 15R polytypes is a high-temperature type powder that is substantially synthesized at a temperature of 2000 ° C. or higher, and the Acheson method is generally used as a manufacturing method. It can also be synthesized by treating a 3C, 2H polytype at a high temperature of 2000 ° C. or higher.

Here, the addition amount of the SiC powder consisting of at least one of 6H, 4H, and 15R polytypes to be added is limited to 5.0 to 0.1 wt%, because the plate-shaped α-SiC particles are more than 5.0 wt%. As the aspect ratio becomes smaller and the characteristics deteriorate, 0.1w
This is because if it is less than t%, the effect of addition is lost.

Moreover, the particle size of the SiC powder consisting of at least one of the 6H, 4H, 15R polytypes was limited to less than twice that of the 3C, 2H polytypes because the open porosity during the primary firing was doubled or more. Because a large amount remains, it does not densify even after HIP treatment.

The amount of boron as an additive is limited to 0.1 to 5.0 wt% because if it is less than 0.1 wt%, the effect of the addition is not recognized and the densification becomes insufficient. This is because a large amount remains and the high temperature characteristics deteriorate. Also,
The amount of carbon as an additive is limited to 0.1 to 5.0 wt% because if it is less than 0.1 wt%, the SiO ₂ film on the SiC surface cannot be removed and the densification is insufficient. This is because a large amount of free-C remains in the body and the characteristics deteriorate.

The reason for limiting the amount of MgO to 0.1-5.0 wt% is that the effect of addition is not observed below 0.1 wt%, and there is no change in the properties of the sintered body after HIP treatment as compared with the case where MgO is not added. on the other hand,
If it exceeds 5.0 wt%, the primary sintered body will not be sufficiently densified and will not be closed porosity, so that the effect of HIP treatment cannot be obtained.

Furthermore, the primary firing temperature before HIP treatment was limited to 1900 to 2300 ° C because open pores remained below 1900 ° C and densification did not occur even after HIP treatment, and when it exceeded 2300 ° C due to the decomposition of SiC. This is because the surface becomes rough. In addition, the temperature in the HIP treatment was limited to 1800 to 2200 ° C and 100 atm or more. If the temperature is less than 1800 ° C, the densification is insufficient, and if it exceeds 2200 ° C, it becomes too costly and meaningless. This is because if the pressure is less than 100 atm, the densification is insufficient. Furthermore, if the particle size of the 6H, 4H, 15R polytype SiC powder to be added is about the same as the particle size of the 3C, 2H polytype SiC powder, the mixing among the SiC powders can be made uniform. Therefore, it is more preferable.

(Example) FIG. 1 is a flow chart showing an example of a manufacturing process of the manufacturing method of the present invention. First, a high temperature type SiC powder made of at least one of 6H, 4H, 15R polytypes having an average particle size of 5 μm or less produced by the Acheson method and 3C having an average particle size of 5 μm or less produced by a silica reduction carbonization method, Low temperature type SiC consisting of at least one of 2H polytypes
Prepare powder and B, C and MgO as additives
To prepare. Table 1 shows the chemical composition of each SiC powder.

Next, the prepared SiC raw material powders and predetermined amounts of B ₄ C, C and MgO additives are pulverized and mixed by a wet ball mill using isopropyl alcohol. The raw materials after crushing and mixing are once dried and then granulated. Then, the granulated powder is preformed, and is further formed into a predetermined shape by isostatic pressing. Next, after primary baking in a vacuum or an inert atmosphere at a temperature of 1900 to 2300 ° C, in an inert atmosphere of 1800 to
A hot isostatic pressing (HIP) process is performed at a temperature of 2200 ° C and a pressure of 100 atm or more to obtain a SiC sintered body.

Hereinafter, an actual example will be described.

Example SiC raw material powder consisting of at least one of 6H, 4H, 15R polytype having an average particle size of 0.42 μm, 3 having an average particle size of 0.45 μm
SiC raw material powder consisting of at least one of C and 2H polytypes, and B ₄ C (boron carbide), C (carbon black) and MgO (magnesium oxide) as additives in isopropyl alcohol at the ratio shown in Table 2. 3 ton / c after pre-molding after mixing and drying in a wet ball mill
A square plate of 60 × 60 × 6 mm was prepared by a hydrostatic press of m ² . Next, the produced square plate was primarily fired in vacuum under the conditions shown in Table 2. The square plate after the primary firing was further subjected to HIP treatment under the conditions shown in Table 2 to obtain sintered bodies of Examples of the present invention and Comparative Examples, respectively. 6H, 4H, 15R in Comparative Examples 5 and 6
As the poly-type SiC raw material powder, a powder having an average particle size of 1.5 μm was used.

For each of the obtained sintered bodies before and after HIP treatment, the density and open porosity were measured by the Archimedes method to evaluate the denseness, and JIS R-1601 (bending strength test method for fine ceramics) was used at room temperature. A four-point bending test was followed to evaluate room temperature strength. Furthermore, the toughness was evaluated by obtaining each K _IC by the chevron notch method at room temperature, and the presence or absence of abnormal grain growth was examined by microscopic observation of the polished-etched surface. The results are shown in Table 2.

As is clear from the results in Table 2, S consisting of 6H, 4H, 15R
When the amount of iC powder is less than 0.05 wt% (Comparative Examples 1 and 2), abnormal grain growth of SiC occurs in the primary fired body, the densification by HIP becomes insufficient, and the strength and K _IC decrease. . 6H, 4H, 1
When the amount of 5R SiC powder exceeds 5.0wt% (Comparative example
3,4), abnormal grain growth does not occur in the primary fired body, but α-S
The aspect ratio of iC particles becomes small, and the strength and K _IC become low. The average particle size of SiC powder consisting of 6H, 4H, 15R is 3C, 2
When the amount is more than twice that of SiC powder made of H (Comparative Example 5,
6), the density of the primary fired body is small and a large number of open pores remain, so the density does not increase even after HIP treatment. B ₄ C addition amount is less than 0.1 wt% (Comparative Example 7), C addition amount is 0.1 wt%
When the temperature is less than (Comparative Example 8) and the primary firing temperature is less than 1900 ° C. (Comparative Example 9), the density of the primary fired body is low, and a large number of open pores remain, so that the HIP treatment does not increase the density. HIP
Treatment temperature is less than 1800 ℃ (Comparative example 10), HIP treatment pressure is 100
When the pressure is lower than the atmospheric pressure (Comparative Example 11), the densification by HIP treatment is insufficient, and the strength and K _IC are low. From the above, Examples 1 to 9 satisfying the range of the present invention have higher density and higher strength than Comparative Examples 1 to 11 not satisfying the range of the present invention, and exhibit a high K _IC value to improve toughness. You can see that

Further, it is understood that when MgO is added, the density and strength are increased as compared with the case where the sintered body MgO after HIP treatment is not added (Examples 10 to 13). However, the addition of MgO was 5.0wt
If it exceeds%, the density of the primary sintered body is low and a large amount of open pores remain, so that the density does not increase even after HIP treatment (Comparative Example 12).

(Effect of the Invention) As is clear from the above description in detail, according to the method for producing a high-density SiC sintered body of the present invention, a predetermined composition of SiC mixed powder is subjected to HIP treatment after primary firing to obtain a wide composition. It is possible to easily and stably obtain a high-density SiC sintered body under the range, primary firing conditions, and HIP treatment conditions. Further, the SiC sintered body obtained by the present invention has a higher density than that of α-SiC, β-SiC alone, and has a large aspect ratio of plate-shaped α-SiC.
Since it has a composite structure with finer β-SiC particles, the mechanical properties are also high.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of the manufacturing process of the manufacturing method of the present invention.

Claims (2)

[Claims] 1. A method for obtaining a high-density SiC sintered body by hot isostatic pressing after firing a compact made of SiC powder and a sintering aid, which comprises at least one of 3C and 2H polytypes. Made of at least one of SiC powder 95.0-99.9wt% and 6H, 4H, 15R polytype with an average particle size of 3
SiC powder 5.0 to 0, which is less than twice that of C, 2H polytype.
SiC mixed powder with 1wt% 90.0-99.8wt%, boron or a compound containing boron is converted to boron 0.1-5.0wt%, carbon or an organic compound that produces carbon is converted to carbon 0.1.
~ 5.0wt% compounded powder is mixed and molded, then fired in vacuum or in inert atmosphere at temperature of 1900 ~ 2300 ℃, then in inert atmosphere at temperature of 1800 ~ 2200 ℃, under pressure of 100 atm or more. A method for producing a high-density SiC sintered body, which comprises hot isostatic pressing at. 2. The method for producing a high-density SiC sintered body according to claim 1, wherein a compounded powder containing 0.1 to 5.0 wt% of MgO is used.