JPH07115927B2 - SiC-based ceramics and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a SiC-based ceramics and a method for producing the same,
In particular, the present invention relates to a SiC-based ceramic having high strength and high toughness up to high temperatures and a method for producing the same.

[Conventional technology]

Ceramics have been actively used in various structural parts and mechanical parts by taking advantage of heat resistance, oxidation resistance, high strength, and high hardness. Candidate materials for such purpose include Si ₃ N ₄ , sialon, SiC, ZrO ₂ . Among them, SiC is a material having extremely excellent characteristics that it has high strength up to high temperatures as compared with other materials. However, these ceramics have the drawback of being brittle, which is a major reason why ceramics are not used as structural or mechanical parts. For this reason,
Various studies have been made to improve the brittleness of ceramics. Proceeding of 9th Anniversary Conference on Compositates and Advanced Ceramic Materials, Florida (1985) [proc.of 9th, Annual Conference on Compo
sites and Advanced Ceramic Materials, Florida (198
5)] in DKShett
y) As announced by others, there is a method of reinforcing fibers by dispersing high-strength fibers in ceramics. But,
In this method, the properties of the interface between the ceramic of the base material and the fiber cannot be said to be appropriate, and the material does not have a sufficiently large fracture toughness value. Also, Bretain of American Ceramic Society, Volume 65, No. 2, No.
351-56 (1986) [Am. Ceram. Soc. Bull., 62 (2) 35
1-56 (1986)] describes a ceramic compound in which SiC whiskers are compounded with Si ₃ N ₄ . The maximum fracture toughness value of 12.5 MPa · m ^1/2 was obtained in this system. Since the heat resistance of this material is not described in this paper, details are unknown, but since the base material is Si ₃ N ₄ ,
It is estimated that there is a problem in using at high temperature of 300 ° C or higher. Also, the Bretain of American Ceramic Society Vol. 65, No. 2, 336-38 (1986
) Describes a ceramic composed of SiC fiber and SiC. This ceramic has a fracture toughness value of about 25MP.
It is described that the ceramics does not have such a characteristic that the value can be maintained up to a high temperature of about 1500 ° C at a · m ^1/2 . However, in this ceramic, the matrix is formed by the CVD infiltration method. Therefore, there is a problem in terms of mass productivity as a method for producing members such as structural parts and mechanical parts.

[Problems to be solved by the invention]

As described above, each of the conventional techniques has problems such as high temperature strength, toughness, mass productivity, and the like.

It is an object of the present invention to provide a ceramics which has a large strength and fracture toughness value from room temperature to a high temperature of 1500 ° C. and is suitable for manufacturing structural parts and mechanical parts, and a manufacturing method thereof.

[Means for solving problems]

Briefly describing the present invention, the first invention of the present invention relates to SiC-based ceramics, in which the stoichiometric ratio of Si and C is
0.98 to 1.02, the average particle size of amorphous is 0.7 μm by X-ray diffraction
The following powder composition, B or B compound as a sintering aid is 0.1 to 5% by weight as B with respect to the above powder composition,
And a SiC whisker having a diameter of 0.2 μm or more and a length of 5 μm or more is obtained by heating and pressing a homogeneous mixed powder containing 5 to 40% by weight of the above powder composition as an essential component. It is characterized by being a sintered body of high density, high strength and high toughness.

The second invention of the present invention is an invention relating to the method for producing the Si-based ceramics of the first invention, wherein the homogeneous mixed powder described in the first invention is not oxidized in a mold. 1600 to 200 under a pressure of 10 MPa or less in a neutral atmosphere
It is characterized in that heating and pressurization are simultaneously performed at a temperature of 0 ° C. to produce a high density, high strength and high toughness sintered body.

In order to achieve the above-mentioned object, in the present invention, as the matrix, SiC is used as a starting material, which is a powder having an extremely fine sinterability and is sintered at a temperature of 2000 ° C. or less to reduce the crystal grains of the matrix. Furthermore, SiC whiskers are added to increase the fracture toughness value of the sintered body.
More preferably, in addition to SiC whiskers, SiC powder having a large particle size is added.

Since it is difficult to densify the sintered body because SiC whiskers are added, it is densified by simultaneously heating and pressing. Specifically, it is sintered by a hot press method or a hot isostatic press (HIP) method.

In order to achieve the above object, as a material in the present invention
It consists of SiC whiskers and a system that uses SiC as a matrix. In the present invention, the SiC forming the matrix is a SiC powder having an average particle size of 0.7 μm or less, or a powder composition having a stoichiometric ratio of Si and C in the range of 0.98 to 1.02. Preferably, the grain size is 0.1 to 0.3 μm and the stoichiometric ratio of Si and C is 0.98 to 1.
An amorphous powder having no SiC diffraction peak which is clear according to X-ray diffraction in the range of 02 is used. B or B compound as an additive for promoting sintering is added in an amount of 0.1 to
Add 5% by weight. As the B compound, B alone, B ₂ O ₃ , BN, B
₄ C, Bp, H ₃ BO ₃ are preferred. The reason why B or B compound is selected as an additive is that by adding this, the addition of about 1400-
Since densification progresses rapidly at 1700 ° C, when Al or Be simple substance or these compounds, which are well known as sintering aids for SiC, are added, the rapid densification at about 1400 to 1700 ° C. Does not occur, so when trying to obtain a dense sintered body,
It is necessary to sinter under a high temperature of 2000 ° C or higher. When B alone or B compound is added as a sintering aid, approximately 1400
It is not clear what causes the rapid densification at temperatures as low as ~ 1700 ℃. The amount of B alone or B compound added as B is 0.
The reason why it is 1 to 5% by weight is that if this amount is less than 0.1% by weight, rapid densification does not occur at low temperatures of about 1400 to 1700 ° C. Further, if it exceeds 5% by weight, too much, the oxidation resistance and corrosion resistance of the sintered body deteriorate. For the sintered body, 5-40% by weight of SiC whiskers is added to the above powder composition in order to achieve high toughness. If the amount of SiC whiskers added is less than 5% by weight, the amount of SiC whiskers is small enough. If it does not achieve high toughness, on the other hand, if it exceeds 40% by weight, it will be extremely difficult to densify it because the amount of SiC whiskers is too large, and a density of 3.0 g / cm ³ or more will be obtained at a temperature of 2000 ° C or less. Therefore, the obtained sintered body is low in both strength and fracture toughness, and has a large number of pores, so that the oxidation resistance is not good. For the SiC whiskers, use whiskers with a diameter of 0.2 μm or more and a length of 5 μm or more. If the diameter of the SiC whisker is less than 0.2 μm, the strength of the whisker itself is low, and the fracture toughness value of the resulting sintered body is not large. Moreover, the length of the SiC whiskers must be 5 μm or more. When the length of the SiC whisker is short, the crack that progresses in the sintered body cannot be sufficiently stopped due to the short length of the SiC whisker, and therefore the fracture toughness value of the sintered body does not increase. is there.

In order to increase the fracture toughness value of the sintered body,
It is effective to add large SiC crystal grains, specifically particles having a grain size of 5 to 80 μm, in an amount of less than 30% by weight with respect to the above powder composition. This large SiC crystal grain has the effect of stopping cracks that have progressed through the small crystal grain in the matrix and causing it to bend significantly, which increases the fracture toughness value. This is because if the grain size is smaller than 5 μm, there is no great effect in improving the fracture toughness value. If the particle size is larger than 80 μm, the SiC
Since the particles themselves are too large, the SiC crystal grains that are too large serve as a fracture generation source in the sintered body, resulting in low strength. Also, if the addition amount of large SiC crystal grains is 5% by weight or less, there is almost no effect on the improvement of fracture toughness, and if the addition amount is 30% by weight or more, the addition amount is too high and the temperature is higher than 2000 ° C. If it is not sintered, it will not become a dense sintered body. Therefore, the strength and fracture toughness of the obtained sintered body are small, and the oxidation resistance is poor.

The sintered body of the present invention can be manufactured in a non-oxidizing atmosphere, specifically in vacuum, in any of argon, nitrogen, hydrogen and helium gas. These gases may be mixed and used.
The sintered body can be manufactured by either the hot press method or the HIP method. At this time, the sintering temperature is 1600 ~ 20
A temperature range of 00 ° C is chosen. The reason for this is that if the temperature is lower than 1600 ° C, it is not possible to obtain a sufficiently compacted sintered body, and the obtained sintered body has low strength and fracture toughness values and poor oxidation resistance. When the temperature exceeds 2000 ° C, the densification of the sintered body proceeds sufficiently, but at the same time, grain growth of the SiC matrix also occurs. In addition, the chemical bond between the crystal grains of the SiC whiskers and the SiC matrix becomes extremely strong, and when cracks progress in the sintered body, the mode of failure is intragranular fracture, and the SiC whiskers are pulled from the matrix. It is also difficult for slip-out to occur and a large fracture toughness value cannot be obtained. Pressure is applied during sintering to promote densification. The pressure applied depends on the amount of SiC whiskers and the amount of large SiC crystal grains of 5 to 80 μm, and the degree of densification varies, but in the case of the hot press method, a dense sintered body must be applied if pressure of at least 10 MPa is not applied. Can't get In the case of the HIP method, a pressure higher than that of the hot press method can be applied, so that the densification can be performed more easily, and the parts having a more complicated shape can be sintered.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples.

Example 1 Si powder and ethane gas were reacted at 1300 ° C. in an argon gas atmosphere containing hydrogen, and the stoichiometric ratio of Si and C was 0.99.
As a result, a fine powder having a particle size of 0.1 to 0.3 μm was obtained. This powder was amorphous by X-ray diffraction (hereinafter referred to as amorphous SiC powder). 1% by weight of B ₄ C powder having an average particle size of 1.0 μm, SiC having a diameter of about 0.5 μm and a length of about 10 to 100 μm were added to this powder.
Whiskers were added in an amount of 20% by weight, and acetone was further added to obtain a suspension, which was stirred with an agitator while applying ultrasonic waves so that the whole mixture became a homogeneous mixture. Further, acetone was volatilized while continuing stirring to obtain a homogeneous powder mixture. The powder mixture was placed in a graphite mold and placed under vacuum at 30 MPa.
While increasing the pressure, the temperature was raised from room temperature to 1800 ° C. in about 1.5 hours, and hot-pressed at this temperature and pressure for 0.5 hour to obtain a sintered body. As a result of X-ray diffraction, the sintered body was found to be composed mainly of β-type SiC. Further, most of the sintered bodies are composed of fine equiaxed crystal grains having a grain size of 1 μm or less, and have a fine structure in which SiC whiskers are dispersed. Further, in the same manner as above, the amount of SiC whiskers was changed within the range of 2 to 50% by weight to manufacture sintered bodies.

Table 1 shows the characteristics of the obtained SiC sintered body. SiC to add
When the amount of whiskers is 5 to 40% by weight, a sintered body having high strength and high fracture toughness value can be obtained.

Example 2 The amorphous SiC powder used in Example 1 has an average particle size of 1.0.
20 μm of B ₄ C powder of 0.05 μm to 10% by weight was added, and the same SiC whiskers as those used in Example 1 were added.
% By weight, and hot pressed in the same manner as in Example 1 to obtain a sintered body. As a result of X-ray diffraction, it was found that the sintered body was composed mainly of β-SiC. The microstructure of the sintered body was almost the same as in Example 1.

Table 2 shows the characteristics of the obtained SiC sintered body. Add B ₄ C
When the amount is 0.13 to 6.4 wt% (0.1 to 5 wt% as B), a sintered body having high strength, high fracture toughness value, and high oxidation resistance can be obtained.

Note 1) The oxide film thickness is the thickness after 100 hours of oxidation of the sample in the air at 1500 ° C. Example 3 The amorphous SiC powder used in Example 1 has an average particle size of 1.0.
1% by weight of B ₄ C powder of μm and 20% by weight of the same SiC whiskers used in Example 1 were added, and the average particle size was 20
By changing the α-type SiC powder of μm in the range of 2 to 40% by weight,
The following operation was hot pressed in the same manner as described in Example 1 to obtain a sintered body. In this example, the temperature of the hot press was set to 1900 ° C. and the pressure was increased to 50 MPa. As a result of X-ray diffraction, the sintered body was found to have β-SiC and α-SiC as the main components. The microstructure of the sintered body has a grain size of 1μ.
SiC whiskers and coarse α-type SiC crystal grains with an average grain size of 20 μm are dispersed in fine equiaxed crystal grains of m or less.

Table 3 shows the characteristics of the obtained sintered body. Α type to be added
When the amount of SiC powder is less than 30% by weight, a sintered body having high strength and high fracture toughness value can be obtained.

Further, similarly to the above, the addition amount of α-type SiC powder was set to 20% by weight, and powders having different average particle diameters were added to obtain a sintered body. The sintered body in this case was composed mainly of β-SiC, and the microstructure was almost the same as above.

Table 4 shows the characteristics of the obtained sintered body. Α type to be added
When the grain size of the SiC powder is 5 to 80 μm, a sintered body having high strength and high fracture toughness value can be obtained.

Example 4 Amorphous SiC powder was obtained in the same manner as in Example 1, but the grain size of the amorphous SiC powder was different in this example. 1% by weight of B ₄ C powder having an average particle size of 1.0 μm, 20% by weight of SiC whiskers having a diameter of around 0.5 μm and a length of around 10 to 100 μm, and α having an average particle size of 20 μm in the amorphous SiC powder. 20 type SiC powder
% Was added, and the following operations were hot pressed in the same manner as in Example 1 to obtain a sintered body. The hot press conditions in this example were a temperature of 1800 ° C. and a pressure of 50 MPa. As a result of X-ray diffraction, the main components of the obtained sintered body were β-SiC and α.
-It had become SiC.

Table 5 shows the characteristics of the obtained sintered body. If the grain size of the amorphous SiC is 0.7 μm or less, it can be densified, and a sintered body with high strength and large fracture toughness value can be obtained.

Example 5 As the amorphous SiC powder, the same powder as that described in Example 1 was used, and 1% by weight of B ₄ C powder having an average particle size of 1.0 μm was used.
And 20 SiC whiskers with different aspect ratios and different diameters
% By weight, and the following operation was hot pressed in the same manner as described in Example 1 to obtain a sintered body. The hot press conditions were a temperature of 1800 ° C and a pressure of 30 MPa.

Table 6 shows the characteristics of the obtained sintered body. When the SiC whiskers have a diameter of 0.2 μm or more, they become a sintered body with high strength and high fracture toughness.

Example 6 A sintered body was manufactured in the same manner as that described in Example 1. In this example, the amount of SiC whiskers was kept constant at 20% by weight, and the hot press conditions were changed.

Table 7 shows the characteristics of the obtained sintered body. When the hot press temperature is 1600 to 2000 ° C and the pressure is 10 MPa or more,
High strength and high fracture toughness value.

Example 7 A powder mixture was obtained by the same method as described in Example 1. The powder mixture was placed in a rubber mold, and a pressure of 200 MPa was applied to the powder mixture to mold it by a cold isostatic pressing method. It was then machined to the desired shape. The processed product was vacuum-sealed in a Pyrex glass. Next, the glass-encapsulated compact was sintered by the HIP method in an argon atmosphere. The HIP conditions were a temperature of 1800 ° C, a pressure of 200 MPa, and a holding time of 0.5 h. As a result of X-ray diffraction, the obtained sintered body was
It was found that the main component was β-type SiC. The fine structure of the sintered body was the same as in Example 1.

Table 8 shows the characteristics of the obtained sintered body. When the amount of SiC whiskers added is 5 to 40% by weight, it is possible to obtain a crystal having high strength and a large fracture toughness value.

Furthermore, α-SiC having a large particle size obtained in the same manner as in Example 3
The powder composition to which the powder was added was HIP-treated in the same manner as above to obtain a sintered body. As a result of X-ray diffraction, the obtained sintered body was
It was found that β-SiC and α-SiC are the main components. The microstructure of the sintered body was the same as in Example 3.
The characteristics of the obtained sintered body were almost the same as those of the hot press shown in Tables 3 and 4.

Example 9 In Example 1, the amount of SiC whiskers added was kept constant at 20% by weight, and the sintering aid was changed from B ₄ C to B alone, B ₂ O ₃ , BN, BP, H ₃ BO ₃ to obtain a sintered body. Got In this case, the properties of the obtained sintered bodies were all the same as those when B ₄ C was used as the sintering aid.

Example 10 A sintered body was obtained in the same manner as in Example 1, except that the amount of SiC whiskers added was kept constant at 20% by weight and the atmosphere during hot pressing was changed.
The atmosphere of the hot press was an atmosphere of argon gas, nitrogen gas, hydrogen gas, and helium gas. The properties of the obtained sintered bodies were all the same as those in vacuum.

Comparative Example 1 B ₄ C having an average particle size of 1 μm was added as a sintering aid to SiC powder having a β-type crystal form having an average particle size of 0.3 μm, and the mixture was mixed and molded. 0.5h at ℃ and pressure of 30MPa
Hot-pressed to obtain a sintered body. Room temperature bending strength
The fracture toughness value was in the range of 3.8 to 4.1 from room temperature to 1500 ℃ at a bending strength of 577MPa at 560MPa and 1500 ℃.

Example 11 The sintered body obtained according to the present invention has a sintering temperature of 1600 to 2000 ° C., which is lower than that of a conventionally known dense SiC sintered body by several hundred degrees Celsius.
Therefore, the bonding force between the crystal grains in the sintered body is
Weaker than C sintered body. Therefore, in the SiC sintered body of the present invention, the composite SiC whiskers are more easily pulled out from the sintered body during the propagation of cracks, and the fracture toughness value of the sintered body of the present invention is increased. The advantage of the bonding strength between the crystal grains of the sintered body of the present invention being weaker than that of the conventional SiC sintered body lies in the excellent machinability of the SiC sintered body of the present invention.
That is, the sintered body of No. 3 in Table 1 and the N in Table 3 of the present invention
The grinding resistances of the o.13 sintered body and the conventional SiC sintered body when ground with a diamond grindstone were compared. When the working resistance when grinding the SiC sintered body of the conventional method was set to 1, the sintered body of NO.3 had a working resistance of 0.7, and the sintered body of NO.13 had a working resistance of 0.8 times.

〔The invention's effect〕

As described above, according to the present invention, a SiC sintered body that is a composite of SiC whiskers densified at a temperature of 2000 ° C. or less can be obtained, which is extremely economical. In particular, 18
In case of hot pressing at 00 ℃, the temperature is 300 ℃, compared with the case of manufacturing hot-press sintered SiC.
It has the remarkable effect of being able to lower the temperature and save about 20% of electricity.

Claims (8)

[Claims] 1. A powder composition having a stoichiometric ratio of Si and C of 0.98 to 1.02 and an amorphous average particle size of 0.7 μm or less in X-ray diffraction, and B or a B compound as a sintering aid. 0.1 to 5% by weight of B for the above powder composition, and 5 to 40% by weight of SiC whiskers having a diameter of 0.2 μm or more and a length of 5 μm or more as essential components for the above powder composition. A SiC-based ceramics characterized by being a high-density, high-strength and high-toughness sintered body obtained by heating and pressurizing the contained homogeneous mixed powder. 2. The SiC-based ceramics according to claim 1, wherein the mixed powder contains less than 30% by weight of SiC powder having a particle diameter of 5 to 80 μm with respect to the powder composition. 3. The sintered body has a density of 3.0 g / cm ³ or more and 400 MPa.
Three-point bending strength from room temperature to 1500 ℃ above, and 10 MPa
The SiC-based ceramics according to claim 1 or 2, which has a fracture toughness value of m ^1/2 or more. 4. The sintering aid is B simple substance, B ₂ O ₃ , BN, B ₄ C, BP,
Alternatively, the SiC-based ceramics according to any one of claims 1 to _3, which is H ₃ BO ₃ . 5. A powder composition having a stoichiometric ratio of Si to C of 0.98 to 1.02 and an amorphous average particle size of 0.7 μm or less in X-ray diffraction, and B or a B compound as a sintering aid. 0.1 to 5% by weight of B for the above powder composition, and 5 to 40% by weight of SiC whiskers having a diameter of 0.2 μm or more and a length of 5 μm or more as essential components for the above powder composition. The homogeneous mixed powder contained in the mold is heated in a non-oxidizing atmosphere under a pressure of 10 MPa or less at a temperature of 1600 to 2000 ° C at the same time and pressed to obtain a high density, high strength and high toughness baking. A method for producing a SiC-based ceramics, which comprises forming a bond. 6. The production of SiC-based ceramics according to claim 5, wherein the mixed powder contains less than 30% by weight of SiC powder having a particle size of 5 to 80 μm with respect to the powder composition. Happo. 7. The method for producing a SiC-based ceramic according to claim 5 or 6, wherein the sintering is carried out by a hot press method or a hot isostatic press method. 8. The production of SiC-based ceramics according to any one of claims 5 to 7, wherein the non-oxidizing atmosphere is vacuum, argon gas, nitrogen gas, hydrogen gas, or helium gas. Method.