JP2920482B2 - Silicon carbide sintered body excellent in toughness and manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to corrosion resistance used in the fields of chemical plants, liquid transport pumps, engine parts, etc.
The present invention relates to a silicon carbide sintered body having excellent wear resistance and toughness, and a method for producing the same.

[0002]

2. Description of the Related Art Ceramics have excellent properties such as high strength and high hardness at low and high temperatures unlike other materials. Above all, silicon carbide-based ceramics have been put into practical use as corrosion-resistant and wear-resistant mechanical parts used under severe conditions. Silicon carbide can be obtained by ordinary normal pressure sintering.
It is a difficult-to-sinter material requiring a high temperature of 00 ° C., and various proposals have been made to improve sinterability. The best known method is to use B, C or a compound containing them as a sintering aid, and to sinter a low-temperature stable β powder. In this method, conditions are controlled such that the phase transition from β to α is suppressed during sintering, and the resulting sintered product is a sintered body mainly composed of β type. Since the raw material particles grow into columns during sintering, the sintered body has a structure almost composed of columnar particles. Also, the sintering aid
Solid solution in the particles without remaining at the grain boundaries. for that reason,
The phenomenon in which cracks progress in the grains facilitates the destruction. For this reason, the silicon carbide sintered body has a
Although it has the advantage that the strength does not decrease to about 0 ° C., it has a drawback that the fracture toughness has a low value of about 2-4 MPa · m ^1/2 . It is also known to use the same sintering aids for sintering α powder to produce sintered bodies with similar mechanical properties. Also in this case, the particles become columnar and their aspect ratio (length / diameter ratio) is smaller than that in the structure of the β powder or the sintered body obtained. In addition, it is necessary to perform sintering at a high temperature, and low fracture toughness is a practical disadvantage.

[0003]

SUMMARY OF THE INVENTION To solve these problems, alumina or alumina-yttria is added,
Liquid phase sintering of silicon carbide raw material powder has been proposed. In this case, β-type sintering material is used, and 1900 ° C.
When sintering at the above temperature, a phase transition from β to α occurs, so that columnar particles develop. Further, a glass phase in which the liquid phase has solidified remains at the grain boundaries of the sintered body. In such a sintered body, the crack caused by the application of the external force proceeds preferentially at the grain boundary. Therefore, the columnar particles effectively work to increase the toughness of the sintered body, and the toughness value is increased to 4 to 6 MPa · m ^1/2 . However, since the phase transition is used, 1900
A high temperature of at least ℃ is required, and there is a problem of high-temperature sintering as in the conventional method. Also, since the speed of the phase transition is very sensitive to temperature, a high degree of temperature control is required, making the sintering operation difficult. Therefore, it is difficult to intentionally control the structure by controlling the raw materials and manufacturing conditions, and to control the fracture toughness and strength. The present invention has been devised to solve such a problem, and uses a β-powder having high sinterability with fine grains,
An object of the present invention is to provide a silicon carbide sintered body having a structure in which columnar particles are developed and having excellent toughness by sintering at a relatively low temperature at which a phase transition from β to α does not occur.

[0004]

In order to achieve the object, a silicon carbide sintered body of the present invention has a structure comprising 85 to 98% by weight of silicon carbide particles and 2 to 15% by weight of a grain boundary phase. The β-type content in the silicon carbide particles is 50% by weight or more, and the columnar particles having an average particle diameter of 1 to 10 μm and an average aspect ratio of 3 or more are 5% by weight or more of all the silicon carbide particles, and are broken. The toughness is characterized by being 4 to 8 MPa · m ^1/2 . This sintered body is composed of Li, Mg, Al, Y ,,
It is preferable to use a glass containing an oxide of two or more metals selected from a rare earth metal and Si as a component or a glass containing a crystal phase as the grain boundary phase. This sintered body has a β-type content of 70% by weight or more of the total silicon carbide particles and an average particle size of 0.3%.
A structure composed of 40 to 95% by weight of matrix particles of 5 to 3 μm and 5 to 60% by weight of columnar particles having an average particle size of 3 to 10 μm, or a β-type content of 50% of all silicon carbide particles
Column particles 60 having an average particle diameter of 1 to 5 μm, and 40% by weight or less of matrix particles having an average particle diameter of 1 to 5 μm.
Has an organization composed of more than weight%. The sintered body of the present invention has an average particle size of 0.3 μm or less and a β-type content of 80 or less.
1900 ° C after liquid phase sintering of raw material fine powder of at least
It is manufactured by heat treatment at the following temperature. In the raw material powder, 0.5 to 5% by weight of β-type particles having an average particle diameter of 0.6 μm or more, or 0.5 to 5% by weight of α-type particles
It is preferable to add by weight.

[0005]

The reason that a silicon carbide sintered body having high toughness cannot be produced at a low sintering temperature is that the conventional method utilizes a phase transition. In the present invention, by using a fine-grained and highly sinterable β powder, sintering at a low temperature of 1900 ° C. or less at which a phase transition from β to α does not occur, and developing columnar particles, a high toughness This allows the compact to be produced at low temperatures.
As described above, a sintered body containing β type as a main component and containing columnar particles can be a sintered body having excellent toughness while utilizing the inherent advantages of silicon carbide such as strength and wear resistance. The silicon carbide sintered body thus obtained is composed of silicon carbide particles mainly of β type and an oxide-based grain boundary phase, and has an average particle diameter of 1 to 1.
It has a structure containing columnar long particles of 10 μm and an average aspect ratio of 23 or more, and shows a fracture toughness of 4 to 8 MPa · m ^1/2 .

[0006] In the sintering of ceramics, the particle size of the sintering raw material used greatly affects the sintering temperature. Powders having an average particle size of 0.5 to 0.6 μm are commercially available as sintering raw materials. This kind of powder has a particle size distribution over a wide range of about 0.1 to 3 μm, and even if an alumina-yttria-based sintering agent usually used for liquid phase sintering is used.
High-temperature sintering at 900 ° C. or higher is required. The sintering temperature can be reduced by preparing β-type fine particles from which large particles of 0.5 μm or more that reduce sinterability have been removed and using an appropriate oxide as an auxiliary agent. The sintering temperature is further reduced by using pressure such as hot pressing or hot isostatic sintering (HIP). And heat treatment for an appropriate time,
Relatively large particles in the sintered body grow into columns, and a high toughness sintered body composed of fine particles and large columnar particles is obtained.
Tissue control is further facilitated by the addition of small amounts of β-type particles. The β-type particles become nuclei during sintering and grow selectively into columnar shapes, thereby improving toughness. The α-type particles act as nuclei during sintering regardless of the particle size. In this case, the α-type particles are mostly sintered particles having columnar particles.

If the sintering and heat treatment are performed at a low temperature of 1900 ° C. or less at which no phase transition from β to α occurs, large columnar particles grow with β still. In this way, by adding a single β-fine powder having a fine and uniform particle size or adding a small amount of β- or α-particles and sintering and heat-treating at a relatively low temperature, high-toughness sintering can be performed without using phase transition. The body is manufactured. The silicon carbide sintered body thus obtained has a structure composed of 85 to 98% by weight of silicon carbide particles and 2 to 15% by weight of a grain boundary phase, and has a β-type content in the silicon carbide particles. Is 5
0% by weight or more, columnar particles having an average particle diameter of 1 to 10 μm and an average aspect ratio of 3 or more account for 5% by weight or more of the total silicon carbide. By controlling the organization in this way, 4
A high toughness silicon carbide sintered body having a fracture toughness of about 8 MPa · m ^1/2 is obtained. This sintered body is densified by liquid phase sintering using an oxide as a sintering aid. In this case, after cooling, a glass phase including an oxide glass phase or a crystal phase in which a liquid phase is solidified is formed at the grain boundary. The glass phase at the grain boundaries contains oxides of two or more metals such as Li, Mg, Al, Y, rare earth metals, and Si as constituents. Preferably, the amount of glass phase is in the range from 2 to 15% by weight. 2
If the content is less than 15% by weight, sintering becomes difficult, and if the content exceeds 15% by weight, the strength of the sintered body is reduced.

The columnar particles effective for improving toughness have an average particle size of 1 to 10 μm and an average aspect ratio of 3 or more. If the average particle size is less than 1 μm, there is no effect on the improvement of fracture toughness, and if it exceeds 10 μm, extremely long time is required for sintering and heat treatment. When the average aspect ratio is less than 3, the properties become almost the same as those of the matrix, and the effect of the columnar particles contributing to the improvement of toughness is reduced. The range of the average particle diameter of the columnar particles differs depending on the size of the matrix particles. In a matrix of 0.5 to 3 μm, the average particle diameter of the columnar particles is 3 to 10 μm, and the amount of the columnar particles is 5 to 6 μm.
0 wt%, β-type content is 70 wt% of all silicon carbide particles
That is all. When the amount of the columnar particles is 5% by weight or less, there is no effect in improving the fracture toughness. When the amount is 60% by weight or more, there is no problem in the characteristics, but heating for an extremely long time is required.

Such a sintered body has an average particle size of 0.3 μm.
It is manufactured by subjecting a raw material powder having a fineness of not more than m and a β-type content of not less than 80% by weight to liquid phase sintering, followed by heating at a temperature of 1900 ° C. or less and heat treatment. During the heat treatment, some large particles in the particles become nuclei and columnar particles develop, so that the fracture toughness of the obtained sintered body increases. When large β-type particles having an average particle diameter of 0.6 μm or more are added to the raw material powder as nuclei for grain growth in an amount of 0.5 to 5% by weight, the number and size of columnar particles can be more easily controlled. When α-type particles are added to the raw material powder, α-type particles having any size function as nuclei for grain growth. In this case, the addition amount of the α-type particles is preferably adjusted in the range of 0.5 to 5% by weight. The sintered body of the present invention is manufactured by sintering at 1900 ° C. or less and heat treatment. By this sintering and heat treatment, high toughness carbonized sintered bodies composed of 40% by weight or less of matrix particles having an average particle size of less than 1 μm and 60% by weight or more of columnar particles having an average particle size of 1 to 5 μm are obtained. Can be Since α-type particles all act as nuclei for grain growth, β
The amount of matrix is smaller than in the case where the type particles are added as nuclei, and the number of columnar particles increases. Thus, the addition of α-type particles promotes the development of columnar particles. Further, by performing sintering and heat treatment at 1900 ° C. or lower, even if α-type particles are added as nuclei, phase transition is not remarkable, and columnar particles mainly containing β-type particles can be obtained. In this manner, production at a low temperature becomes possible, and as a result, a high-toughness silicon carbide sintered body having a β-type content of 50% by weight or more is obtained.

For measuring the particle size of the silicon carbide sintered body, a sample is cut and polished, treated with microwave plasma of CF ₄ gas, and observed with a scanning electron microscope (SEM). The silicon carbide particles are removed by this treatment, and the oxide glass at the grain boundaries remains, so that the shape of the particles can be easily observed. Using 500 or more particles from the SEM photograph, the diameter, length and area of the particles are calculated by an image processing method. The diameter of the particles is the shortest diameter of the particles on the polishing surface. The average particle diameter is a number average of a large number of measured diameters, and the ratio of the measured particle length to diameter is an apparent aspect ratio. Then, the aspect ratios are arranged in descending order, and the average of 10% values from the top is defined as the true aspect ratio. By using the image analysis in this way, data on the three-dimensional particle distribution and particle shape (aspect ratio) can be obtained from the information on the two-dimensional cross section.

By plotting the measured diameter and the total area of the particles within a certain diameter range, a particle size distribution inside the sintered body is obtained. In the sintered body of the present invention, the particle size is divided into two distributions, and the smaller one is defined as a matrix, and the larger one is defined as a columnar particle. Then, the average particle size and the aspect ratio of each of the matrix and the columnar particles are determined. The β type content in the sintered body can be determined by powder X-ray diffraction of the pulverized sample. The fracture toughness was investigated in accordance with JIS 1607 by pressing a Vickers-type diamond indenter at 98 N against the polished surface of the sample and measuring the size of the indentation and the size of the crack grown from the corner.

[0012]

【Example】

Example 1: A commercially available silicon carbide ultrafine powder (β-SiC ultrafine powder manufactured by Sumitomo Osaka Cement Co., Ltd.) as a raw material for sintering, having a concentration of 0.1 such that the slurry concentration becomes 5% by weight.
A weight% aqueous solution of carboxymethyl cellulose (CMC) was added, and wet-dispersed and pulverized with a silicon carbide ball mill for 3 hours. The slurry was then centrifuged at 2800
The mixture was centrifuged under the conditions of G for 90 minutes to remove free carbon in the silicon carbide powder as a supernatant, and then washed and dried to prepare a fine silicon carbide powder. The average particle size was difficult to measure by the laser scattering method, and was calculated on the assumption of a sphere from the specific surface area, but was extremely fine as 0.09 μm. Next, to the adjusted silicon carbide fine powder of 90% by weight, Al ₂ was added.
O ₃ (AKP-20 manufactured by Sumitomo Chemical Co., Ltd.) 7% by weight, Y ₂ O
₃ Add 2% by weight (fine powder manufactured by Shin-Etsu Chemical Co., Ltd.) and 1% by weight of CaO (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.), and add 2% by weight in ethanol with a planetary ball mill using a silicon carbide container and balls.
Wet mixed for hours. After the powders were dried, about 3 g of these powders were formed into a disk shape at 20 MPa using a mold having a diameter of 15 mm, and further pressed to 200 MPa by a hydrostatic press. BN
The raw material compact is housed in a carbon crucible coated with powder,
Heated to 1750 ° C. in Ar for 60 minutes.

The obtained sintered body has a relative density of 97.5%, a uniform structure, and a fracture toughness of 1.9 MPa · m.
It was ^1/2 . The sintered body is cooled without lowering the temperature.
After holding at 00 ° C. for 2 hours, the mixture was cooled, and its structure (average particle size and aspect ratio of matrix and columnar particles) and fracture toughness were evaluated. The results are shown in Table 1. As a result of powder X-ray diffraction of the sintered body, the β-type content was 73%. The structure was obtained by cutting and polishing a sample cut out of the sintered body, plasma etching, and observing with a scanning electron microscope (SEM). Further, quantitative evaluation was performed using an image analyzer (Luzex III manufactured by NIRECO) using 500 or more particles. Also, the β content and fracture toughness were measured,
The results in Table 1 were obtained. As is evident from Table 1, a sintered body having high toughness was obtained having a structure in which columnar particles were developed as shown in FIG.

Example 2 As a raw material for sintering, a concentration of 0.1% by weight of a commercially available silicon carbide powder (Beta Random Ultrafine manufactured by Ibiden Co., Ltd.) was adjusted so that the slurry concentration became 10% by weight. Add CMC aqueous solution,
The mixture was wet-dispersed and pulverized for 3 hours using a ball mill made of silicon carbide. Next, this slurry was centrifuged at a centrifugal force of 1400 G for 5 minutes, and a slurry containing fine silicon carbide powder as a supernatant was separated, washed and dried to prepare fine silicon carbide powder. The average particle size of the obtained silicon carbide fine powder was measured by a laser scattering method.
It was 8 μm. 6% by weight of Al ₂ O ₃ (AKP-20 manufactured by Sumitomo Chemical Co., Ltd.), ₂ % by weight of Y ₂ O ₃ (fine powder manufactured by Shin-Etsu Chemical Co., Ltd.), 91% by weight of the adjusted silicon carbide fine powder, 91% by weight, MgO
Example 1 (1% by weight of a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added.
The same wet mixing was carried out. After the powders were dried, about 4 g of these powders were filled in a carbon die having a diameter of 15 mm, and the pressure was increased to 1850 ° C. under a press pressure of 20 MPa in an argon atmosphere.
Hot press sintering for 5 minutes. Then, after releasing the pressure, a heat treatment of continuously heating to 1850 ° C. for 8 hours was performed. The obtained sintered body had a relative density of 99.5% and a β-type content of 88%. The evaluation results of the structure and the fracture toughness were as shown in Table 1. Also in this case, it is understood that the sintered body is a high toughness sintered body containing columnar particles while having β-type as a main component.

Example 3 To the fine powder of Example 1 and a sintering aid, 2% by weight of a coarse powder was added as a core for grain growth. As the coarse powder, β-type powder having an average particle diameter of 1.2 μm recovered as a precipitate in Example 2 was used. The actual operation was such that an auxiliary agent was added to the fine powder, wet-mixed for 2 hours in the same manner as in Example 1, then a coarse powder was added, and the mixture was further mixed for 15 minutes. Using this powder, hot press sintering was performed at 1750 ° C for 15 minutes.
Heat treatment was performed at 850 ° C. × 4 hours. The obtained sintered body had a relative density of 99.2% and a β-type content of 75%. As shown in Table 1, the results show that a high-toughness sintered body was obtained by the heat treatment at a low temperature as compared with the case of Example 1 in which the coarse powder was not added as a core.

Example 4 To the same raw material powder and sintering aid as in Example 3, 2% by weight of α-type powder was added as a core for grain growth. As the α-type powder, the remaining coarse powder (average particle size: 0.9 μm) obtained by separating the fine powder from the α-type powder (A-1 manufactured by Showa Denko KK) in the same manner as in Example 2 was used. Hot press sintering was performed under the same conditions as in Example 3 and heat treatment was performed at 1900 ° C. for 2 hours.
The obtained sintered body had a relative density of 99.6% and a β-type content of 63%. As shown in FIG. 2, the sintered body had a structure composed of substantially only columnar particles, and the matrix had almost disappeared. As shown in Table 1, the evaluation of the microstructure and the fracture toughness show that a high toughness sintered body was obtained by a short heat treatment as compared with the case of Example 1 in which the coarse powder was not added as a core. To indicate that

[0017]

Example 5 When the hot-pressed sintered body of Example 3 (without heat treatment) was compressed at 1700 ° C. under a pressure of 30 MPa, a superplastic deformation of 1.5 × 10 ^-4 / sec was exhibited. The tissue after deformation is almost the same as the tissue before deformation,
The average particle size was as fine as about 0.1 μm. After the deformation, heat treatment was performed under the same conditions as in Example 3 to obtain a sintered body having a fracture toughness of 6.2 MPa · m ^1/2 . That is, it was found that a high toughness material can be obtained by forming a sintered body having a fine structure into a predetermined shape by superplastic working and then performing a heat treatment.

Example 6: When the hot-pressed sintered body of Example 4 (without heat treatment) was compressed at 1650 ° C. under a pressure of 30 MPa, a superplastic deformation of 8.2 × 10 ^-4 / sec was exhibited. The tissue after deformation is almost the same as the tissue before deformation,
The average particle size was as fine as about 0.1 μm. After the deformation, heat treatment was performed under the same conditions as in Example 3 to obtain a sintered body having a fracture toughness of 7.5 MPa · m ^1/2 . Also in this case, it was found that a high-toughness material was obtained by forming a sintered body having a fine structure into a predetermined shape by superplastic working and then performing a heat treatment.

[0020]

As described above, in the silicon carbide sintered body of the present invention, the β-type is the main component, and the average particle diameter, the aspect ratio, the ratio to the total silicon carbide particles, etc. of the columnar particles are specified. This makes it possible to utilize the high-temperature strength, corrosion resistance, abrasion resistance and the like of the silicon carbide main body and to use it as a product having excellent toughness. This sintered body can be manufactured by sintering at a lower temperature compared to the conventional method, and the amount and size to improve the fracture toughness can be controlled from the synthesis conditions, so that the structure can be controlled with good reproducibility and quality reliability. Used in a wide range of fields as a high product.

[Brief description of the drawings]

FIG. 1 is a photograph showing the structure of a silicon carbide sintered body manufactured in Example 1.

FIG. 2 is a photograph showing a structure of a silicon carbide sintered body manufactured in Example 4.

Claims (7)

(57) [Claims] 1 to 85 to 98% by weight of silicon carbide particles;
Columnar particles having a structure consisting of a grain boundary phase of 2 to 15% by weight, a β-type content in the silicon carbide particles of 50% by weight or more, an average particle diameter of 1 to 10 μm, and an average aspect ratio of 3 or more. A silicon carbide sintered body that is 5% by weight or more of all silicon carbide particles and has a fracture toughness of 4 to 8 MPa · m ^1/2 . 2. The method according to claim 1, wherein the grain boundary phase is a glass containing an oxide of two or more metals selected from the group consisting of Li, Mg, Al, Y, a rare earth metal and Si, or a glass containing a crystal phase. Item 4. The sintered silicon carbide according to Item 1. 3. The silicon carbide particles have an average particle size of 0.5 to 3 μm.
40 to 95% by weight of matrix particles having an average particle size of 3 to
3. The silicon carbide sintered body according to claim 1, comprising 5 to 60% by weight of 10 [mu] m columnar particles, and having a [beta] -type content of 70% by weight or more of all silicon carbide particles. 4. The method according to claim 1, wherein the silicon carbide particles have an average particle diameter of 40% by weight or less and an average particle diameter of 1 to 5 μm or less.
m, comprising at least 60% by weight of columnar particles having a β-type content of at least 50% by weight of all silicon carbide particles.
3. The sintered silicon carbide according to any one of 3. 5. A raw material fine powder having an average particle size of 0.3 μm or less and a β-type content of 80% by weight or more is subjected to liquid phase sintering,
The method for producing a silicon carbide sintered body according to claim 1, wherein the heat treatment is performed at a temperature of 0 ° C. or lower. 6. The raw material fine powder according to claim 5, wherein β-type particles having an average particle size of 0.6 μm or more are used as nuclei for grain growth in an amount of from 0.5 to 0.5 μm.
A method for producing a silicon carbide sintered body in which 5% by weight is added. 7. A method for producing a silicon carbide sintered body, wherein α-type particles are added to the raw material fine powder according to claim 5 as nuclei for grain growth in an amount of 0.5 to 5% by weight.