JP3127022B2 - Method for producing alumina-based composite sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a compact structure and a high hardness.
Manufacture of alumina-based composite sintered body with high fracture toughness
The present invention relates to a method for producing an alumina-based composite sintered body .

[0002]

2. Description of the Related Art In general, alumina ceramics are thermally and chemically stable among many ceramics.
In addition, since it has relatively high hardness and mechanical strength, its use is expanding in recent years. In particular, alumina ceramics have the highest hardness among oxide ceramics. Utilizing this high hardness and the high wear resistance obtained therefrom, powders such as blast devices and powder classifiers are used. It is widely used for wear parts of equipment.

[0003] In a sand blasting apparatus, which is a type of blasting apparatus, sand containing corundum having a hardness as high as that of alumina ceramics is sometimes used in order to further improve the working efficiency. in this case,
The walls made of alumina ceramics are damaged by the impact of corundum sand particles and cause erosion wear. The erosion wear resistance of the vessel wall improves as the difference in hardness between the vessel wall material and the solid particles impinging thereon increases. It is also known that when the hardness difference is within a narrow range, the higher the fracture toughness value, the better.

[0004] However, in such an apparatus, the hardness and fracture toughness of alumina ceramics as a wall material are both smaller than those of corundum particles, so that their wear resistance (erosion wear resistance) is insufficient. Improvement is desired. Generally, as a method of increasing the hardness and fracture toughness of a ceramic material, ceramic material particles having higher hardness and elastic modulus than the material forming the matrix of the ceramic material are dispersed in the matrix, and the hardness is added. There is known a technique that utilizes the property and the deflection of a crack caused by dispersed particles. Among them, a method for increasing the hardness and fracture toughness of alumina ceramics is Si
It is often employed to disperse non-oxide ceramic particles having a higher hardness and elastic modulus than alumina, such as C, TiC, or TiN, in alumina ceramics.

[0005]

However, since the above-mentioned non-oxide ceramic particles are difficult to sinter, the non-oxide ceramic particles are mixed and dispersed in an alumina powder matrix by a usual method. Then, even if the obtained mixed powder is sintered under normal pressure, the structure of the sintered body is dense and has high hardness and high fracture toughness, in other words, fine particles of non-oxide ceramics are uniformly dispersed inside the particles of the matrix powder. It is difficult to obtain a dispersed sintered body.

Therefore, in order to solve such a problem, conventionally, means such as using a hot press method or adding a sintering aid have been adopted. However, even in such a solution, a hot press method can produce only a simple shape, and thus it is almost impossible to produce a component having a complicated shape such as a mechanical component. However, even if an attempt is made to form a part having a complicated shape by cutting or the like, the machining cost is significantly increased due to the high hardness of the material itself.

[0007] When a method using a sintering aid is employed, the hardness of the alumina itself is reduced due to the reaction of the sintering aid with the alumina. Inconveniences such as offsetting occur. Furthermore, even if the mixed powder of the alumina powder and the non-oxide ceramic particles is forcibly sintered at normal pressure, large aggregates of the non-sinterable dispersed particles are interposed at the grain boundaries of the alumina powder particles, Since the sintering of the alumina powder particles is inhibited, the mechanical strength of the obtained product is reduced, and the sintered product is broken or its strength is deteriorated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an alumina-based composite sintered body having a sufficiently dense structure and high hardness and fracture toughness.
Can be produced without using a sintering aid,
An object of the present invention is to provide a method for manufacturing a composite sintered body .

[0009]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object, and as a result, uniformly mixed alumina and fine powder of silicon carbide using ultrasonic vibration and further heat-treated. As a result, it has been found that fine particles of silicon carbide are dispersed in alumina particles, and the present invention has been completed. That is, the method for producing the alumina-based composite sintered body of the present invention
Method, γ-type alumina powder having an average particle size of 0.05 μm or less
Powder and β-type silicon carbide powder having an average particle size of 0.05 μm or less.
80-97% by volume of alumina powder and silicon carbide powder
Ultrasonic wave of 10 to 50 kHz so as to be 3 to 20% by volume
Mixed in a solvent oscillating at
Heat treatment at a temperature of 1150-1350 ° C under an inert atmosphere
The heat-treated mixed powder is molded and molded
And then press the molded body under normal pressure in an inert atmosphere
And sintering at a temperature of 1500 to 1900 ° C. as a means for solving the above-mentioned problem.

Hereinafter, the present invention will be described in detail.

[0011] The method for producing the alumina-based composite sintered body of the present invention
In, First alumina particles, each average particle diameter as the silicon carbide particles have the following particle 0.05 .mu.m. These fine particles have a very small diameter and a large specific surface area, and therefore have excellent surface activity. Here, the reason for using fine particles having an average particle diameter of 0.05 μm or less as silicon carbide particles is that if the average particle diameter exceeds 0.05 μm, it becomes difficult to disperse the particles inside the alumina particles grown by the heat treatment. is there. And, as such silicon carbide fine powder, a powder composed of β-type crystal is used.
Is done .

Further, the average particle diameter of alumina powder is 0.1.
The reason for using fine particles having a particle size of not more than 05 μm is that when the average particle size of the alumina powder is larger than the silicon carbide powder, it becomes difficult to mix both powders uniformly. And such alumina fine powder is composed of γ-type crystals.
Things are used .

Next, the alumina powder and the silicon carbide powder were mixed in an amount of 80 to 97% by volume with the alumina powder and 3% with silicon carbide.
２０20% by volume and 10 to 50 kHz
The mixture is placed in a solvent such as methanol vibrated by ultrasonic waves of z and wet-mixed at a particle level while loosening aggregation between powders.
Here, the reason that the alumina powder is 80 to 97% by volume and the silicon carbide powder is 3 to 20% by volume is that the proportion of the silicon carbide powder in the mixed powder is less than 3% by volume.
If the hardness of the obtained sintered body is insufficiently improved, and if the content of silicon carbide powder exceeds 20% by volume, the silicon carbide powder cannot be completely dispersed in the alumina particles grown by the heat treatment, so that a large amount exists at the grain boundaries. This is because the entire sinterability is impaired.

Further, the mixing operation was carried out in a solvent vibrated by an ultrasonic wave because the raw material powder used was a fine powder and the adhesion and cohesion of the powder particles were large. Because it is difficult to mix them. Here, the reason why the ultrasonic wave is set to 10 to 50 kHz is that an ultrasonic wave having a frequency of less than 10 kHz and exceeding 50 kHz does not sufficiently obtain the effect of dispersing the powder particles and loosening the aggregates.

Next, the obtained mixed powder is heated at a temperature of 1150-1350 ° C. for 30 minutes under an atmospheric pressure under an inert atmosphere.
Heat treatment for about 2 hours. When heat treatment is performed in this manner, alumina particles grow preferentially due to the difference in the particle growth rate between alumina and silicon carbide, and as a result, silicon carbide is formed inside the grown alumina particles or at the grain boundaries of the alumina particles. The fine particles are dispersed, and alumina-based composite particles are formed. In other words, by this heat treatment, the alumina particles grow together and grow into particles having a particle size of 1.0 to 10.0 μm, but the particle size of the silicon carbide particles is at most 0.3.
Only about μm. Therefore, the particle size is 1.0.
Particle size of 0.3 μm inside alumina particles of 10.0 μm
The following silicon carbide particles are dispersed and included to form alumina-based composite particles.

The reason why the heating temperature is set to 1150 to 1350 ° C. is that if the temperature is lower than 1150 ° C., the fusion growth of the alumina powder becomes insufficient and it becomes difficult to disperse silicon carbide particles therein. On the other hand, when the temperature exceeds 1350 ° C., the fusion growth of the alumina powder becomes excessive, the obtained alumina-based composite particles become excessively large, and the densification by sintering is hindered. As an inert atmosphere at the time of such heat treatment, an atmosphere of an inert gas such as helium, argon, or nitrogen, or a vacuum atmosphere is employed. Gas may be generated due to the above, and it is more preferable to perform the treatment in a vacuum atmosphere.

Next, the obtained alumina-based composite particles are molded into a desired size and shape by a known molding method such as a pressure molding method. Heat sintering at a temperature of １1900 ° C. to obtain a desired molded sintered body. Here, the sintering temperature is set to 1
The reason why the temperature is set to 500 to 1900 ° C. is that if the temperature is lower than 1500 ° C., the densification of the sintered body becomes insufficient, and the porosity does not become 2% or less. This is because it becomes insufficient. On the other hand, when the sintering temperature exceeds 1900 ° C., the particles of the sintered body are coarsened, and defects and cracks are easily generated in the obtained molded sintered body, and the manufacturing cost is increased. As an atmosphere for sintering, an atmosphere using an inert gas such as helium, argon, or nitrogen, or a vacuum atmosphere is used.

The alumina-based composite sintered body thus obtained contains alumina particles having a particle size of 1.0 to 10.0 μm in an amount of 8 μm.
A normal pressure sintered body containing 0 to 97% by volume and 3 to 20% by volume of silicon carbide particles having a particle size of 0.3 μm or less, wherein the silicon carbide particles are contained in alumina particles or have a grain boundary. And a dense structure having a porosity of 2% or less of the whole. Here, the reason why the particle size of the sintered alumina particles was set in the above range was that the particle size was 1.0 μm.
If it is less than m, the dispersion of the silicon carbide particles inside the alumina particles will be almost nil. On the other hand, if it exceeds 10.0 μm, the porosity of the obtained sintered body will be larger than 2%, This is because the mechanical properties become insufficient. The reason why the particle size of the sintered silicon carbide particles is 0.3 μm or less is that if the particle size is larger than this, it is difficult to disperse the particles in the alumina particles.

[0019]

According to the method for producing an alumina-based composite sintered body of the present invention,
If silicon carbide particles do not form large aggregates,
Al is uniformly dispersed in the grain and grain boundaries of
Sintering at the interface of the mina particles proceeds smoothly. So the gain
Alumina-based composite sintered body
In which fine particles of silicon carbide are dispersed and contained.
Therefore, a sufficiently dense structure is obtained.

[0020]

EXAMPLES The present invention will be specifically described with reference to examples. Example 1 95% by volume of γ-alumina powder (average particle size: 0.004 μm, BET specific surface area: 300 m ² / g)
And 5% by volume of β-silicon carbide powder (average particle size: 0.02 μm, BET specific surface area: 50 m ² / g) synthesized by high-frequency plasma CVD in methanol vibrated by 19 kHz ultrasonic waves. The mixture was wet-mixed for 10 hours and then dried to obtain a mixed powder. Next, the obtained mixed powder was heat-treated in a vacuum at 1200 ° C. for 2 hours to prepare an alumina-silicon carbide-dispersed composite powder. After the composite powder was crushed to adjust the particle size to about 0.5 to 1.0 μm, it was formed into a plate having a length of 45 mm, a width of 35 mm and a thickness of 5 mm. Thereafter, the molded product was heated and sintered at 1650 ° C. for 1 hour in a nitrogen gas atmosphere at normal pressure to obtain an alumina-based composite sintered body.

[0021] (implementation example 2) 90% by volume of γ- alumina powder (average particle diameter: 0.004
μm, BET specific surface area: 300 m ² / g) and 10% by volume of β -silicon carbide powder synthesized by high frequency plasma CVD ( average particle size: 0.02 μm, BET specific surface area: 5)
0 m ² / g), and the subsequent operation was performed in the same manner as in Example 1 to obtain an alumina-based composite sintered body. Comparative Example 1 90% by volume of γ-alumina powder (average particle diameter: 0.004)
μm, BET specific surface area: 300 m ² / g) and 10% by volume of β-silicon carbide powder synthesized by high frequency plasma CVD (average particle size: 0.02 μm, BET specific surface area: 5)
0 m ² / g) was wet-mixed for 72 hours in methanol to which no ultrasonic vibration was applied, and then dried to prepare a mixed powder. The subsequent operations were the same as in Example 1 to obtain an alumina-based composite sintered body. (Comparative Example 2) An alumina-based composite sintered body was obtained in the same manner as in Example 1 except that a silicon carbide raw material powder having an average particle diameter of 0.3 µm was used. (Comparative Example 3) An alumina-based composite sintered body was obtained in the same manner as in Example 1 except that only alumina powder was used without using silicon carbide powder.

The densities of the sintered bodies of Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the Archimedes method using water displacement, and the relative densities were calculated from the theoretical densities and the actually measured values. The hardness and fracture toughness of each sintered body were measured by a Vickers hardness meter and an indentation method, respectively. Table 1 shows the obtained results.

[Table 1] From Table 1, it was confirmed that the sintered body according to the present invention had a higher density, a dense structure, and excellent hardness and fracture toughness values as compared with the sintered body of the comparative example.

[0023]

As described above, the alumina base of the present invention
The manufacturing method of the composite sintered body is based on the alumina powder (flat
Uniform particle size: 0.05 μm or less, same as γ-type crystal)
Silicon carbide powder with physical properties (average particle size: 0.05 μm or less, β
And the mixing operation was ultrasonically vibrated
In a solvent, heat treatment (1150 to 1350) before sintering
℃), the silicon carbide fine particles
And disperses uniformly in alumina grains and at grain boundaries
Sintering at the alumina particle interface proceeds smoothly
This method requires sintering aids, etc.
And normal pressure sintering using only alumina and silicon carbide
The porosity is 2% or less, resulting in a dense structure.
It has natural high thermal and chemical stability,
Silicon carbide fine particles dispersed and contained in alumina particles
Has excellent hardness and fracture toughness values.
Alumina-based composite sintered body with excellent wear resistance
Can be efficiently and stably manufactured.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/10 C04B 35/626

Claims (1)

(57) [Claims] 1. A γ-type alumina powder having an average particle size of 0.05 μm or less and a β-type silicon carbide powder having an average particle size of 0.05 μm or less, wherein alumina powder is 80 to 97% by volume, The silicon carbide powder is mixed in a solvent vibrating by ultrasonic waves at 10 to 50 kHz so as to have a volume of 3 to 20% by volume, and then the mixed powder is heated at a temperature of 1150 to 1350 ° C under an inert atmosphere. Alumina-based composite characterized by heat-treating and further molding the heat-treated mixed powder into a compact, and then sintering the compact at 1500 to 1900 ° C. under normal pressure under an inert atmosphere. A method for manufacturing a sintered body.