JPH0753615B2 - Method for manufacturing silicon nitride sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automobiles, mechanical devices,
A fine ceramic material that can be used as a raw material for various structural parts used in a wide range of fields such as chemical equipment and aerospace equipment, and that uses inexpensive β-type silicon nitride powder as a raw material and that has a particularly high fracture toughness value and excellent strength The present invention relates to a method for producing a silicon nitride-based sintered body suitable for obtaining.

[0002]

2. Description of the Related Art Sintered bodies containing silicon nitride as a main component are chemically stable at room temperature and high temperature and have high mechanical strength. Therefore, sliding members such as bearings and engine members such as turbocharger rotors are used. Is a suitable material.

Conventionally, in order to obtain a high-strength silicon nitride sintered body, a raw material powder containing α-type as a main component has been required. Generally, a powder having an α-type content of 90% by weight or more is required. It is commercially available. Here, the raw material powder mainly composed of α type is used as follows. 1. The α type is a fine powder and has high sinterability, This is because the phase transition from α-type to β-type occurs during sintering and the columnar crystals develop into a structure, which improves strength and toughness.

[0004]

However, in the above-mentioned silicon nitride powder starting from α-type as a starting material, it is necessary to control the content of α-type, so that the synthesis process of the raw material powder is complicated and the raw material is expensive. There was a problem that it would be something like.

On the other hand, as a silicon nitride powder containing β-type as a main component, a powder used as a raw material of a refractory is known. As a sintered body made of silicon nitride containing β type as a main component as a raw material, J. Am. Ceram. Soc. 57
Volume 25 (1974), JP-A-58-15137
No. 1 is known.

However, the powder containing β-type as the main component has coarse particles, and since the content of α-phase is low, a columnar structure cannot be obtained and a high-strength sintered body cannot be obtained. It was not used as a raw material powder for manufacturing the body.

One of the inventors of the present invention previously developed a gas pressure sintering method which enables sintering at high temperature under high nitrogen (Japanese Patent No. 1,247,183). In addition, according to the gas pressure sintering method, it was shown that β-type silicon nitride powder, which was conventionally considered to have low sinterability, can be sintered to a high density (Journal of Materials Science No. 1).
1 1103 to 1107 (1976) and JP-A-58-151371. Further, it was shown that a high-strength sintered body can be obtained by adjusting the particle size distribution of high-purity β-type silicon nitride powder (Japanese Patent Laid-Open No. 225555/1990).
No. 73).

However, it is necessary to use pure high-purity β-type powder as a starting material, and there is a problem that it becomes expensive.

Therefore, the process of synthesizing the raw material powder is not complicated, and it is not necessary to use the high-purity β-type powder, and the inexpensive refractory-grade β-type silicon nitride powder is used as the raw material and is excellent in strength and toughness. It has been a problem to be able to obtain a silicon nitride sintered body.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, in which an inexpensive refractory grade β-type silicon nitride powder is used as a raw material, and the raw material powder is subjected to a pulverizing / classifying treatment to obtain a particle size. It is an object of the present invention to provide a silicon nitride sintered body excellent in strength and toughness by using a raw material powder whose distribution is controlled.

[0011]

In the method for manufacturing a silicon nitride sintered body according to the present invention, an inexpensive refractory grade β-type silicon nitride powder is used as a raw material, and the raw material powder is subjected to an appropriate pulverization and classification treatment. By using a raw material powder with a controlled particle size distribution, it is possible to obtain a silicon nitride sintered body with excellent strength and toughness comparable to a silicon nitride sintered body using a high-purity powder as a starting material. The present invention has been completed and the present invention has been completed.

That is, in the method for producing a silicon nitride sintered body according to the present invention, the silicon nitride raw material powder having α type and β type contains β type in an amount of 80% by weight or more and has an average particle size of 2.0 μm or more. Using the silicon nitride raw material powder of
After pulverizing and classifying the raw material powder, the raw material powder is classified into fine particles of 0.8 μm or less powder and coarse particles of 1.5 μm or more and 5.0 μm or less, and the fine particles and coarse particles are mixed. And the proportion of 0.8 μm or less is 70% by weight or more and 95% by weight or less, and the proportion of 1.5 μm or more and 5.0 μm or less is controlled to be 5% by weight or more and 30% by weight or less. After adding the sintering aid to and molding
The present invention is characterized in that it is fired in a nitrogen atmosphere, and the constitution of the invention relating to the method for producing a silicon nitride sintered body is a means for solving the above-mentioned conventional problems.

In the method for manufacturing a silicon nitride sintered body according to the present invention, a sintering aid selected from oxides and nitrides can be used. Also,
When firing in a nitrogen atmosphere, 1600 to 2000
Temperatures of ° C can be employed.

In the method for producing a silicon nitride sintered body according to the present invention, the starting raw material powder is a silicon nitride raw material powder having α type and β type, and β type is 80% by weight.
A silicon nitride raw material powder containing the above and having an average particle diameter of 2.0 μm or more is used. In this case, in the present invention, since the particle size distribution and firing conditions are set in accordance with the sinterability of β-type silicon nitride, if the α-type content increases, abnormal grain growth occurs and the strength decreases. Then, it is necessary to obtain fine particles of 0.8 μm or less powder and coarse particles of 1.5 μm or more and 5.0 μm or less by subjecting the silicon nitride raw material powder to pulverizing and classifying treatment. It is necessary that the raw material powder has an average particle size of 2.0 μm or more.

Next, the silicon nitride raw material powder is subjected to a pulverizing and classifying treatment to reduce the ratio of 0.8 μm or less to 70%.
% To 95% by Weight and 1.5 μm to 5.0
The particle size distribution is controlled such that the proportion of μm or less is 5% by weight or more and 30% by weight or less. In this case, it is not limited to the case where it is composed only of powder of 0.8 μm or less and the powder of 1.5 μm or more and 5.0 μm or less, and the powder of other than 0.8 μm and less than 1.5 μm within the range satisfying the above ratio. And 5.
It also includes the case where a small amount of powder exceeding 0 μm is contained.
And, the powder of 0.8 μm or less (hereinafter referred to as “fine particles”) has a function of promoting the densification of the sintered body,
If the maximum particle size of the fine particles exceeds 0.8 μm, the sinterability decreases. Further, if the proportion of fine particles is less than 70% by weight, the sinterability is deteriorated. On the other hand, when the proportion of fine grains exceeds 95% by weight, the proportion of particles in the range of 1.5 μm or more and 5.0 μm or less (hereinafter referred to as “coarse grains”), which are cores of grain growth for structure control, is produced. Since the amount becomes small, the columnar structure does not develop although it is densified, and the strength and toughness values decrease.

The particle size of the coarse particles is from 1.5 μm to 5.0 μm.
m or less is preferable. That is, when the thickness is less than 1.5 μm, there is little function as a nucleus of columnar grain growth, and a columnar structure cannot be obtained. On the other hand, if it exceeds 5.0 μm, a columnar structure having a large particle size can be obtained, but since the growth rate is low, the strengthening mechanism is small and the strength and toughness are not improved. The proportion of coarse particles is preferably 5% by weight or more and 30% by weight or less. That is,
When it is less than 5% by weight, columnar crystals do not develop due to the small number of nuclei. On the other hand, if it exceeds 30% by weight, the proportion of fine particles decreases and the sinterability decreases. Further, when aiming at further higher strength, it is desirable to remove the giant particles of 10.0 μm or more by a precipitation method or a sieve.

Any method can be used for the pulverizing / classifying treatment as long as the above-mentioned particle size distribution can be obtained. An example will be described below.

First, the raw material powder is dispersed in water, then pulverized by using an attrition mill, the treated slurry is put in a water tank, and then the particles are classified by a precipitation method to obtain a necessary amount of fine particles. And remove the coarse particles from the water tank. The coarse particles left over from the classification are charged again into the attrition mill together with the raw materials, and the crushing process is repeated. In this way, it is good in terms of efficiency to obtain a raw material powder having a predetermined particle size distribution by pulverizing and classifying the same powder.

A sintering aid such as an oxide or a nitride is added to the silicon nitride raw material powder whose particle size has been adjusted in this manner. The sintering aid used here is usually selected from the sintering aids used for sintering α-type or β-type silicon nitride. Examples of the oxide sintering aid include MgO, Al ₂ O ₃ , and
One or a mixture of two or more selected from Y ₂ O _{3 and} lanthanide metal oxides is used. In addition, for example, AlN is used as the sintering aid for the nitride. The addition amount of this sintering aid is usually 5 to 15% by weight.

Further, when molding the above-mentioned powder, it is possible to carry out molding by a usual molding method such as die press molding, isostatic press molding, injection molding, casting molding and the like. After that, the organic binder required for molding is removed and firing is performed.

Firing is performed in a nitrogen atmosphere at 1600 to 200.
It is better to carry out at a temperature of 0 ° C. In this case, nitrogen is necessary to prevent thermal decomposition of silicon nitride, and the higher the temperature, the higher the pressure of the nitrogen atmosphere used. The minimum pressure required for this firing is 1 atm at a firing temperature of 1600 to 1750 ° C, 2 atm at a firing temperature of 1800 ° C, 5 atm at a firing temperature of 1900 ° C, and 10 atm at a firing temperature of 2000 ° C. If the pressure is lower than the predetermined pressure, silicon nitride undergoes thermal decomposition and releases nitrogen to become silicon, which is not preferable. The preferable firing temperature varies depending on the sintering method and the type and amount of the auxiliary agent used, but a temperature of 1600 to 2000 ° C. is used. As the sintering method, hot pressing, atmospheric pressure sintering method, gas pressure sintering method and the like are adopted in consideration of the product shape, the type and amount of the sintering aid to be used, and the like.

[0022]

In the method for producing a silicon nitride sintered body according to the present invention, the silicon nitride raw material powder having a large average particle size of 2.0 μm or more is used as a raw material, and the powder is pulverized and classified to obtain the β-type powder. Is used as a silicon nitride raw material powder having a particle size distribution matched to the sintering characteristics of silicon nitride, and in the silicon nitride raw material powder having α type and β type, β type is contained in an amount of 80% by weight or more and the average particle size is 2.
A raw material powder of 0 μm or more of silicon nitride is used, and the raw material powder is pulverized and classified to obtain fine particles of 0.8 μm or less and coarse particles of 1.5 μm or more and 5.0 μm or less. Classifying and mixing the fine particles and the coarse particles, the ratio of 0.8 μm or less is 70% by weight or more and 95% by weight or less.
After controlling the particle size distribution such that the ratio of 1.5 μm or more and 5.0 μm or less is 5% by weight or more and 30% by weight or less, and adding a sintering aid to this silicon nitride raw material powder,
Since it is fired in a nitrogen atmosphere, even when an inexpensive refractory grade β-type silicon nitride powder is used, it has an excellent strength and a strength not inferior to that of a silicon nitride-based sintered body using a high-purity powder as a starting material. A silicon nitride sintered body having a fracture toughness value and excellent characteristics can be obtained.

[0023]

【Example】

(Embodiment 1) FIG. 1 shows an outline of the pulverizing / classifying treatment adopted in Embodiment 1 of the present invention.

In Example 1, first, the average particle size was 2.5 μm, the maximum particle size was 20 μm, and the β-type content was 99.
Water and beads of the silicon nitride sintered body are added to the silicon nitride powder of weight%, continuous crushing is performed using an attrition mill, the crushed slurry is put in a water tank, and coarse particles are put from the lower part of the water tank. 0.8μ by removing fine particles from the top
90% by weight of fine particles of m or less, exceeding 0.8 μm 1.
The ratio of less than 5 μm is 1% by weight, 1.5 μm or more and 5.0 μm
8% by weight of coarse particles of m or less, exceeding 5.0 μm 10.
The particle size was adjusted so that the ratio of less than 0 μm was 1% by weight. At this time, the giant particles (1
0.0μm or more) is removed and discarded, and the remaining 1.5μ
The powder having a particle size of m or more and less than 10.0 μm was collected and again charged into the attrition mill together with the raw material powder.

Next, 6% by weight of yttrium oxide and 2% by weight of aluminum oxide were added to the raw material powder of silicon nitride whose particle size was adjusted, and they were mixed in a ball mill for 2 hours. continue,
20M after drying with a spray dryer in air
Mold press molding with pressure of Pa, 200MP
By applying a rubber press with a pressure of a, 6 mm ×
A 6 mm × 50 mm molded body was obtained.

Next, after firing the molded body under various firing conditions shown in Table 1, various sintered bodies are obtained, and then the porosity of each sintered body is determined by the Archimedes method using water to obtain the density. Was calculated. Further, it was surface ground with an 800 mesh diamond wheel, processed into a shape of 3 mm x 4 mm x 40 mm, and the bending strength was determined by room temperature three-point bending according to JIS R 1601, and JIS R 16
The fracture toughness value was determined by the SEPB method according to 07 (a method in which Vickers indentation is added to the surface of a test piece of 3 × 40 mm, a precrack is generated from this, and fracture is performed from this precrack).
The results are also shown in Table 1.

[0027]

[Table 1]

As is clear from the results shown in Table 1, it was confirmed that a high-strength and high-toughness silicon nitride sintered body was obtained under any of the conditions.

(Embodiment 2) FIG. 2 shows an embodiment 2 of the present invention.
The outline of the pulverizing and classifying process adopted in is shown below.

In this Example 2, first, the average particle size was 1
Water and balls of a silicon nitride sintered body were added to silicon nitride powder having a particle size of 0 μm, a maximum particle size of 200 μm, and a β-type content of 90% by weight, ground with a ball mill for 200 hours, dried, and then dried with a jet grinder. Pulverizing and classifying using a classifier of 0.8 μm and fine particles of 0.8 μm or less and 0.8 μm or more 1.5
Particles of less than μm, coarse particles of 1.5 μm or more and 5.0 μm or less, and particles of more than 5.0 μm and less than 10.0 μm were obtained. And the thing of 10.0 micrometers or more was abandoned. Then, by mixing the powders, the ratio of fine particles of 0.8 μm or less is 80% by weight, the ratio of 0.8 μm or more and less than 1.5 μm is 3% by weight, and the ratio of 1.5 μm or more and 5.0 μm or less is added. 1
5% by weight, ratio of more than 5.0 μm and less than 10.0 μm is 2
The particle size was adjusted so that the weight% was obtained.

Next, the sintering aid having the composition shown in Table 2 was added to the silicon nitride raw material powder whose particle size was adjusted, and mixed for 2 hours in a ball mill. Then, after drying in air using a spray dryer, mold molding was performed at a pressure of 20 MPa, and a rubber press was further performed at a pressure of 200 MPa to obtain a molded body of 6 mm × 6 mm × 50 mm.

Next, after firing the molded body under various firing conditions similarly shown in Table 2 to obtain respective sintered bodies,
The density was calculated by obtaining the porosity of each sintered body by the Archimedes method using water. Furthermore, the surface is ground with an 800-mesh diamond wheel and 3 mm x 4 mm x 40 m.
It is processed into the shape of m and the bending strength is obtained by room temperature three-point bending according to JIS R 1601.
SEPB method according to 1607 (Vickers indentation was added to the surface of the test piece of 3 × 40 mm to generate a pre-crack,
The fracture toughness value was determined by the method of fracture from this precrack. The results are also shown in Table 2.

[0033]

[Table 2]

As is clear from the results shown in Table 2, it was confirmed that a high-strength and high-toughness silicon nitride sintered body was obtained under any of the conditions.

(Comparative Example 1) The raw material powder was pulverized and classified by the same steps as in Example 2, and fine particles of 0.8 µm or less, fine particles of 0.8 µm or more and less than 1.5 µm, and 1.5 µm or more and 5.0 µm or more were used. The following coarse particles and particles with a size exceeding 5.0 μm were obtained.
And the thing of 10.0 micrometers or more was abandoned. Then
By mixing the powders, fine particles of 0.8 μm or less, fine particles of more than 0.8 μm and less than 1.5 μm, and 1.5 μm
The particle size was adjusted so that the ratio of coarse particles of m or more and 5.0 μm or less and particles of more than 5.0 μm was as shown in Table 3.

Next, the particle size-adjusted silicon nitride powder was added,
Similarly, a sintering aid having the composition shown in Table 3 was added and mixed by a ball mill for 2 hours. Then, after performing the same molding as in Example 2, each sintered body was obtained by firing the molded body under the firing conditions shown in Table 3 as well, and the same evaluation as in Example 2 was performed. The results are also shown in Table 3.

[0037]

[Table 3]

As is clear from the results shown in Table 3,
No. 1 containing no coarse particles of 1.5 μm or more and 5.0 μm or less.
No. 9 has a high density but a low bending strength and fracture toughness value, and the ratio of fine particles of 0.8 μm or less is too small. In Nos. 10 and 11, it was confirmed that the density, bending strength and fracture toughness were low. Comparative Example 2 As a comparative example to Example 1, an average particle size of 2.5 μm,
Water and beads of a silicon nitride sintered body were added to silicon nitride powder having a maximum particle size of 20 μm, an impurity amount of Fe: 1200 ppm, oxygen: 2.0% by weight and a β-type content of 99% by weight,
Continuous crushing is performed using an attrition mill, the crushed slurry is put in a water tank, and the powder is taken out from the lower part of the water tank. Particles of 1.5 μm or more and 5.0 μm or less are
Coarse particles of 0% by weight were obtained. On the other hand, average particle size 0.5μ
m, maximum particle size 2.5 μm, impurity amount Fe: 80 ppm,
Oxygen: 0.8% by weight and β-type content of 95% by weight of silicon nitride powder (that is, another silicon nitride powder having different impurities, β-type content, etc., from the above-mentioned silicon nitride powder) with the coarse particles. 9% by weight was added and mixed, the ratio of fine particles of 0.8 μm or less was 89% by weight, the ratio of fine particles of more than 0.8 μm and less than 1.5 μm was 2% by weight, and of coarse particles of 1.5 μm or more and 5.0 μm or less The particle size was adjusted so that the ratio was 8% by weight and the ratio of more than 5.0 μm and less than 10.0 μm was 1% by weight. Then, using this as a raw material, a sintered body was prepared by the same method as in Example 1, and the characteristics were measured by the same method as in Example 1. As a result, as shown in Table 4, the strength was lower than that of the example. When the fracture starting point of the sintered body was examined, glass-like defects of 50 to 100 μm were generated in the comparative example, and it was confirmed that segregation of impurities was a cause of strength reduction.

[Table 4]

[0039]

In the method for producing a silicon nitride sintered body according to the present invention, the silicon nitride raw material powder having α type and β type contains β type in an amount of 80% by weight or more and has an average particle size of 2.0 μm or more. After using the silicon nitride raw material powder as a raw material and subjecting the raw material powder to pulverizing and classifying treatment, the raw material powder is classified into fine particles of 0.8 μm or less and coarse particles of 1.5 μm or more and 5.0 μm or less, Fine particles and coarse particles are mixed, and
The proportion of 8 μm or less is 70% by weight or more and 95% by weight or less, and the proportion of 1.5 μm or more and 5.0 μm or less is 5% by weight or more and 30% by weight or less, and the particle size distribution is controlled and sintered to this silicon nitride raw material powder. After the auxiliary agent was added and molded, it was fired in a nitrogen atmosphere, so even when inexpensive refractory grade β-type silicon nitride powder was used as the raw material, it was pulverized and classified to have a specific particle size. It is remarkably possible to obtain a silicon nitride sintered body having excellent strength and toughness comparable to that of a silicon nitride sintered body using a high-purity powder as a starting material, by blending a specific amount of Excellent effect is brought about.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a pulverizing / classifying process used in Example 1 of the present invention.

FIG. 2 is an explanatory diagram showing an outline of a pulverizing / classifying process used in Example 2 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motohide Ando 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) Reference JP-A-2-255573 (JP, A)

Claims (3)

[Claims] 1. A silicon nitride raw material powder having α-type and β-type, wherein the raw material is silicon nitride raw material powder containing 80% by weight or more of β-type and having an average particle diameter of 2.0 μm or more, and pulverized and classified into the raw material powder. After the treatment, it is classified into fine particles of 0.8 μm or less powder and coarse particles of 1.5 μm or more and 5.0 μm or less, and the fine particles and coarse particles are mixed to obtain 0.8 μm or less. Of 70% to 95% by weight
After controlling the particle size distribution such that the ratio of 1.5 μm or more and 5.0 μm or less is 5% by weight or more and 30% by weight or less, and adding a sintering aid to this silicon nitride raw material powder,
A method for producing a silicon nitride sintered body, which comprises firing in a nitrogen atmosphere. 2. The method for producing a silicon nitride sintered body according to claim 1, wherein the sintering aid is selected from oxides and nitrides. 3. The method for producing a silicon nitride sintered body according to claim 1, wherein the firing temperature is 1600 to 2000 ° C.