JPS63242970A - Manufacture of silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a high-strength silicon nitride sintered body useful for mechanical parts, wear-resistant members, sliding members, etc.

[Conventional technology] Conventionally, silicon nitride sintered bodies have been manufactured as follows.

First, the silicon nitride raw material and the sintering aid are mixed, and after pulverizing, the process is usually carried out at
Passed through the sieve of Lum. Next, after granulating the raw material mixture after passing through a sieve, the amount of water in the raw material mixture is controlled by aging or adding water, and after further passing through a sieve, it is molded using a die press or cold isostatic press. A sintered body is obtained by firing at a predetermined temperature.

[Problems to be Solved by the Invention] However, in the above-described conventional method for producing a silicon nitride sintered body, it is difficult to remove coarse particles and foreign substances contained in the raw material after pulverization, and to remove foreign substances contained in the granulated powder. Since the water content was not actively homogenized, there were cases where coarse particles and foreign matter contained in the raw materials were mixed in, or the amount of water in the granulated powder varied. As a result, pores are generated in the compact due to uneven particle collapse due to the contamination of coarse particles and foreign substances contained in the raw materials and variations in moisture content, and these pores remain after sintering, resulting in high-strength silicon nitride sintering. The drawback was that it was impossible to obtain a body.

[Means for Solving the Problems] Therefore, an object of the present invention is to provide a method for manufacturing a high-strength silicon nitride sintered body that eliminates the above-mentioned conventional drawbacks. According to the present invention, the purpose is to provide a method for manufacturing a silicon nitride sintered body by mixing a silicon nitride raw material and a sintering aid, pulverizing it, granulating it, shaping it, and then firing the molded body. Using a silicon nitride raw material with an α-type silicon nitride content of at least 90%, the granulated powder is once forcibly dried and then molded, and the obtained molded body is then pretreated, This is achieved by a method for producing a silicon nitride sintered body, which is characterized by performing hot isostatic pressing in a nitrogen atmosphere.

In the method for producing a silicon nitride sintered body according to the present invention, selection of the silicon nitride raw material is important.

That is, the content of α-type silicon nitride is at least 90% or more,
It is necessary that the silicon nitride raw material is prepared so that it preferably has a content of 95% or more. When the content of α-type silicon nitride is lower than 90%, the amount of acicular β-type silicon nitride crystals precipitated due to the α→β transition that increases strength during sintering decreases, and high strength is achieved. The disadvantage is that it cannot be done.

In the present invention, preferably after pulverizing the raw material and before granulating,
Pass through a sieve of 2 μm or less, then force dry the granulated powder, add moisture as necessary, pass through a sieve, and then mold, and then pre-process the obtained molded product. give,
A high-strength silicon nitride sintered body can be manufactured by performing hot isostatic pressing in a nitrogen atmosphere. That is, particularly important points in the method for producing a silicon nitride sintered body of the present invention are the selection of the silicon nitride raw material and the forced drying of the granulated powder. If this forced drying is not performed, the granulated powder will not collapse homogeneously due to the molding pressure in the subsequent molding process, and a homogeneous molded product with few pores will not be obtained. H
Coarse pores remain even after IP), making it impossible to obtain a fired product with low porosity.

In addition, the granulation of the silicon nitride raw material and sintering aid is
Conventionally known methods can be used, but in the spray drying method, the granulated powder is spherical, and the powder has good fluidity and filling properties, so close packing during molding is possible. Furthermore, it is preferable from the point of view that the size of the granulated powder can be arbitrarily controlled to suit the desired shape.

Examples of auxiliary agents used in spray drying include polyvinyl alcohol (PVA) and polyethylene glycol (PEG).
), methylcellulose (MC), stearic acid, sodium polyacrylate, polyacrylic acid amide, tannic acid,
Examples include urea, glycerin, etc., but polyvinyl alcohol (PVA), polyethylene glycol (PEG)
It is preferable to use at least one selected from the group consisting of , methyl cellulose (MC), and stearic acid.

Forced drying is performed using a constant temperature dryer, a hot air circulation dryer, a dryer using an infrared heater, or the like.

In addition, after force drying the granulated powder, adding moisture as necessary and passing it through a sieve eliminates the difference in moisture content between the granulated powders, resulting in a more uniform granulated powder. This is preferable because it can be done.

Furthermore, it is preferable to pass the pulverized raw material through a sieve of 321 Lm or less before granulation, since using a sieve with a larger opening will effectively remove coarse particles and foreign substances contained in the raw material after pulverization. This is because it cannot be eliminated and it is difficult to maintain the uniformity of the granulated powder.

Further, in the present invention, molding is performed after the above-mentioned forced drying, and then preliminary treatment and hot isostatic pressing treatment are performed.
Among these, the pretreatment process can be divided into two types: a process of primarily firing the molded body (secondary sintering process), and a process of encapsulating the molded body in a capsule (capsule treatment process). In the second sintering step of the pre-treatment step, the compact is heated at 1400° C., preferably under a nitrogen atmosphere at normal pressure.
Primarily fired at ~1600°C. Firing temperature is 1400
If the temperature is lower than °C, open pores will not disappear even after firing, and a dense sintered body will not be obtained even after hot isostatic pressing. Furthermore, if the firing temperature is higher than 1aoo''c, the beta conversion reaction of silicon nitride will proceed, making it impossible to obtain a high-strength sintered body after hot isostatic pressing.

On the other hand, in the capsule treatment step, the molded body is preferably vacuum degassed and then encapsulated in glass containing SiO2 as a main component. Glass is preferred as a capsule because of its ability to deform and seal as a capsule during hot isostatic pressing.

After performing these preliminary treatments, hot isostatic pressing treatment is preferably performed for 1 hour under a nitrogen atmosphere of 200 to 1500 atm.
It is carried out at 500-1900°C.

The present invention combines the above-mentioned selection of the predetermined raw material silicon nitride, the forced drying process of the granulated powder, the 1,000 IA% processing process and the hot isostatic pressing process of the molded body obtained thereby, and furthermore, Preferably, by performing a sieving step after pulverizing the raw material, it was possible to produce a silicon nitride sintered body having a maximum pore diameter of 10 μm or less and a four-point bending strength at room temperature of 120 kg/mm or more. be.

In terms of composition, the silicon nitride sintered body produced as described above preferably consists of 90% or more of β-type silicon nitride crystals, and the proportion of the β-type silicon nitride crystals is at room temperature. 4-point bending strength at 120 kg/m
This is thought to be directly connected to the high strength properties of m 2 or more.

The type of sintering aid used in the present invention is not particularly limited, and generally known sintering aids can be used.

[Examples] Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited to these Examples.

The drawing is a flowchart showing one embodiment of the method for manufacturing a silicon nitride sintered body of the present invention. In addition, as shown in the drawings, each process is represented by steps 1 to 9.

First, a silicon nitride raw material with an α-type silicon nitride content of 90% or more and a sintering aid are mixed and pulverized (Step 1), and then foreign substances such as fragments of cobblestone used during pulverization and coarse particles are preferably removed. Therefore, it is preferable to pass through a sieve of 32 Bm or less to obtain a raw material with an average particle size of IJl,m or less (
Step 2).

Next, after granulation (step 3), the granulated powder is forcedly dried preferably at a temperature of 60 to 100°C to reduce the difference in moisture content of the granulated powder and make it a homogeneous granulated powder (step 4)
. Next, if necessary, add moisture from O-S to 5.0% by weight to the granulated powder (Step 5) to obtain a granulated powder with a uniform moisture content, and then pass through a sieve to remove moisture. Coarse particles aggregated by the addition are removed (step 6). The obtained granulated powder is molded in a conventional manner (step 7), the molded body is subjected to pretreatment (step 8), and then fired by hot isostatic pressing (step 9), thereby producing the present invention. It is possible to produce a silicon nitride sintered body.

More specific examples will be described below.

(Example 1) Average particle size: 0. MgO and 5rO1Ce are added as sintering aids to the full m silicon nitride raw material powder with an α-type silicon nitride content of 97%.
Each powder of O2 was 3.5% by weight, 1.5% by weight,
After mixing at a ratio of 5% by weight, adding 60% water to it, and mixing and pulverizing it using a batch type pulverizer, the mesh size was 20ILm.
The slurry was passed through a sieve to obtain a slurry with an average particle size of 0.5 g, m. Polyvinyl alcohol (PVA) is added to this slurry.
2% by weight was added to form a granulated powder using a spray dryer.

Furthermore, after drying the granulated powder for 24 hours at the temperature shown in the forced drying temperature in Table 1 using a constant temperature dryer and adding moisture as necessary, the sieve opening after water addition as shown in Table 1 As shown in the figure, sieving was carried out using a JIS standard sieve to obtain granulated powders of sample numbers 1 to 8. This granulated powder was subjected to cold isostatic press molding at a pressure of 3 tons/cm'' to produce a molded body of 65 mm (φ) x 50 mm (length).

After that, after degreasing at a temperature of 500°C for 3 hours, nitrogen (N
2) Normal pressure sintering was performed in an atmosphere at a temperature of 1460'C for 6 hours (-next sintering step). Next, this second sintered body is
The sintered bodies of the present invention were obtained by hot isostatic pressing (HIP) treatment at a pressure of 400 atm and a temperature of 1680° C. in an N2 atmosphere (sample numbers 1 to 8). Separately, as a comparative example of the present invention, sintered bodies (sample numbers 9 to 1
1) was produced.

・Characteristics of the obtained sintered body sample are shown in Table 1.

The bending strength, maximum pore diameter, and porosity of these sintered bodies were measured and shown in Table 1. The bending strength was measured by the four-point bending strength method of JIS R-1601r Fine Ceramics Bending Strength Test Method.

The maximum pore diameter and porosity were measured by mirror polishing the surface of the sintered body and using an optical microscope at a magnification of 400 times. The pore diameter was determined by measuring the maximum length of the pores, and the maximum pore diameter was determined by measuring the number of 1000 pores, and the maximum diameter among them was determined as the maximum pore diameter. Moreover, the porosity is a value obtained by calculating the total pore area by actually measuring the area of 1000 measured pores, and dividing the pore area by the total visual field area required for measurement.

As is clear from Table 1, the HIP sintered body using the prepared raw material of the present invention, which was subjected to forced drying, water was added as necessary, and passed through a sieve, had significantly fewer pores than the comparative example. It was found that the sintered body has excellent mechanical properties.

(Example 2) In order to investigate the influence of passing through a sieve after pulverization and the average particle size after pulverization, α-type silicon nitride raw material (α-type silicon nitride content: 99.
5%) and the types and proportions of sintering aids shown in Table 2,
After adding 60% water and mixing and pulverizing, the mixture was pulverized as shown in Table 2, and a slurry was obtained using a sieve opening. The average particle diameter was as shown in Table 2. To this slurry were added 1% by weight of polyvinyl alcohol and 0.5% by weight of stearic acid, and a granulated powder was obtained using a spray dryer. The granulated powder was dried at 70° C. for 20 hours using a drier, then 4% by weight of water was added, and the powder was passed through a sieve with an opening of 149 μm. This powder was cold isostatically pressed at a pressure of 6 tons/cm2 to form a 30 mm (φ) x 60 m
A molded body having a length of m (length) was obtained. After that, it was degreased at 500°C for 3 hours, and then vacuum-sealed into a silica glass capsule. This capsule is then inserted into the HIP device and a pressure of 1
HIP treatment was performed at 500 atm and a temperature of 1700°C to obtain silicon nitride sintered bodies of sample numbers 12 to 17.

From Table 2, it was found that among the products of the present invention, those that passed through a sieve with a particle size of 32 pm or less after pulverization and those with an average particle size of 1 gm or less after pulverization were more preferable.

(Hereinafter, blank space) (Example 3) α-type silicon nitride content of α-type silicon nitride raw material 85%, 92%
, 95% of each raw material, 6% by weight of Y2O and 34% by weight of Alt 0 as sintering aids were added, mixed and pulverized, and then passed through a sieve with an opening of 32 μm to obtain a slurry. 1% by weight of methylcellulose was added to this slurry, and after drying in a drier, a granulated powder was prepared. Further, it was dried at 100°C for 30 hours using a constant temperature dryer. This granulated powder was cold isostatically pressed at a pressure of 3 tons/cm" and
A molded body of m (φ) x 50 mm (length) was produced. Thereafter, after degreasing at 450°C for 5 hours, the capsule was vacuum sealed in a silica glass capsule, and then this capsule was placed in a HIP device at a pressure of 11000at and a temperature of 1600.165°C.
HIP treatment was performed at 0.1700°C for 30 minutes each to obtain silicon nitride sintered bodies of sample numbers 18 to 24 as shown in Table 3.

As is clear from Table 3, the α-type silicon nitride content is 90
% or more of silicon nitride raw material had higher strength.

[Effects of the Invention] As explained above, according to the present invention, selection of a predetermined raw material silicon nitride, forced drying of the granulated powder, subsequent preliminary treatment, and HIP treatment are combined, and more preferably raw material pulverization By performing subsequent sieving and adding water if necessary, a silicon nitride sintered body with a small maximum pore diameter and high strength can be obtained. Therefore, the silicon nitride sintered body of the present invention can be extremely effectively used as wear-resistant members, sliding members, etc. in addition to mechanical parts.

[Brief explanation of drawings]

The drawing is a flowchart showing an embodiment of the manufacturing method of the present invention.

Claims (10)

[Claims] (1) In a method of manufacturing a silicon nitride sintered body by mixing, pulverizing, granulating and shaping a silicon nitride raw material and a sintering aid, and then firing the molded body, α-type silicon nitride is used as the silicon nitride raw material. Using a material with a content rate of at least 90% or more,
A silicon nitride sintered product characterized in that the powder after granulation is once forcibly dried and then molded, and then the obtained molded body is pretreated and subjected to hot isostatic pressing treatment in a nitrogen atmosphere. Method for producing solids. (2) The silicon nitride sintered body has a maximum pore diameter of 10 μm or less,
The manufacturing method according to claim 1, which has a four-point bending strength of 120 kg/mm^2 or more at room temperature. (3) The manufacturing method according to claim 1 or 2, in which 90% or more of the silicon nitride sintered body is composed of β-type silicon nitride crystals. (4) Once the granulated powder is forcibly dried, water is added as needed and the powder is passed through a sieve,
The manufacturing method according to claim 1, wherein a uniform granulated powder having a predetermined moisture content is obtained. (5) The manufacturing method according to any one of claims 1 to 4, wherein the pulverized raw material is passed through a sieve of 32 μm or less before granulation. (6) The manufacturing method according to any one of claims 1 to 5, wherein the average particle diameter of the powder after pulverization is 1 μm or less. (7) Pre-treatment under nitrogen atmosphere, 1400-1600
Claims 1 to 2 are those that are primarily fired at °C.
The manufacturing method according to any one of Item 6. (8) The manufacturing method according to any one of claims 1 to 6, wherein the pretreatment includes encapsulating the molded body in a capsule. (9) The manufacturing method according to any one of claims 1 to 8, wherein the granulation is performed by spray drying. (10) As auxiliary agents used for spray drying, polyvinyl alcohol, polyethylene glycol, methyl cellulose,
The manufacturing method according to claim 9, wherein at least one selected from the group consisting of stearic acid is used.