JPH05294733A - Silicon nitride-carbon fiber composite and its production - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a silicon nitride-carbon fiber composite having excellent crush strength and toughness. [Structure] Short fiber carbon fibers 0.1 to 30 in silicon nitride
Disperse and mix the volume% uniformly. [Effect] The crush strength and toughness of the composite are significantly improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a novel silicon nitride-carbon fiber composite molded body and silicon nitride obtained by sintering the same.
The present invention relates to a carbon fiber composite sintered body and a method for producing them. More specifically, the present invention relates to a silicon nitride-carbon fiber composite molded body having excellent crush strength and a silicon nitride-carbon fiber composite sintered body having excellent toughness.

[0002]

2. Description of the Related Art Conventionally, a silicon nitride sintered body is resistant to heat and
It has excellent corrosion resistance and high strength, so it can be used with metals and plastics.
Active research and development as a structural material to replace
Came. However, the silicon nitride sintered body is
It is a brittle material similar to cous. Therefore, external stress is generated.
If used, stress concentration will occur in the internal defect, causing cracking.
It has the drawback that it grows rapidly and leads to catastrophic destruction.
is doing. And the fracture toughness value of the silicon nitride sintered body
(K_{I c}) Is usually 5-6MPam^1/2Is. Therefore, K
_{I c}To improve the value of the gas turbine engine,
Indispensable for application as structural members such as Zell engine
It is considered. Therefore, K of the silicon nitride sintered body_{I c}The value of
As a method of improving silicon carbide whiskers, silicon nitride
Method of dispersing in sintered body (J.Am.Ceram.SOC 67 (12) C-26
7 (1984)) or long-fiber carbon fiber to reinforce the silicon nitride sintered body.
Method (powder and powder metallurgy 37.1108 (1990)) is proposed
Has been done.

[0003]

However, in the method of dispersing silicon carbide whiskers in the silicon nitride sintered body, the K _IC value of the obtained composite sintered body is about 7 to 9 MPam ^1/2, which is an improvement. The width is small and not yet satisfactory. In addition, whiskers themselves have a problem that they are harmful to the human body as well as asbestos. Next, in the method of reinforcing a silicon nitride sintered body with long fiber carbon fibers, it is said that the obtained composite sintered body has a K _IC value of 10 MPam ^1/2 or more and can achieve high toughness. However, since such a composite sintered body is reinforced in only one direction, it is greatly limited in practical application as a structural member. The difference in thermal expansion coefficient between carbon fiber and silicon nitride, which is the matrix phase, is large,
There is a problem that cracks are likely to occur in the cooling process after sintering, and further, since the molding method and the sintering method are special molding / sintering methods such as the filament winding method-hot pressing method, the obtained molded body is obtained. However, there is a problem in that it is difficult to manufacture a product having a complicated shape due to being limited to a plate shape.

Further, the green strength of a ceramic molded body such as a silicon nitride molded body is generally low because it is mainly bonded by the van der Waals force of the powder, so that it is damaged in the steps such as mold release, drying and pre-baking. easy. For this reason, a lot of know-how is required to manufacture various products made of silicon nitride, and it is difficult for even a skilled person to maintain a high product yield. In addition, the tendency is that the larger the product becomes, the more difficult it is to manufacture the product. Therefore, improving the strength of the molded product before firing is one of the problems that must be solved in order to reduce the manufacturing cost of silicon nitride products.

[0005]

The inventors of the present invention have made extensive studies to solve the above problems, and as a result, a novel silicon nitride-carbon fiber composite molded product having a specific structure and a sintered product thereof can be obtained. The inventors have found that the above problems can be solved by a silicon nitride-carbon fiber composite sintered body, and further by a specific manufacturing method, and arrived at the present invention. That is, the object of the present invention is to solve the problems of the conventional silicon nitride composite sintered body using silicon carbide whiskers and long fibrous carbon fibers, and to manufacture a high-strength silicon nitride-carbon fiber composite molded body which can be manufactured by a general ceramics manufacturing method. Another object of the present invention is to provide a sintered body thereof and a method for producing them easily.

The object is (1) a silicon nitride-carbon fiber composite fired body in which carbon fibers are uniformly dispersed and mixed in a silicon nitride sintered body, wherein the carbon fibers are short fibrous carbon fibers. And a silicon nitride-carbon fiber composite fired body characterized by containing the carbon fiber in a range of 0.1 to 30% by volume, (2) the carbon fiber was uniformly dispersed and mixed in the silicon nitride molded body. A silicon nitride-carbon fiber composite molded body,
The carbon fiber is a short fibrous carbon fiber, and the carbon fiber is contained in a range of 0.1 to 30% by volume, and a silicon nitride-carbon fiber composite molded body, (3) a silicon nitride aqueous slurry 0.1 to 30% by volume of short fibrous carbon fiber
Of the carbon fiber-containing silicon nitride aqueous slurry added in the range of 1), then the aqueous slurry is molded by a slip cast molding method, and then sintered under pressure. Manufacturing method, and (4) A carbon fiber-containing silicon nitride aqueous slurry is prepared by adding short fibrous carbon fibers to the silicon nitride aqueous slurry in the range of 0.1 to 30% by volume, and then the aqueous slurry is slip-cast molded. It is easily achieved by a method for producing a silicon nitride-carbon fiber composite molded body, which is characterized by being molded by.

The present invention will be described in detail below. The silicon nitride, which is a raw material of the silicon nitride compact or the sintered body in the present invention, can be used without particular limitation as long as it is a silicon nitride powder used in the production of ordinary silicon nitride products. Specifically, the particle size of the silicon nitride powder is 0.1
.About.2 .mu.m, preferably about 0.1 to 0.3 .mu.m is used. Further, it is preferable to preliminarily mix a sintering aid with the silicon nitride powder. As the sintering aid, known sintering aids used in producing a silicon nitride sintered body can be used, and specific examples thereof include alumina, yttrium oxide, magnesium oxide and the like. The amount of the sintering aid compounded is usually 2 to 20 parts by weight, preferably 8 to 13 parts by weight, based on 100 parts by weight of the silicon nitride powder. Further, it is preferable that the particle size of the sintering aid be substantially the same as the particle size of the silicon nitride powder to be used because it is uniformly sintered in the sintering process.

The carbon fiber used in the present invention is not particularly limited as long as it is a known carbon fiber such as rayon-based carbon fiber, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and the like. Among these carbon fibers, it is important to use short fibrous carbon fibers.
The short fibrous carbon fiber is a carbon obtained by any method as long as it is obtained by cutting a long fibrous carbon fiber into a short fibrous form by an arbitrary method or a prefabricated short fibrous form by a centrifugal spinning method or the like. Fibers can also be used. Specifically, the average fiber length is 50 μm to 10 mm, preferably 100 μm to 6 mm
It is good to use those having an aspect ratio (fiber length / fiber cross-sectional diameter) of 5 to 1000, preferably 10 to 600. If the average fiber length is less than 50 μm, it becomes difficult to improve the fracture toughness value of the sintered body, and
This is because if it exceeds 10 mm, it becomes difficult to uniformly disperse the fibers.

The compact and sintered body of the present invention contain 0.1 to 30% by volume, preferably 0.5 to 1% by volume of the above-mentioned short fibrous carbon fiber in the above-mentioned silicon nitride compact or silicon nitride sintered body.
It is uniformly dispersed in the range of 5% by volume.

Next, the method for producing the molded body and the sintered body of the present invention will be described. First, the above-mentioned silicon nitride powder is added to water to prepare a silicon nitride aqueous slurry. At that time, it is preferable to add the above-mentioned sintering aid. As the silicon nitride aqueous slurry, 40 to 60 parts by weight, preferably 45 to 55 parts by weight of water is prepared with respect to 100 parts by weight of silicon nitride powder. 11 parts by weight of the sintering aid is added and mixed with 100 parts by weight of the silicon nitride powder. Note that, if necessary, a known dispersant used when preparing an aqueous slurry of ceramic powder may be added and mixed when preparing such an aqueous slurry of silicon nitride. The dispersant is not particularly limited, and examples thereof include polycarboxylic acid-based dispersants and polyacrylic acid-based dispersants. The amount of these dispersants added is water 1
About 0.5 parts by weight may be added and blended with respect to 00 parts by weight.

Then, short fibrous carbon fibers are added to the silicon nitride aqueous slurry while stirring the aqueous slurry so that the short fibrous carbon fibers are uniformly dispersed in the aqueous slurry, and the silicon nitride-carbon fibers are added. Prepare a mixed aqueous slurry. The short fibrous carbon fiber is added in an amount of 0.1 to 30% by volume, preferably 0.5 to 15% by volume, based on the silicon nitride-carbon fiber composite molded body or its sintered body. To do. If the addition amount of the short fibrous carbon fiber is less than 0.1% by volume, the effect of the addition is difficult to be exhibited, and 30% by volume
This is because if it exceeds 1.0, uniform dispersion becomes difficult. The short fibrous carbon fibers may be added all at once to the silicon nitride aqueous slurry, but in order to disperse the carbon fibers more uniformly, the short fibrous carbon fibers are gradually added while stirring the aqueous slurry. Good to do.

The silicon nitride-carbon fiber mixed aqueous slurry thus obtained is molded by the slip cast molding method. The slip cast molding method itself is a known method as a ceramic molding method. That is, it is a method in which the above-mentioned mixed aqueous slurry is poured into a gypsum mold having a desired shape, and only the water in the mixed aqueous slurry is dehydrated through the gypsum mold and molded. The molded product obtained by such a method is usually in air at 10 to 100 ° C., preferably 1
The silicon nitride-carbon fiber composite molded body of the present invention is obtained by drying at 0 to 70 ° C. The molded product thus obtained exhibits extremely high crush strength as compared with a molded product to which short fibrous carbon fibers are not added and blended. Further, since it can be molded by the slip cast molding method, it is possible to manufacture various complicated shaped silicon nitride molded bodies.

Next, a sintered body of the present invention is obtained by adding the above-mentioned molded body.
It is obtained by firing under pressure. Sintering process is non-oxidizing
Under an atmosphere, preferably a non-oxidizing atmosphere having a partial pressure of nitrogen gas
100 to 2000 kg / cm under ambient atmosphere²Under the pressure of
Ku-500-2000kg / cm ²Under pressure of 1500 ℃
The temperature is preferably 1600 to 1800 ° C.
Be seen. The sintered body thus obtained is a conventional sintered body.
Higher than K_{I c}Slip value
Since it can be formed by the strike forming method, it has various complexities.
It is possible to manufacture a silicon nitride sintered body having various shapes. Na
By incorporating short fibrous carbon fiber, high toughness is obtained.
Although it has not been fully clarified that this is a sintered body
The interface of the carbon fiber inside was as smooth as before sintering, and
The reaction product with silicon nitride, which is a trick, is not formed.
And, as a result, carbon fiber on the fracture surface of the sintered body.
Due to the fact that most of the fibers have a pull-out effect
Presumed to be.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. [Measurement Method of Crushing Strength of Molded Article] The crushing strength of each sample was measured by the method shown in FIG. 1 using a cylindrical sample having a diameter of 26 mm manufactured in the following Examples and Comparative Examples.

Crush strength was calculated as crush strength = crush load / sample length, and relative comparison was performed.

Cylindrical sample shape: Φ26 (mm) × L (20 to 25 mm) Test speed: 0.5 mm / min Crushing strength = Crushing load / Sample length (constant sample diameter) [Example 1] (silicon nitride -Carbon Fiber Composite Molded Body) Silicon nitride powder containing 5% by weight of alumina and yttrium oxide (UBE-SN-C5A manufactured by Ube Industries, Ltd.) 1
000 g, ion-exchanged water 430 g, and polycarboxylic acid-based dispersant (A-6114 manufactured by Toagosei Co., Ltd.) 5 g were mixed in a ball mill for 24 hours to obtain an aqueous slurry. Short fibrous carbon fibers having an average length of 600 μm and a diameter of 10 μm (aspect ratio 60) were added dry to this aqueous slurry through a # 40 mesh so as to be 2% by volume with respect to the silicon nitride powder.

At this time, the aqueous slurry was slowly stirred to prevent the carbon fibers from aggregating. The silicon nitride-carbon fiber mixed aqueous slurry thus obtained was slip cast molded into a plaster mold having a diameter of 26 mm and a length of 30 mm to produce a molded body. After the molded body was dried at room temperature, a crushing strength test was conducted on three samples by the above method. Table 1 shows the average values of the results.

Example 2 (Silicon Nitride-Carbon Fiber Composite Molded Product) The same procedure as in Example 1 was carried out except that the amount of the short fibrous carbon fiber was 5% by volume. The results are shown in Table 1.

Example 3 (Silicon Nitride-Carbon Fiber Composite Molded Product) The same procedure as in Example 1 was carried out except that the amount of the short fibrous carbon fiber blended was 10% by volume. The results are shown in Table 1.

Example 4 (Silicon Nitride-Carbon Fiber Composite Molded Product) The same procedure as in Example 1 was carried out except that the blending amount of the short fibrous carbon fiber was changed to 15% by volume. The results are shown in Table 1.

Comparative Example 1 (Silicon Nitride Molded Body) The same procedure as in Example 1 was carried out except that short fibrous carbon fibers were not added. The results are shown in Table 1.

Example 5 (Silicon Nitride-Carbon Fiber Composite Molded Product) As short fibrous carbon fibers, short fibrous carbon fibers having an average length of 3 mm and a diameter of 10 μm (aspect ratio 300) were contained in a volume percentage of the silicon nitride powder. Example 1 except that 0.5% by volume was blended in
I went the same way. The results are shown in Table 1.

Example 6 (Silicon Nitride-Carbon Fiber Composite Molded Product) Short fibrous carbon fibers having an average length of 3 mm and a diameter of 10 μm (aspect ratio 300) were used as the short fibrous carbon fibers in a volume percentage of the silicon nitride powder. The same procedure as in Example 1 was performed except that 2% by volume was blended. The results are shown in Table 1.

Example 7 (Silicon Nitride-Carbon Fiber Composite Molded Product) As short fibrous carbon fibers, short fibrous carbon fibers having an average length of 6 mm and a diameter of 10 μm (aspect ratio 600) were used in a volume percentage of the silicon nitride powder. The same procedure as in Example 1 was carried out except that 5% by volume was added. The results are shown in Table 1.

[Example 8] (Silicon Nitride-Carbon Fiber Composite Sintered Body) The silicon nitride-carbon fiber composite molded body obtained in Example 2 was enclosed in a Pyrex glass tube, and 1750 ° C. for 2 hours.
The sintering process was performed under the condition of 2000 atm. The relative density of the obtained sintered body was 98% or more, and the K _IC value measured by the IM method was 8 MPam ^1/2 .

[Comparative Example 2] (Silicon Nitride Sintered Body) The silicon nitride molded body obtained in Comparative Example 1 was sealed in a Pyrex glass tube and sintered at 1750 ° C. for 2 hours under 2000 atmospheres. It was Relative density of the obtained sintered body 9
It is 8% or more, and the K _IC value measured by the IM method is 6.
It was 5MPam ^1/2 .

Example 9 (Silicon Nitride-Carbon Fiber Composite Sintered Body) The silicon nitride-carbon fiber composite molded body obtained in Example 3 was sealed in a Pyrex glass tube, and 1750 ° C. for 2 hours.
The sintering process was performed under the condition of 2000 atm. The relative density of the obtained sintered body was 98% or more, and the K _IC value measured by the IM method was 10 MPam ^1/2 .

[0028]

[Table 1]

[0029]

According to the present invention, as is clear from the above examples, the strength of the obtained molded body is remarkably high as compared with the case where the short fiber carbon fibers are not added and the carbon fibers are not contained. It increases, and sufficient strength is exhibited even when 2% by volume is added. In addition, since a product obtained by sintering these compacts can be manufactured into a product having a complicated shape by an ordinary ceramics manufacturing method and can exhibit high toughness, it is industrially and mechanically excellent in terms of the conventional composite structure. Superior to silicon nitride sintered bodies.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a method for measuring the crushing strength of a molded product of the present invention. Where 1 is a cylindrical sample, 2 and 3
Is an indenter, and 4 is a crush load direction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Mori 3-7, Shinsenrihigashi-cho, Toyonaka-shi, Osaka A40-107 (72) Inventor Mihiro 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd. Corporate Research Institute (72) Inventor Toshiaki Katayama 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd.

Claims (4)

[Claims] 1. A silicon nitride-carbon fiber composite fired body in which carbon fibers are uniformly dispersed and mixed in a silicon nitride sintered body,
A silicon nitride-carbon fiber composite fired body, wherein the carbon fiber is a short fibrous carbon fiber, and the carbon fiber is contained in a range of 0.1 to 30% by volume. 2. A silicon nitride-carbon fiber composite molded body in which carbon fibers are uniformly dispersed and mixed in a silicon nitride molded body,
The carbon fiber is a short fibrous carbon fiber, and the carbon fiber is contained in a range of 0.1 to 30% by volume, the silicon nitride-carbon fiber composite molded body. 3. A carbon fiber-containing silicon nitride aqueous slurry is prepared by adding short fibrous carbon fibers to a silicon nitride aqueous slurry in a range of 0.1 to 30% by volume, and then the aqueous slurry is molded by a slip cast molding method. And then sintering under pressure, a method for producing a silicon nitride-carbon fiber composite fired body. 4. A carbon fiber-containing silicon nitride aqueous slurry is prepared by adding short fibrous carbon fibers to a silicon nitride aqueous slurry in a range of 0.1 to 30% by volume, and then the aqueous slurry is molded by a slip cast molding method. A method for producing a silicon nitride-carbon fiber composite molded body, comprising: