JPH06107466A - Production of composite ceramics - Google Patents

Abstract

PURPOSE:To produce a fiber reinforced composite body by pressureless sintering and to make the resulting composite body dense and highly strong. CONSTITUTION:A long fiber 2a is dipped in a slurry 1 consisting of silicon powder and an org. binder and the long fiber with the stuck slurry is wound up to form a formed body. This formed body is subjected to pressureless sintering in a flow of gaseous nitrogen at 1,300-1,500 deg.C by utilizing heat generated at the time of converting the silicon into silicon nitride. The objective composite ceramics contg. the long fiber and silicon nitride is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a complex-shaped composite ceramic having excellent strength and toughness at high temperatures.

[0002]

2. Description of the Related Art Ceramics have high hardness and strength at high temperatures of 1000 ° C. or more, and have excellent thermal shock resistance, so that they are used as high-temperature structural materials, particularly in the fields of aircraft materials and automobile engine materials. It is expected that its applications will be expanded.

However, the greatest drawback of ceramics is that they have a low toughness and are easily broken. Therefore, in order to expand the applications of the ceramics, improving the toughness is a major issue. As a method for improving the toughness of ceramics, for example, there is a method for improving the structure of the ceramic simple substance composed of Al ₂ O ₃ , Si ₃ N ₄ , SiC or the like. This method, for example, develops columnar crystals in the structure by changing the conditions of heat treatment and, as a result, improves toughness. However, depending on this method, only about 2 to 3 times the original material is used. The toughness cannot be improved,
It does not lead to a significant improvement in toughness.

There is also a method for improving the toughness by compounding whiskers with ceramics, but this method can be expected to have only the same effect as the above method.

At present, as the most effective method for improving the toughness of ceramics, there has been proposed a method in which a long fiber material is compounded with ceramics to form a long fiber reinforced composite. In this method, for example, a ceramic powder and an organic binder such as polycarbosilane are mixed in an organic solvent to form a slurry, and long fibers are immersed in this slurry, which is wound by a winding frame to obtain a molded body. Is carried out by sintering and densifying it by a hot pressing method or the like. Since the composite obtained by this method contains the long fibers, it has a strength equal to or higher than that of the ceramic alone. In addition, the fracture toughness value is 20 or more, which is one digit higher than that of ceramics alone.

[0006]

However, in the above manufacturing method, the long fiber reinforced composite is densified by a high pressure sintering method such as a hot pressing method. Since the shrinkage rates of the ceramics and the long fiber material are different when they are treated, there is a disadvantage that only a simple composite such as a plate can be produced. That is, a complex having a complicated shape such as an automobile engine cannot be produced by a high pressure sintering method such as a hot pressing method. In short, when making a complex-shaped composite, it is necessary to sinter under normal pressure so that the ceramic powder that is the raw material does not shrink, but it is necessary to densify and increase the strength of the composite by atmospheric sintering. I can't. Therefore, the present invention makes it possible to produce a fiber-reinforced composite material by an atmospheric pressure sintering method, and further to make the obtained fiber-reinforced composite material dense and high in strength.

[0007]

The present invention does not use a ceramic powder as a raw material as in the prior art, but uses a silicon powder as one component of the raw material to prepare a molded body, which is heat treated in a nitrogen stream. Then, it is intended to obtain a dense and high-strength silicon nitride-containing composite ceramic by the atmospheric pressure sintering method by reacting and sintering by utilizing the heat generated when the silicon powder is converted into silicon nitride. That is, the present invention is
A long fiber is dipped in a slurry composed of silicon powder and an organic binder, and the long fiber to which the slurry is adhered is wound to form a molded body. The molded body generates heat when the silicon powder becomes silicon nitride. Use 1300
Provided is a method for producing a silicon nitride-containing composite ceramic, which comprises obtaining a composite ceramic containing silicon nitride and long fibers by pressureless sintering in a nitrogen stream at ˜1500 ° C.

The above silicon powder has an average particle size of 0.1 to 5 μm, preferably 0.5 to 2 μm and a purity of 9
5% or more, preferably 99% or more is preferably used. If the average particle size of the silicon powder is less than 0.1 μm, the particles may aggregate to form large secondary particles, resulting in poor sinterability. If the average particle size is greater than 5 μm, the sinterability of the ceramic matrix is poor. This causes deterioration of mechanical properties. If the purity of the silicon powder is less than 95%, the impurity component may reduce the strength, which is not preferable.

The organic binder serves as a binder for molding the silicon powder and long fibers, and examples thereof include organic silicon compounds. By using the organic silicon compound as the organic binder, the densification of the matrix can be promoted as a part of the sintering aid. Specific examples of the organic silicon compound include polysilazane, polycarbosilane, polysilastyrene, and the like. Among these organic silicon compounds, polysilazane is particularly preferable. Silicon nitride can be obtained by using polysilazane as the above-mentioned organosilicon compound and performing heat treatment in a N ₂ gas flow.

In the manufacturing method of the present invention, the silicon powder and the organic binder are well mixed in an organic solvent to form a slurry. As the organic solvent, for example, a xylene solution, a toluene solution or the like can be used.

The mixing ratio of the silicon powder and the organic binder is 95-80% by weight / 5-20% by weight, preferably 90-85% by weight / 10-15% by weight. By setting the mixing ratio within this range, a slurry having good viscosity can be obtained.

In the method of the present invention, long fibers such as carbon fibers are immersed in the slurry thus obtained to adhere the slurry to the long fibers. At this time, by adjusting the viscosity of the slurry, the ratio of the slurry and the long fibers is preferably 40 to 70% by weight / 60 to 30% by dry weight. By setting the amount of the slurry adhered to the long fibers within this range, the density and strength of the sintered body can be increased. Carbon fibers are preferable as the above long fibers, and when carbon fibers are used, there is no great difference in the characteristics obtained by using either PAN type or pitch type. Since carbon fiber is originally high in strength and hardly deteriorates even at a high temperature of 100 ° C. or higher, the composite ceramic obtained by using the carbon fiber can be kept at a high temperature.

Next, the long fiber to which the slurry has adhered is wound by, for example, a winding frame to form a molded body. The winding frame used at this time is not particularly limited, and a convenient one can be used depending on the shape of the obtained composite ceramic product.

In the molding method of the present invention, for example, as shown in FIG.
As shown in FIG. 3, a filament-winding method of winding the long fibers 2 a soaked in the slurry 1 with the winding frame 3 is used to form a molded body 4 around which the long fibers 2 b with the slurry attached are wound around the winding frame 3. According to this method, a molded body can be continuously manufactured. In addition, in FIG. 1, 5 is a long fiber bundle.

In the method of the present invention, the obtained molded product is then heated in an N ₂ stream at 300 to 1000 ° C., preferably 6
Heat treatment is performed at 00 to 800 ° C. When an organic silicon compound is used as the organic binder, the heat treatment makes the organic silicon compound an inorganic substance.

In the method of the present invention, after the heat treatment is performed, the heat generated when the silicon powder is converted into silicon nitride in the N ₂ gas stream is used for 1300.
˜1500 ° C., preferably 1450 to 1480 ° C., and reaction sintering under normal pressure. By this reaction sintering under normal pressure, the molded body becomes dense and has high strength, and a composite ceramic composed of silicon nitride and long fibers is obtained.

[0017]

[Operation] According to the method for producing a composite ceramics of the present invention, the reaction sintering can be performed under normal pressure by utilizing the exothermic reaction of silicon powder to silicon nitride. Moreover,
The obtained sintered body is dense, has high strength and high toughness, despite being sintered under normal pressure. That is, according to the method of the present invention, a composite ceramic having high toughness, denseness, and high strength because long fibers are contained,
It can be manufactured in any shape. Further, in the manufacturing method of the present invention, since a sintered body is obtained by reaction sintering, it is possible to perform heat treatment (sintering) without using a sintering aid, etc., and to obtain a composite ceramic obtained by a conventional method. The high temperature strength is superior in comparison. Further, since the reaction from silicon powder to silicon nitride is an exothermic reaction, it is possible to perform heat treatment (sintering) at a lower temperature than the conventional method of sintering silicon nitride powder.

[0018]

[Examples] The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 90 g of silicon powder (manufactured by Kanto Chemical Co., Ltd.) having an average particle size of 1.0 μm and a purity of 99%, and 10 g of polysilazane (manufactured by Chisso Corporation, NCP-200).
Was placed in a xylene solution (60 g), and this solution was mixed by a ball mill for 16 hours to prepare a slurry. PAN-based carbon fiber (made by Asahi Kasei Corporation: AT-4
00) was immersed in the slurry to attach the slurry to the carbon fibers.
This carbon fiber to which the slurry adheres is molded by a filament winding method, and the ratio of the slurry and the carbon fiber is 50% by weight / 50% by dry weight.
A molded product of 50 × 10 mm was obtained. The molded body was heat-treated in N ₂ gas at 800 ° C. for 1 hour to convert polysilazane into silicon nitride. After that, the powder is further heated in a N ₂ gas stream to convert the silicon powder into silicon nitride, and the reaction heat generated at this time is used to perform normal pressure sintering at 1450 ° C. for 3 hours to burn the compact. Tied up. The obtained sintered body was processed into a test piece shape of 3 × 4 × 40 mm, and then the porosity, the three-point bending strength at 1200 ° C., and the fracture toughness value (chevron notch method) were measured. The porosity and 3
The methods for measuring the point bending strength and the fracture toughness value are as follows. Porosity: Dry weight, underwater weight, and saturated water weight of the test piece were measured and calculated by the Archimedes method. Three-point bending strength: The distance between spans was 30 mm, loading was performed at a crosshead speed of 0.5 mm / min, and the strength was calculated from the breaking load. Fracture toughness value (chevron notch method): A test piece introduced with a chevron notch was loaded at a span distance of 30 mm and a crosshead speed of 0.5 mm / min, and the fracture toughness value was calculated from the breaking load. The results are shown in Table 1.

[Examples 2 to 22] Silicon nitride-containing composite ceramics were produced in the same manner as in Example 1 by using the raw material silicon powder and carbon fiber shown in Table 1, and the porosity and 120
Three-point bending strength at 0 ° C. and fracture toughness value (chevron notch method) were measured. The results are shown in Table 1.

[0021]

[Table 1]

[Comparative Example 1] Silicon nitride powder having an average particle size of 0.3 μm and an α conversion rate of 90% (manufactured by Ube Industries, Ltd .: SN-E)
10) 81 g, Y ₂ O ₃ powder (purity 99.9%) 9 g and polysilazane (manufactured by Chisso Corporation: NCP-20).
0) 10 g was put into a xylene solution (60 g) and mixed by a ball mill for 16 hours to prepare a slurry. This carbon fiber to which the slurry adheres is molded by a filament winding method, and the ratio of the slurry and the carbon fiber is 50% by weight / 50% by weight in terms of dry weight 50 × 50 ×
A 10 mm compact was obtained. This molded body was placed in N ₂ gas for 8 hours.
After heat treatment at 00 ° C. for 1 hour to convert polysilazane into silicon nitride, normal pressure sintering was further performed at 1800 ° C. for 3 hours in a N ₂ gas stream. 3 x 4 x 4 of the obtained sintered body
After processing into a 0 mm test piece shape, porosity and 1200
Three-point bending strength at 0 ° C and fracture toughness value (chevron notch method) were measured. As a result, the porosity is 37%
And the bending strength is 100 MPa and the fracture toughness value is 8 M.
It was Pam.

[0023]

In the method for producing a silicon nitride-containing composite ceramics of the present invention, since silicon powder is used as a raw material and the reaction heat at the time of forming silicon nitride is used to perform sintering under normal pressure, It is possible to obtain a complex-shaped composite that could not be produced by the conventional method of pressure sintering. Moreover, despite being sintered under normal pressure, a dense and high-strength composite can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing how a composite of the present invention is molded by a filament winding method.

[Explanation of symbols]

 1 Slurry 2a Long fiber 2b Long fiber with slurry attached 3 Winding frame 4 Formed body 5 Long fiber bundle

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hideto Yoshida 5-4-7 Jyouji Temple, Kamakura City, Kanagawa Prefecture (72) Inventor Chijo Yamagishi 2-17-4 Ogikubo, Suginami-ku, Tokyo

Claims (1)

[Claims] 1. A molded body is molded by immersing long fibers in a slurry composed of silicon powder and an organic binder, and winding the long fibers to which the slurry adheres. The molded body is converted into silicon nitride containing silicon powder. A composite ceramic containing silicon nitride and long fibers is obtained by performing normal pressure sintering in a nitrogen stream at 1300 to 1500 ° C. by utilizing the heat generated at the time of producing a composite ceramic containing silicon nitride. Method.