JPH06122564A - Production of composite ceramic - Google Patents

Abstract

PURPOSE:To provide a carbon fiber-reinforced composite ceramic excellent in mechanical strength and toughness. CONSTITUTION:Carbon fibers are dipped in a slurry 1 composed of ceramic powder and an organic hinder, and the resulting slurry-adhered carbon fibers 29 are wound to make a form which is then heat treated, thus affording the objective carbon fiber-reinforced composite ceramic. In this case, each of the carbon fibers has been coated with a carbon film 0.05-10mum thick and this carbon film has been coated with a silicon carbide film 0.05 1.0mum thick; that is, the surface-modified carbon fibers are used.

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 carbon fiber reinforced composite ceramic having excellent strength and toughness.

[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 of compounding carbon fibers with ceramics to form a carbon fiber-reinforced composite. This method is, for example, mixing ceramic powder and an organic binder in an organic solvent to form a slurry, immersing carbon fiber in this slurry, and winding it with a winding frame to form a molded body, which is then hot pressed, etc. It is carried out by sintering and densifying. Since the composite obtained by this method contains carbon fibers, it has a strength equal to or higher than that of the ceramic alone. Further, the fracture toughness value is 20 MPam or more, which is one digit higher than the toughness of ceramics.

[0006]

However, the carbon fiber reinforced composite ceramics obtained by the above method still has low strength and toughness in view of the original characteristics of the fiber. This is because the surface of the carbon fiber is not sufficiently dense, and during the sintering of the molded body, impurities infiltrate into the carbon fiber from the ceramic powder, which is the matrix, and deteriorate the characteristics of the carbon fiber. It is considered that the cracks that strongly bond and integrate with each other due to the interfacial reaction of the fibers and progress in the ceramics cause the carbon fibers to be cut very easily. Therefore, in order to improve the mechanical properties such as strength and toughness of the carbon fiber reinforced composite ceramics, it is necessary to develop a method for suppressing the deterioration of the properties of the carbon fibers and controlling the interfacial strength between the ceramics and the carbon fibers. I won't.

[0007]

Therefore, according to the present invention, a carbon fiber reinforced composite material that fully utilizes the characteristics of the carbon fibers by controlling the interfacial strength between the carbon fibers and the ceramics without deteriorating the characteristics of the carbon fibers. It is intended to improve mechanical properties such as strength and toughness of the obtained composite by providing a method for producing ceramics. That is, according to the present invention, a carbon fiber is immersed in a slurry composed of ceramic powder and an organic binder, a molded body is molded by winding the carbon fiber to which the slurry adheres, and the resulting molded body is heat-treated. In the method for producing a composite ceramic for producing a reinforced composite ceramic, as the carbon fiber, the outer peripheral surface is covered with a carbon film having a thickness of 0.05 to 1.0 μm, and the outer peripheral surface is further provided with a thickness of 0.05 to 1 The present invention provides a method for producing a composite ceramic, which is characterized by using a surface-modified carbon fiber coated with a silicon carbide film having a thickness of 0.0 μm.

As the ceramic powder, those containing alumina, mullite, silicon nitride, silicon carbide, sialon, etc. as main components can be used, and these main components can be used alone or in combination of two or more kinds. . The average particle size of the main component of the ceramic powder is preferably 0.1 to 5 μm, more preferably 0.5 to 2 μm. If the average particle size is less than 0.1, the ceramic powders may agglomerate to form large secondary particles and deteriorate the sinterability. If the average particle size is larger than 5 μm, the sinterability of the ceramic matrix deteriorates. Cause deterioration of the physical characteristics. As a trace component, boron carbide powder, carbon powder, aluminum nitride powder, aluminum oxide powder, aluminum boride powder or the like can be added to the ceramic powder. By mixing these trace components, the sinterability of the ceramic can be improved.

The organic binder is preferably an organic silicon compound which can be converted into silicon carbide by heat treatment.
Specific examples of the organosilicon compound include polysilazane, polycarbosilane, and polysilastyrene.

In the manufacturing method of the present invention, the ceramic 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 ceramic 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, the carbon fibers are immersed in the slurry thus obtained to adhere the slurry to the carbon fibers. At this time, by adjusting the viscosity of the slurry, the ratio of the slurry and the carbon fibers is preferably 40 to 70% by weight / 60 to 30% by dry weight. By setting the amount of the slurry adhered to the carbon fibers within this range, the density and strength of the sintered body can be increased.

In the method for producing the composite ceramics of the present invention, the surface-modified carbon fiber whose outer peripheral surface is covered with the carbon film and the silicon carbide film is used as the carbon fiber.

As the carbon fiber, PAN type, pit type
Although any of the ch type can be used, the pitch type is preferable when the sintering temperature at the time of sintering the molded body of the carbon fiber reinforced composite ceramics is high, and the PAN type is used when the sintering temperature is low. Are preferred. Although the fiber diameter of the carbon fiber is not particularly limited, it is preferable to use a carbon fiber having a fiber diameter of about 10 μm when the molded body is formed by the filament winding method.

The surface-modified carbon fiber used in the production method of the present invention has an outer peripheral surface of the carbon fiber having a thickness of 0.05 to
A carbon film having a thickness of 1.0 μm is coated on the outer peripheral surface of the silicon carbide film having a thickness of 0.05 to 1.0 μm. The surface modification means is not particularly limited, but chemical vapor deposition (C
The most effective method is the VD) method. For surface modification by the CVD method, first of all, a reactor containing carbon fiber
Heating to 000-1300 ° C. and adding C ₃ H ₈ ,
The outer peripheral surface of the carbon fiber is coated with a carbon film by introducing a raw material gas composed of a hydrocarbon gas such as C ₂ H ₆ and CH ₄ and a carrier gas such as H ₂ . Then, the reactor is
After heating to 00 to 1500 ° C., SiCl ₄ ,
A raw material gas consisting of a silicon compound gas such as SiHCl ₃ , SiH ₂ Cl ₂ and SiCl ₄ , a hydrocarbon gas such as C ₃ H ₈ , C ₂ H ₆ and CH ₄ and a carrier gas such as H ₂ is introduced. As a result, a silicon carbide film is further coated on the above carbon film. The pressure in the furnace when performing the CVD method is not particularly limited, and for example, carbon or silicon carbide can be deposited at a low pressure of 1 torr to a normal pressure of 760 torr, but about 10 torr is preferable in consideration of the reaction rate and the like.

In the manufacturing method of the present invention, the thicknesses of the carbon film and the silicon carbide film are each 0.05 to 1.0 μm.
To When the film thickness is less than 0.05 μm, impurities are mixed in the carbon fiber and the interface strength between the carbon fiber and the ceramic cannot be controlled. Also, the film thickness is 1.0 μm
If it is thicker than this, the handling property is deteriorated.

In the method of the present invention, the surface-modified carbon fiber having the slurry adhered thereto is wound to form a compact, and the obtained compact is heat-treated to obtain a carbon fiber reinforced composite ceramics. .

The forming method of the above-mentioned molded body is not particularly limited, but as shown in FIG. 1, for example, by winding the carbon fiber 2a soaked in the slurry 1 with the winding frame 3 around the winding frame 3 by a filament winding method. It is possible to obtain the molded body 4 in which the carbon fibers 2b to which the slurry is attached are wound, and according to this method, the molded body can be continuously manufactured. In addition, in FIG. 1, 5 is a carbon fiber bundle.

The molded body thus obtained is then heat treated to obtain carbon fiber reinforced composite ceramics. The heat treatment includes both a decomposition treatment in which the organic binder is made inorganic and decomposes, and a sintering treatment in which the molded body is sintered using a hot press or the like to be densified. The decomposition treatment is performed, for example, in a reducing atmosphere such as N ₂ or Ar for 30 times.
It can be performed at 0 to 1000 ° C. In addition, the sintering treatment is performed, for example, in a reducing atmosphere at 1700 to 2000 ° C. and 1
It can be performed at 0 to 50 MPa. When the winding frame in the molded body is a flammable one such as a wooden frame, it can be easily removed from the sintered body by burning it.

[0020]

[Operation] According to the method for producing the composite ceramics of the present invention, the outer peripheral surface of the carbon fiber has a thickness of 0.05 to 1.
It is covered with a carbon film having a thickness of 0 μm, and the outer peripheral surface thereof has a thickness of 0.
By using the surface-modified carbon fiber coated with a silicon carbide film having a thickness of 05 to 1.0 μm, it is possible to suppress the mixing of impurities into the carbon fiber when sintering the molded body and suppress the deterioration of the carbon fiber, Controls the interfacial strength between carbon fiber and ceramics. That is, since the composite ceramics obtained by the method of the present invention uses the surface-modified carbon fiber having the carbon film and the silicon carbide film surface-coated as the carbon fiber, impurities may be mixed into the carbon fiber during sintering. And the interface strength between the carbon fiber and the ceramic in the sintered body is controlled. Therefore, the characteristics of the carbon fibers in the composite ceramics are sufficiently maintained, the carbon fibers are less likely to be broken by cracks, and the mechanical properties such as strength and toughness of the resulting composite ceramics are significantly improved.

[0021]

EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples.
However, the present invention is not limited to this.
Yes. [Examples 1 to 24] Silicon carbide as ceramic powder
Powder (manufactured by Ibiden Co., Ltd .: Beta Random Ultra
Fine) 86.2g, B_FourC powder (Made by Stark: F
1500) 0.4 g, carbon powder (Mitsubishi Kasei Co., Ltd.
Manufactured by: MA-200RB) 2.7 g and AlN powder (Toku)
Sansoda Co., Ltd .: F grade) 0.7g and organic
Polycarbosilane as a binder (Nippon Light Metal Co., Ltd.
Made: 10 g of Ceraresin M-3) in xylene solution (60
g) in a ball mill for 16 hours to make a slurry.
Made On the other hand, pitch carbon fiber (Mitsubishi Kasei Co., Ltd.
Co., Ltd .: K133) is coated on the outer peripheral surface by the CVD method
It was That is, a reactor containing a pitch-based carbon fiber
Heat to 1000 to 1300 ° C and set the furnace pressure to 1 to 760
C as the reaction gas in this reaction furnace at torr ₃H
₈50 to 250 liters / minute, as a carrier gas
H₂Introduce 950 to 750 liters / min, pitch
A carbon film was deposited on the outer peripheral surface of the system carbon fiber. Then in the furnace
Temperature 1000 ~ 1500 ℃, furnace pressure 1 ~ 760t
Orc, SiCl as the reaction gas_Four10 to 10
0 liter / min, C₃H₈10-100 liters / minute
And H as carrier gas₂300-480 liters
/ Minute is introduced, and a pitch-based carbon fiber coated with a carbon film
A silicon carbide film was deposited on the outer peripheral surface of the fiber. Examples 1-24
Table 1 (coating conditions for carbon film) and
And Table 2 (coating conditions for the silicon carbide film).

The surface-modified carbon fiber thus obtained was dipped in the above slurry to obtain a carbon fiber to which the slurry was attached. By winding the obtained carbon fiber by a filament winding method, 50 × 50 × 10
A mm shaped body was formed into a long-fiber-reinforced composite ceramic preform. After heat-treating this molded body in Ar gas at 1000 ° C. to convert polycarbosilane into silicon carbide, the temperature inside the furnace is 2050 ° C. using a hot press furnace.
Sintering was performed in an Ar gas atmosphere at a pressure of 40 MPa. The fiber content (that is, surface-modified carbon fiber / slurry) in the obtained sintered body was determined. The results are shown in Table 3.
Moreover, after processing the obtained sintered body into a test piece shape of 3 × 4 × 40 mm, the porosity, the three-point bending strength at 1200 ° C., and the fracture toughness value (chevron notch method) were measured. The methods of measuring the porosity, the three-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: With a span distance of 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.

[Comparative Example 1] The same slurry as in Example 1 was used, and the same pitch-based carbon fiber as in Example 1 was immersed in the slurry except that the surface modification was not carried out to remove the carbon fiber to which the slurry was attached. Obtained. A preform was formed from the obtained carbon fiber and sintered in the same manner as in Example 1. Table 3 shows the fiber content in the obtained sintered body, the porosity after processing into a test piece shape of 3 × 4 × 40 mm, the three-point bending strength at 1200 ° C., and the fracture toughness value (chevron notch method). .

[0024]

[Table 1]

[Table 2]

[Table 3]

[Examples 25 to 48] Ceramic powder
Sialon powder (made by Nippon Cement Co., Ltd., average
90 g with a particle size of 0.2 to 1.0 μm and an organic binder
Polysilazane (manufactured by Chisso Corporation: NCP-20
0) 10 g in a xylene solution (60 g) in a ball mill
And mixed for 16 hours to prepare a slurry. On the other hand, pi
of tch carbon fiber (Mitsubishi Kasei Co., Ltd .: K133)
The outer peripheral surface was covered by the CVD method. That is, pit
1000 ~ 1300 ℃ the reaction furnace containing ch carbon fiber
To 1 to 760 torr in the furnace,
C as a reaction gas in the reactor ₃H₈50-250 lit
R / min and H as carrier gas₂950 to 750
Introducing a bottle / minute to the outer peripheral surface of the pitch-based carbon fiber
A carbon film was deposited. Next, the furnace temperature is set to 1000 to 15
The reaction gas is set at 00 ° C and the furnace pressure is set to 1 to 760 torr.
SiCl as a substrate_Four10-100 liters / min, C₃
H₈10 to 100 liters / minute as carrier gas
H₂Introduce 300 to 480 liters / min and use a carbon film
Silicon carbide film on the outer peripheral surface of the coated pitch-based carbon fiber
Was deposited. Each coating condition in Examples 1 to 24 is
Table 3 (coating conditions of carbon film) and Table 4 (covering of silicon carbide film)
Cover conditions).

The surface-modified carbon fiber thus obtained was dipped in the above slurry to obtain a carbon fiber to which the slurry was attached. By winding the obtained carbon fiber by a filament winding method, 50 × 50 × 10
A mm shaped body was formed into a long-fiber-reinforced composite ceramic preform. This molded body was heat-treated at 1000 ° C. in N ₂ gas to convert polysilazane into silicon nitride, and then sintered in a N ₂ gas atmosphere at a furnace temperature of 1800 ° C. and a pressure of 40 MPa using a hot press furnace. . The fiber content (that is, surface-modified carbon fiber / slurry) in the obtained sintered body was determined. The results are shown in Table 6. Moreover, after processing the obtained sintered body into a test piece shape of 3 × 4 × 40 mm, the porosity, the three-point bending strength at 1200 ° C., and the fracture toughness value (chevron notch method) were measured. The results are shown in Table 6.

[Comparative Example 2] The same slurry as in Example 25 was used, and the same pitch-based carbon fiber as in Example 25 was immersed in this slurry except that the surface modification was not carried out, to remove the carbon fiber to which the slurry was attached. Obtained. From the obtained carbon fiber,
A preform was molded and sintered in the same manner as in Example 25. Fiber content in this sintered body, as well as 3 × 4 × 40 mm
Table 6 shows the porosity, the three-point bending strength at 1200 ° C., and the fracture toughness value (chevron notch method) after being processed into the test piece shape.

[0028]

[Table 4]

[Table 5]

[Table 6]

[0029]

INDUSTRIAL APPLICABILITY In the production method of the present invention, since the composite ceramic is produced by using the surface-modified carbon fiber whose surface is coated with the carbon film and the silicon carbide film, mechanical strength such as strength and toughness of the obtained composite is obtained. The characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing how a composite ceramic 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 carbon fiber is formed by immersing carbon fiber in a slurry comprising ceramic powder and an organic binder, winding the carbon fiber to which the slurry is attached to form a molded body, and heat-treating the resulting molded body. In the method for producing a composite ceramic for producing a reinforced composite ceramic, the outer peripheral surface of the carbon fiber has a thickness of 0.0
A method for producing a composite ceramic, which comprises using a surface-modified carbon fiber coated with a carbon film having a thickness of 5 to 1.0 μm and further having an outer peripheral surface coated with a silicon carbide film having a thickness of 0.05 to 1.0 μm.