JPH05194028A - Fiber-reinforced ceramic and its production - Google Patents

Abstract

PURPOSE:To provide a highly reliable ceramic material excellent in such high- temperature characteristics as not to decline in mechanical strength and toughness even at elevated temperatures ranging from room temperature to ca. 1500 deg.C along with being excellent in the above characteristics at room temperature. CONSTITUTION:A form is first made using 4 carbon fiber fabric, and then impregnated with a metal alkoxide sol, which is then gelled to contain a gel-like metal alkoxide among the carbon fibers. Thence, this composite is calcinated to develop zircon crystallites from the metal alkoxide followed by sintering, thus obtaining the objective fiber-reinforced ceramic sintered compact where the carbon fibers and zircon are monolithically bound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fiber used as a material for parts for mechanical structures used in a wide range of fields such as automobile parts, spacecraft parts, industrial machine parts, electric equipment parts, chemical equipment parts and the like. The present invention relates to a reinforced ceramic and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, attempts have been made actively to use ceramic materials instead of conventional metal materials, and some of them have been put into practical use.

Ceramics are generally lighter in weight and superior in heat resistance and corrosion resistance than metals,
Although it has characteristics such as electrical and thermal insulation properties, it can be mentioned as its characteristics that it has low ductility and brittleness, and attempts have been made to improve toughness.

[0004] In an attempt to improve the toughness of ceramics, it has been attempted to improve the characteristics of the ceramic itself by considering the sintering aid, the sintering conditions, etc., and to combine the fibers. It is also being strengthened by.

Such fiber-reinforced ceramics (FR
Examples of C) include mullite (Al ₆ Si ₂ O ₁₃ ), silicon nitride (Si ₃ N ₄ ), and glassy ceramics (LA).
Some ceramics such as S; Li ₂ O-Al ₂ O ₃ -SiO ₂ ) are reinforced with carbon fiber or silicon carbide (SiC) fiber, and the ceramic reinforced by the fiber has a large fracture toughness (K _IC ). Will be improved.

For example, comparing the fracture toughness of the ceramic itself with the fracture toughness of the fiber-reinforced ceramic, as shown in Table 1, the fracture toughness is significantly improved by reinforcing the ceramic with the fiber. ..

[0007]

[Table 1]

Regarding the fiber-reinforced ceramics of this type, a special issue of the Japan Institute of Metals, September 1990,
CERAMIC BULLETIN Vol. 68, N
o. 2 1989, pp. 395-400.

[0009]

However, although these fiber reinforced ceramics have considerably excellent values in fracture toughness, the melting point of mullite (Al ₆ Si ₂ O _{1 3} ) constituting the base material is high. Is about 1810 ° C, the decomposition temperature of silicon nitride (Si ₃ N ₄ ) is about 1900 ° C, and the melting point of glassy ceramics (LAS) is about 1350 ° C. However, there is a problem that development of a ceramic material which is excellent in strength especially at high temperature is desired.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and not only has excellent strength and toughness at room temperature, but also high strength and toughness even at high temperatures from room temperature to about 1500 ° C. It is an object of the present invention to provide a highly reliable fiber reinforced ceramic having excellent high temperature characteristics, which does not deteriorate.

[0011]

The fiber-reinforced ceramics according to the present invention is characterized in that it has zircon (ZrSiO ₄ ) as a main matrix phase and is reinforced with carbon fibers. The configuration of the related invention serves as a means for solving the above-mentioned conventional problems.

Further, in the method for producing a fiber-reinforced ceramics according to the present invention, a molded body (prepreg) is prepared using a carbon fiber cloth, and the molded body is impregnated with a sol (solution) of a metal alkoxide, The sol (solution) of the alkoxide is gelled (solidified), the gelled metal alkoxide is interposed between the carbon fibers, and then calcined to generate zircon microcrystals from the metal alkoxide. It is characterized in that the formed carbon fiber compact is sintered to obtain a carbon fiber reinforced zircon sintered body in which carbon fibers and zircon are integrated, and is adopted as necessary. In an embodiment, the carbon fiber reinforced zircon sintered material is impregnated with a sol (solution) of a metal alkoxide and then sintered to obtain pores of the carbon fiber reinforced zircon sintered material. And characterized in that a configuration to fill, and a means for solving the conventional problems described above with a configuration of the invention relating to the method for producing a fiber-reinforced ceramic.

The fiber-reinforced ceramics according to the present invention is
It has zircon as a main matrix phase, and this zircon is represented by ZrSiO ₄ and has a high melting point of about 2420 ° C.

As the carbon fibers mainly composed of zircon for reinforcing the matrix phase, those having various high strengths and / or high elastic moduli such as pitch type, PAN type, mesophase type and vapor phase growth type Is used and is appropriately selected from carbonaceous (carbon-based) and graphite (graphite-based) materials.

It is desirable that the amount of the carbon fiber mainly containing zircon for reinforcing the matrix is in the range of 10 to 60% by volume so that the reinforcing action of the carbon fiber is sufficient.

In the production of such fiber-reinforced ceramics, for example, a molded body (prepreg) is prepared using a cloth such as a woven or non-woven fabric of carbon fibers, and then, only the metal alkoxide is added to the molded body or Impregnate a sol (solution) consisting of a mixture containing metal alkoxide,
The sol (solution) of the metal alkoxide is gelated (solidified) by allowing it to stand, and the gelled metal alkoxide is interposed between the carbon fibers, and then calcined to generate zircon microcrystals from the metal alkoxide. By sintering a molded body of carbon fiber on which zircon microcrystals are formed in an inert atmosphere or the like, a dense carbon fiber reinforced zircon sintered body in which carbon fiber and zircon are integrated is obtained.

In this case, since sintering is carried out in the state of fine crystals of zircon, since it is possible to obtain a dense sintered body by pressureless sintering, pressure sintering is inevitable. There is nothing you have to do. Therefore, it becomes possible to deal with the manufacture of a ceramic member having a complicated shape.

If necessary, the carbon fiber reinforced zircon sintered material is impregnated with a sol (solution) consisting of a metal alkoxide alone or a mixture containing the metal alkoxide, and then sintered to obtain the carbon fiber. It is possible to obtain a denser sintered body by adding the step of filling the pores of the strengthened zircon sintered body, and it has the same excellent characteristics as ceramics pressure-sintered by pressureless sintering. It can be ceramics.

[0019]

The fiber-reinforced ceramics according to the present invention has a structure in which zircon is the main matrix phase and is reinforced with carbon fibers. Therefore, high melting point zircon (Zr
The matrix phase mainly composed of SiO ₄ ) is reinforced with carbon fiber having high strength and high elastic modulus and excellent heat resistance and corrosion resistance, so that not only the strength and toughness at room temperature are excellent,
The strength and toughness are not deteriorated at a high temperature from room temperature to about 1500 ° C., and the high temperature characteristics are excellent and the reliability is high.

Further, in the method for producing the fiber-reinforced ceramics according to the present invention, since the carbon fiber cloth is used, the productivity of the molded body (prepreg) is remarkably excellent, unlike the filament winding method.
Furthermore, since it is decided to sinter the molded body of carbon fiber in which microcrystals of zircon are produced, a dense sintered body can be obtained by pressureless sintering, and pressure sintering is inevitable. A dense sintered body can be obtained regardless of the above.

Then, if necessary, the carbon fiber reinforced zircon sintered material is impregnated with a sol of metal alkoxide and re-sintered, thereby filling the pores of the sintered material to obtain a denser sintering. The body is obtained, and it becomes a ceramic having excellent characteristics which is not inferior to the pressure sintering by the normal pressure sintering.

Therefore, since fiber-reinforced ceramics having sufficient characteristics are manufactured by pressureless sintering, not only is it suitable for mass production, but it is also applicable to ceramic parts having complicated shapes.

[0023]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

Example 1 The zircon powder was adhered to the carbon fiber by immersing the carbon fiber in a slurry mainly containing zircon (ZrSiO ₄ ) powder and an organic solvent and then drying it.

Next, the carbon fiber to which the zircon powder is attached is cut into a predetermined length, and is cut into a molding space 3 formed by a graphite side mold 1 and a graphite lower mold 2 shown in FIG. The carbon fibers 4 having a predetermined length to which the zircon powder was attached were laminated, heated by a heater 5 and calcined to remove the binder.

Subsequently, after the calcination, pressure is applied by the graphite lower mold 2 and the graphite upper mold 6 and the temperature is further raised by the heater 5, and a temperature of 1650 ° C. is applied while applying a pressure of 30 MPa in an inert atmosphere. By performing hot press sintering under the conditions of C, time: 1 Hr, a fiber-reinforced ceramics in which carbon fibers and zircon were integrated was obtained.

The carbon fiber content thus obtained is 40
When the mechanical strength of the carbon fiber / zircon composite ceramics having a volume% was examined, the results shown in Table 2 were obtained.

For comparison, Table 2 also shows the mechanical strength of zircon (ZrSiO ₄ ) based ceramics not reinforced with carbon fibers.

[0029]

[Table 2]

As is clear from the results shown in Table 2, the ceramic of Example 1 of the present invention is not only significantly superior in strength and fracture toughness at room temperature to the ceramics of Comparative Examples, but also It was confirmed that the material is a highly reliable room temperature or high temperature structural material with little decrease in strength and toughness even when the temperature rises to 1500 ° C.

(Examples 2 and 3) After forming a molded body (prepreg) using a woven fabric of carbon fiber, the molded body was
In the case of Example 2, a mixed solution of a metal alkoxide (here, tetraethoxysilane: Si (OC ₂ H ₅ ) ₄ + zirconium propoxide: Zr (OC ₃ H ₇ ) ₄ ) and zircon (ZrSiO ₄ ) powder. Also, in the case of Example 3, the solution of metal alkoxide (sol) was solidified (gel) by impregnating the solution of metal alkoxide alone and then leaving it to stand at 80 ° C.

In this way, the molded body in which the voids of the carbon fiber woven cloth are filled with the gel-like metal alkoxide is calcined at 800 ° C. in an inert atmosphere, and the metal alkoxide is converted to a fine zircon (ZrSiO ₄ ) powder. Crystals were formed.

Next, the carbon fiber molded body in which fine crystals of zircon were formed was subjected to 200 kgf in an inert atmosphere.
By applying hot press sintering under the conditions of temperature: 1650 ° C., time: 1 hr while applying a pressure of / cm ² , a fiber-reinforced ceramics in which carbon fibers and zircon were integrated was obtained.

The mechanical strength of each of the carbon fiber / zircon composite ceramics thus obtained in Example 2 having a carbon fiber content of 40% by volume and Example 3 having a carbon fiber content of 50% by volume was examined. The results are shown in Table 3.

[0035]

[Table 3]

As is clear from the results shown in Table 3, the ceramics of Examples 2 and 3 of the present invention are significantly superior in strength and fracture toughness at room temperature to the comparative ceramics. It was confirmed that it was a room-temperature or high-temperature structural material having high reliability and little decrease in strength and toughness even when the temperature increased to 1500 ° C.

[0037]

Since the fiber-reinforced ceramics according to the present invention has a constitution in which zircon is used as a mother phase and is reinforced with carbon fibers, it is excellent not only in strength and toughness at room temperature but also from room temperature to 1500. It is a highly reliable ceramic material with excellent high-temperature characteristics that does not show any decrease in strength or toughness even at high temperatures up to ° C, and is particularly required to have excellent high-temperature characteristics, heat resistance, corrosion resistance, and light weight. It has a remarkably excellent effect that it is suitable as a material for automobile engine parts, aerospace device parts, chemical device parts and the like.

In the method for producing fiber-reinforced ceramics according to the present invention, after forming a molded body using a cloth of carbon fiber, the molded body is impregnated with a sol of metal alkoxide to gel the sol of metal alkoxide. A carbon-fiber reinforced zircon in which carbon fibers and zircon are integrated by interposing a gel metal alkoxide between carbon fibers and then calcining to generate zircon microcrystals from the metal alkoxide Of the carbon fiber reinforced zircon sintered body is filled with the sol of the metal alkoxide and then sintered to fill the pores of the carbon fiber reinforced zircon sintered body. Therefore, it is possible to obtain a dense sintered body by pressureless sintering, and it is inevitable that the ceramics portion will have excellent characteristics regardless of pressure sintering. Suitable for mass production since it is possible to obtain, and also results in significantly excellent effect that it is possible to cope with the ceramic member of complicated shape.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a schematic configuration of a hot press device used in an example of the present invention.

Claims (4)

[Claims] 1. A fiber-reinforced ceramics comprising zircon as a matrix phase and reinforced with carbon fibers. 2. The fiber-reinforced ceramics according to claim 1, wherein zircon is used as a mother phase and reinforced with 10 to 60% by volume of carbon fiber. 3. After forming a molded body using a cloth of carbon fibers, the molded body is impregnated with a sol of metal alkoxide, and the sol of metal alkoxide is gelled to form a gel metal alkoxide between the carbon fibers. Intervening and then calcining to generate zircon crystallites from the metal alkoxide,
A method for producing fiber-reinforced ceramics, which is characterized by obtaining a carbon fiber-reinforced zircon-based sintered body in which carbon fibers and zircon are integrated by sintering thereafter. 4. The carbon fiber reinforced zircon sintered material is impregnated with a sol of metal alkoxide and then sintered to fill the pores of the carbon fiber reinforced zircon sintered material. Method for producing fiber-reinforced ceramics.