JPH11171658A - Crystalline silicon carbide-based fiber-reinforced ceramic composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a crystalline silicon carbide-based fiber reinforced ceramic composite material having excellent strength, modulus of elasticity and creep characteristics. SOLUTION: This composite material comprises a crystalline silicon carbide- based fiber having >=2.7 g/cm<3> density, >=2 GPa strength and >=250 GPa modulus of elasticity and composed of SiC sintered structure as reinforcing fibers and a ceramic as a matrix. Preferably the composite material comprises a crystalline silicon carbide-based fiber having >=2.7 g/cm<3> density, constituted of 55-70 wt.% of Si, 28-45 wt.% of C, 0.06-3.8 wt.% of Al and 0.06-0.5 wt.% of B and composed of SiC sintered structure as reinforcing fibers and a ceramic as a matrix.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber-reinforced ceramic composite material comprising a crystalline silicon carbide fiber having high mechanical properties and extremely excellent heat resistance as a reinforcing fiber and a ceramic matrix.

[0002]

2. Description of the Related Art Silicon carbide fibers are utilized as ceramic reinforcing fibers by utilizing their excellent heat resistance and mechanical properties. As the silicon carbide fiber, an amorphous or microcrystalline fiber obtained by a heat treatment at a relatively low temperature, for example, a temperature of 1500 ° C. or lower (hereinafter, this fiber is referred to as “amorphous silicon carbide fiber” Is widely known.

[0003] Many proposals have been made for this amorphous silicon carbide fiber and its production method. For example, Japanese Patent Publication No. 58-38535 discloses that an organosilicon polymer containing silicon and carbon as main skeleton components is spun, and the spun fiber is heated at low temperature in an oxidizing atmosphere to make it infusible. A method for producing a silicon carbide fiber by firing at a high temperature is disclosed.

Japanese Patent Publication No. Sho 62-52051 discloses a silicon carbide fiber composed of silicon-carbon-titanium-oxygen. Japanese Patent Publication No. 58-5286 discloses spinning polycarbosilane. , Make the spun fiber infusible,
A method is disclosed in which the infusibilized fiber is fired to produce the silicon carbide-based fiber composed of silicon-carbon-titanium-oxygen.

[0005]

The amorphous silicon carbide fiber has excellent heat resistance and mechanical properties, and has an appropriate elongation, so that it can be used as a complex woven fabric. On the other hand, at a high temperature exceeding 1300 ° C., oxygen in the fiber becomes CO gas and / or SiO
As a result, there is a disadvantage that the mechanical properties are deteriorated due to rapid growth of the β-SiC crystal. Therefore, the ceramic composite material using this as a reinforcing fiber has a problem that the mechanical properties are not sufficient and the fiber is liable to be deteriorated during the composite.

[0006]

Means for Solving the Problems The present inventors have proposed Si,
When a crystalline silicon carbide fiber having a sintered structure of SiC containing C, Al, and B, or Y and / or Mg at a specific ratio is used as a reinforcing fiber, the obtained ceramic composite material has excellent properties. They have been found to exhibit strength, modulus and creep properties.

According to the present invention, the density is 2.7 g / cm ^3.
As described above, the strength and the elastic modulus are 2 GPa or more and 2
A fiber-reinforced ceramic composite material having a strength of at least 50 GPa and having a crystalline silicon carbide fiber having a sintered structure of SiC as a reinforcing fiber and a ceramic as a matrix is provided. Further, the density is 2.7 g / cm ³ or more, and Si: 55 to 70%, C: 28 to 45%, A
1: 0.06 to 3.8% and B: 0.06 to 0.5%, a fiber reinforced ceramic comprising crystalline silicon carbide based fibers having a sintered structure of SiC as reinforcing fibers and ceramic as a matrix. A composite material is provided.

According to the present invention, the density is 2.7 g /
cm ³ or more, and Si: 55 to 70% by weight,
C: 28 to 45%, Al: 0.06 to 3.8%, and Y: 0.06 to 3.8% and / or Mg: 0.06 to
A fiber-reinforced ceramic composite material comprising 3.8% and having a crystalline silicon carbide-based fiber having a sintered structure of SiC as a reinforcing fiber and a ceramic as a matrix is provided.

First, the crystalline silicon carbide fiber of the present invention will be described. This crystalline silicon carbide fiber has S
It has an excellent mechanical property of a sintered structure of iC, a density of 2.7 g / cm ³ or more, and a strength and an elastic modulus of 2 GPa or more and 250 GPa or more, respectively.

[0010] The crystalline silicon carbide fiber of the present invention contains Si and C as main components, and contains Al and B or Y and / or Mg as a sintering aid component. A preferable ratio of these components is Si: 55 to 70%,
C: 28 to 45%, Al: 0.06 to 3.8%, particularly 0.13 to 1.25%, B: 0.06 to 0.5%, particularly 0.06 to 0.19%. .

When Y and / or Mg is contained, Si: 55 to 70%, C: 28 to 45%, Al:
0.06-3.8%, especially 0.13-1.25%,
Y: 0.06 to 3.8%, especially 0.13 to 1.25 and / or Mg: 0.06 to 3.8%, especially 0.13 to 1.
25%. In this case, B may be contained in a ratio of up to 0.2%.

If the proportion of Al is excessively small, the sintered fiber does not become a sufficiently sintered crystalline fiber, and the density of the fiber decreases. If the proportion is excessively high, the mechanical properties at high temperatures deteriorate. become. If the proportion of boron is excessively small, the fiber does not become a sufficiently sintered crystalline fiber, and the density of the fiber decreases.On the other hand, if the proportion is excessively high, the mechanical properties decrease, so that it is preferable. Absent. On the other hand, Y
If the proportion of Mg is too small, the crystalline fiber does not become a sufficiently sintered crystalline fiber, and the density of the fiber decreases. Conversely, if the proportion is too high, the mechanical properties deteriorate. Is not preferred.

The crystalline silicon carbide fiber may contain a small amount of oxygen and an excessive amount of carbon, and it is preferable that each of the fibers is 2% by weight or less. As used herein, the term “excess carbon” means carbon present in excess of the stoichiometric composition that can be present as SiC with respect to Si contained in the fiber. Although there is no particular limitation on the fiber diameter of the crystalline silicon carbide fiber, it is usually 50 μm or less.

The form of the crystalline silicon carbide fiber is not particularly limited, and may be a continuous fiber or a chopped short fiber obtained by cutting the continuous fiber. It may be a woven or non-woven fabric such as an axial weave or a three-dimensional weave, or may be a sheet-like material in which continuous fibers are aligned in one direction or a laminate thereof. The ratio of the crystalline silicon carbide fiber in the composite material is not particularly limited, but is generally 30 to 70% by weight.

The crystalline silicon carbide fiber may be subjected to a surface treatment before being compounded. Examples of the surface treatment include a method of forming a coating of carbon, boron nitride, silicon carbide, or the like on a crystalline silicon carbide fiber by a known method.

Next, a method for producing a crystalline silicon carbide fiber according to the present invention will be described. This crystalline silicon carbide fiber contains 0.05 to 3% by weight of Al, preferably 0.1 to 3% by weight.
1% by weight, and 0.05 to 0.4% by weight, preferably 0.05 to 0.15% by weight of B, and 1% by weight or more of excess carbon, preferably 1.5 to 2.5% by weight. Weight percent of amorphous or microcrystalline silicon carbide-based fiber
It is prepared by heating to a temperature in the range of 0-2100 ° C.

Al is 0.05 to 3% by weight, preferably 0.1 to 1% by weight, Y is 0.05 to 3% by weight, preferably 0.1 to 1% by weight and / or Mg is 0 to 0% by weight. .05-
3% by weight, preferably 0.1-1% by weight, B is 0-0.
An amorphous or microcrystalline silicon carbide fiber containing 1% by weight and 1% by weight or more of excess carbon is 1600-2100.
It is prepared by heating to a temperature in the range of ° C. This heat treatment is performed in an atmosphere of an inert gas such as argon or helium.

The amorphous or microcrystalline silicon carbide fiber preferably contains 8 to 16% by weight of oxygen. This oxygen plays an important role in desorbing the above-mentioned surplus carbon as CO gas when heating these fibers in a later step.

When the crystalline silicon carbide fiber is used in the form of a non-woven fabric or a woven fabric, the crystalline silicon carbide fiber has a very high elastic modulus. Since it is difficult, amorphous or microcrystalline silicon carbide based fibers having good weaving properties are preliminarily formed into a nonwoven fabric or a woven fabric, and subjected to a heat treatment corresponding to each fiber composition to be crystallized. Thus, a nonwoven fabric or a woven crystalline silicon carbide fiber having a complicated shape can be obtained. In addition, since the woven fabric generally causes a volume shrinkage of 10 to 20% by the heat treatment,
It is desirable to determine the dimensions of the woven fabric in consideration of the shrinkage of the raw fibers.

The above-mentioned amorphous or microcrystalline silicon carbide fiber can be prepared, for example, by the following method. First, a chain or cyclic polysilane is prepared by subjecting one or more dichlorosilanes to a dechlorination reaction with sodium, for example, according to the method described in "Chemistry of Organosilicon Compounds", Kagaku Dojin (1972). The number average molecular weight of the polysilane is usually from 300 to 1,000. In the present specification, the polysilane is obtained by heating the above-mentioned chain or cyclic polysilane to a temperature in the range of 400 to 700 ° C., or adding a phenyl group-containing polyborosiloxane to the above-mentioned chain or cyclic polysilane. 250-500
It also includes a polysilane having a carbosilane bond in part, which is obtained by heating to a temperature in the range of ° C. The polysilane can have a hydrogen atom, a lower alkyl group, an aryl group, a phenyl group or a silyl group as a side chain of silicon.

The phenyl group-containing polyborosiloxane is prepared by a dehydrochlorination condensation reaction between boric acid and one or more diorganochlorosilanes according to the methods described in JP-A-53-42330 and JP-A-53-50299. Whose number average molecular weight is usually 500 to 1000
0.

Then, a predetermined amount of an aluminum alkoxide, an acetylacetoxide compound, a carbonyl compound, or a cyclopentadienyl compound is added to the polysilane, and the mixture is heated in an inert gas at a temperature usually in the range of 250 to 350 ° C. By reacting for 1 to 10 hours, an aluminum-containing organosilicon polymer as a spinning raw material can be prepared. When yttrium and / or magnesium are contained, an yttrium and / or magnesium compound is added together with the aluminum compound.

The spun fiber is prepared by spinning the aluminum-containing organosilicon polymer by a method known per se, such as melt spinning or dry spinning. Next, the spun fiber is infusibilized to prepare an infusible fiber. As the infusibilizing method, generally employed heating in air or a method in which heating in air and heating in an inert gas are combined can be preferably employed.

The infusibilized fiber is heated in an inert gas such as nitrogen or argon at a temperature in the range of 800 ° C. to 1500 ° C. to obtain a precursor fiber of the crystalline silicon carbide fiber.
An amorphous or microcrystalline silicon carbide fiber is prepared.

Next, the ceramics forming the matrix in the present invention will be described. Examples of the matrix include crystalline or amorphous oxide ceramics, crystalline or amorphous non-oxide ceramics, glass, crystallized glass, mixtures thereof, and ceramic composite materials in which these ceramics are particle-dispersion-reinforced. can do.

Specific examples of oxide ceramics include aluminum, magnesium, silicon, yttrium, indium, uranium, calcium, scandium, tantalum, niobium, neodymium, lanthanum, ruthenium, rhodium, beryllium, titanium, tin, strontium, barium, Examples include oxides of elements such as zinc, zirconium, and iron, and composite oxides of these metals.

Specific examples of non-oxide ceramics include:
Carbides, nitrides, borides. Specific examples of carbides include silicon, titanium, zirconium,
Elements carbides such as aluminum, uranium, tungsten, tantalum, hafnium, boron, iron, manganese,
Composite carbides of these elements are included. Examples of the composite carbide include an inorganic substance obtained by heating and calcining polytitanocarbosilane or polyzirconocarbosilane.

Specific examples of the nitride include nitrides of elements such as silicon, boron, aluminum, magnesium and molybdenum, composite oxides of these elements, and sialon. Specific examples of borides include borides of elements such as titanium, yttrium, and lanthanum, and CeCo.
Platinum boride lanthanoids such as ₃ B ₂ , CeCo ₄ B ₄ and ErRh ₄ B ₄ are mentioned.

Specific examples of the glass include amorphous glass such as silicate glass, phosphate glass and borate glass. Specific examples of the crystallized glass include LiO ₂ —Al ₂ O ₃ in which the main crystal phase is β-spdumene.
-MgO-SiO ₂ based glass and LiO ₂ -Al ₂ O ₃ -M
gO-SiO ₂ -Nb ₂ O ₅ based glass, a main crystal phase co _{- MgO-Al 2 O 3 -SiO} 2 based glass is cordierite,
BaO-MgO whose main crystal phase is barium osmilite
—Al ₂ O ₃ —SiO ₂ glass, BaO—Al ₂ O ₃ —SiO ₂ whose main crystal phase is mullite or hexacelsian
Glass, CaO-Al whose main crystal phase is anosite
₂ O ₃ —SiO ₂ based glass is exemplified. The crystal phase of these crystallized glasses may include crustbarite. Examples of the ceramic in the present invention include solid solutions of the above various ceramics.

Specific examples of the ceramic composite material in which ceramics are dispersed and strengthened are selected from silicon nitride, silicon carbide, zirconium oxide, magnesium oxide, potassium titanate, magnesium borate, zinc oxide, titanium boride and mullite. Ceramics in which spherical particles, polyhedral particles, plate-like particles, and rod-like particles of an inorganic substance are uniformly dispersed in 0.1 to 60% by volume are exemplified. The particle size of the spherical particles and the polyhedral particles is generally 0.1 μm to 1 mm, and the aspect ratio of the plate-like particles and the rod-like particles is generally 1.5 to 1000.

The composite material of the present invention can be obtained by subjecting a mixture of crystalline silicon carbide fiber and ceramic raw material powder to heat treatment, or adding a precursor polymer of ceramic to the crystalline silicon carbide fiber, for example, polycarbosilane, It is manufactured by impregnating with polymetallocarbosilane, polysilazane or the like and then performing heat treatment.

In the former method, when the crystalline silicon carbide fiber is chopped, a mixture of the chopped fiber and the ceramic raw material powder is used, and the fiber is a long fiber, woven fabric, nonwoven fabric or sheet. When the product is a product, the fiber layer and the ceramic material powder layer are alternately laminated to form a laminate, and after molding into a desired shape or simultaneously with the molding, heat treatment is performed to sinter the ceramic material powder. , A composite material can be obtained.

In the latter method, a solution prepared by dissolving a ceramic precursor polymer in an aromatic hydrocarbon solvent such as toluene or xylene is usually impregnated into crystalline silicon carbide fibers, and the solvent is removed from the impregnated material. The composite material is prepared by a subsequent heat treatment. In this method, it is preferable to repeat a cycle of impregnation of the precursor polymer, removal of the solvent, and heat treatment a plurality of times in order to obtain a composite material having no pores therein. In this method, mineralization and sintering of the precursor polymer proceed.

The heat treatment temperature is usually from 800 to 1800 ° C. The heat treatment is performed in an atmosphere of an inert gas such as nitrogen, argon, or carbon monoxide. The heat treatment temperature is preferably higher than the temperature at which the obtained composite material is actually used.

[0035]

EXAMPLES Examples and comparative examples are shown below. In the following, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively, unless otherwise specified. Reference Example 1 1 l of dimethyldichlorosilane was added dropwise to anhydrous xylene containing 400 g of sodium while heating and refluxing xylene under a nitrogen gas stream, followed by heating and refluxing for 10 hours to produce a precipitate. The precipitate is filtered, washed with methanol and then with water to give white polydimethylsilane 4
20 g were obtained.

By heating 750 g of diphenyldichlorosilane and 124 g of boric acid in n-butyl ether at 100 to 120 ° C. under a nitrogen gas atmosphere, and further heating the resulting white resinous material at 400 ° C. in vacuum for 1 hour, 530 g of phenyl group-containing polyborosiloxane was obtained.

REFERENCE EXAMPLE 2 To 100 parts of the polydimethylsilane obtained in Reference Example 1, 4 parts of phenyl group-containing polyborosiloxane was added and thermally condensed at 350 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight organic compound. A silicon polymer was obtained. Aluminum-tri- (se) was added to a xylene solution in which 100 parts of the organosilicon polymer was dissolved.
c-butoxide) and add 31 parts under a nitrogen gas stream.
A polyaluminocarbosilane was synthesized by performing a crosslinking reaction at 0 ° C.

This polyaluminocarbosilane is heated at 245 ° C.
After heat-spinning at 140 ° C. for 5 hours in air, this was further heated in nitrogen at 300 ° C. for 10 hours to obtain infusible fibers. The infusible fiber was continuously fired in nitrogen at 1500 ° C. to obtain an amorphous silicon carbide fiber. The chemical composition of the amorphous silicon carbide fiber is as follows: Si: 56%, C:
30%, O: 13%, Al: 0.6%, B: 0.05%
Met.

REFERENCE EXAMPLE 3 To 100 parts of the polydimethylsilane obtained in Reference Example 1, 0.5 part of a phenyl group-containing polyborosiloxane was added and thermally condensed at 410 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight polymer. Was obtained. This organosilicon polymer 10
0 parts of the xylene solution was dissolved in aluminum tri-
(Sec-butoxide) (4 parts) and magnesium acetylacetonate (3 parts) were added, and the mixture was heated to 310 ° C. under a nitrogen gas stream.
To obtain a modified polycarbosilane into which aluminum and magnesium were introduced.

The modified polycarbosilane was melt-spun at 255 ° C., heat-treated in air at 150 ° C. for 3 hours, and further heated in nitrogen at 300 ° C. for 9 hours to obtain infusible fibers. The infusibilized fiber was continuously fired at 1450 ° C. to synthesize an amorphous silicon carbide fiber. The chemical composition of this amorphous silicon carbide fiber is as follows: Si: 53%, C: 33.4%, O: 1
3%, Al: 0.34%, B: 0.01%, Mg: 0.1%
30%.

Reference Example 4 0.2 parts of a phenyl group-containing polyborosiloxane was added to 100 parts of the polydimethylsilane obtained in Reference Example 1 and thermally condensed at 420 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight polymer. Was obtained. This organosilicon polymer 10
0 parts of the xylene solution was dissolved in aluminum tri-
(Sec-butoxide) (4 parts) and yttrium acetylacetonate (4 parts) were added, and the mixture was heated to 300 ° C. under a nitrogen gas stream.
To obtain a modified polycarbosilane into which aluminum and yttrium have been introduced.

The modified polycarbosilane was melt-spun at 265 ° C., heat-treated at 155 ° C. for 3 hours in air, and further heated at 300 ° C. for 10 hours in nitrogen to obtain infusible fibers. The infusibilized fibers were continuously fired in argon at 1450 ° C. to synthesize amorphous silicon carbide fibers. The chemical composition of the amorphous silicon carbide fiber is as follows: Si: 52.5%, C:
34.5%, O: 12%, Al: 0.35%, B: 0.
005%, Y: 0.56%.

Reference Example 5 To 100 parts of the polydimethylsilane obtained in Reference Example 1, 8 parts of a phenyl group-containing polyborosiloxane was added, and thermally condensed at 350 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight organic polymer. A silicon polymer was obtained. To a xylene solution in which 100 parts of this organosilicon polymer was dissolved, 1 part of titanium tetrabutoxide was added.
By adding 0 parts and performing a cross-linking reaction at 320 ° C. under a nitrogen gas stream, polytitanocarbosilane was synthesized. Reference Example 6 The polytitanocarbosilane obtained in Reference Example 5 was heated at 225 ° C.
, And heat-treated in air at 170 ° C. for 1 hour, and further heated in nitrogen at 300 ° C. for 10 hours to obtain infusible fibers. The infusibilized fiber was continuously fired at 1300 ° C. in nitrogen to obtain an amorphous silicon carbide fiber. The chemical composition of the amorphous silicon carbide fiber is as follows: Si: 54%,
C: 31%, O: 12.6%, Ti: 2%, B: 0.0
5%.

Example 1 The amorphous silicon carbide fiber obtained in Reference Example 2 was formed into a three-dimensional woven fabric (fiber ratio: X: Y: Z = 1: 1: 0.5). The three-dimensional fabric was crystallized by heating to 1900 ° C. in a 700 torr argon stream. The chemical composition of the obtained crystalline silicon carbide fiber is as follows: Si: 67%,
C: 31%, O: 0.3%, Al: 0.8%, B: 0.
06%, Si: C: O: Al = 1: 1.0 in atomic ratio
8: 0.008: 0.012. The tensile strength of the crystalline silicon carbide fiber constituting the three-dimensional fabric is 27.
It was 0 kg / mm ² , the elastic modulus was 32 t / mm ² , and it had a dense sintered structure of SiC. The density was 2.9 g / cm ³ .

Phenol formaldehyde resin (Bellpearl S type, Kanebo Co., Ltd.) is applied to the obtained three-dimensional fabric.
Was melted in an argon atmosphere, impregnated with the mixture, and cured by heating at 200 ° C., and then carbonized at 1000 ° C. Next, the obtained molded product was immersed in a solution in which 100 parts of the polytitanocarbosilane obtained in Reference Example 5 was dissolved in 100 parts of xylene, and impregnated at 5 atm in an argon atmosphere. Furthermore, it was heated at 150 ° C. in an argon stream to remove xylene by evaporation, and then calcined at 1200 ° C. Subsequently, the immersion, impregnation, and firing were repeated eight times to obtain a crystalline silicon carbide fiber reinforced composite material. The bending strength of the obtained composite material was 65 kg / mm ² . The composite was subjected to a bending stress of 20 kg / mm ² in argon,
It was kept at 00 ° C. for 200 hours, but no change was observed.

Comparative Example 1 The amorphous silicon carbide fiber obtained in Reference Example 6 was formed into a three-dimensional woven fabric (fiber ratio: X: Y: Z = 1: 1: 0.5). Using the obtained three-dimensional woven fabric, a composite material was prepared in the same manner as in Example 1. The bending strength of the obtained composite material was 67 kg / mm ² . The composite material was subjected to a bending stress of 20 kg / mm ² in argon at 1200 ° C. for 200 hours.
When held for a time, the test piece was curved, but did not break, but did not return to its original state even after the load was removed.

Example 2 The amorphous silicon carbide fiber obtained in Reference Example 3 was heated at 1850 ° C.
Was continuously heated in argon to synthesize crystalline silicon carbide fibers. The chemical composition of the obtained silicon carbide continuous inorganic fiber is as follows: Si: 66.5%, C: 32.5%, O: 0.
2%, Al: 0.43%, B: 0.01%, Mg: 0.1%
38%, Si: C: O: Al: Mg = 1: atomic ratio
1.14: 0.005: 0.0067: 0.0066. This fiber has a tensile strength of 230 kg / mm ² , an elastic modulus of 31 t / mm ² , a density of 2.87 g / cm ³ and a dense S
It consisted of a sintered structure of iC. The obtained fiber was continuously passed through a cordierite powder water slurry and then wound up to obtain a one-way sheet. Twenty of these unidirectional sheets were laminated and hot-pressed in argon at 1200 ° C. to obtain a crystalline silicon carbide fiber reinforced composite material. The obtained composite material had a tensile strength of 80 kg / mm ² and an elastic modulus of 24 t / mm ² .

Example 3 The amorphous silicon carbide fiber obtained in Reference Example 4 was heated at 1900 ° C.
Was continuously heated in argon to synthesize crystalline silicon carbide fibers. The chemical composition of the obtained silicon carbide continuous inorganic fiber is as follows: Si: 67%, C: 31.5%, O: 0.1
%, Al: 0.41%, B: 0.01%, Y: 0.73
%: Si: C: O: Al: Y = 1: 1.1:
0.0026: 0.0064: 0.0034.
This fiber has a tensile strength of 245 kg / mm ² and an elastic modulus of 32 t /
mm ² , the density was 3.01 g / cm ³ and consisted of a dense SiC sintered structure. The obtained fiber was cut into a length of 1 mm to obtain a chopped fiber. The chopped fibers and the silicon nitride powder were sufficiently mixed at a ratio of 1: 9 using a ball mill. This mixture was placed in a graphite mold and hot-pressed in argon at 1750 ° C. and 100 kg / cm ² to obtain a crystalline silicon carbide fiber reinforced composite material. The bending strength of the obtained composite material was 80 kg / mm ² .

Comparative Example 2 The amorphous silicon carbide fiber obtained in Reference Example 6 was 1 mm in length.
And chopped fibers were obtained. Using this chopped fiber, a composite material was obtained in the same manner as in Example 3. The bending strength of the obtained composite material was 12 kg / mm ² . Further, when the chopped fibers in the fractured surface were observed with a microscope, deterioration due to crystallization was observed.

Claims (6)

[Claims] Claims: 1. A crystalline silicon carbide-based fiber having a density of 2.7 g / cm ³ or more, a strength and an elastic modulus of 2 GPa or more and 250 GPa or more, and a sintered structure of SiC, is used as a reinforcing fiber. Fiber-reinforced ceramic composite material used as matrix. 2. Density is 2.7 g / cm ³ or more, and Si: 55 to 70%, C: 28 to 45%, A
1: 0.06 to 3.8% and B: 0.06 to 0.5%, a fiber reinforced ceramic comprising crystalline silicon carbide based fibers having a sintered structure of SiC as reinforcing fibers and ceramic as a matrix. Composite materials. 3. Density is 2.7 g / cm ³ or more, and Si: 55 to 70%, C: 28 to 45%, A
l: 0.06 to 3.8%, and Y: 0.06 to 3.8%
And / or Mg: 0.06-3.8%, SiC
A fiber-reinforced ceramic composite material in which a crystalline silicon carbide-based fiber having a sintered structure as described above is used as a reinforcing fiber and a ceramic is used as a matrix. 4. The fiber-reinforced ceramic composite material according to claim 1, wherein the crystalline silicon carbide fiber is a nonwoven fabric or a woven fabric. 5. The fiber-reinforced ceramic composite material according to claim 1, wherein the crystalline silicon carbide fiber is in the form of a unidirectional sheet or a laminate thereof. 6. The fiber-reinforced ceramic composite material according to claim 1, wherein the crystalline silicon carbide fibers are continuous fibers or chopped short fibers obtained by cutting the continuous fibers.