JPH0687673A - Silicon nitride based inorganic fiber reinforced ceramic composite material - Google Patents

Abstract

PURPOSE:To obtain a composite material exhibiting excellent strength and fracture toughness at a room temp. to a high temp. by using a silicon nitride based inorganic fiber as a reinforcing material and an oxide based nanocomposite material as a matrix and compositing them. CONSTITUTION:The silicon nitride based inorganic fiber reinforced ceramic composite material is obtained by using the silicon carbide based inorganic fiber as the reinforcing material and the oxide based nanocomposite material nanocomposited by carbide particles as the matrix. The oxide based nanocomposite material to be the matrix is a ceramic constituted by the structure made by transgranular nanocompositing, intergranular nanocompositing or both trans- and inter-granular nanocompositing at least one kind dispersion particle of the carbide particles and nitride particles with an oxide ceramic. The ratio of the dispersion particles in the oxide based nanocomposite material is usually 1-50 volume % and the ratio of the silicon nitride based inorganic fiber in the composite material is usually 1-70 volume %.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-based inorganic fiber reinforced ceramic composite material having high strength, high toughness and high heat resistance. The ceramic composite material of the present invention is used as a member of a turbine engine such as a rotor, a stator or a combustor, a member of a rocket engine such as a nose cone or a nozzle, a member of an internal combustion engine such as a piston head, an auxiliary combustion chamber or a valve. , Can be preferably used.

[0002]

2. Description of the Related Art Oxide ceramics such as aluminum oxide have excellent heat resistance, but their applications as engineering ceramics have been limited because of their low toughness and insufficient strength. . Recently, attempts have been actively made to improve strength and toughness by compounding oxide ceramics with various reinforcing materials.

For example, "Pro.23rd.Autom
ot. Technol. Dev. Contract C
oord. Meet. In 1986, there are 20
By compounding volume% silicon carbide whiskers,
Bending strength is improved from about 300MPa to about 700MPa, and the critical stress intensity factor (K _1C ) is a measure of fracture toughness.
Is 4.5 MPa · m ^1/2 to about 8.5 MPa · m
It is disclosed that it is improved to ^1/2 . However, the bending strength of this whisker-reinforced alumina composite material sharply decreases when it exceeds 1000 ° C. "The Survey of New Materials for Aircraft" issued by the Japan Aerospace Industry Association in March 1998, page 193 shows that for materials for gas turbine rotors, etc., at temperatures in the range of 1250 ° C to 1450 ° C. It is described that the bending strength needs to be 450 MPa or more. The above-mentioned whisker reinforced alumina composite material cannot satisfy the properties required for the above gas turbine member.

A method of improving the strength or heat resistance of oxide ceramics by nanocompositing is also known.
For example, in “Powder and powder alloys”, Vol. 37, p. 348 (1990), a ceramic nanocomposite material prepared by adding 5% by volume of silicon carbide ultrafine particles to aluminum oxide has a heat resistance temperature of 1200 ° C. and bending. Strength about 155
It is disclosed that it exhibits an excellent property of 0 MPa. However, the K _{1C of} this composite material is approximately 4.8 MPa
m ^1/2 , which is lower than about 6 MPa · m ^1/2 which is K _1C of ordinary monolithic silicon nitride.

[0005]

The object of the present invention is to show excellent strength and high fracture toughness value from room temperature to high temperature, which can be suitably used for various heat engines including automobile engines. It is to provide a ceramic composite material. The above object of the present invention is to use a silicon nitride-based inorganic fiber as a reinforcing material and a matrix of an oxide-based nanocomposite material that is nanocomposited with carbide particles and / or nitride particles as a matrix. Achieved by

Specific examples of the silicon nitride-based inorganic fiber in the present invention include (1) silicon and nitrogen, or an amorphous substance composed of silicon, nitrogen and oxygen, or (2) crystalline Si ₃ N ₄ fine particles and / or Or crystalline Si ₂ N ₂ O fine particles, optionally an aggregate of the crystalline fine particles and amorphous SiO ₂ , (3) a mixture of the amorphous substance of (1) above and the aggregate of (2) above Inorganic fibers composed of can be mentioned. The ratio of the constituent elements in this inorganic fiber is
Generally, Si: 40 to 65% by weight, N: 10 to 40% by weight, O: 0 to 40% by weight. The above-mentioned inorganic fibers are disclosed in, for example, JP-A Nos. 63-235526 and 61-129.
It can be prepared according to the method described in JP-A No. 15 and JP-A No. 62-125012.

The form of the silicon nitride inorganic fiber is not particularly limited, and may be chopped fiber, plain weave woven from continuous fibers, satin weave, multiaxial weave, three-dimensional weave or non-woven fabric, and further continuous. It may be a sheet-shaped product in which fibers are aligned in one direction.

In the oxide-based nanocomposite used as a matrix in the present invention, at least one kind of dispersed particles of carbide particles and nitride particles is intragranular nanocomposite, intergranular nanocomposite or intragranular nanocomposite with oxide ceramics. And a ceramic composed of a nanocomposite structure of both grain boundaries.
The intragranular nanocomposite structure is a structure in which the matrix particles themselves are compounded by dispersing dispersed particles of nano-order in the matrix particles of the oxide-based ceramic, as in the model shown in FIG. On the other hand, the grain boundary nanocomposite structure is
For example, as in the model shown in FIG. 2, it is a structure in which nano-order dispersed particles are dispersed in the matrix grain boundaries of the oxide-based ceramics to form a composite. Such oxide-based nanocomposite
For example, it can be prepared according to the method described in "The Ceramic Society of Japan", Volume 99, pages 947-982 (1991).

Specific examples of the oxide-based ceramics that form the matrix phase in the oxide-based nanocomposite material include aluminum,
Magnesium, silicon, yttrium, indium, uranium, calcium, scandium, tantalum, niobium,
Neodymium, lanthanum, ruthenium, rhodium, beryllium, titanium, tin, strontium, barium, zinc,
Mention may be made of oxides of elements such as zirconium and iron, and complex oxides of these metals. The particle size of these oxide-based ceramics is generally 0.05 to 1000 μm.
Is.

Specific examples of the nitride that becomes the dispersed particles include:
Examples thereof include nitrides of elements such as silicon, boron, aluminum, magnesium, titanium, and molybdenum, composite nitrides of these elements, and sialon. Specific examples of the carbide of the dispersed particles include carbides of elements such as silicon, titanium, zirconium, aluminum, uranium, tungsten, tantalum, hafnium, boron, iron and manganese, and composite carbides of these elements. There is no particular limitation on the shape of the dispersed particles in the oxide-based nanocomposite material, and spherical, polyhedral, plate-shaped,
It may be needle-shaped. In the case of spherical or polyhedral particles, the size of dispersed particles is generally 1 to 100 in terms of equivalent diameter.
In the case of a plate or needle, the maximum length or thickness is 10,000 nm. The proportion of dispersed particles in the oxide-based nanocomposite is generally 1 to 50% by volume with respect to the composite.

The silicon nitride inorganic fiber reinforced ceramics composite material of the present invention can be prepared by blending the silicon nitride inorganic fiber and the oxide nanocomposite material according to a method known per se and sintering. . When the silicon nitride-based inorganic fibers are chopped, a mixture is prepared by mixing the chopped fibers and the oxide-based nanocomposite powder. When the silicon nitride-based inorganic fiber is a long fiber, a woven fabric, a non-woven fabric, or a sheet-like product, a laminate is prepared by alternately laminating a layer composed of these and a layer composed of oxide-based nanocomposite powder. To do. Then, the above-mentioned mixture or laminate is heat-sintered after being formed into a desired shape or at the same time as the formation, whereby the silicon nitride-based inorganic fiber-reinforced ceramic composite material of the present invention can be obtained. The ratio of the silicon nitride inorganic fiber in the composite material is usually 1 to 70% by volume.

As a method for molding the above mixture or laminate, a method known per se, for example, a die pressing method, a rubber pressing method, an extrusion method or a sheet method can be adopted. Known organic polymers such as polyvinyl alcohol, polyethylene oxide and aluminum alkoxide, as well as polycarbosilane and polymetallocarbosilane can be used as the binder during molding.
There is also no particular limitation on the sintering method, and a method known per se such as a method of sintering a molded product under normal pressure or reduced pressure, a hot pressing method or a hot isostatic pressing method in which molding and sintering are simultaneously performed. Can be adopted. The heating and sintering temperature is usually 400 to 2100 ° C. If the heating and sintering temperature is too low, the oxide nanocomposite matrix will not be sufficiently sintered, and if the temperature is too high, the silicon nitride inorganic fibers will be decomposed.

As another method for preparing the silicon nitride-based inorganic fiber reinforced ceramics composite material of the present invention, instead of using the oxide-based nanocomposite powder itself as the raw material powder for the matrix, a raw material for the oxide-based nanocomposite material is used. A method similar to the above can also be adopted, except that a mixed powder obtained by mixing oxide-based ceramic powder to be obtained and carbide particles and / or nitride particles by a known method is used. In this case, during the molding and sintering process, the nanocomposite of the matrix and the composite of the matrix and the silicon nitride-based inorganic fiber occur simultaneously or sequentially, and the silicon nitride-based inorganic fiber-reinforced ceramic composite material of the present invention is obtained. Is prepared.

[0014]

EXAMPLES Examples of the present invention will be shown below. Reference Example 1 Polydimethylsilane synthesized by dechlorinating and condensing dimethyldichlorosilane with sodium metal was placed in a reaction vessel equipped with a reflux condenser, and the temperature in the vessel was kept at 450 ° C. with stirring under a nitrogen stream. Gradually heat to 15 to the same temperature
Held for hours. After cooling, the reaction product was taken out as a xylene solution, filtered, and xylene was evaporated to obtain polycarbosilane having a number average molecular weight of about 2000. After melt-spinning this polycarbosilane, the spun fiber was irradiated with an electron beam of 10 MGy in a vacuum to make it infusible, and then fired at 1300 ° C. in an ammonia gas stream to obtain a silicon nitride-based inorganic fiber. Hereinafter, this inorganic fiber is referred to as an inorganic fiber A. The inorganic fiber A has an oxygen content of 1% by weight or less and a fiber diameter of about 1
1 μm, tensile strength 2.9 GPa, tensile modulus 24
It was 0 GPa (measurement was by the single fiber test method).

Reference Example 2 The polycarbosilane obtained in Reference Example 1 was melt-spun, the spun fiber was heated in oxygen gas at 160 ° C. to be infusible, and then the infusible fiber was fired in ammonia gas at 1300 ° C. Then, a silicon nitride-based inorganic fiber was obtained. Hereinafter, this inorganic fiber is referred to as an inorganic fiber B. The inorganic fiber B had an oxygen content of 12% by weight, a fiber diameter of 11 μm, a tensile strength of 2.8 GPa, and a tensile modulus of elasticity of 190 GPa (measured by a single fiber test method).

Reference Example 3 γ-alumina having an average particle size of 0.5 μm has an average particle size of 0.3 μm.
5% by volume of β-silicon carbide particles of m were added, and the particles were added to 12 in ethanol by a ball mill using alumina balls.
Wet mixed for hours. Then, the mixture was dried, and the powder obtained by dry-mixing for 12 hours was further dried in a nitrogen gas atmosphere.
Hot pressing was performed in a graphite die at a pressure of 30 MPa and a temperature of 1500 to 1800 ° C. to obtain an alumina-based nanocomposite material (SiC particles / Al ₂ O ₃ nanocomposite material) reinforced with silicon carbide particles. The bending strength of this nanocomposite at room temperature is 1.
5 GPa and K _1C were 5 MPa · m ^1/2 , and the maximum operating temperature was 1200 ° C.

Reference Example 4 Magnesia having an average particle size of 0.1 μm has an average particle size of 0.3 μm.
The following silicon carbide particles were added in an amount of 10% by volume, and a silicon nitride ball was used in a ball mill for 24 hours in toluene.
After wet mixing for an hour, the mixture was dried. The mixed powder was placed in a nitrogen gas atmosphere at a pressure of 28 MPa and 1700 to 1700.
Hot-pressed in a graphite die at a temperature of 1900 ° C and strengthened with silicon carbide particles magnesia nanocomposite (Si
C grain / MgO nanocomposite) was obtained. The bending strength of this nanocomposite at room temperature is 700 MPa, and K _1C is 4 MPa · m.
^1/2 , the maximum operating temperature was 1300 ° C.

Example 1 The SiC particles / Al ₂ O ₃ nanocomposite material obtained in Reference Example 3 was crushed for 30 hours in distilled water by a ball mill using a silicon nitride ball and a silicon nitride pot to form a nanocomposite. A slurry of material was obtained. Polyethylene oxide as a binder was added to the slurry in an amount of 10
Add 12% by weight and then use silicon nitride balls
The mixture was wet-mixed for an hour to obtain a matrix raw material slurry.
The bundle of the inorganic fibers A obtained in Reference Example 1 was opened by blowing air and then dipped in the slurry of the above matrix raw material to attach the matrix powder around each inorganic fiber A. A bundle of the inorganic fibers A to which the matrix powder was adhered was wound on a square drum and then sufficiently dried to prepare a prepreg sheet. After cutting this prepreg sheet into a desired shape, the prepreg sheet was laminated in a graphite die coated with boron nitride as a mold release agent, and then, in an argon gas atmosphere, 1
Hot pressing was performed at a temperature of 550 ° C. and a pressure of 60 MPa to obtain an inorganic fiber-reinforced ceramics composite material using the SiC particles / Al ₂ O ₃ nanocomposite material as a matrix. The ratio of the inorganic fibers A in the composite material was 45% by volume. The bending strength of this composite material is 1.62 GPa, 1300 at room temperature.
It was 1.49 GPa at 0 ° C. The fracture toughness value (K _1C ) of the composite material measured by the chevron notch method is 18.5.
It was MPa · m ^1/2 .

Example 2 γ-alumina having an average particle size of 0.4 μm has an average particle size of 0.3 μm.
5% by volume of α-silicon nitride particles of m was added, and alumina balls were used for 15 minutes in ethanol by a ball mill.
The mixed powder, which was wet-mixed for an hour, sufficiently dried, and further dry-mixed for 11 hours, was used as a raw material powder for the matrix. A graphite die in which a sheet of inorganic fibers B obtained by opening the bundle of inorganic fibers B obtained in Reference Example 2 by blowing it into air and the matrix raw material powder are coated with boron nitride as a release agent. The layers were alternately laminated inside and hot-pressed at a temperature of 1000 ° C. and a pressure of 50 MPa in an argon gas atmosphere to obtain a temporary sintered body. After applying boron nitride as a release agent to this temporary sintered body, it is vacuum-sealed in a glass capsule and hot isostatically pressed at 140 MPa to obtain S.
An inorganic fiber reinforced ceramics composite material having a matrix of i ₃ N ₄ grains / Al ₂ O ₃ nanocomposite material was obtained. The ratio of the inorganic fibers B in the composite material was 60% by volume. The flexural strength of this composite material was 1.89 GPa at room temperature and 1.52 GPa at 1300 ° C. Fracture toughness value (K _1C ) of composite material measured by chevron notch method is 22.5MP
It was a · m ^1/2 .

Example 3 The inorganic fiber B obtained in Reference Example 2 was cut into a chopped fiber having a length of 1 to 2 mm. The chopped fibers were dispersed in ethanol using ultrasonic waves and an omni mixer together. After the slurry of the matrix raw material prepared in Example 1 was added to the dispersion liquid, it was wet-mixed for 4 hours in ethanol by a ball mill using nylon balls. From this mixed slurry, a thin plate prepreg sheet having a thickness of 1 mm in which chopped fibers were uniformly dispersed was prepared by a filtration method. After cutting this prepreg sheet into a desired shape, it is laminated in a graphite die coated with boron nitride as a release agent,
In argon gas atmosphere, temperature of 1400 ° C, 75 MPa
By hot pressing at pressure of SiC grain / Al
An inorganic fiber reinforced ceramic composite material having a ₂ O ₃ nano composite material as a matrix was obtained. The ratio of the inorganic fibers B in the composite material was 30% by volume. The flexural strength of this composite material was 1.5 GPa at room temperature and 1.35 GPa at 1300 ° C. The fracture toughness value (K _1C ) of the composite material measured by the chevron notch method was 9.5 MPa · m ^1/2 .

Example 4 The SiC particles / MgO nanocomposite material obtained in Reference Example 4 was crushed for 30 hours in a mixed solvent of ethanol and distilled water by a ball mill using a silicon nitride ball and a silicon nitride pot to prepare a nano-sized nanoparticle. A slurry of composite material was prepared. After adding 8% by weight of polyethylene oxide as a binder to this slurry with respect to the nanocomposite material, wet mixing was performed for 12 hours using silicon nitride balls to obtain a matrix raw material slurry. In the same manner as in Example 1, the inorganic fiber A was opened, the matrix raw material was attached to the inorganic fiber A, wound, and dried to prepare a prepreg sheet. This prepreg sheet was cut into a desired shape, laminated, and then degreased. After applying boron nitride as a release agent to this laminated body and vacuum-sealing it in a glass capsule, in argon gas at a temperature of 1700 ° C. and 140 M
Perform hot isostatic pressing at a pressure of Pa to obtain SiC grains / M
A fiber-reinforced ceramic composite material having a gO nanocomposite material as a matrix was obtained. The ratio of the inorganic fibers A in this composite material was 40% by volume. The bending strength of this composite material was 1.2 GPa at room temperature and 1.28 GPa at 1300 ° C. The fracture toughness value (K _1C ) of the composite material measured by the chevron notch method was 18.5 MPa · m ^1/2 .

[0022]

[Brief description of drawings]

FIG. 1 is a model of intragranular nanocomposite.

FIG. 2 is a model of a grain boundary nanocomposite material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhiko Sato 5 Ogushi, Ube City, Yamaguchi Prefecture, 1978, No. 5 1978, Ube Industries, Ltd., Inorganic Materials Laboratory (72) Inventor, Makoto Tamura 5 1978, Ogushi, Ube, Yamaguchi Prefecture, Ube Kosan Inorganic Materials Research Center

Claims (1)

[Claims] 1. A silicon nitride-based inorganic fiber reinforced ceramics composite material comprising a silicon nitride-based inorganic fiber as a reinforcing material and an oxide-based nanocomposite material which is nanocomposited with carbide particles and / or nitride particles as a matrix.