JP3001126B2 - Silicon nitride based inorganic fiber reinforced ceramic composite - Google Patents

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, or a member of an internal combustion engine such as a piston head, an auxiliary combustion chamber, or a valve. Can be suitably used.

[0002]

2. Description of the Related Art Oxide ceramics such as aluminum oxide have excellent heat resistance, but their use as engineering ceramics has 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.

[0003] For example, "Pro.23rd.Autom"
ot. Technol. Dev. Contract C
oord. Meet. 1986 "has 20
By compounding volume% silicon carbide whisker,
The bending strength is increased from about 300 MPa to about 700 MPa, and the critical stress intensity factor (K _1C ) which is a measure of fracture toughness
Is from 4.5 MPa · m ^1/2 to about 8.5 MPa · m
It is disclosed that it is improved by ^half . However, when the whisker reinforced alumina composite material exceeds 1000 ° C., the bending strength is sharply reduced. The “Investigation of New Materials for Aircraft” published by the Japan Aerospace Industry Association in March 1998, page 193, shows that materials for rotors of gas turbines, etc., have a temperature in the range of 1250 ° C to 1450 ° C. It is described that the bending strength needs to be 450 MPa or more. The whisker reinforced alumina composite material cannot satisfy the characteristics required for the gas turbine member.

[0004] A method of improving the strength or heat resistance of oxide ceramics by nanocompositing is also known.
For example, in “Powder and Powder Alloy”, Vol. 37, p. 348 (1990), a ceramic nanocomposite made by adding 5% by volume of silicon carbide ultrafine particles to aluminum oxide has a heat resistance temperature of 1200 ° C. and a bending temperature of 1200 ° C. Strength about 155
It is disclosed that it exhibits an excellent property of 0 MPa. However, the K _{1C of} this composite material is about 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]

SUMMARY OF THE INVENTION An object of the present invention is to exhibit excellent strength and high fracture toughness from room temperature to high temperature, which can be suitably used for various heat engines including automobile engines. An object of the present invention is to provide a ceramic composite material. An object of the present invention is to provide a silicon nitride-based inorganic fiber reinforced ceramic composite material comprising a silicon nitride-based inorganic fiber as a reinforcing material and an oxide-based nanocomposite nanocomposited with carbide particles and / or nitride particles as a matrix. Achieved by

Specific examples of the silicon nitride-based inorganic fibers in the present invention include (1) an amorphous substance comprising silicon and nitrogen, or silicon, nitrogen and oxygen, or (2) fine particles of crystalline Si ₃ N ₄ and / or Or, crystalline Si ₂ N ₂ O fine particles, in some cases, an aggregate of the crystalline fine particles and amorphous SiO ₂ , (3) a mixture of the amorphous substance of (1) and the aggregate of (2) And inorganic fibers composed of The ratio of the constituent elements in this inorganic fiber is
Generally, Si: 40 to 65% by weight, N: 10 to 40% by weight, and O: 0 to 40% by weight. The inorganic fibers are described in, for example, JP-A-63-235526 and JP-A-61-129.
No. 15, JP-A-61-225012.

The form of the silicon nitride-based inorganic fiber is not particularly limited, and may be plain weave, satin weave, multiaxial weave, three-dimensional weave, or nonwoven fabric knitted from chopped fibers or continuous fibers. It may be a sheet-like material in which fibers are aligned in one direction.

[0008] In the present invention, the oxide-based nanocomposite serving as a matrix is characterized in that at least one kind of dispersed particles of carbide particles and nitride particles is composed of oxide ceramic and intragranular nanocomposite, grain boundary nanocomposite or intragranular. And ceramics composed of both nanocomposite structures of grain boundaries.
The intragranular nanocomposite structure is, for example, a structure obtained by dispersing nano-order dispersed particles in a matrix particle of an oxide ceramic and compounding the matrix particle itself as shown in a model in FIG. On the other hand, the grain-boundary nanocomposite structure
For example, as shown in the model shown in FIG. 2, the composite structure is obtained by dispersing nano-order dispersed particles in a matrix boundary of an oxide ceramic and dispersing them. Such an oxide-based nanocomposite is
For example, it can be prepared according to the method described in “Academic Transactions of the Ceramic Society of Japan”, Vol. 99, pages 947 to 982 (1991).

[0009] Specific examples of the oxide-based ceramics serving as a matrix in the oxide-based nanocomposite include aluminum,
Magnesium, silicon, yttrium, indium, uranium, calcium, scandium, tantalum, niobium,
Neodymium, lanthanum, ruthenium, rhodium, beryllium, titanium, tin, strontium, barium, zinc,
Examples include oxides of elements such as zirconium and iron, and composite oxides of these metals. The particle size of these oxide ceramics is generally 0.05 to 1000 μm.
It is.

[0010] Specific examples of the nitride to be dispersed particles include:
Examples include nitrides of elements such as silicon, boron, aluminum, magnesium, titanium, and molybdenum, and composite nitrides of these elements, or 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 are no particular restrictions on the shape of the dispersed particles in the oxide-based nanocomposite, such as spherical, polyhedral, plate,
Any of a needle shape may be used. The size of the dispersed particles is generally 1 to 100 in the case of spherical or polyhedral.
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 between 1 and 50% by volume relative to the composite.

The silicon nitride-based inorganic fiber-reinforced ceramic composite material of the present invention can be prepared by blending a silicon nitride-based inorganic fiber and an oxide-based nanocomposite in accordance with a method known per se and sintering. . If the silicon nitride-based inorganic fibers are chopped, a mixture of chopped fibers and oxide-based nanocomposite powder is prepared. When the silicon nitride-based inorganic fiber is a long fiber, a woven fabric, a nonwoven fabric or a sheet-like material, a laminate is prepared by alternately laminating a layer composed of these and a layer composed of powder of an oxide-based nanocomposite. I do. Then, the above-mentioned mixture or laminate is heat-sintered after or simultaneously with molding into a desired shape, whereby the silicon nitride-based inorganic fiber reinforced ceramic composite material of the present invention can be obtained. The proportion of the silicon nitride-based inorganic fibers in the composite material is usually from 1 to 70% by volume.

As a method for forming the above-mentioned mixture or laminate, a method known per se, for example, a die pressing method, a rubber pressing method, an extrusion method, and 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 a binder at the time of molding.
There is 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 press method or a hot isostatic press method in which molding and sintering are performed simultaneously. Can be adopted. The heating sintering temperature is usually 400 to 2100 ° C. If the heat sintering temperature is too low, the oxide nanocomposite as the matrix will not be sufficiently sintered, and if the temperature is too high, decomposition of the silicon nitride-based inorganic fibers will occur.

As another method for preparing the silicon nitride-based inorganic fiber reinforced ceramic composite material of the present invention, instead of using the oxide-based nanocomposite powder itself as the matrix raw material powder, a raw material for the oxide-based nanocomposite material is used. The same method as described above can be adopted except that a mixed powder obtained by mixing an oxide ceramic powder and carbide particles and / or nitride particles by a known method is used. In this case, during the forming and sintering processes, 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. Prepared.

[0014]

Examples of the present invention will be described below. Reference Example 1 Polydimethylsilane synthesized by dechlorination-condensation of dimethyldichlorosilane with sodium metal was put into a reaction vessel equipped with a reflux condenser, and the inside of the vessel was heated to 450 ° C. while stirring under a nitrogen stream. Gradually heated to 15
Hold for hours. After cooling, the reaction product was taken out as a xylene solution, filtered and then xylene was evaporated to obtain polycarbosilane having a number average molecular weight of about 2,000. After the polycarbosilane was melt-spun, the spun fiber was irradiated with 10 MGy of electron beam in 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 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 is based on a single fiber test method).

Reference Example 2 The polycarbosilane obtained in Reference Example 1 was melt spun, and the spun fiber was heated at 160 ° C. in oxygen gas to make it infusible, and then the infusible fiber was fired at 1300 ° C. in ammonia gas. Thus, a silicon nitride-based inorganic fiber was obtained. Hereinafter, this inorganic fiber is referred to as 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 190 GPa (measurement was performed by a single fiber test method).

Reference Example 3 0.3 μm average particle diameter was applied to γ-alumina having an average particle diameter of 0.5 μm.
m of β-silicon carbide particles were added at 5% by volume, and a
Wet mixed for hours. Thereafter, the mixture was dried, and the powder subjected to dry mixing for further 12 hours was placed 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 (SiC particles / Al ₂ O ₃ nanocomposite) 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 diameter of 0.1 μm was added to magnesia having an average particle diameter of 0.3 μm.
The following silicon carbide particles were added in an amount of 10% by volume, and 24
After wet mixing for hours, the mixture was dried. The mixed powder was placed in a nitrogen gas atmosphere at a pressure of 28 MPa,
Magnesia-based nanocomposite (Si) hot-pressed in a graphite die at a temperature of 1900 ° C and reinforced with silicon carbide particles
C particles / MgO nanocomposite). The bending strength of this nanocomposite at room temperature is 700 MPa, and K _1C is 4 MPa · m.
^The maximum operating temperature was 1/2300.

Example 1 The nanocomposite of the SiC particles / Al ₂ O ₃ nanocomposite obtained in Reference Example 3 was ground in a ball mill for 30 hours in distilled water using a silicon nitride ball and a silicon nitride pot. A slurry of the material was obtained. Polyethylene oxide as a binder is added to the nanocomposite as a binder in the slurry.
% By weight, and then 12% using a silicon nitride ball.
The mixture was wet-mixed for hours to obtain a slurry of the matrix material.
After the bundle of the inorganic fibers A obtained in Reference Example 1 was opened by blowing air, it was immersed in the above-mentioned slurry of the matrix material, and a matrix powder was attached around each inorganic fiber A. The bundle of the inorganic fibers A to which the matrix powder was adhered was wound around a square drum, and then sufficiently dried to produce a prepreg sheet. After the prepreg sheet is cut into a desired shape, the prepreg sheet is laminated on a graphite die coated with boron nitride as a release agent, and is placed in an argon gas atmosphere.
By hot pressing at a temperature of 550 ° C. and a pressure of 60 MPa, an inorganic fiber reinforced ceramic composite material having a matrix of SiC particles / Al ₂ O ₃ nanocomposite was obtained. The ratio of the inorganic fibers A in the composite material was 45% by volume. The flexural strength of this composite material was 1.62 GPa and 1300 at room temperature.
It was 1.49 GPa at ° C. The fracture toughness value (K _1C ) of the composite material measured by the chevron notch method was 18.5.
MPa · m ^1/2 .

Example 2 γ-alumina having an average particle diameter of 0.4 μm was added to an average particle diameter of 0.3 μm.
m-α-silicon nitride particles in an amount of 5% by volume.
After wet-mixing for hours, the mixture was sufficiently dried, and dry-mixed for 11 hours to obtain a mixed powder, which was used as a raw material powder for the matrix. A graphite die in which a sheet of the inorganic fibers B obtained by blowing the bundle of the inorganic fibers B obtained in Reference Example 2 by blowing the air and the above-mentioned matrix raw material powder and boron nitride as a release agent is coated is used. The layers were alternately laminated, and hot-pressed in an argon gas atmosphere at a temperature of 1000 ° C. and a pressure of 50 MPa to obtain a temporarily sintered body. After applying boron nitride as a mold release agent to this pre-sintered body, it is vacuum-sealed in a glass capsule, and hot isostatically pressed at 140 MPa to obtain S
An inorganic fiber reinforced ceramic composite material using i ₃ N ₄ particles / Al ₂ O ₃ nanocomposite as a matrix was obtained. The ratio of the inorganic fibers B in the composite material was 60% by volume. The bending strength of this composite material was 1.89 GPa at room temperature and 1.52 GPa at 1300 ° C. The fracture toughness value (K _1C ) of the composite material measured by the chevron notch method is 22.5MP.
a · m ^1/2 .

Example 3 The inorganic fiber B obtained in Reference Example 2 was cut into a length of 1 to 2 mm into a chopped fiber. The chopped fibers were dispersed in ethanol by using ultrasonic waves and an omni mixer. After the slurry of the matrix material prepared in Example 1 was added to the dispersion, the mixture was wet-mixed for 4 hours in ethanol by a ball mill using nylon balls. From this mixed slurry, a thin 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,
1400 ° C, 75MPa in argon gas atmosphere
Hot pressing at a pressure of SiC grains / Al
An inorganic fiber reinforced ceramic composite material using a ₂ O ₃ nanocomposite as a matrix was obtained. The ratio of the inorganic fibers B in the composite material was 30% by volume. The bending 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 obtained in Reference Example 4 was ground using a ball mill in a mixed solvent of ethanol and distilled water for 30 hours using a silicon nitride ball and a silicon nitride pot. A composite slurry was prepared. After adding 8% by weight of polyethylene oxide as a binder to the nanocomposite material, the slurry was wet-mixed using silicon nitride balls for 12 hours to obtain a matrix material slurry. In the same manner as in Example 1, the prepreg sheet was prepared by opening the inorganic fiber A, adhering the matrix material to the inorganic fiber A, winding and drying. This prepreg sheet was cut into a desired shape, laminated, and then degreased. This laminate is coated with boron nitride as a mold release agent and vacuum-encapsulated in a glass capsule.
Perform hot isostatic pressing at a pressure of Pa to obtain SiC particles / M
A fiber-reinforced ceramic composite material using the gO nanocomposite material as a matrix was obtained. The ratio of the inorganic fibers A in the 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 the drawings]

FIG. 1 is a model of an intragranular nanocomposite.

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

──────────────────────────────────────────────────続 き Continued from the front page Examiner Yuki Yamada (56) References JP-A-5-58751 (JP, A) JP-A-6-87657 (JP, A) JP-A-6-92745 (JP, A) JP-A-6-87670 (JP, A) JP-A-6-87671 (JP, A) JP-A-6-92737 (JP, A) JP-A-6-107468 (JP, A) JP-A-7-149577 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/80

Claims (1)

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