JPH01230475A - High-strength ceramic composite material and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject article having improved strength at normal temperature and reduced lowering of the strength at high temperature, by mixing or laminating inorganic fiber composed of a specific amorphous substance, a solid solution, etc., with powder produced by pulverizing said fiber and sintering the mixture or laminate under specific condition. CONSTITUTION:An inorganic fiber composed of an amorphous substance consisting of Si, C and O, agglomerate of crystalline fine particles of beta-SiC having particle diameter of <=500Angstrom and amorphous SiO2 or a mixture of said amorphous substance and agglomerate is prepared beforehand. The fiber and powder of the fiber are mixed or laminated with each other and the mixture, etc., is formed. The formed article is sintered at 1700-2200 deg.C in an atmosphere of e.g., an inert gas. The composite ceramic material produced by this process has high strength and is composed of uniformly dispersed flaky, granular or acicular SiC crystals and agglomerate of ultrafine SiC crystal particles.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-strength ceramic composite material and a method for producing the same.
Mainly used for internal combustion engine parts, such as piston rings,
It is used for sub-combustion chambers and parts of rocket engines, such as nose cones and nozzles.

[Prior art and problems to be solved by the invention] Conventionally, ceramics with excellent heat resistance include, for example, Al2
Oxide systems such as O3, B4C, MgO, ZrO2, SiO□, SiC, TiC, WC.

Carbide type such as B, C, S L 3 N4, B N-A
Nitride ceramics such as IN, boride ceramics such as TiBz and ZrBz, and silicide ceramics such as MoSi2, WSiz and CrSi2 are known. These ceramic molded bodies have been manufactured at extremely high temperatures;
Recently, sintering aids have been actively investigated with the aim of lowering the sintering temperature and sintering pressure. The sintering aid improves the sinterability of the ceramic inx, suppresses grain growth in the sintered body, prevents pores from remaining between the grains, and fills the grain boundaries with high density. It also has the role of

Examples of additives conventionally used as sintering aids include MgO, Nip, Cab, TiO□, and AI!
, 20. , Y2O3, B4C, B, C, etc., the reason why these additives are selected is because of the reciprocal force between the base ceramic and the additive so as to assist in the sintering of ceramics with poor self-sintering properties. This is because sintering progresses more easily because the additive becomes plasticized and becomes a liquid phase at high temperatures. Also, B and C are SiC
It has the role of lowering the surface energy of particles and improving sinterability.

However, when a sintering aid is present as mentioned above,
It is thought that the second and third phases appear due to the reaction between the base ceramic and the auxiliary agent, and these exist mainly at the grain boundaries, and when the temperature rises, they are likely to be plastically deformed from these grain boundary constituents. In many cases, high-temperature strength cannot be obtained. For example, S
When Mgo is added to i3N4, 51
High density is achieved by forming a glassy phase of MgO3 that fills the grain boundaries, but the mechanical strength of this sintered body at high temperatures decreases by 1, due to the softening of the glassy phase.
At around 0.000"C, the strength deteriorates dramatically. In order to prevent this kind of decline in high-temperature strength, it is best to choose an auxiliary agent that does not become vitrified, but such auxiliary agents are generally The solidity is low and it is not possible to obtain a satisfactory molded product.

As a method to eliminate the above-mentioned disadvantages, an organic silicon polymer whose main skeleton components are silicon and carbon is used as a binder for ceramic powder, and a mixture of the two is heated and sintered to increase its strength at high temperatures. A method of manufacturing a ceramic sintered body with less deterioration has been proposed.

For example, Japanese Patent Publication No. 5B-44630 discloses that a mixture of silicon carbide powder and the above organosilicon polymer is heated and sintered, and the resulting sintered body is further impregnated with an organosilicon polymer and heat treated. A method of manufacturing sintered silicon carbide compacts is described. Also, in Japanese Patent Publication No. 60-54906,
Polycarbosilane containing some siloxane bonds obtained by heating and polymerizing polysilane in the presence of polyporosiloxane is mixed with ceramic powder, and the mixture is heated and sintered after or at the same time as molding. A method of making a body is disclosed.

The organosilicon polymer used as a binder for ceramic powder in the method described in the above publication is converted into an inorganic substance when the mixture is heated and sintered, and since this inorganic substance has a high melting point, the resulting sintered material is The compact has relatively high strength even at high temperatures. The reason for this is that the sintered body obtained by the above method is produced by thermal decomposition of silicon carbide particles and an organosilicon polymer, as described in Japanese Patent Publication No. 58-44630, column 11, lines 20 to 42. S to generate
This is because it consists of a grain boundary phase mainly composed of tC.

Looking at the strength of the sintered bodies obtained by the methods described in these publications, for example, in Example 1 of Japanese Patent Publication No. 5B-44630, the bending strength of the sintered bodies finally obtained is 1.
900kg10ff (19kg/anal 2), and in Example 1 of Japanese Patent Publication No. 60-54906, the bending strength (bending strength) is 12.1kg/CI (12.1kg/CI).
A sintered molded body was obtained (which seems to be a misprint of mm2).

In recent years, engineering ceramics have come to be required to have higher functionality, and for example, there is a demand for sintered bodies that have high strength and have extremely low strength loss at high temperatures.

Therefore, the object of the present invention is to have high mechanical strength at room temperature,
Another object of the present invention is to provide a ceramic composite material whose strength decreases extremely little even at high temperatures, and a method for producing the same.

[Means to solve the problem]

The present invention achieves the above object by providing a high-strength ceramic composite material in which flaky, lump-like, or needle-like SiC crystals and ultrafine SiC crystal aggregates are uniformly dispersed.

Furthermore, the present invention provides the following manufacturing method as a preferred method for manufacturing the high-strength ceramic composite material of the present invention.

Mixing an inorganic fiber made of any of the inorganic substances listed in (i), (ii) or (iii) below and a powder obtained by pulverizing the inorganic fiber or a powder obtained by pulverizing a sintered body having the same composition as the inorganic fiber. or laminated, and this mixture or laminate is molded into a predetermined shape, and at the same time or after the molding, in a vacuum, at least one gas selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas is used. Uniformly dispersed flake-like, lump-like, or needle-like SiC crystals and ultrafine particle SiC crystal aggregates are characterized by heating and sintering in an atmosphere at a temperature range of 1.700 to 2,200"C. A method for manufacturing ceramic composite materials.

(i) Amorphous consisting essentially of Si, C and 0 (ii) Aggregate consisting of crystalline ultrafine particles consisting essentially of β-SiC with a grain size of 500 Å or less and amorphous Sin ( iii) Mixed system of the amorphous material (i) above and the aggregate (ii) above First, the ceramic composite material of the present invention will be explained.

The ceramic composite material of the present invention is composed of flaky, lump-like or needle-like SiC crystals and ultrafine SiC crystal aggregates. Here, flake-like preferably means a scale-like shape with a length of 1 to 20 μm, and lump-like preferably means a lump of grains grown in a three-dimensional direction with a side length of 1 to 20 μm; Acicular shape preferably has a length of 1 to 20 μm
This means a shape with a length to thickness ratio of 1.5 to 20. The size of the SiC particles constituting the ultrafine particle aggregate is usually 500 Å or less.

The ceramic composite material of the present invention preferably contains 40% by weight or more of flake-like, lump-like, or needle-like SiC crystals. If the SiC crystals are too small, the strength of the composite material will decrease. Further, there is no particular restriction on the upper limit of the SiC crystal, but it is usually 95% by weight.

Next, a method for manufacturing the ceramic composite material of the present invention will be explained.

The above (i), (ii) or (iii) used as a raw material in the method for producing a ceramic composite material of the present invention.
) The inorganic fiber containing silicon, carbon and oxygen made of any of the inorganic substances has a thick self-crystallinity (1.700 to 2,200 without adding a sintering aid).
A good sintered body can be obtained by processing at a temperature of 'C. Note that if crystalline ultrafine particles that are a constituent of the inorganic substance (ii) have a particle size of more than 500 Å, the strength of the resulting composite material will decrease.

Inorganic fibers are made by melt-spinning polycarbosilane produced by the method described in, for example, JP-A-51-126300, JP-A-51-139929, etc., and making it infusible by heat treatment in air. 800~ in active gas
1, obtained by firing at 500"C.

There are no particular restrictions on the form in which inorganic fibers are used, and they may be used as continuous fibers or chopped short fibers obtained by cutting continuous fibers, or as plain woven fabrics, three-dimensional woven fabrics, or non-woven fabrics woven from continuous fibers. It may also be used as a sheet-like material drawn in one direction.

As the powder to be mixed or laminated with the inorganic fiber in the production method of the present invention, a powder obtained by pulverizing the inorganic fiber or a powder obtained by pulverizing a sintered body having the same composition as the inorganic fiber is used. The particle size of the powder is generally between 1 and 50 um.

There is no particular restriction on the ratio of the inorganic fibers to the powder, and the inorganic fibers are usually used in an amount of 10 to 70% by weight based on the total amount of the inorganic fibers and powder.

It is preferable that the inorganic fiber and powder are mixed uniformly.

When the inorganic fiber is a chopped material, the chopped material and the powder can be mixed using a mixer known per se, and the inorganic fiber is a long fiber, a woven fabric, a nonwoven fabric, or a sheet-like material. In this case, a laminate in which inorganic fiber layers and powder layers are alternately laminated can be used.

Next, the ceramic composite material of the present invention can be obtained by heating and sintering the mixture or laminate described in "2" after molding it into a desired shape or simultaneously with the molding.

As the sintering method, a method in which the mixture or laminate is primarily formed and then sintered under pressure, normal pressure, or reduced pressure, or a hot press method in which forming and sintering are performed simultaneously can be used.

In the above-mentioned method in which the next forming and sintering are performed separately, the second forming is performed using a mold press method, a rubber press method, an extrusion method, or a sheet method at a rate of 100 to 5,000 kg/c+f.
It is possible to obtain a product in a predetermined shape (for example, sheet-like, rod-like, spherical, etc.) by applying a pressure of 1 liter. In the above molding, polycarbosilane, which is a raw material for inorganic fibers, or a commercially available organic polymer may be used as a binder, if necessary.

Next, the ceramic composite material of the present invention can be obtained by sintering the molded body.

In addition, when sintering is performed by the hot press method, a press mold made of graphite is sprayed with BN as a mold release agent, and the mixture or laminate is pressed at a pressure of 2 to 2,000 kg/cJ. However, at the same time, it can be heated to form a sintered body.

The heating sintering temperature is 1,700 to 2,200°C, preferably 1,900 to 2,100°C. By heating to this temperature, SiC can be formed into flakes, lumps or needles.
A crystal is generated, and this SiC crystal becomes a matrix of S.
A high-strength ceramic composite material uniformly dispersed in the iC ultrafine particle aggregate is obtained. The heating sintering temperature is 1.70
If it is lower than 0, flake-like, lump-like, or needle-like SiC crystals will not be generated, and a high-strength composite material will not be obtained. Also,
When the heating sintering temperature is higher than 2.200℃, the generated Si
Decomposition of the C crystal or matrix begins to occur.

The heating and sintering is performed in a vacuum and in an atmosphere consisting of at least one selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas. Examples of inert gases include:
Examples of reducing gas include hydrogen gas, -carbon oxide gas, etc. Examples of hydrocarbon gas include methane gas, ethane gas, propane gas, butane gas, etc. .

The ceramic composite material of the present invention exhibits extremely high strength at room temperature compared to known ceramic composite materials, and has almost no decrease in strength even at high temperatures;
It has a fracture toughness value of about 2 to 1.5 times. Note that the oxygen and non-stoichiometric amount of carbon contained in the inorganic fibers are changed from 2C+Si○→S i O+C○ during the above sintering.
, 3C-1-3i02→SiC+2CO, and does not remain in the sintered body. This allows SiC
The surface energy of the particles is reduced, resulting in improved sinterability. Furthermore, in order to completely remove the glassy SiO2, a small amount of carbon may be added during the above molding.

Further, if necessary, after impregnating the sintered body with polycarbosilane, which is a raw material for inorganic fibers, in a vacuum, at least one gas selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas is used. 800-1 in an atmosphere
, 1.700-2.200 after preheating at 500℃
Sintering may be carried out at °C.

〔Example〕

The present invention will be explained below with reference to Examples.

(Reference example 1) 5! 2.51 g of anhydrous xylene and 400 g of thorium were placed in a three-ring flask, heated under a nitrogen gas stream to the boiling point of xylene, and dimethyldichlorosilane 11 was added dropwise over 1 hour. After the dropwise addition was completed, the mixture was heated under reflux for 10 hours to form a precipitate. This precipitate was filtered and washed first with methanol and then with water to obtain a white powder of polydimethylsilane 42.
Obtained 0g.

On the other hand, 759 g of diphenyldichlorosilane and 12 g of boric acid
4 g in n-butyl ether under nitrogen gas atmosphere, 10
The resulting white resinous material was heated at a temperature of 0 to 120° C. and further heated in vacuum at 400° C. for 1 hour to obtain 530 g of polyporodiphenylsiloxane.

Next, 8.27 g of the above polyborodiphenylsiloxane was added and mixed to 250 g of the above polydimethylsilane,
2 with reflux tube! in a quartz tube at 350°C under nitrogen flow.
and polymerized for 6 hours. After cooling at room temperature, add xylene and take out as a solution, evaporate xylene,
C. for 1 hour under a nitrogen stream to obtain polycarbosilane, which is a raw material for the inorganic continuous fiber used in the present invention.

(Example 1) After melt-spinning the polycarbosilane obtained in Reference Example 1, it was heated in air at a heating rate of 20°C/hr to 170"C to make it infusible, and then heated to 200°C in a nitrogen atmosphere. The mixture was heated to 1,000° C. at a heating rate of /hr, held for 1 hour, and then cooled to obtain inorganic continuous fibers.

The inorganic continuous fibers are alternately layered with powder of 200 mesh or less crushed in a mortar made of silicon nitride and plain woven fabrics made of the above-mentioned inorganic continuous fibers. ) under argon flow at 700 kg/cM, 2,0
The ceramic composite material of the present invention was obtained by hot pressing at 00°C for 0.5 hours.

The ratio of the plain woven fabric to the powder was 1:3.

The obtained ceramic composite material of the present invention has a bending strength of 7
6kg/mm2 (normal temperature), 73kg/mm2 (L, 4
QQ°C), and the density was 3.0 g/c+fl. Furthermore, the fracture toughness value was 1.4 times higher than that of a ceramic sintered body obtained only from powder without using plain weave.

(Example 2) After melt-spinning the polycarbosolane obtained in Reference Example 1, it was heated to 170°C at a heating rate of 20°C/hr in air to make it infusible, and then spun at 200°C/hr in a nitrogen atmosphere. The mixture was heated to 1,200°C at a heating rate of 1.2 hours, held for 1 hour, and then cooled to obtain inorganic continuous fibers.

This inorganic continuous fiber was ground in a mortar made of silicon nitride, powder of 200 mesh or less, and a plain fabric made of the above-mentioned inorganic continuous fiber were alternately laminated, and the laminate was cut into a carbon die (sheet shape of 3 mm x 10 mm x 10 bars). Set inside, under argon flow 600 kg/c+fl, 2
The ceramic composite material of the present invention was obtained by hot pressing at ,000°C for 0.5 hours.

The ratio of the handmade fabric to the powder was 1:3.

The obtained ceramic composite material of the present invention has a bending strength of 6
8kg/mm2 (room temperature), 63kg/mm2 (]; 4
00°C), and the density was 3.1 g/all. Furthermore, the fracture toughness value was 1.3 times higher than that of a ceramic sintered body obtained only from powder without using plain weave.

(Effects of the Invention) The ceramic composite material of the present invention has high mechanical strength at room temperature (and exhibits very little decrease in strength even at high temperatures. According to the manufacturing method of the present invention, the ceramic composite material described above Can be manufactured industrially.

Patent applicant: Ube Industries Co., Ltd.

Claims (7)

[Claims] (1) A high-strength ceramic composite material in which flaky, lumpy, or acicular SiC crystals and ultrafine SiC crystal aggregates are uniformly dispersed. (2) The ceramic composite material according to claim (1), which does not contain a non-stoichiometric amount of free carbon and/or amorphous SiO_2 relative to silicon atoms. (3) Inorganic fibers made of the inorganic substance of any of the following (i), (ii), or (iii) and powder obtained by pulverizing the inorganic fibers or powder obtained by pulverizing a sintered body having the same composition as the inorganic fibers. This mixture or laminate is molded into a predetermined shape, and at least one gas selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas is mixed or laminated in a vacuum at the same time or after the molding. Uniform flake-like, lump-like, or needle-like SiC crystals and ultrafine particle SiC crystal aggregates are produced by heating and sintering in an atmosphere consisting of seeds at a temperature range of 1,700 to 2,200°C. A method for producing ceramic composite materials dispersed in. (i) Amorphous consisting essentially of Si, C and O (ii) Aggregate consisting of crystalline ultrafine particles consisting essentially of β-SiC with a grain size of 500 Å or less and amorphous SiO_2 (iii) ) A mixed system of the amorphous substance of (i) above and the aggregate of (ii) above. (4) The method for producing a ceramic composite material according to claim (3), wherein the fibers are chopped short fibers. (5) The method for producing a ceramic composite material according to claim (3), wherein the fibers are woven into a plain weave. (6) The method for producing a ceramic composite material according to claim (3), wherein the fibers are woven into a nonwoven fabric or a three-dimensional fabric. (7) Inorganic fibers having the same composition as the inorganic fibers of a nonwoven fabric and/or three-dimensional fabric made of inorganic fibers made of any of the inorganic substances listed in (i), (ii), or (iii) below. After being filled with fine powder obtained by crushing a substance, it is molded into a predetermined shape, and at the same time or after the molding, in a vacuum, it is made of at least one gas selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas. Flaky, lumpy or acicular S obtained by heating and sintering in an atmosphere at a temperature range of 1,700 to 2,200°C.
A high-strength ceramic composite material in which iC crystals and ultrafine SiC crystal aggregates are uniformly dispersed. (i) Amorphous consisting essentially of Si, C and O (ii) Aggregate consisting of crystalline ultrafine particles consisting essentially of β-SiC with a grain size of 500 Å or less and amorphous SiO_2 (iii) ) A mixed system of the amorphous substance of (i) above and the aggregate of (ii) above.