JP2003252694A - SiC-FIBER-COMPOSITED SiC COMPOSITE MATERIAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a strength decrease due to oxidation inside a SiC/SiC substrate; firstly by densifing only the surface of the SiC/SiC substrate containing voids and cracks in its inside; secondly by changing the composition of the SiC matrix near the surface into an Si-rich one to improve the oxidation resistance of the SiC matrix; thirdly by reducing the influence of the difference between the coefficient of thermal expansion of the SiC/SiC substrate and that of a metallic or ceramic covering layer for the prevention of oxidation to prevent voids or cracks from being formed in the cover layer. <P>SOLUTION: The SiC/SiC 10 is one prepared by forming an Si-rich carbon nitride layer 14 on the surface of an SiC/SiC substrate 12, forming a fibrous composite material layer 16 on the surface of the Si-rich carbon nitride layer 14, and forming an SiC covering layer 18 on the surface of the fibrous composite material layer 16. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to SiC (silicon carbide) as a main matrix and SiC as a main dispersoid.
The present invention relates to SiC / SiC having excellent oxidation resistance using fibers and a method for producing the same.

[0002]

2. Description of the Related Art Carbon fiber reinforced carbon composite materials (hereinafter referred to as "C /
It is abbreviated as "C". ), Which has a high covalent bond
Since all of the carbide-based composite materials such as C and Si ₃ N ₄ have a high decomposition temperature and a high high-temperature strength, they are applied as structural materials for equipment used at high temperatures.
In particular, SiC / SiC does not undergo a decrease in strength even at high temperatures up to 1300 ° C., has a damage tolerance that allows local damage even under unexpected overload conditions, and has a thermal shock resistance. Since SiC itself has a high emission reduction, it is expected to be used as a combustor for turbines, gas turbines, and turbine blades.

The present inventors have proposed, as a coating method for the surface of a material having excellent oxidation resistance, a coating method in which carbon fibers are compounded on the C / C surface (Japanese Patent Laid-Open No. 10-90722), and the like. It has been found that by compounding the fibers with the fibers, the progress of cracks in the film can be prevented by the fibers, and as a result, the oxidation resistance can be greatly improved. However, as will be described later in detail, the carbonaceous material to be put into practical use is difficult to densify, and in addition, a material having a high porosity is intentionally used in terms of manufacturing cost and thermal shock resistance. Many. It is very difficult to improve the oxidation resistance of such a material having a high porosity only by coating. Therefore, in addition to a simple method for smoothing the surface of a material, a method for forming an oxidation resistant film for protecting the surface has been required. However, it is difficult to impart the desired oxidation resistance to the target because it is easy to cause defects in the film due to the difference in the thermal and mechanical properties between the base material and the film, simply by smoothing the surface. is there. Therefore, it can be concluded that the oxidation-resistant coating method for the surface of the carbon material having high porosity requires a multilayer coating in which each layer has specialized functionality.

Now, a few mentions will be made of the method of producing SiC / SiC to clarify the extracted problems of these materials here. In order for SiC / SiC to have damage tolerance, it is necessary to improve toughness by accommodating a mechanism of bridging cracks without breaking SiC fibers at the same time even when cracks propagate in the SiC matrix. . To that end, it is important that the matrix pulls out of the fiber in the process of bridging the cracks. For example, in the research on the development of fail-safe type ultra-high temperature fiber reinforced ceramics, one of the original industrial technology research and development projects of 1996 by the New Energy and Industrial Technology Development Organization, in the study of SiC fiber coated with BN (boron nitride) Or by using a fiber having a surface layer rich in C and SiC formed by heat treatment during the production of SiC fiber as a SiC preform,
The interface mechanical properties between the SiC fiber and the SiC matrix were optimized.

However, even if the fibers thus devised are used, the polymer impregnation method (PI
Method P: Polymer Infiltration Pyrolysis)
When the matrix is formed, cracks and pores (voids) are generated in the SiC matrix due to the difference in thermal characteristics between the SiC fiber and the matrix. In addition, as the polymer in this case, an organosilicon compound such as polycarbosilane or polysilazane (hereinafter referred to as “PCS”) is used. The SiC matrix formed by mineralizing this polymer in the usual high temperature heat treatment step contains oxygen and nitrogen derived from the insolubilization step of PCS, and P
SiC deviated to carbon rich due to thermal decomposition process of CS
Since it has a composition, it is inferior in oxidation resistance to SiC having a stoichiometric composition.

The cracks and pores in SiC / SiC described above serve as diffusion paths for oxygen into SiC / SiC when SiC / SiC is heated at a high temperature for a long time.
Therefore, oxygen reacts with SiC to form SiO ₂ ,
The SiO ₂ reacts with BN to form borosilicate glass. This glass becomes a viscous substance at high temperature and protects the interface, which prevents oxygen from being supplied to the surface of the fiber and the matrix and prevents oxidation, but it becomes a brittle phase at room temperature, so cracks caused by breakage easily occur in the fiber. Propagate to. That is, the optimum interface structure between the fiber and the matrix necessary for improving the toughness of the material is lost by the oxidation. Deterioration due to this oxidation is caused by C on the SiC fiber surface without using BN.
Even when a surface layer rich in SiC and SiC is formed, SiO
Similar results occur because ₂ glass forms on the SiC fiber surface. In this case, although the diffusion rate of oxygen in the SiO ₂ glass is lower than that in the borosilicate glass, deterioration due to oxidation tends to be suppressed, but oxidation at the interface between the fiber and the matrix tends to occur when heating for a long time. Therefore, the optimum interface structure described above is lost.

As a method for forming a dense SiC matrix for preventing the oxidation of fibers, there is disclosed in Japanese Patent Laid-Open No. 8-2680.
The methods described in Japanese Patent Laid-Open No. 63-63, Japanese Patent Laid-Open No. 10-59780 and the like are proposed. All of these methods apply the reactive sintering method. The SiC fibers are bundled into a SiC fiber bundle, and the fiber bundle or the intermediate preform is coated with BN. A final preform is formed from the preform, and the final preform is impregnated with C powder, then impregnated with molten Si and subjected to reaction sintering to form a relatively dense matrix having SiC as a main phase. Is the way. However, for preforms in which fibers are coordinated in one or two directions, C
Although it is easy to impregnate powder or molten Si, it is difficult to impregnate them into preforms that are braided in orthogonal triaxial directions. Therefore, it is difficult to suppress the occurrence of voids and cracks in a preform made of such a multidimensional fabric. That is, in the case of SiC / SiC in which fibers are reinforced in multiple dimensions, it is difficult to suppress deterioration due to oxidation even if this method is applied.

As described above, regarding SiC / SiC, which is said to be stable against high temperature oxidation, it is limited to improve the oxidation resistance by densifying the matrix by improving the manufacturing method. There is. Therefore, in order to improve the oxidation resistance of such materials,
There is no choice but to rely on the coating of the material surface.

As a method for suppressing the oxidation of SiC / SiC, "International Clean Energy System Technology for Hydrogen Utilization (W
In the research and development of hydrogen combustion turbine, which is a subtask of "E-NET)", "Development of ultra-high temperature material", Al ₂ O ₃ having a small oxygen diffusion coefficient was used to perform CV on the SiC / SiC surface.
Al ₂ O ₃ using D method, plasma spraying method, and coating method
We are considering the formation of a film. In this result, ironically,
Porous SiC / Si containing pores or cracks
With the C base material, since it is not possible to obtain the effect of suppressing the high temperature oxidation of SiC by using any of the coatings, it is necessary to densify the SiC / SiC base material. It has been reported that the high temperature oxidation resistance is improved only when densified. In addition, when heated at 1300 ° C. or higher for a long time, Al ₂
It has also been reported that a reaction product of Al ₆ Si ₂ O ₁₃ is generated at the interface between the O ₃ film and SiC (fiscal 1997 result report NEDO-WE-NET 9785).

The application of SiC / SiC is a member having a complicated shape such as a cylindrical shape such as a combustor or a radiant tube. Therefore, it is not a practical method to densify these members by hot pressing. In addition, Al ₂ O ₃ and S
Since the difference in the coefficient of thermal expansion from iC is large, the Al ₂ O ₃ film will peel if it is thickened. On the other hand, in order to prevent peeling, A
When the porosity of the l ₂ O ₃ coating is increased, SiO ₂ generated by the oxidation of SiC at the interface between the Al ₂ O ₃ coating and the SiC / SiC substrate reacts with Al ₂ O ₃ ,
As a result, an aluminosilicate-based reaction product having a low melting point and a high oxygen diffusion rate is produced.

A method for improving the oxidation resistance of composite materials other than SiC / SiC will be examined. For example, in Japanese Patent Laid-Open No. 6-116069, ceramic fibers (SiC or Si-Ti) are formed on the surface of C / C. -CO) is arranged, the ceramic fiber layer is fixed using carbon fibers or ceramic fibers, impregnated with petroleum-based pitch or phenol resin, and baked to form a film in which the fibers are made into a composite material. A method has been proposed. Furthermore, the above-mentioned invention by the present inventors (Japanese Patent Laid-Open No. 10-90722)
Then, the particle size is 1μ with respect to the carbon fiber arranged on the surface of the base material.
There has been proposed a method of forming a film in which fibers are composited by impregnating a refractory material of m or less. However, when a composite layer composed of long fibers is formed on the surface of the base material, it is very difficult to densify it so that gas can be blocked, as described in the problem of manufacturing SiC / SiC. Have difficulty. Therefore, it has been difficult to impart sufficient oxidation resistance to these fiber composite coatings. Also,
It has been difficult to impart sufficient oxidation resistance to a material having a high porosity because a single coating alone tends to cause defects in the coating due to the difference in thermal characteristics between the base material and the coating.

[0012]

[Problems to be Solved by the Invention] SiC / Si having a complicated shape is formed by using a preform knitted in three orthogonal directions.
In the method of manufacturing C, SiC is used inside the preform.
The conventional PIP method is the most suitable method for forming the matrix. However, in order to densify the matrix in order to improve the oxidation resistance, it is necessary to repeat the steps of impregnation and firing, which requires a very long time and cost. Further, as described above, the matrix SiC formed of a polymer has a chemical composition that is carbon-rich within a normal firing temperature range, so that the vapor pressure increases and the surface oxide film is easily broken. Therefore, the desired performance for oxidation resistance cannot be obtained with matrix SiC by PIP.

On the other hand, in practical use, SiC / S having a high density is used.
iC is not always necessary, and low density SiC / SiC produced by the PIP method having pores and cracks is often preferable in terms of thermal shock resistance and cost. Therefore, SiC / Si formed with a SiC matrix having a carbon-rich composition while having pores and cracks therein
It is necessary to form an effective oxidation resistant film also on the C surface.

[0014]

Therefore, the object of the present invention is to first densify only the surface of the SiC / SiC substrate having pores and cracks therein, and secondly to change the composition of the SiC matrix near the surface to a Si-rich composition. To improve the oxidation resistance of the SiC matrix, and thirdly to suppress the influence of the difference in the coefficient of thermal expansion between the SiC / SiC base material and the coating layer made of metal or ceramics for preventing oxidation, It is intended to prevent generation of pores and cracks in the coating layer, and as a result, to provide SiC / SiC capable of preventing strength reduction due to oxidation inside the SiC / SiC substrate.

[0015]

Means for Solving the Problems SiC / S according to the present invention
iC is SiC / SiC in which a coating layer made of metal or ceramics is formed on the surface of the SiC / SiC substrate, and SiC is formed between the SiC / SiC substrate surface and the coating layer.
An intermediate layer is formed which fills pores on the surface of the / SiC base material and smoothes it, and absorbs thermal stress generated between the SiC / SiC base material and the coating layer. 1). For example, the intermediate layer is composed of two layers, a metal-rich carbon / nitride layer on the SiC / SiC substrate side and a fiber composite material layer on the coating layer side (claim 2). Here, the metal-rich carbon / nitride layer is a compound of a metal and at least one of carbon and nitrogen, and has a metal composition ratio higher than the stoichiometric composition ratio.

In a porous SiC / SiC base material, the surface thereof is covered with a dense metal-rich carbon / nitride layer, and the upper portion thereof is covered with a fiber composite material layer. Therefore, the thermal stress due to the difference in thermal expansion coefficient generated between the SiC / SiC base material and the coating layer is absorbed by these intermediate layers. Therefore, in the coating layer, generation of cracks due to thermal stress is suppressed.

As the SiC / SiC base material, for example, 10
A three-dimensionally reinforced SiC fiber bundle of 00 is desirable. As the metal-rich carbon / nitride layer for filling and smoothing the pores on the surface of the SiC / SiC base material, Si powder and an organic compound having a polyacetal structure are used, and the Si powder and the carbon-rich SiC of the SiC / SiC base material are used. Si-rich SiC or Si using chemical reaction with matrix
It is desirable that a ₃ N ₄ surface layer is formed. Metal rich carbon / nitride layer means MC, MN, MC, where M is the metal.
A substance represented by a chemical formula such as N and having a ratio of M larger than its stoichiometric composition ratio. Examples of the coating layer, SiC, _Si 3 _{N 4,} ceramics such as mullite, Mo-Si, Re-Ir , Ir-Al, Ta-Al
A two-layer structure such as or an intermetallic compound of both is desirable.

According to a third aspect of the present invention, in the SiC / SiC according to the second aspect, the fiber composite layer comprises a carbide fiber and a matrix of at least one of carbide and metal. As the carbide fiber, carbon fiber or SiC fiber having excellent high-temperature strength characteristics or carbon fiber in the manufacturing process is used.
It is desirable that the iC fibers are converted. The matrix is
It can be easily obtained by reaction sintering of metal powder and a part of solid content in carbon fiber or binder.

According to a fourth aspect of the present invention, in the SiC / SiC according to the third aspect, the melting point or decomposition point of each of the carbide fiber and the matrix is 1600 ° C. or higher. In this case, the SiC / S at a higher temperature than that by the current technology for forming the borosilicate glass described above.
iC can be used for many purposes.

The SiC / SiC according to claim 5 is the SiC / SiC according to any one of claims 2 to 4,
The fiber composite material layer is formed by a reaction sintering method using carbon fibers having a length of 3 mm or less and metal powder as raw materials. In this case, a denser film with better dimensional accuracy can be easily obtained as compared with the case where long fibers are arranged. The fiber composite material layer of these carbides has excellent heat resistance.

The SiC / SiC according to claim 6 is
In the SiC / SiC according to any one of 3 to 5,
The difference in thermal expansion coefficient between the fiber composite material layer and the coating layer is -0.
5 x 10^-6/ K ~ 1.0 x 10^-6In the range of / K
It Generally, ceramics that show brittle fracture are
Excellent resistance to force (positive stress), but residual tension
It is weak against stress (negative stress) and easily cracks easily.
Therefore, when thermal stress is generated, it corresponds to negative stress.
Material composition that reduces tensile residual stress as much as possible
Is desirable, and in the present invention, −0.5 × 10^-6/
K ~ 1.0 x 10 ^-6Set to be within the range of / K
It In addition, -0.5 x 10^-6/ K or less, thermal expansion coefficient
The unfavorable tensile residual stress increases in the coating layer due to the difference in number.
Therefore, cracks are likely to occur in the coating layer. on the other hand,
1.0 x 10^-6/ K and above, the pressure on the coating layer
Since the shrinkage residual stress increases, the buckling of the coating layer
Peeling easily occurs.

The method for producing SiC / SiC according to claim 7 is the SiC / SiC according to any one of claims 2 to 6.
And a step of applying a slurry containing a metal powder to the surface of a SiC / SiC base material and heat-treating it in an inert atmosphere to form a metal-rich carbon / nitride layer. A step of forming a fiber composite material layer and a coating layer by applying a slurry containing carbon fibers having a length of 3 mm or less and metal powder to the surface of the nitride layer and heating the slurry to form a coating layer at the same time. ing. For example, a thermal CVD method is used for forming the coating layer. According to this manufacturing method, a high-quality fiber composite material layer and a coating layer can be easily obtained.

The method for producing SiC / SiC according to claim 8 is the method for producing SiC / SiC according to claim 7, wherein the binder of the slurry in the step of forming the metal-rich carbon / nitride layer has an organic polyacetal structure. The particle size of the metal powder is 44 μm or less in the step of forming the compound-rich carbon / nitride layer and the step of forming the fiber composite material layer and the coating layer. Particle size 4
When the thickness is 4 μm or less, the surface of the porous base material can be easily and densely smoothed, and the homogeneity and coatability of the slurry are improved to facilitate coating. According to this manufacturing method,
The SiC / SiC according to claims 2 to 6 can be easily obtained.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 [1] shows Si according to the present invention.
It is a schematic sectional drawing which shows one Embodiment of C / SiC. Hereinafter, description will be given with reference to this drawing.

The SiC / SiC 10 of this embodiment is Si
Si-rich carbon / nitride layer 1 on the surface of C / SiC substrate 12
4 is formed, the fiber composite material layer 16 is formed on the surface of the Si-rich carbon / nitride layer 14, and the fiber composite material layer 1 is further formed.
6 has a SiC coating layer 18 formed on the surface thereof.

Slurry A (not shown) is applied to the surface of the SiC / SiC base material 12 and heat-treated at a temperature of 1500 ° C. or higher to obtain Si on the surface of the SiC / SiC base material 12.
A rich carbon / nitride layer 14 is formed. This slurry A
Is composed of Si metal powder of 44 μm or less and a binder made of an aqueous solution of an organic material having a polyacetal structure. The organic substance having this polyacetal structure is, for example, [-CH ₂ such as polyvinyl alcohol.
CHOH-] n has a structure having oxygen as shown by the molecular formula, and is 3 even in an inert atmosphere such as Ar or N _2.
It decomposes easily at a relatively low temperature of about 50 ° C, leaving almost no carbon. On the other hand, the reaction between the carbon-based material and the Si powder is
It rapidly progresses near the melting temperature of Si. Therefore, S
Slurry A in which i powder is dispersed is a SiC / SiC substrate 1
By applying to No. 2 and heat-treating in a nitrogen stream, the slurry A initially loses moisture and binder, and the remaining Si powder is melted and covers the surface of the SiC / SiC substrate 12. At this time, the Si powder is S formed by the PIP method.
At the same time as reacting with the carbon-rich SiC matrix of the iC / SiC base material 12 to form the Si-rich carbon / nitride layer 14, the surface depression caused by the gap between the fiber bundles and the PI
The cracks in the SiC matrix caused by the P method are filled. As a result, the surface of the SiC / SiC substrate 12 becomes dense and smooth, so that the SiC / SiC 10
The oxidation resistance of the surface can be improved.

On the surface of the Si-rich carbon / nitride layer 14,
A fiber composite material layer 16 is provided. The fiber composite material layer 16 is formed by applying the slurry B (not shown) to the surface of the Si-rich carbon / nitride layer 14. The slurry B is composed of powder composed of a combination of carbon fibers of 3 mm or less and metal powder, and an organic binder composed of an ethanol solution such as phenol resin.

The carbon fibers used for fiber-compositing the fiber-composite material layer 16 are changed to carbide fibers by the subsequent high temperature process depending on the metal powder to be combined. Further, although the phenol resin used in this slurry B is carbonized by a high temperature process, it can be reacted and sintered with a metal powder to form a carbide matrix.

As the slurry B, a powder of a metal having a thermal expansion coefficient larger than that of SiC is combined with carbon fibers, whereby the thermal expansion coefficient of the fiber composite material layer 16 can be increased. In this case, select the type of metal powder,
By adjusting the ratio of metal powder and carbon fiber,
The coefficient of thermal expansion of the fiber composite material layer 16 can be freely designed. For example, instead of the SiC coating layer 18, Ir
When the coating layer 18 is used, the coefficient of thermal expansion of Ir is about 1
Since it is × 10 ⁻⁵ / K, while suppressing the high temperature reaction between the Ir coating layer 18 and the Si-rich carbon / nitride layer 14, the Re powder and the carbon fiber are used to form the fiber composite material layer 16,
Moreover, the difference in thermal expansion coefficient between the two is −0.5 to 1 × 10 ^−6.
By designing within the range of / K, it is possible to reduce the influence of the difference in thermal expansion coefficient between the SiC / SiC base material 12 and the Ir coating layer 18.

Metals such as Ir are not preferable as a material for a fusion reactor because they are activated. Therefore, the material for the fusion reactor is limited to SiC. In this case, by using a slurry in which carbon fibers and Si powder are combined and using reaction sintering to form the SiC fibers and the SiC matrix, it is possible to form the fiber composite material layer 16 in which cracks are less likely to occur. The influence of the difference in the coefficient of thermal expansion from the SiC coating layer 18 can be reduced.

The thermal stress caused by the difference in thermal expansion coefficient between the SiC / SiC base material 12 and the fiber composite material layer 16 causes cracks in the film starting from the fiber composite material layer 16. At this time, the cracks generated in the composite material layer 16 bend due to the presence of fibers. Therefore, since the effect of suppressing the inflow of the oxidizing gas is exerted, the SiC / Si
The oxidation resistance of the C base material 12 is improved.

The SiC / SiC substrate 12 is not limited to a flat one. For example, in the case of a radiant tube used in a gas turbine, the inner surface of the tube is significantly oxidized, but in this case, the fiber composite material layer 16 and the coating layer 1 have a coefficient of thermal expansion larger than that of SiC.
By designing 8, the coating layer 18 thermally expands during high temperature use and a compressive stress acts on the coating layer 18 itself, so that the coating layer 18 in which cracks are less likely to occur can be obtained.

FIG. 1 [2] shows the SiC in FIG. 1 [1].
FIG. 3 is a conceptual diagram showing a part of a three-dimensional arrangement structure of a SiC fiber bundle that constitutes / SiC base material 12. Hereinafter, FIG. 1 [1],
A description will be given based on [2].

The SiC fiber 121 generally has a diameter of about 10 μm and is available on the market.
When arranging the SiC fibers 121 in three dimensions, there are various ways of weaving the fibers. When imparting isotropic mechanical properties in any of the x, y, and z directions, the arrangement of the orthogonal triaxes shown in FIG. 1 [2] is often used. At this time, although 6 to 16 SiC fiber bundles 122x, ... Are drawn in the figure, for the sake of simplification of fabric production, 1000 or more SiC fiber bundles having a larger number of fibers are actually used. To be
As can be seen from FIG. 1 [2], the SiC fiber bundle 122x,
The larger the cross-sectional area of 122y, 122z,
The gap 123 between the fiber bundles exposed on the surface becomes large. In addition, as a matter of course, the space (not shown) enclosed in the SiC fiber bundle in the x direction, the y direction, and the z direction inside the SiC woven fabric 120 also becomes large. For example, when 1000 fibers are used as a fiber bundle, the gap surrounded by the fiber bundle is a cube whose one side is surrounded by about 300 μm.

Attention is now paid to the depressions on the surface of the SiC fabric 120. It has been described above that the PIP method is used when manufacturing the SiC / SiC substrate 12. The resin used for the impregnation needs to fill the gaps 123 between the inner fiber bundles, so that a resin having a low viscosity is used in order to facilitate the penetration into the gaps. However, filling the internal gap and smoothing the surface are technically contradictory. That is,
The smoothing of the surface is performed by a resin having a high viscosity. However, when such a resin having a high viscosity is used, since the SiC matrix is formed on the surface of the woven fabric and the gap becomes narrow, the filling of the inside is suppressed. It will be difficult. Therefore, SiC / S
In the manufacturing process of the iC substrate 12, the SiC woven fabric 1
Since the main focus is on filling the gaps inside 20, the resulting SiC / SiC base material 12 has remarkable surface irregularities.

Hereinafter, Examples and Comparative Examples will be described based on the respective experimental results.

[0037]

Example (1). The surface of the SiC / SiC substrate was coated with a slurry containing a selected metal powder and using polyvinyl alcohol as a binder. Subsequently, the solvent water was evaporated at 150 ° C. to fix the slurry on the surface of the SiC / SiC substrate. As SiC / SiC base material, 1000 pieces of Tyranno fiber (trade name) manufactured by Ube Industries, Ltd.
Bundles are three-dimensionally arranged and are made of polycarbosilane resin
What was filled with the SiC matrix by the P method was used.

FIG. 2 is a table showing the composition of the slurry applied to the surface of the SiC / SiC substrate and the physical properties of the powder. Hereinafter, description will be given with reference to this drawing.

As the binder constituting the slurry A, S-REC KW-1 (trade name) manufactured by Sekisui Chemical Co., Ltd. was used. Although the details of this binder are unknown, it is generally called a modified polyacetal resin and may be considered to be a kind of an aqueous solution of polyvinyl alcohol. Basically, it is an organic binder that burns and disappears at a relatively low temperature even in an inert atmosphere. When phenolic resin or the like is used as the binder, the reaction between the carbon generated from the binder and the Si powder results in a porous and fragile film, so that the dense smooth surface obtained in the present invention cannot be obtained. Be careful.

As the Si powder, one having a high purity of 99.999% and a central particle size of about 10 μm was used. S
Since i-powder has a larger specific gravity than water, liquid-solid separation occurs during the application of the slurry, making it difficult to make the composition uniform. In order to prevent this, as a dispersant and as an anti-solidifying agent in the static state of the slurry, and to impart the thixotropic property required for coating, SiO ₂
Ultrafine particles Aerosil 2 manufactured by Nippon Aerosil Co., Ltd.
00 (trade name) was used. The amount of the slurry applied to the surface of the SiC / SiC substrate is about 0.13 g / solid matter.
It is cm ² .

After applying the slurry to the surface of the SiC / SiC substrate by the doctor blade method, it is dried at 150 ° C. to fix the slurry, and 1500 ° C. and 3 ° C. in Ar flow.
It is heated for 0 minutes to remove the binder in the slurry, melt the Si powder, and react the molten Si with the SiC matrix on the surface of the SiC / SiC substrate to make the surface smooth and rich in metal. With SiC
A carbide layer on the / SiC substrate surface was obtained.

Regarding SiC / SiC when polycarbosilazane is used as the resin for forming the matrix by the PIP method or when SiC fiber made from polycarbosilazane is used, the Si--C--N matrix is used. Alternatively, in order to suppress the high temperature thermal decomposition of the Si—C—N fiber, the atmosphere for the heat treatment is preferably N ₂ rather than Ar. In this case, when heat-treated in an N ₂ stream to generate a partially reacted with N ₂ carbonitride of molten Si. However, when heated in a vacuum, the partial pressure of oxygen causes the generation of SiO gas, which is called active oxidation, to produce SiC / Si.
Caution is required because thermal decomposition of the C substrate may occur.

(2). Next, the slurry B was applied to the surface of the Si-rich carbon / nitride layer obtained in the step (1) by a doctor blade method. A 25% xylene solution of polycarbosilane (PCS) manufactured by Nippon Carbon Industry Co., Ltd. was used as a binder constituting the slurry B.
Further, as the carbon fiber, a carbon fiber milled fiber HTA-CMF-0160-0H (trade name) manufactured by Toho Rayon Co., Ltd. and pulverized by milling was used. This milled fiber has a diameter of 7 μm and an average length of 170
μm. As the carbon fiber, a long one can be used depending on the coating conditions, and for example, a fiber chopped to 3 mm or less can be used. Rather, longer fibers are preferable because they are considered to have less influence on the human body and the like during the slurry production. The coating amount of the slurry B is about 0.2 g / cm ² in terms of solid content.

(3). Next, an SiC coating layer was formed on the composite green body obtained in the step (2) by a thermal CVD (chemical vapor deposition) method under a reaction temperature condition of 1250 ° C. The conditions for the thermal CVD method are temperature 1
250 ° C., pressure 1.3 kPa, SiCl ₄ flow rate 0.5 liter / min, CH ₄ flow rate 0.5 liter / min,
And so on. Under these conditions, an SiC coating layer having an average film thickness of about 90 μm was formed over 8 hours. Carbon fiber and Si
Considering formation of a SiC matrix by combustion synthesis with powder, the thermal CVD temperature is preferably 1500 ° C. or higher. However, when manufactured in the temperature range over 1500 ° C,
SiC / derived from polycarbosilane (PCS)
Since the matrix of the SiC base material is formed of an amorphous phase due to cross-linking of oxygen for infusibilization, thermal decomposition accompanied by generation of SiO gas and the like may cause the desired material strength to decrease. is there. Therefore, when using such a SiC / SiC base material, it is necessary to set the processing temperature of the thermal CVD to a maximum of 1500 ° C. Heat C
VD is an essential process for forming a dense film,
A method such as reactive sputtering may be used as long as a similar dense film can be formed.

FIG. 3 shows the composition of methane combustion exhaust gas (N ₂ : 73%, CO ₂ : 9%, H ₂ O: 18%) as an example showing the excellent oxidation resistance of SiC / SiC in this example. SiC heated to 1700 ° C. and held for a total of 10 hours in a simulated mixed gas (flow rate 200 ml / min)
Characteristics of oxygen and Si by electron probe microanalysis (EPMA) showing a cross section near the surface of a / SiC test piece
It is an intensity map image of a line. Hereinafter, description will be given with reference to this drawing.

The two parallel white lines sandwiching the crack shown in the cross section of the SiC / SiC surface of FIG. 3 indicate that the probe was scanned between these and the intensities of the characteristic X-rays of O and Si were analyzed. From the map images of O and Si, typical cracks generated in the SiC / SiC film according to the present invention can be seen. Moreover, it can be seen that the crack is bent in the fiber composite material layer. Figure 3
The characteristic X-ray map image of O shown in [1] shows that the characteristic X-ray intensity of oxygen is high near the surface. The width of the crack is narrowed by oxidation near the surface. And
Although the crack width increases as it approaches the surface of the base material, the characteristic X-ray intensity of oxygen decreases, indicating that oxygen has not penetrated to the inside. That is, when the crack bends, the inflow path of the oxidizing gas is extended, whereby SiO ₂ is generated on the wall surface of the crack and the crack is closed, so that the oxidation resistance is improved. on the other hand,
In the characteristic X-ray map image of Si shown in FIG.
/ Indicates that the Si concentration is high on the surface of the SiC substrate. In general, Si-rich SiC is carbon-rich S
It can be seen that since the vapor pressure is lower than that of iC, it exhibits more excellent heat resistance.

[0047]

[Comparative Example] FIG. 4 shows uncoated SiC.
/ SiC (sample a), SiC / SiC (sample b) in which only the fiber composite material layer is formed on the surface of the SiC / SiC substrate, and the surface is coated with SiC, and an intermediate layer consisting of two layers according to the present invention It is the result of comparing the oxidation resistance of three types of SiC / SiC (sample C) that formed
The test conditions for the oxidation test were repeated heating at 1700 ° C. for 2 hours in an atmosphere simulating the above-mentioned methane combustion exhaust gas. As can be seen from FIG. 4, in the sample a, SiC was used.
Since SiO ₂ is generated by the oxidation of, the mass is significantly increased. This generation of SiO ₂ is due to the diffusion of the oxidizing gas into the inside of SiC / SiC, and tends to increase with temperature and time. On the other hand, in sample B, the increase in mass is suppressed more than in sample B, that is, the oxidation of SiC is suppressed. On the other hand, in Sample C, the mass change was below the detection limit.

[0048] When the oxidized SiC at a high temperature gas containing a large amount of steam, the mass loss due to the mass increase due to the formation of SiO _2, and the SiO ₂ high-temperature water vapor to produce a reacted Si _{(OH) 4} Gas And occur at the same time. Further, the generated Si (OH) ₄ may be reoxidized by the oxidizing atmosphere and may be re-precipitated on the surface as SiO ₂ smoke.

In this test, a SiO ₂ oxide film developed on the surface of all the samples was formed. In sample c, no mass change is observed, but this is due to Si (OH)
₄ Gas mass reduction due to generation of gas and Si accompanying oxidation of SiC
This is because the mass did not seem to change as a result of offsetting the increase in mass due to the formation of O ₂ . However, since the masses of Samples a and b are obviously increasing,
The mechanism of mass change is different from that of sample c.

Generally, the mechanism of oxidation of SiC / SiC materials including SiC is as follows: partial pressure of oxidizing gas in the atmosphere, thickness of gas boundary layer due to flow velocity of the atmosphere gas, purity of SiC, porosity, It greatly changes due to the difference in the crystallinity of the generated SiO ₂ . In addition, H ₂ O and C such as combustion exhaust gas
In a high-speed, high-pressure air stream containing a large amount of O ₂ oxidizing gas, passive oxidation for forming a SiO ₂ film occurs. In this oxidation mechanism, if the surface area of the material is large, SiO ₂
Since the production amount of is increased, the mass of the test piece with many pores and cracks inside the material increases. This is based on the above-mentioned "International clean energy system technology using hydrogen (WE
SiC due to the high temperature of in _{H 2} O exposure by -NET) "
It is also clear from the experimental results of the oxidation of.

Further, although SiC has high thermal shock resistance,
As the number of repeated thermal shocks increases, the SiC film cracks. The crack serves as a path for the oxidizing gas to enter the SiC / SiC substrate. Therefore, SiC
With the occurrence of cracks in the coating, internal oxidation of the SiC / SiC substrate proceeds, and as a result, mass increase is accelerated. Further, the diffusion rate of H ₂ O gas in oxide ceramics is higher than that of O ₂ gas. Therefore, even if the coatings have the same antioxidation performance, in the case of a SiC / SiC base material having many pores inside, the internal oxidation of the SiC / SiC base material proceeds and the mass increase becomes larger. That is, these results show that Si (O
H) ₄ mass reduction due to the formation of SiO ₂ diffused inside SiC / SiC through defects in the SiC film
It is shown that the mass increase due to is dominant. As described above, in the samples other than the present invention, it is considered that the mass increase due to the generation of SiO ₂ controls the mass change.
Therefore, the excellent oxidation resistance of the present invention can be demonstrated.

[0052]

According to the SiC / SiC of the present invention,
By providing an intermediate layer that fills the pores on the surface of the SiC / SiC base material to smooth it and absorbs the thermal stress generated between the SiC / SiC base material and the coating layer, the SiC / S
The surface of the iC base material can be densified, and the thermal stress generated between the SiC / SiC base material and the coating layer can be suppressed to prevent the formation of pores and cracks in the coating layer. / It is possible to prevent a decrease in strength due to oxidation inside the SiC substrate.

According to the SiC / SiC of claim 2,
By providing the metal-rich carbon / nitride layer, only the surface of SiC / SiC having a high porosity can be densified. Further, by providing the fiber composite material layer,
Since the cracks generated in the film due to thermal shock bend,
SiC / S through the SiO ₂ film generated on the crack inner wall
It is possible to suppress the infiltration of the oxidizing gas that reaches the iC base material.

According to the SiC / SiC of claim 3,
Since the fiber composite material layer is made of carbide fibers and a matrix of at least one of carbide and metal, the heat resistance of the fiber composite material layer can be improved.

According to the SiC / SiC of claim 4,
The decomposition point or melting point of the carbide fibers and matrix is 160
Since it is 0 ° C or higher, it can be used at higher temperatures.

According to the SiC / SiC of claim 5,
By using a slurry in which carbon fibers having a length of 3 mm or less and metal powder are combined, the coatability can be improved, and at the same time, the reaction sintering method can be used to easily form a thick film of the fiber composite layer.

According to the SiC / SiC of claim 6,
The coefficient of thermal expansion of the fiber composite material layer with respect to the coating layer was set to −0.
By setting it to 5 × 10 ⁻⁶ to 1 × 10 ⁻⁶ / K, the thermal stress generated between the coating layer and the fiber composite material layer can be relaxed, so that the generation of cracks can be suppressed. Moreover, even if a crack occurs, the crack bends in the fiber composite material layer, so that the oxidation resistance can be maintained.

According to the method for producing SiC / SiC of claim 7, the surface of the porous SiC / SiC substrate is coated only with the slurry of the metal powder and heat-treated in an inert atmosphere. Can form a smooth metal-rich charcoal / nitride, and subsequently apply a slurry in which carbon short fibers and metal powder are mixed and then apply, for example, heat CV.
By forming a fiber composite material layer using the D method and forming a coating layer on the surface of this fiber composite material layer,
The SiC / SiC according to the present invention can be easily manufactured by using common equipment without requiring special equipment, and it is possible to deal with even complicated shapes.

According to the method for producing SiC / SiC of claim 8, an organic compound having a polyacetal structure is used in the slurry for the surface treatment of the porous SiC / SiC base material, and the particle size of the metal powder is 44 μm or less. As a result, a dense and uniform surface treatment can be achieved, and metal rich charcoal.
A nitride layer can be formed.

[Brief description of drawings]

FIG. 1 [1] is a schematic cross-sectional view showing one embodiment of SiC / SiC according to the present invention. FIG. 1 [2] is a schematic diagram showing the structure of the SiC woven fabric of the SiC / SiC base material in FIG. 1 [1].

FIG. 2 is a chart showing the composition of the slurry and the physical properties of the powder for forming the intermediate layer in the example of the present invention.

FIG. 3 is a photograph showing a characteristic X-ray image of a cross section of a sample after an oxidation test in an example of the present invention. FIG. 3 [1] shows O (oxygen) and FIG. 3 [2] is Si (silicon). Indicates.

FIG. 4 is a chart showing mass changes due to oxidation of SiC / SiC of the present invention and the prior art.

[Explanation of symbols]

10 SiC / SiC 12 SiC / SiC base material 14 Metal rich carbon / nitride layer 16 Fiber composite material layer 18 SiC coating layer 120 SiC fabric 121 SiC fiber 122x, 122y, 122z SiC fiber bundle 123 Gap between fiber bundles

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C04B 41/90 C04B 35/56 101X 101L (72) Inventor Akihiko Otsuka 573 Ube Oki, Ube City, Yamaguchi Prefecture F-term in ultra-high temperature materials research institute of 3 stock companies (reference) 4F100 AA32C AB01A AB01B AB01D AD00B AD05C AD08A AD08C AH02G AK21G AK52 AK54K AR00C AS00C BA02 BA03 BA04 BA07 BA41 JA51EJ4848514848 EJ01484851 EJ0148 EJ0148 EJ0148D51A EJ0148 DG01C DG01C DG01A DG01C JA04D JB03 JJ05C JK14 JM01C 4G001 BA22 BA86 BB22 BB86 BC72 BD07

Claims (8)

[Claims] 1. A SiC fiber composite SiC composite material (hereinafter, abbreviated as "SiC / SiC"). A SiC / SiC in which a coating layer made of metal or ceramics is formed on the surface of a substrate.
In SiC, the pores on the surface of the SiC / SiC base material are filled between the surface of the SiC / SiC base material and the coating layer so as to be smoothed and generated between the SiC / SiC base material and the coating layer. An SiC / SiC characterized in that an intermediate layer for absorbing thermal stress is formed. 2. The intermediate layer is composed of two layers, a metal-rich carbon / nitride layer on the side of the SiC / SiC base material and a fiber composite material layer on the side of the coating layer, and the metal-rich carbon / nitride layer. Is a compound of a metal and at least one of carbon and nitrogen, and the composition ratio of the metal is higher than the stoichiometric composition ratio, SiC / SiC according to claim 1. 3. The fiber composite material layer comprises carbide fibers,
The SiC / SiC according to claim 2, comprising a matrix of at least one of a carbide and a metal. 4. The SiC / SiC according to claim 3, wherein the carbide fiber and the matrix each have a melting point or a decomposition point of 1600 ° C. or higher. 5. The SiC / SiC according to claim 2, wherein the fiber composite material layer is formed by a reaction sintering method using carbon fibers having a length of 3 mm or less and metal powder as raw materials. . 6. The coefficient of thermal expansion difference of the matrix with respect to the coating layer is −0.5 × 10 ⁻⁶ / K to 1 × 10 ^−6.
SiC / SiC according to any one of claims 3 to 5, which is in the range of / K. 7. Si according to any one of claims 2 to 6.
A method for producing C / SiC, which comprises applying a slurry containing a metal powder to the surface of the SiC / SiC base material and heat-treating it in an inert atmosphere to form the metal-rich carbon / nitride layer, A slurry containing carbon fibers having a length of 3 mm or less and metal powder is applied to the surface of the metal-rich carbon / nitride layer, and the coating layer is formed at the same time as heating the fiber composite material layer and the coating. A step of forming a layer, and a method for producing SiC / SiC, comprising: 8. The step of forming the metal-rich carbon / nitride layer, wherein the binder of the slurry is an organic compound having a polyacetal structure, and the step of forming the metal-rich carbon / nitride layer, and the fiber composite. The method for producing SiC / SiC according to claim 7, wherein the particle diameter of the metal powder in the step of forming the material layer and the coating layer is 44 μm or less.