JPH0952777A - Production of oxidation resistant c/c composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an oxidation resistant C/C composite material on which an SiC coating film can be stably and tightly formed. SOLUTION: Prepreg formed by impregnating a liq. matrix resin into a fabric of carbon fibers is laminate-molded, cured and carbonized by firing to produce a C/C composite material and an SiC coating film having a functional gradient is formed on the composite material as a base material by bringing gaseous SiO into contact with the surface of the material and converting the SiO into SiC. In this method, prepreg layers positioned at the outermost layer parts (top and bottom layers) are formed using fabrics of carbon fibers woven from tow consisting of a larger number of filaments than tow for inner prepreg layers and a C/C composite material having a composite structure produced by laminating the prepreg layers is used as the base material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxidation resistant C / C composite material (carbon fiber reinforced carbon) which has a stable and strong SiC coating formed on the surface layer of a C / C composite substrate by a conversion method. Composite material).

Since C / C composite materials have excellent specific strength and specific elastic modulus as well as excellent heat resistance and chemical stability even at a high temperature of 1000 ° C. or higher, they are used in aerospace and other high temperatures. It has been attracting attention as various structural members used under severe conditions. However, since the C / C composite material is substantially a carbon material, it has an inherent defect that oxidation progresses in an air atmosphere at 500 ° C. or higher, resulting in material deterioration.
For this reason, there have been many attempts to improve the oxidation resistance by coating the surface of the C / C composite material with oxidation resistance. For example, heat resistance of silicon carbide, silicon nitride, zirconia, alumina, etc. Many methods for coating with ceramic materials have been developed. Of these, the coating of silicon carbide is most suitable for industrial application in terms of technical and economical aspects such as the coating layer forming operation and property characteristics.

[0003]

2. Description of the Related Art Conventionally, as a method for coating the surface of a C / C composite substrate with SiC, SiC produced by a gas phase reaction
There are known a CVD method (chemical vapor deposition method) for directly depositing carbon and a conversion method for converting carbon of a base material into SiC by reacting with SiO gas using a reaction source. Among them, the SiC coating layer formed by applying the former CVD method has an extremely high density of structure, but the interface with the substrate is clearly separated, so that it is C
/ C composite substrate and SiC coating layer due to thermal expansion difference Si
There is a drawback that the C coating layer is easily peeled off. This delamination phenomenon occurs because the difference in thermal expansion between the C / C composite substrate and the SiC coating layer is large and the maximum strain cannot be followed. If it is modified so as to approximate the coefficient of thermal expansion, it can be reduced. From such a viewpoint, a pyrolytic carbon layer is formed on the C / C composite substrate surface by a vapor phase pyrolysis method, and then a CVD method or a CV method is used.
A method of coating SiC by method I (Japanese Patent Laid-Open No. 2-111681) has been proposed, but sufficient high temperature oxidation resistance commensurate with the complexity of the operation cannot be expected.

On the other hand, in the latter conversion method, the SiO gas and C /
Since it is based on the mechanism of reacting with the carbon structure of the C composite material to gradually become SiC from the surface to the inside of the surface layer portion of the C / C composite material, the formed SiC coating layer has a degree of SiC formation. It exhibits a continuous functionally graded structure that gradually decreases toward the inside of the material. Therefore, CV
Unlike the SiC coating layer formed by the D method, there is no clear interlayer, and there is an advantage that interlayer delamination does not occur even when subjected to thermal shock. However, on the other hand, S in the surface layer
In addition to the decrease in the density of the iC coating layer, minute cracks are generated in the coating layer during the reaction, and sufficient oxidation resistance cannot be imparted.

Therefore, an attempt has been made to improve the oxidation resistance by forming a SiC coating layer on the surface of a C / C substrate in advance by a conversion method and laminating various coating layers on the SiC coating layer as a base layer. Has been done. For example, as a method of filling fine cracks with a glass seal layer, a SiC coating layer, a SiO ₂ fine particle coating layer, and a SiO ₂ fine particle coating layer are formed on the surface of a C / C substrate.
₂ glass coating layer or B ₂ O ₃ glass coating layer or B
Oxidation-resistant C / C material having a structure in which ₂ O ₃ .SiO ₂ glass coating layers are laminated in three layers and a method for producing the same (Japanese Patent Application Laid-Open No. Hei 4-
42883, JP 4-187583, JP 4-24
3989, JP-A-4-243990, JP-A-4-4336
6, JP-A-5-70228, JP-A-5-229886
JP-A-5-330961, JP-A-6-48872, JP-A-6-144967, JP-A-6-247782, etc.) are known.

These multi-layered coating means can effectively improve the oxidation resistance of the C / C composite material, but if the SiC coating formed as the base layer by the conversion method becomes thicker, the C / C composition becomes larger. Si up to the internal structure of the substrate
There is a problem that the carbonization progresses and the material strength of the C / C base material is lowered. That is, in the coating step by the conversion method, the SiO gas converts the C / C base structure into SiC while permeating and diffusing from the surface of the C / C base into the inside of the structure. Not only that, but the SiC structure progresses to the inside of the relatively deep structure, and the matrix structure, especially the matrix carbon portion which is easily converted into SiC, is preferentially silicified to weaken the entire matrix structure. The degree of crack generation increases due to the difference in thermal expansion from the material.

As a means for solving the above problems and preventing the deterioration of the material inside the tissue by keeping the formation of the SiC coating by the conversion method as the base layer on the surface layer, as a C / C composite base material in the multilayer coating step. A method for producing an oxidation resistant carbon fiber reinforced carbon material, in which a polyacrylonitrile-based carbon fiber layer is present on the surface portion and the inside has a composite structure formed of pitch-based carbon fibers (Japanese Patent Application No. 5-273108). ), S
Carbon fiber volume content (Vf) of surface layer forming iC film
Is higher than the inside, and the carbon fiber volume content (V
f) is a composite structure with at least 65% oxidation resistance C / C
A method for manufacturing a composite material (Japanese Patent Laid-Open No. 6-144968) has been developed by the present applicant.

[0008]

SUMMARY OF THE INVENTION The inventor of the present invention uses the C / C method based on the conversion method from the viewpoint different from the above-mentioned prior art.
As a result of further studies on a method for forming a SiC coating layer on the surface layer of the C base material in a stable and strong manner, the degree of uneven distribution of matrix carbon in the outermost layer of the C / C composite base material is relatively large as compared with the inner layer. Then Si by conversion
The formation of the C coating layer does not proceed to the inside of the tissue, and SiC
It was confirmed that the coating layer and the C / C base material structure inside were strongly bonded by the anchor effect (anchoring effect) of the SiC layer.

The present invention was developed on the basis of the above findings, and its purpose is to stabilize the surface layer of a C / C composite substrate by the conversion method without deteriorating the material quality of the internal structure. It is to provide a method for producing an oxidation resistant C / C composite material capable of forming a strong SiC coating layer.

[0010]

The method for producing an oxidation resistant C / C composite material according to the present invention for achieving the above object comprises:
SiC having a gradient function by a conversion method by using a C / C composite material obtained by laminating a prepreg obtained by impregnating a carbon fiber woven fabric with a matrix resin liquid, and curing and firing and carbonizing the prepreg, and bringing SiO gas into contact with the surface of the substrate to obtain a conversion method. In the method of forming a coating, the C / of a composite structure in which prepregs located in the outermost layers (uppermost layer and lowermost layer) are laminated using a carbon fiber woven fabric braided with a tow having a larger number of filaments than the inner prepreg layer A structural feature is that the C composite material is used as a base material.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A C / C composite substrate is obtained by impregnating a carbon fiber woven fabric with a matrix resin liquid by dipping or coating to form a semi-cured prepreg, and laminating and molding a predetermined number of the prepreg. It is produced by curing and firing carbonization. The kind of carbon fiber woven fabric is not particularly limited, and for example, plain weave, satin weave, twill weave and the like made of various carbon fibers such as polyacrylonitrile type, rayon type and pitch type can be used. Further, as the matrix resin liquid, a liquid type thermosetting resin such as a phenol type having a high carbonization residual rate, a furan type, tar pitch,
A thermoplastic such as phenol-modified tar pitch is used.

In the process of producing the above C / C composite substrate, a prepreg located in the outermost layer (uppermost layer and lowermost layer) is braided with a tow having a larger number of filaments than the internal prepreg layer. Laminating with is a major requirement of the present invention. Usually, the carbon fiber woven cloth has a carbon fiber filament (single fiber) of 1,000 to 15,000.
The braided tow is braided, but the weave and other braided states differ depending on the number of filaments forming the tow. In the present invention, among the prepreg layers to be laminated,
Composed of a relatively large woven fabric in which the carbon fiber woven fabric that is compounded in the prepreg of the uppermost layer and the lowermost layer is braided with a tow having a larger number of filaments than the carbon fiber woven fabric that is compounded in the prepreg laminated inside To do. In this case, the difference in the number of filaments is that the number of filaments of the carbon fiber tow in the prepreg of the outermost layer portion is preferably twice or more the number of filaments of the carbon fiber tow in the inner prepreg, and if it is less than twice, the SiC by the conversion method is used. It becomes impossible to form a layer only on the surface layer portion of the C / C composite substrate. The prepreg to be laminated on the outermost layer may have 1 to 2 layers.

The prepregs laminated in a laminated state are thermocompression-molded in a mold to obtain a molded product having a desired shape such as a flat plate shape or a curved plate shape, and then the matrix resin is completely heat-cured and then subjected to a non-conventional method. 1000-2 under oxidizing atmosphere
It is heated to a temperature of 000 ° C. to be carbonized by firing. The C / C composite substrate thus produced is coated with a SiC film by a conversion method.

The formation of the SiC film by the conversion method is performed by the following operation. First, a silicon source obtained by crushing SiO ₂ -containing substances such as quartz, silica stone, and silica sand to 10 to 500 μm and coke, pitch, graphite, carbon black, etc.
A carbon source of about 500 μm is thoroughly mixed by a mechanical mixing device to form a uniform mixture, which is then placed in a reaction vessel made of a heat resistant material such as graphite. The blending ratio of the silicon source and the carbon source is determined in consideration of the surface area of each powder to be mixed, and is usually 1: 1 to 5: 1 by weight ratio of SiO ₂ : C.
It is blended to a composition of 1 range.

The above reaction vessel is installed in a closed heating furnace,
The C / C composite substrate is embedded in the mixed powder in the reaction vessel or set in the vicinity of the reaction vessel, and heat-treated at a temperature of 1600 to 2000 ° C. while maintaining the system in a non-oxidizing atmosphere. . The SiO gas generated by the heat reduction reaction between the silicon source and the carbonaceous material in the treatment process reacts with the carbon of the C / C base material from the surface of the C / C composite base material, converts into SiC, and permeates and diffuses inside. A SiC coating layer having a functionally graded structure is formed on the surface layer of the C / C substrate.

According to the present invention, C /
When forming the SiC coating layer on the surface of the C composite substrate, C
As a composite structure, the prepregs located in the outermost layers (the uppermost layer and the lowermost layer) as the / C composite substrate are laminated using a carbon fiber woven fabric braided with a tow having a larger number of filaments than the internal prepreg layer. Therefore, the texture of the carbon fiber woven cloth intervening in the outermost layer is larger than that in the inner layer, and in this relationship, the structure after firing and carbonization is the carbon portion relatively converted from the matrix resin in the outermost layer. Presents a complex state in which many

When such a C / C base material is brought into contact with SiO gas by a conversion method to be made into SiC, the carbonization portion of the matrix resin, which is more liable to SiC reaction than carbon fiber, progresses to become SiC, and the upper and lower portions are converted into SiC. The outermost layer portion is preferentially converted to the SiC layer. At the same time, a part of the SiO gas permeates and diffuses into the inside and is converted into SiC in a state where a wedge is driven into the inner layer. Due to such an action of converting to SiC,
The phenomenon in which the internal structure of the C / C composite substrate is converted to SiC is effectively suppressed, and only the surface layer portion is completely covered with the SiC layer, and wedge-shaped SiC formed from the SiC layer toward the inner layer is formed. It exerts an anchor effect (anchor effect) and firmly bonds. Therefore, it is possible to always form a stable and strong oxidation resistant SiC coating without deterioration of the material of the C / C composite substrate.

[0018]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Example 1 (1) Preparation of C / C substrate A plain woven carbon fiber woven fabric (manufactured by Toray Industries, Inc.) in which a polyacrylonitrile-based high strength and high elasticity type carbon fiber tow (3000 filaments) was braided. Then, a phenol resin initial condensate [manufactured by Dainippon Ink and Chemicals, Inc.] was uniformly applied as a matrix resin and air dried for 48 hours to prepare a prepreg sheet. Sixteen prepreg sheets were stacked in the vertical direction and laminated, and one prepreg sheet was prepared by the same method except that carbon fiber tow having 6000 filaments was used on the upper and lower surfaces (outermost layer) of the prepreg sheet. 20
It was placed in a 0 × 200 mm mold and thermocompression molded under the conditions of a heating temperature of 110 ° C. and a pressure of 20 kg / cm ² . The molded body was taken out of the mold, heated to a temperature of 250 ° C. to be completely cured, and then transferred to a firing furnace kept in a nitrogen atmosphere.
The mixture was heated to 1000 ° C. at a temperature rising rate of ° C./hr and kept at this temperature for 5 hours for calcination and carbonization. Then, the obtained C / C
The same phenol resin initial condensate as above was applied to the material at a pressure of 7 kg.
A step of impregnating under a pressure of / cm ² again and firing treatment in the same manner as above was repeated three times, and finally fired at a temperature of 2000 ° C. to prepare a C / C composite substrate. C / C produced
The composite base material (200 mm × 200 mm × 4.5 mm) had a carbon fiber volume content (Vf) of 65% and a bulk density of 1.65 g / cc.

(2) Formation of SiC coating layer Silica sand powder having a particle size of 40 to 500 μm and graphite powder having the same particle size range are blended in a molar ratio of 2: 1 and homogenized using a stirring mixer. Mixed. The mixed powder was put into a graphite crucible, and a C / C composite base material was set on the upper portion thereof. This graphite crucible was transferred into an electric furnace, and after the interior was sufficiently replaced with argon gas, the graphite crucible was heated to 1900 ° C. at a heating rate of 50 ° C./hr and kept for 2 hours to form a surface layer on the C / C composite substrate. A SiC coating layer having a gradient function was formed by the conversion method.

(3) Formation of Glass Sealing Layer Further, in order to seal fine cracks in the SiC coating layer, a B ₂ O ₃ —SiO ₂ glassy coating was coated by the following method and glass sealing was performed. Si (OC ₂ H ₅ ) ₄
The C / C composite base material having the SiC coating layer formed thereon was dipped in a SiO ₂ fine particle suspension obtained by an alkoxide method in which is hydrolyzed in the basic region of NH ₄ OH and impregnated under reduced pressure. After air-drying, the operation of applying the SiO ₂ fine particle suspension and air-drying was repeated 3 times and dried at 100 ° C. to form a coating layer made of SiO ₂ . Next, this C / C base material is put into a B (OC ₄ H ₉ ) ₃ solution, impregnated under reduced pressure, air-dried for a whole day and night, hydrolyzed by moisture in the air, dried at 100 ° C., and further dried at 500 ° C. It was heat-treated at a temperature of ₂ to convert to a B ₂ O ₃ glass layer. Next, Si (OC
SiO ₂ obtained by hydrolyzing ₂ H ₅ ) ₄ in a hydrochloric acid solution
The above C / C substrate was put into a glass precursor solution, impregnated under reduced pressure, and dried at 100 ° C. The treated C / C substrate was again put into the B (OC ₄ H ₉ ) ₃ solution, impregnated under reduced pressure, air-dried for 24 hours, and then hydrolyzed by water in the air. 10
After drying at 0 ° C., it was heated at a temperature of 800 ° C. in an argon atmosphere to form a B ₂ O ₃ —SiO ₂ vitreous coating.

(4) Evaluation of characteristics With respect to the C / C composite material having the SiC coating formed as described above, the film thickness of the SiC coating, Si
The depth of the anchor portion of the C coating layer was measured and the results are shown in Table 1.
Further, the bending strength and the oxidation resistance test of the C / C composite material were performed, and the results are shown in Table 2. Thickness of SiC coating: Part of the C / C composite material on which the SiC coating was formed was cut with a diamond cutter, and the cross section was observed and measured by SEM. Anchor depth of SiC coating layer: A part of C / C composite material on which the SiC coating was formed was cut with a diamond cutter, and its cross section was observed by SEM to observe a mixture layer of SiC and carbon existing under the SiC coating. And then Si by XMA
Was measured from the depth distribution of the mixture layer of SiC and carbon. Bending strength: A test piece of 150 × 12.5 × 4 mm was measured for three-point bending strength under the conditions of a fulcrum distance of 64 mm and a crosshead speed of 6 mm / min. Oxidation resistance test: The C / C composite material on which the SiC film was formed was placed in an electric furnace kept in the atmosphere, kept at a temperature of 1400 ° C. for 30 minutes, and then naturally cooled to room temperature. This operation was repeated 10 times to obtain C /
The weight loss rate of the C composite material and the state of the SiC coating layer were observed.

Examples 2 to 5 prepreg sheets laminated inside and upper and lower (outermost layer)
A C / C composite substrate was produced in the same manner as in Example 1 except that the prepreg sheet to be laminated on the surface was prepared using a carbon fiber woven fabric in which carbon fiber tows having different numbers of filaments were braided. In Example 4, two prepreg sheets were laminated on each of the upper and lower (outermost layer) surfaces. The C / C composite base material was subjected to the same method as in Example 1 to form a SiC coating layer and the glass was sealed, and the obtained C / C composite material with the SiC coating formed was subjected to the same method as in Example 1. The characteristics were evaluated and the results are shown in Tables 1 and 2.

Comparative Examples 1 to 4 A prepreg sheet made of a carbon fiber woven fabric in which carbon fiber tows having the same number of filaments were braided was laminated to form C /
A SiC coating layer was formed and glass was sealed in the same manner as in Example 1 except that a C composite substrate was prepared.
The characteristics of the obtained C / C composite material having the SiC coating formed thereon were evaluated by the same method as in Example 1, and the results are shown in Tables 1 and 2 together. The oxidation resistance test was not conducted because the oxidation resistant coating layer was peeled off.

[0025]

[Table 1] Note) * () is the number of laminated prepreg sheets.

[0026]

[Table 2]

As shown in Table 1, the SiC coating layer of the example has a deep mixture layer of SiC and carbon in the lower layer of the coating as compared with the SiC coating layer of the comparative example, and the SiC is formed in a wedge shape. You can see that the effect is great. as a result,
As shown in Table 2, in the oxidation resistance test, the SiC coatings of the comparative examples all peeled off within the 9th heat cycle, whereas the SiC coatings of the examples slightly floated in Examples 3 and 5. In addition to being observed, all of them are good, and the weight loss rate is small, showing excellent oxidation resistance. Furthermore, Si
The decrease in strength of the C / C composite material due to the formation of the C coating is small,
It is recognized that it has high material strength.

[0028]

As described above, according to the present invention, when a SiC coating is formed on the surface of a C / C substrate by a conversion method, the prepreg located in the outermost layer portion has a filament number larger than that of the internal prepreg layer. By using the C / C composite material having a composite structure in which the woven carbon fiber cloth is laminated as the base material, it becomes possible to stably and firmly form the SiC coating having a large anchor effect. Therefore,
Even if it is exposed to a high temperature oxidizing atmosphere, it can maintain a high level of oxidation resistance without peeling, and also suppresses the deterioration of the material strength of the C / C composite material. Is extremely useful as a manufacturing method of.

Claims (2)

[Claims] 1. A C / C composite material obtained by laminating a prepreg obtained by impregnating a carbon fiber woven cloth with a matrix resin liquid, curing and firing carbonization is used as a base material, and SiO gas is brought into contact with the base material surface to carry out a conversion method. SiC with gradient function
In the method of forming a coating, the C / of a composite structure in which prepregs located in the outermost layers (uppermost layer and lowermost layer) are laminated using a carbon fiber woven fabric braided with a tow having a larger number of filaments than the inner prepreg layer A method for producing an oxidation resistant C / C composite material, which comprises a C composite material as a base material. 2. A carbon fiber woven fabric in which the number of filaments of the carbon fiber tow in the prepreg of the outermost layer portion (uppermost layer and lowermost layer) is twice or more the number of filaments of the carbon fiber tow in the inner prepreg. The oxidation resistant C according to claim 1, wherein the C / C composite material having a composite structure is used as a base material.
/ C composite material manufacturing method.