JPH07309677A - Oxidation-resistant c/c composite material and its production - Google Patents

Abstract

PURPOSE:To provide an oxidation/resistant C/C composite material (carbon fiber reinforced carbon composite material) showing excellent oxidation resistance in a high temp. oxidizing atmosphere, and to provide its production method. CONSTITUTION:This composite material has such a laminated structure that a first coating layer of SiC having a functionally gradient structure, second coating layer of SiO2 fine particles, third coating layer of Al2O3, and fourth coating layer of Al2O3-SiO2 glass are successively formed on a C/C base body. Th first coating layer is formed by the conversion method to bring SiO2 gas into contact with the surface. The second coating layer is formed by impregnating the base body in vacuum with a soln. obtd. from Si(OC2H5)4 by the alkoxide method and then heat treating the layer. The third layer is formed by gas phase deposition according to the pulse CVI method. The fourth layer is formed by impregnating the base body in vacuum with a soln. obtd. by hydrolysis of a mixture soln. of Si(OC2H5)4 and aluminum salt according to the alkoxide method and then heat treating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oxidation resistant C having a coating structure having a high degree of oxidation resistance in a high temperature oxidizing atmosphere.
/ C composite material ("carbon fiber reinforced carbon composite material", same below)
And its manufacturing method.

[0002]

2. Description of the Related Art C / C composite materials have peculiar material properties such as maintaining a high specific strength and a specific elastic modulus even in a temperature range exceeding 1000 ° C. and exhibiting a low coefficient of thermal expansion.
It is useful as a structural material in many fields including aerospace parts. However, because of the inherent material drawback of carbon materials such that oxidation proceeds in the atmosphere of about 500 ° C, use in the high temperature atmosphere is impossible except for a very short time. For this reason, there have been many attempts to modify the surface of the C / C composite material by coating it with an oxidation resistant coating.

Of these, the most general oxidation resistance treatment is a method of forming a ceramic coating layer by CVD (chemical vapor deposition), and the treatment of coating SiC is known as a typical technique. Has been. C according to the CVD method
Although a dense SiC coating can be formed on the / C composite substrate surface, phenomena such as delamination of the SiC coating due to thermal fluctuation and cracking at the layer interface are likely to occur. This phenomenon is caused by the fact that the maximum strain cannot follow because the difference in thermal expansion between the C / C composite base material and the SiC coating layer is large. Therefore, the C / C composite base material surface has a coefficient of thermal expansion of SiC. If it is modified so as to approximate it, it can be reduced. From this point of view, a method of forming a pyrolytic carbon layer on the surface of a C / C composite substrate by a vapor phase pyrolysis method and then coating SiC by CVD or CVI method (JP-A-2-111681) is proposed. However, a sufficient effect cannot be expected.

On the other hand, in the conversion method in which carbon of the C / C composite base material is used as a reaction source to react with the Si component to be converted into SiC, the surface layer portion of the base material forms a SiC layer as a continuous structure. Since it is a functionally graded material that does not cause interfacial peeling. However, in addition to being less dense than the CVD method, there are problems that minute cracks are generated in the coating layer during the reaction and the oxidation resistance is reduced.

In order to solve the above-mentioned problems, the present applicant has adopted C
/ C in SiC coating layer formed by the conversion method in the composite substrate surface, SiO ₂ further through the SiO ₂ fine coating layer,
An oxidation resistant C / C material for forming a glass coating layer such as B ₂ O ₃ and a manufacturing method thereof have already been developed (JP-A-4-42883). However, in this method, the outermost layer of B ₂ O ₃ −
Since the SiO ₂ glass coating layer softens at about 900 ° C,
It was found that when exposed to high temperatures of 1000 ° C or higher, the vapor pressure also increased and the oxidation resistance performance deteriorated over time.

[0006] Therefore, the present applicant has improved this prior application technique, and can exhibit stable oxidation resistance for a long period of time even in a high temperature atmosphere exceeding 1000 ° C. As a material, a first coating layer made of a polycrystalline SiC coating having a gradient function, a second coating layer made of an amorphous or fine polycrystalline SiC coating, and a third coating made of a B ₂ O ₃ —SiO ₂ glass coating. Oxidation-resistant C / C composite material in which layers are laminated (JP-A-4-243989), an inner layer made of a polycrystalline SiC film having a gradient function, an intermediate layer made of a SiO ₂ fine particle film, A
l ₂ O ₃ -SiO ₂ or _{B 2 O 3 -Al 2 O 3} -S
An oxidation-resistant C / C composite material (Japanese Patent Laid-Open No. 5-43366) in which an outer layer made of a glass film of iO ₂ is laminated and coated is proposed.

[0007]

According to these prior application techniques, stable oxidation resistance can be exhibited for a long period of time even in a high temperature atmosphere exceeding 1000 ° C. However, in a severe high temperature oxidizing atmosphere exceeding 1700 ° C,
The problem that the SiC film is consumed by evaporation of the glass that seals the cracks and the sublimation of SiO ₂ caused by the oxidation of the SiC film, and the oxygen is introduced into the inside of the SiC film layer through the cracks, and the base material is oxidized and worn. There is.

Recently, the demand for oxidation resistance of C / C composite materials has become more and more advanced, and C which has stable oxidation resistance performance even in a severe oxidizing atmosphere exceeding 1700 ° C.
The development of the / C composite material has become a major development issue. As a result of continuing research on this problem, the present inventor found that a stable Al ₂ O ₃ coating layer was formed as an outer layer of the SiC coating.
It has been found that sufficient oxidation resistance can be imparted even in a high temperature region around 1900 ° C.

The present invention was developed based on this finding, and its purpose is to provide a coating structure capable of exhibiting stable oxidation resistance for a long period of time even in a severe high temperature oxidizing atmosphere exceeding 1700 ° C. An object is to provide an oxidation resistant C / C composite material and an industrial manufacturing method thereof.

[0010]

The oxidation resistant C / C composite material provided by the present invention for achieving the above object comprises:
Polycrystalline Si with functionally graded structure on the surface of C / C composite substrate
A first coating layer made of a C coating, a second coating layer made of a SiO ₂ fine particle coating, a third coating layer made of an Al ₂ O ₃ coating, and a fourth coating made of a glassy coating of Al ₂ O ₃ —SiO ₂ .
The structural feature is that the coating layers are sequentially laminated.

The C / C composite material used as the base material is a carbon fiber woven cloth, felt, tow or the like impregnated or coated with a matrix resin liquid to form a prepreg, which is laminated and molded, and then subjected to firing and carbonization treatment. The material manufactured by the method is used, and there is no particular limitation on the manufacturing history of the material, the material structure, and the like. If necessary, the process of impregnating with the matrix resin liquid, hardening, and carbonization is repeated to densify the structure.

The first coating layer consisting of a SiC coating that directly coats the surface of the C / C composite substrate is a polycrystalline SiC coating having a functionally graded structure in which the SiC is gradually organized as the surface layer of the substrate goes to the outer surface. And the preferred SiC coating thickness is 50
~ 300 μm. The SiO ₂ fine particle coating forming the second coating layer fills and seals fine cracks and voids (pinholes) in the SiC coating structure forming the first coating layer and is formed as Al ₂ O formed as the third coating layer. ₃ Functions to enhance adhesion with the coating, and the appropriate SiO ₂ coating amount is 0.5
~ 3.0 mg / cm ² . The third coating layer made of an Al ₂ O ₃ coating has a C / C base material and S at a high temperature of 1700 ° C. or higher.
It functions to prevent the oxidation of the iC coating layer, and the preferable film thickness is 25 to 200 μm. Al ₂ O ₃ -SiO
The fourth coating layer composed of the vitreous coating of ₂ is the third
It is a barrier layer that fills and seals cracks and voids in the Al ₂ O ₃ coating of the coating layer and finally makes the outer surface a non-porous structure to completely block the atmosphere and the C / C composite substrate. The preferred coverage is 0.5-3.0 mg / cm ² .

Oxidation resistance C / having the above-mentioned laminated structure structure
The method according to the present invention for producing a C composite material is based on a carbon fiber reinforced carbon composite material obtained by subjecting a carbon fiber to a composite molding together with a matrix resin, curing and firing carbonization treatment, and SiO 2 on the surface of the base material. First coating step of forming a SiC coating by a conversion method by contacting gas, S
Second coating step of forming a SiO ₂ fine particle coating by vacuum impregnation of a fine particle suspension of SiO ₂ obtained by an alkoxide method of hydrolyzing an alcohol solution of i (OC ₂ H ₅ ) _{4 in} an acidic region, AlCl ₃ or aluminum organic The compound was vapor-phase deposited by the pulse CVI method to form Al ₂
Third coating step of forming an O ₃ coating, and Si (OC ₂
H _{5) 4} and Al ₂ O ₃ -SiO ₂ glass precursor solution mixed solution solution was added an alcohol to aluminum salts obtained in hydrolyzed alkoxide process in the acidic region by vacuum impregnation of Al ₂ O ₃ -SiO _The constitutional feature is that the fourth coating step for forming the vitreous coating of No. 2 is sequentially performed, and then heat treatment is performed at a temperature of 500 ° C. or higher.

The carbon fibers constituting the C / C composite substrate include
Woven fabric such as plain weave, twill weave, felt or tow manufactured from various raw materials such as polyacrylonitrile type, rayon type, pitch type, etc., and felt or tow are used, and the matrix resin is phenol type, furan type, etc. Resin is used. The carbon fiber is sufficiently wetted with the matrix resin liquid by means of dipping, impregnation, coating, etc., and then semi-cured to form a prepreg, and then laminated and pressure-molded. The molded body is heated to completely cure the resin component, and subsequently subjected to firing carbonization treatment or further graphitization to obtain a C / C composite substrate. The C / C composite substrate is subjected to a process of impregnating with a matrix resin, curing, and carbonizing, if necessary, to densify the structure.

The first coating step for forming a polycrystalline SiC coating by conversion on the C / C composite substrate is S
The iO ₂ powder is mixed with Si or C powder, housed in a closed heating system, and a C / C composite substrate is set or embedded in the system to carry out a heating reaction. In this case, it is preferable that the molar ratio of SiO ₂ : Si or C is 2: 1, the heating temperature is set in the range of 1800 to 2000 ° C., and the system is reduced or neutralized. When heated, SiO ₂
Is heated and reduced by the Si or C component to generate SiO gas, and this SiO gas reacts with the carbon structure of the C / C composite substrate to convert the surface layer portion into a SiC coating layer having a functionally gradient structure.

The fine particle suspension of SiO ₂ used in the second coating step is prepared by mixing Si (OC ₂ H ₅ ) ₄ and alcohols such as ethanol and methanol and heating and stirring under reflux, and then Si (OC ₂ H ₅ ) It is prepared by an alkoxide method in which water and an acid are added to H ₅ ) ₄ and the mixture is heated and stirred to be hydrolyzed. The acidic region at this time is
It is preferable to adjust the pH within the range of 1-2. The suspension prepared in this way is 0.2-1.2 μm
The SiO ₂ spherical fine particles of 3) are in a uniformly dispersed state. The second coating layer composed of the SiO ₂ fine particle coating is formed by a step of immersing the C / C composite substrate after the first coating step in the above-mentioned SiO ₂ fine particle suspension, impregnating in vacuum and then drying. Further, if necessary, a treatment of applying and drying the SiO ₂ fine particle suspension may be added.

The formation of the Al ₂ O ₃ coating in the third coating step is carried out by setting the C / C composite base material on which the first and second coating layers have been formed in the reaction chamber of the CVI device and mixing the mixed gas of AlCl ₃ and oxygen. Or aluminum triisopropoxide,
This is performed by a pulse CVI method in which a gas of an aluminum organic compound such as trimethylaluminum or triethylaluminum is introduced and Al ₂ O ₃ is vapor-deposited by thermal decomposition, which is intermittently repeated in a short cycle.

Al ₂ O ₃ --SiO used in the fourth coating step
_{The 2} type glass precursor solution includes aluminum salts such as aluminum nitrate, aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum formoacetate, and aluminum acetylacetonate, and Si (OC ₂
It is prepared by an alkoxide method of hydrolyzing and polymerizing a mixed solution obtained by adding alcohol such as methanol, ethanol, propanol, butanol, and ethylene glycol to H ₅ ) ₄ and water in an acidic region. In the fourth coating step, the C / C composite substrate after the third coating step is dipped in the glass precursor solution, vacuum impregnated and dried, and then 500 ° C.
By the heat treatment process in the above temperature range, Al ₂ O ₃
Forming an -SiO ₂ coating layer.

[0019]

In the present invention, polycrystalline Si having a functionally graded structure is used.
The first coating layer composed of the C coating is formed as a dense and highly adhesive film on the surface of the C / C composite substrate. The SiO ₂ fine particle coating formed as the second coating layer fills and seals cracks and voids (pinholes) of the first coating layer, and is formed by the SiC coating of the first coating layer and the third coating step. It functions as an intermediary for forming a strong coating layer by closely adhering to the Al ₂ O ₃ coating. The third coating layer consisting of an Al ₂ O ₃ coating functions to prevent oxidation of the C / C base material and the SiC coating layer at a high temperature of 1700 ° C. or higher, and
The coating layer is a glassy coating of Al ₂ O ₃ —SiO ₂ third.
As a barrier layer that fills and seals cracks and voids (pinholes) in the Al ₂ O ₃ coating of the coating layer and finally makes the outer surface a non-porous structure and completely blocks the atmosphere and the C / C composite substrate Function.

The Al ₂ O ₃ coating and the Al ₂ O ₃ --SiO layered as the third and fourth coating layers in this way are formed.
High temperature of 1700 ℃ or more, such as 1900 due to the glassy coating of ₂
A high degree of oxidation resistance that sufficiently withstands even in an air atmosphere of ° C is imparted.

[0021]

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

Example (1) Preparation of C / C composite substrate A polyacrylonitrile-based high-elasticity type plain woven carbon fiber cloth was immersed in a matrix resin solution containing a phenol resin initial condensation product for impregnation treatment, and then 14 sheets were laminated. Then, it was put into a mold and subjected to composite molding under the conditions of a heating temperature of 110 ° C. and an applied pressure of 20 kg / cm ² . Then, the molded body is heated to a temperature of 250 ° C. to be completely hardened, then transferred to a firing furnace kept in an N ₂ atmosphere, heated to 2000 ° C. at a heating rate of 5 ° C./hr, and held for 5 hours. Carbonized by firing. The obtained C / C material was impregnated with a phenol resin solution under a vacuum pressure, and the same 2000 ° C. firing treatment was repeated three times to produce a two-dimensional orientation type C / C composite substrate.

(2) First coating step SiO ₂ powder and Si powder are mixed in a molar ratio of 2: 1 and the mixed powder is put in a graphite crucible and C is added on top.
A / C composite substrate (width 30 mm, length 50 mm, thickness 5 mm) was set and covered with a graphite lid. This graphite crucible was transferred to an electric furnace and heated at a temperature rising rate of 50 ° C / hr while maintaining the inside and outside in an Ar gas atmosphere, and kept at a temperature of 1850 ° C for 2 hours to form a surface layer on the C / C composite substrate. A first coating layer composed of a 100 μm thick SiC coating having a gradient function was formed. It was confirmed that cracks with a width of about 10 μm were generated in places on the surface of the SiC coating.

(3) Second coating step The C / C composite substrate on which the first coating layer was formed was placed in a vacuum desiccator, and the pressure was reduced to 1 Torr or less by a vacuum pump.
7 mol of ethanol was added to 1 mol of (OC ₂ H ₅ ) ₄ , and 11 mol of water and 0.03 mol of HCl were mixed to adjust the pH to 1.5.
Then, a suspension of SiO ₂ fine particles prepared by hydrolysis and polymerization was injected. After injecting until the C / C composite base material is completely immersed and holding it for 1 hour, the C / C composite base material is taken out of the desiccator and transferred to an electric furnace in the air atmosphere.
The film was heated to 500 ° C. at a temperature rising rate of 10 ° C./min and held for 30 minutes to form a SiO ₂ fine particle film. By this operation, the entire surface was covered with 1.5 mg / cm ² of SiO ₂ .

(4) Third coating step The C / C composite substrate on which the second coating layer was formed was set in a quartz reaction tube of a pulse CVI device, and the inside of the tube was sufficiently replaced with Ar gas, followed by high frequency induction heating. The temperature of the C / C composite substrate was raised to 1100 ° C. Then, the pressure inside the reaction tube was reduced to 2 Torr or less in 2 seconds by a vacuum pump, and immediately AlCl _{3 was} added.
A mixed gas of oxygen and oxygen (5% by volume as Al) was introduced with Ar as a carrier gas so as to be 720 Torr in 1 second.
Hold for a second. The operation of decompressing the inside of the tube, introducing the reaction gas, and holding the same was repeated 3000 times, and 100 μm thick dense Al ₂
An O ₃ coating was applied.

(5) Fourth coating step The C / C composite substrate on which the third coating layer was formed was placed in a vacuum desiccator, and the pressure was reduced to 1 Torr or less by a vacuum pump.
Ethyl orthosilicate and aluminum nitrate were mixed so that the molar ratio of ₂ O ₃ / SiO ₂ was 1.0, and HCl was added to the aqueous solution containing ethylene glycol and water to add p.
Hydrolyzed and polymerized Al ₂ O ₃ -S adjusted to H 1.5
The iO ₂ glass precursor solution was injected. Inject until the C / C composite substrate is completely immersed, hold for 1 hour, then
Take out the C composite substrate and put it in an electric furnace in the air at 500 ℃
The temperature was maintained for 30 minutes to form a glassy coating of Al ₂ O ₃ —SiO ₂ . By this operation, a 1.0 mg / cm ² Al ₂ O ₃ —SiO ₂ glass film was formed on the entire surface.

(5) Evaluation of Oxidation Resistance A plasma irradiation test was performed on the C / C composite base material coated with the above-described four-stage coating under Ar atmosphere using Ar gas. In the irradiation test, the operation of irradiating for 10 minutes and then cooling to room temperature was repeated 5 times, and the weight loss rate due to oxidative consumption of the C / C composite substrate was measured. The results are shown in Table 1. In addition,
The plasma irradiation conditions were such that the plasma diameter was 5 mm, the distance from the irradiation nozzle to the substrate was 10 mm, and the temperature of the irradiation surface was 1900 ° C. measured by a radiation thermometer.

Comparative Example 1 With respect to the C / C composite substrate on which only the first coating layer of Example was formed, the oxidation resistance was evaluated under the same conditions as in Example,
The results are also shown in Table 1.

Comparative Example 2 A SiC coating layer having a film thickness of 150 μm, a SiO ₂ fine particle coating layer, and a method similar to those described in JP-A-4-42883,
C in which glass coating layers of B ₂ O ₃ —SiO ₂ were sequentially formed
The / C composite substrate was evaluated for oxidation resistance under the same conditions as in the examples, and the results are also shown in Table 1.

Comparative Example 3 A SiC coating layer having a thickness of 150 μm, a SiC coating layer having a thickness of 80 μm by the pulse CVI method, and B ₂ O ₃ —SiO ₂ by the same method as that described in Japanese Patent Laid-Open No. 4-243989.
For the C / C composite substrate in which the glass coating layer of 1 was sequentially formed, the oxidation resistance was evaluated under the same conditions as in Example 1,
The results are also shown in Table 1.

[0031]

[Table 1]

From the results shown in Table 1, the coated C / C composite substrates according to the examples of the present invention show a high degree of oxidation resistance even in a high temperature atmosphere of 1900 ° C., but in Comparative Examples 1 and 2, oxidation resistance is high. The coating layer is penetrated by plasma, and Comparative Example 3
It was confirmed that the weight reduction rate due to oxidation was large.

[0033]

As described above, according to the present invention, a polycrystalline SiC coating layer having a gradient function on the surface, a SiO ₂ fine particle coating layer, an Al ₂ O ₃ coating layer, an Al ₂ O ₃ —SiO ₂ glass coating layer. It is possible to provide a C / C composite base material having a high degree of oxidation resistance, which is sequentially laminated and integrally formed. Therefore, it is extremely useful as a structural member exposed to the severe conditions of a high temperature oxidizing atmosphere exceeding 1700 ° C.

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Claims (2)

[Claims] 1. A first coating layer comprising a polycrystalline SiC coating having a functionally graded structure on the surface of a carbon fiber reinforced carbon composite substrate,
A second coating layer made of a SiO ₂ fine particle coating, a third coating layer made of an Al ₂ O ₃ coating, and a fourth coating layer made of a glassy coating of Al ₂ O ₃ —SiO ₂ are sequentially laminated. Characteristic oxidation resistant C / C composite material. 2. A carbon fiber-reinforced carbon composite material obtained by subjecting a carbon fiber to a composite molding together with a matrix resin, curing and firing carbonization as a base material, and contacting SiO gas on the surface of the base material to obtain SiC by a conversion method. In the first coating step for forming a coating, a fine particle suspension of SiO ₂ obtained by an alkoxide method of hydrolyzing an alcohol solution of Si (OC ₂ H ₅ ) _{4 in} an acidic region is vacuum impregnated with S
Second coating step for forming iO ₂ fine particle coating, AlCl ₃
Alternatively, a third coating step in which an aluminum organic compound is vapor-phase deposited by a pulse CVI method to form an Al ₂ O ₃ coating, and a mixed solution obtained by adding alcohol to an aqueous solution of Si (OC ₂ H ₅ ) ₄ and an aluminum salt is acidified. sequentially applying a fourth coating step of forming a glassy coating of Al ₂ O ₃ -SiO ₂ and Al ₂ O ₃ -SiO ₂ glass precursor solution obtained in hydrolyzed alkoxide process in the region by vacuum impregnation, followed A method for producing an oxidation resistant C / C composite material, which comprises performing heat treatment at a temperature of 500 ° C. or higher.