JPH06345572A - Oxidation resistant coating layer of c/c composite material - Google Patents

Abstract

PURPOSE:To improve oxidation resistance by interposing a coating film of only B2O3 glass as a glassy base layer between a coating film of fine particle- shaped SiO2, as an intermediate layer and a heat resistant glassy coating film as a surface layer. CONSTITUTION:A carbon fiber reinforced carbon composite material (C/C composite material) is set in SiO2. powder mixed with Si or C powder in 2:1 molar ratio and the surface layer part of the composite material is converted into an SiC coating layer having functional gradient structure by heating to 1,850-2,000 deg.C. The composite material with the formed underlayer is put in a suspension of Sin. particles and this suspension is vacuum-impregnated to form a coating film as an intermediate layer. The composite material is further put in a boron alkoxide soln. and this soln. is vacuum-impregnated, hydrolyzed and heated to 500-800 deg.C to form a layer of B2O3. A soln. of a precursor of, glass is then vacuum-impregnated into the composite material and dried and a boron alkoxide soln. is vacuum-impregnated, hydrolyzed and heated at about 800 deg.C in an inert atmosphere. A C/C composite material excellent in oxidation resistance is obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oxidation resistant coating formed on the surface of a C / C composite material (“carbon fiber reinforced carbon composite material”; the same applies hereinafter) and which exhibits excellent oxidation resistance in a high temperature oxidizing atmosphere. Regarding layers.

[0002]

2. Description of the Related Art C / C composite materials have peculiar material characteristics 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 drawing attention as a member for aerospace. However, since this material has a peculiar tendency of a carbon material that oxidation progresses in an air atmosphere of 500 ° C. or more, its use in a high temperature atmosphere is a material defect that is limited to an extremely 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, the SiC coating may be delaminated with a slight heat load,
Phenomena such as cracks tend to occur frequently at the layer interface. This phenomenon is mainly 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, so the C / C composite base material surface approximates the thermal expansion coefficient of SiC. If it is modified so that it can be reduced, it can be reduced. Therefore, a pyrolytic carbon layer is formed on the surface of the C / C composite substrate by the vapor phase pyrolysis method, and then the Si layer is formed by the CVD or CVI method.
A method of coating C (Japanese Patent Laid-Open No. 2-111681) has been proposed, but 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 becomes a functionally graded structure 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.

In order to solve such a problem, the inventor of the present invention has proposed that Si having a functionally graded structure on the surface of a C / C composite substrate.
An intermediate coating layer composed of a C coating layer and a fine particle SiO ₂ coating is formed, and a SiO ₂ —B ₂ O ₃ system, Al ₂
Oxidation-resistant C / C composites have been developed, which are laminated and coated with heat-resistant glassy coatings such as O ₃ —SiO ₂ system and B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ system (JP-A-4-42883). Japanese Patent Laid-Open No. 5-
No. 43366).

[0006]

According to the composite coating layer formed by the above-mentioned prior art, the vitreous coating formed as the surface layer is exposed to a high temperature atmosphere to be softened, and the SiC coating layer as the inner layer in a molten state. In order to completely seal fine pores and cracks generated in the particulate SiO ₂ intermediate coating layer and protect the C / C composite material of the base material from the oxidizing atmosphere, 1200
Exhibits excellent oxidation resistance in severe high-temperature oxidizing atmospheres exceeding ℃.

However, in this composite coating structure, 1000
In a relatively low temperature range below ℃, the oxidation resistance may deteriorate. As a result of studying to clarify this phenomenon, the vitreous base layer in contact with the intermediate layer is SiO ₂
It was found that when it was formed of a glass coating, melt softening in a low temperature region did not proceed smoothly, and as a result, a sufficient sealing effect was not exhibited. As a result of further research, the above-mentioned inconvenient phenomenon was improved by interposing a glass coating of B ₂ O ₃ alone having a relatively low melting point between the intermediate layer and the vitreous coating layer, and the low temperature of 1000 ° C. or less was improved. From area 1
It has been clarified that a practical oxidation resistant coating layer can be obtained in a high temperature range exceeding 200 ° C.

The present invention was developed on the basis of the above-mentioned findings, and its purpose is to provide a C / C composite material having a composite coating structure which exhibits stable and sufficient oxidation resistance in a high temperature oxidizing atmosphere at 500 to 1200 ° C. To provide an oxidation resistant coating layer.

[0009]

The oxidation resistant coating layer of a C / C composite material according to the present invention for achieving the above object is a Si having a functionally graded structure on the surface of a carbon fiber reinforced composite material.
In a composite coating structure in which an underlayer made of a C coating, an intermediate layer made of a fine particle SiO ₂ coating, and a surface layer made of a heat resistant glassy coating are sequentially laminated, the intermediate layer made of the fine particle SiO ₂ coating and the surface layer made of a heat resistant glassy coating are formed. A constitutional feature is that a coating of B ₂ O ₃ glass alone is interposed as a glassy base layer therebetween.

In the present invention, the C / C composite material as the base material is a conventional method in which carbon fiber woven cloth, felt, tow and the like are impregnated or applied with a matrix resin liquid, laminated and molded, and then subjected to firing carbonization treatment. The one manufactured in
There is no limitation on the manufacturing history of the material or the material structure.

Si directly coated on the surface of C / C composite
The base layer of the C coating is a polycrystalline SiC layer whose surface layer is C /
A coating layer having a high bonding property, which has a functionally-graded structure in which the generation concentration of SiC gradually decreases toward the inside of the structure of the C composite material,
The preferred film thickness is 100 to 300 μm. The fine particulate SiO ₂ film serving as the intermediate layer functions to fill and seal the fine pores and cracks generated in the SiC film of the underlayer and to enhance the adhesion with the glassy coating layer on the upper surface. A thickness of about 5 μm is sufficient for the intermediate layer.

The heat-resistant vitreous coating of the surface layer is, for example, Si.
O ₂ based, SiO ₂ -B ₂ O ₃ system, Al ₂ O ₃ -SiO ₂
System, SiO ₂ —AlO ₃ —B ₂ O ₃ system, etc., but SiO ₂ —B ₂ O ₃ system glassy coating is most suitable for the purpose of the present invention. In addition, SiO ₂ -B ₂ O ₃
The system means not only a solid solution of these components but also a composite coating in which a SiO ₂ coating and a B ₂ O ₃ coating are continuously laminated. The heat-resistant glassy coating melts and softens in a temperature range exceeding 1000 ° C., uniformly seals the entire surface, and functions as a barrier layer for blocking contact with the outside air.

The main constituent feature of the present invention is that, in the above composite coating structure, B ₂ O ₃ glass alone is used as a vitreous base layer between the intermediate layer made of the particulate SiO ₂ coating and the surface layer made of the heat-resistant vitreous coating. It is where the coating is interposed. The vitreous base layer consisting of this B ₂ O ₃ glass single coating preferentially melts and softens in a temperature range of 1000 ° C. or lower in preference to the surface layer of the heat resistant glassy coating when exposed to a high temperature oxidizing atmosphere, and seals. As a layer, it exhibits effective oxidation resistance.

The above-mentioned oxidation resistant coating layer of the C / C composite material according to the present invention comprises an underlayer coating step of reacting a SiO gas on the surface of the C / C composite material to form an SiC coating film by a conversion method. Si (OC) by alkoxide method
SiO obtained by hydrolyzing ₂ H ₅ ) ₄ with a basic aqueous solution.
Intermediate layer coating step of impregnating the fine particle suspension of ₂ under reduced pressure, and glassy base layer coating in which a B (OC ₄ H ₉ ) ₃ solution is impregnated or adhered and then heat-treated to convert it into a B ₂ O ₃ glassy layer Process and Si by alkoxide method
Al ₂ O ₃ -Si is impregnated or adhered with a glass precursor solution obtained by hydrolyzing (OC ₂ H ₅ ) ₄ with an acidic aqueous solution or an acidic aqueous solution containing an AlCl ₃ aqueous solution and then dried.
An O ₂ -based glassy coating layer is formed, or B (OC ₄
H ₉ ) ₃ solution was used and treated in the same manner as described above to obtain SiO ₂ —B ₂
It can be manufactured by a process of sequentially forming a glassy coating layer of O ₃ system or SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ system. A detailed description of this process is as follows.

As the carbon fiber constituting the C / C composite material, plain weave, twill weave or other woven fabric, felt or tow produced from various raw materials such as polyacrylonitrile type, rayon type and pitch type is used, and as a matrix resin. The liquid thermosetting resin having good carbonization property such as phenol type, furan type or the like 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.

In the base layer coating step, SiO ₂ powder is mixed with Si or C powder and stored in a closed heating system, and C /
It is carried out by a method in which the C composite material is set or embedded and a heating reaction is performed. The conditions at this time are that the molar ratio of SiO ₂ : Si or C is 2: 1 and the heating temperature is 1850 to 20.
It is preferable to set the temperature in the range of 00 ° C. and reduce or neutralize the inside of the system. When heated, SiO ₂ is Si or C
The components are heated and reduced to generate SiO gas.
The iO gas reacts with the carbon structure of the C / C composite material to convert the surface layer portion into a SiC coating layer having a functionally gradient structure.

In the step of coating the intermediate layer, the C / C in which the underlayer is formed on the SiO ₂ fine particle suspension by the alkoxide method.
It is carried out by adding C composite material, impregnating under reduced pressure, and then drying. Further, if necessary, a treatment of applying and drying the SiO ₂ fine particle suspension may be added. At this time, the fine particle suspension of SiO ₂ used is prepared by mixing Si (OC ₂ H ₅ ) ₄ and alcohols such as ethanol and methanol in a molar ratio of 1:10 to 15 and heating and stirring under reflux. Then, the above Si (OC ₂ H
₅ ) It is prepared by an alkoxide method in which NH ₄ OH is added together with water in an amount corresponding to a molar ratio of ₅ ) ₄ to 1:25 to 30 to heat and stir in a basic state to cause hydrolysis. The basic region at this time is preferably adjusted to a pH range of 11.0 to 12.5. The suspension thus produced exhibits a suspension state in which 0.2 to 1.2 μm SiO ₂ spherical fine particles are uniformly dispersed, and sufficiently fills the fine pores and cracks of the underlayer.

The vitreous base layer consisting of a single coating of B ₂ O ₃ glass has a C / C composite material with an intermediate layer formed on it as B (OC
It is formed by a method in which it is placed in a ₄ H ₉ ) ₃ solution, impregnated under reduced pressure, air-dried for a whole day and night, hydrolyzed by moisture in the air, dried and then heat-treated at a temperature of 500 ° C. or higher. When the heat treatment temperature is lower than 500 ° C., it becomes difficult to form a stable B ₂ O ₃ glassy coating layer. A preferable heating temperature range is 500 to 800 ° C.

In order to form a SiO ₂ —B ₂ O ₃ heat-resistant vitreous coating as a surface layer, first, Si (OC ₂ H ₅ ) _{4 is formed.}
And alcohol are mixed at a molar ratio of 1: 1.5 to 7.0, and the mixture is stirred under reflux at room temperature.
After adding an aqueous HCl solution containing HCl together with water in an amount corresponding to 1: 2 to 5 in a molar ratio to i (OC ₂ H ₅ ) ₄ to make an acidic solution (pH 1 to 3), hydrolyze while stirring. A SiO ₂ glass precursor solution is prepared by the alkoxide method. A C / C composite material having a glassy base layer is immersed in this SiO ₂ glass precursor solution for impregnation under reduced pressure, or the surface of the C / C composite material is uniformly sprayed with the SiO ₂ glass precursor solution. And then dried in the temperature range around 100 ° C. Then, soak in B (OC ₄ H ₉ ) ₃ solution and impregnate under reduced pressure or apply by spray spraying, air dry for one day and hydrolyze with moisture in the air, and then heat at a temperature of around 800 ° C in an inert atmosphere. The method of processing is adopted. SiO ₂ -Al ₂
To form an O ₃ -B ₂ O ₃ -based heat-resistant glassy coating,
In the process of preparing the SiO ₂ glass precursor solution described above, A
It may be hydrolyzed with an acidic aqueous solution containing lCl ₃ ,
Further, for the Al ₂ O ₃ —SiO ₂ -based heat-resistant glassy coating, the treatment of the B (OC ₄ H ₉ ) ₃ solution may be omitted in this process.

[0020]

The oxidation resistant coating layer of the C / C composite material according to the present invention comprises:
On the surface of the C / C composite material, a dense and highly adherent SiC film having a functionally graded structure is formed as an underlayer, and as an intermediate layer, minute pores, cracks, etc. of the underlayer are filled and sealed, and a glassy film layer is formed. It is composed of a fine particle SiO ₂ coating for enhancing adhesion, a single coating made of B ₂ O ₃ glass as a glassy base layer, and a composite coating layer in which a heat-resistant glassy coating is sequentially laminated as a surface layer. When a C / C composite material having this coating layer structure is exposed to a high temperature oxidizing atmosphere, 1
In the temperature range of 000 ° C. or lower, the B ₂ O ₃ glass of the vitreous base layer first melts and softens to completely seal the underlayer and the intermediate layer, and functions as a barrier for blocking contact with the outside air. When the ambient temperature is 1000 ° C. or higher, the heat-resistant glassy coating of the surface layer is melted and softened, and the same sealing effect as described above is exhibited.

Owing to the barrier function of blocking the stepwise oxygen diffusion by the glass base layer and the heat-resistant glassy coating, stable oxidation resistance is exhibited for a long period in a wide temperature range of 500 to 1200 ° C. It

[0022]

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

Example 1 (1) Preparation of C / C composite base material Polyacrylonitrile-based high elasticity type plain woven carbon fiber cloth with phenol resin initial condensate [Dainippon Ink and Machinery Co., Ltd.]
Was prepared as a matrix resin and air-dried for 48 hours to prepare a prepreg sheet. The prepreg sheets are laminated and placed in a mold, and the heating temperature is 110 ° C.,
Composite molding was performed under the condition of an applied pressure of 20 kg / cm ² . Then, after heating the molded body to a temperature of 250 ° C. to completely cure it,
It was transferred to a firing furnace maintained in an N ₂ atmosphere, heated to 2000 ° C. at a temperature rising rate of 5 ° C./hr, and held for 5 hours for carbonization by firing. In this way, the carbon fiber volume content (Vf) of 65
%, A C / C composite material having an apparent specific gravity of 1.65 g / cc was produced.

(2) Underlayer 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.
The / C composite was set and covered with a graphite lid. This graphite crucible was transferred to an electric furnace, and while maintaining the inside and outside in an Ar gas atmosphere, the temperature was raised to 1900 ° C. at a rate of 50 ° C./hr and kept for 2 hours to form a functionally graded structure on the surface layer of the C / C composite material. A polycrystalline SiC coating was provided. The formed SiC film had a thickness of about 200 μm, but the surface had a width of 10 μm.
Minute cracks of about μm were generated in some places.

(3) Intermediate layer coating step Si (OC ₂ H ₅ ) ₄ and ethanol were mixed in a molar ratio of 1:12, and the mixture was refluxed and stirred at a temperature of 70 ° C. A mixed solution of 25 mol of water and 0.2 mol of NH ₄ OH with respect to 1 mol of ₂ H ₅ ) was added dropwise with stirring. The pH of the mixed aqueous solution was 12.0. Then, stirring was continued to prepare a suspension in which spherical SiO ₂ fine particles of about 0.2 μm were uniformly suspended. A C / C composite material having an underlayer formed thereon was dipped in this suspension and impregnated under reduced pressure for 15 minutes. Then, after air drying,
Further, the suspension was applied to the surface, and the air drying and drying treatments were repeated three times in the same manner, and the coating was dried at a temperature of 100 ° C. to form an intermediate layer of a fine particle SiO ₂ coating. The thickness of the formed intermediate layer was 5 μm.

(4) Vitreous Base Layer Coating Step The C / C composite material on which the intermediate layer was formed was immersed in a B (OC ₄ H ₉ ) ₃ solution and impregnated for 15 minutes under reduced pressure.
After impregnation, it is air dried for a whole day and night, hydrolyzed by moisture in the air, dried at 100 ° C, and transferred to a heating furnace to 500 ° C.
Heat treatment was carried out for 15 minutes at a temperature of 1 to form a film of B ₂ O ₃ glass alone. The coating film thickness was 2 μm.

(5) Surface layer coating step Si (OC ₂ H ₅ ) ₄ and ethanol were mixed in a molar ratio of 1: 4.5, and the mixture was refluxed and stirred at room temperature. A mixed aqueous solution of 2.5 mol of water and 0.03 mol of HCl was added dropwise to 1 mol of ₂ H ₅ ) ₄ . The solution pH after the dropping was 3.0. Continue 1
The stirring was continued for a while to obtain a SiO ₂ glass precursor solution.
C forming a glassy base layer on this glass precursor solution
/ C composite material is dipped, impregnated under reduced pressure for 15 minutes, air-dried, then 1
It was dried at a temperature of 00 ° C. Subsequently, it was immersed in a B (OC ₄ H ₉ ) ₃ solution, impregnated under reduced pressure for 15 minutes, air-dried for one day and night, hydrolyzed by moisture in the air, and dried at a temperature of 100 ° C. The C / C composite material after the drying treatment was transferred to an electric furnace and heated at 800 ° C. for 60 minutes to form SiO ₂ —B ₂ on the surface.
An O ₃ based glassy film was formed. The heat-resistant vitreous coating thus formed had a thickness of 3 μm.

(6) Evaluation of Oxidation Resistance The oxidation resistant coating layer of the present invention was formed by the above-mentioned process.
/ C composite material was placed in an electric furnace maintained in the atmosphere,
After heating at a temperature of 500 ° C. for 30 minutes, it was taken out of the furnace and naturally cooled to room temperature. This operation was performed every 100 ° C. from 500 to 1200 ° C., and the weight reduction rate due to the oxidation of the final C / C composite substrate was measured. The results are shown in Table 1.

Comparative Example 1 An oxidation resistance test was conducted in the same manner as in Example 1 on the C / C composite material in which only the underlayer of the SiC coating having a functionally graded structure was formed under the same conditions as in Example 1. The results are also shown in Table 1.

Comparative Example 2 Of the steps of Example 1, the B ₂ O ₃ glassy base layer coating step was omitted, and after the SiO ₂ glass precursor treatment of the surface layer coating step, heat treatment was performed at a temperature of 500 ° C. to obtain B ( OC ₄ H ₉ ) ₃
The heating temperature after the treatment was changed to 500 ° C. to form a composite coating layer on the surface of the C / C composite material. For this C / C composite material,
An oxidation resistance test was conducted in the same manner as in Example 1, and the results are also shown in Table 1.

[0031]

From the results shown in Table 1, the C / C composite material provided with the composite coating layer of Example 1 exhibited excellent oxidation resistance in the entire temperature range of 500 to 1200 ° C. On the other hand, in the composite coating layer of Comparative Example 2 in which the glassy base layer was substantially composed of the SiO ₂ coating layer, the oxidation resistance performance was considerably deteriorated.

[0033]

As described above, according to the present invention, the surface of the C / C composite material has an underlayer of a polycrystalline SiC film having a gradient function, an intermediate layer of a particulate SiO ₂ film and a surface of a heat-resistant glassy film. In a composite coating structure in which layers are laminated, by interposing a glassy base layer of B ₂ O ₃ alone coating between the intermediate layer and the surface layer, high oxidation resistance in a wide temperature range of 500 to 1200 ° C. Can be granted. Therefore, the C / C composite material provided with this coating layer is applied to a structural member application exposed to the severe conditions of a high temperature oxidizing atmosphere, and effects such as securing stable performance and extending a durable life are brought about.

Claims (2)

[Claims] 1. An underlayer of a SiC coating having a functionally graded structure on the surface of a carbon fiber reinforced carbon composite material, and a particulate S.
intermediate layer by iO ₂ film, and the composite coating structure obtained by sequentially stacking a surface layer by heat-vitreous coatings, vitreous base-layer between the surface layer by the intermediate layer and the heat-resistant glassy coating according to the particulate SiO ₂ film As B ₂ O ₃
C characterized by interposing a film of glass alone
/ C composite material oxidation resistant coating layer. 2. The heat-resistant glassy coating is SiO ₂ —B ₂ O.
The oxidation resistant coating layer of a C / C composite material according to claim 1, which is a ₃ type glassy coating.