JPH0648872A - Production of oxidation-resistant c/c composite material - Google Patents

Abstract

PURPOSE:To provide a production method of oxidation-resistant C/C composite material (carbon fiber-reinforced carbon composite material) showing high and stable oxidation resistance at high temp. in an oxidative atmosphere. CONSTITUTION:This production method is composed of three processes. In the first process, SiO gas at 1800-2000 deg.C is brought into contact with the surface of a C/C composite base body to form a SiC film having a gradient-function structure. In the second process, an amorphous SiC film and fine polycrystalline SiC film are successively formed at 900-1000 deg.C and 1200-1400 deg.C, respectively, by pulse-CVI method using a mixture gas of CH3SiCl3 and H2. In the third process, the coating film is impregnated in vacuum with a liquid prepared by hydrolysis and polymn. of B(OC12H27)3 and Si(OC2H5)4 by alkoxide method to form a B2O5-SiO2 glass coating film. In the second process, heat treatment at >=1400 deg.C in a nonoxidative atmosphere is added to convert the SiC coating film into a highly crystallized state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxidation resistant C / C composite material (carbon fiber reinforced carbon composite material) having a coating structure layer exhibiting a high degree of oxidation resistance in a high temperature oxidizing atmosphere.

[0002]

2. Description of the Related Art C / C composite materials have excellent heat resistance and chemical stability as well as excellent specific strength and specific elastic modulus, so that they are structural materials in many fields including aerospace. However, this material has a material defect unique to carbon materials, that is, it is easily oxidizable, and this is the biggest bottleneck that impedes versatility. Therefore, C / C
Many attempts have been made to modify the surface of a composite material by applying an oxidation resistant coating, for example, ZrO ₂ , Al ₂ O.
A method of coating with a ceramic material such as ₃ , SiC, Si ₃ N ₄ has been proposed.

Of these, the most practical oxidation resistant layer is S.
iC film. Conventionally, SiC was used on the surface of C / C composite substrate.
As a method of applying the coating of Si, Si produced by a gas phase reaction
A CVD method for directly depositing C (chemical vapor deposition method),
A conversion method is known in which carbon of a base material is used as a reaction source to react with a silicon component to convert it into SiC, but each has its own merits and demerits. That is, in the SiC coating layer formed by applying the CVD method, the interface with the substrate is clearly separated, and when a thermal shock is applied, a delamination phenomenon is likely to occur due to a mutual thermal expansion difference, and thus in a high temperature range. Sufficient oxidation resistance cannot be expected. On the other hand, when the conversion method is used, the surface layer portion of the base material has a functionally graded structure that is continuously converted into the SiC layer, so that interfacial peeling does not occur, but it is inferior in denseness to the CVD method and There is a problem that minute cracks are generated in the coating layer during the reaction.

As a means for solving such a problem, a first SiC film is formed on the surface of a C / C composite base material by a conversion method by contact with SiO gas, and amorphous SiC is further deposited on the surface. CVD under various conditions
Of the second anti-oxidation treatment method for forming a second SiC coating layer by the method (JP-A-4-12078)
Pulse CV for intermittently filling the base material structure with a halogenated organosilicon compound under reduced pressure heating of the coating layer of the above to perform reductive thermal decomposition
Oxidation-resistant treatment method formed by using the I method
Gazette), the coating layer is a SiC coating layer, a SiO ₂ fine particle coating layer, a SiO ₂ glass coating layer or B ₂ O ₃ or B ₂
The present applicant has developed an oxidation resistant C / C material (Japanese Patent Application Laid-Open No. 4-42883) in which an O ₃ —SiO ₂ glass coating layer is formed in three layers.

Further, as a C / C material having oxidation resistance which is a further development of these techniques, the present inventors have formed a polycrystalline SiC coating film having a gradient function on the surface of the base material of the carbon fiber reinforced carbon material. the first coating layer, an amorphous substance or micro polycrystalline second coating layer made of SiC coating, and B ₂ O ₃ -S
We proposed a coating structure in which a third coating layer consisting of an iO ₂ glass coating was laminated (Japanese Patent Application No. 3-25643).

[0006]

The oxidation resistant C / C composite material according to the invention of Japanese Patent Application No. 3-25643 exhibits sufficiently stable durability even in a severe high temperature oxidizing atmosphere. A closer examination revealed that the conditions for forming the second coating layer had a delicate effect on the oxidation resistance.

The present invention is based on this finding and is an improvement of the above-mentioned prior invention from the viewpoint of manufacturing method. The purpose of the present invention is to exhibit high and stable oxidation resistance in a severe high temperature oxidizing atmosphere. There is an attempt to provide a method for manufacturing a C / C composite material.

[0008]

A method for producing an oxidation resistant C / C composite material according to the present invention for achieving the above object is obtained by subjecting a carbon fiber to a composite molding together with a matrix resin, curing and firing carbonization. A carbon fiber reinforced carbon composite material is used as a base material, and a reaction temperature of 1800 to 2000 ° C. is applied to the surface of the base material.
In the first coating step of forming a SiC film having a functionally gradient structure by contacting SiO gas with a conversion method at a heating temperature of 900 to 1000 ° C. by a pulse CVI method using a mixed gas of a halogenated organosilicon compound and hydrogen. First Step Operation for Forming Amorphous SiC Coating and 120
A second coating step in which a second stage operation for forming a fine polycrystalline SiC coating at a heating temperature of 0 to 1400 ° C. is sequentially performed, and then B (OC ₁₂ H ₂₇ ) ₃ and Si (OC ₂ H ₅ ) ₄ are added. The constitutional feature is that it comprises a third coating step in which a glass precursor solution hydrolyzed and polymerized by the alkoxide method is vacuum impregnated to form a surface layer composed of a B ₂ O ₃ —SiO ₂ glass coating film.

Another embodiment of the second coating step according to the present invention is to form an amorphous and / or fine polycrystalline SiC coating by a pulse CVI method using a mixed gas of a halogenated organosilicon compound and hydrogen. After being formed, it is heat-treated at a temperature of 1400 ° C. or higher in a non-oxidizing atmosphere to convert the film properties into highly crystalline SiC.

First, the C / C composite material as the base material of the present invention is
Manufactured by a conventional method of impregnating or applying a matrix resin liquid having a high carbonization residual ratio to reinforcing fibers such as carbon fiber woven cloth, felt, and tow to form a prepreg, which is laminated and then cured and carbonized by firing. To be done. The material used in this case is not particularly limited, and generally, various carbon fiber reinforcing materials such as polyacrylonitrile-based, rayon-based, pitch-based, etc., and the matrix resin of phenol-based, furan-based or other carbonizable Good liquid thermosetting resins can be used. The manufactured C / C composite substrate is subjected to a process of impregnating with a matrix resin, curing, and carbonizing, if necessary, to densify the structure.

S of a functionally graded tissue is obtained by the conversion method.
In the first coating step for forming the iC coating, SiO ₂ powder is added to S
It is carried out by a method in which it is mixed with i or C powder and housed in a closed heating system, and the C / C composite base material is set or embedded in the system and reacted by heating. The process conditions are SiO
It is preferable to set the compounding amount of Si or C to _{2 in} a weight ratio of 2: 1, set the heating temperature to 1800 to 2000 ° C., and maintain the system in a reducing or neutral atmosphere. When heating,
SiO ₂ is heated and reduced by the Si or C component to produce Si
O gas is generated, and this SiO gas reacts with the carbon structure of the C / C composite base material to convert the surface layer portion into a SiC coating layer having a functionally graded structure in which the concentration of SiC continuously changes at the interface. The suitable film thickness of the SiC coating layer formed in the first coating step is 100 to 300 μm.

In the second coating step, an operation of bringing a mixed gas of a halogenated organosilicon compound and hydrogen into contact with a C / C composite substrate heated in a quartz reaction chamber in a gas state is intermittently repeated in a short cycle. The pulse CVI process is performed. Trichloromethylsilane (CH ₃ SiCl ₃ ) is preferably used as the halogenated organosilicon compound and mixed so that the molar ratio with hydrogen gas (CH ₃ SiCl ₃ / H ₂ ) is 0.01 to 0.05. Then, intermittent introduction / stopping is preferably repeated at intervals of a second into the reaction chamber in a reduced pressure state where the C / C composite substrate is heated.

In the second coating step, in order to sequentially form the amorphous SiC coating and the fine polycrystalline SiC coating, the heating conditions of the pulse CVI step are adjusted,
First, the first stage operation is set to a temperature range of 900 to 1000 ° C. to form an amorphous SiC film, and then the second stage operation in which the temperature is raised to 1200 to 1400 ° C. is used to form fine polycrystalline SiC. A method of forming coatings by stacking them is adopted. In setting these conditions, temperature adjustment is particularly important when forming a fine polycrystalline SiC coating, and if the temperature is less than 1200 ° C., the crystal properties become unstable.
If the temperature exceeds 00 ° C, the SiC coating becomes inhomogeneous. The most preferable heating temperature is 1300 ° C. In addition, an appropriate film thickness is 10 to 30 μm for the lower amorphous SiC layer,
The upper fine polycrystalline SiC layer has a thickness of 30 to 50 μm.

On the other hand, in order to form a highly crystalline SiC film,
In the heating furnace in which the heating temperature of the pulse CVI step is set in the range of 900 to 1300 ° C. to form an amorphous and / or fine polycrystalline SiC coating layer in advance, and then the base material is kept in a non-oxidizing atmosphere. And a heat treatment at a temperature of 1500 ° C. or higher to enhance the crystallinity of the SiC coating.

B ₂ O ₃ --SiO ₂ in the third coating step
The glass coating consists of B (OC ₁₂ H ₂₇ ) ₃ and Si (OC ₂ H _2
5 ) ₄ is hydrolyzed and polymerized by an alkoxide method to prepare a glass precursor solution, and this solution is vacuum impregnated into the C / C composite substrate subjected to the second coating step, and then heat treated at a temperature of 500 ° C. or higher. Formed by the method. At this time, the B ₂ O ₃ glass can be formed by directly impregnating B (OC ₁₂ H ₂₇ ) ₃ in vacuum, but the SiO ₂ glass can be formed by Si (O ₂
It is preferable to adjust the pH of C ₂ H ₅ ) ₄ in advance to pH 1 to ₂ for hydrolysis polymerization, and then to impregnate in vacuum. It is also successful to coat the SiO ₂ glass first and then the B ₂ O ₃ glass as the coating sequence.

[0016]

As described above, according to the method of the present invention, the C / C composite substrate surface is subjected to a coating treatment in three steps to form an oxidation resistant coating. Of these, the SiC coating formed in the first coating step is formed as a dense and highly adherent thick film having a functionally graded structure. The amorphous and fine polycrystalline two-layered SiC coating that is coated in the second coating step fills and seals minute voids (pinholes), cracks, and the like in the SiC coating layer in the first coating step, and Compared with a single SiC coating layer made of an amorphous material or a micropolycrystalline material, the dense retention of the SiC coating structure at the time of high temperature use is improved, and the coating properties are extremely stabilized. In addition, in the aspect in which the highly crystalline SiC layer is formed by heat treatment in the second coating step, fine cracks caused by a difference in thermal expansion with the base material during the crystallization process and heating are positively generated, Ensure a tissue morphology that does not cause property changes during use. The B ₂ O ₃ —SiO ₂ glass coating formed in the third coating step fills the fine cracks generated in the second coating SiC layer to ensure the non-porous structure of the coating layer.

The SiC thus formed in the second coating step
By adjusting the crystalline properties of the coating layer in advance,
Even in a high temperature oxidizing atmosphere up to 00 ° C, extremely high and stable oxidation resistance performance is imparted.

[0018]

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

Examples 1 to 3 and Comparative Examples 1 to 4 (1) Preparation of C / C composite base material A polyacrylonitrile-based high elasticity type plain woven carbon fiber cloth was dipped in a matrix resin solution containing a phenol resin initial condensation product. After impregnation, 14 sheets were laminated and placed in a mold, and composite molding was performed under the conditions of a heating temperature of 110 ° C. and an applied pressure of 20 kg / cm ² . After the molded body was heated to a temperature of 250 ° C. to be completely hardened, it was transferred to a firing furnace maintained in a nitrogen atmosphere, heated to 2000 ° C. at a temperature rising rate of 5 ° C./hr, and held for 5 hours to be carbonized. . Then, 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 3 times to repeat the two-dimensional orientation type C / C material.
A C composite substrate was prepared.

(2) First coating step SiO ₂ powder and Si powder are mixed in a mixing ratio of 2: 1 (weight ratio), the mixed powder is put into a graphite crucible and a C / C composite substrate ( Width 30mm, length 50mm, thickness 5mm) was set. This graphite crucible was transferred to an electric furnace and the inside was filled with Ar.
After fully substituting with gas, at 1850 at a rate of 50 ° C / hr
The temperature was raised to 0 ° C. and maintained for 2 hours to form a SiC coating layer having a functionally graded structure on the surface layer of the C / C composite substrate. The thickness of the formed SiC coating layer was about 200 μm, but it was confirmed that many cracks having a width of about 10 μm were generated on the surface.

(3) Second coating step The C / C composite substrate on which the first coating layer was formed was placed in a quartz reaction tube of a pulse CVI device, the inside of the tube was sufficiently replaced with Ar gas, and then C / C was performed by high frequency induction heating. The temperature of the C composite substrate was raised to 1000 ° C. Then, the pressure inside the reaction tube was reduced to 2 Torr or less in 2 seconds by a vacuum pump, and immediately a mixed gas of trichloromethylsilane (CH ₃ SiCl ₃ ) and H ₂ (CH ₃ SiCl ₃ / H ₂ molar ratio 0.05) was applied in 720 Torr for 1 second. Introduced to become 1
Hold for a second. This operation of depressurizing the inside of the tube, introducing the reaction gas, and holding the same was repeated with 4000 pulses to obtain a thickness of about 20 μ
An amorphous SiC film of m 2 was formed. Continuing,
The heating temperature of the C / C composite substrate was raised to 1300 ° C., and the number of pulses was 5000 and the film thickness was about 30 μm.
The coating was laminated.

(4) Third coating step The C / C composite substrate on which the second 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 , 11 mol of water and 0.03 mol of HCl were mixed, and p
2To glass precursor liquid hydrolyzed and polymerized with H1.5
It was flowed under a reduced pressure of rr and filled with the liquid until the C / C composite base material was completely immersed and held for 1 hour. Then, the C / C composite substrate was taken out from the desiccator, transferred to an electric furnace in the atmosphere, and heated to 500 ° C. at a heating rate of 10 ° C./min.
The temperature was kept for 30 minutes to form a film of SiO ₂ glass.

The C / C composite substrate on which the SiO ₂ glass coating was formed was placed in a vacuum desiccator and the pressure was reduced to 1 Torr or less. Then, B (OC ₁₂ H ₂₇ ) ₃ was injected under a reduced pressure of 2 Torr or less to C.
The / C composite substrate was kept immersed for 1 hour. The treated C / C composite substrate was taken out from the desiccator, air-dried in room temperature air for 2 hours, transferred to an electric furnace kept in the air atmosphere, and heated at 500 ° C. for 30 minutes to form a B ₂ O ₃ glass coating film. Formed. As a result, B ₂ O ₃ --SiO ₂ was formed on the entire surface.
A glass coating was formed.

(5) Evaluation of Oxidation Resistance The C / C composite base material subjected to the above-mentioned three-step coating process is put in an electric furnace maintained in the air atmosphere and kept at a temperature of 1500 ° C. for 1 hour.
After holding it for 00 minutes, it was taken out of the furnace and naturally cooled to room temperature.
This step was repeated 10 times, and the weight loss rate of the final C / C composite material due to oxidation was measured. In addition, for comparison, the second coating step is performed in the heating temperature range of 1000 to 1400 ° C.
The C / C composite material in which a single-layer amorphous and / or fine polycrystalline SiC coating was formed by the stepwise operation was also measured for the weight loss on oxidation. The results are shown in Table 1.

[0025]

[Table 1]

From the results shown in Table 1, the examples to which the conditions of the present invention are applied give the C / C composites a high degree of oxidation resistance as compared with the comparative examples, and have excellent high temperature stability in an oxidizing atmosphere. It is accepted to show. Especially, the heating temperature of the second stage is 13
Good results were obtained in Example 2 in which a fine polycrystalline SiC coating was formed at a temperature of 00 ° C.

Example 5 S of a functionally graded structure was subjected to the same first coating step as in Example 1.
The C / C composite substrate on which the iC film was formed was set in the pulse CVI device, and the second coating step was performed by the following operation.
The inside of the system is maintained in an Ar gas atmosphere, and the C / C composite substrate is
After heating to 00 ° C., the same raw material gas as in Example 1 was set under pulse conditions of a gas introduction pressure of 650 Torr, a pressure retention time of 3 seconds, a gas discharge pressure of 5 Torr, and a pressure retention time of 3 seconds. CVI treatment was performed. This pulse CVI is 1
Repeated 0000 times, 50 μm thick amorphous S
An iC coating was formed. Then, the C / C composite substrate was placed in a heating furnace in an argon atmosphere and kept at a temperature of 1500 ° C. for 1 hour to convert the amorphous SiC film into a highly crystalline SiC layer. By this treatment, many fine cracks were generated in the SiC layer.

Subsequently, the third condition is obtained under the same conditions as in the first embodiment.
A coating process was performed to produce an oxidation resistant C / C composite material. The weight reduction rate of this material due to oxidation at high temperature in the atmosphere was measured in the same manner as in Example 1, and it showed a high level of oxidation resistance of 0.2%.

[0029]

As described above, according to the present invention, a crystalline Si film is formed on the SiC film surface of the functionally graded structure formed on the surface layer portion of the C / C composite base material by using the pulse CVI method under specific conditions.
A C / C composite material having a high degree of oxidation resistance and stable durability can be efficiently produced through a three-step process of forming a C coating and then laminating a B ₂ O ₃ —SiO ₂ glass coating on the entire surface. . Therefore, it is extremely useful as an industrial production technology of an oxidation resistant C / C composite material for structural members exposed to the severe conditions of a high temperature oxidizing atmosphere.

Claims (2)

[Claims] 1. A base material is 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 a reaction temperature of 18 on the surface of the base material.
Forming a SiC film having a functionally graded structure by a conversion method by contacting SiO gas at 00 to 2000 ° C.
Covering step, forming an amorphous SiC film at a heating temperature of 900 to 1000 ° C. by a pulse CVI method using a mixed gas of a halogenated organosilicon compound and hydrogen 1
A second coating step of sequentially performing a step operation and a second step operation of forming a fine polycrystalline SiC coating at a heating temperature of 1200 to 1400 ° C., followed by B (OC ₁₂ H ₂₇ ) ₃ and Si
A glass precursor solution obtained by hydrolyzing and polymerizing (OC ₂ H ₅ ) ₄ by an alkoxide method is vacuum impregnated to obtain B ₂ O ₃ —Si.
A method for producing an oxidation resistant C / C composite material, which comprises a third coating step of forming a surface layer made of an O ₂ glass film. 2. In the second coating step, an amorphous and / or fine polycrystalline SiC coating is formed by a pulse CVI method using a mixed gas of a halogenated organosilicon compound and hydrogen, and then a C / C composite is formed. The method for producing an oxidation resistant C / C composite material according to claim 1, wherein the base material is subjected to a heat treatment at a temperature of 1400 ° C. or higher in a non-oxidizing atmosphere to convert the coating property into highly crystalline SiC.