JPH0796473B2 - Oxidation resistance treatment method for carbon fiber reinforced carbon material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a carbon fiber reinforced carbon material (hereinafter referred to as “C / C”) capable of imparting excellent oxidation resistance in a high temperature oxidizing atmosphere.
It is called "C material". ) Related to the oxidation resistance treatment method.

[Conventional technology]

C / C materials have excellent specific strength and specific elastic modulus, and also have excellent heat resistance and corrosion resistance, and are therefore in the spotlight as structural materials for various fields including aerospace applications.

The C / C material is generally made of carbon fiber woven fabric, felt, tow, etc. as a reinforcing material, and is impregnated or coated with a matrix resin liquid having a high carbonization residual rate, and then laminated and molded, followed by curing and firing carbonization treatment. However, this material inherits the material defect inherent to carbon materials such as oxidizability as it is, and this is the biggest bottleneck to impede versatility. For this reason, it has been attempted to modify the surface of the C / C material by applying an oxidation resistant coating,
For example, a method of coating with a ceramic material such as ZrO ₂ , Al ₂ O ₃ and SiC has been proposed. However, a coating layer other than SiC does not exhibit the function of sufficiently preventing the progress of oxidation due to delamination or cracking at the coating interface due to the thermal cycle during use.

Even in the SiC coating layer, delamination often occurs depending on the method of film formation. That is, as a method for coating the surface of the C / C substrate with SiC, a conversion method in which carbon of the substrate is used as a reaction source to be converted into SiC,
There is a CVD (Chemical Vapor Deposition) method in which SiC deposited by a vapor phase reaction is directly deposited. Of these, the former method forms a Si layer on the surface of the substrate by hydrogen reduction of a silicon halide compound such as SiCl ₄ , or forcibly impregnates the substrate with an organosilicon compound such as polycarbosilane in a molten state. , Or SiO produced by reacting SiO ₂ , Si, C, etc. on the surface of the substrate
This is due to the mechanism in which gas is brought into contact with these silicon components and the carbon structure of the base material is heated and reacted to be converted into SiC. Since the base material surface becomes a functionally gradient material that forms a SiC layer as a continuous composition, the coating interface is In other words, it exhibits coating characteristics in which delamination hardly occurs. On the other hand, the latter CVD method is a heating reaction between a silicon compound such as SiCl ₄ and a hydrocarbon (for example, C ₃ H ₈ ) or a halogenated organic compound containing a hydrocarbon such as trichloromethylsilane (CH ₃ SiCl ₃ ). This method deposits and deposits SiC vapor-deposited by reductive thermal decomposition on the surface of the substrate. In this case, the coating interface is clearly separated. Is easy to occur.

Therefore, the conversion method, especially the dense Si
It is desirable to apply the method of contacting the converted SiO gas with the C layer.

However, in the conversion method, the carbon component bonded to oxygen in SiO from the textured surface of the C / C substrate heated in the reaction step of the coating process becomes CO and gas is released,
Due to this, minute voids (pinholes) are formed between the SiC particles. Even in the case of the SiC film formed by the conversion method, minute cracks may occur during the reaction depending on the layer thickness and other conditions, and this causes a decrease in the oxidation resistance together with the minute voids.

As a means to eliminate such minute voids, cracks, etc., it is possible to further form a SiC film by the CVD method on the SiC coated surface, but crystalline SiC precipitated by the ordinary CVD method has large generated particles. Because of the minute void,
The inside of cracks is not filled smoothly and a sufficient filling effect cannot be obtained.

[Problems to be Solved by the Invention]

The present inventor has previously used C / C to solve the above problems.
The first SiC film is formed on the surface of the substrate by the conversion method by contacting with SiO, and then the second SiC film layer is formed by the CVD method under the condition that amorphous SiC is deposited on the surface of the first SiC film. We have developed and proposed an oxidation resistance treatment method for C / C materials that seals cracks, etc. (Japanese Patent Application No. 2-114872).
issue).

However, in the case of this method, the CVD reaction becomes diffusion-controlled, so that the generated SiC deposits prior to the site with a short diffusion path on the surface of the substrate, and does not deposit on the site with a long diffusion path such as inside a crack. The phenomenon of becoming slow occurs. As a result, there is room for improvement in that the filling of the amorphous SiC into the cracks becomes incomplete.

The object of the present invention is to improve the above-mentioned prior invention by making amorphous or fine polycrystalline SiC minute voids,
C / C that reliably fills cracks, etc., and can therefore provide even better oxidation resistance in a high temperature oxidizing atmosphere
The present invention is to provide a method of oxidation-proofing the material.

[Means for Solving the Problems]

Oxidation resistance treatment method of the C / C material according to the present invention to achieve the above objects, a carbon fiber reinforced carbon body obtained by complex molding carbon fiber with matrix resin, curing and firing carbonization, as a base material, A first coating step in which SiO gas is brought into contact with the surface of the base material to form a first SiC coating layer by a conversion method, and then the base material is held in a reduced pressure system.
Amorphous or fine polycrystalline SiC by pulse CVI method in which halogenated organosilicon compounds are intermittently charged while being heated in the temperature range of 0 to 1100 ℃ to carry out reductive thermal decomposition reaction.
Is characterized in that the second coating step of depositing and depositing on the surface of the first SiC coating layer to form the second SiC coating layer is sequentially performed.

Carbon fiber, which is a reinforcing material, includes polyacrylonitrile-based,
Woven fabric such as plain weave and twill weave manufactured from various raw materials such as rayon type and pitch type, felt and tow are used, and as the matrix resin, phenol type, furan type and other liquid thermosetting resin with good carbonization property are used. . The carbon fiber is sufficiently wetted with the matrix resin by means of dipping, impregnation, coating or the like, 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 according to a conventional method to obtain a C / C base material.

The obtained C / C base material may be subjected to a treatment of impregnating with a matrix resin, curing, and carbonization, if necessary, to densify the structure.

The C / C substrate thus obtained is subjected to the first coating step for forming the first SiC coating layer by the conversion method. The first coating step is performed by mixing SiO ₂ powder with Si or C powder, shrinking the mixture into a closed heating system, setting a C / C substrate in the system and heating. By heating, SiO ₂ is reduced by Si or C component, and the SiO gas generated by the reaction reacts with the carbon structure of the C / C base material to convert the surface layer portion into SiC.

At this time, by controlling the concentration of SiO gas generated by the reaction of the components, the reaction temperature, the reaction time, etc., a tissue state having a gradient function in which the C layer of the base material and the SiC of the coating layer continuously change at the interface It is formed. The most preferable conditions are
The molar ratio of SiO ₂ : Si or C is 2: 1 and the heating temperature is 1850-
It is to set in the range of 2000 ℃.

Then, a second coating step for depositing and depositing a second SiC coating layer by the pulse CVI method is performed on the surface of the C / C substrate on which the first SiC coating layer is formed.

Examples of the halogenated organosilicon compound used in the second coating step include trichloromethylsilane (CH ₃ SiCl ₃ ), trichlorophenylsilane (C ₆ H ₅ SiCl ₃ ), dichloromethylsilane (CH ₃ SiHCl ₂ ), dichlorodimethyl. Silane ((CH ₃ )
₂ SiCl ₂ ) and chlorotrimethylsilane ((CH ₃ ) ₃ SiCl). In the pulse CVI method of the present invention, the operation of bringing these halogenated organosilicon compounds into contact with a heated C / C substrate set in a quartz reaction chamber in a gas state while entraining it in H ₂ gas is intermittent in a short cycle. It is performed by repeating the method. In this step, it is an important requirement to carry out the pulse CVI under the condition that the inside of the reaction chamber system is kept under reduced pressure and the heating temperature of the C / C substrate is adjusted in the range of 900 to 1100 ° C. Under conditions out of this range, it is not possible to reliably infiltrate dense, amorphous or fine polycrystalline fine SiC into the minute voids, cracks, etc. of the first coating layer, resulting in high impermeability. It becomes difficult to form the second SiC coating layer provided. The most preferable condition of the second coating step is that the reaction system is trichloromethylsilane (CH ₃ S
iCl ₃ ) and hydrogen gas are mixed so that the molar ratio is in the range of 1:20 to 100, and intermittent introduction / stopping is repeated at intervals of a second under a reduced pressure of 10 ^-1 Torr or less in the reaction chamber. Is.

By performing the second coating step, the surface of the first SiC coating layer is formed as an integral coating layer without pinholes via the second amorphous or fine polycrystalline SiC coating.

[Work]

According to the present invention, the surface layer of the C / C substrate is first converted into the first SiC coating layer having a dense and strong gradient function by the conversion method using the SiO contact mechanism in the first coating step, and the subsequent second coating is performed. Through permeation precipitation of fine amorphous or fine polycrystalline SiC by pulse CVI method
Small voids (pinholes) and cracks in the coating layer are reliably filled and sealed, and the entire surface of the second SiC is dense.
It is integrally and firmly coated with the coating layer.

Due to the action of the two-step coating process, a gas impermeable and highly oxidation resistant coating is formed on the entire surface of the C / C substrate.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 2 (1) Preparation of C / C base material 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. Fourteen of these 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 heating the molded product to a temperature of 250 ° C to completely cure it,
It was transferred to a firing furnace maintained in a nitrogen atmosphere, heated to 1000 ° C. at a temperature rising rate of 5 ° C./hr, and held for 5 hours for firing and carbonization.

The obtained C / C material was impregnated with a phenol resin solution under vacuum pressure, and the treatment of baking at 1000 ° C. was repeated three times in the same manner as above to prepare a C / C base material having a dense structure.

(2) First coating step SiO ₂ powder and Si powder are mixed at a mixing ratio of 2: 1 and the mixed powder is put in a graphite crucible and a C / C base material is set on the upper part of the graphite lid. Covered.

Next, the graphite crucible was transferred to an electric furnace, and the inside of the crucible was replaced with Ar.
After sufficiently substituting with a gas, the temperature is raised to 1850 ° C at a rate of 50 ° C / hr, and the temperature is maintained for 2 hours for reaction to cause the surface layer of the C / C material to have a first SiC coating layer having a gradient function. Converted to.

The thickness of the formed SiC coating layer was about 200 μm, but it was confirmed that cracks with a width of about 10 μm were generated in places on the surface.

(3) Second coating step The C / C substrate on which the first SiC coating layer was formed in the first coating step was set in the quartz reaction tube (capacity 500 ml) of the pulse CVI device, and the inside of the tube was sufficiently replaced with Ar gas. After that, by high frequency induction heating
Raised the temperature of C / C substrate (950 ℃, 1100 ℃).

Subsequently, the pressure inside the reaction tube was reduced to 10 ^-1 Torr in 1.5 seconds, and immediately the mixed reaction gas consisting of trichloromethylsilane (CH ₃ SiCl ₃ ) and H ₂ (molar ratio 1:20) was brought to a pressure of 40 Torr in 1 second. And introduced for 3 seconds and held for 1 second. The operation of depressurizing the inside of the tube, introducing the reaction gas and holding the same was repeated 5000 times to form a second SiC coating layer by the pulse CVI method.

The average film thickness of the second SiC coating layer was 30 μm.

(4) Evaluation of oxidation resistance The C / C material on which the SiC coating layer was formed by the above two-step coating process was put in an electric furnace and heated to 1300 ° C at a rate of 10 ° C / min in the air for 2 hours. A heating / cooling cycle of holding and then naturally cooling was repeated 5 times. The weight loss due to oxidation was measured for the materials treated in this way and the results are shown in Table 1 in comparison with the coating conditions.

Comparative Example 1 A two-step SiC coating layer was formed under the same conditions as in Example except that the reaction temperature in the second coating step was 1200 ° C. The oxidation weight reduction rate of this material was measured by the same method as in the example, and the results are also shown in Table 1.

Comparative Example 2 A C / C substrate on which a first SiC coating layer was formed under the same conditions as in Example was reacted with a mixed reaction gas of trichloromethylsilane (CH ₃ SiCl ₃ ) and H ₂ (molar ratio 1:20). The second Sic coating layer having a film thickness of 30 μm was formed by the CVD method by bringing them into contact with each other at a temperature of 950 ° C. and a pressure of 400 Torr.

The oxidized weight reduction rate of the treated material was measured by the same method as in Example, and the results are also shown in Table 1.

Comparative Example 3 A mixed reaction gas of SiCl ₄ , CH ₄ and H ₂ (molar ratio 1: 1: to a C / C substrate on which a first SiC coating layer was formed under the same conditions as in Example).
7) is contacted at a reaction temperature of 1500 ° C, and a film thickness of 30 is obtained by the CVD method.
A 2 μm second SiC coating layer was formed.

The oxidized weight reduction rate of the treated material was measured by the same method as in Example, and the results are also shown in Table 1.

Comparative Example 4 A SiC coating layer was directly formed on the surface of the same C / C substrate as in Example by the CVD method under the same conditions as in Comparative Example 2. The oxidation weight reduction rate of this material was measured by the same method as in the example, and the results are also shown in Table 1.

Comparative Example 5 A SiC coating layer was directly formed on the surface of the same C / C substrate as in Example by the CVD method under the same conditions as in Comparative Example 3. The oxidation weight reduction rate of this material was measured by the same method as in the example, and the results are also shown in Table 1.

Comparative Example 6 Of the coating steps of the example, only the first coating step was performed to obtain the first
With respect to the material on which the SiC coating layer was formed, the reduction rate of oxidized weight was measured by the same method. The results are also shown in Table 1.

From the results in Table 1, it is clear that the C / C materials of Examples 1 and 2 in which the second SiC coating layer was formed by applying the pulse CVI method had a very small weight reduction rate due to oxidation. However, in Comparative Example 1 in which the reaction temperature in the second coating step was 1200 ° C., the second SiC
Since the crystallization of the coating layer progresses and the crystal grain boundaries also appear clearly, the oxidative consumption increases as compared with the examples. In addition, the materials to which the CVD method is applied as the second coating step as in Comparative Examples 2 and 3 have poor oxidation resistance because the second SiC coating layer is not sufficiently permeated and filled inside the cracks of the first SiC coating layer. Since the materials of Comparative Examples 4 and 5 were formed only by the SiC coating layer by the CVD method, the adhesion was weak and the phenomenon that part of the SiC coating peeled off during the oxidation test occurred.

[Effects of the Invention] As described above, according to the present invention, the first coating step of forming the first SiC coating layer on the surface of the C / C material by the conversion method by the SiO contact mechanism and the pulse CVI method under the specific conditions on the upper surface thereof are performed. A high degree of oxidation resistance can be imparted by combining the second coating steps for forming the amorphous or fine polycrystalline SiC coating layer and sequentially performing the treatment.

Therefore, when applied to structural member applications exposed to severe conditions under a high temperature oxidizing atmosphere, effects such as securing stable performance and extending the useful life are brought about.

Claims (2)

[Claims] 1. A carbon fiber reinforced carbon body 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 2 gas on the surface of the base material. The first coating step for forming the SiC coating layer of
Amorphous or fine polycrystalline SiC by pulse CVI method in which halogenated organosilicon compounds are intermittently charged while being heated in the temperature range of 0 to 1100 ℃ to carry out reductive thermal decomposition reaction.
Is sequentially deposited on the surface of the first SiC coating layer to form a second SiC coating layer, which is successively subjected to a second coating step. 2. The deposition of amorphous or fine polycrystalline SiC in the second coating step is performed by trichloromethylsilane (C
The oxidation resistance treatment method for a carbon fiber reinforced carbon material according to claim 1, wherein the H ₃ SiCl ₃ ) gas is reduced by hydrogen to set the molar ratio of hydrogen to trichloromethylsilane in the range of 1:20 to 100.