JPH0735313B2 - Surface treatment method for carbon / carbon composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention is a carbon / carbon composite used as a material for parts, parts and products that require heat resistance, corrosion resistance, oxidation resistance and the like. TECHNICAL FIELD The present invention relates to a surface treatment method for a carbon / carbon composite material, which is used for further improving the surface characteristics of a carbon material (C / C material).

(Prior Art) With the progress of material development technology in recent years, ceramic-based (oxide-based, nitride-based, carbide-based, nitride-oxygen-based, etc.) materials have been advanced from the conventional metal-based materials. It has been developed, and further, fiber reinforced metal (FRM), fiber reinforced ceramics (FRC), and carbon / carbon composite material (C / C material) have been developed.

The latter C / C material is lightweight, has relatively good corrosion and oxidation resistance, and suffers less wear and strength deterioration due to heat compared to conventional metal-based materials, so it can be used, for example, in rocket nozzles. Suitable for applications exposed to severe heat environment.

This C / C material is manufactured by carbonizing or graphitizing FRP materials such as carbon / phenol and graphite / phenol by primary firing, and then repeating pitch impregnation and firing to further densify the resin. There is a char method and a vapor deposition method (CVD method) that vaporizes carbon produced by pyrolyzing hydrocarbons into aggregates woven with carbon or graphite fibers, and is a two-dimensional (2D) type C
In addition to / C materials, C / C materials with multi-dimensionally oriented fibers such as three-dimensional (3D) and four-dimensional (4D) types have also been developed (for example, regarding C / C materials, " Steel ”70th year (1984)
No. 14, p. 30 to p. 31. ).

Even C / C materials with such excellent properties can be further improved in their surface properties, for example, nose caps and leading edges of reusable winged space vehicles (so-called "space shuttles"). As shown in the figure, the surface of C / C material is applied so that it can be applied to the part where the maximum temperature at the time of re-entry into the atmosphere remarkably exceeds the heat resistance limit of metal structural materials and is required to be thermally severe and strength / rigidity is required. An oxidation-resistant surface treatment method has been developed to diffuse and form SiC (silicon carbide).

An example of this oxidation resistant surface treatment method is described in CERAMIC BULLETIN VOL.60, No.11 (1981). This method uses 10% alumina (Al ₂ O ₃ ),
The powder consisting of 30% silicon (Si) and 60% silicon carbide (SiC) was packed around the C / C material in a graphite retort and heated at about 1650 ° C in an argon atmosphere to obtain the surface of the C / C material. Is converted to SiC, and in the subsequent cooling process, minute cracks caused by the difference in thermal expansion between the C / C material and SiC are treated with tetraethyl orthosilicate (TEOS) to remove the cracks. This is an oxidation resistant surface treatment method of impregnating with SiO ₂ .

(Problems to be solved by the invention) In such a conventional oxidation-resistant surface treatment method for C / C materials, C / C
Since SiC is diffused and formed on the surface of the material, and the minute cracks formed on the surface are impregnated with SiO ₂ , compared with C / C material that is not subjected to oxidation-resistant surface treatment, especially when re-entry into the atmosphere, It is remarkably excellent in corrosion resistance against hot air. However, when the surface is treated by the so-called retort method described above, the smoothness of the surface becomes relatively low, and C /
Since an extremely hard SiC diffusion layer is formed on the surface of C material, and it is difficult to control the thickness of the SiC diffusion layer, it is difficult to secure sufficient dimensional accuracy as a C / C material structure, When applied to curved C / C materials such as the nose and leading edge of space vehicles, problems with the interface that joins this may occur, and further improvement is required. was there.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and it is possible to obtain a surface having high smoothness after the oxidation resistant surface treatment, and the thickness control of the surface treatment layer is controlled. It is easy, and it is possible to secure high dimensional accuracy even when applied to a part having a curved surface such as the leading edge of a space shuttle, heat resistance, corrosion resistance,
Suitable as a material for parts requiring oxidation resistance (especially corrosion and oxidation resistance against hot air) and strength and rigidity,
C / C material (carbon / carbon composite material) that is fully reusable
It is intended to provide.

[Structure of the Invention] (Means for Solving Problems) A surface treatment method for a carbon / carbon composite material (C / C material) according to the present invention is a method for depositing SiC (carbonization) on the surface of the C / C material by vapor deposition. (Silicon) vapor deposition film is formed by coating, and then SiO ₂ is impregnated into fine cracks generated in the SiC vapor deposition film.

The C / C material to which the present invention is applied is not particularly limited in its manufacturing method. For example, a material in an FRP state such as carbon / phenol and graphite / phenol is carbonized or graphitized by primary firing to further increase the density. For this purpose, it was manufactured by the resin char method in which pitch impregnation and firing are repeated, the vapor deposition method in which carbon produced by thermally decomposing hydrocarbons into carbon or graphite fiber knitted aggregate is deposited, or a combination thereof. The present invention can be applied not only to those in which the fiber orientation is two-dimensional (2D), but also to those in which the fiber orientation is multidimensional such as three-dimensional (3D) and four-dimensional (4D).

The vapor deposition method for forming the SiC vapor deposition film on the surface of the C / C material is not particularly limited, and a vapor phase vapor deposition method or the like is adopted.

In addition, the SiC formed on the surface of the C / C material by vapor deposition
The vapor-deposited film has a C / C material (coefficient of thermal expansion of about 1.2 to 2 × 10 ⁻⁶ / ° C.) and a SiC vapor-deposited film (coefficient of thermal expansion of about 3.5 to 4 × 10 ⁻⁶ / ° C.) in the subsequent cooling process. S due to the difference in thermal expansion between
Since microcracks are generated on the surface of the iC vapor deposition film, and the corrosion resistance to hot air is impaired, SiO ₂ is impregnated into the microcracks.

In this case, when impregnating the fine cracks with SiO ₂ , the tetraethyl orthosilicate (TEO
By heat treatment by impregnating the S), and a method to leave as SiO ₂ in fine cracks, a method of leaving as SiO ₂ by heat treatment by impregnating the silicate coating is a silicone modifier to the fine cracks There is.

(Example 1) A C / C material manufactured by the resin char method was prepared, and this C / C material was pre-purified at about 1500 ° C. and then mounted in a high-temperature low-pressure furnace to prepare H ₂ / CH ₃ SiCl ₃ In the mixed gas atmosphere of C, the molecular SiC on the surface of the C / C material by the vapor deposition method (CVD method)
By vapor-depositing, a SiC vapor-deposited film was formed by coating.

The C / C material whose surface has been subjected to oxidation resistance by this vapor deposition method shows a glossy surface state, and unlike the one obtained by the conventional retort method, it can be processed as it is in its original shape. As a result, it is possible to easily treat curved shapes with oxidation resistance, and it is possible to treat complicated shapes.
The thickness of the deposited film could be easily controlled.

In this way, in the process of cooling after forming the SiC vapor-deposited film, the coefficient of thermal expansion of the C / C material (about 1.2 to 2 × 10 ⁻⁶ /
C.) and the coefficient of thermal expansion of SiC (about 3.5 to 4.times.10.sup.- ⁶ / .degree. C.), minute cracks of, for example, about 5 .mu.m are generated in the SiC vapor-deposited film.
A treatment of impregnating with O ₂ was performed.

That is, after the SiC vapor-deposited film was formed, the C / C material was immersed in tetraethyl orthosilicate (TEOS) at 180 ° C for 4 hours and then pulled up to check the impregnation state. Surface treatment with sandpaper and cleaning were performed. Then, it was heated at 315 ° C. for 6 hours to carry out a curing treatment to impregnate SiO ₂ into the fine cracks generated in the SiC vapor deposition film.

Next, according to the above-mentioned Example 1, TEO after the oxidation resistance treatment with SiC was performed.
For comparison, a C / C material that has been completely cracked with S and a C / C material that has not been subjected to SiC oxidation resistance for reference
C / C material that has not undergone crack treatment by TEOS after SiC oxidation resistance, and C / C material that has undergone about 50% crack treatment by TEOS after oxidation resistance treatment by SiC,
As a test material, the corrosion resistance of each C / C material to hot air was evaluated.

At this time, the test material shall be 25 mmφ, the back surface temperature of the test material: 650 ° C, the burner flame temperature using propane gas: 140
Burner flame irradiation was performed at 0 ° C, and the mass loss (g
/ m ² ) was obtained to evaluate the corrosion resistance.

The results are shown in FIG.

As shown in FIG. 1, by completely treating the fine cracks formed on the SiC vapor-deposited film with TEOS,
It was confirmed that it is possible to significantly reduce the mass loss due to burner flame irradiation, and to significantly improve the corrosion resistance to hot air. It was confirmed that when the crack treatment was not completely performed, the corrosion resistance was considerably improved as compared with the case where the TEOS crack treatment was not performed at all, but the corrosion resistance was lower than when the crack treatment was completely performed. This indicates that there is a correlation between the fine cracks and the corrosion resistance to hot air.
It is shown that the corrosion resistance to hot air is reduced when the C / C material is exposed due to the fine cracks in the SiC vapor-deposited film deposited on the surface of the material.

Moreover, when the relationship between the TEOS treatment and the mass loss rate was examined, it was as shown in Table 1.

As shown in Table 1, by completely treating the fine cracks formed on the SiC vapor-deposited film with TEOS in a cooling household, the mass loss rate is about 1/8 of that of the C / C material without crack treatment, It was confirmed that the mass loss rate was about 1/15 compared to the C / C material without oxidation resistance, and the oxidation resistance could be significantly improved.

(Example 2) A C / C material produced by the resin char method was prepared, and this C / C material was preheated to about 1500 ° C in the same manner as in Example 1.
After high-purity treatment with H ₂ / CH ₃ SiC
Vapor deposition method (CVD method) on the surface of C / C material under a mixed gas atmosphere of l ₃
In the same manner as in Example 1, by depositing molecular SiC,
A vapor-deposited film was formed by coating.

In this way, in the process of cooling after forming the SiC vapor-deposited film by coating, fine cracks are generated in the SiC vapor-deposited film due to the difference in thermal expansion between the C / C material and SiC as described above,
The cracks were impregnated with SiO ₂ as follows.

That is, a two-liquid type of (silicic acid, methyl silicon) + organic solvent was used as the silicon modifier, and the C / C material was immersed in the silicon modifier and impregnated by vacuuming. After that, it is dried at room temperature and then 2 at 80 ℃.
Heated and cured for hours. By this heating, 90% of the methyl groups and SiO ₂ remained, so that SiO ₂ could be impregnated into the fine cracks generated in the SiC vapor-deposited film.

Next, a comparison was made between the C / C material which was subjected to the complete crack treatment with the silicon modifier after the oxidation resistance treatment with SiC according to the above Example 2 and the C / C material which was not subjected to the SiC oxidation resistance treatment for reference. For this reason, a C / C material that has not undergone cracking treatment with a silicon modifier after SiC oxidation resistance and an incomplete crack treatment C that has undergone about 50% cracking treatment with a silicon modifier after oxidation resistance treatment with SiC / C material was used as a test material, and the corrosion resistance of each C / C material to hot air was evaluated.

At this time, the test material was 25 mmφ, burner flame irradiation was performed at the back surface temperature of the test material: 650 ° C, propane gas flame temperature: 1400 ° C, and corrosion resistance was evaluated by determining the mass loss (g / m ² ). .

The results are shown in FIG.

As shown in Fig. 2, by completely treating the fine cracks formed on the SiC vapor-deposited film with a silicon modifier, it is possible to significantly reduce the mass loss due to burner flame irradiation, and the corrosion resistance to hot air. It has been confirmed that can be significantly improved. Then, it was confirmed that when the cracking treatment was performed incompletely, the corrosion resistance was lowered as in the case of Example 1.

Further, when the relationship between the treatment with the silicon modifier and the mass loss rate was examined, it was as shown in Table 2.

As shown in Table 2, by completely treating the fine cracks formed in the SiC vapor-deposited film in the cooling process with the silicon modifier, the mass loss is about 1/6 of that of the C / C material without crack treatment. Speed, which is about 1/1 compared to C / C material without oxidation resistance
It was confirmed that the mass loss rate was 1 and the oxidation resistance could be significantly improved.

(Example 3) Fiber-reinforced type R / C / C materials shown in Table 3 were prepared and implemented.

Then, the corrosion resistance of each of the R / C / C-1 to 4 materials shown in Table 3 to hot air was evaluated.

At this time, the test material shall be 25 mmφ, the back temperature of the test material: 1000 ° C, the banner flame temperature using propane gas: 1650
It was evaluated by irradiating a burner flame at ℃ and obtaining the mass loss (g / m ² ). The results are shown in FIG.

As shown in Fig. 3, there is no substantial difference in the mass loss due to the difference in the fiber / matrix of the C / C material, and the mass loss rate of each test material is approximately 13 mass loss / min. It was

Next, each of the R / C / C-1 to 4 materials shown in Table 3 was used in Example 1
In the same manner as above, an oxidation resistance treatment was performed, and a SiC vapor deposition film was formed on the surface of each of the R / C / C-1 to 4 materials by the vapor deposition method (CVD method). At this time, the thickness of the SiC vapor-deposited film of the R · C / C-1 to 3 materials was about 175 μm, and the thickness of the SiC vapor-deposited film of the R · C / C-4 material was about 130 μm.

Next, each of the R / C / C-1 to 4 after the formation of the SiC vapor deposition film
The corrosion resistance of the material to hot air was evaluated.

At this time, the test material shall be 25 mmφ, the back temperature of the test material: 1000 ° C, the burner flame temperature using propane gas: 16
It was evaluated by performing banner flame irradiation at 50 ° C. and determining the mass loss (g / m ² ). The results are shown in FIG.

As shown in FIG. 4, R · C / C-1 to 1 evaluated in FIG.
It was possible to significantly reduce the mass loss with respect to hot air by subjecting the surfaces of the four materials to the oxidation resistance treatment with SiC. In this case, the difference in the corrosion resistance against hot air is observed due to the difference in the fiber / matrix of the R / C / C-1 to 4 materials, and the difference in thermal expansion between the R / C / C material and the SiC vapor-deposited film is large. It has been confirmed that the corrosion resistance tends to be low because the fine cracks on the SiC surface become larger. In this case, the base material composition is 2D R / C / C-1 to 2
Compared with the material, the R / C / C-3 to 4 material, which has a 3D base material, has a higher density, so the coefficient of thermal expansion becomes smaller and
Since the difference in the coefficient of thermal expansion from the C vapor deposition film increases, the size of the microcracks becomes larger in the 3D material than in the 2D material, and it is considered that the corrosion resistance to hot air is reduced.

Next, in order to prevent deterioration of corrosion resistance due to generation of fine cracks on the SiC surface, Example 1 was applied to the cracks.
In the same manner as above, a crack treatment using TEOS was performed to impregnate the fine cracks with SiO ₂ .

Next, each R / C / that has been completely cracked by TEOS
The corrosion resistance of C-1 to 4 materials against hot air was evaluated.

At this time, the test material shall be 25 mmφ, the back temperature of the test material: 1000 ° C, the burner flame temperature using propane gas: 16
The banner flame was irradiated at 50 ° C., and the mass loss (g / m ² ) was determined to evaluate the corrosion resistance. The results are shown in FIG.

As shown in FIG. 5, by completely treating the fine cracks formed in the SiC vapor-deposited film with TEOS,
It was confirmed that it is possible to significantly reduce the mass loss due to burner flame irradiation, and to significantly improve the corrosion resistance to hot air. In this case, the 2D material (R / C / C-1 to 2 material) is superior to the 3D material (R / C / C-3 to 4 material) in corrosion resistance due to burner flame irradiation. It was confirmed that the corrosion resistance to air does not depend on the composition of the R / C / C material but depends on the fine cracks generated by the difference in thermal expansion.

(Comparative Example 1) A C / C material manufactured by the resin char method was prepared, and alumina (Al ₂ O ₃ ) / 10%, silicon (Si): 30%, silicon carbide (S
iC): A mixture powder consisting of 60% is put into the retort together with the above C / C material, and heat-treated at about 1600 ° C. in an argon atmosphere to cause the surface of the C / C material to undergo a diffusion reaction with Si to produce a surface. By converting the C / C of SiC into SiC,
A diffusion layer was formed.

C / C whose surface was subjected to oxidation resistance treatment by this retort method
The surface of the material is covered with an extremely hard SiC diffusion layer, and the thickness (depth) of this SiC diffusion layer is difficult to control. To prevent oxidation of the curved C / C material surface, Was required to be improved, and was not suitable for a complicated shape.

In the process of cooling after forming the SiC diffusion layer in this way, a minute crack is generated on the surface due to the difference in thermal expansion between the C / C material and the SiC diffusion layer. _The treatment of impregnating ₂ was performed.

That is, tetraethyl orthosilicate (TE
To impregnate the OS), repeating the curing several impregnation step process, the orthosilicate tetraethyl denatured to SiO ₂ in the curing step, impregnated with SiO ₂ in the cracks.

Next, in Example 1, C / C subjected to oxidation resistance by the CVD method
Material, C / C material subjected to oxidation resistance by the retort method in Comparative Example 1, and C / C not subjected to oxidation resistance for reference
As a test material, the corrosion resistance of each C / C material against hot air was evaluated.

At this time, the test material shall be 50 mmφ, and the backside temperature of the test material
1000 ℃, Burner flame temperature using propane gas: 1650
Corrosion resistance was evaluated by irradiating a burner flame at ℃ and obtaining the mass loss (g / m ² ). The results are shown in FIG.

As shown in FIG. 6, by subjecting the surface of the C / C material to oxidation resistance treatment with SiC, it is possible to significantly reduce the mass loss with respect to hot air, and the retort-treated C / C material of Comparative Example 1 is used. It was confirmed that the CVD-treated C / C material of Example 1 was more excellent in oxidation resistance than the above.

Further, the relationship between the burner flame irradiation time and the mass loss was linearly approximated and expressed by the mass loss rate (mass loss / min).

As shown in Table 4, by performing SiC oxidation resistance treatment on the surface of C / C material, the mass loss rate is about 1/12 to 1/15 compared to the case without treatment, and the CVD treated C / C material Retort processing
It was confirmed that the mass loss rate was lower than that of C / C material.
This is because the CVD-deposited C / C material has a uniformly deposited SiC film on the surface, whereas the retort-treated C / C material has a SiC diffusion layer with a uniform depth. It is presumed that there is a part that is not.

[Effects of the Invention] As described above, the surface treatment method for a carbon / carbon composite material (C / C material) according to the present invention forms a SiC vapor deposition film on the surface of the C / C material by vapor deposition. And then the SiC
Since the minute cracks generated in the vapor-deposited film were impregnated with SiO ₂ , the surface-treated C / C material had heat resistance, corrosion resistance and oxidation resistance (especially corrosion resistance and oxidation resistance against hot air). It is remarkably suitable as a material for parts, parts and products that are required to have excellent strength and rigidity,
The excellent effect of being a lightweight material that is fully reusable is provided. And, for example, when it is used for a nose cap and a leading edge that are the most thermally severe in a reusable wing space vehicle, it is possible to increase the dimensional accuracy of the part. It is possible to significantly reduce the problems on the interface to be joined and to significantly improve the corrosion resistance to hot air, and it is a great effect that it can be a C / C material with a large oxidation resistance when re-entering the atmosphere. Is brought about.

[Brief description of drawings]

FIG. 1 is a graph showing the results of examining the relationship between the presence or absence of fine crack treatment by TEOS and the mass loss due to burner flame irradiation in Example 1 of the present invention, and FIG. FIG. 3 is a graph showing the results of examining the relationship between the presence or absence of crack treatment and the mass loss due to burner flame irradiation. FIG. 3 shows the fiber / matrix structure of the R / C / C material alone and the mass loss due to burner flame irradiation in Example 3. 4 is a graph showing the results of examining the relationship between R and C after the oxidation resistance treatment with SiC in Example 3 as well.
FIG. 5 is a graph showing the results of investigating the relationship between the fiber / matrix structure of the C / C material and the mass loss due to burner flame irradiation, and FIG.
A graph showing the results of examining the relationship between the fiber / matrix structure of the R / C / C material after the fiber crack treatment by EOS and the mass loss due to burner flame irradiation, and FIG.
It is a graph which shows the result of having investigated the relation between the oxidation resistance processing method by SiC and the mass loss by burner flame irradiation.

Claims (1)

[Claims] 1. A surface of carbon / carbon composite material is deposited by a vapor deposition method.
A method for surface treatment of a carbon / carbon composite material, which comprises forming an SiC vapor-deposited film as a coating and then impregnating fine cracks generated in the SiC vapor-deposited film with SiO ₂ .