JP2976368B2 - Heat and oxidation resistant carbon fiber reinforced carbon composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation-resistant coated carbon fiber reinforced carbon composite material, and more particularly, to a repetitive use in a high-temperature oxidizing atmosphere such as a structural material for a spacecraft, a turbine blade, and a member for a nuclear reactor. A carbon fiber reinforced carbon composite material for providing a durable material.

[0002]

2. Description of the Related Art Carbon fiber reinforced carbon composite materials (hereinafter referred to as C / C)
Is generally 50) in an oxidizing atmosphere.
Oxidized from about 0 ° C, has excellent physical properties of its own,
Due to the reduced chemical properties, use in a high temperature atmosphere was not possible except for very short periods of time. In order to prevent this phenomenon, various studies have been made on the oxidation-resistant treatment method of the carbon fiber reinforced carbon composite material.

[0003] Among these methods, ceramic coating on a carbon fiber reinforced carbon composite material substrate by a vapor phase chemical vapor deposition (hereinafter sometimes referred to as CVD) is one of the most common methods. A dense film can be obtained by the method. According to this method, SiC, TiC, HfC, Ta
Coating such as carbides such as C, nitrides such as Si ₃ N ₄ , TiN, BN, and ZrN, oxides such as Al ₂ O ₃ and ZrO ₂ , and other borides can be performed. In general, in this method, the deposition temperature is about 1000 ° C., so that the ceramic coating on the surface often peels off or cracks occur when the substrate is cooled. This is due to the large difference in the coefficient of thermal expansion between the substrate and the ceramic to be deposited,
The problem can be solved by making the expansion coefficient of the base material approximately equal to that of the ceramic to be deposited. Therefore, in order to improve the adhesion between the substrate and the ceramic, a method has been adopted in which the surface of the substrate is converted into ceramics by a diffusion method and then coated by a chemical vapor deposition method.

[0004] Among CVD coated ceramics, silicon carbide
Silicon and silicon nitride have excellent heat and oxidation resistance.
Widely used as oxidation-resistant coating of carbon fiber reinforced carbon composites
Have been. However, the nose cone of the spacecraft, Leadin
At high temperatures of 1400-1700 ° C, such as
When exposed to a reduced pressure environment of ~ 4000 Pa, silicon carbide
Silicon and silicon nitride are combined with SiO gas by active oxidation.
It becomes exhausted. As a method to prevent active oxidation,
Compounds or metals that do not contain silicon on silicon carbide coatings
As an intermediate layer and coating the outermost layer with an oxide
It has been devised, as disclosed in JP-A-2-106337 and JP-A-4-285068.
HfC, TaC, ZrC, W _TwoC, Nb
C, ThC, ZrB_Two, HfB_Two, BN, HfN, Zr
N, AlN, Pt, Ir, Os, Rh, Ru, outermost layer
ThO for oxide_Two, ZrO_Two, HfO _Two, La_TwoO_Three,
Y_TwoO_ThreeOf oxide and the outermost layer of oxide SiO_Twosystem
A method for coating glass is disclosed. But this
Oxidize the coating layer and_TwoBetween base glass and silicon carbide
Therefore, the life time is short and lacks practicality. Also acti
ve A metal coating has been devised as an antioxidant film,
When metal is used, erosion of silicon carbide and coating metal
Oxidation of the body becomes a problem.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an outermost layer of a mixture of a high melting point metal silicide and metallic silicon for preventing active oxidation of a silicon carbide or silicon nitride layer which is an oxidation-resistant barrier of a carbon fiber reinforced carbon composite material. It is an object of the present invention to provide a heat-resistant and oxidation-resistant carbon fiber reinforced carbon composite material having excellent durability, which is coated with carbon.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a high melting point metal silicide having extremely small chemical interaction with silicon carbide and having excellent heat resistance and oxidation resistance; By combining metal silicon that forms a liquid phase at operating temperature with a very small interaction,
Metal silicon that forms a liquid phase at the operating temperature in cracks and pores due to the difference in thermal expansion coefficient from the underlying silicon carbide in the refractory metal silicide layer quickly penetrates to form a dense film with a self-healing effect By doing so, the present inventors have found that active oxidation of silicon carbide, which is a main oxidation-resistant barrier, can be effectively prevented, and have reached the present invention. The melting point of the high melting point metal silicide must be higher than the expected attainment temperature of space equipment of 1700 ° C. If the melting point is lower than 1700 ° C, the molten metal silicide is scattered by the air flow and is consumed. I will. The liquid-phase metallic silicon densifies the refractory metal silicide layer by a self-healing effect, and also blocks the contact between refractory metal silicide and oxygen and protects the refractory metal silicide layer from oxidation.
This has the effect of significantly extending the lifetime as compared with the conventional non-oxide coating. In addition, it can be easily repaired by re-coating as necessary.

That is, the present invention provides a silicon carbide-coated carbon in which the surface of a carbon fiber reinforced carbon composite material serving as a base material is converted into a silicon carbide layer by a diffusion method, and then a silicon carbide layer is formed by a gas phase chemical vapor deposition method. A heat-resistant and oxidation-resistant carbon fiber-reinforced carbon composite material characterized in that a fiber-reinforced carbon composite material is coated with a mixture of a high melting point metal silicide having a melting point of 1700 ° C. or more and metal silicon. .

Hereinafter, the present invention will be described in more detail. First, the structure of the heat-resistant and oxidation-resistant carbon fiber-reinforced carbon composite material of the present invention will be described with reference to a preferred embodiment shown in FIG. As shown in FIG. 1, a preferred material of the present invention is a porous SiC layer which is formed on a C / C base material 1 made of a carbon fiber reinforced carbon composite material by a diffusion method and serves as a thermal stress relaxation layer, that is, Conve.
It has a rsion-SiC layer 2 and further has a CVD-SiC layer 3 which is a dense SiC layer formed by CVD. The outermost layer is provided with a mixture coating layer of a high melting point metal silicide 4 and metal silicon 5. As the carbon fibers constituting the carbon fiber reinforced carbon composite material as the base material, plain weave, satin weave, twill weave, and other two-way laying, one-way laying, three-way laying, n-direction alignment material, felt, tow, and the like are used. As the binder, a thermosetting resin such as a phenol resin and a furan resin, and a thermoplastic resin such as tar and pitch can be used. As a method for producing the carbon fiber reinforced carbon composite material, for example, the carbon fiber is prepregted by a method such as impregnation with a binder, coating, or the like, and is formed into a molded product by heating under pressure. The binder is completely cured by heat treatment, then fired by a conventional method, and if necessary, graphitized to obtain a carbon fiber reinforced carbon composite material. Thereafter, depending on the application, the thermosetting substance pitches and the like are impregnated, and the densification is repeatedly performed by an impregnation method of performing re-carbonization, for example, a CVD method of thermally decomposing a hydrocarbon gas such as methane and propane to obtain carbon, and the like. Further, a carbon fiber reinforced carbon composite material having higher strength can be obtained.

As the silicon carbide (porous SiC layer) coating by the diffusion method to the above-mentioned material, carbon fiber reinforced in a mixed powder of silicon / silicon carbide / alumina = 15-50 / 25-85 / 3-25% by weight. Buried carbon composite material, 1500 ~
The surface layer of the above material is converted into SiC by heat treatment at 1800 ° C. The reaction time can be selected according to the desired coating film thickness. The film thickness may be 1 μm or more, preferably 10 to 200 μm. This layer becomes a thermal stress relaxation (Conversion) SiC layer.

As a silicon carbide (densified SiC) coating by CVD, for example, CH ₃ SiCl ₃ , S
The carrier gas such as iCl ₂ + CH ₄ is H ₂ or H ₂
Reaction temperature of 900 to 170 using a mixed gas of + Ar, etc.
It is preferable that the reaction is performed at 0 ° C. and a reaction pressure of 760 Torr or less, and the flow rate ratio between the raw material gas and the carrier gas is (raw material gas flow rate) / (carrier gas flow rate) = 1/5 to 10. The film thickness may be 50 μm or more, preferably 10 μm.
It is preferably from 0 to 300 μm.

In the present invention, the carbon fiber reinforced carbon composite material coated with silicon carbide obtained as described above is coated with a mixture of a high melting point metal silicide and metal silicon. As the refractory metal silicide, SiC (decomposition temperature 22
00 ° C), SiB ₆ (melting point 1850 ° C), WSi ₂ (melting point 2160 ° C), MoSi ₂ (melting point 2020 ° C), ReMo
Si ₄ (melting point 2000 ° C.) can be used.
₂ is preferred. The mixing ratio between the high melting point metal silicide and the metal silicon is preferably set to a molar ratio of 10: 1 to 1: 1. This coating is performed by a method of applying a slurry of a mixed powder of a high melting point metal silicide and metallic silicon and then performing a heat treatment, a plasma spraying method or the like. The film thickness may be 1 μm or more, preferably 5 μm.
~ 200 µm is preferred. The same effect can be obtained by a method in which a metal silicide is coated first and then a metal silicon is coated. The coating of the metal silicide is performed by a method of applying a slurry of the metal silicide powder and then performing a heat treatment or a plasma spraying method. The film thickness may be 1 μm or more, preferably 5 to 200 μm. The coating of metal silicon is performed by a method of applying a slurry and then performing a heat treatment under reduced pressure conditions, a vapor deposition method, or the like. The film thickness may be 1 μm or more, preferably 5 to
100 μm is preferred. The slurry of metal silicide or metal silicon is prepared by adding these powders (particle diameter: 1 to 20 μm) to a mixture of an organic binder such as polystyrene and polyvinyl alcohol and an organic solvent such as toluene and xylene, and dispersing the mixture by stirring. Can be used. In the plasma spraying method and the vacuum evaporation method, a mixture of a metal silicide and a metal silicon having a predetermined mixing ratio is sprayed or vapor-deposited. It can also be carried out without prior mixing.

[0012]

According to the present invention, a carbon fiber reinforced carbon composite material coated with CVD silicon carbide is coated with a high melting point metal silicide and metal silicon so that the carbon fiber reinforced carbon composite material is generated in an environment such as when re-entering the atmosphere. Effectively prevent active oxidation of silicon carbide,
A heat-resistant and oxidation-resistant carbon fiber reinforced carbon composite material having excellent durability can be obtained.

[0013]

[Example] Ten prepregs impregnated with phenolic resin in a carbon fiber woven fabric were laminated, pressed and molded, baked in an inert atmosphere, and then densified four times using a coal tar pitch. Then, a carbon fiber reinforced carbon composite material was obtained. After pressurizing the obtained carbon fiber reinforced carbon composite material to a predetermined size, the carbon fiber reinforced carbon composite material is embedded in a mixed powder having a composition ratio of silicon / silicon carbide / alumina = 25/75/5% by weight. 1700 ° C, 2
A diffusion reaction was performed for 40 minutes to convert the surface of the carbon fiber reinforced carbon composite material into silicon carbide. The thickness of this silicon carbide was 20 μm. Next, on the surface of the carbon fiber reinforced carbon composite material coated with silicon carbide by the diffusion method, a dense silicon carbide coating was formed by a vapor phase chemical vapor deposition method. Gas composition is CH ₃ SiCl ₃ / H
_The reaction was carried out for 150 minutes at a gas flow rate of 3 L / min, a pressure of 30 Torr and a reaction temperature of 1300 ° C. so that ₂ = 25/100. The thickness of this CVD silicon carbide is
It was 100 μm.

The mixture layer of a high melting point metal silicide and metal silicon
The formation is SiC, SiB₆, WSi _Two, MoSi_Two, Re
MoSi_FourMixed powder of metallic silicide and metallic silicon
Mixed with a solution of an organic solvent containing
Was. The mixing ratio between the metal silicide and the metal silicon is 4: 1 in molar ratio.
did. Polystyrene for organic binder and organic solvent
Toluene is used, and the mixing ratio is a powder ratio: torue
= 1: 1: 8. This slurry is CVD silicon carbide
Coated on coated substrate and dried at room temperature for more than 6 hours
After that, heat treatment was performed at 1500 ° C for 30 minutes in an argon atmosphere.
Was. The thickness of the mixture layer of the metal silicide and the metal silicon is about
It was 40 μm.

Evaluation method The oxidation resistant coating C / C obtained as described above was
Heating was performed at 1700 ° C. in an atmosphere of 0 Pa. The temperature history is about 3 minutes from room temperature to the set temperature, and 20 minutes at the set temperature.
Minutes, 10 minutes from the set temperature to room temperature. The evaluation was performed by observing the weight loss and the surface and cross section. In addition, as a comparison, a test was performed on a sample in which only the outermost layer was coated with the MoSi ₂ layer of the refractory metal silicide and only the silicon carbide was coated. The weight loss rate _Xn was determined by the following equation. X _n = [(W _o −W _n ) / W _o ] × 100 wt% W _o : initial weight of the sample W _n : weight of the sample after n times of oxidation tests In the example, the mixture layer of the high melting point silicide and metal silicon is used. Damage that was thought to be wear of metallic silicon was observed, but the underlying CVD
-No decrease in the thickness of the SiC layer was observed. On the other hand, the comparative example is C
The erosion of VD-SiC was severe, and C / C of the base material partially appeared.

[0016] * MoSi ₂ single coating ** CVD-SiC only, no coating

[0017]

The coating of a mixture of a high melting point metal silicide and metallic silicon on CVD silicon carbide according to the present invention has a remarkably high effect of suppressing active oxidation, and is a carbon fiber reinforced carbon composite material having high heat and oxidation resistance. Is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a carbon fiber reinforced carbon composite material of the present invention.

[Explanation of symbols]

 Reference Signs List 1 C / C base material 2 Diffusion method-SiC layer 3 CVD-SiC layer 4 Refractory metal silicide 5 Metallic silicon

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihito Sakai 1 Kawasaki-cho, Kakamigahara City, Gifu Prefecture Inside the Gifu Factory of Kawasaki Heavy Industries, Ltd. (56) References JP-A-1-320152 (JP, A) JP Hei 2-74669 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00 C04B 35/80 D06M 11/00-11/84

Claims (2)

(57) [Claims] A porous silicon carbide layer is formed on the surface of a carbon fiber reinforced carbon composite material as a base material, and then dense silicon carbide is coated by a vapor phase chemical vapor deposition method, and the outermost layer has a melting point of 1%.
A heat- and oxidation-resistant carbon fiber reinforced carbon composite material characterized by being coated with a mixture of a metal silicide having a high melting point of 700 ° C or higher and metal silicon. 2. The method according to claim 1, wherein the refractory metal silicide is C, B, Mo,
The heat- and oxidation-resistant carbon fiber reinforced carbon composite material according to claim 1, which is a silicide of one or more metal elements selected from the group consisting of Re, W, and Re.