JPH10167862A - Carbon fiber reinforced carbon composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon fiber reinforced carbon composite material excellent in stability and durability even in a sever space environment at high temp. and under low pressure and further having superior oxidation and erosion resistances. SOLUTION: Gaseous SiO is brought into contact with the surface of a substrate 5 of a carbon fiber reinforced carbon composite material and an SiC coating layer 1 is formed by a conversion method. The top of the layer 1 is coated with SiC by CVD technique and the SiC is highly crystallized by heat treatment. The top of the highly crystallized SiC 2 is coated with a glassy material 3 and an oxidation resistant layer 4 made of a mixture of SiC powder with SiC fibers and a glassy binder is formed on the top of the glassy material 3. By this multiple coating, erosion resistance as well as oxidation resistance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon fiber reinforced carbon composite material having excellent oxidation resistance and erosion resistance even under high temperature and low pressure.

[0002]

2. Description of the Related Art Carbon fiber reinforced composite materials (hereinafter referred to as "C / C")
Material ". ) Is used as a structural material in many fields, including aerospace, because it has excellent specific strength, specific elastic modulus, and excellent heat resistance and chemical stability. Has a shortcoming inherent in carbon materials such as oxidizability, which is the biggest bottleneck in versatility. For this reason, attempts have been made to modify the surface of the C / C material by applying an oxidation-resistant coating thereon, for example, ZrO ₂ , Al ₂ O ₃ , SiC, S
A method of coating with a ceramic material such as i ₃ N ₄ has been proposed. However, except for the SiC coating layer, delamination and cracks occur at the coating interface during a thermal cycle during use, and the function of sufficiently preventing the progress of oxidation is not exhibited.

Conventionally, as a method of coating SiC on the surface of a C / C substrate, a CVD method (chemical vapor deposition method) in which SiC generated by a gas phase reaction is directly deposited, and a carbon of the substrate are reacted. There is known a conversion method of converting SiC by reacting with a silicon component by using it as a source.
However, in the SiC coating layer formed by applying the former CVD method, the interface between the SiC coating layer and the base material is clearly separated, and when a thermal shock is applied, a delamination phenomenon easily occurs due to a difference in thermal expansion between the two. For this reason, sufficient oxidation resistance in a high temperature range cannot be expected. On the other hand, in the case of the latter conversion method, the surface layer portion of the base material becomes a functionally graded material forming a SiC layer as a continuous structure, so that there is no occurrence of interfacial delamination. In addition, there is a problem that minute cracks occur in the coating layer during the reaction.

[0004] In order to solve such problems,
An oxidation-resistant treatment in which a first SiC coating is formed on a C / C substrate surface by a conversion method using SiO contact, and a second SiC coating layer is formed on the surface by a CVD method under such conditions that amorphous SiC is deposited. Method (Japanese Unexamined Patent Publication No.
Oxidation resistance formed by using a pulsed CVI method in which the second coating layer is intermittently filled with a halogenated organosilicon compound in a base material tissue under reduced pressure heating and reduced and thermally decomposed. treatment (JP-a-4-42878) and the second cracks occur in the coating layer B ₂ O ₃ -SiO ₂ oxidation treatment to form a third coating layer is sealed with a glass (Patent 4
-243989). Such B ₂ O ₃
-The oxidation resistant C / C material forming the SiO ₂ glass coating is:
Demonstrate sufficiently stable durability even in severe high temperature oxidizing atmosphere.

[0005] However, even in the case of the oxidation-resistant C / C material forming the third coating layer, in a space environment, a high-temperature, low-pressure operation is performed under the assumption of the back side of a nose cap or the like of a spacecraft. As a result of a detailed study in the test (low-pressure volatilization test), the second coating layer is greatly oxidized and depleted under conditions assuming one emergency entry into the atmosphere, and is inferior in durability under the specific environment described above. There was a problem.

[0006] To solve such problems,
Na ₂ SiO ₃ is used as a glass material on the SiC coating layer, and a mixture of SiC powder and a fibrous substance is used as an inorganic filler. The mixture is slurried and applied on the Si coating to form an acid-resistant material for forming a protective film. (US Patent No. 4471
023) has been proposed. However, Na ₂ SiO ₃ as a binder used in the oxidation-resistant treatment method
Is effective for oxidation resistance up to around 1000 ° C. because of its high vapor pressure. However, under high temperature and low pressure over 1000 ° C., Na ₂ SiO ₃ glass is volatilized, and the coating film is peeled off. There is a problem that does not work as.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a carbon fiber reinforced carbon composite having excellent oxidation resistance and erosion resistance in a high temperature range up to about 1600 ° C. and low pressure, and which can be used repeatedly. To provide materials.

[0008]

Under such circumstances, the present invention has been intensively studied, and as a result, the present invention has been completed.
That is, the present invention provides a first coating layer composed of a polycrystalline SiC coating having a gradient function, a fine polycrystalline SiC coating, or a heat treatment of the same, on a substrate surface of a carbon fiber reinforced carbon composite material. A second coating layer made of a highly crystalline SiC coating, a third coating layer made of a glass coating, and vitreous;
It is an object of the present invention to provide a carbon fiber reinforced carbon composite material characterized in that a fourth coating layer composed of a mixture of one or two kinds of ceramic fillers of iC and MoSi ₂ is laminated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS C / C as a base material is formed by impregnating or applying a matrix resin solution having a high carbonization residual rate to a reinforcing fiber such as a woven fabric of carbon fiber, felt, and tow to form a semi-cured prepreg. Then, after lamination molding, a material produced by a conventional method of hardening and firing and carbonizing is used, and there is no particular limitation on the material. Therefore, the carbon fibers of the reinforcing material usually include polyacrylonitrile, rayon,
Various types such as a pitch type, and a type using a phenol type, a furan type, or a liquid thermosetting resin having a good carbonization property as a matrix resin can be used. Further, if necessary, the process of impregnating, hardening and carbonizing the matrix resin may be repeated to densify the tissue.

The first coating layer is a functionally graded polycrystalline SiC film in which the organization of SiC gradually progresses as the surface layer of the C / C base material moves toward the outer surface.
It is preferable that the thickness be in the range of 0 μm in order to form a good functionally graded structure and to minimize a decrease in the strength of the base material.

The second coating layer is made of SiC in the first coating layer.
A fine polycrystalline or highly polycrystalline SiC film for filling and sealing fine cracks and voids in the structure, and the preferable film thickness is in the range of 10 to 50 μm. If the film thickness is less than 10 μm, the above-mentioned filling and sealing effect becomes insufficient, and a film thickness exceeding 50 μm becomes unnecessary.

The third coating layer is formed in order to plug small cracks generated in the second coating layer. The third coating layer is a glass coating, preferably a simple substance or a composite of SiO ₂ , Al ₂ O ₃ or ZrO _2. And a glass coating of The preferred film thickness is in the range of 5 to 20 μm. Below this, the effect of improving the oxidation resistance is not effectively achieved, and a film thickness exceeding 20 μm is unnecessary.

The fourth coating layer is made of glass, SiC and M
It consists of a mixture of oSi ₂ with one or two ceramic fillers. A preferred film thickness is 100 to 200 μm, and if it is less than 100 μm, the function of the second coating layer as a protective film is not satisfied, and if it exceeds 200 μm, the film is undesirably peeled off when heated. The glassy material is not particularly limited, but is preferably one or more selected from SiO ₂ , Al ₂ O ₃ and ZrO ₂ .

The oxidation resistant C / C material having the above-mentioned laminated structure can be manufactured as follows. The first coating layer is formed by a process in which SiO ₂ powder and Si or C powder are mixed, housed in a closed heating system, and a C / C substrate is set in the system and heat-treated. In the heating step, SiO ₂ is reduced, and the generated SiO gas reacts with the carbon constituting the C / C base material to convert the surface layer into SiC. As the reaction conditions, it is preferable that the blending amount of Si or C with respect to SiO ₂ is 2: 1, the heating temperature is 1800 to 2000 ° C., and the inside of the system is reduced or neutral atmosphere. A textured state with a tilting function is formed in which the SiC of the layer and the coating layer change continuously at the interface. Thereby, it can serve as a thermal stress relieving layer generated between the second coating layer and the C / C material.

The second coating layer is formed by mixing a mixed gas of a halogenated organosilicon compound and hydrogen or a mixed gas of silicon halide, hydrocarbon and hydrogen into a C / C material heated in a quartz reaction chamber. Is carried out by a pulse CVI process in which the operation of contacting is performed intermittently in a short cycle. Examples of the halogenated organic silicate compound include trichloromethylsilane (CH ₃ SiCl ₃ ). The molar concentration of trichloromethylsilane with respect to the total gas amount is 5 to 10%.
It is preferred that The reaction chamber is preferably at normal pressure and the reaction temperature is preferably 1400 to 1500 ° C. By appropriately controlling the reaction temperature, the composition of the precipitated SiC is changed to Si:
A fine polycrystalline SiC film with C = 1: 1 can be obtained. Further, the second coating is transferred to a heating furnace maintained in an inert atmosphere and subjected to a heat treatment at 1600 to 1900 ° C., thereby eliminating crystal defects and crystal irregularities present in the SiC crystal and improving the quality. A crystalline SiC coating can be obtained. With the second coating, the surface of the first coating is formed as a dense and gas-impermeable coating layer.

The formation of the third coating is performed, for example, using SiO ₂ , Al
It is preferable to form a simple substance or a composite substance of ₂ O ₃ , B ₂ O ₃ and ZrO ₂ , which are composed of Si, Al, B and Zr.
For metal alkoxides containing one or more of each atom selected from r, Si, for example, after applying a glass precursor obtained by hydrolyzing tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ), Dry at 100 ° C, then 500 ~
The heat treatment can be performed at 1000 ° C. The formation of the third coating layer further reduces the thermal stress between the C / C material and the coating film, and coats the delicate defects and surface generated in the second coating layer to prevent oxygen from entering the defects. And the oxidation resistance can be improved.

The fourth coating layer is made of, for example, Si, Al and Zr.
A glass precursor containing one or two selected from the following atoms and one or two ceramic fillers of SiC and MoSi ₂ are mixed to form a slurry, which is applied to a carbon material, and then dried and heated. Manufactured by processing.

The above-mentioned glass precursor is not particularly restricted but includes those prepared by a method of hydrolyzing a metal alkoxide and commercially available sols.

In the fourth coating layer, the form of the ceramic filler is not particularly limited, and may be powdery or fibrous, but it is particularly preferable to use a mixture of powdery and fibrous. In the case of the mixture, the compounding ratio of the fibrous substance and the powdery substance is preferably from 0 to 1/1.

When the vitreous precursor and the ceramic filler are mixed, the mixing ratio of the vitreous and the ceramic filler is preferably 1/10 to 1/1, more preferably 3/5 to 1/1, by weight. 1 is preferred.

The method for applying the slurry to the carbon material is not particularly limited, and includes a brush coating method and a spraying method using a spray, and these may be appropriately selected according to the shape of the carbon material. After the slurry is applied, a drying and heating treatment may be performed. The drying and heating temperature is not particularly limited, and may be, for example, a temperature of about 200 ° C.

FIG. 1 shows a schematic view of the structure of the C / C material of the present invention obtained in this manner. As shown in FIG.
The / C material 10 has a laminated structure of a first coating layer 1, a second coating layer 2, a third coating layer 3, and a fourth coating layer 4.

The C / C material of the present invention is durable and can be used repeatedly in a high temperature range of up to about 1600 ° C., and is used for, for example, aerospace materials, turbine blades, and members for nuclear reactors. Applicable. In particular, it is suitable as a member of a spacecraft that is repeatedly used under high temperature and low pressure in a space environment.

[0024]

Next, the present invention will be described in more detail with reference to examples, but this is merely an example and does not limit the present invention.

Example 1 (1) Preparation of C / C Composite Substrate A polyacrylonitrile-based high-strength, high-elasticity type plain woven carbon fiber cloth was sufficiently coated with a phenol resin precondensate (manufactured by Dainippon Ink) as a matrix. Then, it was air-dried for 48 hours to prepare a prepreg sheet. The prepreg sheets were laminated and placed in a mold, and composite-molded under the conditions of a heating temperature of 100 ° C. and an applied pressure of 20 kg / cm ² . After heating this molded body to a temperature of 250 ° C. to completely cure it, it is transferred into a firing furnace maintained in a nitrogen atmosphere, heated to 2000 ° C. at a rate of 5 ° C./hr, and held for 5 hours for firing. Carbonized. Thus, a C / C composite base material having a carbon fiber volume content (Vf) of 65% and an apparent specific gravity of 1.65 g / cc was prepared.

(2) First coating step The SiO ₂ powder and the 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 material is set on the upper part. did. The graphite crucible was transferred into an electric furnace, and the inside was sufficiently replaced with argon gas.
The temperature is raised to 1850 ° C at the rate of hr
A polycrystalline SiC coating layer having a tilt function was formed on the surface layer of the / C base material. The thickness of the formed SiC coating layer is about 5
Although it was 0 μm, it was confirmed that fine cracks having a width of several μm were generated on this surface.

(3) Second Coating Step The C / C material on which the first coating film is formed is placed in a reaction tube of a CVD apparatus, and the inside of the tube is sufficiently replaced with argon gas. The temperature of the material was increased to 1500 ° C. Then, trichloromethylsilane (CH ₃ SiC
l ₃ ) was mixed with hydrogen gas and introduced with a molar concentration of CH ₃ SiCl ₃ of 7.5% to deposit polycrystalline SiC. The thickness of the formed SiC coating layer was 150 μm, and although fine cracks were present, both the width and the number of cracks were smaller than those after the first coating step. Next, this is subjected to a heat treatment at 1800 ° C. in an inert atmosphere to obtain SiC.
The film was highly crystallized, and the thermal stress existing in the SiC film was reduced.

(4) Third Coating Step Si (OC ₂ H ₅ ) ₄ and ethanol were mixed in a molar ratio of 2: 1 and the mixture was refluxed and stirred at a temperature of 70 ° C. 25 moles per mole of Si (OC ₂ H ₅ ) ₄
A mixed aqueous solution of a molar amount of water and a 0.2 molar amount of NH ₄ OH was added dropwise. The pH of the mixed aqueous solution was 12.0. Subsequently, stirring was continued to synthesize a suspension in which spherical SiO ₂ fine particles of about 0.2 μm were uniformly dispersed. The C / C composite material subjected to the second coating step was immersed in the suspension and impregnated under reduced pressure for 15 minutes. Next, after air-drying, the above-mentioned suspension was applied in the same manner, and air-drying was repeated three times, and then dried at a temperature of 100 ° C. to form an intermediate layer composed of SiO ₂ fine particles. Next, the C / C composite material having the intermediate layer formed of the SiO ₂ fine particles was charged into a B (OC ₄ H ₉ ) ₃ solution and impregnated under reduced pressure for 15 minutes. It was air-dried all day and night to hydrolyze with moisture in the air. Then, after air drying, drying was performed at a temperature of 100 ° C., and a heat treatment was further performed at a temperature of 500 ° C. for 15 minutes to form B ₂ O ₃ . Then, a molar ratio of Si (OC ₂ H ₅ ) ₄ and ethanol of 1: 4.
5 in a mixed solution which was stirred under reflux at room temperature, and added to the mixed solution in an amount of 2.5 mol per mol of Si (OC ₂ H ₅ ) _4.
A mixed aqueous solution of a molar amount of water and a 0.03 molar amount of HCl was added dropwise. The pH of the mixed aqueous solution was 3.0. Subsequently, stirring was continued to synthesize a SiO ₂ glass precursor. The C / C composite material on which the intermediate layer composed of the SiO ₂ fine particles / B ₂ O ₃ glass was formed was charged into this glass precursor solution, and 1
Vacuum impregnation was performed for 5 minutes. Next, after air drying, drying was performed at 100 ° C. Finally, the C /
The C composite base material is again put into the B (OC ₄ H ₉ ) ₃ solution,
Vacuum impregnation was performed for 15 minutes. It was air-dried all day and night to decompose by heating with moisture in the air. Then, after air drying, 10
Dry at a temperature of 0 ° C., and further,
By heating at 0 ° C. for 60 minutes, B ₂ O ₃ —Si
An O ₂ glass was formed.

(5) Fourth coating step SiC powder having an average particle diameter of 0.4 μm and a length of 20 to 30 μm
m, SiC fibrous materials having an aspect ratio of 10 to 30 are mixed at a mixing ratio of 1: 1 by weight, and then the mixture is mixed with SiO 2
_{The two} sols were mixed at a weight ratio of 1: 1 to prepare a slurry. This slurry was applied to the carbon composite material formed up to the third coating film and dried at a temperature of 200 ° C. to form a coating film. The thickness of the fourth coating film by coating is about 15
It was 0 μm. Further, Na ₂ O—SiO ₂ and water were mixed at a weight ratio of 1: 1 to prepare a sodium silicate aqueous solution, and this aqueous solution was applied as an outermost coating layer. After the coating, the coating is dried at a temperature of 300 ° C., and Na ₂ O—S
An iO ₂ glass layer was formed. The erosion resistance of the obtained carbon fiber reinforced carbon composite was evaluated by a low pressure volatilization test shown below. Table 1 shows the results.

(Low pressure volatilization test) Apparatus: Low pressure volatilization test device Sample surface temperature: 1550 ° C. (by condensing irradiation of xenon lamp) Irradiation time: 1100 sec Pressure in reaction chamber: 1 or 1000 Pa Evaluation: Oxidation-resistant film Observation of thickness reduction (mg) and appearance

Examples 2 and 3 Instead of the SiO ₂ sol used in the fourth coating step, Al ₂
O ₃ —SiO ₂ sol (Example 2) or ZrO ₂ —SiO
The procedure was performed in the same manner as in Example 1 except that ₂ sol (Example 3) was used. Table 1 shows the results.

Comparative Example 1 The same procedure as in Example 1 was performed except that the fourth coating step was omitted. Table 1 shows the results.

[0033]

[Table 1]

As shown in Table 1, in Comparative Example 1, the vitreous material of the third coating layer volatilizes under high temperature and low pressure, exposing the SiC film, and oxidizing even the C / C material base under high temperature and high pressure. Will be done. In Examples 1 to 3, although the amount of vitreous volatilization is large under high temperature and low pressure, excellent coating properties are exhibited without exposing the underlying SiC film.

[0035]

According to the present invention, excellent oxidation resistance and erosion resistance can be obtained in a high temperature range up to about 1600 ° C. and high and low pressure conditions, and particularly, the fourth coating step can be obtained by a simple method. Therefore, it is effective as a repair method when the coating film is worn out or scratched.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st coating layer 2 2nd coating layer 3 3rd coating layer 4 4th coating layer 5 base material 10 carbon fiber reinforced carbon composite material

Claims (1)

[Claims] 1. A first coating layer made of a polycrystalline SiC coating having a gradient function, a fine polycrystalline SiC coating or a heat treatment of the same on a substrate surface of a carbon fiber reinforced carbon composite material. A second coating layer made of a highly crystalline SiC coating, a third coating layer made of a glass coating, and a fourth coating layer made of a mixture of vitreous and one or two ceramic fillers of SiC and MoSi ₂ are laminated. A carbon fiber reinforced carbon composite material characterized by being formed.