JPH0791137B2 - Oxidation resistant carbon fiber reinforced carbon material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber reinforced carbon material (hereinafter referred to as "C / C material") having a structure showing a high degree of oxidation resistance in a high temperature oxidizing atmosphere.

[0002]

2. Description of the Related Art C / C materials have excellent specific strength and specific elastic modulus, and also have excellent heat resistance and chemical stability, so that they are used as structural materials in many fields including aerospace applications. Although useful, this material has a material defect unique to carbon materials, that is, it is easily oxidized, and this is the biggest bottleneck to its versatility. For this reason, attempts have conventionally been made to modify the surface of the C / C material by applying an oxidation resistant coating, for example, ZrO ₂ , Al ₂ O ₃ and S.
A method of coating with a ceramic material such as iC or Si ₃ N ₄ has been proposed. However, except for the SiC coating layer, delamination and cracks occur at the coating interface during the thermal cycle during use, and the function of sufficiently preventing the progress of oxidation is not exhibited.

Conventionally, as a method for coating the surface of a C / C base material with SiC, a CVD method (chemical vapor deposition method) for directly depositing SiC produced by a vapor phase reaction and a carbon of the base material are reacted. A conversion method is known in which a source is used to react with a silicon component to convert it into SiC.
However, in the SiC coating layer formed by applying the former CVD method, the interface with the substrate is clearly separated, so that when a thermal shock is applied, a delamination phenomenon is likely to occur due to a mutual thermal expansion difference. Therefore, sufficient oxidation resistance in the high temperature range cannot be expected. On the other hand, in the latter conversion method, the surface layer portion of the base material is a functionally graded material that forms the SiC layer as a continuous structure, so interface peeling does not occur, but it is less dense than the CVD method. In addition, there is a problem that minute cracks are generated in the coating layer during the reaction.

In order to solve such a problem, the present inventors have already formed a first SiC coating on the surface of a C / C substrate by a conversion method by contacting with SiO, and further depositing amorphous SiC on the surface. The oxidation resistance treatment method of forming a second SiC coating layer by the CVD method under the following conditions (Japanese Patent Application No. 2-114872), and by further improving this method, the second coating layer is halogenated organic under reduced pressure heating. An oxidation resistant treatment method (Japanese Patent Application No. 2-150640) has been developed, which is formed by using a pulse CVI method in which a silicon compound is intermittently filled in a base material structure and reductively pyrolyzed.

[0005]

Among the above-mentioned oxidation resistant treatment methods, particularly when the latter method is applied, the reaction gas having a high degree of saturation enters each portion of the substrate at each pulse, so that the first layer is formed. Amorphous or fine polycrystalline SiC can be smoothly deposited inside the generated fine cracks, and thus the oxidation resistance of the C / C material can be significantly improved. However, a detailed microscopic investigation revealed that minute cracks were also formed in the SiC of the second coating layer deposited on the surface of the first coating layer, and these cracks were clogged in order to impart complete oxidation resistance. It was recognized that it was necessary to establish the organization.

Therefore, it is an object of the present invention to provide a C / C material having a coating structure property which is further improved from the prior art and has higher oxidation resistance.

[0007]

The oxidation resistant C / C material according to the present invention for achieving the above object is a polycrystalline SiC coating having a gradient function on the surface of a base material of a carbon fiber reinforced carbon material. A first coating layer composed of, a second coating layer composed of an amorphous or fine polycrystalline SiC coating, and B ₂ O ₃
A structural feature is that a third coating layer made of a —SiO ₂ glass coating is laminated.

The C / C as the base material is obtained by 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, and then laminating the same.
What was manufactured by the conventional method of hardening and baking and carbonizing is used, and there is no particular limitation on the material. Therefore, usually, various carbon fibers such as polyacrylonitrile-based, rayon-based, and pitch-based carbon fibers are used as the reinforcing material, and phenol-based, furan-based, and other liquid thermosetting resins having good carbonization properties are used as the matrix resin. Is the target.

The first coating layer is a functionally graded polycrystalline SiC coating in which SiC is gradually organized as the surface layer portion of the C / C base material goes to the outer surface, and an appropriate thickness is 100 to 300.
It is in the μm range. If the film thickness is less than 100 μm, a good functionally graded structure is not formed, and layer formation exceeding 300 μm is no longer necessary.

The second coating layer is SiC in the first coating layer.
Amorphous or fine 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. With a film thickness of less than 10 μm, the above-mentioned filling and sealing effect becomes insufficient, and a film thickness of more than 50 μm becomes unnecessary.

The third coating layer is formed to fill the minute cracks generated in the second coating layer, and is composed of a composite vitreous coating of B ₂ O ₃ and SiO ₂ . A suitable film thickness is in the range of 5 to 20 μm, and if it is less than this, the effect of improving the oxidation resistance is not effectively achieved, and a film thickness exceeding 20 μm is unnecessary.

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 step of mixing SiO ₂ powder and Si or C powder, housing the mixture in a closed heating system, setting a C / C base material in the system, and performing heat treatment. SiO ₂ is reduced in the heating step, and the generated SiO gas reacts with the carbon constituting the C / C base material to convert the surface layer portion into SiC. At this time, S
By controlling the concentration of the iO gas, 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 is formed.

The formation of the second coating layer is carried out by intermittently making a short period of operation in which the halogenated organosilicon compound is brought into contact with the C / C base material heated in the quartz reaction chamber in a gaseous state while being accompanied by hydrogen gas. This is done by a repeating pulse CVI process. Appropriate reaction conditions are trichloromethylsilane (CH ₃ SiCl ₃ ) as a halogenated organosilicon compound, mixed so that the molar ratio with hydrogen gas (CH ₃ SiCl ₃ ) is 0.01 to 0.05, and 900 to 1100. Intermittently introduced into the reaction chamber under reduced pressure where the C / C substrate heated to ℃ is set at intervals of seconds.
To stop repeatedly.

The B ₂ O ₃ --SiO ₂ glass coating of the _third coating layer is obtained by vacuum impregnating the surface of the second coating layer with B (OC ₁₂ H ₂₇ ) ₃ and Si (OC ₂ H ₅ ) ₄ and heat treating at 500 ° C. Formed by the method. At this time, the B ₂ O ₃ glass is B (OC ₁₂ H
₂₇ ) ₃ can be formed by direct vacuum impregnation of SiO ₂ glass, but SiO ₂ glass has Si (OC ₂ H ₅ ) ₄ p.
It is preferable to carry out vacuum impregnation since it is adjusted to H1-2 and hydrolyzed and polymerized. It is also preferable to coat the SiO ₂ glass first and then the B ₂ O ₃ glass as the coating order.

[0015]

In the present invention, the first coating layer composed of a polycrystalline SiC coating having a gradient function is formed as a dense and highly adherent thick film on the surface of the C / C substrate, and is amorphous or fine polycrystalline. The second coating layer made of a high quality SiC coating fills and seals minute voids (pinholes), cracks and the like of the first coating layer, and covers the entire surface as a thin film-like dense layer. Then, the third coating layer made of the B ₂ O ₃ —SiO ₂ glass coating closes the fine cracks generated in the second coating layer to ensure the non-porous structure of the coating layer. The functions of the laminated coating in these three stages act comprehensively to impart high oxidation resistance to the entire surface of the C / C substrate, which can withstand high temperature use in an oxidizing atmosphere.

[0016]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example (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 composed of a phenol resin initial condensation product for impregnation treatment, and then 14 sheets were laminated to form a mold. Then, the composite was molded under the conditions of a heating temperature of 110 ° C. and an applied pressure of 20 kg / cm ² . After heating the molded body to a temperature of 250 ° C to completely cure it, transfer it to a firing furnace kept in a nitrogen atmosphere,
The temperature was raised to 2000 ° C. at a temperature rising rate of 5 ° C./hr, and the temperature was maintained for 5 hours for carbonization by firing. Then, the obtained C / C material was impregnated with a phenol resin solution under vacuum pressure, and the same 2000 ° C. baking treatment as described above was repeated three times to produce a two-dimensional orientation type C / C substrate.

(2) Formation of first coating layer SiO ₂ powder and Si powder are mixed in a molar ratio of 2: 1 and the mixed powder is put in a graphite crucible and C is added on top.
/ C base material (width 30 mm, length 50 mm, thickness 5 mm) was set. The graphite crucible was transferred to an electric furnace, the inside was sufficiently replaced with Ar gas, the temperature was raised to 1850 ° C. at a rate of 50 ° C./hr, and the temperature was maintained for 2 hours so that the surface layer of the C / C base material had a gradient function. A first coating layer of SiC having was formed. SiC formed
The thickness of the coating was about 200 μm, but the width of the coating was 10 μm.
It was confirmed that cracks of about μm were generated in some places.

(3) Formation of second coating layer The C / C 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 by high frequency induction heating. The temperature of the / C 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 trichloromethylsilane (C
H ₃ SiCl ₃ ) and H ₂ mixed gas (molar ratio 5: 100) in 1 second
It was introduced at 720 Torr and held for 1 second. The operation of decompressing the inside of the tube, introducing the reaction gas and holding the same is repeated 3000 times to obtain an amorphous or fine polycrystalline S having a thickness of 20 μm.
A second coating layer of iC was formed. Newly formed fine cracks having a width of 0.5 to 1.0 μm were formed in the formed second coating layer.

(4) Formation of third coating layer The C / C base material on which the second coating layer is formed is placed in a vacuum desiccator and the pressure is reduced to 1 Torr or less by a vacuum pump, and then Si (O) is added.
7 mol of ethanol was added to 1 mol of C ₂ H ₅ ) ₄ ,
A solution obtained by mixing 11 mol of water and 0.03 mol of HCl and performing hydrolysis polymerization at pH 1.5 was injected under a reduced pressure of 2 Torr. C /
The liquid was injected and kept for 1 hour until the C substrate was completely immersed. Then, the C / C base material was taken out from the desiccator, transferred to an electric furnace in an air atmosphere, and heated at a heating rate of 10 ° C / min.
It was heated to 0 ° C. and kept at this temperature for 30 minutes to form a film of SiO ₂ glass.

The C / C 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.
Inject B (OC ₁₂ H ₂₇ ) ₃ under reduced pressure of 2 Torr or less to C / C
The substrate was kept immersed for 1 hour. The C / C substrate was taken out of the desiccator, air-dried in room temperature air for 2 hours, transferred to an electric furnace maintained in an air atmosphere, and heated at 500 ° C. for 30 minutes to form a B ₂ O ₃ glass film. In this way, a third coating layer made of a B ₂ O ₃ —SiO ₂ glass coating film was formed on the entire surface.

(5) Evaluation of oxidation resistance The C / C base material coated with the above three-stage coating was placed in an electric furnace maintained in an air atmosphere, kept at a temperature of 500 ° C. for 30 minutes, and then naturally cooled to room temperature. did. This step was carried out every 100 ° C. from 500 to 1500 ° C., and the final weight loss rate of the C / C substrate due to oxidation was measured. The results are shown in Table 1.

Comparative Example 1 With respect to the C / C substrate having only the first coating layer of the example,
The oxidation resistance was evaluated under the same conditions, and the results are shown in Table 1.
It was also published in.

Comparative Example 2 C / C with SiC coating formed up to the second coating layer of Example
The base material was evaluated for oxidation resistance under the same conditions, and the results are shown in Table 1.

COMPARATIVE EXAMPLE 3 A first coating layer was formed under the same conditions as in Example, placed in a reaction tube kept at atmospheric pressure, heated to 1000 ° C. and then treated with trichloromethylsilane (CH ₃ SiCl ₃ ). H ₂ mixed reaction gas (
The film thickness is increased by a normal CVD process that introduces a molar ratio of 5: 100).
A 20 μm SiC film was formed. With respect to the C / C base material thus formed by two-step coating, the oxidation resistance was evaluated under the same conditions as in the examples, and the results are also shown in Table 1.

[0025]

From the results of Table 1, C according to the embodiment of the present invention
It is recognized that the / C substrate has a high degree of oxidation resistance.
On the other hand, in Comparative Example 1 including only the first coating layer, high oxidative consumption occurs. In Comparative Example 2 in which the second coating layer was formed, the oxidation resistance was considerably improved, but the oxidation resistance was reduced as compared to the Examples because of the presence of minute cracks in the second coating layer. Further, in Comparative Example 3 in which the second coating process is performed by the normal CVD method, the crack filling function of the first coating layer becomes insufficient, and therefore the effect of improving the oxidation resistance is small.

[0027]

As described above, according to the present invention, a polycrystalline SiC first coating layer having a surface gradient function, an amorphous or fine polycrystalline SiC second coating layer, and B ₂ O _3-. It is possible to provide a C / C base material having a high degree of oxidation resistance in which a third coating layer of a SiO ₂ glass coating is laminated. Therefore, when applied to structural member applications exposed to the severe conditions of a high temperature oxidizing atmosphere, effects such as securing stable performance and extending durable life are exhibited.

Claims (2)

[Claims] 1. A first coating layer made of a polycrystalline SiC coating having a gradient function, on a substrate surface of a carbon fiber reinforced carbon material,
The second coating layer made of SiC film amorphous substance or micro polycrystalline, and B ₂ O ₃ -SiO ₂ third coating layer oxidation-resistant carbon fiber, characterized in that formed by stacking formed of glass film reinforced Carbon material. 2. The first coating layer has a thickness of 100 to 300 μm, the second coating layer has a thickness of 10 to 50 μm, and the third coating layer has a thickness of 5 to 5.
The oxidation resistant carbon fiber reinforced carbon material according to claim 1, having a thickness of 20 μm.