JP2607409B2 - Oxidation-resistant treatment of carbon fiber reinforced carbon composites. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for coating a substrate surface of a carbon fiber reinforced carbon composite material (hereinafter referred to as "C / C material") with silicon carbide having excellent oxidation resistance at high temperatures. The present invention relates to an oxidation-resistant treatment method for a C / C material that forms a coating layer except for a predetermined portion.

[0002]

2. Description of the Related Art C / C materials have excellent specific strength and specific elastic modulus and excellent heat resistance and chemical stability. Therefore, C / C materials are used as structural materials in many fields including aerospace. Have been useful. However, this material has a material defect inherent to carbon material that is oxidized in the atmosphere at around 500 ° C., and this is the biggest bottleneck that hinders 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, a method of coating with a heat-resistant ceramic material such as silicon carbide, silicon nitride, zirconia, or alumina has been proposed. Is being developed. Among them, the formation of a silicon carbide film is most suitable for industrial applications from the technical and economical aspects such as the coating layer forming operation and properties.

Conventionally, as a method of coating silicon carbide 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, There is known a conversion method of converting SiC by reacting with SiO gas by using it as a reaction source. Among them, the silicon carbide coating layer formed by applying the former CVD method is liable to cause delamination due to a mutual thermal expansion difference when a thermal shock is applied because the interface with the substrate is clearly separated. However, sufficient oxidation resistance in a high temperature range cannot be expected. On the other hand, in the case of the latter conversion method, since the surface layer portion of the base material is a functionally graded material forming a silicon carbide layer as a continuous structure, no interface separation occurs.

[0004] As an improvement method of the conversion method, for example, a method of previously mixing fine powder of silicon carbide in a raw material filler of a C / C base material and forming an oxidation resistant film at the time of heat treatment (JP-A-2-271963) ) And a method of forming an oxidation-resistant film by burying a C / C base material in a material for coating silicon carbide and heating the same (JP-A-1-179714). A carbon fiber reinforced carbon composite material as an oxidation-resistant treatment means for a C / C material capable of easily and uniformly forming a silicon carbide coating layer even on a large material without causing material defects such as erosion and warpage. The surface is buried in a coating material powder of a composition comprising a silicon source and a carbon material in a state of being covered with a porous carbonaceous material, and heat-treated at 1800 to 2000 ° C. in a non-oxidizing atmosphere to form a silicon carbide film on the substrate surface. A method for forming a coating layer has been developed by the present applicant (Japanese Patent Application No. -124,694).

[0005]

The C / C material subjected to the oxidation-resistant treatment as described above is used in various fields, but depending on the use, a predetermined portion of the member is excluded from the formation of the oxidation-resistant coating layer. Failure to do so may cause inconvenience. For example, when a C / C material coated with silicon carbide is used as an aerospace member, it is usually assembled with bolts or the like. At this time, when a silicon carbide coating layer including bolts and bolt holes is formed, the volume is increased. Due to the increase, the joining operation such as screwing and fitting becomes difficult. Such a situation is unavoidable even when silicon carbide coating is performed by a conversion method in which the volume is relatively small. At the time of connection, the screw portion of the bolt, the bolt hole, and the like do not need to be subjected to oxidation-resistant treatment because they do not come into close contact with the mating member and come into contact with the atmosphere.

Conventionally, in order to prevent the formation of a silicon carbide coating layer at a predetermined portion or to reduce the thickness,
A mask method has been adopted in which a carbon material is brought into contact with a predetermined portion to suppress a silicidation reaction. However, this method is effective for a simple shape such as a flat plate, but is difficult to apply to a member having a complicated shape such as a bolt hole.

SUMMARY OF THE INVENTION It is an object of the present invention to effectively suppress the formation of silicon carbide in a specific portion even in a portion having a complicated shape, and to form a silicon carbide coating layer having a uniform and dense structure in other portions. It is an object of the present invention to provide a method of oxidizing a C / C material which is possible.

[0008]

According to the present invention, there is provided a method for oxidizing a C / C material according to the present invention. To form a gas barrier film by coating with a mixture of
Then, the substrate is coated with a silicon carbide layer by heating to a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere while being buried in a powder having a composition comprising a silicon source and a carbon material. Features.

The carbon fibers constituting the C / C base material include woven fabrics such as plain weave, satin weave and twill weave made of various materials such as polyacrylonitrile, rayon, pitch, etc. in one-dimensional or multi-dimensional directions. Oriented fibrous bodies, felts, tows and the like are used. As the matrix resin, a phenol-based or furan-based highly carbonizable liquid thermosetting resin, or a thermoplastic material such as tar pitch is used. The carbon fiber is sufficiently wetted with a matrix resin by means of impregnation, coating, or the like, then semi-cured to form a prepreg, and then laminated and pressed. The molded body is heated to completely cure the resin component, and subsequently calcined or carbonized or graphitized in a conventional manner to obtain a C / C base material. Depending on the application, the process of impregnation, curing, and carbonization of the matrix resin may be repeated,
The structure can be densified by depositing pyrolytic carbon using methane, propane, or the like as a raw material by using a CVD method.
It is desirable that the temperature during the firing carbonization be set higher than the processing temperature at the time of forming the silicon carbide film.

In the present invention, the mixture of the thermodegradable thermosetting resin and the carbonaceous powder covering a predetermined portion of the C / C base material makes contact between the SiO gas and the base material surface at the time of forming the silicon carbide layer coating. The thermosetting resin functions as a gas blocking film that blocks the heat, and is selected from thermosetting resins that eventually decompose and volatilize. For example, phenol-based, furan-based, and epoxy-based resins are used. As the carbonaceous powder, for example, a powder of graphite, carbon, coke, or the like is used, and it is preferable to use a fine powder having an average particle diameter of 100 μm or less and a nitrogen adsorption specific surface area of 1 m ² / g or more. The thermosetting resin and the carbonaceous powder are mixed at a predetermined ratio to form a paste, which is applied to a predetermined site to cover the same. The mixing ratio of the two components is appropriately adjusted according to the shape of the predetermined portion to be coated, and usually, the adjustment of the mixing is made of a thermosetting resin. 10
It is performed within the range of 50 to 100 parts by weight of carbonaceous powder with respect to 0 to 200 parts by weight.

[0011]

[0012]

Then, a silicon carbide layer is formed on the surface of the C / C substrate on which a predetermined portion is coated, covered or filled by each of the above-mentioned means, using a powder having a composition comprising a silicon source and a carbon material by a conversion method. Is coated. As a silicon source, quartz,
Silica, those obtained by pulverizing SiO ₂ containing material such as silica sand to grain size 10 to 500 [mu] m, but also carbonaceous materials, the particle size 10 to 100 [mu] m
Carbonaceous materials such as coke, pitch, graphite, and carbon black. The composition of the silicon source and the carbonaceous material is determined in consideration of the surface area of each material powder, but is generally adjusted so that the weight ratio of SiO ₂ : C is in the range of 1: 1 to 4: 1. Be blended. The mixture is sufficiently mixed with a mixing device such as a V-type blender and placed in a reaction vessel made of a highly heat-resistant material such as graphite.

The oxidation-resistant treatment is performed in a process in which a C / C base material is buried in a coating material powder in a reaction vessel, and then transferred to a heating furnace and heated to a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere. . By this treatment step, an unnecessary oxidation of C / C material in which silicon carbide is prevented from being formed in predetermined portions and a silicon carbide coating layer having a uniform and dense structure is formed in other portions can be obtained.

[0015]

Since the formation of the silicon carbide coating layer according to the present invention is substantially performed by the conversion method, the SiO gas generated from the coating material powder is brought into contact with the C / C base material to gradually form the surface of the silicon carbide coating layer. Based on the conversion mechanism. When silicon carbide is formed on the entire surface of the C / C base by this reaction mechanism, a silicon carbide layer is formed up to, for example, a portion such as a bolt hole, resulting in a loss of dimensional accuracy formed at the time of the base.

According to the oxidation-resistant treatment method of the present invention, conversion is performed with a gas barrier film of a mixed paste of a thermodegradable thermosetting resin and a carbonaceous powder coated on a predetermined portion not requiring the oxidation resistance treatment. Since the process is transferred to the process, the SiO gas is effectively prevented from contacting the C / C substrate by the gas barrier film during heating. In this case, the thermo-effective resin in the gas barrier film gradually volatilizes during the heating process during the reaction, and completely disappears when the silicon carbide layer is formed in other parts, and remains on the substrate surface as carbide. Never. Further, the carbonaceous powder is carbonized under CO gas generated in the reaction process, and becomes porous to increase the specific surface area.
C Consumed before reaching the substrate surface. The functions of the gas shutoff and the preferential reaction function synergistically, and siliconization of a predetermined portion is effectively suppressed.

[0017]

[0018]

[0019]

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

Comparative Examples 1, 3 A polyacrylonitrile-based plain woven carbon fiber cloth [W6101 manufactured by Toho Rayon Co., Ltd.] was used as a matrix and a phenolic resin precondensate [PR940 manufactured by Sumitomo Durez Co., Ltd.] was used as a matrix and the volume content was 60%. %, And air-dried for 48 hours to prepare a prepreg sheet. Twenty of these prepreg sheets are stacked and put into a mold, and the weight of the prepreg sheet is 20 kg /
applying a pressure of cm ² at a heating temperature of 130 ° C. for 10 hours,
Pressure molding was performed at a heating temperature of 170 ° C. for 3 hours to form a composite. Then, the composite was transferred to a firing furnace maintained in a nitrogen gas atmosphere, and heated at a rate of 20 ° C./hr to 1000 ° C.
And carbonized. This material is impregnated with a furfuryl alcohol precondensate under vacuum and pressure, transferred again to a baking furnace, heated to 2000 ° C. at a heating rate of 50 ° C./hr, and a 6 mm-thick plate-shaped C / C substrate is obtained. Produced. Then, the C / C base material was cut into a length and width of 200 mm, and a fixing bolt hole (M10, processing accuracy ± 0.01 mm) was formed by 10 mm.
After drilling in places, threading was performed to install a screw portion.

A 50% by weight phenol resin acetone solution is coated on the screw surface of the bolt hole of the C / C base material to a thickness of 100 μm.
, And heated at a temperature of 150 ° C. for 2 hours to cure the resin component. In this state, the C / C base material was mixed with silica sand powder (particle size: 40 to 300 μm) and carbonaceous coke powder (particle size: 74
μm) at a weight ratio of 2: 1 and buried in a filled graphite container. Transfer the graphite container to a heating furnace maintained in a nitrogen gas atmosphere and heat it to 1800 ° C for 2 hours to C / C
A silicon carbide coating layer was formed on the surface of the substrate.

The structure and appearance of the C / C material after the treatment were examined. Table 1 shows the results of the formation of silicon carbide in the screw portion of the bolt hole, the change in screw precision, and the screwed state of the bolt. The thickness of the silicon carbide coating layer formed on the entire surface excluding the bolt hole portions was about 150 μm. Further, as Comparative Example 3, the same C / C base material was coated with the same silicon carbide without performing any treatment on the bolt hole,
Table 1 also shows the inspection results of the bolt hole screw portions in that case.

COMPARATIVE EXAMPLE 2 An average particle size of 5 μm was formed in a bolt hole of the same C / C base material as in Comparative Example 1.
m, graphite powder having a nitrogen adsorption specific surface area of 10 m ² / g. In this state, a silicon carbide coating layer was formed on the C / C substrate surface using the conversion method under the same conditions as in Comparative Example 1. Table 1 also shows the results of the inspection performed on the screw portion of the bolt hole in this case. In addition, the thickness of the silicon carbide coating layer formed in the portion excluding the bolt holes was about 150 μm.

Example A paste in which the graphite powder used in Comparative Example 2 was mixed at a ratio of 100 parts by weight with respect to 100 parts by weight of a phenol resin precondensate on the screw surface of a bolt hole of the same C / C substrate as in Comparative Example 1. Was applied and heated at 150 ° C. for 1 hour to cure the resin component. In this state, a silicon carbide coating layer was formed on the C / C substrate surface using the conversion method under the same conditions as in Comparative Example 1. Table 1 also shows the results of the inspection performed on the screw portion of the bolt hole in this case. In addition, the thickness of the silicon carbide coating layer formed in the portion excluding the bolt holes was about 150 μm.

[0025]

[Table 1]

From the results shown in Table 1, it can be seen that in Examples to which the present invention was applied, silicon carbide generation in bolt holes was more effectively suppressed than in Comparative Examples, and there was no hindrance to bolt bonding, and good results were obtained. Obtained.

[0027]

As described above, according to the present invention, a uniform and dense silicon carbide coating layer can be formed except for a specific portion of the C / C substrate surface. Therefore, it is possible to industrially perform oxidation-resistant treatment of the C / C material in a state where high dimensional accuracy is required and silicon carbide is suppressed in a portion that does not come into contact with the atmosphere during use.

Claims (1)

(57) [Claims] 1. A predetermined portion of a carbon fiber reinforced carbon composite substrate is coated with a mixture of a thermodegradable thermosetting resin and a carbonaceous powder, and then buried in a powder having a composition comprising a silicon source and a carbonaceous material. An oxidation-resistant treatment method for a carbon fiber reinforced carbon composite material, wherein the substrate is heated to a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere in a state and the surface of the substrate is coated with a silicon carbide layer.