JPH0274669A - Carbon fiber-reinforced carbon material having oxidation resistance and production thereof - Google Patents

Abstract

PURPOSE:To obtain non-oxidizable base body without generating crack or peeling of film to steep heat cycle with out losing inherent characteristics of carbon fiber-reinforced carbon material base body by forming inner layer of porous silicon carbide film and outer layer of dense silicon carbide under specific conditions on the surface of said base body. CONSTITUTION:The surface of carbon fiber-reinforced carbon material base body is coated with silicon carbide powder and binder solution and calcined in inert atmosphere at a condition of reaction temperature of 600-1500 deg.C, then an inner layer of porous silicon carbide film of 6-100mum film thickness is formed. Next, an outer layer of dense silicon carbide film of 50-800mum film thickness is formed by using ceramic powder containing silicon, boron and silicon carbide and sintering with reaction at 1650-1900 deg.C for 60-600 min.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a carbon material reinforced with carbon fibers, and in particular,
The present invention relates to oxidation-resistant carbon fiber-reinforced carbon materials that can withstand repeated use in high-temperature environments such as in the aerospace industry or as parts for nuclear reactors.

<Conventional technology> As is clear from the historical process of its application, carbon materials are good conductors of electricity and heat, and at the same time have many unique physical and chemical properties such as unparalleled heat resistance, corrosion resistance, and lubricity. It has the properties of artificial graphite electrodes, carbon/graphite products for metallurgy, and radioactive processed electrodes.1. It is used in a wide range of fields such as electrical brushes and mechanical carbon products.

Carbon materials reinforced with carbon fibers (hereinafter referred to as C/C composites) have a particularly high specific strength and also have the characteristics of carbon materials, so they can be used in areas where conventional carbon materials cannot be used, such as rockets. It can be applied to nose cones, nozzles, etc.

However, carbon materials, including C/C composites, generally undergo oxidation from around 500°C and their excellent physical and chemical properties deteriorate, so they can only be used in high-temperature atmosphere for a very short time. It was impossible except for something.

In order to prevent this phenomenon, various studies have been made regarding oxidation-resistant treatment methods for carbon materials.

Among these methods, chemical vapor deposition (CVD)
Ceramic coating on carbon materials is one of the most commonly used methods, and a dense coating can be obtained by this method. In addition, this method can be used to remove carbides such as silicon carbide, titanium carbide, hafnium carbide, and tantalum carbide, nitrides such as titanium nitride, boron nitride, and zirconium nitride, oxides such as alumina and zirconia, and other borides. Coating can be performed.

However, in this method, it is often necessary to heat the carbon material serving as the base material to around 1000°C, and the ceramic coating on the surface often peels or cracks when the base material is cooled. This is because the maximum strain cannot follow the large difference in thermal expansion coefficient between the base material and the ceramic to be deposited.This can be resolved by making the coefficient of thermal expansion of the base material almost the same as that of the ceramic to be deposited. can do.

However, when using a C/C composite as a base material, its coefficient of thermal expansion is restricted by the coefficient of thermal expansion of the carbon fiber itself and cannot be freely adjusted. Since there was no material available, it was not possible to utilize the excellent oxidation-resistant film produced by the CVD method.

JP-A No. 61-26563 discloses that after a C/C composite is forcibly impregnated with an organic silicon high molecular compound in a molten state, the impregnated material is carbonized by firing at a high temperature of 1200 to 2000°C in an inert atmosphere. A method of converting to silicon is disclosed. However, in this method, when the density of the C/C composite is high, it is not possible to uniformly impregnate the molten organic silicon high molecular compound, and as a result, the anchoring effect becomes poor. It is not possible to obtain a silicon carbide film that adheres closely to the surface.
Such silicon carbide films tend to peel off when used repeatedly at high temperatures, and are not suitable as oxidation-resistant protective films for C/C composites.

Further, Japanese Patent Application Laid-Open No. 153164/1984 discloses a method in which a mixture of a thermosetting resin and an organic phosphorus compound is applied to the surface of a C/C composite, and then the mixture is hardened and carbonized. However, as shown in the examples in the same publication, even in the C/C composite treated as described above, there is a weight loss of about 10% at temperatures below 1000°C. 16 when it enters the atmosphere
Considering the fact that the temperature reaches an extremely high temperature of about 00° C., the C/C composite obtained by the above method has insufficient oxidation resistance.

Further, JP-A No. 61-27248 discloses that a C/C composite is coated with silicon carbide by a diffusion method, and its outer surface is coated with a silicon nitride film by a CVD method. According to this method, it is possible to form a somewhat effective oxidation-resistant film, but because silicon nitride is used, the usable temperature is as low as about 1300°C.
Because the adhesion between the two oxidation-resistant films is weak, the dense film, that is, the silicon nitride film deposited by CVD in this method, is prone to minute cracks due to rapid thermal shock, and the fine cracks are likely to occur. Oxygen diffuses through these cracks, reducing the performance of the C/C composite. For this reason, the above-mentioned techniques are not suitable for use in areas that are repeatedly used at high temperatures.

<Problems to be Solved by the Invention> As mentioned above, there are various methods for coating C/C composites with oxidation resistance, but they have the following problems.

(1) The oxidation-resistant film deposited on the C/C composite by the CVD method always suffers from cracks due to differences in thermal expansion coefficient.
Peeling occurs, making it unsuitable for practical use as it is.

(2) When impregnating with a liquid containing oxidation-resistant film components, if the density of the C/C composite used is high, impregnation cannot be carried out to the inside, and therefore the adhesion of the oxidation-resistant film due to the anchor effect is lost. This may cause peeling. Moreover, even if the film appears to have good adhesion, the difference in coefficient of thermal expansion between the film and the C/C composite is too large, so it will easily crack or peel off when subjected to one or more thermal cycles.

(3) According to the multilayer coating method disclosed in JP-A No. 61-27248, it is possible to obtain a much more stable oxidation-resistant film than the above-mentioned two methods (7), but CV
The film coated by this method easily develops fine cracks due to one thermal cycle load, and oxygen diffuses from the cracks, resulting in a decrease in the strength of the C/C composite.

An object of the present invention is to provide a carbon fiber-reinforced carbon material and a method for producing the same, which suppresses peeling of the oxidation-resistant film, which is a drawback of conventional methods, and minimizes microscopic cracks due to thermal cycle loads. .

<Means for Solving the Problems> In order to achieve the above object, according to the first aspect of the present invention, a porous film formed by powder sintering is provided as an oxidation-resistant film on the surface of a carbon fiber-reinforced carbon material base. An oxidation-resistant carbon fiber-reinforced carbon material is provided, which has an inner layer of a silicon carbide film and an outer layer of a silicon carbide film formed by reaction sintering on the inner layer.

Moreover, it is preferable that the inner layer has a thickness in the range of 3 to 100 μm.

The outer layer preferably has a thickness in the range of 50 to 800 μm.

According to the second aspect of the present invention, after applying a solution containing silicon carbide powder and a binder to the surface of a carbon fiber reinforced carbon material substrate, a porous silicon carbide inner layer is formed by powder sintering, m by reaction sintering on the inner layer of the hindlimb.
A method for producing an oxidation-resistant carbon fiber-reinforced carbon material is provided, which comprises forming an outer layer of a dense silicon carbide film.

Further, it is preferable that the inner layer is formed by sintering at a reaction temperature of 600 to 1500° C. in an inert atmosphere after applying the solution.

The outer layer is made of silicon carbide obtained by reaction-sintering ceramic powder containing silicon, boron, and silicon carbide at a temperature of 1650 to 1900°C for a reaction time of 60 to 600 minutes. Preferably, it is a film.

The present invention will be explained in more detail below.

As shown in FIG. 1, the carbon fiber reinforced carbon material of the present invention has an inner layer 2 on a carbon ia fiber reinforced carbon material base 1,
Further, an outer layer 3 is provided on the inner layer. The inner layer 2 has through holes 4 all over it.

Two-dimensional woven fabrics such as plain weave, satin weave, and twill weave, -dimensionally oriented materials, three-dimensionally oriented materials, felt, tow, etc. are used as the carbon fibers constituting the C/C composite that serves as the base, and phenolic resin is used as the binder. , thermosetting materials such as furan resins, and thermoplastic materials such as tar pitch. The carbon fiber is made into a prepreg by a method such as impregnation or coating, and then laminated and pressure-molded to form a molded body. This molded body is made into a C/C composite by hardening the binder by heat treatment, then firing in accordance with a conventional method, and further graphitizing if necessary.
After that, depending on the application, densification is repeated by an impregnation method in which thermosetting substances, pitch, etc. are impregnated and carbonized again, or a CVD method that uses pyrolytic carbon such as methane or propane. It can also be a C composite.

The inner layer 2 is a powder-sintered porous silicon carbide film that bonds the base 1 and the outer layer 3 with good adhesion, and also has C/
Acts as a buffer layer against external stress on the C composite.

In other words, the film of the C/C composite repeatedly expands and contracts due to rapid thermal cycle loads, but in this case, if the inner layer 2, which is the m-plane layer, is dense, the difference in thermal expansion coefficient between the C/C composite and the film will increase. Because the inner layer is too large, the resulting thermal stress cannot be contracted, and cracks 4 and peeling are likely to occur.

For the above reasons, it is necessary that the inner layer has an appropriate amount of voids. There are various methods for measuring the amount of voids, such as image analysis using electron micrographs of fractured surfaces, mercury holotheta, and the like.

The porosity of the inner layer 2 is larger than the porosity of the substrate 1 and the outer FI 3 described below, and is preferably 15 to 85 as measured by electron microscopic observation of the outermost layer of the inner layer 2.
% is good.

If the void ratio of the inner layer 2 is less than 15%, thermal stress may become a relaxing layer, and if it exceeds 85%, the strength will drop rapidly, which is not preferable.

The thickness of the inner layer formed by powder sintering is preferably in the range of 3 to 100 μm. In other words, if the film is less than 3 μm, it will not actually function as an oxidation-resistant film, and on the other hand, even if you try to obtain a film that is more than 100 μm, many defects such as peeling and cracking will occur during firing. undesirable for this reason.

The outer layer 3 is a dense silicon carbide film obtained by a reactive sintering method.

Since the outer layer 3 is formed on the C/C composite substrate 1 via the porous inner layer 2, when it is formed by reaction sintering, the difference in thermal expansion coefficient between the inner layer and the deposited silicon carbide layer is Since there is almost no cracking, the outer layer 3 does not peel off or crack when the C/C composite is cooled, and a dense outer layer 3 with good adhesion can be obtained.

The thickness of the outer layer of silicon carbide obtained by reaction sintering is 5
It is preferably in the range of 0 to 800 μm. If the film thickness is less than 50 μm, it will not function adequately as an oxygen diffusion bath layer to the C/C composite;
If it exceeds μm, it is not preferable because cracking and peeling are likely to occur due to heat load.

Next, a preferred method for producing the oxidation-resistant carbon fiber-reinforced carbon material of the present invention described above will be described.

In the manufacturing method of the present invention, a solution containing silicon carbide powder and a binder is first applied as an oxidation-resistant film of a C/C composite, and then porous silicon carbide is formed on the surface of the C/C composite by powder sintering. A film is created, and then a silicon carbide layer is formed on the surface of the porous silicon carbide film through the surface openings and on the surface thereof using a reaction sintering method.

The first layer on the C/C composite, that is, the silicon carbide coating on the inner layer, is coated with a solution containing silicon carbide powder and a binder, and then heated at 600°C or higher for 1 hour in an inert gas atmosphere.
This can be done by firing at a temperature of 500° C. or lower.

The particle size of silicon carbide particles contained in the coating material used in this method is preferably 10 μm or less. That is, if the particle size exceeds 10 μm, it is difficult to obtain a smooth film, and as a result, even by providing an outer layer, sufficient oxidation resistance cannot be obtained.

Furthermore, the coating must contain a binder for binding the C/C composite and the aforementioned silicon carbide particles. As this binder, thermosetting resins such as phenol resins, epoxy resins, and furan resins, thermosetting inorganic binders containing alumina, silica, etc. are used. This is because, if this binder is not included, no adhesive force will work between the silicon carbide particles and the C/C composite, making it virtually impossible to coat the composite. Further, it is necessary to use isopropyl alcohol, methanol, etc. as a solvent for this binder so that the coating can be carried out smoothly.

The coating method for applying the coating material is to apply it directly to the C/C composite with a brush, roller spray, etc.
A so-called dip method in which the /C composite is immersed is also used.

The coated film needs to be baked in an inert gas atmosphere to firmly adhere the silicon carbide particles to the C/C composite, but the temperature at that time is preferably 600°C or more and 1500°C or less. . That is, 6
If the temperature is below 00°C, the chemical reaction of the binder components will not proceed sufficiently, making it impossible to obtain a silicon carbide film with sufficient adhesion.On the other hand, if the temperature exceeds 1500°C, the binder itself will become brittle, causing the inner layer to deteriorate. It is not preferable when forming.

A solution containing fine silicon carbide powder and a binder is
The operation of firing after coating the C composite is necessary not only for the above-mentioned effect but also for making the obtained silicon carbide film appropriately porous. This porosity is
It is generated when the volatile components contained in the solution evaporate, and is necessary to have a buffering effect to absorb thermal stress.

In the solution application for forming the inner layer, it is possible to coat the inner layer to a predetermined film thickness at -degrees, but in order to minimize coating unevenness, it is better to coat the inner layer in several batches.

The second layer, that is, the outer silicon carbide film, is formed on the first silicon carbide film formed on the C/C composite by the above method. It is obtained by reaction sintering using a ceramic powder containing an element.

The raw materials required for pressureless sintering of silicon carbide are 3 fl of silicon carbide, carbon, and boron, but this alone does not improve the adhesion to the inner layer and C/C composite, so silicon By adding , the adhesion to the C/C composite is improved.

Silicon, boronic, and silicon carbide used in the reaction sintering method must have a purity of 95% or more and a particle size of 100 μm or less. It is particularly preferable that the total content of oxides and/or these oxides is 1% by weight or less. That is, if the purity is less than 95% and the above-mentioned impurities are contained, the oxidation start temperature of the silicon carbide film formed on the surface layer of the C/C composite will be lowered. This tendency is particularly remarkable when magnesium and/or magnesium oxides are included. If the particle size is larger than 100 μm, it is not preferable because it becomes difficult to mix uniformly with silicon when adding the above-mentioned ceramic powder.

The proportion of each substance in the mixture of silicon, boron, and silicon carbide is 5 to 45% by weight, 0.5 to 3% by weight, respectively.
It is preferably in the range of 52 to 94.5% by weight.
When the amount of silicon is less than 51% by weight, sufficient bonding strength between the C/C composite and the inner layer cannot be obtained, and peeling easily occurs due to thermal shock. On the other hand, if it exceeds 45% by weight, sintering progresses to the extent that it becomes difficult to take out the C/C composite buried in the ceramic powder during reaction sintering, which is not preferable. Boron amount is 0.
If it is less than 5% by weight, it will have difficulty working as a sintering aid for silicon carbide, and conversely, even if it is added in an amount greater than 3% by weight, no improvement in the sintering effect will be seen, and rather the silicon carbide film will remain as an unreacted product. It is undesirable because it remains inside and promotes oxidation. If the amount of silicon carbide is less than the stated amount, it will be difficult to obtain a dense film, and if it is above the stated amount, the amount of auxiliary agent and silicon will be insufficient and a dense film will not be obtained, which is not preferable.

The reaction conditions necessary to obtain a dense outer layer are a temperature of 1650°C.
Preferably, the temperature is 60 to 600 minutes. If the temperature is lower than 1650°C or the reaction time is shorter than 60 minutes, the densification of the film will not proceed sufficiently, whereas if it exceeds 1900°C, abnormal grain growth of silicon carbide will easily occur, resulting in a uniform film. This is not preferable because it becomes difficult to obtain. Even if reaction sintering is carried out for a reaction time exceeding 480 minutes, it is difficult to further improve the densification.

According to this reaction sintering method, silicon added as a raw material diffuses through the through holes created in the inner layer and reacts with the C/C composite to form silicon carbide, which is a continuous reaction. As a result, a film with excellent adhesion can be obtained.

Moreover, the inner layer silicon carbide film is made of very fine silicon carbide particles, and the boron added when forming the outer layer becomes a porous and high-strength film due to the sintering aid effect. It is possible to obtain a film with extremely high oxidation resistance, which could not be obtained using conventional methods.

<Example> The present invention will be specifically explained below based on Examples.

(Example 1) A C/C composite used as a substrate was created by the method described below.

A thermosetting phenol formaldehyde resin (manufactured by Kanebo ■, trade name Bell Pearl) was dissolved and diluted with methanol to a concentration of 25%. Carbon fiber cloth "Besphi #3101" (high-strength type carbon) manufactured by Toho Rayon ■ was added to the solution. impregnated with fibers). The resin basis weight is 8 as an amount.
It was 5 g/m'.

Then, dry in an oven at 80°C for 30 minutes to evaporate methanol.5. A resin-impregnated carbon fiber cloth was obtained.
15 sheets of this cloth are stacked and heated to produce a weight of 50 kg.
A carbon fiber-reinforced plastic board was obtained by heat-pressing molding at 150° C. for 60 minutes under a pressure of f/c+n2. Next, the carbon fiber reinforced plastic plate was fired in an argon gas atmosphere at a heating rate of 20°C/Hr to 2000°C to obtain a C/C composite with a thickness of 2mm.

The C/C composite thus obtained was further subjected to a densification process of impregnating and firing with Totchi (Kawasaki Steel ■ pK-QL'') three times, resulting in a bending strength of 27.
kgf/mm2 interlayer shear strength 1, 78 kgf/a
m2, and a high strength C/C composite with a density of 1.63 g/cm3.

The C/C composite obtained by the above method was
Cut it into a size of 00x50x2, add 20% by weight of silicon carbide powder, and use phenolic resin as a binder (Kanebo ■).
An alcohol solution containing 50% by weight (manufactured by Shinyo Shiroenga ■, trade name "N-TAC21") was applied with a spatula.
Number of applications: 1 time, 3 times after application, sx 10-'g/cm
There was an increase in weight of "16" after this to volatilize the alcohol contained in the film and increase adhesion.
It was dried at 60°C for an hour. The thickness of the film at that time is approximately 9
It was confirmed by electron micrographs that there were several through holes with a diameter of about 0.2 μm. Thereafter, sintering was performed in a high frequency induction heating furnace at 1000° C. for 120 minutes.

Next, 30% by weight of silicon (particle size 10 μm or less, purity 99.9%, manufactured by Kojundo Kagaku ■) and silicon carbide (average particle size 1.
0μm, purity 99.8%) 69% by weight (manufactured by Showa Denko ■) and boron (particle size 10μm or less, purity 99.5%, H, C
1% by weight (manufactured by Tark, Inc.) was placed in a graphite crucible so as to be immersed in an inorganic powder mixture which had been mixed for 6 hours in a ball mill. At this time, the silicon yu is C/C
The amount was 3.5 times the amount required to completely silicon carbide the composite. The sample prepared in this manner was placed in a high-frequency induction heating furnace and reacted for 120 minutes at 1650°C under argon gas plasma distribution to coat the C/C composite with a silicon carbide film with an average thickness of 293 μm. did.

The oxidation-resistant coated C/C composite obtained by the above method was irradiated with Matsuha 2 argon gas plasma for 30 minutes in an air atmosphere, and the weight loss and strength change at that time were investigated. In this experiment, the distance from the argon gas nozzle outlet to the C/C composite was 20 mm, and the diameter of the argon gas plasma was about 10 mm. Further, when the temperature of the back surface of the irradiation center on the C/C composite was measured with a thermocouple, it was 1500°C.

The oxidation-resistant coated carbon fiber-reinforced carbon material obtained by the above method was held at a temperature of 1500°C for 30 minutes in an electric furnace in an air atmosphere, and the weight loss rate and bending strength at that time were examined. The results are shown in Table 1.

(Example 2) A C/C composite was coated with silicon carbide in the same manner as in Example 1 except that the reaction sintering temperature was 1800°C. The average film thickness of silicon carbide at this time was 403μ
It was m.

Table 1 shows the weight loss rate and strength change when the same oxidation test as in Example 1 was conducted.

(Example 3) A C/C composite was coated with silicon carbide in the same manner as in Example 1, except that the reaction sintering temperature and time were 1800° C. for 360 minutes. The average film thickness of silicon carbide at this time was 494 μm. This test piece was subjected to the same oxidation test as in Example 1, and the results are shown in Table 1.

(Example 4) In an alcoholic solution containing 20 parts by weight of silicon carbide powder, 1
The silicon carbide coating was carried out in the same manner as in Example 1 except that the silicon carbide coating was performed by dipping the C/C composite cut out to 0.100 x 50 x 2. The thickness of the silicon carbide film obtained by dipping was about 14 μm. Ta. This test piece was subjected to the same oxidation test as in Example 1, and the results are shown in Table 1.

(Comparative Example 1) Alcohol solution containing 20 parts by weight of silicon carbide powder was
A C/C composite cut out to a size of 100x50x2 was overcoated using a spatula to obtain a film thickness of 110 μm.
However, during dealcoholization treatment at 60° C., many large cracks occurred in the film. When this sample was reacted and sintered under the same conditions as in Example 1, a silicon carbide film with a thickness of 384 μm was obtained.

Table 1 <Effects of the Invention> The oxidation-resistant carbon fiber-reinforced carbon material of the present invention has extremely excellent heat resistance, oxidation resistance, and specific strength, and is an indispensable material particularly in the aviation, space, and nuclear industries. It can be used as

The oxidation-resistant film of the present invention has a structure in which fine-grained silicon carbide is appropriately densely laminated, that is, a more dense silicon carbide film is formed on a porous inner layer by a reaction sintering method. , it is possible to produce carbon fiber-reinforced carbon materials in which the substrate, oxidation-resistant film, and oxidation-resistant film are tightly adhered to each other, and the oxidation-resistant film has an anchoring effect, and is oxidation-resistant even under sudden thermal shock and thermal cycle loads. Since the film does not crack or exfoliate, and the original properties of the carbon fiber reinforced carbon material itself are not impaired, it can fully cope with extremely severe usage conditions of heat loads.

[Brief explanation of the drawing]

FIG. 1 is a conceptual cross-sectional view of the oxidation-resistant carbon fiber-reinforced carbon material of the present invention. Explanation of symbols 1...Carbon fiber reinforced carbon material base, 2...Inner layer, 3...Outer layer, 4...Through hole

Claims (6)

[Claims] (1) The surface of the carbon fiber-reinforced carbon material base has an inner layer of a porous silicon carbide film formed by powder sintering as an oxidation-resistant film, and an outer layer of a silicon carbide film formed by reaction sintering on the inner layer. An oxidation-resistant carbon fiber-reinforced carbon material characterized by having. (2) The oxidation-resistant carbon fiber-reinforced carbon material according to claim 1, wherein the inner layer has a thickness in the range of 3 to 100 μm. (3) The oxidation-resistant carbon fiber-reinforced carbon material according to claim 1, wherein the outer layer has a thickness in the range of 50 to 800 μm. (4) After applying a solution containing silicon carbide powder and a binder to the surface of the carbon fiber-reinforced carbon material substrate, a porous silicon carbide inner layer is formed by powder sintering, and then reaction sintering is performed on the inner layer. A method for producing an oxidation-resistant carbon fiber-reinforced carbon material, which comprises forming an outer layer of a dense silicon carbide film by bonding. (5) The method for producing an oxidation-resistant carbon fiber-reinforced carbon material according to claim 4, wherein the inner layer is sintered at a reaction temperature of 600 to 1500° C. in an inert atmosphere after applying the solution. (6) The outer layer is made of ceramic powder containing silicon, boron, and silicon carbide, and is heated at a temperature of 1650 to 1900°C.
The method for producing an oxidation-resistant carbon fiber-reinforced carbon material according to claim 4 or 5, wherein the silicon carbide film is obtained by reaction sintering under conditions of a reaction time of 60 to 600 minutes.