JPH0274670A - Oxidation-resistant carbon fiber-reinforced material and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title material resistant to rapid heat cycle without impairing the characteristics inherent in the base material by forming, under specified conditions, an inner layer of porous silicon carbide film on the surface of a carbon fiber-reinforced carbonaceous material base form followed by forming thereon a porous metal silicide film by a specific metal spray coating. CONSTITUTION:An inner layer of porous silicon carbide film 45-800mum thick is formed on the surface of a carbon fiber-reinforced carbonaceous material base form by treatment in an inert gas atmosphere at 1500-1700 deg.C for 30-60min using a silicon carbide-contg. gas and/or liquid. Thence, a metal selected from barium, titanium, zirconium, vanadium, tantalum, molybdenum and manganese is put to plasma spray coating on the resultant inner layer film to form, as an outer layer, a porous metal silicide film 200-1000mum thick.

Description

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

<Conventional technology> As is clear from the historical process of its application, carbon materials are good conductors of electricity and heat! ,: It has many unique physical and chemical properties such as unparalleled heat resistance, corrosion resistance, and lubricity, and is useful for artificial graphite electrodes, metallurgical carbon and graphite products, electrical discharge machining electrodes, electric brushes, and mechanical carbon. It is used in a wide range of fields including 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 at temperatures as low as 500°C, degrading their own excellent physical and chemical properties. It was impossible except for

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. Also, according to this method, 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 Compound coating can be performed.

However, in this method, the temperature of the carbon material serving as the base material must often be heated 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 difference in thermal expansion coefficient between the base material and the precipitated ceramic is so large that the maximum strain cannot be followed. It can be solved.

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 a C/C composite is forcibly impregnated with an organic silicon high molecular compound in a molten state, and then the impregnated material is baked at a high temperature of 1200 to 2000°C in an inert atmosphere. A method of converting to silicon carbide 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 layers of 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. 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. Ill! ! This causes t to occur. Furthermore, 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 when subjected to one or more thermal cycles.

(3) According to the multilayer coating method disclosed in JP-A-61-27248, it is possible to obtain an oxidation-resistant film that is much more stable than the above two methods. The resulting film easily develops fine cracks due to one thermal cycle load, and oxygen diffuses through 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 that suppresses peeling of an oxidation-resistant film, which is a drawback of conventional methods, and minimizes microscopic cracks caused by thermal cycle loads, and a method for producing the same.

Means for Solving the Problems> In order to achieve the above object, according to a first aspect of the present invention, an inner layer of a porous or dense silicon carbide film is provided on the surface of a carbon fiber-reinforced carbon material substrate. An oxidation-resistant carbon fiber-reinforced carbon material is provided, which further comprises an outer layer of porous metal silicide on the silicon carbide film.

Further, the silicon carbide film of the inner layer has a thickness of 45 to 800 μm.
Good film thickness.

The metal silicide film of the outer layer has a 200 to 1
A range of 000 μm is preferred.

Further, the metal forming the metal silicide is preferably selected from barium, titanium, zirconium, vanadium, tantalum, molybdenum, and manganese.

According to the second aspect of the present invention, an inner layer of a porous or dense silicon carbide film is formed on the surface of the carbon fiber-reinforced carbon material substrate by a diffusion method, and the inner layer is further formed on the silicon carbide film by a plasma spraying method. A method for producing an oxidation-resistant carbon fiber-reinforced carbon material is provided, which comprises forming an outer layer of porous metal silicide.

Here, the silicon carbide film is formed under an atmosphere of inert gas τ.
It is preferably obtained by a chemical reaction between the carbon fiber reinforced carbon material and a silicon-containing gas and/or liquid at a temperature of 500 to 1700° C. for 30 to 600 minutes. Note that the film thicknesses were all measured by electron microscopic observation of the cross section.

The present invention will be explained in more detail below.

The carbon fiber reinforced carbon material of the present invention has an inner layer 2 on a C/C composite base 1 as shown in FIG. 1, and further has an outer layer 3 on the inner layer. 4 is a bore contained in the outer layer.

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 in the present invention is on the surface of the C/C composite,
It has a porous silicon carbide film.

The porosity of the inner layer 2 is preferably in the range of 15 to 85% based on the image analysis results obtained by taking an electron micrograph of the outermost layer. If it is less than 15%, it may become a stress relaxation layer, 8
This is because if it exceeds 5%, the strength will rapidly decrease.

When the inner layer is porous, the base 1 and the outer N3 are bonded with good adhesion, and it also acts as a buffer layer against external stress on the C/C composite.

The thickness of the silicon carbide film of the present invention is preferably in the range of 45 to 800 μm. If the film thickness is less than 45 μm, it is not sufficient to improve the oxidation resistance of the C/C composite 1-, and moreover, it is difficult to act as a thermal stress relaxation layer existing between the outer layer and the C/C composite.

In addition, if the film is thicker than 800 μm,
The silicon carbide film is more likely to be destroyed due to rapid thermal cycle loads. Furthermore, five films are not preferable because they reduce the strength of the C/C composite due to the nature of the diffusion method.

The inner layer 2 may be a layer that does not contain unreacted silicon, but preferably contains 35% by weight or less of silicon. If silicon is contained, even if a crack occurs in the metal silicide film of the outer layer 3, the unreacted silicon vapor existing inside will pass through that part and come out to the surface, preventing oxygen from diffusing into the interior. is suppressed, and the original oxidation resistance properties of the C/C composite itself are not impaired. Furthermore, silica is produced by the reaction between a portion of silicon vapor and oxygen, and this can also function as a sealing agent for sealing cracks that occur in the silicon carbide film.

If the silicon content exceeds 35% by weight, unreacted silicon will flow violently if used at a temperature higher than the melting point of silicon, which will promote peeling of the silicon carbide film, which is not preferable.

Further, as the outer layer 3, a metal silicide film is further formed on the silicon carbide film by a plasma spraying method.

The thickness of the film obtained by plasma spraying is 200 to 1
000 μm range is preferable. 200μ
If it is thinner than m, it is difficult to function sufficiently as an oxidation-resistant film of the C/C composite, and if it exceeds 1000 μm, the thermal stress relaxation ability decreases and cracks often occur, which is not preferable.

The metal forming the metal silicide subjected to plasma spraying is selected from barium, titanium, zirconium, vanadium, tantalum, molybdenum, and manganese, and among these, molybdenum, zirconium, and manganese silicides have particularly excellent oxidation resistance. Show characteristics.

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

In the manufacturing method of the present invention, as an oxidation-resistant film for a C/C composite, a silicon carbide film is first created on the surface of the C/C composite by a diffusion method, and then a porous silicon carbide film is formed on the surface of the silicon carbide film by a plasma spraying method. Forms an outer layer of high quality metal silicide.

The diffusion method involves reacting a silicon-containing gas and/or a silicon-containing liquid with a C/C composite substrate to form a C/C composite substrate.
This method converts the surface of C composite into silicon carbide. According to this method, since the surface layer of the C/C composite is made into silicon carbide, the adhesiveness with the C/C composite is strong, and there is an advantage that peeling does not easily occur even under thermal shock.

Another advantage is that unreacted silicon can be easily interposed in the silicon carbide film.

The specific method is to bury the C/C composite inside the silicon powder bed and heat it under an inert gas atmosphere for 1,500~
The reaction is carried out in a temperature range of 1700° C. for 30 to 600 minutes to convert the surface layer of the C/C composite into silicon carbide.

Here, if the reaction temperature is lower than 1500°C, the formation rate of the silicon carbide film is very slow and it takes a long time to obtain the desired film thickness, which is inefficient. This reaction is not preferable because the silicon carbide reaction of the C/C composite progresses to the inside, impairing the characteristics inherent to the carbon fiber.

Regarding the reaction time, if it is shorter than 30 minutes, the formation of the silicon carbide film will occur unevenly and insufficiently, which is not preferable. On the other hand, if the reaction time exceeds 600 minutes, the silicon carbide reaction progresses to the inside of the C/C composite, which is not preferable because the characteristics of the carbon material are lost.

Also, if only silicon powder is used in the reaction, sintering will occur during the reaction and the C/C composite will not be able to be taken out, so it is recommended to add ceramic powder that is stable at high temperatures, such as silicon carbide, alumina, silica, etc. This improves handling.

However, if the amount of ceramic powder mixed exceeds 85% by weight, it should be avoided since it will have an adverse effect on the silicon carbide reaction of the surface layer of the C/C composite.

The silicon used in the diffusion method has a purity of 95% or more,
The particle size must be 100 μm or less, and the purity must be 99% or more, including magnesium, aluminum,
It is particularly preferable that the total content of iron and/or oxides thereof is 1% by weight or less and the particle size is 10 μm 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 trend is especially true for magnesium and/or
or significant if it contains magnesium oxides. 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 silicon carbide film obtained by this method needs to be porous.

When obtaining a porous membrane, it can be obtained by reacting at a temperature of 1500 to 1700°C for 30 to 300 minutes. In this case, if boron is added as a sintering aid for silicon carbide in an amount of less than 0.5% of the silicon to be added, a porous and high-strength film can be obtained.

In addition, specific methods include non-formation of silicon carbide through the reaction of SiO gas and C/C composite, etc.
The method is not necessarily limited to the above method.

A metal silicide film is further formed on the silicon carbide film obtained by the above method using a plasma spraying method.

Preferably, the metal silicide is formed by plasma spraying.

Plasma spraying consists of a series of actions in which a powder raw material is fed into a plasma jet, melts, accelerates, flies, and collides with the material, where it absorbs heat while getting wet with the material and solidifies to form a film. There is. The advantages of obtaining a film by plasma spraying are: (1) Since the plasma jet flow rate is high, the collision energy of the molten particles becomes large, and a film with strong bonding force can be obtained.

(2) Since the temperature of the material is not normally heated above 200°C, the mechanical strength of the material will not deteriorate or thermal distortion will occur.

(3) The coating speed is fast and a thick film can be obtained at low cost.

The following points can be mentioned.

Since the C/C composite and the silicon carbide film formed on it have many irregularities, it is possible to obtain a film with strong bonding strength due to the anchor effect, and metal silicide has a chemical affinity with silicon carbide. Because of its excellent properties, peeling is less likely to occur.

In addition to the above-mentioned advantages, the coating obtained by plasma spraying is moderately porous, so even when subjected to sudden thermal cycle loads, the stress is absorbed within the coating and cracking does not occur. Generally, it is said that a dense oxidation-resistant film is preferable in order to prevent oxygen diffusion, but the denser the film, the more likely it is that it cannot absorb the stress associated with heat load, leading to destruction. In the present invention, we have succeeded in obtaining an oxidation-resistant coating that will not be destroyed by thermal stress by utilizing the porosity of the plasma sprayed coating and using a material with excellent oxidation resistance.

When performing plasma spraying, the reaction conditions include the amount of raw material supplied,
It is necessary to specify the thermal spraying temperature, etc.

By the above method, oxidation-resistant coating can be applied to the C/C composite. According to this method, it is possible to obtain a film that can withstand thermal cycle loads and has excellent oxidation resistance.

<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 Belbar) was dissolved and diluted with methanol to a concentration of 25% by weight, and carbon fiber cloth "Besphite #3101" (high strength) manufactured by Toho Rayon ■ was added to the solution. (type carbon fiber used) impregnated. The resin basis weight is 8 as an amount.
It was 5 g/m'.

Thereafter, it was dried in an oven at 80° C. for 30 minutes to volatilize methanol to obtain a resin-impregnated carbon fiber cloth. Laminate 15 sheets of this cloth and autoclave it for 50k.
A carbon fiber-reinforced plastic board was obtained by heating and press-forming at 159°C for 60 minutes under a pressure of "gf/cm". Next, the carbon fiber-reinforced plastic board was heated at a temperature of 20°C/Hr in an argon gas atmosphere. A C/C composite with a thickness of 2 mm was obtained by firing at a speed of up to 2000°C.The C/C composite thus obtained was further subjected to a densification process of pitch impregnation and firing four times. Bending strength: 15 kgf/mm' Interlaminar shear strength: 1,01 k
High strength C/C with gf/mm2 and density 1.53g/cm3
Composite.

The C/C composite obtained by the above method was
Cut it out to a size of 00x50x2, and add silicon (particle size 10
μm or less, purity 99.9%, made by Kojundo Kagaku ■) 60% by weight, silicon carbide (average particle size 1.0μm, purity 99.7%)
40 wt. The sample thus prepared was placed in a high-frequency reading heating furnace and reacted for 600 minutes at 1550°C with argon gas flowing at 10°C/min. Covered with a bare film. The unreacted silicon contained in this silicon carbide film was calculated from the weight loss due to the pickling method, and was 12.7% by weight based on the silicon carbide film.

The C/C composite having a silicon carbide film obtained by the diffusion method obtained by the above method was further coated with molybdenum silicide by a plasma spraying method. The equipment used was manufactured by Plasma Giken ■.

The average particle size of the molybdenum silicide used was 1.5 μm.
30 g/mi by outside powder feeding method
This was done by supplying n. The plasma gas used was argon, and the speed of the plasma jet was Matsuha 1.

This plasma melt Q] coated the film with a molybdenum silicide film of about 500 μm.

The oxidation-resistant coated C/C composite obtained by the above method was exposed to Matsuha 2 argon plasma in air for 30 minutes, and the weight loss rate at that time was measured. The temperature at the center of exposure of the argon plasma to the C/C composite was 1500°C. The results are shown in Table 1.

(Example 2) A C/C composite obtained by the same method as Example 1 was
It was cut into a size of 0.100 x 50.0 x 2 and placed in a high frequency induction heating furnace. Silicon and 5t0 as SiO sources
2 were mixed at a weight ratio of 1:1 and placed in a graphite crucible, which was similarly inserted into the high frequency induction heating furnace described above. In this state, Ar gas 5 fl/m i
The C/C composite was subjected to a SiC reaction by raising the temperature to 1700° C. over 2 hours under n-flow and holding it at that temperature for 3 hours. The thickness of the obtained film was 4
It was 10 μm.

After obtaining a C/C composite having a silicon carbide film by this method, a 500 μm thick molybdenum silicide film was formed in the same manner as in Example 1.

The sample thus obtained was subjected to an air oxidation test in the same manner as in Example 1, and then its physical properties were measured.

(Comparative Example 1) The same method as in Example 1 was carried out except that the reaction conditions for the diffusion method were changed to 1400° C. for 200 minutes. C/C
The thickness of the silicon carbide film formed on the composite is
The diameter was 34 μm when observed using an electron microscope.

Thereafter, a plasma flame exposure test was conducted in the same manner as in Example 1, and an oxidation test was also conducted.

(Comparative Example 2) Coating was carried out in the same manner as in Example 1, except that the thickness of the molybdenum silicide film was 146 μm. The film thickness was measured by electron microscopy.

Thereafter, a plasma flame exposure test was conducted in the same manner as in Example 1, and an oxidation test was also conducted.

(Comparative Example 3) The same method as in Example 1 was carried out except that the film thickness of molybdenum silicide was set to 1500 μm. Film thickness measurement is
This was done using electron micrographs.

Thereafter, a plasma flame exposure test was conducted in the same manner as in Example 1, and then physical properties were measured.

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 manufacturing method of the present invention first converts the surface of a carbon fiber reinforced carbon material base into silicon carbide by a diffusion method, and then forms a porous metal silicide on the surface of the carbon fiber reinforced carbon material by a plasma spraying method. Carbon fiber-reinforced carbon materials can be produced in which the substrate, oxidation-resistant film, and metal silicide are in close contact with each other, and the oxidation-resistant film has an anchoring effect, and the oxidation-resistant film remains strong even under sudden thermal shock and thermal cycle loads. ,
No cracking or peeling occurs, and the original properties of the carbon fiber reinforced carbon material itself are not impaired.

[Brief explanation of the drawing]

FIG. 1 shows a schematic cross-sectional view of a C/C composite provided with an oxidation-resistant coating obtained according to the present invention. Explanation of symbols 1... C/C composite, 2... Inner layer, 3... Outer layer, 4... Bore (hole)

Claims (6)

[Claims] (1) Oxidation resistance characterized by having an inner layer of a porous silicon carbide film on the surface of the carbon fiber-reinforced carbon material base, and further having an outer layer of porous metal silicide on the silicon carbide film. carbon fiber reinforced carbon material. (2) The inner layer silicon carbide film has a thickness of 45 to 800 μm.
The oxidation-resistant carbon fiber-reinforced carbon material according to claim 1, which has a film thickness of . (3) The oxidation-resistant carbon fiber-reinforced carbon material according to claim 1 or 2, wherein the metal silicide film of the outer layer has a thickness in the range of 200 to 1000 μm. (4) The oxidation-resistant carbon fiber reinforced carbon according to any one of claims 1 to 3, wherein the metal forming the metal silicide is selected from barium, titanium, zirconium, vanadium, tantalum, molybdenum, and manganese. material. (5) A porous or dense inner layer of silicon carbide film is formed on the surface of the carbon fiber-reinforced carbon material substrate by a diffusion method, and an outer layer of porous metal silicide is further formed on the silicon carbide film by a plasma spraying method. A method for producing an oxidation-resistant carbon fiber-reinforced carbon material. (6) The silicon carbide film is heated for 15 minutes under an inert gas atmosphere.
The oxidation-resistant carbon fiber-reinforced carbon material according to claim 5 obtained by chemically reacting the carbon fiber-reinforced carbon material with a silicon-containing gas and/or liquid at a temperature of 00 to 1700°C for 30 to 600 minutes. Production method.