JPH01320152A - Carbon fiber reinforced carbon material - Google Patents

Abstract

PURPOSE:To enable to obtain a carbon fibre reinforced carbon material with an extremely excellent heat resistance, anticorrosion and specific intensity by coating the inner layer of a silicon carbide covering film containing metallic silicon on the surface of a carbon fibre reinforced carbon material basement, and further coating the outer layer of a silicon carbide covering film on the inner layer. CONSTITUTION:A C/C composit (carbon fibre reinforced carbon material) is buried into metallic silicon powder, and reacted under the inactive gas atmosphere at the temperature of melting point or more of the metallic silicon so as to make the surface layer part of the C/C composit to be a silicon carbide. Moreover, by adding silicon carbide, alumina, boric acid and the like beside the metallic silicon powder, the content of unreacted metallic silicon into the silicon carbide covering film is made to be 1-35wt.% relative to the silicon carbide, and the film thickness of the silicon carbide film is made to be 45-700mu. Furthermore, on the silicon carbide covering film 2 of the first layer of the C composite, the silicon carbide film 3 of an outer layer is covered by CVD method.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a carbon fiber-reinforced carbon material that can withstand repeated use in the field of aerospace industry or in high-temperature atmospheres such 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 certain characteristics. Carbon fiber reinforced carbon material (hereinafter referred to as C
/C composite) has particularly high specific strength and also has the characteristics of carbon materials.
It can be used in areas where conventional carbon materials cannot be used, such as rocket nose cones and nozzles.

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. 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, 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 extremely high temperatures of around 00°C are reached, the above-mentioned method is not practical.

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 approximately 1300'C, and it has a fatal flaw. There is little possibility that it will be put to practical use. In other words, the fatal defect is the dense membrane,
In other words, with this method, the silicon nitride film deposited by the CVD method will inevitably develop minute cracks due to rapid thermal bombardment, and oxygen will diffuse from these minute cracks, improving the performance of the C/C composite. This results in a decrease in

The above-mentioned technology does not take measures to deal with this phenomenon, and therefore is not suitable for use in parts 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 has cracks and cracks due to differences in the coefficient of thermal expansion.
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 multi-layer coating method disclosed in JP-A-61-27248, it is possible to obtain a much more stable oxidation-resistant film than the two methods mentioned above, but the CVD method 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.

The present invention suppresses the peeling of the oxidation-resistant film, which is a drawback of conventional methods, and also has a self-healing function that prevents oxidative deterioration even when microscopic cracks occur due to thermal cycle loads. The aim is to provide reinforced carbon materials.

Means for Solving the Problems> In order to achieve the above object, according to the present invention, an inner layer of a silicon carbide film containing metallic silicon is provided on the surface of a carbon fiber-reinforced carbon material base material as an oxidation-resistant film. Provided is a carbon fiber-reinforced carbon material, further comprising an outer layer of silicon carbide film on the inner layer.

The inner layer contains 1 to 35% by weight of silicon metal, and 4
The outer layer has a thickness of 5 to 700 μm, and the outer layer has a thickness of 50 to 50 μm.
Preferably, the film thickness is 0 μm.

Moreover, it is preferable that the inner layer is formed by a diffusion method.

Furthermore, it is preferable that the inner layer contains boron.

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 fiber-reinforced carbon material base material 1, and further has an outer layer 3 on the inner layer. 4 is metal silicon contained in the inner 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 is the base material, and phenol is used as the binder. Thermosetting substances such as resins and furan resins, and thermoplastic substances such as tar pitch can be used. 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.
Thereafter, a C/C composite with even higher strength can be obtained by repeating #densification by an impregnation method, a CVD method, etc. depending on the application.

The first or inner silicon carbide coating on the C/C composite can be formed by a diffusion method. This method is a method in which a silicon-containing gas and/or a silicon-containing liquid reacts with a C/C composite to convert the surface of the C/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.

Furthermore, a dense silicon carbide film can be obtained by adding a suitable silicon carbide sintering aid, such as boron, in a few percent to the amount of silicon metal. The advantage of the diffusion method is not only that, but also that unreacted metallic silicon can be easily interposed in the silicon carbide film.

As a specific method, C/
The C composite is buried and the reaction is carried out at a temperature higher than the melting point of silicon metal (1390°C) in an inert gas atmosphere,
A typical method is to convert the surface layer of a C/C composite into silicon carbide.

At this time, by using metal silicon in an amount of 1.3 to 7.5 times the weight of the metal silicon required to silicon carbide the entire C/C composite, the metal in the silicon carbide film obtained is The amount of silicon can be adjusted. Furthermore, if only a metal silicon powder bundle is used in the reaction, sintering will occur during the reaction and the C/C composite cannot be taken out.
Handling properties are improved by adding alumina, silica, etc.

The silicon carbide film formed on the surface layer of the C/C composite by the diffusion method is necessary to interpose unreacted silicon metal, but the silicon carbide film formed by the CVD method in the second layer described below It is necessary to improve the adhesion strength of the walnut film. That is, even if an attempt is made to directly deposit a uniform silicon carbide film on a C/C composite by the CVD method, peeling will inevitably occur due to the difference in the coefficient of thermal expansion.

Metallic silicon used in the diffusion method must have a purity of 95% or more and a particle size of 100 μm or less, and in particular must have a purity of 99% or more and contain magnesium, aluminum, iron, and/or their oxides. It is particularly preferred that the total amount 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 carbonized silica 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 metal silicon when adding the above-mentioned ceramic powder.

The content of unreacted metallic silicon in the silicon carbide film is
The amount is preferably 1 to 35% by weight based on the carbonized silica film. If the content is less than 1% by weight, C
If cracks occur in the silicon carbide film deposited by the VD method, it becomes difficult to work as a sealing agent, and conversely, if it exceeds 35% by weight, it may become unreacted if used at a temperature above the melting point of silicon metal. This is not preferable because the flow of silicon metal becomes intense and promotes peeling of the silicon carbide film.

The thickness of the silicon carbide film in which a small amount of unreacted metal silicon is present is preferably in the range of 45 to 700 μm.

If the film thickness is less than 45 μm, a strong bond between the carbonized silica film formed by the CVD method described below and the C/C composite cannot be obtained. In other words, the first layer not only functions as an oxidation-resistant film, but also as a buffer layer that alleviates the difference in coefficient of thermal expansion. On the other hand, it is possible to form a coating with a thickness exceeding 700 μm using the diffusion method, but if the film is made too thick, the carbonized silica film is likely to be destroyed by rapid thermal cycles. Furthermore, due to the nature of the diffusion method, it is undesirable because it reduces the strength of the C/C composite.

The second layer, ie, the outer layer, of the carbonized silicone film formed on the first layer of the carbonized silicone film of the C/C composite can be formed by a CVD method. Silicon carbide coating by CVD is one of the most commonly used methods, for example, using a mixed gas of silicon tetrachloride, methane, hydrogen, and argon (volume ratio 1:1:5:1). , 5°~400
2 at a temperature of 1000-150°C under a reduced pressure of mmHg.
It can be obtained by reacting for about 0 to 300 minutes. However, the reaction conditions of the CVD method vary greatly depending on the crystal structure of silicon carbide to be deposited and the type of raw material gas used, and are not necessarily limited to the above-mentioned reaction conditions.

The thickness of the silicon carbide film coated by the CVD method is
It is necessary that the thickness be in the range of 50 to 500 μm. If the film thickness is less than 50 μm, it will not function sufficiently as a barrier for oxygen diffusion into the C/C composite, and if the film thickness exceeds 500 μm, the time required for precipitation will be extremely long, making it impractical and causing heat problems. This is not preferable because the film is likely to crack or chip due to impact.

C/C composites made using conventional oxidation-resistant coating methods do not have the ability to repair cracks even if the coating is of a certain level, so under severe usage conditions, Oxygen diffuses from the crack and the base material C
/C usually deteriorated the properties of the composite. In contrast, in the C/C composite of the present invention, even if cracks occur in the outer silicon carbide film,
The vapor of unreacted metal silicon existing inside comes out to the surface through that part, suppressing the diffusion of oxygen and causing C/
The original properties of the C composite itself are not impaired. Furthermore, silica is produced by the reaction of a portion of the metal silicon vapor with oxygen, and this can also function as a sealing agent for sealing cracks that occur in the silicon carbide film.

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

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

Phenol formaldehyde resin (manufactured by Kanebo Co., Ltd., part name: Belbar), which exhibits heat-fusibility, was dissolved and diluted with methanol to 25% by weight, and then carbon fiber cross "Besphite"#3101 (manufactured by Toho Rayon Co., Ltd.) was dissolved and diluted with methanol to a concentration of 25% by weight. High-strength type carbon fiber is used) and the resin basis weight is 85g/rn.
Impregnated with '.

Thereafter, it was dried in an oven at 80° C. for 30 minutes to volatilize methanol to obtain a resin-impregnated carbon fiber sheet. Stack 10 of these sheets and press them to produce 100 kg.
/crn' at 150° C. for 60 minutes to obtain a carbon fiber reinforced plastic board. Next, the carbon fiber reinforced plastic plate was placed in an argon gas atmosphere for 2 hours.
A C/C composite with a thickness of 2 mm was obtained by firing to 2000° C. at a temperature increase rate of 0° C./Hr. The C/C composite thus obtained was further subjected to a densification process of furan resin impregnation and firing four times, resulting in a bending strength of 24 kg/mm" and a glabella shear strength of 1.86 kg/m.
m2 and a high strength C/C composite with a density of 1.65 g/cm3.

The C/C composite obtained by the above method was
Cut into 00 x 30 x 2 pieces of metal silicon (particle size 10 μm or less, purity 99.9%, manufactured by Kojundo Kagaku Co., Ltd.)
70% by weight, silicon carbide (average particle size 1.0μm, purity 9
9.7% manufactured by Showa Denko Co., Ltd.) 28% by weight and boron (
Particle size 10μm or less, purity 99.5%, H, C, 5tar
2 wt. The amount of metallic silicon at this time is 3.5, which is the amount required to completely convert the C/C composite into silicon carbide.
It was doubled. The sample prepared in this way was placed in a high-frequency induction heating furnace, and the sample was placed in a high-frequency induction heating furnace for 16 hours under a flow of argon gas at 101/min.
The reaction was carried out at 50° C. for 4 hours, and the C/C composite was coated with a silicon carbide film having an average thickness of 485 μm. The unreacted metallic silicon contained in this silicon carbide film was calculated from the weight loss due to the pickling method, and was 18% by weight based on the silicon carbide film.

The C/C composite having a silicon carbide film with free metal silicon interposed therein obtained by the above method was further coated with a silicon carbide film by a CVD method. This CVD method uses a pulse C that repeats the operation of reducing the pressure and returning it to normal pressure.
The VD method was used, and hydrogen gas containing about 5% by weight of methyltrichlorosilane was fed into the reaction chamber as a reaction gas.

The temperature inside the reaction chamber was 1200° C., the reaction time per pulse was 1.5 seconds, and the number of pulses was 6000. The reason why the pulse CVD method was selected as the CVD method was to cause the reaction gas to diffuse quickly and to obtain a silicon carbide film of a predetermined thickness in as short a time as possible. By this method, a silicon carbide film with a thickness of 150 μm was produced.

The oxidation-resistant coated C/C composite obtained by the above method was placed in the argon plasma of Matsuha 2 in the air for 30 minutes.
The weight loss amount and strength change during that time were examined. The temperature on the C/C composite irradiated with argon plasma was 1500°C. The results are shown in Table 1.

(Comparative Example 1) When coating a C/C composite with a silicon carbide film by the diffusion method, the amount of metallic silicon is reduced to 1 of the amount required for the entire C/C composite to be completely silicon carbide. Silicon carbide coating was performed using the same materials and method as in Example 1, except that the thickness was increased to 0.0 times. The average thickness of the film at this time is 4
It was 79 μm. Further, this C/C composite was further held at 1800° C. for 12 hours to completely convert remaining unreacted metallic silicon to silicon carbide. Thereafter, a silicon carbide film was further formed by CVD in the same manner as in Example 1.

The oxidation-resistant coated C/C composite obtained by the above method was tested in the same manner as in Example 1.
The results are shown in Table 1.

(Comparative Example 2) C/C without oxidation-resistant coating, same as that used in Example 1
The composite was cut into a size of 100 x 30 x 2 mm, and the average film thickness was 482 μm using the same diffusion method as in Example 1.
A silicon carbide film was formed. The amount of unreacted metal silicon contained in this silicon carbide film was calculated from the weight loss due to the pickling method, and it was found that the amount of unreacted metal silicon contained in the silicon carbide film was 17.4% compared to the silicon carbide film.
% by weight.

The C/C composite having a silicon carbide film with unreacted metal silicon interposed therein obtained by the above method was exposed to Matsuha 2's argon plasma in the air for 30 minutes, and the amount of weight loss and strength change at that time was investigated. Ta.
Note that the temperature on the C/C composite to which the argon plasma was irradiated was 1500°C. The results are shown in Table 1.

(Comparative Example 3) When coating a C/C composite with a silicon carbide film by a diffusion method, 30% by weight of metallic silicon and 70% by weight of silicon carbide were used.
Silicon carbide coating was performed in the same manner as in Example 1, except that powder containing no boron at % by weight was used. The thickness of the obtained film was approximately 460 μm. Furthermore, the CVD method was applied to the upper part in the same manner as in Example 1, and the film thickness was 150.
A micron silicon carbide film was deposited.

The sample thus obtained was subjected to an oxidation test according to the method of Example 1. The results are shown in Table 1.

Table 1 <Effects of the Invention> Since the present invention is configured as explained above, its heat resistance, corrosion resistance, and specific strength are extremely excellent, and it is a material that is indispensable especially in the aerospace industry and the nuclear power industry. It can be used as

The C/C composite of the present invention has a special two-layer structure consisting of a silicon carbide film with unreacted metal silicon interposed therein and a silicon carbide film formed thereon. Even if a crack occurs in the silicon film, the metal silicon vapor that exists in the underlying layer will pass through the crack and come out to the surface, suppressing the diffusion of oxygen from the outside.
The original characteristics of C/C composite are not impaired,
Moreover, since silica is produced by the reaction between metal silicon vapor and oxygen, it has the function of a sealing agent that seals cracks that occur in the outer silicon carbide film.

The C/C composite of the present invention has a C/C composite as a base material.
Since damage to the C composite can be kept to a minimum, it can adequately handle even extremely severe thermal cycle loads.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the carbon fiber reinforced carbon material of the present invention. Explanation of symbols 1...Carbon fiber reinforced carbon material base material, 2...Inner layer, 3...Outer layer, 4...Silicon

Claims (4)

[Claims] (1) The surface of the carbon fiber-reinforced carbon material base material has an inner layer of a silicon carbide film containing metal silicon as an oxidation-resistant film, and further has an outer layer of a silicon carbide film on the inner layer. Carbon fiber reinforced carbon material. (2) the inner layer contains 1 to 35% by weight of silicon metal,
and has a film thickness of 45 to 700 μm, and the outer layer has a thickness of 50 to 700 μm.
The carbon fiber reinforced carbon material according to claim 1, which has a film thickness of 500 μm. (3) The carbon fiber reinforced carbon material according to claim 1 or 2, wherein the inner layer is formed by a diffusion method. (4) Claims 1 to 3, wherein the inner layer contains boron.
The carbon fiber-reinforced carbon material according to any one of the above.