JPH03197377A - Carbon fiber-reinforced composite material and its production - Google Patents

Abstract

PURPOSE:To obtain the subject composite material capable of preventing fine cracks due to cyclic load by calcining a carbon fiber preform impregnated with an Mo powder-containing resin, modifying the surface layer into an Mo carbide material layer and subsequently applying a metal silicide thereto. CONSTITUTION:A carbon fiber preform and an Mo powder-blended resin contained in the surface layer and/or the whole body of the carbon fiber preform structure are calcined in a monolithic state to modify the surface layer into a molybdenum carbide layer and the surface layer is subsequently coated with a metal silicide to obtain the objective composite material. As the metal constituting the above-mentioned metal silicide, titanium, zirconium, tantalum, molybdenum or manganese is preferable. The content of the above-mentioned powdery metal is preferably within a range of 10-50wt.% based on the amount of the impregnated resin.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to carbon fiber-reinforced carbon composite materials, which are used in the fields of the aerospace industry, nuclear reactor components, etc. The present invention relates to a carbon fiber-reinforced carbon composite material and a method for producing the same.

<Conventional technology> Carbon materials are good conductors of electricity and heat, and at the same time have heat resistance and
It has many unique physical and chemical properties such as corrosion resistance and lubricity, and is used in a wide range of fields such as artificial graphite electrodes, metallurgical carbon and graphite products, electrical discharge machining electrodes, electrical brushes, and mechanical carbon products. It is used.

Carbon fiber reinforced carbon composite material (-hereinafter referred to as C70)
Because it has particularly high specific strength and also has the excellent properties of carbon materials, it can be applied to areas where conventional materials cannot be used, such as rocket nose cones and nozzles.

However, carbon materials including C70 are generally 50
Since it undergoes oxidation from about 0°C and its own excellent physical and chemical properties deteriorate, it was difficult to use it in a high-temperature oxidizing atmosphere.

In order to prevent this phenomenon, various studies have been made regarding oxidation-resistant treatment methods for carbon materials. Among these, ceramic coating on carbon materials by chemical vapor deposition (hereinafter referred to as CVD) is one of the most commonly used methods.For example, silicon carbide, titanium carbide,
Carbides such as hafnium carbide and tantalum carbide, nitrides such as silicon nitride, titanium nitride, boron nitride, and zirconium nitride, oxides such as alumina, zirconia, and silica, borides such as hefnium hydride, etc. coating can be performed.

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

However, when C70 is used as a substrate, its coefficient of thermal expansion is restricted by the coefficient of thermal expansion of the carbon mill itself and cannot be freely adjusted. Since there was no material available, the ceramic coating 2 deposited on C701 by the CVD method as shown in FIG. 1 caused cracking as indicated by 3 and peeling as indicated by 4, and could not be used as an oxidation-resistant coating.

JP-A No. 61-26583 discloses that after C70 is forcibly impregnated with an organosilicon polymer compound in a molten state, the impregnated material is converted into silicon carbide by firing at a temperature of 1200 to 2000°C in an inert atmosphere. A method is disclosed. However, with this method, when the density of C70 is high, it is not possible to uniformly impregnate the organosilicon polymer compound in a molten state, and as a result, a film with high adhesion due to the anchor effect cannot be obtained. Such a film easily peels off when used repeatedly at high temperatures, making it unsuitable as an oxidation-resistant film.

Further, Japanese Patent Application Laid-open No. 153164/1984 discloses a method in which a thermosetting resin and an organic phosphorus compound are applied to the C/C surface, and then the mixture is hardened and carbonized. However, as shown in the Examples of the same publication, even C70 subjected to the above treatment has a weight loss of about 10% by weight at temperatures below 1000° C., so it is difficult to apply it to areas with large heat loads.

Furthermore, in JP-A No. 61-27248, C70 is coated with silicon carbide by a diffusion method, and its outer surface is coated with CVD.
A method of forming a silicon nitride film by a method is disclosed. According to this method, it is possible to form a somewhat effective oxidation-resistant film, but since silicon nitride is used, the usable temperature is as low as approximately 1400°C, and the strength decreases significantly at high temperatures, so the heat load is reduced. Difficult to apply to large areas.

Patents that apply silicon carbide coating to general carbon materials include:
JP-A-60-155586 is mentioned. In this method, a carbon substrate is buried in silicon carbide rice powder and heat-treated in a gas stream containing halogen to form a silicon carbide film on the surface of the carbon substrate. The principle of this method is thought to be that a halogen-containing gas promotes a reaction in which SL gas generated by decomposition of silicon carbide reacts with a carbon base material and converts its surface into silicon carbide.

According to this method, it is possible to form an effective oxidation-resistant film on special high-density carbon materials, but on the other hand, in the case of C70, which cannot be made so dense, the silicon carbide film obtained is Since a large number of through holes are generated, it cannot be an effective oxidation-resistant film.

As mentioned above, there are various methods for coating C70 with oxidation resistance, but they have the following problems.

(1) The oxidation-resistant film deposited on C/C by the CVD method always cracks and peels due to the difference in thermal expansion coefficient, so it is not suitable for practical use as it is.

(2) When impregnating with a liquid containing oxidation-resistant film components, if the density of C70 used is high, impregnation cannot be performed to the center;
Therefore, the adhesion of the oxidation-resistant film due to the anchor effect is lost, resulting in peeling. Moreover, even if the film appears to have good adhesion, the difference in thermal expansion coefficient from that of C70 is too large, so it will easily crack and peel when subjected to one or more thermal cycles.

(3) According to the multi-layer coating method disclosed in JP-A No. 61-27274, it is possible to obtain a much more stable oxidation-resistant film than the above two methods, but the high-temperature strength of the film is It is difficult to apply it to areas with large heat loads because of its poor performance.

An object of the present invention is to provide a carbon fiber-reinforced carbon composite material having oxidation resistance 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. With the goal.

Means for Solving the Problems> According to a first aspect of the present invention, there is provided a carbon fiber-reinforced carbon composite material characterized by having a surface layer portion containing molybdenum carbide and a metal silicide film thereon. Ru.

Here, it is preferable that the metal constituting the metal silicide is at least one selected from titanium, zirconium, tantalum, molybdenum, and manganese.

According to the second aspect of the present invention, a carbon fiber preform and a resin mixed with molybdenum powder impregnated into the surface layer and/or the entire structure of the carbon fiber preform are integrally fired. Thereby, a method for manufacturing a carbon fiber reinforced carbon composite material is provided, which comprises modifying the surface layer to a molybdenum carbide layer and coating the surface layer of the hind leg with metal silicide.

In the above invention, the metal powder is preferably contained in an amount of 10 to 50% by weight based on the amount of the impregnated resin.

Moreover, it is preferable that the particle size of the molybdenum powder is 100 μm or less.

The impregnation amount of the resin is 25 to 25% in the prepreg state.
It is preferably in the range of 60% by weight.

Further, it is preferable that the firing temperature is in a range of 1400 to 3000°C.

The metal silicide coating is preferably carried out by plasma spraying, and the thickness of the metal silicide film is preferably in the range of 100 to 11,000 u.

<Specific structure of the invention> The present invention will be explained in more detail below.

The carbon fiber preform used in the present invention includes a dimensionally oriented material preform, a two-dimensional woven fabric laminated preform such as plain weave, satin weave, and twill weave, a three-dimensionally oriented material preform, felt,
Tow etc. are used.

Typical resins that can be used in the present invention include pitch as a thermoplastic type, and phenolic resin, furan resin, and eboshiki resin as thermosetting types. The content of the resin is preferably in the range of 25 to 60% by weight in the form of blibrig. In other words, if it is less than 25% by weight, the interlayer adhesive strength of the resulting C70 will decrease. Only weak and low-strength C70 can be obtained, which does not meet the field of application of the present invention.

On the other hand, if the resin content exceeds 601% by weight, more pyrolysis gas will be generated during firing, interlayer cracking will occur due to resin contraction, and the carbon fiber content will decrease relatively. , it becomes difficult to obtain high strength C/C.

The molybdenum mixed in the resin is preferably in powder form for ease of handling and mixing, and the particle size is 100 ttn or less, the finer the better. If the particle size exceeds 100 μm, it cannot be used as a carbon fiber preform. Not only is it difficult to mix in the molybdenum powder, but also the density is impaired when C/C is formed, making it impossible to obtain a high-strength product, which is undesirable. It is preferable that the content is in the range of 50% by weight.

If the content is less than 10% by weight, conversion to molybdenum carbide in the C/C surface layer does not progress sufficiently, and therefore, a so-called thermal stress relaxation layer that suppresses peeling of the oxidation-resistant film is not sufficiently formed, which is not preferable. Moreover, if the molybdenum powder exceeds 50% by weight, most of the C/C is converted into molybdenum carbide, which is not preferable because it not only loses the characteristics of the C/C itself but also causes a decrease in glabellar strength.

A method for impregnating carbon fiber preforms with molybdenum powder and resin is, for example, dissolving molybdenum powder and resin in a low boiling point organic solvent such as acetone, methanol, toluene, or a mixed solvent thereof, and then impregnating the carbon fiber preform with the solution. , by removing the organic solvent using an oven or vacuum dryer, or by stacking release paper coated with a mixture of molybdenum powder and resin on at least one side of the carbon fiber preform, and heating and pressing with heating rolls. There are methods such as treating the mixture and impregnating carbon fiber with δ, etc.
Any method may be used as long as the carbon 1am preform can be uniformly impregnated with the mixture, and the present invention is not limited to the method of impregnating the carbon fiber preform with molybdenum powder and resin.

In the step of integrally firing a carbon fiber preform and a resin mixed with metal powder that is impregnated into the surface layer and/or the entire structure of the carbon fiber preform,
The firing temperature is preferably in the range of 1400°C to 3000°C. If the firing temperature is lower than 1400°C, the reaction between molybdenum and carbon is difficult to occur, and the obtained molybdenum carbide is also unstable and has low strength. In addition, it is impractical to manufacture a furnace with a firing temperature of over 3000°C because it is extremely difficult in practice, and it is impractical to create a furnace with a firing temperature of over 3000°C, which is the purpose of the invention. Since a sufficient chemical reaction between carbon and molybdenum proceeds even at a temperature of It is thought that the chemical formula of M o Cs-x, which is not stable in terms of stability, is also included.

By the method described above, a molybdenum carbide layer that can serve as a thermal stress relaxation layer can be formed on the C/C surface layer.

However, this layer is quite porous, and if left as is in heated air, it will inevitably deteriorate due to oxidation. Therefore, a metal silicide film that is stable even in high-temperature oxidizing atmospheres is added to the surface layer by plasma spraying. It is formed.

The formation of metal silicide is preferably performed by plasma spraying. In plasma spraying, a powder raw material is supplied into a plasma jet, melts, accelerates, flies, and collides with the material, absorbing heat while getting wet with the material. It consists of a series of behaviors such as stopping on the side and forming a film. The advantages of obtaining a coating by plasma spraying are as follows.

(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 usually not 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. Because C70 and the molybdenum carbide layer formed on it have many irregularities,
A film with strong bonding strength due to the anchor effect can be obtained, and since metal silicide has excellent chemical affinity with molybdenum carbide, peeling is less likely to occur.

The thickness of the metal silicide film formed by plasma spraying is preferably in the range of 100 to 1000 μm, because if it is thinner than 100 μm, it will not work sufficiently as an oxidation-resistant film for C70, whereas if it exceeds 1000 μm, it will not work as a heat resistant film. This is not preferable because the film is more likely to break (crack) due to impact.

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

As mentioned above, according to the method of surface modification of C70 by mixing carbonizable metal powder in advance in the carbon fiber preform and heat-treating it, the film formation rate is lower than that of the conventional film forming method. Because it provides excellent adhesion, it can prevent the film from peeling off in an oxidizing atmosphere.
As a result, it contributes to improving oxidation resistance.

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

Molybdenum powder (Molybdenum powder
Made by Showa Denko ■, purity 99%, average particle size 40 μm) 6
40g (403i weight % of phenol formaldehyde resin) was added and mixed for 30 minutes with a DC stirrer. The obtained mixed solution was poured into an impregnating tank, and carbon fiber cloth (two-dimensional woven fabric) cut into a size of 310 x 310 mm (east cloth) was poured.
(Using high elastic carbon fiber, 3 to 8 pieces of satin weave) was immersed in the tank for impregnation.

Thereafter, the methanol was volatilized by drying in an oven at 80°C for 30 minutes to obtain a resin-impregnated carbon fiber cloth (prepreg) containing molybdenum powder.The resin content of this prepreg was 37wt% (not including metal molybdenum powder). , the content of metallic molybdenum is 610g/m
Six sheets of this prepreg were laminated and heated at 150°C under a pressure of 2 kgf/cm in an autoclave.
Heat and pressure mold for 0 minutes, carbon fiber reinforced plastic (F
RP).

Next, the carbon fiber reinforced plastic plate was fired to 1000°C at a heating rate of 10°C/Hr in an argon gas atmosphere to obtain C70 with a thickness of 1.9 mm. Furthermore, the surface layer of the C/C was modified into a molybdenum carbide layer by heating to 2600° C. and holding it for 6 hours in the same firing furnace.

C70 having the recycled surface layer thus obtained was further coated with Mo5iz by plasma spraying. The equipment used was manufactured by Plasma Giken ■.

The Mo5t used had an average particle size of 1.5 μm, and thermal spraying was carried out using an outside powder supply method at a spraying rate of 30 g/min. The plasma gas used was argon, and the plasma jet speed was Matsuha 1. A 500 μm thick MoS iz film was coated by this plasma spraying.

The oxidation-resistant coated C70 obtained by the above method was held at a temperature of 1300°C for 1 hour in an electric furnace in an air atmosphere, and the weight loss rate at that time was examined, and it was found to be 0.
It was 91 wt%.

<Effects of the Invention> The oxidation-resistant C/C obtained as a result of the present invention has excellent heat resistance, oxidation resistance, and specific strength, and can be used as an indispensable material in the aerospace field and the nuclear industry. can.

In addition, the coating method of the present invention is a simple method in which the surface of C70 is first modified using molybdenum contained in the prepreg, and then the metal silicide is coated by plasma spraying, so it is practically limited to the size of the sample. This makes it possible to uniformly coat the entire surface without any damage.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an overview of applying a ceramic coating to C70 directly by the CVD method. Explanation of symbols 1...Carbon fiber reinforced carbon composite material, 2...Ceramic film, 3...Crack, 4...Peeling part FIG, 1

Claims (9)

[Claims] (1) A carbon fiber-reinforced carbon composite material characterized by having a surface layer containing molybdenum carbide and a metal silicide film thereon. (2) The metal constituting the metal silicide is titanium,
The carbon fiber reinforced carbon composite material according to claim 1, which is at least one selected from zirconium, tantalum, molybdenum, and manganese. (3) By integrally firing the carbon fiber preform and the resin mixed with molybdenum powder that is impregnated into the surface layer and/or the entire structure of the carbon fiber preform, the surface layer becomes molybdenum carbide. A method for producing a carbon fiber-reinforced carbon composite material, which comprises modifying the material into layers, and then coating the surface layer with metal silicide. (4) The metal powder has a content of 10 to 50% relative to the amount of impregnated resin.
The method for producing a carbon fiber-reinforced carbon composite material according to claim 3, wherein the carbon fiber-reinforced carbon composite material is contained in a range of % by weight. (5) The method for producing a carbon fiber-reinforced carbon composite material according to claim 3 or 4, wherein the molybdenum powder has a particle size of 100 μm or less. (6) When the amount of resin impregnated is in the prepreg state,
The method for producing a carbon fiber reinforced carbon composite material according to any one of claims 3 to 5, wherein the content is in the range of 25 to 60% by weight. (7) The method for producing a carbon fiber reinforced carbon composite material according to any one of claims 3 to 6, wherein the firing temperature is in a range of 1400 to 3000°C. (8) The method for producing a carbon fiber reinforced carbon composite material according to any one of claims 3 to 7, wherein the metal silicide coating is performed by plasma spraying. (9) The method for producing a carbon fiber reinforced carbon composite material according to claim 8, wherein the metal silicide film has a thickness in the range of 100 to 1000 μm.