JPH08253874A - High adhesion oxidation resistant coating film for c/c composite material and its formation - Google Patents

Abstract

PURPOSE: To form a high adhesion oxidation resistant coating film for preventing the oxidation of a C/C composite material on the surface of the C/C composite material. CONSTITUTION: A metal coating film layer 3 of one or more kinds of B, Cr Mo and W, which are >=500 deg.C in m.p., is formed on the surface of the C/C composite material 2, silicon carbide 4 is applied thereon and the change of adhesive strength due to the difference of thermal expansion between the C/C composite material 2 and the silicon carbide 4 is absorbed by the plastic deformation of the metal coating film layer 3 at a high temp. Further, it is more preferable to provide a vitreous coating film layer 5 on the silicon carbide 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber reinforced carbon (hereinafter referred to as C / C) composite material, which is a high-performance C / C composite material which can be used repeatedly for a long time in a high temperature atmosphere. An adhesive oxidation resistant coating and a method for forming the same are provided.

[0002]

2. Description of the Related Art A C / C composite material is a composite material in which carbon fiber is used as a reinforcing material and carbon is used as a matrix, and is excellent in heat resistance, chemical resistance, and abrasion resistance, and has high strength and light weight. Is. Therefore, it is used for rocket nozzles and aircraft disc brakes. The C / C composite material is oxidized in an oxygen atmosphere from about 500 ° C, and its excellent physical and chemical performance deteriorates. Therefore, use in a high temperature atmosphere except for an extremely short time It was impossible.
In order to prevent this phenomenon, various studies have hitherto been made on a method of enhancing the oxidation resistance performance of the carbon material.
Among these methods, chemical vapor deposition (hereinafter referred to as CVD) coating of ceramics is one of the most widely used methods, and a dense coating film can be obtained by this method. However, in this method, it is often necessary to heat the base material C / C composite material to a temperature of around 1000 ° C. at the time of coating, and the ceramic coating on the surface peels off when cooled to room temperature after the coating treatment is completed. And often cracked. This is C /
The main cause is the large difference in the coefficient of thermal expansion between the C composite material and the ceramics. The thermal expansion coefficient of the C / C composite material is determined by the thermal expansion coefficient of the carbon fiber itself, and there is no ceramic coating material having the same thermal expansion coefficient as the C / C composite material. It was difficult to use a ceramic coating film.

In Japanese Patent Publication No. 2-54778, C
Before coating the ceramics layer by the VD method, the surface conversion layer of the C / C composite material is provided with a SiC conversion coating obtained by reacting metallic silicon with the C / C composite material by the pack diffusion method to form SiC, thereby forming a CVD-SiC. Techniques for increasing adhesion to layers are described. Although this technique is excellent in improving the adhesion, a problem that the material strength of the C / C composite material is extremely lowered because a part of the reinforcing fibers in the surface layer of the C / C composite material is converted to SiC. was there.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems in the prior art, and to prevent the C / C composite material and the silicon carbide coating from being deteriorated without lowering the material strength of the base material C / C composite material. It is an object of the present invention to provide a high adhesion and oxidation resistant coating for C / C composite materials, which has excellent adhesion to a covering film and exhibits high oxidation resistance and a method for forming the same.

[0005]

In order to solve the above-mentioned problems, the present inventors have found that the difference in the coefficient of thermal expansion between the C / C composite material in the plane direction and the thickness direction, and the C / C composite material. As a result of repeated intensive research focusing on the difference in the coefficient of thermal expansion between silicon carbide,
It was concluded that the difference in thermal expansion coefficient between the two can be relaxed by a metal layer that plastically deforms at high temperature. That is, the present invention has a melting point of 15 on the surface of the C / C composite material.
It is intended to provide a C / C composite material which is coated with at least one kind of metal having a temperature of 00 ° C. or higher, and is further coated with silicon carbide, which shows high oxidation resistance, and a method for producing the same.

Hereinafter, the present invention will be described in more detail. C
As the reinforcing carbon fiber of the / C composite material, PAN-based, rayon-based or tar-pitch-based carbon fiber can be used,
The most excellent one is obtained by using a PAN-based one in terms of strength. For example, commercially available products such as "High Strength Vesphite (HTA)" and "High Elasticity Vesphite (HM40)" manufactured by Toho Rayon can be used.

As the form of the reinforcing fiber, a roving obtained by bundling 100 to 12000 long fiber filaments in one direction and / or a woven fabric can be used. In terms of strength, the reinforcing carbon fiber preferably has a length of 50 mm or more, and when the length is less than 50 mm, the base material C is used.
The strength of the / C composite material cannot be increased sufficiently.

The present invention works most effectively when the reinforcing carbon fiber is a long fiber and exhibits high oxidation resistance performance without deteriorating the strength of the C / C composite material having high strength. A protective coating can be provided. As the binder of the reinforcing carbon fiber, a thermosetting substance such as phenol resin or furan resin, or a thermoplastic substance such as pitch can be used.

As a method for producing a C / C composite material, for example, a prepreg sheet is prepared by impregnating and coating a carbon fiber with a binder, laminating, heating and pressing to form a compact, and the compact is made of nitrogen, argon or the like. After firing in an inert atmosphere, and further graphitizing as necessary, a C / C composite material is obtained. Then, depending on the required performance, densification is repeatedly performed by an impregnation method in which a thermosetting material or a thermoplastic material is impregnated and firing, or a CVI method in which a hydrocarbon gas such as methane or propane is thermally decomposed to obtain carbon. ,
A method for increasing the density and strength of the C / C composite material can be given. In the present invention, when the density of the C / C composite material is increased to 1.5 g / cm ³ or more and the strength of the C / C composite material base material is sufficiently high, it acts particularly effectively,
The effect of not lowering the material strength of the base material C / C composite material, which is a feature of the present invention, can be sufficiently exerted.

On the surface of the C / C composite material obtained as described above, at least one metal having a melting point of 1500 ° C. or higher, preferably at least one metal selected from B, Cr, Mo and W. To cover. The reason why the metal is selected is that a metal having a melting point of less than 1500 ° C. is melted at a temperature of 1500 ° C. or higher at which a C / C composite material is usually used and the outermost silicon carbide coating layer is peeled off. Because you can't. As a method for coating a metal, a method usually used for metal coating such as a vapor deposition method and a sputtering method can be used.

The film thickness of the high melting point metal is 0.5 μm or more and 100 or more.
μm or less. If it is less than 0.5 μm, the effect of relaxing the thermal stress becomes low, and the outermost silicon carbide layer peels off. More preferably, the thickness is 2 μm or more. 10
When it exceeds 0 μm, it takes time and material cost for the obtained oxidation resistance, which is not preferable. A more preferable upper limit is 50 μm.

A silicon carbide coating layer is formed on the high melting point metal coating layer. In particular, these are selected because of their high temperature stability, low vapor pressure at high temperature, low reactivity with carbon, and low oxygen permeability. The CVD method is suitable as a coating method, and the most dense layer can be obtained, and in the present invention, it is particularly effective in increasing the adhesion of the silicon carbide film by the CVD method. The thickness of the silicon carbide coating layer is 5μ
m-500 μm is preferable, and if it is less than 5 μm, the oxidation resistance performance in an oxidizing atmosphere deteriorates. More preferably 50
It is preferable that the thickness is at least μm. It is not preferable to obtain a coating thickness of more than 500 μm because it takes too much time and material cost for the obtained oxidation resistance performance. More preferably 300μ
m or less.

The coated silicon carbide coating layer is apt to have defects such as fine cracks during cooling. Oxygen that has entered through this defect will start oxidation of the C / C composite at about 50
In the temperature range from 0 ° C. up to several hundreds of degrees Celsius where thermal expansion closes fine cracks in the silicon carbide coating layer, significant oxidation is caused. Therefore, for example, boron oxide, silicon oxide,
A glass-like substance containing aluminum oxide, zirconium oxide or the like as a main component is applied. These glassy substances are 500 ° C
When the C / C composite material in the vicinity melts at a temperature at which oxidation starts and prevents cracks, and when the fine cracks in the silicon carbide coating layer start to close due to thermal expansion, they have fluidity, so when the cracks close. In addition, it can easily deform and flow, and keeps cracks sealed. The present invention works more effectively due to the presence of this vitreous substance. Examples of the method for coating the vitreous substance include, for example, triethyl borate, tetraethyl silicate, a method of applying a solution that vitrifies by a reaction of aluminum phosphate, an aluminum-alkoxide, an organic compound which precipitates an oxide by a reaction of zirconium-alkoxide, etc. The method of applying the solution of can be mentioned. Usually, since it contains a volatile substance or bubbles inside only by coating and drying, it may be heated to a temperature near the melting point of the glass or more once in order to obtain a more dense glass.

[0014]

The high-adhesion, oxidation-resistant coating for high-strength and high-density C / C composite material according to the present invention causes a reaction caused by a difference in coefficient of thermal expansion between the C / C composite material and silicon carbide coating the outer layer thereof.
Since it is relaxed by the metal layer that plastically deforms at a high temperature, without lowering the strength of the base material C / C composite material,
The adhesiveness between the C / C composite material and silicon carbide can be enhanced, and the adhesive strength at the interface hardly decreases even when subjected to cycle heating from room temperature to 1000 ° C.

[0015]

EXAMPLE FIG. 1 shows the high strength and high density C / C of the example of the present invention.
A schematic cross-sectional view of the high adhesion and oxidation resistant coating 1 for a composite material is shown. A refractory metal layer 3 is formed on a C / C composite material 2, a layer of silicon carbide 4 is formed on the refractory metal layer 3, and a vitreous coating layer 5 is coated on the uppermost portion.

The present invention will be specifically described below based on Examples and Comparative Examples. [Example 1] Phenolic resin (Sumitomo Bakelite Co., Ltd.)
"PR-50273" manufactured by Toray Co., Ltd.) was dissolved and diluted in acetone so that the non-volatile component was 28% by weight, and then carbon fiber woven cloth (manufactured by Toho Rayon Co., Ltd., "High strength vesphite"# 3)
121) was impregnated. 80 degrees 30 minutes in the oven, 1
It was dried at 00 degrees for 30 minutes to obtain a carbon fiber sheet having a resin basis weight of 35% by weight. Six of these sheets are laminated and hot-pressed under a pressure of 10 kg / cm ² at 150 ° C. 60.
It was heated and pressed for a minute to obtain a carbon fiber reinforced plastic plate. Next, the material was heated to 2000 ° C. at a temperature rising rate of 10 ° C. per minute in an Ar gas atmosphere to obtain a material having a thickness of about 2 mm.

This material was impregnated with furan resin for 4 hours as a densification treatment in a vacuum, and then under a pressure of 10 kg / cm ² for 4 hours, and this was heated in an oven at 100 ° C. for 1 hour.
After heating for 5 hours to cure the furan resin, it was baked at 2000 ° C. in an Ar gas atmosphere. This densification treatment was repeated until the density reached 1.55 g / cm ³ , to produce a high density and high strength C / C composite material.

The obtained high-density and high-strength C / C composite material was coated with molybdenum by 10 μm by a sputtering method. After that, a mixed gas of silicon tetrachloride, methane, hydrogen and argon was added.
A C / C composite material was coated with 100 μm of silicon carbide by a CVD method introduced into a furnace heated to about 1300 ° C. to impart oxidation resistance performance to the C / C composite material. When the C / C composite material was inserted into a furnace heated to 1400 ° C. in an air atmosphere, held for 6 minutes, and then taken out and rapidly cooled, an oxidation test was conducted. No peeling of the film was observed, and the weight loss was 1.8%.

Example 2 The C / C composite material was provided with oxidation resistance in exactly the same manner as in Example 1, except that the refractory metal in Example 1 was changed to boron 5 μm, chromium 15 μm, and dungsten 7 μm. When the C / C composite material was subjected to an oxidation test in the same manner as in Example 1, no peeling of the silicon carbide film was observed,
The weight loss was 1.8%, 1.8% and 1.9%, respectively.

Example 3 A C / C composite material having the same oxidation resistance as that of Example 1 was coated with a solution of tetraethyl silicate polymerized by a polymerization reaction under an acid catalyst in advance. After drying at 500 ° C. for 30 minutes, the glass was once melted by heating to 1000 ° C., and the surface of the C / C composite material was coated with glass. The C / C composite material was subjected to an oxidation test in the same manner as in Example 1. As a result, peeling of the silicon carbide coating was not observed, and the weight loss was 0.5%.

COMPARATIVE EXAMPLE 1 In the same manner as in Example 1, except that the refractory metal was changed to zirconium 7 μm and hafnium 7 μm, 100 μm of silicon carbide was coated by the CVD method. The C composite material surface could not be uniformly coated and floated on the C / C composite material surface.

[Comparative Example 2] The thickness of the silicon nitride coating layer was 5
Oxidation resistance was imparted and an oxidation test was performed in the same manner as in Example 1 except that the thickness was changed to μm, and the silicon nitride film was peeled off during the 10th heating and cooling. [Comparative Example 3] Except that the coating of the refractory metal was not performed,
When oxidation resistance was given and an oxidation test was conducted in exactly the same manner as in Example 1, the silicon nitride film was peeled off during the first heating and cooling.

[0023]

As described above, the high-adhesion oxide coating for high-density and high-strength C / C composite materials according to the present invention does not impair the mechanical properties of the high-density and high-strength C / C composite materials. Since it is possible to impart high oxidation resistance to C / C composite materials, oxidation resistance treatment of high density and high strength C / C composite materials designed and manufactured for space related structural materials such as space shuttles It can be used as a coating.

[Brief description of drawings]

1 is a partial cross-sectional view of a coating of an example.

[Explanation of symbols]

1 coating 2 C / C composite material 3 refractory metal layer 4 silicon carbide 5 vitreous coating layer

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // D06M 101: 40

Claims (7)

[Claims] 1. A high adhesion oxidation resistance for C / C composite material, comprising a coating layer of refractory metal on the surface of C / C composite material, and further having a coating layer of silicon carbide thereon. Coating. 2. The high adhesion oxidation resistant coating for a C / C composite material according to claim 1, wherein the high melting point metal is at least one kind of metal having a melting point of 1500 ° C. or higher. 3. The high adhesion property for C / C composite material according to claim 1, wherein the refractory metal is at least one kind of metal selected from the group consisting of B, Cr, Mo and W. Oxidation resistant coating. 4. The film thickness of the refractory metal is 0.5 μm to 1
C / C according to claim 1, characterized in that
High adhesion and oxidation resistant coating for composite materials. 5. The silicon carbide is vapor phase chemical vapor deposition (CVD).
2. A high adhesion and oxidation resistant coating for C / C composite materials according to claim 1, which is a silicon carbide coating layer according to the method). 6. The C / C composite material according to claim 1, further comprising a glassy coating layer made of at least one kind of oxides of silicon, aluminum and zirconium on the coating layer of silicon carbide. High adhesion and oxidation resistant coating for use. 7. B, Cr, Mo on the surface of the C / C composite material.
And at least one metal selected from the group consisting of W by a vapor deposition method or a sputtering method to a film thickness of 0.5 μm to 100 μm.
to form a coating layer having a thickness of 5 to 500 μm of silicon carbide on the deposited metal by a CVD method, and forming a high adhesion and oxidation resistant coating for a C / C composite material. Method.