JPH11199354A - Oxidation-resistant c/c composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an oxidation-resistant C/C composite material having an SiC coating layer excellent in thermal shock resistance, durability and material strength formed on the surface layer part of a C/C composite substrate and to provide a method for producing the C/C composite material. SOLUTION: This oxidation-resistant C/C composite material having an SiC coating layer formed on the surface layer part of a C/C composite substrate prepared by compounding and molding carbon fibers with a matrix resin and carrying out the curing, baking and carbonizing according to a conversion method and having <=50 ppm metal impurity content and >=300 cPs intensity of an SiC (111) plane according to an X-ray diffraction. The maximum film thickness of the SiC coating layer locally silicidized in the surface layer part is 1.0-1.2 times based on the average film thickness. The method for producing the C/C composite material comprises preparing a C/C composite material having 1.55-1.75 g/cm<3> bulk density, 0.1-10 μm maximum mode diameter of voids and <=20 ppm metal impurity content and bringing the resultant C/C composite material into contact with SiO2 gas produced by thermally reacting a mixed powder of a silicon source having <=100 ppm metal impurity content and <=300 μm particle diameter with a carbon source having <=10 ppm metal impurity content and <=100 μm particle diameter in a temperature region of 1,600-2,000 deg.C in a nonoxidizing atmosphere and forming the SiC coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SiC coating having excellent thermal shock resistance and durability and high material strength on the surface layer of a C / C composite substrate by silicifying the surface layer by a conversion method. The present invention relates to an oxidation-resistant C / C composite (carbon fiber reinforced carbon composite) in which a layer is formed stably and firmly, and a method for producing the same.

[0002]

2. Description of the Related Art A C / C composite material has excellent heat resistance and chemical stability in a high temperature range exceeding 1000 ° C. in addition to being lightweight and high strength. It is useful as a structural material used under severe conditions at high temperatures. However, the C / C composite material has a disadvantage inherent in carbon material that it is oxidized at about 500 ° C. in the atmosphere, and this is the biggest obstacle to restricting the application. For this reason, attempts to improve the oxidation resistance by forming a coating layer having high oxidation resistance on the surface of the C / C composite material have been made for a long time. For example, heat-resistant materials such as silicon carbide, silicon nitride, zirconia, and alumina have been used. A method for coating a ceramic material has been developed. Among them, the coating treatment with silicon carbide is excellent in technical and economical aspects, and is practically used as the most suitable industrialization means.

As a typical method of forming a coating layer of silicon carbide on the surface of a C / C composite material, a CVD method (chemical vapor deposition method) in which SiC generated by a gas phase reaction is directly deposited.
And carbon utilizing the carbon in the surface layer of the C / C composite material as a reaction source.
There is known a conversion method of converting SiC by reacting with iO gas. However, each of the silicon carbide coating layers formed by these methods has advantages and disadvantages. That is, although the SiC coating layer formed by the former CVD method is excellent in denseness, when a thermal shock is applied because the interface with the base material is clearly separated, a difference in thermal expansion between the two occurs. There is a disadvantage that the delamination phenomenon easily occurs. This delamination phenomenon is mainly caused by C / C
Since the difference in thermal expansion coefficient between the composite substrate and the SiC coating layer is large and the maximum strain cannot follow,
If the surface of the C composite base material is modified so as to approximate the thermal expansion coefficient of SiC, it can be reduced. From such a viewpoint, a method is proposed in which a pyrolytic carbon layer is formed on the surface of a C / C composite base material by a vapor phase pyrolysis method and then coated with SiC by a CVD or CVI method (Japanese Patent Laid-Open No. 2-111681). However, sufficient high-temperature oxidation resistance that is commensurate with the complexity of the operation cannot be expected.

On the other hand, in the latter conversion method, SiO gas and C gas generated by heating and reacting a silicon source and a carbon source are used.
/ C composite material is formed based on a mechanism of reacting the carbon structure constituting the C / C composite material and gradually forming SiC from the surface to the inside of the surface layer portion of the C / C composite material. It exhibits a continuous functionally graded tissue that gradually decreases as it goes into the interior of the material. Therefore, there is no interlayer such as the SiC coating layer formed by the CVD method, and there is an advantage that the interlayer delamination hardly occurs even when subjected to thermal shock. On the other hand, there is a disadvantage that the denseness of the SiC coating layer in the surface layer portion is reduced and sufficient oxidation resistance cannot be provided. Further, in the conversion method, since a part of the carbon structure of the surface layer of the C / C composite material is silicified and converted into SiC, there is a disadvantage that the material strength is reduced. In particular, the internal structure of the C / C composite substrate is partially reduced. In the case where the silicon is silicified, the strength decreases greatly.

[0005] Therefore, as a SiC-coated C / C composite material which does not decrease in strength and has excellent thermal shock resistance, C / C
SiC coating C / C
In the C composite material, a silicide layer containing at least unreacted carbon fibers having a large number of protrusions protruding from the surface in an inward direction from the surface is present on a surface layer of the C / C composite base material. An SiC-coated C / C composite material has been proposed (Japanese Patent Laid-Open No. 4-19081). This Japanese Patent Laid-Open No. 4
The SiC coated C / C composite disclosed in -149081
After forming a porous SiC film on the surface of the / C composite base material by a CVD method, the surface layer is subjected to a silicidation treatment, and the SiC film is further formed by a CVD method. Therefore, the disadvantage of the above-mentioned CVD method, C,
The problem of interface separation between the / C composite substrate and the SiC coating is not solved, and the improvement in thermal shock resistance is not sufficient.

On the other hand, conversion to SiC by the conversion method has a problem of essentially impairing the material strength of the C / C composite base material itself. That is, SiC by the conversion method
In the process of forming the coating layer, the SiO gas converts the C / C base structure into SiC while penetrating and diffusing from the surface of the C / C composite base into the inside of the structure, but exists in the C / C base. Along the voids such as pores and cracks, the SiO gas easily permeates and diffuses to a relatively deep substrate structure. Therefore, not only the surface of the C / C composite, but also the deep internal structure
As the formation of iC proceeds, the matrix structure, particularly the matrix carbon portion that is easily converted to SiC, is preferentially silicided to easily form a SiC product in a saw-like or island-like shape. Will be invited.

Therefore, when the SiC coating layer is formed by the conversion method, the generated SiC coating layer is made uniform,
In view of the fact that it is necessary to suppress the phenomenon that the internal structure of the C / C composite base material is densified and converted into SiC, in order to ensure the material strength, the applicant of the present invention has proposed that the carbon fiber and the matrix resin be composite-molded. Forming a SiC coating layer by a conversion method on the surface of a C / C composite substrate obtained by calcining and carbonizing a polyimide resin film spread on the outer peripheral surface of a cured and cured carbon fiber composite resin molded body (Japanese Patent Application Laid-Open No. 8-169786) or a method of forming a graphitizable carbon coating layer on the surface of a C / C composite base material and then forming a SiC coating layer by a conversion method (Japanese Patent Application No. 8-169786).
No. 346730).

In these methods, a dense carbon coating layer or a graphitizable carbon coating layer formed on a surface layer of a C / C composite base material allows a SiO gas to penetrate into the internal structure of the C / C composite base material. By acting as a barrier to suppress the phenomenon of diffusion,
It is intended to suppress a decrease in material strength.

[0009]

SUMMARY OF THE INVENTION The present inventor has proposed that a surface layer of a C / C composite base material is silicified by a conversion method to obtain Si.
Regarding the oxidation-resistant C / C composite material having the C coating layer formed thereon, S
In order to improve the durability and thermal shock resistance of the iC coating layer, or to prevent the material strength from decreasing, further studies were conducted on the properties of the SiC coating layer. As a result, the crystallinity and purity of the SiC, and the C / C composite Si penetrated into the voids in the surface layer of the base material
It was confirmed that the maximum thickness of the SiC coating layer locally formed by the O gas was related.

The present invention has been developed on the basis of the above findings, and the object of the present invention is to provide a C / C composite base material having excellent thermal shock resistance and durability, and high material strength. An object of the present invention is to provide an oxidation-resistant C / C composite material in which a provided SiC coating layer is formed stably and firmly, and a method for producing the same.

[0011]

In order to achieve the above object, an oxidation-resistant C / C composite material according to the present invention comprises a C / C composite material obtained by molding a carbon fiber together with a matrix resin, and curing and calcining and carbonizing. The SiC coating layer formed by silicidizing the surface layer portion of the material by the conversion method has a metal impurity content of 50 ppm or less, a strength of the SiC (111) surface by X-ray diffraction of 300 cps or more, and a C / C composite. The maximum thickness of the locally silicified SiC coating layer on the surface layer of the base material is SiC
It is a structural feature that the average thickness of the coating layer is 1.01 to 1.2 times.

The method for producing an oxidation-resistant C / C composite material according to the present invention is characterized in that carbon fiber is composite-molded together with a matrix resin, cured and calcined, and further subjected to a high-purification treatment and a graphitization treatment to obtain a bulk. A C / C composite base material having a density of 1.55 to 1.75 g / cm ³ , a maximum mode diameter of voids of 0.1 to 10 μm, and a metal impurity content of 20 ppm or less was prepared.
A composite substrate is produced by heating and reacting a mixed powder of a silicon source having a metal impurity content of 100 ppm or less and a particle size of 300 μm or less and a carbon source having a metal impurity content of 10 ppm or less and a particle size of 100 μm or less. In SiO gas and non-oxidizing atmosphere 1
The surface layer of the C / C composite base material is silicified by a conversion method by contacting in a temperature range of
Forming the coating layer is a structural feature.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Fibers made from various raw materials such as polyacrylonitrile, rayon, pitch, etc. are woven in two-dimensional or three-dimensional directions into carbon fibers as reinforcing materials for C / C composites. A fibrous body, felt, tow, etc. are used.
A highly carbonized liquid thermosetting resin such as furan or a thermoplastic substance such as tar pitch is used. The carbon fiber is immersed, fully filled with the matrix resin by means such as coating, and then semi-cured to form a prepreg, then the prepreg is laminated and pressed to form a composite, and then heated to completely cure the resin component, 1 in a non-oxidizing atmosphere according to the usual method
A C / C composite base material is produced by heating and carbonizing at a temperature of 000 to 2000 ° C. If necessary, the C / C composite substrate is further densified by repeatedly impregnating, curing and calcining with a matrix resin, and is then subjected to a high-purification treatment and a graphitization treatment to improve the base material. Purify.

In order to silicify the surface layer of the C / C composite base material by the conversion method and to maintain the formed SiC coating layer with high durability, it is important to improve the purity and crystallinity of SiC. . That is, if metal impurities exist in the SiC coating layer, the material deterioration of the SiC proceeds,
For example, the content of metal impurities such as iron, nickel, boron, and calcium needs to be 50 ppm or less.

Further, the crystallinity of SiC of the SiC coating layer is low, and if there is a crystal defect, the durability of the SiC coating layer is reduced. In particular, metal impurities and crystal defects existing in the SiC coating layer act synergistically to promote the deterioration of SiC. Therefore, in order to improve the corrosion resistance of the SiC coating layer, the strength of the SiC (111) plane by X-ray diffraction must be 3
Set to 00 cps or more. Si below 300 cps
This is because the crystallinity of C is low and the corrosion resistance is reduced due to the presence of crystal defects.

The oxidation-resistant C / C composite of the present invention comprises SiC
The coating layer has the above-mentioned metal impurity content of 50 ppm or less, the purity and crystallinity of the SiC (111) plane by X-ray diffraction of 300 cps or more, and locally silicide the surface layer of the C / C composite base material. The maximum thickness of the SiC coating layer
It is necessary to be 1.01 to 1.2 times the average thickness of the C coating layer. The process of forming the SiC coating layer on the surface layer of the C / C composite base material by the conversion method is SiO
While the gas permeates and diffuses from the surface of the C / C composite base material into the interior, the carbon structure is silicified and converted into SiC. In this process, part of the SiO gas is present in the C / C composite base material Along the voids such as pores and cracks, which penetrate and diffuse into the internal structure of the base material. Therefore, the SiO gas that has entered the inside of the C / C composite substrate sequentially reacts with the carbon structure and is converted into SiC, and a saw-toothed SiC layer is generated along the void.

That is, as shown in the schematic diagram of FIG. 1, the SiC coating layer formed on the surface layer of the C / C composite base material has a C / C
A locally silicified portion 3 which is locally silicified is formed on a surface layer portion of the C composite base material 1. In FIG. 1, 1 is a C / C composite substrate, 2 is a SiC coating layer, 3 is a locally silicified portion, 4 is a maximum film thickness, and 5 is an average film thickness. As described above, when the internal structure of the C / C composite material is partially converted to SiC, the material strength is significantly reduced. Therefore, in the oxidation-resistant C / C composite material of the present invention, the surface layer of the C / C composite substrate is locally silicified by the SiO gas that has permeated and diffused along the voids of the C / C composite substrate. The maximum thickness 4 of the formed SiC coating layer is S
By controlling the average thickness 5 of the iC coating layer to 1.01 to 1.2 times, it is possible to suppress a decrease in material strength,
The thermal stress acting on the internal structure generated during rapid heating and rapid cooling can be relaxed, and the thermal shock resistance can be maintained at a high level.

This oxidation-resistant C / C composite material has a bulk density of 1.55 to 1.75 g / cm ³ and a maximum mode diameter of voids of 0.5.
1 to 10 μm, C /
A C composite substrate is prepared, and the C / C composite substrate is mixed with a silicon source having a metal impurity amount of 100 ppm or less and a particle diameter of 300 μm or less, a metal impurity amount of 10 ppm or less and a particle diameter of 100 μm
S generated by heating and reacting a mixed powder with the following carbon source
It is manufactured by contacting with iO gas in a non-oxidizing atmosphere in a temperature range of 1600 to 2000 ° C.

The C / C composite substrate is produced by compound-molding a carbon fiber with a matrix resin, curing and firing and carbonizing. The C / C composite substrate is impregnated with the matrix resin, cured, The process of firing and carbonizing is repeatedly performed to adjust and control the bulk density to be in the range of 1.55 to 1.75 g / cm ³ . If the bulk density is less than 1.55 g / cm ³ , there are many voids in the internal structure, and the ratio of silicification of the internal structure of the C / C composite base material increases, resulting in a large decrease in strength. However, even if the bulk density is increased to more than 1.75 g / cm ³ , the effect of suppressing the strength decrease hardly changes.

The C / C composite base material used is one in which the size of voids such as pores and cracks existing in the base material is adjusted to a maximum mode diameter of 0.1 to 10 μm by densification.
If there is a large void having a maximum mode diameter exceeding 10 μm, the SiO gas easily penetrates into the inside of the substrate structure, and C / C
This is because the surface layer portion of the composite base material is locally silicified, and SiC formation in the internal structure becomes remarkable. It should be noted that even if the void portion is densified so that the maximum mode diameter is less than 0.1 μm, the effect of preventing the invasion of the SiO gas is not significantly increased. Also, C
The / C composite substrate preferably has a purity as high as possible, and the content of metal impurities such as iron, nickel, boron and calcium is 2
Less than 0 ppm is used. 2 metal impurity content
If it exceeds 0 ppm, impurities migrate into the formed SiC coating layer and act as a metal catalyst to lower the corrosion resistance. C / C
In order to reduce the content of metal impurities in the composite substrate, the produced C / C composite substrate can be heat-treated with a halogen-containing gas such as fluorine or chlorine at a high temperature and then subjected to a high-purity treatment. .

The bulk density thus produced is 1.55
１1.75 g / cm ³ , maximum mode diameter of air gap is 0.1〜１０10
Using a C / C composite substrate having a metal impurity content of 20 ppm or less, the surface layer is silicified by a conversion method to form a SiC coating layer. As a silicon source for generating a SiO gas that undergoes a silicidation reaction, a metal impurity content of 100 ppm
Hereinafter, an SiO ₂ -containing substance such as quartz, silica stone, silica sand or the like having a particle diameter of 300 μm or less is used. As the carbon source, a carbonaceous powder having a metal impurity content of 10 ppm or less and a particle diameter of 100 μm or less, such as coke, pitch, graphite, and carbon black, is used. The composition of the silicon source and the carbon source is
It is determined in consideration of the surface area of each material powder.
It is blended so that the weight ratio of iO ₂ : C is in the range of 1: 1 to 5: 1. The mixture is sufficiently mixed by a mixing device such as a V-type blender to form a uniform mixture, and then placed in a reaction vessel made of a highly heat-resistant material such as graphite.

The above reaction vessel is placed in a closed heating furnace,
While the C / C composite base material is buried in the mixed powder in the reaction vessel or set in the vicinity of the reaction vessel, the inside of the system is maintained in a reducing or neutral non-oxidizing atmosphere while being 1600 to 2000.
Heat to a temperature of ° C. In the process, the SiO gas generated by the heat-reduction reaction between the silicon source and the carbon source silicifies the carbon structure of the C / C substrate while contacting the surface layer of the C / C composite substrate to form a SiC coating layer. Is done. In this silicidation process, the SiO gas penetrates into the internal structure of the C / C composite substrate by using a C / C composite substrate having properties such as bulk density, maximum mode diameter of voids, and metal impurity content within a specific range. Since the diffusion phenomenon is suppressed, SiC conversion in the internal structure can be reduced, and the content of metal impurities can be reduced. Therefore, the metal impurity content is 50 ppm or less, the intensity of the SiC (111) plane is 300 cps or more by X-ray diffraction, and the locally silicified S
It is possible to manufacture an oxidation-resistant C / C composite material having an SiC coating layer in which the maximum thickness of the iC coating layer is 1.01 to 1.2 times the average thickness.

[0023]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 5 and Comparative Examples 1 to 5 A polyacrylonitrile-based plain-woven carbon fiber woven fabric [W6101 manufactured by Toho Rayon Co., Ltd.] was mixed with a phenol resin precondensate [PR940 manufactured by Sumitomo Durez Co., Ltd.] as a matrix resin. And applied so that the volume content of carbon fiber becomes 60%.
It was air-dried for 8 hours to prepare a prepreg sheet. 20 sheets of this prepreg sheet are stacked and put in a mold,
The mixture was heated and pressurized at a temperature of 170 ° C. for 3 hours while applying a pressure of / cm ² to form a composite. This complex was placed in a firing furnace maintained in a nitrogen gas atmosphere, and was heated at a rate of 20 ° C./hr to 1000
C. and carbonized. Further, a densification treatment of impregnating a furfuryl alcohol initial condensate, transferring the mixture again to a baking furnace, and heating it to 1000 ° C. at a heating rate of 50 ° C./hr was repeated several times until a desired bulk density was obtained. Then
After heat-treating to 2000 ° C. at a heating rate of 70 ° C./hr, in an electric furnace under an atmosphere introduced with chlorine gas,
It was heated to a temperature of ° C. to perform a high purification treatment. In this way, C / C composite substrates (250 mm in length and 4 mm in thickness) having different bulk densities, maximum void mode diameters, and metal impurity contents were produced.

The C / C composite substrate is covered with a graphite fiber felt having a porosity of 90%, a pore diameter of 10 μm, and a thickness of 10 mm.
Using quartz powder with different amounts of metal impurities and particle diameter as the silicon source and coke powder with different amounts of metal impurities and particle size as the carbon source, mixed powders mixed at a weight ratio of 3: 1 are placed above and below the graphite fiber felt. Placed in a graphite container. The graphite container is transferred to a heating furnace maintained in a nitrogen gas atmosphere and heated to a predetermined temperature at a heating rate of 50 ° C./hr to cause a conversion reaction to form a SiC coating layer on the surface of the C / C composite base material. did. Table 1 shows the production conditions of the oxidation-resistant C / C composite material having the SiC coating layer formed thereon.

[0026]

[Table 1]

With respect to the SiC coating layer thus formed, the metal impurity content and the SiC (1
11) The properties of the SiC coating layer such as the X-ray diffraction intensity and the film thickness of the surface were measured. Further, the oxidation-resistant C / C composite material having the SiC coating layer formed thereon was subjected to a tensile strength test, an oxidation resistance test, and a thermal shock resistance test by the following methods to evaluate its oxidation resistance performance. Table 2 shows the obtained results.

(1) Properties of SiC Coating Layer Content of metal impurities: The residue obtained by incineration at 800 ° C. in air was measured by plasma emission analysis. X-ray diffraction intensity of SiC (111) surface;
The peak intensity of the (111) plane of iC was measured. Film thickness: The film thickness of SiC was measured by an eddy current measurement method.

(2) Evaluation of oxidation resistance Tensile strength: From a sample cut out to a thickness of 4 mm and a length of 160 mm, the gripping portion was set to a length of 40 mm and a width of 25.4 mm, and the gauge portion was 40 mm in length and 12 in width. It was processed into a dumbbell shape of 7 mm to obtain a tensile strength test specimen. A tensile load was applied to this test piece at a crosshead speed of 1.3 mm / min, and the breaking load was measured. Oxidation resistance test: The C / C composite material on which the SiC coating layer was formed was placed in an electric furnace, and the weight loss rate when the temperature was maintained at 1400 ° C. for 30 minutes in an air atmosphere was measured. Thermal shock resistance test: A C / C composite material having a SiC coating layer formed thereon was placed in an electric furnace, kept at a temperature of 1550 ° C. for 5 minutes in an air atmosphere, taken out to room temperature, and rapidly cooled, repeated 5 times. Then, the state of peeling of the coating layer at that time was observed.

[0030]

[Table 2]

From the results shown in Tables 1 and 2, the C / C composite material of the example in which the properties of the SiC coating layer satisfy the characteristic requirements of the present invention is as follows:
It can be seen that the tensile strength is higher than that of the C / C composite material of the comparative example, and the weight loss rate due to oxidation is small even in a high-temperature atmosphere. Also, it is recognized that it is excellent in thermal shock resistance when a thermal shock due to rapid heating and cooling in the air atmosphere is given. A C / C composite material having such excellent oxidation resistance is obtained by performing a conversion reaction under specific conditions using a C / C composite base material whose properties such as bulk density and voids are controlled to obtain a SiC composite material. It can be produced by controlling the properties of the coating layer.

[0032]

As described above, according to the present invention, the properties of the SiC coating layer formed on the surface layer of the C / C composite substrate by silicification by the conversion method are specified, whereby the thermal shock resistance, durability and heat resistance are improved. An oxidation-resistant C / C composite material in which a SiC coating layer having excellent material strength is formed stably and firmly can be obtained. Further, the oxidation-resistant C / C composite material can be manufactured by specifying the conditions for producing the C / C composite substrate and the conditions for silicidation by the conversion method. Therefore, it is extremely useful as a C / C composite material used under high temperature and severe atmosphere and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is a schematic view of a SiC coating layer formed on a surface layer portion of a C / C composite base material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 C / C composite base material 2 SiC coating layer 3 Local silicide part 4 Maximum film thickness 5 Average film thickness

Claims (2)

[Claims] 1. A Si layer formed by subjecting a carbon fiber to composite molding with a matrix resin and silicifying a surface layer of a C / C composite base material cured and calcined by a conversion method.
The C coating layer has a metal impurity content of 50 ppm or less, a strength of the SiC (111) plane by X-ray diffraction of 300 cps or more, and a locally silicified S on the surface layer of the C / C composite base material.
The oxidation resistant C, wherein the maximum thickness of the iC coating layer is 1.01 to 1.2 times the average thickness of the SiC coating layer.
/ C composite. 2. Carbon fiber is composite-molded with a matrix resin, cured and calcined, and then subjected to a high-purification treatment and a graphitization treatment to obtain a bulk density of 1.55 to 1.75 g.
/ cm ^3, the maximum mode diameter voids 0.1 to 10 [mu] m, the metal impurity content is prepared following C / C composite base material 20 ppm,
The C / C composite substrate has a metal impurity content of 100 ppm or less,
A silicon source having a particle diameter of 300 μm or less, and a metal impurity amount of 1
0 ppm or less, a mixed powder with a carbon source having a particle diameter of 100 μm or less is brought into contact with SiO gas generated by heating and reacting in a non-oxidizing atmosphere in a temperature range of 1600 to 2000 ° C.
A method for producing an oxidation-resistant C / C composite material, comprising forming a SiC coating layer by silicifying a surface layer portion of a C composite base material by a conversion method.