JP2006290670A - Fiber reinforced silicon carbide composite material, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber reinforced silicon carbide composite material which is manufactured in a simple process without using a special manufacturing apparatus, can shorten a manufacturing process and reduce cost, has strength and toughness similar to those of a sintered SiC in the physical property, and is free from anisotropy. <P>SOLUTION: A carbon fiber reinforced silicon carbide base material is formed by mixing a plurality of kinds of carbon fibers each having different reactivity with silicon, graphite powder and powdery resin and heating and press-forming to form a carbon fiber reinforced base material and carbonizing the carbon fiber reinforced base material and siliconizing the carbon fiber reinforced carbon base material to form the carbon fiber reinforced silicon carbide base material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon fiber reinforced silicon carbide composite material (hereinafter, appropriately referred to as a C / SiC composite material) suitable for large-scale telescopes for space and ground use and high-temperature structural members, and a method for producing the same.

  Silicon carbide ceramics are widely used in applications such as high-temperature corrosion-resistant members, heater materials, wear-resistant members, and even abrasives and grindstones, but they are practical as high-temperature structural members because of their low fracture toughness values. It has not been converted.

  For this reason, for the purpose of improving the toughness of the ceramic, a ceramic composite material in which a fibrous reinforcing material is combined has been proposed. In general, the fiber reinforced silicon carbide composite material is manufactured by impregnation with an organometallic polymer, repeated thermal decomposition firing method, chemical vapor deposition method (CVI method), silicon melt impregnation method (reaction sintering method), or the like.

  However, in the method of manufacturing by repeated impregnation of organometallic polymer and pyrolysis firing, only those having low density and strength characteristics can be obtained by one impregnation. In order to improve the strength characteristics by this method, it is necessary to reduce the open porosity to at least 10% by repeating impregnation and firing about 10 times. For this reason, a manufacturing period becomes long and there exists a big problem in practical use.

  In addition, chemical vapor deposition can produce a complex shape at a relatively low temperature of about 1100 ° C. However, it takes a long time of several weeks for filling and has disadvantages such as toxic gas used. is there. Moreover, it is very difficult to obtain a composite material having an open porosity of 5% or less only by the method or the method of manufacturing by repeating the impregnation of the above-described organometallic polymer and thermal decomposition firing.

  The reaction sintering method has the advantages that the reaction time is short and a dense composite material can be produced in a short time. In the production of fiber reinforced silicon carbide based composite materials by the conventional silicon melt impregnation method, the fiber bundle portion is densely covered with glassy carbon from the resin, and the silicon carbide with volume reduction of silicon and carbon from the resin is involved. There has been proposed a method in which a porous portion generated by a generation reaction is generated only in a specific portion of a matrix and silicon is impregnated with the porous portion. Thereby, it is possible to manufacture the fiber reinforced silicon carbide composite material without coating the fiber surface with BN or the like.

  For example, Patent Document 1 discloses a method for producing a fiber-reinforced silicon carbide composite material by the above-described silicon melt impregnation method. Briefly explaining this method, first, a prepreg made of silicon powder and a resin and a fiber as a carbon source is manufactured and molded, or a fiber prepreg containing resin, and a prepreg containing silicon powder and resin are alternately used. Laminate and mold.

  Next, carbonization is performed at a temperature of about 900 to 1350 ° C. in an inert atmosphere. Subsequently, the obtained composite material is impregnated with resin, and again carbonized at a temperature of about 900 to 1350 ° C. in an inert atmosphere. After repeating this resin impregnation and carbonization treatment, reaction sintering is performed at a temperature of 1300 ° C. or higher in a vacuum or an inert atmosphere.

  Thereafter, silicon is finally melt impregnated at a temperature of about 1300 to 1800 ° C. in a vacuum or an inert atmosphere. Thereby, a fiber reinforced silicon carbide composite is obtained. The composite material thus obtained is considered to be dense with non-linear fracture behavior.

JP 2000-313676 A

  In the conventional method for producing a C / SiC composite material, a prepreg is produced by using continuous fibers as carbon fibers as reinforcing fibers, and these are laminated and molded. For this reason, anisotropy occurs in the material properties of the C / SiC composite material due to the effect of the orientation of the reinforcing fibers, and the structural design becomes complicated when this molded body is applied to various structural members, resulting in low versatility. .

  In addition, the C / SiC composite material is manufactured by repeatedly impregnating and carbonizing the resin (900 to 1350 ° C.), and further subjecting it to reactive sintering at a temperature of 1300 ° C. or higher in a vacuum or an inert atmosphere. Was manufactured by melt impregnation of silicon at a temperature of about 1300 to 1800 ° C. in a vacuum or an inert atmosphere. For this reason, a manufacturing process is comparatively long and requires a long time for manufacture. Furthermore, it is necessary to perform the treatment at a temperature of 1300 ° C. or higher in carbonization or reaction sintering, and equipment with a very special specification is required as a firing furnace. For this reason, there existed a subject that manufacturing cost increased.

  Furthermore, the material properties of the conventional C / SiC composite material have a problem that the carbon fiber and carbon matrix content is high, thereby lowering the strength and rigidity compared to sintered SiC.

  The present invention has been made to solve the above-described problems. It is a simple process that does not use any special manufacturing equipment, and can shorten the manufacturing process and reduce the cost. It aims at obtaining the fiber reinforced silicon carbide composite material which has the intensity | strength and rigidity of this, and there is no anisotropy, and its manufacturing method.

  The fiber-reinforced silicon carbide composite material according to the present invention contains a plurality of types of carbon fibers having different reactivity with silicon and graphite powder, and a part of the contained carbon fibers is siliconized.

  According to the present invention, the carbon fiber containing a plurality of types of carbon fibers having different reactivity with silicon and graphite powder, and a part of the contained carbon fibers are siliconized, so that the types of carbon having different reactivity with silicon are obtained. By controlling the combination and blending ratio of the fibers and the carbon matrix, it becomes possible to leave part of the contained carbon fibers without reacting with silicon and react the remaining carbonaceous parts with silicon to form silicon carbide. . Thereby, SiC-ization can be accelerated | stimulated and a structure | tissue with a high SiC ratio is obtained. As a result, it becomes possible to manufacture a carbon fiber reinforced silicon carbide base material having excellent strength and rigidity comparable to sintered SiC, and the adaptability to a heat-resistant structural member can be improved.

  Further, in the present invention, in the molding of the carbon fiber base material, a mixture of a plurality of types of carbon short fibers having different reactivity with silicon, graphite powder and powder resin is heated and molded at a low pressure. There is no need for high pressure as in the molding of ceramics. Thereby, there is an effect that isotropic physical properties can be obtained because the internal carbon fibers are randomly oriented without being oriented.

  Further, since the densification treatment of the carbon fiber substrate is unnecessary and the pitch or resin impregnation process is not performed, no impregnation equipment is required. Furthermore, the reaction sintering process is not required, and the carbonization treatment is sufficient at a temperature of about 800 ° C., no special carbonization firing furnace is required, and it can be manufactured in a general-purpose firing furnace. Cost can be greatly reduced compared to the prior art.

Embodiment 1 FIG.
In the present invention, materials that satisfy the conditions shown in the following (1) to (4) are considered as materials suitable for heat-resistant structural members.
(1) A material having high specific strength and specific rigidity and high fracture toughness.
(2) There is no anisotropy in the physical properties as in conventional C / SiC materials and is isotropic.
(3) The manufacturing process is simple and the shape manufacturability is excellent.
(4) It can be manufactured with general-purpose equipment and has excellent material processability.

  In order to obtain various properties required for the above heat-resistant structural member, the present invention provides a combination of components in a carbon fiber reinforced silicon carbide (hereinafter referred to as C / SiC) composite material, control of the mixing ratio, and improvement of the manufacturing process. In addition, the SiC ratio is increased and the physical properties are made isotropic. Embodiments will be described below.

  FIG. 1 is a diagram showing a method for manufacturing a fiber-reinforced silicon carbide composite material according to Embodiment 1 of the present invention, and is a C / SiC composite material in which reinforcing carbon fibers are dispersed in a matrix substantially made of silicon carbide. Shows a process of forming a heat-resistant structural material. First, in the process shown in FIG. 1 (a), each short fiber 1, 2 of a pitch-based carbon fiber and a PAN (PolyAcryloNitrile) -based carbon fiber, which are two types of carbon fibers having different reactivity with silicon, graphite powder 3 , And powder resin 4 are mixed at a specific weight ratio, loaded into a mixer and mixed uniformly to obtain mixture 5.

  In the step shown in FIG. 1 (b), the uniformly mixed mixture 5 is transferred to a mold and heated and pressurized to be molded into a fixed shape. Then, it removes from a type | mold and the carbon fiber molded object (carbon fiber base material) 6 which consists of the hybrid carbon fiber by 2 types of different carbon fibers 1 and 2, the resin binder, and the graphite powder 3 is obtained. Next, the process proceeds to the step shown in FIG. In this step, the carbon fiber molded body 6 is heated in a vacuum or an inert atmosphere to carbonize the resin binder component, and a C / C molded body 7 made of a carbon fiber reinforced carbon (hereinafter referred to as C / C) composite material is formed. obtain.

  In the step of FIG. 1D, the C / C molded body 7 is cut into the shape of the heat-resistant structural member to obtain the heat-resistant structural member 8. Thereafter, the process proceeds to the step shown in FIG. 1 (e), and the heat-resistant structural member 8 is impregnated with molten metal silicon in a vacuum and subjected to silicon carbide (C / SiC) treatment to obtain a C / SiC molded body 9. Finally, in the process of FIG. 1 (e), detailed dimensional finishing is performed on the heat-resistant structural member C / SiC molded body 9 made of a matrix including carbon fibers 1 and 2 and a small amount of carbon mainly composed of SiC and silicon. By applying, the heat-resistant structural member 10 of a C / SiC composite material is obtained.

  In the first embodiment, pitch carbon fiber short fiber 1 and PAN carbon fiber short fiber 2 are mixed as starting raw materials because pitch carbon fiber hardly reacts with silicon, but PAN carbon. This is because the fiber reacts more easily with silicon than the pitch-based carbon fiber, and this difference in reactivity is used to cause the carbon fiber portion to undergo a SiC reaction to increase the production ratio of SiC.

  The reason why graphite powder is added is that if the carbon matrix is produced by carbonization using only a resin in the production of the carbon matrix, the carbon matrix is aggregated and unevenly distributed in the carbon fiber molded body. Thus, by adding the graphite powder 3 and improving the uneven distribution due to the aggregation of the carbon matrix, the reactivity with silicon is improved, and the production ratio of SiC can be increased.

  When only pitch-based carbon fibers are used, it is necessary to increase the silicon impregnation temperature and further increase the reaction time in order to promote SiC conversion. However, since the silicon impregnation treatment is performed under reduced pressure, if the temperature is increased or the treatment time is lengthened, silicon is easily vaporized, and a large amount of voids are generated in the substrate due to vaporization / disappearance.

  This void is not preferable because it causes a decrease in strength. In addition, when silicon is vaporized, a large amount of silicon adheres to the inside of the processing equipment, and there is an influence such as deterioration inside the equipment due to reaction with silicon and drawing of silicon vapor into the exhaust line. Therefore, impregnation treatment at high temperature and long-time treatment are practically difficult.

  On the other hand, when it is made using only PAN-based carbon fibers, it easily becomes brittle and a desired material strength cannot be obtained.

  Furthermore, when only pitch-based carbon fibers and PAN-based carbon fibers are used and graphite powder is not used, it is necessary to increase the amount of powder resin used, and the carbon matrix produced by carbonization is agglomerated to form SiC. hard. In order to promote the formation of SiC under these conditions, it is necessary to increase the silicon impregnation temperature and extend the reaction time, which is not preferable.

  As described above, according to the first embodiment, in the forming process of the carbon fiber base material as the starting raw material for the production of the C / SiC composite material used for the heat-resistant structural member, two short types of pitch type and PAN type are used. The carbon fiber molded body 6 obtained by mixing and molding the carbon fibers 1 and 2, the graphite powder 3, and the powder resin 4 is further carbonized to obtain a C / C molded body 7. By using such raw materials, there is an effect that excellent properties such as high strength and high rigidity can be obtained in the C / SiC composite material. As a result, a high-performance composite material heat-resistant structural member having high versatility can be manufactured.

Embodiment 2. FIG.
In the heat resistant structural member of the composite material described in the first embodiment, the second embodiment has an average fiber length of pitch-based carbon fibers used as a component of the carbon fiber base material of 1 mm or less, and the PAN-based carbon fiber. The average fiber length is defined as 0.5 mm or less, and the particle size of the graphite powder is defined as 100 μm or less.

  When the average fiber length of the pitch-based carbon fiber exceeds 1 mm, or the average fiber length of the PAN-based carbon fiber exceeds 0.5 mm and the particle size of the graphite powder exceeds 100 μm, There is a problem that uniform dispersion of fibers is difficult to obtain, and isotropic material properties may not be obtained.

  Therefore, in the second embodiment, the average fiber length of the pitch-based carbon fibers used as the constituent elements of the carbon fiber substrate is 1 mm or less, the average fiber length of the PAN-based carbon fibers is 0.5 mm or less, and the particle diameter of the graphite powder is It is defined as 100 μm or less. As a result, the carbon fibers are uniformly dispersed in the base material, the reaction between silicon and the PAN-based carbon fibers is promoted to a preferable level in the silicon carbide step, and the SiC ratio in the C / SiC molded body is moderate. And the effect of uniformly dispersing the SiC structure. As a result, the C / SiC molded article does not exhibit anisotropic physical properties, has isotropic physical properties, and improves mechanical strength and rigidity.

Embodiment 3 FIG.
In the present third embodiment, the volume content of the carbon fiber in the carbon fiber substrate is 15% or more and 40% or less in the first embodiment or the second embodiment, and the porosity in the carbon fiber substrate is 30. % To 40%.

  That is, in the third embodiment, the volume content of the carbon fiber is within the above range in order to obtain various characteristics that are practical as a heat-resistant structural member. When the total volume content of the two types of carbon fibers of pitch and PAN in the carbon fiber substrate is less than 15%, the C / C substrate before the silicon impregnation has the dispersibility and inclusion of the matrix and the carbon fibers. The amount is insufficient. For this reason, SiC reaction by metal silicon impregnation becomes inadequate, a lot of unreacted silicon is inherent, and the carbon fiber content after reaction becomes small.

  As a result, there may be a problem that sufficient mechanical strength and rigidity cannot be obtained or the thermal expansion coefficient becomes large. Further, when the volume content of the carbon fiber exceeds 40%, it becomes difficult to uniformly disperse the fiber, so that anisotropy occurs in the physical properties and there is a problem that silicon impregnation is difficult.

  Therefore, in Embodiment 3, by defining the volume content of carbon fiber in the carbon fiber base material within the appropriate range as described above, in the heat-resistant structural member of the C / SiC composite material as the final product, etc. It has isotropic physical properties, and superior characteristics in terms of bending strength, fracture toughness and the like can be obtained, and a heat-resistant structural member suitable for practical use can be obtained. In particular, there is an effect of obtaining excellent mechanical strength and rigidity.

Examples of the present invention will be described below.
Example 1.
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powder resin are mixed at a weight ratio of 56: 117: 99: 12.4, and mixed using a V-type mixer to form a uniform mixture. I let you. Thereafter, the mixture was transferred to a mold and pressed with a press to be molded into a certain shape. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin. The volume content of the carbon fibers contained in this molded body was about 31.5%, and the volume content of the graphite powder was about 2%.

  Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of this C / C molded body was about 38.5%. Subsequently, the formed C / C shaped body was heated to 1700 ° C. in a vacuum, and metallic silicon was melted and impregnated to form C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, the matrix carbon and the PAN-based carbon fiber almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber almost reacted. Not confirmed. Moreover, the void of the C / SiC composite material molded body was almost completely filled with silicon impregnation, and the void was 1% or less.

  When the characteristics of the composite material molded body were evaluated, the values shown in the table of FIG. 2 were obtained. The strength was about 3 times that of the conventional C / SiC composite material, the Young's modulus was 1.5 times higher, The fracture toughness value was doubled or more, and the anisotropy of the physical properties was eliminated, resulting in isotropic physical properties.

Example 2
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powder resin are mixed at a weight ratio of 61.9: 119.2: 106: 31 using a V-type mixer so as to form a uniform mixture. It was. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 33%, and the volume content of the graphite powder was about 5%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of this C / C molded body was about 32%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum, and metallic silicon was melted and impregnated to form C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, the matrix carbon and the PAN-based carbon fiber almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber almost reacted. Not confirmed. Moreover, the void of the C / SiC composite material molded body was almost completely filled with silicon impregnation, and the void was 1% or less.

  When the properties of this composite material compact were evaluated, the values shown in the table in FIG. 2 were obtained, and the strength, Young's modulus, and fracture toughness values were improved from the conventional C / SiC composite material, and the physical properties became isotropic. It was confirmed that

Example 3
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powdered resin are uniformly mixed using a V-type mixer at a weight ratio of 108.9: 55.7: 97.2: 24.7. Were mixed as such. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was about 4%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C compact was about 38.5%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, the matrix carbon and the PAN-based carbon fiber almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber almost reacted. Not confirmed. Moreover, the void of the C / SiC composite material molded body was almost completely filled with silicon impregnation, and the void was 1% or less.

  When the properties of this composite material compact were evaluated, the values shown in the table in FIG. 2 were obtained, and the strength, Young's modulus, and fracture toughness values were improved from the conventional C / SiC composite material, and the physical properties became isotropic. It was confirmed that

Comparative Example 1
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powdered resin are uniformly mixed using a V-type mixer at a weight ratio of 61.9: 103.7: 6.2: 144.9. Were mixed as such. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was about 1%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C molded body was about 28%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, cracks were observed in the C / SiC molded body due to the formation of SiC by silicon impregnation. Further, it was confirmed that the matrix carbon and the PAN-based carbon fiber almost changed to SiC by reacting with the impregnated silicon, but the pitch-based carbon fiber hardly reacted.

  When the porosity of the carbon fiber reinforced carbon substrate is reduced to 28% as in Comparative Example 1, the C / SiC molded body has cracks due to volume expansion due to the SiC conversion reaction as in the above results. appear. For this reason, it became clear that it is not preferable to make the porosity of the carbon fiber reinforced carbon substrate too small.

Comparative Example 2
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fibers, PAN-based carbon fibers, graphite powder, and powder resin are mixed in a uniform ratio using a V-type mixer in a weight ratio of 61.9: 103.7: 30.9: 81.3. Were mixed as such. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was about 5%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C molded body was about 42%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, the matrix carbon and the PAN-based carbon fiber almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber almost reacted. Not confirmed. Moreover, it was confirmed that there was a lot of Si that could not be reacted in the C / SiC composite material molded body.

  When the porosity of the carbon fiber reinforced carbon substrate is increased to 42% as in Comparative Example 2, the SiC conversion reaction becomes insufficient in the C / SiC molded body as in the above results, and there is a large amount of unreacted silicon. Since it exists, it became clear that strength and rigidity were lowered, which was not preferable.

Comparative Example 3
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powder resin are in a uniform mixture using a V-type mixer at a weight ratio of 61.9: 103.7: 37.1: 84.8. Were mixed as such. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was about 6%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C molded body was about 40%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, cracks were observed in the C / SiC molded body due to the formation of SiC by silicon impregnation.

  Even if the porosity of the carbon fiber reinforced carbon substrate is increased to 40% as in Comparative Example 3, if the graphite powder is increased to 6%, the SiC conversion reaction is performed on the C / SiC molded body as shown above. Cracks occur in the C / SiC molded body due to the volume expansion caused by the above. For this reason, it became clear that it is not preferable to increase the blending ratio of the carbon powder.

Comparative Example 4
Pitch-based carbon fiber having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) and PAN-based carbon fiber having an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.) Of milled fiber). Further, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  Pitch-based carbon fiber, PAN-based carbon fiber, graphite powder, and powder resin are each in a weight ratio of 61.9: 103.7: 0: 141.4 so that a uniform mixture is obtained using a V-type mixer. Mixed. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was 0%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C compact was about 30%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, part of the matrix carbon remained without reacting with silicon, and the SiC conversion reaction was insufficient.

  When the porosity of the carbon fiber reinforced carbon substrate is set to 30% as in Comparative Example 4 and the graphite powder is not added, the carbon matrix increases, and the C / SiC molded body is unreacted as in the above results. Matrix carbon is generated and the SiC conversion reaction becomes insufficient. For this reason, it became clear that it is not preferable to reduce the porosity of the carbon fiber reinforced carbon base material and not add graphite powder.

Comparative Example 5
Pitch-based carbon fibers were not used, and PAN-based carbon fibers having an average fiber length of 130 μm (MLD-300 milled fiber manufactured by Toray Industries, Inc.) were used. In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These PAN-based carbon fibers, graphite powder, and powder resin were mixed at a weight ratio of 155.5: 6.2: 120.2 using a V-type mixer so as to form a uniform mixture. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was 1%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C compact was about 35%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, cracks were observed in the C / SiC molded body due to the formation of SiC by silicon impregnation.

  As in Comparative Example 5, when the carbon fiber of the carbon fiber reinforced carbon base material is not pitch-based carbon fiber but only PAN-based carbon fiber is used, the C / SiC molded body is subjected to SiC conversion reaction as shown above. Cracks occur in the C / SiC molded body due to volume expansion. For this reason, it became clear that it is not preferable to use only PAN-based carbon fibers.

Comparative Example 6
PAN-based carbon fibers were not used, and pitch-based carbon fibers having an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation) were used. Further, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was used as the graphite powder, and PG652 manufactured by Gunei Chemical Co., Ltd. was used as the powder resin.

  These pitch-based carbon fibers, graphite powder, and powder resin were mixed at a weight ratio of 185.6: 24.7: 109.6 using a V-type mixer so as to form a uniform mixture. Thereafter, the mixture was transferred to a mold and pressed into a fixed shape by pressing. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and powder resin.

  The volume content of the carbon fibers contained in this molded body was about 30%, and the volume content of the graphite powder was 4%. Next, this molded body was carbonized to C / C by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon). The porosity of the C / C compact was about 35%. Subsequently, the formed C / C molded body was heated to 1700 ° C. in a vacuum to melt and impregnate the metal silicon to obtain C / SiC.

  When the C / SiC composite material molded body thus obtained was analyzed, the matrix carbon and the graphite powder almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber hardly reacted. It was confirmed that the carbon fibers were oriented in the molding surface.

  As in Comparative Example 6, when the PAN-based carbon fiber is not used as the carbon fiber of the carbon fiber-reinforced carbon base material and only the pitch-based carbon fiber is used, the carbon fiber is oriented as in the above result. For this reason, since anisotropy arises in the physical property of a C / SiC molded object, it is not preferable.

  The carbon fiber reinforced silicon carbide composite material according to the present invention has the same strength and rigidity as sintered SiC, and has material properties without anisotropy. It is applicable to.

It is a figure which shows the manufacturing method of the fiber reinforced silicon carbide composite material by Embodiment 1 of this invention. It is a table | surface which shows the material physical property of the Example of this invention, conventional C / SiC, and a comparative example.

Explanation of symbols

1 short fiber of pitch-based carbon fiber, 2 short fiber of PAN-based carbon fiber, 3 graphite powder, 4 powder resin, 5 mixture, 6 carbon fiber molded body (carbon fiber base material), 7 C / C molded body, 8 Heat-resistant structural member, 9 C / SiC molded body, 10 C / SiC composite material heat-resistant structural member.

Claims (5)

  A fiber-reinforced silicon carbide composite material containing a plurality of types of carbon fibers having different reactivity with silicon and graphite powder, wherein a part of the carbon fibers contained is siliconized.   The fiber-reinforced silicon carbide composite material according to claim 1, wherein the carbon fibers are pitch-based carbon fibers and PAN-based carbon fibers.   The fiber-reinforced silicon carbide composite according to claim 2, wherein the average fiber length of the pitch-based carbon fibers is 1 mm or less, the average fiber length of the PAN-based carbon fibers is 0.5 mm or less, and the particle size of the graphite powder is 100 µm or less. material.   A first step of mixing a plurality of types of carbon fibers having different reactivity with silicon, graphite powder and powdered resin, heating and pressure forming to form a carbon fiber substrate, and the carbon fiber base by heat treatment A second step of carbonizing the material to form a carbon fiber reinforced carbon base material; and a third step of forming the carbon fiber reinforced silicon carbide base material by siliconizing the carbon fiber reinforced carbon base material by melt impregnation of silicon. A method for producing a fiber-reinforced silicon carbide composite material comprising: In the first step, pitch-based carbon fibers and PAN-based carbon fibers are included as carbon fibers, the carbon fiber volume content is 15% to 40%, the volume content of the graphite powder is 5% or less, and the porosity is 30% to 40%. % Carbon fiber base material is formed, The manufacturing method of the fiber reinforced silicon carbide composite material of Claim 4 characterized by the above-mentioned.

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