JP2017145181A - METHOD FOR PRODUCING SiC/SiC COMPOSITE MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a ceramic composite material, in which fracture toughness can be raised even in the interior of the ceramic composite material.SOLUTION: The method for producing a SiC/SiC composite material includes: an impregnation step of impregnating a fiber aggregate including SiC fibers with a SiC precursor, thereby obtaining an impregnated body; a burning step of heating the impregnated body under inert atmosphere, thereby thermally decomposing the SiC precursor and obtaining a burned body; and a CVD step of forming a CVD-SiC layer on a surface of the burned body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a SiC / SiC composite material.

Ceramic materials such as silicon carbide (SiC) and silicon nitride (Si ₃ N ₄ ) are excellent in heat resistance, chemical stability, mechanical properties, and the like. Therefore, these ceramic materials are being developed as materials used in harsh environments such as the nuclear field, aerospace field, and power generation field, and in general fields such as pump mechanical seals. Of these ceramic materials, SiC is a structural material that is promising in a wide range of fields because of its excellent properties.

  However, since SiC itself is a brittle material, in order to improve this, a SiC fiber / SiC composite material composed of a SiC fiber and a SiC matrix has been proposed. However, even in the SiC fiber / SiC composite material, when a crack occurs in the SiC matrix, the crack propagates in the matrix and the crack may propagate to the SiC fiber.

  Patent Document 1 discloses a ceramic composite including an impregnation step of impregnating a fiber assembly made of ceramic fibers with a slurry containing a matrix precursor and a hollow body to obtain an impregnation body, and a firing step of firing the impregnation body. A material manufacturing method and a ceramic composite material are described.

  When a hollow body exists in the matrix, in the ceramic composite material of Patent Document 1, even if a crack occurs in the matrix, the hollow body existing in the matrix prevents the crack from progressing, and the crack propagates to the ceramic fiber. This can be prevented.

  In addition, when the hollow body is substantially spherical, energy due to cracks generated by external impact is dispersed to the surroundings, and the progress of cracks can be prevented. It is described that the strength of the ceramic composite material can be increased by such an action.

Japanese Patent Laying-Open No. 2015-30632

  In the ceramic composite material manufactured by the manufacturing method described in Patent Document 1, since the slurry containing the hollow body is impregnated, the hollow body is separated during the impregnation process, and the matrix precursor is disposed inside the ceramic composite material. Only the body penetrates and the hollow body is difficult to reach. For this reason, on the surface layer side of the ceramic composite material, the hollow body acts to increase the fracture toughness, while the hollow body hardly reaches the inner side, and the ceramic fibers and the matrix are easily integrated, and the effect of increasing the fracture toughness is achieved. It's not enough.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing a ceramic composite material capable of increasing fracture toughness to the inside.

  The manufacturing method of the SiC / SiC composite material of the present invention for solving the above problems is as follows.

(1) An impregnation step of impregnating a SiC fiber with a SiC precursor to obtain an impregnated body, and heating the impregnated body in a reducing or inert atmosphere to thermally decompose the SiC precursor. A method for producing a SiC / SiC composite material, comprising: a firing step for obtaining a fired body; and a CVD step for forming a CVD-SiC layer on a surface of the fired body.

  According to the method for producing a SiC / SiC composite material of the present invention, since the SiC precursor is heated in a reducing atmosphere or an inert atmosphere in the firing step, the SiC precursor is converted into SiC without being sufficiently infusible. To do. For this reason, since a porous (porous) SiC matrix surrounds the periphery of the fiber and a buffer layer is formed, cracks generated in the CVD-SiC layer can be made difficult to progress into the SiC fiber.

(2) In the firing step, the SiC precursor is foamed and thermally decomposed.

  According to the method for producing a SiC / SiC composite material of the present invention, since the SiC precursor is foamed with decomposition gas or the like in the firing step, the SiC fibers are not easily exposed on the surface of the fired body and are generated in the CVD-SiC layer. It is possible to make it difficult for the cracks to be developed by the SiC fiber.

(3) The SiC precursor is polycarbosilane-based or polysilane-based.

  According to the method for producing a SiC / SiC composite material of the present invention, a polycarbosilane-based or polysilane-based SiC precursor is used as the SiC precursor. A polycarbosilane-based or polysilane-based SiC precursor can efficiently obtain SiC by thermal decomposition. Further, in the present invention, since the polycarbosilane-based or polysilane-based SiC precursor is subjected to infusibilization treatment using a method such as oxygen or electron beam irradiation, pores are formed around the SiC fiber by thermal decomposition. Many SiC matrices can be formed. Since the SiC matrix having many pores serves as a buffer layer and stops the growth of cracks, the cracks generated in the CVD-SiC layer can be made difficult to progress due to the SiC fibers.

  Examples of the polycarbosilane-based SiC precursor include polycarbosilane, polymetallocarbosilane, and hydridocarbosilane. Examples of the polysilane-based SiC precursor include polysilane and polyvinylsilane.

(4) In the impregnation step, a carbon precursor is impregnated together with the SiC precursor.

  The impregnation of the carbon precursor together with the SiC precursor is preferably performed by mixing the SiC precursor with the carbon precursor. The carbon precursor is heated to carbon in a reducing atmosphere or an inert atmosphere, and carbon is mixed into the decomposition product of the SiC precursor. The crack which the carbon which is this extraneous material generate | occur | produces in a CVD-SiC layer can be made hard to progress by SiC fiber.

(5) The reducing atmosphere or the inert atmosphere is an atmosphere of one or more gases selected from a rare gas, nitrogen, hydrogen, and a hydrocarbon gas.

  According to the method for producing a SiC / SiC composite material of the present invention, the firing step of the impregnated body impregnated with the SiC precursor is performed in a reducing atmosphere or inert atmosphere of any of rare gas, nitrogen, hydrogen, and hydrocarbon gas. Since it is carried out under heating, a crosslinking reaction of the SiC precursor hardly occurs, and a SiC matrix having many pores can be formed around the SiC fiber. The reducing atmosphere or the inert atmosphere may be an atmosphere of a reducing gas such as hydrogen or hydrocarbon and an inert gas such as nitrogen or a rare gas, or a mixed gas atmosphere thereof, and is not particularly limited. .

  According to the method for producing a SiC / SiC composite material of the present invention, since the SiC precursor is heated in a reducing atmosphere or an inert atmosphere in the firing step, the SiC precursor is converted into SiC without being sufficiently infusible. To do. For this reason, a porous SiC matrix surrounds the fiber and forms a buffer layer. For this reason, the crack which generate | occur | produces in a CVD-SiC layer can be made hard to progress to a SiC fiber.

It is a flowchart which shows the manufacturing process of the SiC / SiC composite material of this invention. It is explanatory drawing which shows the manufacturing process of the SiC / SiC composite material which uses the woven fabric of the SiC fiber of embodiment of this invention as a fiber assembly.

(Detailed description of the invention)
As shown in FIG. 1, the SiC / SiC composite material manufacturing method of the present invention includes an impregnation step (step S1) of impregnating an SiC precursor by impregnating a fiber assembly made of SiC fibers with an impregnated body. A baking process (step S2) for heating in a reducing atmosphere or an inert atmosphere to thermally decompose the SiC precursor to obtain a fired body, and a CVD process for forming a CVD-SiC layer on the surface of the fired body (step S3) Have.

  In the method for producing a SiC / SiC composite material of the present invention, the SiC precursor is heated in a reducing atmosphere or an inert atmosphere in the firing step, so that the SiC precursor is converted to SiC without being sufficiently infusible. For this reason, a porous SiC matrix surrounds the fiber and forms a buffer layer. For this reason, the crack which generate | occur | produces in a CVD-SiC layer can be made hard to progress to a SiC fiber.

  In the method for producing a SiC / SiC composite material of the present invention, it is desirable that the SiC precursor is foamed and thermally decomposed in the firing step.

  When the SiC precursor is foamed with decomposition gas or the like in the firing step, the SiC fibers are hardly exposed on the surface of the fired body, and cracks generated in the CVD-SiC layer can be made difficult to progress due to the SiC fibers.

  In the method for producing a SiC / SiC composite material of the present invention, the SiC precursor is preferably a polycarbosilane-based or polysilane-based material.

A polycarbosilane-based or polysilane-based SiC precursor can efficiently obtain SiC by thermal decomposition. Further, in the present invention, since the polycarbosilane-based or polysilane-based SiC precursor is subjected to infusibilization treatment using a method such as oxygen or electron beam irradiation, pores are formed around the SiC fiber by thermal decomposition. Many SiC matrices can be formed. Since the SiC matrix having many pores serves as a buffer layer and stops the growth of cracks, the cracks generated in the CVD-SiC layer can be made difficult to progress due to the SiC fibers.
Examples of the polycarbosilane-based SiC precursor include polycarbosilane, polymetallocarbosilane, and hydridocarbosilane. Examples of the polysilane-based SiC precursor include polysilane and polyvinylsilane.

  In the method for producing a SiC / SiC composite material of the present invention, the carbon precursor is impregnated with the SiC precursor in the impregnation step.

  The impregnation of the carbon precursor together with the SiC precursor is preferably performed by mixing the SiC precursor with the carbon precursor. The carbon precursor is heated to carbon in a reducing atmosphere or an inert atmosphere, and carbon is mixed into the decomposition product of the SiC precursor. The crack which the carbon which is this extraneous material generate | occur | produces in a CVD-SiC layer can be made hard to progress by SiC fiber.

  In the method for producing a SiC / SiC composite material of the present invention, the reducing atmosphere or the inert atmosphere is an atmosphere of at least one gas selected from the group consisting of a rare gas, nitrogen, hydrogen, and a hydrocarbon gas. Is desirable.

  In the method for producing a SiC / SiC composite material according to the present invention, the firing step of the impregnated body impregnated with the SiC precursor is performed under a reducing atmosphere or inert atmosphere of any of rare gas, nitrogen, hydrogen, and hydrocarbon gas By carrying out the heating, a crosslinking reaction of the SiC precursor hardly occurs and the yield can be lowered, so that a SiC matrix having many pores can be formed around the SiC fiber. The reducing atmosphere or the inert atmosphere may be an atmosphere of a reducing gas such as hydrogen or hydrocarbon and an inert gas such as nitrogen or a rare gas, or a mixed gas atmosphere thereof, and is not particularly limited. .

  In the manufacturing method of the SiC / SiC composite material of the present invention, the thickness of the SiC fiber to be used is not particularly limited. For example, the diameter of the SiC fiber is preferably 3 μm or more. Moreover, it is preferable that the diameter of a SiC fiber is 20 micrometers or less. A plurality of SiC fibers can be bundled and used as SiC fiber yarns. It is preferable that the number of SiC fibers constituting one SiC fiber yarn is, for example, 100 or more. Moreover, it is preferable that the number of the SiC fiber which comprises one SiC fiber yarn is 5000 or less, for example.

  In the manufacturing method of the SiC / SiC composite material of the present invention, the fiber assembly made of SiC fibers to be used is not particularly limited. As the fiber assembly, a woven fabric, a mat, a filament winding body, a braiding body, or the like can be used, or a combination thereof may be used.

  The woven fabric is formed using SiC fiber yarn. The weaving method is not particularly limited, and for example, a plain weave or a twill weave can be used. The mat is formed by laminating SiC fibers or SiC fiber yarns.

  The filament winding body can be obtained by winding a SiC fiber yarn around a mandrel. For winding around the mandrel, hoop winding that is perpendicular to the mandrel axis and helical winding that rotates around the mandrel axis can be used. Filament winding is a combination of hoop winding and helical winding. A body fiber assembly may be formed.

  The braiding body is formed by knitting SiC fiber yarn. The braided body is a structure in which SiC fiber yarns that extend helically in the right direction and the left direction on the cylindrical surface are alternately combined. Furthermore, a triaxial woven structure in which SiC fiber yarns are arranged in the axial direction can also be used.

(Mode for carrying out the invention)
Hereinafter, an embodiment of a method for producing a SiC / SiC composite material of the present invention will be described with reference to FIG. The fiber assembly 10 of the embodiment shown in FIG. 2A is a woven fabric of SiC fiber yarns 2. In this example, SiC fiber yarn 2A corresponding to warp and SiC fiber yarn 2B corresponding to weft are knitted to constitute a woven fabric. The SiC fiber yarn 2 is configured by bundling a plurality of SiC fibers 1.

  Next, as shown in FIG. 2B, the fiber assembly 10 is impregnated with the SiC precursor 3 to obtain an impregnated body 20. For impregnation, various methods such as pressure impregnation, vacuum impregnation, vacuum pressure impregnation, and immersion can be used. If the wettability between the SiC fiber and the SiC precursor is good, the SiC precursor permeates into the impregnated body 20 only by immersing the fiber assembly 10 in the SiC precursor 3. A gap between the SiC fibers 1 of the fiber assembly 10 is impregnated with a solution of the SiC precursor 3.

  Next, as shown in FIG. 2C, the impregnated body 20 is heated in a reducing atmosphere or an inert atmosphere to obtain a fired body 30. The SiC precursor 3 impregnated with the start of heating is thermally decomposed to increase the viscosity, and foams with a decomposition gas or the like. The structure is such that the porous SiC precursor decomposition product 4 surrounds the SiC fiber 1 by further heating and raising the temperature.

  Next, as shown in FIG. 2 (d), the fired body 30 is put in a CVD furnace, the CVD-SiC layer 5 is formed on the surface, and the newly formed CVD-SiC layer 5 and the SiC precursor 3 are formed. The SiC precursor decomposition product 4 obtained by thermal decomposition becomes the SiC matrix 6 of the SiC / SiC composite material 40.

  Hereinafter, the manufacturing method of the SiC / SiC composite material of this invention is demonstrated using an Example.

  In the embodiment, a method for producing a cylindrical SiC / SiC composite material using a filament winding body as a fiber assembly made of SiC fibers will be described.

  A SiC fiber thread is wound around a graphite mandrel having a diameter of 100 mm and a length of 300 to form a fiber assembly made of SiC fibers. A resin sheet is wound around the mandrel in advance. The SiC fiber yarn is configured by bundling 1600 SiC fibers having a diameter of 7 μm.

  The SiC fiber yarn is wound until the entire surface of the mandrel is covered by helical winding so that the inclination angle becomes 45 °, and then similarly wound by hoop winding until the entire surface is covered, and then helical winding is repeated until the entire surface is covered. Through the above steps, a fiber assembly having an inner diameter of 100 mm, an outer diameter of 105 mm, and a length of 250 mm can be obtained. A SiC / SiC composite material is manufactured using the obtained fiber assembly.

(Impregnation process)
The fiber assembly made of the SiC fibers is impregnated with a SiC precursor to obtain an impregnated body. As the SiC precursor, a xylene solution of polycarbosilane is used. The concentration of polycarbosilane is 45% by mass. The fiber assembly can be immersed in a xylene solution of polycarbosilane to obtain an impregnated body. A gap between the SiC fibers of the fiber assembly is impregnated with a xylene solution of polycarbosilane. In the impregnation step, after the impregnation is completed, the solvent may be removed by natural drying or using a dryer.

(Baking process)
In the firing step, the impregnated body impregnated with the xylene solution of polycarbosilane is heated in a reducing atmosphere or an inert atmosphere to obtain a fired body. Argon is used as an inert gas. As heating is started, the remaining xylene evaporates and the concentration of polycarbosilane gradually increases. Since polycarbosilane is heated in a reducing atmosphere or an inert atmosphere, the infusibilization reaction hardly occurs. Polycarbosilane decreases in xylene content, gradually increases in boiling point, increases in viscosity, and foams due to generation of decomposition gas and evaporation of xylene. By further heating and raising the temperature, the polycarbosilane is converted to SiC while being foamed.

  The calcination temperature of the impregnated body is 1100 ° C., and is heated up to 500 ° C. at 5 ° C./h and in the range of 500 to 1100 ° C. at a temperature rising rate of 20 ° C./h. By baking, the resin sheet wound around the mandrel is thermally decomposed and disappears. Since the resin sheet disappears, a gap is formed between the fired body obtained by firing the impregnated body and the mandrel, and the fired body can be separated from the mandrel.

  The obtained fired body has a structure in which a porous SiC matrix surrounds the periphery of the SiC fiber.

(CVD process)
The fired body separated from the mandrel is placed in a CVD furnace to form a CVD-SiC layer on the surface (step S3 in FIG. 1). The newly formed CVD-SiC layer and the SiC porous body (SiC matrix), which is a decomposition product of the SiC precursor, become the SiC matrix of the SiC / SiC composite material.

  The SiC / SiC composite material thus obtained has a porous SiC matrix around the SiC fiber. Therefore, even if a crack occurs in the CVD-SiC layer, the development of the crack stops at the SiC matrix around the SiC fiber. The breakage of the SiC fiber can be prevented.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the matters shown in the above embodiments, and those skilled in the art will understand the scope of the claims and the description, and based on well-known techniques. Modifications or applications are also contemplated by the present invention and are within the scope of seeking protection.

DESCRIPTION OF SYMBOLS 1 SiC fiber 2 SiC fiber thread 3 SiC precursor 4 SiC precursor decomposition product 5 CVD-SiC layer 6 SiC matrix 10 Fiber assembly 20 Impregnation body 30 Firing body 40 SiC / SiC composite material

Claims (5)

An impregnation step of impregnating an SiC precursor into a fiber assembly composed of SiC fibers to obtain an impregnated body;
A firing step of heating the impregnated body in a reducing atmosphere or an inert atmosphere to thermally decompose the SiC precursor to obtain a fired body;
A CVD step of forming a CVD-SiC layer on the surface of the fired body;
The manufacturing method of the SiC / SiC composite material which has this. A method for producing a SiC / SiC composite material according to claim 1,
The baking step is a method for producing a SiC / SiC composite material in which the SiC precursor is foamed and thermally decomposed. The manufacturing method of the SiC / SiC composite material of Claim 1 or 2.
The SiC precursor is a polycarbosilane-based or polysilane-based manufacturing method of a SiC / SiC composite material. A method for producing the SiC / SiC composite material according to any one of claims 1 to 3,
In the impregnation step, a SiC / SiC composite material manufacturing method in which a carbon precursor is impregnated together with the SiC precursor. A method for producing a SiC / SiC composite material according to any one of claims 1 to 4,
The method for producing a SiC / SiC composite material, wherein the reducing atmosphere or the inert atmosphere is an atmosphere of at least one gas selected from the group consisting of a rare gas, nitrogen, hydrogen, and a hydrocarbon gas.

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