JP2010070421A - METHOD FOR MANUFACTURING SiC FIBER-REINFORCED SiC COMPOSITE MATERIAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an SiC fiber-reinforced SiC composite material capable of exhibiting excellent heat characteristics and strength characteristics than the SiC fiber-reinforced SiC composite material of a conventional technology. <P>SOLUTION: The method for manufacturing the SiC fiber-reinforced SiC composite material includes (1) a first process for obtaining a preliminarily molded body by impregnating a slurry containing an SiC fine powder and a sintering aid and also containing no organic silicon polymer to a coated SiC fiber obtained by forming a coated layer containing at least one of carbon, boron nitride and silicon carbide on the SiC fiber surface and (2) a second process for pressure-sintering the preliminarily molded body. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a SiC fiber-reinforced SiC composite material.

Materials used in equipment such as aerospace, nuclear power, nuclear fusion, and power generation using fossil fuels are exposed to harsh environments subject to high heat loads. As materials used in such an environment, various ceramic materials such as SiC and Si ₃ N ₄ having excellent heat resistance, chemical stability, and mechanical properties have been developed. Ceramic materials are also used as members exposed to severe conditions such as heat exchangers and mechanical seals. Among these, SiC is not only heat resistant, but also has high strength, excellent wear resistance, and excellent chemical stability. Utilizing these advantages, it is a promising structural material in a wide range of fields ranging from aerospace applications to nuclear power, nuclear fusion, and power generation. Furthermore, it exhibits excellent properties not only in thermal properties but also in wear resistance, corrosion resistance, and the like.

  SiC has a melting point of 2600 ° C. and excellent high-temperature characteristics, but is a brittle material by itself. Accordingly, SiC fiber / SiC composite materials reinforced with SiC fibers have been proposed, and various manufacturing processes such as a hot press method and a liquid phase sintering method have been studied as manufacturing methods thereof. However, it is not easy to obtain a SiC fiber / SiC composite material having high heat conduction characteristics, high density, high strength characteristics, and excellent fracture behavior characteristics by any manufacturing method. By repeating the same process, etc. The characteristics are improved. The repetition of the process means the complexity of the manufacturing process and increases the manufacturing cost. In addition, restrictions on the product shape are added due to manufacturing problems, making it difficult to manufacture parts having complicated shapes. The restrictions imposed on complicated manufacturing processes and product shapes become a bottleneck in popularizing SiC fiber reinforced SiC composite materials as practical materials.

  On the other hand, there is also a method for producing a SiC fiber reinforced SiC composite material having a composition close to stoichiometry and using a highly crystalline SiC fiber excellent in heat resistance as a reinforcing material and forming a matrix by a liquid phase sintering method Are known. The SiC fiber reinforced SiC composite material produced by this method exhibits excellent thermal properties at high density, but is still unresolved with respect to achieving both high fracture strength and toughness.

  On the other hand, a slurry in which SiC fine powder and a sintering aid are dispersed is prepared, and the slurry is impregnated with SiC fiber coated with one or more of carbon, boron nitride, and silicon carbide, and a preform is obtained. And a method for producing a SiC fiber reinforced SiC composite material, characterized in that the preform is hot-pressed (Patent Document 1).

Further, after impregnating the silicon carbide fiber woven fabric or silicon carbide short fiber, which is a reinforcing fiber, with polycarbosilane, which is an organosilicon polymer, a molded body is formed, which is irradiated with ionizing radiation to become infusible. There has been proposed a method for producing a ceramic reinforced fiber / ceramic matrix composite (hereinafter referred to as a ceramic composite) by firing an infusibilized molded article in an inert gas and converting it into a ceramic (Patent Document 2).
JP 2002-356181 A JP 11-130552 A

  However, the composite materials obtained by these conventional manufacturing methods have room for further improvement in terms of thermal characteristics, strength characteristics, and the like.

  Accordingly, a main object of the present invention is to provide a SiC fiber reinforced SiC composite material that can exhibit thermal characteristics, strength characteristics, and the like superior to those of prior art SiC fiber reinforced SiC composite materials.

  As a result of intensive studies in view of the problems of the prior art, the present inventor has not intentionally formulated an organosilicon polymer (such as polycarbosilane) that is required for increasing the density of materials in the prior art. When pressure-sintering a preform made using the prepared slurry, a composite material with unexpectedly higher strength and high thermal conductivity was obtained, thereby achieving the above objective. The present inventors have found that this can be done and have completed the present invention.

That is, this invention relates to the manufacturing method of the following SiC fiber reinforcement type | mold SiC composite material.
1. A method for producing a SiC fiber reinforced SiC composite material, comprising:
(1) A coated SiC fiber formed by forming a coating layer containing at least one of carbon, boron nitride, and silicon carbide on the surface of the SiC fiber, including SiC fine powder and a sintering aid, and an organosilicon polymer A SiC fiber reinforced SiC composite material, comprising: a first step of obtaining a preform by impregnating a slurry containing no pre-treatment and (2) a second step of pressure-sintering the preform. Method.
2. Item 2. The method according to Item 1, wherein the SiC fine powder has an average particle size of 200 nm or less.
3. Item 2. The manufacturing method according to Item 1, wherein the sintering aid is at least one of Al ₂ O ₃ , Y ₂ O ₃ , SiO ₂ and CaO.
4). Item 2. The production method according to Item 1, wherein the pressure sintering is performed at 1600 to 1900 ° C under a pressure of 5 MPa or more.
5). Item 2. The method according to Item 1, wherein the coating layer is formed by a vapor phase method.
6). The manufacturing method of said claim | item 1 whose fiber length of SiC fiber is 20 mm or more.
7). The manufacturing method of said claim | item 1 whose fiber diameter of a SiC fiber is 20 micrometers or less.
8). The SiC fiber reinforced SiC composite material obtained by the manufacturing method according to any one of Items 1 to 7.
9. Item 9. The SiC fiber-reinforced SiC composite material according to Item 8, wherein the maximum strength by a three-point bending test at room temperature (20 ° C.) is 800 MPa or more.
10. Item 9. The SiC fiber-reinforced SiC composite material according to Item 8, wherein the thermal conductivity is 22 W / m · k or more at 800 ° C., 20 W / m · k or more at 1000 ° C., and 18 W / m · k or more at 1200 ° C. .

  According to the manufacturing method of the present invention, a SiC fiber reinforced SiC composite material, which has been conventionally required, is used to manufacture a SiC fiber reinforced SiC composite material. A composite material can be obtained. In particular, when SiC fine powder having an average particle diameter of 200 nm or less is used as a raw material, the effect can be obtained more reliably. In the case of adopting such means, it is considered that a phenomenon such as higher crystallinity occurs as a result of further promoting the denseness of the obtained sintered body.

  The SiC fiber reinforced SiC composite material obtained by the production method of the present invention is particularly excellent in strength and thermal conductivity, and can be effectively used for various structural materials, aerospace materials, nuclear reactor materials, and the like. .

The production method of the present invention is a method of producing a SiC fiber-reinforced SiC composite material,
(1) A coated SiC fiber formed by forming a coating layer containing at least one of carbon, boron nitride, and silicon carbide on the surface of the SiC fiber, including SiC fine powder and a sintering aid, and an organosilicon polymer It includes a first step of obtaining a preform by impregnating a slurry that does not contain, and (2) a second step of pressure-sintering the preform.

First step In the first step, the coated SiC fiber in which a coating layer containing at least one of carbon, boron nitride and silicon carbide is formed on the surface of the SiC fiber contains SiC fine powder and a sintering aid, and Then, a preform is obtained by impregnating a slurry containing no organosilicon polymer.

  SiC fiber should just be a fiber which consists of crystalline SiC, and a well-known or commercially available thing can be used for it. Since the fiber length of the SiC fiber is particularly preferably long fibers (filament yarn), it can be suitably selected within a range of, for example, 20 mm or more.

  Moreover, the fiber diameter of SiC fiber can be suitably set according to the use etc. of this invention composite material, and it is preferable to set it especially in the range of 5-20 micrometers.

  A coating layer containing at least one of carbon, boron nitride, and silicon carbide is formed on the surface of the SiC fiber. In the present invention, the coating layer exhibits effects such as a) load transmission (distributed load is distributed to the fiber and the matrix), b) a crack growth suppressing function, and c) suppression of material diffusion between the fiber and the matrix. be able to.

  The component of a coating layer should just contain at least 1 sort (s) of carbon, boron nitride, and silicon carbide, and the other component may be contained as needed. In this invention, the coating layer which consists of at least 1 sort (s) of carbon, boron nitride, and silicon carbide can be employ | adopted suitably. Examples thereof include a coating layer made of carbon (pyrolytic carbon), a coating layer made of boron nitride, and a coating layer made of silicon carbide.

  The thickness of the coating layer is not limited, but is usually about 0.1 to 1 μm, and particularly preferably 0.3 to 0.6 μm. By forming a coating layer with the above thickness, a large frictional force is generated on the peeled surface after peeling between the matrix and the interface. ) Can be obtained.

The method for forming the coating layer on the SiC fiber is not particularly limited, and a known thin film forming technique can be employed. For example, any of a liquid phase method, a gas phase method, and a solid phase method may be used. In particular, in the present invention, it is preferable to form the coating layer by a vapor phase method from the standpoint of adhesion to SiC fibers. Specifically, a CVD method, a thermal evaporation method (vacuum evaporation method), a sputtering method, an ion plating method, and the like can be given. In the present invention, for example, a pyrolytic carbon layer or a boron nitride layer can be suitably formed as a coating layer by a CVD method. The thin film formation conditions for the CVD method may be, for example, a substrate temperature of 900 to 1100 ° C. and H ₂ or the like as a carrier gas.

  The coated SiC fiber is impregnated in the slurry. As this slurry, a slurry containing SiC fine powder and a sintering aid and containing no organosilicon polymer is used.

  It is preferable to use a SiC fine powder having an average particle diameter of 200 nm or less. By using such fine powder, it is possible not only to obtain an excellent sinterability without using an organosilicon polymer, but also to more reliably obtain a composite material having excellent strength, thermal conductivity, etc. be able to. In the present invention, SiC fine powder having an average particle diameter of 100 nm or less, and most preferably an average particle diameter of 50 nm or less is used. A known or commercially available SiC fiber fine powder can be used. The lower limit value of the average particle diameter is not limited, but is usually about 5 nm.

The content of the SiC fine powder in the slurry is not particularly limited, but generally it is preferably about 40 to 80% by weight (solid content).

As the sintering aid, any common one used for the production of a silicon carbide sintered body can be used. In particular, in the present invention, it is desirable to use at least one of Al ₂ O ₃ , Y ₂ O ₃ , SiO ₂ and CaO.

  The content of the sintering aid in the slurry is not limited, and can be appropriately set according to the desired characteristics and application of the sintered body, usually within a range of 5 to 20% by weight (solid content). For example, when trying to obtain a sintered body excellent in high-temperature characteristics (strength and thermal conductivity), the content is preferably 5 to 10% by weight. For example, when relatively mild production conditions (temperature, pressure, etc.) are required, the content is preferably 10 to 20% by weight. As the sintering aid, a powdery one is usually used. In that case, the average particle size is usually about 0.5 to 3 μm.

  In the present invention, a slurry containing substantially no organosilicon polymer is used as a starting material. By using such a slurry, excellent thermal conductivity, strength, and the like can be achieved as compared with the case containing an organosilicon polymer. Examples of the organosilicon polymer include silicon-based polymers such as polycarbosilane, polyvinylsilane, and polymethylsilane described in Patent Document 1 and the like. In the present invention, a slurry containing an organic silicon polymer and not containing an organic polymer binder is preferably used, and more preferably a slurry composed of a two-component system of SiC fine powder and a sintering aid is used as a solid content.

  As the solvent, water or an organic solvent can be used. Examples of the organic solvent that can be used include hydrocarbon organic solvents such as hexane, toluene, and xylene, and alcohol organic solvents such as ethanol and isopropanol.

  In preparing the slurry, the method is not limited as long as these components can be mixed uniformly. For example, the slurry may be prepared using a known mixing and stirring device such as a mixer or a kneader.

  The method for preparing the preform by impregnating the coated SiC fiber into the slurry is not particularly limited. For example, 1) a method of impregnating the slurry into a nonwoven fabric composed of coated SiC short fibers and drying, 2) gold Examples include a method in which a bundle of coated SiC long fibers is placed in a mold, and a slurry is filled thereon, followed by drying. 3) A method in which a woven fabric of coated SiC long fibers is immersed in the slurry and then dried. .

Second Step In the second step, the preform is pressure sintered. Thereby, the composite material of the present invention can be obtained.

  The sintering temperature is usually about 1600 to 1900 ° C, particularly 1800 to 1900 ° C. By performing pressure sintering in the above temperature range, more excellent strength, heat conduction characteristics, and the like can be obtained.

  The pressure is usually 5 MPa or more, particularly 10 MPa or more, and preferably 15 to 30 MPa. By applying pressure within such a range, it is possible to obtain a composite material having higher density, higher strength, thermal conductivity, etc. while utilizing the characteristics of SiC fibers.

  The sintering atmosphere may be a non-oxidizing atmosphere, and may be any of an inert gas atmosphere, a reducing atmosphere, a vacuum atmosphere, and the like. In particular, in the present invention, an inert gas atmosphere is desirable. As the inert gas, for example, hydrogen, nitrogen, helium, argon or the like can be used.

  What is necessary is just to implement the method of pressure sintering using a well-known method and an apparatus. For example, any of a hot press (HP) method, a hot isostatic press (HIP) method, and the like can be employed.

  The present invention includes the SiC fiber-reinforced SiC composite material (the composite material of the present invention) obtained as described above.

  The composite material of the present invention has a configuration in which coated SiC fibers are present in a SiC matrix. The ratio of the coated SiC fiber in the composite material is not limited, and may be appropriately set in accordance with the application and the like within a range of usually 20 to 80% by weight (preferably 40 to 60% by weight). The composite material of the present invention is dense with a relative density of 98% or more. For this reason, higher strength, thermal conductivity, etc. can be achieved. For example, the maximum strength by a three-point bending test at room temperature (20 ° C.) can exhibit a characteristic of 800 MPa or more. Moreover, the bending elastic modulus by the 3 point | piece bending test at room temperature (20 degreeC) can exhibit the characteristic of 250 GPa or more. Furthermore, the thermal conductivity is 30 W / m · k or more at room temperature (20 ° C.), 22 W / m · k or more at 800 ° C., 20 W / m · k or more at 1000 ° C., 18 W / m · k at 1200 ° C. The characteristic of k or more is shown.

  The features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the examples.

<Reference Example 1>
Tyranno ^TM- SA fiber (manufactured by Ube Industries, fiber diameter 7.5 μm, heat resistant temperature to 2000 ° C.) is used as a highly crystalline SiC fiber having a composition close to stoichiometry, and pyrolytic carbon is formed by a CVD method. By depositing on the surface of the SiC fiber, a C (carbon) coating layer having a film thickness of about 0.5 μm was formed on the surface of the SiC fiber to produce a surface-coated SiC fiber.

Next, a slurry for impregnating the surface-coated SiC fiber was prepared. Ultrafine β-SiC particles (average particle size 30 nm): sintering aid Al ₂ O ₃ (average particle size 0.3 μm): polycarbosilane = 4.5: 0.5: 5 (mass ratio) hexane ( A slurry was obtained by dispersing in a solvent.

  Next, a fiber bundle in which dozens of surface-coated SiC fibers were arranged in a row in parallel without gaps was placed in a pressure-resistant sealed container. Thereafter, the slurry is introduced by vacuum suction from the container opening, and the surface-coated SiC fiber bundle is impregnated with the slurry, whereby a surface-coated SiC fiber: slurry = 4: 6 (solid content mass ratio) preform is obtained. Produced.

  The obtained preform was set in a hot press machine and sintered at a pressure of 20 MPa and a temperature of 1780 ° C. to obtain a SiC fiber reinforced SiC composite material sintered body. The pressing direction in this case was a direction perpendicular to the longitudinal direction of the surface-coated SiC fiber. The density and relative density of the obtained sintered body are shown in Table 1 (with organosilicon polymer).

<Example 1>
A SiC fiber reinforced SiC composite material sintered body was obtained in the same manner as in Reference Example 1 except that polycarbosilane, which is an organosilicon polymer, was not used in Reference Example 1. The characteristics of the obtained sintered body are shown in Table 1 (no organosilicon polymer).

<Test Example 1>
The sintered bodies obtained in Reference Example 1 and Example 1 were examined for mechanical properties at room temperature. Specifically, the maximum strength and bending elastic modulus by a three-point bending test, the proportional limit stress, the maximum strength and elastic modulus by a tensile test were measured. The results are shown in Table 1.

<Test Example 2>
About the sintered compact obtained in Example 1, the stress strain curve was calculated | required (room temperature, 1300 degreeC, and 1500 degreeC). The result is shown in FIG. In a similar composite material using a conventional organosilicon polymer, significant strength deterioration is observed at a high temperature range of 1400 ° C. (reference: Key Engineering Materials Vol.247 (2003) pp191-194)). It can be seen that such a sintered body does not show such deterioration and exhibits excellent high temperature characteristics.

<Test Example 3>
About the sintered compact obtained by the reference example 1 and Example 1, the thermal conductivity in room temperature-high temperature (800 degreeC, 1000 degreeC, and 1200 degreeC) was investigated. The results are shown in Table 2.

<Test Example 4>
The microstructure of the sintered bodies obtained in Reference Example 1 and Example 1 was examined with a scanning electron microscope (SEM). The result is shown in FIG. As is clear from FIG. 2, the sintered body of Example 1 has a matrix formed more densely between the fiber bundles and inside the fiber bundle, whereas in Reference Example 1, formation of a SiC matrix having poor crystallinity. In addition, macro segregation of the sintering aid is more pronounced, and it can be seen that these are associated with deterioration of strength characteristics particularly at high temperatures.

<Test Example 5>
The microstructure of the sintered bodies obtained in Reference Example 1 and Example 1 was examined with a transmission electron microscope (TEM). The result is shown in FIG. As is clear from FIG. 3, in the sintered body of Reference Example 1, in addition to the high crystalline SiC crystal growing only up to about 200 nm, finer crystal grains at the initial stage of crystallization were observed. In addition, a poor degree of alignment at the grain boundary is recognized (the degree of matching is good when there are few defects at the grain boundary). Compared to this, in the sintered body of Example 1, highly crystalline SiC crystals grow relatively uniformly up to about ~ 500 nm, and the degree of alignment of grain boundaries is good. In the sintered body of Example 1 having such a fine structure, high thermal conductivity and strength can be maintained from room temperature to a high temperature range.

The stress-strain curve of the composite material obtained in Example 1 is shown. The result of having observed the composite material obtained by the reference example 1 and Example 1 with the scanning electron microscope (SEM) is shown. The result of having observed the composite material obtained by the reference example 1 and Example 1 with the transmission electron microscope (TEM) is shown.

Claims (10)

A method for producing a SiC fiber reinforced SiC composite material, comprising:
(1) A coated SiC fiber formed by forming a coating layer containing at least one of carbon, boron nitride, and silicon carbide on the surface of the SiC fiber, including SiC fine powder and a sintering aid, and an organosilicon polymer A SiC fiber reinforced SiC composite material, comprising: a first step of obtaining a preform by impregnating a slurry containing no pre-treatment and (2) a second step of pressure-sintering the preform. Method. The manufacturing method of Claim 1 whose average particle diameter of SiC fine powder is 200 nm or less. Sintering _aid, an _{Al 2 O 3, Y 2 O} 3, at least one of SiO ₂ and CaO, the manufacturing method according to claim 1. The manufacturing method according to claim 1, wherein the pressure sintering is performed at 1600 to 1900 ° C. under a pressure of 5 MPa or more. The manufacturing method according to claim 1, wherein the coating layer is formed by a vapor phase method. The manufacturing method of Claim 1 whose fiber length of a SiC fiber is 20 mm or more. The manufacturing method of Claim 1 whose fiber diameter of a SiC fiber is 20 micrometers or less. A SiC fiber-reinforced SiC composite material obtained by the production method according to claim 1. The SiC fiber reinforced SiC composite material according to claim 8, wherein the maximum strength by a three-point bending test at room temperature (20 ° C) is 800 MPa or more. The SiC fiber-reinforced SiC composite material according to claim 8, wherein the thermal conductivity is 22 W / m · k or more at 800 ° C, 20 W / m · k or more at 1000 ° C, and 18 W / m · k or more at 1200 ° C. .