JP7085388B2 - Method for manufacturing SiC fiber reinforced SiC composite material - Google Patents

Description

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

SiC is a material having excellent 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 power field, aerospace field, and power generation field, and in general fields such as pump mechanical seals.

However, since SiC as a sintered body is a ceramic material, it has low fracture toughness, and a SiC fiber-reinforced SiC composite material has been developed in order to eliminate the weaknesses thereof.
There are various manufacturing methods for a SiC fiber reinforced SiC composite material in which a matrix made of SiC is filled between aggregates made of SiC fibers.

In the CVI method, a matrix composed of SiC is formed between aggregates of SiC fibers by a vapor phase growth method. In the PIP method, a SiC precursor is impregnated between the aggregates of SiC fibers and then fired to be ceramicized to form a SiC matrix. In the MI method, the gaps between the SiC fibers are impregnated with a carbon source, then fused silicon is impregnated, and carbon and silicon are internally reacted to form a SiC matrix.

Patent Document 1 describes the MI method, which is one of the methods for producing a SiC fiber-reinforced SiC composite material. The scope of the patent claim of Patent Document 1 is a method for forming a ceramic matrix composite (CMC) article, which comprises a ceramic matrix composite base material containing a ceramic fiber reinforced material in a ceramic matrix material having a free silicon content. The process of forming by melt impregnation and the outer layer of the ceramic matrix composite containing the ceramic fiber reinforced material in the ceramic matrix material having no free silicon content, which is placed on at least a part of the substrate, is formed by chemical vapor phase impregnation. Methods including steps are described.

According to the above method for producing a CMC article, it is possible to obtain a CMC article having a creep resistance larger than the creep resistance of the CMC article having no outer layer. The CMC outer layer without free elemental silicon or silicon alloy can withstand higher temperatures (eg, higher than the melting point of silicon) compared to the CMC substrate (which may contain free silicon), resulting in It is described that it can result in a CMC article that can withstand higher temperatures than that of a CMC article that does not have an outer layer.

Japanese Unexamined Patent Publication No. 2016-185901

However, the CMC article described in Patent Document 1 has a structure in which the inner CMC article having a small creep resistance is reinforced by an outer layer having no free silicon, and does not enhance the heat resistance of the inner layer itself. .. Therefore, there is a problem that the heat resistance and strength of the inner layer are insufficient.

In view of the above problems, the present invention provides a method for producing a SiC fiber-reinforced SiC composite material, which can obtain a SiC fiber-reinforced SiC composite material having few residual silicon, unreacted carbon or pores and excellent heat resistance by a simple method. The purpose is to provide.

The method for producing a SiC fiber-reinforced SiC composite material of the present invention includes a first impregnation step of impregnating an aggregate made of SiC fibers with a slurry consisting of water, SiC particles and graphite particles and drying the first impregnation step. It is characterized by having a second impregnation step of impregnating the molten silicon after the above.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, a slurry composed of water, SiC particles and graphite particles is impregnated in advance in the first impregnation step, so that the SiC particles and the SiC particles are more efficiently used than the conventional method. Graphite particles can be impregnated inside the pores. In addition, water is used for the slurry, and since water is less likely to cause aggregation of SiC particles and graphite particles than other solvents, the viscosity of the slurry is less likely to increase, and high-concentration SiC particles and the slurry of graphite particles are impregnated. Suitable for.

In the second impregnation step after the first impregnation step, the remaining pores in the SiC fiber are impregnated with high-temperature molten silicon and react with the graphite particles to form reaction-sintered SiC. If there are many pores left after the first impregnation step, the amount of fused silicon to be impregnated increases, and the amount of graphite particles required increases. Further, as the amount of the obtained reaction sintered SiC increases, the amount of silicon remaining inside the base material also increases with the reaction shrinkage.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, by filling the SiC particles together with the graphite particles, the pores left after the first impregnation step are reduced, and the amount of graphite particles required for forming the SiC is reduced. Therefore, residual silicon and residual carbon can be reduced. Further, the reaction sintered SiC is formed by impregnating the molten silicon in the second impregnation step. Therefore, it is possible to fill the voids that could not be filled in the first impregnation step with Si and convert it into SiC to obtain a dense SiC fiber-reinforced SiC composite material.

Further, since the SiC particles are filled in the first impregnation step, it is possible to prevent the graphite particles from becoming excessive and leaving unreacted graphite particles. Further, since the graphite particles having a higher true density than the carbonaceous particles are crystallized, the reaction with the molten silicon is slow, and the molten silicon reacts slowly after it has spread to the inside. Therefore, it is possible to obtain a SiC fiber-reinforced SiC composite material having few pores, because the graphite particles in the vicinity of the surface are less likely to be clogged by being converted into SiC first.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the solid content content in the slurry is preferably 50 to 80% by weight.

In the method for producing a SiC fiber-reinforced SiC composite material by the MI method of impregnating molten silicon and forming SiC by reaction sintering, when completely impregnated with silicon, it is contained in the aggregate after the first impregnation step of impregnating the slurry. The amount of pores in the above becomes the amount of impregnation of the fused silicon as it is. When the amount of impregnated silicon is large, the amount of graphite particles required for the reaction increases, and the volume shrinkage due to the reaction further impregnates silicon between the SiC fibers to increase the amount of residual silicon.

As mentioned above, water is less likely to cause aggregation of SiC particles than other solvents. In addition, since many dispersants can be applied to water, it is easy to select a dispersant that does not easily aggregate, and it is suitable as a solvent. Therefore, in the method for producing a SiC fiber-reinforced SiC composite material of the present invention, even if the solid content in the slurry is as high as 50 to 80% by weight, the viscosity of the slurry is unlikely to increase and the content is high. Therefore, SiC particles and graphite particles can be impregnated between the SiC fibers.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the solid content is as high as 50% by weight or more, SiC particles and graphite particles can be efficiently filled between the SiC fibers. .. Further, when the content ratio of the SiC particles is 80% by weight or less, the viscosity of the slurry can be maintained in a low state, so that the SiC particles and the graphite particles can be sufficiently filled between the SiC fibers.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the true density of graphite particles in the above slurry is 2.05 to 2.26 g / cm ³ .

In the second impregnation step of the method for producing a SiC fiber-reinforced SiC composite material of the present invention, graphite particles react with molten silicon to form reaction-sintered SiC. The density of molten silicon is about 2.57 g / cm ³ , and the density of SiC is about 3.2 g / cm ³ . On the other hand, the density of graphite varies, and even the largest theoretical value is 2.26 g / cm ³ . Therefore, SiC has a higher density than either silicon or graphite. Therefore, shrinkage always occurs due to the reaction between the graphite particles and the molten silicon. In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the reaction shrinkage can be reduced by setting the true density of the graphite particles in the slurry as high as 2.05 to 2.26 g / cm ³ . A dense SiC fiber reinforced SiC composite material can be obtained.

In addition, in the graphite crystal, when the hexagonal mesh surface and the edge are compared, the edge reacts more easily. As the true density of graphite increases, the hexagonal mesh surface expands and the edge ratio decreases. For this reason, graphite crystals and carbon materials having a true density of less than 2.05 g / cm ³ become solid SiC as soon as they come into contact with molten silicon, which closes the pores and suppresses the penetration of molten silicon. When graphite particles having a true density of 2.05 g / cm ³ or more are used, the reaction shrinkage is suppressed and the reaction is slow, so that it is difficult to prevent the permeation of molten silicon and a dense SiC fiber-reinforced SiC composite material can be obtained. can.

ρ_Si：溶融シリコン密度
ρ_c：黒鉛真密度
ｕ：スラリー含浸前の骨材の気孔率
Ｖｐ：スラリー含浸後、溶融シリコン含浸前の骨材の気孔率
ｓ：ＳｉＣ粒子と黒鉛粒子の和に対する黒鉛粒子の体積比 In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the volume ratio of graphite particles to the total volume of SiC particles and graphite particles in the slurry is calculated by the following formulas (1) and (2). It is desirable that it is within 10%.

ρ _Si : Molten silicon density ρ _c : Graphite true density u: Porosity of aggregate before slurry impregnation Vp: Porosity of aggregate after slurry impregnation and before molten silicon impregnation s: Graphite for sum of SiC particles and graphite particles Particle volume ratio

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the volume ratio of graphite particles to the total volume of SiC particles and graphite particles in the slurry is calculated by the formulas (1) and (2) with respect to the above s. If it is within 10%, the original pores inside the SiC fiber are almost filled with the SiC particles and the reaction sintered SiC, and only the reaction shrinkage portion is filled with the molten silicon, so that the pores are small and dense. A SiC fiber reinforced SiC composite material can be obtained.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the number of times of impregnation of the slurry in the first impregnation step is one.

In the first impregnation step of the present invention, in which a slurry composed of water and SiC particles is impregnated and dried, the main purpose is to fill the SiC particles and the graphite particles between the SiC fibers, and the SiC particles and the graphite particles are formed. It is difficult to fix SiC particles and graphite particles between SiC fibers in the filled state. Therefore, the SiC particles and the graphite particles filled between the SiC fibers are not sufficiently fixed, and easily fall off from between the SiC fibers. Therefore, if the impregnation step is repeated two or more times, the SiC particles and the graphite particles once filled will flow out. According to the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the number of times of impregnation of the slurry is one, so that the SiC particles and the graphite particles can be efficiently filled between the SiC fibers.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the average particle diameter (diameter) of the SiC particles is 0.1 to 10 μm.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the average particle size of the SiC particles is 0.1 μm or more, a slurry having low viscosity can be obtained with a small amount of water, and the SiC particles can be efficiently produced. It can be filled between SiC fibers. Further, when the average particle diameter of the SiC particles is 10 μm or less, the SiC particles are likely to be filled in the voids even if the voids between the SiC fibers are narrow.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the average particle diameter (diameter) of the graphite particles is 0.1 to 10 μm.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the average particle size of the graphite particles is 0.1 μm or more, a slurry having low viscosity can be obtained with a small amount of water, and the graphite particles can be efficiently produced. It can be filled between SiC fibers. Further, when the average particle diameter of the graphite particles is 10 μm or less, the graphite particles are likely to be filled inside the voids even if the voids between the SiC fibers are narrow.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the slurry contains 2 to 5 parts by weight of the dispersant with respect to 100 parts by weight of the total of the SiC particles and the graphite particles.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the slurry contains 2 parts by weight or more of the dispersant with respect to 100 parts by weight of the total of SiC particles and graphite particles, the SiC particles are sufficiently dispersed and the slurry is prepared. Liquidity can be ensured. On the other hand, since the dispersant exhibits performance in a small amount, the viscosity of the slurry is not significantly affected even if it is added in an excessive amount. By setting the content to 5% by weight or less based on 100 parts by weight of the particles and the graphite particles in total, the viscosity of the slurry can be sufficiently reduced with a small amount.

FIG. 1A is a cross-sectional view schematically showing an example of a fixing jig used for producing a plate-shaped aggregate in the method for producing a SiC fiber-reinforced SiC composite material of the present invention. b) is a perspective view of the fixing jig. 2 (A) to 2 (C) are band graphs showing changes when the carbon particles and the initially impregnated molten silicon have the same number of moles and the pores are completely impregnated with the molten silicon. 3 (A) to 3 (C) are band graphs showing changes when the number of moles of the molten silicon impregnated with carbon particles is larger than that of the initially impregnated molten silicon and the pores are completely impregnated with the molten silicon. 4 (A) to 4 (C) are band graphs showing changes when the number of moles of the molten silicon impregnated with carbon particles is smaller than that of the initially impregnated molten silicon and the pores are completely impregnated with the molten silicon. 5 (A) to 5 (C) are band graphs showing changes when the carbon particles and the initially impregnated molten silicon have the same number of moles and the pores are sufficiently impregnated with the molten silicon. 6 (A) to 6 (C) are band graphs showing changes when the number of moles of molten silicon impregnated with carbon particles is larger than that of the initially impregnated molten silicon and the impregnation of the molten silicon into the pores is insufficient. 7 (A) to 7 (C) are band graphs showing changes when the number of moles of molten silicon impregnated with carbon particles is smaller than that of the initially impregnated molten silicon and the impregnation of the molten silicon into the pores is insufficient.

(Detailed description of the invention)
Hereinafter, the method for producing the SiC fiber-reinforced SiC composite material of the present invention will be described in detail.
The method for producing a SiC fiber-reinforced SiC composite material of the present invention includes a first impregnation step of impregnating an aggregate made of SiC fibers with a slurry consisting of water, SiC particles and graphite particles and drying the first impregnation step. It is characterized by having a second impregnation step of impregnating the molten silicon.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, since a slurry composed of water, SiC particles and graphite particles is impregnated in advance in the first impregnation step, SiC and graphite are more efficiently used than the conventional method. Particles can be impregnated inside the pores. In addition, water is used for the slurry, and since water is less likely to cause aggregation of SiC particles and graphite particles than other solvents, the viscosity of the slurry is less likely to increase, and high-concentration SiC particles and the slurry of graphite particles are impregnated. Suitable for.

In the second impregnation step after the first impregnation step, the remaining pores in the SiC fiber are impregnated with high-temperature molten silicon and react with the graphite particles to form reaction-sintered SiC. If there are many pores left after the first impregnation step, the amount of fused silicon to be impregnated increases, and the amount of graphite particles required increases. Further, as the amount of the obtained reaction sintered SiC increases, the amount of silicon remaining inside the base material also increases with the reaction shrinkage.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, by filling the SiC particles together with the graphite particles, the pores left after the first impregnation step are reduced, and the amount of graphite particles required for forming the SiC is reduced. Therefore, residual silicon and residual carbon can be reduced. Further, the reaction sintered SiC is formed by impregnating the molten silicon in the second impregnation step. Therefore, it is possible to fill the voids that could not be filled in the first impregnation step with Si and convert it into SiC to obtain a dense SiC fiber-reinforced SiC composite material.

Further, since the SiC particles are filled in the first impregnation step, it is possible to prevent the graphite particles from becoming excessive and leaving unreacted graphite particles. Further, since the graphite particles having a higher true density than the carbonaceous particles are crystallized, the reaction with the molten silicon is slow, and the molten silicon reacts slowly after it has spread to the inside. Therefore, it is possible to obtain a SiC fiber-reinforced SiC composite material having few pores, because the graphite particles in the vicinity of the surface are less likely to be clogged by being converted into SiC first.

SiC fiber is used as an aggregate, and carbon (graphite) particles and SiC particles, which are carbon sources, are pre-filled in the gaps via a slurry, and then impregnated with high-temperature molten silicon to form reaction-sintered SiC. The following six patterns will be illustrated and described as a method for producing a fiber-reinforced SiC composite material.

Specifically, in the above manufacturing method, pores, filled SiC particles, reaction sintered SiC, unreacted carbon, and residue existing in the aggregate made of SiC fibers after the first impregnation step and after the second impregnation step. Consider the amount of silicon, etc.
Pore: Means a space that is not filled with anything in the aggregate.
Unreacted carbon: Filled carbon particles that do not react with molten silicon and remain.
Residual Silicon: Silicon that does not react with the filled carbon particles and remains.

In each pattern, the progress of the manufacturing process of the SiC fiber reinforced SiC composite material and the volume ratio occupied by each member to the total volume of the aggregate made of SiC fibers are shown in the band graphs (A), (B) and (C). It is shown by.
That is, FIGS. 2A to 2C are band graphs showing changes when the carbon particles and the first impregnated molten silicon have the same number of moles and the pores are completely impregnated with the molten silicon.
3A to 3C are band graphs showing changes when the number of moles of molten silicon impregnated with carbon particles is larger than that of the initially impregnated molten silicon and the pores are completely impregnated with the molten silicon.
4 (A) to 4 (C) are band graphs showing changes when the number of moles of the molten silicon impregnated with carbon particles is smaller than that of the initially impregnated molten silicon and the pores are completely impregnated with the molten silicon.
5 (A) to 5 (C) are band graphs showing changes when the carbon particles and the initially impregnated molten silicon have the same number of moles and the pores are sufficiently impregnated with the molten silicon.
6 (A) to 6 (C) are band graphs showing changes when the number of moles of molten silicon impregnated with carbon particles is larger than that of the initially impregnated molten silicon and the impregnation of the molten silicon into the pores is insufficient.
7 (A) to 7 (C) are band graphs showing changes when the number of moles of molten silicon impregnated with carbon particles is smaller than that of the initially impregnated molten silicon and the impregnation of the molten silicon into the pores is insufficient.

(A): Volume ratio of each member after filling an aggregate made of SiC fiber with a slurry made of SiC particles and carbon particles (B): Volume ratio of each member after impregnation with molten silicon and immediately before the occurrence of reaction sintering. (C): Volume ratio of each member in consideration of volume shrinkage due to reaction sintering after reaction sintering In addition, "first impregnated" means that the material was impregnated before the reaction shrinkage due to the formation of reaction sintered SiC. Is shown.

The symbols used in the graph above and the description below are summarized in Table 1 below.

(Pattern 1) When the carbon particles and the first impregnated molten silicon have the same number of moles and the pores are completely impregnated with the molten silicon (see FIG. 2).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled.
(B)
The pores Vp are completely filled with molten silicon and Vp is replaced by the molten silicon Vsi.
(Vp = Vsi)
(C)
Vrsic is generated by reaction sintering, and the molten silicon Vsi and carbon particles Vc are completely consumed, but the generated Vrsic is smaller than the total volume of Vsi and Vc and shrinks, so that the formed gaps The molten silicon Vsi2 is newly filled.

In (Pattern 1), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vsi2, and only silicon remains in the aggregate in addition to SiC, and no pores are formed.

(Pattern 2) When the number of carbon particles is larger than the number of moles of the molten silicon initially impregnated, and the pores are completely impregnated with the molten silicon (see FIG. 3).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled. The amount of Vc is larger than that of pattern 1.
(B)
The pores Vp are completely filled with molten silicon and Vp is replaced by the molten silicon Vsi.
(Vp = Vsi)
(C)
Vrsic is generated by reaction sintering, and excess carbon particles Vc2 remain. Since the generated Vrsic is smaller than the total volume of Vsi and Vc and is contracted, the formed gap is newly filled with molten silicon Vsi2.

In (Pattern 2), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vc2 + Vsi2, and carbon Vc2 and silicon Vsi2 remain in the aggregate in addition to SiC, and pores are not formed.

(Pattern 3) When the number of carbon particles is smaller than the number of moles of the molten silicon initially impregnated, and the pores are completely impregnated with the molten silicon (see FIG. 4).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled. The amount of Vc is smaller than that of pattern 1.
(B)
The pores Vp are completely filled with molten silicon and Vp is replaced by the molten silicon Vsi.
(Vp = Vsi)
(C)
Vrsic is generated by reaction sintering, and excess silicon Vsi3 remains. Since the generated Vrsic is smaller than the total volume of Vsi and Vc and is contracted, the formed gap is newly filled with molten silicon Vsi2.

In (Pattern 3), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vsi2 + Vsi3, and silicon (Vsi2, Vsi3) remains in the aggregate in addition to SiC, and pores are not formed. In addition, Vsi2 is the molten silicon impregnated afterwards with the reaction shrinkage, and Vsi3 is the first impregnated molten silicon remaining without participating in the reaction.

(Pattern 4) When the number of moles of the molten silicon initially impregnated with the carbon particles is the same, but the impregnation of the molten silicon into the pores is insufficient (see FIG. 5).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled.
(B)
The pore Vp is filled with molten silicon, but the Vp is not completely filled, and the pore Vp2 remains in addition to Vsi. (Vp = Vsi + Vp2)
(C)
Vrsic is produced by reaction sintering, and the molten silicon Vsi and carbon particles Vc are completely consumed. At this point, Vsi and Vc are equimolar. Since the generated Vrsic is smaller than the total volume of Vsi and Vc and is contracted, the formed gap is newly filled with the molten silicon Vsi2, but the pores Vp2 remain.

In (Pattern 4), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vsi2 + Vp2, and silicon (Vsi2) and pores Vp2 remain in the aggregate in addition to SiC.

(Pattern 5) When the number of carbon particles is larger than the number of moles of the molten silicon initially impregnated, and the impregnation of the molten silicon into the pores is insufficient (see FIG. 6).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled. The amount of Vc is larger than that of pattern 4.
(B)
The pore Vp is filled with molten silicon, but the Vp is not completely filled, and the pore Vp2 remains in addition to Vsi. (Vp = Vsi + Vp2)
(C)
Vrsic is generated by reaction sintering, and excess carbon particles Vc2 remain. Since the generated Vrsic is smaller than the total volume of Vsi and Vc and is contracted, the formed gap is newly filled with the molten silicon Vsi2, but the pores Vp2 remain.

In (Pattern 5), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vc2 + Vsi2 + Vp2, and carbon particles (Vc2), silicon (Vsi2) and pores (Vp2) remain in the aggregate in addition to SiC. Will be.

(Pattern 6) When the number of carbon particles is smaller than the number of moles of the molten silicon initially impregnated, and the impregnation of the molten silicon into the pores is insufficient (see FIG. 7).
(A)
The gaps between the SiC fibers Vf are filled with the carbon particles Vc and the SiC particles Vsic, but pores Vp are formed in the portion where the carbon particles and the SiC particles are not filled. The amount of Vc is smaller than that of pattern 4.
(B)
The pore Vp is filled with molten silicon, but the Vp is not completely filled, and the pore Vp2 remains in addition to Vsi. (Vp = Vsi + Vp2)
(C)
Vrsic is generated by reaction sintering, and excess silicon Vsi3 remains. Since the generated Vrsic is smaller than the total volume of Vsi and Vc and is contracted, the formed gap is newly filled with the molten silicon Vsi2, but the pores Vp2 remain.

In (Pattern 6), the SiC fiber-reinforced SiC composite material finally becomes Vf + Vsic + Vrsic + Vsi2 + Vsi3 + Vp2, and silicon (Vsi2, Vsi3) and pores (Vp2) remain in the aggregate in addition to SiC. In addition, Vsi2 is the molten silicon impregnated afterwards with the reaction shrinkage, and Vsi3 is the first impregnated molten silicon remaining without participating in the reaction.

The members and pores of the SiC fiber-reinforced SiC composite material obtained by the above-mentioned patterns of the six manufacturing conditions are summarized in Table 1 below.

Here, regardless of any of the patterns 1 to 6 (patterns 1 to 6), volume shrinkage occurs when SiC is generated by reaction sintering, and molten silicon invades the portion where the volume shrinks, and Si (Vsi2). Remains.
Further, when the carbon (graphite) is excessive (patterns 2 and 5), the generated reaction sintered SiC has no fluidity, so that it is difficult to react with the residual carbon and the Si invaded by shrinkage, and the residual silicon (Vsi2). And carbon particles (Vc2) remain together.
When there is an excess of silicon (patterns 3 and 6), Si (Vsi2) that has invaded after reaction sintering and Si (Vsi3) that was originally excessive remain.
Further, in patterns 4 to 6, the molten silicon does not reach the central portion of the aggregate due to the sealing effect of the generated reaction-sintered SiC, and pores remain.

As is clear from Table 1 above, pattern 1 is most desirable, and in addition to SiC, there is only silicon filled in the portion whose volume has shrunk due to reaction sintering. It is a SiC fiber reinforced SiC composite material with excellent heat resistance without leaving pores.

The method for producing an ideal SiC fiber-reinforced SiC composite material as described above will be further considered based on pattern 1.

ρ_Si：溶融シリコン密度
ρ_c：黒鉛真密度
ｕ：スラリー含浸前の骨材の気孔率
Ｖｐ：スラリー含浸後、溶融シリコン含浸前の骨材の気孔率
ｓ：ＳｉＣ粒子と黒鉛粒子の和に対する黒鉛粒子の体積比 In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the volume ratio of graphite particles to the total volume of SiC particles and graphite particles in the slurry is calculated by the following formulas (1) and (2). It is desirable that it is within 10%.

ρ _Si : Molten silicon density ρ _c : Graphite true density u: Porosity of aggregate before slurry impregnation Vp: Porosity of aggregate after slurry impregnation and before molten silicon impregnation s: Graphite for sum of SiC particles and graphite particles Particle volume ratio

The symbols described below are as shown in Table 1.

First, in order to simplify the calculation, the volume ratio t other than the SiC fiber and the SiC particles after the slurry impregnation is defined as the formula (3) in Table 3, and the volume (pores + graphite particles) other than the SiC after the slurry impregnation is defined. The volume ratio k of the graphite particles occupying is defined as the formula (4) in Table 3.

Since the number of moles of the graphite particles and the molten silicon when the silicon is melted is the same, the formula (5) in Table 3 holds. Since the pores are completely replaced by the molten silicon, the formula (6) in Table 3 holds, and the volume ratios of the graphite particles and the silicon particles are used by using the formulas (3), (4) and (6). When (Vc, Vsi) is obtained, equations (7) and (8) are obtained.

When the equation (5) is modified, the equation (9) is obtained. By combining the formulas (7), (8), and (9), the formula (1) described in the claims can be obtained.

The ratio of graphite particles to SiC particles will be examined.
The pores before the slurry impregnation are the sum of Vp which becomes pores after the slurry impregnation, the volume ratio Vc of the filled graphite particles, and the volume ratio Vsic of the filled SiC particles, and the total porosity u is the formula in Table 4. It is represented by (10). Since V _P + V _C + V _SiC + V _f = 1, the equation (10) is simplified as in the equation (11).
The volume ratio s of the graphite particles to the SiC particles in the slurry is defined by the formula (12).

Here, the equation (13) in Table 4 is derived from the equations (7) and (8).
When the equation (11) is transformed and the equation (13) is substituted, the equation (14) is obtained.
Further, by substituting the formulas (13) and (14) into the formula (12), the formula (2) described in the scope of the patent claim is obtained, and the volume ratio of the graphite particles to the sum of the SiC particles and the graphite particles ( Ideal value) s can be determined, and by setting the volume ratio of the graphite particles to the total volume of SiC particles and graphite particles within 10% with respect to s, it is dense and excellent in heat resistance and mechanical strength. A SiC fiber reinforced SiC composite material can be manufactured.

By determining the above numerical values, the appropriate volume ratio of the graphite particles in the slurry can be set. Vp can be calculated from the volume densities of graphite particles and SiC particles contained in the slurry and the porosity before impregnation with the slurry.

The capacitance ratio of the residual silicon Vsi2 at this time can be expressed by the equation (15), and by substituting k of the equation (1) and t obtained by transforming the equation (8) into the equation (15), the equation (16). Substituting k again into equation (16), the porosity (Vp) of the aggregate after impregnation with the slurry and before impregnation with the molten silicon, the true density of the graphite particles (ρc), the density of the molten silicon (ρsi), and the density of SiC. The volume ratio of residual silicon Vsi2 under ideal conditions determined only by (ρsic) is calculated [Equation (17)].

Hereinafter, the production conditions and the like in each step of the method for producing the SiC fiber-reinforced SiC composite material of the present invention will be described.
(1) First Impregnation Step In the first impregnation step in the method for producing a SiC fiber-reinforced SiC composite material of the present invention, an aggregate made of SiC fibers is impregnated with a slurry made of water, SiC particles and graphite particles and dried. do.

The form of the aggregate made of SiC fibers is not particularly limited, and examples thereof include a cloth, a papermaking body, a filament winding body, and a braiding body.

The cloth is woven using strands of ceramic fibers bundled together. The papermaking body is manufactured using short fibers, long fibers, and the like of ceramic fibers. The filament winding body is formed by winding a strand in which ceramic fibers are bundled around a mandrel. In the braiding body, strands are knitted in a spiral direction facing each other to form a cylindrical aggregate.

The number of ceramic fibers used in one strand is not particularly limited, but is, for example, 100 to 5000.

The method for producing an aggregate having a predetermined shape using SiC fibers is not particularly limited, but for example, when a plate-like body having a predetermined thickness is produced by stacking cloths, abstracts, or the like. After stacking multiple pieces of cloth or the like, grip them from both sides using a fixing jig such as a plate made of graphite, and use the CVI method or the like to deposit SiC between the cloth-like bodies, etc. A method of adhering the body to form a plate-shaped aggregate having a predetermined thickness can be adopted.

FIG. 1A is a cross-sectional view schematically showing an example of a fixing jig used for producing a plate-shaped aggregate in the method for producing a SiC fiber-reinforced SiC composite material of the present invention. b) is a perspective view of the fixing jig.

The fixing jig 1 shown in FIGS. 1A and 1B is composed of an upper surface side member 11 and a lower surface side member 12. The laminated cloth-like body 10 is sandwiched between the upper surface side member 11 and the lower surface side member 12, so that the laminated cloth-like body 10 is gripped by the fixing jig 1.

The upper surface side member 11 is a support member arranged on the upper surface side of the laminated cloth-like body 10.
The upper surface side member 11 is a flat plate made of graphite, and has a first main surface 11a on the side in contact with the laminated cloth-like body 10 and a second main surface 11b on the opposite side to the first main surface 11a. The upper surface side member 11 has a plurality of through holes 13 penetrating from the first main surface 11a to the second main surface 11b.

The lower surface side member 12 is a support member arranged on the lower surface side of the laminated cloth-like body 10.
The lower surface side member 12 is also a flat plate made of graphite, and has a first main surface 12a on the side in contact with the laminated cloth-like body 10 and a second main surface 12b on the side opposite to the first main surface 12a. The lower surface side member 12 has a plurality of through holes 14 penetrating from the first main surface 12a to the second main surface 12b.

Although not shown in FIG. 1, the upper surface side member 11 and the lower surface side member 12 are fixed to each other by fixing members such as screws, bolts, and nuts.

In FIG. 1, the upper surface side member 11 is arranged vertically above and the lower surface side member 12 is arranged vertically below, as long as the laminated cloth-like body 10 is sandwiched between the upper surface side member 11 and the lower surface side member 12. The direction is not particularly limited.

After grasping the laminated cloth-like body with a fixing jig as described above, the cloth-like body is placed in a CVD furnace, a SiC layer is formed between the laminated cloth-like bodies by the CVI method, and a plurality of cloth-like bodies are adhered to each other. A flat plate-shaped aggregate having a predetermined thickness is used. Since the fixing jig has a mesh-like through hole, the raw material gas reaches between the multiple cloth-like bodies, and when the fixing jig is removed, the flat-plate-like bone to which the multiple cloth-like bodies are adhered. It becomes a material.

The shape of the aggregate is not limited to the flat plate shape, but is desired by changing the shape of the part gripped by the fixing jig (the part in contact with the laminated cloth-like body or the like) according to the shape of the target aggregate. It is possible to form an aggregate in the shape of.
As a matter of course, even if the above preparation is not performed, if the aggregate made of SiC fiber has a predetermined shape, it can be used as it is as an aggregate.

Next, the aggregate having a predetermined shape prepared as described above is impregnated with a slurry composed of water, SiC particles and graphite particles.
The solid content in the slurry is preferably 50 to 80% by weight.

Since water is less likely to cause aggregation of SiC particles than other solvents, the viscosity of the slurry is less likely to increase, and even at such a high content ratio, the SiC particles and graphite particles in the slurry are satisfactorily placed between the SiC fibers. Can be filled in.

In the first impregnation step of impregnating and drying a slurry composed of water and SiC particles, the main purpose is to fill the SiC particles and the graphite particles between the SiC fibers, and the SiC particles and the graphite particles are filled. It is difficult to fix SiC particles and graphite particles between SiC fibers in the state. Therefore, the SiC particles and the graphite particles filled between the SiC fibers are not sufficiently fixed, and easily fall off from between the SiC fibers. Therefore, if the impregnation step is repeated two or more times, the SiC particles and the graphite particles once filled will flow out. In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the number of times of impregnation of the slurry is set to one, SiC particles and graphite particles can be efficiently filled between the SiC fibers.

The average particle size of the SiC particles in the first impregnation step is preferably 0.1 to 10 μm.
When the average particle size of the SiC particles is within the above range, a slurry having a low viscosity can be obtained with a small amount of water, and the SiC particles can be efficiently filled between the SiC fibers. Further, even in a small void, SiC particles are likely to be filled between the SiC fibers.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the average particle size of the graphite particles is 0.1 to 10 μm.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the average particle size of the graphite particles is 0.1 μm or more, a slurry having low viscosity can be obtained with a small amount of water, and the graphite particles can be efficiently produced. It can be filled between SiC fibers. Further, when the average particle diameter of the graphite particles is 10 μm or less, the graphite particles are likely to be filled inside the voids even if the voids between the SiC fibers are narrow.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, it is desirable that the slurry contains 2 to 5 parts by weight of the dispersant with respect to 100 parts by weight of the total of the SiC particles and the graphite particles.

In the method for producing a SiC fiber-reinforced SiC composite material of the present invention, when the slurry contains 2 parts by weight or more of the dispersant with respect to 100 parts by weight of the total of SiC particles and graphite particles, the SiC particles are sufficiently dispersed and the fluidity is improved. Can be secured. On the other hand, since the dispersant exhibits performance in a small amount, the viscosity of the slurry is not significantly affected even if it is added in excess, but in the method for producing a SiC fiber-reinforced SiC composite material of the present invention, the sum of SiC particles and graphite particles is used. By setting the content to 5% by weight or less with respect to 100 parts by weight, the viscosity of the slurry can be sufficiently reduced with a small amount.

Examples of the dispersant include sodium polycarboxylate, ammonium polycarboxylate, amino alcohol polyphosphate, condensed ammonium naphthalene sulfonate, polyethylene glycol and the like, as well as polyurethane-based and acrylic-based dispersants.

Examples of the impregnation method in the first impregnation step include dipping, spraying, coating, coater, vacuum pressure impregnation, and the like, but any method may be used.
In the vacuum pressure impregnation method, first, an aggregate made of SiC fibers is immersed in a slurry in a container in which a slurry made of water, SiC particles and graphite particles is charged. Subsequently, the container in which the aggregate is immersed is carried into the pressure vessel, and once vacuumed, the gas existing inside the SiC fiber or the like is removed, and then pressure is applied to make SiC between the SiC fibers or on the surface thereof. Fill the particles.

Then, the aggregate impregnated with SiC particles and graphite on the inside and its surface is dried at, for example, 60 to 120 ° C. for 0.5 to 3 hours to remove water.

(2) Second Impregnation Step In the second impregnation step in the method for producing a SiC fiber-reinforced SiC composite material of the present invention, high-temperature molten silicon is impregnated after the first impregnation step. Specifically, an aggregate made of SiC fibers filled with graphite particles and SiC particles is immersed in the molten silicon through a first impregnation step. The temperature of the molten silicon at this time is preferably 1420 to 1500 ° C. When the molten silicon penetrates between the SiC fibers, the filled graphite particles react with the molten silicon to form reaction-sintered SiC.

Since the reaction-sintered SiC produced by the reaction sintering becomes smaller than the total capacity of the pores and the graphite particles and shrinks, the molten silicon further penetrates into the space formed by the shrinkage, and the SiC fiber-reinforced SiC composite material is manufactured. Will be done. In the above step, the graphite particles filled inside are completely consumed, and the amount of silicon that invades the space formed by the shrinkage after the reaction is set to be as small as possible, so that it is dense and heat resistant. , A SiC fiber reinforced SiC composite material having high mechanical strength can be obtained.

(Example)
Hereinafter, specific examples for explaining the present invention more specifically will be shown, but the present invention is not limited to these examples.

(Example 1)
A plain weave cloth using SiC fibers was prepared. As the cloth made of SiC fiber, Tyranno SA manufactured by Ube Kosan Co., Ltd. was used. The thickness of the SiC fiber was 10 μm, and the number of filaments in the fiber bundle was 800. It was carried into a CVD furnace in a cloth state, and the surface of the SiC fiber was coated with a pyrolytic carbon and a CVD-SiC layer. The pyrolytic carbon layer formed on the surface of the SiC fiber plays a role of preventing the matrix made of SiC formed in the subsequent step from being integrated with the SiC fiber. The thickness of the obtained pyrolytic carbon layer was 420 nm.
Specifically, seven plain weave cloths are laminated, and the cloth laminated between the upper surface side member and the lower surface side member is grasped by using the fixing jigs shown in FIGS. 1 (a) and 1 (b), and then the laminated cloth is grasped. It was placed in a CVD furnace, and a pyrolytic carbon layer and a SiC layer were formed in this order between the cloth-like bodies laminated by the CVI method, and a plurality of cloth-like bodies were bonded to each other to form an aggregate. The porosity of the aggregate thus obtained was 70%.

Next, it is assumed that the obtained aggregate is impregnated with a slurry consisting of carbon (particles) and SiC particles in the first impregnation step (porosity 10%), and further impregnated with molten silicon in the second impregnation step. And simulated.

(First impregnation step)
The aggregate prepared by the above method is impregnated with a slurry composed of SiC particles, graphite particles and water. The slurry is composed of water, graphite particles (true density 2.10 g / cm ³ ), and SiC particles (true density 3.20 g / cm ³ ). The true density of molten silicon is 2.57 g / cm ³ .
Based on the above conditions, the volume ratio of graphite particles to the sum of SiC particles and graphite particles in the slurry when the amount of residual silicon is the smallest (s = 0.0874), and the volume ratio of residual silicon (Vsi2 = 0. 03772 ) was obtained. (Table 5)

In addition, assuming the second impregnation step, in order to confirm the impregnation property of the molten silicon, water, graphite particles (Nika beads average particle size 4 μm made by Nippon Carbon), SiC particles (β-SiC average particle size 0. A verification test was conducted by impregnating a solid material obtained by impregnating a dried solid matter of 35 μm) with molten silicon. (Verification test 1)
The mixing ratio at that time was carbon (graphite) particles: SiC particles = 1: 1 (vol), and the impregnation conditions were 1450 ° C. for 1 hour under a vacuum of 0.1 torr or less. (Table 6)

(Comparative Example 1)
In Comparative Example 1, a simulation and a verification test were similarly performed using carbon particles (Carbon Black N991: True Density 1.84 manufactured by Cancarb) instead of the graphite particles of the Example.
Based on the above conditions, the volume ratio of graphite particles to the sum of SiC particles and graphite particles in the slurry when the amount of residual silicon is the smallest (s = 0.0998), and the volume ratio of residual silicon (Vsi2 = 0. 04513 ) was obtained. The conditions are shown in Table 5.

Further, assuming the second impregnation step, in order to confirm the impregnation property of the molten silicon, water, carbon particles (Carbon Black N991: average particle size 0.28 μm manufactured by Cancarb), and SiC particles (β-SiC manufactured by Superior Graphite). A solid matter having an average particle size of 0.35 μm) was impregnated with molten silicon and a verification test was conducted. (Verification test 2)
The mixing ratio at that time was carbon particles: SiC particles = 1: 1 (vol), and the impregnation conditions were 1450 ° C. for 1 hour under a vacuum of 0.1 torr or less. (Table 6)

By comparing the numerical values of Example 1 and Comparative Example 1 with the simulation values, it was confirmed that the residual silicon was reduced more efficiently in the example.
Further, by comparing the cross sections of the samples obtained in the verification test, in the verification test 1 using graphite particles, the molten silicon was uniformly impregnated, whereas in the verification test 2, the verification test 2 using carbon particles (carbon black) was used. Then, when the molten silicon was impregnated, carbon aggregates were confirmed probably because the graphite was rapidly formed, and it was confirmed that the molten silicon was not uniformly impregnated.

Based on the above, a first impregnation step of impregnating an aggregate made of SiC fibers with a slurry of water, SiC particles, and graphite particles and drying the aggregate, and a second impregnation step of impregnating molten silicon after the first impregnation step. It is considered that a method for producing a SiC fiber-reinforced SiC composite material having few pores, residual silicon, and a small amount of residual carbon can be obtained by the process and the method for producing the SiC fiber-reinforced SiC composite material.

1 Fixing jig 10 Laminated cloth-like body 11 Upper surface side member 11a First main surface of upper surface side member 11b Second main surface of upper surface side member 12 Lower surface side member 12a First main surface of lower surface side member 12b First main surface of lower surface side member 2 Main surface 13,14 Through hole

Claims (8)

The first impregnation step of impregnating an aggregate made of SiC fibers with a slurry of water, SiC particles, and graphite particles and drying the aggregate.
After the first impregnation step, a second impregnation step of impregnating molten silicon and a second impregnation step,
A method for producing a SiC fiber-reinforced SiC composite material, which comprises. The method for producing a SiC fiber-reinforced SiC composite material according to claim 1, wherein the solid content in the slurry is 50 to 80% by weight. The method for producing a SiC fiber-reinforced SiC composite material according to claim 1 or 2, wherein the true density of graphite particles in the slurry is 2.05 to 2.26 g / cm ³ . The volume ratio of the graphite particles to the total volume of the SiC particles and the graphite particles in the slurry is within 10% with respect to the following s calculated by the following formulas (1) and (2), according to claims 1 to 3. The method for producing a SiC fiber-reinforced SiC composite material according to any one of the above.

ρ _Si : Molten silicon density ρ _c : Graphite true density u: Porosity of aggregate before slurry impregnation Vp: Porosity of aggregate after slurry impregnation and before molten silicon impregnation s: Graphite for sum of SiC particles and graphite particles Particle volume ratio The method for producing a SiC fiber-reinforced SiC composite material according to any one of claims 1 to 4, wherein the number of times the slurry is impregnated in the first impregnation step is one. The method for producing a SiC fiber-reinforced SiC composite material according to any one of claims 1 to 5, wherein the average particle size of the SiC particles is 0.1 to 10 μm. The method for producing a SiC fiber-reinforced SiC composite material according to any one of claims 1 to 6, wherein the average particle size of the graphite particles is 0.1 to 10 μm. The method for producing a SiC fiber-reinforced SiC composite material according to any one of claims 1 to 7, wherein the slurry contains 2 to 5 parts by weight of a total of 100 parts by weight of SiC particles and graphite particles.

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