JP7495280B2 - Manufacturing method of SiC/SiC composite material - Google Patents

Description

The present invention relates to a SiC/SiC composite reinforced with SiC fibers and a method for manufacturing the same.

SiC/SiC composite materials have heat resistance, strength, and toughness, and are therefore expected to be used in a variety of fields, such as in components for high-temperature reactors, nuclear reactors, and gas turbines.
A SiC/SiC composite is a component that combines a base material (matrix) made of SiC with aggregate containing SiC fibers. Although SiC used as the base material has heat resistance and strength, it is a brittle material due to its high elastic modulus. Therefore, various SiC/SiC composites have been proposed that improve the brittleness of the ceramic base material by combining ceramic fibers as aggregate with the ceramic base material (matrix).

One method for manufacturing such SiC/SiC composites is the polymer infiltration and pyrolysis (PIP) method. The PIP method involves impregnating an aggregate made of SiC fibers with a SiC precursor and then firing it. With the PIP method, the aggregate is impregnated with a liquid SiC precursor, so that even if the aggregate is thick, the liquid SiC precursor can penetrate to the inside, and a SiC/SiC composite with the desired thickness can be obtained.

For example, Patent Document 1 proposes a method for producing a SiC fiber-reinforced SiC composite material, which is characterized by having a first impregnation step in which aggregate made of SiC fibers is impregnated with a slurry made of water and SiC particles and dried, and a second impregnation step in which, after the first impregnation step, the aggregate is impregnated with a SiC precursor solution made of a SiC precursor and an organic solvent, dried, and fired. Patent Document 1 describes that a dense SiC fiber-reinforced SiC composite material (SiC/SiC composite) can be obtained by a simple method.

JP 2019-172503 A

The high heat resistance of SiC/SiC composites is due to the heat resistance of SiC itself and the action of a thin oxide film ( _SiO2 film) formed on the surface of the SiC/SiC composite. For this reason, for SiC/SiC composites manufactured in an environment in which a _SiO2 film cannot be formed, such as a dilute oxygen atmosphere, an environmentally resistant coating different from the _SiO2 film is formed to improve the oxidation resistance, thereby improving the performance.

However, while the technology described in Patent Document 1 provides a dense SiC/SiC composite material in a simple manner, the increased density results in a smooth surface, and when an environmentally resistant coating is formed, sufficient adhesion cannot be obtained between the coating and the surface of the SiC/SiC composite material.

In view of the above problems, the present invention aims to provide a SiC/SiC composite material that can obtain a desired strength and has excellent adhesion to a coating formed on the surface, and a method for manufacturing the same.

The above object is achieved by the SiC/SiC composite material according to the present invention as described below in (1).

(1) A method for producing a composite material comprising: an aggregate containing SiC fibers; SiC pulverized particles having corners; and a sintered body of a SiC precursor that bonds adjacent SiC pulverized particles to each other;
The bulk density is 2.0 g/cm ³ or more and 2.8 g/cm ³ or less,
A SiC/SiC composite material characterized in that voids are formed in areas other than the aggregate, the SiC crushed particles, and the sintered body of the SiC precursor, and corners of the SiC crushed particles protrude into the voids.

In the SiC/SiC composite of the present invention, the corners of the SiC crushed particles protrude into the voids, increasing the surface area of the voids and providing an anchor effect due to the corners, thereby increasing the bonding strength with the environmentally resistant coating formed on the surface of the SiC/SiC composite.
In addition, since the bulk density is appropriately set, the desired strength can be obtained and the amount of voids can be secured, thereby ensuring the bonding strength with the environmentally resistant coating formed on the surface of the SiC/SiC composite.

The SiC/SiC composite material according to the present invention is preferably as follows (2):

(2) The SiC/SiC composite material described in (1) is characterized in that the void portion has a recess that is recessed at an acute angle in a cross-sectional view.

If the void has a concave portion that is recessed at an acute angle in cross section, when an environmentally resistant coating is formed on the surface of the SiC/SiC composite, the material of the environmentally resistant coating will penetrate into the concave portion, providing an anchor effect and further improving the bonding strength between the surface of the SiC/SiC composite and the environmentally resistant coating.

The above object is achieved by the manufacturing method of the SiC/SiC composite material according to the present invention as described below in (3).

(3) an impregnation step of impregnating an aggregate containing SiC fibers with a slurry containing water, crushed SiC particles having corners, and polycarbosilane particles to obtain an impregnated body;
A drying step of drying the impregnated body to obtain a dried body;
A firing step of heating and firing the dried body,
The method for producing a SiC/SiC composite material is characterized in that the firing process is a process for obtaining a fired body of a SiC precursor that bonds adjacent SiC crushed particles to each other after melting and polymerizing the polycarbosilane particles.

According to the method for producing a SiC/SiC composite of the present invention, since the polycarbosilane particles, which are the SiC precursor, are not dissolved in the slurry, in the impregnation process, adjacent SiC crushed particles are selectively held at the contact points close to each other while remaining in particulate form. Then, in the firing process, the polycarbosilane particles are melted while remaining in particulate form, polymerized, and converted into ceramics. In the SiC/SiC composite after firing, the fired body of the SiC precursor firmly bonds adjacent SiC crushed particles, and multiple voids are generated on the surface and inside. In addition, the corners of the SiC crushed particles that are not covered by the polycarbosilane particles protrude into the voids. Therefore, the surface area of the voids is increased, and an anchor effect is obtained by the corners, so that a SiC/SiC composite with excellent bonding strength with the environmental resistance coating can be produced.

The manufacturing method of the SiC/SiC composite material according to the present invention is preferably the following (4) to (8).

(4) The method for producing a SiC/SiC composite material described in (3) is characterized in that the number average molecular weight of the polycarbosilane constituting the polycarbosilane particles is 800 or more and 3500 or less.

When the number-average molecular weight of polycarbosilane is adjusted to the above range, the fluidity can be controlled, increasing the yield of the SiC precursor and selectively bonding the contact points with the crushed SiC particles, thereby increasing the strength of the SiC/SiC composite.

(5) The method for producing a SiC/SiC composite material according to (3) or (4), characterized in that the average particle size of the polycarbosilane particles is 1 μm or more and 100 μm or less.

When the average particle size of the polycarbosilane particles is adjusted to fall within the above range, they can be easily dispersed in water, making it easy to obtain a uniform slurry, and also making it easier to impregnate the slurry into the interior of the aggregate during the impregnation process.

(6) A method for producing a SiC/SiC composite material according to any one of (3) to (5), characterized in that the average particle size of the SiC crushed particles is 0.1 μm or more and 5.0 μm or less.

When the average particle size of the crushed SiC particles contained in the slurry is adjusted to the above range, a small amount of water can be used to obtain a slurry with a viscosity that is easy to impregnate into the aggregate, which increases the yield after the firing process and makes it easier to impregnate the slurry into the inside of the aggregate during the impregnation process.

(7) A method for producing a SiC/SiC composite material according to any one of (3) to (6), characterized in that the content of the polycarbosilane particles relative to the mass of the slurry is 5 mass% or more and 30 mass% or less.

When the content of polycarbosilane particles relative to the mass of the slurry is adjusted to the above range, adjacent crushed SiC particles can be bonded with sufficient bonding strength, and the corners of the crushed SiC particles can be reliably exposed, making it easier to form corners that protrude toward the voids.

(8) A method for producing a SiC/SiC composite material according to any one of (3) to (7), characterized in that the content of the SiC crushed particles relative to the mass of the slurry is 10 mass% or more and 70 mass% or less.

When the content of SiC crushed particles relative to the mass of the slurry is adjusted to the above range, the viscosity of the slurry can be reduced, making it easier to impregnate the inside of the aggregate with the slurry, and the content of polycarbosilane particles can be adjusted relatively, so that the yield of the matrix precursor can be increased and corners protruding into the voids can be sufficiently formed.

In the SiC/SiC composite material of the present invention, the corners of the SiC crushed particles protrude into the voids, increasing the surface area of the voids and providing an anchor effect due to the corners, thereby increasing the bonding strength with the environmental resistant coating formed on the surface of the SiC/SiC composite material.
In addition, since the bulk density is appropriately set, the desired strength can be obtained and the amount of voids can be secured, thereby ensuring the bonding strength with the environmentally resistant coating formed on the surface of the SiC/SiC composite.
According to the method for producing a SiC/SiC composite material of the present invention, the polycarbosilane particles are fired while still in the form of particles, and adjacent crushed SiC particles are firmly bonded to each other, and a plurality of voids are generated on the surface and inside. In addition, the corners of the SiC crushed particles that are not covered by the polycarbosilane particles protrude into the voids, so that the surface area of the voids is increased and an anchor effect is obtained by the corners, making it possible to produce a SiC/SiC composite material with excellent bonding strength with the environmental resistant coating.

FIG. 1 is a cross-sectional view that typically illustrates a method for producing a SiC/SiC composite material according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the state of gaps in the aggregate of FIG. 1 in an enlarged manner in the order of steps. FIG. 3 is a schematic diagram showing, in enlarged scale, the state of gaps in aggregate in the order of steps in a conventional method for producing a SiC/SiC composite material. FIG. 4 is a photograph showing a cross section of the SiC/SiC composite material obtained by the manufacturing method according to Example 1. FIG. 5 is a photograph showing a cross section of a SiC/SiC composite material obtained by the manufacturing method according to Comparative Example 1. FIG. 6 is a schematic diagram showing, in enlarged scale, the state of gaps in the aggregate in the order of steps in the manufacturing method of the SiC/SiC composite material of Comparative Example 2. FIG. 7 is a photograph showing a cross section of a SiC/SiC composite material obtained by the manufacturing method according to Comparative Example 2.

The inventors conducted extensive research to obtain a SiC/SiC composite material and a method for producing the same that can obtain the desired strength and have excellent adhesion to the coating formed on the surface. As a result, they discovered that if the matrix region of the SiC/SiC composite material excluding the aggregate has voids and the corners of the SiC crushed particles protrude into these voids, an anchor effect is obtained by the corners when a coating is formed on the surface, improving adhesion between the coating and the surface of the SiC/SiC composite material. They also discovered that the desired strength can be obtained in the SiC/SiC composite material by appropriately setting the bulk density.

The present invention is based on these findings, and first, a method for producing a SiC/SiC composite material according to an embodiment of the present invention will be described in detail below.
The present invention is not limited to the embodiments described below, and can be modified as desired without departing from the scope of the present invention. In addition, in this specification, the term "to" indicating a range of values is used to mean that the values before and after the range are included as the lower and upper limits.

[Method of manufacturing SiC/SiC composite material]
Fig. 1 is a cross-sectional view showing a method for producing a SiC/SiC composite according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing the state of gaps in the aggregate in Fig. 1 in an enlarged manner in the order of steps. The schematic diagrams shown in Fig. 2(a) to Fig. 2(d) correspond to the regions in Fig. 1(a) to Fig. 1(d) excluding the aggregate, respectively.

<Preparation of aggregate>
As shown in Fig. 1(a), an aggregate 2 is prepared. The aggregate 2 is constructed by weaving strands 5, which are bundles of a plurality of SiC fibers 4, as warp and weft threads to form a woven fabric 6, and then stacking a plurality of the obtained woven fabrics 6. Note that, as shown in Fig. 2(a), there are gaps 2a inside the aggregate 2.

<Impregnation process>
Next, as shown in Fig. 1(b) and Fig. 2(b), the aggregate 2 is impregnated with the slurry 1a to obtain an impregnated body 3 in which the gaps 2a are filled with the slurry 1a. The slurry 1a is obtained by dispersing SiC crushed particles 11 and powdered polycarbosilane particles 12 in water 13 to form a slurry. The SiC crushed particles 11 are obtained by crushing SiC particles, and the corners 11a are formed by the crushing. The polycarbosilane particles 12 may be particles containing polycarbosilane as the main component and containing alumina, _SiO2 , etc., or may be particles consisting of only polycarbosilane.
In this embodiment, the content of the SiC pulverized particles 11 relative to the mass of the slurry 1a is, for example, 60 mass%, the average particle diameter is, for example, 0.6 μm, and the content of the polycarbosilane particles 12 relative to the mass of the slurry 1a is, for example, 20 mass%, the average particle diameter is, for example, 10 μm, and the number average molecular weight of polycarbosilane is, for example, 3,500.

As a method for impregnating the slurry 1a into the inside of the aggregate 2, it is preferable to use the reduced pressure pressure impregnation method, in which the aggregate 2 is placed in a vacuum atmosphere, the gas inside the aggregate 2 is removed, and then the slurry 1a is permeated into the inside of the aggregate 2 by applying pressure. By applying the reduced pressure pressure impregnation method, the slurry 1a can be easily impregnated into the inside of the aggregate 2 without leaving any gaps.

<Drying process>
1(c) and 2(c), the obtained impregnated body 3 is heated at a heating rate of, for example, 1° C./min, and then heated at a temperature of 80° C. for 3 hours to evaporate the water 13 in the slurry 1a impregnated in the aggregate 2, thereby obtaining a dried body 7. In the region of the dried body 7 other than the aggregate 2, a mixture 1b of SiC crushed particles 11 and polycarbosilane particles 12 exists, and voids 14 are formed in the other regions.
The heating conditions in the drying step are not particularly limited as long as the temperature is such that the water 13 can be evaporated. For example, the heating temperature may be 80 to 150° C. for 1 to 10 hours.

<Firing process>
Next, as shown in Fig. 1(d) and Fig. 2(d), the dried body 7 is heated to 1200°C at a heating rate of, for example, 200°C/hour, and then held for 1 hour to sinter the polycarbosilane particles 12, thereby producing a SiC/SiC composite material 8. This sintering process melts and polymerizes the polycarbosilane particles 12, forming a sintered body 12a of the SiC precursor that bonds adjacent SiC pulverized particles 11, and a SiC matrix 1c having voids 14 is formed. In addition, the voids 14 are formed in the SiC/SiC composite material 8 obtained by this sintering process. Furthermore, in the voids 14, the corners 11a of the SiC pulverized particles 11 are exposed and protrude, forming recesses 14a that are recessed at acute angles in cross-sectional view.

Next, in order to explain in more detail the effects of the manufacturing method for the SiC/SiC composite material according to this embodiment, a conventional manufacturing method for the SiC/SiC composite material will be described below with reference to FIG. 3. FIG. 3 is a schematic diagram showing the gaps in the aggregate in the order of process steps in the conventional manufacturing method for the SiC/SiC composite material. In FIG. 3, parts that are the same as or equivalent to the embodiment shown in FIG. 2 above are given the same reference numerals in the drawing, and their description will be omitted or simplified.

<Preparation of aggregate>
The structure of the aggregate is the same as that of the above embodiment, and has gaps 2a as shown in FIG.

<Impregnation process>
Next, as shown in Fig. 3(b), the aggregate is impregnated with the slurry by vacuum pressure impregnation to obtain an impregnated body. The slurry used is a mixture of a solution 23 in which polycarbosilane is dissolved in xylene and the SiC crushed particles 11. As in the above embodiment, the SiC crushed particles 11 have corners 11a.

<Drying process>
Next, as shown in Fig. 3(c), the impregnated body is dried in the same manner as in the above embodiment. During this drying process, bubbles 24 made of xylene gas are generated from inside the aggregate, and a highly viscous dissolving liquid 23a is generated and ejected to the outside of the aggregate.

<Curing process>
3D, the polycarbosilane in the solution 23 impregnated in the aggregate is hardened to obtain a hardened body, whereby the polycarbosilane becomes a hardened SiC precursor 23b.

<Firing process>
3(e), the hardened body is fired in the same manner as in the firing step in the above embodiment, whereby the SiC precursor 23b is converted into a ceramic, a SiC matrix 25 is formed, and a SiC/SiC composite material is obtained.

As described above, in the conventional manufacturing method, a slurry is used in which the solution 23 in which polycarbosilane is dissolved in xylene is mixed with the SiC pulverized particles 11. The solution 23 is gelled in the curing step while covering the corners 11a of the SiC pulverized particles 11, so that in the obtained SiC/SiC composite material, the corners 11a of the SiC pulverized particles 11 are covered with the SiC matrix 25.
Furthermore, the bubbles 24 generated in the drying process remain in the subsequent hardening and firing processes to form a matrix, so that in the obtained SiC/SiC composite material, the bubbles 24 have an approximately spherical surface.

As a result, the surface of the obtained SiC/SiC composite is almost smooth, and when an environmentally resistant coating is formed on this surface, the adhesion between the SiC/SiC composite and the environmentally resistant coating is poor, resulting in the coating being easily peeled off.
In the present invention, the environmentally resistant coating refers to a coating having various functions, such as a coating having heat resistance or a coating having oxidation resistance, and the functions are not particularly limited.

In contrast, in the present embodiment, a slurry 1a containing water 13, SiC crushed particles 11 having corners 11a, and polycarbosilane particles 12 is used, and the polycarbosilane particles 12 are not dissolved in the slurry 1a. Therefore, the polycarbosilane particles 12, which are precursors of the SiC matrix, are impregnated into the gaps 2a of the aggregate 2 while remaining in the form of particles, and then selectively held at the contact points where adjacent SiC crushed particles 11 are close to each other.
That is, according to the conventional manufacturing method, polycarbosilane is dissolved in xylene and impregnated into the aggregate, so that the polycarbosilane covers the entire surface of the SiC crushed particles 11, but in this embodiment, the polycarbosilane particles 12 do not wet the entire surface of the SiC crushed particles 11.

Then, in the firing process after the drying process, the particulate polycarbosilane particles 12, which are held at the contact points where the SiC crushed particles 11 are close to each other, melt while still in particulate form and polymerize to form a ceramic, thereby forming a fired SiC precursor body 12a. As a result, in the fired SiC/SiC composite material 8, the fired SiC precursor body 12a firmly bonds adjacent SiC crushed particles 11, and multiple voids 14 are generated on the surface and inside. In addition, the corners 11a of the SiC crushed particles 11 that are not covered by the polycarbosilane particles 12 protrude from the voids 14, increasing the surface area.

When an environmentally resistant coating is formed on the surface of the SiC/SiC composite 8 configured in this manner, the material of the environmentally resistant coating penetrates into the surface of the SiC/SiC composite 8 and the voids 14 near the surface. At this time, a wide contact area can be obtained between the inner surface of the voids 14 and the environmentally resistant coating, and an anchor effect can be obtained by the corners 11a inside the voids 14. Therefore, the adhesion between the surface of the SiC/SiC composite 8 and the environmentally resistant coating can be improved.

In this embodiment, the gap 14 has a recess 14a that is recessed at an acute angle in cross section.
When such recesses 14a are formed, when an environmentally resistant coating is formed on the surface of the SiC/SiC composite 8, the material of the environmentally resistant coating penetrates into the recesses 14a of the voids 14, and as with the corners 11a, an anchor effect is obtained by the recesses 14a, thereby improving the bonding strength between the surface of the SiC/SiC composite 8 and the environmentally resistant coating.

Next, the slurry 1a that can be used in the manufacturing method of this embodiment, the SiC crushed particles 11 and polycarbosilane particles 12 in the slurry 1a, the SiC fibers 4 that make up the aggregate 2, and the shape of the aggregate 2 will be described in detail below.

(Slurry 1a)
The slurry 1a is obtained by mixing and dispersing water 13, crushed SiC particles 11, and polycarbosilane particles 12. Since the polycarbosilane particles 12 are dispersed in water to form a slurry, the viscosity of the slurry 1a does not increase easily even if a polycarbosilane with a large molecular weight is used, and the effect of temperature and concentration on the viscosity is small, so that the slurry 1a can be stably impregnated into the aggregate 2.

In this embodiment, the content of the SiC pulverized particles 11 relative to the mass of the slurry 1a is not particularly limited, but is preferably, for example, 10 mass % or more and 70 mass % or less.
By setting the content of the SiC crushed particles 11 relative to the mass of the slurry 1a to 70 mass % or less, the viscosity of the slurry 1a can be reduced, and the slurry 1a can be easily impregnated into the inside of the aggregate 2. On the other hand, by setting the content of the SiC crushed particles 11 relative to the mass of the slurry 1a to 10 mass % or more, the content of the polycarbosilane particles 12, the weight of which is reduced by firing, can be reduced, so that the yield of the matrix precursor can be increased and the corners 11a protruding into the voids 14 can be sufficiently formed.

In this embodiment, the content of the polycarbosilane particles 12 relative to the mass of the slurry 1a is not particularly limited, but is preferably, for example, 5 mass % or more and 30 mass % or less.
By making the content of the polycarbosilane particles 12 to be 5% by mass or more relative to the mass of the slurry 1a, it is possible to bond adjacent SiC crushed particles 11 with sufficient bonding strength. On the other hand, if the content of the polycarbosilane to the mass of the slurry 1a is 30% by mass or less, it is possible to reliably expose the corners 11a of the SiC crushed particles 11, and it is possible to easily form the corners 11a protruding toward the voids 14.

(SiC pulverized particles 11)
The average particle size of the SiC crushed particles 11 contained in the slurry 1a is not particularly limited, but it is preferable to use SiC crushed particles 11 having an average particle size of, for example, 0.1 μm or more and 10.0 μm or less. If the average particle size of the SiC crushed particles 11 is 0.1 μm or more, the specific surface area can be reduced, so that a small amount of water 13 can be used to obtain a slurry 1a with a viscosity that allows easy impregnation into the aggregate 2, and the yield after the firing process can be increased.
On the other hand, when the average particle diameter of the SiC crushed particles 11 is 10.0 μm or less, the slurry 1 a can be easily impregnated into the inside of the aggregate 2 without being trapped by the SiC fibers 4 constituting the aggregate 2 in the impregnation process.
The average particle size of the SiC pulverized particles 11 can be measured by using a laser diffraction type particle size distribution measuring device.

(Polycarbosilane Particles 12)
The number average molecular weight of the polycarbosilane constituting the polycarbosilane particles 12 in the slurry 1a is not particularly limited, but it is preferable to use, for example, polycarbosilane having a number average molecular weight of 800 to 3500. When the number average molecular weight of the polycarbosilane is 800 or more, even if the polycarbosilane starts to flow when heated, it does not become so fluid that it flows out of the aggregate 2, so that the yield of the SiC precursor can be increased and the contact parts with the SiC crushed particles 11 can be selectively bonded.
On the other hand, if the number average molecular weight of polycarbosilane is 3,500 or less, sufficient fluidity can be ensured to bond adjacent SiC crushed particles 11 when heated and melted, so that the SiC crushed particles 11 can be firmly bonded to each other and the strength of the SiC/SiC composite material 8 can be increased.
The number average molecular weight can be analyzed by gel permeation chromatography (GPC) using xylene as a solvent.

In this embodiment, the average particle diameter of the polycarbosilane particles 12 is not particularly limited, but it is preferable to use polycarbosilane particles 12 having an average particle diameter of, for example, 1 μm or more and 100 μm or less. When the average particle diameter of the polycarbosilane particles 12 is 1 μm or more, the polycarbosilane particles 12 can be easily dispersed in the water 13, and a uniform slurry 1a can be easily obtained. On the other hand, when the average particle diameter of the polycarbosilane particles 12 is 100 μm or less, the slurry 1a can be easily impregnated into the inside of the aggregate 2 without being trapped by the SiC fibers 4 constituting the aggregate 2 in the impregnation step.
The average particle size of the polycarbosilane particles 12 can be measured using a laser diffraction particle size distribution measuring device.

The slurry 1a that can be used in the present invention may be composed only of the SiC pulverized particles 11, the polycarbosilane particles 12, and the water 13, but may further contain a dispersant. When the slurry 1a contains a dispersant, the SiC pulverized particles 11 and the polycarbosilane particles 12 can be uniformly dispersed when mixed with the water 13.
Examples of the dispersant include sodium polycarboxylate, ammonium polycarboxylate, amino alcohol polyphosphate, condensed ammonium naphthalenesulfonate, polyethylene glycol, as well as polyurethane-based and acrylic-based dispersants.

The slurry 1a may contain liquids other than water 13, but in the present invention, it is important that the corners 11a of the SiC crushed particles 11 protrude into the voids 14, and a liquid that does not dissolve the polycarbosilane particles 12 can be selected to prevent the corners 11a from being covered by the SiC matrix.

(SiC fiber)
The thickness of the SiC fibers 4 is not particularly limited, but for example, those having an average diameter of 7.5 to 15 μm can be used. If the thickness of the SiC fibers 4 is 7.5 μm or more, even if there are scratches or defects on the surface, a decrease in strength can be prevented, and a high-strength SiC fiber 4 can be obtained. On the other hand, if the thickness of the SiC fibers 4 is 15 μm or less, the tensile stress generated on the surface when the fibers are bent can be reduced, and a high-strength SiC fiber 4 can be obtained.

Furthermore, in the present invention, in addition to the above-mentioned SiC fibers 4, SiC fibers having a coating layer on the surface may be used as the fibers forming the aggregate 2. The coating layer may be a coating layer made of a component different from SiC, such as a carbon layer or a BN layer, or a coating layer made of SiC may be formed on the surface of the SiC fiber on top of a coating layer made of a component different from SiC.

These coating layers may be formed by any method, including, but not limited to, CVI (vapor phase impregnation) or a method in which the SiC fibers are impregnated with a dilute precursor diluted with a solvent, followed by drying, curing, and firing. When using a precursor to form the coating layer, it is not necessary to ensure an amount of impregnation sufficient to form a matrix. By using such a coating layer, the shape of the aggregate can be fixed in advance. Furthermore, forming a coating layer of a different component can prevent the SiC fibers from integrating with the matrix.

(aggregate)
The form of the aggregate 2 that can be used in this embodiment is not particularly limited, and various forms of aggregate 2 can be used. For example, aggregates using continuous fibers such as a cloth (woven fabric 6) obtained by weaving a strand formed by bundling a plurality of SiC fibers 4, a filament winding body obtained by winding the above-mentioned strand around a mandrel, and a braiding body in which the above-mentioned strand is woven into a braided cord can be used as the aggregate, as well as a paper body, a nonwoven fabric, a mat, and the like obtained by laminating short fibers.
The woven fabric 6 may be of any weaving type, including, but not limited to, plain weave, twill weave, satin weave, and 3D weave.

The number of SiC fibers 4 per strand is not particularly limited, but can be, for example, 100 to 10,000. Within the above range, the strands will have an appropriate thickness, so when they are used to form, for example, a woven fabric 6, the desired thickness can be achieved.

[SiC/SiC composite material]
The present invention also relates to a SiC/SiC composite obtained by the method for producing a SiC/SiC composite according to the above embodiment.
As described above, the SiC/SiC composite material 8 includes the aggregate 2 containing SiC fibers, the SiC crushed particles 11 having corners 11a, and the sintered bodies 12a of the SiC precursor that bond adjacent SiC crushed particles 11. Also, voids 14 are formed in the regions excluding the SiC crushed particles 11 and the sintered bodies 12a of the SiC precursor, and the corners 11a of the SiC crushed particles 11 protrude into the voids 14.

The effects obtained by the configuration of the SiC/SiC composite material 8 are the same as those described in the manufacturing method of the SiC/SiC composite material 8. That is, the corners 11a are exposed in the voids 14, and the corners 11a protrude toward the voids 14, increasing the surface area of the voids 14 and providing an anchor effect due to the corners 11a, thereby increasing the bonding strength with the environmentally resistant coating formed on the surface of the SiC/SiC composite material 8.

In the present invention, it is important to appropriately set the bulk density of the SiC/SiC composite 8. The difference between the bulk density of the SiC/SiC composite 8 and the true density of SiC corresponds to the amount of voids 14 in the SiC/SiC composite 8. In other words, a higher bulk density indicates a denser SiC/SiC composite.
If the bulk density of the SiC/SiC composite is less than 2.0 g/ ^cm3 , the strength is reduced due to a decrease in denseness, making it difficult to use as a high-temperature furnace component or structural material. On the other hand, if the bulk density exceeds 2.8 g/ ^cm3 , the amount of voids 14 is reduced, and the effect of increasing the bonding strength of the environmentally resistant coating to the surface of the SiC/SiC composite cannot be obtained.
Therefore, the bulk density of the SiC/SiC composite material 8 is set to be 2.0 g/cm ³ or more and 2.8 g/cm ³ or less.

In addition, the bulk density of the SiC/SiC composite material 8 can be adjusted to the above range by adjusting the content of the SiC crushed particles 11 and the content of polycarbosilane in the slurry 1a, etc.

Furthermore, in this embodiment, the void 14 formed in the SiC/SiC composite 8 preferably has a recess 14a recessed at an acute angle in cross section. The effect obtained by the recess 14a is as described above, and when an environmentally resistant coating is formed on the surface of the SiC/SiC composite 8, the material of the environmentally resistant coating penetrates into the recess 14a, providing an anchor effect and improving the bonding strength between the surface of the SiC/SiC composite 8 and the environmentally resistant coating.

The manufacturing method according to the present embodiment described above can be used to manufacture the SiC/SiC composite material according to the present embodiment described above, but there are no particular limitations on the manufacturing conditions as long as the desired structure can be obtained.

Below, examples of the SiC/SiC composite material according to this embodiment are described, but the present invention is not limited to these examples.

1 and 2, a SiC/SiC composite material of Example 1 was produced, and a SiC/SiC composite material of Comparative Example 1 and Comparative Example 2 was produced by a conventional production method. The production methods and production conditions of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below.
In Table 1 below, the columns for the drying step, hardening step, and firing step show the conditions for each step and the structure of the member obtained after each step.

Example 1
(Preparation of aggregate)
As shown in Fig. 1(a), strands 5 each made of bundled SiC fibers 4 were woven together to produce a woven fabric 6, and eight sheets of the resulting woven fabric 6 were laminated to form an aggregate 2 measuring 70 mm x 70 mm x 2 mm. The SiC fibers 4 used had an average diameter of 10 µm, and one strand 5 was produced by bundling 800 SiC fibers 4 together.
A coating layer made of SiC was formed by CVI on the surface of the SiC fiber 4. Since these coating layers were formed after lamination, the eight layers of the woven fabric 6 were bonded together so as not to fall apart, and the plate shape was maintained.

(Impregnation process)
As shown in Fig. 1(b) and Fig. 2(b), the obtained aggregate 2 was impregnated with the slurry A shown in Table 1 using the vacuum pressure impregnation method, and the gaps in the aggregate 2 were filled to obtain an impregnated body. An anionic dispersant was used as the dispersant. The average particle size of the SiC crushed particles was 0.6 µm, the average particle size of the polycarbosilane particles was 10 µm, and the number average molecular weight was 3500. Furthermore, the pressure in the vacuum pressure impregnation method was 0.9 MPa.

(Drying process)
As shown in Fig. 1(c) and Fig. 2(c), the obtained impregnated body was placed in a dryer and dried under the conditions shown in Table 1 to obtain a dried body in which the inside of the aggregate was filled with crushed SiC particles and polycarbosilane particles. At this time, no blowing out from inside the aggregate was confirmed.

(Firing process)
As shown in FIG. 1(d) and FIG. 2(d), the obtained dried body was fired under the conditions shown in Table 1 above and then allowed to cool naturally to room temperature to obtain a SiC/SiC composite material having a bulk density of 2.32 g/ ^cm3 .

Fig. 4 is a drawing substitute photograph showing a cross section of the SiC/SiC composite material obtained by the manufacturing method according to Example 1, where 10 divisions of the scale are 5 μm. As shown in Fig. 4, in the SiC/SiC composite material of Example 1, adjacent SiC pulverized particles 11 are bonded to each other by sintered bodies 12a of the SiC precursor, forming voids 14, and the corners 11a of the SiC pulverized particles 11 protrude into the voids 14. In addition, the voids 14 also have recesses 14a recessed at acute angles.
This is thought to be because the polycarbosilane particles, which are the SiC precursor, are in powder form and are not diluted with a solvent or the like, and therefore when the SiC precursor was sintered, the sintered body was not formed to cover the surface of the SiC crushed particles 11.
Since the SiC/SiC composite of Example 1 has the configuration described above, it is believed that when an environmentally resistant coating or the like is formed on the surface, a strong adhesive strength can be obtained between the SiC/SiC composite and the environmentally resistant coating.

<Comparative Example 1>
In Comparative Example 1, xylene is used instead of the water in Example 1, and polycarbosilane, which is a SiC precursor, is impregnated into the aggregate in the form of a solution. In addition, a hardening process is carried out between the drying process and the firing process in Example 1 to reduce the fluidity of polycarbosilane and gel it. The manufacturing conditions of Comparative Example 1 will be described below with reference to FIG. 3, focusing on the differences from Example 1.

(Impregnation process)
As shown in Figures 3(a) and 3(b), the same aggregate 2 as in Example 1 was impregnated with the impregnating liquid A shown in Table 1 to obtain an impregnated body. The impregnating liquid used was one in which polycarbosilane was dissolved in xylene and in which crushed SiC particles were dispersed. The average particle size of the crushed SiC particles was 0.6 μm.

(Drying process)
Next, as shown in Fig. 3(c), the impregnated body was dried in the same manner as in Example 1 to obtain a dried body. During drying, bubbles 24 consisting of xylene gas generated from inside the aggregate 2 were generated, and the bubbles 24 were pushed out and blown out. This is thought to be because the concentration of polycarbosilane in the xylene solution increased with drying, and the viscosity increased, making the bubbles 24 less likely to break and more likely to be pushed out by the gas pressure. Furthermore, this drying process produced a highly concentrated solution 23a, and the polycarbosilane became binder-like.

(Curing process)
Next, as shown in Fig. 3(d), the polycarbosilane impregnated inside the aggregate was hardened under the conditions shown in Table 1 above to obtain a hardened body. In the hardening process, gelation and softening occur in opposition to each other, but the process is completed when gelation progresses and hardened SiC precursor 23b is generated. If softening proceeds too quickly, the SiC precursor will be pushed out from inside the aggregate by the pressure of the gas generated from the solvent, so the SiC precursor was slowly heated while observing the balance between softening and gelation, and hardened so as not to blow out.

(Firing process)
Next, as shown in FIG. 3( e ), the obtained hardened body was fired under the same conditions as in Example 1 to form a SiC matrix 25, and then the hardened body was allowed to cool naturally to room temperature to obtain a SiC/SiC composite material having a bulk density of 2.25 g/cm ³ .

Fig. 5 is a drawing substitute photograph showing a cross section of a SiC/SiC composite material obtained by the manufacturing method according to Comparative Example 1. As shown in Fig. 5, in the SiC/SiC composite material of Comparative Example 1, bubbles 24 generated in the drying process remain in the subsequent hardening and firing processes and are turned into a matrix, so that in the obtained SiC/SiC composite material, bubbles 24 having a substantially spherical shape are formed. In addition, the corners 11a of the SiC pulverized particles 11 are covered with a SiC matrix 25, and the corners 11a of the bubbles 24 do not protrude as in Example 1.
This is believed to be because the aggregate was impregnated with the SiC precursor polycarbosilane in the form of a solution dissolved in xylene, and the aggregate was fired after the solution had covered the surfaces of the crushed SiC particles.
Furthermore, the SiC/SiC composite material of Comparative Example 1 obtained in this manner had a smooth surface, and therefore when an environmentally resistant coating or the like was formed on the surface, sufficient adhesion could not be obtained between the SiC/SiC composite material and the environmentally resistant coating.

<Comparative Example 2>
Comparative Example 2 differs from Example 1 in that the impregnation step was performed twice. In the first impregnation step, the aggregate was impregnated with a slurry containing water and crushed SiC particles, and in the second impregnation step, the dried body was impregnated with an impregnation liquid in which polycarbosilane, a SiC precursor, was dissolved in an organic solvent. In addition, in Comparative Example 2, a hardening step was performed between the second drying step and the firing step to reduce the fluidity of polycarbosilane and gel it. Hereinafter, the manufacturing conditions of Comparative Example 2 will be described with reference to FIG. 6, focusing on the differences from Example 1.

(Impregnation process)
As shown in Fig. 6(a) and Fig. 6(b), the same aggregate 2 as in Example 1 was prepared, and the gaps 2a of the aggregate 2 were impregnated with slurry B, which was a mixture of water 13 and crushed SiC particles 11 in the ratio shown in Table 1, to obtain an impregnated body. An anionic dispersant was used as the dispersant. The average particle size of the crushed SiC particles was 0.6 µm.

(Drying process)
Next, as shown in Fig. 6(c), the impregnated body was dried in the same manner as in Example 1 to obtain a dried body. During drying, only the water in the slurry B impregnated in the aggregate 2 could be removed, and the slurry did not erupt from the aggregate. Note that voids 14 were formed in the area excluding the SiC crushed particles 11.

(Impregnation process (second time))
Next, as shown in FIG. 6(d), the above-mentioned dried body was impregnated with the impregnation liquid B (dissolving liquid 23) shown in Table 1 to obtain an impregnated body.

(Drying process (second time))
Next, as shown in Fig. 6(e), the impregnated body obtained by the second impregnation step was dried under the same conditions as in Example 1 to obtain a dried body. At this time, the xylene in the dissolving solution 23 became gas, generating bubbles 24, and a highly concentrated dissolving solution 23a was generated, causing polycarbosilane to become binder-like. Also, a small amount of the impregnating solution B impregnated in the aggregate 2 was blown out.

(Curing process)
Next, as shown in Fig. 6(f), the polycarbosilane impregnated inside the aggregate was hardened under the conditions shown in Table 1 above to obtain a hardened body. In the hardening process, gelation and softening occur in opposition to each other, but the process is completed when gelation eventually progresses and hardened SiC precursor 23b is produced. If softening proceeds too quickly, the SiC precursor will be pushed out of the aggregate by the pressure of the gas generated from the solvent, so the SiC precursor was slowly heated while observing the balance between softening and gelation, and hardened so as not to blow out.

(Firing process)
Next, as shown in FIG. 6( g ), the obtained hardened body was fired under the same conditions as in Example 1 to form a SiC matrix 25, and then the hardened body was allowed to cool naturally to room temperature to obtain a SiC/SiC composite material having a bulk density of 2.31 g/cm ³ .

Fig. 7 is a drawing substitute photograph showing a cross section of a SiC/SiC composite material obtained by the manufacturing method according to Comparative Example 2. As shown in Fig. 7, in the SiC/SiC composite material of Comparative Example 2, as in Comparative Example 1, approximately spherical bubbles 24 were formed. In addition, the corners 11a of the SiC pulverized particles 11 are covered with a SiC matrix 25, and the corners 11a of the bubbles 24 do not protrude as in Example 1.
This is believed to be because the aggregate is impregnated with the SiC precursor polycarbosilane in the form of a solution dissolved in xylene, and the aggregate is fired after the solution has covered the surfaces of the SiC crushed particles 11.
Furthermore, the SiC/SiC composite material of Comparative Example 2 obtained in this manner also has a smooth surface, so when an environmentally resistant coating or the like is formed on the surface, sufficient adhesion cannot be obtained between the SiC/SiC composite material and the environmentally resistant coating.

The bulk density of the SiC/SiC composite material of Example 1 was 2.32 g/ ^cm3 , which was almost the same as the bulk density of the SiC/SiC composite materials of Comparative Examples 1 and 2. This shows that the SiC/SiC composite material obtained by the manufacturing method of the present invention has high density and excellent strength, similar to conventional SiC/SiC composite materials.

Reference Signs List 1a Slurry 2 Aggregate 3 Impregnated body 4 SiC fiber 5 Strand 6 Woven fabric 7 Dried body 8 SiC/SiC composite 9, 24 Air bubbles 11 SiC crushed particles 11a Corner 12 Polycarbosilane particles 12a Sintered body of SiC precursor 13 Water 14 Void 14a Recess 25 SiC matrix

Claims (3)

an impregnation step of impregnating an aggregate containing SiC fibers with a slurry consisting of only water, crushed SiC particles having corners, and polycarbosilane particles, or with a slurry consisting of only water, crushed SiC particles having corners, polycarbosilane particles, and a dispersant to obtain an impregnated body;
A drying step of drying the impregnated body to obtain a dried body;
A firing step of heating and firing the dried body,
The firing step is a step of melting and polymerizing the polycarbosilane particles, and then obtaining a fired body of the SiC precursor in which adjacent SiC pulverized particles are bonded to each other,
The average particle size of the polycarbosilane particles is 1 μm or more and 100 μm or less,
The content of the polycarbosilane particles relative to the mass of the slurry is 5 mass% or more and 30 mass% or less,
A method for producing a SiC/SiC composite material, characterized in that the content of the SiC crushed particles relative to the mass of the slurry is 10 mass% or more and 70 mass% or less . 2. The method for producing a SiC/SiC composite material according to claim 1 , wherein the number average molecular weight of the polycarbosilane constituting the polycarbosilane particles is 800 or more and 3,500 or less. 3. The method for producing a SiC/SiC composite material according to claim 1 , wherein the average particle size of the SiC crushed particles is 0.1 μm or more and 5.0 μm or less.

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