Method for filling open pores in ceramic matrix composite material and ceramic matrix composite material

Abstract

To provide a method for filling an open pore in the matrix of a ceramic base composite material with a ceramic, even when the open pore formed in the matrix of the ceramic base composite material has a size (for example, width) of several μm or less.SOLUTION: A method for filling an open pore formed in the matrix of a ceramic base composite material including reinforcing fiber in the matrix, with a ceramic to make the matrix, comprises repeating the following steps (A) and (B), in a state with the ceramic base composite material disposed in a liquid material as the raw material of the matrix. (A) Heating the ceramic base composite material to make the liquid material in a film boiling state, which forms a ceramic derived from the liquid material in the open pore. (B) Cooling the ceramic base composite material to a temperature lower than the boiling point of the liquid material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for filling open pores generated in the matrix of a ceramic-based composite material with ceramics. [Background technology]

[0002] Ceramic matrix composites are materials that have a matrix of ceramics such as silicon carbide and reinforced fibers within the matrix. They are used as high-temperature structural components in rocket engines, aircraft jet engines, and other applications.

[0003] A matrix is ​​formed on reinforcing fibers (for example, a fibrous body that is a woven or knitted fabric of reinforcing fibers) by a chemical vapor infiltration (CVI) method, a polymer impregnation pyrolysis (PIP) method, a metal melt infiltration (MI) method, etc. The above-mentioned fibrous body is also called a preform.

[0004] In the CVI method, reactive gas is passed through a heated fibrous body, and the reactants of the reactive gas are precipitated as a matrix in the gaps within the fibrous body. In the PIP method, a polymer such as polycarbosilane is impregnated into the fibrous body, and the impregnated polymer is sintered to form a matrix. In the MI method, a matrix (e.g., a matrix of silicon carbide and silicon metal) is formed by melting and pouring a metal component (e.g., silicon metal) into a fibrous body with powder material (e.g., silicon carbide or carbon powder) mixed inside.

[0005] During the process of forming such a matrix, small open pores such as cracks tend to occur in the matrix. Open pores are pores that are open to the outside (hereinafter simply referred to as open pores). Conventionally, in order to fill such open pores with a matrix material, the matrix forming process has been carried out for a long time or repeatedly.

[0006] For example, in Patent Document 1, a dense matrix with few open pores is formed by performing polymer impregnation and baking twice and chemical vapor impregnation. In addition, in Patent Document 2 and Non-Patent Document 3, an attempt is made to increase the density of the matrix by immersing a carbon fiber preform in a precursor liquid of low molecular weight liquid polycarbosilane and repeatedly performing pulse heating. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-343176 [Patent Document 2] China Patent Publication CN102795871A [Non-patent literature]

[0008] [Non-Patent Document 1] C. Besnarda et al. “Synthesis of hexacelsian barium aluminosilicate by film boiling chemical vapor process”, Journal of the European Ceramic Society 40 (2020) 3494-3497 [Non-Patent Document 2] Masanori SHIMIZU et al. "Crystallization Behavior and Change in Surface Area of ​​Alkoxide-Derived Mullite Precursor Powders with Different Compositions", Journal of the Ceramic Society of Japan 105 [2] 131-135 (1997) [Non-Patent Document 3] Min Mei et al. “Preparation of C / SiC composites by pulse chemical liquid-vapor deposition process”, Materials Letters 82 (2012) 36-38 Summary of the Invention [Problem to be solved by the invention]

[0009] When an open pore is entirely or partially elongated and has a narrow width of several μm or less, the conventional techniques have the following problems (a) and (b). (a) The processing time required to fill the open pores with the matrix ceramics is longer. (b) Conventionally, it has been difficult to fill narrow open pores having a width of a few μm or less (for example, a width of 1 to 2 μm or less) with ceramics.

[0010] For example, even with the techniques of Patent Document 2 and Non-Patent Document 3, it is difficult to prevent open pores having a width of several μm or less from remaining in the matrix of the produced ceramic-based composite material.

[0011] Therefore, an object of the present invention is to provide a technique that can solve at least one of the above problems, i.e., to provide a technique that can fill open pores generated in the matrix of a ceramic-based composite material with ceramics in a short time, or can fill narrow portions having a width of several μm or less in at least some of the open pores generated in the matrix of a ceramic-based composite material with ceramics, or can achieve both of these. [Means for solving the problem]

[0012] In order to achieve the above object, the open pore filling method according to the present invention is a method for filling open pores generated in a matrix of a ceramic-based composite material having reinforcing fibers provided in the matrix with a ceramic to serve as the matrix, the method comprising the steps of: In a state where the ceramic matrix composite material is placed in a liquid material that is a matrix raw material, (A) heating the ceramic matrix composite material to bring the liquid material into a film boiling state, thereby generating ceramics derived from the liquid material in the open pores; (B) cooling the ceramic matrix composite material to a temperature below the boiling point of the liquid material; By repeating steps (A) and (B), the open pores are filled with the ceramics.

[0013] Furthermore, the ceramic matrix composite material according to the present invention has open pores filled with ceramics by carrying out the above-mentioned open pore filling method. Effect of the Invention

[0014] According to the present invention, open pores generated in the matrix of a ceramic-based composite material can be filled with ceramics in a short period of time, or open pores generated in the matrix of a ceramic-based composite material can be filled with ceramics even if the size (e.g., width) of the open pores is several μm or less, or both of these can be achieved. [Brief description of the drawings]

[0015] [Figure 1] 1 is a flowchart showing a method for filling open pores of a ceramic-based composite material with ceramics according to a first embodiment of the present invention. [Figure 2A] 1 shows an example of a fixture used to attach a ceramic matrix composite material to a heater. [Figure 2B] FIG. 2B is a view taken along the line 2B-2B of FIG. 2A. [Figure 2C] 2C-2C in FIG. 2A. [Diagram 3] This shows a state in which the ceramic matrix composite material attached to the heater by the fixture of FIG. 2A is placed in a liquid material. [Figure 4] 5 is a flowchart showing a method for filling open pores in a ceramic-based composite material according to a second embodiment of the present invention. [Diagram 5] 2B shows a state in which the fibrous body attached to the heater body by the fixture of FIG. 2A is placed in a liquid material. [Figure 6] 1 is a graph showing temperature changes in an open hole filling method in an example. [Figure 7] 1 is a scanning electron microscope image of a ceramic matrix composite material in which open pores are filled with ceramic according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are used to designate the same parts, and duplicated explanations will be omitted.

[0017] [First embodiment] The method for filling open pores in a ceramic matrix composite material according to a first embodiment of the present invention is a method for filling open pores present in a matrix of the ceramic matrix composite material with ceramics. The ceramic matrix composite material has a large number of reinforcing fibers provided as reinforcing materials in the matrix. The ceramic matrix composite material may be used as a high-temperature structural member in a rocket engine, an aircraft jet engine, or the like.

[0018] The ceramic matrix composite material to which the open pore filling method according to the present embodiment is applied may be one formed by performing a process for forming a matrix on a large number of reinforcing fibers. The process may be the above-mentioned CVI method, PIP method, or MI method, or a film boiling method described below. The matrix may be one formed of silicon carbide, but may also be one formed of other materials (e.g., mullite).

[0019] The reinforcing fibers may be fibers mainly composed of silicon carbide or carbon. For example, the reinforcing fibers are silicon carbide fibers or carbon fibers. However, according to the present invention, the reinforcing fibers are not limited to these, and may be heat-resistant oxide fibers such as alumina fibers, mullite fibers, and zirconia fibers. In addition, the multiple reinforcing fibers may be provided in the matrix as a fibrous body formed by multiple reinforcing fibers. This fibrous body may be a woven or knitted fabric of reinforcing fibers.

[0020] FIG. 1 is a flow chart showing a method for filling open pores of a ceramic-based composite material with ceramics according to a first embodiment of the present invention.

[0021] In step S1, a target ceramic matrix composite material is placed in a liquid material. This ceramic matrix composite material may be a prefabricated ceramic matrix composite material. The liquid material used in step S1 is a liquid and is a ceramic raw material to be generated in open pores in the matrix of the ceramic matrix composite material, as described below.

[0022] Step S1 includes steps S11 and S12. In step S11, the ceramic-based composite material is attached to the heating body by a fixture. As a result, the ceramic-based composite material, the heating body, and the fixture may be integrated with one another. The number of ceramic-based composite materials attached to the heating body in this manner may be one or more (two in the example of FIG. 2A described later). In a state in which the ceramic-based composite material is attached to the heating body by the fixture, the ceramic-based composite material may or may not be in contact with the heating body.

[0023] Fig. 2A shows an example of a fixture that can be used in step S11. However, the fixture is not limited to the configuration example of Fig. 2A, and may be any fixture that maintains the ceramic-based composite material attached to the heating body.

[0024] In the case of FIG. 2A, in step S11, the ceramic-based composite material is attached to the heating body by the fixture 20. FIG. 2B is a view taken along the line 2B-2B of FIG. 2A. FIG. 2A shows a state in which two ceramic-based composite materials 10 are attached to the heating body 1 by the fixture 20 (hereinafter, also simply referred to as the attached state). In the example of FIG. 2A, in the attached state, each ceramic-based composite material 10 is in contact with the heating body 1. The fixture 20 includes a pair of insulating plates 2, a porous body 3, an action mechanism 4, a thermal insulator 5, and a hanging portion 7.

[0025] The heating body 1 is formed of a material that can be induction heated (e.g., graphite) and is disposed between a pair of insulating plates 2. Each insulating plate 2 is formed of a material that has insulating properties (e.g., alumina). When viewed from the thickness direction of the insulating plate 2, each insulating plate 2 and the heating body 1 may be, for example, circular with approximately the same radius. In the above-mentioned mounting state, the porous body 3 is disposed between the heating body 1 and each insulating plate 2. Each porous body 3 has a large number of holes formed therein through which a fluid can pass, and may be, for example, a stack of multiple wire meshes.

[0026] The action mechanism 4 has a bolt 4a and a nut 4b. The bolt 4a passes through the two heat insulating plates 2 and the heater 1 with a gap therebetween, and a nut 4b is screwed onto both ends of each bolt 4a. In the attached state, the nut 4b is tightened onto the bolt 4a in a direction in which the two heat insulating plates 2 approach each other, thereby holding each of the porous bodies 3, the heater 1, and each of the ceramic-based composite materials 10 between the pair of heat insulating plates 2. A plurality of such action mechanisms 4 (two in the example of FIG. 2A) may be provided.

[0027] The heat insulating material 5 covers the outer periphery of the heating body 1 and the two ceramic-based composite materials 10 in the attached state. That is, the heating body 1 and each ceramic-based composite material 10 have outer peripheries 1a, 10a surrounding the central axis facing the thickness direction of the insulation plate 2, respectively, and these outer peripheries 1a, 10a are covered by the heat insulating material 5 as shown in FIG. 2B. In FIG. 2A, only the parts of the heat insulating material 5 located on both sides (the left and right sides of this figure) of the heating body 1 and each ceramic-based composite material 10 are illustrated by two-dot chain lines. The heat insulating material 5 is formed of a material having heat insulating properties. For example, the heat insulating material 5 may be a glass heat insulating cloth (woven fabric). In addition, in the example of FIG. 2A and FIG. 2B, a wire 6 is wound around the heat insulating material 5 from the outside in order to fix the heat insulating material 5 to the heating body 1, but the heat insulating material 5 may be fixed by other means.

[0028] In addition, in the attached state, each porous body 3 is open to the outer periphery side. That is, each porous body 3 has an outer periphery 3a surrounding a central axis facing the thickness direction of the heat insulating board 2, and the outer periphery 3a is open to the outside radially outward from the central axis.

[0029] The suspending part 7 is for suspending the ceramic-based composite material 10 and the heater 1 in step 12 described later. FIG. 2C is a view taken along the arrow 2C-2C in FIG. 2A. The suspending part 7 has a plate-shaped member 7a and a rod-shaped member 7b. The plate-shaped member 7a extends elongatedly in the left-right direction of FIG. 2A and FIG. 2C along the upper surface of the upper heat insulating plate 2. The bolts 4a penetrate both ends of the plate-shaped member 7a with gaps. Both ends of the plate-shaped member 7a are sandwiched between the upper heat insulating plate 2 and the upper nut 4b, respectively. A joint 7a1 is provided in the center of the plate-shaped member 7a. The rod-shaped member 7b is joined to this joint 7a1. The rod-shaped member 7b extends upward from the joint 7a1. Although not shown in the figure, for example, a protrusion as a bolt may be formed on the upper surface of the connecting portion 7a1, and a bolt hole may be formed in the lower end surface of the rod-shaped member 7b, and the connecting portion 7a1 and the rod-shaped member 7b may be connected by screwing the bolt into the bolt hole.

[0030] In step S12, the ceramic-based composite material attached to the heating body by a fixture (e.g., fixture 20 in FIG. 2A) is placed in the liquid material. At this time, as shown in FIG. 3, ceramic-based composite material 10 is placed in liquid material 9 together with fixture 20 and heating body 1, and ceramic-based composite material 10 and heating body 1 are suspended by suspension unit 7 so that fixture 20, heating body 1, and ceramic-based composite material 10 do not come into contact with the inner surface (bottom surface and inner peripheral surface) of treatment vessel 8. At this time, rod-shaped member 7b of suspension unit 7 is disposed so as to penetrate through through-hole 8a1 of lid member 8a that closes the opening at the top surface of treatment vessel 8, and the upper end portion of rod-shaped member 7b may be connected to and supported by a structure (not shown) by appropriate means.

[0031] In step S12, the hanging part is not limited to the configuration examples shown in Figures 2A and 2C, etc., as long as it can hang the ceramic-based composite material 10 and the heating body 1 so that the mounting fixture 20, the heating body 1, and the ceramic-based composite material 10 do not come into contact with the inner surface of the processing vessel 8 (i.e., so as to be separated from the inner surface of the processing vessel 8).

[0032] The processing vessel 8 is made of a non-conductive material (e.g., glass) that is not induction heated. The processing vessel 8 may be formed with a gas inlet hole 8b for introducing nitrogen gas into the gas phase portion in the processing vessel 8 in step S2 described later, and a gas outlet hole 8a2 for discharging gas from the gas phase portion in the processing vessel 8 in step S2.

[0033] By step S12, the entire ceramic matrix composite material is placed in the liquid material, and as a result, the liquid material enters (permeates) into each open pore in the matrix of the ceramic matrix composite material.

[0034] The liquid material may be, for example, liquid polycarbosilane (LPCS), which is a silicon carbide liquid material, although the liquid material is not limited thereto, as will be described later.

[0035] In step S2, a film boiling gas of a liquid material is generated, and open pores (hereinafter simply referred to as open pores) in the matrix of the ceramic-based composite material are filled with ceramics, which are precipitates from the film boiling gas. Step S2 includes steps S21 and S22.

[0036] In step S21, the ceramic matrix composite material located in the liquid material is heated to a target temperature equal to or higher than the boiling point of the liquid material, thereby generating ceramics derived from the liquid material in the open pores. That is, the liquid material is heated by the heated ceramic matrix composite material, and becomes a film boiling gas (i.e., enters a film boiling state) at the interface between the matrix of the ceramic matrix composite material (the inner surface of the open pores) and the liquid material, and this film boiling gas generates and deposits ceramics (i.e., ceramic pyrolysis precipitates) in the open pores. This ceramics may be generated by one or both of the following (i) and (ii).

[0037] (i) When the film boiling gas collides with the inner surface of the open pores, it receives further thermal energy, which causes thermal decomposition and mineralization, resulting in precipitation of solid ceramics on the inner surface of the open pores.

[0038] (ii) Some of the gases contained in the film boiling gas have already been thermally decomposed into pyrolysis gas. When this pyrolysis gas collides with the inner surface of the heated open pores, it undergoes mineralization and precipitates as solid ceramics on the inner surface of the open pores.

[0039] In step S21, the ceramic may be precipitated at the interface between the ceramic-based composite material and the liquid material in places other than the inner surfaces of the open pores of the matrix.

[0040] In step S21, the ceramic-based composite material may be heated by induction heating the heating body. For example, as shown in FIG. 3, the heating body 1 is induction heated by an alternating magnetic field generated by the coil 11 by passing an alternating current through the coil 11. The ceramic-based composite material and the liquid material are heated by heat generated by the heated heating body. In order to fill minute open pores with ceramics, the heating rate of the heating body (ceramic-based composite material) in step S21 is desirably 3000° C. / hour or less, 2000° C. / hour or less, or 1500° C. / hour or less. In this case, the heating rate may be 500° C. / hour or more. Also, in this case, the heating rate is more desirably about 1000° C. / hour or less than 1000° C. / hour. However, the heating rate is not limited to this. For example, the heating rate may be lower than 500° C. / hour (in this case, the heating rate may be, for example, 100° C. / hour or more).

[0041] In step S21, when the ceramic matrix composite material reaches the target temperature, which is equal to or higher than the boiling point of the liquid material, the process proceeds to step S22. For example, a temperature sensor may be attached to the ceramic matrix composite material or to the surface of the heater, and the temperature measured by the temperature sensor may be taken as the temperature of the ceramic matrix composite material. When the measured temperature reaches the target temperature, the process proceeds to step S22. The target temperature may be an approximate standard. That is, since it may be difficult to start step S22 at the timing when the target temperature is reached, the timing to start step S22 may be when the temperature of the ceramic matrix composite material reaches the target temperature, or when the temperature of the ceramic matrix composite material exceeds the target temperature to some extent.

[0042] In step S22, the ceramic matrix composite material is cooled to a target temperature lower than the boiling point of the liquid material. This stops the boiling phenomenon of the liquid material at the interface between the matrix (the inner surface of each open pore) and the liquid material in step S22 (in contrast to this, Patent Document 2 and Non-Patent Document 3 do not mention stopping the boiling phenomenon). As a result, in a state where new film boiling gas is no longer generated, the film boiling gas that has already been generated is replaced with the liquid material, and the liquid material again enters (permeates) each open pore in the ceramic matrix composite material that is not completely filled with ceramic. For example, the liquid material again enters the open pores that are partially filled with ceramic in step S21 in step S22. The cooling rate of the heating body (ceramic matrix composite material) in step S22 is preferably 3000°C / hour or less, more preferably 1000°C / hour, but is not limited thereto.

[0043] The cooling in step S22 may be performed by stopping the heating of the ceramic-based composite material and maintaining this stopped state. Alternatively, in step S22, in addition to stopping the heating of the ceramic-based composite material, the liquid material may be cooled. For example, in FIG. 3, the liquid material 9 may be circulated by causing a part of the liquid material 9 in the processing vessel 8 to flow outside the processing vessel 8, cooling the liquid material 9 by a heat exchanger, and then returning the cooled liquid material 9 to the processing vessel 8. In this case, piping and a pump (not shown) for circulating the liquid material 9 in this manner may be provided.

[0044] When the ceramic matrix composite material in step S22 is cooled to the target temperature lower than the boiling point of the liquid material, step S21 is started again. For example, assuming that the temperature measured by the temperature sensor is the temperature of the ceramic matrix composite material, when the measured temperature falls below the target temperature, step S21 is started again. The target temperature may be an approximate standard. That is, since it may be difficult to start step S21 again at the timing when the target temperature is reached, the timing to start step S21 again may be when the temperature of the ceramic matrix composite material reaches the target temperature, or when the temperature of the ceramic matrix composite material falls below the target temperature to some extent.

[0045] Furthermore, after step S22, before starting step S21 again, it is confirmed that no air bubbles are generated from the ceramic-based composite material in the liquid material in the processing vessel 8, and once this confirmation is made, step S21 is started. This confirmation may be made, for example, by visually checking the transparent glass processing vessel 8 from the outside. Since no air bubbles are generated, it can be determined that the liquid material has completely permeated into the ceramic-based composite material.

[0046] In this manner, step S21 is started again, and steps S21 and S22 are repeated. As a result, the ceramics generated in each open pore in the matrix increases, and these open pores are filled with the ceramics. Steps S21 and S22 are repeated until each open pore is sufficiently (for example, completely) filled with the ceramics. The number of times this is repeated may be, for example, 10 times or more and 20 times or less, but is not limited to this.

[0047] When the liquid material is the above-mentioned LPCS, the above-mentioned ceramic becomes silicon carbide. In this case, the LPCS undergoes polymerization in the repeated process of steps S21 and S22, and its boiling point rises from about 180°C to about 250°C. In addition, in this case, the maximum temperature of the ceramic-based composite material reached by step S21 is, for example, 800°C or higher, preferably 1000°C or higher and 1400°C or lower. By setting the maximum temperature to 1000°C or higher, sufficient progress of mineralization of the ceramics can be expected, and by setting the maximum temperature to 1400°C or lower, it is possible to prevent the precipitation rate of the ceramics from becoming too high or the occurrence of intense thermal decomposition to the extent that the ceramics do not deposit. This is expected to make it easier for the ceramics to be filled into the minute open pores.

[0048] Furthermore, when the liquid material is the above-mentioned LPCS, the minimum temperature of the ceramic matrix composite material reached by step S22 is a temperature lower than the boiling point of the LPCS. The boiling point of the LPCS rises from about 180° C. to about 250° C. as described above during the repeated process of steps S21 and S22. Therefore, in each step S22, the ceramic matrix composite material is cooled to a temperature lower than the boiling point, so that the liquid material permeates each open pore in the ceramic matrix composite material in a liquid state without boiling.

[0049] (Effects of the first embodiment) According to the open pore filling method of this embodiment, the following effects (A) to (G) can be obtained.

[0050] (A) A ceramic matrix composite is placed in a liquid material, so that the liquid material penetrates (permeates) into the open pores in the matrix, and then the ceramic matrix composite is heated to a temperature equal to or higher than the boiling point of the liquid material. This causes the liquid material in the open pores of the matrix to become a film boiling gas, and ceramics are generated from this film boiling gas to fill some of the open pores. The ceramic matrix composite is then cooled to a temperature lower than the boiling point. This stops the boiling of the liquid material in the open pores, and the liquid material penetrates (permeates) into the open pores again. The ceramic matrix composite is then heated to a temperature equal to or higher than the boiling point. By repeating this heating and cooling process, each open pore in the matrix can be filled with ceramics.

[0051] (B) This also blocks open pores that serve as paths for oxygen and combustion gas to penetrate into the ceramic matrix composite, and further reduces the number of open pore tips that serve as starting points for crack propagation, thereby improving the oxidation resistance, strength, and fatigue properties of the ceramic matrix composite.

[0052] (C) In the open pore filling method of this embodiment, the ceramic matrix composite material is cooled to a temperature lower than the boiling point of the liquid material in each repeated cooling process (step S22 described above). This allows the liquid material to enter the open pores in the matrix as described above, so that even if the open pores are small (e.g., open pores having a width of 1 to 2 μm or less) in size, the liquid material can enter the open pores, and film boiling gas of the liquid material can be generated in the open pores. Therefore, even if the open pores are small, the open pores can be filled with ceramics.

[0053] (D) The above-mentioned heating and cooling do not take much time, so by repeating the above-mentioned heating and cooling, ceramics can be filled (for example, completely) into relatively large open pores and minute open pores of several μm or less in a short time (for example, several hours). For example, one cycle of steps S21 and S22 takes about 30 minutes to 1 hour, and it is expected that ceramics with a maximum size of about 5 to 10 μm can be grown in the open pores in one cycle. In addition, since heating is performed by induction heating of a heater in contact with the ceramic matrix composite material, the ceramic matrix composite material can be heated rapidly.

[0054] (E) Furthermore, when a plurality of ceramic matrix composite materials (two in FIG. 2A) are attached to a heater, the open pore filling method can be carried out simultaneously on the plurality of ceramic matrix composite materials.

[0055] (F) The heat insulating plates 2 and the heat insulating material 5 in the mounting fixture 20 in FIG. 2A can suppress heat radiation from the heater 1 and the ceramic matrix composite material 10.

[0056] (G) In the above-mentioned step S21, when the heating element 1 is induction heated, the treatment vessel 8 made of a non-conductive material is not induction heated. In addition, at this time, as shown in Fig. 3, the heating element 1, the ceramic-based composite material 10, and the fixture 20 are suspended by the suspending part 7 so as not to come into contact with the inner surface of the treatment vessel 8, so that the treatment vessel 8 is prevented from being damaged by contact with the high-temperature heating element 1, the ceramic-based composite material 10, and the fixture 20.

[0057] (H) In the above-mentioned open pore filling method, the heater 1 may be omitted, and in step S21, a fibrous body (e.g., a fibrous body formed of carbon fiber or silicon carbide fiber) in a ceramic matrix composite material having a sufficiently large heat capacity (volume) may be induction-heated to generate the above-mentioned film boiling gas, and ceramics may be deposited in the open pores of the matrix of the ceramic matrix composite material by one or both of the above (i) and (ii). In this case, for example, in FIG. 2A and FIG. 3, the heater 1 may be omitted, the number of ceramic matrix composite materials 10 may be one, one ceramic matrix composite material 10 may contact the porous body 3 from above and below, and the heat insulating material 5 may cover the outer periphery 10a of the ceramic matrix composite material 10, and the other points may be the same as those described above. In addition to or instead of omitting the heater 1, the heat insulating plate 2 may be omitted. [Second embodiment] A method for filling open pores in a ceramic-based composite material according to a second embodiment of the present invention will be described below. The second embodiment may be the same as the first embodiment in respects that will not be described below.

[0058] In the second embodiment, the ceramic matrix composite material to be the subject of the open pore filling method is a material in which a matrix is ​​formed by a film boiling method (FB: Film Boiling) on ​​a large number of reinforcing fibers (for example, the above-mentioned fibrous body). In the film boiling method, each reinforcing fiber (fibrous body) is heated while a large number of reinforcing fibers (fibrous body) are arranged in a liquid material of the matrix. This heating causes ceramics derived from the liquid material to be deposited on each reinforcing fiber as a matrix, thereby forming a matrix. That is, the liquid material becomes a film boiling gas by being heated by the heated reinforcing fibers, and this film boiling gas generates ceramics on the reinforcing fibers. The ceramics on the reinforcing fibers may be generated by one or both of the following (1) and (2).

[0059] (1) When the film boiling gas collides with the heated reinforcing fibers, it receives additional thermal energy, causing thermal decomposition and mineralization, which precipitates on the reinforcing fibers as solid ceramics.

[0060] (2) Some of the gas contained in the film boiling gas has already been thermally decomposed into pyrolysis gas. When this pyrolysis gas collides with the heated reinforcing fibers, it undergoes mineralization and precipitates on the reinforcing fibers as solid ceramics.

[0061] The open pore filling method according to the second embodiment can be carried out with the ceramic matrix composite material having a matrix formed therein by such a film boiling method (FB) while it is placed in the above-mentioned liquid material. That is, before carrying out the above-mentioned step S2, a matrix is ​​formed in the liquid material by the film boiling method on the fibrous body placed in the liquid material, so that the ceramic matrix composite material is placed in the liquid material. That is, the matrix formation process by the film boiling method replaces the above-mentioned step S1.

[0062] FIG. 4 is a flow chart showing the process for producing a ceramic-based composite material and the process for filling open pores carried out successively in this order in the second embodiment.

[0063] In step S101, a fibrous body made of reinforcing fibers is attached to a heating body by a mounting tool, and the fibrous body is placed in a liquid material together with the heating body. In this state, the fibrous body may or may not be in contact with the heating body. The liquid material is a liquid that is a raw material for the matrix. When the liquid material is the above-mentioned LPCS, the matrix is ​​mainly formed of silicon carbide.

[0064] The fixture used in step S101 may be the same as the fixture in Fig. 2A. In this case, the state immediately after performing step S101 is the same as the state in Fig. 2A where each ceramic-based composite material 10 is replaced with a fibrous body. That is, in step S101, the fibrous body is attached to the heating body by the fixture instead of the ceramic-based composite material. In step S101, the state in which the fibrous body attached to the heating body in this way is placed in the liquid material is shown in Fig. 5. In Fig. 5, reference numeral 13 denotes the fibrous body, and reference numeral 13a denotes the outer periphery of the fibrous body 13.

[0065] 5, with the fibrous body 13 placed in the liquid material 9, the fibrous body 13 and the heater 1 are suspended by the suspension part 7 so that the fixture 20, the heater 1, and the fibrous body 13 do not come into contact with the inner surface (bottom surface and inner peripheral surface) of the treatment vessel 8. In this state, the upper end side portion of the rod-shaped member 7b may be connected to and supported by a structure (not shown) by appropriate means, as described above. This state is maintained until the end of step S2.

[0066] In step S102, a matrix is ​​formed on the fibrous body by the film boiling method as described above to obtain a ceramic-based composite material. Step S102 includes steps S121 and S122.

[0067] In step S121, the reinforcing fibers (fibrous body) are heated until their temperature reaches or exceeds a high-temperature target temperature. The high-temperature target temperature is a temperature higher than the temperature at which ceramics begin to be generated in each reinforcing fiber of the fibrous body by the film boiling gas described above.

[0068] The heating in step S121 may be performed by induction heating the heating body. For example, as shown in FIG. 5, the heating body 1 is induction heated by an alternating magnetic field generated by the coil 11 by passing an alternating current through the coil 11. The fibrous body and the liquid material are heated by the heat generated by the heated heating body. When the temperature of the fibrous body (reinforced fiber) reaches or exceeds the target temperature on the high temperature side in step S121, the process proceeds to step S122. For example, when the measured temperature of a temperature sensor attached to the surface of the heating body reaches or exceeds the target temperature, the process proceeds to step S122. The heating rate of the fibrous body (or heating body) in step S121 may be, for example, 3000° C. / hour or less, 2000° C. / hour or less, or 1500° C. / hour or less. In this case, the heating rate may be 1000° C. / hour or more (or higher than 1000° C. / hour).

[0069] In step S122, the fibrous body is cooled. That is, in step S122, the heating of the fibrous body is stopped, and the state in which the heating of the fibrous body is stopped is maintained until the temperature of the fibrous body (or the heating body) becomes equal to or lower than the target temperature on the low temperature side. The target temperature on the low temperature side is equal to or lower than the temperature at which the formation of ceramics on each reinforcing fiber by the film boiling gas described above stops. This target temperature may be equal to or higher than the boiling point of the liquid material. In addition to stopping the heating of the reinforcing fibers in step 122, the liquid material may be cooled by a heat exchanger as described above.

[0070] When the liquid material is the above-mentioned LPCS, the high-temperature side target temperature in step S121 is preferably within a range of 800° C. or more and 1600° C. or less, and the low-temperature side target temperature in step S122 is preferably less than 800° C., more preferably 500° C. or less (e.g., 500° C.), and may be, for example, a value within a range of 300° C. to 400° C. Note that these target temperatures may be approximate standards as described above.

[0071] When the temperature of the fiber body (or the heater) becomes equal to or lower than the target temperature on the low temperature side in step S122 (for example, when the temperature measured by the temperature sensor attached to the surface of the heater becomes equal to or lower than the target temperature on the low temperature side), step S121 is started again, and steps S121 and S122 are repeated. In this repetition, the process may proceed from step S121 to step S122 while the boiling state of the liquid material is maintained. By performing step S121 and step S122 once, one layer of the matrix is ​​formed for each reinforcing fiber by ceramics generated for each reinforcing fiber by thermal decomposition from the film boiling gas described above. One cycle is performed by performing step S121 and step S122 once, and the number of cycles is the same as the number of layers formed for each reinforcing fiber.

[0072] By repeating steps S121 and S122, ceramics are sequentially deposited around each reinforcing fiber, forming a ceramic matrix. This completes the formation of the matrix. This matrix has a layered structure in which a plurality of the above-mentioned layers are sequentially stacked (around each reinforcing fiber). In this case, the heating rate of the fibrous body (or the heater) in step S121 is slow enough to form a matrix with a layered structure. For example, the heating rate may be 3000°C / hour or less, 2000°C / hour or less, or 1500°C / hour or less. In this case, the heating rate may be 1000°C / hour or more, or may be higher than 1000°C / hour. From another point of view, in order to form a layer structure of the matrix, it is preferable to heat the fibrous body for a suitable period of time. For example, in one step S121, the time during which the temperature of the fibrous body is raised (i.e., the total time during which the temperature of the fibrous body is raised) may be longer than 10 minutes, 15 minutes or more, 20 minutes or more, or 30 minutes or more. In this case, the time during which the temperature of the fibrous body is raised may be, for example, within 40 minutes, within 50 minutes, or within 60 minutes, but is not limited thereto, and may be longer than 60 minutes.

[0073] However, according to the present invention, step S122 may be omitted. In this case, in step S121, the formation of the matrix may be completed by continuing to heat the fibrous body in the liquid material at a temperature of, for example, 1000° C. to 1400° C. for a predetermined time. In this case, a matrix without a layer structure is formed.

[0074] By repeating steps S121 and S122, or by performing step S102 with step S122 omitted, the formation of the matrix is ​​completed, thereby obtaining a ceramic-based composite material (two ceramic-based composite materials in FIG. 5).

[0075] In the second embodiment, when the formation of the matrix is ​​completed as described above, the open pore filling method is started without taking out the ceramic-based composite material from the liquid material (e.g., liquid material 9 in FIG. 5) in step S102. That is, the above-mentioned step S2 (step S21) of the open pore filling method is started without performing step S1.

[0076] When the formation of the matrix is ​​completed by the fixture 20 in Fig. 5, each fibrous body 13 in Fig. 5 becomes a ceramic-based composite material, resulting in the state shown in Fig. 3. Therefore, step S2 (step S21) is started without performing step S1. That is, the process of the open pore filling method is started.

[0077] Hereinafter, the open hole filling method is the same as that in the first embodiment, and therefore the description thereof will be omitted. The heater, fixture, coil, processing vessel, liquid material in the processing vessel, and the like used in the above-mentioned manufacturing method are used as they are in the next open hole filling method (step S2). The target temperature in the above-mentioned step S22 in the open hole filling method is lower than the low temperature side target temperature in the above-mentioned step S122.

[0078] (Effects of the second embodiment) In the second embodiment, after a ceramic-based composite material is obtained by forming a matrix on a fibrous body by film boiling, the open pore filling process can be started without carrying out step S1 of the first embodiment.

[0079] (Example) In the example of the second embodiment, the fibrous body in step S101 was formed of silicon carbide fiber as a reinforcing fiber, and the liquid material was the above-mentioned LPCS. Also, using the configuration shown in FIG. 5, the process shown in the flowchart of FIG. 4 was performed.

[0080] 6 is a graph showing an example of the temperature change in the above-mentioned step S2 in the example. In Fig. 6, the solid line indicates the surface temperature of the heater, the dashed line indicates the temperature of the upper surface of the ceramic-based composite material 10 on the upper side of Fig. 4, and the dashed line indicates the temperature of the liquid material in Fig. 4.

[0081] Fig. 7 is a scanning electron microscope image of a ceramic matrix composite material in which ceramics are filled into open pores according to another embodiment. Fig. 7 shows the state obtained by carrying out the above-mentioned step S2 treatment for 2.5 hours with the temperature change shown in Fig. 6. In Fig. 7, the parts indicated by the multiple arrows and sandwiched between these arrows are open pores as cracks. These cracks are about 1 to 2 µm wide and extend thinly from the position of the reinforcing fibers. These cracks could be filled with ceramics in step S2 for 2.5 hours.

[0082] [Third embodiment] A method for filling open pores in a ceramic matrix composite material according to a third embodiment of the present invention will be described below. The third embodiment may be the same as the first embodiment except for the points described below.

[0083] The liquid material for generating the above-mentioned ceramics in the open pores (the liquid material used in step S1) may be a liquid material other than the above-mentioned LPCS. For example, the liquid material may be borazine, methyltrichlorosilane, cyclohexane, a silicon alkoxide solution, an aluminum alkoxide solution, a mixture of a silicon alkoxide solution and an aluminum alkoxide solution, or a zirconium alkoxide solution.

[0084] When the liquid material used in step S1 is borazine, the ceramics generated by heating in the above-mentioned step S21 are boron nitride (BN), which is a ceramic. Boron nitride has low adhesion to silicon carbide. Therefore, when the matrix is ​​mainly formed of silicon carbide, the boron nitride filled in the open pores has the function of suppressing the propagation of cracks at the interface with the matrix.

[0085] When the liquid material used in step S1 is methyltrichlorosilane, the ceramics generated by heating in the above-mentioned step S21 will be silicon carbide (SiC), which is a ceramic, in the same way as when the liquid material is polycarbosilane (LPCS).

[0086] When the liquid material used in step S1 is cyclohexane, the ceramics generated by heating in the above-mentioned step S21 is carbon. This carbon has the function of suppressing the propagation of cracks, similar to the case of the above-mentioned boron nitride.

[0087] When the liquid material used in step S1 is a silicon alkoxide solution, the ceramics generated by heating in the above-mentioned step S21 will be silicon dioxide (SiO2). The silicon alkoxide solution is cheaper than LPCS.

[0088] When the liquid material used in step S1 is an aluminum alkoxide solution, the ceramics generated by heating in the above-mentioned step S21 will be alumina (Al2O3). The aluminum alkoxide solution is cheaper than LPCS.

[0089] When the liquid material used in step S1 is a mixture of a silicon alkoxide solution and an aluminum alkoxide solution, the ceramics generated by heating in the above-mentioned step S21 will be mullite (Al2O3-SiO2).

[0090] When the liquid material used in step S1 is a zirconium alkoxide solution, the ceramics generated by heating in the above-mentioned step S21 will be zirconia (ZrO2). Zirconia is a ceramic with a higher melting point than silicon carbide, so it does not melt even in an ultra-high temperature environment and functions as part of the matrix.

[0091] According to the present invention, the liquid material used in step S1 is not limited to the above specific example, and may be other liquid materials. For example, other metal alkoxide solutions may be used as the liquid material used in step S1. In this case, the ceramics generated by heating in the above-mentioned step S21 may be oxide ceramics. In this case, the liquid material used in step S1 may be, for example, a mixture of three alkoxydes solutions, as described in Non-Patent Document 1, so that the ceramics generated in the open pores in step S21 is barium aluminosilicate (BaAl2Si2O8).

[0092] The present invention is not limited to the above-described embodiment, and various modifications may be made within the scope of the technical concept of the present invention. For example, the following modifications may be adopted. In this case, the other points may be the same as those described above.

[0093] (Example of change) The liquid material used in the second embodiment may be a liquid material other than LPCS. In this case, an inorganic polymer material that is a ceramic raw material containing an alkoxide solution and has a molecular weight low enough to be in a liquid state can be used as the liquid material in the film boiling method described above.

[0094] For example, as described in the above-mentioned non-patent document 1, the liquid material used in the above-mentioned film boiling method may be a mixture of three alkoxydes solutions, and in this case, the matrix may be formed of barium aluminosilicate (BaAl2Si2O8).

[0095] In another example, as described in the above-mentioned non-patent document 2, the liquid material used in the above-mentioned film boiling method may be a mixture of multiple alkoxydes, in which case the matrix is ​​formed of mullite.

[0096] Furthermore, the liquid material used in the second embodiment may be any of the liquid materials described in the third embodiment above. [Explanation of symbols]

[0097] REFERENCE SIGNS LIST 1 heating body, 1a outer periphery, 2 insulating plate, 3 porous body, 3a outer periphery, 4 action mechanism, 4a bolt, 4b nut, 5 insulating material, 6 wire, 7 hanging part, 7a plate-shaped member, 7a1 connecting part, 7b rod-shaped member, 8 treatment vessel, 8a lid member, 8a1 through hole, 8a2 gas exhaust hole, 8b gas introduction hole, 9 liquid material, 10 ceramic-based composite material, 10a outer periphery, 11 coil, 13 fibrous body, 20 mounting fixture

Claims

1. A method for filling open pores generated in a matrix of a ceramic-based composite material having reinforcing fibers provided in the matrix with a ceramic to form the matrix, comprising the steps of: In a state where the ceramic matrix composite material is disposed in a liquid material that is a matrix raw material, (A) heating the ceramic matrix composite material to bring the liquid material into a film boiling state, thereby generating ceramics derived from the liquid material in the open pores; (B) cooling the ceramic matrix composite material; By repeating steps (A) and (B), the open pores are filled with the ceramics, In the repetition of (A) and (B), When the ceramic matrix composite material reaches a target temperature equal to or higher than the boiling point of the liquid material in each of the steps (A), heating of the ceramic matrix composite material is stopped and the step (B) is started; The method for filling open pores in a ceramic matrix composite material, wherein in each step of (B), the ceramic matrix composite material is cooled to a temperature lower than the boiling point of the liquid material.

2. 2. The method for filling open pores in a ceramic matrix composite material according to claim 1, further comprising the step of placing the produced ceramic matrix composite material in the liquid material prior to the step (A).

3. Prior to the step (A), the matrix is ​​formed on a fibrous body placed in the liquid material by a film boiling method, thereby forming the ceramic-based composite material in the liquid material; 2. The method for filling open pores in a ceramic matrix composite material according to claim 1, wherein the step (A) is then started while the ceramic matrix composite material is still placed in the liquid material.

4. In the arrangement state, the ceramic-based composite material and a heater are arranged inside a processing vessel that holds the liquid material, 4. The method for filling open pores in a ceramic matrix composite material according to claim 1, wherein in the step (A), the ceramic matrix composite material is heated by induction heating the heater.

5. In the method (A), an AC current is applied to a coil disposed outside the processing vessel to generate an AC magnetic field, thereby inductively heating the heating body, and the ceramic-based composite material is heated by the induction-heated heating body.

5. The method for filling open pores in a ceramic matrix composite material according to claim 4, wherein said treatment vessel is made of a non-conductive material.

6. A method for filling open pores generated in a matrix of a ceramic-based composite material having reinforcing fibers provided in the matrix with a ceramic to serve as the matrix, comprising the steps of: In a state where the ceramic matrix composite material is disposed in a liquid material that is a matrix raw material, (A) heating the ceramic matrix composite material to bring the liquid material into a film boiling state, thereby generating ceramics derived from the liquid material in the open pores; (B) cooling the ceramic matrix composite material to a temperature below the boiling point of the liquid material; By repeating steps (A) and (B), the open pores are filled with the ceramics, In the arrangement state, the ceramic-based composite material and a heater are arranged inside a processing vessel that holds the liquid material, In the step (A), the ceramic matrix composite material is heated by induction heating the heating body, In the method of (A), the ceramic matrix composite material is attached to the heating body by a mounting fixture, and the mounting fixture, the ceramic matrix composite material, and the heating body are suspended so as not to come into contact with the inner surface of the processing vessel.

7. The method for filling open pores in a ceramic-based composite material according to any one of claims 1 to 5, wherein the liquid material is polycarbosilane, borazine, methyltrichlorosilane, cyclohexane, a silicon alkoxide solution, an aluminum alkoxide solution, a mixed solution of a silicon alkoxide solution and an aluminum alkoxide solution, or a zirconium alkoxide solution.

8. A ceramic-based composite material in which the open pores are filled with ceramics by carrying out the open pore filling method according to any one of claims 1 to 5 and 7.

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