BN-coated ceramic fiber, ceramic matrix composite material including the same, and method for producing BN-coated ceramic fiber

Abstract

To provide a BN-coated ceramic fiber in which a decrease in strength in a BN layer formation process is suppressed, and which has higher strength than before; a ceramic matrix composite material including the BN-coated ceramic fiber; and a method for producing a BN-coated ceramic fiber.SOLUTION: A BN-coated ceramic fiber (1) according to the present disclosure comprises: a ceramic fiber (2) containing SiC as a main component; and a BN layer (3) containing BN as a main component and coating the surface of the ceramic fiber. The BN layer includes a first BN layer (3a), which is an amorphous phase, and a second BN layer (3b), which is a crystalline phase. The first BN layer is located adjacent to the ceramic fiber and is sandwiched between the ceramic fiber and the second BN layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a BN-coated ceramic fiber, a ceramic-based composite material including the same, and a method for producing the BN-coated ceramic fiber. [Background technology]

[0002] In the aircraft industry, with a view to improving engine combustion efficiency, there are high hopes for the use of ceramic matrix composites (CMCs), which are about one-third lighter than conventional metallic materials (nickel alloys) and have excellent heat resistance.

[0003] One type of ceramic matrix composite known is silicon carbide (SiC) matrix composite, in which a matrix mainly made of SiC is formed between fibers mainly made of SiC. In first-generation ceramic matrix composites using SiC fibers, a carbon (C) layer that provides damage tolerance was formed on the surface of the SiC fibers. However, C is oxidized and disappears at temperatures above 600°C, turning into SiO 2 is formed, and an event (Pest behavior) occurs in which damage tolerance is lost.

[0004] First-generation SiC fibers had low heat resistance and were difficult to coat at high temperatures, but with the development of second-generation SiC fibers with heat resistance, a boron nitride (BN) layer was formed on the surface of the SiC fibers (see Patent Documents 1 and 2). The formation of the BN layer increases the bonding strength between the SiC fibers and the matrix. This is said to result in a composite material with higher strength than the matrix material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2001-505864 [Patent Document 2] Patent Publication No. 2021-42100 Summary of the Invention [Problem to be solved by the invention]

[0006] The formation of the BN layer is carried out at high temperatures. Although the SiC fiber on which the BN layer is formed is a material with improved heat resistance, the strength is reduced by about 10-30% due to exposure to high temperatures for the formation of the BN layer.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a BN-coated ceramic fiber that suppresses the decrease in strength during the BN layer formation process and maintains strength close to that of the original ceramic fiber, a ceramic-based composite material including the BN-coated ceramic fiber, and a method for manufacturing the BN-coated ceramic fiber. [Means for solving the problem]

[0008] In order to solve the above problems, the BN-coated ceramic fiber, the ceramic-based composite material including the same, and the method for producing the BN-coated ceramic fiber of the present disclosure employ the following means.

[0009] The present disclosure provides a BN-coated ceramic fiber comprising: a ceramic fiber mainly composed of SiC; and a BN layer mainly composed of BN coating a surface of the ceramic fiber, the BN layer including a first BN layer which is an amorphous phase and a second BN layer which is a crystalline phase, the first BN layer being adjacent to the ceramic fiber and being sandwiched between the ceramic fiber and the second BN layer.

[0010] The present disclosure provides a ceramic-based composite material including the above-mentioned BN-coated ceramic fiber and a matrix containing SiC as a main component.

[0011] The present disclosure provides a method for producing a BN-coated ceramic fiber, in which the surface of a ceramic fiber mainly composed of SiC is covered with a first BN layer which is an amorphous phase, and then the surface of the first BN layer is covered with a second BN layer which is a crystalline phase. Effect of the Invention

[0012] By forming an amorphous phase as the first layer on the ceramic fiber surface, the degree of decrease in strength of the ceramic fiber when the BN layer is formed can be made smaller than before, resulting in a BN-coated ceramic fiber and a ceramic-based composite material equipped with the same that are stronger than before. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view of a BN-coated ceramic fiber. [Diagram 2] FIG. 1 is a conceptual diagram of an example of a CVD apparatus. [Diagram 3] FIG. 1 is a schematic diagram of a ceramic-based composite material according to one embodiment. [Figure 4] FIG. 4 is an enlarged schematic diagram of the BN-coated ceramic fiber in FIG. 3 and the Si-based compound layer coating it. [Diagram 5] FIG. 1 shows the results of a single fiber tensile test. [Figure 6] 1 is a TEM image of an embodiment. [Figure 7] 7 shows an enlarged image of the squared area in FIG. 6 and an electron beam diffraction pattern of the circled area in the enlarged image. [Figure 8] 1 is a TEM image of a comparative example. [Figure 9] 9 shows an enlarged image of the squared area in FIG. 8 and an electron beam diffraction pattern of the circled area in the enlarged image. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a BN-coated ceramic fiber, a ceramic-based composite material including the same, and a method for producing the BN-coated ceramic fiber according to the present disclosure will be described with reference to the drawings.

[0015] The BN-coated ceramic fiber according to this embodiment and the ceramic-based composite material including the same are suitable for use as components for aircraft engines and gas turbines.

[0016] (BN coated ceramic fiber) 1 is a cross-sectional view of a BN-coated ceramic fiber 1. The BN-coated ceramic fiber 1 includes a ceramic fiber 2 and a BN layer 3 that coats the surface of the ceramic fiber 2.

[0017] The ceramic fiber 2 is mainly composed of silicon carbide (SiC). More specifically, the ceramic fiber 2 contains 98 wt% or more of SiC, and the oxygen content is 1 wt% or less. The ceramic fiber 2 may contain aluminum (Al), titanium (Ti), zirconium (Zr), and boron (B) in addition to oxygen. The ceramic fiber 2 is used in the form of a fiber bundle having about 500 to 1000 single fibers. The ceramic fiber 2 may be Hi-Nicalon (registered trademark) Type S (manufactured by Nippon Carbon Co., Ltd.), Tyranno Fiber (registered trademark) SA (manufactured by UBE Corporation), Sylramic (registered trademark) fiber (manufactured by COI Ceramics Inc.), or the like.

[0018] The BN layer 3 is mainly composed of boron nitride (BN). The BN layer 3 has higher oxidation resistance than a conventional carbon (C) layer. The BN layer 3 includes a first BN layer 3a and a second BN layer 3b.

[0019] The first BN layer 3a is an amorphous phase. The first BN layer 3a is adjacent to the ceramic fiber 2 and is sandwiched between the ceramic fiber 2 and the second BN layer 3b. By providing the first BN layer 3a of an amorphous phase as the first layer of the layer that covers the surface of the ceramic fiber 2, it is possible to reduce thermal damage to the surface of the ceramic fiber 2 caused by the BN layer 3 formation process. The thickness of the first BN layer 3a is preferably 200 nm or less.

[0020] The second BN layer 3b is a crystalline phase. The second BN layer 3b is the outermost layer of the BN-coated ceramic fiber 1. The second BN layer 3b plays a role in strengthening the bond between the ceramic fiber 2 and the matrix described below, preventing the progress of matrix cracks, and suppressing the transmission of stress to the ceramic fiber 2. The thickness of the second BN layer 3b is preferably 250 nm or more.

[0021] The BN layer 3 (first BN layer 3a and second BN layer 3b) can be formed by chemical vapor deposition (CVD). The first BN layer 3a is preferably formed by CVD using a precursor as a raw material. Raw materials containing halides are not used in forming the first BN layer 3a. Using raw materials that do not contain halides makes it unnecessary to perform a process to remove hydrogen halides from exhaust gas. In addition, damage to the ceramic fibers 2 caused by active raw material gases or by-products generated as a result of the CVD method can be reduced.

[0022] The first BN layer 3a, which is an amorphous phase, is formed (deposited) directly on the surface of the ceramic fibers 2. The deposition temperature of the first BN layer 3a is 600° C. or less, preferably 550° C. or less, and more preferably 500° C. or less. The first BN layer 3a deposited at this temperature becomes an amorphous phase.

[0023] The second BN layer 3b, which is a crystalline phase, is formed on the first BN layer 3a. The film formation temperature of the second BN layer 3b is preferably 1000°C or higher. The second BN layer 3b formed at this temperature will be a crystalline phase. The second BN layer 3b can be formed by any of the following CVD methods: CVD using a precursor as a raw material, thermal CVD using a raw material containing a halide, or plasma CVD. Since the second BN layer 3b is formed on the first BN layer 3a, even if a CVD method using a raw material containing a halide is used to form the second BN layer 3b, the first BN layer 3a protects the ceramic fiber 2, and damage to the ceramic fiber 2 is small.

[0024] As an example, a conceptual diagram of a CVD apparatus for a CVD method using a precursor as a raw material is shown in Fig. 2. The CVD apparatus 10 in Fig. 2 has a raw material supply chamber 11 and a film formation chamber 12.

[0025] A raw material (precursor 13) for the BN layer 3 is placed in the raw material supply chamber 11. The precursor 13 is, for example, ammonia borane (H 3 NBH 3 ), cyclotriborazane (B 3 H 6 N 3), borazene (aminoborane) or their polymers.

[0026] The raw material supply chamber 11 has a raw material heating unit 11a and a gas supply port 11b. The raw material heating unit 11a is a coil heater or the like. At least a part of the precursor is heated by the raw material heating unit 11a, and a carrier gas (e.g., N 2 By supplying the raw material supply chamber 11 with the raw material gas, a -(BN)-based gas or a -(BNC)-based gas is generated. The heating temperature by the raw material heating unit 11a is preferably set to 55 to 200° C. The -(BN)-based gas or the -(BNC)-based gas generated in the raw material supply chamber 11 flows into the film formation chamber 12.

[0027] The film formation chamber 12 has a film formation heating unit 12a and a gas exhaust port 12b. The film formation heating unit 12a is a coil heater or the like. The gas exhaust port 12b is connected to a pressure reducing unit 16 via a pressure controller 15. The pressure reducing unit 16 is a pump or the like. The pressure reducing unit 16 and the pressure controller 15 can control the pressure inside the film formation chamber 12 to a predetermined pressure.

[0028] The inside of the raw material supply chamber 11 and the film formation chamber 12 of the CVD apparatus 10 are filled with N 2 After replacing the atmosphere with a gas with low activity such as nitrogen gas or Ar gas, the inside of the deposition chamber 12, which is controlled to a predetermined pressure, is heated by the deposition heating unit 12a, and when a -(BN)-based gas or a -(BNC)-based gas is introduced into the deposition chamber 12, a BN layer 3 containing boron nitride (BN) as a main component is deposited on the ceramic fibers 2. A dilution gas (N 2 Gas) may be supplied.

[0029] The first BN layer 3a formed at 600°C or less is a -(BN-Hy)n- layer or -(BN-Cx-Hy)n- layer with a semi-inorganic structure that has not yet been completely converted into ceramic. Therefore, if it is exposed to the atmosphere as it is, it will react with water vapor and oxygen in the atmosphere and decompose. Therefore, when the ceramic fiber 2 with the first BN layer 3a formed thereon is exposed to the atmosphere, after the first BN layer 3a is formed at 600°C or less, the inside of the film formation chamber 12 is filled with N gas controlled at a predetermined pressure before being exposed to the atmosphere. 2 The first BN layer 3a is stabilized by heating (heat treatment) at 900° C. or higher using the film formation heating unit 12a in an atmosphere of low activity gas such as Ar gas or Ar gas.

[0030] When forming the crystalline second BN layer 3b on the first amorphous BN layer 3a after forming the first amorphous BN layer 3a on the surface of the ceramic fiber 2, the layer is formed by any of the following CVD methods: CVD using a precursor as a raw material, thermal CVD using a raw material containing a halide, or plasma CVD. In this case, the deposition temperature for the second BN layer 3b is preferably 1000°C or higher.

[0031] When the second BN layer 3b is formed by a CVD method using the same precursor as that used for forming the first BN layer 3a, the first BN layer 3a and the second BN layer 3b may be formed successively. For example, when the CVD apparatus 10 shown in FIG. 2 is used, the first BN layer 3a is formed on the surface of the ceramic fiber 2 under predetermined conditions using a part of the precursor in the raw material heating section 11a. Next, the carrier gas from the gas source 14 is stopped, and the material is heated (heat-treated) at 1000°C or higher by the film-forming heating section 12a only under the gas flow from the gas source 17. Thereafter, the carrier gas is again supplied from the gas source 14 to the raw material supply chamber 11, and the precursor remaining in the raw material supply chamber 11 is heated to 55 to 200°C by the raw material heating section 11a, and the -(BN)-based gas or -(BNC)-based gas generated from the precursor is allowed to flow into the film-forming chamber 12. As a result, a crystalline second BN layer 3b is formed on the first BN layer 3a.

[0032] (Ceramics-based composite materials) Fig. 3 is a schematic diagram of the ceramic-based composite material according to this embodiment, and Fig. 4 is an enlarged schematic diagram of the BN-coated ceramic fiber and the Si-based compound layer coating it in Fig. 3.

[0033] The ceramic-based composite material 20 includes a BN-coated ceramic fiber 1 and a matrix 21. The ceramic-based composite material 20 may include a Si-based compound layer 22 between the BN-coated ceramic fiber 1 and the matrix 21.

[0034] The BN-coated ceramic fiber 1 is as described above.

[0035] The matrix 21 is mainly composed of SiC. More specifically, the matrix 21 contains 50% or more of SiC. The matrix 21 may also contain carbon (C) and / or silicon (Si).

[0036] The ceramic-based composite material 20 can be manufactured by melt infiltration method (MI method), vapor phase impregnation method (CVI method), liquid phase impregnation method (PIP method), etc. The ceramic-based composite material 20 is preferably manufactured by melt infiltration method (MI method).

[0037] The Si-based compound layer 22 is mainly composed of a Si-based compound. More specifically, the Si-based compound contains 90% or more of a Si-based compound. The Si-based compound is SiC or Si 3 N 4 The Si-based compound layer 22 may contain carbon (C) and nitrogen (N). The Si-based compound layer 22 protects the BN layer from high-temperature oxidation (particularly molten Si) and plays a role in preventing oxidation degradation.

[0038] The Si-based compound layer 22 can be formed on the surface of the BN-coated ceramic fiber 1 by a CVD method, a PVD method, a liquid phase sintering method, or the like. The Si-based compound layer 22 is preferably manufactured by a CVD method, and is formed so as to cover the entire surface of the BN-coated ceramic fiber 1.

[0039] Next, the effects of the above embodiment will be described. (BN layer deposition temperature) For the BN-coated ceramic fibers on which the BN layer was formed at different deposition temperatures, single fiber tensile tests were carried out in accordance with JIS standard R1657 "Testing method for reinforcement properties of long fiber reinforced ceramic composite materials." When calculating the tensile strength, the thickness of the BN layer was ignored.

[0040] The ceramic fiber used was Hi-Nicalon (registered trademark) Type S (manufactured by Nippon Carbon Co., Ltd.). The raw material for the BN layer was H 3 NBH 3 (precursor) and N 2 (Carrier gas) was used. Film formation was performed under the same conditions except for the film formation temperature. The film formation temperature was the set temperature of the film formation heating unit. The CVD apparatus shown in FIG. 2 was used to form the BN layer.

[0041] The test results are shown in Figure 5. The average tensile strength of the BN-coated ceramic fiber with a BN layer formed at 1000°C was 3.35 GPa. The average tensile strength of the BN-coated ceramic fiber with a BN layer formed at 500°C was 3.76 GPa. The average tensile strength of the BN-coated ceramic fiber with a BN layer formed at 450°C was 3.83 GPa.

[0042] Although not shown in Figure 5, the average tensile strength of the untreated ceramic fiber before the BN layer was formed was approximately 3.7 GPa. When the coating was formed at 1000°C, the strength decreased by about 10% compared to the untreated case. On the other hand, when the coating was formed at 500°C and 450°C, no decrease in strength was observed. The difference in the average tensile strength value from the untreated one is within the margin of error.

[0043] In addition, when the BN layer was repeatedly deposited at the same temperature, a clear decrease in strength was only observed in the first deposition at 1000°C, and no decrease in strength was observed in the second or subsequent depositions.

[0044] From the above results, it became clear that the decrease in fiber strength due to the film formation process can be avoided by lowering the temperature during the initial formation of the BN layer that is formed directly on the surface of the ceramic fiber.

[0045] (Deposition temperature and crystal structure of BN layer) A ceramic matrix composite material was manufactured according to the above embodiment, and its cross section was observed with a transmission electron microscope (Example). For comparison, a ceramic matrix composite material was manufactured in the same manner as in the Example, using a BN-coated ceramic fiber in which the deposition order of the first BN layer and the second BN layer was reversed, and its cross section was observed (Comparative Example). The other deposition conditions were the same.

[0046] The ceramic fiber used was Hi-Nicalon (registered trademark) Type S (manufactured by Nippon Carbon Co., Ltd.). The raw material for the BN layer was H 3 NBH 3 (Precursor), N 2 (carrier gas) was used. Silicon tetrachloride (SiCl 4 ) and methane (CH 4 ) was used. Silicon (Si) metal and carbon (C) powder were used as the matrix raw materials. The CVD apparatus shown in Figure 2 was used to form the BN layer.

[0047] The deposition conditions for the first BN layer were as follows. Raw material heating section temperature: 115℃ Film-forming heating section temperature: 500℃ (actual temperature inside the furnace 460~480℃) Pressure inside the deposition chamber: 10.6 to 10.9 kPa

[0048] The deposition conditions for the second BN layer were as follows. Raw material heating section temperature: 115℃ Film-forming heating section temperature: 1150℃ (actual temperature inside the furnace 1100℃) Pressure inside the deposition chamber: normal pressure

[0049] The film formation conditions for the Si-based compound layer are as follows. Raw material heating section temperature: 60℃ Film-forming heating section temperature: 900℃ (actual temperature inside the furnace 860~880℃) Pressure inside the deposition chamber: 10.7kPa

[0050] The manufacturing conditions for the ceramic matrix composite material are as follows: Silicon impregnation heating temperature: 1400℃ Furnace atmosphere: Argon (Ar), normal pressure

[0051] Figure 6 is a TEM image of the example. Figure 7 is an enlarged image of the squared area in Figure 6 and an electron beam diffraction pattern of the circled area in the enlarged image.

[0052] In the example where the first BN layer and the second BN layer were formed in this order, it was confirmed that the BN layer on the surface of the ceramic fiber had a two-layer structure (see Figure 6). According to the electron beam diffraction pattern, it was observed that the first BN layer (AREA 1) was amorphous, and the second BN layer (AREA 2, 3) was crystalline.

[0053] Fig. 8 is a TEM image of a comparative example, and Fig. 9 is an enlarged image of the squared area in Fig. 8 and an electron beam diffraction pattern of the circled area in the enlarged image.

[0054] In the comparative example, in which the second BN layer was formed followed by the first BN layer, no clear boundary between the first and second BN layers could be confirmed in the BN layer on the surface of the ceramic fiber (see Figure 7). In the electron diffraction pattern, crystalline characteristics were observed in AREA1, 2, and 3.

[0055] For the BN-coated ceramic fibers used in the examples and comparative examples, single fiber tensile tests were carried out in accordance with JIS standard R1657 "Testing method for reinforcement properties of long fiber reinforced ceramic composite materials." When calculating the tensile strength, the thickness of the BN layer was ignored.

[0056] The average tensile strength of the example in which the first BN layer and the second BN layer were formed in this order was 3.84 GPa. In contrast, the average tensile strength of the comparative example in which the second BN layer and the first BN layer were formed in this order was about 3.2 GPa. The average tensile strength of the untreated ceramic fiber was about 3.7 GPa. In the comparative example, the strength decreased by about 14% during the process of forming the BN layer. On the other hand, no decrease in strength was observed in the examples.

[0057] These results suggest that by forming the first layer of the BN layer as an amorphous phase, it is possible to prevent a decrease in strength during the process of forming the BN layer. In the CVD method using a precursor as a raw material, an amorphous BN layer can be formed by setting the film formation temperature at 600°C or less.

[0058] <Additional Notes> The BN-coated ceramic fiber, the ceramic-based composite material including the same, and the method for producing the BN-coated ceramic fiber according to the above-described embodiments can be understood, for example, as follows.

[0059] A BN-coated ceramic fiber (1) according to a first aspect of the present disclosure comprises a ceramic fiber mainly composed of SiC, and a BN layer (3) mainly composed of BN that coats the surface of the ceramic fiber, the BN layer including a first BN layer (3a) which is an amorphous phase, and a second BN layer (3b) which is a crystalline phase, the first BN layer being adjacent to the ceramic fiber and being sandwiched between the ceramic fiber and the second BN layer.

[0060] A BN layer in the amorphous phase can be formed at a lower temperature than a BN layer in the crystalline phase. By making the first layer of the BN layer that touches the ceramic fiber surface an amorphous phase, the degree of decrease in strength of the ceramic fiber when the BN layer is formed can be reduced. This results in a BN-coated ceramic fiber that retains the original strength of the ceramic fiber.

[0061] A ceramic-based composite material (20) according to a second embodiment of the present disclosure includes the BN-coated ceramic fiber according to the first embodiment and a matrix (21) mainly composed of SiC.

[0062] A ceramic matrix composite material produced by using the BN-coated ceramic fiber according to the first embodiment is a ceramic matrix composite material having higher strength than conventional ceramic matrix composite materials.

[0063] The ceramic matrix composite material according to a third aspect of the present disclosure is the second aspect, further comprising a Si-based compound layer (22) containing a Si-based compound as a main component between the BN-coated ceramic fiber and the matrix.

[0064] Si-based compounds have high oxidation resistance, so by placing a layer of Si-based compounds between the BN-coated ceramic fiber and the matrix, the BN layer can be protected from high-temperature oxidation in the operating environment.

[0065] A method for producing a BN-coated ceramic fiber according to a fourth aspect of the present disclosure involves covering the surface of a ceramic fiber mainly composed of SiC with a first BN layer, which is an amorphous phase, and then covering the surface of the first BN layer with a second BN layer, which is a crystalline phase.

[0066] An amorphous BN layer can be formed at a lower temperature than a crystalline BN layer. By forming the first BN layer at a low temperature, the decrease in strength of the ceramic fibers during the formation of the BN layer can be reduced. [Explanation of symbols]

[0067] 1. BN-coated ceramic fiber 2. Ceramic Fibers 3 BN layer 3a 1st BN layer 3b 2nd BN layer 10 CVD equipment 11 Raw material supply room 11a Raw material heating section 11b Gas supply port 12 Deposition chamber 13 Precursors 14,17 Gas Source 15 Pressure control gauge 16 Pressure reducing section 20 Ceramic-based composite materials 21. Matrix 22 Si-based compound layer

Claims

1. Ceramic fibers mainly composed of SiC; A BN layer containing BN as a main component and coating a surface of the ceramic fiber, the BN layer includes a first BN layer having an amorphous phase and a second BN layer having a crystalline phase; The first BN layer is adjacent to the ceramic fiber and is sandwiched between the ceramic fiber and the second BN layer.

2. The BN-coated ceramic fiber according to claim 1; A ceramic matrix composite material comprising: a matrix mainly composed of SiC.

3. 3. The ceramic-based composite material according to claim 2, further comprising a Si-based compound layer, the Si-based compound being a main component, between the BN-coated ceramic fiber and the matrix.

4. The surface of the ceramic fiber mainly composed of SiC is covered with a first BN layer, which is an amorphous phase, and then A method for producing a BN-coated ceramic fiber, comprising covering the surface of the first BN layer with a second BN layer which is a crystalline phase.

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