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

Abstract

Provided are: a BN-coated ceramic fiber in which the 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. 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) that is an amorphous phase and a second BN layer (3b) that 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.

Description

BN-coated ceramic fiber, ceramic-based composite material including the same, and method for manufacturing BN-coated ceramic fiber

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

[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] As a ceramic matrix composite material, a SiC matrix composite material in which a matrix mainly composed of SiC is formed between fibers mainly composed of silicon carbide (SiC) is known. In the first generation ceramic matrix composite material using SiC fibers, a carbon (C) layer that provides damage tolerance was formed on the surface of the SiC fiber. However, C is oxidized and disappears at temperatures above 600°C, and SiO ２ is formed, and a phenomenon of loss of damage tolerance (Pest behavior) occurs.

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

[0005] JP 2001-505864 A JP 2021-42100 A

[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 same, and a method for manufacturing a BN-coated ceramic fiber.

[0008] In order to solve the above problems, the BN-coated ceramic fiber, the ceramic matrix 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 primarily composed of SiC and a BN layer primarily composed of BN that coats the surface of the ceramic fiber, wherein the BN layer includes a first BN layer that is an amorphous phase and a second BN layer that is a crystalline phase, and the first BN layer is adjacent to the ceramic fiber and is sandwiched between the ceramic fiber and the second BN layer.

[0010] The present disclosure provides a ceramic matrix composite material including the above-described 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, which comprises covering the surface of a ceramic fiber whose main component is 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.

[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 in the past, resulting in a BN-coated ceramic fiber and a ceramic matrix composite material containing the same that are stronger than in the past.

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

[0014] Hereinafter, an embodiment of a BN-coated ceramic fiber, a ceramic-based composite material including the same, and a method for manufacturing a 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 matrix composite material including the same are suitable for use as components for aircraft engines and gas turbines.

[0016] (BN-coated ceramic fiber) Fig. 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 primarily composed of silicon carbide (SiC). More specifically, the ceramic fiber 2 contains 98 wt% or more of SiC, and its oxygen content is 1 wt% or less. In addition to oxygen, the ceramic fiber 2 may contain aluminum (Al), titanium (Ti), zirconium (Zr), or boron (B). The ceramic fiber 2 is used in the form of a fiber bundle containing approximately 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 3 a and a second BN layer 3 b.

[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 amorphous first BN layer 3a as the first layer that covers the surface of the ceramic fiber 2, thermal damage to the surface of the ceramic fiber 2 caused by the BN layer 3 formation process can be reduced. 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 serves to strengthen the bond between the ceramic fiber 2 and the matrix described below, to prevent the progression of matrix cracks, and to suppress 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. When forming the first BN layer 3a, raw materials containing halides are not used. Using raw materials that do not contain halides eliminates the need for a process to remove hydrogen halide from the 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 process can be reduced.

[0022] The first BN layer 3a, which is an amorphous phase, is formed (deposited) directly on the surface of the ceramic fiber 2. The deposition temperature for 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 for the second BN layer 3b is preferably 1000°C or higher. The second BN layer 3b formed at this temperature has 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. Because 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 fibers 2, and damage to the ceramic fibers 2 is minimal.

[0024] 2 shows a conceptual diagram of a CVD apparatus for a CVD method using a precursor as a raw material, as an example. 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 a polymer thereof.

[0026] The raw material supply chamber 11 has a raw material heating section 11a and a gas supply port 11b. The raw material heating section 11a is a coil heater or the like. At least a part of the precursor is heated by the raw material heating section 11a, and a carrier gas (e.g., N ) is supplied from a gas source 14 into the raw material supply chamber 11 via the gas supply port 11b. ２ By supplying the raw material (a gas), a -(B-N)-based gas or a -(B-N-C)-based gas is generated. The heating temperature by the raw material heating unit 11a is preferably set to 55°C to 200°C. The -(B-N)-based gas or the -(B-N-C)-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 part 12a and a gas exhaust port 12b. The film formation heating part 12a is a coil heater or the like. A pressure reducing part 16 is connected to the gas exhaust port 12b via a pressure controller 15. The pressure reducing part 16 is a pump or the like. The pressure reducing part 16 and the pressure controller 15 can control the pressure inside the film formation chamber 12 to a predetermined level.

[0028] The inside of the raw material supply chamber 11 and the film formation chamber 12 of the CVD device 10 is filled with N ２ After the atmosphere is replaced with a gas with low activity such as nitrogen or Ar gas, the film-forming chamber 12, which is controlled to a predetermined pressure, is heated by the film-forming heater 12a, and a -(B-N)-based gas or a -(B-N-C)-based gas is introduced into the chamber, whereby a BN layer 3 containing boron nitride (BN) as a main component is formed on the ceramic fiber 2. The film-forming chamber 12 is supplied with a dilution gas (N ２ gas) may be supplied.

[0029] The first BN layer 3a formed at 600°C or less is a -(B-N-Hy)n- layer or -(B-N-Cx-Hy)n- layer with a semi-inorganic structure that has not yet been completely ceramicized. 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 on which the first BN layer 3a is formed 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 ventilated in a N atmosphere 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 in the film formation heating unit 12a in an atmosphere of low-activity gas such as nitrogen gas or Ar gas.

[0030] When the crystalline second BN layer 3b is to be formed on the surface of the ceramic fiber 2 after the amorphous first BN layer 3a has been formed, the film 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 film formation temperature for the second BN layer 3b is preferably 1000°C or higher.

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

[0032] (Ceramic-based composite material) Fig. 3 is a schematic diagram of a ceramic-based composite material according to this embodiment. 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 silicon (Si).

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

[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 firing 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 Formation Temperature) For BN-coated ceramic fibers on which BN layers were formed at different deposition temperatures, single fiber tensile tests were conducted in accordance with JIS standard R1657 "Testing Methods for Reinforcement Properties of Long Fiber-Reinforced Ceramic Composite Materials." The thickness of the BN layer was ignored when calculating the tensile strength.

[0040] The ceramic fiber used was Hi-Nicalon (registered trademark) Type S (manufactured by Nippon Carbon Co., Ltd.). 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 in which the BN layer was formed at 1000°C was 3.35 GPa. The average tensile strength of the BN-coated ceramic fiber in which the BN layer was formed at 500°C was 3.76 GPa. The average tensile strength of the BN-coated ceramic fiber in which the BN layer was 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 from the untreated case is within the margin of error.

[0043] Furthermore, when the BN layer was repeatedly deposited at the same temperature, a clear decrease in strength was observed only 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] (Coating temperature and crystal structure of BN layer) A ceramic matrix composite material was produced 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 produced in the same manner as in Example, using a BN-coated ceramic fiber in which the first BN layer and the second BN layer were formed in the reversed order, and its cross section was observed (Comparative Example). The other coating conditions were the same.

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

[0047] The deposition conditions for the first BN layer were as follows: Temperature of source material heating section: 115° C. Temperature of deposition heating section: 500° C. (Actual temperature measured inside the furnace: 460° C. to 480° C.) Pressure inside the deposition chamber: 10.6 kPa to 10.9 kPa

[0048] The deposition conditions for the second BN layer were as follows: Temperature of source material heating section: 115° C. Temperature of deposition heating section: 1150° C. (Actual temperature measured inside the furnace: 1100° C.) Pressure inside the deposition chamber: normal pressure

[0049] The conditions for forming the Si-based compound layer were as follows: Temperature of source material heating section: 60° C. Temperature of film forming heating section: 900° C. (Actual temperature measured inside the furnace: 860° C. to 880° C.) Pressure inside the film forming chamber: 10.7 kPa

[0050] The manufacturing conditions for the ceramic matrix composite material are as follows: Si impregnation heating temperature: 1400°C; furnace atmosphere: argon (Ar), normal pressure

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

[0052] In the example where the first BN layer and then the second BN layer were formed, 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, the first BN layer (AREA 1) was amorphous, and the second BN layers (AREA 2 and 3) were 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 first and then 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 patterns, crystalline characteristics were observed for AREA 1, 2, and 3.

[0055] The BN-coated ceramic fibers used in the examples and comparative examples were subjected to single fiber tensile tests in accordance with JIS standard R1657, "Testing methods 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 then the second BN layer were formed was 3.84 GPa. In contrast, the average tensile strength of the Comparative Example in which the second BN layer and then the first BN layer were formed was approximately 3.2 GPa. The average tensile strength of the untreated ceramic fiber was approximately 3.7 GPa. In the Comparative Example, the strength decreased by approximately 14% during the process of forming the BN layer. On the other hand, no decrease in strength was observed in the Example.

[0057] These results suggest that forming the initial BN layer as an amorphous phase can prevent a decrease in strength during the BN layer formation process. In the CVD method using precursors as raw materials, an amorphous BN layer can be formed by setting the film formation temperature at 600°C or below.

[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 described in 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 whose main component is SiC, and a BN layer (3) whose main component is BN and which 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] An amorphous BN layer can be formed at a lower temperature than a crystalline BN layer. By making the initial BN layer that touches the ceramic fiber surface amorphous, the degree of decrease in strength of the ceramic fiber during BN layer formation can be reduced. This results in a BN-coated ceramic fiber that maintains the original strength of the ceramic fiber.

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

[0062] A ceramic matrix composite material produced 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) mainly composed of a Si-based compound between the BN-coated ceramic fiber and the matrix.

[0064] Si-based compounds have high oxidation resistance, so by disposing a Si-based compound layer between the BN-coated ceramic fiber and the matrix, the BN layer can be protected from high-temperature oxidation in the usage 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 whose main component is 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] Amorphous BN layers can be formed at lower temperatures than crystalline BN layers. By forming the first BN layer at a low temperature, the degree of decrease in strength of the ceramic fibers during BN layer formation can be reduced.

[0067] REFERENCE SIGNS LIST 1 BN-coated ceramic fiber 2 Ceramic fiber 3 BN layer 3a First BN layer 3b Second BN layer 10 CVD apparatus 11 Source material supply chamber 11a Source material heating section 11b Gas supply port 12 Film formation chamber 13 Precursor 14, 17 Gas source 15 Pressure controller 16 Pressure reduction section 20 Ceramic-based composite material 21 Matrix 22 Si-based compound layer

Claims

1. A BN-coated ceramic fiber comprising: a ceramic fiber whose main component is SiC; and a BN layer whose main component is BN and which coats the surface of the ceramic fiber, wherein the BN layer includes a first BN layer which is an amorphous phase and a second BN layer which is a crystalline phase, and the first BN layer is adjacent to the ceramic fiber and is sandwiched between the ceramic fiber and the second BN layer.

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

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

4. A method for producing BN-coated ceramic fibers, comprising covering the surface of a ceramic fiber whose main component is 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.

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