Ceramic matrix composite and method for producing ceramic matrix composite

Abstract

Provided is a ceramic matrix composite comprising: fibers that contain silicon carbide; a coating layer of boron nitride that is formed on the surfaces of the fibers and that has a film thickness zero ratio of not more than 50%; and a silicon carbide layer that is formed on the surface of the coating layer and that has a film thickness within the range of 0.1-50 μm. A fiber bundle including the fibers forms a structure including at least one of a fiber laminate and a fabric. Also provided is a method for producing a ceramic matrix composite, said method comprising: a step for forming a coating layer on fibers included in a fiber bundle by a continuous process; a step for forming a structure with the fiber bundle including the fibers on which the coating layer is formed; and a step for forming a silicon carbide layer on the surface of the coating layer by chemical vapor infiltration with respect to the structure.

Description

Ceramic matrix composite material and method for manufacturing ceramic matrix composite material

[0001] The present disclosure relates to a ceramic matrix composite material and a method for manufacturing a ceramic matrix composite material.

[0002] Patent Document 1 discloses that by forming a boron nitride interphase layer on the surface of silicon carbide fibers and using this to form a matrix, a strong boron nitride (BN) interphase layer, i.e., a BN interfacial layer, can be formed between the fiber and the matrix. According to this, the BN interfacial layer enhances the bonding strength between the BN interfacial layer and the fiber and between the BN interfacial layer and the matrix, resulting in a composite material with higher strength than the matrix material. Such ceramic matrix composites (CMCs) have attracted attention as high-temperature structural components for engine parts, gas turbine parts, spacecraft, and the like, due to their excellent mechanical properties and light weight in high-temperature environments. CMCs (SiC / SiC composites) with silicon carbide fibers as reinforcement and a silicon carbide matrix are expected to be next-generation high-temperature structural materials due to their excellent heat resistance, oxidation resistance, and corrosion resistance.

[0003] Special Publication No. 2001-505864

[0004] When high-temperature processes are performed on fibers to form a BN interfacial layer on the fibers, as described in Patent Document 1, non-uniformities occur in the thickness, composition, crystallinity, and frequency of contact between fibers of the BN interfacial layer, resulting in variations in the strength of the fibers after the process. Furthermore, when the fibers are broken during the high-temperature process, the process of forming the BN interfacial layer on the fibers frequently stops, which is a problem. This results in reduced manufacturing efficiency and variations in quality, making it difficult to obtain a ceramic-based composite material with stable high strength.

[0005] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a ceramic matrix composite material and a method for manufacturing the ceramic matrix composite material that can suppress variations in fiber strength and prevent fiber breakage after a process for forming a BN interfacial layer on the fiber has been carried out.

[0006] The ceramic matrix composite material according to the present disclosure comprises fibers containing silicon carbide, a coating layer of boron nitride formed on the surface of the fibers and having a zero ratio of 50% or less, and a silicon carbide layer formed on the surface of the coating layer and having a thickness in the range of 0.1 to 50 μm. Also, a structure including at least one of a fiber laminate and a woven fabric is formed by fiber bundles containing the fibers.

[0007] The coating layer may have an average thickness of 100 to 1000 nm.

[0008] The interplanar distance (d002) in the C-axis direction in the coating layer may be 3.5 Å or less.

[0009] The coating layer may have a nitrogen to boron ratio of 0.7 to 1.3, and the amount of oxygen mixed therein may be 10 atomic percent or less.

[0010] The silicon carbide layer may have a thickness of 0.5 μm or more inside the fiber bundle and 5 to 30 μm outside the fiber bundle.

[0011] The method for producing a ceramic matrix composite material according to the present disclosure includes a step of forming a coating layer on fibers contained in a fiber bundle by a continuous process, a step of forming a structure from the fiber bundle containing the fibers with the coating layer, and a step of forming a silicon carbide layer on the surface of the coating layer by chemical vapor impregnation of the structure.

[0012] A continuous process may be a process in which a coating layer is formed on an area of ​​the surface of the fibers to be treated while the area is moved in the direction of extension of the fiber bundle.

[0013] The heating temperature of the region may be set to 1300° C. or higher, and the time for the region to pass through each point of the fiber in the extension direction may be set to within one minute.

[0014] The fiber bundle may be moved through the regions by being transported in the extending direction at a speed of 1 to 10 m per minute.

[0015] When multiple fiber bundles are processed simultaneously by a continuous process, the fiber bundles may be spaced apart by 5 mm or more.

[0016] When processing the fiber bundles through a continuous process, a tension of 200 grams force or less may be applied to the fiber bundles.

[0017] When treating the fiber bundle by the continuous process, the fiber bundle may be exposed to a gas containing a raw material in which the ratio of ammonia to boron trichloride is in the range of 1 to 3, the gas pressure may be set to 100 to 500 Pa, and the direction of gas flow may be set to be opposite to the direction of transport of the fiber bundle.

[0018] In the steps of the manufacturing method after forming the silicon carbide layer, the fibers may be heated to a temperature that does not exceed the temperature at which the coating layer is formed.

[0019] According to the present disclosure, it is possible to provide a ceramic matrix composite material and a method for manufacturing the ceramic matrix composite material that can suppress variations in fiber strength and fiber breakage after a process for forming a BN interfacial layer on the fiber, thereby enabling efficient production of high-strength ceramic matrix composite materials with stable quality.

[0020] FIG. 1 is a schematic diagram of a fiber bundle included in a ceramic matrix composite material according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing an example of a coating layer and a silicon carbide layer formed on the surface of a fiber. FIG. 3 is a diagram showing a flowchart of a method for producing a ceramic matrix composite material according to an embodiment of the present disclosure. FIG. 4 is a schematic diagram of an application device for forming a boron nitride coating layer by a continuous process. FIG. 5 is a diagram showing an example of the relationship between the zero film thickness rate and tensile strength. FIG. 6 is a diagram showing an example of a diffraction chart corresponding to the heat treatment temperature. FIG. 7 is a diagram showing an example of the relationship between the heat treatment temperature and the interplanar distance (d002) in the C-axis direction of the BN interface layer. FIG. 8 is a diagram showing an example of the relationship between creep rupture time and applied stress. FIG. 9 is a diagram showing differences in the amount of impurities mixed in the coating layer.

[0021] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that common parts in the drawings are given the same reference numerals, and duplicated explanations will be omitted.

[0022] [Configuration of ceramic matrix composite material] Fig. 1 is a schematic diagram of a fiber bundle included in a ceramic matrix composite material according to an embodiment of the present disclosure. Fig. 2 is a schematic diagram showing an example of a coating layer and a silicon carbide layer formed on the surface of a fiber. Fig. 1 shows a cross-sectional view of a fiber bundle FB. Fig. 2 shows a cross-sectional view of a fiber CF.

[0023] The ceramic matrix composite material includes fibers CF, a coating layer LB, and a silicon carbide layer LS. In the ceramic matrix composite material, a woven fabric is formed from fiber bundles FB containing the fibers CF. This woven fabric can be molded into products having three-dimensional shapes and can be used, for example, as high-temperature structural components such as engine parts, gas turbine parts, and heat exchanger parts. The fiber bundles FB are composed of multiple fibers CF.

[0024] Here, the fiber CF is a fiber containing silicon carbide. The coating layer LB is a boron nitride coating layer formed on the surface of the fiber CF, and has a zero thickness ratio of 50% or less. The definition of "zero thickness ratio" will be described later. The thickness of the silicon carbide layer LS is in the range of 0.1 to 50 μm.

[0025] The coating layer LB has a graphite structure (crystalline structure). In the crystalline structure, the bonds between atoms in a plane perpendicular to the C-axis direction are covalent bonds, while the bonds between atoms in the C-axis direction are van der Waals bonds. The plane perpendicular to the C-axis direction in the crystalline structure is parallel to the surface of the fiber CF. Therefore, a crack propagating from the outside of the coating layer LB delaminates in the coating layer LB on a plane parallel to the surface of the fiber CF. As a result, the crack is prevented from propagating into the fiber CF. This crack deflection mechanism improves the toughness of the entire composite material and enhances its ability to absorb fracture energy.

[0026] In this way, by forming the coating layer LB on the surface of the fiber CF, the strength of the fiber CF can be improved. Therefore, by examining the extent to which the coating layer LB is formed on the surface of the fiber CF, it can be used as an index for measuring the degree of improvement in the strength of the fiber CF.

[0027] Next, the "zero film thickness rate" will be described. For example, the "zero film thickness rate" can be defined by observing the cross section of the fiber bundle FB as shown in FIG.

[0028] First, fields of view R1 to R4 are set on the cross section of the fiber bundle FB. Here, fields of view R1 and R3 are set inside the fiber bundle FB. Fields of view R2 and R4 are set on the outer periphery of the fiber bundle FB. Each field of view is set to be large enough to observe at least five or more fibers CF that fit the entire circumference.

[0029] For example, according to Figure 1, there are six fibers CF that fit completely around the field of view R1, five fibers CF that fit completely around the field of view R2, six fibers CF that fit completely around the field of view R3, and seven fibers CF that fit completely around the field of view R4.

[0030] Next, a secondary electron image of each field of view is taken at a magnification of 20,000 times. For example, observation is performed using a scanning electron microscope (SEM). The maximum and minimum thicknesses of the coating layer LB formed on the surface of each fiber CF are recorded in the obtained secondary electron image. The percentage of fibers CF whose entire circumference falls within fields of view R1 to R4 and whose coating layer LB has a minimum thickness of 0 is defined as the "zero film thickness rate."

[0031] Therefore, a state in which the "zero film thickness rate" is 100% means that the minimum thickness of the coating layer LB is 0 for all of the observed fibers CF. Also, a state in which the "zero film thickness rate" is 0% means that the minimum thickness of the coating layer LB is not 0 for all of the observed fibers CF. In the present disclosure, by controlling the zero film thickness rate to 50% or less, a uniform coating layer is formed over the entire surface of the fiber, thereby achieving improved strength and stability.

[0032] The average thickness of the coating layer LB may be 100 to 1000 nm. Here, the "average thickness" is obtained by measuring the thickness of the coating layer LB for the fibers CF whose entire circumference falls within the fields of view R1 to R4 and calculating the average value. The thicknesses may also be obtained for each fiber CF at positions arranged at a predetermined angular interval in the circumferential direction and then averaged.

[0033] If the average thickness of the coating layer LB is less than 100 nm, the effect of the coating layer LB in inhibiting crack propagation is insufficient. Furthermore, if the average thickness of the coating layer LB is greater than 1000 nm, the coating layer LB itself is more likely to peel off from the fiber CF, which does not improve strength. Furthermore, increasing the thickness of the coating layer LB also increases costs. Therefore, in order to obtain a sufficient effect of improving strength by providing the coating layer LB on the surface of the fiber CF, the average thickness of the coating layer LB is set to a range of 100 to 1000 nm.

[0034] The interplanar distance (d002) in the C-axis direction of the coating layer LB may be 3.5 Å or less. The interplanar distance in the C-axis direction of boron nitride crystals is an important parameter that serves as an indicator of crystallinity. The smaller the interplanar distance, the higher the crystallinity and the improved mechanical properties. Furthermore, the ratio of nitrogen to boron in the coating layer LB may be 0.7 to 1.3, and the amount of oxygen mixed in may be 10 atomic percent or less. This allows a coating layer LB having a refined crystal structure to be formed on the surface of the fiber CF, thereby achieving the effect of suppressing crack propagation by the coating layer LB. In particular, keeping the oxygen content low prevents oxidative degradation in high-temperature environments and ensures long-term stability. Note that, according to the manufacturing method of the ceramic-based composite material disclosed herein, a crystal structure with an interplanar distance in the C-axis direction of 3.5 Å or less can be obtained without performing additional heat treatment after forming the coating layer LB. Furthermore, the ratio of nitrogen to boron in the coating layer LB may be 0.7 to 1.3, and the amount of oxygen mixed in may be 10 atomic percent or less.

[0035] Furthermore, the thickness of the silicon carbide layer LS may be 0.5 μm or more inside the fiber bundle FB and 5 to 30 μm outside the fiber bundle FB. The thickness distribution of the silicon carbide layer inside and outside the fiber bundle significantly affects the mechanical properties of the entire composite material. This reduces the situation in which cracks that occur in the ceramic matrix composite material propagate and lead to fracture of the entire ceramic matrix composite material. In particular, the growth of cracks that do form is suppressed by the coating layer LB formed on the surface of the fibers CF contained in the fiber bundle FB. This results in improved strength of the ceramic matrix composite material.

[0036] If the thickness of the silicon carbide layer LS inside the fiber bundle FB is less than 0.5 μm, the boundary between the coating layer LB formed on the surface of the fibers CF contained in the fiber bundle FB and the silicon carbide layer LS will be reduced. Furthermore, if the thickness of the silicon carbide layer LS outside the fiber bundle FB is greater than 30 μm, the silicon carbide layer will preferentially deposit on the outside of the fiber bundle, resulting in reduced boundaries between the coating layer LB formed on the surface of the fibers CF contained in the fiber bundle FB and the silicon carbide layer LS. Therefore, in order to obtain a sufficient strength improvement effect by providing the coating layer LB on the surface of the fibers CF, the thickness of the silicon carbide layer LS inside the fiber bundle FB is set to 0.5 μm or more. Furthermore, the thickness of the silicon carbide layer LS outside the fiber bundle FB is set to 5 to 30 μm.

[0037] [Method for Manufacturing Ceramic Matrix Composite Material] FIG. 3 is a flowchart showing a method for manufacturing a ceramic matrix composite material according to an embodiment of the present disclosure.

[0038] In step S101, a coating layer LB is formed on the fibers CF included in the fiber bundle FB by a continuous process. Details of the "continuous process" will be described later. This step allows for efficient formation of a boron nitride coating layer with stable quality.

[0039] In step S103, a structure including at least one of a fiber laminate and a woven fabric is formed using fiber bundles FB containing fibers CF on which coating layers LB are formed. For example, the fiber bundles FB are woven together to form a woven fabric so as to obtain a ceramic matrix composite material of a predetermined shape. Specifically, two-dimensional woven fabrics such as plain weave, twill weave, and satin weave, three-dimensional woven fabrics, and braid structures can be formed. Also applicable are a method of laminating multiple layers of unidirectionally oriented fiber bundles, and a method of arranging them in the form of a nonwoven fabric.

[0040] In step S105, a silicon carbide layer LS is formed on the surface of the coating layer LB by chemical vapor impregnation of the structure. For example, the silicon carbide layer LS is formed using methyltrichlorosilane in the chemical vapor impregnation. The gas used in the chemical vapor impregnation is not limited to the example given here.

[0041] Next, the "continuous process" will be explained. Figure 4 is a schematic diagram of a coating device for forming a boron nitride coating layer by a continuous process.

[0042] The "continuous process" is a process in which a fiber bundle FB is continuously fed into a reactor FR, and a coating layer LB is formed on the surface of the fibers CF contained in the fiber bundle FB within the reactor FR. In particular, the "continuous process" is a process in which a coating layer LB is formed on a treatment target area of ​​the surface of the fibers CF while the treatment target area is moved in the extension direction of the fiber bundle FB. This method allows for the formation of a coating layer with more efficient and uniform quality than conventional batch processing.

[0043] 4 shows a state in which the fiber bundle FB is fed from the feeding device P1 and moves in the transport direction AR1 within the reactor FR. The feeding device P1 is equipped with a spool around which the fiber bundle is wound and a tension control mechanism that controls the tension of the fiber bundle, and can feed the fiber bundle under stable conditions.

[0044] Then, in the reactor FR, the fibers CF are heated in the raw material gas flowing in the flow direction AR2, and a coating layer LB is formed on the surface of the fibers CF. The reactor FR is equipped with a heating zone and a gas supply system, and is capable of accurate temperature control and gas composition control.

[0045] Here, in the reactor FR, the heating temperature of the region to be treated on the surface of the fiber CF is set to 1300°C or higher, and the time it takes for each point of the fiber CF in the extension direction to pass through that region is set to within one minute. In other words, the time it takes each point of the fiber bundle FB to pass through the reactor FR is set to within one minute, and the heating temperature in the reactor FR is set to 1300°C or higher. This is a feature that significantly differs from conventional batch-type processing.

[0046] Such high-temperature, short-time processing conditions make it possible to form a coating layer LB having a fine crystalline structure on the surface of the fiber CF while preventing the strength of the fiber CF from being reduced due to the effects of heating.

[0047] When forming the coating layer LB, the fiber bundle FB may be conveyed in the extending direction of the fiber bundle FB at a speed of 1 to 10 m / min to move the area of ​​the surface of the fibers CF that is to be treated in the reactor FR. For example, if the conveying speed of the fiber bundle FB exceeds 10 m / min, it becomes necessary to increase the length of the reactor FR along the extending direction of the fiber bundle FB in order to form a sufficient coating layer LB. From the viewpoint of reducing the cost of the reactor FR, it is better to have a slower conveying speed of the fiber bundle FB.

[0048] On the other hand, if the conveying speed of the fiber bundle FB is less than 1 m per minute, the reaction between the raw material gas and the surface of the fiber CF will occur over a short distance. From the viewpoints of controlling the flow of the raw material gas and discharging unnecessary gas after the reaction, it is preferable that the length of the reactor FR along the extending direction of the fiber bundle FB is equal to or greater than a predetermined length, and the conveying speed of the fiber bundle FB is equal to or greater than a predetermined speed.

[0049] Alternatively, when multiple fiber bundles FB are processed simultaneously by a continuous process, the fiber bundles FB may be spaced apart by 5 mm or more. For example, consider a case where multiple fiber bundles FB are introduced into a reactor FR. If adjacent fiber bundles FB are placed too close to each other, there is a risk of interference between the fiber bundles FB, making it impossible to stably form a coating layer LB. Therefore, it is preferable that the fiber bundles FB are spaced apart by 5 mm or more.

[0050] Alternatively, when processing the fiber bundle FB by a continuous process, the tension applied to the fiber bundle FB may be 200 grams by weight or less. In order to efficiently form a coating layer LB on the surface of the fibers CF contained in the fiber bundle FB, it is necessary to transport the fiber bundle FB with gaps between the fibers CF. If the tension applied to the fiber bundle FB exceeds 200 grams by weight, the gaps between the fibers CF become smaller, making it difficult for the raw material gas to enter the gaps. To prevent this from happening, the tension applied to the fiber bundle FB may be set to 200 grams by weight or less.

[0051] Furthermore, when treating the fiber bundle FB using a continuous process, the fiber bundle FB may be exposed to a gas containing a raw material in which the ratio of ammonia to boron trichloride is in the range of 1 to 3. The gas pressure may be set to 100 to 500 Pa, and the conveying direction AR1 of the fiber bundle FB and the flow direction of the gas (flow direction AR2) may be set to be opposite. This allows a coating layer LB with a fine crystalline structure to be formed on the surface of the fiber CF, thereby realizing the effect of suppressing crack propagation by the coating layer LB. Setting the gas flow direction opposite to the conveying direction of the fiber bundle has the following advantages: First, fresh gas is always supplied to the fiber bundle; Reaction by-products are discharged as the fiber bundle moves; A more uniform coating can be achieved by utilizing the gradient of gas concentration and temperature; and, finally, gas utilization efficiency is improved, resulting in reduced material costs.

[0052] In particular, a crystal structure having an interplanar distance in the C-axis direction of 3.5 Å or less can be obtained without performing additional heat treatment after forming the coating layer LB. Furthermore, the ratio of nitrogen to boron in the coating layer LB is 0.7 to 1.3, and the amount of oxygen mixed in can be 10 atomic percent or less. Therefore, there is no need to reheat the fibers CF in the process included in the method for producing a ceramic-based composite material after forming the silicon carbide layer LS. In the process after forming the silicon carbide layer LS, there is no need to perform heat treatment at a temperature exceeding that used to form the coating layer LB.

[0053] [Characteristics of Ceramic Matrix Composite Material] Next, the characteristics of the ceramic matrix composite material of the present disclosure will be described. Fig. 5 is a diagram showing an example of the relationship between the zero thickness rate and the tensile strength. The ceramic matrix composite material corresponding to the data plotted in region B1 in Fig. 5 is the ceramic matrix composite material produced by the production method of the present disclosure.

[0054] The ceramic matrix composite materials corresponding to the data plotted in region B1 have a zero thickness ratio of 50% or less, resulting in a strength of 85% or more. The strength here is shown as a relative value, with the fiber strength before coating treatment taken as 100%. This means that the method of the present disclosure allows the fiber to maintain 85% or more of its original strength even after being coated with boron nitride.

[0055] In contrast, the ceramic matrix composite materials corresponding to the data plotted in region B2 in FIG. 5 are ceramic matrix composite materials produced under conditions other than those disclosed in the present disclosure.

[0056] According to a forming method other than the conditions of the present disclosure, the zero film thickness rate is greater than 50%. This means that there are many areas on the fiber surface where no coating layer is formed. In addition, the crystalline structure of the coating layer is not sufficiently refined. As a result, it is not possible to achieve a strength of 85% or more. With conventional methods, the fiber strength is significantly reduced, limiting the improvement of performance as a composite material.

[0057] Therefore, it can be seen that by using an optimal process such as the manufacturing method of the present disclosure, a coating layer LB having a fine crystalline structure is formed on the surface of the fiber CF, resulting in a sufficient improvement in strength, which is an important property that directly leads to improved reliability when used as a high-temperature structural material.

[0058] FIG. 6 shows an example of a diffraction chart corresponding to the heat treatment temperature. FIG. 7 shows an example of the relationship between the heat treatment temperature and the interplanar distance (d002) in the C-axis direction of the BN interface layer. FIG. 6 shows the results of a diffraction chart obtained for a ceramic-based composite material of the present disclosure in a state in which no heat treatment was applied after forming the coating layer LB and the silicon carbide layer LS. Also shown are the results of diffraction charts obtained for each state in which heat treatments were performed at 1500°C, 1600°C, 1700°C, and 1800°C. The diffraction intensity peak PK corresponds to the interplanar distance in the C-axis direction included in the crystal structure. Furthermore, FIG. 7 shows the results of calculating the interplanar distance in the C-axis direction based on the diffraction intensity peaks included in the diffraction chart shown in FIG. 6.

[0059] 6, the diffraction intensity peak PK in the diffraction chart is almost constant regardless of the heat treatment temperature. Therefore, as shown in FIG. 7, the interplanar distance in the C-axis direction is almost constant (a value of 3.5 Å or less) regardless of whether or not heat treatment is performed and the heat treatment temperature.

[0060] This means that the coating layer LB has a sufficiently refined crystal structure without heat treatment. Therefore, in the method for producing a ceramic-based composite material according to the present disclosure, an additional heat treatment for refining the crystal structure of the coating layer LB is not required. This simplifies the production process, and is expected to reduce production costs and improve production efficiency.

[0061] Fig. 8 is a graph showing an example of the relationship between creep rupture time and applied stress. Fig. 9 is a graph showing the difference in the amount of impurities mixed in the coating layer. Fig. 8 shows the relationship between creep rupture time and applied stress, comparing a ceramic matrix composite material in which a coating layer LB is formed by a continuous process and a ceramic matrix composite material in which a coating layer is formed by a batch process.

[0062] As shown in Figure 8, the ceramic matrix composite material produced by the continuous process of the present disclosure has stronger creep rupture toughness than the ceramic matrix composite material produced by the batch process. In particular, the ceramic matrix composite material produced by the continuous process has a larger load stress than the ceramic matrix composite material produced by the batch process when compared at the same creep rupture time.

[0063] Such high creep rupture toughness is due to the difference in the amount of impurities contained in the coating layer LB. In the ceramic matrix composite material produced by the continuous process, the amount of impurities, primarily oxygen, is 10 atomic percent or less. In contrast, in the ceramic matrix composite material produced by the batch process, the amount of impurities, primarily oxygen, is greater than 10 atomic percent. Thus, according to the method for producing a ceramic matrix composite material disclosed herein, after forming the coating layer LB, the ratio of nitrogen to boron in the coating layer LB is 0.7 to 1.3, and the amount of oxygen contained therein can be reduced to 10 atomic percent or less. Impurities such as oxygen reduce the chemical stability of the coating layer in high-temperature environments and promote deterioration of the crystalline structure. The continuous process disclosed herein results in a low amount of impurities, thereby exhibiting excellent stability even during long-term use at high temperatures. This is an extremely important characteristic for structural materials used at high temperatures for long periods of time, such as engine parts and gas turbine parts.

[0064] As described above in detail, the ceramic matrix composite material according to the present disclosure comprises fibers containing silicon carbide, a boron nitride coating layer formed on the surface of the fibers and having a zero ratio of 50% or less, and a silicon carbide layer formed on the surface of the coating layer and having a thickness in the range of 0.1 to 50 μm. In addition, a structure including at least one of a fiber laminate and a woven fabric is formed by fiber bundles containing the fibers.

[0065] This reduces the variation in fiber strength after the process of forming the BN interfacial layer (coating layer) on the fiber, and also reduces fiber breakage. In particular, the coating layer formed on the surface of the fibers in the fiber bundle prevents cracks from growing in the ceramic matrix composite material. This results in improved strength of the ceramic matrix composite material.

[0066] The coating layer may have an average thickness of 100 to 1000 nm, which allows the coating layer to have a sufficient effect of suppressing crack propagation and also prevents the coating layer itself from peeling off from the fiber.

[0067] The interplanar distance (d002) in the C-axis direction in the coating layer may be 3.5 Å or less. The ratio of nitrogen to boron in the coating layer may be 0.7 to 1.3, and the amount of oxygen mixed in may be 10 atomic percent or less. This allows a coating layer with a fine crystalline structure to be formed on the surface of the fiber, thereby realizing the effect of suppressing crack propagation by the coating layer. Reducing the amount of oxygen mixed in also improves long-term stability in high-temperature environments.

[0068] The silicon carbide layer may have a thickness of 0.5 μm or more inside the fiber bundle and 5 to 30 μm outside the fiber bundle. This reduces the possibility of cracks occurring in the ceramic matrix composite material propagating and leading to fracture of the entire ceramic matrix composite material. In particular, the growth of any cracks that do form is suppressed by the coating layer formed on the surfaces of the fibers contained in the fiber bundle. This results in improved strength of the ceramic matrix composite material.

[0069] The method for producing a ceramic matrix composite material according to the present disclosure includes a step of forming a coating layer on fibers contained in a fiber bundle by a continuous process, a step of forming a structure from the fiber bundle containing the fibers with the coating layer, and a step of forming a silicon carbide layer on the surface of the coating layer by chemical vapor impregnation of the structure.

[0070] This reduces the variation in strength of the fibers after the process of forming the BN interfacial layer (coating layer) on the fibers, and prevents the fibers from breaking. The coating layer can be efficiently formed on the surface of the fibers while suppressing the variation in strength. As a result, the strength of the ceramic matrix composite material can be improved.

[0071] The continuous process may be a process in which a coating layer is formed on a region of the fiber surface to be treated while the region is moved in the direction of extension of the fiber bundle. This allows for efficient formation of a coating layer on the fiber surface while suppressing variations in strength. Furthermore, this improves production efficiency, making the manufacturing method suitable for mass production.

[0072] The heating temperature of the region may be set to 1300° C. or higher, and the time for the region to pass through each point of the fiber in the extension direction may be set to 1 minute or less. This makes it possible to form a coating layer with a fine crystalline structure on the surface of the fiber while suppressing a decrease in fiber strength due to the influence of heating.

[0073] The fiber bundle may be transported in the extension direction at a speed of 1 to 10 m / min to move through the regions. This eliminates the need to increase the length of the reactor along the extension direction of the fiber bundle in order to form a sufficient coating layer. Furthermore, it is possible to easily control the flow of the raw material gas and to easily discharge unnecessary gases after the reaction. As a result, it is possible to reduce the cost and load associated with the equipment used to apply the coating layer.

[0074] When multiple fiber bundles are processed simultaneously by a continuous process, the fiber bundles may be spaced apart by 5 mm or more. This prevents interference between the fiber bundles in the reactor, even when multiple fiber bundles are introduced into the reactor to form a coating layer. As a result, the coating layer can be formed stably. Furthermore, simultaneous processing of multiple fiber bundles improves production efficiency.

[0075] When treating the fiber bundle by the continuous process, the tension applied to the fiber bundle may be 200 grams by weight or less. This prevents the gaps between the fibers from becoming small due to excessive tension applied to the fiber bundle. As a result, it is possible to ensure that the raw material gas can sufficiently penetrate into the gaps between the fibers. As a result, it is possible to form a fine coating layer on the surface of the fiber.

[0076] When treating a fiber bundle using a continuous process, the fiber bundle may be exposed to a gas containing a raw material in which the ratio of ammonia to boron trichloride is in the range of 1 to 3, the gas pressure may be set to 100 to 500 Pa, and the gas flow may be set in the opposite direction to the fiber bundle transport direction. This allows a coating layer with a fine crystalline structure to be formed on the fiber surface, thereby realizing the effect of suppressing crack propagation by the coating layer. Furthermore, by flowing the gas in the opposite direction to the fiber bundle movement direction, fresh gas is supplied and by-products are efficiently discharged.

[0077] In the manufacturing process after forming the silicon carbide layer, the fibers may be heated to a temperature that does not exceed the temperature used to form the coating layer. This eliminates the need for additional heat treatment to refine the crystalline structure of the coating layer, reducing the overall cost of the manufacturing process for ceramic matrix composites. Furthermore, minimizing the thermal history of the fibers also improves the quality and reliability of the final product.

[0078] According to the present disclosure, it is possible to improve the strength of various products made of composite materials, which can contribute to, for example, Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

[0079] Although several embodiments have been described, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, unless they contradict each other.

[0080] The entire contents of Japanese Patent Application No. 2024-135231 (filing date: August 14, 2024) are incorporated herein by reference.

[0081] AR1 Conveying direction AR2 Flow direction CF Fiber FB Fiber bundle FR Reactor LB Coating layer LS Silicon carbide layer P1 Delivery device P2 Winding device PK Peak position R1 to R4 Field of view

Claims

1. A ceramic matrix composite material comprising: fibers containing silicon carbide; a coating layer of boron nitride formed on the surface of the fibers and having a zero film thickness ratio of 50% or less; and a silicon carbide layer formed on the surface of the coating layer and having a film thickness in the range of 0.1 to 50 μm; wherein a structure including at least one of a fiber laminate and a woven fabric is formed by fiber bundles containing the fibers.

2. The ceramic matrix composite material according to claim 1, wherein the coating layer has an average thickness of 100 to 1,000 nm.

3. The ceramic matrix composite material according to claim 1, wherein the interplanar distance (d002) in the C-axis direction in the coating layer is 3.5 Å or less.

4. The ceramic matrix composite material according to claim 1, wherein the ratio of nitrogen to boron in said coating layer is 0.7 to 1.3, and the amount of oxygen mixed in is 10 atomic percent or less.

5. A ceramic matrix composite material according to claim 1, wherein the silicon carbide layer has a thickness of 0.5 μm or more inside the fiber bundle and 5 to 30 μm outside the fiber bundle.

6. A method for producing a ceramic matrix composite material according to any one of claims 1 to 5, comprising the steps of: forming the coating layer on the fibers contained in the fiber bundle by a continuous process; forming the structure from the fiber bundle containing the fibers on which the coating layer is formed; and forming the silicon carbide layer on the surface of the coating layer by chemical vapor impregnation of the structure.

7. The method for producing a ceramic matrix composite material according to claim 6, wherein the continuous process is a process in which the coating layer is formed on a treatment target area of ​​the surface of the fiber while the treatment target area is moved in the extension direction of the fiber bundle.

8. A method for producing a ceramic matrix composite material as described in claim 7, wherein the heating temperature of the region is set to 1,300 degrees Celsius or higher, and the time it takes for the fiber to pass through the region at each point in the extension direction is set to within one minute.

9. The method for producing a ceramic matrix composite material according to claim 7, wherein the fiber bundle is transported in the extending direction at a speed of 1 to 10 m / min to move through the region.

10. The method for producing a ceramic matrix composite material according to claim 6, wherein when a plurality of said fiber bundles are simultaneously processed by said continuous process, the fiber bundles are spaced apart by an interval of 5 mm or more.

11. The method for producing a ceramic matrix composite material according to claim 6, wherein a tension of 200 grams force or less is applied to the fiber bundle when the fiber bundle is processed through the continuous process.

12. The method for producing a ceramic matrix composite material according to claim 6, wherein, when treating the fiber bundles by the continuous process, the fiber bundles are exposed to a gas containing raw materials in which the ratio of ammonia to boron trichloride is in the range of 1 to 3, the pressure of the gas is set to 100 to 500 Pa, and the direction of transport of the fiber bundles and the flow of the gas are set to be opposite to each other.

13. The method for producing a ceramic matrix composite material according to claim 6, wherein in a step included in the production method after forming the silicon carbide layer, the heating temperature of the fibers does not exceed the heating temperature used to form the coating layer.

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