Method for coating at least one fiber with a boron nitride interphase

Abstract

The invention relates to a method for coating at least one fiber (11) with a boron nitride interphase, comprising treating the at least one fiber with a treatment medium containing ammonia borane, the treatment medium having a temperature of 100°C or more and a pressure of 1 bar or more.

Description

Technical Field

[0001] The present invention relates to a method for processing at least one fiber, particularly fibers made of ceramic and, for example, fibers made of silicon carbide, by coating them with a boron nitride (BN) mesophase. Background Technology

[0002] Ceramic matrix composites (“CMC materials”) possess excellent mechanical properties, making them suitable for forming structural elements and advantageously retaining these properties at high temperatures. They are a promising alternative to commonly used metal components because they allow for lighter structures.

[0003] CMC materials can be produced by forming fiber preforms that resemble the shape of the final component, which are then densified within a ceramic matrix. The functionality of CMC materials requires specific management of the interfacial bonding between the fibers and the matrix to achieve the damage-resistant properties of the final composite. This interfacial conditioning is typically achieved by incorporating an intermediate phase between the fibers and the matrix. In the context of thermostructural applications, using boron nitride as the intermediate phase may be advantageous compared to pyrolytic carbon (PyC) due to its more favorable oxidation behavior.

[0004] Boron nitride mesophases can be deposited on fibers of preforms via chemical vapor infiltration (CVI). This technique has relatively slow deposition kinetics, which increases manufacturing time and cost. One problem with CVI is the mass transfer of reactive species to the matrix core, which can limit deposition kinetics. Furthermore, CVI can induce different reactivity at the core and exterior of the preform, leading to inhomogeneity in the resulting material. Boron nitride can be obtained via CVI from boron trichloride (BCl3) or boron trifluoride (BF3) as starting materials, both of which are toxic compounds. Alternative precursors, such as alkylboranes, which contain carbon atoms in their structure, can lead to carbon contamination in the mesophase deposits.

[0005] We desire methods for forming boron nitride mesophases that avoid the use of boron trichloride and boron trifluoride and limit contamination in sediments. Furthermore, we hope these methods will exhibit higher deposition kinetics than the CVI method while producing a uniform coating. Summary of the Invention

[0006] The present invention relates to a method for coating at least one fiber with a boron nitride mesophase, comprising treating the at least one fiber with a treatment medium containing ammonia borane, wherein the temperature of the treatment medium is greater than or equal to 100°C and the pressure is greater than or equal to 1 bar.

[0007] The use of a processing medium makes it possible to obtain higher boron nitride mesophase formation kinetics than CVI technology by avoiding mass transfer phenomena, particularly encountered in CVI technology. This invention proposes using ammoniaborane (chemical formula BH3NH3) as a precursor for the boron nitride to be obtained to produce the mesophase. Ammoniaborane does not present any particular hazard during use and is a stable solid compound under environmental conditions. Therefore, the formation of the boron nitride mesophase is simplified and safer compared to conventional CVI technology. The mesophase is formed by the decomposition of ammoniaborane under temperature. This decomposition can be used to obtain hexagonal boron nitride and release molecular hydrogen. The molecular hydrogen produced by the decomposition of ammoniaborane does not present significant toxicity or safety risks. Furthermore, this reactivity is part of the development of sustainable chemistry, especially at the atom economy level. Moreover, the choice of ammoniaborane particularly avoids the use of carbon-containing precursors, such as alkylboranes, thereby avoiding the introduction of contamination into the formed boron nitride mesophase. The processing medium can be liquid, gaseous, or supercritical.

[0008] In one exemplary embodiment, the processing medium comprises ammonia borane dissolved in ammonia (NH3).

[0009] This property is advantageous because of the high solubility of ammonia borane in ammonia. However, the present invention is not limited to using ammonia as the solvent for the ammonia borane treatment medium. Tetrahydrofuran (THF) (critical temperature: 267°C, critical pressure: 51.9 bar) can also be used as the solvent for ammonia borane, optionally as a co-solvent with ammonia to promote nitriding conditions.

[0010] Specifically, especially when ammonia is used as the ammonia borane solvent, the temperature of the treatment medium can be greater than or equal to 600°C, for example, between 600°C and 1600°C, and the pressure of the treatment medium can be greater than or equal to 10 bar, for example, between 10 bar and 300 bar.

[0011] More specifically, especially when ammonia is used as the ammonia borane solvent, the temperature of the processing medium is between 800°C and 1600°C, for example, between 900°C and 1600°C, and the pressure of the processing medium is between 100 bar and 150 bar.

[0012] These conditions constitute a compromise that allows for the utilization of the high solubility of ammonia borane while benefiting from improved mass transfer, thereby achieving higher deposition kinetics. Furthermore, these pressures are feasible for the industrial development of this method.

[0013] In one exemplary embodiment, the at least one fiber is microwave heated during processing.

[0014] A microwave field can bring the surface of the treated fiber to a sufficiently high temperature to locally achieve the desired conditions and initiate the decomposition of ammonia borane. The microwave field can heat the entire fiber to ensure uniform formation of the mesophase. Furthermore, since the fiber is heated directly rather than the entire treatment chamber, the energy required to form the mesophase is reduced. However, using another heating method, such as radiation from a susceptor, would not be outside the scope of this invention.

[0015] In one exemplary embodiment, the at least one fiber moves through the processing chamber during processing. The movement of the fiber within the processing chamber can be in the same direction as or against the circulation direction of the processing medium.

[0016] Using a treatment medium can avoid limitations due to mass transfer and accelerate deposition kinetics, which is particularly advantageous for continuous deposition on fibers moving through the treatment chamber, thereby significantly increasing the rate of mesophase formation.

[0017] In one exemplary embodiment, the at least one fiber is made of ceramic or carbon.

[0018] Specifically, the at least one fiber may be made of silicon carbide with an oxygen content of less than or equal to 1% atomic percentage.

[0019] Specifically, the treatment can be carried out in a treatment chamber, and the at least one fiber is made of silicon carbide. Prior to the treatment, the at least one fiber has been pretreated in the treatment chamber by placing the fiber in contact with an ammonia phase at a temperature greater than or equal to 100°C and a pressure greater than or equal to 1 bar to remove the surface layer of the fiber.

[0020] In this case, the fibers are pretreated to remove a surface layer that could reduce the adhesion quality between the fibers and the boron nitride mesophase. This feature utilizes an ammonia phase and is carried out in the same chamber as the boron nitride mesophase coating, which eliminates the need to manipulate the treated fibers, thus simplifying the method and reducing its duration.

[0021] Specifically, the temperature of the ammonia phase can be greater than or equal to 600°C, for example, between 600°C and 1600°C, and the pressure of the ammonia phase can be greater than or equal to 1 bar, for example, between 1 bar and 300 bar. The ammonia phase can be in a gaseous, liquid, or supercritical state.

[0022] The present invention also relates to a method for manufacturing a composite material component, comprising forming a matrix at least in the pores of a fiber reinforcement, the fibers of which have been coated with a boron nitride mesophase by performing one of the methods described above.

[0023] It will be understood that in the above-described manner, a fiber reinforcement can be obtained by coating multiple fibers with an intermediate phase. Alternatively, a fiber reinforcement can first be formed from multiple fibers, and then the reinforcement can be treated with a processing medium to form an intermediate phase on the fibers.

[0024] Composite material components can be, for example, turbine components, such as turbine blades or vanes or turbine ring segments. Attached Figure Description

[0025] [ Figure 1 ] Figure 1 This schematically illustrates the treatment of fibers in a processing chamber in one embodiment or scope of the method according to the invention.

[0026] [ Figure 2 ] Figure 2 This is a schematic cross-sectional view showing the structure of treated fibers coated with a boron nitride mesophase.

[0027] [ Figure 3 ] Figure 3 An embodiment of a processing facility that can be used to implement the method according to the invention is illustrated schematically.

[0028] [ Figure 4 ] Figure 4 It is a schematic cross-sectional view representing the structure of silicon carbide fibers initially having a surface layer.

[0029] [ Figure 5 ] Figure 5 It is a schematic representation. Figure 4 Cross-sectional view of the structure of medium silicon carbide fibers after the surface layer is removed and before the deposition of the boron nitride mesophase. Detailed Implementation

[0030] Figure 1 This illustrates the treatment of fiber 11 in one embodiment of the method according to the invention, enabling it to be coated with a boron nitride mesophase.

[0031] In the considered embodiment, fiber 11 travels along during processing Figure 1 The direction indicated by the middle arrow D is through the processing chamber 10. In the processing chamber 10, the deposition of the mesophase can be continuous without interrupting the movement of the fiber 11. Alternatively, the fiber can be segmented, with the fiber segment to be treated fixed in the processing chamber 10, and the mesophase deposited on that segment. Then, an adjacent fiber segment 11 is introduced into the chamber 10 for deposition on that adjacent segment. The treated fiber 11 is unwound from a spool (not shown), enters the processing chamber 10, and then wound back onto the spool after treatment. The travel speed of the fiber 11 in the processing chamber 10 can be between 0.1 cm / s and 50 cm / s.

[0032] Processing chamber 10 is filled with a fluid medium 20 containing ammonia borane. Ammonia borane can be dissolved in fluid medium 20. Fluid medium 20 can contain a solvent for ammonia borane, such as ammonia. Fluid medium 20 can essentially consist of ammonia borane and a solvent for ammonia borane. Advantageously, fluid medium 20 contains no other atoms besides B, N, and H atoms, particularly no carbon atoms, to avoid any risk of contamination in the mesophase deposit. Fluid medium 20 can be in liquid form. Fluid medium 20 can be pressurized, for example, at a pressure greater than or equal to the critical pressure of the solvent. During processing of fiber 11 in processing chamber 10, fiber 11 is immersed in fluid medium 20. In the illustrated embodiment, fiber 11 is directly heated, for example by applying a microwave field. Heating makes it possible to obtain a high temperature at least in the vicinity of fiber 11 in order to obtain processing medium 22 by bringing, for example, fluid medium 20 to supercritical conditions. Direct heating of fiber 11 can trigger the decomposition of ammonia borane upon contact with such heated fiber 11, forming a boron nitride mesophase.

[0033] The fluid medium 20 can continuously move through the processing chamber 10, or alternatively, the processing chamber 10 can be initially filled with the fluid medium 20 and then processed without introducing or draining the fluid medium 20. In the case of continuous circulation of the fluid medium, a duration greater than or equal to 0.00016 s can be applied during the entire or partial processing period. -1 The ratio [flow rate of fluid medium introduced into the chamber] / [chamber volume], for example, in 0.00016s -1 and 0.16s -1 Between or within 0.0016s -1 and 0.016s -1 Between or within 0.0016s -1 and 0.16s -1 For example, for a treatment chamber 10 with a volume between 0.1 mL and 100 mL, the fluid medium 20 can be introduced into the chamber 10 at a flow rate of 0.1 mL / min to 10 mL / min (e.g., 0.1 mL / min to 3 mL / min) throughout or part of the treatment. Generally, the molar concentration of ammonia borane in the fluid medium 20 can be greater than or equal to 0.001 mol / L, for example, between 0.001 mol / L and 10 mol / L.

[0034] For mesophase deposition, fiber 11 can be contacted with a pressurized fluid medium 20, which includes ammonia borane. When using ammonia as a solvent, fiber 11 can be contacted with the fluid medium containing a mixture of ammonia and ammonia borane at a pressure between 1 bar and 300 bar, for example, between 10 bar and 300 bar, for example, between 100 bar and 150 bar. Heating of fiber 11 is then initiated. Thus, a processing medium 22 is formed at least in the vicinity of fiber 11. At least in the vicinity of the fiber, the fluid medium 20 is heated to a sufficient temperature to decompose the ammonia borane and form boron nitride. For example, when using ammonia as a solvent, at least in the vicinity of the fiber, the fluid medium 20 can be heated to a temperature greater than or equal to 600°C, for example, greater than or equal to 800°C or greater than or equal to 900°C. This temperature can be between 600°C and 1600°C, or between 800°C and 1600°C, or between 900°C and 1600°C.

[0035] Therefore, a boron nitride mesophase 24 is obtained deposited on the surface S of the fiber 11. The thickness e24 of the mesophase 24 can be greater than or equal to 1 nm, for example, greater than or equal to 10 nm. This thickness e24 can be between 10 nm and 1 mm, for example, between 10 nm and 10 μm.

[0036] The obtained mesophase 24 has a controlled and uniform thickness throughout the circumference of the treated fiber, wherein the boron:nitrogen stoichiometry is close to 1. The obtained boron nitride can be crystalline. Using crystalline materials is beneficial for increasing crack deflection performance. Hexagonal boron nitride mesophases can be obtained.

[0037] The duration of the coating treatment with boron nitride mesophase can be greater than or equal to 10 seconds, for example, between 10 seconds and 30 minutes, or between 1 minute and 10 minutes.

[0038] Once the intermediate phase has deposited, the treatment chamber 10 can be cleaned by injecting a pressurized solvent. For example, liquid ammonia can be injected at a flow rate of 0.5 mL / min to 10 mL / min to remove unreacted excess ammonia borane.

[0039] The treated fiber 11 can be made of ceramic or carbon. Fiber 11 can also be made of silicon carbide, optionally with an oxygen content of less than or equal to 1% atomic percentage. Such fibers include, for example, fibers sold under the name "Hi-Nicalon S" or "Hi-Nicalon". Alternatively, Si-CO fibers with a higher oxygen content can be treated. Such fibers include, for example, fibers sold under the name "Nicalon".

[0040] An embodiment of the method according to the invention has just been described, in which a single fiber 11 is processed. However, it is certainly not beyond the scope of the invention to process multiple fibers simultaneously to form an intermediate phase 24 on each fiber. It should be noted that each fiber can be in the form of a roving comprising multiple filaments. It is also not beyond the scope of the invention if the intermediate phase is no longer formed on one or more unconnected fibers, but on an already formed texture comprising multiple fibers, movable or immovable within the processing chamber. Thus, fibers can be processed in any form, such as yarn, roving, ply, strand, fibrous fabric, felt, pad, and even two-dimensional or three-dimensional textures. Fibers processed according to the method of the invention can be advantageously used for the production of fiber preforms for composite material components. Regardless of the form in which the fibers are processed, the conditions described above for depositing the intermediate phase still apply.

[0041] This will be explained in more detail in the following description. Figure 3 An embodiment of an apparatus that can be used to implement the method of the present invention is shown.

[0042] Figure 3 The device 1 shown includes an injection pump 4, which can operate at a constant flow rate or a constant pressure. It also includes means for generating microwaves capable of heating the fiber 11 through such radiation, and a tube 9 made of a microwave-transparent material containing the fiber 11 to be heated. The device 1 includes a pressure regulator 15, which can stabilize the pressure throughout the device when the injection pump operates at a constant flow rate.

[0043] To process fiber 11 to remove the boron nitride mesophase, storage tank 6 is first filled with ammonia borane and then connected to the rest of the unit. Injection pump 4 is filled with solvent and cooled using a cryostat. Injection pump 4 is then turned on, and valves 7, 8, 13, and 14 are closed. The injection pump operates at a constant pressure, thus filling storage tank 6 with ammonia at the operating pressure. The valve of storage tank 5 is then closed and valve 7 is opened, bringing the entire unit under pressure. Valve 13 is then opened, and the injection pump is operated in constant flow mode. The pressure is then stabilized via pressure regulator 15.

[0044] Once the pressure in the system stabilizes, valve 7 is closed and valves 5 and 8 of tank 5 are opened to inject a solution consisting of ammonia borane and solvent into treatment chamber 10. When constant flow rate operation is stable, the fibers 11 contained in chamber 10 are brought to operating temperature within a given time using a microwave heating device. After all precursors have been injected, pressurized solvent is injected (via an injection pump) to remove any trace precursors that may remain.

[0045] A method for coating fibers with a boron nitride mesophase and a facility for implementing this method have just been described. Below, we will attempt to combine... Figure 4 and Figure 5An optional embodiment is described, wherein the fibers are pretreated to remove the surface layer in order to improve the bonding with the boron nitride mesophase.

[0046] Figure 4 A cross-sectional view of a silicon carbide fiber 16 prior to pretreatment is shown schematically. The oxygen content of the fiber may be less than or equal to 1% (atomic percentage). The fiber 16 has a surface layer 12 comprising silicon carbide (composed of silicon, carbon, and oxygen) and / or carbon, which is preferably removed before the deposition of the boron nitride mesophase 24. The thickness e12 of the surface layer 12 is typically between 1 nm and 1 mm, for example, between 1 nm and 1 μm. The silicon carbide fiber 16 consists of a silicon carbide core 11 and a surface layer 12 located near the surface of the fiber 16. The surface layer 12 has a non-uniform surface state. The surface layer 12 may lead to a decrease in the adhesion quality of the fiber to the coating covering it.

[0047] The surface layer 12 can be removed by contacting the fibers 16 with an ammonia phase at a temperature of 600°C to 1600°C and a pressure of 1 bar to 300 bar. As described above, the fibers 16 can first be contacted with pressurized ammonia at a pressure of 1 bar to 300 bar, and then the fibers are heated and this process is continued until the surface layer 12 is removed. During pretreatment, ammonia can be injected into the chamber 10 continuously or intermittently. If there is continuous circulation of a fluid medium containing ammonia during all or part of the treatment, the ratio [flow rate of the fluid medium flowing into the chamber] / [volume of the chamber] can be set to be greater than or equal to 0.00016 s. -1 For example, at 0.00016s -1 and 0.16s -1 Between or within 0.0016s -1 and 0.16s -1 Between or within 0.0016s -1 and 0.016s -1 Between. The surface carbon of fiber 16 can react with ammonia to generate removed hydrogen cyanide (HCN). Carbon oxide compounds are also removed by the ammonia medium. Thus, fiber 11 with an improved surface state is obtained, which is then coated with boron nitride mesophase 24 as described above. The duration of the pretreatment can be greater than or equal to 10 seconds, for example, between 5 minutes and 30 minutes. The advantage of this pretreatment is that the steps of eliminating non-uniformity and mesophase coating are carried out in the same chamber 10, which avoids the fiber returning to ambient air and reduces the number of operations. Furthermore, if the solvent of ammonia borane is ammonia, the fact that the same medium is used for pretreatment and as a solvent avoids chemical compatibility issues between the two steps.

[0048] A method for coating fibers with a boron nitride mesophase has just been described, which optionally includes a pretreatment designed to eliminate surface non-uniformity of the fibers prior to the coating step. The remainder of the method for obtaining composite parts from such treated fibers is now attempted to be described.

[0049] The fibers treated as described above can be used to form fiber preforms of the desired components. The preforms are formed using textile operations known per se, such as weaving, optionally three-dimensional weaving. Therefore, the preforms can, for example, have an "interlocking" weaving pattern; in other words, a weaving pattern in which each layer of weft yarn connects multiple layers of warp yarn, and all yarns in the same row of weft yarns have the same movement within the same weaving plane. Of course, other types of three-dimensional weaving can be used to produce the preforms. As mentioned above, if the preform is first formed from fibers, and then the boron nitride mesophase is deposited on the fibers of the preform thus obtained as described above, it also falls within the scope of this invention.

[0050] This method can be carried out by forming at least one matrix phase in the pores of a fiber preform, the fibers of which are coated with a boron nitride mesophase. The resulting matrix can be at least partially made of ceramic, for example, primarily made of ceramic material, or entirely made of ceramic. The matrix formation uses techniques known per se, such as liquid densification (by impregnation with a precursor resin of the matrix and by crosslinking and pyrolysis transformation, a process that is repeatable) or gaseous techniques (chemical vapor infiltration of the matrix), or even by melt infiltration (MI).

[0051] This invention is particularly applicable to the production of components made of ceramic matrix composites, which are formed of fiber reinforcements having silicon carbide fibers densified by a ceramic matrix (particularly refractory carbides, nitrides, or oxides). A typical example of such CMC materials is SiC-SiC materials (consisting of silicon carbide fibers and reinforcements made of a silicon carbide matrix).

[0052] The obtained component can be an aerospace or industrial turbine part. For example, the component can be a turbine blade or blade or a turbine annular plate.

[0053] Example

[0054] like Figure 1 As schematically shown, a fiber passes through processing chamber 10, which has a volume of 1 cm³. 3 The treated fiber is a silicon carbide fiber with an oxygen content of less than or equal to 1% atomic percentage, corresponding to the commercially available fiber called "Hi-Nicalon S". Before treatment, the fiber has a surface layer 12 with a thickness of approximately 100 nm.

[0055] The fiber was first pretreated by exposing it to a supercritical ammonia phase in chamber 10. During pretreatment, the fiber was heated to 1000°C using a microwave field, and the pressure of the supercritical ammonia phase was increased to 120 bar. Ammonia was continuously injected into the treatment chamber at a flow rate of 6 mL / min, and the fiber moved at a speed of 30 cm / min. This resulted in the removal of surface-exfoliated silicon carbide, such as… Figure 5 As shown.

[0056] Then, in the same processing chamber, a boron nitride mesophase was deposited on the peeled fibers. During this deposition, the fibers moved within the processing chamber at a speed of 30 cm / min. A mixture of ammonia and ammoniaborane (molar concentration of 1 mol / L in the mixture) was continuously introduced into the processing chamber at a flow rate of 1 mL / min. During processing, the fiber surface temperature was raised to 1100 °C by a microwave field, and the fluid medium was subjected to a pressure of 120 bar. The processing was carried out over a time period of 15 minutes, and in this way, a 1000 nm BN mesophase was obtained on the surface of the silicon carbide fibers. The expression "between..." should be understood to include limiting values.

Claims

1. A method of coating at least one fiber with a boron nitride mesophase, comprising contacting the at least one fiber with a processing medium containing ammonia borane, wherein the processing medium has a temperature greater than or equal to 100°C and a pressure greater than or equal to 1 bar, wherein the processing medium contains ammonia borane dissolved in ammonia.

2. The method according to claim 1, wherein the temperature of the processing medium is greater than or equal to 600°C, and the pressure of the processing medium is greater than or equal to 10 bar.

3. The method according to claim 2, wherein the temperature of the processing medium is between 800°C and 1600°C, and the pressure of the processing medium is between 100 bar and 150 bar.

4. The method of claim 1, wherein the at least one fiber is heated by microwave during the contact.

5. The method of claim 1, wherein during the contact, the at least one fiber moves through the processing chamber.

6. The method of claim 1, wherein the at least one fiber is made of ceramic or carbon.

7. The method of claim 6, wherein the contact is performed in a processing chamber, and the at least one fiber is made of silicon carbide, and wherein the at least one fiber has undergone pretreatment in the processing chamber prior to the contact, the pretreatment being for removing the surface layer of the fiber by contacting the fiber with an ammonia phase at a temperature greater than or equal to 100°C and a pressure greater than or equal to 1 bar.

8. The method according to claim 7, wherein in the pretreatment, the temperature of the ammonia is between 600°C and 1600°C, and the pressure of the ammonia is between 1 bar and 300 bar.

9. A method of manufacturing a composite material component, comprising at least forming a matrix in the pores of a fiber reinforcement, the fibers of the fiber reinforcement having been coated with a boron nitride mesophase by performing the method according to claim 1.

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