High temperature metal carbide coating

Abstract

A method for forming a high temperature coating includes applying a carbon powder to a surface of a carbon / carbon (C / C) composite substrate to force the carbon powder into one or more surface voids of the surface of the C / C composite substrate. The carbon powder has substantially the same composition and morphology as surface portions of the C / C composite substrate. The method includes applying a metal slurry to the surface of the C / C composite substrate after applying the carbon powder and reacting a metal of the metal slurry with carbon of the carbon powder and carbon of the surface portions of the C / C composite substrate to form a metal-rich oxidation barrier layer of metal carbide on the C / C composite substrate.

Description

Technical Field

[0001] This disclosure relates to high-temperature coatings. Background Technology

[0002] Carbon-carbon (C / C) composites can be used in high-temperature applications. For example, the aerospace industry uses C / C composite components as friction materials for commercial and military aircraft, such as brake friction materials. In high-temperature applications, C / C composites may be susceptible to oxidation, which can lead to a deterioration of their physical and mechanical properties. Summary of the Invention

[0003] This disclosure describes a high-temperature coating for protecting carbon-carbon (C / C) composite substrates from oxidation at high temperatures, and techniques for preparing said coatings. In some examples, the high-temperature coating comprises a metal-rich antioxidant layer of metal carbides on the surface of the C / C composite substrate. During the formation of the metal carbides, the carbon substrate may react with a metal (such as silicon, titanium, or tungsten) in stoichiometric excess. Carbon powder may be used to enhance the formation of a continuous coating. The carbon powder at the surface of the C / C composite substrate has substantially the same composition and morphology as the C / C composite substrate, such as microstructure and phase composition. For example, the carbon powder may be generated from the surface of the C / C composite substrate, such as by grinding, or by matching and applying it to the surface of the C / C composite substrate. The carbon powder may be forced into one or more surface voids on the surface of the C / C composite substrate and react with the metal along with a portion of the surface of the C / C composite substrate. The resulting metal carbides can be formed from both carbon in the carbon powder within the surface pores and carbon in the surface portion of the C / C composite substrate, and can extend into the surface pores to partially bridge the surface pores with the metal carbides on the C / C composite substrate, thereby forming a dense antioxidant coating with high-quality, uniformly crystalline metal carbides that is essentially free of defects. Metal-rich antioxidant layers can be applied to relatively large parts for which forming a substantially defect-free metal carbide coating may be difficult or expensive.

[0004] In one example, a method for forming a high-temperature coating includes applying carbon powder to the surface of a carbon / carbon (C / C) composite substrate to force the carbon powder into one or more surface pores on the surface of the C / C composite substrate. The carbon powder has a composition and morphology substantially the same as the surface portion of the C / C composite substrate. The method includes applying a metal slurry to the surface of the C / C composite substrate after applying the carbon powder, and reacting the metal of the metal slurry with the carbon of the carbon powder and the carbon of the surface portion of the C / C composite substrate to form a metal-rich antioxidant layer of metal carbides on the C / C composite substrate.

[0005] In another example, the high-temperature article includes a carbon / carbon (C / C) composite substrate and a high-temperature coating on the surface of the C / C composite substrate. The high-temperature coating includes a metal-rich antioxidant layer of metal carbides on the surface of the C / C composite substrate. The metal carbides in the metal-rich antioxidant layer are formed from carbon in carbon powder and carbon in the surface portion of the C / C composite substrate. The carbon powder has substantially the same composition and morphology as the surface portion of the C / C composite substrate. The metal-rich antioxidant layer extends into one or more surface voids on the surface of the C / C composite substrate and may be able to form a defect-free metal carbide coating on a relatively large substrate.

[0006] Details of one or more examples of this disclosure are set forth in the following drawings and description. Other features, objects, and advantages of this disclosure will be apparent from the description and drawings, as well as from the claims. Attached Figure Description

[0007] Figure 1 This is a schematic diagram illustrating an exemplary aircraft brake assembly according to an example of the present disclosure, which includes a composite brake disc having a formed high-temperature coating.

[0008] Figure 2 This is a cross-sectional side view showing an exemplary article including a high-temperature coating according to an example of this disclosure.

[0009] Figure 3 This is a flowchart illustrating an exemplary technique for forming a high-temperature coating according to an example of this disclosure.

[0010] Figure 4A This is a cross-sectional side view showing a portion of an exemplary C / C composite substrate including surface voids, according to an example of this disclosure.

[0011] Figure 4B This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate, wherein carbon powder fills surface voids.

[0012] Figure 4C This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate, wherein carbon powder fills surface voids and metal paste is present on the C / C composite substrate.

[0013] Figure 4D This illustrates an example according to this disclosure. Figure 4A A portion of an exemplary C / C composite substrate and a cross-sectional side view of a metal-rich antioxidant layer including surface voids.

[0014] Figure 4EThis illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate and a first metal-rich antioxidant layer in which carbon powder fills surface voids in a metal-rich antioxidant coating.

[0015] Figure 4F This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of an exemplary C / C composite substrate, a first metal-rich antioxidant layer in which carbon powder fills surface voids in a metal-rich antioxidant coating, and a metal paste on the metal-rich antioxidant coating.

[0016] Figure 4G This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate, a metal-rich antioxidant layer, and an outer oxide layer.

[0017] Figure 4H This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate, a metal-rich antioxidant layer, and an outer oxide layer.

[0018] Figure 5 This is a schematic diagram illustrating an exemplary system for forming a high-temperature coating on a C / C composite substrate according to an example of this disclosure.

[0019] Figure 6 This is a micrograph of a cross-section of an exemplary article comprising a C / C composite substrate and a high-temperature coating, according to an example of this disclosure.

[0020] Figure 7A This is a micrograph of a cross-section at the outer diameter of an exemplary aircraft rotor segment comprising a C / C composite substrate and a high-temperature coating, according to an example of this disclosure.

[0021] Figure 7B This is a micrograph of a cross-section at the inner diameter of an exemplary aircraft rotor segment comprising a C / C composite substrate and a high-temperature coating, according to an example of this disclosure.

[0022] Figure 7C This is a micrograph of a cross-section of an exemplary aircraft rotor segment comprising a C / C composite substrate and a high-temperature coating, according to an example of this disclosure.

[0023] Figure 8 The image shows an exemplary C / C composite substrate coated under various vapor pressures to form a high-temperature coating, according to examples of this disclosure. Detailed Implementation

[0024] This disclosure describes a high-temperature coating for carbon-carbon (C / C) composite articles, comprising a C / C composite substrate and a metal-rich antioxidant layer made of metal carbides on the C / C composite substrate for ultra-high temperature (e.g., greater than 1500 degrees Celsius (°C)) applications.

[0025] Carbon-carbon composite components offer excellent mechanical properties and have a low mass density compared to other materials, such as metal alloys. However, at high temperatures, carbon-carbon composite components can be susceptible to oxidation, environmental corrosion, and degradation of their physical and mechanical properties. Antioxidant coatings based on metal carbides can improve resistance to oxidation and / or environmental corrosion at high temperatures experienced in aerospace applications (such as aircraft brakes, e.g., temperatures up to 1600°C) and hypersonic applications (such as leading edges and rocket nozzles).

[0026] Prior to use in an oxidizing atmosphere, the high-temperature carbon composite substrate may be coated with a metal carbide-based antioxidant coating, which reduces oxidation of the substrate's outer surface. However, the surface of the C / C composite substrate may include one or more surface voids extending into the substrate, such as defects, cracks, holes, ripples, or machining textures. If a surface portion of the C / C composite substrate including surface voids reacts with a metal to form a metal carbide coating, the resulting metal carbide coating may be discontinuous on the C / C composite substrate.

[0027] The high-temperature coating described herein may include a metal-rich antioxidant layer that extends into the surface voids of a C / C composite substrate and forms a dense barrier against oxidizing agents. The metal-rich antioxidant layer of the coating of the present invention may include a metal carbide phase formed from reactive carbon of both a metal (such as silicon, titanium, or tungsten) and carbon powder from the surface portion and surface voids of the C / C composite substrate. The reactive carbon powder may be packed into the surface voids prior to reaction with the metal. This carbon powder may have substantially the same composition and / or morphology as the carbon matrix of the surface portion of the C / C composite substrate, such that the carbon powder and the carbon matrix may have substantially similar reaction thermodynamics and kinetics. Therefore, during reaction with the metal, the carbon of the surface portion of the C / C composite substrate and the carbon powder in the surface voids may react with the metal at substantially the same temperature and at substantially the same rate to form a uniform antioxidant coating that bridges the metal carbides in the voids with the metal carbides in the surface portion of the substrate. One or more additional applications of carbon powder (e.g., slurry or dry rubbing), and subsequent reaction with metal, can further repair any remaining surface voids to produce a continuous metal carbide coating.

[0028] By filling surface voids with reactive carbon powder having the same composition and / or morphology as the carbon matrix of the surface portion of the C / C composite substrate, the resulting metal-rich antioxidant coating can exhibit high uniformity and / or continuity compared to a metal carbide coating formed from carbon powder that does not have the same composition and / or morphology as the carbon matrix of the surface portion of the C / C composite substrate. This excludes the possibility that carbon powder with substantially the same composition and / or morphology may react with the metal earlier or later than the carbon matrix of the surface portion of the C / C composite substrate, resulting in the metal carbide phase not consolidating with the metal carbide formed from the surface portion of the C / C composite substrate. For example, before the surface portion of the C / C composite substrate reacts with the metal, the carbon powder reacting with the metal can migrate out of the surface voids as metal carbide powder, thus leaving the surface voids unsealed.

[0029] The high-temperature coatings described in this article can be used in a variety of high-temperature applications. Because components are subjected to high temperatures in high-speed, frictional, or combustion environments, high-temperature coatings may be particularly suitable for aerospace applications. Figure 1 This is a schematic diagram illustrating an exemplary aircraft brake assembly according to an example of the present disclosure, comprising a composite brake disc having a formed high-temperature coating. For ease of description, examples of the present disclosure will be described primarily with respect to aircraft brake assemblies. However, the article of the present disclosure can be used to form brake components that are not aircraft brake discs, and for applications that are not brake components. As an example, the brake component can be used as a friction material in other types of braking applications and vehicles. As another example, the article can be used in leading edges, hypersonic vehicles or weapons, rocket nozzles, and other applications involving high-temperature and oxidizing environments.

[0030] exist Figure 1 In the example, the wheel and brake assembly 10 includes a wheel 12, an actuator assembly 14, a brake stack 16, and an axle 18. The wheel 12 includes a hub 20, wheel support flanges 22, bead seals 24A and 24B, lug bolts 26, and lug nuts 28. The actuator assembly 14 includes an actuator housing 30, actuator housing bolts 32, and a plunger 34. The brake stack 16 includes alternating rotor brake discs 36 and stator brake discs 38; the rotor brake discs 36 are configured to move relative to the stator brake discs 38. The rotor brake discs 36 are mounted on the wheel 12, and specifically on the hub 20, via beam keys 40. The stator brake discs 38 are mounted to the axle 18, and specifically on torque tubes 42, via key teeth 44. The wheel and brake assembly 10 can support any kind of private, commercial, or military aircraft or other types of vehicles.

[0031] Wheel and brake assembly 10 includes wheel 12, in Figure 1In the example, wheel 12 is defined by hub 20 and wheel support flange 22. Wheel support flange 22 is mechanically attached to hub 20 by lug bolts 26 and lug nuts 28. Wheel 12 defines bead seals 24A and 24B. During assembly, an inflatable tire (not shown) can be placed above hub 20 and secured to opposite sides by wheel support flange 22. Thereafter, lug nuts 28 can be fastened to lug bolts 26, and the inflatable tire can be inflated using bead seals 24A and 24B, thereby providing an airtight seal for the inflatable tire.

[0032] The wheel and brake assembly 10 can be mounted to the vehicle via torque tube 42 and axle 18. Figure 1 In the example, torque tube 42 is attached to shaft 18 by a plurality of bolts 46. Torque tube 42 supports actuator assembly 14 and stator brake disc 38. Shaft 18 may be mounted on a strut of landing gear (not shown) or other suitable component of the vehicle to connect wheels and brake assembly 10 to the vehicle.

[0033] During vehicle operation, braking may be required periodically, such as during the landing and taxiing of an aircraft. The wheel and brake assembly 10 is configured to provide braking functionality to the vehicle via actuator assembly 14 and brake stack 16. Actuator assembly 14 includes actuator housing 30 and plunger 34. Actuator assembly 14 may include one or more of different types of actuators, such as, for example, electromechanical actuators, hydraulic actuators, pneumatic actuators, etc. During operation, plunger 34 may extend away from actuator housing 30 to axially compress brake stack 16 against a compression point for braking.

[0034] The brake stack 16 includes alternating rotor brake discs 36 and stator brake discs 38. The rotor brake discs 36 are mounted on the hub 20 for common rotation via a beam key 40. The stator brake discs 38 are mounted to the torque tube 42 via key teeth 44. Figure 1 In the example, brake stack 16 includes four rotors and five stators. However, in other examples, brake stack 16 may include different numbers of rotors and / or stators.

[0035] In some examples, the rotor brake disc 36 and stator brake disc 38 may be mounted in the wheel and brake assembly 10 via beam keys 40 and key teeth 44, respectively. In some examples, the beam keys 40 may be circumferentially spaced around the inner portion of the hub 20. For example, the beam keys 40 may be shaped to have opposing ends (e.g., opposite sides of a rectangle) and may have one end mechanically attached to the inner portion of the hub 20 and an opposing end mechanically attached to the outer portion of the hub 20. The beam keys 40 may be integrally formed with the hub 20, or may be separate from the hub 20 and mechanically attached to it, for example, to provide a thermal barrier between the rotor brake disc 36 and the hub 20. For this purpose, in various examples, the wheel and brake assembly 10 may include a heat shield (not shown) extending radially outward and surrounding the brake stack 16, for example, to limit heat transfer between the brake stack 16 and the wheel 12.

[0036] In some examples, the key teeth 44 may be circumferentially spaced around the outer portion of the torque tube 42. Accordingly, the stator brake disc 38 may include a plurality of radially inwardly disposed lugs along the inner diameter of the brake disc, the lugs being configured to engage with the key teeth 44. Similarly, the rotor brake disc 36 may include a plurality of radially inwardly disposed lugs along the outer diameter of the brake disc, the lugs being configured to engage with the beam key 40. Thus, the rotor brake disc 36 will rotate with the movement of the wheel, while the stator brake disc 38 remains stationary, allowing the friction surfaces of adjacent stator brake discs 38 and rotor brake discs 36 to engage with each other, thereby slowing the rotation of the wheel 12.

[0037] Rotor brake disc 36 and stator brake disc 38 provide relative friction surfaces for braking an aircraft. As the kinetic energy of a moving aircraft is converted into heat energy in the brake stack 16, the temperature in the brake stack 16 can rise rapidly. Accordingly, the rotor brake disc 36 and stator brake disc 38 forming the brake stack 16 may include coatings capable of operating at very high temperatures and blocking various oxidizing substances.

[0038] In some examples, the articles or components described above (such as...) Figure 1 The brake discs 36 and / or 38 may include a high-temperature coating to protect the underlying substrate from oxidation, such as the non-friction surfaces of the brake discs. The non-friction surfaces of the brake discs 36 may include those surfaces of the brake discs 36 that do not engage with another opposing surface when the friction surfaces of the brake discs 36 are engaged, for example, during braking operation of the assembly 10. Figure 2 This is a cross-sectional side view illustrating an exemplary high-temperature article including a high-temperature coating according to an example of this disclosure.

[0039] The high-temperature article 50 includes a carbon / carbon (C / C) composite substrate 52. The substrate 52 may include carbon-based reinforcing fibers and a carbon-based matrix material at least partially surrounding the carbon-based reinforcing fibers. In some examples, the substrate 52 may be formed from a porous preform comprising carbon fibers or carbon precursor fibers. Examples of porous preforms that can be used to produce the substrate 52 include, but are not limited to: fiber preforms such as woven fiber preforms, nonwoven fiber preforms, chopped fiber and binder preforms, binder-treated random fiber preforms, carbon fiber preforms, or ceramic fiber preforms; foam preforms; porous carbon matrix preforms; or porous ceramic matrix preforms.

[0040] In some examples, the porous preform comprises multiple mechanically bonded layers, which may be, for example, multiple fiber layers, such as multiple woven or nonwoven fabric layers, joined together, for example by an adhesive (such as a resin adhesive) or via needle punching. In some examples, the layers comprise one or more tow layers, one or more web layers, or combinations thereof. The tow layer may comprise one or more fiber tows. The fiber tows may be arranged in any suitable arrangement, including, for example, linear, radial, chordal, etc. The web layer may comprise web fibers, which may include relatively short, chopped, and entangled fibers. In other examples, the porous preform may not include predefined layers but may be formed from, for example, a bundle of fibers mechanically bonded together via needle punching. In other examples, any combination of the aforementioned types of porous preforms may be used.

[0041] The substrate 52 may also include a matrix material that at least partially encapsulates carbon fibers. The matrix material can be introduced into the porous preform using one or more of a variety of techniques, including, for example, chemical vapor deposition / chemical vapor infiltration (CVD / CVI), resin transfer molding (RTM), vacuum / pressure infiltration (VPI), high-pressure impregnation / carbonization (PIC), etc.

[0042] The substrate 52 can withstand high temperatures during operation. As an example, a carbon-carbon composite brake disc can withstand temperatures up to about 3,000 degrees Fahrenheit (°F) (about 1,649 °C) during braking events. To protect the substrate 52 from oxidation, the article 50 includes a high-temperature coating 54 on one or more surfaces of the substrate 52. The coating 54 can be stable at temperatures up to about 3,600 °F (about 2,000 °C). In this context, "stable" can mean that the coating 54 does not degrade into its constituent elements, does not react with carbon, and / or does not react (including but not limited to oxidation) with other elements or compounds present in the environment in which the coating 54 is used, and persists for a certain period of time (e.g., several minutes or several hours). The coating 54 can have any suitable thickness. In some examples, the thickness of the coating 54 can be between about 1 micrometer (μm) and about 30 μm. In some examples, the thickness of the coating 54 can be self-terminating and determined by the diffusion characteristics of the metallic carbon system.

[0043] The high-temperature coating 54 includes a metal-rich antioxidant layer 56 on the surface of the substrate 52. The metal-rich antioxidant layer 56 comprises a metal carbide. The metal carbide may have high strength, abrasion resistance, and temperature resistance, and may be chemically compatible with the underlying substrate 52. In some examples, the metal carbide includes at least one of silicon carbide, titanium carbide, or tungsten carbide.

[0044] As shown below Figures 4A-4F Further explanation is given regarding the metal-rich antioxidant layer (in...) Figure 2 In the example, layer 56 extends into one or more surface voids (such as defects or pores) on the surface of the C / C composite substrate 52 to form a continuous layer that substantially encapsulates the substrate 52. For example, the substrate 52 may include surface voids extending from the outer surface of the substrate 52 into the body of the substrate 52. Surface voids may include defects such as cracks, inherent structures such as surface pores, or other voids or roughness in the surface that extend into the substrate 52, and may have a relatively complex or irregular surface. These surface voids may form discontinuities in the metal carbide layer formed by the substrate 52 and allow oxidizing substances to react with the underlying substrate 52. The metal-rich antioxidant layer 56 can be formed by reacting a metal with both a surface portion of the C / C composite substrate 52 and carbon powder filled into the surface voids, such that a portion of the metal-rich antioxidant layer 56 extends into and substantially fills the surface voids (such as defects or pores) on the surface of the substrate 52, and bridges with a portion of the remaining unreacted metal-rich antioxidant layer 56 on the C / C composite substrate 52 to form a substantially continuous coating.

[0045] To form a uniform, defect-free coating, the metal-rich antioxidant layer 56 may comprise a metal carbide formed from both a carbon matrix of the surface portion of the C / C composite substrate 52 and carbon powder within surface pores having substantially the same composition and morphology as the surface portion of the C / C composite substrate 52. For example, prior to reaction with a metal, the substrate 52 may comprise a surface portion (e.g., the outermost 10-20 micrometers) comprising a carbon matrix capable of reacting with the metal to form the metal carbide. Without being limited by any particular theory, the carbon matrix of the surface portion may have a specific composition and / or morphology, such as microstructure, phase composition, geometry of the component phases, morphology of the component phases, and / or size and distribution of ceramic fibers or pores, crystal structure, presence and type of impurities, particle morphology and size, crystal surface termination (e.g., active facets), crystal defects, and / or surface functionalization. This specific composition and / or morphology may lead to reaction with the metal depending on specific reaction thermodynamics and kinetics, such as reaction temperature and reaction rate.

[0046] Similarly, prior to reacting with the metal, the carbon powder filling the surface voids may have a composition and / or morphology similar to the surface portion of the substrate 52. Due to its substantially similar composition and / or morphology to the surface portion of the substrate 52, the carbon powder may exhibit substantially similar reaction thermodynamics and kinetics. By forming metal carbides from both the carbon matrix of the C / C composite substrate 52 and the carbon powder having substantially the same composition and / or morphology as the C / C composite substrate 52, a metal-rich antioxidant layer 56 can be formed at substantially the same time and rate, thereby bridging the metal carbides in the surface voids with the unreacted metal carbides on the C / C composite substrate 52.

[0047] The metal-rich antioxidant layer 56 may be metal-rich, such that it may contain a metal carbide with a stoichiometric excess of metal. For example, during the formation of the metal carbide from the carbon matrix of the surface portion of the substrate 52 and the carbon powder in the surface voids, a portion of the excess metal may be retained in the metal-rich antioxidant layer 56. During operation of the article 50, the metal may form a metal oxide, which may migrate to form a passivation layer, such as the outer layer 58 described below, or may fill small cracks or pores in the metal-rich antioxidant layer 56 caused by the difference in the coefficients of thermal expansion between the substrate 52 and the metal-rich antioxidant layer 56, such as by the expansion of the excess metal at high temperatures in the presence of oxidation during operation. As a result, the metal of the metal-rich antioxidant layer 56 may perform passivation and / or self-healing functions to further protect the substrate 52.

[0048] In some examples, coating 54 includes a metal oxide outer layer 58 on a metal-rich antioxidant layer 54. For example, during the formation of the metal-rich antioxidant layer 56, a metal that reacts with carbon powder in the carbon matrix and surface voids of the surface portion of the C / C composite substrate 52 may be applied to the surface of the C / C composite substrate 52 in the form of metal powder or particles. This metal powder may include a metal oxide surface layer formed in an oxidizing atmosphere, such as an oxide of the underlying metal or an oxide of a different element. For example, the metal oxide surface layer may have a thickness between about 1 nanometer and about 1 micrometer. During the formation of the metal-rich antioxidant layer 56, the metal oxide may migrate to the surface of the metal-rich antioxidant layer 56 and form the outer layer 58. The outer layer 58 may have a relatively high temperature resistance, such as greater than about 1500°C. In this way, metal oxides that may otherwise exist as impurities in the metal powder may form an additional protective layer to protect the substrate 52 from oxidation.

[0049] The high-temperature antioxidant coating described herein (such as the above) can be formed in situ on a C / C composite substrate. Figure 2 The coating 54) is used to form a denser coating that can continuously encapsulate the C / C composite substrate. Figure 3 This is a flowchart illustrating an exemplary technique for forming a high-temperature coating according to an example of this disclosure. Figure 3 Exemplary technologies will be about Figures 4A-4F The description illustrates various steps for forming a high-temperature antioxidant coating, and Figure 5 An exemplary system or system sequence for forming a high-temperature coating is shown.

[0050] As mentioned above Figure 2 The substrate 52 described herein may include various surface voids, which, if left unsealed or partially sealed, may allow oxidizing substances to penetrate into and react with the substrate 52. Figure 4AThis is a cross-sectional side view showing a portion 60 of an exemplary C / C composite substrate 52 according to an example of this disclosure. The substrate 52 defines an initial outer surface 62A. Surface 62A includes one or more surface voids 64A, 64B, 64C (individually “void 64” and collectively “void 64”). Voids 64 may include any irregularity or deviation from the general plane of surface 62A, which may otherwise create discontinuities in a metal carbide coating formed from the surface portion of the substrate 52 unless filled. For example, a hole with high curvature may result in inhibited reaction with metal and is therefore likely to be a void 64 to be filled, while a shallow depression with low curvature may not result in inhibited reaction with penetrating metal and is therefore likely not a void 64 to be filled. In some examples, voids 64 may include one or more holes 64A, one or more cracks 64B, and / or one or more surface protrusions or depressions 64C. These voids 64 may be formed during the formation of the substrate 52, and the manufacturing effort to reduce voids 64 may be relatively expensive. The void 64 may have a relatively complex surface, which defines a relatively complex volume that may be difficult to fill. For example, a relatively large reactant particle size and / or high slurry viscosity may limit the penetration of metallic reactants into the void 64.

[0051] See again Figure 3 An exemplary technique includes applying carbon powder to the surface of a carbon / carbon (C / C) composite substrate to fill surface voids in the C / C composite substrate (70). Applying carbon powder to the surface may include coating the surface of the C / C composite substrate with carbon powder and forcing the carbon powder into one or more surface voids in the surface of the C / C composite substrate. Figure 4B This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion 60 of an exemplary C / C composite substrate 52, wherein carbon powder 66A fills surface voids 64. Applying carbon powder 66A to surface 62B may include distributing carbon powder 66A onto surface 62B and forcing carbon powder 66A into one or more voids 64 of surface 62B (e.g., filling or at least partially filling surface voids with powder). Thus, carbon powder 66A can penetrate into voids 64.

[0052] Carbon powder 66A may have substantially the same composition and morphology as the surface portion of the C / C composite substrate 52 at or near surface 62B. For example, the microstructure and / or crystallinity of carbon powder 66A may be substantially the same as the microstructure and / or crystallinity of the material of substrate 52 near surface 62B and voids 64. Carbon powder 66A having substantially the same composition and morphology as the surface portion of the C / C composite substrate 52 may have substantially the same reaction thermodynamics and kinetics as the surface portion of the C / C composite substrate 52, such that the reaction of the penetrating metal with the carbon matrix of carbon powder 66A and the surface portion of the C / C composite substrate 52 can occur at substantially the same temperature and at substantially the same rate. As described above, the reaction thermodynamics and kinetics of each of carbon powder 66A and the carbon matrix of the C / C composite substrate 52 may be a product of the respective type of carbon powder 66A and the C / C composite substrate 52, the source of raw materials, the processing history, and other characteristics and conditions, which affect the temperature and rate at which the carbon matrix of carbon powder 66A and the C / C composite substrate 52 can react with the penetrating metal.

[0053] In some examples, applying carbon powder 66A to surface 62B of substrate 52 may include applying carbon powder 66A as a separate powder in a slurry or mixture to surface 62B of substrate 52. As an example, carbon powder 66A may be milled from one or more portions of substrate 52 and / or from raw materials with a composition and / or morphology similar to that of substrate 52 and applied to surface 62B. For example, carbon powder may be generated during the processing of C / C composite substrate 52 through various milling or other operations. This carbon powder may be further processed, such as by milling, to produce carbon powder 66A with a processing history similar to that of C / C composite substrate 52. As another example, carbon powder 66A with a composition and / or morphology substantially matching that of a surface portion of substrate 52 may be selected or obtained and applied to surface 62. For example, carbon powder 66A may be selected or obtained from raw materials produced under processing conditions similar to those of C / C composite substrate 52.

[0054] In some examples, applying carbon powder 66A to surface 62B of substrate 52 may include applying a force to surface 62B to force and fill the voids 64 with carbon powder 66A. For example, the force may include a normal force on surface 62B and / or any lateral force for dispersing and / or filling voids 64. The force applied to carbon powder 66A may force carbon powder 66A into surface voids 64, thereby forming a metal carbide and filling the surface voids 64 with carbon powder 66A, such that carbon powder 66A is retained in surface voids 64, for example, at most between about 50% and about 60% by volume. In some cases, a carrier medium, such as a volatile medium, may be applied to carbon powder 66A to aid in dispersing carbon powder 66A into voids 64. For example, carbon powder 66A may be dispersed in a carrier medium to form a slurry corresponding to a relatively high filler. A variety of methods can be used to force and fill carbon powder 66A into the surface voids 64, including but not limited to: rotational forces, such as polishing or abrasion; linear forces, such as plastering; manual forces, such as manual sanding (e.g., to generate and force carbon powder 66A); etc.

[0055] In some examples, such as Figure 4B As shown, applying carbon powder 66A to the surface 62B of a C / C composite substrate 52 may include generating carbon powder 66A directly from the substrate 52 by mechanically grinding the surface 62A of the C / C composite substrate 52. Figure 4B In the example, substrate 52 has been ground from surface 62A to surface 62B, as shown by the dashed line. For example, grinding surface 62A can, in a single step, both generate carbon powder 66A having substantially the same composition and / or morphology as substrate 52 and force carbon powder 66A into the voids 64, rather than separately applying carbon powder 66A that may be difficult to match with substrate 52 and forcing carbon powder 66A into the voids in a separate step. Even within substrate 52, the composition and / or morphology can vary, such as due to different temperatures during the formation of substrate 52, allowing carbon powder 66A obtained directly from a portion of substrate 52 near surface 62 to generate carbon powder with a composition and / or morphology matching the material surrounding voids 64. The resulting carbon powder 66A can have the same composition and morphology as substrate 52 near surface 62B, can be generated close to voids 64, and can penetrate into voids 64 without the use of a carrier medium.

[0056] Excess carbon powder 66A can be removed from surface 62 prior to reaction with the metal slurry or mixture, such that surface voids 64 may include carbon powder 66A, while the low-curvature or flat surface of surface 62B may not contain carbon powder 66A. For example, if carbon powder 66A remains on the low-curvature or flat portion of surface 62B and subsequently reacts with the metal, the resulting metal carbide may not adhere strongly to the surface of the C / C composite substrate 52 and may undergo delamination. In some examples, excess carbon powder 66A can be removed from the non-void surface of surface 62B during the filling of carbon powder 66A, such as by polishing surface 62B to force carbon powder 66A into voids 64 while wiping away carbon powder 66A on the low-curvature or flat surface of surface 62B.

[0057] See Figure 5 System 80 may include a polishing system 82 configured to mechanically polish the surface 62 of substrate 52. Polishing system 82 may include a polishing surface 86 configured to polish the surface of substrate 52. Polishing system 82 may include an actuation system 84 coupled to polishing surface 86. In some examples, actuation system 84 may be configured to generate a rotational force to rotate polishing surface 86 or a linear force to drive polishing surface 86 (e.g., a belt). In some examples, actuation system 84 may be configured to apply a lateral force to move polishing surface 86 to different portions of substrate 52 and apply a downward force on polishing surface 86 to polish the surface of substrate 52 and force carbon powder generated by polishing into the surface voids of substrate 52.

[0058] See again Figure 3 Exemplary techniques include applying a metal paste to the surface of a C / C composite substrate (71). Figure 4C This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion 60 of an exemplary C / C composite substrate 52, wherein carbon powder 66A fills voids 64 and metal paste 68A is on the C / C composite substrate 52. Although shown in the form of metal paste 68A, the metal can be applied in any form, including in the form of liquid or gas.

[0059] Metal paste 68A may include metal particles in an application medium. In some examples, the metal particles of metal paste 68A include at least one of silicon, titanium, or tungsten. The metal particles may be coated with a thin layer of metal oxide, such as that formed in an oxidizing atmosphere during the formation or storage of the metal particles. For example, relatively pure metal particle raw materials can be very expensive due to inert storage, making the use of metal particles comprising a metal oxide film a way to broaden the available raw materials for the metal particles and / or reduce the cost of the metal particles.

[0060] See Figure 5System 80 may include a metal application system 88. The metal application system 88 may be configured to apply a metal paste to the surface of substrate 52. Although Figure 5 The system shown is a spraying system, but the metal application system 88 may include any system configured to apply a metal paste to the surface of the substrate 52, such as a brushing system.

[0061] See again Figure 3 Exemplary techniques include reacting the metal of a metal slurry with the carbon of a carbon powder and the carbon of a surface portion of a C / C composite substrate to form a metal carbide-rich antioxidant layer (72) on the C / C composite substrate. Figure 4D This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion 60 of an exemplary C / C composite substrate 52 and a metal-rich antioxidant layer 56A. To allow the metal of the metal paste 68A to react with the carbon of the carbon powder 66A and the carbon of the surface portion of the C / C composite substrate 52, the metal may be fluidized (e.g., melted or sublimated) so that the metal can penetrate into the carbon powder 66A and the surface portion of the C / C composite substrate 52, and react with the carbon of the carbon powder 66A and the carbon matrix of the surface portion of the C / C composite substrate 52 to form a metal carbide. This metal carbide can form a continuous metal-rich antioxidant layer 56A to substantially seal the C / C composite substrate 52.

[0062] In some cases, this reaction can be limited by the diffusion of metal into the surface portion of the C / C composite substrate 52 and into the carbon powder 66A. When the metal reacts with the surface portion of the C / C composite substrate 52 to form a metal carbide, the newly formed metal carbide can form a diffusion barrier layer separating the reactants (e.g., carbon and metal), which can prevent thickening and further formation to form a thicker metal carbide (e.g., by preventing the metal from penetrating further into a certain depth of the surface portion of the C / C composite substrate 52 and / or preventing carbon from diffusing from the C / C composite substrate 52 to react with the metal). On the other hand, when the metal reacts with the carbon powder 66A to form a metal carbide, the powder form of the carbon powder 66A allows the metal to continue to permeate around the carbon powder 66A, such that the thickness of the metal carbide in the surface voids 64 can be greater than the thickness of the metal carbide on the C / C composite substrate 52. In some examples, the size of the carbon powder 66A may correspond to the size at which the metal can permeate and react (e.g., less than the diffusion limit), such as less than about 20 micrometers (μm), or between about 1 μm and about 5 μm. In contrast, the size of the surface voids 64 may be greater than about 100 μm, such as between about 100 μm and about 1000 μm. Metal may be applied to the surface 62B of the C / C composite substrate 52 until the reaction ends by diffusion limitation, metal evaporation or depletion, or both. For example, any remaining metal on the surface 62 may be removed, such as by evaporation. The resulting layer 56A may be a relatively uniform metal carbide with a relatively uniform thickness, which may include some deviations in the filling air 64. In some examples, the thickness of the metal-rich antioxidant layer 56A at the surface of the C / C composite substrate 52 is less than about 50 micrometers, such as between about 10 micrometers and about 20 micrometers. In some examples, the thickness of the metal-rich antioxidant layer 56A in the surface voids 64 can be significantly thicker than the thickness of the metal-rich antioxidant layer 56A at the surface of the C / C composite substrate 52.

[0063] The reaction of the metal in the metal paste 68A with the carbon in the carbon powder 66A and the carbon matrix of the surface portion of the C / C composite substrate 52 can be carried out in a stoichiometric excess of metal, such that the resulting metal carbide antioxidant layer 56 is metal-rich. The metal-rich layer may include a metal carbide phase comprising an excess of free metal. For example, the metal-rich metal carbide phase may include a stoichiometric ratio of metal to carbon in the carbon powder greater than 1.1, such as greater than about 1.001:1. By reacting in a stoichiometric excess of metal, the resulting metal-rich antioxidant layer 56A may include excess metal. During the formation of the metal-rich antioxidant layer 56A or during operation of the substrate 52 (e.g., as a component), the excess metal may form metal oxides. In some cases, such as... Figure 4HAs described, the metal oxide can form a passivation layer that further protects the substrate 52. In some cases, the metal oxide can perform a self-healing function on the metal-rich antioxidant layer 56A. For example, the metal oxide can migrate into small cracks that may form during operation, such as mismatches due to CTE or volume expansion, and seal the cracks.

[0064] In some examples, reacting the metal of the metal paste 68A with the carbon of the carbon powder 66A may include heating the surface 62 of the substrate 52 to above the melting point of the metal and maintaining the metal vapor pressure at the surface 62 of the substrate 52 in stoichiometric excess. Various parameters, such as the temperature at the surface 62, the metal concentration at the surface 62 (e.g., as indicated by pressure), and the reaction time, can be controlled to maintain the metal in stoichiometric excess and to promote metal migration into the carbon powder 66A and the carbon in the surface portion of the C / C composite substrate 52 and to react with the carbon powder and carbon. As an example, for silicon metal, the temperature may be maintained above about 1400°C, the pressure may be maintained between about 0.1 mTorr and about 300 mTorr, and the temperature and pressure may be maintained for more than about one hour.

[0065] See Figure 5 System 80 may include a furnace 90 configured to enclose a substrate 52. The furnace 90 may include one or more heaters configured to heat the metal particles of the metal slurry 68A to above the melting point of the metal. The furnace 90 may be configured to maintain the temperature and pressure of the metal such that the metal maintains a stoichiometric excess to form a dense first layer 56A. In some cases, the furnace 90 may be configured to heat the substrate 52 to conduct heat to the metal slurry 68A. For example, although... Figure 5 Not shown, but one or more heaters or electrical contacts may be configured to heat substrate 52 (or generate heat within the substrate) to heat metal paste 68A and cause the metal of metal paste 68A to react with the carbon of carbon powder 66A.

[0066] In some cases, the resulting metal-rich antioxidant layer may still include one or more surface voids. As an example, the surface voids in the C / C composite substrate can be significantly large, such that the carbon powder within the surface voids may not react simultaneously, resulting in smaller residual surface voids. As another example, the surface voids in the metal-rich antioxidant layer can extend to the surface of the C / C composite substrate, such as due to pinholes in the metal-rich antioxidant layer. Figure 4D In the example, the metal-rich antioxidant layer 56 includes smaller surface defects 64D and 64E at the previous surface defects 64A and 64B, respectively. To fill surface defects 64D and 64E, Figure 3Methods may include repairing one or more remaining surface voids on a C / C composite substrate and / or surface voids generated during the formation of a metal-rich antioxidant layer.

[0067] See again Figure 3 Exemplary techniques may include applying a second carbon powder to the surface of a metal-rich antioxidant layer and applying a second metal paste to the surface of other metal-rich antioxidant layers (73). Figure 4E This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of portion 60 of an exemplary C / C composite substrate 52, and of a metal-rich antioxidant layer 56A in which carbon powder 66B fills surface voids 64D and 64E in an antioxidant coating 56A. Figure 4E In some examples, a second carbon powder 66B may be applied to the surface of the metal-rich antioxidant layer 56A. In some examples, the carbon powder 66B has substantially the same composition or morphology as the carbon powder 66A used to form the metal-rich antioxidant layer 56A. The carbon powder 66B may be applied in the form of a slurry or dry powder, rather than by grinding the surface 62 of the substrate 52 to generate the carbon powder.

[0068] See again Figure 3 In some examples, exemplary techniques may include applying a second metal slurry to the surface of a metal-rich antioxidant layer (74). Figure 4F This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion 60 of an exemplary C / C composite substrate 52, a metal-rich antioxidant layer 56A with carbon powder 66B filling surface voids 64D and 64E in a metal-rich antioxidant coating 56A, and a metal paste 68B on the metal-rich antioxidant coating 56A. For example, the metal-rich antioxidant coating 56A may include surface voids 64E extending to the surface of the C / C composite substrate 52. Applying the second metal paste 68B may be similar to applying the first metal paste 68A (71).

[0069] See again Figure 3 Exemplary techniques may include reacting the metal of a second metal slurry with the carbon of a second carbon powder to form a metal carbide (75) in one or more surface voids. Figure 4G This illustrates an example according to this disclosure. Figure 4AA cross-sectional side view of portion 60 of an exemplary C / C composite substrate 52 and a metal-rich antioxidant layer 56. The metal of the metal paste 68B can react with the carbon of the carbon powder 66B to form metal carbides in the previously existing surface defects 64D. Therefore, the metal-rich antioxidant layer 56 may include fewer surface voids than a metal-rich antioxidant layer 56A formed by a single application of carbon powder and metal paste alone. The reaction of the metal of the metal paste 68B with the carbon of the carbon powder 66B can be carried out under similar conditions and using a method (72) similar to the reaction of the metal of the metal paste 68A with the carbon of the carbon powder 66A.

[0070] Although Figures 4E-4G The example shown is a single additional patching process, but in some examples, Figure 3 Steps 73-75 may be repeated iteratively multiple times to form a continuous, substantially defect-free metal-rich antioxidant layer 56, and may include additional processing steps, such as cleaning or brushing the metal-rich antioxidant layer 56A, so that any loose carbides or carbon powder are removed before additional coating.

[0071] See again Figure 3 In some examples, exemplary techniques include forming a metal oxide layer on a high-temperature antioxidant coating. Figure 4H This illustrates an example according to this disclosure. Figure 4A A cross-sectional side view of a portion of an exemplary C / C composite substrate, a metal-rich antioxidant layer 56, and an outer oxide layer 58. Figure 4C and Figure 4E The metal pastes 68A and 68B may comprise metal particles coated with a metal oxide layer, such as silicon oxide, titanium oxide, and / or tungsten oxide. During heating of surface 62, at least a portion of the metal oxide from the metal particles may enter the solution and migrate from the respective metal paste 68A or 68B to the surface of the metal-rich antioxidant layer 56. Upon cooling, the metal oxide may form an outer oxide layer 58 on the metal-rich antioxidant layer 56. In some examples, at least a portion of the metal oxide may remain in the metal-rich antioxidant layer 56, except for forming the outer oxide layer 56, such that during operation of the assembly including substrate 52, the metal oxide may be available to migrate to one or more cracks formed in the metal-rich antioxidant layer 56.

[0072] Experimental methods

[0073] In a first embodiment, a high-temperature silicon carbide coating is formed on a C / C composite substrate. The surface of the C / C composite substrate is ground using a rotary mill to generate carbon powder and force the carbon powder into one or more surface pores of the C / C composite substrate. A slurry of coated silicon particles, which may already contain a layer of natural oxide (such as silicon dioxide), is applied to the surface of the C / C composite substrate in a stoichiometric excess sufficient to react up to a surface area of ​​20-30 micrometers, and to compensate for evaporation and other losses (e.g., about 0.02 g / cm² to 0.2 g / cm² for silicon). The C / C composite substrate is heated at a temperature of about 1400°C and a pressure of about 100 mTorr for about one hour.

[0074] Figure 6 These are micrographs of a cross-section of an exemplary article 100 comprising a C / C composite substrate 102 and a high-temperature coating 104 according to embodiments of the present disclosure. Figure 6 As shown, silicon migrates into various surface voids (such as pores and defects) on the surface of substrate 102 to react with carbon powder and form a dense high-temperature coating 104.

[0075] In a second embodiment, a high-temperature silicon carbide coating is formed on an exemplary aircraft rotor segment comprising a C / C composite substrate. As described above, a high-temperature coating is formed on the aircraft rotor segment.

[0076] According to embodiments of this disclosure, Figure 7A This is a micrograph of a cross-section of a portion 110 of a C / C composite substrate at the outer diameter of an exemplary aircraft rotor section. Figure 7B This is a micrograph of a cross-section of a portion 120 of a C / C composite substrate at the inner diameter of an exemplary aircraft rotor section, and... Figure 7C This is a magnified photomicrograph of a cross-section of a portion 130 of an exemplary aircraft rotor segment. Figure 7A and Figure 7B As shown, silicon carbide coatings 112 and 122 extend through the surface of the C / C substrate 114 to form a relatively uniform and homogeneous high-temperature antioxidant coating. Figure 7C As shown, the silicon carbide coating 132 can extend into the voids 134 of the C / C composite substrate 114 to substantially seal the voids 134 from the effects of oxidizing substances.

[0077] In the third embodiment, a high-temperature silicon carbide coating is formed on six C / C composite substrates. Different vapor pressures are used to form the high-temperature coating as described in the first embodiment above, in order to control the concentration of stoichiometric excess silicon metal during the reaction between carbon and silicon.

[0078] Figure 8The image shows an exemplary C / C composite substrate coated under various vapor pressures to form a high-temperature coating, according to examples of this disclosure.

[0079] Example 1: A method for forming a high-temperature coating includes: applying carbon powder to the surface of a carbon / carbon (C / C) composite substrate to force the carbon powder into one or more surface voids on the surface of the C / C composite substrate, wherein the carbon powder has a composition and morphology substantially the same as the surface portion of the C / C composite substrate; after applying the carbon powder, applying a metal paste to the surface of the C / C composite substrate; and reacting the metal of the metal paste with the carbon of the carbon powder and the carbon of the surface portion of the C / C composite substrate to form a metal-rich antioxidant layer of metal carbides on the C / C composite substrate.

[0080] Example 2: According to the method of Example 1, applying the carbon powder to the surface of the C / C composite substrate includes mechanically grinding the surface portion of the C / C composite substrate to generate the carbon powder from the surface portion of the C / C composite substrate and forcing the carbon powder into the one or more surface voids.

[0081] Example 3: The method according to any one of Examples 1 and 2, wherein during the reaction, the metal in the metal slurry is maintained in stoichiometric excess to form the metal-rich antioxidant layer of the metal carbide.

[0082] Example 4: The method according to any one of Examples 1 to 3, wherein reacting the metal of the metal slurry with the carbon of the carbon powder comprises: heating the surface of the C / C composite substrate to above the melting point of the metal; and maintaining the vapor pressure of the metal at the surface of the C / C composite substrate in accordance with a stoichiometric excess of the metal.

[0083] Example 5: The method according to any one of Examples 1 to 4, wherein the metal slurry comprises metal particles coated with a metal oxide layer, and wherein the method further comprises forming an outer layer of metal oxide on a metal-rich antioxidant layer using at least a portion of the metal oxide from the metal slurry.

[0084] Example 6: The method according to any one of Examples 1 to 5, wherein the metal paste comprises at least one of silicon, titanium or tungsten.

[0085] Example 7: The method according to any one of Examples 1 to 6, wherein the thickness of the metal-rich antioxidant layer is less than about 30 micrometers.

[0086] Example 8: The method according to any one of Examples 1 to 7, wherein the average diameter of the carbon powder is less than about 20 micrometers.

[0087] Example 9: The method according to any one of Examples 1 to 8, wherein the carbon powder is a first carbon powder, wherein the metal paste is a first metal paste, and wherein the method comprises: applying a second carbon powder to the surface of the metal-rich antioxidant layer to force the second carbon powder into one or more surface voids in the surface of the metal-rich antioxidant layer; applying a second metal paste to the surface of the metal-rich antioxidant layer; and reacting the metal of the second metal paste with the carbon of the second carbon powder to form a metal carbide in the one or more surface voids in the surface of the metal-rich antioxidant layer.

[0088] Example 10: The method according to any one of Examples 1 to 9, wherein applying the carbon powder to the surface of the C / C composite substrate comprises applying a carbon powder slurry or a dry rub containing the carbon powder to the surface of the C / C composite substrate.

[0089] Example 11: The method according to Example 10, wherein the carbon powder is generated by processing the C / C composite substrate.

[0090] Example 12: The method according to any one of Examples 1 to 11, wherein the high-temperature coating comprises a single metal-rich antioxidant layer.

[0091] Example 13: A high-temperature article includes: a carbon / carbon (C / C) composite substrate; and a high-temperature coating on the surface of the C / C composite substrate, wherein the high-temperature coating includes a metal-rich antioxidant layer of metal carbides on the surface of the C / C composite substrate, wherein the metal carbides of the metal-rich antioxidant layer are formed from carbon of carbon powder and carbon of the surface portion of the C / C composite substrate, wherein the carbon powder has substantially the same composition and morphology as the surface portion of the C / C composite substrate, and wherein the metal-rich antioxidant layer extends into one or more surface voids on the surface of the C / C composite substrate.

[0092] Example 14: The article according to Example 13, wherein the carbon powder is generated from the surface portion of the C / C composite substrate.

[0093] Example 15: The article according to any one of Examples 13 and 14, wherein the metal carbide comprises at least one of silicon carbide, titanium carbide or tungsten carbide.

[0094] Example 16: The article according to any one of Examples 13 to 15 further includes an outer layer of metal oxide on the high-temperature coating.

[0095] Example 17: The article according to any one of Examples 13 to 16, wherein the thickness of the metal-rich antioxidant layer is less than about 30 micrometers.

[0096] Example 1 8: The article according to Example 17, wherein the thickness of the metal-rich antioxidant layer is between about 1 micrometer and about 5 micrometers.

[0097] Example 19: An article according to any one of Examples 13 to 18, wherein the metal carbide comprises a stoichiometric ratio of a metal carbide of a metal to the carbon of the carbon powder of a ratio greater than 1:1.

[0098] Example 20: The article according to any one of Examples 13 to 19, wherein the high-temperature coating comprises a single metal-rich antioxidant layer.

[0099] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for forming a high-temperature coating, the method comprising: Carbon powder is applied to the surface of a carbon / carbon (C / C) composite substrate to force the carbon powder into one or more surface voids of the C / C composite substrate, wherein applying the carbon powder to the surface of the C / C composite substrate includes mechanically grinding a portion of the surface of the C / C composite substrate to generate the carbon powder from the portion of the surface of the C / C composite substrate and forcing the carbon powder into the one or more surface voids, such that the carbon powder has substantially the same composition and morphology as the portion of the surface of the C / C composite substrate; After the carbon powder is applied, a metal slurry is applied to the surface of the C / C composite substrate; as well as The metal in the metal slurry reacts with the carbon in the carbon powder and the carbon in the surface portion of the C / C composite substrate to form a metal carbide-rich antioxidant layer on the C / C composite substrate.

2. The method of claim 1, wherein during the reaction, the metal in the metal slurry is maintained in stoichiometric excess to form the metal-rich antioxidant layer of the metal carbide.

3. The method of claim 1, wherein reacting the metal of the metal slurry with the carbon of the carbon powder comprises: The surface of the C / C composite substrate is heated to a temperature higher than the melting point of the metal; as well as Corresponding to a stoichiometric excess of the metal, the vapor pressure of the metal at the surface of the C / C composite substrate is maintained.

4. The method according to claim 1, The metal paste comprises metal particles coated with a metal oxide layer, and The method further includes forming an outer layer of the metal oxide on the metal-rich antioxidant layer using at least a portion of the metal oxide from the metal slurry.

5. The method of claim 1, wherein the carbon powder is a first carbon powder, the metal paste is a first metal paste, and the method comprises: The second carbon powder is applied to the surface of the metal-rich antioxidant layer to force the second carbon powder into one or more surface voids in the surface of the metal-rich antioxidant layer; A second metal paste is applied to the surface of the metal-rich antioxidant layer; as well as The metal of the second metal slurry reacts with the carbon of the second carbon powder to form metal carbides in one or more surface voids on the surface of the metal-rich antioxidant layer.

6. A high-temperature product, comprising: Carbon / carbon (C / C) composite substrate; and A high-temperature coating on the surface of the C / C composite substrate, wherein the high-temperature coating comprises a metal carbide-rich antioxidant layer on the surface of the C / C composite substrate. The metal carbide in the metal-rich antioxidant layer is formed from carbon in the carbon powder and carbon in the surface portion of the C / C composite substrate. The carbon powder is formed by mechanically grinding the surface portion of the C / C composite substrate to generate carbon powder from the surface portion of the C / C composite substrate, such that the carbon powder has substantially the same composition and morphology as the surface portion of the C / C composite substrate. The metal-rich antioxidant layer extends into one or more surface voids of the surface of the C / C composite substrate.

7. The article of claim 6 further comprises an outer layer of metal oxide on the high-temperature coating.

8. The article of claim 6, wherein the thickness of the metal-rich antioxidant layer is between 1 micrometer and 5 micrometers.

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