Heat-resistant material
By adding silicide carbon powder to the thermally resisted material and forming a silicon oxide phase, the problem that existing thermally resisted materials are easily eroded by oxides in high-temperature oxidation environments is solved, and the high-temperature mechanical strength and corrosion resistance of the material are significantly improved.
Patent Information
- Application Number
- JP2024148297
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-09-15
- Filing Date
- 2024-08-30
- Publication Date
- 2025-03-28
AI Technical Summary
Existing thermal resistance materials are easily eroded by oxides in high-temperature oxidation environments, resulting in degradation of mechanical properties and corrosion of components. A thermal resistance material that can effectively prevent oxide corrosion at high temperatures is needed.
Using a silicon-rich thermal resistance material system, by adding silicide carbon powder to the silicide ene carbide matrix and forming a silicon oxide phase during the heat treatment process, the density and mechanical strength of the material are enhanced and the barrier ability to the oxide is improved.
It achieves a significant improvement in the mechanical strength and corrosion resistance of thermally resisted materials in high-temperature oxidation environments, extends the service life of the materials, and reduces the maintenance and replacement frequency.
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Figure 2025043291000001_ABST
Abstract
Description
[Technical field]
[0001] The present disclosure relates to heat resistant materials. [Background technology]
[0002] Refractory materials can be used in high temperature applications to aid in handling molten metal. For example, in foundries, refractory materials can be used to form or coat metalworking units, such as ladles and furnaces. The harsh conditions encountered during metalworking can cause the metalworking units to corrode and erode, which can lead to replacement of the entire metalworking unit. Summary of the Invention
[0003] The present disclosure describes systems and techniques for forming components or coatings from one or more heat-resistant materials. The substrate or component, such as an aerospace or cast component, may be part of a device or system that is exposed to relatively high temperature oxidizing and abrasive environments, such as hypersonic aerospace applications having temperatures above about 1200 degrees Celsius (°C), or cast applications exposed to slag or other oxidizing species. To prevent the chemical species from degrading the component, the surfaces of the heat-resistant components that may be exposed to the oxidizing species are dense and have high resistance to penetration of the oxidizing species.
[0004] In some examples, the coating or component is formed from a relatively dense refractory material using inexpensive raw materials that resist degradation from particulates or other wear sources. The dense refractory material includes a polymer-derived silicon carbide matrix and silicon carbide powder in a silicon carbide matrix. To enhance the mechanical properties of the refractory material, such as mechanical strength, corrosion resistance, and impact resistance, the refractory material includes a silicon dioxide phase formed at the grain boundaries of the silicon carbide powder.
[0005] The refractory material is derived from a silicon-rich refractory mixture. The silicon-rich refractory mixture includes a small amount of a relatively expensive silicon carbide preceramic polymer and a large amount of a relatively inexpensive silicon carbide powder. In a first heating step, the mixture is pyrolyzed to form a silicon-rich refractory material. In a second heating step, the excess silicon in the silicon-rich refractory material is oxidized to form a silicon dioxide phase that further reduces porosity and increases the mechanical strength of the reinforced refractory material. In this manner, a dense refractory component suitable for casting applications can be formed using relatively simple processing and inexpensive raw materials.
[0006] In some examples, the refractory material may be used to form a coating on a substrate of an aerospace component. The coating may be applied to a surface of the substrate as a paste having a silicon-rich refractory mixture. The resulting coating may be resistant to both migration of oxidizing species and abrasion by particles in the fluid. In other examples, the refractory material may be used to form a refractory component of a casting system. The refractory component may be formed from a near-net-shape preform and molded from the silicon-rich refractory mixture. The resulting refractory component may be resistant to both migration of oxidizing species and damage caused by equipment contacting the surface of the refractory component.
[0007] In one example, the method includes forming a coating on a substrate. The coating is formed from a silicon-rich refractory mixture including a silicon-rich silicon carbide preceramic polymer and silicon carbide powder. The method further includes heating the coating to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material. The silicon-rich refractory material includes silicon carbide powder and excess silicon in a silicon carbide matrix. The method further includes heating the silicon-rich refractory material to oxidize at least a portion of the excess silicon and form a reinforced refractory material. The reinforced refractory material includes a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0008] In another example, an article includes a substrate and a coating overlying the substrate, the coating comprising a reinforced heat-resistant material including a polymer-derived silicon carbide matrix, silicon carbide powder in the silicon carbide matrix, and a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0009] In another example, the method includes forming a preform of a refractory component from a silicon-rich refractory mixture. The silicon-rich refractory mixture includes a silicon-rich silicon carbide preceramic polymer and silicon carbide powder. The method further includes heating the preform to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material. The silicon-rich refractory material includes silicon carbide powder and excess silicon in a silicon carbide matrix. The method further includes heating the silicon-rich refractory material to oxidize at least a portion of the excess silicon and form a reinforced refractory material. The reinforced refractory material includes a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0010] In another example, the heat resistant component includes a reinforced heat resistant material that includes a polymer-derived silicon carbide matrix, silicon carbide powder in the silicon carbide matrix, and a silicon dioxide phase at the grain boundaries of the silicon carbide powder.
[0011] The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will become apparent from the description, drawings, and claims. [Brief description of the drawings]
[0012] [Figure 1] 1 is an enlarged cross-sectional view of an exemplary heat-resistant material formed according to the techniques of the present disclosure. [Diagram 2] FIG. 2 is a close-up view of an exemplary heat-resistant mixture according to the techniques of the present disclosure. [Diagram 3] 1 is a side cross-sectional view of a portion of an exemplary aerospace component formed in accordance with the techniques of the present disclosure. [Figure 4]FIG. 1 is a flow diagram illustrating an exemplary technique for forming a coating for an aerospace component in accordance with techniques of the present disclosure. [Diagram 5] 1 is a cross-sectional perspective view illustrating an exemplary container including a heat-resistant component formed in accordance with the techniques of the present disclosure. [Figure 6] FIG. 1 is a flow diagram illustrating an exemplary technique for forming a heat resistant component according to techniques of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The present disclosure describes articles, such as high temperature articles of aerospace or casting systems, that include heat-resistant materials. Aerospace coatings and / or heat-resistant components made from heat-resistant materials may be capable of operating in relatively high temperature oxidizing environments. As an example, aerospace heat-resistant materials can help protect the exterior components of a spacecraft from damage during re-entry. As another example, cast heat-resistant materials can help with handling molten metal during metal processing, such as steelmaking. Various casting systems, such as ladles, slide gates, and furnaces, may include heat-resistant components, such as bricks, bulk materials, or liners, to help maintain the high temperatures of the molten metal and to shield the more sensitive components of the processing units and the workers operating the processing units from the high temperatures. These heat-resistant components can provide high resistance to oxidation and / or environmental attack at the high temperatures that occur during the operation or fabrication of aerospace components as well as other types of components.
[0014] Refractory materials can be formed from relatively inexpensive refractory ceramic particles dispersed in a ceramic matrix. Despite the relatively high thermal and chemical stability of refractory materials, the harsh environment of wear particles or molten metal can erode and corrode the ceramic matrix of the refractory material. As an example, a coating made from a refractory material can deteriorate when in contact with airborne particles or other wear materials. As another example, a ladle for processing steel can be formed from a refractory material that includes refractory particles bound by a carbon matrix. Slag and other by-products of steel processing can oxidize the carbon and cause cracks or other deterioration in the refractory material. As a result, refractory coatings or components may be periodically replaced or rebuilt.
[0015] To withstand high temperatures, to withstand migration of oxidizing species, and / or to withstand wear or other impacts, the refractory materials described herein include silicon carbide particles fused by a silicon carbide matrix and reinforced with silicon dioxide phases. FIG. 1 is an enlarged cross-sectional view of an exemplary reinforced refractory material 10 formed according to the techniques of the present disclosure. The reinforced refractory material 10 may be a portion of a refractory coating or component having one or more surfaces 12 that are exposed to high temperatures and oxidizing conditions during operation. As an example, hypersonic applications may be exposed to temperatures exceeding 3000 degrees Fahrenheit (°F) (about 1650 degrees Celsius (°C)) during re-entry. As another example, metalworking components may be exposed to temperatures exceeding 2200 degrees Fahrenheit (°F) (about 1200 degrees Celsius (°C)) during processing of oxidizing species such as superalloys and silicon.
[0016] The reinforced refractory material 10 includes a silicon-rich polymer-derived silicon carbide matrix 16 and silicon carbide powder (or aggregates) 14 in the silicon carbide matrix 16. The silicon carbide powder 14 may form a closely packed phase that comprises a high volume fraction of the reinforced refractory material 10. The silicon carbide matrix 16 may form a binder phase that comprises a low volume fraction of the reinforced refractory material 10.
[0017] The polymer-derived silicon carbide matrix 16 may include a silicon carbide ceramic material formed from the decomposition of a preceramic polymer and the subsequent formation of amorphous and / or crystalline silicon carbide phases that maintain thermal and chemical stability at high temperatures, such as above about 1500° C. Silicon carbide may have properties that make it particularly suitable for high temperature oxidative environments, including a high decomposition temperature, a relatively low crystallization temperature of one or more crystalline phases of the polymer-derived ceramic material, a low coefficient of thermal expansion, and compatibility and adhesion with silicon carbide powder 14.
[0018] In some examples, silicon carbide matrix 16 may be present as a substantially crystalline phase (e.g., greater than 95% by volume). As described further below, silicon carbide matrix 16 may be substantially crystallized by heating silicon carbide matrix 16 above a crystallization temperature after pyrolysis of the preceramic polymer such that silicon carbide matrix 16 is substantially free of glass / amorphous phase. For example, silicon carbide matrix 16 may include one or more crystalline phases distributed in an amorphous phase such that the amorphous phase is less than about 5% by volume of the ceramic matrix.
[0019] The silicon carbide matrix 16 may be present in the reinforced refractory material 10 in a distribution and volume fraction sufficient to bond the particles of the silicon carbide powder 14 together. For example, the silicon carbide powder 14 may form closely packed agglomerates with small voids between the particles. The silicon carbide matrix 16 may fill these voids to secure and seal the particles. However, although the silicon carbide matrix 16 may have a relatively high thermal and oxidation resistance, the preceramic polymer used to form the silicon carbide matrix 16 may be relatively expensive, so the volume fraction of the silicon carbide matrix 16 may be kept relatively small. In some examples, the silicon carbide matrix 16 defines less than about 10 volume percent of the reinforced refractory material 10.
[0020] The silicon carbide powder 14 maintains thermal and chemical stability at temperatures of about 1500° C. or greater. The silicon carbide powder 14 may exist as a powder with relatively loose particles or as agglomerates with relatively constrained (e.g., packed) particles. Various parameters of the particles, such as particle size, particle shape, and particle size distribution of the silicon carbide powder 14, may be selected to form a densely packed, mechanically robust material when the silicon carbide powder 14 is bonded to the silicon carbide matrix 16. In some examples, the particle size may be from about 0.1 micrometers to about 500 micrometers.
[0021] In some examples, the reinforced refractory material 10 is configured with a particular average particle size or shape and / or particle size distribution of the silicon carbide powder 14 within the silicon carbide matrix 16. The density of the reinforced refractory material 10 may be related to the compaction or packing density of the silicon carbide powder 14. To increase the density of the reinforced refractory material 10 and improve its properties (e.g., pyrolysis, oxidation, and optionally crystallization), the refractory mixture used to form the reinforced refractory material 10 may include a wide distribution of particle sizes, such as a bimodal or trimodal distribution of particle sizes. The bimodal or trimodal particle size distribution may be configured to form a highly packed refractory material and increase the overall density and performance of the material. The particle size distribution may vary based on the composition of the silicon carbide powder 14 and the volume ratio of the silicon carbide powder 14 to the silicon carbide matrix 16. The distribution may determine the packing ratio. In some examples, the packing percentage can be at least about 60% by volume, such as about 60% to about 75%, depending on the particle size distribution. "About" a particular packing percentage can be within 10%, e.g., within 5% or 1%, of that value and can refer to the precision and capabilities of the equipment used to measure the packing percentage and / or the manufacturing control of the particle size and / or particle size distribution.
[0022] In some examples, such as those in which the reinforced refractory material 10 is used to form a refractory component, the reinforced refractory material 10 is configured to maintain the near net shape of the refractory component before and after processing. A refractory component having a near net shape may not shrink or shrink very little during pyrolysis. For example, prior to pyrolysis, a preform formed from a refractory mixture including silicon carbide powder 14 may be defined by a first volume that corresponds to a first set of dimensions of a corresponding mold. After pyrolysis, the refractory component may be defined by a second volume that corresponds to the final shape of the refractory component. In some examples, the near net shape is a difference between the first volume and the second volume that is less than about 5 volume percent.
[0023] Prior to pyrolysis, the silicon carbide powder 14 may be densely packed such that grains of the silicon carbide powder 14 particles contact adjacent grains. During pyrolysis of the silicon carbide preceramic polymer, the silicon carbide preceramic polymer may decompose into a denser silicon carbide matrix. In a refractory mixture where the refractory particles are not densely packed, the refractory component may shrink and maintain a high density with a relatively low porosity. However, in a refractory mixture where the silicon carbide powder 14 particles are densely packed, the grains of the particles may continue to reinforce the shape of the refractory material.
[0024] When used as a bulk material to form a refractory component, the reinforced refractory material 10 can maintain the near-net shape of the refractory component by resisting shrinkage. During pyrolysis, the silicon carbide preceramic polymer may shrink locally to form the silicon carbide matrix 16 and may include small voids such that the refractory material may have a slightly lower density. In some examples, the refractory material may include a substantially closed porosity, such as greater than about 80 volume percent closed pores. In this way, by tightly packing the particles of silicon carbide powder 14, the refractory component may have a high density, improved mechanical properties, a near-net shape, a relatively high percentage of closed pores, and / or a small amount of relatively expensive silicon carbide matrix.
[0025] In some examples, the refractory material 10 may include two or more particle compositions of silicon carbide powder 14. Various properties of the refractory material 10, such as the effective coefficient of thermal expansion, may result from a combination of properties of the silicon carbide powder 14 and the silicon carbide matrix 16. In some examples, the silicon carbide powder 14 may be part of a mix of two or more species such that the enhanced refractory material 10 may have properties resulting from a blend of refractory powders. For example, the mix of two or more species may be configured to enhance thermal shock by including a blend of refractory powders having different elastic moduli, thermal conductivities, and / or thermal expansion coefficients to produce a refractory material with a particular bulk elastic modulus, thermal conductivity, and / or thermal expansion. In some examples, the refractory powder may include an active species configured to interact with other species. For example, the mix of two or more species may include a species configured to react with an oxidizing species, such as oxygen. In some examples, the mix of two or more species may be configured to produce a particular grade of refractory material associated with a price point. For example, a mix of two or more species can balance the cost of the various species with the qualities (eg, strength or stability) of the heat-resistant material.
[0026] In some examples, the reinforced refractory material 10 includes a particular volume ratio of silicon carbide matrix 16 to silicon carbide powder 14. As mentioned above, the volume ratio of silicon carbide matrix 16 to silicon carbide powder 14 can be kept relatively small to maintain a large amount of the more chemically and thermally stable silicon carbide powder 14 and / or to reduce the cost of the refractory material. For example, the cost of the refractory material can be kept relatively low, such as by maintaining a relatively small amount of silicon carbide matrix 16 sufficient to bond the silicon carbide powder 14 together, since silicon carbide preceramic polymers can be relatively expensive. Such relatively low costs can be particularly important for components of a casting system that may use a large amount of refractory material in one piece of equipment that may have a high replacement schedule. In some examples, the silicon carbide matrix 16 can define less than about 10 volume percent of the refractory material, and the silicon carbide powder 14 can define more than 90 volume percent of the reinforced refractory material 10.
[0027] Refractory materials including silicon carbide powder 14 in a silicon carbide matrix 16 can be thermally stable at high temperatures and resistant to oxidation. However, such refractory materials may still be susceptible to oxidation over time. To further improve the mechanical and / or chemical properties of the refractory material, the reinforced refractory material 10 further includes silicon dioxide phases 18A, 18B (collectively "silicon dioxide phase 18"). The silicon dioxide phase 18 can be configured to improve various mechanical and / or chemical properties of the refractory material, including, but not limited to, increased mechanical strength, increased wear resistance, increased hardness, increased corrosion resistance, and increased thermal shock resistance.
[0028] Without being limited to any particular theory, the silicon dioxide phase 18 may function as an intermediate phase within the reinforced refractory material 10 to further adhere the silicon carbide powder 14 to the silicon carbide matrix 16, such as by increasing intergranular strength or grain boundary bond strength. In the example of FIG. 1 , the silicon dioxide phase 18 includes a silicon dioxide phase at the grain boundaries of the silicon carbide powder 14 ("boundary phase 18A") and a silicon dioxide phase at the pores ("pore phase 18B"). The boundary phase 18A may be present at the interface between the silicon carbide powder 14 and the silicon carbide matrix 16. The pore phase 18B may be present within the silicon carbide matrix 16.
[0029] The silicon dioxide phase 18 may comprise a relatively small volume fraction of the reinforced refractory material 10. In small amounts, silicon dioxide may improve the mechanical properties of the reinforced refractory material 10, but in large amounts, silicon dioxide may adversely affect the reinforced refractory material 10. For example, as the silicon content increases, various properties of the reinforced refractory material 10 may become closer to silicon than to silicon carbide, such as reduced thermal resistance, reduced hardness, and reduced corrosion resistance. In some examples, the silicon dioxide phase 18 is less than about 1 volume percent of the reinforced refractory material 10.
[0030] In some examples, the silicon dioxide phase 18 may densify the reinforced refractory material 10 by reducing the porosity of the reinforced refractory material 10. For example, the pore phase 18B may form in portions of the silicon carbide matrix 16 that may have contained open pores before the silicon dioxide formed within the pores. By filling at least a portion of the open pores with silicon dioxide, the reinforced refractory material 10 can have an even lower porosity than a refractory material formed solely from silicon carbide powder 14 and silicon carbide matrix 16. In some examples, the reinforced refractory material 10 has a porosity of about 5 volume percent (vol%) or less.
[0031] In some examples, the reinforced refractory material 10 further comprises silicon powder. As discussed below, the reinforced refractory material 10 may be formed from a silicon-rich refractory mixture that forms a silicon-rich refractory material intermediate silicon carbide powder 14 and silicon carbide matrix 16. The excess silicon in the silicon-rich refractory material may be provided by the silicon powder. A portion of the silicon powder may not oxidize and remain dispersed within the silicon carbide matrix 16.
[0032] The heat-resistant materials described herein are formed from a silicon-rich heat-resistant mixture that includes silicon carbide powder and a silicon-rich silicon carbide preceramic polymer. Figure 2 is an enlarged view of an exemplary silicon-rich heat-resistant mixture 20 according to the techniques of the present disclosure. The heat-resistant mixture 20 includes a liquid component 22 and silicon carbide powder 14 dispersed in the liquid component.
[0033] The liquid component 22 includes a silicon-rich silicon carbide preceramic polymer. The silicon-rich silicon carbide preceramic polymer is configured to decompose to form an amorphous and / or crystalline silicon carbide phase that maintains thermal and chemical stability at high temperatures, such as above about 1500° C. The preceramic polymer can be relatively inexpensive to form a silicon carbide matrix, as compared to chemical and physical deposition methods, such as chemical vapor deposition (CVD). The preceramic polymer can be selected for cost and desired properties of the resulting pyrolyzed and optionally crystallized silicon carbide matrix, such as silicon carbide matrix 16 of FIG. 1. A variety of silicon-rich silicon carbide preceramic polymers can be used, including, but not limited to, polycarbosilanes, such as allylhydridopolycarbosilane (AHPCS), polycarbosiloxanes, polycarbosilazanes, and the like.
[0034] In some examples, the silicon-rich silicon carbide preceramic polymer may be selected for desired properties of the refractory mixture 20 or a preform formed from the refractory mixture 20. As one example, for a refractory coating, the preceramic polymer may be selected for fluid properties related to its ability to be applied as a paste and conform to the surface of the underlying substrate. As another example, for a refractory component, the preceramic polymer may be selected for fluid properties related to the ability of the refractory mixture 20 to flow during application to a mold, fluid or adhesive properties related to the ability of the refractory mixture 20 to compact and maintain a compacted form as a preform prior to complete pyrolysis, and other properties related to the dispersion and compaction of the refractory mixture 20.
[0035] In some examples, the silicon-rich silicon carbide preceramic polymer is configured to aid in the application of a coating formed from the refractory mixture 20. For example, the preceramic polymer can function as a carrier to allow the refractory mixture 20 to flow to a desired thickness and with a desired conformability prior to pyrolysis of the preceramic polymer. The preceramic polymer can wet the surface of the silicon carbide powder 14 and the surface of the underlying substrate. As a result, the coating formed from the silicon carbide powder 14 and the preceramic polymer can be continuous and substantially uniform. In examples of forming a coating from the reinforced refractory material 10, the preceramic polymer in the refractory mixture 20 is present in a weight concentration of about 3% to about 10% by weight.
[0036] In some examples, the silicon-rich silicon carbide preceramic polymer is configured to aid in adhesion of a preform formed from the refractory mixture 20. For example, the preceramic polymer can function as a binder to adhere the refractory mixture 20 as a preform in a desired shape prior to pyrolysis of the preceramic polymer. The preceramic polymer can wet the surface of the silicon carbide powder 14 and bond the silicon carbide powder 14. As a result, a preform formed from the consolidated silicon carbide powder 14 and the preceramic polymer can be structurally solid to withstand at least the forces of gravity and light handling. In an example for forming a coating from the reinforced refractory material 10, the preceramic polymer in the refractory mixture 20 is present in a weight concentration of about 1% to about 5% by weight.
[0037] The silicon carbide preceramic polymer is silicon rich. The silicon carbide preceramic polymer is configured to decompose to form both a silicon carbide matrix, such as silicon carbide matrix 16, and excess silicon. The excess silicon may be available for oxidation and subsequent formation of a silicon dioxide phase, such as silicon dioxide phase 18 in FIG. 1. In some examples, the silicon rich silicon carbide preceramic polymer may be a silicon carbide preceramic polymer that has been modified with excess silicon groups, such as a polycarbosilane mixed with a polysiloxane, or other preceramic polymer with silicon-containing functional groups.
[0038] In some examples, the heat-resistant mixture 20 further comprises silicon powder. For example, in addition to the excess silicon provided by the silicon-rich silicon carbide polymer, the silicon powder may provide additional silicon for subsequent oxidation within the silicon dioxide phase 18. In some examples, the particle size of the silicon powder is from about 10 nanometers to about 10 micrometers. For example, nano-range particle sizes can disperse more completely than larger particles and do not form large pores when melted. However, such particles may be difficult to process because silicon dioxide may form on the surface of the particles. In some examples, the particle size is from about 500 nanometers to about 1 micrometer.
[0039] In some examples, the preceramic polymer may be cured, for example, by heating, prior to complete pyrolysis to form a cured coating or preform with improved integrity. For example, application or compaction of a paste may form the heat-resistant mixture into a coating or preform with a uniform thickness or compacted consistency, but the coating or preform may still be brittle and susceptible to damage upon dropping or rough handling. A portion of the preceramic polymer, such as a portion near the surface of the heat-resistant coating or component, may be heated above a curing temperature to cure the portion of the preceramic polymer and protect the coating or preform from damage. In some examples, the curing temperature may be greater than about 100° C. and less than about 250° C. and may depend on the particular preceramic polymer.
[0040] In some examples, the heat-resistant mixture 20 may be configured to be applied as a paste that is subsequently heated. The paste may be formed into a coating having a predetermined thickness that corresponds to the desired thickness of the final coating. Thus, the heat-resistant mixture 20 may have various flow properties related to the ability of the heat-resistant mixture 20 to flow or move over the surface of the substrate, and / or various adhesion properties related to the ability of the heat-resistant mixture 20 to form a relatively uniform and conforming coating after application. As an example, for substrates having relatively complex features, the heat-resistant mixture 20 may have a relatively low viscosity so that the heat-resistant mixture 20 can be applied to the surface of the substrate and flow over the portions of the surface that have relatively complex features. On the other hand, for substrates having relatively simple features, the heat-resistant mixture 20 may have a relatively high viscosity corresponding to a lower volume fraction of the preceramic polymer, thereby reducing the amount of preceramic polymer.
[0041] In some examples, the refractory mixture 20 may be configured to be cast into a preform that is subsequently heated. The preform may have a predetermined shape that generally corresponds to the final shape of the refractory component. As such, the refractory mixture 20 may have different flow properties related to the ability of the refractory mixture 20 to flow or move into a mold, and / or different adhesion properties related to the ability of the refractory mixture 20 to form a preform after pressing. As an example, for components with relatively complex features, the refractory mixture 20 may have a relatively low viscosity so that the refractory mixture 20 can be poured into a mold and flow into the portion of the mold that has the relatively complex features. On the other hand, for components with relatively simple features, the refractory mixture 20 may have a relatively high viscosity so that the refractory mixture 20 can be consolidated into the mold using a pellet press or the like.
[0042] In some examples, the refractory mixture 20 may have a particular ratio of liquid component 22 to silicon carbide powder 14. The ratio of liquid component 22 to silicon carbide powder 14 may relate to some flow or adhesion properties of the refractory mixture 20, such as viscosity and / or dispersibility. For example, the ratio of liquid component 22 to silicon carbide powder 14 may be high enough so that the preceramic polymer and silicon carbide powder 14 can be uniformly distributed throughout the refractory mixture 20, high enough so that the refractory mixture 20 can flow onto a surface or into a mold, and / or low enough so that the refractory mixture 20 can maintain a uniform coating after application or maintain a solid consolidated preform after consolidation and before complete pyrolysis. In some examples, the refractory mixture 20 has a volume ratio of liquid component 22 to silicon carbide powder 14 that is about 1:5 or less. For example, as described above, the heat-resistant mixture 20 may have a relatively lower volume ratio of liquid component 22 to silicon carbide powder 14 to form a heat-resistant component that may use compaction than the volume ratio to form a coating that may use spraying or other lower force delivery methods.
[0043] In some examples, the composition, particle size or shape, and / or particle size distribution of the refractory mixture 20 may be selected to produce a resulting refractory material that is relatively free of thermal defects, such as cracks, caused by temperature changes during pyrolysis or crystallization. For example, during pyrolysis of the preceramic polymer, the preceramic polymer may change dimensions due to shrinkage from the release of various volatiles, thermal expansion, or other dimensional changes with temperature. This dimensional change may be different from the dimensional change of the silicon carbide powder 14 due to, for example, the different thermal expansion coefficients or relatively low chemical stability of the preceramic polymer. Thus, the refractory mixture 20 used to form the refractory material may be configured with a composition, particle size or shape, and / or particle size distribution such that the refractory material and various intermediates of the refractory material are not degraded during various processing steps, such as painting, casting, pressing, drying, and / or heating.
[0044] The heat-resistant components described herein can be used in a variety of high temperature applications. In some examples, the heat-resistant materials can be used as coatings to protect substrates in high temperature oxidative environments, such as aerospace applications. FIG. 3 is a side cross-sectional view of a portion of an example component 30 of an aerospace system formed according to the techniques of the present disclosure. The component 30 can include any component of an aerospace system configured to be compatible with an environment having a temperature greater than about 1200° C., such as a combustion system component and / or an external component configured to contact air.
[0045] The component 30 includes a substrate 32. The substrate 32 may include any material that is thermally stable at temperatures of about 1200° C. or greater. In some examples, the substrate 32 is a ceramic matrix composite (CMC). For example, the substrate 32 may include reinforcing fibers and a matrix material that at least partially surrounds the reinforcing fibers. Although the substrate 32 may be relatively resistant to relatively high temperatures, the substrate 32 may be susceptible to degradation by oxidizing species and / or thermal degradation at very high temperatures, such as above about 1500° C. CMCs that may be used for the substrate 32 include, but are not limited to, carbon / carbon, carbon / silicon carbide, silicon carbide / silicon carbide, and the like.
[0046] To protect the substrate 32 from oxidizing species, the component 30 includes one or more coatings on a surface 38 of the substrate 32. In the example of Figure 3, the component 30 includes a silicon carbide coating 36 overlying the substrate 32 and a heat resistant coating 34 overlying the silicon carbide coating 36. The surface 38 may include the surface intended to be in contact with an oxidizing environment or may be only a portion of the substrate 32.
[0047] The heat-resistant coating 34 is formed from a reinforced heat-resistant material, such as the reinforced heat-resistant material 10 of FIG. 1. As described above, the reinforced heat-resistant material 10 includes a silicon-rich polymer-derived silicon carbide matrix 16 and silicon carbide powder 14 in the silicon carbide matrix 16. The silicon carbide powder 14 may form a closely packed phase that constitutes a high volume fraction of the reinforced heat-resistant material 10. The silicon carbide matrix 16 may form a binder phase that constitutes a low volume fraction of the reinforced heat-resistant material 10. The coating 34 may be stable at temperatures up to about 3600° F. (about 2000° C.), such that the coating 34 does not decompose into its constituent elements, react with carbon, and / or react with other elements or compounds present in the environment in which the coating 34 is used (including, but not limited to, oxidation) over a period of time (e.g., minutes or hours). The coating 34 may have any suitable thickness. In some examples, the thickness of the coating 34 may be from about 1 micrometer (μm) to about 100 μm. The reinforced heat-resistant material can have various properties to support the substrate 112, such as high mechanical strength, high thermal stability, low porosity, and / or good adhesion to the substrate 32.
[0048] In some examples, the heat resistant coating 34 may not adhere strongly directly to the substrate 32. For example, the substrate 32 may include a carbon matrix with substantial surface porosity such that the substrate 32 and the coating 34 have low compatibility. To improve adhesion of the heat resistant coating 34 to the substrate 32, the component 30 includes a metal carbide layer 36 between the substrate 32 and the heat resistant coating 34. The metal carbide layer 36 may be configured to adhere to the underlying substrate 32 and form a relatively uniform surface for adhesion to the coating 34. The layer 36 may have any suitable thickness. In some examples, the thickness of the layer 36 may be from about 1 micrometer (μm) to about 100 μm and may be non-uniform within the layer 36. In some examples, the thickness of the layer 36 may be self-terminating and may be determined by the diffusion characteristics of the metal carbon system and / or the deposition characteristics of the carbon layer.
[0049] The metal carbide layer 36 includes silicon carbide. The metal carbide may have high strength, wear resistance, and temperature resistance, especially compared to the substrate 32, and may be chemically compatible with the underlying substrate 32. In some examples, the metal carbide includes at least one of silicon carbide, titanium carbide, or tungsten carbide. In some examples, the metal carbide layer 36 includes silicon carbide. Silicon carbide may have properties that are particularly suitable for high temperature oxidizing environments, including a high decomposition temperature, a relatively low crystallization temperature of one or more crystalline phases of the metal carbide layer 36, a low coefficient of thermal expansion, an ability to form a passivating oxide layer, and compatibility and adhesion with the porous refractory substrate 32. The metal carbide layer 36 extends across surface voids on the surface of the substrate 32, filling the surface, and forming a uniform, defect-free, continuous layer that substantially encapsulates the substrate 32.
[0050] In some examples, the metal carbide layer 36 is formed by reacting a metal, such as in a metal slurry, with carbon at or on the surface of the substrate 32. For example, the substrate 32 may include a carbon matrix or a carbon layer overlying a matrix that extends across the surface 38 of the substrate 32. Portions of the metal carbide layer 36 may extend across surface voids of the surface of the substrate 32 to form a substantially continuous layer and substantially seal the surface (e.g., seal all surface voids or nearly all surface voids, such as 90% or more).
[0051]
[0023] Figure 4 is a flow diagram illustrating an exemplary technique for forming a coating for a component, such as an aerospace component, according to the techniques of the present disclosure. Figure 4 will be described with respect to the reinforced heat resistant material 10 of Figure 1 and the heat resistant mixture 20 of Figure 2 applied to the component 30 of Figure 3.
[0052] In some examples, the technique of FIG. 4 includes forming a metal carbide layer on a substrate, such as a metal carbide layer 36 on the substrate 32. The articles described herein may include a metal carbide layer 36 formed in situ on the substrate 32 to form a dense intermediate coating that may encapsulate the substrate 32. The substrate 32 may define an exterior surface that includes one or more surface voids. The voids may include any irregularities or deviations from a generally flat surface that may otherwise be susceptible to migration of oxidizing species, such as one or more pores, one or more cracks, and / or one or more surface protrusions or recesses. These voids may be formed during formation of the substrate 32 and may have relatively complex surfaces that define relatively complex volumes that may be difficult to fill. For example, relatively large reactant particle sizes and / or high slurry viscosities may limit penetration of the metal reactants into the voids.
[0053] To form the metal carbide layer 36, the technique of FIG. 4 may include forming a carbon layer on the surface of the substrate 32. Forming the carbon layer may include depositing a carbon layer on the surface of the substrate 32 or abrading an outer layer of the surface of the substrate 32 such that the carbon of the carbon layer fills surface voids on the surface of the substrate 32. Depositing a carbon layer on the surface may include depositing carbon on exposed portions of the surface, including the surface within voids (e.g., at least partially filling the surface voids with carbon), such that the carbon may penetrate into and extend across the surface voids. The carbon may be deposited until a desired thickness of the carbon layer is reached. In some examples, the carbon layer is formed from a solid carbon form, such as carbon powder.
[0054] In such examples, depositing a carbon layer on the surface of the substrate 32 may include applying carbon powder, such as from a slurry or mixture, to the surface of the substrate 32. For example, a carbon powder having a particular composition and / or morphology may be selected or obtained and applied to the surface. In some examples, depositing a carbon layer on the surface of the substrate 32 includes applying a force to the surface to force and fill the carbon powder into voids. For example, the force may include a normal force to the surface and / or any lateral force to spread and / or fill the voids. The force applied to the carbon powder may force the carbon powder into the surface voids before forming the metal carbide to form the carbon layer, and may fill the surface voids such that the carbon powder is retained in the surface voids, such as up to about 50% to about 60% by volume. In some cases, a carrier medium, such as a volatile medium, may be applied to the carbon powder to help disperse the carbon powder into the voids. For example, the carbon powder may be dispersed in the carrier medium to form a slurry corresponding to a relatively high fill rate. A variety of methods can be used to force and fill the carbon powder into surface voids, including, but not limited to, one or more of rotational forces such as grinding or abrasion, linear forces such as spackling, manual forces such as manual sanding (e.g., to generate and force the carbon powder), and the like.
[0055] In some examples, the carbon layer is formed from a gaseous precursor, such as by using chemical vapor deposition (CVD). For example, depositing a carbon layer on a surface may include placing the substrate 32 in a reaction chamber, introducing a carbon precursor into an atmosphere in contact with the surface of the substrate 32, and creating operating conditions, such as temperature and / or pressure conditions, configured to decompose the carbon precursor to form a carbon layer. Various operating parameters of the CVD may include, but are not limited to, temperature, pressure, precursor / gas flow, type of precursor (e.g., methane, other hydrocarbon, or carbon source). Microstructural properties of the carbon layer that may result from controlling various operating parameters include, but are not limited to, good bonding to the surface (e.g., surface compatibility, adhesion, etc.), thickness uniformity, bridging of defects and voids, smooth surfaces, fast coating times, etc.
[0056] In some examples, the carbon layer has a substantially uniform composition and morphology across the surface. For example, the microstructure and / or crystallinity of the carbon layer may be substantially the same in various portions of the carbon layer and therefore may have substantially the same reaction thermodynamics and kinetics across the carbon layer, such that the reaction between the infiltrated metal and the carbon layer may occur at substantially the same temperature and at substantially the same rate across the carbon layer. As explained above, the reaction thermodynamics and kinetics of the carbon layer may be a product of the respective species, raw material source, processing history, and other properties and conditions of the carbon layer that affect the temperature and rate at which the carbon layer may react with the infiltrated metal. The resulting carbon layer may have a uniform composition and morphology, may be produced in close proximity to the voids, and may infiltrate the voids with or without the use of a carrier medium.
[0057] After the carbon layer is deposited, a metal slurry may be applied to the surface of the carbon layer. The metal slurry may include metal particles in an application medium. In some examples, the metal particles of the metal slurry include at least one of silicon, titanium, or tungsten. The metal particles may be coated with a thin layer of metal oxide, such as may be formed in an oxidizing atmosphere during the formation or shelf life of the metal particles. For example, a relatively pure source of metal particles may be prohibitively expensive due to inert storage, and thus the use of metal particles including a metal oxide film may broaden the available source of material for the metal particles and / or reduce the cost of the metal particles.
[0058] The metal of the metal slurry is reacted with the carbon of the carbon layer to form the metal carbide layer 36 on the substrate 32 such that the metal carbide layer 36 fills surface voids on the surface of the substrate 32. To react the metal of the metal slurry with the carbon of the carbon layer, the metal may be fluidized (e.g., melted or sublimated) so that the metal penetrates the carbon layer and reacts with the carbon of the carbon layer to form the metal carbide. This metal carbide can form a continuous metal carbide layer 36 to substantially seal the substrate 32. In some examples, the metal of the metal slurry includes silicon and the metal carbide of the metal carbide layer 36 includes silicon carbide. In some cases, this reaction may be limited by diffusion of the metal into the carbon layer. As the metal reacts with the carbon of the carbon layer to form the metal carbide, the newly formed metal carbide can form a diffusion barrier separating the reactants (e.g., carbon and metal) that can stop the thickening and further formation of thicker metal carbides (e.g., by preventing the metal from penetrating further into the carbon layer and / or by preventing the carbon from diffusing out of the carbon layer to react with the metal). For example, the metal carbide can have a low surface porosity, such as less than about 1%. The resulting layer 36 can be a relatively homogenous metal carbide having a relatively uniform thickness that may include some deviations to fill voids. In some examples, the thickness of the metal carbide layer 36 is less than about 50 micrometers, such as between about 10 micrometers and about 20 micrometers.
[0059] The reaction between the metal of the metal slurry and the carbon of the carbon layer may be carried out under a stoichiometric excess of the metal such that the resulting metal carbide layer 36 is metal-rich. Metal-rich may include a metal carbide phase that includes excess free metal. For example, a metal-rich metal carbide phase may include a stoichiometric ratio of metal to carbon of the carbon layer that is greater than 1:1, such as greater than about 1.001:1. By carrying out the reaction with a stoichiometric excess of metal, the resulting metal carbide layer 36 may include excess metal. During the formation of the metal carbide layer 36 or during operation of the refractory component (e.g., as a component), the excess metal may form a metal oxide. In some cases, the metal oxide may form a passivation layer that further protects the substrate 32. In some cases, the metal oxide may perform a self-healing function for the metal carbide layer 36. For example, the metal oxide may migrate into and seal small cracks that may form during operation, such as due to mismatch in coefficient of thermal expansion (CTE) or volume expansion.
[0060] In some examples, reacting the metal of the metal slurry with the carbon of the carbon layer includes heating the surface of the substrate 32 containing the carbon layer and the metal slurry above the melting point of the metal and maintaining a vapor pressure of the metal in stoichiometric excess at the surface of the substrate 32. Various parameters such as the temperature at the surface, the concentration of the metal at the surface (e.g., as indicated by pressure), and the reaction time can be controlled to maintain the metal in stoichiometric excess and promote migration of the metal to and reaction with the carbon layer.
[0061] The technique of FIG. 4 includes forming a silicon-rich refractory mixture (42), such as refractory mixture 20 of FIG. 2. Refractory mixture 20 includes a silicon-rich silicon carbide preceramic polymer and silicon carbide powder 14. Refractory mixture 20 may be formed by at least mixing the silicon-rich silicon carbide preceramic polymer, the silicon carbide powder 14, and any solvents and / or dispersants. In some examples, the silicon-rich silicon carbide preceramic polymer is present in an amount such that the resulting silicon carbide matrix defines less than about 10 weight percent of the reinforced refractory material 10, such as less than about 20 weight percent. In some examples, refractory mixture 20 further includes silicon powder. The silicon content of the silicon-rich silicon carbide preceramic polymer and / or the volume fraction of the silicon powder in the refractory mixture 20 may be selected such that the excess silicon forms a silicon dioxide phase 18 having a low volume fraction, such as less than about 1 volume percent.
[0062] The heat-resistant mixture 20 can include a sufficient proportion of solvent to substantially mix the heat-resistant mixture 20 into a well-dispersed mixture, which can depend on the particular silicon carbide preceramic polymer and mixing method. In some examples, the solvent is present at a concentration of greater than about 5 volume percent, such as about 5 volume percent to about 10 volume percent. In some examples, the proportion of solvent in the silicon-rich heat-resistant mixture 20 can be varied to adjust the viscosity of the silicon-rich heat-resistant mixture 20. For example, the amount of solvent that is ideal for uniformly mixing the silicon-rich heat-resistant mixture 20 may be different from the amount of solvent that is ideal for dispersing the silicon-rich heat-resistant mixture 20 into a mold or other form. Thus, an amount of solvent can be added or removed to provide a desired consistency of the heat-resistant mixture 20 prior to forming a coating.
[0063] 4 further includes forming (44) a coating from the heat resistant mixture on a substrate, such as coating 34 from the heat resistant mixture 20 on surface 38 of substrate 32. For example, heat resistant mixture 20 may be applied, such as by spraying, painting, dipping, or other deposition methods, to one or more surfaces of an aerospace system component that may encounter high temperature oxidative environments.
[0064] The method includes heating the coating (46) to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material. The coating may be heated to a heat treatment temperature in an inert atmosphere or under vacuum. The heat treatment temperature is sufficiently high, such as above the pyrolysis temperature, to pyrolyze the preceramic polymer of the coating and form the silicon carbide matrix 16. For example, a typical silicon carbide preceramic polymer, such as AHPCS, may begin to pyrolyze at about 450° C. and be completely pyrolyzed by 900° C. Heating the preform at least partially (e.g., substantially completely) pyrolyzes the silicon carbide preceramic precursor. The decomposition of the preceramic polymer into the silicon carbide matrix 16 may result in shrinkage of the preceramic polymer. For example, the preceramic polymer may decompose to amorphous silicon carbide having a density of about 2.5 g / cm, such as from a density of about 1 gram per centimeter (g / cm). The resulting silicon-rich refractory material includes silicon carbide powder 14 and excess silicon in a silicon carbide matrix 16. In some examples, the excess silicon includes silicon particles in the silicon carbide matrix 16.
[0065] In some exemplary processes, the heat treatment temperature is sufficiently high, such as above the crystallization temperature, to crystallize the silicon carbide matrix 16. Continuing with the AHPCS example above, the silicon carbide matrix 16 may be heated above 900°C, and may begin to crystallize at about 1200°C, with full crystallization occurring at about 1500°C-1600°C. The heat treatment temperature may be high enough to convert most or all of the glass phase to one or more crystalline phases. In some examples, the heat treatment temperature may be above about 950°C, for example, about 1425°C, for several hours. The resulting refractory material includes silicon carbide powder 14 and excess silicon in a silicon carbide matrix 16.
[0066] The method includes heating 48 the coating to oxidize at least a portion of the excess silicon and form a reinforced refractory material, such as the reinforced refractory material 10 of FIG. 1. The excess silicon, either present as silicon powder or formed from pyrolysis of a silicon-rich silicon carbide preceramic polymer, may be distributed throughout the silicon carbide matrix 16. Upon heating, the excess silicon may migrate to grain boundaries of the silicon carbide powder 14 and / or voids within the refractory material and react with oxygen to oxidize and form silicon dioxide phases 18. As a result, the reinforced refractory material 10 includes silicon dioxide phases 18 that are in the grain boundaries of the silicon carbide powder 14.
[0067] To form the silicon dioxide phase 18, the refractory material may be heated above 800° C. in an oxidizing atmosphere. The heat treatment temperature may be high enough to thermally convert most or all of the excess silicon to silicon dioxide. In some examples, the heat treatment temperature may be above about 800° C., for example up to about 1200° C., for several hours.
[0068] Although the heat-resistant materials described herein may be used as heat-resistant components for aerospace applications, the heat-resistant materials may also be used in other applications where high temperature oxidative environments are present, such as metal processing applications. FIG. 5 is a cross-sectional perspective view illustrating an exemplary vessel 50 including a heat-resistant component 56 formed according to the techniques of the present disclosure. FIG. 5 illustrates an example of an exemplary high temperature article (vessel 50) configured to handle molten materials. Such high temperature articles may include one or more surfaces that contact molten metal and experience high temperatures that result in oxidation, and thus include a heat-resistant component that resists oxidation.
[0069] The vessel 50 includes a casing 52, an insulating layer 54, a heat-resistant component 56, and a bottom 58 that may include a heating system (not shown). The heat-resistant component 56 is the innermost component in contact with the contents of the vessel 50, the insulating layer 54 is disposed around the heat-resistant component 56 to retain heat within the vessel 50, and the casing 52 is disposed around the insulating layer 54 to house the insulating layer 54 and provide structure to the vessel 50. The vessel 50 may be configured to process molten metals, such as steel. For example, the vessel 50 may be a crucible for melting metals or a ladle for transporting molten metals. Surfaces of the vessel 50 that come into contact with the molten metal may experience oxidation and corrosion due to impurities in the metal. For example, melting various metals used in steel may cause calcium and silicon to go into solution and form by-products, such as calcium-rich silicates.
[0070] To help resist corrosion and oxidation from these by-products, the vessel 50 includes a refractory component 56. The refractory component 56 may form at least a portion of the interior portion of the vessel 50 and may include an oxidation-resistant surface 60 configured to contact the molten metal. Although the refractory component 56 is illustrated as a monolithic component, the refractory component 56 may be formed from one or more pieces, such as bricks. As discussed above, in some examples, the refractory component 56 includes a refractory material formed from silicon carbide particles fused together by a silicon carbide matrix that includes a reinforcing and strengthening silicon dioxide phase.
[0071] FIG. 6 is a flow diagram illustrating an exemplary technique for forming a heat-resistant component according to the techniques of the present disclosure. FIG. 6 is described with respect to the reinforced heat-resistant material 10 of FIG. 1 and the heat-resistant mixture 20 of FIG. 2. The technique of FIG. 6 includes forming a silicon-rich heat-resistant mixture (70), such as the heat-resistant mixture 20 of FIG. 2, similar to step 42 of FIG. 4. However, the heat-resistant mixture 20 may include a sufficient proportion of solvent to substantially mix into a well-dispersed mixture capable of compacting the heat-resistant mixture 20 into a preform. In some examples, the solvent is present at a concentration of greater than about 5 volume percent, for example, between about 5 volume percent and about 10 volume percent. In some examples, the proportion of solvent in the silicon-rich heat-resistant mixture 20 may be varied to adjust the viscosity of the silicon-rich heat-resistant mixture 20. For example, the amount of solvent that is ideal for homogeneously mixing the silicon-rich refractory mixture 20 may be different from the amount of solvent that is ideal for dispersing the silicon-rich refractory mixture 20 into a mold or other form. Thus, an amount of solvent can be added or removed to provide a desired consistency of the refractory mixture 20 prior to forming the preform.
[0072] The technique of FIG. 6 includes forming a preform from a silicon-rich refractory mixture (72). Initially, the refractory mixture 20 may include silicon carbide powder 14 and a liquid component 22 including a preceramic polymer and optionally a solvent or dispersant as a fluid or paste. To form the preform, the silicon carbide powder 14 may be compressed and the refractory mixture 20 may be consolidated to increase the density of the refractory mixture 20. The preform may be formed to a near net shape since the dimensions of the preform and the dimensions of the final refractory component may be substantially similar. For example, the preform may be defined by a first volume and the refractory component is defined by a second volume, with the difference between the first volume and the second volume being less than about 5 volume percent.
[0073] In some examples, forming a preform from the refractory mixture 20 includes pressure casting the refractory mixture 20 into a predetermined shape of the preform. Pressure casting the refractory mixture 20 may include applying the refractory mixture 20 into a mold having a predetermined shape and compressing the refractory mixture 20 in the mold using a pressure system to at least partially cure the refractory mixture 20 into the preform.
[0074] The technique of FIG. 6 includes heating the preform (74) to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material, and heating the preform (76) to oxidize at least a portion of the excess silicon and form a reinforced refractory material, such as the reinforced refractory material 10 of FIG. 1 as described in steps 46 and 48 of FIG. 4.
[0075] Example 1: A method includes forming a coating on a substrate, the coating being formed from a silicon-rich refractory mixture including a silicon-rich silicon carbide preceramic polymer and silicon carbide powder; heating the coating to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material, the silicon-rich refractory material including silicon carbide powder and excess silicon in a silicon carbide matrix; and heating the silicon-rich refractory material to oxidize at least a portion of the excess silicon and form a reinforced refractory material, the reinforced refractory material including a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0076] Example 2: The method of example 1, wherein the silicon carbide matrix defines less than about 10 volume percent of the reinforced refractory material.
[0077] Example 3: The method of any of Examples 1 and 2, wherein the porosity of the reinforced refractory material has a porosity that is less than or equal to about 5 volume percent (vol%).
[0078] Example 4: The method of any one of Examples 1 to 3, wherein the silicon-rich refractory mixture further comprises silicon powder.
[0079] Example 5: The method of any one of Examples 1-4, further comprising forming a heat resistant mixture by at least mixing a silicon-rich silicon carbide preceramic polymer and a silicon carbide powder.
[0080] Example 6: The method of any one of Examples 1-5, wherein the substrate comprises a component of an aerospace system.
[0081] Example 7: The method of any one of Examples 1-6, wherein heating the coating further comprises heating the silicon carbide preceramic polymer above a pyrolysis temperature to pyrolyze the silicon carbide preceramic polymer into a silicon carbide matrix.
[0082] Example 8: The method of example 7, wherein heating the coating further comprises heating the silicon carbide matrix above a crystallization temperature to crystallize the silicon carbide matrix.
[0083] Example 9: The method of any one of Examples 1-8, further comprising forming a metal carbide layer on the substrate prior to forming the coating on the substrate, wherein the coating is formed on a surface of the metal carbide layer.
[0084] Example 10: The method of Example 9, wherein forming the metal carbide layer further comprises depositing a carbon layer on a surface of the substrate, the melting point of the substrate being equal to or greater than about 1500 degrees Celsius (°C); applying a metal slurry to the surface of the carbon layer after depositing the carbon layer; and reacting the metal of the metal slurry with the carbon of the carbon layer to form a metal carbide layer on the substrate.
[0085] Example 11: The method of example 10, wherein the substrate has a porosity greater than about 10 volume percent (vol%) and the metal carbide layer has a porosity less than about 5 vol%.
[0086] Example 12: The method of any of examples 10 and 11, wherein the metal of the metal slurry comprises silicon and the metal carbide layer comprises silicon carbide.
[0087] Example 13: An article includes a substrate and a coating overlying the substrate, the coating comprising a reinforced heat resistant material including a polymer-derived silicon carbide matrix, silicon carbide powder in the silicon carbide matrix, and a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0088] Example 14: The article of example 13, wherein the silicon carbide matrix comprises less than about 10 volume percent of the reinforced refractory material.
[0089] Example 15: The article of any one of Examples 13 and 14, wherein the silicon dioxide phase comprises less than about 1 volume percent of the reinforced heat-resistant material.
[0090] Example 16: The article of any one of Examples 13-15, wherein the porosity of the reinforced heat resistant material is less than or equal to about 5 volume percent (vol%).
[0091] Example 17: The article of any one of Examples 13-16, wherein the reinforced heat resistant material further comprises silicon powder.
[0092] Example 18: The article of any one of Examples 13-17, wherein the substrate comprises a component of an aerospace system.
[0093] Example 19: The article of any one of Examples 13-18, further comprising a metal carbide layer on the surface of the substrate, the coating covering the metal carbide layer, and the melting point of the substrate being greater than or equal to about 1500 degrees Celsius (°C).
[0094] Example 20: The article of example 19, wherein the metal carbide layer comprises silicon carbide.
[0095] Example 21: A method includes forming a preform of a refractory component from a silicon-rich refractory mixture, the silicon-rich refractory mixture including a silicon-rich silicon carbide preceramic polymer and silicon carbide powder; heating the preform to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material, the silicon-rich refractory material including silicon carbide powder and excess silicon in a silicon carbide matrix; and heating the silicon-rich refractory material to oxidize at least a portion of the excess silicon and form a reinforced refractory material, the reinforced refractory material including a silicon dioxide phase at grain boundaries of the silicon carbide powder.
[0096] Example 22: The method of example 21, wherein the silicon carbide matrix defines less than about 10 volume percent of the reinforced refractory material.
[0097] Example 23: The method of any of Examples 21 and 22, wherein the porosity of the reinforced refractory material has a porosity that is less than or equal to about 5 volume percent (vol%).
[0098] Example 24: The method of any one of Examples 21-23, wherein the silicon-rich refractory mixture further comprises silicon powder.
[0099] Example 25: The method of any one of Examples 21-24, further comprising forming a heat resistant mixture by at least mixing a silicon-rich silicon carbide preceramic polymer and a silicon carbide powder.
[0100] Example 26: The method of any one of Examples 21-25, wherein the preform is defined by a first volume and the heat-resistant component is defined by a second volume, and the difference between the first volume and the second volume is less than about 5 volume percent.
[0101] Example 27: The method of any one of Examples 21-26, wherein forming a preform from the heat-resistant mixture includes applying the heat-resistant mixture into a mold having a predetermined shape and compressing the heat-resistant mixture in the mold.
[0102] Example 28: The method of example 27, wherein heating the preform further comprises heating the preform in the mold after compressing the heat-resistant mixture.
[0103] Example 29: The method of any one of Examples 21-28, wherein heating the preform further comprises heating the silicon carbide preceramic polymer above a pyrolysis temperature to pyrolyze the silicon carbide preceramic polymer into a silicon carbide matrix.
[0104] Example 30: The method of example 29, wherein heating the preform further comprises heating the silicon carbide matrix above a crystallization temperature to crystallize the silicon carbide matrix.
[0105] Example 31: The method of any one of Examples 21-30, wherein the heat-resistant component defines an oxidation-resistant surface configured to contact the molten metal.
[0106] Example 32: The method of any one of Examples 21-31, wherein the refractory component comprises at least one of an inner portion of a vessel for contacting the molten metal, a ladle, a slide gate, or a liner.
[0107] Example 33: A heat-resistant component includes a reinforced heat-resistant material including a polymer-derived silicon carbide matrix, silicon carbide powder in the silicon carbide matrix, and a silicon dioxide phase at the grain boundaries of the silicon carbide powder.
[0108] Example 34: The heat-resistant component of Example 33, wherein the silicon carbide matrix comprises less than about 10 volume percent of the reinforced heat-resistant material.
[0109] Example 35: The heat-resistant component of any one of Examples 33 and 34, wherein the silicon dioxide phase constitutes less than about 1 volume percent of the reinforced heat-resistant material.
[0110] Example 36: The heat-resistant component of any one of Examples 33-35, wherein the porosity of the reinforced heat-resistant material is less than or equal to about 5 volume percent (vol%).
[0111] Example 37: The heat-resistant component according to any one of Examples 33 to 36, wherein the reinforced heat-resistant material further comprises silicon powder.
[0112] Example 38: The heat-resistant component of any one of Examples 33-37, wherein the heat-resistant component defines an oxidation-resistant surface configured to contact a molten metal.
[0113] Example 39: The heat-resistant component of example 38, wherein the heat-resistant component comprises an interior portion of the vessel, and the oxidation-resistant surface of the heat-resistant component is configured to contact the molten metal.
[0114] Example 40: The heat-resistant component of any one of Examples 33 to 39, wherein the heat-resistant component comprises at least one of an inner portion of a vessel for contacting molten metal, a ladle, a slide gate, or a liner.
[0115] Various implementations have been described. These and other implementations are within the scope of the following claims.
Claims
1. Forming a coating on a substrate, the coating being formed from a silicon-rich heat-resistant mixture, the silicon-rich heat-resistant mixture comprising: a silicon-rich silicon carbide preceramic polymer; and forming a silicon carbide powder; heating the coating to pyrolyze the silicon-rich silicon carbide preceramic polymer and form a silicon-rich refractory material, the silicon-rich refractory material comprising the silicon carbide powder and excess silicon in a silicon carbide matrix; and heating the silicon-rich refractory material to oxidize at least a portion of the excess silicon and form a reinforced refractory material, wherein the reinforced refractory material comprises a silicon dioxide phase located at grain boundaries of the silicon carbide powder.
2. Heating the coating comprises heating the silicon carbide preceramic polymer above a pyrolysis temperature to pyrolyze the silicon carbide preceramic polymer into the silicon carbide matrix; The method of claim 1 , further comprising heating the silicon carbide matrix above a crystallization temperature to crystallize the silicon carbide matrix.
3. An article, A substrate; a coating overlying the substrate, the coating comprising an enhanced heat resistant material, the enhanced heat resistant material comprising: Polymer-derived silicon carbide matrix, silicon carbide powder in the silicon carbide matrix; and a silicon dioxide phase located at the grain boundaries of said silicon carbide powder.