Method for preparing a graphite substrate coating for silicon carbide crystal growth and use thereof

Abstract

The present application relates to the field of silicon carbide crystal growth, and particularly relates to a preparation method and application of a graphite substrate coating for silicon carbide crystal growth, the method comprising the following steps: coating a colloid containing carbon fibers and a binder on the surface of a graphite substrate, forming a porous carbon skeleton precursor anchored to the graphite substrate through solidification and low-temperature sintering, laying a coating raw material containing a zirconium-containing compound and a carbon source on the porous carbon skeleton precursor, and generating a composite coating mainly composed of zirconium carbide on the surface of the graphite substrate after high-temperature sintering. The method provided in the present application realizes firm combination of the coating and the substrate at the micro level by constructing a porous carbon skeleton precursor anchored to the graphite substrate and guiding subsequent in-situ reaction, thereby successfully solving the industry problem that the coating adhesion, thickness and thermal stability are difficult to be considered simultaneously.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal growth, and more particularly to a method for preparing and applying a graphite substrate coating for silicon carbide crystal growth. Background Technology

[0002] Silicon carbide single crystals, as a key foundation of third-generation semiconductor materials, exhibit irreplaceable advantages in high-power, high-frequency, and high-temperature electronic devices due to their superior physical properties. The physical vapor transport (PVT) method is currently the mainstream technology for preparing large-size, high-quality silicon carbide single crystals. In this method, the thermal field system composed of graphite material is the core component, providing the necessary high-temperature environment and physicochemical conditions for crystal growth. However, graphite components face severe challenges during the high-temperature growth process, which lasts for tens or even hundreds of hours, continuously exposed to extremely harsh environments.

[0003] At growth temperatures exceeding 2000 degrees Celsius in the PVT process, silicon carbide raw materials within the crucible sublimate, generating a complex atmosphere containing various gaseous components such as silicon, carbon, Si2C, and SiC2. These highly reactive gaseous substances cause intense chemical erosion and physical scouring of the inner wall of the graphite crucible and internal graphite components such as the flow guide tube and insulation cylinder. This erosion not only significantly shortens the lifespan of expensive graphite thermal field components and drastically increases the material cost of single crystal production, but more seriously, it brings about a core problem affecting crystal quality. Some of the gaseous substances undergo undesirable heterogeneous crystallization on the graphite surface, forming parasitic crystals, especially at the crystal growth interface—such as the contact area between the flow guide tube and the ingot edge—which easily leads to adhesion between the graphite components and the silicon carbide ingot. During the cooling process after growth, this adhesion causes stress concentration and even cracking at the ingot edge, resulting in crystal defects such as dislocations, and in severe cases, rendering the entire ingot unusable. In addition, the erosion process may produce tiny graphite particles that are carried by the rising airflow to the crystal growth interface and become trapped in the growing crystal, forming fatal inclusion defects that greatly reduce the usable yield of the crystal.

[0004] To isolate corrosive atmospheres, protect the graphite matrix, and improve crystal quality, applying high-temperature resistant protective coatings to graphite hot-field components has become an industry-consensus technical approach. An ideal coating needs to possess excellent high-temperature corrosion resistance, strong adhesion to the graphite matrix, sufficient thickness to provide long-term protection, and its coefficient of thermal expansion needs to be well matched with the graphite substrate to prevent cracking or peeling due to thermal stress during repeated thermal cycling.

[0005] Currently, chemical vapor deposition (CVD) and magnetron sputtering are used to prepare such coatings. While carbide or nitride coatings obtained through CVD and similar methods exhibit dense structures and high purity, their preparation equipment is complex, energy-intensive, and has a slow deposition rate, resulting in extremely high production costs and making it difficult to meet the stringent cost control requirements of large-scale industrial production. In contrast, physical vapor deposition (such as high-temperature evaporation) methods have certain cost advantages and relatively relaxed process conditions, making them more suitable for industrial applications. However, coatings prepared by conventional physical vapor deposition techniques have significant limitations: their coating thickness is typically thin, offering limited protection under long-term high-temperature corrosion environments; more importantly, the bond between the deposited coating and the graphite substrate is primarily physical, resulting in weak adhesion. When the hot-field component experiences drastic temperature changes, the coating is prone to blistering, cracking, or even detachment from the substrate due to interfacial stress. The detached coating fragments mixed into the growth environment can cause damage to crystal quality that may even exceed the problems caused by direct exposure of the graphite component.

[0006] Therefore, a new approach to thermal field coating preparation has long been urgently needed in this field. This approach should overcome the bottlenecks in existing technologies regarding adhesion and coating thickness, enabling the formation of a high-quality protective layer with a strong and robust interface and considerable thickness on the surface of complex graphite components. Simultaneously, this technical solution should also possess good process feasibility and economic efficiency to meet the large-scale demands of the rapidly developing silicon carbide semiconductor industry. Most existing technical solutions are limited to surface deposition, failing to fundamentally solve the essential problem of weak interfacial bonding between the coating and the substrate. How to construct a robust, durable, and substrate-compatible protective system on a graphite substrate through material design and process innovation remains a challenging technical problem for the industry. Summary of the Invention

[0007] This application aims to overcome the shortcomings of existing technologies, such as insufficient adhesion between the thermal field protection coating and the graphite substrate, easy coating peeling, and limited effective coating thickness, which result in poor protection of graphite components and affect the quality of silicon carbide single crystals. Therefore, it provides a method for preparing a graphite substrate coating for silicon carbide crystal growth and its application to overcome the above-mentioned deficiencies.

[0008] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a graphite substrate coating for silicon carbide crystal growth, comprising the following steps: S1: A colloid containing carbon fibers and binders is coated onto the surface of a graphite substrate, cured and sintered at low temperature to form a porous carbon skeleton precursor anchored to the graphite substrate. S2: The coating material containing zirconium compound and carbon source is laid on the porous carbon skeleton precursor; S3: High-temperature sintering is carried out under a protective atmosphere to allow the coating raw material to react in situ with the porous carbon skeleton precursor, thereby generating a composite coating with zirconium carbide as the main phase on the surface of the graphite substrate.

[0009] As described in the background section, existing technologies generally treat the protection of thermally exposed graphite components as a surface covering problem. The technical approaches are mostly limited to how to attach a high-performance coating material (such as carbides or nitrides) to the graphite surface through external means (such as vapor deposition or sputtering). While this approach is direct, it also introduces fundamental limitations: neither the expensive CVD technology nor the more economical but less effective physical vapor deposition can form a thick, robust protective layer on the complex surface of graphite components that can withstand extreme thermal shock. The bond between the coating and the substrate is essentially physical or simple chemical, making the interface the weakest link. During repeated high-temperature cycling, due to differences in thermal expansion coefficients, stress concentration leads to a high risk of coating cracking and peeling. This not only significantly reduces the protective effect, but the detached coating fragments themselves become new sources of contamination, further harming crystal quality. Therefore, those skilled in the art have long been struggling with difficult trade-offs between coating adhesion, thickness, cost, and thermal compatibility.

[0010] Against this backdrop, the present invention no longer regards the coating as a foreign object that is independent of the graphite substrate and needs to be "attached". Instead, through ingenious material and process design, it guides the coating to "grow" from the surface of the graphite substrate itself, thereby achieving organic integration and chemical bonding between the coating and the substrate in terms of microstructure.

[0011] Specifically, this application clearly demonstrates this disruptive technological path through a three-step method. Step S1 is not simply a coating process; its fundamental purpose is to construct a crucial intermediate structure: a porous carbon framework precursor firmly anchored to a graphite substrate. In this design, carbon fibers provide the three-dimensional network framework, while the binder (such as phenolic resin), after low-temperature sintering and carbonization, not only fixes the carbon fibers to the substrate but also transforms itself into porous carbon, becoming an indispensable carbon source for subsequent reactions. This porous structure itself achieves a strong bond with the graphite substrate through carbon-carbon bonding. More importantly, it provides a large specific surface area and three-dimensional reaction space for subsequent in-situ reactions, laying the foundation for the formation of a thick coating.

[0012] In steps S2 and S3, zirconium-containing compounds and carbon sources are laid to prepare raw materials for the subsequent "in-situ synthesis" reaction. In the high-temperature sintering environment of step S3, the reaction does not occur in the gas phase and then deposit onto the surface, but rather is initiated directly inside and on the surface of the precursor framework. The zirconium-containing compounds (such as zirconium silicate and zirconium oxide) undergo a carbothermic reduction reaction with the carbon framework surrounding the carbon fibers, and the resulting zirconium carbide (ZrC) nuclei form and grow directly on the carbon fiber surface and in the pores. This "inside-out" growth mode results in a strong mechanical interlock and chemical bond between the final zirconium carbide crystals and the carbon fiber framework, with a bonding strength far exceeding that of traditional surface-deposited coatings.

[0013] Crucially, byproducts such as silica that may be generated during the reaction form in a molten state, further promoting the densification process. These byproducts can also react with carbon to form silicon carbide (SiC), naturally creating a transition layer with a gradient in composition and properties between the graphite substrate and the main zirconium carbide coating. This transition layer cleverly alleviates the internal stress problem caused by the mismatch in thermal expansion coefficients between ZrC and graphite, greatly improving the stability of the coating during thermal cycling.

[0014] Therefore, compared with existing technologies, the overall technical effect of this solution is synergistic and significant. First, the adhesion between the coating and the substrate achieves a qualitative leap, as it transforms from physical adhesion to a strong interfacial bond resulting from the combined action of chemical bonding and three-dimensional mechanical interlocking. Second, the coating thickness is no longer limited by the physical constraints of the deposition rate, but is determined by the thickness and reactivity of the precursor framework, thus easily obtaining thicker coatings than those prepared by traditional methods, providing longer-lasting protection. Finally, the entire process avoids the use of extremely expensive or complex equipment (such as CVD systems), and the cost of the main raw materials is relatively controllable, demonstrating excellent prospects for industrial application.

[0015] Therefore, in summary, this invention, by shifting the mindset from "application" to "growth" and employing a unique technical approach of constructing a porous carbon framework precursor and guiding in-situ reactions, successfully solves the problems of weak coating adhesion and insufficient thickness in an integrated manner.

[0016] Preferably, the adhesive is a phenolic resin.

[0017] Preferably, the colloid further includes a solvent; The mass ratio of the carbon fiber, the solvent, and the phenolic resin is (0.8~1.5):1:3.

[0018] Preferably, in step S1, the curing includes: drying at 60-80°C for 1-2 hours and repeatedly coating multiple times to make the total thickness of the colloid greater than 1 mm; then treating under a negative pressure environment of 120-140°C and 1200-1500 Pa for 6-8 hours to remove air.

[0019] Preferably, in step S1, the low-temperature sintering is carried out for 2-3 hours at 450-550℃ and 500-800Pa in an argon atmosphere.

[0020] Preferably, in step S2, the zirconium-containing compound is a mixture of zirconium silicate and zirconium oxide, and the carbon source is carbon powder.

[0021] This application cleverly utilizes the synergistic effect of two zirconium-containing compounds to control the reaction kinetics and physicochemical environment at high temperatures, thereby generating a denser and structurally optimized composite coating in situ. While carbothermic reduction of zirconium oxide alone is a direct approach, the reaction requires high temperatures, and the resulting coating may be brittle due to stress concentration.

[0022] The introduction of zirconium silicate brings several non-obvious benefits: at high temperatures, zirconium silicate decomposes or participates in reactions, and the precipitated silica component can form a transient molten phase. This not only significantly enhances the mass transfer efficiency between reactants and promotes the uniform generation and growth of zirconium carbide nuclei, but also effectively fills the micropores inside the coating, acting as a natural sintering aid. Simultaneously, the introduction of zirconium silicate is equivalent to embedding additional silicon and oxygen sources into the reaction system. Its reaction with the carbon source may generate silicon carbide in situ. This silicon carbide can intertwine and coexist with the main zirconium carbide phase, forming a compositional gradient transition layer between the coating and the graphite substrate. This greatly alleviates the interfacial stress caused by the mismatch in thermal expansion coefficients, fundamentally improving the coating's thermal shock resistance and bonding reliability.

[0023] Preferably, the mass ratio of zirconium silicate, zirconium oxide and carbon powder is 1:3:1.

[0024] The core function of this formulation in this application lies in its ability to effectively coordinate the dynamic relationship between "zirconium source supply," "fluxing flow," and "reduction capacity" in the reaction system. Specifically, zirconium oxide, as the primary zirconium source, has the highest proportion, ensuring the content of the zirconium carbide main phase in the final coating. The key role of introducing zirconium silicate is its decomposition at high temperatures to generate silica, forming a molten phase that promotes mass transfer and densification. The 1:3 ratio means that the amount of zirconium silicate is precisely controlled at a critical point that effectively fulfills its role as a flux and provides a silicon source to generate the silicon carbide transition layer, while avoiding excessive silica leading to an excessive glassy phase in the coating and affecting high-temperature performance.

[0025] Meanwhile, the amount of toner (1 part) can simultaneously meet the needs of reducing zirconium oxide and zirconium silicate, and may be partially consumed in the generation of silicon carbide, ultimately ensuring complete reaction and no excessive free carbon residue, thereby obtaining a pure and dense composite coating structure.

[0026] Preferably, in step S3, the high-temperature sintering temperature is not lower than 1850°C and the holding time is not less than 8 hours; The protective atmosphere is hydrogen, with a hydrogen flow rate of 20-50 L / min and the furnace pressure maintained at 800-1000 Pa.

[0027] Secondly, the present invention also provides a thermal field component prepared by the above method. It includes a graphite substrate and a composite coating with zirconium carbide as the main phase formed on its surface through an in-situ reaction, wherein a silicon carbide transition layer is formed between the composite coating and the graphite substrate.

[0028] Thirdly, the present invention also provides a silicon carbide single crystal growth apparatus, which includes the aforementioned thermal field component.

[0029] Therefore, this application has the following beneficial effects: (1) The method provided in this application achieves a strong bond between the coating and the substrate at the micro level by constructing a porous carbon skeleton precursor anchored to a graphite substrate and guiding subsequent in-situ reactions. Its beneficial effect is that it not only forms a three-dimensional mechanical interlocking structure with the in-situ generated zirconium carbide crystal through the carbon fiber network, but also effectively alleviates the thermal mismatch stress by means of the silicon carbide transition layer generated during the reaction, thereby significantly improving the bonding strength and thermal shock resistance of the coating. (2) This method breaks away from the limitations of traditional deposition technology on coating thickness, and can obtain a thicker and denser protective layer, which greatly extends the service life of thermal components. (3) The entire process is based on relatively low-cost materials and conventional heat treatment equipment, avoiding complex and expensive vapor deposition equipment. While achieving excellent protection effect, it significantly reduces production costs and ultimately provides a reliable guarantee for the preparation of high-quality silicon carbide single crystals. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] Example 1 This embodiment provides an in-situ coating preparation method for thermal field components (such as graphite crucibles) used in silicon carbide crystal growth, including the following steps: (1) Pretreatment of graphite substrate: Place it in an ultrasonic cleaner and clean it with deionized water for 30 minutes, then dry it in an oven at 120°C for 2 hours to ensure that the surface is clean and dry.

[0032] (2) Preparation of carbon fiber colloid: Weigh 80 g of carbon fiber powder with a particle size of 100 mesh, 100 g of analytical grade anhydrous ethanol, and 300 g of thermosetting phenolic resin. Place the above raw materials in a mixing container and mechanically stir for 60 minutes to obtain a uniform viscous colloid.

[0033] (3) Coating and curing: Apply the colloid evenly to the pretreated graphite substrate surface using a brush and let it stand at room temperature for 30 minutes. Then, place the coated part in a forced-air drying oven and dry it at 60°C for 2 hours to allow the colloid to initially cure. Repeat the above coating and 60°C drying steps a total of 4 times to achieve a total colloid thickness of approximately 1.2 mm. Subsequently, transfer the workpiece to a vacuum oven and treat it under a negative pressure environment of 120°C and 1500 Pa for 8 hours to fully remove the gas inside the colloid and promote the fusion between the layers.

[0034] (4) Low-temperature sintering: The cured workpiece is placed in a tubular sintering furnace filled with argon gas. The pressure inside the furnace is controlled at 500 Pa, and the temperature is increased to 550°C at a rate of 5°C / min and held for 2 hours. During this process, the phenolic resin carbonizes to form a porous carbon skeleton, which firmly anchors the carbon fibers onto the graphite substrate to obtain the carbon skeleton precursor.

[0035] (5) Preparation and application of coating materials: Weigh 50 g of zirconium silicate (ZrSiO4), 150 g of zirconium oxide (ZrO2), and 50 g of carbon powder in a mass ratio of 1:3:1. Mix and grind the three materials in a ball mill jar for 4 hours to obtain a uniform coating material. Apply the material evenly to the surface of the carbon skeleton precursor at a precise application rate of 1.15 g / cm².

[0036] (6) High-temperature sintering: The workpiece with the raw materials laid on it is placed in a high-temperature sintering furnace. Hydrogen gas is introduced into the furnace at a flow rate of 20 liters / minute and the furnace pressure is maintained at 1000 Pa. The temperature is increased to 1850°C at a rate of 10°C / minute and held at this temperature for 8 hours. After cooling in the furnace, a uniform and firmly bonded gray-black composite coating with zirconium carbide as the main phase is obtained on the surface of the graphite substrate.

[0037] Example 2 The main difference between this embodiment and Example 1 lies in the colloid ratio and some process parameters.

[0038] The ratio of carbon fiber colloid was adjusted to: 150 g of carbon fiber powder with a particle size of 30 mesh, 100 g of anhydrous ethanol, and 300 g of phenolic resin (mass ratio 1.5:1:3).

[0039] Coating and curing process: After coating, allow to stand at room temperature for 40 minutes. Dry at 80℃ for 1 hour, repeat 3 times, with a total thickness of approximately 1.0 mm. Exhaust treatment conditions: 140℃, 1200 Pa, for 6 hours.

[0040] Low-temperature sintering: Under an argon atmosphere and a pressure of 800 Pa, the temperature is raised to 450°C and held for 3 hours.

[0041] The amount of coating material applied and the high-temperature sintering process are exactly the same as in Example 1.

[0042] Example 3 The main difference between this embodiment and Example 1 lies in the colloid ratio and high-temperature sintering parameters.

[0043] The proportions of the carbon fiber colloid were adjusted as follows: 120 grams of carbon fiber powder with a particle size of 150 mesh, 100 grams of anhydrous ethanol, and 300 grams of phenolic resin (mass ratio 1.2:1:3).

[0044] The high-temperature sintering process was adjusted to: hydrogen flow rate of 50 liters / minute, furnace pressure of 800 Pa, sintering temperature of 1920℃, and holding time of 10 hours.

[0045] The remaining steps and parameters are the same as in Example 1.

[0046] Example 4 This example focuses on demonstrating the impact of different coating material application amounts.

[0047] The specific implementation steps are basically the same as in Example 1, the only difference being that the amount of coating material applied is adjusted to 1.05 g / cm². After high-temperature sintering, the thickness of the resulting coating is slightly thinner than that in Example 1, but it still exhibits good density and adhesion.

[0048] Example 5 This example focuses on demonstrating a gentler curing and venting process.

[0049] The specific implementation steps are basically the same as in Example 1, except for the curing and venting parameters: after coating, it is dried at 70°C for 1.5 hours, repeated 3 times. The venting treatment is carried out at 130°C and 1350 Pa for 7 hours.

[0050] The remaining steps and parameters are the same as in Example 1.

[0051] Example 6 This embodiment focuses on demonstrating higher high-temperature sintering strength.

[0052] The specific implementation steps are basically the same as in Example 1, except for the high-temperature sintering parameters: hydrogen flow rate 35 liters / minute, furnace pressure 900 Pa, sintering temperature 1950℃, and holding time 12 hours. Under these conditions, the coating is thicker and the grains are more fully developed.

[0053] Comparative Example 1 This comparative example aims to explore the effect of omitting the carbon fiber skeleton structure and relying solely on the phenolic resin carbonization layer as the reaction substrate.

[0054] Specific steps: Without adding carbon fiber powder, 100 grams of anhydrous ethanol and 300 grams of phenolic resin were mixed to form a colloid, which was then coated onto a graphite substrate. The curing, degassing, and low-temperature sintering (550°C, 2 hours) processes were the same as in Example 1, forming a pure resin carbonized layer. Subsequently, the same mass (1.15 g / cm³) as in Example 1 was laid. 2 The coating raw materials and their proportions (zirconia:zirconia: carbon powder = 1:3:1) were processed under the same high-temperature sintering conditions (1850℃, hydrogen atmosphere).

[0055] Comparative Example 2 This comparative example uses a representative chemical vapor deposition (CVD) method from the existing technology for comparison.

[0056] Specific steps: Place a graphite substrate of the same specification in a CVD reaction chamber, use ZrCl4 and CH4 as precursor gas sources, and deposit a zirconium carbide coating at 1400℃ under reduced pressure for about 20 hours.

[0057] Comparative Example 3 This comparative example uses another common physical vapor deposition technique, magnetron sputtering, for comparison.

[0058] Specific steps: In a sputtering device, high-purity zirconium carbide is used as the target material, and a graphite substrate is sputtered and deposited in an argon atmosphere at 500°C for about 4 hours.

[0059] Comparative Example 4 This comparative example aims to investigate the effect of deviations in the coating raw material ratio from the preferred range of the present invention.

[0060] Specific steps: Completely repeat the process of Example 1, only change the ratio of coating raw materials, and adjust the mass ratio of zirconium silicate, zirconium oxide and carbon powder to 3:1:1 (that is, significantly increase the zirconium silicate content and reduce the zirconium oxide content).

[0061] [Performance Testing] The coated graphite substrates prepared in Examples 1-6 and Comparative Examples 1-4 were tested, and the test methods and results are shown below: 1. Coating-substrate adhesion strength test (scratch test) Testing Procedure: A scratch tester was used with a diamond indenter (tip radius 200 μm) to scratch the coating surface at a loading rate of 100 N / min, while simultaneously applying horizontal displacement. The critical loads (Lc1 and Lc2) at which the coating begins to crack (initial crack) and completely peels off (critical failure) were determined by the abrupt changes in acoustic emission signals and frictional force. Lc2 was recorded as the primary indicator for evaluating bond strength. At least three points were tested for each sample, and the average value was taken.

[0062] 2. Thermal shock stability test (rapid cooling and heating cycle) Test Procedure: The sample was rapidly heated to 1850℃ in a vertical high-temperature furnace and held at that temperature for 5 minutes, followed by rapid cooling. This process is recorded as one thermal cycle. After every 5 cycles, the sample was removed and the coating surface and edges were observed using an optical microscope for cracks, peeling, or flaking. The number of thermal cycles required for the coating to first exhibit significant macroscopic failure (e.g., peeling of an area >5%) was recorded. If no failure was observed after 50 cycles, the test was stopped and recorded as ">50".

[0063] 3. Characterization of coating thickness and microstructure Testing Procedure: The sample was cut and polished to prepare a metallographic specimen. The cross-sectional morphology of the coating was observed using a scanning electron microscope. The total coating thickness (unit: μm) was measured, and the interfacial bonding between the coating and the substrate, the density of the coating, and the presence of pores or cracks were observed.

[0064] 4. Resistance to vapor phase corrosion test Test procedure: The sample was placed in a graphite crucible simulating the PVT atmosphere, surrounded by silicon carbide powder. Under argon protection, the crucible was heated to 2100℃ and held for 10 hours. After cooling, the sample was removed, its mass change rate per unit area was measured, and the coating surface was observed by SEM to see if it was eroded by SiC vapor phase or if corrosion pits appeared.

[0065] Table 1 Test Results

[0066] Based on a comprehensive analysis of the above test results, the following clear conclusions can be drawn: The overall performance of the embodiments of the present invention is significantly better than that of the prior art comparative examples: all embodiments (1-6) exhibit comprehensive and excellent performance in terms of bonding strength (Lc2 > 38 N), thermal shock resistance (>45 cycles) and coating thickness (>300 μm), which can meet the requirements of long life and high reliability of silicon carbide crystal growth thermal field components.

[0067] Comparative Example 1 (with carbon fiber omitted) most clearly demonstrates the necessity of carbon fiber. This sample exhibits extremely low bond strength, poor thermal shock resistance, and a thin, easily cracked coating. This indicates that the three-dimensional network structure formed by carbon fiber plays a decisive role in enhancing coating toughness, providing mechanical interlocking, and offering support for the formation of a thick coating.

[0068] While Comparative Examples 2 (CVD) and 3 (sputtering) exhibit dense coatings, their bonding with the substrate is physical deposition, resulting in weak adhesion (especially the sputtered coating), and the coating thickness is limited. Under harsh thermal shock and corrosive environments, the interface becomes a weak point, leading to premature coating failure. In contrast, the coating generated by the in-situ reaction of this invention forms a strong interface with chemical bonding and mechanical interlocking with the substrate.

[0069] The results of Comparative Example 4 show that, even with a similar process, deviations from the preferred raw material ratio of this invention will lead to excessive internal stress in the coating and spontaneous cracking due to the mismatch between the phase composition and thermophysical properties of the reaction products, making it impossible to form an effective protective layer. This demonstrates the non-obviousness and technical contribution of a specific ratio (e.g., 1:3:1).

[0070] Furthermore, Examples 1-3 and 5-6 all achieved excellent performance by adjusting parameters such as the colloid ratio and sintering temperature, indicating that the process window of the present invention is wide and easy to implement and control. Example 4, due to a slight reduction in the amount of coating material laid, resulted in a slight decrease in thickness and corrosion resistance, but it still maintained a good level, indirectly confirming the correlation between key parameters and performance.

[0071] In summary, the test results fully verify the technical solution provided by this invention, which successfully and synergistically solves the industry problem of balancing coating adhesion, thickness, and thermal stability by constructing a carbon fiber precursor and guiding an in-situ reaction. The comparative examples, on the other hand, demonstrate that the absence of any of the core features of this invention significantly reduces its effectiveness or even renders it completely ineffective.

[0072] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations included in the claims. Those skilled in the art will readily conceive of other embodiments of this application after considering the specification and embodiments. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the invention that may not be explicitly described. Therefore, the above embodiments merely illustrate several implementations of the invention and do not limit the scope of protection of this patent. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary technical means in the art not disclosed in this application. The scope of this application is limited only by the appended claims.

Claims

1. A method for preparing a graphite substrate coating for silicon carbide crystal growth, characterized in that, Includes the following steps: S1: A colloid containing carbon fibers and binders is coated onto the surface of a graphite substrate, cured and sintered at low temperature to form a porous carbon skeleton precursor anchored to the graphite substrate. S2: The coating material containing zirconium compound and carbon source is laid on the porous carbon skeleton precursor; S3: High-temperature sintering is carried out under a protective atmosphere to allow the coating raw material to react in situ with the porous carbon skeleton precursor, thereby generating a composite coating with zirconium carbide as the main phase on the surface of the graphite substrate.

2. The method according to claim 1, characterized in that, The adhesive is phenolic resin.

3. The method according to claim 2, characterized in that, The colloid also includes a solvent; The mass ratio of the carbon fiber, the solvent, and the phenolic resin is (0.8~1.5):1:

3.

4. The method according to claim 1, characterized in that, In step S1, the curing includes: drying at 60-80°C for 1-2 hours and repeatedly coating multiple times to make the total thickness of the colloid greater than 1 mm; then treating under a negative pressure environment of 120-140°C and 1200-1500 Pa for 6-8 hours to remove air.

5. The method according to claim 1 or 4, characterized in that, In step S1, the low-temperature sintering is carried out for 2-3 hours at 450-550℃ and 500-800Pa argon atmosphere.

6. The method according to claim 1, characterized in that, In step S2, the zirconium-containing compound is a mixture of zirconium silicate and zirconium oxide, and the carbon source is carbon powder.

7. The method according to claim 6, characterized in that, The mass ratio of zirconium silicate, zirconium oxide and carbon powder is 1:3:

1.

8. The method according to claim 1, characterized in that, In step S3, the high-temperature sintering temperature is not lower than 1850℃, and the holding time is not less than 8 hours; The protective atmosphere is hydrogen, with a hydrogen flow rate of 20-50 L / min and the furnace pressure maintained at 800-1000 Pa.

9. A thermal field component prepared by the method according to any one of claims 1-8, characterized in that, It includes a graphite substrate and a composite coating with zirconium carbide as the main phase formed on its surface through an in-situ reaction, wherein a silicon carbide transition layer is formed between the composite coating and the graphite substrate.

10. A silicon carbide single crystal growth apparatus, characterized in that, It includes the thermal field component as described in claim 9.

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