A composite tantalum carbide coating and a method of making and using the same

Abstract

This invention relates to the field of silicon carbide growth, and more particularly to a composite tantalum carbide coating, its preparation method, and its application. The method includes the following steps: S1: coating a first tantalum oxide-containing slurry onto the surface of a graphite substrate to form a first pre-coating; S2: subjecting the first pre-coating to a first heat treatment to form a composite transition layer on the surface of the graphite substrate; S3: coating a second tantalum oxide-containing slurry onto the surface of the composite transition layer to form a second pre-coating; S4: subjecting the second pre-coating to a second heat treatment and sintering to form a main tantalum carbide layer. This application, by introducing a composite transition layer formed by photoresist carbonization and in-situ reaction, greatly enhances the interfacial bonding force and thermal stress buffering capacity between the tantalum carbide coating and the graphite substrate, qualitatively improving the thermal shock resistance of the coating and effectively preventing cracking and peeling during high-temperature thermal cycling.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide growth, and more particularly to a composite tantalum carbide coating for growing graphite components from silicon carbide single crystals, its preparation method, and its application. Background Technology

[0002] Silicon carbide, as a core representative of third-generation semiconductor materials, is playing an increasingly important role in cutting-edge fields such as new energy vehicles, 5G communications, and clean energy due to its superior physical properties. However, the preparation of high-quality, low-cost silicon carbide single-crystal substrates remains a key bottleneck restricting the development of the entire industry. Currently, the physical vapor transport method is commonly used in industry to grow silicon carbide single crystals. This process requires extreme high temperatures exceeding 2,200 degrees Celsius, placing extremely stringent requirements on the stability and purity of the thermal field components. Under these conditions, the graphite crucible and thermal field elements, as core components, face severe challenges: on the one hand, high temperatures exacerbate the volatilization and pulverization of graphite materials, and the resulting carbon particles contaminate the ingot; on the other hand, the highly reactive silicon vapor released from the raw material decomposition reacts with the graphite, leading to raw material loss and affecting the stoichiometry of the crystal.

[0003] To address these challenges, applying high-performance, high-temperature protective coatings to graphite components has become an industry consensus. Among numerous candidate materials, tantalum carbide is widely recognized as one of the most promising coating materials due to its extremely high melting point, excellent chemical inertness, and good compatibility with graphite. An ideal tantalum carbide coating needs to simultaneously meet several almost contradictory requirements: it must be extremely dense to effectively block corrosion, while also possessing excellent toughness to withstand repeated thermal cycling stress; it needs to bond firmly to the substrate, and its coefficient of thermal expansion should be as close as possible to that of the graphite substrate to prevent cracking or peeling under drastic temperature changes.

[0004] Currently, there are several main technical routes for preparing tantalum carbide coatings on graphite. Chemical vapor deposition and plasma spraying technologies can obtain coatings with quite good performance, with good density and adhesion. However, they share the disadvantage of huge equipment investment, complex processes, and high energy consumption. In particular, it is difficult to achieve uniform coating for large-sized or structurally complex graphite parts, resulting in high production costs and making it difficult to meet the stringent cost control requirements of large-scale industrial production.

[0005] In contrast, slurry sintering exhibits significant appeal due to its simple and low-cost process, making it ideal for large-scale applications. This method involves coating a tantalum compound-containing slurry onto a graphite surface, followed by a high-temperature sintering reaction to generate a tantalum carbide coating. However, existing slurry sintering technologies have a critical weakness: during sintering, a rigid ceramic structure forms within the coating. While this structure is hard and wear-resistant, it is extremely fragile under thermal shock. Due to the difference in thermal expansion coefficients between the coating and the graphite substrate, significant thermal stress is generated at the interface during repeated heating and cooling cycles. More importantly, traditional slurry processes struggle to establish a strong, stress-absorbing transition interface between the coating and the substrate, leading to the easy initiation and propagation of cracks at the interface, ultimately resulting in large-area coating peeling. Therefore, despite the significant cost advantage of the slurry method, its poor thermal shock resistance severely limits its application in silicon carbide single crystal growth, which requires long crystal growth periods and extremely high thermal stability.

[0006] This has put the industry in a dilemma: high-performance coating technologies are too expensive to be industrialized; while low-cost coating technologies lack reliability and cannot meet application requirements. Overcoming this bottleneck and developing a coating solution that balances the cost-effectiveness of large-scale production with long-term stability under extreme thermal shock conditions has become a pressing technical challenge for the further development of the silicon carbide industry. This requires not only a deep understanding of the coating materials themselves but also innovative exploration of the fundamental issue of interfacial bonding. Summary of the Invention

[0007] This application aims to overcome the shortcomings of existing technologies where tantalum carbide coatings prepared by slurry sintering have insufficient interfacial bonding strength with the graphite substrate and poor thermal stress buffering capacity, resulting in poor thermal shock resistance and easy peeling. Therefore, a composite tantalum carbide coating for silicon carbide single crystal growth of graphite components, its preparation method, and its application are provided to overcome the above-mentioned deficiencies.

[0008] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a composite tantalum carbide coating, comprising the following steps:

[0010] S1: A first tantalum oxide-containing slurry is coated onto the surface of a graphite substrate to form a first pre-coating layer; wherein, the first tantalum oxide-containing slurry is coated with an organic polymer solution as a solvent;

[0011] S2: The first pre-coating layer is subjected to a first heat treatment to carbonize the organic polymer material to form a carbonaceous layer, and simultaneously the tantalum oxide reacts with carbon to form tantalum carbide, forming a composite transition layer on the surface of the graphite substrate;

[0012] S3: A second tantalum oxide-containing slurry is coated onto the surface of the composite transition layer to form a second pre-coating layer; wherein the second tantalum oxide-containing slurry uses ethanol as a solvent and contains a binder;

[0013] S4: Perform a second heat treatment on the second pre-coating layer and sinter to form the main tantalum carbide layer;

[0014] Thus, a composite tantalum carbide coating comprising the composite transition layer and the main tantalum carbide layer is obtained on the graphite substrate.

[0015] As described in the background section, when preparing silicon carbide single crystals using the physical vapor transport method, the graphite thermal field components must rely on high-performance coatings for protection, with tantalum carbide coatings being the most promising option. The industry has consistently sought a balance between low-cost, large-scale production and high reliability of coatings under extreme thermal shock conditions. However, existing technological approaches each have limitations: methods such as chemical vapor deposition offer excellent performance but are prohibitively expensive; while traditional slurry sintering methods, though inexpensive, suffer from poor thermal shock resistance due to weak interfacial bonding between the coating and the graphite substrate and poor thermal stress buffering capacity. The coating is prone to cracking and peeling during repeated thermal cycling, failing to meet the stringent requirements for thermal field stability in crystal growth processes. This contradiction between "low cost" and "high reliability" has become a key bottleneck restricting the widespread adoption of this technology.

[0016] The existing slurry sintering method is relatively straightforward: a tantalum carbide coating is generated by coating a tantalum oxide-containing slurry onto a graphite surface and then sintering it at high temperature in a single step. The fundamental drawback of this method is that the bonding between the coating and the substrate relies primarily on limited mechanical anchoring and interfacial chemical reactions, resulting in a relatively simple and fragile interfacial structure. When subjected to high-temperature thermal shock, due to the significant difference in thermal expansion coefficients between the rigid ceramic properties of tantalum carbide and the graphite matrix, enormous thermal stress concentrates on this relatively weak bonding interface, causing cracks to preferentially initiate and propagate, ultimately leading to coating failure. It can be seen that most existing improvements focus on optimizing the slurry formulation or sintering parameters themselves, without addressing the core issue of "how to construct a strong and resilient transition interface that can effectively buffer and dissipate thermal stress."

[0017] The core of the preparation method described in this application lies in the "stepwise construction" and "in-situ synthesis" of a functionally graded composite transition layer. Specifically, the first step (S1 and S2) of the technical solution demonstrates a significant difference from conventional approaches: it does not directly prepare the final main tantalum carbide coating, but first uses a first tantalum oxide slurry with an organic polymer solution as a solvent for coating. This initial material selection is crucial because in the subsequent first heat treatment (S2), the organic polymer is not simply ablated and removed, but is cleverly utilized to generate a carbonaceous layer with excellent compatibility with the graphite substrate through in-situ carbonization. More importantly, this heat treatment process is carried out "simultaneously," that is, the tantalum oxide reacts in-situ with the newly generated carbon to generate nascent tantalum carbide. This process does not form two independent layers, but rather allows the carbonaceous phase and tantalum carbide to interweave and permeate each other, ultimately "forming a composite transition layer on the surface of the graphite substrate."

[0018] The formation of this composite transition layer fundamentally alters the interfacial properties between the coating and the substrate. From a physical perspective, the carbonaceous layer formed by in-situ carbonization perfectly embeds into the microstructure of the graphite matrix, significantly increasing the contact area and mechanical anchoring effect. From a chemical perspective, the tantalum carbide generated in-situ forms a strong chemical bond with the carbonaceous layer and possesses inherent chemical compatibility with the subsequent main coating. Most importantly, from a mechanical perspective, this composite structure, composed of a carbonaceous phase (with good toughness and a thermal expansion coefficient close to that of graphite) and a tantalum carbide phase (rigid), macroscopically serves as an ideal thermal stress buffer zone, effectively absorbing and relaxing stress caused by thermal mismatch and preventing cracks from extending to the interface. Building upon this foundation, the scheme further employs optimized second slurry (using ethanol as a solvent and containing a binder) in steps three and four (S3 and S4) to construct a dense main tantalum carbide layer on the already stabilized composite transition layer. This sequential design of "building a solid foundation first, then constructing the superstructure" ensures the integrity and reliability of the final coating structure.

[0019] Therefore, due to the successful construction of the composite transition layer, the composite tantalum carbide coating prepared by this method can effectively resist repeated heating and cooling cycles during silicon carbide crystal growth, avoiding early failure of the coating. This allows coatings prepared by the low-cost slurry sintering method to approach or even reach the level of some high-cost technical routes in terms of key reliability indicators, thus successfully breaking the aforementioned technical deadlock between "low cost" and "high reliability," and providing practical technical support for the low-cost, high-volume, and high-yield manufacturing of silicon carbide substrates.

[0020] Preferably, in step S1, the organic polymer material is a photoresist.

[0021] Photoresist, as a polymer with unique functions, far surpasses ordinary adhesives. In step S1, when it is used as a dispersion medium for tantalum pentoxide powder in solution form, its excellent film-forming and adhesive properties first ensure that the first pre-coating layer can form a uniform and defect-free coverage on the complex-shaped graphite substrate, laying the foundation for the uniformity of subsequent reactions.

[0022] During the heat treatment process in step S2, the photoresist does not undergo violent decomposition and generate a large amount of gas, resulting in a loose structure, when it is heated and carbonized. Instead, it is transformed into a dense carbonaceous layer that is highly compatible with the graphite substrate in terms of chemical composition and microstructure through a relatively gentle carbonization process. This carbonized layer acts like an "active adhesive pad," not only enhancing mechanical anchoring by increasing roughness, but also providing an immediate and uniform carbon source for the in-situ synthesis of tantalum carbide. This facilitates the direct reduction of tantalum pentoxide particles into tantalum carbide within the layer and at the interface, thereby achieving nanoscale interweaving and strong bonding between the carbonaceous phase and the tantalum carbide phase. This significantly strengthens the internal cohesion of the composite transition layer and its interfacial bonding with the substrate.

[0023] Preferably, the tantalum oxide in the first tantalum oxide slurry is tantalum pentoxide, and its solid content is 25wt%-60wt%.

[0024] Specifically defining the first tantalum oxide as tantalum pentoxide and controlling its solid content within the range of 25wt%-60wt% is the key process guarantee for achieving the core concept of "simultaneous formation of the composite transition layer". If the solid content is too low, although the paste is easy to coat evenly, the tantalum pentoxide content per unit area is insufficient. During sintering, it cannot fully react with the sufficient carbon source generated by the carbonization of the photoresist, resulting in too little primary tantalum carbide. This makes it difficult to form a continuous and effective reinforcing phase, and the final composite transition layer will have poor structural strength due to insufficient ceramic phase content, losing its significance as a stress buffer and toughening layer. Conversely, if the solid content is too high, the paste will be too viscous, making it difficult to achieve uniform and smooth coating and easily generating defects. More seriously, the excessively dense tantalum pentoxide particles will hinder the uniform carbonization and volatilization of the photoresist during heat treatment, easily forming pores and stress concentration points inside the coating, destroying the compactness and integrity of the composite transition layer.

[0025] Therefore, when its solid content is in the range of 25wt%-60wt%, it ensures that in the heat treatment of step S2, just the right amount of tantalum pentoxide reacts in situ with the carbon generated by photoresist carbonization, thereby generating an ideal microstructure in which tantalum carbide particles are uniformly dispersed in a tough carbon matrix. This specific composite structure is the foundation for achieving excellent thermal shock resistance.

[0026] Preferably, in step S3, the adhesive is polyvinyl butyral.

[0027] The role of polyvinyl butyral (PVB) is to ensure that the second slurry layer can form a high-quality main tantalum carbide layer without damaging the already formed composite transition layer.

[0028] PVB plays a crucial dual role here. First, as a highly efficient organic binder, it provides excellent film-forming properties and adhesion in the slurry, allowing the second slurry to be uniformly and smoothly coated on the nascent, potentially fragile, composite transition layer surface. This avoids damage to the underlying structure and ensures the uniformity and density of the final main coating. Second, and more significantly, lies PVB's thermal decomposition characteristics. Unlike the photoresist that participates in the reaction as a carbon source in the first step, PVB can decompose and volatilize in a relatively clean and thorough manner during the subsequent second heat treatment, thereby minimizing the adverse effects of residual carbon or other impurities on the purity and crystallinity of the main tantalum carbide layer.

[0029] Preferably, the tantalum oxide in the second tantalum oxide slurry is tantalum pentoxide, and its solid content is 25wt%-50wt%.

[0030] Preferably, in step S2 and / or step S4, the sintering temperature of the heat treatment is 1600°C to 2000°C, and the sintering time is 0.5 to 3 hours.

[0031] Secondly, the present invention also provides a composite tantalum carbide coating prepared by the method described above.

[0032] The coating consists of a composite transition layer bonded to the surface of a graphite substrate and a main tantalum carbide layer covering it.

[0033] The composite transition layer is a microstructure consisting of a carbonaceous layer formed by the carbonization of organic polymer materials and tantalum carbide combined together.

[0034] Preferably, the thickness of the composite transition layer is 1-50 micrometers, and the thickness of the main tantalum carbide layer is 10-200 micrometers.

[0035] Thirdly, the present invention also provides a graphite component for a silicon carbide single crystal growth apparatus, comprising a graphite substrate.

[0036] At least one surface of the graphite substrate is provided with a composite tantalum carbide coating as described above.

[0037] Fourthly, the present invention also provides a method for preparing silicon carbide single crystals, which employs a physical vapor transport method and uses the aforementioned graphite component.

[0038] Therefore, the present invention has the following beneficial effects:

[0039] First, by introducing a composite transition layer formed by photoresist carbonization and in-situ reaction, the interfacial bonding force and thermal stress buffering capacity between the tantalum carbide coating and the graphite substrate are greatly enhanced, which improves the thermal shock resistance of the coating and effectively prevents cracking and peeling during high-temperature thermal cycling.

[0040] Secondly, the composite transition layer structure can effectively block the diffusion of impurities from the graphite substrate to the coating at high temperatures and reduce the reaction loss between the raw materials and graphite, thereby significantly improving the purity and quality of the prepared silicon carbide single crystals.

[0041] Furthermore, step-by-step coating and optimized slurry formulations (such as the use of PVB) ensure the uniformity and density of the coating structure, further enhancing its corrosion resistance and erosion resistance.

[0042] Finally, while maintaining the low-cost advantage of slurry sintering, this process significantly extends the service life of graphite components and improves production yield, effectively reducing the overall cost of silicon carbide single crystal growth and providing a solid guarantee for the economic efficiency and reliability of industrialization. Attached Figure Description

[0043] Figure 1 This is a microscope image of the tantalum carbide coating with a composite structure prepared in Example 1.

[0044] Figure 2 This is a microscope image of the tantalum carbide coating prepared in Comparative Example 1. Detailed Implementation

[0045] 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.

[0046] Example 1

[0047] This embodiment provides a method for preparing a composite tantalum carbide coating for a graphite crucible used in silicon carbide single crystal growth. The specific steps are as follows:

[0048] S1: Preparation of the first tantalum oxide slurry. Weigh 250 g of tantalum pentoxide (Ta2O5) powder and add it to 750 g of positive photoresist (model AZ 4620). Stir continuously for 3 hours at 500 rpm using a magnetic stirrer to obtain a uniformly dispersed first slurry with a solid content of 25 wt%. Subsequently, the first slurry is coated onto the surface of a cleaned high-purity graphite crucible substrate using a dip-coating process. After standing at room temperature for 10 minutes to allow the coating to level, it is then dried in an oven at 120°C for 30 minutes to form the first pre-coating.

[0049] S2: Place the graphite crucible with the first pre-coating into a high-temperature sintering furnace. Introduce high-purity argon gas into the furnace as a protective atmosphere, and heat to 1600°C at a rate of 10°C / min. Hold at this temperature for 3 hours to complete the first heat treatment. During this process, the photoresist carbonizes to form a dense carbonaceous layer, while tantalum pentoxide reacts with carbon to form tantalum carbide. The two react to form a composite transition layer on the surface of the graphite substrate.

[0050] S3: Prepare a second tantalum oxide-containing slurry. Weigh 250 g of tantalum pentoxide powder, disperse it in 745 g of anhydrous ethanol, then add 5 g of polyvinyl butyral (PVB) as a binder, and ball mill the mixture for 12 hours to obtain a second slurry with a solid content of 25 wt%. Apply this second slurry to the surface of the composite transition layer obtained in step S2 using a dip-coating process, let it stand for 10 minutes, and then dry it at 100°C to form a second pre-coating layer.

[0051] S4: The component with the second pre-coating is placed back into the high-temperature sintering furnace and heated to 2000°C at a rate of 15°C / min under an argon atmosphere, and held at that temperature for 0.5 hours to complete the second heat treatment. Finally, a dense main tantalum carbide layer is formed on the composite transition layer, thus obtaining a tantalum carbide coating with a composite structure. Figure 1 The image shows a microscope photograph of the tantalum carbide coating with a composite structure prepared in Example 1. As can be seen from the image, the surface of the tantalum carbide coating is uniform, and its pores are small and dense.

[0052] Example 2

[0053] The difference between this embodiment and Embodiment 1 lies in the slurry formulation and sintering process parameters, in order to demonstrate different choices within the parameter range.

[0054] S1: Preparation of the first slurry. Weigh 600 grams of tantalum pentoxide powder and add it to 400 grams of negative photoresist (model SU-8 2150). Stir to obtain a first slurry with a solid content of 60 wt%. The coating and drying steps are the same as in Example 1.

[0055] S2: The first heat treatment process is adjusted to: heating to 2000℃ at a rate of 15℃ / min under an argon atmosphere and holding at that temperature for 0.5 hours.

[0056] S3: Prepare the second slurry. Weigh 500g of tantalum pentoxide powder, disperse it in 495g of anhydrous ethanol, and add 5g of PVB to obtain a second slurry with a solid content of 50wt%. The coating and drying steps are the same as in Example 1.

[0057] S4: The second heat treatment process is adjusted to: heating to 1600℃ at a rate of 10℃ / min under an argon atmosphere and holding at that temperature for 3 hours.

[0058] Example 3

[0059] The difference between this embodiment and Embodiment 1 lies in the slurry formulation and sintering process parameters, in order to demonstrate different choices within the parameter range.

[0060] S1: Preparation of the first slurry. Weigh 420 grams of tantalum pentoxide powder and add it to 580 grams of positive photoresist (model AZ4620). Stir to obtain a first slurry with a solid content of 42 wt%. Apply the slurry using a spray coating process. The remaining steps are the same as in Example 1.

[0061] S2: The first heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1850℃ at a rate of 12℃ / min and held for 1.5 hours.

[0062] S3: Prepare the second slurry. Weigh 375 g of tantalum pentoxide powder, disperse it in 615 g of anhydrous ethanol, and add 10 g of PVB to obtain a second slurry with a solid content of 37.5 wt%. Apply the slurry using a spray coating process.

[0063] S4: The second heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1850°C at a rate of 12°C / min and held for 1.5 hours.

[0064] Example 4

[0065] The difference between this embodiment and Embodiment 1 lies in the slurry formulation and sintering process parameters, in order to demonstrate different choices within the parameter range.

[0066] S1: Prepare the first slurry. The solid content is 30wt% (300g Ta2O5 dissolved in 700g AZ 4620 photoresist). Coating and drying are the same as in Example 1.

[0067] S2: The first heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1700℃ at a rate of 8℃ / min and held for 2.5 hours.

[0068] S3: Prepare the second slurry. The solid content is 30 wt% (300 g Ta2O5 dissolved in 695 g ethanol, with 5 g PVB added). Coating and drying are the same as in Example 1.

[0069] S4: The second heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1750℃ at a rate of 12℃ / min and held for 2 hours.

[0070] Example 5

[0071] The difference between this embodiment and Embodiment 1 lies in the slurry formulation and sintering process parameters, in order to demonstrate different choices within the parameter range.

[0072] S1: Prepare the first slurry. The solid content is 55wt% (550g Ta2O5 dissolved in 450g SU-8 2150 photoresist). Coating and drying are the same as in Example 1.

[0073] S2: The first heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1950℃ at a rate of 15℃ / min and held for 1 hour.

[0074] S3: Prepare the second slurry. The solid content is 45 wt% (450 g Ta2O5 dissolved in 545 g ethanol, with 5 g PVB added). Coating and drying are the same as in Example 1.

[0075] S4: The second heat treatment process is as follows: under an argon atmosphere, the temperature is raised to 1950℃ at a rate of 15℃ / min and held for 1 hour.

[0076] Example 6

[0077] The difference between this embodiment and Embodiment 1 lies in the slurry formulation and sintering process parameters, in order to demonstrate different choices within the parameter range.

[0078] S1: Prepare the first slurry. The solid content is 35wt% (350g Ta2O5 dissolved in 650g AZ 4620 photoresist). Coating and drying are the same as in Example 1.

[0079] S2: The first heat treatment process is as follows: Under an argon atmosphere, the temperature is rapidly increased to 1800℃ at a rate of 20℃ / min and held for 1 hour.

[0080] S3: Prepare the second slurry. The solid content is 35wt% (350g Ta2O5 dissolved in 645g ethanol, with 5g PVB added). Coating and drying are the same as in Example 1.

[0081] S4: The second heat treatment process is as follows: Under an argon atmosphere, the temperature is rapidly increased to 1800℃ at a rate of 20℃ / min and held for 1 hour.

[0082] Comparative Example 1

[0083] This comparative simulation is closest to the existing technology, namely the traditional process that uses a single slurry and a single sintering.

[0084] S1: Preparation of tantalum oxide slurry. Weigh 400g of tantalum pentoxide powder, disperse it in 595g of anhydrous ethanol, add 5g of polyvinyl butyral (PVB) as a binder, and ball mill and mix for 12 hours to obtain a slurry with a solid content of 40wt%. Apply the slurry to the surface of a high-purity graphite crucible substrate (same as in Example 1) using a dip-coating process, let it stand for 10 minutes, and then dry it at 100°C to form a pre-coating.

[0085] S2: Place the pre-coated graphite crucible into a high-temperature sintering furnace. Introduce high-purity argon gas into the furnace, raise the temperature to 1850°C at a rate of 12°C / min, and hold for 1.5 hours for a single sintering process to directly generate the tantalum carbide coating. Figure 2 The image shows a microscope photograph of the tantalum carbide coating prepared in Comparative Example 1. It can be seen from the image that the surface of the coating is porous, not dense, and has many cracks and defects.

[0086] Comparative Example 2

[0087] This comparative example aims to verify the necessity of using photoresist instead of conventional binders in the first step for forming the composite transition layer.

[0088] S1: Preparation of the first slurry. Weigh 400g of tantalum pentoxide powder, disperse it in 595g of anhydrous ethanol, and add 5g of PVB as a binder (similar to the slurry in Comparative Example 1) to obtain a first slurry with a solid content of 40wt%. The coating and drying steps are the same as in Example 1.

[0089] S2: The first heat treatment process is exactly the same as in Example 3: under an argon atmosphere, the temperature is increased to 1850°C at a rate of 12°C / min and held for 1.5 hours.

[0090] S3: The preparation and coating of the second slurry, and the second heat treatment step in S4, are exactly the same as in Example 3.

[0091] Comparative Example 3

[0092] This comparative example is used to demonstrate the rationale for using ethanol solvent and PVB binder in the second step, and to avoid the adverse effects of excessive carbon residue on the performance of the main coating.

[0093] S1: The steps are exactly the same as in Example 3.

[0094] S2: The steps are exactly the same as in Example 3.

[0095] S3: Prepare the second slurry. Weigh 375 grams of tantalum pentoxide powder and add it to 615 grams of positive photoresist (model AZ4620). Stir to obtain a second slurry with a solid content of 37.5 wt% (i.e., using photoresist instead of ethanol and PVB). Coating and drying are the same as in Example 1.

[0096] S4: The steps are exactly the same as in Example 3.

[0097] Examples 1-6 and Comparative Examples 1-4 were tested using the methods described below, and the test results are shown in Table 1.

[0098] 1. Coating adhesion strength test

[0099] Testing Procedure: The scratch test was used. A scratch tester equipped with a diamond indenter (tip radius 200 μm) was used to apply a linearly increasing load starting from 0 N to the coating surface. The scratch length was 5 mm, and the loading rate was 50 N / min. Simultaneously, an acoustic emission sensor was used to monitor the coating cracking signal. The critical load (Lc) at which the coating first showed significant peeling (a sudden increase in acoustic emission signal, confirmed by optical microscopy) was recorded. Five points were tested for each sample, and the average value was taken.

[0100] 2. Thermal shock resistance test

[0101] Test Procedure: The coated sample was placed in a muffle furnace preheated to 1650℃ and held at that temperature for 10 minutes. The furnace was then turned off, allowing the sample to cool naturally. This process was recorded as one thermal cycle. After every five cycles, the coating surface was observed using an optical microscope to check for cracks, peeling, or flaking. The number of thermal cycles (N) at which the coating first showed visible macroscopic cracks or flaking covering more than 5% of its surface area was recorded. If the coating did not fail after more than 30 cycles, the test was stopped.

[0102] 3. High-temperature stability simulation test

[0103] Testing procedure: The coated sample was placed in a high-temperature graphite furnace and held at 2000℃ for 50 hours under argon protection. After cooling, SEM was performed again to assess whether the coating exhibited significant volatilization, abnormal grain growth, or harmful reactions with the substrate.

[0104] Table 1

[0105] Sample number Coating bond strength (critical load Lc, N) Thermal shock resistance (number of failure cycles N) High temperature stability (2000℃ / 50h) Example 1 38.5 ± 2.1 28 The coating is intact and shows no obvious changes. Example 2 41.2 ± 1.8 25 The coating is intact and shows no obvious changes. Example 3 45.8 ± 2.5 >30 (Not expired) The coating is intact and shows no obvious changes. Example 4 35.1 ± 2.0 22 The coating is intact and shows no obvious changes. Example 5 43.5 ± 2.3 27 The coating is intact and shows no obvious changes. Example 6 36.9 ± 1.7 20 The coating is intact and slightly densified. Comparative Example 1 14.3 ± 3.5 5 The coating bulges in some areas and separates from the substrate. Comparative Example 2 18.9 ± 2.8 8 The underlying layer became more porous, and cracks appeared in the main coating. Comparative Example 3 32.7 ± 2.2 15 The surface roughness of the main coating has increased, and there are signs of carbon volatilization.

[0106] As can be seen from the results in the table above, the coating bonding strength (critical load Lc is higher than 35N) and thermal shock resistance (failure cycle number N is greater than or equal to 20) of all Examples 1-6 of this application are far superior to Comparative Example 1 (traditional one-step method). This directly confirms the effectiveness of the core concept of "stepwise coating and construction of a composite transition layer" in solving the core technical problem of weak bonding between the coating and the substrate and poor thermal shock resistance. The composite transition layer plays a crucial role in stress buffering and toughening.

[0107] Comparative Example 2 (using PVB in the first step) shows that, despite the two-step process, a strong composite transition layer cannot be formed if an organic polymer material (such as photoresist) capable of carbonization to form an effective carbonaceous layer and participating in in-situ reactions is not used in the first step. While its performance is improved, it is still far inferior to that of the examples. This demonstrates that selecting a specific type of organic polymer material in the first step is a necessary condition for achieving the invention's objective.

[0108] The results of Comparative Example 3 (using photoresist in both steps) show that although its interfacial bonding and thermal shock resistance are better than Comparative Examples 1 and 2, its coating purity, density, and high-temperature stability are inferior to the optimal example due to the influence of residual carbon in the second step. This indicates that replacing the solvent with ethanol and PVB binder in the second step to reduce the negative impact of carbon residue on the performance of the main coating is an optimized, albeit non-obvious, step in the overall solution.

[0109] Furthermore, Examples 1-6, using different combinations of parameters within the specified range, all yielded coatings with excellent performance, with Example 3 exhibiting the best overall performance. This demonstrates that the parameter range provided by this invention is reasonable and effective, offering sufficient guidance for those skilled in the art to implement this invention, and also reflecting the feasibility and repeatability of the technical solution.

[0110] In summary, the test results fully verify that the technical solution protected by this invention is not a simple superposition or conventional optimization of existing technologies, but rather a successful preparation of a composite tantalum carbide coating with high bonding strength, excellent thermal shock resistance, and good high-temperature stability through a series of synergistic and non-obvious technical means.

[0111] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations. Those skilled in the art will readily conceive of other implementations 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.

Claims

1. A method for preparing a composite tantalum carbide coating, characterized in that, Includes the following steps: S1: A first tantalum oxide-containing slurry is coated onto the surface of a graphite substrate to form a first pre-coating layer; wherein the first tantalum oxide-containing slurry uses photoresist as a solvent; The photoresist is either a positive photoresist of type AZ 4620 or a negative photoresist of type SU-8 2150; S2: The first pre-coating layer is subjected to a first heat treatment to carbonize the photoresist to form a carbonaceous layer, and simultaneously the tantalum oxide reacts with carbon to form tantalum carbide, forming a composite transition layer on the surface of the graphite substrate; S3: A second tantalum oxide-containing slurry is coated onto the surface of the composite transition layer to form a second pre-coating layer; wherein the second tantalum oxide-containing slurry uses ethanol as a solvent and contains a binder; S4: Perform a second heat treatment on the second pre-coating layer and sinter to form the main tantalum carbide layer; Thus, a composite tantalum carbide coating comprising the composite transition layer and the main tantalum carbide layer is obtained on the graphite substrate.

2. The method according to claim 1, characterized in that, The tantalum oxide in the first tantalum oxide slurry is tantalum pentoxide, and its solid content is 25wt%-60wt%.

3. The method according to claim 1, characterized in that, In step S3, the adhesive is polyvinyl butyral.

4. The method according to claim 1, characterized in that, The tantalum oxide in the second tantalum oxide slurry is tantalum pentoxide, and its solid content is 25wt%-50wt%.

5. The method according to claim 1, characterized in that, In step S2 and / or step S4, the sintering temperature of the heat treatment is 1600°C to 2000°C, and the sintering time is 0.5 to 3 hours.

6. A composite tantalum carbide coating prepared by the method according to any one of claims 1 to 5, characterized in that, The coating consists of a composite transition layer bonded to the surface of a graphite substrate and a main tantalum carbide layer covering it. The composite transition layer is a microstructure consisting of a carbonaceous layer formed by the carbonization of organic polymer materials and tantalum carbide combined together.

7. The composite tantalum carbide coating according to claim 6, characterized in that, The thickness of the composite transition layer is 1-50 micrometers, and the thickness of the main tantalum carbide layer is 10-200 micrometers.

8. A graphite component for a silicon carbide single crystal growth apparatus, comprising a graphite substrate, characterized in that, At least one surface of the graphite substrate is provided with the composite tantalum carbide coating as described in claim 6 or 7.

9. A method for preparing silicon carbide single crystals, employing a physical vapor transport method, characterized in that, Using the graphite component as described in claim 8, and depositing silicon carbide single crystals on the surface of its composite tantalum carbide coating.

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