Graphite anti-ablation composite coating and preparation method thereof

Abstract

The invention discloses a graphite anti-ablation composite coating and a preparation method thereof, and belongs to the technical field of coatings. The invention discloses a graphite anti-ablation composite coating. A SiC compact transition and sealing layer, a ZrC porous heat insulation and strain tolerance layer and an HfC-TaC compact ultrahigh-temperature ablation coating are sequentially arranged on the surface of a graphite matrix from inside to outside; the linear expansion coefficients of the SiC compact transition and sealing layer, the ZrC porous heat insulation and strain tolerance layer and the HfC-TaC compact ultrahigh-temperature ablation coating are gradually reduced from outside to inside. The coating provided by the invention is in gradient distribution in the aspects of components, mechanical properties and thermal expansion coefficients, and the continuous change can effectively relieve the performance mismatching between the matrix and the coating, so that the outermost layer is subjected to smaller tensile stress in the ablation process. The obtained coating is stable in adhesive force under the action of thermal stress, free of layering and cracking and good in ablation resistance.

Description

Technical Field

[0001] This invention relates to a graphite ablation-resistant composite coating and its preparation method, and more particularly to a novel graphite ablation-resistant composite coating and its preparation method, belonging to the field of coating technology. Background Technology

[0002] Graphite materials are prone to cracking and peeling under external forces due to their low strength and weak bonding. Therefore, after high-energy discharge ablation under extreme conditions such as high temperature, high pressure, high current density and high-speed airflow, the mass loss and volume ablation rate of graphite surface are much greater than those of alloy materials such as tungsten and copper, which restricts its application in high-energy discharge environments.

[0003] Graphite ablation failure refers to the arc discharge caused by the extremely high energy of an electric arc during electrical and thermal conduction, resulting in a significant transfer and exchange of electrical charge. This raises the surface temperature of the graphite, which has a layered, loose crystalline structure, to its phase transition temperature, causing the surface graphite to sublimate and remelt, ultimately leading to breakdown or fracture failure and unnecessary mass and volume loss. The ablation process can be divided into graphite heating and material removal. The heat input from the electric arc at the arc root region to the graphite surface generates Joule heating; simultaneously, the heat input heats the electrode material, causing a phase transition, leading to solid-liquid and solid-gas transformations, oxidation, and detachment from the surface.

[0004] Ultra-high temperature ceramic materials, represented by TaC, possess excellent high-temperature performance, enabling them to effectively protect graphite materials in high-temperature environments such as corrosive solutions and aerobic atmospheres, thereby improving the substrate's oxidation and corrosion resistance. However, graphite and tantalum carbide have significantly different coefficients of thermal expansion and mechanical properties. This significant performance mismatch leads to thermal stress and dislocations. Under thermal stress, the adhesion of the coating begins to decrease, and it is highly susceptible to delamination, cracking, and even peeling. Therefore, composite coatings are urgently needed to reduce this performance mismatch. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a graphite ablation-resistant composite coating with good ablation resistance and strong inter-film-substrate bonding.

[0006] Another objective of this invention is to provide a method for preparing a graphite ablation-resistant composite coating with a shorter preparation time, higher uniformity, and greater thickness. Technical solution

[0007] The present invention discloses a graphite anti-ablation composite coating, which is disposed on the surface of a graphite substrate. The graphite substrate surface is provided with a SiC dense transition and sealing layer, a ZrC porous heat insulation and strain tolerance layer, and an HfC-TaC dense ultra-high temperature ablation coating in sequence from the inside to the outside. The coefficient of linear expansion of the SiC dense transition and sealing layer, the ZrC porous heat insulation and strain tolerance layer, and the HfC-TaC dense ultra-high temperature ablation coating gradually decreases from the outside to the inside.

[0008] Furthermore, the thickness of the SiC dense transition and sealing layer is 3-4 μm, the thickness of the ZrC porous thermal insulation and strain-tolerant layer is 4.5-8 μm, and the thickness of the HfC-TaC dense ultra-high temperature ablation coating is 21-24 μm.

[0009] Furthermore, in the HfC-TaC dense ultra-high temperature ablation coating, the molar ratio of HfC-TaC is 1:1-1:3.

[0010] The method for preparing the above-mentioned ablation-resistant composite coating of cylindrical graphite includes the following steps: Step 1: Plasma activation pretreatment of the graphite substrate surface; Step 2: A dense SiC transition and sealing layer is generated on the surface of the graphite matrix after pretreatment by the three-stage reaction melting infiltration method. Step 3: Deposit a porous ZrC thermal insulation and strain-tolerant layer on the surface of the SiC dense transition and sealing layer using slurry coating; Step 4: Prepare a dense, ultra-high temperature ablation coating of HfC-TaC on the surface of the ZrC porous thermal insulation and strain-tolerant layer using plasma spraying.

[0011] Furthermore, in step one, the plasma activation pretreatment involves introducing argon gas with a purity greater than 99.99%, at a power of 100-200W, a pressure of 10-20Pa, and a time of 10-20min.

[0012] Further, in step two, argon gas with a purity greater than 99.99% is introduced, and the temperature is raised from room temperature to 1430-1470℃ at a rate of 5-10℃ / min, held for 30-60 minutes, and then cooled with the furnace. The outer shell containing free Si is then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process is repeated for a second reaction infiltration, raising the temperature from room temperature to 1530-1570℃ at a rate of 5-10℃ / min, and holding for 40-80 minutes. The outer shell containing free Si is then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process is repeated for a third reaction infiltration, raising the temperature from room temperature to 1630-1670℃ at a rate of 5-10℃ / min, and holding for 60-120 minutes.

[0013] Furthermore, in step two, high-purity silicon is used as the silicon infiltration source for the reactive melting infiltration method, and the silicon block is placed around the workpiece (i.e., the graphite substrate).

[0014] Further, step three specifically involves coating the surface of the graphite substrate, which has already undergone SiC dense transition and sealing layer deposition, with a slurry to deposit a ZrC porous thermal insulation and strain-tolerant layer. The raw material is ZrC powder (balance) with a particle size range of 0.8-2.0 μm, the pore-forming agent is polymethyl methacrylate (PMMA) with a pore-forming agent weight percentage of 10%-20%, the binder is PVB with a binder weight percentage of 3%-4%, the dispersant is PVP with a dispersant weight percentage of 1%-2%, and the solvent is anhydrous ethanol with a weight percentage of 20%-30%. Sintering is carried out under a high-purity argon atmosphere for a holding time of 60-120 min, a temperature of 1800℃-2000℃, a heating rate of 5-7℃ / min, and a porosity of 30%-50%.

[0015] Furthermore, in step four, the plasma spraying method uses a powder-feeding spray gun with the spraying angle perpendicular to the graphite substrate surface.

[0016] Furthermore, in step four, the powder used in the plasma spraying method is HfC-TaC powder, which is a composite powder with a molar ratio of 1:1 to 1:3. The plasma gas is Ar, the power is 40-60kW, the spraying distance is 100-140mm, the powder feeding rate is 20-30g / min, and the spray gun moving speed is 500-800mm / s.

[0017] This invention provides a graphite ablation-resistant composite coating with a surface hardness of 1351.63-1589.24 HV. Its flexural strength is 300-600 MPa at room temperature, 200-400 MPa at 1500℃, and 100-250 MPa at 2000℃. The thermal conductivity at room temperature is 20-40 W / (m·K), and at 2000℃ it is 15-25 W / (m·K). The high-temperature steady-state emissivity at 2000℃ is 0.7-0.9. The critical load for film-substrate separation is 0.27-0.29 N. The depth of 40 ablation pits is 39.85-45.03 μm, and the diameter of the 40 ablation pits is 1237.74-1527.44 μm.

[0018] The present invention relates to the application of a graphite ablation-resistant composite coating in a high-energy discharge environment.

[0019] Principle of Preparation: The design of graphite-based ablation-resistant coatings must first address the problem of delamination and cracking caused by the significant difference in thermal expansion coefficients and mechanical properties between graphite and the outermost layer. A transition layer is needed to alleviate this issue. This invention sequentially incorporates a dense SiC transition and sealing layer, a porous ZrC thermal insulation and strain-tolerant layer, and a dense HfC-TaC ultra-high temperature ablation coating. These layers exhibit a gradient distribution from the inside out in terms of composition, mechanical properties, and thermal expansion coefficients. This continuously varying transition effectively mitigates the performance mismatch between the coating and the substrate. By introducing a carefully designed porous layer within the coating, efficient thermal insulation and strain tolerance are actively achieved, while the dense layer provides oxidation resistance and sealing. This is a "rigid on the outside, flexible on the inside" intelligent structure designed to simultaneously optimize thermal protection efficiency and thermal shock resistance life.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features: 1. HfC and TaC can form a continuous solid solution, and their oxidation resistance and ablation resistance can be synergistically improved through composition optimization. In the prior art, the oxidation product HfO2 (hafnium oxide) undergoes a phase transition from monoclinic to tetragonal phase at about 1700°C, accompanied by a volume shrinkage of about 3-5%. This phase transition leads to increased internal stress in the oxide film during thermal cycling, making it prone to cracking and spalling, thus compromising the integrity of the protective layer. Furthermore, the oxidation product Ta2O5 (tantalum pentoxide) has a high vapor pressure at high temperatures (>1800°C), making it easily volatilized and causing rapid thinning and failure of the oxide film. However, this invention, through the co-oxidation of HfC and TaC, can suppress the phase transition, stabilize the structure, and significantly increase its phase transition temperature (up to above 2000°C), even completely suppressing harmful phase transitions at service temperatures, thereby greatly improving the structural stability of the oxide film during thermal cycling and reducing cracking. It can also reduce volatilization and enhance adhesion: the addition of HfO2 can effectively reduce the overall vapor pressure of the composite oxide film and inhibit the volatilization of Ta2O5 components. Simultaneously, the formed composite oxide has higher viscosity and lower oxygen diffusivity, making the oxide film denser, more firmly adhered, and able to cover the coating surface more persistently, isolating oxygen. Furthermore, the different atomic radii of Hf and Ta, when mutually dissolved, introduce a stress field in the crystal lattice, hindering dislocation movement, thereby increasing the material's hardness and high-temperature strength, making it more resistant to high-speed particle erosion. It can also improve ablation resistance. TaC typically has a higher thermal conductivity than HfC. By forming a solid solution, its thermal conductivity can be moderately adjusted while maintaining the material's high melting point. A slightly higher thermal conductivity is beneficial for diffusing high surface heat flux along the surface direction, avoiding localized overheating; at the same time, the composite oxide surface may have a better thermal radiation coefficient, which is beneficial for radiative heat dissipation.

[0021] 2. The ZrC porous insulation and strain-tolerant layer significantly reduces thermal conductivity, providing a powerful insulation effect. This allows heat to accumulate in the outer layer, thereby significantly reducing the actual operating temperature of the inner layer and the substrate. Simultaneously, the pore-forming agent is polymethyl methacrylate, which increases porosity; the binder is PVB, used to enhance green strength; and the dispersant is PVP, used to prevent powder agglomeration. The ZrC porous insulation and strain-tolerant layer significantly reduces thermal conductivity, providing a powerful insulation effect. This allows heat to accumulate in the outer layer, thereby significantly reducing the actual operating temperature of the inner layer and the substrate.

[0022] 3. Significantly improves strain tolerance. The pores in the ZrC porous insulation and strain-tolerant layer can serve as termination points for microcracks and give the layer compressibility similar to a "honeycomb" structure, thereby efficiently absorbing and releasing thermal stress transmitted from the dense outer layer.

[0023] 4. The coating of the present invention has a gradient distribution in terms of composition, mechanical properties and coefficient of thermal expansion. This continuous change can effectively alleviate the performance mismatch between the substrate and the coating, so that the outermost layer is subjected to less tensile stress during the ablation process.

[0024] 5. The SiC dense transition and sealing layer acts as a "gate" for the inner layer, ensuring that no oxygen can penetrate into the substrate through the porous second layer (ZrC porous thermal insulation and strain-tolerant layer). It completely confines the ablation and oxidation processes to the outer layer (HfC-TaC dense ultra-high temperature ablation coating) and the second layer (ZrC porous thermal insulation and strain-tolerant layer). This provides a robust mechanical support substrate for the porous second layer (ZrC porous thermal insulation and strain-tolerant layer). The three-stage reaction melting infiltration method of this invention can improve the excellent interfacial bonding strength and enhance the strong chemical bond formed between the coating and the substrate. The reaction process is usually accompanied by a small volume expansion, which effectively fills the pores and cracks inside the substrate, thus achieving densification.

[0025] 6. The HfC-TaC dense ultra-high temperature ablation coating-ZrC porous thermal insulation and strain-tolerant layer-SiC dense transition and sealing layer and graphite have good compatibility and good matching of thermal expansion coefficients.

[0026] 7. In this invention, a dense transition and sealing layer of SiC is generated on the surface of a graphite matrix through a three-stage reaction melting infiltration method. The molten infiltrator (Si) undergoes an in-situ chemical reaction with the components (C) in the graphite matrix, and the resulting new phase (SiC) is atomically bonded to the matrix. The coating / composite material forms a strong chemical bond with the matrix, rather than a physical adhesion, which greatly improves the coating's resistance to peeling under extreme thermal shock and enhances interfacial strength. The three-stage melting infiltration process is accompanied by minute volume expansion, which effectively fills the pores and cracks inside the graphite matrix, simultaneously completing the "synthesis" and "densification" steps to obtain a product with low porosity and high density, with a relatively short process cycle. High-efficiency densification is achieved.

[0027] 8. The second layer of the present invention, the ZrC porous thermal insulation and strain tolerance layer, can significantly reduce thermal conductivity and achieve a strong thermal insulation effect, causing heat to accumulate in the outer layer, thereby greatly reducing the actual working temperature of the inner layer and the substrate.

[0028] 9. In this invention, HfC and TaC can form a continuous solid solution. Through composition optimization, their antioxidant and ablation resistance properties can be synergistically improved. The addition of HfO2 can effectively reduce the overall vapor pressure of the composite oxide film and inhibit the volatilization of the Ta2O5 component. Simultaneously, the formed composite oxide has higher viscosity and lower oxygen diffusivity, making the oxide film denser, more firmly adhered, and able to cover the coating surface more persistently, isolating oxygen. Furthermore, the different atomic radii of Hf and Ta, when mutually dissolved, introduce a stress field in the crystal lattice, hindering dislocation movement, thereby increasing the material's hardness and high-temperature strength, making it more resistant to high-speed particle erosion. This improves ablation resistance. TaC typically has a higher thermal conductivity than HfC. By forming a solid solution, the thermal conductivity can be moderately adjusted while maintaining the material's high melting point. A slightly higher thermal conductivity facilitates the diffusion of high surface heat flux along the surface direction, avoiding localized overheating; simultaneously, the composite oxide surface has a better thermal radiation coefficient, which is beneficial for radiative heat dissipation.

[0029] In summary, this invention achieves a stable oxide film resistant to erosion and burning by forming a continuous solid solution using highly dense HfC and TaC. A porous ZrC layer with a porosity of 30%–50% provides thermal insulation and strain tolerance. Near-dense reactive sintered SiC strengthens the bond between the film and substrate, resulting in an ablation-resistant coating.

[0030] This invention discloses a graphite-resistant ablation composite coating and its preparation method. The ablation-resistant composite coating is disposed on the surface of a graphite substrate. From the outside to the inside, the graphite substrate is sequentially composed of an HfC-TaC dense ultra-high temperature ablation coating, a ZrC porous heat insulation and strain tolerance layer, and a SiC dense transition and sealing layer. The coefficients of linear expansion of the HfC-TaC dense ultra-high temperature ablation coating, the ZrC porous heat insulation and strain tolerance layer, and the SiC dense transition and sealing layer gradually decrease from the outside to the inside. The preparation method includes the following steps: pre-treating the graphite substrate surface; generating the SiC dense transition and sealing layer on the pre-treated graphite substrate using a three-stage reaction infiltration method; depositing the ZrC porous heat insulation and strain tolerance layer on the surface of the SiC dense transition and sealing layer using a slurry coating; and preparing the HfC-TaC dense ultra-high temperature ablation coating on the surface of the ZrC porous heat insulation and strain tolerance layer using a plasma spraying method. The coating obtained by this invention exhibits stable adhesion under thermal stress, does not delamination or cracking, and has good ablation resistance. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the present invention, wherein 1-graphite matrix, 2-SiC dense transition and sealing layer, 3-ZrC porous heat insulation and strain tolerance layer, and 4-HfC-TaC dense ultra-high temperature ablation coating. Figure 2 This is a SEM image of the coating surface obtained by the present invention. Detailed Implementation

[0032] The following description, in conjunction with the accompanying drawings and embodiments of the present invention, will further clarify the objectives, technical solutions, and advantages of the present invention. The specific embodiments described are merely illustrative and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all materials and reagents used in the following embodiments are commercially available. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or as recommended by the manufacturer. Experimental materials selected include TaC and HfC powders with a purity greater than 99%, high-purity silicon blocks with a purity greater than 99.99%, ZrC powder with a purity greater than 99.99%, Ar gas, and isostatically pressed special high-purity graphite. Example 1

[0034] A method for preparing an ablation-resistant composite coating on a graphite surface includes the following steps: (1) The surface of the graphite substrate 1 is sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC, HfC and ZrC powders are placed in a drying oven.

[0035] (2) The surface of the graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 100W, the pressure was 10Pa, and the time was 10min.

[0036] (3) A dense transition and sealing layer 2 of SiC is formed on the surface of graphite substrate 1 by a three-stage reaction melting infiltration method. The silicon source is a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% is introduced, and the temperature is raised from room temperature to 1450℃ at a heating rate of 8℃ / min, held for 45min, and then cooled with the furnace. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, leaving the high-quality coating part. The above process is repeated for a second melting infiltration, raising the temperature from room temperature to 1550℃ at a heating rate of 8℃ / min, and holding for 60min. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, leaving the high-quality coating part. The above process is repeated for a three-stage reaction melting infiltration, raising the temperature from room temperature to 1650℃ at a heating rate of 8℃ / min, and holding for 90min.

[0037] (4) The surface of the graphite substrate 1, on which the SiC dense transition and sealing layer 2 has been deposited, is coated with a slurry to deposit a ZrC porous thermal insulation and strain-tolerant layer 3. The raw material is ZrC powder with a particle size of approximately 1.4 μm, the pore-forming agent is polymethyl methacrylate (PMMA) at a weight percentage of 15%, the binder is PVB at a weight percentage of 3.5%, the dispersant is PVP at a weight percentage of 1.5%, and the solvent is anhydrous ethanol at a weight percentage of 25%. Sintering is carried out under a high-purity argon atmosphere for 90 min at a temperature of 1900 °C and a heating rate of 6 °C / min. The porosity is 40%.

[0038] (5) A dense ultra-high temperature ablation coating 4 of HfC-TaC was prepared on the surface of ZrC porous heat insulation and strain tolerance layer 3 by plasma spraying. The powder used in plasma spraying was HfC-TaC composite spherical powder with a molar ratio of 1:2. The plasma gas was Ar, the power was 50kW, the spraying distance was 120mm, the powder feeding rate was 25g / min, and the spray gun moving speed was 600mm / s.

[0039] like Figure 1 As shown, the thickness of the SiC dense transition and sealing layer 2 obtained in this embodiment is 3.5 μm, the thickness of the ZrC porous heat insulation and strain tolerance layer 3 is 7 μm, the thickness of the HfC-TaC dense ultra-high temperature ablation coating 4 is 22 μm, and the total thickness is 32.5 μm.

[0040] The hardness of the ablation-resistant coating obtained in this embodiment was tested, and the surface hardness of the coating was 1589.24 HV.

[0041] The coating of this embodiment was subjected to high-temperature strength testing. Its flexural strength was 600 MPa at room temperature, 400 MPa at 1500°C, and 250 MPa at 2000°C.

[0042] The thermal conductivity of the coating in this embodiment was tested, and the thermal conductivity at room temperature was 40 W / (m·k), and the thermal conductivity at 2000℃ was 25 W / (m·k).

[0043] The thermal radiation coefficient of this embodiment was tested, and it was found that the high-temperature steady-state emissivity was 0.9 at 2000℃.

[0044] The adhesion performance of the coating obtained in this embodiment was further investigated using the scratch method. The critical load at which the film and substrate separate was used to characterize the adhesion force between the film and substrate. The critical load in this embodiment was 0.28 N.

[0045] The ablation resistance of the coating in this embodiment was tested using a YLS-2000 high-power fiber laser. The specific process was as follows: after being impacted by a high-energy laser beam, the coating material and the substrate material underwent surface melting, evaporation, or sublimation, forming ablation pits on the surface. The laser spot diameter was 1.2 mm, the distance from the laser head to the sample surface was 10 mm, the duration of a single ablation was 100 ms, and the ablation power was 900 W. After undergoing the above 40 ablation cycles, the coating obtained in this embodiment exhibited good ablation resistance. The overall depth of the 40 ablation pits was approximately 39.85 μm, and the diameter was approximately 1237.74 μm.

[0046] like Figure 1 As shown, a graphite anti-ablation composite coating is provided on the surface of a graphite substrate 1, from the inside out, consisting of a SiC dense transition and sealing layer 2, a ZrC porous heat insulation and strain tolerance layer 3, and an HfC-TaC dense ultra-high temperature ablation coating 4; the coefficients of linear expansion of the SiC dense transition and sealing layer 2, the ZrC porous heat insulation and strain tolerance layer 3, and the HfC-TaC dense ultra-high temperature ablation coating 4 gradually decrease from the outside to the inside.

[0047] like Figure 2 As shown, the synergistic effect of HfC-TaC forms a distinct mesh coating, indicating a high coating density. The mesh structure can limit the propagation of coating cracks and improve the coating's resistance to ablation. The gaps in the mesh can act as stress buffers to relax stress. Example 2

[0048] A method for preparing an ablation-resistant composite coating on a graphite surface includes the following steps: (1) The surface of the graphite substrate 1 is sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC, HfC and ZrC powders are placed in a drying oven.

[0049] (2) The surface of the graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 150W, the pressure was 15Pa, and the time was 15min.

[0050] (3) A dense SiC transition and sealing layer 2 is formed on the surface of graphite substrate 1 by a three-stage reaction melting infiltration method. Argon gas with a purity greater than 99.99% is introduced, and the temperature is raised from room temperature to 1430℃ at a heating rate of 5℃ / min, held for 30min, and then cooled with the furnace. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. The above process is repeated for a second melting infiltration, raising the temperature from room temperature to 1530℃ at a heating rate of 5℃ / min, and holding for 40min. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. The above process is repeated for a three-stage reaction melting infiltration, raising the temperature from room temperature to 1630℃ at a heating rate of 5℃ / min, and holding for 60min.

[0051] (4) The surface of the graphite substrate on which the SiC dense transition and sealing layer 2 has been deposited is coated with a slurry to deposit a ZrC porous thermal insulation and strain-tolerant layer 3. The raw material is ZrC powder with a particle size of approximately 0.8 μm, the pore-forming agent is polymethyl methacrylate (PMMA) at a weight percentage of 10%, the binder is PVB at a weight percentage of 3%, the dispersant is PVP at a weight percentage of 1%, and the solvent is anhydrous ethanol at a weight percentage of 20%. Sintering is carried out under a high-purity argon atmosphere for 60 min at a temperature of 1800 °C and a heating rate of 5 °C / min. The porosity is 30%.

[0052] (5) A dense ultra-high temperature ablation coating 4 of HfC-TaC was prepared on the surface of ZrC porous heat insulation and strain tolerance layer 3 by plasma spraying. The powder used in plasma spraying was HfC-TaC composite spherical powder with a molar ratio of 1:1. The plasma gas was Ar, the power was 40W, the spraying distance was 100mm, the powder feeding rate was 20 / min, and the spray gun moving speed was 500mm / s.

[0053] In this embodiment, the thickness of the SiC dense transition and sealing layer 2 is 3 μm, the thickness of the porous heat insulation and strain tolerance layer 3 is 4.5 μm, and the thickness of the HfC-TaC dense ultra-high temperature ablation coating 4 is 21 μm, with a total thickness of 28.5 μm.

[0054] The hardness of the ablation-resistant coating obtained in this embodiment was tested, and the surface hardness of the coating was 1359.11 HV.

[0055] The high-temperature strength test of this embodiment showed that its bending strength was 450 MPa at room temperature, 300 MPa at 1500℃, and 200 MPa at 2000℃.

[0056] Thermal conductivity tests were conducted on this embodiment. The thermal conductivity at room temperature was 30 W / (m·k), and the thermal conductivity at 2000℃ was 20 W / (m·k).

[0057] The thermal radiation coefficient of this embodiment was tested, and it was found that the high-temperature steady-state emissivity was 0.8 at 2000℃.

[0058] The bonding performance of the anti-ablation coating obtained in this embodiment was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load in this embodiment was 0.27 N.

[0059] The ablation resistance performance of this embodiment was tested using a YLS-2000 high-power fiber laser. The specific process was as follows: after being impacted by a high-energy laser beam, the coating and substrate materials underwent surface melting, evaporation, or sublimation, forming ablation pits on the surface. The laser spot diameter was 1.2 mm, the distance from the laser head to the sample surface was 10 mm, the duration of a single ablation was 100 ms, and the ablation power was 900 W. After undergoing 40 ablation cycles, the coating obtained in this embodiment exhibited good ablation resistance. The overall depth of the 40 ablation pits was 45.03 μm, and the diameter was approximately 1527.44 μm. Example 3

[0060] A method for preparing an ablation-resistant composite coating on a graphite surface includes the following steps: (1) The surface of the graphite substrate 1 is sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC, HfC and ZrC powders are placed in a drying oven.

[0061] (2) The surface of the graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 200W, the pressure was 20Pa, and the time was 20min.

[0062] (3) A dense SiC transition and sealing layer 2 is formed on the inner wall surface of the graphite substrate 1 by a three-stage reaction melting infiltration method. Argon gas with a purity greater than 99.99% is introduced, and the temperature is raised from room temperature to 1470℃ at a heating rate of 10℃ / min, held for 60min, and then cooled with the furnace. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. The above process is repeated for a second melting infiltration, raising the temperature from room temperature to 1570℃ at a heating rate of 10℃ / min, and holding for 80min. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. The above process is repeated for a three-stage reaction melting infiltration, raising the temperature from room temperature to 1670℃ at a heating rate of 10℃ / min, and holding for 120min.

[0063] (4) The surface of the graphite substrate on which the SiC dense transition and sealing layer 2 has been deposited is coated with a slurry to deposit a ZrC porous thermal insulation and strain-tolerant layer 3. The raw material is ZrC powder with a particle size of approximately 2.0 μm, the pore-forming agent is polymethyl methacrylate (PMMA) at a weight percentage of 20%, the binder is PVB at a weight percentage of 4%, the dispersant is PVP at a weight percentage of 2%, and the solvent is anhydrous ethanol at a weight percentage of 30%. Sintering is carried out under a high-purity argon atmosphere for 120 min at a temperature of 2000 °C and a heating rate of 7 °C / min. The porosity is 50%.

[0064] (5) A dense ultra-high temperature ablation coating 4 of HfC-TaC was prepared on the surface of ZrC porous heat insulation and strain tolerance layer 3 by plasma spraying. The powder used in plasma spraying was HfC-TaC composite spherical powder with a molar ratio of 1:3. The plasma gas was Ar, the power was 60W, the spraying distance was 140mm, the powder feeding rate was 30 / min, and the spray gun moving speed was 800mm / s.

[0065] In this embodiment, the thickness of the SiC dense transition and sealing layer 2 is 4 μm, the thickness of the ZrC porous heat insulation and strain tolerance layer 3 is 8 μm, and the thickness of the HfC-TaC dense ultra-high temperature ablation coating 4 is 24 μm, with a total thickness of 36 μm.

[0066] The hardness of the ablation-resistant coating obtained in this embodiment was tested, and the surface hardness of the coating was 1351.63 HV.

[0067] The bonding performance of the anti-ablation coating obtained in this embodiment was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load in this embodiment was 0.29 N.

[0068] The high-temperature strength test of this embodiment showed that its bending strength was 300 MPa at room temperature, 200 MPa at 1500℃, and 100 MPa at 2000℃.

[0069] Thermal conductivity tests were conducted on this embodiment. The thermal conductivity at room temperature was 20 W / (m·k), and the thermal conductivity at 2000℃ was 15 W / (m·k).

[0070] The thermal emissivity of this embodiment was tested, and it was found that the high-temperature steady-state emissivity was 0.7 at 2000℃.

[0071] The ablation resistance performance of this embodiment was tested using a YLS-2000 high-power fiber laser. The specific process was as follows: after being impacted by a high-energy laser beam, the coating material and the substrate material underwent surface melting, evaporation, or sublimation, forming ablation pits on the surface. The laser spot diameter was 1.2 mm, the distance from the laser head to the sample surface was 10 mm, the duration of a single ablation was 100 ms, and the ablation power was 900 W. After undergoing the above 40 ablation cycles, the coating obtained in this embodiment exhibited good ablation resistance. The overall depth of the ablation pits after 40 ablation cycles was 43.06 μm, and the diameter was approximately 1425.46 μm.

[0072] Comparative Example 1

[0073] The method for preparing a dense transition and sealing layer 2 of pure SiC includes the following steps: (1) The surface of the graphite substrate 1 is sanded, ultrasonically cleaned with selected ethanol cleaning agent, and dried.

[0074] (2) Plasma activation of graphite substrate 1 and pretreatment of the substrate surface. The equipment is a plasma cleaner, with Ar of purity greater than 99.99% introduced, power of 100W, gas pressure of 10Pa, and time of 10min.

[0075] (3) A dense transition and sealing layer 2 of SiC is generated on the surface of graphite substrate 1 by multiple reactive melting infiltration. The silicon source is a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% is introduced, and the temperature is raised from room temperature to 1450℃ at a heating rate of 8℃ / min, held for 45min, and then cooled with the furnace. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, leaving the high-quality coating. The above process is repeated for a second melting infiltration, raising the temperature from room temperature to 1550℃ at a heating rate of 8℃ / min, and holding for 60min. Afterwards, the outer shell containing free Si is removed by mechanical grinding with a diamond wheel, leaving the high-quality coating. The above process is repeated for a third reactive melting infiltration, raising the temperature from room temperature to 1650℃ at a heating rate of 8℃ / min, and holding for 90min.

[0076] The thickness of the SiC dense transition and sealing layer 2 obtained in this comparative example is 7 μm.

[0077] The hardness of the ablation-resistant coating obtained in Comparative Example 1 was tested, and the surface hardness of the coating was 254.95 HV.

[0078] The bonding performance of the anti-ablation coating obtained in Comparative Example 1 was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load of Comparative Example 1 was 0.8 N.

[0079] The ablation resistance of this comparative example was tested using a YLS-2000 high-power fiber laser. The specific process was as follows: after being impacted by a high-energy laser beam, the coating and substrate materials underwent surface melting, evaporation, or sublimation, forming ablation pits on the surface. The laser spot diameter was 1.2 mm, the distance from the laser head to the sample surface was 10 mm, the duration of a single ablation was 100 ms, and the ablation power was 900 W. The coating obtained in this example exhibited good ablation resistance after undergoing 40 ablation cycles. The overall depth of the 40 ablation pits was 90.12 μm, and the diameter was 2304.67 μm.

[0080] Comparative Example 2

[0081] A method for preparing a dense, ultra-high temperature ablation coating of pure HfC-TaC includes the following steps: (1) The surface of the graphite substrate 1 is sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC and HfC powders are placed in a drying oven.

[0082] (2) Plasma activation of graphite substrate 1 and pretreatment of the substrate surface. The equipment is a plasma cleaner, with Ar of purity greater than 99.99% introduced, power of 100W, gas pressure of 10Pa, and time of 10min.

[0083] (3) A dense ultra-high temperature ablation coating 4 of HfC-TaC was prepared on the surface of graphite substrate 1 by plasma spraying. The powder used in plasma spraying was a composite spherical powder with a molar ratio of HfC-TaC of 1:2. The plasma gas was Ar, the power was 50kW, the spraying distance was 120mm, the powder feeding rate was 25g / min, and the spray gun moving speed was 600mm / s.

[0084] The thickness of the HfC-TaC dense ultra-high temperature ablation coating 4 obtained in this comparative example is 19 μm.

[0085] The thermal shock resistant coating obtained in Comparative Example 2 was subjected to a hardness test, and the surface hardness of the coating was 667.83 HV.

[0086] The bonding performance of the anti-ablation coating obtained in Comparative Example 2 was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load of Comparative Example 2 was 0.08 N.

[0087] The comparative example was subjected to high-temperature strength tests. Its bending strength was 150 MPa at room temperature, 100 MPa at 1500℃, and 50 MPa at 2000℃.

[0088] Thermal conductivity tests were conducted on this comparative example. The thermal conductivity at room temperature was 15 W / (m·k), and the thermal conductivity at 2000℃ was 12 W / (m·k).

[0089] The thermal radiation coefficient of this comparative example was tested, and it was found that the high-temperature steady-state emissivity was 0.4 at 2000℃.

[0090] Comparative Example 2 tested the ablation resistance using a YLS-2000 high-power fiber laser. The process involved the coating and substrate materials being subjected to a high-energy laser beam, causing surface melting, evaporation, or sublimation, resulting in ablation pits. The laser spot diameter was 1.2 mm, the distance from the laser head to the sample surface was 10 mm, the duration of a single ablation was 100 ms, and the ablation power was 900 W. The coating obtained in this comparative example exhibited good ablation resistance after 40 ablation cycles. The overall depth of the 40 ablation pits was 93.42 μm, and the diameter was 2007.34 μm.

[0091] In summary, the optimal embodiment is Embodiment 1.

[0092] Comparative Example 3

[0093] The only difference between this comparative example and Example 1 is that: A dense SiC transition and sealing layer 2 was formed on the surface of a graphite substrate 1 using a one-step reactive melting infiltration method. The silicon source was a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% was introduced, and the temperature was raised from room temperature to 1450℃ at a rate of 8℃ / min, held for 45 min, and then cooled with the furnace. The surface hardness of the coating was 631.21 HV; its flexural strength was 150 MPa at room temperature, 100 MPa at 1500℃, and 75 MPa at 2000℃. The thermal conductivity at room temperature was 12 W / (m·K), and at 2000℃ it was 10 W / (m·K). The high-temperature steady-state emissivity at 2000℃ was 0.4. The critical load for film-substrate separation was 0.12 N. The depth of the 40 ablation pits was 87.29 μm, and the diameter of the 40 ablation pits was 3003.56 μm.

[0094] Comparative Example 4

[0095] The only difference between this comparative example and Example 1 is that: A dense SiC transition and sealing layer 2 was formed on the surface of a graphite substrate 1 using a two-stage reactive melting infiltration method. The silicon source was a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% was introduced, and the temperature was raised from room temperature to 1450℃ at a rate of 8℃ / min, held for 45 min, and then cooled with the furnace. The outer shell containing free Si was then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. The second melting infiltration process was repeated, raising the temperature from room temperature to 1550℃ at a rate of 8℃ / min, and holding for 60 min. The surface hardness of the coating was 727.83 HV; its flexural strength was 170 MPa at room temperature, 120 MPa at 1500℃, and 90 MPa at 2000℃. The thermal conductivity at room temperature was 13 W / (m·K), and at 2000℃ it was 11 W / (m·K). At 2000℃, the high-temperature steady-state emissivity is 0.45. The critical load for film-substrate separation is 0.14 N. The depth of the 40 ablation pits is 84.33 μm, and the diameter of the 40 ablation pits is 2784.23 μm.

[0096] Comparative Example 5

[0097] The only difference between this comparative example and Example 1 is that: A dense SiC transition and sealing layer 2 was formed on the surface of a graphite substrate 1 using a three-stage reaction infiltration method. The silicon source was a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% was introduced, and the temperature was raised from room temperature to 1400℃ at a rate of 8℃ / min, held for 70 min, and then cooled with the furnace. The outer shell containing free Si was then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process was repeated for a second infiltration, raising the temperature from room temperature to 1500℃ at a rate of 8℃ / min, and holding for 90 min. The outer shell containing free Si was then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process was repeated for a third infiltration, raising the temperature from room temperature to 1600℃ at a rate of 8℃ / min, and holding for 150 min. The coating surface hardness is 889.34 HV; its flexural strength is 190 MPa at room temperature, 150 MPa at 1500℃, and 95 MPa at 2000℃. The thermal conductivity at room temperature is 17 W / (m·K), and at 2000℃ it is 15 W / (m·K). The high-temperature steady-state emissivity at 2000℃ is 0.6. The critical load for film-substrate separation is 0.21 N. The depth of the 40 ablation pits is 67.33 μm, and the diameter of the 40 ablation pits is 2009.45 μm.

[0098] Comparative Example 6

[0099] The only difference between this comparative example and Example 1 is that: A dense SiC transition and sealing layer 2 was formed on the surface of a graphite substrate 1 using a three-stage reaction infiltration method. The silicon source was a high-purity silicon block with a purity greater than 99.99%. Argon gas with a purity greater than 99.99% was introduced, and the temperature was raised from room temperature to 1500℃ at a rate of 8℃ / min, held for 25 min, and then cooled with the furnace. The outer shell containing free Si was then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process was repeated for a second infiltration, raising the temperature from room temperature to 1600℃ at a rate of 8℃ / min, and holding for 30 min. The outer shell containing free Si was then removed by mechanical grinding with a diamond wheel, retaining the high-quality coating portion. This process was repeated for a third infiltration, raising the temperature from room temperature to 1700℃ at a rate of 8℃ / min, and holding for 50 min. The coating surface hardness is 833.22 HV; its flexural strength is 180 MPa at room temperature, 140 MPa at 1500℃, and 90 MPa at 2000℃. The thermal conductivity at room temperature is 16 W / (m·K), and at 2000℃ it is 13 W / (m·K). The high-temperature steady-state emissivity at 2000℃ is 0.55. The critical load for film-substrate separation is 0.19 N. The depth of the 40 ablation pits is 70.71 μm, and the diameter of the 40 ablation pits is 2398.34 μm.

[0100] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0101] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A graphite-resistant ablation composite coating, characterized in that: The graphite substrate surface is sequentially configured from the inside out with a SiC dense transition and sealing layer, a ZrC porous heat insulation and strain tolerance layer, and an HfC-TaC dense ultra-high temperature ablation coating; the coefficient of linear expansion of the SiC dense transition and sealing layer, the ZrC porous heat insulation and strain tolerance layer, and the HfC-TaC dense ultra-high temperature ablation coating gradually decreases from the outside to the inside.

2. The graphite ablation-resistant composite coating according to claim 1, characterized in that: The thickness of the SiC dense transition and sealing layer is 3-4 μm, the thickness of the ZrC porous thermal insulation and strain-tolerant layer is 4.5-8 μm, and the thickness of the HfC-TaC dense ultra-high temperature ablation coating is 21-24 μm.

3. The graphite ablation-resistant composite coating according to claim 1, characterized in that: The surface hardness of the coating is 1351.63-1589.24 HV; Its flexural strength at room temperature is 300-600 MPa, at 1500℃ it is 200-400 MPa, and at 2000℃ it is 100-250 MPa. Its thermal conductivity at room temperature is 20-40 W / (m·K), and at 2000℃ it is 15-25 W / (m·K). At 2000℃, its high-temperature steady-state emissivity is 0.7-0.

9. The critical load for film-substrate separation is 0.27-0.29 N. The depth of the 40 ablation pits is 39.85-45.03 μm, and the diameter of the 40 ablation pits is 1237.74-1527.44 μm.

4. A method for preparing a graphite ablation-resistant composite coating according to any one of claims 1 to 3, characterized in that: Includes the following steps: Step 1: Plasma activation pretreatment of the graphite substrate surface; Step 2: A dense SiC transition and sealing layer is generated on the surface of the graphite matrix after pretreatment by the three-stage reaction melting infiltration method. Step 3: Deposit a porous ZrC thermal insulation and strain-tolerant layer on the surface of the SiC dense transition and sealing layer using slurry coating; Step 4: Prepare a dense, ultra-high temperature ablation coating of HfC-TaC on the surface of the ZrC porous thermal insulation and strain-tolerant layer using plasma spraying.

5. The preparation method according to claim 4, characterized in that: In step one, the plasma activation pretreatment process is as follows: argon gas is introduced at a power of 100-200W, a pressure of 10-20Pa, and a time of 10-20min.

6. The preparation method according to claim 4, characterized in that: In step two, the pretreatment process of the three-stage reaction infiltration method involves placing the silicon block around the graphite substrate. One-stage reaction melting and infiltration: Argon gas is introduced, and the temperature is raised from room temperature to 1430-1470℃ at a rate of 5-10℃ / min. The temperature is held for 30-60 minutes and then cooled with the furnace; then the outer shell is removed by grinding. Secondary reaction melting and infiltration: heat from room temperature to 1530-1570℃ at a rate of 5-10℃ / min, hold at that temperature for 40-80min, and then cool with the furnace; then grind to remove the outer shell; Three-stage reaction melting and infiltration: heating from room temperature to 1630-1670℃ at a rate of 5-10℃ / min, holding at that temperature for 60-120min, and then cooling with the furnace; then polishing to remove the outer shell.

7. The preparation method according to claim 4, characterized in that: In step three, the graphite substrate surface, after the SiC dense transition and sealing layer deposition has been completed, is coated with a slurry to deposit a ZrC porous heat insulation and strain tolerance layer. The raw materials include 10%-20% by weight of pore-forming agent, 3%-4% by weight of binder, 1%-2% by weight of dispersant, 20%-30% by weight of solvent, and the balance ZrC powder. Sintering is carried out under an argon atmosphere for 60-120 min at a temperature of 1800℃-2000℃, with a heating rate of 5-7℃ / min, and a porosity of 30%-50%.

8. The preparation method according to claim 7, characterized in that: The pore-forming agent includes polymethyl methacrylate; the binder includes PVB; the dispersant includes PVP; and the solvent includes anhydrous ethanol.

9. The preparation method according to claim 4, characterized in that: In step four, the plasma spraying method involves the powder-feeding spray gun being perpendicular to the graphite substrate surface. The powder used in the plasma spraying method is HfC-TaC powder, which is a composite powder with a molar ratio of 1:1 to 1:

3. The plasma gas is Ar, the power is 40-60kW, the spraying distance is 100-140mm, the powder feeding rate is 20-30g / min, and the spray gun moving speed is 500-800mm / s.

10. The application of a graphite ablation-resistant composite coating according to any one of claims 1 to 3 in a high-energy discharge environment.

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