An anti-ablation coating with a grass grid structure and its preparation method

Abstract

This invention relates to an anti-ablation coating with a grass-grid structure and its preparation method. First, uniformly sized spherical carbide and oxide powders are prepared using spray granulation technology as raw materials for coating preparation. Next, the substrate material is fixed in a tooling mold, and a strip-shaped metal mesh is passed through narrow slots on both sides of the tooling mold and secured with bolts, ensuring close adhesion between the metal mesh and the substrate material surface. Then, spherical carbide powder is sprayed onto the substrate surface using atmospheric plasma spraying to prepare a carbide inner coating with a columnar array structure. Finally, an oxide layer is sprayed onto the substrate material surface with the carbide coating to seal the gaps between the columns, completing the preparation of the grass-grid coating. By introducing the grass-grid structure, the interfacial bonding area between coating layers is increased, forming a mechanically interlocking structure, achieving windproof and erosion-resistant functional characteristics similar to grass-grid, and realizing long-life ablation resistance of the coating in ultra-high temperature, high-erosion plasma ablation environments.

Description

Technical Field

[0001] This invention belongs to the field of coating technology and relates to an anti-ablation coating with a grass grid structure and its preparation method. Background Technology

[0002] With the continuous increase in the carrying capacity demands of commercial space launch vehicles, their hot-end components, such as engine combustion chambers, nozzles, and diffusers, need to withstand higher service temperatures and more intense airflow erosion and thermochemical ablation. Traditional ablation protection technologies for hot-end components of launch vehicles are no longer adequate to meet the urgent needs of high-load flights, necessitating the introduction of ablation-resistant coatings on the surface of these components to ensure reliable service under extreme conditions. However, the ultra-high temperatures and strong airflow erosion in ablation environments continuously act on the coating surface, easily causing coating peeling, cracking, and substrate oxidation failure, severely shortening the service life of hot-end components and restricting their overall service reliability and endurance. Against this backdrop, higher and more stringent technical requirements have been placed on the ablation resistance, erosion resistance, thermal stability, and long service life performance of protective coatings for hot-end components of launch vehicles. High-performance, long-life ablation-resistant coatings have become a key research focus and breakthrough direction for core protection technologies of launch vehicles.

[0003] Currently, various ablation-resistant coating structures have been developed both domestically and internationally to meet the technical requirements for ablation protection of hot-end components of aircraft. The authors systematically reviewed and summarized these structures in the literature "XX Li, QG Fu, ZH Wen, et al. Research Progress on Ultra-high Temperature Ceramic Structural Materials for Extreme Environments [J], Journal of Inorganic Materials, 2025, 40(10): 1045-1078". Most existing mainstream ablation-resistant coatings adopt a multi-layer composite structure design, generally using composition gradient control and alternating stacking of multiple materials to balance the coating's high-temperature resistance, thermal expansion matching, and interfacial bonding performance, thereby adapting to ultra-high temperature service environments and achieving effective protection for hot-end components of aircraft. Although existing ablation-resistant coatings can effectively alleviate the technical drawbacks of poor thermal stability, interfacial stress concentration, and easy delamination of single coating materials, they can exhibit good ablation resistance under short-term ultra-high temperature and strong erosion ablation conditions, meeting the protection requirements of short-term, intermittent flight. However, under prolonged high-load flight conditions, existing multilayer coatings have significant technical shortcomings. The interfaces between alternating layers are highly susceptible to defects such as interface debonding, microcrack propagation, and interlayer peeling under the combined effects of long-term thermal shock and high-speed, high-temperature airflow. Furthermore, compositional gradient structures can experience elemental diffusion and component failure in long-term high-temperature environments, leading to a rapid decline in the overall protective performance of the coating. Therefore, existing traditional multilayer ablation-resistant coatings can only provide short-term effective protection under extreme conditions and cannot meet the ablation resistance requirements of long-term stable service for hot-end components of aircraft.

[0004] Therefore, given the technical bottleneck of existing multi-layered alternating and compositional gradient ablation-resistant coatings that are prone to cracking and peeling after long-term ablation, it is urgent to develop a new coating structure that does not experience catastrophic cracking and peeling in long-term, high-impact ablation environments. This would enable long-term stable protection of hot-end components of spacecraft under extreme conditions of ultra-high temperature and high impact, significantly extending the service life of hot-end components and perfectly meeting the technical requirements of the next generation of long-endurance commercial space launch vehicles. Summary of the Invention

[0005] Technical problems to be solved To overcome the shortcomings of existing technologies, this invention proposes an anti-ablation coating with a grass checkerboard structure and its preparation method. By referencing the principle of windbreak and sand fixation using grass checkerboard structures in deserts, a double-layer coating composed of carbides on the inside and oxides on the outside is designed. By introducing a special structure that couples a columnar array of carbides with the oxide gap-sealing, the bottleneck problem of existing anti-ablation coatings easily cracking and peeling off in ultra-high temperature and strong erosion environments, thus failing to provide protection, is solved.

[0006] Technical solution A lattice-structured ablation-resistant coating is characterized by: a double-layer structure consisting of an outer lattice-resistant oxide layer and an inner ultra-high temperature ceramic carbide layer; the inner ultra-high temperature ceramic carbide layer is attached to the substrate material and has an array column structure; an lattice-resistant oxide layer is sprayed onto the surface of the ultra-high temperature ceramic carbide layer to seal the gaps between the columns, thus obtaining a lattice-structured ablation-resistant coating; the carbide layer and oxide layer in the lattice structure form an interfacial mechanical interlock; the mass ablation rate and linear ablation rate of the ablation-resistant coating after being subjected to Ar-H2 plasma ablation at an internal pressure of 3.0-3.5 MPa and a high temperature of 3000-3200 ℃ for 500 s are as low as -0.16 mg / s and -0.78 μm / s, respectively.

[0007] The size of the array pillars is 250-450 μm.

[0008] A method for preparing an ablation-resistant coating with a grass-grid structure, characterized by the following steps: Step 1: Prepare spherical oxide powder and carbide powder with uniform particle size using spray granulation technology; the average particle size of the spherical carbide and oxide powder is 50~75 μm; Step 2: Cover the surface of the substrate material with a metal mesh that serves as a mask, and ensure that the metal mesh adheres tightly to the substrate material; Step 3: Using spherical carbide powder as raw material, an inner carbide coating is prepared by atmospheric plasma spraying on the surface of the substrate material to obtain a carbide inner coating with an array column structure; after spraying, the coating is allowed to cool to room temperature in a mold fixture. During the process of spraying the carbide inner coating, the power of the plasma spray gun is 38-44 kW, the flow rate of the main gas Ar is 70-75 L / min, the flow rate of the auxiliary gas H2 is 2-4 L / min, the flow rate of the powder carrier gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 2.5-4.0 rpm. Step 4: Remove the metal mesh and tooling mold, perform ultrasonic cleaning and drying on the coated substrate material; then use spherical oxide powder as raw material and use atmospheric plasma spraying to prepare an oxide layer on the surface of the carbide inner coating to obtain an ablation-resistant coating with a grass grid structure. During the process of spraying the oxide layer, the power of the plasma spray gun is 45-55 kW, the flow rate of the main gas Ar is 65-70 L / min, the flow rate of the auxiliary gas H2 is 3-5 L / min, the flow rate of the powder carrier gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 1.5-2.5 rpm.

[0009] The mask is a metal mesh with a aperture size of 40-80 mesh, and the mesh shape is square. The metal mesh is made of high melting point metals such as Fe, Ni, Ti, Ta, and W.

[0010] Step 2 uses a tooling mold to fix the metal mesh and the base material. The tooling mold has a groove in the middle that matches the size of the base material, and narrow slits on both sides. The base material is fixed in the groove, the metal mesh covers the base material, and is fixed in the tooling mold with bolts after passing through the narrow slits on both sides.

[0011] Before each spraying, the substrate needs to be pretreated. The first time, compressed air of 0.8-1.0 MPa is used to blow and clean the surface of the substrate material to fully remove impurities and improve the bonding strength of the subsequent carbide coating. The second time, the substrate material with the carbide coating is placed in anhydrous ethanol and cleaned and dried using an ultrasonic cleaner and an electric heating drying oven, respectively.

[0012] The types of matrix materials include carbon / carbon composite materials, ceramic matrix composite materials, or ceramic-modified carbon / carbon composite materials.

[0013] In step 1, when preparing spherical oxide powder and carbide powder, the initial powder raw material is selected with a particle size of 300 mesh sieve, PVA aqueous solution with a solid content of 2.0 wt.% is used as binder, and anhydrous ethanol and deionized water are used as solvents. The above four are mixed in a mass ratio of 4:4 to 6:1:1 to prepare the slurry. The spherical carbide powder in step 1 includes monocomponent carbides, multiphase carbides, multicomponent carbides, high-entropy carbides, micro-nano toughened carbides, or biomimetic carbides based on plant roots; the composition consists of transition metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W or rare earth metals Sc, Y and La-series elements and C.

[0014] The spherical oxide powder contains monocomponent oxides, multicomponent oxides, and high-entropy oxides with melting points higher than 2500 °C; the constituent elements are 1 to 2 of Hf and Zr, and it contains 0 mol.% to 25 mol.% of Ti, Ta, Sc, Y, and La-based elemental modifiers.

[0015] Beneficial effects This invention proposes an anti-ablation coating with a checkerboard structure and its preparation method. Inspired by the windbreak and sand-fixing principle of checkerboard structures in deserts, a coating microstructure similar to checkerboard is designed. First, uniformly sized spherical carbide and oxide powders are prepared using spray granulation technology as raw materials for coating preparation. Next, the substrate material is fixed in a tooling mold, and a strip-shaped metal mesh is passed through narrow slots on both sides of the tooling mold and secured with bolts, ensuring close adhesion between the metal mesh and the substrate surface. Then, spherical carbide powder is sprayed onto the substrate surface using atmospheric plasma spraying to prepare a carbide inner coating with a columnar array structure. Finally, an oxide layer is sprayed onto the substrate surface with the carbide coating to seal the gaps between the columns, completing the preparation of the checkerboard coating. By introducing the checkerboard structure, the interfacial bonding area between coating layers is increased, forming a mechanically interlocking structure, achieving windbreak and erosion resistance similar to checkerboard structures, and realizing long-life ablation resistance in ultra-high temperature, high-erosion plasma ablation environments.

[0016] The ablation-resistant coating with a checkerboard artificial structure prepared by the method of this invention exhibits excellent ablation resistance and protective reliability in high-temperature, high-impact ablation environments. The ablation-resistant coating with a checkerboard artificial structure prepared in the examples of this invention, after being subjected to Ar-H2 plasma ablation at an internal pressure of 3.0-3.5 MPa and a high temperature of 3000-3200 ℃ for 500 s, showed a mass ablation rate and a linear ablation rate as low as -0.16 mg / s and -0.78 μm / s, respectively, which are 112%~132% lower than that of traditional double-layer ablation-resistant coatings, demonstrating superior ablation resistance. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation process of the ablation-resistant coating with a grass-grid artificial structure in this invention. Figure 2 The diagram illustrates the grass checkerboard coating structure and its preparation process according to the present invention, wherein: (a) a reference photograph of an artificial grass checkerboard structure in the desert; (b) a schematic diagram of the preparation process of the grass checkerboard coating; and (c) a schematic diagram of the structure of the grass checkerboard coating. During the spraying process, a carbide coating is deposited inside the mesh to form a columnar coating, followed by further spraying of an oxide coating to fill the pores between the columns and form an oxide coating. The carbide coating and the oxide coating combine to form a checkerboard microstructure, which is highly similar to the target grass checkerboard structure. Figure 3 This invention provides a tooling mold for preparing a grass checkerboard coating, comprising: a schematic diagram of the mold structure; mold drawings and detailed dimensions; Figure 4These are macroscopic and microscopic images of the surface morphology of the carbide internal coating prepared according to the present invention, wherein: (ab) is a ZrC internal coating prepared using a metal mesh with an 80-mesh mask; (cd) is a ZrC internal coating prepared using a metal mesh with a 60-mesh mask; and (ef) is a ZrC internal coating prepared using a metal mesh with a 40-mesh mask. The carbide coating exhibits a typical columnar array morphology, with intact carbide column structures and no obvious collapse or cracking. The size of the carbide columns is 250-450 μm, showing a regular and ordered array arrangement. Figure 5 The images show the macroscopic surface morphology of the checkered pattern coating in this invention before and after plasma ablation, where: (ab) YSZ / ZrC coating; (cd) YSZ / ZrC-80 coating; (ef) YSZ / ZrC-60 coating; (gh) YSZ / ZrC-40 coating. After 500 s of plasma ablation, the comparative YSZ / ZrC double-layer coating was completely eroded away, exposing the substrate material. The mass ablation rate and linear ablation rate of the coating were 1.32 mg / s and 2.43 μm / s, respectively, indicating that the protective effect of the coating had completely failed. The YSZ / ZrC-80 and YSZ / ZrC-60 coatings showed local cracking and peeling after ablation, indicating their effective protection against high-temperature and high-pressure plasma flow. The YSZ / ZrC-40 coating exhibits optimal ablation resistance. After ablation, the surface shows no obvious large-sized cracks or pores. The mass ablation rate and linear ablation rate are -0.16 mg / s and -0.78 μm / s, respectively, representing a reduction of 112%–132% compared to the comparative YSZ / ZrC bilayer coating. Figure 6 This is an example of fixing the substrate material in the tooling mold in an embodiment of the present invention; a photo of the mold fixing the substrate during the spraying process. The tooling mold can stably fix the substrate material and make the metal mesh closely adhere to the surface of the substrate material. This can ensure that the substrate material is not swept away or moved by the plasma flame during the spraying process, and can also ensure that the carbide coating with columnar array structure is effectively deposited. Detailed Implementation The present invention will now be further described in conjunction with the embodiments and accompanying drawings: To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0018] This invention is achieved through the following technical solution: The primary objective of this invention is to propose an ablation-resistant coating with a grass-grid artificial structure. The coating comprises a two-layer structure: an outer ablation-resistant oxide layer and an inner ultra-high temperature ceramic carbide layer. The inner coating is prepared by plasma spraying using a 40-80 mesh metal mesh as a mask, giving the ultra-high temperature ceramic carbide layer a columnar array microstructure with column dimensions of 250-450 μm. Subsequently, the gaps between the array columns are filled by spraying an ablation-resistant oxide layer, constructing a unique grass-grid-like coating structure. The oxide layer, possessing high bonding strength and high erosion resistance, exhibits a grid network structure at the interface between the two coating layers, which can be considered as the sand barrier portion of a grass-grid artificial structure in a desert. The carbide layer, with its antioxidant and ablation-resistant properties, exhibits an array of columnar microstructures at the interface, which can be considered as the inner grid region suitable for plant growth in a desert grass-grid artificial structure. The oxide and carbide layers are tightly bonded at the interface, and the larger contact area promotes a stronger physical bond between the two layers through intermolecular forces. By introducing this grass-like grid structure, the interfacial bonding area between the inner and outer coatings is increased, forming a mechanical interlocking structure. This achieves windproof and erosion-resistant functional characteristics similar to grass grids, enabling the coating to have a long lifespan and resist ablation in plasma ablation environments with high-speed flame erosion.

[0019] The second objective of this invention is to provide a method for preparing an ablation-resistant coating with a grass-grid artificial structure, comprising the following steps: S1, using spray granulation technology to prepare spherical oxide powder and carbide powder with uniform particle size; Preferably, the spray granulation process uses carbide and oxide powders with a particle size of 300 mesh as raw materials, PVA aqueous solution with a solid content of 2.0 wt.% as binder, and anhydrous ethanol and deionized water as solvents. The above four are mixed in a mass ratio of 4:4 to 6:1:1 to prepare the slurry.

[0020] Further optimization revealed that a uniform slurry of carbides and oxides was prepared by ball milling. The ball milling speed and time were 300-400 rpm and 4-8 hours, respectively, to ensure that the carbide powder and oxide powder were fully dispersed in the slurry.

[0021] Further optimization revealed that a peristaltic pump was used to transport the slurry to a spray dryer to prepare spherical carbide and oxide powders, with the peristaltic pump rotating at 18-22 rpm.

[0022] Further optimization revealed that the atomizing nozzle speed and inlet / outlet temperature of the spray dryer were set to 35~38 rpm, 330~350 ℃, and 100~120 ℃, respectively.

[0023] Further optimization revealed that the obtained spherical carbide and spherical oxide powders need to be sieved sequentially through a 200-mesh sieve and a 300-mesh sieve to homogenize the powder particle size to 50~75 μm.

[0024] S2, use bolts to fix the base material in the tooling mold, cut the metal mesh into strips, pass the metal mesh through the narrow slots on both sides of the tooling mold and tighten it with bolts, so that the metal mesh is closely attached to the surface of the base material; Preferably, the tooling mold for fixing the base material and the metal mesh is a hollow square, with a narrow slit of 1 mm width on each side of the hollow part for inserting the metal mesh. The metal mesh in the narrow slit is fixed by bolts on both sides to ensure that the metal mesh is tightly attached to the surface of the base material.

[0025] More preferably, the metal mesh used has an aperture size of 40-80 mesh, a square mesh shape, and is made of high-melting-point metals such as Fe, Ni, Ti, Ta, or W.

[0026] Preferably, compressed air at 0.8-1.0 MPa is used to purge and clean the surface of the substrate material to fully remove impurities from the surface of the substrate material and improve the bonding strength of the carbide coating prepared by subsequent plasma spraying.

[0027] S3 uses spherical carbide powder as raw material and atmospheric plasma spraying equipment to prepare an inner layer of carbide coating on the surface of the substrate material. Molten carbide powder passes through the holes of the metal mesh and is deposited on the substrate surface to form an inner coating with an array column structure. More preferably, during the carbide coating spraying process, the plasma spray gun has a power of 38-44 kW, the main gas Ar flow rate is 70-75 L / min, the auxiliary gas H2 flow rate is 2-4 L / min, the powder carrier gas Ar flow rate is 6-10 L / min, and the powder feeder rotation speed is 2.5-4.0 rpm.

[0028] Preferably, after the carbide coating is applied, the coated substrate is left to stand in the mold fixture for 5-10 minutes to allow the sample to cool fully to room temperature.

[0029] More preferably, the substrate material with the carbide coating is placed in anhydrous ethanol and cleaned in an ultrasonic cleaner for 5-15 minutes, and then placed in an electric heating drying oven at 70-90 ℃ for 10-30 minutes to dry thoroughly.

[0030] S4, Remove the metal mesh and tooling mold, use spherical oxide powder as raw material, and use atmospheric plasma spraying equipment to prepare an oxide layer on the surface of the carbide inner coating to construct a grass grid structure, thus completing the preparation of the anti-ablation coating of the present invention.

[0031] More preferably, during the oxide coating spraying process, the plasma spray gun has a power of 45-55 kW, the main gas Ar flow rate is 65-70 L / min, the auxiliary gas H2 flow rate is 3-5 L / min, the powder carrier gas Ar flow rate is 6-10 L / min, and the powder feeder rotation speed is 1.5-2.5 rpm.

[0032] The ablation-resistant coating with a checkerboard artificial structure prepared by the above-described method exhibits excellent ablation resistance and reliable protection in high-temperature, high-scouring ablation environments. The ablation-resistant coating with a checkerboard artificial structure prepared in the examples described in this invention, after being subjected to Ar-H2 plasma ablation at an internal pressure of 3.0-3.5 MPa and a high temperature of 3000-3200 ℃ for 500 s, showed a mass ablation rate and a linear ablation rate as low as -0.16 mg / s and -0.78 μm / s, respectively. Compared with traditional double-layer ablation-resistant coatings, these figures are reduced by 112%~132%, demonstrating superior ablation resistance. Specific implementation examples: See Figure 1 This is a schematic diagram of the preparation process of the ablation-resistant coating with a grass checkerboard artificial structure in this invention, specifically including the following steps: Step 1: Weigh the carbide powder and oxide powder with a 2.0 wt.% solid content PVA aqueous solution, anhydrous ethanol, and deionized water at a mass ratio of 4:4~6:1:1 and place them in a polytetrafluoroethylene ball mill jar. Use ZrO2 ceramic balls as the grinding media and ball mill for 4~8 hours to obtain a uniformly mixed slurry. Set the milling speed to 300~400 rpm. Use a peristaltic pump to deliver the slurry to a spray dryer at a speed of 18~22 rpm. Atomize the slurry through a nozzle at a speed of 35~38 rpm and spray granulate at 330~350 ℃. Finally, sieve using 200 mesh and 300 mesh screens to obtain spherical carbide and oxide powder with a particle size of 50~75 μm.

[0034] Step 2: Use bolts to fix the base material in the tooling mold. Use scissors to cut the 40-80 mesh metal mesh into strips. Pass the cut metal mesh through the narrow slots on both sides of the tooling mold. Use M5 stainless steel bolts to tighten the metal mesh in the narrow slots to prevent the metal mesh from moving under the action of the flame during the subsequent plasma spraying process, and press it to make the metal mesh fit tightly against the surface of the base material.

[0035] Step 3: The mold with the substrate material is placed in an atmospheric plasma spraying device, and the surface of the substrate material is purged and cleaned using compressed air at 0.8-1.0 MPa. Subsequently, a carbide coating is prepared on the surface of the substrate material using spherical carbide powder as raw material. During the spraying process, the power of the plasma spray gun is 38-44 kW, the flow rate of the main gas Ar is 70-75 L / min, the flow rate of the auxiliary gas H2 is 2-4 L / min, the flow rate of the powder-carrying gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 2.5-4.0 rpm. During the spraying process, the carbide powder melts in the ultra-high temperature plasma flame to form droplets, which are rapidly deposited on the substrate surface under the drive of the Ar gas flow, forming a carbide inner coating with a columnar array structure.

[0036] Step 4: After the carbide coating is applied, allow the sample to cool to room temperature. Loosen the M5 stainless steel bolts on both sides of the mold fixture and remove the metal mesh and the mold fixture. Place the sample in anhydrous ethanol and clean it with an ultrasonic cleaner for 5-15 minutes to thoroughly remove any unmelted carbide powder residue on the surface. Place the cleaned sample in an electric heating drying oven at 70-90 ℃ and let it stand for 10-30 minutes to remove any residual wastewater ethanol. Subsequently, using spherical oxide powder as raw material, an oxide layer is prepared on the surface of the substrate material with the carbide coating using an atmospheric plasma spraying device, completing the preparation of the grass checkerboard coating described in this invention. During the spraying process, the power of the plasma spray gun is 45-55 kW, the flow rate of the main gas Ar is 65-70 L / min, the flow rate of the auxiliary gas H2 is 3-5 L / min, the flow rate of the powder carrier gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 1.5-2.5 rpm.

[0037] Example 1 Commercial ZrC powder with a particle size of 1-3 μm and 12 mol.% yttrium-stabilized zirconia (YSZ) powder with a particle size of 10-12 μm were weighed with 2.0 wt.% PVA aqueous solution, anhydrous ethanol and deionized water at a mass ratio of 4:4:1:1 and placed in a polytetrafluoroethylene ball mill jar. The ball mill jar was fixed in a planetary ball mill and mixed for 8 hours to obtain a uniform slurry. ZrO2 ceramic balls were used as grinding media during the mixing process, and the speed of the planetary ball mill was set to 400 rpm. The uniformly mixed slurry and ZrO2 ceramic balls were separated using a filter screen. The uniformly mixed slurry was placed in a beaker and transported to a spray dryer using a peristaltic pump at a speed of 18 rpm. The inlet and outlet temperatures of the spray dryer were set to 350 ℃ and 120 ℃, respectively. The slurry was atomized and dried by a nozzle at a speed of 35 rpm to form spherical ZrC powder and YSZ powder. Finally, the powder was sieved using 200-mesh and 300-mesh screens to obtain spherical ZrC powder and YSZ powder with a particle size of 50~75 μm.

[0038] Use bolts to fix the C / C composite material in the tooling mold. Use scissors to cut the 40-mesh iron mesh into strips. Pass the cut metal mesh through the narrow slots on both sides of the tooling mold. Use M5 stainless steel bolts to tighten the metal mesh in the narrow slots to prevent the metal mesh from moving under the action of the flame during the subsequent plasma spraying process, and press it to make the metal mesh fit tightly against the surface of the substrate material.

[0039] A tooling mold containing C / C composite material was placed in an atmospheric plasma spraying device, and the surface of the C / C substrate was purged and cleaned using compressed air at 1.0 MPa. Spherical ZrC powder prepared by spray granulation was used as raw material to prepare a ZrC coating on the C / C substrate surface. During the spraying process, the plasma spray gun power was 44 kW, the main gas Ar flow rate was 70 L / min, the auxiliary gas H2 flow rate was 3 L / min, the powder carrier gas Ar flow rate was 6 L / min, and the powder feeder rotation speed was 2.5 rpm. During the spraying process, the ZrC powder melted in the ultra-high temperature plasma flame to form droplets, which, driven by the Ar gas flow, rapidly passed through the pores of the metal mesh and deposited on the substrate surface to form an array of ZrC pillars, with the ZrC pillars having a size of approximately 450 μm.

[0040] After the ZrC coating is applied, the coated sample is left to stand for 10 minutes to cool to room temperature. The M5 stainless steel bolts on both sides of the mold fixture are loosened, and the 40-mesh iron mesh and mold fixture are removed. The sample is placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 10 minutes to thoroughly remove any unmelted ZrC powder residue from the surface. The cleaned ZrC-coated C / C sample is then placed in an 80°C electric heating drying oven and left to stand for 30 minutes to remove any residual wastewater ethanol. Using spherical YSZ powder as raw material, an atmospheric plasma spraying device is used to prepare a YSZ coating on the surface of the ZrC-coated substrate material, completing the preparation of the checkered pattern coating described in this invention. During the spraying process, the plasma spray gun power is 55 kW, the main gas Ar flow rate is 70 L / min, the auxiliary gas H2 flow rate is 5 L / min, the powder carrier gas Ar flow rate is 10 L / min, and the powder feeder speed is 2.5 rpm.

[0041] Example 2 ZrC powder was prepared by carbothermal reduction at 1900 ℃. ZrC powder with a particle size of 300 mesh and commercial YSZ powder with a particle size of 10-12 μm were weighed with PVA aqueous solution with a solid content of 2.0 wt.%, anhydrous ethanol and deionized water in a mass ratio of 4:5:1:1 and placed in a polytetrafluoroethylene ball mill jar. The ball mill jar was fixed in a planetary ball mill and mixed for 6 hours to obtain a uniform slurry. ZrO2 ceramic balls were used as grinding media during the mixing process and the speed of the planetary ball mill was set to 350 rpm. The uniformly mixed slurry and ZrO2 ceramic balls were separated using a filter screen. The uniformly mixed slurry was placed in a beaker and transported to a spray dryer using a peristaltic pump at a speed of 20 rpm. The inlet and outlet temperatures of the spray dryer were set to 330℃ and 100℃, respectively. The slurry was atomized and dried by a nozzle at a speed of 37 rpm to form spherical ZrC powder and YSZ powder. Finally, the powder was sieved using 200-mesh and 300-mesh screens to obtain spherical ZrC powder and YSZ powder with a particle size of 50~75 μm.

[0042] Use bolts to fix the C / C-SiC composite material in the tooling mold. Use scissors to cut a 60-mesh tungsten mesh into strips. Pass the cut metal mesh through the narrow slots on both sides of the tooling mold. Use M5 stainless steel bolts to tighten the metal mesh in the narrow slots to prevent the metal mesh from moving under the action of the flame during the subsequent plasma spraying process, and press it to make the metal mesh fit tightly against the surface of the substrate material.

[0043] The mold for the C / C-SiC composite material was placed in an atmospheric plasma spraying device, and the surface of the C / C-SiC substrate was purged and cleaned using compressed air at 0.95 MPa. Spherical ZrC powder prepared by spray granulation was used as raw material to prepare a ZrC coating on the C / C-SiC substrate surface. During the spraying process, the plasma spray gun power was 40 kW, the main gas Ar flow rate was 72 L / min, the auxiliary gas H2 flow rate was 2.5 L / min, the powder carrier gas Ar flow rate was 8 L / min, and the powder feeder rotation speed was 3.0 rpm. During the spraying process, the ZrC powder melted in the ultra-high temperature plasma flame to form droplets, which, driven by the Ar gas flow, rapidly passed through the pores of the metal mesh and deposited on the substrate surface to form an array of ZrC pillars, with the ZrC pillars having a size of approximately 330 μm.

[0044] After the ZrC coating is applied, the coated sample is left to stand for 8 minutes to cool to room temperature. The M5 stainless steel bolts on both sides of the mold fixture are loosened, and the 60-mesh tungsten mesh and mold fixture are removed. The sample is placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 5 minutes to thoroughly remove any unmelted ZrC powder residue from the surface. The cleaned ZrC-coated C / C sample is then placed in a 90°C electric heating drying oven and left to stand for 10 minutes to remove any residual wastewater ethanol. Using spherical YSZ powder as raw material, an atmospheric plasma spraying device is used to prepare a YSZ coating on the surface of the ZrC-coated substrate material, completing the preparation of the checkered pattern coating described in this invention. During the spraying process, the plasma spray gun power is 50 kW, the main gas Ar flow rate is 68 L / min, the auxiliary gas H2 flow rate is 4.2 L / min, the powder carrier gas Ar flow rate is 6 L / min, and the powder feeder speed is 1.5 rpm.

[0045] Example 3 ZrC powder was prepared by carbothermal reduction at 1900 ℃, and YSZ powder was prepared by solid-state reaction sintering at 1600 ℃. ZrC powder and YSZ powder with a particle size of 300 mesh were weighed with PVA aqueous solution with a solid content of 2.0 wt.% in a mass ratio of 4:6:1:1 and placed in a polytetrafluoroethylene ball mill jar. The ball mill jar was fixed in a planetary ball mill and mixed for 4 hours to obtain a uniform slurry. ZrO2 ceramic balls were used as grinding media during the mixing process, and the speed of the planetary ball mill was set to 300 rpm. The uniformly mixed slurry and ZrO2 ceramic balls were separated using a filter screen. The slurry was then placed in a beaker and pumped into a spray dryer at 22 rpm using a peristaltic pump. The inlet and outlet temperatures of the spray dryer were set to 340 ℃ and 110 ℃, respectively. The slurry was atomized and dried by a nozzle at 38 rpm to form spherical ZrC powder and YSZ powder. Finally, the powder was sieved using 200-mesh and 300-mesh screens to obtain spherical ZrC powder and YSZ powder with a particle size of 50~75 μm.

[0046] Use bolts to fix the C / C-ZrC-SiC composite material in the tooling mold. Use scissors to cut the 80-mesh tungsten mesh into strips. Pass the cut metal mesh through the narrow slots on both sides of the tooling mold. Use M5 stainless steel bolts to tighten the metal mesh in the narrow slots to prevent the metal mesh from moving under the action of the flame during the subsequent plasma spraying process, and press it to make the metal mesh fit tightly against the surface of the substrate material.

[0047] The mold for the C / C-ZrC-SiC composite material was placed in an atmospheric plasma spraying device, and the surface of the C / C-ZrC-SiC substrate was purged and cleaned with compressed air at 0.8 MPa. A ZrC coating was prepared on the C / C-ZrC-SiC substrate surface using spherical ZrC powder prepared by spray granulation. During the spraying process, the plasma spray gun power was 38 kW, the main gas Ar flow rate was 75 L / min, the auxiliary gas H2 flow rate was 2 L / min, the powder carrier gas Ar flow rate was 10 L / min, and the powder feeder rotation speed was 4.0 rpm. During the spraying process, the ZrC powder melted in the ultra-high temperature plasma flame to form droplets, which, driven by the Ar gas flow, rapidly passed through the pores of the metal mesh and deposited on the substrate surface to form an array of ZrC pillars with a size of approximately 250 μm.

[0048] After the ZrC coating is applied, the coated sample is left to stand for 5 minutes to cool to room temperature. The M5 stainless steel bolts on both sides of the mold fixture are loosened, and the 80-mesh tungsten mesh and mold fixture are removed. The sample is placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 15 minutes to thoroughly remove any unmelted ZrC powder residue from the surface. The cleaned ZrC-coated C / C sample is then placed in a 70°C electric heating drying oven and left to stand for 20 minutes to remove any residual wastewater ethanol. Using spherical YSZ powder as raw material, an atmospheric plasma spraying device is used to prepare a YSZ coating on the surface of the ZrC-coated substrate material, completing the preparation of the checkered pattern coating described in this invention. During the spraying process, the plasma spray gun power is 45 kW, the main gas Ar flow rate is 65 L / min, the auxiliary gas H2 flow rate is 3 L / min, the powder carrier gas Ar flow rate is 8 L / min, and the powder feeder speed is 2.0 rpm.

[0049] Comparative Example 1 To compare the ablation resistance of the grass-grid coating prepared in this invention, a double-layer YSZ / ZrC coating without the grass-grid artificial structure was prepared using a conventional atmospheric plasma spraying process. The composition of each layer and its spraying process parameters were consistent with those of Comparative Examples 1-3. The conventional double-layer YSZ / ZrC coating suffered severe peeling after 500 s of high-temperature, high-abrasion-intensity plasma flame ablation, fully exposing the substrate material. This indicates that the protective capability of the double-layer YSZ / ZrC coating is insufficient to withstand the erosion and ablation of high-temperature, high-speed flame. The mass ablation rate and linear ablation rate of the coating after ablation were 1.32 mg / s and 2.43 μm / s, respectively. Compared with the YSZ / ZrC-40 coating in Example 3 (-0.16 mg / s and -0.78 μm / s), the ablation rates were reduced by 112% and 132%, respectively. This demonstrates that the ablation-resistant coating with the grass-grid artificial structure proposed in this invention and its preparation technology can significantly improve the protective life and performance of the coating in ultra-high temperature, high-abrasion ablation environments.

[0050] Test example: Figure 1 This is a flowchart illustrating the preparation process of the ablation-resistant coating with a grass-grid artificial structure in this invention. Figure 2 The diagram shows the structure of the grass checkerboard coating prepared according to the present invention and its preparation process, wherein: (a) a reference photograph of the artificial grass checkerboard structure in the desert; (b) a schematic diagram of the preparation process of the grass checkerboard coating; and (c) a schematic diagram of the structure of the grass checkerboard coating. It can be seen that the grass checkerboard used for sand control in the desert is formed by artificially burying windbreak straw or stalks, which can prevent the growth of plants inside the checkerboard from being eroded and damaged by wind and sand. The present invention uses a metal mesh as a mask, allowing the carbide coating to deposit inside the mesh openings during the spraying process, forming a columnar coating. Subsequently, an oxide coating is further sprayed to fill the gaps between the columns and form an oxide coating. The oxide coating with anti-ablation flame erosion properties is considered as a simulation of the artificial grass checkerboard structure, avoiding the pulverization and oxidation failure of the carbide coating inside the checkerboard during the ablation process due to high-speed flame erosion, thus achieving the beneficial effect of improving the coating's long lifespan and ablation resistance.

[0051] Figure 3 This is the tooling mold used in the present invention for preparing the grass checkerboard coating. During the spraying process, the substrate material is placed in the center of the mold. A metal mesh of appropriate size is passed through the narrow slits on both sides of the tooling mold and fixed with stainless steel bolts, so that the metal mesh is tightly and securely attached to the surface of the substrate material. Subsequently, the mold tooling with the substrate material is fixed together on the spraying worktable of the atmospheric plasma spraying equipment for subsequent preparation of the grass checkerboard coating.

[0052] Figure 4 These are macroscopic and microscopic images of the carbide internal coatings prepared in Examples 1-3 of this invention, wherein: (ab) is a ZrC internal coating prepared using a metal mesh with an 80-mesh mask; (cd) is a ZrC internal coating prepared using a metal mesh with a 60-mesh mask; and (ef) is a ZrC internal coating prepared using a metal mesh with a 40-mesh mask. It can be seen that voids with a metal mesh shape are formed on the surface of the substrate material, and the carbide coating exhibits a typical columnar array morphology. The microscopic images show that the carbide column structure in the coating is intact, without obvious collapse or cracking. The size of the carbide columns is 250-450 μm, exhibiting a regular and ordered array arrangement.

[0053] Figure 5The images show the surface macroscopic morphology of the YSZ / ZrC checkerboard coating and the YSZ / ZrC double-layer coating prepared in Examples 1-3 and Comparative Example 1 of this invention before and after plasma ablation for 500 s at an internal pressure of 3.0-3.5 MPa and a high temperature of 3000-3200 ℃. The coatings are: (ab) YSZ / ZrC coating; (cd) YSZ / ZrC-80 coating; (ef) YSZ / ZrC-60 coating; and (gh) YSZ / ZrC-40 coating. Before ablation, all four coatings exhibited a dense and complete macroscopic morphology without obvious cracks or pores. A faint array of microscopic morphological features can be observed on the surfaces of the three checkerboard coatings. After 500 s of plasma ablation, the comparative YSZ / ZrC bilayer coating was completely eroded away, exposing the substrate material. The mass ablation rate and linear ablation rate of the coating were 1.32 mg / s and 2.43 μm / s, respectively, indicating that the protective effect of the coating had completely failed. The YSZ / ZrC-80 and YSZ / ZrC-60 coatings showed localized cracking and peeling after ablation, demonstrating their effectiveness against high-temperature, high-pressure plasma flow. The YSZ / ZrC-40 coating exhibited the best ablation resistance; after ablation, the surface showed no obvious large cracks or pores, with a mass ablation rate of -0.16 mg / s and a linear ablation rate of -0.78 μm / s, respectively, representing a reduction of 112%–132% compared to the comparative YSZ / ZrC bilayer coating.

[0054] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An ablation-resistant coating with a grass-grid structure, characterized in that: The coating has a double-layer structure of an outer anti-ablation oxide layer and an inner ultra-high temperature ceramic carbide layer; the inner ultra-high temperature ceramic carbide layer is attached to the substrate material and has an array column structure; the anti-ablation oxide layer is sprayed on the surface of the ultra-high temperature ceramic carbide layer to seal the gaps between the columns, thus obtaining an anti-ablation coating with a grass grid structure. The carbide and oxide layers in the grass grid structure form an interlocking interface; the mass ablation rate and linear ablation rate of the anti-ablation coating after being subjected to Ar-H2 plasma ablation at an internal pressure of 3.0-3.5 MPa and a high temperature of 3000-3200 ℃ for 500 s are as low as -0.16 mg / s and -0.78 μm / s, respectively.

2. The ablation-resistant coating with a checkerboard structure according to claim 1, characterized in that: The size of the array pillars is 250-450 μm.

3. A method for preparing an anti-ablation coating with a grass-grid structure as described in claim 1 or 2, characterized in that... The steps are as follows: Step 1: Prepare spherical oxide powder and carbide powder with uniform particle size using spray granulation technology; the average particle size of the spherical carbide and oxide powder is 50~75 μm; Step 2: Cover the surface of the substrate material with a metal mesh that serves as a mask, and ensure that the metal mesh adheres tightly to the substrate material; Step 3: Using spherical carbide powder as raw material, an inner carbide coating is prepared by atmospheric plasma spraying on the surface of the substrate material to obtain a carbide inner coating with an array columnar structure. After spraying, allow the material to cool completely to room temperature in the mold fixture. During the process of spraying the carbide inner coating, the power of the plasma spray gun is 38-44 kW, the flow rate of the main gas Ar is 70-75 L / min, the flow rate of the auxiliary gas H2 is 2-4 L / min, the flow rate of the powder carrier gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 2.5-4.0 rpm. Step 4: Remove the metal mesh and tooling mold, perform ultrasonic cleaning and drying on the coated substrate material; then use spherical oxide powder as raw material and use atmospheric plasma spraying to prepare an oxide layer on the surface of the carbide inner coating to obtain an ablation-resistant coating with a grass grid structure. During the process of spraying the oxide layer, the power of the plasma spray gun is 45-55 kW, the flow rate of the main gas Ar is 65-70 L / min, the flow rate of the auxiliary gas H2 is 3-5 L / min, the flow rate of the powder carrier gas Ar is 6-10 L / min, and the rotation speed of the powder feeder is 1.5-2.5 rpm.

4. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: The mask is a metal mesh with a aperture size of 40-80 mesh, and the mesh shape is square. The metal mesh is made of high melting point metals such as Fe, Ni, Ti, Ta, and W.

5. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: Step 2 uses a tooling mold to fix the metal mesh and the base material. The tooling mold has a groove in the middle that matches the size of the base material, and narrow slits on both sides. The base material is fixed in the groove, the metal mesh covers the base material, and is fixed in the tooling mold with bolts after passing through the narrow slits on both sides.

6. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: Before each spraying, the substrate needs to be pretreated. The first time, compressed air of 0.8-1.0 MPa is used to blow and clean the surface of the substrate material to fully remove impurities and improve the bonding strength of the subsequent carbide coating. The second time, the substrate material with the carbide coating is placed in anhydrous ethanol and cleaned and dried using an ultrasonic cleaner and an electric heating drying oven, respectively.

7. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: The types of matrix materials include carbon / carbon composite materials, ceramic matrix composite materials, or ceramic-modified carbon / carbon composite materials.

8. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: In step 1, when preparing spherical oxide powder and carbide powder, the initial powder raw material is selected with a particle size of 300 mesh sieve, a PVA aqueous solution with a solid content of 2.0 wt.% is used as a binder, and anhydrous ethanol and deionized water are used as solvents. The above four are mixed in a mass ratio of 4:4 to 6:1:1 to prepare the slurry.

9. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: The spherical carbide powder in step 1 includes monocomponent carbides, multiphase carbides, multicomponent carbides, high-entropy carbides, micro-nano toughened carbides, or biomimetic carbides based on plant roots; the composition consists of transition metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W or rare earth metals Sc, Y and La-series elements and C.

10. The method for preparing the ablation-resistant coating with a grass-grid structure according to claim 3, characterized in that: The spherical oxide powder contains monocomponent oxides, multicomponent oxides, and high-entropy oxides with melting points higher than 2500 °C; the constituent elements are 1 to 2 of Hf and Zr, and it contains 0 mol.% to 25 mol.% of Ti, Ta, Sc, Y, and La-based elemental modifiers.

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