Based on SiC@M x O y Laser in-situ repair method for SiC ceramics or their composites coated with powder

Abstract

This invention discloses a SiC@M x O y A laser-assisted in-situ repair method for SiC ceramics or their composites coated with powder. The method includes: pretreatment of the damaged area; using a sol-gel method to gel a metal oxide precursor on the pretreated SiC surface and then crystallizing it through heat treatment to prepare a SiC-based composite material. x O y The shell is coated with powder; it is prepared into a repair slurry and coated onto the damaged area, dried to form a pre-formed layer; finally, laser in-situ sintering is used, utilizing M x O y The liquid-phase sintering of the shell promotes the tight bonding of SiC particles. This invention combines core-shell structured coated powder with laser in-situ forming technology, which not only reduces the sintering temperature and avoids overall high-temperature thermal damage, but also significantly improves the density and bonding strength of the repair layer, restoring the flexural strength of the material to more than 80% of its undamaged state.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramics technology, and more specifically, to a method based on SiC@M x O y A laser in-situ repair method for SiC ceramics or their composites coated with powder. Background Technology

[0002] SiC ceramics or their composites possess high specific strength, high specific modulus, excellent oxidation resistance, and low density, making them widely used in extreme service environments such as hot-end components of aerospace engines, gas turbine blades, and nuclear reactor cladding. However, during manufacturing and actual service, SiC ceramics or their composites are highly susceptible to microscopic and macroscopic damage, such as surface cracks, porosity, and localized erosion, caused by external factors like thermal shock, oxidation ablation, or mechanical wear. The continuous accumulation of these microscopic defects not only leads to a significant decrease in the material's mechanical properties and airtightness but may also induce localized thermal instability and catastrophic failure, severely limiting their service life and system reliability.

[0003] For the structural damage repair of SiC ceramics or their composites, the commonly used traditional processes in industry mainly include chemical vapor deposition (CVD), slurry coating, and repair agent repair. However, although CVD can obtain a high-density repair layer, its process is extremely complex, the repair cycle is long, and the manufacturing cost is high; although the slurry coating process is simple, the repair layer has extremely low density and limited interfacial bonding strength with the substrate; and the repair agent repair method is significantly insufficient in precision when dealing with complex morphologies or microscale defects, making it difficult to achieve accurate filling and microstructural reconstruction of localized damaged areas.

[0004] In recent years, the development of additive manufacturing and laser processing technologies has provided new ideas for the forming and repair of ceramic materials. For example, the paper "Core-shell powder strategy for additive manufacturing of ceramics: application to direct powder bed selective laser processing of silicon carbide" proposes a method to prepare core-shell structured powder by conformally coating SiC pre-ceramic onto the surface of SiC particles, thus solving the problem of directly using binder-free SiC for laser sintering. This has brought a technological breakthrough to the laser processing of ceramic materials. However, this research focuses on the field of additive manufacturing and does not provide a complete solution for the interfacial bonding and in-situ densification problems in the repair of local damage.

[0005] In specific laser repair and cladding applications, Chinese patent application CN 111455375 A discloses a laser cladding repair method for C / C composite SiC coatings. This method uses a Si-C-SiC composite slurry with silicon powder as a binder, pre-placed at the damaged area for laser cladding. Furthermore, the document "Spray drying as a one-step production method of SiC-based granules for direct reactive laser sintering of Reaction Bonded Silicon Carbide (RBSiC)" also introduces a latex carbon source into a mixed system and performs spray drying, using continuous laser to achieve reactive sintering of silicon carbide. However, the above-mentioned laser reactive sintering technologies have revealed significant drawbacks in practical applications: Si powder is commonly used as a binder, which easily leads to highly uneven cladding layer structure and high porosity due to uneven melt flow and insufficient reaction. More critically, low-melting-point Si phases remain, severely weakening the coating's density and high-temperature service stability.

[0006] To overcome the shortcomings of the aforementioned single process, the paper "Fabrication of SiC composites by selective laser sintering and reactive melt infiltration" proposes a new method for preparing SiC composites by combining selective laser sintering (SLS) and reactive melt infiltration (RMI). Although this process shows certain advantages in near-net-shape forming, its process flow is too cumbersome, highly dependent on multi-stage processes, and is also prone to introducing unstable phases such as residual Si and residual C. Moreover, this method requires overall high-temperature treatment, which not only easily causes secondary thermal damage to the matrix but also cannot meet the needs of local laser in-situ repair under complex working conditions.

[0007] In summary, current research on in-situ ceramic repair typically relies on simple physically mixed powders as raw materials. These powders exhibit low reactivity under laser irradiation and insufficient sintering driving force, readily initiating pores, microcracks, and loose interface phases in the repair zone, resulting in very limited bonding strength between the repair layer and the undamaged substrate. Although traditional ceramic sintering often incorporates oxide additives to improve densification, under conventional mechanical mixing conditions, oxides readily agglomerate and exhibit extremely uneven distribution, failing to exert an effective synergistic effect of liquid-phase reaction sintering during the rapid laser heating and cooling process.

[0008] Given the numerous shortcomings of existing technologies that use traditional physical powder mixing for repair, such as low reactivity, insufficient sintering driving force, easy retention of low-melting-point phases and microcracks, weak interfacial bonding strength, and difficulty in achieving both in-situ local repair and high density, there is an urgent need for a laser in-situ repair method for SiC ceramics or their composites that can significantly reduce sintering temperature, improve interfacial bonding strength, and avoid overall high-temperature damage. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a SiC@M x O y A laser in-situ repair method for SiC ceramics or their composites coated with powder is proposed to address the problems of low reactivity, insufficient sintering driving force, and low interfacial bonding strength of the repair layer caused by the traditional physical mixing of powders in the existing technology.

[0010] To overcome the shortcomings of the prior art, the present invention provides a SiC@M x O y A laser-assisted in-situ repair method for SiC ceramics or their composites coated with powder includes the following steps: S1: Damaged area pretreatment: The damaged area of ​​SiC ceramic or its composite material is flattened and cleaned to obtain a clean repair area; S2: Preparation of coated powder: SiC@M powder was prepared using the sol-gel method. x O y Core-shell coated powders include: S21: The surface-pretreated SiC powder is dispersed in a solvent to form a SiC suspension; S22: M containing metal oxide x O y The precursor is dissolved in a solvent, and a complexing agent is added to mix and form a precursor sol; S23: The precursor sol is mixed and reacted with the SiC suspension and the solvent is evaporated to gel the precursor on the surface of SiC particles, thus obtaining a wet gel. S24: The wet gel is dried and ground, and then heat-treated in a controlled atmosphere to decompose and crystallize the precursor, obtaining a SiC-based, M... x O y SiC@M shell x O y Coated powder; S3: Preparation of repair slurry: The SiC@M x O y The coated powder is mixed with binder, dispersant and solvent to prepare a repair slurry; S4: Coating and Drying: The repair slurry is coated onto the surface of the damaged area after step S1, and then dried to form a pre-coated layer; S5: Laser in-situ sintering repair: Under a protective atmosphere or vacuum environment, a laser is used to sinter the dried pre-coated layer, so that the M coating on the surface of the powder is repaired. x O y Liquid phase sintering occurs to promote the bonding of SiC powder and achieve in-situ densification of the repair area.

[0011] This invention provides a SiC@M x O y Compared with existing technologies, the laser in-situ repair method for coated SiC ceramics or their composites has the following advantages: This invention replaces the existing physical mixed powder repair system, which suffers from low reactivity and easy agglomeration, with a synergistic repair mechanism that combines core-shell structured powder prepared by a sol-gel method with laser in-situ densification. By enabling metal oxide precursors to undergo in-situ heterogeneous nucleation, gelation, and heat treatment crystallization on the surface of SiC particles, the technical bottleneck of uneven distribution of sintering aids in traditional physical mixed systems is eliminated, endowing the composite powder with extremely high interfacial reactivity and a uniform microstructure. During the repair and forming stage, the high-energy-density laser beam and the core-shell structured powder generate a strong thermophysical synergistic effect, uniformly coating the outer layer of SiC with M... x O y The shell preferentially absorbs laser energy and rapidly undergoes liquid-phase sintering, instantly constructing continuous and uniform liquid-phase mass transfer channels between adjacent SiC particles, significantly reducing the overall sintering activation energy and densification temperature of SiC. The underlying design of the material structure provided by this invention, deeply adapted to the high-energy beam forming process, provides abundant sintering driving force, strictly confining the heat-affected zone of the repair process to the damaged area. This avoids the severe thermal damage and thermal stress accumulation caused by traditional overall high-temperature furnace-based sintering to the original composite fiber and surrounding matrix. At the same time, the abundant and uniform liquid phase greatly promotes the rapid diffusion and bonding of internal SiC nuclei and interface wetting, eliminating low-melting-point residual phases and loose microcracks caused by component segregation. This results in a highly dense repair layer with continuous structure and strong interface bonding in the damaged area, solving the problem that conventional in-situ repair cannot simultaneously achieve local temperature control and high-strength densification.

[0012] In one possible implementation, step S21, the method for surface pretreatment of the SiC powder includes: treating the SiC powder with HNO3 solution, H2O2 solution or HNO3 / H2O2 mixed solution to introduce hydroxyl functional groups on the surface of the SiC powder.

[0013] Compared with existing technologies, the above-mentioned technical solution treats chemically inert SiC powder with a strong oxidizing solution of HNO3, H2O2, or a mixture of both, introducing a large number of highly active hydroxyl functional groups on its surface. These hydroxyl functional groups directly serve as heterogeneous nucleation sites in the subsequent sol-gel process, strongly adsorbing metal precursor complexes through chemical bonding. This inhibits the spontaneous homogeneous nucleation of metal precursors in the solvent, ensuring that the metal oxide shell can achieve dense, uniform, and firmly bonded conformal coating on the SiC particle surface, thereby improving the structural integrity of the core-shell powder and the uniformity of the final repair layer.

[0014] In one possible implementation, in steps S21, S22 and S3, the solvent is selected from one or more of deionized water, anhydrous ethanol, isopropanol and ethyl acetate.

[0015] Compared with existing technologies, this embodiment selects deionized water or specific low-carbon alcohols and esters with suitable polarity and excellent volatility. With their good solubility and dispersion ability, the metal oxide precursor is fully dissociated to form a uniform true solution. This ensures that the SiC powder after surface pretreatment can achieve long-term stable dispersion in the suspension by steric hindrance or electrostatic repulsion, avoiding powder agglomeration. Moreover, the solvent can evaporate smoothly and completely during the subsequent heating, stirring and gelation process, without introducing non-volatile impurities that would cause sintering pores into the coated powder and repair slurry. Thus, it provides an excellent liquid phase mass transfer medium and forming carrier for constructing a high-purity coating shell and a high-density repair layer.

[0016] In one possible implementation, in step S22, the metal oxide M x O y The metal element M is selected from at least one of Y, Al, Yb, Er, Mg, Ho, and La; the metal oxide M x O y The precursor is selected from one of the nitrate, acetate, or chloride of the corresponding metal M.

[0017] Compared with existing technologies, this embodiment selects specific rare earth, alkaline earth, or aluminum metal elements as coating layer components, which can rapidly react with the SiC matrix and the trace amount of silicon oxide on its surface under high laser temperature to form a silicate liquid phase with a low eutectic point. This endows the repair system with extremely high liquid phase sintering driving force and excellent interfacial wettability. Furthermore, the use of metal nitrates, acetates, or chlorides with extremely high solubility in the selected solvents as precursors ensures the uniform molecular-level distribution of metal cations in the sol, further eliminating component segregation in the coating layer due to excessively high local concentration of precursors. This makes the liquid phase sintering behavior under laser action more uniform and controllable, significantly improving the recovery rate of mechanical properties in the repaired area.

[0018] In one possible implementation, in step S22, the complexing agent is selected from citric acid or ethylenediaminetetraacetic acid, and the molar ratio of the complexing agent to the metal cation in the precursor is (1-4):1.

[0019] Compared with existing technologies, in this embodiment, citric acid or ethylenediaminetetraacetic acid has multiple coordinating groups, which can form highly stable soluble chelates with metal cations. This strictly controls and delays the hydrolysis and condensation rate of the metal precursor, preventing premature formation of large particle precipitates. Precisely controlling the molar ratio of the complexing agent to the metal cation within the range of (1-4):1 ensures complete complexation of metal ions to maintain the uniformity and stability of the precursor sol. This avoids the generation of large amounts of gas during subsequent heat treatment and descaling due to excessive introduction of organic carbon chains. Microscopically, this eliminates the formation of residual carbonates or porous defects within the coating shell, ensuring the high purity and density of the core-shell powder, thereby guaranteeing high-strength structural regeneration in the laser in-situ repair area.

[0020] In one possible implementation, step S24, the heat treatment process includes: first holding at 300-400°C to remove organic components, and then raising the temperature to 600-900°C and holding at that temperature to allow the metal oxide to crystallize and form a shell, wherein the heat treatment is carried out in air, oxygen or an inert atmosphere.

[0021] Compared with existing technologies, by precisely dividing the heat treatment process into two-stage stepped heat preservation curves, the complexing agent and nitrate, as well as other organic and inorganic volatile components inside the coating layer, are slowly and completely decomposed and discharged in the low-temperature stage of 300-400℃, preventing the instantaneous release of large amounts of gas caused by a single rapid temperature rise, which could break or tear the pre-formed gel layer. Subsequently, in the high-temperature stage of 600-900℃, the amorphous metal oxides are fully crystallized, completing the in-situ construction of a dense shell at the microscale. Furthermore, the targeted control of air, oxygen, or inert atmosphere ensures the full oxidation and removal of organic matter, preventing the excessive oxidation of the internal silicon carbide core. This provides a core-shell structured powder carrier with excellent fluidity, pure composition, and high energy absorption activity for subsequent laser sintering.

[0022] In one possible implementation, in step S3, the binder is selected from polyvinyl alcohol or polyethylene glycol, and its addition amount accounts for 0.5%-5% of the powder mass in the repair slurry; the dispersant is selected from sodium carboxymethyl cellulose or polyethyleneimine, and its addition amount accounts for 1%-3% of the solvent mass in the repair slurry.

[0023] Compared with existing technologies, this embodiment uses a specific amount of polyvinyl alcohol or polyethylene glycol as a polymer binder, and a specific amount of sodium carboxymethyl cellulose or polyethyleneimine as a dispersant. By utilizing the steric hindrance effect and electrostatic repulsion of the long polymer chains, the core-shell structure powder forms a highly stable suspension network in the solvent, which significantly reduces the settling rate of the powder and endows the slurry with excellent thixotropy and coating ability. Furthermore, the amount of binder and dispersant added is strictly limited to an extremely low mass fraction range, which satisfies the requirement of maintaining the macroscopic morphology and structural bonding force of the pre-coated layer after drying. It also eliminates the possibility of low-density amorphous carbon or explosive pores remaining due to excessive combustion of organic carbon sources under subsequent high-energy laser heating, thus ensuring the phase purity and compactness of the final repair layer.

[0024] In one possible implementation, in step S4, the thickness of the pre-coated layer after drying is controlled at 500-2000 μm; the drying temperature is 60-100 ℃ and the time is 6-12 h.

[0025] Compared with existing technologies, the above-mentioned technical solution strictly controls the thickness of the pre-coated layer after drying to 500-2000 μm, covering the typical geometric depth of microcracks and erosion damage on the surface of most ceramic components. It also achieves thermophysical matching with the energy penetration depth of the selected laser spot, avoiding the problem of insufficient fusion at the bottom due to excessive coating thickness or thermal damage to the substrate caused by excessively thin coating. Combined with a temperature of 60-100 ℃, the solvent inside the pre-coated layer exhibits a uniform and slow evaporation gradient from the surface to the interior, eliminating the capillary shrinkage stress that is easily induced by rapid drying, and preventing the pre-coated layer from cracking, peeling, or flaking before laser sintering.

[0026] In one possible implementation, in step S5, the protective atmosphere is argon, and the vacuum level of the vacuum environment does not exceed 500 Pa.

[0027] Compared with existing technologies, the above-mentioned technical solution introduces an argon protective atmosphere or controls the vacuum level to no more than 500 Pa during the laser in-situ sintering process. This effectively eliminates the interference of ambient oxygen in the repair area, greatly suppresses the oxidation and burn-off of silicon carbide matrix, composite fiber and carbon elements in the coating layer under extreme high temperature conditions, avoids closed-pore defects left in the repair layer due to poor gas escape, and improves the high temperature oxidation resistance and mechanical load-bearing performance of the repair area under extreme service conditions.

[0028] In one possible implementation, in step S5, the laser providing the laser includes a continuous fiber laser, a pulsed laser, or a semiconductor laser; the laser sintering process parameters are: laser power 100-1000 W, laser scanning speed 100-1000 mm / min, laser spot diameter 1-10 mm, and a multi-pass reciprocating scanning repair process is adopted.

[0029] Compared with existing technologies, this embodiment limits the output laser power, scanning speed, and spot diameter to the aforementioned ranges, ensuring that the transient linear energy density of the input prefabricated layer just crosses the liquid phase nucleation threshold of the metal oxide shell, while avoiding the sublimation damage point of the internal silicon carbide nucleus. This achieves an optimal balance between the amount and viscosity of the liquid phase. Furthermore, in conjunction with a multi-channel reciprocating scanning repair strategy, the thermal overlap effect between adjacent melt channels is used to gradually smooth the overall temperature gradient, alleviating the residual thermal stress that is easily generated in ceramic materials during the rapid thermal cycling of the laser. This eliminates the tendency for macroscopic cracking at the repair interface and reconstructs a large-area, high-quality repair layer with strong metallurgical bonding and uniform stress distribution on a wide-area damage surface. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the repair process provided in an embodiment of the present invention; Figure 2This is a schematic diagram of the laser in-situ sintering repair mechanism provided in an embodiment of the present invention. Detailed Implementation

[0031] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0032] This invention provides a SiC@M x O y A laser-assisted in-situ repair method for SiC ceramics or their composites coated with powder includes the following steps: S1: Damaged area pretreatment: The damaged area of ​​SiC ceramic or its composite material is flattened and cleaned to obtain a clean repair area; S2: Preparation of coated powder: SiC@M powder was prepared using the sol-gel method. x O y Core-shell coated powders include: S21: The surface-pretreated SiC powder is dispersed in a solvent to form a SiC suspension; S22: M containing metal oxide x O y The precursor is dissolved in a solvent, and a complexing agent is added to mix and form a precursor sol; S23: The precursor sol is mixed and reacted with the SiC suspension and the solvent is evaporated to gel the precursor on the surface of SiC particles, thus obtaining a wet gel. S24: The wet gel is dried and ground, and then heat-treated in a controlled atmosphere to decompose and crystallize the precursor, obtaining a SiC-based, M... x O y SiC@M shell x O y Coated powder; S3: Preparation of repair slurry: The SiC@M x O y The coated powder is mixed with binder, dispersant and solvent to prepare a repair slurry; S4: Coating and Drying: The repair slurry is coated onto the surface of the damaged area after step S1, and then dried to form a pre-coated layer; S5: Laser in-situ sintering repair: Under a protective atmosphere or vacuum environment, a laser is used to sinter the dried pre-coated layer, so that the M coating on the surface of the powder is repaired. x O y Liquid phase sintering occurs to promote the bonding of SiC powder and achieve in-situ densification of the repair area.

[0033] As a preferred embodiment, in step S21, the method for surface pretreatment of the SiC powder includes: treating the SiC powder with HNO3 solution, H2O2 solution or HNO3 / H2O2 mixed solution to introduce hydroxyl functional groups on the surface of the SiC powder.

[0034] As a preferred embodiment, in steps S21, S22 and S3, the solvent is selected from one or more of deionized water, anhydrous ethanol, isopropanol and ethyl acetate.

[0035] As a preferred embodiment, in step S22, the metal oxide M x O y The metal element M is selected from at least one of Y, Al, Yb, Er, Mg, Ho, and La; the metal oxide M x O y The precursor is selected from one of the nitrate, acetate, or chloride of the corresponding metal M.

[0036] As a preferred embodiment, in step S22, the complexing agent is selected from citric acid or ethylenediaminetetraacetic acid, and the molar ratio of the complexing agent to the metal cation in the precursor is (1-4):1.

[0037] As a preferred embodiment, in step S24, the heat treatment process includes: first holding at 300-400 ℃ to remove organic components, and then raising the temperature to 600-900 ℃ and holding at 600-900 ℃ to crystallize the metal oxide to form a shell. The heat treatment is carried out in air, oxygen or an inert atmosphere.

[0038] As a preferred embodiment, in step S3, the binder is selected from polyvinyl alcohol or polyethylene glycol, and its addition amount accounts for 0.5%-5% of the powder mass in the repair slurry; the dispersant is selected from sodium carboxymethyl cellulose or polyethyleneimine, and its addition amount accounts for 1%-3% of the solvent mass in the repair slurry.

[0039] As a preferred embodiment, in step S4, the thickness of the pre-coated layer after drying is controlled at 500-2000 μm; the drying temperature is 60-100 ℃ and the time is 6-12 h.

[0040] As a preferred embodiment, in step S5, the protective atmosphere is argon, and the vacuum level of the vacuum environment does not exceed 500 Pa.

[0041] As a preferred embodiment, in step S5, the laser providing the laser includes a continuous fiber laser, a pulsed laser, or a semiconductor laser; the laser sintering process parameters are: laser power 100-1000 W, laser scanning speed 100-1000 mm / min, laser spot diameter 1-10 mm, and a multi-pass reciprocating scanning repair process is adopted.

[0042] The following are embodiments incorporating specific data to further elaborate on the above-described technical solutions of the present invention: Example 1 This embodiment provides a laser in-situ repair method for SiC ceramics or their composites based on SiC@Y2O3 coated powder, specifically including the following steps: S1: Pretreatment of damaged areas: Select SiC ceramic or its composite material samples containing surface damage, remove the surface oxide layer and loose cracks by sanding with sandpaper, then ultrasonically clean with anhydrous ethanol for 10 min, and dry for later use.

[0043] S2: Preparation of coated powder: SiC@Y2O3 core-shell structured coated powder was prepared using the sol-gel method, specifically including: S21: The SiC powder cleaned in S1 is immersed in hydrogen peroxide solution, heated and stirred to introduce -OH hydroxyl groups on the SiC surface; then the treated SiC powder is dispersed in ethanol and subjected to ultrasonic treatment for 30-60 min to form a stable and uniform SiC suspension. S22: Yttrium nitrate, as a precursor, is dissolved in ethanol and stirred until completely dissolved to form a clear solution. Citric acid is added as a complexing agent, and the molar ratio of citric acid to metal ions is controlled at 2:1. The pH is adjusted to about 7.0 by adding ammonia dropwise to form a precursor sol. S23: Under continuous stirring, the precursor sol is slowly added dropwise to the SiC suspension. The system is kept under continuous stirring and gentle heating at 60 °C to allow the solvent to evaporate slowly and the precursor to gel on the surface of the SiC particles, resulting in a wet gel. S24: The obtained wet gel was dried in an oven at 80 °C to remove most of the solvent and obtain a dry gel. The dry gel was then ground to restore it to a powder state. Subsequently, it was placed in a tube furnace and heat-treated in an air atmosphere. First, the temperature was slowly raised to 400 °C to fully decompose, oxidize and remove the organic components and anions. Then, the temperature was raised to 800 °C to crystallize the amorphous Y2O3 into a dense shell. After holding at this temperature for 2 h, the powder was cooled with the furnace to obtain SiC@Y2O3 coated powder.

[0044] S3: Preparation of repair slurry: The obtained SiC@Y2O3 coated powder is mixed with ethanol solvent, polyvinyl alcohol (PVA) binder and a small amount of sodium carboxymethyl cellulose (CMC) dispersant, and the solid volume fraction is controlled at 40% to prepare the repair slurry.

[0045] S4: Coating and Drying: The repair slurry is uniformly coated on the surface of the pretreated damaged area with a thickness of about 1000 μm, and then dried at 80 ℃ for 2 h to form a pre-coated layer.

[0046] S5: Laser in-situ sintering repair: A continuous fiber laser is used to sinter and repair the dried pre-coated layer. The laser power is set to 400 W and the scanning speed is 100 mm / min. During the laser scanning process, the SiC@Y2O3 coated powder undergoes local melting and reactive sintering to form a dense SiC repair layer, achieving in-situ densification.

[0047] Performance testing: The flexural strength of the repaired specimen was determined using a three-point bending test method, with a support span of 30 mm and a loading rate of 0.5 mm / min. The results show that the flexural strength of the repaired specimen in this embodiment recovered to 82.25% of the strength of the undamaged specimen.

[0048] Example 2 This embodiment provides a laser in-situ repair method for SiC ceramics or their composites based on SiC@AL2O3 coated powder, specifically including the following steps: S1: Pretreatment of damaged areas: Select SiC ceramic or its composite material samples containing surface damage, remove the surface oxide layer and loose cracks by sanding with sandpaper, then ultrasonically clean with anhydrous ethanol for 10 min, and dry for later use.

[0049] S2: Preparation of coated powder: SiC@AL2O3 core-shell structured coated powder was prepared using the sol-gel method, specifically including: S21: The cleaned SiC powder is immersed in hydrogen peroxide solution, heated and stirred to introduce -OH hydroxyl groups, then dispersed in ethanol and ultrasonically treated for 30-60 min to form a SiC suspension; S22: Dissolve aluminum isopropoxide, which is a precursor, in ethanol and stir until completely dissolved to form a clear solution. Add a small amount of acetic acid to control the hydrolysis rate of aluminum isopropoxide. Adjust the pH to about 4.0 by adding hydrochloric acid dropwise to form a precursor sol. S23: Under continuous stirring, the precursor sol is slowly added dropwise to the SiC suspension. The system is kept at 60 °C with continuous stirring and gentle heating to evaporate the solvent, yielding a wet gel; S24: The wet gel was dried at 80 °C to obtain a dry gel, which was then ground and placed in a tube furnace for heat treatment in an air atmosphere: the temperature was first slowly raised to 400 °C to decompose the organic components, and then raised to 800 °C and held for 2 h. The powder was then cooled in the furnace to obtain SiC@AL2O3 coated powder.

[0050] S3: Preparation of repair slurry: SiC@AL2O3 coated powder is mixed with ethanol, PVA binder and a small amount of CMC dispersant, and the solid volume fraction is controlled at 40%.

[0051] S4: Coating and Drying: Apply the repair slurry evenly to the damaged area to a thickness of about 1000 μm, and dry it at 80°C for 2 h.

[0052] S5: Laser in-situ sintering repair: The same laser as in Example 1 was used for sintering repair at a laser power of 400 W and a scanning speed of 100 mm / min. Due to the weak laser absorption of the AL2O3 coating layer, slight porosity appeared in some parts of the repair layer, resulting in a slightly lower density than the Y2O3 system.

[0053] Performance testing: Bending strength was determined under the same test conditions. The results showed that the bending strength of the repaired specimen in this embodiment recovered to 80.79% of the strength of the undamaged specimen.

[0054] Comparative Example This comparative example provides a laser repair method for SiC ceramics or their composite materials using conventional mixed powders, for comparison with the above embodiments. The difference between this comparative example and the embodiments is that this comparative example does not use core-shell structured coating powder prepared by the sol-gel method, but directly uses a physical mixture of ordinary SiC powder and metal oxide powder to prepare the repair slurry.

[0055] S1: Pretreatment of damaged areas: Select SiC ceramic or its composite material samples containing surface damage, polish with sandpaper and ultrasonically clean with anhydrous ethanol for 10 min, and dry for later use.

[0056] S3: Preparation of repair slurry (without using the coating process of this invention): ordinary SiC powder, AL2O3 powder, ethanol, PVA binder and a small amount of CMC dispersant are directly mixed and stirred, and the solid volume fraction is controlled at 40%.

[0057] S4: Coating and Drying: The repair slurry is uniformly coated on the pretreated damaged area to a thickness of approximately 1000 μm and dried at 80 ℃ for 2 h.

[0058] S5: Laser Sintering Repair: Due to the lack of coated powder and low reactivity, the laser power needed to be increased to 500W and the scanning speed to 200 mm / min for sintering. Under these conditions, cracks appeared in the repair layer, and the porosity increased significantly.

[0059] Performance testing: Bending strength was measured. The results showed that the bending strength of the sample repaired with ordinary mixed powder was only 74.21% of that of the undamaged sample. Compared with Examples 1 and 2, there were significant differences in both density and mechanical property recovery rate, which fully demonstrates the superiority of the core-shell structure coated powder of the present invention in laser in-situ repair.

[0060] like Figure 1 and Figure 2 As shown, the present invention involves coating the damaged area of ​​SiC ceramics or their composites with SiC@M prepared by the sol-gel method. x O y A repair slurry containing coated powder is prepared and sintered locally using a high-energy laser beam, achieving in-situ reaction and rapid densification of the coated powder. Under laser irradiation, the metal oxide coating preferentially undergoes liquid-phase sintering, promoting diffusion bonding and performance reconstruction among internal SiC particles, thereby forming a highly dense repair layer bonded to the original material in the damaged area. This repair layer exhibits a continuous structure and strong interfacial bonding, effectively inhibiting crack propagation and delamination failure, and significantly improving the structural integrity and high-temperature service performance of the damaged material.

[0061] Based on the test results of the above embodiments and comparative examples, it can be seen that the method of the present invention exhibits significant advantages in the laser in-situ repair process: In the comparative examples, ordinary physically mixed powders, due to uneven distribution of metal oxides and low interfacial reactivity, are unable to overcome the defect of insufficient sintering driving force even with a forced increase in laser input power, resulting in the repair layer being prone to the initiation of pores and microcracks; while the present invention, based on the sol-gel process, achieves dense surface mattification of SiC particles at the microscale. x O y In-situ coating of the shell fundamentally solves the problem of component agglomeration in traditional powders. During the repair process, the high energy density of the laser and the core-shell structure of the coated powder produce a strong synergistic effect: the metal oxide shell coating the SiC surface preferentially absorbs laser energy and rapidly undergoes liquid-phase sintering, forming uniform liquid-phase mass transfer channels between SiC particles. This greatly promotes the diffusion and bonding of the internal SiC nuclei and interface wetting, reducing the sintering temperature. The synergistic effect of the above material structure design and laser forming process effectively avoids crack defects induced by high-temperature thermal stress, and also achieves high density and uniform reconstruction of the repair layer structure, enabling the macroscopic flexural strength of the material to recover to more than 80%, proving the inventiveness and engineering application value of the core technical solution of this invention.

[0062] In the description of the embodiments of the present invention, it should be noted that the terms "inner" and "outer" and other terms indicating the direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0063] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A SiC@M x O y A laser-assisted in-situ repair method for SiC ceramics or their composites coated with powder, characterized in that, Includes the following steps: S1: Damaged area pretreatment: The damaged area of ​​SiC ceramic or its composite material is flattened and cleaned to obtain a clean repair area; S2: Preparation of coated powder: SiC@M powder was prepared using the sol-gel method. x O y Core-shell coated powders include: S21: The surface-pretreated SiC powder is dispersed in a solvent to form a SiC suspension; S22: M containing metal oxide x O y The precursor is dissolved in a solvent, and a complexing agent is added to mix and form a precursor sol; S23: The precursor sol is mixed and reacted with the SiC suspension and the solvent is evaporated to gel the precursor on the surface of SiC particles, thus obtaining a wet gel. S24: The wet gel is dried and ground, and then heat-treated in a controlled atmosphere to decompose and crystallize the precursor, obtaining a SiC-based, M... x O y SiC@M shell x O y Coated powder; S3: Preparation of repair slurry: The SiC@M x O y The coated powder is mixed with binder, dispersant and solvent to prepare a repair slurry; S4: Coating and Drying: The repair slurry is coated onto the surface of the damaged area after step S1, and then dried to form a pre-coated layer; S5: Laser in-situ sintering repair: Under a protective atmosphere or vacuum environment, a laser is used to sinter the dried pre-coated layer, so that the M coating on the surface of the powder is repaired. x O y Liquid phase sintering occurs to promote the bonding of SiC powder and achieve in-situ densification of the repair area.

2. The laser in-situ repair method according to claim 1, characterized in that, In step S21, the method for surface pretreatment of the SiC powder includes: treating the SiC powder with HNO3 solution, H2O2 solution or HNO3 / H2O2 mixed solution to introduce hydroxyl functional groups on the surface of the SiC powder.

3. The laser in-situ repair method according to claim 1, characterized in that, In steps S21, S22 and S3, the solvent is selected from one or more of deionized water, anhydrous ethanol, isopropanol and ethyl acetate.

4. The laser in-situ repair method according to claim 1, characterized in that, In step S22, the metal oxide M x O y The metal element M is selected from at least one of Y, Al, Yb, Er, Mg, Ho, and La; the metal oxide M x O y The precursor is selected from one of the nitrate, acetate, or chloride of the corresponding metal M.

5. The laser in-situ repair method according to claim 1, characterized in that, In step S22, the complexing agent is selected from citric acid or ethylenediaminetetraacetic acid, and the molar ratio of the complexing agent to the metal cation in the precursor is (1-4):

1.

6. The laser in-situ repair method according to claim 1, characterized in that, In step S24, the heat treatment process includes: first holding at 300-400 °C to remove organic components, and then raising the temperature to 600-900 °C and holding at that temperature to allow the metal oxide to crystallize and form a shell. The heat treatment is carried out in air, oxygen or an inert atmosphere.

7. The laser in-situ repair method according to claim 1, characterized in that, In step S3, the binder is selected from polyvinyl alcohol or polyethylene glycol, and its addition amount accounts for 0.5%-5% of the powder mass in the repair slurry; the dispersant is selected from sodium carboxymethyl cellulose or polyethyleneimine, and its addition amount accounts for 1%-3% of the solvent mass in the repair slurry.

8. The laser in-situ repair method according to claim 1, characterized in that, In step S4, the thickness of the pre-coated layer after drying is controlled at 500-2000 μm; the drying temperature is 60-100 ℃ and the time is 6-12 h.

9. The laser in-situ repair method according to claim 1, characterized in that, In step S5, the protective atmosphere is argon, and the vacuum level of the vacuum environment does not exceed 500 Pa.

10. The laser in-situ repair method according to claim 1, characterized in that, In step S5, the laser providing the laser includes a continuous fiber laser, a pulsed laser, or a semiconductor laser; the laser sintering process parameters are: laser power 100-1000 W, laser scanning speed 100-1000 mm / min, laser spot diameter 1-10 mm, and a multi-pass reciprocating scanning repair process is adopted.

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