One-time sintering repairing method for reactive sintering silicon carbide material defects

Abstract

The invention relates to the technical field of ceramic material repairing, in particular to a one-time sintering repairing method for reactive sintering silicon carbide material defects. Comprising the following steps: measuring the defect size of reactive sintering silicon carbide, and cutting a silicon-based alloy block slightly larger than the defect size; carrying out ultrasonic cleaning on the defect part of the reactive sintering silicon carbide by adopting an organic solvent, wherein the ultrasonic time is 20-40 minutes; placing the silicon-aluminum alloy block above the defect of the reactive sintering silicon carbide, and uniformly paving silicon powder on the surface of the reactive sintering silicon carbide; the mass fraction of the silicon powder is 3-8% of that of the reactive sintering silicon carbide; setting a proper sintering temperature, heating according to a heating rate of 3-10 DEG C / min, and keeping the temperature for 1-3 hours after the sintering temperature is reached; the sintering temperature is higher than the melting point of the silicon-based alloy; and polishing the surface of the repaired reactive sintering silicon carbide to obtain the repaired reactive sintering silicon carbide. The method has the advantages that low-porosity and high-density repair of the crack area is guaranteed, and the optical performance of the reflector is not reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic material repair, and in particular to a one-time sintering repair method for defects in reaction-sintered silicon carbide materials. Background Art

[0002] Reaction-bonded silicon carbide (RB-SiC) boasts excellent properties, including high modulus, high strength, and low linear expansion coefficient, making it a prime candidate material for space optical mirrors. With the continuous advancement of space exploration technology, the aperture of optical mirrors is gradually increasing. A Chinese patent application, Publication No. CN107903068A, published on April 13, 2018, entitled "Process for Reducing Internal Stress in Large-Aperture Reaction-Bonded Silicon Carbide," indicates that defects such as holes and cracks are highly susceptible to formation during the fabrication of large-aperture RB-SiC mirrors (diameter ≥ 1m). Because ceramic materials are extremely sensitive to defects, these defects can severely reduce the mirror's yield and operational reliability.

[0003] Defects in RB-SiC mirrors can arise from thermal defects caused by high-temperature fields and vibration and collision defects generated during the mirror processing process. Defect sizes range from nanometers to millimeters. However, no effective repair methods for RB-SiC defects have been reported. Existing reports primarily focus on research into welding and joining technologies for RB-SiC materials. The difference between welding and defect repair lies in the fact that the former involves joining two objects into a single entity, while the latter involves repairing local defects within a single entity. Despite the fundamental differences between welding and repair, welding technology can still provide a reference and inspiration for defect repair technology. Existing RB-SiC welding technologies include brazing, laser welding, and arc welding. For example, the Chinese patent application with publication number CN117817066A, publication date April 5, 2024, and invention title "A Method for Joining Reaction-Sintered Silicon Carbide, and RB-SiC Connector" discloses a method for welding RB-SiC base material with a metal brazing flux. This method involves preparing the brazing material, pre-treating the surfaces to be welded, coating the surfaces with brazing material, laminating the two surfaces to be welded, and high-temperature brazing. The brazing method is cumbersome and complex, and to ensure that the joint has good mechanical properties, a certain amount of pressure is usually applied to the two base materials during the welding process to achieve the preparation of pore-free, high-performance welds. However, unlike the process of connecting two base materials, in the process of repairing ceramic defects, the base material is a whole. It is inconvenient to apply pressure after the brazing fills the weld, and the comprehensive performance of the repaired area cannot be guaranteed. In particular, according to the results disclosed in the Chinese patent application with publication number CN119263891A, publication date January 7, 2025, and invention name "A method for repairing crack damage of silicon carbide ceramic-based composite parts of aircraft engines", when the RB-SiC crack width is greater than 0.2mm, brazing technology cannot be used for efficient repair. A Chinese patent application, publication number CN115626776A, date of publication January 20, 2023, and titled "Glass Powder for Laser-Assisted Joining of Silicon Carbide Ceramic Materials, Preparation Method, and Application thereof," discloses a laser-assisted SiC ceramic joining method. Because the laser instantly generates high-energy heat, improper processing can create a large temperature gradient within the heat-affected zone of the weld surface, which can easily lead to thermal stress. Inappropriate release of thermal stress can easily lead to secondary cracks, resulting in more serious defects in the substrate. Furthermore, arc welding is a typical fusion welding technique, and its use significantly affects the microstructure and properties of the parent material.

[0004] In summary, RB-SiC defects range in size from nanometers to millimeters, with depths ranging from millimeters to centimeters. Existing brazing techniques have strict requirements for defect size, requiring widths to be less than 0.2 mm. However, even deep defects make it difficult to ensure uniform brazing. Laser welding and arc welding can both adversely affect the base material, making process parameters difficult to control. Therefore, developing a technology that has no impact on the RB-SiC base material and can achieve cross-scale defect repair is crucial for the efficient production and long-life service of large-scale RB-SiC mirrors. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials.

[0006] The present invention aims to provide a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically comprises the following steps: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-sintered silicon carbide and cut the silicon-based alloy block to a size 2-3 times the defect width and 1-1.5 times the defect height. S2. Surface pretreatment of the reaction-bonded silicon carbide: Ultrasonic cleaning of defects in the reaction-bonded silicon carbide is performed using an organic solvent for 20 to 40 minutes. S3. Sample loading: Place the SiAl alloy block over a defect in the reaction-sintered SiC and evenly spread silicon powder on the surface of the reaction-sintered SiC. The silicon powder should constitute 3-8% of the mass fraction of the reaction-sintered SiC. S4. Primary sintering: Set the appropriate sintering temperature based on the melting point of the silicon-based alloy, increase the temperature at a rate of 3-10°C / min, and hold the temperature for 1-3 hours after reaching the sintering temperature. The sintering temperature should be greater than the melting point of the silicon-based alloy. S5. Polishing the surface of the repaired reaction-sintered silicon carbide to obtain repaired reaction-sintered silicon carbide.

[0007] Preferably, the silicon-based alloy includes silicon-aluminum alloy, silicon-molybdenum alloy, silicon-titanium alloy, silicon-copper alloy, and silicon-nickel alloy; the silicon content in the silicon-based alloy is greater than 5%.

[0008] Preferably, in step S1, defects of the reaction-sintered silicon carbide include cracks and holes; and the cutting is performed using a diamond cutting machine.

[0009] Preferably, the organic solvent in step S2 includes acetone, alcohol, methanol, n-hexane, n-propanol, and isopropanol; and the ultrasonic time is 30 min.

[0010] Preferably, step S2 further includes: before ultrasonic cleaning, using a sandblasting process to treat the defective surface of the reaction-sintered silicon carbide to increase the roughness of the defective surface.

[0011] Preferably, the silicon powder in step S3 is 5-8% of the mass fraction of the reaction-bonded silicon carbide.

[0012] Preferably, the silicon powder in step S3 is 5% of the mass fraction of the reaction-bonded silicon carbide.

[0013] Preferably, the heating rate of step S4 is 5°C / min and the holding time is 1 hour.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention uses a silicon-based alloy with controllable composition to achieve a solid-liquid phase transition of the silicon-based alloy within a temperature range below the melting point of silicon. Under the action of gravity and vacuum conditions, the molten silicon-based alloy is prompted to fill defects such as holes and cracks. After 1-3 hours of heat preservation treatment, the alloy elements in the silicon-based alloy are promoted to undergo mutual diffusion reaction with the silicon in the matrix to improve the bonding strength between the repair area and the matrix. In addition, silicon powder with a mass fraction of 3 to 8% is added to the surface of RB-SiC to prevent the loss of silicon in the RB-SiC matrix during the sintering process and cause secondary defects. The present invention proposes a technology for sandblasting the crack surface to improve the roughness for large-scale defects, i.e., defects with a width or diameter greater than 0.2 mm and a depth greater than 5 mm. On the basis of metallurgical bonding, the high-roughness surface increases the mechanical bonding force between the repair area and the matrix, better solving the technical problem of large-scale defects being difficult to repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The microstructure of surface cracks in reaction-bonded silicon carbide (RB-SiC) provided in an embodiment of the present invention is shown.

[0016] Figure 2 Figures 2 and 3 show the morphology and elemental analysis results of the reaction-sintered silicon carbide surface crack repaired according to an embodiment of the present invention. (a) shows the surface morphology after the crack repair; (b) shows the carbon (C) distribution in the repaired area; (c) shows the aluminum (Al) distribution in the repaired area; and (d) shows the silicon (Si) distribution in the repaired area. DETAILED DESCRIPTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical modules are denoted by identical reference numerals. In the case of identical reference numerals, their names and functions are also identical. Therefore, their detailed description will not be repeated.

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0019] The present invention provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically comprises the following steps: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-bonded silicon carbide (RB-SiC) and cut the silicon-based alloy block to a size 2-3 times the defect width and 1-1.5 times the defect height. The silicon-based alloy block should be slightly larger than the defect size. Specifically, the defects of reaction-bonded silicon carbide (RB-SiC) include cracks and holes. The width or diameter of the defect of reaction-bonded silicon carbide is greater than 0.2mm and the depth is greater than 5mm. When the defect is a crack, the silicon-based alloy block is cut to 2 to 3 times the width of the crack and 1 to 1.5 times the height. When the defect is a hole, the silicon-based alloy block is cut to 2 to 3 times the diameter of the hole and 1 to 1.5 times the height. Cutting is done with a diamond cutting machine; Silicon-based alloys include silicon-aluminum alloys, silicon-molybdenum alloys, silicon-titanium alloys, silicon-copper alloys, and silicon-nickel alloys; the silicon content in silicon-based alloys is >5%.

[0020] S2. Surface pretreatment of the reaction-bonded silicon carbide: Ultrasonic cleaning of defects in the reaction-bonded silicon carbide is performed using an organic solvent for 20 to 40 minutes to remove surface contaminants and prevent them from affecting the wettability of the silicon-aluminum alloy. Specifically, the organic solvent includes acetone, alcohol, methanol, n-hexane, n-propanol, isopropanol, etc. In a specific embodiment, the ultrasonic time is 30 minutes; Before ultrasonic cleaning, the crack surface of RB-SiC was treated by sandblasting to appropriately increase the surface roughness of the crack, which was conducive to the mechanical engagement between the alloy and the matrix after melting and solidification.

[0021] S3. Sample Furnace Loading: A silicon-aluminum alloy block is placed on a defective surface of reaction-sintered silicon carbide (RB-SiC). To prevent silicon flow or evaporation in the RB-SiC due to poor temperature control during the sintering process, a 3-8% by mass silicon powder is evenly spread on the surface of the RB-SiC before the primary sintering. This increased amount of silicon powder compensates for potential silicon loss during the sintering process, ensuring sintering process stability and final product performance. Preferably, the silicon powder accounts for 5-8% of the mass fraction of the reaction-bonded silicon carbide; in a specific embodiment, the silicon powder accounts for 5% of the mass fraction of the reaction-bonded silicon carbide.

[0022] S4. Primary sintering: Set the appropriate sintering temperature based on the melting point of the silicon-based alloy, increase the temperature at a rate of 3-10°C / min, and hold the temperature for 1-3 hours after reaching the sintering temperature. The sintering temperature should be greater than the melting point of the silicon-based alloy. Specifically, the heating rate is 5°C / min and the holding time is 1 h.

[0023] S5. Polishing the surface of the repaired reaction-bonded silicon carbide (RB-SiC) to obtain a repaired reaction-bonded silicon carbide; Specifically, the polishing process is grinding polishing.

[0024] Example 1 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically includes the following steps: S1. Prepare a silicon-aluminum alloy (Si-Al) sample: Measure the crack size of the RB-SiC sample. Using a diamond saw, prepare a Si-Al alloy block with a width twice the crack width and a height once the crack depth. The Si-Al alloy is a commercially available sample with a silicon content of 80%.

[0025] S2. Surface pretreatment of RB-SiC samples: Use acetone, alcohol and other solutions to ultrasonically clean the cracks of RB-SiC for 30 minutes to remove surface dirt and prevent it from affecting the wettability of silicon-aluminum alloy.

[0026] S3. Sample loading: The silicon-aluminum alloy block prepared in step S1 is placed on the cracked surface of the RB-SiC treated in step S2. To prevent the silicon in the RB-SiC from flowing or evaporating due to poor temperature control during the sintering process, a 5% by mass silicon powder is evenly spread on the surface of the RB-SiC before sintering.

[0027] S4. Primary sintering: According to the Si-Al binary phase diagram, the melting point of the silicon-aluminum alloy in step S1 is about 1330°C. Therefore, the sintering temperature is set to 1350°C; the temperature is increased at a heating rate of 5°C / min, and the temperature is maintained for 1 hour after reaching the sintering temperature.

[0028] S5. The surface of the repaired reaction-sintered silicon carbide is ground and polished to obtain a repaired reaction-sintered silicon carbide; Compare the microstructural changes of the crack area before and after repair, and analyze the microstructural changes between the crack repair area and the substrate after repair. Figure 1 As shown in Figure 1, there are cracks of about 500 μm in RB-SiC. After sintering once through the above steps, Figure 2 The crack area shown is completely filled. Energy spectrum analysis shows that the aluminum in the silicon-aluminum alloy diffuses into the matrix and forms an intermediate phase with the silicon in the matrix.

[0029] The above results show that: (1) the low-temperature one-time sintering repair technology can eliminate RB-SiC surface cracks, prevent further crack expansion, and prevent component failure; (2) the silicon-aluminum alloy can diffuse and react with the silicon in the matrix material to form an intermediate phase, which is beneficial to the improvement of the bonding strength between the repair area and the matrix.

[0030] Example 2 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically includes the following steps: S1. Prepare a silicon-aluminum alloy (Si-Al) sample: Measure the crack size of the RB-SiC sample. Using a diamond cutter, prepare a Si-Al alloy block with a width twice the crack width and a height once the crack depth. The Si-Al alloy is a commercially available sample with a silicon content of 12.6%.

[0031] Step S2 and step S3 are the same as those in Example 1.

[0032] S4. Primary sintering: According to the Si-Al binary phase diagram, the melting point of the silicon-aluminum alloy in step S1 is about 577°C. Therefore, the sintering temperature is set to 600°C; the temperature is increased at a heating rate of 5°C / min, and the temperature is maintained for 1 hour after reaching the sintering temperature.

[0033] S5. The surface of the repaired reaction-sintered silicon carbide is ground and polished to obtain a repaired reaction-sintered silicon carbide; The apparent porosity of the repaired RB-SiC was measured and compared with that of the crack-free RB-SiC to analyze the effect of the repair technology on the surface density of the RB-SiC material. In addition, scanning electron microscopy and optical microscopy were used to evaluate the bonding between the repaired area and the substrate.

[0034] Example 3 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically includes the following steps: S1. Prepare a silicon-aluminum alloy (Si-Al) sample: Measure the crack size of the RB-SiC sample. Using a diamond saw, prepare a Si-Al alloy block with a width three times the crack width and a height one times the crack depth. The Si-Al alloy is a commercially available sample with a silicon content of 70%.

[0035] S2. Surface pretreatment of RB-SiC samples: The crack surface of RB-SiC was treated by sandblasting to appropriately increase the surface roughness of the crack, which is conducive to the mechanical bite between the alloy and the matrix after melting and solidification. The crack of RB-SiC was ultrasonically cleaned for 30 minutes using acetone, alcohol and other solutions to remove surface dirt and prevent it from affecting the wettability of silicon-aluminum alloy.

[0036] S3. Sample loading: Place the silicon-aluminum alloy block prepared in step S1 on the crack surface of the RB-SiC prepared in step S2. To prevent the silicon in the RB-SiC from flowing or evaporating due to poor temperature control during the sintering process, evenly spread 5% by mass of silicon powder on the surface of the RB-SiC before sintering.

[0037] S4. Primary sintering: According to the Si-Al binary phase diagram, the melting point of the silicon-aluminum alloy in step S1 is about 1200°C. Therefore, the sintering temperature is set to 1280°C; the temperature is increased at a heating rate of 5°C / min, and the temperature is maintained for 1 hour after reaching the sintering temperature.

[0038] S5. The surface of the repaired reaction-sintered silicon carbide is ground and polished to obtain a repaired reaction-sintered silicon carbide; The repaired RB-SiC surface was ground and polished, and the microstructural changes in the cracked area were compared before and after the repair. Sandblasting the cracked area resulted in a high-strength connection between the alloy and the substrate, achieved through the coupling of mechanical engagement and metallurgical bonding.

[0039] Example 4 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically includes the following steps: S1. Prepare a silicon-copper (Si-Cu) alloy sample: Measure the RB-SiC pore size and use a diamond saw to prepare a Si-Cu alloy block with a pore diameter three times that of the pore diameter and a height one times that of the pore depth. The Si-Cu alloy is a commercially available sample with a silicon content greater than 5%.

[0040] S2. Surface decontamination of RB-SiC samples: Use acetone, alcohol and other solutions to ultrasonically clean the pores of RB-SiC for 30 minutes to remove surface dirt and prevent it from affecting the wettability of silicon-copper alloy.

[0041] S3. Sample loading: Place the silicon-copper alloy block prepared in step S1 above the RB-SiC hole in step S2. To prevent poor temperature control during the sintering process, which may cause the silicon in the RB-SiC to flow or evaporate, evenly spread 5% by mass of silicon powder on the surface of the RB-SiC before sintering.

[0042] S4. Primary sintering: According to the Si-Cu binary phase diagram, the melting point of the silicon-copper alloy in step S1 is approximately 900°C. Therefore, the sintering temperature is set to 920°C. The temperature is increased at a rate of 5°C / min and maintained at the sintering temperature for 1 hour.

[0043] S5. Polishing the surface of the repaired reaction-sintered silicon carbide to obtain repaired reaction-sintered silicon carbide.

[0044] Compare the microstructural changes in the crack area before and after repair. Analyze the distribution of copper within the defect and the matrix. Perform porosity testing to assess the surface density of the repaired sample.

[0045] Example 5 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, which specifically includes the following steps: S1. Prepare a silicon-nickel alloy sample: Measure the crack size of the RB-SiC. Use a diamond cutting machine to prepare a silicon-nickel alloy block with a width three times the hole diameter and a height one times the hole depth. The silicon-nickel alloy is a commercially available sample with a silicon content greater than 5%.

[0046] Step S2 and step S3 are the same as those in Example 1.

[0047] S4. Primary sintering: The sintering temperature was set to 1280°C according to the Si-Ni binary phase diagram; the temperature was increased at a rate of 5°C / min and maintained at the sintering temperature for 1 hour.

[0048] S5. Polishing the surface of the repaired reaction-sintered silicon carbide to obtain repaired reaction-sintered silicon carbide.

[0049] Compare the microstructural changes in the hole area before and after repair. Porosity testing was performed to evaluate the surface density of the repaired sample.

[0050] The key technical points and advantages of this invention lie in: addressing the problems of defects caused by thermal stress during the fabrication of large-aperture RB-SiC mirrors, or defects caused by collision and vibration during processing, by providing a technical solution for repairing RB-SiC cracks using a low-temperature, single-shot sintering method using a silicon-based alloy. This solution ensures low porosity and high-density repair of the cracked area without degrading the optical performance of the mirror. A silicon-based alloy block, shaped similarly to the crack but slightly larger in volume, is prepared using a wire saw and placed above the RB-SiC crack. A single-shot sintering schedule is designed based on the binary phase diagram of the silicon-based alloy. After holding the block for 1-3 hours, a highly densified RB-SiC material is obtained in the cracked area.

[0051] By designing the component system of silicon-based alloys and regulating the primary sintering temperature regime, we studied the coupling effect between silicon-based alloy components and the sintering temperature field, and the impact on defects and the composition and performance changes of the matrix, achieving high-density repair of RB-SiC defects and ensuring the service stability of RB-SiC.

[0052] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0053] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A single-sintering repair method for defects in reaction-sintered silicon carbide materials, characterized by: The specific steps include: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-sintered silicon carbide and cut the silicon-based alloy block to a size 2-3 times the defect width and 1-1.5 times the defect height. S2. Surface pretreatment of the reaction-bonded silicon carbide: Ultrasonic cleaning of defects in the reaction-bonded silicon carbide is performed using an organic solvent for 20 to 40 minutes. S3. Sample loading: Place the SiAl alloy block over a defect in the reaction-sintered SiC and evenly spread silicon powder on the surface of the reaction-sintered SiC. The silicon powder should constitute 3-8% of the mass fraction of the reaction-sintered SiC. S4. Primary sintering: Set the sintering temperature appropriately based on the melting point of the silicon-based alloy. Raise the temperature at a rate of 3-10°C / min. Hold at the sintering temperature for 1-3 hours. The sintering temperature should be above the melting point of the silicon-based alloy. S5. Polishing the surface of the repaired reaction-sintered silicon carbide to obtain repaired reaction-sintered silicon carbide.

2. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: The silicon-based alloy includes silicon-aluminum alloy, silicon-molybdenum alloy, silicon-titanium alloy, silicon-copper alloy and silicon-nickel alloy; the silicon content in the silicon-based alloy is greater than 5%.

3. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: In the step S1, defects of the reaction-sintered silicon carbide include cracks and holes; the cutting is performed using a diamond cutting machine.

4. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: The organic solvent in step S2 includes acetone, alcohol, methanol, n-hexane, n-propanol, and isopropanol; and the ultrasonic time is 30 minutes.

5. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: The step S2 further includes: before ultrasonic cleaning, using a sandblasting process to treat the defective surface of the reaction-sintered silicon carbide to increase the roughness of the defective surface.

6. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: The silicon powder in step S3 accounts for 5-8% of the mass fraction of the reaction-sintered silicon carbide.

7. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 6, characterized in that: The silicon powder in step S3 is 5% of the mass fraction of the reaction-bonded silicon carbide.

8. The one-time sintering repair method for defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: The heating rate of step S4 is 5°C / min, and the holding time is 1 hour.

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