A method for repairing defects in a reaction sintered silicon carbide material by a primary sintering

Abstract

The present application relates to ceramic material repair technical field, especially to a kind of reaction sintered silicon carbide material defect one-time sintering repair method.The present application includes: the defect size of reaction sintered silicon carbide is measured, and silicon-based alloy block slightly larger than the defect size is cut;Reaction sintered silicon carbide defect is ultrasonically cleaned using organic solvent, and ultrasonic time is 20~40min;Silicon-aluminum alloy block is placed above the defect of reaction sintered silicon carbide, and silicon powder is evenly laid on the surface of reaction sintered silicon carbide;Silicon powder is 3~8% of the mass fraction of reaction sintered silicon carbide;Set appropriate sintering temperature, heat at a rate of 3~10℃ / min, heat for 1~3h after reaching sintering temperature;Sintering temperature is greater than the melting point of silicon-based alloy;The surface of the repaired reaction sintered silicon carbide is polished to obtain the repaired reaction sintered silicon carbide.The advantage is that the crack area is repaired with low porosity and high density, and the optical performance of the mirror is not reduced.

Description

Technical Field

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

[0002] Reaction-bonded silicon carbide (RB-SiC) possesses excellent comprehensive properties such as high modulus, high strength, and low coefficient of linear expansion, making it one of the main candidate materials for space optical mirrors. Currently, with the continuous development of space exploration technology, the aperture of optical mirrors is gradually moving towards larger diameters. Chinese patent application CN107903068A, published on April 13, 2018, entitled "Process for Reducing Internal Stress in Large-Aperture Reaction-Bonded Silicon Carbide," indicates that defects such as voids and cracks are easily generated during the fabrication of large-aperture RB-SiC mirrors (aperture ≥ 1m). Since ceramic materials are extremely sensitive to defects, the occurrence of defects will seriously reduce the yield and reliability of the mirror's service performance.

[0003] The formation of defects in RB-SiC mirrors involves thermal defects caused by high-temperature fields and vibration and collision defects generated during mirror processing, with defect sizes ranging from nanometers to millimeters. However, no effective repair methods have been reported for RB-SiC defects. Existing reports mainly focus on the research of RB-SiC material welding and joining technologies. The difference between welding and defect repair lies in the fact that the former connects two objects into a whole, while the latter repairs local defects in a whole. Although welding and repair are fundamentally different, welding technology can still provide reference and inspiration for defect repair technology. Existing RB-SiC welding technologies include brazing, laser welding, and arc welding. For example, Chinese patent application CN117817066A, published on April 5, 2024, entitled "A joining method for reaction-sintered silicon carbide, RB-SiC connector," discloses a method for welding RB-SiC base material with metal flux. This method involves processes such as brazing filler metal preparation, pretreatment of the surfaces to be welded, coating the surfaces to be welded with brazing filler metal, bonding the two surfaces to be welded, and high-temperature brazing. Brazing is a complex and cumbersome process. To ensure good mechanical properties of the joint, pressure is typically applied to both base materials during welding to create a porosity-free, high-performance weld. However, unlike the connection of two base materials, in ceramic defect repair, the base materials are a single unit. Once the brazing filler filler fills the weld, it's difficult to apply pressure, thus compromising the overall performance of the repaired area. Specifically, according to the results of Chinese patent application CN119263891A, published on January 7, 2025, entitled "A Method for Repairing Cracks in Silicon Carbide Ceramic Matrix Composite Parts for Aero-engines," brazing technology cannot be used efficiently to repair RB-SiC cracks wider than 0.2 mm. Chinese patent application CN115626776A, published on January 20, 2023, entitled "A Glass Powder for Laser-Assisted Joining of Silicon Carbide Ceramic Materials and Its Preparation Method and Application," discloses a laser-assisted SiC ceramic joining method. However, due to the instantaneous high-energy heat generated by the laser, improper processing can lead to a large temperature gradient in the heat-affected zone of the weld surface, easily causing thermal stress. If this thermal stress is not properly released, secondary cracks can easily occur, resulting in more severe defects in the substrate. Furthermore, arc welding is a typical fusion welding technique, and its application significantly affects the microstructure and properties of the base material.

[0004] In summary, RB-SiC defects range in size from nanometers to millimeters, and their depths range from millimeters to centimeters. Existing brazing techniques have requirements regarding defect size, requiring a width of less than 0.2 mm, while ensuring uniform coating of the brazing filler metal is difficult when the defect depth is large. Laser welding and arc welding both adversely affect the base material, and process parameters are difficult to control. Therefore, researching a technology that does not affect the RB-SiC base material and can repair defects across scales is crucial for the high-efficiency production and long-life service of large-size RB-SiC mirrors. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials.

[0006] The purpose of this invention is to provide a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, specifically including the following steps: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-sintered silicon carbide, and cut silicon-based alloy blocks to a size of 2 to 3 times the defect width and 1 to 1.5 times the height; S2. Surface pretreatment of reactive sintered silicon carbide: Defects in reactive sintered silicon carbide are ultrasonically cleaned with organic solvent for 20-40 minutes. S3. Sample loading: Place the silicon-aluminum alloy block above the defects in the reaction-bonded silicon carbide, and evenly spread silicon powder on the surface of the reaction-bonded silicon carbide; the silicon powder should be 3-8% of the mass fraction of the reaction-bonded silicon carbide. S4. Single sintering: Set an appropriate sintering temperature according to the melting point of the silicon-based alloy, and heat at a rate of 3~10℃ / min. After reaching the sintering temperature, hold for 1~3 hours. The sintering temperature should be higher than the melting point of the silicon-based alloy. S5. Polish the surface of the repaired reactive sintered silicon carbide to obtain the repaired reactive 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 >5%.

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

[0009] Preferably, the organic solvent in step S2 includes acetone, alcohol, methanol, n-hexane, n-propanol, and isopropanol; 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 surface roughness of the defects.

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

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

[0013] Preferably, the heating rate in step S4 is 5℃ / min, and the holding time is 1h.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention utilizes a silicon-based alloy with controllable composition to achieve a solid-liquid phase transformation within a temperature range below the melting point of silicon. Under gravity and vacuum conditions, the molten silicon-based alloy fills defects such as pores and cracks. After a 1-3 hour heat treatment, the alloying elements in the silicon-based alloy undergo interdiffusion reactions with the silicon in the matrix, improving the bonding strength between the repaired area and the matrix. Furthermore, 3-8% by mass of silicon powder is added to the RB-SiC surface to prevent secondary defects caused by silicon loss in the RB-SiC matrix during sintering. For large-sized defects (width or diameter greater than 0.2 mm and depth greater than 5 mm), this invention proposes a sandblasting technique to improve the surface roughness of cracked surfaces. Based on metallurgical bonding, the high-roughness surface increases the mechanical bonding force between the repaired area and the matrix, better solving the technical challenge of repairing large-sized defects. Attached Figure Description

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

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

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

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0019] This invention provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, specifically including the following steps: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-bonded silicon carbide (RB-SiC), and cut silicon-based alloy blocks to a size of 2 to 3 times the defect width and 1 to 1.5 times the height; the silicon-based alloy blocks should be slightly larger than the defect size; Specifically, defects in reactive sintered silicon carbide (RB-SiC) include cracks and pores; defects in reactive sintered silicon carbide have a width or diameter greater than 0.2 mm and a depth greater than 5 mm; when the defect is a crack, a silicon-based alloy block with a crack width of 2 to 3 times and a height of 1 to 1.5 times is cut; when the defect is a pore, a silicon-based alloy block with a pore diameter of 2 to 3 times and a height of 1 to 1.5 times is cut. Cutting is done using 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 greater than 5%.

[0020] S2. Surface pretreatment of reaction-bonded silicon carbide: Defects in reaction-bonded silicon carbide are ultrasonically cleaned with organic solvent for 20-40 minutes to remove surface contaminants and prevent them from affecting the wettability of the silicon-aluminum alloy. Specifically, the organic solvents include acetone, alcohol, methanol, n-hexane, n-propanol, isopropanol, etc.; in a specific embodiment, the ultrasonic time is 30 minutes. Before ultrasonic cleaning, the surface of the RB-SiC crack was treated with sandblasting to appropriately increase the surface roughness of the crack, which is conducive to the formation of mechanical interlocking between the alloy and the matrix after melting and solidification.

[0021] S3. Sample loading: Place the silicon-aluminum alloy block on the defective surface of the reaction-bonded silicon carbide (RB-SiC). To prevent poor temperature control during the sintering process from causing silicon flow or evaporation in the RB-SiC, uniformly spread 3-8% by mass of silicon powder on the surface of the RB-SiC before the first sintering. By increasing the amount of silicon powder, the silicon loss that may occur during the sintering process can be compensated, ensuring the stability of the sintering process and the performance of the final product. Preferably, the silicon powder is 5-8% of the mass fraction of reaction-bonded silicon carbide; in a specific embodiment, the silicon powder is 5% of the mass fraction of reaction-bonded silicon carbide.

[0022] S4. Single sintering: Set an appropriate sintering temperature according to the melting point of the silicon-based alloy, and heat at a rate of 3~10℃ / min. After reaching the sintering temperature, hold for 1~3 hours. The sintering temperature should be higher than the melting point of the silicon-based alloy. Specifically, the heating rate is 5℃ / min, and the holding time is 1h.

[0023] S5. Polish the repaired reactive sintered silicon carbide (RB-SiC) surface to obtain the repaired reactive sintered silicon carbide; Specifically, the polishing process is grinding and polishing.

[0024] Example 1 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, specifically including the following steps: S1. Prepare silicon-aluminum alloy (Si-Al) samples: Measure the crack size of RB-SiC, and use a diamond cutter to prepare a silicon-aluminum alloy block with a width of 2 times the crack width and a height of 1 times the crack depth. The silicon-aluminum alloy is a commercially available sample with a silicon content of 80%.

[0025] S2. RB-SiC sample surface pretreatment: The RB-SiC crack was ultrasonically cleaned for 30 minutes with acetone, alcohol and other solutions to remove surface contaminants and prevent them from affecting the wettability of the silicon-aluminum alloy.

[0026] S3. Sample loading: Place the silicon-aluminum alloy block prepared in step S1 on the cracked surface of RB-SiC treated in step S2. To prevent poor temperature control during sintering from causing silicon to flow or evaporate in RB-SiC, spread silicon powder with a mass fraction of 5% evenly on the surface of RB-SiC before sintering.

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

[0028] S5. Grind and polish the repaired reactive sintered silicon carbide surface to obtain the repaired reactive sintered silicon carbide. The changes in microstructure of the cracked area before and after repair were compared. Simultaneously, the changes in microstructure between the repaired cracked area and the matrix were analyzed. For example... Figure 1 As shown, a crack of approximately 500 μm exists in RB-SiC. After one sintering process as described above, as... Figure 2 The cracked area shown is completely filled. Energy dispersive spectroscopy analysis shows that aluminum in the silicon-aluminum alloy diffuses into the matrix and forms an intermediate phase with silicon in the matrix.

[0029] The above results show that: (1) the low-temperature one-time sintering repair technology can eliminate surface cracks of RB-SiC, prevent further crack propagation, and prevent component failure; (2) the silicon-aluminum alloy can undergo a diffusion reaction with silicon in the matrix material to form an intermediate phase, which is beneficial to improving 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, specifically including the following steps: S1. Prepare silicon-aluminum alloy (Si-Al) samples: Measure the crack size of RB-SiC, and use a diamond cutter to prepare silicon-aluminum alloy blocks with a width of 2 times the crack width and a height of 1 times the crack depth. The silicon-aluminum alloy is a commercially available sample with a silicon content of 12.6%.

[0031] Steps S2 and S3 are the same as in Example 1.

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

[0033] S5. Grind and polish the repaired reactive sintered silicon carbide surface to obtain the repaired reactive sintered silicon carbide. The apparent porosity of the repaired RB-SiC was measured and compared with that of crack-free RB-SiC to analyze the effect of the repair technique on the surface density of the RB-SiC material. Furthermore, scanning electron microscopy and optical microscopy were used to evaluate the bonding state 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, specifically including the following steps: S1. Prepare silicon-aluminum alloy (Si-Al) samples: Measure the crack size of RB-SiC, and use a diamond cutter to prepare a silicon-aluminum alloy block with a width of 3 times the crack width and a height of 1 times the crack depth. The silicon-aluminum alloy is a commercially available sample with a silicon content of 70%.

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

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

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

[0038] S5. Grind and polish the repaired reactive sintered silicon carbide surface to obtain the repaired reactive sintered silicon carbide. The repaired RB-SiC surface was ground and polished, and the changes in microstructure in the crack area were compared before and after repair. After sandblasting treatment of the crack area, a high-strength connection can be achieved between the alloy and the matrix in the crack area through the coupling effect of mechanical interlocking and metallurgical bonding.

[0039] Example 4 This embodiment provides a one-time sintering repair method for defects in reaction-sintered silicon carbide materials, specifically including the following steps: S1. Prepare silicon-copper alloy (Si-Cu) samples: Measure the pore size of RB-SiC, and use a diamond cutter to prepare a silicon-copper alloy block with a pore diameter of 3 times and a height of 1 times the pore depth. The silicon-copper alloy is a commercially available sample with a silicon content of >5%.

[0040] S2. RB-SiC sample surface cleaning treatment: The pores of RB-SiC were ultrasonically cleaned for 30 minutes using solutions such as acetone and alcohol to remove surface contaminants and prevent them from affecting the wettability of the silicon-copper alloy.

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

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

[0043] S5. Polish the surface of the repaired reactive sintered silicon carbide to obtain the repaired reactive sintered silicon carbide.

[0044] The changes in microstructure in the cracked area before and after repair were compared. The distribution of copper at the defect and in the matrix was also analyzed. Porosity testing was performed to evaluate 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, specifically including the following steps: S1. Prepare silicon-nickel alloy samples: Measure the crack size of RB-SiC, and use a diamond cutter to prepare silicon-nickel alloy blocks with a width of 3 times the hole diameter and a height of 1 times the hole depth. The silicon-nickel alloy is a commercially available sample with a silicon content of >5%.

[0046] Steps S2 and S3 are the same as in Example 1.

[0047] S4. First sintering: The sintering temperature is set to 1280℃ according to the Si-Ni binary phase diagram; the temperature is increased at a rate of 5℃ / min, and the temperature is held for 1 hour after reaching the sintering temperature.

[0048] S5. Polish the surface of the repaired reactive sintered silicon carbide to obtain the repaired reactive sintered silicon carbide.

[0049] The changes in microstructure in the pore area before and after repair were compared. Porosity tests were performed to evaluate the surface density of the repaired sample.

[0050] The key technical points and advantages of this invention are as follows: Addressing the problems of defects caused by thermal stress during the fabrication of large-diameter RB-SiC mirrors or defects caused by collisions and vibrations during processing, this invention provides a technical solution for repairing RB-SiC cracks using a low-temperature, one-step sintering process with silicon-based alloys. This ensures low porosity and high density repair of the cracked area without reducing the optical performance of the mirror. A silicon-based alloy block, with a shape approximating the crack and a volume slightly larger than the crack, is prepared using a wire cutting machine and placed on top of the RB-SiC crack. Based on the binary phase diagram of the silicon-based alloy, a one-step sintering process is designed. After holding at temperature 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 controlling the primary sintering temperature regime, the study investigates the coupling effect between silicon-based alloy components and the sintering temperature field on defects and changes in the composition and properties of the matrix. This enables high-density repair of defects in RB-SiC and ensures the service stability of RB-SiC.

[0052] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0053] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A one-time sintering repair method for defects in reaction-sintered silicon carbide materials, characterized in that: Specifically, the steps include the following: S1. Prepare silicon-based alloy samples: Measure the defect size of reaction-sintered silicon carbide, and cut silicon-based alloy blocks to a size of 2 to 3 times the defect width and 1 to 1.5 times the height; S2. Surface pretreatment of reactive sintered silicon carbide: Defects in reactive sintered silicon carbide are ultrasonically cleaned with organic solvent for 20-40 minutes. S3. Sample loading: Place the silicon-aluminum alloy block above the defects in the reaction-bonded silicon carbide, and evenly spread silicon powder on the surface of the reaction-bonded silicon carbide; the silicon powder should be 3-8% of the mass fraction of the reaction-bonded silicon carbide. S4. Single sintering: Set an appropriate sintering temperature according to the melting point of the silicon-based alloy, and heat at a rate of 3~10℃ / min. After reaching the sintering temperature, hold at that temperature for 1~3 hours. The sintering temperature should be higher than the melting point of the silicon-based alloy. S5. Polish the surface of the repaired reactive sintered silicon carbide to obtain the repaired reactive sintered silicon carbide.

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

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

4. The method for one-time sintering repair of 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; the ultrasonic time is 30 minutes.

5. The method for one-time sintering repair of defects in reaction-sintered silicon carbide materials according to claim 1, characterized in that: 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 surface roughness of the defects.

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

7. The method for one-time sintering repair of 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 reaction-sintered silicon carbide.

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

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