Method for repairing microcracks of silicon carbide fiber reinforced silicon carbide composite material

Abstract

The invention relates to the field of silicon carbide composite material repairing, in particular to a silicon carbide fiber reinforced silicon carbide composite material microcrack repairing method which comprises the following steps: spraying a silicon-containing coating on the surface of a pretreated to-be-repaired silicon carbide fiber reinforced silicon carbide composite material, the silicon-containing coating covers the whole surface of the silicon carbide fiber reinforced silicon carbide composite material to be repaired, the thickness of the silicon-containing coating ranges from 30 micrometers to 80 micrometers, the silicon carbide fiber reinforced silicon carbide composite material to be repaired sprayed with the silicon-containing coating is heated, the heating temperature ranges from 1420 DEG C to 1500 DEG C, and finishing is conducted after cooling. The problems that an existing repairing method is long in repairing period, complex in operation and poor in safety are solved.

Description

Technical Field

[0001] The present invention relates to the field of silicon carbide composite material repair, and in particular to a method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material. Background Art

[0002] Silicon carbide fiber-reinforced silicon carbide composites (SiC / SiC composites) are a key material choice for high-temperature, hot-end components of aircraft engines due to their low density, high-temperature resistance, and oxidation resistance. As aircraft engines develop toward higher thrust-to-weight ratios, SiC / SiC composites are increasingly used in hot-end components such as the liner, turbine outer ring, and turbine guide vanes. These composites not only withstand complex mechanical loads and vibration stresses, but also are subject to oxidative corrosion from high-temperature combustion gases. When SiC / SiC composite components are subjected to excessive local loads during service, microcracks and other microdefects can easily develop in the matrix. These microcracks serve as pathways for oxygen attack, allowing high-temperature oxygen to further oxidize the SiC fibers and their interfacial layers, causing a sharp drop in the strength of the SiC / SiC composite, severely impacting the safe long-term service life of SiC / SiC composite components. Therefore, when microcracks develop in the matrix, appropriate methods must be employed to bridge the cracks, thereby blocking the oxygen pathways and extending the component's service life. The prepreg-infiltration process for preparing SiC / SiC composites offers advantages such as short cycle times, low cost, and high density, making it the mainstream preparation process for SiC / SiC composites used in aircraft engines. Existing repair methods typically involve cleaning and drying the SiC / SiC composite specimen to be repaired using HF etching. The specimen is then placed in a vacuum heat treatment furnace, where gases such as trichloromethylsilane, H2, NH3, and BCl3 are introduced. A high-temperature chemical reaction, known as chemical vapor deposition (CVD), deposits SiC on the specimen surface. However, CVD is slow, requires a long repair cycle, is sensitive to process parameters, requires precise control, and is complex to operate. Furthermore, the repair process involves the use of toxic gases, resulting in poor safety. Summary of the Invention

[0003] In view of this, the present invention provides a method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite materials to solve the problems of long repair cycle, complex operation and poor safety of existing repair methods.

[0004] The present invention provides a method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material, comprising the following steps:

[0005] A silicon-containing coating is sprayed on the surface of the pretreated silicon carbide fiber reinforced silicon carbide composite material to be repaired. The silicon-containing coating covers the entire surface of the silicon carbide fiber reinforced silicon carbide composite material to be repaired and has a thickness of 30μm-80μm. The silicon carbide fiber reinforced silicon carbide composite material to be repaired after being sprayed with the silicon-containing coating is heated at a temperature of 1420℃-1500℃ and is trimmed after cooling.

[0006] The present invention provides a method for repairing microcracks in a silicon carbide fiber-reinforced silicon carbide composite material. By spraying a silicon-containing coating onto the entire surface of the silicon carbide fiber-reinforced silicon carbide composite material and then performing a heat treatment, the method has a short implementation cycle, high production efficiency, no harmful gas generation, and enhanced safety. Furthermore, since free silicon within the matrix melts at high temperatures and can escape through interconnected internal pores or microcracks, the integrally sprayed silicon provided by the present invention effectively prevents the escape of free silicon within the matrix during the heat treatment process, while simultaneously providing a silicon source for the microcracks, thereby healing the cracks and achieving a good repair effect.

[0007] The thickness of the silicon-containing coating is 30μm-80μm because when the coating is too thin, it is impossible to fill and repair microcracks. When the coating is too thick, the bonding strength between silicon and the substrate is reduced, and there is a risk of falling off. In addition, it also makes the processing allowance during subsequent mechanical processing larger. The above range limitation can achieve both the microcrack repair function and the bonding strength between the coating and the substrate.

[0008] The heating temperature is 1420℃-1500℃ because the melting point of silicon is 1414℃. Heating temperature above 1420℃ can make silicon melt and have fluidity, and under the action of capillary force, it can infiltrate and fill the micro cracks of the matrix to play a repairing role. At the same time, the heat treatment temperature cannot be too high to prevent damage to the silicon carbide fiber and the matrix.

[0009] In an optional embodiment, the silicon-containing coating is sprayed using a plasma spraying process or a physical vapor deposition process.

[0010] The plasma spraying process has a fast deposition rate, does not require a vacuum environment, can be operated at normal pressure, and has low cost. The physical vapor deposition process has relatively high equipment requirements and a slow deposition rate, making it difficult to achieve large-area rapid coating. However, both processes are less sensitive to process parameters than the chemical vapor deposition process, are simple to operate, do not produce harmful gases, and are relatively safe.

[0011] In an optional embodiment, silicon powder or silicon alloy powder is used to spray the silicon-containing coating.

[0012] Silicon powder or silicon alloy powder has a high silicon content and can be quickly filled into the microcracks of the matrix after melting, while minimizing the introduction of other impurities and ensuring the repair effect.

[0013] In an optional embodiment, the silicon alloy powder is any one of Si-Mo, Si-Ti or Si-Zr.

[0014] In an optional embodiment, the silicon carbide fiber reinforced silicon carbide composite material to be repaired after being sprayed with the silicon-containing coating is heated in a vacuum atmosphere or an inert gas atmosphere.

[0015] Heating is performed in a vacuum atmosphere or an inert gas atmosphere to prevent silicon from oxidizing and ensure the repair effect.

[0016] In an optional embodiment, the pretreatment includes cleaning and then drying the silicon carbide fiber reinforced silicon carbide composite material to be repaired.

[0017] In an optional embodiment, the silicon carbide fiber reinforced silicon carbide composite material to be repaired is ultrasonically cleaned using anhydrous ethanol or deionized water, and the cleaning time is 10 minutes to 20 minutes.

[0018] Ultrasonic cleaning with anhydrous ethanol or deionized water can ensure the cleaning effect without damaging the silicon carbide fiber reinforced silicon carbide composite material to be repaired. The cleaning time is sufficient to visually check that there is no dirt on the surface.

[0019] In an optional embodiment, the drying temperature is 80°C-120°C.

[0020] Anhydrous ethanol evaporates at 80°C and deionized water evaporates at 100°C. Setting the drying temperature at 80°C-120°C will accelerate the removal of anhydrous ethanol and water on the surface of the component and improve the repair efficiency.

[0021] In an optional embodiment, a diamond grinding head or a diamond tool is used to trim the assembly surface of the repaired silicon carbide fiber reinforced silicon carbide composite material.

[0022] In an optional embodiment, the width of the microcracks in the silicon carbide fiber reinforced silicon carbide composite material is less than or equal to 200 μm. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0024] Next, embodiments of the present invention will be described.

[0025] According to an embodiment of the present invention, a method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material is provided, comprising the following steps:

[0026] A silicon-containing coating is sprayed on the surface of the pretreated silicon carbide fiber reinforced silicon carbide composite material to be repaired. The silicon-containing coating covers the entire surface of the silicon carbide fiber reinforced silicon carbide composite material to be repaired and has a thickness of 30μm-80μm. The silicon carbide fiber reinforced silicon carbide composite material to be repaired after being sprayed with the silicon-containing coating is heated at a temperature of 1420℃-1500℃ and is trimmed after cooling.

[0027] The repair target is a silicon carbide fiber-reinforced silicon carbide composite material produced using a prepreg-infiltration process. It has microcracks no wider than 200 μm, but no macrocracks or chipping. The silicon-containing coating can be sprayed in either air or vacuum, with vacuum being preferred to prevent oxidation of the silicon.

[0028] The method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material provided by the present invention is to spray a silicon-containing coating on the surface of the silicon carbide fiber reinforced silicon carbide composite material as a whole and then perform heat treatment. The implementation cycle is short, the production efficiency is high, no harmful gas is generated, and the safety is higher. Moreover, since the free silicon in the matrix melts at high temperatures, it can escape through the connected internal pores or microcracks, and the overall sprayed silicon provided by the present invention can effectively prevent the free silicon in the matrix from escaping during the heat treatment process, and at the same time provide a silicon source for the microcrack site, so that the cracks are bridged and the repair effect is good. Since the present invention is prepared by a prepreg-infiltration process, there is residual silicon in the matrix of the silicon carbide fiber reinforced silicon carbide composite material. The method of the present invention can effectively prevent the free silicon in the matrix from escaping and prevent the reduction of the mechanical properties of the composite material.

[0029] The thickness of the silicon-containing coating is 30μm-80μm because when the coating is too thin, it is impossible to fill and repair microcracks. When the coating is too thick, the bonding strength between silicon and the substrate is reduced, and there is a risk of falling off. In addition, it also makes the processing allowance during subsequent mechanical processing larger. The above range limitation can achieve both the microcrack repair function and the bonding strength between the coating and the substrate.

[0030] The heating temperature is 1420°C-1500°C because silicon has a melting point of 1414°C. Heating above 1420°C allows silicon to melt and become fluid, allowing it to infiltrate and fill microcracks in the substrate under capillary action, thus repairing the substrate. At the same time, the heat treatment temperature should not be too high to prevent damage to the substrate. Of course, the thickness of the silicon-containing coating and the heating temperature can be selected based on the degree of damage to the silicon carbide fiber-reinforced silicon carbide composite material to be repaired and the actual needs.

[0031] In one embodiment, the silicon-containing coating is sprayed using a plasma spraying process or a physical vapor deposition process.

[0032] The silicon-containing coating is sprayed evenly onto the surface of the silicon carbide fiber-reinforced silicon carbide composite material to be repaired. The preferred spray thickness is 50μm-70μm. The plasma spraying process has a fast deposition rate, does not require a vacuum environment, can be operated at normal pressure, and is low-cost. The physical vapor deposition process has relatively high equipment requirements and a slow deposition rate, making it difficult to achieve rapid coating of large areas. However, both processes are less sensitive to process parameters than the chemical vapor deposition process, are simple to operate, do not produce harmful gases, and are relatively safe.

[0033] In one embodiment, silicon powder or silicon alloy powder is used to spray the silicon-containing coating.

[0034] Silicon powder or silicon alloy powder has a high silicon content and can be quickly filled into the microcracks of the matrix after melting, while minimizing the introduction of other impurities and ensuring the repair effect.

[0035] In one embodiment, the silicon alloy powder is any one of Si-Mo, Si-Ti or Si-Zr.

[0036] In one embodiment, the silicon carbide fiber reinforced silicon carbide composite material to be repaired after being sprayed with the silicon-containing coating is heated in a vacuum atmosphere or an inert gas atmosphere.

[0037] Heating is performed in a vacuum atmosphere or an inert gas atmosphere to prevent silicon oxidation and ensure the repair effect. Specifically, the silicon carbide fiber-reinforced silicon carbide composite material to be repaired, after being sprayed with a silicon-containing coating, can be placed in a closed box. The closed box is vacuumed in advance or filled with an inert gas, such as helium or argon, to isolate oxygen.

[0038] In one embodiment, the pretreatment includes cleaning and then drying the silicon carbide fiber reinforced silicon carbide composite material to be repaired.

[0039] In one embodiment, the silicon carbide fiber reinforced silicon carbide composite material to be repaired is ultrasonically cleaned using anhydrous ethanol or deionized water, and the cleaning time is 10 minutes to 20 minutes.

[0040] Ultrasonic cleaning with anhydrous ethanol or deionized water can ensure the cleaning effect without damaging the silicon carbide fiber reinforced silicon carbide composite material to be repaired. The cleaning time is sufficient to visually check that there is no dirt on the surface.

[0041] In one embodiment, the drying temperature is 80°C-120°C.

[0042] Anhydrous ethanol evaporates at 80°C and deionized water evaporates at 100°C. Setting the drying temperature at 80°C-120°C will accelerate the removal of anhydrous ethanol and water on the surface of the component and improve the repair efficiency.

[0043] In one embodiment, a diamond grinding head or a diamond tool is used to trim the assembly surface of the repaired silicon carbide fiber reinforced silicon carbide composite material to remove excess residual silicon on the assembly surface.

[0044] In order to further verify the repair effect of the method of this embodiment, the following examples are provided:

[0045] Example 1

[0046] A 100mm x 10mm tensile strip of silicon carbide fiber-reinforced silicon carbide composite was stretched to a strain of 0.2%. This strain produced numerous microcracks in the matrix, but the strip did not break. The strip was then ultrasonically cleaned with anhydrous ethanol for 10 minutes and then dried at 80°C.

[0047] A layer of silicon was sprayed on the upper and lower surfaces and side surfaces of the tensile specimen using a plasma spraying process, with a spraying thickness of 50 μm.

[0048] The tensile specimens with the silicon-containing coating were placed in a high-temperature furnace for vacuum heat treatment at a temperature of 1420°C and a heating time of 30 min.

[0049] Testing revealed that the tensile strength of the original tensile specimens was (286±23) MPa, while that of the repaired specimens was (278±29) MPa, indicating that the repair treatment had little effect on the tensile strength. Both the microcracked and repaired specimens were oxidized in an oxygen environment at 1200°C for 300 hours. The tensile strength of the microcracked specimens was (213±17) MPa, while that of the repaired specimens was (265±32) MPa, demonstrating that the repair treatment significantly improved the material's service life.

[0050] Example 2

[0051] During testing, the outer ring of a certain turbine model experienced localized excessive stress, resulting in damage to the surface and internal structure of the reinforced structure. Microcracks were observed on the surface using a stereoscope. The outer ring was ultrasonically cleaned with anhydrous ethanol for 20 minutes and then dried at 120°C.

[0052] A layer of silicon is sprayed on the entire surface of the turbine outer ring using a plasma spraying process with a spraying thickness of 30 μm.

[0053] The silicon-coated turbine outer ring was vacuum-heat treated in a high-temperature furnace at 1450°C for 30 minutes. No defects, such as microcracks, were observed on the surface after treatment.

[0054] After cooling, diamond tools are used to trim the mounting holes and outer surface of the turbine outer ring.

[0055] Example 3

[0056] During the assessment of a certain flame tube, excessive stress at the installation site caused microcracks near the mounting hole. These defects were observed using a stereoscope. The flame tube was ultrasonically cleaned with deionized water for 15 minutes and then dried at 100°C.

[0057] A layer of silicon is sprayed on the entire surface of the flame tube using a physical vapor deposition process, with a spraying thickness of 80μm.

[0058] The silicon-coated flame tube was placed in a high-temperature furnace for vacuum heat treatment at 1500°C for 30 minutes. No defects such as microcracks were observed on the surface after the treatment.

[0059] After cooling, use a diamond tool to trim the area around the flame tube mounting hole.

[0060] Although the embodiments of the present invention have been described in conjunction with experimental examples, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material, characterized in that: The following steps are involved: A silicon-containing coating is sprayed on the surface of the pretreated silicon carbide fiber reinforced silicon carbide composite material to be repaired. The silicon-containing coating covers the entire surface of the silicon carbide fiber reinforced silicon carbide composite material to be repaired and has a thickness of 30μm-80μm. The silicon carbide fiber reinforced silicon carbide composite material to be repaired after being sprayed with the silicon-containing coating is heated at a temperature of 1420℃-1500℃ and is trimmed after cooling.

2. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to claim 1, characterized in that: The silicon-containing coating is sprayed using a plasma spraying process or a physical vapor deposition process.

3. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to claim 1, characterized in that: Silicon powder or silicon alloy powder is used to spray the silicon-containing coating.

4. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to claim 3, characterized in that: The silicon alloy powder is any one of Si-Mo, Si-Ti or Si-Zr.

5. The method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material according to any one of claims 1 to 4, characterized in that: The silicon carbide fiber reinforced silicon carbide composite material to be repaired is heated and sprayed with a silicon-containing coating in a vacuum atmosphere or an inert gas atmosphere.

6. The method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material according to any one of claims 1 to 4, characterized in that: The pretreatment includes cleaning and then drying the silicon carbide fiber reinforced silicon carbide composite material to be repaired.

7. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to claim 6, characterized in that: The silicon carbide composite material to be repaired is ultrasonically cleaned using anhydrous ethanol or deionized water, and the cleaning time is 10 minutes to 20 minutes.

8. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to claim 7, characterized in that: The drying temperature is 80℃-120℃.

9. The method for repairing microcracks in a silicon carbide fiber reinforced silicon carbide composite material according to any one of claims 1 to 4, characterized in that: A diamond grinding head or a diamond tool is used to trim the assembly surface of the repaired silicon carbide fiber reinforced silicon carbide composite material.

10. The method for repairing microcracks in silicon carbide fiber reinforced silicon carbide composite material according to any one of claims 1 to 4, characterized in that: The width of the microcracks in the silicon carbide fiber reinforced silicon carbide composite material is less than or equal to 200 μm.