Preparation method and application of a low-shrinkage, high-bending-strength precision ceramic core material

Abstract

The present invention discloses a preparation method and application of a precision ceramic core material with low shrinkage and high flexural strength, which is made of multi-level structured silicon carbide fibers, silicon nitride microspheres and silicon-based ceramic slurry through electrostatic spinning, sol-gel, chemical grafting and high-temperature calcination. The interwoven and cross-linked structure of silicon carbide fibers can increase the structural stability of the material, thereby improving the flexural strength of the material in a high-temperature environment. Silicon carbide fibers contain a certain porosity and can adsorb and diffuse the gas generated during the sintering process, reducing the pressure of the gas and thus reducing the shrinkage of the material. Silicon nitride microspheres have a lower density and higher porosity and can be used to fill the gaps between materials to hinder the mutual contact and bonding between their particles, thereby reducing the sintering shrinkage of the material. The amino functional groups contained on its surface can form strong hydrogen bonds with the oxides on the surface of the silicon-based ceramic material, thereby improving the compatibility and bonding strength of the interface, thereby improving the flexural strength of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of precision ceramic material casting, and in particular to a preparation method and application of a precision ceramic core material with low shrinkage and high bending strength. Background Art

[0002] In recent years, with the rapid development of my country's aerospace industry, research on aircraft engines has received significant attention. Increased demand for military aircraft engines has led to a 20-30% profit increase for some aircraft engine manufacturers compared to last year, while increased demand for civilian aircraft engines has resulted in a 10.09% profit increase for some manufacturers. Ceramic core materials are a key component of aircraft engine manufacturing. Currently, commonly used ceramic core materials include zirconia, alumina, and silicon-based ceramic cores. However, while these single ceramic core materials offer advantages such as excellent corrosion resistance and low thermal conductivity, they still exhibit issues such as high brittleness, phase transitions at high temperatures, and grain growth caused by prolonged sintering, resulting in high sintering shrinkage, low high-temperature flexural strength, and susceptibility to cracking. These issues, in turn, affect the engine's high-temperature resistance.

[0003] In view of the advantages and disadvantages of the above-mentioned ceramic core materials, the researchers' research on modifying single ceramic core materials and synthesizing new ceramic core materials with high high-temperature resistance is of great significance in the field of precision ceramic core material casting. At present, researchers have obtained new ceramic core materials by chemically modifying the above-mentioned materials, adding plasticizers, binders, etc. Although the high-temperature flexural strength and sintering shrinkage of these new ceramic core materials have been improved, such as the ceramic core material prepared by mixing and sintering quartz glass powder, zirconium silicate powder, mica powder and reinforcing phase powder has a certain flexural strength (at a temperature of 1500°C, the flexural strength is 25-34MPa) and sintering shrinkage (sintering shrinkage is 0.62%), but in actual applications, there is still the problem of poor flexural strength at high temperatures due to phase transformation caused by high temperature during the reaction. In addition, due to factors such as the generation of gas in the reaction of the matrix material and its own large porosity, the shrinkage rate is high during the high-temperature sintering process, which in turn limits its application in the field of precision ceramic core material casting.

[0004] Chinese patent application number CN202210921970.X, "A Silica-Based Ceramic Core and Its Preparation Method," uniformly mixes zircon powder, quartz glass powder, and quartz glass fiber coated with alumina to form a ceramic core blank, which is then sintered to produce a ceramic core material. While this ceramic core material exhibits a certain degree of deformation resistance during sintering (deformation ranges from 0.09 to 5.96 mm), it still suffers from high shrinkage and poor high-temperature resistance.

[0005] The Chinese patent application number CN202210559518.3, “A photocurable 3D printed alumina-based ceramic core and its preparation method”, uses coarse, medium and fine alumina ceramic powders for grading to obtain a photocurable alumina-based ceramic core slurry, and obtains a ceramic core by photocuring 3D printing, degreasing and sintering. The ceramic core material has a certain flexural strength (when the open porosity is 34.4%, its flexural strength can reach 52.4MPa), but there is still a problem of gas expansion in the pores during high-temperature sintering due to the high porosity of the material, thereby increasing the shrinkage rate of the material. In addition, the high porosity of the material can easily lead to uneven shrinkage and stress concentration during the sintering process, which further affects the shrinkage rate of the material, thereby affecting the overall flexural strength of the material, limiting its application in the field of precision ceramic material casting technology.

[0006] The Chinese patent application number CN202111419333.4, “A Process for Preparing Ceramic Cores for Aeroengines”, uses quartz glass powder, zirconium silicate powder, mica powder and reinforcing phase powder and uses a plasticizer for bonding and mixing. After compression molding and sintering, a ceramic core material is obtained. The ceramic core material has good temperature resistance (the bending strength is 25-34 MPa at a temperature of 1500°C), but there is still a problem that the quartz glass powder, zirconium silicate powder, mica powder and reinforcing phase powder will form particle accumulation during the mixing process, and pores or particles will be rearranged and reorganized during high-temperature sintering, resulting in a change in the volume of the material, which in turn affects the shrinkage rate of the material (when the porosity is 31.5%, the sintering shrinkage rate is 0.62%). In addition, the above-mentioned particles cause interfacial reactions and phase changes between different materials during the mixing process, and the grain boundaries and interface areas of the material become brittle, thereby causing the material to have low bending strength during use.

[0007] The Chinese patent application number CN202110047872.3, "A Spinel-Magnesium-Based Ceramic Core and Its Preparation Method," uses spinel powder, zirconium oxide powder, titanium dioxide powder, and magnesium oxide powder as raw materials, adds an appropriate amount of binder to mix and prepare a slurry, and uses hot injection molding and sintering to prepare the spinel-magnesium-based ceramic core. This ceramic core material has good high-temperature resistance (18 thermal shock cycles at 1600-1950°C), but there is still the problem of phase transformation of the material structure during high-temperature sintering, which in turn affects the sintering shrinkage of the material (sintering shrinkage is 0.7% to 3%), thereby limiting its application in the field of precision ceramic material casting technology.

[0008] In view of the problems of high sintering shrinkage and low bending strength at high temperature caused by the generation of gas by the matrix raw materials during the mixed sintering process and the interface reaction and phase change between the materials in the ceramic core material in the above patent, it is of great research significance to design a low shrinkage and high bending strength precision ceramic core material for use in aircraft engines. Summary of the Invention

[0009] The present invention provides a preparation method and application of a precision ceramic core material with low shrinkage and high flexural strength, which solves the problems of low shrinkage and low flexural strength of existing ceramic core materials during high-temperature sintering. The present invention adopts electrospinning to prepare multi-level structured silicon carbide fibers, and its interwoven and cross-linked structure can increase the structural stability of the material, thereby improving the flexural strength of the material in a high-temperature environment. At the same time, the multi-level structured silicon carbide fibers contain a certain porosity, which can adsorb and diffuse the gas generated during the sintering process, reduce the pressure of the gas, and thus reduce the shrinkage of the material. In addition, the silicon nitride microspheres prepared for grafting silicon carbide fibers have a low density and a high porosity, which can be used to fill the gaps between materials to hinder the mutual contact and bonding between their particles, thereby reducing the sintering shrinkage of the material. At the same time, the amino functional groups contained on its surface can form strong hydrogen bonds with the oxides on the surface of the silicon-based ceramic material, thereby improving the compatibility and bonding strength of the interface, thereby improving the flexural strength of the material. Therefore, the two are combined, and the carbon-based functional groups are broken under high temperature to form activated carbon intermediates, which undergo recombination reactions with nitrogen atoms to form strong silicon-oxygen bonds, silicon-nitrogen bonds and silicon-carbon bonds, forming a silicon nitride grafted layer on the surface of the silicon carbide fiber, increasing the surface activity and interfacial compatibility of the fiber, thereby further increasing the high-temperature flexural strength of the material, while reducing gas pressure, thereby further reducing the sintering shrinkage of the material.

[0010] The present invention uses silicon carbide and silicon nitride to prepare composite fibers for the preparation of ceramic core materials. First, the prepared multi-level structured silicon carbide fiber has a high surface area and pore structure and has a high melting point (can be heated to 1200-1500°C in a vacuum or inert gas) and thermal stability (at 1200°C, its flexural strength can reach 1960-4410MPa), thereby reducing the sintering shrinkage of the material during high-temperature sintering. And its multi-level structure can maintain the structural integrity and mechanical properties of the fiber at high temperatures, thereby improving the high-temperature flexural strength of the material. Secondly, with the help of the low density of silicon nitride microspheres (3.12g / cm 3) and thermal stability at high temperatures (its flexural strength is ≥980MPa at 1200°C), thereby reducing the mutual collision and solid-phase diffusion between particles during high-temperature sintering, improving the compatibility and bonding strength of the interface in the material, thereby further reducing the sintering shrinkage of the material and improving the high-temperature flexural strength of the material. Combining the advantages of the above-mentioned silicon carbide fibers and silicon nitride microspheres with a multi-level structure, the present invention constructs a precision ceramic core material with low shrinkage and high flexural strength by chemically grafting and modifying the two.

[0011] The present invention provides a method for preparing a precision ceramic core material with low shrinkage and high bending strength, comprising the following steps:

[0012] Step S1, preparing silicon carbide fibers with a multi-level structure by electrospinning: tetraethyl orthosilicate or tetramethyl orthosilicate, anhydrous ethanol, polyvinyl pyrrolidone or polyvinyl alcohol and N,N-dimethylformamide or dimethyl sulfoxide are uniformly mixed and then a precursor fiber is prepared using an electrospinning device. After spinning, the precursor fiber is dried and cured. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on the fiber. The crucible is buried in a sagger filled with graphite powder to perform a siliconization reaction to obtain the silicon carbide fibers with a multi-level structure.

[0013] Step S2, preparing silicon nitride ceramic microspheres by a sol-gel method: mixing hexamethylenetetramine or hexamethylene-tert-butyltetramine and urea or aminosilane and adding them to deionized water to obtain a mixed solution B; stirring ZrO(NO3)2 and the mixed solution B uniformly, adding concentrated nitric acid solution, then adding deionized water and stirring until viscous, adding nano-silicon powder and ultrasonically dispersing it uniformly to obtain a glue solution; adding the glue solution to hot silicone oil, curing it after completion, taking it out and drying it to obtain gel microspheres; calcining the gel microspheres to obtain the silicon nitride ceramic microspheres;

[0014] Step S3, preparation of silicon carbide / silicon nitride composite fibers: taking the silicon nitride ceramic microspheres, silane coupling agent, photoinitiator and the silicon carbide fibers in anhydrous ethanol, stirring them uniformly and sealing them to obtain a mixed solution C; placing the sealed mixed solution C in an ultraviolet lamp for reaction to obtain composite fibers, then taking out the composite fibers and washing them, and drying them after completion to obtain the silicon carbide / silicon nitride composite fibers;

[0015] Step S4, preparation of precision ceramic core material: uniformly dispersing the silicon carbide / silicon nitride composite fiber in a silicon-based ceramic slurry by ultrasonic dispersion, and then calcining the dispersion to obtain the precision ceramic core material.

[0016] In the above technical solution, the specific preparation process of step S1 includes the following steps:

[0017] S11, 10-20 mL of tetraethyl orthosilicate or tetramethyl orthosilicate, 10-25 mL of anhydrous ethanol, 1-3 g of polyvinyl pyrrolidone or polyvinyl alcohol, and 0.5-1.5 mL of N,N-dimethylformamide or dimethyl sulfoxide, stirred for 15-35 minutes until uniformly mixed to obtain a mixed solution A;

[0018] S12, preparing precursor fibers by electrospinning the mixed solution A using an electrospinning device, wherein the spinning voltage is 15 to 30 kV, the spinning flow rate is 1 to 5 mL / h, and the receiving distance is 10 to 20 cm;

[0019] S13, after the spinning is completed, the precursor fiber is dried at 60-90° C. for 8-14 hours and cured at 100-200° C. for 1-4 hours, and after curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber;

[0020] S14, burying the crucible in a sagger filled with graphite powder, and performing siliconization reaction at 1300-1600° C. for 7-9 hours to obtain the silicon carbide fiber with a multi-level structure.

[0021] In the above technical solution, the specific preparation process of step S2 includes the following steps:

[0022] S21, mixing hexamethylenetetramine or hexamethylenetetramine and urea or aminosilane in a molar ratio of 1:1 to 1:4 and adding the mixture to 50 to 100 mL of deionized water to obtain a mixed solution B;

[0023] S22, stirring ZrO(NO3)2 and the mixed solution B in a molar ratio of 1:1.2 to 1:3.5 for 5 to 20 minutes until uniformly mixed, and adding 0.5 to 1.5 mL of concentrated nitric acid solution dropwise, then adding 50 to 100 mL of deionized water and stirring for 1 to 2 hours until viscous, and adding 0.5 to 2 g of nano-silicon powder and ultrasonicating for 1 to 2 hours until uniformly dispersed to obtain a glue;

[0024] S23, dripping the glue solution dropwise into hot silicone oil at 80-120° C. using a dropper, curing for 12-36 hours, removing the solution and drying it at 40-70° C. for 12-24 hours to obtain gel microspheres;

[0025] S24, calcining the gel microspheres at 1000-2000° C. for 3-7 hours to obtain the silicon nitride ceramic microspheres.

[0026] In the above technical solution, the specific preparation process of step S3 includes the following steps:

[0027] S31, weighing 0.5-1.5 g of the silicon nitride ceramic microspheres, 0.01-0.03 g of a silane coupling agent, 0.005-0.015 g of a photoinitiator, and the silicon carbide fiber in 100-400 mL of anhydrous ethanol, stirring for 1-4 h until uniform, and sealing the mixture to obtain a mixed solution C;

[0028] S32, placing the sealed mixed solution C in an ultraviolet lamp to react for 3 to 5 hours to obtain composite fibers, then taking out the composite fibers and washing them, and drying them at 60 to 90°C for 12 to 24 hours to obtain the silicon carbide / silicon nitride composite fibers.

[0029] In the above technical solution, the silane coupling agent is one of tris(3-mercaptopropionic acid)propyltrimethoxysilane, trichloromethylsilane and tris(2-aminoethyl)aminopropyltrimethoxysilane;

[0030] The photoinitiator is benzoyl diisopropyl dimethyl ammonium chloride or benzoyl diisopropyl malonate.

[0031] In the above technical solution, the specific preparation process of step S4 includes the following steps:

[0032] The silicon carbide / silicon nitride composite fiber is ultrasonically dispersed in a silicon-based ceramic slurry for 3 to 6 hours until uniformly dispersed. After completion, the fiber is calcined at 1500 to 2000° C. at a speed of 3° / min or 5° / min for 5 to 11 hours and kept warm for 1 to 3 hours to obtain the precision ceramic core material.

[0033] In the above technical solution, the silicon carbide fiber obtained in step S1 has a length of 20 to 200 μm and a diameter of 0.1 to 2 μm.

[0034] The present invention also provides application of the precision ceramic core material prepared by the preparation method in casting of precision ceramic materials.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] First, the present invention uses electrospinning to produce silicon carbide fibers with a multi-level structure. Silicon carbide fibers inherently have a high melting point (can be heated to 1200-1500°C in a vacuum or inert atmosphere) and thermal stability (at 1200°C, their flexural strength can reach 1960-4410 MPa), thus enhancing the material's high-temperature flexural strength during use. The silicon carbide fibers produced by the present invention have a multi-level structure, and their interwoven and cross-linked structures enhance the material's structural stability, thereby improving its flexural strength in high-temperature environments. Furthermore, the multi-level structure effectively hinders the shrinkage of the silicon-based ceramic core material during sintering, adsorbs and diffuses gases generated during sintering, reduces gas pressure, and thus reduces shrinkage of the core material. Furthermore, leveraging the high-temperature thermal stability of silicon nitride microspheres (at 1200°C, their flexural strength is ≥980 MPa), the silicon carbide fibers are chemically grafted onto the microspheres to form strong chemical bonds, such as silicon-oxygen and silicon-carbon bonds, further enhancing the material's high-temperature flexural strength and thus improving its high-temperature resistance. At the same time, the composite fiber is combined with the silicon-based ceramic slurry to prepare the ceramic core material, which can be injection molded in the application with the help of the toughness of the fiber, and the operation is simple.

[0037] Secondly, silicon nitride is a kind of material with low thermal expansion coefficient (2.35×10 6 K), materials with good corrosion resistance and good mechanical properties. The present invention uses silicon nitride microspheres to chemically graft and modify silicon carbide fibers, and through activated carbon intermediates and recombination reactions with nitrogen atoms to form strong silicon-oxygen bonds, silicon-nitrogen bonds and silicon-carbon bonds, a silicon nitride grafting layer is formed on the surface of the silicon carbide fiber, which increases the surface activity and interface compatibility of the fiber, thereby reducing the sintering shrinkage of the material and improving the high-temperature flexural strength of the material. In addition, silicon nitride can carry a large load. After combining with silicon carbide fibers, when subjected to stress concentration, it can disperse stress and reduce damage to the ceramic core material, thereby further improving the high-temperature flexural strength of the material. At the same time, silicon nitride has a relatively low density (3.12g / cm 3 ), which can absorb or disperse gases during use, thereby reducing the shrinkage rate of the material during high-temperature sintering.

[0038] Third, the low shrinkage and high flexural strength precision ceramic core material prepared by the present invention has a flexural strength test results, and its flexural strength (flexural strength is 2000-2500 MPa at 1500-2000°C) is higher than that of zirconia ceramic core material (flexural strength is 200-1000 MPa at 1200-1600°C) and spinel-magnesium-based ceramic core material (flexural strength is 100-200 MPa at 1100-1400°C).

[0039] Fourthly, the low-shrinkage, high-flexural-strength precision ceramic core material prepared by the present invention has a shrinkage of only 0.01-0.05% as measured by dimensional measurement of samples after high-temperature sintering. This ceramic core material can be directly applied to aircraft engines through injection molding. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic diagram of flexural strength determination;

[0041] Among them, 1. Upper pressure head; 2. Sample; 3. Sample fixture. DETAILED DESCRIPTION

[0042] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0043] Example 1

[0044] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0045] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 10mL of tetraethyl orthosilicate, 10mL of anhydrous ethanol, 1g of polyvinyl pyrrolidone and 0.5mL of N,N-dimethylformamide were stirred for 15min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 15kV, the spinning flow rate was 5mL / h, and the receiving distance was 20cm. After the spinning is completed, the precursor fiber is dried at 60°C for 14h and cured at 100°C for 4h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1300°C for 7h to obtain silicon carbide fiber with a multi-level structure;

[0046] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexamethylenetetramine and urea in a molar ratio of 1:1 and add them to 50mL of deionized water to obtain a mixture B. Stir ZrO(NO3)2 and the mixture B in a molar ratio of 1:1.2 for 5 minutes until evenly mixed and add 0.5mL of concentrated nitric acid solution dropwise, then add 50mL of deionized water and stir for 1 hour until viscous and add 0.5g of nano-silicon powder and ultrasonicate for 1 hour until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 80℃ hot silicone oil. After completion, solidify for 12 hours, take out and dry at 40℃ for 24 hours to obtain gel microspheres; finally, calcine the gel microspheres at 1000℃ for 3 hours to obtain silicon nitride ceramic microspheres;

[0047] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 0.5g of silicon nitride ceramic microspheres, 0.01g of silane coupling agent tris(3-mercaptopropionic acid)propyltrimethoxysilane, 0.005g of photoinitiator benzoyldiisopropyldimethylammonium chloride and silicon carbide fiber in 100mL of anhydrous ethanol, stir for 1h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 3h; then, take out and wash the composite fiber, and after completion, dry it at 60°C for 24h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 3h until it is uniformly dispersed, and after completion, calcine at 1500°C at 5° / min for 5h, and keep warm for 1h to obtain a precision ceramic core material.

[0048] Example 2

[0049] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0050] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 10mL of tetramethyl orthosilicate, 10mL of anhydrous ethanol, 1g of polyvinyl alcohol and 0.5mL of dimethyl sulfoxide were stirred for 15min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 15kV, the spinning flow rate was 5mL / h, and the receiving distance was 20cm. After the spinning is completed, the precursor fiber is dried at 60°C for 14h and cured at 100°C for 4h. After curing, it was placed in a crucible containing silicon powder and a carbon fiber plate was placed on top of the fiber; finally, the crucible was buried in a sagger filled with graphite powder and siliconized at 1300°C for 7h to obtain silicon carbide fiber with a multi-level structure;

[0051] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexadibutyltetramine and urea in a molar ratio of 1:1 and add them to 50mL of deionized water to obtain a mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:1.2 for 5 minutes until evenly mixed and add 0.5mL of concentrated nitric acid solution dropwise, then add 50mL of deionized water and stir for 1 hour until viscous and add 0.5g of nano-silicon powder and ultrasonicate for 1 hour until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 80℃ hot silicone oil. After completion, solidify for 12 hours, take out and dry at 40℃ for 24 hours to obtain gel microspheres; finally, calcine the gel microspheres at 1000℃ for 3 hours to obtain silicon nitride ceramic microspheres;

[0052] Step 3: Preparation of silicon carbide / silicon nitride composite fibers: First, weigh 0.5g of silicon nitride ceramic microspheres, 0.01g of the silane coupling agent trichloromethylsilane, 0.005g of the photoinitiator benzoyldiisopropyldimethylammonium chloride, and silicon carbide fibers in 100mL of anhydrous ethanol, stir for 1 hour until uniform, and seal to obtain a mixture C. Next, place the sealed mixture C under a UV lamp to react for 3 hours. The composite fibers are then removed and washed, and dried at 60°C for 24 hours to obtain silicon carbide / silicon nitride composite fibers. Finally, the composite fibers are ultrasonically dispersed in a silicon-based ceramic slurry for 3 hours until uniformly dispersed. After completion, the fibers are calcined at 1500°C at 3°C / min for 8 hours and held at this temperature for 1 hour to obtain a precision ceramic core material.

[0053] Example 3

[0054] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0055] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 14mL of tetraethyl orthosilicate, 15mL of anhydrous ethanol, 1.5g of polyvinyl pyrrolidone and 1.2mL of N,N-dimethylformamide were stirred for 20min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 20kV, the spinning flow rate was 3mL / h, and the receiving distance was 16cm. After the spinning is completed, the precursor fiber is dried at 70°C for 12h and cured at 140°C for 3h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1400°C for 7.6h to obtain silicon carbide fiber with a multi-level structure;

[0056] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexamethylenetetramine and aminosilane in a molar ratio of 1:2 and add them into 70mL deionized water to obtain mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:2.5 for 10 minutes until mixed evenly and add 0.7mL concentrated nitric acid solution dropwise, then add 70mL deionized water and stir for 1.5h until viscous and add 1g nano-silicon powder and ultrasonicate for 1.5h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 90℃ hot silicone oil, after completion of curing for 16h, take out and dry at 50℃ for 20h to obtain gel microspheres; finally, calcined the gel microspheres at 1300℃ for 4h to obtain silicon nitride ceramic microspheres;

[0057] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.0g of silicon nitride ceramic microspheres, 0.015g of silane coupling agent tris(2-aminoethyl)aminopropyltrimethoxysilane, 0.01g of photoinitiator diisopropyl benzoylmalonate and silicon carbide fiber in 200mL of anhydrous ethanol, stir for 2h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 4h; then, take out and wash the composite fiber, and after completion, dry it at 70°C for 20h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 4h until it is uniformly dispersed, and after completion, calcine at 1700°C at 5° / min for 6h, and keep warm for 2h to obtain a precision ceramic core material.

[0058] Example 4

[0059] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0060] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 14mL of tetramethyl orthosilicate, 15mL of anhydrous ethanol, 1.5g of polyvinyl alcohol and 1.2mL of dimethyl sulfoxide were stirred for 20min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 20kV, the spinning flow rate was 3mL / h, and the receiving distance was 16cm. After the spinning is completed, the precursor fiber is dried at 70°C for 12h and cured at 140°C for 3h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1400°C for 7.6h to obtain silicon carbide fiber with a multi-level structure;

[0061] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexadibutyltetramine and aminosilane in a molar ratio of 1:2 and add them into 70mL deionized water to obtain mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:2.5 for 10 minutes until mixed evenly and add 0.7mL concentrated nitric acid solution dropwise, then add 70mL deionized water and stir for 1.5h until viscous and add 1g nano-silicon powder and ultrasonicate for 1.5h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 90℃ hot silicone oil, after completion of curing for 16h, take out and dry at 50℃ for 20h to obtain gel microspheres; finally, calcined the gel microspheres at 1300℃ for 4h to obtain silicon nitride ceramic microspheres;

[0062] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.0g of silicon nitride ceramic microspheres, 0.015g of silane coupling agent tris(2-aminoethyl)aminopropyltrimethoxysilane, 0.01g of photoinitiator diisopropyl benzoylmalonate and silicon carbide fiber in 200mL of anhydrous ethanol, stir for 2h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 4h; then, take out and wash the composite fiber, and after completion, dry it at 70°C for 20h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 4h until it is uniformly dispersed, and after completion, calcine at 1700°C at 3° / min for 9h, and keep warm for 2h to obtain a precision ceramic core material.

[0063] Example 5

[0064] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0065] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 16mL of tetraethyl orthosilicate, 20mL of anhydrous ethanol, 2g of polyvinyl pyrrolidone and 1.4mL of N,N-dimethylformamide were stirred for 25min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 25kV, the spinning flow rate was 2mL / h, and the receiving distance was 14cm. After the spinning is completed, the precursor fiber is dried at 80°C for 10h and cured at 180°C for 2h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1500°C for 8.2h to obtain silicon carbide fiber with a multi-level structure;

[0066] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexamethylenetetramine and urea in a molar ratio of 1:3 and add them to 90mL deionized water to obtain mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:3 for 15 minutes until mixed evenly and add 1.0mL concentrated nitric acid solution dropwise, then add 90mL deionized water and stir for 1.7h until viscous and add 1.5g nano-silicon powder and ultrasonicate for 1.7h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 110℃ hot silicone oil, after completion of curing for 20h, take out and dry at 60℃ for 16h to obtain gel microspheres; finally, calcine the gel microspheres at 1700℃ for 6h to obtain silicon nitride ceramic microspheres;

[0067] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.3g of silicon nitride ceramic microspheres, 0.02g of silane coupling agent trichloromethylsilane, 0.013g of photoinitiator benzoyldiisopropyldimethylammonium chloride and silicon carbide fiber in 300mL of anhydrous ethanol, stir for 3h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 4.5h; then, take out and wash the composite fiber, and after completion, dry it at 80°C for 16h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 5h until it is uniformly dispersed. After completion, calcine at 1900°C at 5° / min for 6.5h and keep it warm for 2.5h to obtain a precision ceramic core material.

[0068] Example 6

[0069] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0070] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 16mL of tetramethyl orthosilicate, 20mL of anhydrous ethanol, 2g of polyvinyl alcohol and 1.4mL of dimethyl sulfoxide were stirred for 25min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 25kV, the spinning flow rate was 2mL / h, and the receiving distance was 14cm. After the spinning is completed, the precursor fiber is dried at 80°C for 10h and cured at 180°C for 2h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1500°C for 8.2h to obtain silicon carbide fiber with a multi-level structure;

[0071] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexadibutyltetramine and urea in a molar ratio of 1:3 and add them to 90mL deionized water to obtain a mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:3 for 15 minutes until evenly mixed and add 1.0mL concentrated nitric acid solution dropwise, then add 90mL deionized water and stir for 1.7h until viscous and add 1.5g nano-silicon powder and ultrasonicate for 1.7h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 110℃ hot silicone oil, after completion of curing for 20h, take out and dry at 60℃ for 16h to obtain gel microspheres; finally, calcine the gel microspheres at 1700℃ for 6h to obtain silicon nitride ceramic microspheres;

[0072] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.3g of silicon nitride ceramic microspheres, 0.02g of silane coupling agent tris(2-aminoethyl)aminopropyltrimethoxysilane, 0.013g of photoinitiator benzoyldiisopropyldimethylammonium chloride and silicon carbide fiber in 300mL of anhydrous ethanol, stir for 3h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 4.5h; then, take out and wash the composite fiber, and after completion, dry it at 80℃ for 16h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 5h until it is uniformly dispersed. After completion, calcine at 1900℃ at 3° / min for 10h and keep warm for 2.5h to obtain a precision ceramic core material.

[0073] Example 7

[0074] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0075] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 20mL of tetraethyl orthosilicate, 25mL of anhydrous ethanol, 3g of polyvinyl pyrrolidone and 1.5mL of N,N-dimethylformamide were stirred for 35min to obtain a mixed solution A; secondly, the mixed solution A was used to prepare the precursor fiber using an electrospinning device, wherein the spinning voltage was 30kV, the spinning flow rate was 1mL / h, and the receiving distance was 10cm. After the spinning is completed, the precursor fiber is dried at 90°C for 8h and cured at 200°C for 1h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1600°C for 9h to obtain silicon carbide fiber with a multi-level structure;

[0076] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexamethylenetetramine and aminosilane in a molar ratio of 1:4 and add them to 100mL deionized water to obtain a mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:3.5 for 20 minutes until evenly mixed and add 1.5mL concentrated nitric acid solution dropwise, then add 100mL deionized water and stir for 2h until viscous and add 2g nano-silicon powder and ultrasonicate for 2h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 120℃ hot silicone oil. After completion, solidify for 24h, take out and dry at 70℃ for 12h to obtain gel microspheres; finally, calcine the gel microspheres at 2000℃ for 7h to obtain silicon nitride ceramic microspheres;

[0077] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.5g of silicon nitride ceramic microspheres, 0.03g of silane coupling agent tris(3-mercaptopropionic acid)propyltrimethoxysilane, 0.015g of photoinitiator diisopropyl benzoylmalonate and silicon carbide fiber in 400mL of anhydrous ethanol, stir for 4h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 5h; then, take out and wash the composite fiber, and after completion, dry it at 90°C for 12h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 6h until uniformly dispersed, and after completion, calcine at 2000°C at 5° / min for 7h, and keep warm for 3h to obtain a precision ceramic core material.

[0078] Example 8

[0079] A method for preparing a precision ceramic core material with low shrinkage and high bending strength, the specific process is as follows:

[0080] Step 1, electrospinning to prepare multi-level structure silicon carbide fiber: First, 20mL of tetramethyl orthosilicate, 25mL of anhydrous ethanol, 3g of polyvinyl alcohol and 1.5mL of dimethyl sulfoxide are stirred for 35min to obtain a mixture A; secondly, the above-mentioned mixture A is used for precursor fiber preparation using an electrospinning device, wherein the spinning voltage is 30kV, the spinning flow rate is 1mL / h, and the receiving distance is 10cm. After the spinning is completed, the above-mentioned precursor fiber is dried at 90°C for 8h and cured at 200°C for 1h. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; finally, the crucible is buried in a sagger filled with graphite powder and siliconized at 1600°C for 9h to obtain silicon carbide fiber with a multi-level structure;

[0081] Step 2, prepare porous silicon nitride by sol-gel method: First, mix hexadibutyltetramine and aminosilane in a molar ratio of 1:4 and add them to 100mL deionized water to obtain mixed solution B. Stir ZrO(NO3)2 and mixed solution B in a molar ratio of 1:3.5 for 20 minutes until evenly mixed and add 1.5mL concentrated nitric acid solution dropwise, then add 100mL deionized water and stir for 2h until viscous and add 2g nano-silicon powder and ultrasonicate for 2h until evenly dispersed to obtain a glue solution. Use a dropper to add the above glue solution dropwise into 120℃ hot silicone oil, after completion of curing for 24h, take out and dry at 70℃ for 12h to obtain gel microspheres; finally, calcine the gel microspheres at 2000℃ for 7h to obtain silicon nitride ceramic microspheres;

[0082] Step 3, preparation of silicon carbide / silicon nitride composite fiber: First, weigh 1.5g of silicon nitride ceramic microspheres, 0.03g of silane coupling agent trichloromethylsilane, 0.015g of photoinitiator diisopropyl benzoylmalonate and silicon carbide fiber in 400mL of anhydrous ethanol, stir for 4h until uniform and seal it to obtain a mixed solution C; secondly, place the above-mentioned sealed mixed solution C in an ultraviolet lamp to react for 5h; then, take out and wash the composite fiber, and after completion, dry it at 90°C for 12h to obtain silicon carbide / silicon nitride composite fiber; finally, ultrasonicate the above-mentioned composite fiber in silicon-based ceramic slurry for 6h until it is uniformly dispersed, and after completion, calcine at 2000°C at 3° / min for 11h, and keep warm for 3h to obtain a precision ceramic core material.

[0083] Comparative Example 1, a currently available zirconia ceramic core material, was tested for flexural strength using a three-point bending method using a compression and flexural testing machine. The results showed that at a calcination temperature of 1450°C, the material's flexural strength reached 1200 MPa. The sintering shrinkage of the sample was measured using a thermogravimetric / differential thermal analyzer (STA449F3, Germany) according to the "Determination of Sintering Shrinkage" standard, Part 2, of the "Aviation Industry Standard of the People's Republic of China (HB 5353.3-2004)." The results showed that at a sintering temperature of 1550°C, the linear shrinkage was 18.31%.

[0084] Comparative Example 2 is a currently available spinel-magnesium-based ceramic core material. It was tested using the method for determining the firing shrinkage rate in Part 2 of the "Aviation Industry Standard of the People's Republic of China (HB 5353.3-2004)". The sample was placed in a vertical molybdenum disilicide rod heating furnace for high-temperature calcination. After calcination, the sample shrinkage rate was 0.7% to 3%. The flexural strength test was performed using an AG-Xplus 100KN electronic universal testing machine produced by Shimadzu Corporation of Japan and the method for determining the flexural strength in Part 3 of the "Aviation Industry Standard of the People's Republic of China (HB 5353.3-2004)". The results showed that the flexural strength of the sample in this comparative example was 20 to 60 MPa.

[0085] The test standards used in the experiments of the present invention are specifically:

[0086] The sintering shrinkage of the ceramic core material was tested according to the "Determination of Firing Shrinkage" in Part 2 of the "Aviation Industry Standard of the People's Republic of China (HB 5353.3-2004)." A cylindrical specimen of the ceramic core material of the present invention, measuring Φ4 mm x 50 mm, was prepared to ensure that it was free of defects such as cracks, bubbles, and deformation. The specimen was placed at 20°C ± 2°C for 2 hours, the length of the specimen was measured, and the specimen was sintered according to the above-described sintering process. After completion, the length of the specimen was measured and the shrinkage was calculated according to formula (1).

[0087]

[0088] In the formula: δ——specimen sintering shrinkage, expressed as percentage (%);

[0089] L——length of sample before calcination, millimeter (mm);

[0090] L1 - length of the sample after calcination, millimeters (mm).

[0091] The flexural strength of the ceramic core material is tested in accordance with the flexural strength test in Part 3 of the Aviation Industry Standard of the People's Republic of China (HB 5353.3-2004). The ceramic core material of the present invention is prepared into a test sample according to the standard sample size of 60 mm × 10 mm × 4 mm and mounted on a special fixture (such as Figure 1 (as shown in the figure), heat the sample to 1500-2000°C at a heating rate of 300-400°C / h and hold at this temperature for 30 minutes. Then, apply a load to the middle of the working part of the sample at a rate of 6-8 mm / min until the sample breaks. Record the load value at the time of sample fracture and calculate the flexural strength according to formula (2).

[0092]

[0093] Where: σ w — flexural strength, MPa;

[0094] P——The load when the specimen breaks, Newton (N);

[0095] L——the span between two supports, millimeter (mm);

[0096] b——width of the specimen, millimeter (mm);

[0097] h——specimen thickness, millimeter (mm).

[0098] Table 1 shows the comparative test results of the low shrinkage, high bending strength precision ceramic core material in the embodiment and the existing zirconia ceramic core material and spinel-magnesium-based ceramic core material in the comparative example.

[0099] Table 1 Comparison of shrinkage and flexural strength of ceramic core materials of the present invention and comparative examples

[0100]

[0101] As can be seen from the above table, compared with the currently available zirconia ceramic core materials and spinel-magnesium-based ceramic core materials, the present invention prepares a low-shrinkage, high-flexural strength precision ceramic core material, which is made from multi-level structured silicon carbide fibers, silicon nitride microspheres and silicon-based ceramic slurry through electrostatic spinning, sol-gel, chemical grafting and high-temperature calcination. When preparing the above-mentioned multi-level structured silicon carbide fibers, their interwoven and cross-linked structures can increase the structural stability of the material, thereby improving the material's flexural strength in a high-temperature environment. In addition, the multi-level structured silicon carbide fibers contain a certain porosity, which can adsorb and diffuse the gases generated during the sintering process, reducing the gas pressure and thus reducing the shrinkage of the material. At the same time, with the help of the silicon nitride microspheres having a lower density and higher porosity, they can be used to fill the gaps between the materials to hinder the mutual contact and bonding between the particles, thereby reducing the sintering shrinkage of the material. And the amino functional groups on its surface can form strong hydrogen bonds with the oxides on the surface of the silicon-based ceramic material, thereby improving the compatibility and bonding strength of the interface, thereby improving the flexural strength of the material. Therefore, the two are combined, and the carbon-based functional groups are broken under high temperature to form activated carbon intermediates, which undergo recombination reactions with nitrogen atoms to form strong silicon-oxygen bonds, silicon-nitrogen bonds, and silicon-carbon bonds, forming a silicon nitride grafting layer on the surface of the silicon carbide fiber, thereby increasing the surface activity and interfacial compatibility of the fiber, thereby further increasing the high-temperature flexural strength of the material, and reducing the gas pressure at the same time, thereby further reducing the sintering shrinkage of the material. In summary, the low-shrinkage, high-flexural-strength precision ceramic core material prepared by the present invention has the characteristics of low sintering shrinkage and high flexural strength, and is expected to have broad application prospects in the field of precision ceramic core casting.

[0102] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a low-shrinkage, high-bending-strength precision ceramic core material, characterized in that: The steps include: Step S1, electrospinning to prepare silicon carbide fibers with a multi-level structure: tetraethyl orthosilicate or tetramethyl orthosilicate, anhydrous ethanol, polyvinyl pyrrolidone or polyvinyl alcohol, N,N-dimethylformamide or dimethyl sulfoxide are uniformly mixed and then a precursor fiber is prepared using an electrospinning device. After spinning, the precursor fiber is dried and cured. After curing, it is placed in a crucible containing silicon powder and a carbon fiber plate is placed on the fiber. The crucible is buried in a sagger filled with graphite powder to perform a siliconization reaction to obtain the silicon carbide fibers with a multi-level structure. Step S2, preparing silicon nitride ceramic microspheres by a sol-gel method: mixing hexamethylenetetramine or hexamethylene-tert-butyltetramine, urea or aminosilane and adding them to deionized water to obtain a mixed solution B; stirring ZrO(NO3)2 and the mixed solution B uniformly, adding concentrated nitric acid solution, then adding deionized water and stirring until viscous, adding nano-silicon powder and ultrasonically dispersing it uniformly to obtain a glue solution; adding the glue solution to hot silicone oil, curing it after completion, taking it out and drying it to obtain gel microspheres; calcining the gel microspheres to obtain the silicon nitride ceramic microspheres; Step S3, preparation of silicon carbide / silicon nitride composite fibers: taking the silicon nitride ceramic microspheres, silane coupling agent, photoinitiator and the silicon carbide fibers in anhydrous ethanol, stirring them uniformly and sealing them to obtain a mixed solution C; placing the sealed mixed solution C in an ultraviolet lamp for reaction to obtain composite fibers, then taking out the composite fibers and washing them, and drying them after completion to obtain the silicon carbide / silicon nitride composite fibers; Step S4, preparation of precision ceramic core material: uniformly dispersing the silicon carbide / silicon nitride composite fiber in a silicon-based ceramic slurry by ultrasonic dispersion, and then calcining the dispersion to obtain the precision ceramic core material.

2. The preparation method according to claim 1, wherein: The specific preparation process of step S1 includes the following steps: S11, 10-20 mL of tetraethyl orthosilicate or tetramethyl orthosilicate, 10-25 mL of anhydrous ethanol, 1-3 g of polyvinyl pyrrolidone or polyvinyl alcohol, and 0.5-1.5 mL of N,N-dimethylformamide or dimethyl sulfoxide are stirred for 15-35 minutes until the mixture is uniformly mixed to obtain a mixed solution A; S12, preparing precursor fibers by electrospinning the mixed solution A using an electrospinning device, wherein the spinning voltage is 15-30 kV, the spinning flow rate is 1-5 mL / h, and the receiving distance is 10-20 cm; S13, after the spinning is completed, the precursor fiber is dried at 60-90° C. for 8-14 hours and cured at 100-200° C. for 1-4 hours, and after curing, is placed in a crucible containing silicon powder and a carbon fiber plate is placed on top of the fiber; S14, burying the crucible in a sagger filled with graphite powder, and performing siliconization reaction at 1300-1600° C. for 7-9 hours to obtain the silicon carbide fiber with a multi-level structure.

3. The preparation method according to claim 1, wherein: The specific preparation process of step S2 includes the following steps: S21, mixing hexamethylenetetramine or hexamethylenetetramine and urea or aminosilane in a molar ratio of 1:1 to 1:4 and adding the mixture to 50 to 100 mL of deionized water to obtain a mixed solution B; S22, ZrO (NO 3 ) 2 and the mixed solution B are stirred at a molar ratio of 1:1.2 to 1:3.5 for 5 to 20 minutes until the mixture is uniformly mixed, and 0.5 to 1.5 mL of concentrated nitric acid solution is added dropwise, followed by adding 50 to 100 mL of deionized water and stirring for 1 to 2 hours until the mixture becomes viscous, and then 0.5 to 2 g of nano-silicon powder is added and ultrasonicated for 1 to 2 hours until the mixture is uniformly dispersed to obtain a glue solution; S23, dripping the glue solution dropwise into hot silicone oil at 80-120° C. using a dropper, curing for 12-36 hours, removing the solution, and drying it at 40-70° C. for 12-24 hours to obtain gel microspheres; S24, calcining the gel microspheres at 1000-2000° C. for 3-7 hours to obtain the silicon nitride ceramic microspheres.

4. The preparation method according to claim 1, wherein: The specific preparation process of step S3 includes the following steps: S31, weighing 0.5-1.5 g of the silicon nitride ceramic microspheres, 0.01-0.03 g of a silane coupling agent, 0.005-0.015 g of a photoinitiator, and the silicon carbide fiber in 100-400 mL of anhydrous ethanol, stirring for 1-4 h until uniform, and sealing the mixture to obtain a mixed solution C; S32, placing the sealed mixed solution C in an ultraviolet lamp to react for 3 to 5 hours to obtain composite fibers, then taking out and washing the composite fibers, and drying them at 60 to 90°C for 12 to 24 hours to obtain the silicon carbide / silicon nitride composite fibers.

5. The preparation method according to claim 4, characterized in that: The silane coupling agent is one of tris(3-mercaptopropionic acid)propyltrimethoxysilane, trichloromethylsilane and tris(2-aminoethyl)aminopropyltrimethoxysilane; The photoinitiator is benzoyl diisopropyl dimethyl ammonium chloride or benzoyl diisopropyl malonate.

6. The preparation method according to claim 1, characterized in that: The silicon carbide fiber obtained in step S1 has a length of 20-200 μm and a diameter of 0.1-2 μm.

7. Use of the precision ceramic core material prepared by the preparation method according to any one of claims 1 to 6 in the casting of precision ceramic materials.

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