Raw materials for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof

Abstract

The present invention discloses a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. The raw material for the ceramic core includes refractory powder, zirconium silicate powder, and metallic zirconium powder. The refractory powder, zirconium silicate powder, and metallic zirconium powder are mixed in proportion to form the raw material for the ceramic core. The raw material for the ceramic core is added to liquid paraffin to form a ceramic core slurry. The ceramic core green body is obtained by using the ceramic core slurry through a hot pressing injection molding method. The ceramic core green body is sintered by powder embedding to obtain the ceramic core. In the present invention, the in-situ self-generated oxidation expansion of the metallic zirconium powder compensates for the volume shrinkage generated during the sintering process of the ceramic core. At the same time, the generated zirconium dioxide also compensates for the shrinkage of the ceramic core due to the phase change effect. Under the dual action of the in-situ oxidation and phase change effects, near-zero shrinkage of the silicon-based ceramic core during the sintering process is achieved, improving its dimensional accuracy. At the same time, the generated zirconium dioxide improves the room temperature bending strength and high temperature bending strength of the ceramic core.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic core preparation, and particularly relates to a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. Background Art

[0002] As a key hot-end component of an aero-engine, the temperature-bearing capacity of the turbine blade of the aero-engine plays an important role in improving the overall performance of the aero-engine. At present, simply improving the alloy material to further increase its temperature-bearing capacity has reached its limit. The design of the hollow air-cooled structure of the blade has become the main means to improve the temperature-bearing capacity of the blade, and the design and preparation of complex ceramic cores are the key to realizing the hollow air-cooled structure of the blade. With the continuous improvement of the air-cooling efficiency, the internal cavity structure of the blade is becoming more and more complex, and the size of some channels is becoming smaller and smaller, which requires the ceramic core to have precise and fine dimensions, such as a double-wall ceramic core. While these complex structures require higher performance of the ceramic core, they also require higher dimensional accuracy of the ceramic core, that is, the ceramic core needs to have high dimensional accuracy.

[0003] At present, the method actually applied to manufacture complex-shaped ceramic cores is investment casting. When the ceramic cores prepared by this technology encounter complex internal cavity structures, due to poor dimensional accuracy of the cores, local fine structures often deform or break, resulting in unqualified casting of the blades. At the same time, the dimensional stability of the ceramic core is poor, and it is extremely easy to cause core mismatch due to large high-temperature deflection during the high-temperature pouring stage, resulting in unqualified casting of the blades. Therefore, in order to improve the dimensional accuracy of the internal cavity of the turbine blade and improve the casting yield, it is of great significance to develop ceramic cores with high dimensional accuracy and stability.

[0004] In terms of improving the dimensional accuracy and stability of ceramic cores, domestic and foreign researchers have also carried out a lot of work, such as introducing inert mineralizers to inhibit the shrinkage of ceramic cores during sintering.

[0005] The existing patent CN115894051A discloses a special sintering shrinkage regulator for silicon-based ceramic cores and a preparation method thereof. The special sintering shrinkage regulator for silicon-based ceramic cores includes: 10-30 parts of kyanite powder, 20-45 parts of cristobalite powder, 10-40 parts of mullite powder, 10-20 parts of activated alumina powder, 0-10 parts of elemental silicon powder, 0-10 parts of silicon carbide powder, and 0-10 parts of silicon nitride powder. This method can freely adjust the sintering size of the ceramic core by adding this regulator almost without changing the performance of the ceramic core, and avoid sacrificing the performance of the ceramic core in order to ensure sintering shrinkage.

[0006] The existing patent CN115108818A discloses a raw material for a silicon-based ceramic core with low shrinkage and low deflection and a preparation method thereof, which includes refractory powder and a mineralizer. The mineralizer is a composite mineralizer, and the composite mineralizer includes zirconium silicate and aluminum silicate. The weight percentage of aluminum silicate in the ceramic core raw material is 1-15%, and the weight percentage of zirconium silicate in the ceramic core raw material is 5-10%. Using the present invention, a silicon-based ceramic core with low sintering shrinkage and low high-temperature deformation can be prepared, thereby improving the sintering success rate of the ceramic core. Existing research results show that by adding such mineralizers, the dimensional accuracy of the ceramic core can be effectively improved, and then the manufacturing of hollow blades with high dimensional accuracy can be realized. However, such methods are still limited in improving the dimensional accuracy of the ceramic core, and at the same time, a large amount of inert oxides or non-oxide raw materials will be introduced, affecting the removability of the ceramic core.

[0007] In summary, the above two existing patents have not completely solved the problem that the dimensional accuracy and stability of ceramic cores in the existing technology need to be improved. Summary of the Invention

[0008] Based on the above technical problems, the present invention proposes a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof, which solves the problem that the dimensional accuracy and stability of ceramic cores in the existing technology need to be further improved.

[0009] To achieve the above object, the present invention proposes a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. The specific technical solutions are as follows:

[0010] A raw material for a near-zero shrinkage silicon-based ceramic core includes refractory powder, zirconium silicate powder and zirconium metal powder. The weight percentage of the refractory powder in the raw material is 70-89%, the weight percentage of the zirconium silicate powder in the raw material is 10-20%, and the weight percentage of the zirconium metal powder in the raw material is 1-10%.

[0011] Further, the weight percentage of the refractory powder in the raw material is 80-89%, the weight percentage of the zirconium silicate powder in the raw material is 10-15%, and the weight percentage of the zirconium metal powder in the raw material is 1-5%.

[0012] Further, the weight percentage of the refractory powder in the raw material is 85-88%, the weight percentage of the zirconium silicate powder in the raw material is 10.5-12%, and the weight percentage of the zirconium metal powder in the raw material is 1.5-3%.

[0013] Further, the particle size range of the refractory powder is 1-60 μm and the powder purity is not less than 99.95%, the particle size range of the zirconium silicate powder is 1-50 μm and the powder purity is not less than 98.99%, and the particle size range of the metallic zirconium powder is 1-10 μm and the powder purity is not less than 99.99%.

[0014] Further, the refractory powder is quartz glass powder.

[0015] The present invention also provides a preparation method of a near-zero shrinkage silicon-based ceramic core, using the raw materials of the above-mentioned near-zero shrinkage silicon-based ceramic core to prepare the ceramic core. The preparation method specifically includes:

[0016] S1. Mix the ceramic core raw materials to form a ceramic core slurry;

[0017] S2. Use the ceramic core slurry to form a green body of the ceramic core;

[0018] S3. Sinter the green body of the ceramic core by powder embedding to obtain the ceramic core.

[0019] Further, in step S1, the ceramic core raw materials are added to the dispersant in batches, and vacuum stirring is performed until uniform to obtain the ceramic core slurry.

[0020] Further, in step S1, the ceramic core raw materials are added to the melted paraffin in batches, and vacuum stirring is performed until uniform to obtain the ceramic core slurry;

[0021] The melting temperature of the paraffin is 80-95 °C.

[0022] Further, in step S2, the ceramic core slurry is added to a core pressing machine, and a green body of the ceramic core is obtained by a hot pressing injection molding method;

[0023] The forming pressure of the core pressing machine is 5-10 MPa.

[0024] Further, in step S3, the final sintering temperature is 1100-1300 °C, and the heat preservation time is 4-15 h;

[0025] The heating process of the sintering includes multiple stages. The heating rate of each stage is 150-300 °C, the heating rate of each stage is 2-8 °C / min, and the heat preservation time after heating in each stage is 4-15 h;

[0026] The multiple stages include: the first stage: from room temperature to 200 °C, with a heating rate of 2 °C / min and holding for 4 h at 200 °C; the second stage: from 200 °C to 400 °C, with a heating rate of 2 °C / min and holding for 5 h at 400 °C; the third stage: from 400 °C to 650 °C, with a heating rate of 3 °C / min and holding for 8 h at 650 °C; the fourth stage: from 650 °C to 950 °C, with a heating rate of 5 °C / min and holding for 10 h at 950 °C; the fifth stage: from 950 °C to 1250 °C, with a heating rate of 8 °C / min and holding for 12 h.

[0027] Based on the above technical solutions, the present invention has at least the following beneficial effects:

[0028] 1. The present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. The in-situ self-generated oxidation expansion of zirconium metal powder compensates for the volume shrinkage generated during the sintering process of the ceramic core. At the same time, the generated zirconium dioxide compensates for the shrinkage of the ceramic core due to the phase change effect. Under the dual action of in-situ oxidation and phase change effects, near-zero shrinkage of the ceramic core during the sintering process is achieved, improving its dimensional accuracy.

[0029] 2. The present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. The zirconium dioxide generated by zirconium metal powder improves the room-temperature bending strength and high-temperature bending strength of the silicon-based ceramic core.

[0030] 3. The present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. The component content of zirconium metal powder in the raw material of the ceramic core is specifically designed, enabling the raw material of the ceramic core to achieve excellent technical effects.

[0031] 4. The present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof, which is also applicable to the design and development of ceramic cores in other systems and has important promotion value. Specific embodiments

[0032] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0033] The following further describes the present invention in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present invention.

[0034] To solve the problem that the dimensional accuracy and stability of ceramic cores in the prior art need to be improved, the present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof.

[0035] To achieve the above object, the present invention provides a raw material for a near-zero shrinkage silicon-based ceramic core and a preparation method thereof. Based on refractory powder and mineralizer, metallic zircon powder is introduced. During high-temperature sintering, the in-situ oxidation expansion of the metallic zircon powder compensates for the shrinkage of the ceramic core, and at the same time, the generated zirconia also compensates for the shrinkage of the ceramic core due to the phase change effect. Under the dual action of in-situ oxidation and phase change effect, near-zero shrinkage of the silicon-based ceramic core during sintering is achieved, improving its dimensional accuracy. At the same time, the generated zirconia will improve the room-temperature and high-temperature bending strength of the ceramic core.

[0036] The raw material for a near-zero shrinkage silicon-based ceramic core provided by the present invention includes refractory powder, mineralizer, and metallic zircon powder. The weight percentage of the refractory powder in the raw material of the ceramic core is 70%-89%, the mineralizer is selected as zirconium silicate powder, and the weight percentage of the zirconium silicate powder in the raw material of the ceramic core is 10-20%, and the weight percentage of the metallic zircon powder in the raw material of the ceramic core is 1-10%.

[0037] Among them, the refractory powder is selected as quartz glass powder, and the chemical composition of the zirconium silicate powder includes 64-67% of ZrO 2 and 33-36% of SiO 2 . The powder particle size range of the refractory powder is 1-60μm, and the powder purity ≥99.95%. The powder particle size range of the zirconium silicate powder is 1-50μm, and the powder purity ≥98.99%. The powder particle size range of the metallic zircon powder is 1-10μm, and the powder purity ≥99.99%.

[0038] The present invention also provides a preparation method for a near-zero shrinkage silicon-based ceramic core, using the above raw material of the ceramic core to prepare the ceramic core, specifically including:

[0039] S1. Mix the raw material of the ceramic core to form a ceramic core slurry;

[0040] Specifically, weigh the refractory powder, zirconium silicate powder, and metallic zircon powder according to the ratio, place the refractory powder and zirconium silicate powder in a vacuum dryer for drying; then mix the refractory powder, zirconium silicate powder, and metallic zircon powder evenly to obtain the raw material of the ceramic core; add the raw material of the ceramic core to the melted paraffin wax, and achieve uniform mixing of the powder and paraffin wax through vacuum stirring to form a ceramic core slurry.

[0041] Among them, the drying temperature of the vacuum dryer is 95-120°C, and the drying time is 10-24h. The weight percentage of the paraffin wax in the ceramic core slurry is 10-20%, and the melting temperature of the paraffin wax is 80-95°C.

[0042] S2. Use the ceramic core slurry to form a ceramic core green body;

[0043] Specifically, the obtained ceramic core paste is added to a core pressing machine, and a green body of the ceramic core is obtained by hot pressing injection molding method.

[0044] Among them, the forming pressure of the core pressing machine is 5-10 MPa.

[0045] S3. The green body of the ceramic core is sintered with buried powder to obtain the ceramic core.

[0046] Specifically, the green body of the ceramic core is buried with powder in an air atmosphere and sintered at high temperature to obtain the ceramic core. Among them, the final sintering temperature is 1100-1300 °C. The heating process of sintering includes multiple stages, the heating rate of each stage is 150-300 °C, the heating speed of each stage is 2-8 °C / min, and the holding time after heating in each stage is 4-15 h.

[0047] The preparation method of the above near-zero shrinkage silicon-based ceramic core is described below through specific data values.

[0048] Example 1

[0049] S1. Prepare 10 kg of ceramic core raw materials, and weigh quartz glass powder with an average particle size of 20 μm and a purity of 99.95%, zirconium silicate powder with an average particle size of 30 μm and a purity of 98.99%, and metallic zirconium powder with an average particle size of 5 μm and a purity of 99.99% according to the weight percentages of 89%, 10%, and 1% respectively; place the quartz glass powder and zirconium silicate powder in a vacuum dryer and dry for 12 h at a temperature of 120 °C, and fully and evenly mix the dried quartz glass powder and zirconium silicate powder with the metallic zirconium powder to obtain the ceramic core raw materials;

[0050] Weigh paraffin according to 20% of the weight of the ceramic core paste, put it into a vacuum mixer for melting, add the evenly mixed ceramic core raw materials to the melted paraffin in batches, the temperature of the paraffin is 90 °C, evacuate and stir until evenly mixed to obtain the ceramic core paste;

[0051] S2. Transfer the ceramic core paste to the barrel of the core pressing machine, use a mold to press the green body, the forming pressure of the core pressing machine is 5 MPa, and obtain the green body of the ceramic core;

[0052] S3. Place the green body of the ceramic core in a sagger, fill it with filler, and then sinter it. The sintering process is as follows: in the first stage, heat from room temperature to 200 °C at a heating rate of 2 °C / min and hold at 200 °C for 5 h; in the second stage, heat from 200 °C to 400 °C at a heating rate of 2 °C / min and hold at 400 °C for 5 h; in the third stage, heat from 400 °C to 700 °C at a heating rate of 3 °C / min and hold at 700 °C for 8 h; in the fourth stage, heat from 700 °C to 1000 °C at a heating rate of 5 °C / min and hold at 1000 °C for 10 h; in the fifth stage, heat from 1000 °C to 1300 °C at a heating rate of 8 °C / min and hold for 12 h; finally, cool it in the furnace to room temperature to obtain the ceramic core.

[0053] Calculate the shrinkage rate using the dimensions of the green body of the ceramic core measured before and after sintering and the dimensions of the ceramic core. The shrinkage rate of the ceramic core prepared in this example is 0.42% and the high-temperature deflection is 0.47 mm after measurement and calculation.

[0054] Example 2

[0055] S1. Prepare 10 kg of ceramic core raw materials. Weigh quartz glass powder with an average particle size of 20 μm and a purity of 99.96%, zirconium silicate powder with an average particle size of 30 μm and a purity of 99.09%, and metallic zirconium powder with an average particle size of 5 μm and a purity of 99.99% according to the weight percentages of 85%, 12%, and 3% respectively. Place the quartz glass powder and zirconium silicate powder in a vacuum dryer and dry for 10 h at a temperature of 110 °C. Then, fully and evenly mix the dried quartz glass powder and zirconium silicate powder with the metallic zirconium powder to obtain the ceramic core raw materials.

[0056] Weigh paraffin according to 15% of the weight of the ceramic core slurry and put it into a vacuum mixer for melting. Add the evenly mixed ceramic core raw material powder to the melted paraffin in batches. The temperature of the paraffin is 95 °C. Vacuumize and stir until it is uniform to obtain the ceramic core slurry.

[0057] S2. Transfer the ceramic core slurry to the hopper of a core pressing machine and use a mold to press the green body. The forming pressure of the core pressing machine is 6 MPa to obtain the green body of the ceramic core.

[0058] S3. Put the ceramic core blank into a sagger, fill it with fillers and then sinter it. According to the first stage, the temperature is from room temperature to 250℃, the heating rate is 2℃ / min, and it is kept at 250℃ for 5h; the second stage is from 250℃ to 450℃, the heating rate is 2℃ / min, and it is kept at 450℃ for 5h; the third stage is from 450℃ to 650℃, the heating rate is 3℃ / min, and it is kept at 650℃ for 8h; the fourth stage is from 650℃ to 950℃, the heating rate is 5℃ / min, and it is kept at 950℃ for 10h; finally, the temperature is increased from 950℃ to 1250℃, the heating rate is 5℃ / min, and it is kept at 12h; finally, the ceramic core is obtained after cooling to room temperature with the furnace.

[0059] The shrinkage rate is calculated using the ceramic core blank size and the ceramic core size measured before and after sintering. The ceramic core prepared in this embodiment is measured and calculated to have a shrinkage rate of 0.03% and a high-temperature deflection of 0.20 mm.

[0060] Example 3

[0061] S1. Prepare 10 kg of ceramic core raw material, weigh quartz glass powder with an average particle size of 20 μm and a purity of 99.97%, zirconium silicate powder with an average particle size of 30 μm and a purity of 99.29%, and metal zirconium powder with an average particle size of 5 μm and a purity of 99.99% in 80%, 15% and 5% by weight respectively; dry the quartz glass powder and zirconium silicate powder in a vacuum dryer for 24 h at a temperature of 95° C., and fully and evenly mix the dried quartz glass powder and zirconium silicate powder with the metal zirconium powder to obtain a ceramic core raw material;

[0062] Weigh paraffin wax according to 12% of the weight of the ceramic core slurry and put it into a vacuum mixer for melting. Add the evenly mixed ceramic core raw material powder into the melted paraffin wax in batches. The temperature of the paraffin wax is 85°C. Vacuum and stir until uniform to obtain ceramic core slurry.

[0063] S2, transferring the ceramic core slurry to the barrel of the core pressing machine, using a mold to press the green blank, the molding pressure of the core pressing machine is 10MPa, and obtaining the ceramic core green blank;

[0064] S3. Put the ceramic core blank into a sagger, fill it with fillers and then sinter it. According to the first stage, the temperature is from room temperature to 150℃, the heating rate is 2℃ / min, and it is kept at 150℃ for 5h; the second stage is from 150℃ to 300℃, the heating rate is 2℃ / min, and it is kept at 300℃ for 5h; the third stage is from 300℃ to 500℃, the heating rate is 3℃ / min, and it is kept at 500℃ for 8h; the fourth stage is from 500℃ to 800℃, the heating rate is 5℃ / min, and it is kept at 800℃ for 10h; finally, the temperature is increased from 800℃ to 1100℃, the heating rate is 5℃ / min, and it is kept at 15h; finally, the ceramic core is obtained after cooling to room temperature with the furnace.

[0065] The shrinkage rate was calculated using the ceramic core blank size and the ceramic core size measured before and after sintering. The ceramic core prepared in this embodiment was measured and calculated to have a shrinkage rate of -0.19% and a high-temperature deflection of 0.50 mm.

[0066] Example 4

[0067] S1. Prepare 10 kg of ceramic core raw material, weigh quartz glass powder with an average particle size of 40 μm and a purity of 99.98%, zirconium silicate powder with an average particle size of 20 μm and a purity of 99.39%, and metal zirconium powder with an average particle size of 5 μm and a purity of 99.99% in accordance with weight percentages of 70%, 20% and 10% respectively; dry the quartz glass powder and zirconium silicate powder in a vacuum dryer for 10 h at a temperature of 1115° C., and fully and evenly mix the dried quartz glass powder and zirconium silicate powder with the metal zirconium powder to obtain a ceramic core raw material;

[0068] Weigh paraffin wax according to 10% of the weight of the ceramic core slurry and put it into a vacuum mixer for melting. Add the evenly mixed ceramic core raw material powder into the melted paraffin wax in batches. The temperature of the paraffin wax is 80°C. Vacuum and stir until uniform to obtain ceramic core slurry.

[0069] S2, transferring the ceramic core slurry to the barrel of the core pressing machine, using a mold to press the green blank, the molding pressure of the core pressing machine is 8MPa, and obtaining the ceramic core green blank;

[0070] S3. Place the green ceramic core in a sagger, fill it with packing material, and then sinter it. The sintering process is as follows: in the first stage, heat from room temperature to 200 °C at a heating rate of 2 °C / min and hold at 200 °C for 5 h; in the second stage, heat from 200 °C to 400 °C at a heating rate of 2 °C / min and hold at 400 °C for 5 h; in the third stage, heat from 400 °C to 700 °C at a heating rate of 3 °C / min and hold at 700 °C for 8 h; in the fourth stage, heat from 700 °C to 1000 °C at a heating rate of 5 °C / min and hold at 1000 °C for 8 h; finally, heat from 1000 °C to 1300 °C at a heating rate of 5 °C / min and hold for 10 h. Then, cool it in the furnace to room temperature to obtain the ceramic core.

[0071] Calculate the shrinkage rate using the dimensions of the green ceramic core and the ceramic core measured before and after sintering. The shrinkage rate of the ceramic core prepared in this example is -0.05% and the high-temperature deflection is 0.38 mm after measurement and calculation.

[0072] Example 5

[0073] S1. Prepare 10 kg of ceramic core raw materials. Weigh quartz glass powder with an average particle size of 50 μm and a purity of 99.99%, zirconium silicate powder with an average particle size of 10 μm and a purity of 99.59%, and metallic zirconium powder with an average particle size of 10 μm and a purity of 99.99% according to the weight percentages of 88%, 10.5%, and 1.5% respectively. Place the quartz glass powder and zirconium silicate powder in a vacuum dryer and dry for 20 h at a temperature of 100 °C. Then, thoroughly and evenly mix the dried quartz glass powder and zirconium silicate powder with the metallic zirconium powder to obtain the ceramic core raw materials.

[0074] Weigh paraffin wax according to 18% of the weight of the ceramic core slurry and melt it in a vacuum mixer. Add the evenly mixed ceramic core raw material powder to the melted paraffin wax in batches. The temperature of the paraffin wax is 85 °C. Vacuumize and stir until it is uniform to obtain the ceramic core slurry.

[0075] S2. Transfer the slurry to the hopper of a core press and use a mold to press the green body. The forming pressure of the core press is 7 MPa to obtain the green ceramic core.

[0076] S3. Put the ceramic core blank into a sagger, fill it with fillers and then sinter it. According to the first stage, the temperature is from room temperature to 200°C, the heating rate is 3°C / min, and it is kept at 200°C for 5 hours; the second stage is from 200°C to 400°C, the heating rate is 3°C / min, and it is kept at 400°C for 5 hours; the third stage is from 400°C to 650°C, the heating rate is 5°C / min, and it is kept at 650°C for 8 hours; the fourth stage is from 650°C to 900°C, the heating rate is 5°C / min, and it is kept at 900°C for 10 hours; finally, the temperature is increased from 900°C to a maximum of 1200°C, the heating rate is 8°C / min, and it is kept at 12 hours; finally, the ceramic core is obtained after cooling to room temperature with the furnace.

[0077] The shrinkage rate was calculated using the ceramic core blank size and the ceramic core size measured before and after sintering. The ceramic core prepared in this embodiment was measured and calculated to have a shrinkage rate of 0.02% and a high-temperature deflection of 0.10 mm.

[0078] Example 6

[0079] S1. Prepare 10 kg of ceramic core raw material, weigh quartz glass powder with an average particle size of 30 μm and a purity of ≥99.95%, zirconium silicate powder with an average particle size of 15 μm and a purity of ≥98.99%, and metal zirconium powder with an average particle size of 3 μm and a purity of ≥99.99% according to weight percentages of 87%, 11% and 2% respectively; place the quartz glass powder and zirconium silicate powder in a vacuum dryer and dry them for 15 hours at a temperature of 100 ° C. Fully and evenly mix the dried quartz glass powder and zirconium silicate powder with the metal zirconium powder to obtain a ceramic core raw material;

[0080] Weigh paraffin wax according to 16% of the weight of the ceramic core slurry and put it into a vacuum mixer for melting. Add the evenly mixed ceramic core raw material powder into the melted plasticizer paraffin wax in batches. The temperature of the paraffin wax is 90°C. Vacuum and stir until uniform to obtain ceramic core slurry.

[0081] S2, transferring the slurry to the barrel of a core pressing machine, using a mold to press the blank, the molding pressure of the core pressing machine is 9 MPa, and obtaining a ceramic core blank;

[0082] S3. Place the green ceramic core in a sagger, fill it with packing material, and then sinter it. The sintering process is as follows: in the first stage, from room temperature to 200 °C, the heating rate is 2 °C / min, and keep it at 200 °C for 4 h; in the second stage, from 200 °C to 400 °C, the heating rate is 2 °C / min, and keep it at 400 °C for 5 h; in the third stage, from 400 °C to 650 °C, the heating rate is 3 °C / min, and keep it at 650 °C for 8 h; in the fourth stage, from 650 °C to 950 °C, the heating rate is 5 °C / min, and keep it at 950 °C for 10 h; in the fifth stage, from 950 °C to 1250 °C, the heating rate is 8 °C / min, and keep it at 1250 °C for 12 h; finally, cool it in the furnace to room temperature to obtain the ceramic core.

[0083] Calculate the shrinkage rate using the dimensions of the green ceramic core and the ceramic core measured before and after sintering. The shrinkage rate of the ceramic core prepared in this example is 0.01% and the high-temperature deflection is 0.05 mm after measurement and calculation.

[0084] Comparative Example 1

[0085] S1. Prepare 10 kg of ceramic core raw materials. Weigh quartz glass powder with an average particle size of 20 μm and a purity of 99.95% and zirconium silicate powder with an average particle size of 30 μm and a purity of 98.99% according to the weight percentages of 90% and 10% respectively. Place the quartz glass powder and zirconium silicate powder in a vacuum dryer and dry for 12 h at a temperature of 120 °C; add the dried and evenly mixed ceramic core raw material powder to the melted paraffin in batches. The temperature of the paraffin is 90 °C, and evacuate and stir until it is uniform to obtain the ceramic core slurry.

[0086] S2. Transfer the ceramic core slurry to the hopper of a core pressing machine, and use a mold to press the green body. The forming pressure is 5 MPa to obtain the green ceramic core.

[0087] S3. Place the green ceramic core in a sagger, fill it with packing material, and then sinter it. The final sintering temperature is 1250 °C, and the holding time is 10 h. Take it out after cooling in the furnace to room temperature to obtain the ceramic core.

[0088] Calculate the shrinkage rate using the dimensions of the green ceramic core and the ceramic core measured before and after sintering. The shrinkage rate of the ceramic core prepared in this comparative example is 1.15% and the high-temperature deflection is 0.71 mm after measurement and calculation.

[0089] By comparing the above examples and comparative examples, it is found that the dimensional accuracy of the ceramic cores prepared by the technologies and parameters adopted in Examples 1-6 is higher than that of the comparative example without the introduction of zirconium metal. This shows that the introduction of zirconium metal can effectively control the dimensional accuracy and stability of the ceramic core.

[0090] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0091] It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

Claims

1. A raw material for a near-zero shrinkage silicon-based ceramic core, comprising refractory powder and a mineralizer, characterized in that: It also includes metal zirconium powder, the mineralizer is zirconium silicate powder, the refractory powder is quartz glass powder, the weight percentage of the refractory powder in the raw material is 80-89%, the weight percentage of the zirconium silicate powder in the raw material is 10-15%, and the weight percentage of the metal zirconium powder in the raw material is 1-5%; The particle size range of the refractory powder is 1-60 μm and the powder purity is not less than 99.95%, the particle size range of the zirconium silicate powder is 1-50 μm and the powder purity is not less than 98.99%, and the particle size range of the metal zirconium powder is 1-10 μm and the powder purity is not less than 99.99%; The raw materials of the ceramic core are formed into a ceramic core blank, which is then subjected to powder embedding sintering in an air atmosphere to obtain a ceramic core. The final sintering temperature is 1200-1300°C, and the sintering heating process includes multiple stages. The heating amplitude of each stage is 150-300°C, the heating rate of each stage is 2-8°C / min, and the insulation time after heating in each stage is 4-15h.

2. The raw material of the near-zero shrinkage silicon-based ceramic core according to claim 1, characterized in that: The weight percentage of the refractory powder in the raw material is 85-88%, the weight percentage of the zirconium silicate powder in the raw material is 10.5-12%, and the weight percentage of the metal zirconium powder in the raw material is 1.5-3%.

3. A method for preparing a near-zero shrinkage silicon-based ceramic core, using the raw material of the near-zero shrinkage silicon-based ceramic core as described in any one of claims 1-2 to prepare a ceramic core, characterized in that: The preparation method specifically comprises: S1, mixing ceramic core raw materials to form ceramic core slurry; S2, forming a ceramic core blank using the ceramic core slurry; S3, burying the ceramic core blank with powder and sintering to obtain a ceramic core.

4. The method for preparing a near-zero shrinkage silicon-based ceramic core according to claim 3, characterized in that: In step S1, the ceramic core raw material is added to the dispersant in batches, and vacuum-stirred until uniform to obtain a ceramic core slurry.

5. The method for preparing a near-zero shrinkage silicon-based ceramic core according to claim 4, characterized in that: In step S1, the ceramic core raw material is added to the melted paraffin in batches, and the mixture is vacuumed and stirred until uniform to obtain a ceramic core slurry; the melting temperature of the paraffin is 80-95°C.

6. The method for preparing a near-zero shrinkage silicon-based ceramic core according to claim 3, characterized in that: In step S2, the ceramic core slurry is added into a core pressing machine, and a ceramic core blank is obtained by a hot pressing injection molding method; the molding pressure of the core pressing machine is 5-10 MPa.

7. The method for preparing a near-zero shrinkage silicon-based ceramic core according to claim 3, characterized in that: In step S3, the temperature rising process of the buried powder sintering includes multiple stages, which include: the first stage: room temperature to 200°C, the heating rate is 2°C / min, and the temperature is kept at 200°C for 4 hours; the second stage: 200°C to 400°C, the heating rate is 2°C / min, and the temperature is kept at 400°C for 5 hours; the third stage: 400°C to 650°C, the heating rate is 3°C / min, and the temperature is kept at 650°C for 8 hours; the fourth stage: 650°C to 950°C, the heating rate is 5°C / min, and the temperature is kept at 950°C for 10 hours; the fifth stage: 950°C to a maximum of 1250°C, the heating rate is 8°C / min, and the temperature is kept for 12 hours.