Highly Collapsible Ceramic Core with Dense Surface and Porous Core and its Preparation Method

Abstract

This invention discloses a highly collapsible ceramic core with a dense outer surface and a porous core, and its preparation method. The ceramic core is composed of a porous core ceramic core and a densified inert coating on its outer surface. The porous core ceramic core comprises 42-51 wt% ceramic powder, 35-40 wt% hollow glass microspheres, 4-9 wt% fiber, 3-7 wt% graphite, and 2-8 wt% starch. The densified inert coating comprises 67-75 wt% sol and 25-33 wt% nanoparticles. The preparation method includes the following steps: preparing a porous core ceramic core and a densified inert coating slurry; impregnating the porous core ceramic core with the densified inert coating slurry under segmented vacuum pressure using a gradient pressure reduction method; and then sintering it in a heat treatment furnace. The ceramic core prepared by this invention exhibits excellent collapsibility, which can solve the problem of blade thermal cracking. The inert coating avoids interfacial reactions, and the porous core structure facilitates efficient core removal.

Description

Technical Field

[0001] This invention belongs to the field of ceramic core material design and preparation technology, specifically relating to a high-collapse ceramic core with a dense outer surface and a porous core structure and its preparation method. This technology is particularly suitable for casting blades with complex internal cavity structures in hot-end components such as aero-engines and gas turbines. Background Technology

[0002] In high-end equipment manufacturing industries such as aerospace and energy, hot-end components such as aero-engine turbine blades and gas turbine guide vanes are facing increasingly harsh working environments and more complex structural designs as equipment demands higher thrust-to-weight ratios and efficiency. To improve the cooling efficiency and mechanical properties of blades, the internal cavity is often designed as a complex structure with multiple channels and blind cavities. This places extremely high demands on the ceramic cores used to form such complex internal cavity structures, and traditional ceramic cores face numerous technical challenges in practical applications.

[0003] First, there is insufficient high-temperature resilience. Traditional ceramic cores are mostly monolithically dense or have low porosity structures. During high-temperature casting, the molten metal solidifies and shrinks, but the ceramic core, due to its dense structure and poor high-temperature deformation capacity, cannot adapt to the alloy shrinkage, resulting in huge solidification stress in the blade cavity. In thin-walled, complex-cavity blades, at weak points such as corners and blind holes, stress concentration can easily lead to solidification thermal cracking or recrystallization of the internal metal, reducing the blade's mechanical properties and causing a blade scrap rate of over 30%.

[0004] Secondly, interfacial reaction issues are prominent. As the turbine inlet temperature of aero-engines increases, highly reactive alloys such as high-Hf alloys, high-Y alloys, and cobalt-based alloys are widely used. However, the reactive elements in these alloys (such as Hf, Y, and Co) easily react with components such as SiO2 in traditional silicon-based ceramic cores to generate low-melting-point eutectic phases or brittle compounds, which contaminate the alloy matrix, form a hard and brittle layer at the interface, and cause early cracking of the blades. At the same time, they damage the core surface and affect the dimensional accuracy and aerodynamic performance of the blade cavity.

[0005] Furthermore, core removal is difficult. Traditional ceramic cores, to ensure dimensional stability, often have a dense structure or low porosity. However, the internal cavity of a blade is complex, with numerous curved channels, blind cavities, and blind holes. This dense core structure makes it difficult for core-removing agents (such as strong alkaline solutions) to penetrate. Therefore, it is necessary to extend the core removal time, increase the core removal temperature, or increase the concentration of the core-removing agent. This not only increases costs and energy consumption but may also corrode the blade substrate. Even so, more than 30% of blades with complex internal cavity structures still have residual cores, leading to blockage of the blade's internal flow channels, affecting cooling efficiency, and even causing blade overheating failure. In existing technologies, even with improved ceramic cores, it is difficult to simultaneously achieve multiple performance characteristics. For example, while some porous cores can improve yielding and core removal performance, their high surface activity makes them prone to reacting with highly reactive alloys; some surface-modified cores, while reducing the risk of interfacial reactions, suffer from insufficient yielding due to core density. Therefore, developing a ceramic core that combines high yielding properties, low surface activity, and excellent core removal performance has become a key technical challenge that urgently needs to be solved in the field of precision casting technology. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a high-yield ceramic core with a dense outer surface and a porous core structure. The high-yield ceramic core is composed of a porous core ceramic core and a densified inert coating on its outer surface. The mass percentage of each component in the porous core ceramic core is as follows: ceramic powder component 42-51 wt%, hollow glass microsphere component 35-40 wt%, fiber component 4-9 wt%, graphite component 3-7 wt%, and starch component 2-8 wt%. The mass percentage of each component in the densified inert coating is as follows: sol component 67-75 wt% and nanoparticle component 25-33 wt%.

[0007] Preferably, the amount of hollow glass microspheres added increases with the amount of ceramic powder added. Within the mass percentage range of the hollow glass microspheres and the ceramic powder, the amount of hollow glass microspheres added increases by 1.5-2 wt% for every 3 wt% increase in the amount of ceramic powder added.

[0008] In any of the above embodiments, it is preferred that the mass percentage of each substance in the ceramic powder component is 48-55 wt% quartz glass powder, 24-28 wt% white corundum powder, and 20-24 wt% zirconium silicate powder.

[0009] In any of the above embodiments, it is preferred that the quartz glass powder, the white corundum powder, and the zirconium silicate powder each include three particle sizes: 30-40μm, 18-30μm, and 10-18μm, respectively, and the mass ratio of the 30-40μm, 18-30μm, and 10-18μm particles is 2-3:1-2:1.

[0010] In any of the above embodiments, it is preferred that the mass percentage of each substance in the hollow glass microsphere component is 50-60 wt% for silicon oxide hollow glass microspheres, 21-27 wt% for alumina hollow glass microspheres, and 18-24 wt% for zirconium silicate hollow glass microspheres.

[0011] In any of the above embodiments, it is preferred that the silica hollow glass microspheres, the alumina hollow glass microspheres, and the zirconium silicate hollow glass microspheres all include three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm, respectively, and the mass ratio of the 20-30 μm, 10-20 μm, and 0-10 μm particles is 2-3:1-2:1.

[0012] In any of the above embodiments, it is preferred that the mass percentage of each substance in the fiber component is 42-72 wt% chopped carbon fiber and 28-58 wt% chopped aramid fiber; the diameter of both the chopped carbon fiber and the chopped aramid fiber is controlled within the range of 2-8 μm, and the aspect ratio is controlled within the range of 10-25:1.

[0013] In any of the above embodiments, it is preferred that the particle size of the graphite is controlled within the range of 1-5 μm.

[0014] In any of the above embodiments, it is preferred that the mass percentage of each substance in the sol component is 42-47 wt% for silica sol, 30-35 wt% for aluminum sol, and 21-25 wt% for yttrium sol.

[0015] In any of the above embodiments, it is preferred that the mass percentage of each substance in the nanopowder component is 24-31 wt% nano-silica, 17-24 wt% nano-alumina, 10-17 wt% nano-yttrium oxide, and 34-41 wt% nano-zirconium silicate; and the particle size of the nano-silica, the nano-alumina, the nano-yttrium oxide, and the nano-zirconium silicate is controlled within the range of 10-30 nm.

[0016] This invention also provides a method for preparing a highly collapsible ceramic core with a dense outer surface and a porous core, the preparation method comprising the following steps in sequence:

[0017] Step 1: Weigh out each raw material according to the designed material ratio and set aside;

[0018] Step 2: Prepare a porous ceramic core according to the designed process and parameters;

[0019] Step 3: Prepare a dense inert coating slurry according to the designed process and parameters;

[0020] Step 4: Use a positioning fixture to suspend the porous ceramic core in the impregnation chamber of the vacuum impregnation equipment, so that the porous ceramic core maintains an appropriate gap with the inner wall of the impregnation chamber. Then, slowly inject the densification inert coating slurry into the impregnation chamber until the densification inert coating slurry completely submerges the porous ceramic core.

[0021] Step 5: Start the vacuum system of the vacuum impregnation equipment and use a gradient pressure reduction method to impregnate the porous ceramic core with a densifying inert coating slurry under segmented vacuum pressure. This allows the densifying inert coating slurry to fully penetrate into the pores on the outer surface of the porous ceramic core, forming a densifying inert coating on its outer surface.

[0022] Step Six: Place the porous ceramic core with the densified inert coating into a heat treatment furnace for sintering treatment, so that the densified inert coating is tightly bonded to the outer surface of the porous ceramic core, thus obtaining a high-yield ceramic core with a dense outer surface and a porous core.

[0023] Preferably, in step two, the method for preparing the porous ceramic core includes the following steps in sequence:

[0024] Step 2.1: Weigh each raw material according to the designed material ratio and set aside;

[0025] Step 2.2: Put all the quartz glass powder, white corundum powder and zirconium silicate powder of each particle size into a V-type mixer and mix at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to make the substances mix evenly and obtain ceramic powder components.

[0026] Step 2.3: Put all the silica hollow glass microspheres, alumina hollow glass microspheres and zirconium silicate hollow glass microspheres of various particle sizes into a V-type mixer and mix them at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to ensure that the substances are mixed evenly and to obtain the hollow glass microsphere component.

[0027] Step 2.4: Place the plasticizer in a mixer and heat it while stirring at a speed of 100-200 r / min. After the temperature reaches 90-130℃, continue stirring for 20-30 minutes to completely melt it. The amount of plasticizer added is 15-25% of the mass of the porous ceramic core. The plasticizer is composed of 93wt% paraffin wax, 5wt% beeswax and 2wt% polyethylene.

[0028] Step 2.5: Keep the stirring temperature and stirring speed constant, add the ceramic powder components to the mixer and continue stirring for 1-2 hours to allow the substances to blend together;

[0029] Step 2.6: Keep the stirring temperature and stirring speed constant, add the hollow glass microsphere component into the mixer and continue stirring for 1-2 hours to allow the substances to blend together;

[0030] Step 2.7: Keep the stirring temperature and stirring speed constant, add the chopped carbon fibers and chopped aramid fibers to the mixer and continue stirring for 2-3 hours to ensure that the fiber components are evenly dispersed;

[0031] Step 2.8: Keep the stirring temperature and stirring speed constant, add graphite and starch to the mixer and continue stirring for 3-5 hours to ensure that the substances are mixed evenly and to obtain ceramic core slurry;

[0032] Step 2.9: Press the ceramic core blank using the prepared ceramic core slurry at a pressing temperature of 90-130℃, a pressing pressure of 3-7MPa, and a holding time of 120-180s; then place the ceramic core blank into a firing furnace for low-temperature debinding and high-temperature sintering to decompose and volatilize the organic matter in the ceramic core blank, forming a porous structure, thus obtaining a porous ceramic core.

[0033] The process parameters for low-temperature debinding and high-temperature sintering are as follows: The ceramic core blank is placed in a firing furnace. First, the temperature is increased from room temperature to 400-600℃ at a rate of 5-10℃ / min and held for 10-20 hours to complete the low-temperature debinding process. Then, the temperature is increased from 400-600℃ to 1100-1250℃ at a rate of 3-5℃ / min and held for 4-8 hours. The blank is then cooled to room temperature in the furnace to complete the high-temperature sintering process. No protective atmosphere is required during the entire process of low-temperature debinding and high-temperature sintering.

[0034] In any of the above schemes, it is preferred that, in step three, the method for preparing the densified inert coating slurry includes the following steps in sequence:

[0035] Step 3.1: Weigh each raw material according to the designed material ratio and set aside;

[0036] Step 3.2: Put all the silica sol, aluminum sol and yttrium sol into a mixer and stir at room temperature for 2-3 hours at a stirring speed of 220-350 r / min to make the substances evenly dispersed and fused to obtain the sol component;

[0037] Step 3.3: Put all the nano-silica, nano-alumina, nano-yttrium oxide and nano-zirconium silicate into a V-type mixer and mix at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to make the substances mix evenly and obtain nano-powder components.

[0038] Step 3.4: Add the obtained nanoparticle components to the mixer and continue stirring with the sol components for 6-10 hours to allow the substances to fuse together, thus obtaining a dense inert coating slurry.

[0039] In any of the above schemes, it is preferred that, in step four, a densifying inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densifying inert coating slurry reaches a position 20-25 mm above the highest point of the porous ceramic core.

[0040] In any of the above schemes, it is preferred that, in step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 2-5min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 10-15min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 5-8min.

[0041] In this invention, the first stage of impregnation can eliminate most of the free gas, the second stage of impregnation can prevent the gas in the pores from expanding suddenly, and the third stage of impregnation can ensure that the slurry fully penetrates into the pores.

[0042] In any of the above schemes, it is preferred that in step six, the sintering temperature is 700-950℃ and the calcination time is 3-6h.

[0043] In this invention, the V-type mixer, agitator, vacuum impregnation equipment, heat treatment furnace, core pressing machine, and calcining furnace used are all traditional equipment, with no special requirements on equipment structure or model. The positioning fixtures used can be selected according to the actual situation. Quartz glass powder, white corundum powder, and zirconium silicate powder all include three particle size ranges: 30-40μm, 18-30μm, and 10-18μm, i.e., 30μm≤particle size≤40μm, 18μm≤particle size<30μm, and 10μm≤particle size<18μm. Silica hollow glass microspheres, alumina hollow glass microspheres, and zirconium silicate hollow glass microspheres all include three particle size ranges: 20-30μm... The particle sizes are defined as follows: 10-20 μm and 0-10 μm, i.e., 20 μm ≤ particle size ≤ 30 μm, 10 μm ≤ particle size < 20 μm, and 0 μm < particle size < 10 μm; the particle sizes of nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are all controlled within the range of 10-30 nm, i.e., 10 nm ≤ particle size ≤ 30 nm; the particle size of graphite is controlled within the range of 1-5 μm, i.e., 1 μm ≤ particle size ≤ 5 μm. For each particle size range, the particle size obtained after passing the material through two sieves (upper and lower) sequentially is between the upper and lower sieve openings. For example, a particle size of 18-30 μm means the material is passed through a 30 μm sieve and an 18 μm sieve sequentially, resulting in a particle size between 18 and 30 μm.

[0044] This invention utilizes hollow glass microspheres, which effectively improve the collapsibility, collapseability, and removability of the ceramic core. Silica hollow glass microspheres and quartz glass powder possess good thermal stability and a low coefficient of thermal expansion, maintaining structural stability at high temperatures while providing a certain strength to the core. Alumina hollow glass microspheres and white corundum powder further enhance the high-temperature strength of the core. Zirconia hollow glass microspheres and zirconium silicate powder improve the chemical stability of the material. Graphite has a lubricating effect, helping to improve the collapsibility of the core and increase porosity. Starch decomposes at high temperatures to form pores, increasing the porosity of the core. Short-cut carbon fibers and short-cut aramid fibers enhance the toughness of the core, prevent cracking, and increase porosity.

[0045] In this invention, silica sol, aluminum sol, and yttrium sol act as binders in the coating, enabling the nanoparticles to bond tightly together. Nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate have high chemical stability and low activity, effectively isolating the highly active alloy from the ceramic core substrate and preventing interfacial reactions.

[0046] The present invention relates to a highly collapsible ceramic core with a dense outer surface and a porous core, and its preparation method thereof, which has the following beneficial effects:

[0047] (1) High yielding capacity: The porous core structure designed in this invention is the core of achieving high yielding capacity, which can fundamentally solve the problems of hot cracking of blades and recrystallization of internal cavity metal. In the high-temperature casting environment, the porous core structure can achieve active yielding in size through the compression and deformation of pores, accurately matching the solidification shrinkage requirements of the alloy; at the same time, the porous structure makes the core strength exhibit a moderate decrease with increasing temperature, achieving strength yielding. This dual yielding mechanism can effectively disperse and alleviate the solidification stress in the blade cavity, especially in stress concentration areas such as corners and blind holes of thin-walled blades, which can completely avoid hot cracking defects caused by excessive stress, and at the same time prevent the recrystallization of internal cavity metal due to stress.

[0048] (2) Low interfacial reactivity: The densified inert coating of this invention has extremely low chemical activity, forming an effective isolation layer between the ceramic core and the highly reactive alloy. During the casting process, the coating prevents the active elements in the alloy from reacting with the ceramic core matrix, ensuring that the microstructure and performance of the blade are not contaminated or damaged. Testing of blades cast with high-Hf alloys showed that after using the ceramic core prepared according to this invention, the thickness of the interfacial reaction layer was reduced from 10-30 μm in traditional cores to below 2 μm, significantly improving the high-temperature performance and service life of the blade.

[0049] (3) Excellent core removal performance: The porous structure of the core facilitates the core removal process. During core removal, the core removal agent, such as alkali solution, can quickly penetrate into the core through the porous structure, fully contact and react with the core material, causing the core to disintegrate rapidly, achieving efficient core removal without any residual core. Compared with traditional dense cores, the core removal time of this invention can be shortened by more than 50%, and there is no residual core in the inner cavity of the blade after core removal, with good surface quality, effectively improving the processing efficiency and quality of the blade. Attached Figure Description

[0050] Figure 1 Microscopic photograph of a porous ceramic core prepared according to a preferred embodiment of the present invention and its preparation method;

[0051] Figure 2 for Figure 1 A photograph of the densified inert coating slurry prepared in the illustrated embodiment;

[0052] Figure 3 for Figure 1 A photograph of a porous ceramic core (test rod) in the illustrated embodiment before it is impregnated with a densified inert coating slurry;

[0053] Figure 4 for Figure 1 A photograph of a porous ceramic core (test rod) in the illustrated embodiment after being impregnated with a densified inert coating slurry;

[0054] Figure 5 for Figure 1 Photographs of the interface morphology between the ceramic core and the blade prepared in the illustrated embodiment;

[0055] Figure 6 To adopt Figure 1 The ceramic core prepared in the illustrated embodiment was further used to cast blades, and the morphology of the blade's inner cavity is shown in the photograph.

[0056] The diagram shows the following labels: 1 - hollow glass microspheres, 2 - pores. Detailed Implementation

[0057] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0058] Example 1:

[0059] According to a preferred embodiment of the high-yield ceramic core with a dense outer surface and a porous core structure of the present invention, the high-yield ceramic core is composed of a porous core ceramic core and a densified inert coating on its outer surface. The mass percentage of each substance in the porous core ceramic core is as follows: ceramic powder component 42wt%, hollow glass microsphere component 35wt%, fiber component 9wt%, graphite component 7wt%, and starch component 7wt%. The mass percentage of each substance in the densified inert coating is as follows: sol component 67wt% and nanopowder component 33wt%.

[0060] The amount of hollow glass microspheres added increases with the amount of ceramic powder added. Within the mass percentage range of the hollow glass microspheres and ceramic powder, the amount of hollow glass microspheres added increases by 1.5-2 wt% for every 3 wt% increase in the amount of ceramic powder added. In this embodiment, both the ceramic powder and hollow glass microspheres are added at the minimum amount.

[0061] The ceramic powder composition comprises, by mass percentage, 48 wt% quartz glass powder, 28 wt% white fused alumina powder, and 24 wt% zirconium silicate powder. The quartz glass powder, white fused alumina powder, and zirconium silicate powder each have three particle sizes: 30-40 μm, 18-30 μm, and 10-18 μm. The mass ratio of the 30-40 μm, 18-30 μm, and 10-18 μm particles is 2:1:1.

[0062] The hollow glass microspheres are composed of the following components at the following mass percentages: 50 wt% silica hollow glass microspheres, 27 wt% alumina hollow glass microspheres, and 23 wt% zirconium silicate hollow glass microspheres. Each of the silica, alumina, and zirconium silicate hollow glass microspheres comprises three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm. The mass ratio of each particle size (20-30 μm, 10-20 μm, and 0-10 μm) is 2:1:1.

[0063] The fiber composition comprises 42 wt% chopped carbon fibers and 58 wt% chopped aramid fibers by mass. The diameters of both the chopped carbon fibers and chopped aramid fibers are controlled within the range of 2-8 μm, and their aspect ratios are controlled within the range of 10-25:1. The graphite particle size is controlled within the range of 1-5 μm.

[0064] The sol component comprises, by mass percentage, 42 wt% silica sol, 34 wt% aluminum sol, and 24 wt% yttrium sol. The nanopowder component comprises, by mass percentage, 24 wt% nano-silica, 18 wt% nano-alumina, 17 wt% nano-yttrium oxide, and 41 wt% nano-zirconium silicate; the particle sizes of the nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are all controlled within the range of 10-30 nm.

[0065] This embodiment also provides a method for preparing a highly collapsible ceramic core with a dense outer surface and a porous core, the preparation method comprising the following steps in sequence:

[0066] Step 1: Weigh out each raw material according to the designed material ratio and set aside;

[0067] Step 2: Prepare a porous ceramic core according to the designed process and parameters;

[0068] Step 3: Prepare a dense inert coating slurry according to the designed process and parameters;

[0069] Step 4: Use a positioning fixture to suspend the porous ceramic core in the impregnation chamber of the vacuum impregnation equipment, so that the porous ceramic core maintains an appropriate gap with the inner wall of the impregnation chamber. Then, slowly inject the densification inert coating slurry into the impregnation chamber until the densification inert coating slurry completely submerges the porous ceramic core.

[0070] Step 5: Start the vacuum system of the vacuum impregnation equipment and use a gradient pressure reduction method to impregnate the porous ceramic core with a densifying inert coating slurry under segmented vacuum pressure. This allows the densifying inert coating slurry to fully penetrate into the pores on the outer surface of the porous ceramic core, forming a densifying inert coating on its outer surface.

[0071] Step Six: Place the porous ceramic core with the densified inert coating into a heat treatment furnace for sintering treatment, so that the densified inert coating is tightly bonded to the outer surface of the porous ceramic core, thus obtaining a high-yield ceramic core with a dense outer surface and a porous core.

[0072] In step two, the preparation method of the porous ceramic core includes the following steps in sequence:

[0073] Step 2.1: Weigh each raw material according to the designed material ratio and set aside;

[0074] Step 2.2: Put all the quartz glass powder, white corundum powder and zirconium silicate powder of each particle size into a V-type mixer and mix them at room temperature for 20 minutes at a mixing speed of 200 r / min to make the materials evenly mixed and obtain ceramic powder components.

[0075] Step 2.3: Put all the silica hollow glass microspheres, alumina hollow glass microspheres and zirconium silicate hollow glass microspheres of various particle sizes into a V-type mixer and mix them at room temperature for 20 minutes at a mixing speed of 200 r / min to make the substances mix evenly and obtain the hollow glass microsphere component.

[0076] Step 2.4: Put the plasticizer into a mixer and heat it while stirring. The stirring speed is 200 r / min. After the temperature reaches 90℃, continue stirring for 20 minutes to make it completely melted. The amount of plasticizer added is 15% of the mass of the porous ceramic core. The plasticizer is composed of 93wt% paraffin wax, 5wt% beeswax and 2wt% polyethylene.

[0077] Step 2.5: Keep the stirring temperature and stirring speed constant, add the ceramic powder components to the mixer and continue stirring for 1 hour to allow the substances to blend together;

[0078] Step 2.6: Keep the stirring temperature and stirring speed constant, add the hollow glass microsphere component into the mixer and continue stirring for 1 hour to allow the substances to blend together;

[0079] Step 2.7: Keeping the stirring temperature and stirring speed constant, add the chopped carbon fibers and chopped aramid fibers to the mixer and continue stirring for 2 hours to ensure that the fiber components are evenly dispersed;

[0080] Step 2.8: Keep the stirring temperature and stirring speed constant, add graphite and starch to the mixer and continue stirring for 3 hours to mix the substances evenly and obtain ceramic core slurry;

[0081] Step 2.9: Press the ceramic core blank using the prepared ceramic core slurry at a pressing temperature of 90℃, a pressing pressure of 3MPa, and a holding time of 180s; then place the ceramic core blank into a calcining furnace for low-temperature debinding and high-temperature sintering to decompose and volatilize the organic matter in the ceramic core blank, forming a porous structure, thus obtaining a porous ceramic core.

[0082] The process of low-temperature debinding and high-temperature sintering is as follows: the ceramic core blank is placed in a firing furnace and first heated from room temperature to 400°C at a heating rate of 5°C / min, and held at that temperature for 20 hours to complete the low-temperature debinding process; then the temperature is increased from 400°C to 1100°C at a heating rate of 3°C / min, held at that temperature for 8 hours, and then cooled to room temperature in the furnace to complete the high-temperature sintering process; no protective atmosphere is required during the entire low-temperature debinding and high-temperature sintering process.

[0083] In step three, the preparation method of the densified inert coating slurry includes the following steps in sequence:

[0084] Step 3.1: Weigh each raw material according to the designed material ratio and set aside;

[0085] Step 3.2: Put all the silica sol, aluminum sol and yttrium sol into a mixer and stir at room temperature for 2 hours at a stirring speed of 350 r / min to make the substances evenly dispersed and fused to obtain the sol component;

[0086] Step 3.3: Put all the nano-silica, nano-alumina, nano-yttrium oxide and nano-zirconium silicate into a V-type mixer and mix at room temperature for 20 minutes at a mixing speed of 200 r / min to make the substances mix evenly and obtain nano-powder components.

[0087] Step 3.4: Add the obtained nanoparticle components to the mixer and continue stirring with the sol components for 6 hours to allow the substances to fuse together, thus obtaining a dense inert coating slurry.

[0088] In step four, the densification inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densification inert coating slurry reaches 20 mm above the highest point of the porous ceramic core.

[0089] In step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 2min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 10min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 5min.

[0090] In step six, the sintering temperature is 700℃ and the calcination time is 6 hours.

[0091] The microstructure of the porous ceramic core prepared in this embodiment is as follows: Figure 1 As shown, hollow glass microspheres 1 and pores 2 are clearly visible in the core. The designed porous core structure is the core of achieving high yielding, which can fundamentally solve the problems of hot cracking of blades and recrystallization of internal metal. In the high-temperature casting environment, the porous core structure can achieve active yielding in size through the compression and deformation of pores, accurately matching the solidification shrinkage requirements of alloy. At the same time, the porous structure makes the core strength show a moderate decrease as the temperature rises, thus achieving strength yielding.

[0092] The densified inert coating slurry prepared in this embodiment is as follows: Figure 2 As shown, the states of the porous ceramic core (test rod) before and after impregnation with the densified inert coating slurry are as follows: Figure 3 and Figure 4 As shown.

[0093] The interface morphology between the ceramic core and the blade prepared in this embodiment is as follows: Figure 5 As shown in the figure, no interfacial reaction occurred. The ceramic core prepared in this embodiment was used to further cast blades, and the morphology of the blade's inner cavity is shown in the figure. Figure 6 As shown in the figure, no metal recrystallization occurred in the inner cavity of the blade.

[0094] The high-yield ceramic core with a dense outer surface and a porous core, and its preparation method, as described in this embodiment, have the following beneficial effects: high yieldability, as the designed porous core structure is the core to achieve high yieldability, fundamentally solving the problems of blade thermal cracking and internal cavity metal recrystallization; low interfacial reactivity, as the dense inert coating has extremely low chemical activity, forming an effective isolation layer between the ceramic core and the highly reactive alloy; and excellent core removal performance, as the porous core structure facilitates the core removal process.

[0095] Example 2:

[0096] Another preferred embodiment of the high-collapse ceramic core with a dense outer surface and a porous core according to the present invention and its preparation method is basically the same as that of Embodiment 1 in terms of material selection and proportioning, process flow and parameters, technical principles, and beneficial effects, except that:

[0097] The porous ceramic core comprises the following components by mass percentage: 45 wt% ceramic powder, 36.5 wt% hollow glass microspheres, 8 wt% fiber, 6 wt% graphite, and 4.5 wt% starch. The densified inert coating comprises the following components by mass percentage: 70 wt% sol-gel and 30 wt% nanoparticles. In this embodiment, for every 3 wt% increase in the amount of ceramic powder, the amount of hollow glass microspheres increases by 1.5 wt% to ensure it remains within the range of 1.5-2 wt%.

[0098] The ceramic powder composition comprises, by mass percentage, 50 wt% quartz glass powder, 27 wt% white fused alumina powder, and 23 wt% zirconium silicate powder. The quartz glass powder, white fused alumina powder, and zirconium silicate powder each have three particle sizes, with a mass ratio of 2.5:1.5:1 for particles of 30-40 μm, 18-30 μm, and 10-18 μm.

[0099] The hollow glass microspheres are composed of the following components by mass percentage: 53 wt% silica hollow glass microspheres, 25 wt% alumina hollow glass microspheres, and 22 wt% zirconium silicate hollow glass microspheres. Each of the silica, alumina, and zirconium silicate hollow glass microspheres comprises three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm, with a mass ratio of 2.5:1.5:1.

[0100] The fiber composition comprises 52 wt% chopped carbon fibers and 48 wt% chopped aramid fibers by mass. The diameters of both the chopped carbon fibers and chopped aramid fibers are controlled within the range of 2-8 μm, and their aspect ratios are controlled within the range of 10-25:1. The particle size of the graphite is controlled within the range of 1-5 μm.

[0101] The sol component comprises, by mass percentage, 44 wt% silica sol, 33 wt% aluminum sol, and 23 wt% yttrium sol. The nanopowder component comprises, by mass percentage, 26 wt% nano-silica, 20 wt% nano-alumina, 15 wt% nano-yttrium oxide, and 39 wt% nano-zirconium silicate, with the particle size of each component controlled within the range of 10-30 nm.

[0102] In step two, the preparation method of the porous ceramic core includes the following main parameters: Step 2.2: Quartz glass powder, white corundum powder, and zirconium silicate powder are placed in a V-type mixer and mixed at room temperature for 23 minutes at a mixing speed of 160 r / min to obtain ceramic powder components; Step 2.3: Silica hollow glass microspheres, alumina hollow glass microspheres, and zirconium silicate hollow glass microspheres are placed in a V-type mixer and mixed at room temperature for 23 minutes at a mixing speed of 160 r / min to obtain hollow glass microsphere components; Step 2.4: 18% plasticizer is added to a mixer and heated while stirring at a stirring speed of 160 r / min until the temperature is reached. After reaching 103℃, continue stirring for 23 minutes; Steps 2.5-2.8: Keeping the stirring temperature and speed constant, add the ceramic powder component to the mixer and continue stirring for 1.3 hours, add the hollow glass microsphere component to the mixer and continue stirring for 1.3 hours, add the chopped carbon fiber and chopped aramid fiber to the mixer and continue stirring for 2.3 hours, add the graphite and starch to the mixer and continue stirring for 3.6 hours to obtain the ceramic core slurry; Step 2.9: Use the ceramic core slurry to press the ceramic core blank at a pressing temperature of 103℃, a pressing pressure of 4MPa, and a holding time of 160s. After low-temperature debinding treatment and high-temperature sintering treatment, a porous ceramic core is obtained.

[0103] The process of low-temperature debinding and high-temperature sintering is as follows: the ceramic core blank is placed in the firing furnace and first heated from room temperature to 460°C at a heating rate of 7°C / min and held for 16 hours to complete the low-temperature debinding process; then the temperature is increased from 460°C to 1150°C at a heating rate of 3.7°C / min and held for 6 hours, and then cooled to room temperature with the furnace to complete the high-temperature sintering process.

[0104] In step three, the preparation method of the densified inert coating slurry includes the following main parameters: Step 3.2: Silica sol, aluminum sol, and yttrium sol are placed in a mixer and stirred at room temperature for 2.3 hours at a stirring speed of 308 r / min to obtain a sol component; Step 3.3: Nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are placed in a V-type mixer and mixed at room temperature for 23 minutes at a mixing speed of 160 r / min to obtain a nano-powder component; Step 3.4: The nano-powder component is added to the mixer and stirred with the sol component for another 7 hours to obtain the densified inert coating slurry.

[0105] In step four, the densification inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densification inert coating slurry reaches 22 mm above the highest point of the porous ceramic core.

[0106] In step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 3min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 12min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 6min.

[0107] In step six, the sintering temperature is 780℃ and the calcination time is 5 hours.

[0108] Example 3:

[0109] Another preferred embodiment of the high-collapse ceramic core with a dense outer surface and a porous core according to the present invention and its preparation method is basically the same as that of Embodiment 1 in terms of material selection and proportioning, process flow and parameters, technical principles, and beneficial effects, except that:

[0110] The porous ceramic core comprises, by mass percentage, 48 wt% ceramic powder, 38 wt% hollow glass microspheres, 5 wt% fiber, 5 wt% graphite, and 4 wt% starch. The densified inert coating comprises, by mass percentage, 72 wt% sol-gel and 28 wt% nanoparticles. In this embodiment, for every 3 wt% increase in the amount of ceramic powder, the amount of hollow glass microspheres increases by 1.5 wt% to ensure it remains within the range of 1.5-2 wt%.

[0111] The ceramic powder composition comprises, by mass percentage, 52 wt% quartz glass powder, 26 wt% white fused alumina powder, and 22 wt% zirconium silicate powder. The quartz glass powder, white fused alumina powder, and zirconium silicate powder each have three particle sizes, with a mass ratio of 2.8:1.8:1 for particles of 30-40 μm, 18-30 μm, and 10-18 μm.

[0112] The hollow glass microspheres are composed of the following components by mass percentage: 56 wt% silica hollow glass microspheres, 23 wt% alumina hollow glass microspheres, and 21 wt% zirconium silicate hollow glass microspheres. Each of the silica, alumina, and zirconium silicate hollow glass microspheres comprises three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm, with a mass ratio of 2.8:1.8:1.

[0113] The fiber composition comprises 62 wt% chopped carbon fibers and 38 wt% chopped aramid fibers by mass. The diameters of both the chopped carbon fibers and chopped aramid fibers are controlled within the range of 2-8 μm, and their aspect ratios are controlled within the range of 10-25:1. The graphite particle size is controlled within the range of 1-5 μm.

[0114] The sol component comprises, by mass percentage, 45 wt% silica sol, 33 wt% aluminum sol, and 22 wt% yttrium sol. The nanopowder component comprises, by mass percentage, 29 wt% nano-silica, 23 wt% nano-alumina, 12 wt% nano-yttrium oxide, and 36 wt% nano-zirconium silicate, with the particle size of each component controlled within the range of 10-30 nm.

[0115] In step two, the preparation method of the porous ceramic core includes the following main parameters: Step 2.2: Quartz glass powder, white corundum powder, and zirconium silicate powder are placed in a V-type mixer and mixed at room temperature for 26 minutes at a mixing speed of 130 r / min to obtain ceramic powder components; Step 2.3: Silica hollow glass microspheres, alumina hollow glass microspheres, and zirconium silicate hollow glass microspheres are placed in a V-type mixer and mixed at room temperature for 26 minutes at a mixing speed of 130 r / min to obtain hollow glass microsphere components; Step 2.4: 21% plasticizer is added to a mixer and heated while stirring at a stirring speed of 130 r / min until the temperature is reached. After reaching 116℃, continue stirring for 26 minutes; Steps 2.5-2.8: Keeping the stirring temperature and speed constant, add the ceramic powder component to the mixer and continue stirring for 1.6 hours, add the hollow glass microsphere component to the mixer and continue stirring for 1.6 hours, add the chopped carbon fiber and chopped aramid fiber to the mixer and continue stirring for 2.6 hours, add the graphite and starch to the mixer and continue stirring for 4.2 hours to obtain the ceramic core slurry; Step 2.9: Use the ceramic core slurry to press the ceramic core blank at a pressing temperature of 116℃, a pressing pressure of 5MPa, and a holding time of 140s. After low-temperature debinding treatment and high-temperature sintering treatment, a porous ceramic core is obtained.

[0116] The process of low-temperature debinding and high-temperature sintering is as follows: the ceramic core blank is placed in the firing furnace and first heated from room temperature to 520°C at a heating rate of 8°C / min and held for 13 hours to complete the low-temperature debinding process; then the temperature is increased from 520°C to 1200°C at a heating rate of 4.4°C / min and held for 5 hours, and then cooled to room temperature with the furnace to complete the high-temperature sintering process.

[0117] In step three, the preparation method of the densified inert coating slurry includes the following main parameters: Step 3.2: Silica sol, aluminum sol, and yttrium sol are placed in a mixer and stirred at room temperature for 2.6 hours at a stirring speed of 265 r / min to obtain a sol component; Step 3.3: Nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are placed in a V-type mixer and mixed at room temperature for 26 minutes at a mixing speed of 130 r / min to obtain a nano-powder component; Step 3.4: The nano-powder component is added to the mixer and stirred with the sol component for another 8 hours to obtain the densified inert coating slurry.

[0118] In step four, the densification inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densification inert coating slurry reaches 23 mm above the highest point of the porous ceramic core.

[0119] In step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 4min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 13min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 7min.

[0120] In step six, the sintering temperature is 870℃ and the calcination time is 4 hours.

[0121] Example 4:

[0122] Another preferred embodiment of the high-collapse ceramic core with a dense outer surface and a porous core according to the present invention and its preparation method is basically the same as that of Embodiment 1 in terms of material selection and proportioning, process flow and parameters, technical principles, and beneficial effects, except that:

[0123] The porous ceramic core comprises the following components by mass percentage: 51 wt% ceramic powder, 40 wt% hollow glass microspheres, 4 wt% fiber, 3 wt% graphite, and 2 wt% starch. The densified inert coating comprises the following components by mass percentage: 75 wt% sol-gel and 25 wt% nanoparticles. In this embodiment, for every 3 wt% increase in the amount of ceramic powder, the amount of hollow glass microspheres increases by 2 wt% to ensure it remains within the range of 1.5-2 wt%.

[0124] The ceramic powder composition comprises, by mass percentage, 55 wt% quartz glass powder, 25 wt% white fused alumina powder, and 20 wt% zirconium silicate powder. The quartz glass powder, white fused alumina powder, and zirconium silicate powder each have three particle sizes, with a mass ratio of 3:2:1 for particles of 30-40 μm, 18-30 μm, and 10-18 μm.

[0125] The hollow glass microspheres are composed of the following components at the following mass percentages: 60 wt% silica hollow glass microspheres, 22 wt% alumina hollow glass microspheres, and 18 wt% zirconium silicate hollow glass microspheres. Each of the silica, alumina, and zirconium silicate hollow glass microspheres comprises three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm, with a mass ratio of 3:2:1.

[0126] The fiber composition comprises 72 wt% chopped carbon fibers and 28 wt% chopped aramid fibers by mass. The diameters of both the chopped carbon fibers and chopped aramid fibers are controlled within the range of 2-8 μm, and their aspect ratios are controlled within the range of 10-25:1. The graphite particle size is controlled within the range of 1-5 μm.

[0127] The sol component comprises, by mass percentage, 47 wt% silica sol, 32 wt% aluminum sol, and 21 wt% yttrium sol. The nanopowder component comprises, by mass percentage, 31 wt% nano-silica, 24 wt% nano-alumina, 11 wt% nano-yttrium oxide, and 34 wt% nano-zirconium silicate, with the particle size of each component controlled within the range of 10-30 nm.

[0128] In step two, the preparation method of the porous ceramic core includes the following main parameters: Step 2.2: Quartz glass powder, white corundum powder, and zirconium silicate powder are placed in a V-type mixer and mixed at room temperature for 30 minutes at a mixing speed of 100 r / min to obtain ceramic powder components; Step 2.3: Silica hollow glass microspheres, alumina hollow glass microspheres, and zirconium silicate hollow glass microspheres are placed in a V-type mixer and mixed at room temperature for 30 minutes at a mixing speed of 100 r / min to obtain hollow glass microsphere components; Step 2.4: 25% plasticizer is added to a mixer, and the mixture is heated while stirring at a stirring speed of 100 r / min until... After heating to 130℃, continue stirring for 30 minutes; Steps 2.5-2.8: Keeping the stirring temperature and speed constant, add the ceramic powder component to the mixer and continue stirring for 2 hours, add the hollow glass microsphere component to the mixer and continue stirring for 2 hours, add the chopped carbon fiber and chopped aramid fiber to the mixer and continue stirring for 3 hours, add the graphite and starch to the mixer and continue stirring for 5 hours to obtain the ceramic core slurry; Step 2.9: Use the ceramic core slurry to press the ceramic core blank at a pressing temperature of 130℃, a pressing pressure of 7MPa, and a holding time of 120s. After low-temperature debinding treatment and high-temperature sintering treatment, a porous ceramic core is obtained.

[0129] The process of low-temperature debinding and high-temperature sintering is as follows: the ceramic core blank is placed in the firing furnace and first heated from room temperature to 600℃ at a heating rate of 10℃ / min and held for 10 hours to complete the low-temperature debinding process; then the temperature is increased from 600℃ to 1250℃ at a heating rate of 5℃ / min and held for 4 hours, and then cooled to room temperature with the furnace to complete the high-temperature sintering process.

[0130] In step three, the preparation method of the densified inert coating slurry includes the following main parameters: Step 3.2: Silica sol, aluminum sol, and yttrium sol are placed in a mixer and stirred at room temperature for 3 hours at a stirring speed of 220 r / min to obtain a sol component; Step 3.3: Nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are placed in a V-type mixer and mixed at room temperature for 30 minutes at a mixing speed of 100 r / min to obtain a nano-powder component; Step 3.4: The nano-powder component is added to the mixer and stirred with the sol component for another 10 hours to obtain the densified inert coating slurry.

[0131] In step four, the densification inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densification inert coating slurry reaches 25 mm above the highest point of the porous ceramic core.

[0132] In step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 5min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 15min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 8min.

[0133] In step six, the sintering temperature is 950℃ and the calcination time is 3 hours.

[0134] Comparative Example 1:

[0135] A dense ceramic core was prepared using a traditional formula. 60wt% quartz glass powder, 25wt% white corundum powder, and 15wt% zirconium silicate powder were weighed by mass percentage. A plasticizer accounting for 20wt% of the total powder mass was added. After mixing and pressing, the core was calcined at 1200℃ for 5 hours to obtain an integrally dense ceramic core.

[0136] Comparative Example 2:

[0137] The porous ceramic core of this embodiment is prepared using the material formulation, process flow and process parameters, but without the impregnation treatment of the densification inert coating.

[0138] The ceramic cores prepared using the above four embodiments and two comparative examples were further used for casting high Hf alloy blades with complex internal cavity structures in a certain type of aero-engine, and the castings were subjected to quality inspection. The inspection results are shown in Table 1.

[0139] Table 1. Test results of blade castings prepared using different ceramic cores

[0140]

[0141] The test results above show that the ceramic cores prepared in the four embodiments have high yielding properties, low surface activity and excellent core removal performance. Using the ceramic cores of the four embodiments to further cast blades can effectively solve the problems of hot cracking defects and recrystallization in the blade cavity. The thickness of the reaction layer at the interface can be reduced to less than 2μm. Moreover, there are no residual cores in the blade cavity after core removal, and the casting qualification rate is as high as 90% or more.

[0142] The ceramic powder components, hollow glass microsphere components, fiber components, graphite, starch, sol components, nanopowder components, plasticizers, and other raw materials used in the above embodiments were purchased from Aladdin Reagent Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd.

[0143] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0144] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification and the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A highly collapsible ceramic core with a dense outer surface and a porous core, characterized in that, The high-yield ceramic core is composed of a porous ceramic core and a dense inert coating on its outer surface. The mass percentage of each component in the porous ceramic core is as follows: ceramic powder 42-51 wt%, hollow glass microspheres 35-40 wt%, fiber 4-9 wt%, graphite 3-7 wt%, and starch 2-8 wt%. The mass percentage of each component in the dense inert coating is as follows: sol 67-75 wt% and nanoparticles 25-33 wt%. The ceramic powder composition comprises the following mass percentages: 48-55 wt% quartz glass powder, 24-28 wt% white corundum powder, and 20-24 wt% zirconium silicate powder. The quartz glass powder, white corundum powder, and zirconium silicate powder each have three particle sizes: 30-40 μm, 18-30 μm, and 10-18 μm. The mass ratio of the 30-40 μm, 18-30 μm, and 10-18 μm particles is 2-3:1-2:

1. The mass percentage of each substance in the hollow glass microsphere component is as follows: 50-60 wt% silica hollow glass microspheres, 21-27 wt% alumina hollow glass microspheres, and 18-24 wt% zirconium silicate hollow glass microspheres. The hollow glass microspheres of silica, alumina, and zirconium silicate all include three particle sizes: 20-30 μm, 10-20 μm, and 0-10 μm. The mass ratio of the 20-30 μm, 10-20 μm, and 0-10 μm particles is 2-3:1-2:

1. The mass percentage of each substance in the fiber component is 42-72 wt% chopped carbon fiber and 28-58 wt% chopped aramid fiber; the diameter of both the chopped carbon fiber and the chopped aramid fiber is controlled within the range of 2-8 μm and the aspect ratio is controlled within the range of 10-25:

1. The mass percentages of each substance in the sol component are as follows: silica sol 42-47 wt%, aluminum sol 30-35 wt%, and yttrium sol 21-25 wt%. The mass percentages of each substance in the nanopowder composition are as follows: 24-31 wt% nano-silica, 17-24 wt% nano-alumina, 10-17 wt% nano-yttrium oxide, and 34-41 wt% nano-zirconium silicate; the particle sizes of the nano-silica, nano-alumina, nano-yttrium oxide, and nano-zirconium silicate are all controlled within the range of 10-30 nm.

2. The high-yield ceramic core with a dense outer surface and porous core structure according to claim 1, characterized in that, The amount of hollow glass microspheres added increases with the amount of ceramic powder added. Within the mass percentage range of the hollow glass microspheres and the ceramic powder, the amount of hollow glass microspheres added increases by 1.5-2 wt% for every 3 wt% increase in the amount of ceramic powder added.

3. A method for preparing a highly collapsible ceramic core with a dense outer surface and a porous core according to claim 1 or 2, characterized in that, The preparation method includes the following steps in sequence: Step 1: Weigh out each raw material according to the designed material ratio and set aside; Step 2: Prepare a porous ceramic core according to the designed process and parameters; Step 3: Prepare a dense inert coating slurry according to the designed process and parameters; Step 4: Use a positioning fixture to suspend the porous ceramic core in the impregnation chamber of the vacuum impregnation equipment, so that the porous ceramic core maintains an appropriate gap with the inner wall of the impregnation chamber. Then, slowly inject the densification inert coating slurry into the impregnation chamber until the densification inert coating slurry completely submerges the porous ceramic core. Step 5: Start the vacuum system of the vacuum impregnation equipment and use a gradient pressure reduction method to impregnate the porous ceramic core with a densifying inert coating slurry under segmented vacuum pressure. This allows the densifying inert coating slurry to fully penetrate into the pores on the outer surface of the porous ceramic core, forming a densifying inert coating on its outer surface. Step Six: Place the porous ceramic core with the densified inert coating into a heat treatment furnace for sintering treatment, so that the densified inert coating is tightly bonded to the outer surface of the porous ceramic core, thus obtaining a high-yield ceramic core with a dense outer surface and a porous core.

4. The method for preparing a high-collapse ceramic core with a dense outer surface and a porous core according to claim 3, characterized in that, In step two, the preparation method of the porous ceramic core includes the following steps in sequence: Step 2.1: Weigh each raw material according to the designed material ratio and set aside; Step 2.2: Put all the quartz glass powder, white corundum powder and zirconium silicate powder of each particle size into a V-type mixer and mix at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to make the substances mix evenly and obtain ceramic powder components. Step 2.3: Put all the silica hollow glass microspheres, alumina hollow glass microspheres and zirconium silicate hollow glass microspheres of various particle sizes into a V-type mixer and mix them at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to ensure that the substances are mixed evenly and to obtain the hollow glass microsphere component. Step 2.4: Place the plasticizer in a mixer and heat it while stirring at a speed of 100-200 r / min. After the temperature reaches 90-130℃, continue stirring for 20-30 minutes to completely melt it. The amount of plasticizer added is 15-25% of the mass of the porous ceramic core. The plasticizer is composed of 93wt% paraffin wax, 5wt% beeswax and 2wt% polyethylene. Step 2.5: Keep the stirring temperature and stirring speed constant, add the ceramic powder components to the mixer and continue stirring for 1-2 hours to allow the substances to blend together; Step 2.6: Keep the stirring temperature and stirring speed constant, add the hollow glass microsphere component into the mixer and continue stirring for 1-2 hours to allow the substances to blend together; Step 2.7: Keep the stirring temperature and stirring speed constant, add the chopped carbon fibers and chopped aramid fibers to the mixer and continue stirring for 2-3 hours to ensure that the fiber components are evenly dispersed; Step 2.8: Keep the stirring temperature and stirring speed constant, add graphite and starch to the mixer and continue stirring for 3-5 hours to ensure that the substances are mixed evenly and to obtain ceramic core slurry; Step 2.9: Press the ceramic core blank using the prepared ceramic core slurry at a pressing temperature of 90-130℃, a pressing pressure of 3-7MPa, and a holding time of 120-180s; then place the ceramic core blank into a sintering furnace for low-temperature debinding and high-temperature sintering to decompose and volatilize the organic matter in the ceramic core blank, forming a porous structure, thus obtaining a porous ceramic core. The process parameters for low-temperature debinding and high-temperature sintering are as follows: The ceramic core blank is placed in a firing furnace. First, the temperature is increased from room temperature to 400-600℃ at a rate of 5-10℃ / min and held for 10-20 hours to complete the low-temperature debinding process. Then, the temperature is increased from 400-600℃ to 1100-1250℃ at a rate of 3-5℃ / min and held for 4-8 hours. The blank is then cooled to room temperature in the furnace to complete the high-temperature sintering process. No protective atmosphere is required during the entire process of low-temperature debinding and high-temperature sintering.

5. The method for preparing a high-collapse ceramic core with a dense outer surface and a porous core according to claim 4, characterized in that, In step three, the preparation method of the densified inert coating slurry includes the following steps in sequence: Step 3.1: Weigh each raw material according to the designed material ratio and set aside; Step 3.2: Put all the silica sol, aluminum sol and yttrium sol into a mixer and stir at room temperature for 2-3 hours at a stirring speed of 220-350 r / min to make the substances evenly dispersed and fused to obtain the sol component; Step 3.3: Put all the nano-silica, nano-alumina, nano-yttrium oxide and nano-zirconium silicate into a V-type mixer and mix at room temperature for 20-30 minutes at a mixing speed of 100-200 r / min to make the substances mix evenly and obtain nano-powder components. Step 3.4: Add the obtained nanoparticle components to the mixer and continue stirring with the sol components for 6-10 hours to allow the substances to fuse together, thus obtaining a dense inert coating slurry.

6. The method for preparing a high-collapse ceramic core with a dense outer surface and a porous core according to claim 5, characterized in that, In step four, the densification inert coating slurry is slowly injected into the impregnation chamber until the liquid level of the densification inert coating slurry reaches a position 20-25mm above the highest point of the porous ceramic core.

7. The method for preparing a high-collapse ceramic core with a dense outer surface and a porous core according to claim 6, characterized in that, In step five, a gradient pressure reduction method is used to impregnate the porous ceramic core with a densified inert coating slurry under segmented vacuum pressure, that is, impregnation in three stages: the first stage impregnation, 0.08MPa≤vacuum pressure<0.1MPa, impregnation time is 2-5min; the second stage impregnation, 0.05MPa≤vacuum pressure<0.08MPa, impregnation time is 10-15min; the third stage impregnation, 0.02MPa≤vacuum pressure<0.05MPa, impregnation time is 5-8min.

8. The method for preparing a high-collapse ceramic core with a dense outer surface and a porous core according to claim 7, characterized in that, In step six, the sintering temperature is 700-950℃ and the calcination time is 3-6 hours.

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