A ceramic core for nickel-based high-temperature alloy equiaxed crystal hollow turbine blades and a preparation method thereof

Abstract

The present invention relates to the technical field of precision casting of turbine blades, and specifically to a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade and a preparation method thereof. The ceramic core is prepared by mixing a refractory powder and a paraffin-based plasticizer and then sintering at high temperature, wherein the mass ratio of the refractory powder to the paraffin-based plasticizer is (75-85): (15-25); the refractory powder is composed of quartz glass powder, alumina powder and natural flake graphite, and the mass ratio of the quartz glass powder: alumina powder: natural flake graphite is (72-77): (20-25): (0.5-3); the paraffin-based plasticizer is composed of refined paraffin, beeswax and low-density polyethylene, and the mass ratio of the refined paraffin, beeswax and low-density polyethylene is (40-50): (40-50): (5-10). The present invention creatively adds natural flake graphite to the ceramic core raw material, improves the fluidity of the slurry, increases the high-temperature bending strength of the ceramic core, and improves the core removal performance.

Description

Technical Field

[0001] The invention relates to the technical field of precision casting of turbine blades, and in particular to a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade and a preparation method thereof. Background Art

[0002] Turbine blades are one of the hot end components in aircraft engines that have the worst service environment, the highest performance requirements, and the greatest manufacturing difficulty. In order to improve the thrust-to-weight ratio and fuel efficiency of aircraft engines, the engine turbine inlet temperature must be continuously increased, so the temperature bearing capacity of turbine blades also needs to be continuously improved.

[0003] The most effective technical approach to improve the temperature bearing capacity of aircraft engine turbine blades is to make the turbine blades into hollow structures. Hollow turbine blades are usually mass-produced using precision casting technology (lost wax method). The principle is to embed the ceramic core in the metal mold, use injection molding to make a wax mold with a built-in ceramic core, turn the ceramic mold shell on the surface of the wax mold, and then melt the wax mold to obtain a mold shell with a built-in ceramic core. Melt the molten metal and pour it into the ceramic mold shell. After the molten metal cools, the ceramic mold shell is broken and removed, and the internal ceramic core is removed by alkali boiling to obtain a hollow turbine blade.

[0004] Ceramic cores are essential key adapters for the preparation of hollow turbine blades. Due to the complex internal cooling structure of aircraft engine turbine blades and the large number of fine features, the ceramic core slurry must have good fluidity on the one hand to ensure that the ceramic core blank can fill the mold cavity during injection molding. On the other hand, the ceramic core must have sufficient high-temperature bending strength to avoid the risk of core breakage during the casting process. Finally, the ceramic core must have good core removal performance to improve production efficiency and reduce the risk of residual cores inside the blades. However, the current preparation technology of ceramic cores still restricts the production qualification rate of precision casting of aircraft engine turbine blades.

[0005] Chinese patent application CN116477960 A discloses a composite ceramic core for single crystal turbine blades and a preparation method thereof, wherein the preparation method comprises: mixing quartz glass powder, zircon powder, cristobalite powder and glass fiber uniformly, adding a plasticizer, pressing to form a ceramic core embryo, and calcining the ceramic core embryo to form a composite ceramic core for single crystal turbine blades. The patent improves the creep resistance of the ceramic core at high temperature by adding glass fiber, and the technical problem solved is: solving the problem that the traditional ceramic core will have obvious thermal deformation when in use. However, the patent is only beneficial to single crystal turbine blades, while the ceramic core of the present invention is used for equiaxed hollow turbine blades, and generally does not need to consider the performance index of thermal deformation resistance. In addition, the glass fiber added in the patent will greatly reduce the rheological properties and filling properties of the ceramic slurry, and there is also a risk of uneven mixing with the refractory powder during the batching process, resulting in unstable quality of the ceramic core. Summary of the invention

[0006] In view of the technical problems existing in the background technology, an object of the present invention is to provide a ceramic core for a nickel-based high-temperature alloy equiaxed hollow turbine blade.

[0007] Another object of the present invention is to provide a method for preparing a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade.

[0008] The technical solution adopted to achieve one purpose of the present invention is: a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade, the ceramic core is made by mixing a refractory powder and a paraffin-based plasticizer and then sintering at a high temperature, wherein the mass ratio of the refractory powder to the paraffin-based plasticizer is (75-85): (15-25);

[0009] The refractory powder is composed of quartz glass powder, alumina powder and natural flake graphite, and the mass ratio of the quartz glass powder: alumina powder: natural flake graphite is (72-77): (20-25): (0.5-3);

[0010] The paraffin-based plasticizer is composed of refined paraffin, beeswax and low-density polyethylene, and the mass ratio of the refined paraffin, beeswax and low-density polyethylene is (40-50): (40-50): (5-10).

[0011] Preferably, the average particle size of the quartz glass powder of the present invention is 20-40 μm.

[0012] Preferably, the alumina powder of the present invention is pretreated by calcining at 1300-1400°C for 2-4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into structurally stable α-Al2O3; the average particle size of the alumina powder is 5-15 μm.

[0013] Preferably, the natural flake graphite of the present invention is pretreated, and the pretreatment method is: drying the natural flake graphite at a temperature of 100-150° C. for at least 6 hours; the specification of the natural flake graphite is 16-30 mesh.

[0014] Preferably, the shrinkage of the ceramic core of the present invention is ≤0.8%, the porosity is 24%-35%, and the flexural strength at 1400° C. is 18-31 MPa.

[0015] Preferably, the refractory powder of the present invention is prepared by the following method:

[0016] The quartz glass powder is ball-milled into a powder with an average particle size of 20-40 μm; the alumina powder is calcined at 1300-1400°C for 2-4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then the calcined alumina powder is ball-milled to an average particle size of 5-15 μm; the natural flake graphite with a specification of 16-30 mesh is dried at 100-150°C for at least 6 hours; the treated quartz glass powder, alumina powder and natural flake graphite are evenly mixed in a planetary ball mill to obtain a refractory powder.

[0017] Preferably, the paraffin-based plasticizer of the present invention is prepared by the following method:

[0018] 1) Weigh paraffin, beeswax and low-density polyethylene in proportion;

[0019] 2) Heat the paraffin wax until it is molten; then add the beeswax. When the beeswax starts to melt, start the mixer and stir until the beeswax and paraffin wax are evenly mixed.

[0020] 3) Increase the temperature of the mixer, add low-density polyethylene, and continue stirring until the low-density polyethylene is evenly mixed with paraffin and beeswax;

[0021] 4) Lower the temperature of the mixer and continue stirring to obtain the paraffin-based plasticizer. Stop stirring and heating, take out the paraffin-based plasticizer and cool it for later use.

[0022] The technical solution used to achieve another purpose of the present invention is: a method for preparing a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade, which includes the following preparation steps:

[0023] 1) Preparation of refractory powder

[0024] The quartz glass powder is ball-milled into a powder with an average particle size of 20-40 μm; the alumina powder is calcined at 1300-1400°C for 2-4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then the calcined alumina powder is ball-milled to an average particle size of 5-15 μm; the natural flake graphite with a specification of 16-30 mesh is dried at 100-150°C for at least 6 hours; the treated quartz glass powder, alumina powder and natural flake graphite are evenly mixed in a planetary ball mill to obtain a refractory powder;

[0025] 2) Preparation of paraffin-based plasticizer

[0026] Weigh refined paraffin, beeswax and low-density polyethylene in proportion; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it and set it aside;

[0027] 3) Preparation of ceramic slurry

[0028] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in proportion; dry the refractory powder at 100-120° C. for at least 6-12 hours; melt and stir the paraffin-based plasticizer at 110-130° C.; add the dried refractory powder to the melted paraffin-based plasticizer in 4-6 portions, and continue stirring for 30-50 hours to prepare a ceramic slurry;

[0029] 4) Preparation of sintered ceramic core

[0030] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1180-1250° C. for a holding time of 4-8 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0031] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0032] A ethyl silicate hydrolyzate solution is prepared, and the sintered ceramic core is impregnated and strengthened, and dried in an ammonia atmosphere for 30-50 minutes to improve the high-temperature bending strength of the ceramic core; a phenolic resin solution is prepared, and the ceramic core is further impregnated and strengthened, and dried at 100-130°C for 30-60 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade is obtained.

[0033] Preferably, the ethyl silicate hydrolyzate described in the present invention is obtained by taking ethyl orthosilicate as a raw material and adding distilled water and hydrochloric acid for hydrolysis; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 18-22%.

[0034] Preferably, the phenolic resin solution of the present invention is an ethanol solution of phenolic resin, wherein the volume ratio of the phenolic resin to ethanol is 1:1.

[0035] Compared with the prior art, the technical advantages of the present invention are:

[0036] 1) The present invention provides a method for preparing a ceramic core suitable for precision casting of hollow turbine blades of nickel-based high-temperature alloy equiaxed crystals. Natural flake graphite is creatively added to the ceramic core raw material to improve the fluidity of the ceramic slurry, increase the high-temperature bending strength of the ceramic core, and improve the core removal performance of the ceramic core.

[0037] 2) The present invention adds a certain proportion of natural flake graphite. Due to the lamellar morphology of graphite and the easy failure of weak van der Waals bonds in the direction perpendicular to the hexagonal structure layer, the graphite has lubrication properties, thereby improving the fluidity of the ceramic slurry and reducing the viscosity. Therefore, without changing the proportion of plasticizer in the ceramic slurry and the injection temperature, better filling performance can be obtained, and the final mechanical properties and dimensional control accuracy of the ceramic core can be improved.

[0038] 3) After adding flake graphite to the raw material of the ceramic core, the phase analysis found that the addition of natural flake graphite can significantly reduce the amount of cristobalite in the core. The reason is that during sintering, graphite will react on the surface of the quartz glass powder particles to generate SiC, reducing the nucleation of the in-situ cristobalite phase on the surface of the quartz glass. On the other hand, the presence of graphite and SiC will change the crystallization free energy of cristobalite, so that the amount of cristobalite crystallization inside the ceramic core is reduced due to the addition of graphite, thereby reducing the microcracks caused by the crystal transformation of cristobalite and improving the high-temperature bending strength of the ceramic core. Furthermore, SiC, as a refractory phase with higher intrinsic strength, can further improve the high-temperature bending strength of the ceramic core.

[0039] 4) After the turbine blades are cast and cooled, it is usually necessary to dissolve the internal ceramic core by chemical reaction to obtain hollow blades. The core removal performance is beneficial to improving production efficiency and reducing the risk of residual cores inside the blades. The method of adding natural flake graphite inside the ceramic core proposed in the present invention can improve the core removal performance of the ceramic core because the graphite will be oxidized and burned during sintering, and the remaining pores can improve the core removal performance of the ceramic core.

[0040] 5) Compared with the traditional turbine blade ceramic core preparation technology, the present invention has a simpler composition ratio, which can effectively improve the quality stability of industrial mass production, while reducing production costs and saving energy and increasing efficiency, because the raw materials of the ceramic core are refractory powder and non-degradable paraffin, etc., and the simpler the raw materials, the more beneficial it is to cost reduction, energy saving and environmental protection. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to Examples and Comparative Examples.

[0042] The present invention discloses a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade. The ceramic core is prepared by mixing a refractory powder and a paraffin-based plasticizer and then sintering at a high temperature, wherein the mass ratio of the refractory powder to the paraffin-based plasticizer is (75-85): (15-25);

[0043] The refractory powder is composed of quartz glass powder, alumina powder and natural flake graphite, and the mass ratio of the quartz glass powder: alumina powder: natural flake graphite is (72-77): (20-25): (0.5-3);

[0044] The paraffin-based plasticizer is composed of refined paraffin, beeswax and low-density polyethylene, and the mass ratio of the refined paraffin, beeswax and low-density polyethylene is (40-50): (40-50): (5-10).

[0045] In the composition of paraffin-based plasticizers, paraffin is the base material, beeswax is added to increase the hardness (needle penetration) of the plasticizer, and low-density polyethylene is added to increase the strength of the plasticizer. For thin-walled and slender ceramic cores, a high ratio of low-density polyethylene and beeswax can be selected. When the configured plasticizer is used for ceramic slurry configuration, the ceramic slurry has higher hardness (not easy to deform) and filling performance (easier to fill the mold) under the premise of the same ratio of plasticizer to refractory powder.

[0046] The purpose of the plasticizer is to make the refractory powder in the ceramic slurry obtain rheological properties. It is also a key factor in adjusting the shrinkage and porosity of the ceramic core. When the ceramic core structure is complex and there are too many small and fine features, the ceramic slurry is required to have good rheological properties so that the ceramic slurry can be smoothly filled into the mold during the manufacturing process of the ceramic core blank. In addition, according to the actual needs of the turbine blades, the shrinkage and porosity can be adjusted by adjusting the plasticizer ratio. For example, when a large shrinkage is required, a high plasticizer ratio can be selected, but if the plasticizer ratio is too high, it will reduce the high temperature strength of the ceramic core, which needs to be considered comprehensively.

[0047] The quartz glass powder of the present invention is purchased from Lianyungang Longxin Quartz High-tech Co., Ltd.; alumina powder is purchased from Aluminum Corporation of China Limited; zircon powder is purchased from Xiamen Kaili Import and Export Co., Ltd.; natural flake graphite is purchased from Qingdao Dongkai Graphite Co., Ltd.; refined paraffin is purchased from Sinopec, specification: No. 58 refined wax; beeswax is purchased from Dongguang County Dongsheng Beeswax Factory; low-density polyethylene is purchased from Sinopec Beijing Yanshan Branch; tetraethyl orthosilicate is purchased from Guangdong Jiudian Biotechnology Co., Ltd., specification: molecular weight 264.26, purity ≥95.0%; phenolic resin is purchased from Shaanxi Baotashan New Material Technology Co., Ltd., specification: F01-36 alcohol-soluble phenolic baking varnish. Embodiment 1:

[0048] 1) Preparation of refractory powder

[0049] Quartz glass powder is ball-milled into an average particle size (D 50 ) is a powder of 30μm; calcining alumina powder at 1300℃ for 4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then ball-milling the calcined alumina powder to an average particle size of 15μm; drying natural flake graphite with a specification of 20 mesh at 100℃ for at least 6 hours; mixing the treated quartz glass powder, alumina powder and natural flake graphite in a mass ratio of 77:20:3 in a planetary ball mill to obtain a refractory powder;

[0050] 2) Preparation of paraffin-based plasticizer

[0051] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 50:45:5; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it for use;

[0052] 3) Preparation of ceramic slurry

[0053] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 15:85; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at 120° C.; add the dried refractory powder into the melted paraffin-based plasticizer in four portions, and continue stirring for 30 hours to prepare a ceramic slurry;

[0054] 4) Preparation of sintered ceramic core

[0055] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1200° C. for a holding time of 4 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0056] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0057] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 20%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 30 minutes to improve the high-temperature bending strength of the ceramic core;

[0058] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 100°C for 60 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed hollow turbine blade is obtained.

[0059] The refractory powder formula described in Example 1, wherein 3% of natural flake graphite is selected, can make the ceramic slurry have better fluidity. Therefore, adding a lower proportion of plasticizer can also obtain good filling performance, which helps to reduce the shrinkage rate of the blank (the shrinkage rate during injection molding of the blank is actually the shrinkage of the plasticizer from the molten state to the solid state at room temperature) and the porosity of the ceramic core after sintering (the porosity of the ceramic is determined by the holes left after the plasticizer is burned out). In addition, alumina powder, as a mineralizer, can promote the sintering of the matrix material quartz glass powder to obtain high high-temperature bending strength. The ceramic core prepared by the preparation process described in this embodiment has a shrinkage rate of ≤0.5%, a porosity of 26%, and a bending strength of 25MPa at 1400℃, and is suitable for turbine guide blade ceramic cores with large thickness differences and slightly smaller sizes. Embodiment 2:

[0060] 1) Preparation of refractory powder

[0061] Quartz glass powder is ball-milled into an average particle size (D 50 ) is a powder of 20μm; calcining alumina powder at 1300℃ for 4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into structurally stable α-Al2O3, and then ball-milling the calcined alumina powder to an average particle size of 8μm; drying natural flake graphite with a specification of 16 mesh at 150℃ for at least 6 hours; mixing the treated quartz glass powder, alumina powder and natural flake graphite in a mass ratio of 72:25:3 in a planetary ball mill to obtain a refractory powder;

[0062] 2) Preparation of paraffin-based plasticizer

[0063] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 50:40:10; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it for use;

[0064] 3) Preparation of ceramic slurry

[0065] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 25:75; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at a temperature of 110° C.; add the dried refractory powder to the melted paraffin-based plasticizer in 6 portions, and continue stirring for 48 hours to prepare a ceramic slurry;

[0066] 4) Preparation of sintered ceramic core

[0067] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1180° C. for a holding time of 8 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0068] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0069] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 18%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 40 minutes to improve the high-temperature bending strength of the ceramic core;

[0070] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 110°C for 40 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade is obtained.

[0071] The process described in Example 2 is designed to obtain the most excellent filling performance while taking into account a certain high-temperature flexural strength. In the plasticizer component, a high proportion of polyethylene is selected to increase the strength of the plasticizer and even the ceramic core blank, and reduce the risk of deformation of the ceramic core blank; when configuring the ceramic slurry, a higher ratio of plasticizer and natural flake graphite is selected to obtain excellent filling performance, and the blank pressed by the ceramic slurry with a higher proportion of plasticizer is easier to correct, which is suitable for the preparation of slender thin-walled ceramic cores; the refractory powder selects a high proportion of alumina mineralizer content, so that the ceramic core has appropriate high-temperature flexural strength. The ceramic core prepared by the preparation process described in this embodiment has a shrinkage rate of ≤0.8%, a porosity of 35%, and a flexural strength of 18MPa at 1400℃, which is suitable for thin-walled and slender power turbine blade ceramic cores. Embodiment 3:

[0072] 1) Preparation of refractory powder

[0073] Quartz glass powder is ball-milled into an average particle size (D 50 ) is a powder of 40μm; calcining alumina powder at 1300℃ for 4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then ball-milling the calcined alumina powder to an average particle size of 8μm; drying natural flake graphite with a specification of 30 mesh at 100℃ for at least 6 hours; mixing the treated quartz glass powder, alumina powder and natural flake graphite in a mass ratio of 74.5:25:0.5 in a planetary ball mill to obtain a refractory powder;

[0074] 2) Preparation of paraffin-based plasticizer

[0075] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 40:50:10; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it down and set it aside;

[0076] 3) Preparation of ceramic slurry

[0077] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 15:85; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at a temperature of 130° C.; add the dried refractory powder to the melted paraffin-based plasticizer in 5 portions, and continue stirring for 50 hours to prepare a ceramic slurry;

[0078] 4) Preparation of sintered ceramic core

[0079] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1250° C. for a holding time of 4 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0080] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0081] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 22%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 50 minutes to improve the high-temperature bending strength of the ceramic core;

[0082] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 130°C for 30 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade is obtained.

[0083] The ceramic core prepared in Example 3 aims to prepare a core with excellent high-temperature bending strength, which is suitable for preparing thick and large-sized turbine blade ceramic cores. The proportion of low-melting-point beeswax in the paraffin-based plasticizer reaches 50%, and adding a small amount of natural flake graphite can also ensure that the ceramic slurry still has appropriate fluidity. The ceramic core prepared by the preparation process described in this embodiment has a shrinkage rate of ≤0.5%, a porosity of 24%, and a bending strength of 31MPa at 1400℃.

[0084] Comparative Example 1:

[0085] No natural flake graphite is added to the formula of the refractory powder, and the rest is the same as in Example 1. The specific preparation steps are as follows:

[0086] 1) Preparation of refractory powder

[0087] Quartz glass powder is ball-milled into an average particle size (D 50 ) is a powder of 30 μm; the alumina powder is calcined at 1300°C for 4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then the calcined alumina powder is ball-milled to an average particle size of 15 μm; the treated quartz glass powder and alumina powder are evenly mixed in a planetary ball mill at a mass ratio of 80:20 to obtain a refractory powder;

[0088] 2) Preparation of paraffin-based plasticizer

[0089] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 50:45:5; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it for use;

[0090] 3) Preparation of ceramic slurry

[0091] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 15:85; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at 120° C.; add the dried refractory powder into the melted paraffin-based plasticizer in four portions, and continue stirring for 30 hours to prepare a ceramic slurry;

[0092] 4) Preparation of sintered ceramic core

[0093] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1200° C. for a holding time of 4 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0094] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0095] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 20%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 30 minutes to improve the high-temperature bending strength of the ceramic core;

[0096] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 100°C for 60 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed hollow turbine blade is obtained.

[0097] The raw materials described in Comparative Example 1 do not contain natural flake graphite, and the proportion of plasticizer is 15%. The prepared slurry has poor fluidity, but has low shrinkage and porosity. The prepared ceramic core has a shrinkage rate of ≤0.5%, a porosity of 28%, and a flexural strength of 27MPa at 1400°C. It is suitable for thick and large ceramic cores with simple structures. However, for slender and thin-walled ceramic cores, there is a high proportion of lack of meat (i.e., the cavity cannot be filled) and the core is scrapped.

[0098] Comparative Example 2:

[0099] The formula of the refractory powder selected a low alumina ratio and a high natural flake graphite ratio, and the rest was the same as in Example 2. The specific preparation steps are as follows:

[0100] 1) Preparation of refractory powder

[0101] Quartz glass powder is ball-milled into an average particle size (D 50 ) is a powder of 20μm; calcining alumina powder at 1300℃ for 4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then ball-milling the calcined alumina powder to an average particle size of 8μm; drying natural flake graphite with a specification of 16 mesh at 150℃ for at least 6 hours; mixing the treated quartz glass powder, alumina powder and natural flake graphite in a mass ratio of 94:3:3 in a planetary ball mill to obtain a refractory powder;

[0102] 2) Preparation of paraffin-based plasticizer

[0103] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 50:40:10; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it for use;

[0104] 3) Preparation of ceramic slurry

[0105] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 25:75; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at a temperature of 110° C.; add the dried refractory powder to the melted paraffin-based plasticizer in 6 portions, and continue stirring for 48 hours to prepare a ceramic slurry;

[0106] 4) Preparation of sintered ceramic core

[0107] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1180° C. for a holding time of 8 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0108] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0109] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 18%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 40 minutes to improve the high-temperature bending strength of the ceramic core;

[0110] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 110°C for 40 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade is obtained.

[0111] The ceramic core formula described in Comparative Example 2 selects a low alumina ratio and a high natural flake graphite ratio. The ceramic slurry has good fluidity, and a low plasticizer ratio can also obtain a low tendency of ceramic green body deformation. The prepared ceramic core has a shrinkage rate of ≤0.6% and a porosity of 29%, but the high-temperature flexural strength at 1400°C is 16MPa, and the risk of core breakage during pouring is very high. The reason is that the appropriate proportion of alumina mineralizer has the effect of promoting the crystallization of quartz, which can ensure that the ceramic core quickly precipitates a large amount of quartz crystal phase during the heating process of the mold shell, so that the ceramic core quickly builds high-temperature strength. When the alumina content is too low, the crystallization rate of quartz in the prepared ceramic core is slow, and the high-temperature flexural strength is insufficient.

[0112] Comparative Example 3:

[0113] Zircon powder was selected to replace alumina powder, and the rest was the same as in Example 1. The specific preparation steps are as follows:

[0114] 1) Preparation of refractory powder

[0115] Quartz glass powder is ball-milled into an average particle size (D 50 ) of 30μm; select zircon powder with an average particle size of 5μm; dry natural flake graphite with a specification of 20 mesh at 100℃ for at least 6 hours; mix the treated quartz glass powder, zircon powder and natural flake graphite in a planetary ball mill at a mass ratio of 77:20:3 to obtain refractory powder;

[0116] 2) Preparation of paraffin-based plasticizer

[0117] Weigh refined paraffin, beeswax and low-density polyethylene in a mass ratio of 50:45:5; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it for use;

[0118] 3) Preparation of ceramic slurry

[0119] Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in a mass ratio of 15:85; dry the refractory powder at 100° C. for at least 12 hours; melt and stir the paraffin-based plasticizer at 120° C.; add the dried refractory powder into the melted paraffin-based plasticizer in four portions, and continue stirring for 30 hours to prepare a ceramic slurry;

[0120] 4) Preparation of sintered ceramic core

[0121] The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1200° C. for a holding time of 4 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core;

[0122] 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades

[0123] Prepare ethyl silicate hydrolyzate (the ethyl silicate hydrolyzate is prepared by adding distilled water and hydrochloric acid to ethyl orthosilicate as a raw material and hydrolyzing it; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 20%), perform impregnation strengthening treatment on the sintered ceramic core, and dry it in an ammonia atmosphere for 30 minutes to improve the high-temperature bending strength of the ceramic core;

[0124] A phenolic resin solution is prepared (the phenolic resin solution is an ethanol solution of phenolic resin, and the volume ratio of the phenolic resin to ethanol is 1:1), and the ceramic core is continuously impregnated and strengthened, and dried at 100°C for 60 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed hollow turbine blade is obtained.

[0125] In the ceramic core formula of Comparative Example 3, due to the addition of 3% natural flake graphite, the ceramic slurry still has good fluidity, the ceramic core has a small shrinkage rate and a low deformation tendency. However, zircon powder is used as a mineralizer. Since zircon powder has no effect on the crystallization of quartz and zircon powder cannot be sintered (solid phase reaction) with quartz glass powder, the ceramic core prepared in Comparative Example 3 has a shrinkage rate of ≤0.5% and a porosity of 25%, but the high temperature flexural strength at 1400°C is 13MPa, and the risk of core breakage during casting is very high.

[0126] In Examples 1-3 and Comparative Examples 1-3, the porosity was determined according to the test standard: HB 5353.1-2004 Test method for properties of investment casting ceramic cores Part 1: Determination of apparent porosity, water absorption and bulk density.

[0127] Determination of shrinkage rate Select test standard: HB 5353.2-2004 Test method for properties of investment casting ceramic cores Part 2: Determination of firing shrinkage rate.

[0128] Determination of flexural strength Select the test standard: HB 5353.3-2004 Investment casting ceramic core performance test method Part 3: Determination of flexural strength.

Claims

1. A ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade, characterized in that: The ceramic core is prepared by mixing refractory powder and paraffin-based plasticizer and then sintering at high temperature, wherein the mass ratio of the refractory powder to the paraffin-based plasticizer is (75-85): (15-25); The refractory powder is composed of quartz glass powder, alumina powder and natural flake graphite, and the mass ratio of the quartz glass powder, alumina powder and natural flake graphite is (75-95): (5-25): (0.5-3); The paraffin-based plasticizer is composed of paraffin, beeswax and low-density polyethylene, and the mass ratio of the paraffin, beeswax and low-density polyethylene is (40-60): (40-50): (3-10); The refractory material is prepared by the following method: The quartz glass powder is ball-milled into a powder with an average particle size of 20-40 μm; the alumina powder is calcined at 1300-1400°C for 2-4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then the calcined alumina powder is ball-milled to an average particle size of 5-20 μm; the natural flake graphite with a specification of 16-30 mesh is dried at 100-150°C for at least 6 hours; the treated quartz glass powder, alumina powder and natural flake graphite are evenly mixed in a planetary ball mill to obtain a refractory powder; The paraffin-based plasticizer is prepared by the following method: 1) Weigh paraffin, beeswax and low-density polyethylene in proportion; 2) Heat the paraffin wax until it is molten; then add the beeswax. When the beeswax starts to melt, start the mixer and stir until the beeswax and paraffin wax are evenly mixed. 3) Increase the temperature of the mixer, add low-density polyethylene, and continue stirring until the low-density polyethylene, paraffin and beeswax are evenly mixed; 4) Lower the temperature of the mixer and continue stirring to obtain the paraffin-based plasticizer. Stop stirring and heating, take out the paraffin-based plasticizer and cool it for later use.

2. A method for preparing a ceramic core for a nickel-based high-temperature alloy equiaxed hollow turbine blade as claimed in claim 1, characterized in that: The preparation steps include: 1) Preparation of refractory powder The quartz glass powder is ball-milled into a powder with an average particle size of 20-40 μm; the alumina powder is calcined at 1300-1400°C for 2-4 hours to transform the metastable phase γ-Al2O3 in the alumina powder raw material into a structurally stable α-Al2O3, and then the calcined alumina powder is ball-milled to an average particle size of 5-20 μm; the natural flake graphite with a specification of 16-30 mesh is dried at 100-150°C for at least 6 hours; the treated quartz glass powder, alumina powder and natural flake graphite are evenly mixed in a planetary ball mill to obtain a refractory powder; 2) Preparation of paraffin-based plasticizer Weigh refined paraffin, beeswax and low-density polyethylene in proportion; first heat the refined paraffin to a molten state, then add the beeswax, and when the beeswax begins to melt, start stirring until the beeswax and the refined paraffin are evenly mixed; increase the temperature of the mixer, add the low-density polyethylene, and continue stirring until the low-density polyethylene, the refined paraffin and the beeswax are evenly mixed; then lower the temperature of the mixer, continue stirring, and obtain a paraffin-based plasticizer, and finally turn off the mixer and the heating power supply, take out the paraffin-based plasticizer, cool it and set it aside; 3) Preparation of ceramic slurry Weigh the refractory powder prepared in step 1) and the paraffin-based plasticizer prepared in step 2) in proportion; dry the refractory powder at 100-120° C. for at least 6-12 hours; melt and stir the paraffin-based plasticizer at 110-130° C.; add the dried refractory powder to the melted paraffin-based plasticizer in 4-6 portions, and continue stirring for 30-50 hours to prepare a ceramic slurry; 4) Preparation of sintered ceramic core The ceramic slurry prepared in step 3) is transferred to a core pressing machine, and a ceramic green blank is made by injection molding. The ceramic green blank is placed in a sagger, and is buried and compacted with industrial alumina powder. The sagger is placed in a muffle furnace and sintered in an atmospheric atmosphere at a sintering temperature of 1180-1250° C. for a holding time of 4-8 hours. The sintered ceramic core is taken out, and the surface powder and flash are removed to obtain a sintered ceramic core; 5) Preparation of ceramic core for nickel-based high-temperature alloy equiaxed hollow turbine blades A ethyl silicate hydrolyzate solution is prepared, and the sintered ceramic core is impregnated and strengthened, and dried in an ammonia atmosphere for 30-50 minutes to improve the high-temperature bending strength of the ceramic core; a phenolic resin solution is prepared, and the ceramic core is further impregnated and strengthened, and dried at 100-130°C for 30-60 minutes to improve the room temperature strength of the ceramic core, and finally a ceramic core for a nickel-based high-temperature alloy equiaxed crystal hollow turbine blade is obtained.

3. The method according to claim 2, characterized in that: The ethyl silicate hydrolyzate is obtained by taking ethyl orthosilicate as a raw material and adding distilled water and hydrochloric acid for hydrolysis; wherein the content of SiO2 in the ethyl silicate hydrolyzate is 18-22%.

4. The method according to claim 2, characterized in that: The phenolic resin solution is an ethanol solution of phenolic resin, wherein the mass volume ratio of the phenolic resin to ethanol is 1:1.