Yttrium oxide inert coating applied to silicon-based ceramic surface as well as preparation method and application of yttrium oxide inert coating

Abstract

The invention relates to the technical field of ceramic additive manufacturing, and discloses an yttrium oxide inert coating applied to a silicon-based ceramic surface as well as a preparation method and application of the yttrium oxide inert coating. The yttrium oxide inert coating is prepared from a coating additive and yttrium oxide-based composite ceramic powder, the yttrium oxide-based composite ceramic powder is prepared from a matrix material, a mineralization modifier and a sintering additive, and the coating additive is prepared from a binder, a flatting agent, a defoaming agent and a coloring agent. The preparation method of the yttrium oxide inert coating comprises the following steps: mixing and ball-milling a coating additive and yttrium oxide-based composite ceramic powder, carrying out vacuum-pumping treatment, then carrying out coating treatment on the surface of silicon-based ceramic, and finally sintering to obtain the yttrium oxide inert coating. The method can be used for precision casting of the ceramic core. According to the invention, the chemical stability of the surface of the ceramic core can be effectively improved, the generation of interface reaction in the casting process of the ceramic core can be avoided, and the silicon-based ceramic core with excellent comprehensive performance can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic additive manufacturing, and in particular to an yttria inert coating applied to the surface of silicon-based ceramics, and a preparation method and application thereof. Background Art

[0002] Nickel-based high-temperature alloy single-crystal hollow turbine blades have good high-temperature comprehensive properties and have been commonly used in hot section components of advanced aircraft engines and industrial gas turbines. In recent years, in order to improve the high-temperature performance of single-crystal turbine blades, a new generation of high-melting-point high-temperature alloys, such as CMSX-4, CMSX-10, TMS-138 and PWA1497, have been used to prepare single-crystal blades. Ceramic cores, as key adapters for forming the complex air-cooled structure of aircraft engine turbine blades, can effectively improve the performance of aircraft engines. Silica-based ceramics are widely used in the field of ceramic cores due to their excellent high-temperature stability and easy removal. However, due to the increase in the melting point of high-temperature alloys and the increase in blade size, the casting temperature and casting time are high during the preparation of single-crystal blades. Therefore, the interface reaction trend between high-temperature alloys and silica-based ceramic cores is more prominent, which seriously affects the element composition and quality near the blade surface.

[0003] Therefore, how to avoid the interfacial reaction of ceramic cores during the casting process is the main problem facing silicon-based ceramic cores. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an yttria inert coating applied to the surface of silicon-based ceramics and its preparation method and application in view of the deficiencies of the above-mentioned prior art. The method can avoid the interface reaction between the silicon-based ceramic core and the high-temperature alloy during the casting process, so as to promote the application in the field of hollow turbine blade precision casting.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides an inert yttrium oxide coating applied to the surface of silicon-based ceramics. The inert yttrium oxide coating applied to the surface of silicon-based ceramics is made of the following raw materials in parts by weight: 90 to 96 parts of a base material, 0 to 2 parts of a mineralization modifier, and 4 to 8 parts of a sintering aid;

[0007] The coating additive is composed of the following raw materials in mass fraction: 97% to 99.5% of a binder, 0.05% to 0.2% of a defoamer, 0.3% to 1% of a leveling agent, and 0.5% to 2% of a dye;

[0008] The matrix material is yttrium oxide, the mineralization modifier is boron carbide, the sintering aid is a mixture of aluminum oxide and titanium dioxide, the binder is a mixture of silica sol and polyvinyl alcohol, the defoamer is n-octanol, the leveling agent is BYK333, and the colorant is cobalt aluminate or chromium oxide.

[0009] Preferably, the yttrium oxide includes yttrium oxide in three particle size ranges: 50nm<d1≤150nm, 1μm<d2≤45μm, and 45μm<d3≤75μm.

[0010] Preferably, the binder is composed of the following raw materials in parts by weight: 0 to 30 parts of silica sol, 1.4 to 2 parts of polyvinyl alcohol, and 68.6 to 98 parts of deionized water.

[0011] Preferably, the mineralization modifier is a powder with a particle size of 10 nm to 200 nm.

[0012] The present invention also provides a method for preparing the above-mentioned yttrium oxide inert coating applied to the surface of silicon-based ceramics, the method comprising the following steps:

[0013] S1. Ball milling the coating additive and yttrium oxide composite ceramic powder at a rotation speed of 200 rpm to 500 rpm for 2 h to 5 h to obtain a ceramic slurry that can be used to prepare an inert coating;

[0014] S2, vacuuming the ceramic slurry obtained in S1 for preparing an inert coating for 10 to 20 minutes;

[0015] S3, taking out the ceramic slurry obtained in S2, preparing 1 to 5 layers of coating on the silicon-based ceramic by dipping method or spraying method, the dipping time of the dipping method is 0 to 5 minutes, and the spray gun muzzle is placed at a distance of 5 cm to 20 cm from the test piece for spraying, and the test piece after each spraying is naturally air-dried before the next coating;

[0016] S4, placing the silicon-based ceramic body with the yttrium oxide inert coating obtained in S3 in a sintering furnace, heating the body from room temperature to 850°C to 1100°C at a heating rate of 0.5°C / min to 3°C / min in an air atmosphere, and keeping the temperature for 2h to 6h to obtain a silicon-based ceramic with the yttrium oxide inert coating;

[0017] Preferably, the coating thickness of the silicon-based ceramic with the yttria inert coating in S4 is 8 μm to 60 μm, and the porosity is 20% to 23.5%.

[0018] The present invention also provides an application of the above-mentioned yttria inert coating applied to the surface of silicon-based ceramics. The yttria inert coating applied to the surface of silicon-based ceramics is used in the field of precision casting of hollow turbine blades.

[0019] Compared with the related art, the yttrium oxide inert coating applied to the surface of silicon-based ceramics provided by the present invention and its preparation method and application have the following beneficial effects:

[0020] 1. The present invention uses yttrium oxide as the coating material matrix. Based on its excellent inertness, it can effectively isolate the silicon oxide-based ceramic core matrix from the high-temperature alloy in the casting process, significantly preventing its interface reaction with the high-temperature alloy during the casting process of the ceramic core, which is helpful for the dimensional accuracy of the hollow turbine blades. By introducing boron carbide, which has extremely high hardness and wear resistance, it is oxidized during the high-temperature sintering process to generate boron oxide to promote the sintering process of the material, making the material more dense, reducing the porosity, and better improving the strength and toughness of the ceramic core;

[0021] 2. The porosity of the yttria inert coating applied to the surface of silicon-based ceramics prepared by the present invention is 20% to 23.5%, the coating thickness is 8 μm to 60 μm, and the interface bonding strength between the yttria inert coating and the silicon oxide-based ceramics is 0.75 MPa to 1 MPa, thereby achieving high-precision precision casting of hollow turbine blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a microscopic morphology of a silicon-based ceramic with an inert yttria coating prepared in Example 1 of the present invention;

[0023] Figure 2 A physical picture of the casting sample prepared by the present invention;

[0024] Figure 3 The microscopic morphology of the casting sample prepared by the present invention;

[0025] Figure 4 for Figure 3 EDS test chart in;

[0026] Figure 5 This is a diagram of the physical properties of the ceramic cores of Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0028] Example 1

[0029] The yttrium oxide inert coating applied to the surface of silicon-based ceramics in this embodiment is made of the following raw materials in parts by weight: 68.55 parts of coating additives and the balance of yttrium oxide-based composite ceramic powder;

[0030] The yttrium oxide-based composite ceramic powder is composed of the following raw materials in parts by weight: 95.7 parts of matrix material, 0.48 parts of mineralization modifier, and 3.82 parts of sintering aid;

[0031] The coating additive is composed of the following raw materials in mass fractions: 98.24% of binder, 0.11% of defoamer, 0.55% of leveling agent, and the balance of dye;

[0032] The matrix material is yttrium oxide; the yttrium oxide powder includes yttrium oxide powders of two particle size ranges with a mass ratio of 37:3: 50nm<d1≤150nm, 45μm<d3≤75μm;

[0033] The mineralization modifier is boron carbide powder with a particle size of 100 nm;

[0034] The sintering aid is a powder mixture of aluminum oxide and titanium dioxide with a particle size of 100 nm and a mass ratio of 3:1;

[0035] The binder is composed of the following raw materials in parts by weight: 5.55 parts of silica sol, 1.89 parts of polyvinyl alcohol, and 92.56 parts of deionized water.

[0036] The defoaming agent is n-octanol, the coloring agent is cobalt aluminate, and the leveling agent is BYK333.

[0037] This embodiment also provides a method for preparing the above-mentioned yttrium oxide inert coating applied to the surface of silicon-based ceramics, the method comprising the following steps:

[0038] S1, using zirconium oxide ball milling beads as a medium, the coating additive and the yttria-based composite ceramic powder are ball milled at a speed of 300 rpm for 2 hours to obtain a ceramic slurry that can be used to prepare an inert coating;

[0039] S2, vacuuming the ceramic slurry obtained in S1 for preparing the inert coating for 10 minutes;

[0040] S3. Take out the ceramic slurry obtained in S2, prepare a coating layer on the silicon-based ceramic by using an immersion method, and obtain the silicon-based ceramic with an inert yttrium oxide coating after the test piece is naturally air-dried.

[0041] S4, placing the silicon-based ceramic body with the yttrium oxide inert coating obtained in S3 in a sintering furnace, heating it from room temperature to 200°C at a heating rate of 1°C / min in an air atmosphere, keeping it warm for 1 hour, heating it from 200°C to 900°C at a heating rate of 1°C / min, keeping it warm for 1 hour, and obtaining the silicon-based ceramic with the yttrium oxide inert coating;

[0042] The physical properties of the yttrium oxide inert coating applied to the surface of silicon-based ceramics prepared in this embodiment were tested. The results showed that the porosity was 22.07%, the coating thickness was 18.82 μm, and the interface bonding strength between the yttrium oxide inert coating and the silicon oxide-based ceramics was 0.77 MPa.

[0043] This embodiment also provides an application of the above-mentioned yttria inert coating applied to the surface of silicon-based ceramics, wherein the yttria inert coating applied to the surface of silicon-based ceramics is used in the field of hollow turbine blade precision casting.

[0044] This embodiment can effectively avoid the interface reaction problem during the casting process, and can obtain a silicon-based ceramic core with an yttria inert coating having excellent comprehensive performance.

[0045] like Figure 1 As shown in (a), the coating is dense after sintering, and there are some fine microcracks that increase the porosity of the specimen. A certain porosity can promote the dissolution of the core and improve the air permeability during the casting process. Figure 1 As shown in (b), the coating thickness of this embodiment is 18.82 μm. The moderate thickness is beneficial to improving the precision of the hollow turbine blades during the casting process.

[0046] Comparative Example 1

[0047] The preparation method and raw materials of the silicon-based ceramic substrate of this comparative example are the same as those of Example 1, except that the silicon-based ceramic substrate of this comparative example has no coating.

[0048] Physical property tests were conducted on the silicon-based ceramics of the comparative example, and the results showed that the porosity was 22.22%. Casting tests were conducted on the silicon-based ceramics of the comparative example, and interface reactions occurred at the interfaces of the silicon-based ceramics with a large amount of high-temperature alloys.

[0049] Based on casting experiment analysis, the yttrium oxide inert coating can avoid the contact between the silicon-based ceramic core and the high-temperature alloy during the casting process, prevent the occurrence of interface reaction, which is beneficial to dimensional accuracy and also helps investment casting.

[0050] Example 2

[0051] The yttrium oxide inert coating applied to the surface of silicon-based ceramics in this embodiment is made of the following raw materials in parts by weight: 68.55 parts of coating additives and the balance of yttrium oxide-based composite ceramic powder;

[0052] The yttrium oxide-based composite ceramic powder is composed of the following raw materials in parts by weight: 95.7 parts of matrix material, 0.48 parts of mineralization modifier, and 3.82 parts of sintering aid;

[0053] The coating additive is composed of the following raw materials in mass fractions: 98.24% of binder, 0.11% of defoamer, 0.55% of leveling agent, and the balance of dye;

[0054] The matrix material is yttrium oxide; the yttrium oxide powder includes yttrium oxide powders of two particle size ranges with a mass ratio of 37:3: 50nm<d1≤150nm, 45μm<d3≤75μm;

[0055] The mineralization modifier is boron carbide powder with a particle size of 100 nm;

[0056] The sintering aid is a powder mixture of aluminum oxide and titanium dioxide with a particle size of 100 nm and a mass ratio of 3:1;

[0057] The binder is composed of the following raw materials in parts by weight: 11.1 parts of silica sol, 1.778 parts of polyvinyl alcohol, and 87.122 parts of deionized water.

[0058] The defoaming agent is n-octanol, the coloring agent is cobalt aluminate, and the leveling agent is BYK333.

[0059] This embodiment also provides a method for preparing the above-mentioned yttrium oxide inert coating applied to the surface of silicon-based ceramics, the method comprising the following steps:

[0060] S1, using zirconium oxide ball milling beads as a medium, the coating additive and the yttria-based composite ceramic powder are ball milled at a speed of 300 rpm for 2 hours to obtain a ceramic slurry that can be used to prepare an inert coating;

[0061] S2, vacuuming the ceramic slurry obtained in S1 for preparing the inert coating for 10 minutes;

[0062] S3. Take out the ceramic slurry obtained in S2, prepare a coating layer on the silicon-based ceramic by using an immersion method, and obtain the silicon-based ceramic with an inert yttrium oxide coating after the test piece is naturally air-dried.

[0063] S4, placing the silicon-based ceramic body with the yttrium oxide inert coating obtained in S3 in a sintering furnace, heating it from room temperature to 200°C at a heating rate of 1°C / min in an air atmosphere, keeping it warm for 1 hour, heating it from 200°C to 900°C at a heating rate of 1°C / min, keeping it warm for 1 hour, and obtaining the silicon-based ceramic with the yttrium oxide inert coating;

[0064] The physical properties of the yttrium oxide inert coating applied to the surface of silicon-based ceramics prepared in this embodiment were tested. The results showed that the porosity was 21.15%, the coating thickness was 20.29 μm, and the interface bonding strength between the yttrium oxide inert coating and the silicon oxide-based ceramics was 0.84 MPa.

[0065] This embodiment also provides an application of the above-mentioned yttria inert coating applied to the surface of silicon-based ceramics, wherein the yttria inert coating applied to the surface of silicon-based ceramics is used in the field of hollow turbine blade precision casting.

[0066] Example 3

[0067] The yttrium oxide inert coating applied to the surface of silicon-based ceramics in this embodiment is made of the following raw materials in parts by weight: 68.55 parts of coating additives and the balance of yttrium oxide-based composite ceramic powder;

[0068] The yttrium oxide-based composite ceramic powder is composed of the following raw materials in parts by weight: 95.7 parts of matrix material, 0.48 parts of mineralization modifier, and 3.82 parts of sintering aid;

[0069] The coating additive is composed of the following raw materials in mass fractions: 98.24% of binder, 0.11% of defoamer, 0.55% of leveling agent, and the remainder of dye;

[0070] The matrix material is yttrium oxide; the yttrium oxide powder includes yttrium oxide powders of two particle size ranges with a mass ratio of 37:3: 50nm<d1≤150nm, 45μm<d3≤75μm;

[0071] The mineralization modifier is boron carbide powder with a particle size of 100 nm;

[0072] The sintering aid is a powder mixture of aluminum oxide and titanium dioxide with a particle size of 100 nm and a mass ratio of 3:1;

[0073] The binder is composed of the following raw materials in parts by weight: 16.65 parts of silica sol, 1.667 parts of polyvinyl alcohol, and 81.683 parts of deionized water.

[0074] The defoaming agent is n-octanol, the coloring agent is cobalt aluminate, and the leveling agent is BYK333.

[0075] This embodiment also provides a method for preparing the above-mentioned yttrium oxide inert coating applied to the surface of silicon-based ceramics, the method comprising the following steps:

[0076] S1, using zirconium oxide ball milling beads as a medium, the coating additive and the yttria-based composite ceramic powder are ball milled at a speed of 300 rpm for 2 hours to obtain a ceramic slurry that can be used to prepare an inert coating;

[0077] S2, vacuuming the ceramic slurry obtained in S1 for preparing the inert coating for 10 minutes;

[0078] S3. Take out the ceramic slurry obtained in S2, prepare a coating layer on the silicon-based ceramic by using an immersion method, and obtain the silicon-based ceramic with an inert yttrium oxide coating after the test piece is naturally air-dried.

[0079] S4, placing the silicon-based ceramic body with the yttrium oxide inert coating obtained in S3 in a sintering furnace, heating it from room temperature to 200°C at a heating rate of 1°C / min in an air atmosphere, keeping it warm for 1 hour, heating it from 200°C to 900°C at a heating rate of 1°C / min, keeping it warm for 1 hour, and obtaining the silicon-based ceramic with the yttrium oxide inert coating;

[0080] The physical properties of the yttrium oxide inert coating applied to the surface of silicon-based ceramics prepared in this embodiment were tested. The results showed that the porosity was 20.93%, the coating thickness was 23.99 μm, and the interface bonding strength between the yttrium oxide inert coating and the silicon oxide-based ceramics was 0.97 MPa.

[0081] This embodiment also provides an application of the above-mentioned yttria inert coating applied to the surface of silicon-based ceramics, wherein the yttria inert coating applied to the surface of silicon-based ceramics is used in the field of hollow turbine blade precision casting.

[0082] Example 4

[0083] The yttrium oxide inert coating applied to the surface of silicon-based ceramics in this embodiment is made of the following raw materials in parts by weight: 68.55 parts of coating additives and the balance of yttrium oxide-based composite ceramic powder;

[0084] The yttrium oxide-based composite ceramic powder is composed of the following raw materials in parts by weight: 95.7 parts of matrix material, 0.48 parts of mineralization modifier, and 3.82 parts of sintering aid;

[0085] The coating additive is composed of the following raw materials in mass fractions: 98.24% of binder, 0.11% of defoamer, 0.55% of leveling agent, and the remainder of dye;

[0086] The matrix material is yttrium oxide; the yttrium oxide powder includes yttrium oxide powders of two particle size ranges with a mass ratio of 37:3: 50nm<d1≤150nm, 45μm<d3≤75μm;

[0087] The mineralization modifier is boron carbide powder with a particle size of 100 nm;

[0088] The sintering aid is a powder mixture of aluminum oxide and titanium dioxide with a particle size of 100 nm and a mass ratio of 3:1;

[0089] The binder is composed of the following raw materials in parts by weight: 22.2 parts of silica sol, 1.556 parts of polyvinyl alcohol, and 76.244 parts of deionized water.

[0090] The defoaming agent is n-octanol, the coloring agent is cobalt aluminate, and the leveling agent is BYK333.

[0091] This embodiment also provides a method for preparing the above-mentioned yttrium oxide inert coating applied to the surface of silicon-based ceramics, the method comprising the following steps:

[0092] S1, using zirconium oxide ball milling beads as a medium, the coating additive and the yttria-based composite ceramic powder are ball milled at a speed of 300 rpm for 2 hours to obtain a ceramic slurry that can be used to prepare an inert coating;

[0093] S2, vacuuming the ceramic slurry obtained in S1 for preparing the inert coating for 10 minutes;

[0094] S3, taking out the ceramic slurry obtained in S2, preparing a coating layer on the silicon-based ceramic by an impregnation method, and obtaining a silicon-based ceramic with an yttrium oxide inert coating after the test piece is naturally air-dried;

[0095] S4, placing the silicon-based ceramic body with the yttrium oxide inert coating obtained in S3 in a sintering furnace, heating it from room temperature to 200°C at a heating rate of 1°C / min in an air atmosphere, keeping it warm for 1 hour, heating it from 200°C to 900°C at a heating rate of 1°C / min, keeping it warm for 1 hour, and obtaining the silicon-based ceramic with the yttrium oxide inert coating;

[0096] The physical properties of the yttrium oxide inert coating applied to the surface of silicon-based ceramics prepared in this embodiment were tested. The results showed that the porosity was 23.26%, the coating thickness was 27.89 μm, and the interface bonding strength between the yttrium oxide inert coating and the silicon oxide-based ceramics was 0.81 MPa.

[0097] This embodiment also provides an application of the above-mentioned yttria inert coating applied to the surface of silicon-based ceramics, wherein the yttria inert coating applied to the surface of silicon-based ceramics is used in the field of hollow turbine blade precision casting.

[0098] like Figure 2 FIG. 1 is an alloy specimen after a casting test using K3030 alloy according to the present invention.

[0099] like Figure 3 As shown, Figure 2 From the microscopic morphology of the cross-section of the casting specimen after cutting, it can be seen that the alloy part is almost completely dense, without pores and microcracks. The alloy specimens obtained by casting experiments using the silicon-based ceramic with yttria inert coating of this invention have very high dimensional accuracy.

[0100] like Figure 4 As shown, Figure 3 The key elements of the EDS test at the micro-morphology, where Si is concentrated in the ceramic part and Ni is concentrated in the alloy part, can prove that no interface reaction occurs.

[0101] Figure 5(a) shows the effect of different mass fractions of Si sol on porosity. With the increase of Si sol dosage, the porosity of the ceramic core decreases and then increases. The reason is that Si sol contains a large number of nano-SiO2 particles, which can fill the pores between large particles during sintering. With the increase of nano-particles, sintering tends to be densified. When the silica content is too high, cristobalite will undergo α-β phase transformation at 180-270℃ during the cooling process, resulting in volume shrinkage (2.7%), thereby forming microcracks, resulting in the core having a higher porosity and pore diameter. Figure 5 (b) shows the effect of different mass fractions of Si sol on the coating thickness. As the amount of Si sol increases, the thickness of the yttrium oxide inert coating gradually increases from 18.82μm to 27.89μm. The reason is that the nanoparticles have a larger specific surface area, which makes them more likely to diffuse during the sintering process and form larger particle agglomerates, resulting in an increase in the thickness of the coating. Figure 5 (c) shows the effect of different mass fractions of Si sol on the bonding strength between the yttrium oxide inert coating and the silicon-based ceramic core. As the amount of Si sol increases, the bonding strength increases first and then decreases. The reason is that Si sol contains a large amount of nano-SiO2 particles. The increase in the amount of nano-particles will make the specimens tend to densify during the sintering process, thereby leading to an increase in bonding strength. When the silica content is too high, cristobalite will undergo an α-β phase transition at 180-270°C during the cooling process, resulting in volume shrinkage (2.7%), thereby forming microcracks, resulting in the core having a higher porosity and pore diameter, which has a certain impact on the stability and mechanical properties of the ceramic core, resulting in a decrease in the interface bonding strength.

[0102] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An inert yttrium oxide coating applied to the surface of silicon-based ceramics, characterized in that: The yttrium oxide inert coating applied to the surface of silicon-based ceramics is made of the following raw materials in parts by weight: 65 to 72 parts of coating additives, and the balance is yttrium oxide composite ceramic powder; The yttrium oxide composite ceramic powder is composed of the following raw materials in parts by weight: 90 to 96 parts of matrix material, 0 to 2 parts of mineralization modifier, and 4 to 8 parts of sintering aid; The coating additive is composed of the following raw materials in mass fraction: 97% to 99.5% of a binder, 0.05% to 0.2% of a defoamer, 0.3% to 1% of a leveling agent, and 0.5% to 2% of a dye; The matrix material is yttrium oxide, the mineralization modifier is boron carbide or metallic silicon powder, the sintering aid is a mixture of aluminum oxide and titanium dioxide, the binder is a mixture of silica sol and polyvinyl alcohol, the defoamer is n-octanol or tert-butanol, the leveling agent is BYK333, and the colorant is cobalt aluminate, which may also be chromium oxide.

2. The yttrium oxide inert coating applied to the surface of silicon-based ceramics according to claim 1, characterized in that: The yttrium oxide includes yttrium oxide with three particle size ranges: 50nm<d1≤150nm, 1μm<d2≤45μm, and 45μm<d3≤75μm.

3. The yttrium oxide inert coating applied to the surface of silicon-based ceramics according to claim 1, characterized in that: The binder is composed of the following raw materials in parts by weight: 0 to 30 parts of silica sol, 0.4 to 4 parts of polyvinyl alcohol solution, and 66 to 99.6 parts of deionized water.

4. The yttrium oxide inert coating applied to the surface of silicon-based ceramics according to claim 1, characterized in that: The mineralization modifier is a powder with a particle size of 10nm to 200nm.

5. A method for preparing an inert yttrium oxide coating as claimed in any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1. ball milling the coating additive and yttrium oxide composite ceramic powder at a rotation speed of 200 rpm to 500 rpm for 2 h to 5 h to obtain a ceramic slurry that can be used to prepare an inert coating; S2, vacuuming the ceramic slurry obtained in S1 for preparing an inert coating for 10 to 20 minutes; S3, taking out the ceramic slurry obtained in S2, preparing 1 to 5 layers of coating on the silicon-based ceramic by dipping method or spraying method, the dipping time of the dipping method is 0 to 5 minutes, and the spray gun muzzle is placed at a distance of 5 cm to 20 cm from the test piece for spraying, and the test piece after each spraying is naturally air-dried before the next coating; S4. Place the silicon-based ceramic body with an inert yttrium oxide coating obtained in S3 in a sintering furnace, and heat it from room temperature to 850°C to 1100°C at a heating rate of 0.5°C / min to 3°C / min in an air atmosphere. Keep the temperature for 2h to 6h to obtain a silicon-based ceramic with an inert yttrium oxide coating.

6. The yttrium oxide inert coating applied to the surface of silicon-based ceramics as claimed in claim 5, and its preparation method and application, characterized in that: The coating thickness of the silicon-based ceramic with the yttria inert coating in S4 is 8 μm to 60 μm, the porosity is 20% to 23.5%, and the interface bonding strength between the yttria inert coating and the silicon-based ceramic core is 0.70 MPa to 1 MPa.

7. An application of a silicon-based ceramic with an inert yttria coating prepared by the preparation method as claimed in claim 5, characterized in that: The silicon-based ceramic with yttria inert coating is used for ceramic core precision casting.

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