Method for preparing yttria coating by modified ceramic core ultrasonic immersion

Abstract

The present application relates to the field of nickel-based single crystal superalloy blade investment casting, in particular to a method for preparing yttria coating on modified ceramic core by ultrasonic impregnation. The surface of the silicon-based ceramic core is modified by using silane coupling agent to improve the adhesion of the coating and reduce the risk of coating peeling. During the preparation of the coating, the ultrasonic impregnation can increase the permeability of the liquid coating, promote the penetration of the coating solution into the small pores of the silicon-based ceramic core, and further enhance the adhesion of the coating, so as to form a uniform and firm protective coating on the surface of the silicon-based ceramic core. The scheme is green and environmentally friendly, easy to operate, and suitable for various types of coatings, including metal, oxide, polymer and other materials, and has wide applicability.

Description

TECHNICAL FIELD

[0001] The application relates to the field of nickel-based single crystal superalloy blade investment casting, in particular to a method for preparing a yttrium oxide coating on a modified ceramic core through ultrasonic impregnation. BACKGROUND

[0002] Silicon-based ceramic cores are widely used in aerospace, automobile manufacturing, energy industry and other fields as the main body of the inner cavity of high-temperature alloy castings due to their excellent high-temperature resistance, excellent mechanical strength, low expansion coefficient and good chemical stability. However, in actual application, the core will react with alloying elements in the high-temperature alloy during the casting process, thereby affecting the surface quality of the high-temperature alloy casting. Surface treatment of the silicon-based ceramic core can solve the problem of interfacial reaction between the silicon-based ceramic core and the alloy. At present, the main problems of the surface treatment of the silicon-based ceramic core are poor uniformity of the surface coating, weak adhesion and easy failure. Extensive research shows that the key to solving this problem is to select appropriate coating materials and coating methods.

[0003] The selection of coating materials is mainly based on the modification purpose. To improve the high-temperature resistance of the silicon-based ceramic core, aluminate coating, aluminum oxide and yttrium oxide coating are mainly selected. Among them, the yttrium oxide coating not only protects the durability of the silicon-based ceramic core at high temperatures and reduces the degree of erosion of the silicon-based ceramic core by alloying elements in the interfacial reaction, but also ensures that the coating has excellent density and continuity. This is due to the high melting point of yttrium oxide, which is 2400 DEG C, which ensures that the coating will not melt and fail in a high-temperature environment. Moreover, yttrium oxide is chemically inert and is not prone to oxidation-reduction, displacement and other chemical reactions with alloying elements at high temperatures. More importantly, yttrium oxide usually has excellent density, which is conducive to the formation of a continuous and dense coating, thereby effectively isolating the silicon-based ceramic core from direct contact with the casting alloy, prolonging the service life of the silicon-based ceramic core and improving the quality of the casting.

[0004] At present, the preparation techniques of the yttrium oxide coating on the surface of the silicon-based ceramic core mainly include chemical vapor deposition, physical vapor deposition, thermal spraying and sol-gel method. Among them, the sol-gel method is simple, flexible, low in cost and good in coating uniformity, and has controllability and can realize uniform coating. The impregnation method, as a classic sol-gel method for preparing the coating, can control the thickness of the coating. Especially for the complex shape of the silicon-based ceramic core, the impregnation method can cover the recessed or narrow part of the substrate with the impregnation liquid, realizing the uniformity and density of the coating. However, the coating prepared by the impregnation method often has the characteristics of poor adhesion and poor stability, resulting in easy peeling and failure of the coating in a high-temperature environment. Therefore, it is of great significance to provide a modification scheme with wide applicability to improve the adhesion of the yttrium oxide coating on the surface of the silicon-based ceramic core prepared by the impregnation method for the development of the silicon-based ceramic core coating. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, so as to improve the problems of easy peeling, poor uniformity and insufficient density of the current surface coating of the silicon-based ceramic core, and to improve the surface treatment quality of the silicon-based ceramic core for controlling the alloy casting quality and stability.

[0006] The present application is realized by the following technical solutions:

[0007] A method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, comprising the following steps:

[0008] (1) preparing a silicon-based ceramic core;

[0009] (2) pretreating the silicon-based ceramic core, and drying after modification by a silane coupling agent;

[0010] (3) immersing the modified silicon-based ceramic core in a yttrium nitrate aqueous solution, and drying after ultrasonic immersion;

[0011] (4) sintering treatment in a muffle furnace after drying.

[0012] In step (2) of the method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, the silane coupling agent is KH550 (γ-aminopropyl triethoxysilane).

[0013] In step (2) of the method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, the surface of the silicon-based ceramic core is modified by the KH550 silane coupling agent to improve the adhesion of the yttrium oxide coating.

[0014] In step (2) of the method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, the silane coupling agent is hydrolyzed in an alcohol-water solution prepared by mixing 90-95 vol% of ethanol and 5-10 vol% of H2O, and acetic acid is added to adjust the pH to 3.5-4.5; under stirring, the silane coupling agent is added to a concentration of 1-5 vol%, and after hydrolysis for 5-15 min, a hydrolysate containing Si-OH is generated; the silicon-based ceramic core is immersed in the hydrolysate under stirring for 5-10 min, taken out and rinsed twice in ethanol, and then dried in an oven at 90-120℃.

[0015] In step (3) of the method for preparing a yttrium oxide coating by ultrasonic immersion of a modified ceramic core, the content of yttrium nitrate in the yttrium nitrate aqueous solution for ultrasonic immersion is 25-35 mol / L.

[0016] The temperature in the ultrasonic immersion environment in step (3) is 60-70 DEG C, the ultrasonic frequency is 20KHz-50KHz, the heating power is 100-200W, and the immersion time is 0.5-1.5h, and after the immersion, the silicon-based ceramic core and the solution attached to the surface thereof are placed in an oven together and dried at 60-90 DEG C.

[0017] The ultrasonic immersion in step (3) increases the permeability of the liquid coating, promotes the penetration of the coating solution into the micro-pores of the silicon-based ceramic core, further enhances the adhesion of the coating, and forms a uniform and firm protective coating on the surface of the silicon-based ceramic core.

[0018] In step (4), the sintering atmosphere is an air atmosphere, the heating rate is 4-10 DEG C / min, the temperature is heated to 800-900 DEG C, and the temperature is kept for 2-4h.

[0019] The design idea of the present application is:

[0020] The present application adopts the ultrasonic immersion method to prepare the yttrium oxide coating on the surface of the silane coupling agent modified silicon-based ceramic core.

[0021] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0022] (1) The silane coupling agent, as a common organic silicon compound for improving the actual bonding strength, can form a chemical bond on the surface of the silicon-based ceramic core and form a more stable bonding effect with the immersion liquid, thereby significantly improving the adhesion of the coating and improving the bonding strength between the coating and the silicon-based ceramic core.

[0023] (2) The present application utilizes ultrasonic immersion method to prepare yttria coating on the surface of silicon-based ceramic cores, which can improve the uniformity of the coating. On the one hand, ultrasonic waves can generate strong acoustic vibrations in the immersion liquid, which helps to disperse the coating material, reduces the aggregation of bubbles and particles, and improves the density and consistency of the coating, thereby improving the quality of the coating. On the other hand, the vibration of ultrasonic waves can make the coating liquid better penetrate the surface of the substrate, improving the adhesion between the coating and the substrate. For the ceramic surface with complex shape, ultrasonic immersion method can better ensure the uniform coverage of the coating, especially in the narrow gap and recessed parts, to ensure the uniformity of immersion. Moreover, the ultrasonic immersion equipment is simple and widely applicable, and by adjusting the ultrasonic time, ultrasonic power, immersion liquid concentration and other parameters, yttria coating with controllable thickness can be prepared.

[0024] (3) The present application obtains uniform and dense yttria coating, which can ensure the long-term stability of silicon-based ceramic cores at high temperature, reduce the degree of erosion of silicon-based ceramic cores by alloy elements in the interface reaction, effectively isolate the direct contact between silicon-based ceramic cores and casting alloy, prolong the service life of silicon-based ceramic cores, and improve the quality of castings. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The micro-morphology of the yttria coating sample prepared by ultrasonic immersion after the surface of the silicon-based ceramic core was modified with KH550 (γ-aminopropyl triethoxysilane).

[0026] Figure 2 The micro-morphology of the yttria coating sample prepared on the surface of the unmodified silicon-based ceramic core.

[0027] Figure 3 The XRD patterns of the yttria coating sample prepared on the surface of the unmodified silicon-based ceramic core and the yttria coating sample prepared on the surface of the silicon-based ceramic core modified with KH550 (γ-aminopropyl triethoxysilane). In the figure, the horizontal coordinate 2-Theta is the diffraction angle (°), and the vertical coordinate Intensity is the relative intensity (a.u.). DETAILED DESCRIPTION

[0028] In the specific implementation process, the present application proposes a method for preparing yttria coating on modified ceramic cores by ultrasonic immersion, which utilizes silane coupling agent to modify the surface of silicon-based ceramic cores, improves the adhesion of the coating, and reduces the risk of coating peeling. During the preparation of the coating, ultrasonic immersion can increase the permeability of the liquid coating, promote the penetration of the coating solution into the small pores of the silicon-based ceramic core, and further enhance the adhesion of the coating, thereby forming a uniform and firm protective coating on the surface of the silicon-based ceramic core.

[0029] In the following, the present application will be further described in detail in conjunction with the drawings and specific examples.

[0030] Example 1

[0031] In this embodiment, a method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core includes the following steps:

[0032] (1) Preparation of silicon-based ceramic core;

[0033] (2) Pretreatment of silicon-based ceramic cores: Silane coupling agent KH550 (γ-aminopropyltriethoxysilane) was hydrolyzed in an alcohol-water solution prepared with 90% ethanol and 10% H2O, and acetic acid was added to adjust the pH to 4.2. The silane coupling agent was added under stirring to a concentration of 2%, and after hydrolysis for 10 minutes, a Si-OH-containing hydrolysate was generated. The silicon-based ceramic core was immersed in the solution under stirring for 10 minutes. The silicon-based ceramic core modified with the silane coupling agent was then removed and rinsed twice in ethanol. After air drying, it was transferred to an oven and dried at 100℃ for later use.

[0034] (3) The modified silicon-based ceramic core was immersed in a 30 mol / L yttrium nitrate aqueous solution. The ultrasonic impregnation environment temperature was 60℃, the ultrasonic frequency was 40KHz, the heating power was 150W, and the impregnation time was 1h. After impregnation, it was placed in an oven and dried at 80℃.

[0035] (4) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air, the heating rate was 5℃ / min, the temperature was raised to 850℃, and the temperature was held for 3h.

[0036] like Figure 1 As shown, the microstructure of the yttrium oxide coating prepared on the surface of the silicon-based ceramic core modified with KH550 (γ-aminopropyltriethoxysilane) shows that the ceramic surface is uniformly and continuously covered with a dense coating.

[0037] like Figure 3 As shown, the XRD spectrum of the yttrium oxide coating prepared on the surface of the KH550 (γ-aminopropyltriethoxysilane) modified silicon-based ceramic core is sharper than that of the yttrium oxide coating prepared on the unmodified ceramic surface. This indicates that the yttrium oxide content is higher, the exposed ceramic substrate is less, and the coating is more compact.

[0038] Example 2

[0039] In this embodiment, a method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core includes the following steps:

[0040] (1) Preparation of silicon-based ceramic core;

[0041] (2) Pretreatment of silicon-based ceramic cores: Silane coupling agent KH550 (γ-aminopropyltriethoxysilane) was hydrolyzed in an alcohol-water solution prepared with 90% ethanol and 10% H2O, and acetic acid was added to adjust the pH to 4.2. The silane coupling agent was added under stirring to a concentration of 2%, and after hydrolysis for 10 minutes, a Si-OH-containing hydrolysate was generated. The silicon-based ceramic core was immersed in the solution under stirring for 10 minutes. The silicon-based ceramic core modified with the silane coupling agent was then removed and rinsed twice in ethanol. After air drying, it was transferred to an oven and dried at 100℃ for later use.

[0042] (3) The modified silicon-based ceramic core was immersed in a 30 mol / L yttrium nitrate aqueous solution. The ultrasonic impregnation environment temperature was 60℃, the ultrasonic frequency was 40KHz, the heating power was 150W, and the impregnation time was 0.5h. After impregnation, it was placed in an oven and dried at 80℃.

[0043] (4) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air, the heating rate was 5℃ / min, the temperature was raised to 850℃, and the temperature was held for 3h.

[0044] Compared with Example 1, this example reduces the ultrasonic impregnation time to 0.5h, and the yttrium oxide coating is successfully attached to the surface of the silicon-based ceramic core.

[0045] Comparative Example 1

[0046] In this comparative example, a method for preparing yttrium oxide coating by ultrasonic impregnation of a ceramic core includes the following steps:

[0047] (1) Preparation of silicon-based ceramic core;

[0048] (2) Immerse the silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution. The ultrasonic impregnation environment temperature is 60℃, the ultrasonic frequency is 40KHz, the heating power is 150W, the impregnation time is 1h, and after impregnation, place it in an oven and dry it at 80℃.

[0049] (3) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air, the heating rate was 5℃ / min, the temperature was raised to 850℃, and the temperature was held for 3h.

[0050] like Figure 2 As shown, the microstructure of the yttrium oxide coating prepared on the surface of the unmodified silicon-based ceramic core shows that most of the ceramic substrate particles are exposed outside the coating, and the coating fails to effectively cover the surface of the silicon-based ceramic core.

[0051] like Figure 3As shown in the XRD spectrum of the yttria coating prepared on the surface of the unmodified silicon-based ceramic core, the yttria characteristic peaks of the yttria coating prepared on the surface of the silicon-based ceramic core are weak, indicating that the content of yttria is small, the exposed ceramic substrate is more, and the coating density is insufficient.

[0052] Comparative Example 2

[0053] In the present comparative example, a method for preparing a yttria coating by modifying a ceramic core by impregnation comprises the following steps:

[0054] (1) preparing a silicon-based ceramic core;

[0055] (2) pretreating the silicon-based ceramic core, hydrolyzing silane coupling agent KH550 (γ-aminopropyl triethoxysilane) in an alcohol-water solution prepared by mixing 90% ethanol and 10% H2O, and adding acetic acid to adjust the pH to 4.2. Stirring is added to the silane coupling agent to make the concentration reach 2%, and after hydrolysis for 10 min, the hydrolysate containing Si-OH is generated. Immerse the silicon-based ceramic core in the solution for 10 min, take out the silicon-based ceramic core modified by the silane coupling agent and rinse it in ethanol for 2 times, dry it after drying in an oven at 100℃, and then move it into the oven for drying;

[0056] (3) immersing the modified silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution, the impregnation temperature is 60℃, the impregnation time is 1h, and after the impregnation is completed, it is placed in an oven at 80℃ for drying;

[0057] (4) placing the dried sample in a muffle furnace for sintering treatment. The sintering atmosphere is air atmosphere, the heating rate is 5℃ / min, the temperature is heated to 850℃, and the temperature is kept for 3h.

[0058] Compared with the examples, when the ultrasonic method is not used for impregnation, the yttria coating attached to the ceramic surface modified by KH550 is discontinuous, has low coverage and poor density.

[0059] The results of the examples show that after the surface of the silicon-based ceramic core is modified by the silane coupling agent, the yttria coating prepared by ultrasonic impregnation for a suitable time can improve the adhesion, density and continuity of the coating. In particular, the coating prepared by ultrasonic impregnation for 1h after the surface of the silicon-based ceramic core is modified by the silane coupling agent KH550 (γ-aminopropyl triethoxysilane) has better coating of the ceramic substrate and less exposed ceramic substrate. At the same time, the present application meets the characteristics of simple and flexible process and strong applicability. The present application is green and environmentally friendly, easy to operate, and suitable for a variety of different types of coatings, including metals, oxides, polymers and other materials, and has wide applicability.

[0060] Those skilled in the art can understand that the above description is only an embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core for investment casting of nickel-based single-crystal superalloy blades, characterized in that, Includes the following steps: (1) Preparation of silicon-based ceramic core; (2) The silicon-based ceramic core is pretreated, modified with a silane coupling agent, and then dried; In step (2), the silane coupling agent is hydrolyzed in an alcohol-water solution prepared with 90-95 vol% ethanol and 5-10 vol% H2O, and acetic acid is added to adjust the pH to 3.5-4.5; the silane coupling agent is added under stirring to make its concentration reach 1-5 vol%, and after hydrolysis for 5-15 min, a hydrolysate containing Si-OH is generated; the silicon-based ceramic core is immersed under stirring for 5-10 min, taken out and rinsed twice in ethanol, air-dried, and then transferred to an oven to dry at 90-120℃. (3) The modified silicon-based ceramic core was immersed in yttrium nitrate aqueous solution, ultrasonically impregnated, and then dried; In step (3), the yttrium nitrate content in the ultrasonically impregnated yttrium nitrate aqueous solution is 25-35 mol / L; the temperature in the ultrasonic impregnation environment is 60-70℃, the ultrasonic frequency is 20KHz-50KHz, the heating power is 100-200W, and the impregnation time is 0.5-1.5h. After impregnation, the silicon-based ceramic core and the solution attached to its surface are placed in an oven and dried at 60-90℃. (4) After drying, it is placed in a muffle furnace for sintering treatment; In step (4), the sintering atmosphere is air, the heating rate is 4-10℃ / min, the temperature is heated to 800-900℃, and the temperature is held for 2-4 hours.

2. The method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core as described in claim 1, characterized in that, In step (2), the silane coupling agent selected is KH550 (γ-aminopropyltriethoxysilane).

3. The method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core as described in claim 2, characterized in that, In step (2), the surface of the silicon-based ceramic core is modified by KH550 silane coupling agent to improve the adhesion of the yttrium oxide coating.

4. The method for preparing yttrium oxide coating by ultrasonic impregnation of a modified ceramic core as described in claim 1, characterized in that, In step (3), ultrasonic impregnation is used to increase the permeability of the liquid coating, promote the coating solution to penetrate into the tiny pores of the silicon-based ceramic core, further enhance the adhesion of the coating, and form a uniform and firm protective coating on the surface of the silicon-based ceramic core.

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