Method for preparing yttrium oxide coating through ultrasonic impregnation of modified ceramic core

Abstract

The invention relates to the field of investment casting of nickel-based single-crystal high-temperature alloy blades, in particular to a method for preparing an yttrium oxide coating through ultrasonic impregnation of a modified ceramic core. And the silane coupling agent is utilized to modify the surface of the silicon-based ceramic core, so that the adhesive force of the coating is improved, and the risk of coating stripping is reduced. In the preparation process of the coating, the permeability of the liquid coating can be improved by utilizing ultrasonic impregnation, a coating solution is promoted to permeate into tiny pores of the silicon-based ceramic core, and the adhesive force of the coating is further enhanced, so that a uniform and firm protective coating is formed on the surface of the silicon-based ceramic core. The scheme is green and environment-friendly, is simple and easy to operate, is suitable for various different types of coatings including materials such as metals, oxides and polymers, and has wide applicability.

Description

Technical Field

[0001] The invention relates to the field of nickel-based single crystal high-temperature alloy blade investment casting, in particular to a method for preparing an yttrium oxide coating by ultrasonic impregnation of a modified ceramic core. Background Art

[0002] As the inner cavity molding body of high-temperature alloy castings, silicon-based ceramic cores have excellent high-temperature resistance, excellent mechanical strength, low expansion coefficient and good chemical stability, and are widely used in aerospace, automobile manufacturing, energy industry and other fields. However, in actual applications, the core will react with the 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 silicon-based ceramic cores can solve the problem of interface reaction between silicon-based ceramic cores and alloys. At present, the surface treatment problems of silicon-based ceramic cores mainly lie in poor uniformity of surface coatings, weak adhesion, and easy failure. Extensive research has shown that selecting suitable coating materials and using suitable coating methods are the key to solving this problem.

[0003] The selection of coating materials is mainly based on the purpose of modification. Aluminate coatings, aluminum oxide, yttrium oxide coatings, etc. are mainly selected to improve the high temperature resistance of silicon-based ceramic cores. Among them, yttrium oxide coatings can not only protect the long-term stability of silicon-based ceramic cores at high temperatures and reduce the degree of corrosion of silicon-based ceramic cores by alloy elements in interface reactions, but also ensure that the coating has excellent density and continuity. This is attributed to the high melting point of yttrium oxide of 2400°C, which ensures that the coating will not melt and fail in a high temperature environment, and yttrium oxide is chemically inert and is not easy to undergo oxidation-reduction, replacement and other chemical reactions with alloy 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 direct contact between the silicon-based ceramic core and the casting alloy, extending the service life of the silicon-based ceramic core, and improving the quality of the casting.

[0004] At present, the preparation technologies of yttrium oxide coating on the surface of silicon-based ceramic cores mainly include chemical vapor deposition, physical vapor deposition, thermal spraying, sol-gel method, etc. Among them, the sol-gel method is simple and flexible, low-cost, good coating uniformity, and controllable, and can achieve uniform coating. The dipping method, as a classic sol-gel method, is used to prepare the coating to achieve the control of the coating thickness, especially for the complex shape of silicon-based ceramic cores. The dipping method can make the dipping liquid cover the concave or slit parts of the substrate to achieve the uniformity and density of the coating. However, the coating effect prepared by the dipping method often has the characteristics of poor adhesion and poor stability, which makes the coating easy to fall off and fail 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 dipping method for the development of silicon-based ceramic core coatings. Summary of the invention

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

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing an yttrium oxide coating by ultrasonic impregnation of a modified ceramic core comprises the following steps:

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

[0009] (2) pre-treating the silicon-based ceramic core, modifying it with a silane coupling agent, and then drying it;

[0010] (3) immersing the modified silicon-based ceramic core in an aqueous solution of yttrium nitrate, ultrasonically immersing it, and then drying it;

[0011] (4) After drying, the mixture is placed in a muffle furnace for sintering.

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

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

[0014] The modified ceramic core ultrasonic impregnation method for preparing yttrium oxide coating comprises the following steps: in step (2), hydrolyzing a silane coupling agent in an alcohol-water solution composed of 90-95 vol% ethanol and 5-10 vol% H2O, adding acetic acid to adjust the pH to 3.5-4.5; adding a silane coupling agent under stirring to a concentration of 1-5 vol%, and generating a hydrolyzate containing Si-OH after hydrolysis for 5-15 min; immersing the silicon-based ceramic core under stirring for 5-10 min, taking out and immersing the core in ethanol for rinsing twice, drying it, and then transferring it to an oven for drying at 90-120°C.

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

[0016] The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core, in step (3), the temperature in the ultrasonic impregnation environment is 60-70°C, the ultrasonic frequency is 20KHz-50KHz, the heating power is 100-200W, the impregnation time is 0.5-1.5h, and after the impregnation is completed, the silicon-based ceramic core and the solution attached to the surface are placed in an oven and dried at 60-90°C.

[0017] In the method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core, 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.

[0018] In the method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core, in step (4), the sintering atmosphere is air atmosphere, the heating rate is 4-10°C / min, the temperature is heated to 800-900°C, and the temperature is kept for 2-4h.

[0019] The design concept of the present invention is:

[0020] The present invention adopts an ultrasonic impregnation method to prepare an yttrium oxide coating on the surface of a silicon-based ceramic core modified by a silane coupling agent. From the practical perspectives of simple process design and strong applicability, the impregnation method is optimized for the purpose of improving the adhesion, density, continuity, etc. of the yttrium oxide coating on the surface of the silicon-based ceramic core.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0022] (1) As a common organic silicon compound that improves the actual bonding strength, silane coupling agent can form chemical bonds on the surface of silicon-based ceramic cores and form a more stable bonding effect with the impregnation liquid, thereby significantly improving the adhesion of the coating and improving the bonding strength between the coating and the silicon-based ceramic core. On the other hand, the surface properties of the silicon-based ceramic core modified by silane coupling agent are controllable and can be adjusted to hydrophilicity or hydrophobicity by selecting different types of silane coupling agents, making it more suitable for specific coating applications.

[0023] (2) The present invention utilizes ultrasonic impregnation to prepare yttrium oxide coating on the surface of silicon-based ceramic core, which can improve the uniformity of the coating. On the one hand, ultrasonic waves can generate strong sonic vibrations in the impregnation liquid, which helps to disperse the coating material, reduce bubble and particle aggregation, improve the density and consistency of the coating, and thus improve the quality of the coating. On the other hand, ultrasonic vibrations can enable the coating liquid to better penetrate into the surface of the substrate, thereby improving the adhesion between the coating and the substrate. For ceramic surfaces with complex shapes, the ultrasonic impregnation method can better ensure uniform coverage of the coating, especially in slits and recessed areas, to ensure the uniformity of impregnation. Moreover, the ultrasonic impregnation equipment is simple and has a wide range of applicability. By adjusting parameters such as ultrasonic time, ultrasonic power, and impregnation liquid concentration, it is possible to prepare an yttrium oxide coating with controllable thickness.

[0024] (3) The present invention obtains a uniform and dense yttrium oxide coating, which can ensure the long-term stability of the silicon-based ceramic core at high temperatures, reduce the degree of corrosion of the silicon-based ceramic core by alloy elements in the interface reaction, effectively isolate the direct contact between the silicon-based ceramic core and the casting alloy, extend the service life of the silicon-based ceramic core, and improve the quality of the casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The microstructure of the yttrium oxide coating sample prepared by ultrasonic impregnation after modifying the surface of the silicon-based ceramic core with KH550 (γ-aminopropyltriethoxysilane).

[0026] Figure 2 The microstructure of the yttrium oxide coating sample prepared on the surface of the unmodified silicon-based ceramic core.

[0027] Figure 3 The XRD patterns of the yttrium oxide coating samples prepared on the surface of the unmodified silicon-based ceramic core and the yttrium oxide coating samples prepared on the surface of the silicon-based ceramic core modified with KH550 (γ-aminopropyltriethoxysilane). In the figure, the abscissa 2-Theta is the diffraction angle (°), and the ordinate Intensity is the relative intensity (au). DETAILED DESCRIPTION

[0028] In the specific implementation process, the present invention proposes a method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core, using silane coupling agent to modify the surface of silicon-based ceramic core, improve the adhesion of coating, and reduce the risk of coating peeling. In the process of coating preparation, ultrasonic impregnation can increase the permeability of liquid coating, promote the penetration of coating solution into the tiny pores of silicon-based ceramic core, further enhance the adhesion of coating, and thus form a uniform and firm protective coating on the surface of silicon-based ceramic core.

[0029] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

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

[0032] (1) preparing a silicon-based ceramic core;

[0033] (2) Pre-treat the silicon-based ceramic core by hydrolyzing the silane coupling agent KH550 (γ-aminopropyltriethoxysilane) in an alcohol-water solution composed of 90% ethanol and 10% H2O, and add acetic acid to adjust the pH to 4.2. Add the silane coupling agent while stirring to a concentration of 2%. After hydrolysis for 10 minutes, a hydrolyzate containing Si-OH is generated. Immerse the silicon-based ceramic core in the core for 10 minutes while stirring. Take out the silicon-based ceramic core modified with the silane coupling agent and rinse it twice in ethanol. After drying, move it into an oven and dry it at 100°C for use.

[0034] (3) immersing the modified silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution, with an ultrasonic immersion environment temperature of 60° C., an ultrasonic frequency of 40 kHz, a heating power of 150 W, and an immersion time of 1 h. After the immersion is completed, the core is placed in an oven and dried at 80° C.;

[0035] (4) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air atmosphere, the heating rate was 5°C / min, the temperature was heated to 850°C, and the temperature was kept for 3 hours.

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

[0037] like Figure 3 As shown in the figure, the XRD spectrum of the yttrium oxide coating prepared on the surface of the silicon-based ceramic core modified with KH550 (γ-aminopropyltriethoxysilane) shows that compared with the yttrium oxide coating prepared on the unmodified ceramic surface, the characteristic peak of yttrium oxide on the surface of the KH550-modified silicon-based ceramic core is sharper, indicating that the yttrium oxide content is higher, the exposed ceramic substrate is less, and the coating is denser.

[0038] Example 2

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

[0040] (1) preparing a silicon-based ceramic core;

[0041] (2) Pre-treat the silicon-based ceramic core by hydrolyzing the silane coupling agent KH550 (γ-aminopropyltriethoxysilane) in an alcohol-water solution composed of 90% ethanol and 10% H2O, and add acetic acid to adjust the pH to 4.2. Add the silane coupling agent while stirring to a concentration of 2%. After hydrolysis for 10 minutes, a hydrolyzate containing Si-OH is generated. Immerse the silicon-based ceramic core in the core for 10 minutes while stirring. Take out the silicon-based ceramic core modified with the silane coupling agent and rinse it twice in ethanol. After drying, move it into an oven and dry it at 100°C for use.

[0042] (3) immersing the modified silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution, with an ultrasonic immersion environment temperature of 60° C., an ultrasonic frequency of 40 kHz, a heating power of 150 W, and an immersion time of 0.5 h. After the immersion is completed, the core is placed in an oven and dried at 80° C.;

[0043] (4) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air atmosphere, the heating rate was 5°C / min, the temperature was heated to 850°C, and the temperature was kept for 3 hours.

[0044] Compared with Example 1, when the ultrasonic immersion time in this example is reduced to 0.5 h, 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 an yttrium oxide coating by ultrasonic impregnation of a ceramic core comprises the following steps:

[0047] (1) preparing a silicon-based ceramic core;

[0048] (2) immersing the silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution, with an ultrasonic immersion environment temperature of 60° C., an ultrasonic frequency of 40 kHz, a heating power of 150 W, and an immersion time of 1 h. After the immersion, the core is placed in an oven and dried at 80° C.;

[0049] (3) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air atmosphere, the heating rate was 5°C / min, the temperature was heated to 850°C, and the temperature was kept for 3 hours.

[0050] like Figure 2 As shown in the microscopic morphology of the yttrium oxide coating prepared on the surface of the unmodified silicon-based ceramic core, it can be observed that most of the ceramic base 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 yttrium oxide coating prepared on the surface of the unmodified silicon-based ceramic core, the yttrium oxide characteristic peak of the yttrium oxide coating prepared on the surface of the silicon-based ceramic core is weak, indicating that the yttrium oxide content is low, the exposed ceramic substrate is large, and the coating density is insufficient.

[0052] Comparative Example 2

[0053] In this comparative example, a method for preparing an yttrium oxide coating by dipping a modified ceramic core comprises the following steps:

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

[0055] (2) Pre-treat the silicon-based ceramic core by hydrolyzing the silane coupling agent KH550 (γ-aminopropyltriethoxysilane) in an alcohol-water solution composed of 90% ethanol and 10% H2O, and add acetic acid to adjust the pH to 4.2. Add the silane coupling agent while stirring to a concentration of 2%. After hydrolysis for 10 minutes, a hydrolyzate containing Si-OH is generated. Immerse the silicon-based ceramic core in the core for 10 minutes while stirring. Take out the silicon-based ceramic core modified with the silane coupling agent and rinse it twice in ethanol. After drying, move it into an oven and dry it at 100°C for use.

[0056] (3) immersing the modified silicon-based ceramic core in a 30 mol / L yttrium nitrate aqueous solution at a temperature of 60° C. for 1 h, and drying in an oven at 80° C. after immersion;

[0057] (4) The dried sample was placed in a muffle furnace for sintering. The sintering atmosphere was air atmosphere, the heating rate was 5°C / min, the temperature was heated to 850°C, and the temperature was kept for 3 hours.

[0058] Compared with the embodiment, in this comparative example, when the ultrasonic method is not used for impregnation, the yttrium oxide coating attached to the surface of the ceramic modified by KH550 is discontinuous, has a low coverage rate, and has poor density.

[0059] The results of the embodiments show that after the surface of the silicon-based ceramic core is modified by a silane coupling agent, the yttrium oxide coating is prepared by ultrasonic impregnation for an appropriate period of time, which can improve the adhesion, density and continuity of the coating. In particular, the coating prepared by ultrasonic impregnation for 1 hour after the surface of the silicon-based ceramic core is modified by the silane coupling agent KH550 (γ-aminopropyltriethoxysilane) has better coating properties on the ceramic substrate and less exposed ceramic substrate. At the same time, the invention meets the characteristics of simple and flexible process and strong applicability. The scheme is green and environmentally friendly, easy to operate, and is applicable to many different types of coatings, including metals, oxides, polymers and other materials, and has a wide range of applicability.

[0060] Those skilled in the art will easily understand that the above description is only an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core, characterized in that: The steps include: (1) preparing a silicon-based ceramic core; (2) pre-treating the silicon-based ceramic core, modifying it with a silane coupling agent, and then drying it; (3) immersing the modified silicon-based ceramic core in an aqueous solution of yttrium nitrate, ultrasonically impregnating and then drying; (4) After drying, the mixture is placed in a muffle furnace for sintering.

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

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

4. The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core according to claim 1 or 2, characterized in that: In step (2), the silane coupling agent is hydrolyzed in an alcohol-water solution composed of 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 a concentration of 1-5 vol%, and after hydrolysis for 5-15 minutes, a hydrolyzate containing Si-OH is generated; the silicon-based ceramic core is immersed in the core for 5-10 minutes under stirring, and the core is taken out and immersed in ethanol for rinsing twice, and after drying, it is moved into an oven and dried at 90-120°C.

5. The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core according to claim 1, characterized in that: In step (3), the yttrium nitrate content in the ultrasonically impregnated yttrium nitrate aqueous solution is 25 to 35 mol / L.

6. The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core according to claim 1, characterized in that: In step (3), the temperature in the ultrasonic immersion environment is 60-70°C, the ultrasonic frequency is 20KHz-50KHz, the heating power is 100-200W, and the immersion time is 0.5-1.5h. After the immersion is completed, the silicon-based ceramic core and the solution attached to its surface are placed in an oven and dried at 60-90°C.

7. The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core according to claim 1 or 6, 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.

8. The method for preparing yttrium oxide coating by ultrasonic impregnation of modified ceramic core according to claim 1, characterized in that: In step (4), the sintering atmosphere is air atmosphere, the heating rate is 4-10°C / min, the temperature is heated to 800-900°C, and the temperature is kept for 2-4h.

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