Preparation method of diffusion coating based on rare earth oxide modification

Abstract

The invention relates to the technical field of surface protective coatings, in particular to a preparation method of a diffusion coating based on rare earth oxide modification, which comprises the steps of matrix pretreatment, permeation agent preparation and coating preparation. The permeation agent is composed of an aluminum supply agent, a filling agent, an activating agent and a permeation accelerating agent, wherein nano cerium oxide serves as the permeation accelerating agent and can remarkably improve the coating performance. By optimizing process parameters, the aluminizing temperature is reduced to 630 DEG C, and the time is shortened to be within 5 hours. The oxidation resistance, the hot corrosion resistance and the matrix bonding strength of the coating can be remarkably improved, and the coating is suitable for TiAl intermetallic compounds and other high-temperature alloy materials and has wide application prospects in the fields of aerospace and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface treatment and coating technology, and specifically relates to a preparation method of a diffusion coating modified based on rare earth oxides. Background Art

[0002] With the rapid development of modern industry, the demand for a high thrust-to-weight ratio is becoming increasingly stringent, as power efficiency is closely related to the engine's thrust-to-weight ratio. Consequently, increasing the horizontal thrust of the engine and reducing its net weight have become the goals pursued by many engine researchers. TiAl intermetallic compounds, due to their high specific strength and modulus, possess certain oxidation resistance and creep resistance. In particular, their density, approximately 4.0 g / cm³, is only half that of nickel-based superalloys. They have now partially replaced superalloys in the manufacture of key components such as compressor blades, casings, combustion chamber diffusers, vortex finders, and low-pressure turbine blades. However, as engine operating conditions become increasingly demanding, the inferior high-temperature oxidation resistance of TiAl intermetallic compounds above 800°C has become a key factor limiting their widespread use. Achieving the protection and life extension of TiAl intermetallic compounds has become one of the most pressing issues in engine materials research.

[0003] Improving the high-temperature oxidation resistance of TiAl intermetallic compound components through surface engineering techniques has become a widely used and effective approach. Among these, the most widely used key technology is the powder embedding method for preparing diffusion-type aluminide coatings on alloy surfaces. This is primarily due to the simplicity of the embedded aluminizing coating preparation process, and the resulting aluminide protective coating exhibits a certain degree of high-temperature oxidation resistance, significantly extending the service life of the alloy substrate under harsh operating conditions. However, this approach also presents several drawbacks and deficiencies during service. For example, the coating itself is inherently brittle, and during service, the mismatch in thermal expansion coefficients between the coating and the alloy substrate can lead to cracking and flaking of the coating or oxide film. Furthermore, the coating exhibits weak resistance to sulfidation and hot corrosion, making it susceptible to accelerated corrosion in saline environments. Consequently, the addition of the rare earth element Ce to the aluminide coating, leveraging its active element effect to enhance its thermal properties and resistance to high-temperature oxidation and hot corrosion, has become an important approach for improving existing technologies. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a method for preparing a diffusion coating modified with rare earth oxides. By optimizing the infiltrant formulation and process parameters, this method significantly reduces the temperature and time required to prepare the aluminide coating, while also improving the coating's oxidation resistance, thermal corrosion resistance, and bonding strength to the substrate.

[0005] The technical solution of the present invention is: A method for preparing a diffusion coating modified by rare earth oxides comprises the following steps: S1. Matrix pretreatment: The TiAl intermetallic compound matrix was processed into the desired shape, polished with 400-grit sandpaper to remove the surface oxide layer, cleaned with anhydrous ethanol, and then sandblasted. The matrix was ultrasonically cleaned with anhydrous ethanol for 15 minutes and dried. S2. Preparation of the penetrant: Weigh 20wt%-40wt%, 50wt%-80wt% of the filler, 2wt%-6wt% of the activator, and 1wt%-3wt% of the catalyst by weight, mix them evenly, and put them into a crucible, wherein the aluminum supply agent is aluminum powder, the filler is aluminum oxide, the activator is ammonium chloride, and the catalyst is nano-cerium oxide; S3. Coating preparation: insert the pretreated substrate vertically into the upper middle position of the penetrant, place the crucible in a horizontal tube furnace, and evacuate to 10 -2 Pa, introduce high-purity argon and replace it repeatedly for more than 3 times, heat to 630℃ at a heating rate of 10℃ / min, keep warm for 5 hours and then cool naturally to room temperature.

[0006] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, the ratio of the aluminum supply agent to the filler is controlled between 1:1.5 and 1:4.

[0007] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, the particle size of the nano-cerium oxide is in the range of 10nm-50nm.

[0008] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, the amount of the activator ammonium chloride added is adjusted according to the volatility characteristics of the penetrant system, and the ammonia gas and hydrogen chloride gas generated by decomposition form a dynamic equilibrium in the system.

[0009] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, during the substrate pretreatment process, sandblasting is used to increase the surface roughness of the substrate to improve the mechanical bonding force between the coating and the substrate.

[0010] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, the holding stage in the horizontal tube furnace is a critical period for aluminum atoms to quickly migrate to the substrate surface through the preferential channel provided by nano-cerium oxide.

[0011] Furthermore, in the above-mentioned method for preparing a diffusion coating modified by rare earth oxide, the mass ratio of the substrate to the penetrant is less than 1:50 to ensure that the penetrant is sufficient to form an aluminide coating.

[0012] Furthermore, the above-mentioned method for preparing a diffusion coating modified by rare earth oxide is applicable to the field of surface protection of TiAl intermetallic compound matrix and other high-temperature alloy materials.

[0013] The key innovations of the present invention are as follows: Rare earth oxide modified coating design: By introducing nano-cerium oxide into the infiltrant, its lattice distortion effect and vacancy generation mechanism are fully utilized to significantly improve the diffusion efficiency of aluminum atoms, while enhancing the density and uniformity of the coating.

[0014] Synergistic Effect of Infiltrant Components: The optimized ratios of the aluminizing agent, filler, activator, and catalyst form a highly efficient aluminizing system. The gaseous environment generated by the decomposition of ammonium chloride and the catalytic effect of nano-cerium oxide further promote the rapid formation of the aluminide coating.

[0015] Wide range of applications: This coating is not only suitable for TiAl intermetallic compounds, but can also be extended to the surface protection of other high-temperature alloy materials, such as nickel-based and cobalt-based high-temperature alloys. Its excellent oxidation resistance and hot corrosion resistance give it broad application prospects in aerospace, shipbuilding, chemical equipment and other fields.

[0016] Process flexibility and adaptability: By adjusting the nano-cerium oxide content in the infiltrator and the aluminizing process parameters, coating performance can be customized for different application scenarios. For example, when higher oxidation resistance is required in high-temperature environments, the nano-cerium oxide dosage can be appropriately increased; when stronger thermal corrosion resistance is required in saline environments, the coating quality can be further improved by extending the holding time.

[0017] Advantages and beneficial effects of the present invention: The aluminized coating preparation temperature was reduced from the conventional 800-1000°C to 630°C, and the preparation time was shortened from over 10 hours to less than 5 hours. This improvement significantly reduces the damage to the TiAl intermetallic matrix structure caused by high temperatures, while also reducing energy consumption.

[0018] The introduction of nano-cerium oxide significantly improves the density and uniformity of the coating. The coating surface has no holes or cracks and is tightly bonded to the substrate.

[0019] In the high temperature oxidation test, the oxidation weight gain rate of the coating is less than 0.3 mg / cm 2 ·h, showing excellent antioxidant properties. In contrast, the oxidation weight gain rate of the coating without adding nano-cerium oxide is higher than 1.2mg / cm 2 ·h.

[0020] The coating's thermal corrosion resistance in a salty environment is significantly improved, and the stability of the oxide film formed on its surface is enhanced, which can effectively inhibit the corrosion of sulfides and chlorides. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the surface morphology of the coating obtained in Example 1; Figure 2 is the oxidation weight gain rate of the coating obtained in Example 1 in the high temperature oxidation experiment; Figure 3 This is the surface morphology of the coating obtained in Comparative Example 1; Figure 4 The coating oxidation weight gain rate of the coating obtained in Comparative Example 1 in the high temperature oxidation experiment; Figure 5 This is the surface morphology of the coating obtained in Comparative Example 2; Figure 6 The coating oxidation weight gain rate of the coating obtained in Comparative Example 2 in the high temperature oxidation experiment; DETAILED DESCRIPTION

[0022] In a specific embodiment, a diffusion coating modified with rare earth oxides is prepared, wherein the infiltrant is composed of the following raw materials in parts by weight: 20-40 wt% of the aluminum-supplying agent, 50-80 wt% of the filler, 2-6 wt% of the activator, and 1-3 wt% of the catalyst. The aluminum-supplying agent is aluminum powder, the filler is aluminum oxide, the activator is ammonium chloride, and the catalyst is nano-cerium oxide. The composition ratio of these components has been rigorously optimized to ensure the rapid formation of a uniform, dense aluminide coating at relatively low temperatures while avoiding the adverse effects of prolonged high-temperature treatment on the substrate structure.

[0023] Nano-cerium oxide, the core component of the penetration catalyst, possesses high surface activity and chemical reactivity. Its particle size distribution ranges from 10 to 50 nm, allowing it to effectively penetrate the micropores on the substrate surface and undergo physical adsorption and chemical bonding with the substrate surface. This mechanism of action not only enhances the bonding strength between the coating and the substrate, but also significantly improves the density and uniformity of the coating. Furthermore, upon entering the substrate, nano-cerium oxide undergoes lattice distortion, generating a vacancy effect that provides a preferential path for the diffusion of aluminum atoms, thereby accelerating the formation of the aluminide coating.

[0024] In the design of the penetrant ratio, the ratio of aluminum supply agent to filler is controlled between 1:1.5-4. This ratio ensures sufficient aluminum source while preventing excessive aluminum powder from increasing coating brittleness. The amount of ammonium chloride added as an activator is adjusted according to the volatility of the penetrant system. The ammonia and hydrogen chloride gases produced by its decomposition form a dynamic equilibrium within the system, promoting the diffusion of aluminum atoms and inhibiting oxidation reactions. The addition of nano-cerium oxide as a penetrant catalyst is strictly limited to 1-3 parts to avoid excessive addition that can cause internal stress concentration in the coating.

[0025] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention. Example 1

[0026] This embodiment provides a method for preparing a diffusion coating modified with rare earth oxides, comprising the following steps: 1) Matrix Pretreatment: Use an EDM machine to machine the TiAl intermetallic compound matrix. After sanding with 400-grit sandpaper to remove rust, soak it in anhydrous ethanol solution and store it for later use. Remove the matrix, dry it, sandblast it, and then ultrasonically clean it with anhydrous ethanol for 15 minutes before drying it for later use.

[0027] 2) Preparation of penetrant: Prepare 100g of penetrant by mixing Al:Al2O3:NH4Cl:CeO2=30:66:3:1 (wt%), select CeO2 with a particle size of 50nm, and put the evenly mixed penetrant into a crucible.

[0028] 3) Coating preparation: Polish the substrate surface again and dry it, then quickly insert the substrate vertically into the middle and upper part of the penetrant. Then place the crucible in a horizontal tube furnace and evacuate to 10 -2 Pa, and then introduce 99.99% argon gas and replace it repeatedly for more than 3 times. Heat to 630℃ at a heating rate of 10℃ / min, keep it at this temperature for 5 hours, then cool it naturally to room temperature and take out the sample.

[0029] Example 2

[0030] This embodiment provides a method for preparing a diffusion coating modified with rare earth oxides, comprising the following steps: 1) Matrix Pretreatment: Use an EDM machine to machine the TiAl intermetallic compound matrix. After sanding with 400-grit sandpaper to remove rust, soak it in anhydrous ethanol solution and store it for later use. Remove the matrix, dry it, sandblast it, and then ultrasonically clean it with anhydrous ethanol for 15 minutes before drying it for later use.

[0031] 2) Preparation of penetrant: Prepare 100g of penetrant by mixing Al:Al2O3:NH4Cl:CeO2=30:65:3:2 (wt%), select CeO2 with a particle size of 10nm, and put the evenly mixed penetrant into a crucible.

[0032] 3) Coating preparation: Polish the substrate surface again and dry it, then quickly insert the substrate vertically into the middle and upper part of the penetrant. Then place the crucible in a horizontal tube furnace and evacuate to 10 -2 Pa, and then introduce 99.99% argon gas and replace it repeatedly for more than 3 times. Heat to 630℃ at a heating rate of 10℃ / min, keep it at this temperature for 5 hours, then cool it naturally to room temperature and take out the sample.

[0033] Comparative Example 1: In this comparative example, Y2O3 is selected to replace CeO2, and the remaining process steps and proportions are the same as those in Example 1.

[0034] Comparative Example 2: In this comparative example, Y2O3 is selected to replace CeO2, and the remaining process steps and proportions are the same as those in Example 1.

[0035] like Figure 1-6 As shown, The coating modified with rare earth element Ce in Example 1 has a dense, uniform surface, free of holes and cracks. The aluminide coating modified with Y in Comparative Example 1 has an uneven surface and exhibits holes. The aluminide coating modified with La has a relatively uniform surface, but exhibits cracks. The comparison shows that the Ce-modified aluminide coating has superior film quality to those modified with Y and La.

[0036] Example 1 The oxidation weight gain of the rare earth Ce modified coating is 0.3 mg / cm 2 h, significantly lower than the 1.2 mg / cm2 of the rare earth Y modified coating in Comparative Example 1. 2 ·h and comparative example 2 with rare earth La modified coating of 0.6 mg / cm 2 This result shows that the introduction of nano-cerium oxide significantly improves the oxidation resistance of the coating. Its excellent lattice distortion effect and vacancy generation mechanism provide preferential channels for the diffusion of aluminum atoms, thereby accelerating the formation of the aluminide coating.

[0037] The coating preparation method of the present invention is not only applicable to TiAl intermetallic compound matrices, but can also be extended to the field of surface protection of other high-temperature alloy materials. For example, in the application of nickel-based high-temperature alloys and cobalt-based high-temperature alloys, by adjusting the content of nano-cerium oxide in the infiltrant and the aluminum infiltration process parameters, the coating performance can be customized for different application scenarios. When higher antioxidant performance is required in a high-temperature environment, the amount of nano-cerium oxide added can be appropriately increased; when stronger thermal corrosion resistance is required in a salty environment, the coating quality can be further improved by extending the holding time. The process flexibility and adaptability of the present invention give it broad application prospects in the fields of aerospace, shipbuilding, chemical equipment, etc.

Claims

1. A method for preparing a diffusion coating modified by rare earth oxide, characterized in that: The following steps are involved: S1. Matrix pretreatment: The TiAl intermetallic compound matrix was processed into the desired shape, polished with 400-grit sandpaper to remove the surface oxide layer, cleaned with anhydrous ethanol, and then sandblasted. The matrix was ultrasonically cleaned with anhydrous ethanol for 15 minutes and dried. S2. Preparation of the penetrant: Weigh 20wt%-40wt% of an aluminum supply agent, 50wt%-80wt% of a filler, 2wt%-6wt% of an activator, and 1wt%-3wt% of a catalyst by weight, mix them evenly, and put them into a crucible, wherein the aluminum supply agent is aluminum powder, the filler is aluminum oxide, the activator is ammonium chloride, and the catalyst is nano-cerium oxide; S3, coating preparation: insert the pretreated substrate vertically into the middle and upper part of the penetrant, place the crucible in a horizontal tube furnace, and evacuate to 10 -2 Pa, introduce high-purity argon and replace it repeatedly for more than 3 times, heat to 630℃ at a heating rate of 10℃ / min, keep warm for 5 hours and then cool naturally to room temperature.

2. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The ratio of the aluminum supply agent to the filler is controlled between 1:1.5 and 1:

4.

3. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The particle size of the nano-cerium oxide is in the range of 10nm-50nm.

4. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The amount of ammonium chloride added as the activator is adjusted according to the volatility characteristics of the penetrant system, and the ammonia gas and hydrogen chloride gas generated by decomposition form a dynamic equilibrium in the system.

5. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: During the substrate pretreatment process, sandblasting is used to increase the surface roughness of the substrate to improve the mechanical bonding force between the coating and the substrate.

6. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The holding stage in the horizontal tube furnace is a critical period for aluminum atoms to quickly migrate to the surface of the substrate through the preferential channel provided by nano-cerium oxide.

7. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The mass ratio of the substrate to the penetrant is less than 1:50 to ensure that the penetrant is sufficient to form an aluminide coating.

8. The method for preparing a diffusion coating modified by rare earth oxide according to claim 1, characterized in that: The method is applicable to the field of surface protection of TiAl intermetallic compound matrix and other high-temperature alloy materials.

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