A modified aluminide coating based on ni2al3 powder, method of preparation and use thereof

Abstract

This invention discloses a modified aluminide coating based on Ni2Al3 powder, its preparation method, and its application, belonging to the field of high-temperature alloy surface protection technology. The invention uses Ni2Al3 powder and aluminum powder as the aluminum source, silicon powder and rare earth oxides as modifiers, and polyvinyl alcohol aqueous solution as a binder. These are mixed to form a slurry, which is then coated onto the surface of an alloy substrate. After high-temperature sintering, a coating is formed on the substrate surface. This invention introduces Ni2Al3 alloy powder to replace traditional pure Al powder as the aluminum source, fully utilizing the advantages of Ni2Al3 alloy powder, overcoming the limitations of existing coating preparation methods, and effectively improving the stability of the coating under high-temperature environments. It has significant engineering application value and broad industrial prospects in the field of anti-oxidation protection in high-temperature environments such as aero-engine turbine blades.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy surface protection technology, specifically relating to a modified aluminide coating based on Ni2Al3 powder, its preparation method, and its application. Background Technology

[0002] Nickel-based superalloys are widely used in turbine blades of aero-engines due to their excellent high-temperature mechanical properties. They can operate for extended periods in environments above 650°C, exhibiting excellent surface stability and good resistance to oxidation and high-temperature corrosion. However, at temperatures above 1000°C, nickel-based superalloys are prone to severe oxidation and corrosion, significantly shortening component lifespan. Therefore, a high-temperature protective coating is required on the alloy surface, and the coating preparation process must balance performance and efficiency to meet the demands of industrial mass production. Aluminide coatings can form a dense Al2O3 protective film at high temperatures, effectively blocking the corrosion of elements such as oxygen and sulfur, making it one of the most widely used coating types for nickel-based superalloys. Traditional slurry aluminizing often uses pure Al powder as the aluminum source, but pure Al powder has significant drawbacks: its high reactivity makes it prone to oxidation with air, forming an oxide film on the powder surface and affecting coating purity; pure Al powder particles are also prone to agglomeration, leading to uneven slurry dispersion and consequently, coating thickness fluctuations and insufficient density. To address the aforementioned issues, an attempt was made to mix Ni2Al3 powder with Al powder. Adding Al powder promotes liquid-phase sintering, improving the coating's sintering efficiency and interfacial adhesion with the substrate. However, variations in their ratio significantly impact the coating's structure and performance. When the Al powder ratio is too high, the reaction during high-temperature melting is violent, resulting in poor adhesion between the coating and the substrate. Conversely, when the Ni2Al3 powder ratio is too high, insufficient Al powder fails to promote good interfacial adhesion between the substrate and the coating. Only when the Ni2Al3 and Al powder ratios are within a specific range can the coating achieve a suitable growth rate and a dense microstructure. Ni2Al3 alloy powder, as an aluminum source, offers significant advantages: first, it can rapidly form a uniform and dense aluminide protective layer on the substrate surface; second, Ni2Al3 powder particles exhibit better stability, are less prone to agglomeration, and reduce air bubbles in the slurry. In addition, compared with CVD, embedding aluminizing and other processes, the slurry melting method has significant advantages such as simple process, high production efficiency and low cost. It does not require complex processes and long reaction cycles, and can achieve rapid batch preparation of coatings, which has significant advantages in the preparation of aluminide coatings.

[0003] To further improve the high-temperature oxidation resistance and structural stability of aluminide coatings, multi-element composite modification and gradient structures are often employed. The addition of Si can promote the formation of the β-NiAl phase in the coating, inhibit the formation of brittle phases, and reduce the formation of Kirkendal pores during oxidation, thus delaying coating failure. Rare earth element modification (such as Y, Ce, and La) can refine the coating grains and improve the adhesion of the oxide film. Gradient coating design achieves gradient control of modifying elements in the coating by changing the coating composition and controlling the slurry ratio from the surface to the interior. However, the preparation of modified aluminide coatings still has many shortcomings. Pure Al powder, as the aluminum source, has high reactivity, making the reaction process difficult to control. Inappropriate binder selection can easily lead to poor slurry dispersion, weak bonding between the coating layer and the substrate, and defects such as cracks and pores during sintering. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a modified aluminide coating based on Ni2Al3 powder, its preparation method, and its application. This invention solves the technical problems in existing technologies where using pure aluminum powder as the aluminum source results in high reactivity, easy oxidation and agglomeration, poor coating density, insufficient bonding strength with the substrate, and poor slurry dispersion, weak coating adhesion, and easy generation of cracks and pores during sintering due to unreasonable selection of binders.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a modified aluminide coating based on Ni2Al3 powder includes the following steps: Step 1, preparing the adhesive: Mix polyvinyl alcohol with water and heat to obtain a polyvinyl alcohol aqueous solution.

[0006] Step 2, preparation of slurry: Mix Ni2Al3 powder, Al powder, Si powder, Y2O3 powder and polyvinyl alcohol aqueous solution, and ball mill to obtain slurry.

[0007] Step 3, substrate preparation: The high-temperature alloy substrate is successively ground, chamfered, ultrasonically cleaned and dried.

[0008] Step 4, Coating preparation: The slurry obtained in Step 2 is coated onto the surface of the high-temperature alloy substrate and cured to form a single-layer slurry layer; then, slurry is uniformly coated onto the single-layer slurry layer and cured; the above coating and curing operations are repeated until the required number of slurry layers is reached, and then final curing is performed to obtain a material with a slurry layer.

[0009] Step 5, high-temperature sintering: The material with slurry layer obtained in step 4 is placed in a vacuum environment for sintering; after sintering, it is cooled with the furnace to obtain a material with a modified aluminide coating.

[0010] This invention also protects a modified aluminide coating based on Ni2Al3 powder prepared by the method described above, comprising an inner layer and an outer layer. The outer layer comprises a NiAl phase, a Cr-Si compound phase, and Y2O3, and the inner layer comprises a NiAl phase, a TCP phase, and a carbide phase. It is prepared using the following raw materials: 35–46 wt.% Ni2Al3 powder, 1–5 wt.% Al powder, 1–7 wt.% Si powder, 0.5–3 wt.% Y2O3 powder, 2–5 wt.% polyvinyl alcohol, and 40–54.5 wt.% water. The solid-liquid ratio of the raw material slurry is (45.5–60 wt.%):(54.5–40 wt.%).

[0011] The present invention also protects the application of the modified aluminide coating based on Ni2Al3 powder as described above as a protective coating for alloy surfaces in aerospace applications.

[0012] The present invention also has the following technical features: Specifically, in step one, the heating method is water bath heating.

[0013] Specifically, in step one, the heating temperature is 80–95°C, and the heating time is 1–1.5 h. Preferably, the heating temperature is 95°C, and the heating time is 1 h.

[0014] Specifically, in step one, the preferred mass ratio of polyvinyl alcohol to water is (4-6):(94-96). More preferably, the mass ratio of polyvinyl alcohol to water is 5:95.

[0015] Specifically, in step two, the ball milling speed is 200–400 rpm, and the ball milling time is ≥4 hours. Preferably, the ball milling speed is 400 rpm, and the ball milling time is 5 hours.

[0016] Preferably and optionally, in step two, the slurry is a type of material in which the mass ratio of Ni2Al3 powder, Al powder, Si powder, Y2O3 powder and polyvinyl alcohol aqueous solution is (38-40):(1-2):(2-3):1:(55-57).

[0017] Preferably and optionally, in step two, the slurry is of two types: an inner slurry and an outer slurry; in the inner slurry, the mass ratio of Ni2Al3 powder, Al powder, Si powder, Y2O3 powder, and polyvinyl alcohol aqueous solution is 40:2:2:1:55; in the outer slurry, the mass ratio of Ni2Al3 powder, Al powder, Si powder, Y2O3 powder, and polyvinyl alcohol aqueous solution is 39.5:2:4:0.5:54.

[0018] Specifically, in step three, the high-temperature alloy matrix is ​​a nickel-based high-temperature alloy. Preferably, the high-temperature alloy matrix is ​​a K447A nickel-based high-temperature alloy.

[0019] Specifically, in step three, the high-temperature alloy substrate is polished using 80-400 grit SiC sandpaper.

[0020] Preferably and optionally, when the slurry in step two is of one type, each slurry layer in step four is formed using that type of slurry.

[0021] Preferably and optionally, when there are two types of slurry in step two, the innermost slurry layer in step four is made from the inner slurry, and the other layers are made from the outer slurry.

[0022] Specifically, in step four, the slurry is applied by brushing or dipping, and the number of applications is 2 to 5.

[0023] Specifically, in step four, the curing temperature is 100℃~120℃, and the curing time is 10~20min. Preferably, the curing temperature is 100℃, and the curing time is 15min.

[0024] Specifically, in step four, the final curing temperature is 100℃~120℃, and the final curing time is 60~90min. Preferably, the final curing temperature is 100℃, and the final curing time is 90min.

[0025] Specifically, in step four, the mass per unit area of ​​the slurry layer is 20–30 mg / cm³. 2 .

[0026] Specifically, in step five, the vacuum level of the vacuum environment is 1×10⁻⁶. -3 ~3×10 -3 Pa.

[0027] Specifically, in step five, the sintering conditions are as follows: first, the temperature is increased to 300–500°C at a rate of 4–6°C / min, and held for 1–2 hours; then, the temperature is increased to 950–1150°C at a rate of 8–12°C / min, and held for 1–2 hours. Preferably, the sintering conditions are as follows: first, the temperature is increased to 500°C at a rate of 5°C / min, and held for 1 hour; then, the temperature is increased to 1000–1100°C at a rate of 10°C / min, and held for 1 hour.

[0028] Specifically, in step five, the thickness of the modified aluminide coating is 40–60 μm. Preferably, the thickness of the modified aluminide coating is 50 μm.

[0029] Compared with the prior art, the present invention has the following technical effects: (I) This invention uses a mixture of Ni2Al3 alloy powder and Al powder as an aluminum source, and adds Si powder and rare earth oxides as modifiers to directly prepare a multi-component modified aluminum compound coating by slurry melting method. This eliminates the complicated pretreatment steps in the traditional embedding and infiltration method, eliminates the need for long-term homogenization heat treatment, and shortens the slurry melting process, thus greatly improving the efficiency of coating preparation.

[0030] (II) The coating obtained by the method of the present invention is dense, tightly bonded to the substrate, and has a dark gray surface, providing reliable protection. Combined with optimized pretreatment and coating methods, it can accelerate the evaporation of moisture in the slurry, prevent the formation of bubbles in the coating, improve coating uniformity, effectively reduce defects such as cracks, and further ensure coating quality.

[0031] (III) The slurry used in this invention is composed of Ni2Al3 alloy powder, Al powder, Si powder, rare earth oxide powder, polyvinyl alcohol and deionized water. It is non-toxic and dust-free during the coating process and does not release toxic gas products. After high-temperature heating treatment, the organic matter in the slurry is completely decomposed and volatilized, and the final aluminum oxide coating is free of impurities, significantly improving the purity of the coating.

[0032] (IV) This invention is not only applicable to the preparation of Si and rare earth modified aluminide coatings, but can also generate aluminide coatings modified with other elements by adding other modified powders to Ni2Al3 powder. Furthermore, this process can achieve localized coating of workpieces, adapting to the protection requirements of parts of different specifications. The coating operation can be completed at room temperature, and the process is simple and efficient.

[0033] (V) This invention introduces Ni2Al3 alloy powder to replace traditional pure Al powder as the aluminum source, giving full play to the advantages of Ni2Al3 alloy powder, solving the limitations in existing coating preparation, and effectively improving the stability of the coating in high-temperature environments. It has important engineering application value and broad industrialization prospects in the field of anti-oxidation protection in high-temperature environments such as aero-engine turbine blades. Attached Figure Description

[0034] Figure 1 This is a cross-sectional microstructure diagram of the Si / Y co-modified aluminide coating of Example 1 of the present invention.

[0035] Figure 2 This is a cross-sectional microstructure image of the Si / Y co-modified aluminide coating after a high-temperature oxidation test in Example 1 of this invention.

[0036] Figure 3 This is a microscopic morphology image of the surface of the Si / Y co-modified aluminide coating after an oxidation resistance test in Example 1 of the present invention.

[0037] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0038] It should be noted that all raw materials used in this invention, unless otherwise specified, are those known in the art. For example, the molecular weight of polyethanol is 77,000 g / mol (this molecular weight is obtained by multiplying the degree of polymerization by the molecular unit; the degree of polymerization is approximately 1750, and the molecular weight of a single unit is 44.05).

[0039] The coating slurry of this invention is composed of the following raw materials: Ni2Al3 alloy powder, Al powder, Si powder, Y2O3 powder, polyvinyl alcohol, and deionized water; wherein, the composite aluminum source of Ni2Al3 powder and Al powder is the core component of the slurry. Compared with pure aluminum powder, the alloy powder can form a more uniform slurry during mixing and ball milling, significantly reducing air bubbles in the slurry and cracks and unevenness during the coating process. Polyvinyl alcohol, as an environmentally friendly and easily degradable water-soluble binder, has good adhesion and dispersibility, which can effectively prevent slurry agglomeration and shorten the slurry preparation cycle. Using polyvinyl alcohol aqueous solution as a binder can fully adsorb Ni2Al3 powder and Al powder to form a slurry with moderate viscosity and uniformity.

[0040] Following the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solution of this application fall within the protection scope of the present invention.

[0041] Example 1 This embodiment provides a method for preparing a modified aluminide coating based on Ni2Al3 powder to form a multi-component modified aluminide coating on the surface of a nickel-based superalloy substrate, including the following steps: Step 1, preparing the binder: Mix polyvinyl alcohol with deionized water and heat in a water bath at 95°C for 1 hour. The mass fraction ratio of polyvinyl alcohol to water is 5%:95%. Obtain a polyvinyl alcohol aqueous solution with suitable viscosity to be used as the binder for the slurry.

[0042] Step 2, prepare slurry: Mix Ni2Al3 powder, Al powder, Si powder, Y2O3 powder and the polyvinyl alcohol aqueous solution obtained in step 1 in a mass fraction ratio of 40%:2%:2%:1%:55%, mix evenly, ball mill for 5 hours at a ball milling speed of 400 rpm to obtain a uniform slurry for later use.

[0043] Step 3, Matrix Preparation: A matrix sample measuring 20mm × 10mm × 2mm was cut from the K447A nickel-based superalloy using wire electrical discharge machining. The alloy matrix sample was then polished and chamfered using 80# to 400# SiC sandpaper. Afterward, the sample was ultrasonically cleaned and dried.

[0044] Step four, prepare the slurry layer: Apply the slurry from step two to each surface of the sample using a brush, and dry it in a 100℃ oven for 15 minutes to form a layer with a unit area mass of approximately 5 mg / cm². 2 The first layer of slurry is applied. Another layer of slurry is then evenly applied over the first layer, and this process is repeated until the final layer is applied. The sample is then dried in a 100°C oven for 90 minutes to obtain a mass per unit area of ​​approximately 25 mg / cm³. 2 The slurry layer.

[0045] Step 5, High-temperature sintering: Place the dried slurry sample from Step 4 under a vacuum of 2*10 -3 In an environment of Pa, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 hour, then increased to 1000℃ at a rate of 10℃ / min and held for 1 hour. The sample is then cooled to room temperature in the furnace and removed.

[0046] In this embodiment, the microstructure of the finally obtained modified aluminide coating sample was observed, and the results are as follows: Figure 1 As shown, the slurry forms a coating with a thickness of about 50 μm after sintering, which has a double-layer structure: the outer layer is composed of β-NiAl phase and Cr-Si compound, with a small amount of Y2O3 at the top and on the surface of the coating; the inner layer is composed of β-NiAl phase + topologically close-packed phase (TCP phase) + carbide phase.

[0047] In this embodiment, the modified aluminide coating sample was subjected to an oxidation resistance test (held at 1150℃ for 20h). Figure 2 The cross-sectional microstructure of the coating after oxidation is shown. It can be seen that after the sample was oxidized at 1150℃ for 20h, the coating was still intact and dense, and there was no peeling or cracking on the surface of the coating. Figure 3 The image shows the surface microstructure of the coating after oxidation. A dense Al2O3 film is visible on the surface, with a small amount of Y2O3 mixed in. There are no other oxidation products and no obvious defects such as cracks or holes.

[0048] Example 2 This embodiment provides a method for preparing a modified aluminide coating based on Ni2Al3 powder, including the following steps: Step 1, preparing the binder: Mix polyvinyl alcohol with deionized water and heat in a water bath at 95°C for 1 hour. The mass fraction ratio of polyvinyl alcohol to water is 5%:95%. Obtain a polyvinyl alcohol aqueous solution with suitable viscosity to be used as the binder for the slurry.

[0049] Step 2, slurry preparation: The inner layer slurry is prepared by uniformly mixing Ni₂Al₃ powder, Al powder, Si powder, Y₂O₃ powder, and the polyvinyl alcohol aqueous solution obtained in Step 1, with a mass fraction ratio of 40%:2%:2%:1%:55%. The outer layer slurry is prepared by uniformly mixing Ni₂Al₃ powder, Al powder, Si powder, Y₂O₃ powder, and the polyvinyl alcohol aqueous solution obtained in Step 1, with a mass fraction ratio of 39.5%:2%:4%:0.5%:54%. Both slurries are mixed uniformly and ball-milled for 5 hours at 400 rpm to obtain a homogeneous slurry for later use.

[0050] Step 3, substrate preparation: The process flow for this step is the same as in Example 1.

[0051] Step 4, Preparation of the slurry layer: Apply the inner layer slurry from Step 2 to each surface of the sample using a brush, and dry in a 100℃ oven for 30 minutes to form a sample with a unit area mass of approximately 10 mg / cm². 2 The inner layer of slurry is applied; then the outer layer of slurry is evenly coated on top of the inner layer, until the final layer of slurry is applied; the sample is then dried in an oven at 100℃ for 60 minutes to obtain a unit area mass of 30 mg / cm³. 2 The slurry layer.

[0052] Step 5, High-temperature sintering: Place the dried slurry sample from Step 4 under a vacuum of 2*10 -3 In an environment of Pa, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 1 hour, then increased to 1050℃ at a rate of 10℃ / min and held for 1 hour. The sample was then cooled to room temperature in the furnace and removed.

[0053] The modified aluminide coating samples obtained above were subjected to microscopic morphology observation and oxidation resistance test (1150℃ for 20h). The results showed that the Al2O3 film on the coating surface was dense, with a small amount of Y2O3 dispersed on the surface, no obvious defects in the oxide film, and the coating structure was stable.

[0054] Example 3 This embodiment provides a method for preparing a modified aluminide coating based on Ni2Al3 powder, including the following steps: Step 1, preparing the binder: Mix polyvinyl alcohol with deionized water and heat in a water bath at 95°C for 1 hour. The mass fraction ratio of polyvinyl alcohol to water is 5%:95%. Obtain a polyvinyl alcohol aqueous solution with suitable viscosity to be used as the binder for the slurry.

[0055] Step 2, prepare slurry: Mix Ni2Al3 powder, Al powder, Si powder, Y2O3 powder and the polyvinyl alcohol aqueous solution obtained in step 1 in a mass fraction ratio of 38%:1%:3%:1%:57% evenly, ball mill for 5 hours at a ball milling speed of 400 rpm to obtain a uniform slurry for later use.

[0056] Step 3, substrate preparation: The process flow for this step is the same as in Example 1.

[0057] Step 4, prepare the slurry layer: The process flow for this step is the same as in Example 1.

[0058] Step 5, High-temperature sintering: Place the dried slurry sample from Step 4 under a vacuum of 2*10 -3 In an environment of Pa, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 1 hour, then increased to 1100℃ at a rate of 10℃ / min and held for 1 hour. The sample was then cooled to room temperature in the furnace and removed.

[0059] The modified aluminide coating samples obtained above were subjected to microscopic morphology observation and oxidation resistance test (1150℃ for 20h). The results showed that the coating had good oxidation resistance, the surface Al2O3 film was dense and without obvious defects, and Y2O3 was dispersed on the oxide film surface.

Claims

1. A method for preparing a modified aluminide coating based on Ni2Al3 powder, characterized in that, The method includes: mixing aluminum source, silicon source, rare earth oxide and binder to prepare a slurry, coating it on the surface of an alloy substrate, and then sintering it at high temperature to form a coating on the substrate surface; The aluminum source is Ni2Al3 powder and aluminum powder; the silicon source is silicon powder; the rare earth oxide is yttrium oxide; and the binder is an aqueous solution of polyvinyl alcohol.

2. The method for preparing a modified aluminide coating based on Ni2Al3 powder as described in claim 1, characterized in that, The method includes the following steps: Step 1, preparing the adhesive: Polyvinyl alcohol is mixed with water and heated to obtain the adhesive; Step 2, preparation of slurry: Ni2Al3 powder, aluminum powder, silicon powder, yttrium oxide and polyvinyl alcohol aqueous solution are mixed and ball-milled to obtain slurry; Step 3, substrate preparation: The high-temperature alloy substrate is successively ground, chamfered, ultrasonically cleaned and dried; Step 4, Coating preparation: The slurry obtained in Step 2 is coated onto the surface of the high-temperature alloy substrate and cured to form a single-layer slurry layer; then, slurry is uniformly coated onto the single-layer slurry layer and cured; the above coating and curing operations are repeated until the required number of slurry layers is reached, and then final curing is performed to obtain a material with a slurry layer. Step 5, high-temperature sintering: The material with slurry layer obtained in step 4 is placed in a vacuum environment for sintering; after sintering, it is cooled with the furnace to obtain a material with a modified aluminide coating.

3. The method for preparing a modified aluminide coating based on Ni2Al3 powder as described in claim 2, characterized in that, In step two, the ball milling speed is 200-400 rpm, and the ball milling time is at least 4 hours.

4. The method for preparing a modified aluminide coating based on Ni2Al3 powder as described in claim 2, characterized in that, In step four, the curing temperature is 100℃~120℃ and the curing time is 10~20min; the final curing temperature is 100℃~120℃ and the final curing time is 60~90min.

5. The method for preparing a modified aluminide coating based on Ni2Al3 powder as described in claim 2, characterized in that, In step five, the sintering conditions are as follows: first, heat the temperature to 300-500℃ at a rate of 4-6℃ / min and hold for 1-2 hours, then heat the temperature to 950-1150℃ at a rate of 8-12℃ / min and hold for 1-2 hours.

6. The method for preparing a modified aluminide coating based on Ni2Al3 powder as described in claim 2, characterized in that, In step two, the slurry may be one type or two types; When the slurry in step two is of one type, each slurry layer in step four shall be formed using that type of slurry. When there are two types of slurry in step two, namely inner slurry and outer slurry, the innermost slurry layer in step four is made from the inner slurry, and all other layers are made from the outer slurry.

7. A modified aluminide coating based on Ni2Al3 powder prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The following raw materials were used to prepare the product: Ni₂Al₃ powder 35–46 wt.%, Al powder 1–5 wt.%, Si powder 1–7 wt.%, Y₂O₃ powder 0.5–3 wt.%, polyvinyl alcohol 2–5 wt.%, and water 40–54.5 wt.%. Ni2Al3 powder and Al powder are used as aluminum sources, Si powder and Y2O3 powder are used as modifiers, and a mixture of polyvinyl alcohol and water is used as a binder.

8. The modified aluminide coating based on Ni2Al3 powder prepared by the method described in claim 7, characterized in that, The coating thickness is 40–60 μm.

9. The modified aluminide coating based on Ni2Al3 powder as described in claim 8 is used as a protective coating for alloy surfaces in aerospace applications.

10. The application as described in claim 9, characterized in that, The alloy is a nickel-based high-temperature alloy.

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