Method for preparing Al2O3 / Ni (Al, Si) / Al2O3 composite coating on surface of nickel-based high-temperature alloy

Abstract

The invention discloses a method for preparing an Al2O3 / Ni (Al, Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy. The method comprises the following steps: 1, carrying out oil removal cleaning and plating assistance on the surface of the nickel-based superalloy; secondly, a pure aluminum liquid melt pool and an Al-Si alloy liquid melt pool are arranged in a hot dipping box protected by argon; 3, forming a dendritic Ni-Al intermediate phase and Al-Si liquid phase mixed layer on the surface of the nickel-based high-temperature alloy by adopting a two-step hot dipping method; and fourthly, the nickel-based high-temperature alloy subjected to two-step hot dipping is subjected to long-time high-temperature pre-oxidation, and finally the Al2O3 / Ni (Al, Si) / Al2O3 composite coating is obtained on the surface of the nickel-based high-temperature alloy. The method of combining two-step hot dipping and long-time high-temperature pre-oxidation treatment is adopted, the coating has excellent high-temperature oxidation resistance, and the preparation method is simple, convenient, low in cost and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of nickel-based high-temperature alloy surface treatment, and in particular to a method for preparing an Al2O3 / Ni(Al, Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy. Background Art

[0002] Nickel-based superalloys, due to their excellent casting properties, high-temperature strength, and excellent heat-corrosion resistance, are widely used in critical hot-end components of aerospace engines and gas turbines, such as those in modern aerospace engines, spacecraft, and rocket engines. Despite their numerous excellent properties and widespread use in aerospace, nickel-based superalloys also have some drawbacks. The aluminum content in these alloys is typically low, which limits their ability to form a continuous, stable Al2O3 protective film at high temperatures. This is one of the key factors limiting the long-term service life of nickel-based superalloys in high-temperature environments. Therefore, to improve the high-temperature oxidation resistance of nickel-based superalloys, various surface modification methods have been employed. Initially, a layer of aluminum coating was formed on the surface of nickel-based superalloys, aiming to produce a dense Al2O3 film and a NiAl phase, as the NiAl intermetallic compound has a high melting point and excellent stability and oxidation resistance.

[0003] However, single aluminide coatings are prone to degradation, making them unable to meet the requirements of long-term service at high temperatures. Studies have shown that adding Si to the surface of aluminide coatings can help form a dense Al2O3 protective film, thereby extending the coating's service life. However, directly introducing Si can lead to uneven Si-enriched layers in the aluminide coating, resulting in varying degrees of Al oxidation. This allows other elements, such as Ni, to diffuse outward from the coating, ultimately causing the oxide layer to flake off.

[0004] In thermal barrier coating systems, the TGO layer (Thermally Grown Oxide) at the interface between the bonding layer and the ceramic layer is one of the key factors for the coating's excellent high-temperature oxidation resistance, while traditional diffused aluminide coatings do not have a TGO layer. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy. This method utilizes a step-by-step coating process, first hot-dip plating pure aluminum and then hot-dip plating Al-Si, to form a dendritic Ni(Al,Si)3 phase. This is then followed by a high-temperature pre-oxidation treatment, ultimately forming a stable multiphase layer structure on the surface of the nickel-based high-temperature alloy. From the substrate outward, the structure comprises a thermally grown oxide Al2O3 layer (TGO), a Ni(Al,Si) layer, and an Al2O3 oxide film. The present invention is suitable for preparing Al2O3 / Ni(Al,Si) / Al2O3 composite coatings on nickel-based high-temperature alloy workpieces. A TGO layer forms at the junction of the coating and the substrate, giving the coating excellent thermal stability and high-temperature oxidation resistance. The present method also offers the advantages of ease of implementation and low cost.

[0006] Another object of the present invention is to provide a method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy, characterized in that the preparation method comprises the following steps:

[0007] Step 1: Degrease and clean the surface of the nickel-based high-temperature alloy with a metal cleaning agent, then immerse it in a plating flux of NaF:KF:KCl:deionized water (mass ratio) heated in a 90°C water bath for 3 minutes, remove it and place it in a drying oven to dry;

[0008] Step 2: Two independently temperature-controlled melt pools are placed in a hot-dip plating box filled with argon protection. Melt pool 1 contains pure aluminum liquid, and melt pool 2 contains Al-Si alloy liquid with a Si content of 10-20wt.%;

[0009] Step 3: immerse the nickel-based superalloy with the flux coated on the surface in step 1 into pure aluminum liquid for hot dip plating. After holding the nickel-based superalloy for a certain period of time, quickly extract the nickel-based superalloy from the pure aluminum liquid and then quickly immerse the nickel-based superalloy in Al-Si alloy liquid for hot dip plating. After holding the nickel-based superalloy for a certain period of time, extract the nickel-based superalloy from the Al-Si alloy liquid, remove excess hot dip plating liquid from the surface of the nickel-based superalloy, quench with water, and then dry.

[0010] Step 4: Place the nickel-based high-temperature alloy that has undergone two-step hot-dip plating in step 3 in a box furnace for long-term high-temperature pre-oxidation treatment, and finally obtain an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of the nickel-based high-temperature alloy.

[0011] A preparation scheme for an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on a nickel-based high-temperature alloy surface that is subjected to two-step hot-dip plating followed by high-temperature pre-oxidation is disclosed. The method comprises the following steps: first, hot-dip plating pure aluminum liquid on the nickel-based high-temperature alloy, and then hot-dip plating Al-Si alloy liquid to introduce Si atoms, thereby forming a dendritic Ni(Al,Si)3 phase; and then performing a high-temperature pre-oxidation treatment. Ultimately, a stable multiphase layer structure is formed on the nickel-based high-temperature alloy surface, comprising a thermally grown oxide layer Al2O3 layer, a Ni(Al,Si) layer, and an Al2O3 oxide film layer from the substrate outward.

[0012] The preparation scheme of the Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of the nickel-based high-temperature alloy after two-step hot-dip plating and high-temperature pre-oxidation of the present invention combines the advantages of the two-step hot-dip plating method and the high-temperature pre-oxidation method. By controlling the two-step hot-dip plating temperature and the two-step hot-dip plating time, the content of the generated Ni(Al,Si)3 phase is controlled, thereby forming a protective coating composed of the Ni(Al,Si)3 phase and the Al-Si liquid phase residual from the hot-dip plating step on the surface of the nickel-based high-temperature alloy. The high-temperature pre-oxidation treatment is then performed to allow the nickel-based high-temperature alloy coating to continue to undergo diffusion reaction to form a stable multi-phase layer structure. From the substrate to the outside, there are respectively a thermally grown oxide layer Al2O3 layer, a Ni(Al,Si) layer and an Al2O3 oxide film layer. The formed thermally grown oxide layer Al2O3 layer can greatly improve the high-temperature oxidation resistance of the coating. In addition, the coating has good thermal stability, a simple preparation process and low cost, which can greatly improve the operating temperature and service life of the nickel-based high-temperature alloy workpiece.

[0013] The present invention can also control the Si concentration in the Al-Si alloy solution and the content of the Ni-Al compound phase by controlling the two-step hot-dip plating temperature and the two-step hot-dip plating time according to actual use requirements. The thickness of the Ni(Al,Si) phase layer can also be controlled by controlling the high-temperature pre-oxidation time and temperature. Therefore, the Ni(Al,Si) phase layer formed by the high-temperature pre-oxidation after the two-step hot-dip plating is controllable.

[0014] The above-mentioned method for preparing Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of nickel-based high-temperature alloy is characterized in that the protective coating composed of dendritic Ni(Al,Si)3 phase and residual Al-Si liquid phase generated after the two-step hot dip plating in step three has a thickness of 30-50 microns.

[0015] The above-mentioned method for preparing Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of nickel-based high-temperature alloy is characterized in that the temperature of hot-dip plating in pure aluminum liquid in step 3 is 700-800℃ and the hot-dip plating time is 60-150 seconds; then the temperature of hot-dip plating in Al-Si alloy liquid is 700-800℃ and the hot-dip plating time is 60-150 seconds. The above-mentioned temperature range can ensure that the hot-dip plating is mainly an internal diffusion reaction, ensuring the formation of the target product NiAl3 phase after hot-dip plating, while avoiding the occurrence of external diffusion reaction to form Kirkendall holes. The above-mentioned hot-dip plating time range can control the NiAl3 phase content and the Si element content in the coating, and obtain the above-mentioned protective coating with a thickness of 30-50 microns composed of the Ni(Al,Si)3 phase and the Al-Si liquid phase residual from the hot-dip plating step. It ensures the formation of a uniform Ni(Al,Si) phase during the subsequent long-term high-temperature pre-oxidation treatment, which is beneficial to the high-temperature oxidation resistance of the Al2O3 / Ni(Al,Si) / Al2O3 composite coating and avoids the waste of raw materials.

[0016] The above-mentioned method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy is characterized in that the thickness of the multiphase layer structure described in step 4 is 40-70 microns.

[0017] The above-mentioned method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of a nickel-based high-temperature alloy is characterized in that the long-term high-temperature pre-oxidation temperature described in step 4 is 950°C-1000°C, and the long-term high-temperature pre-oxidation time is 15-20 hours. The above-mentioned long-term high-temperature pre-oxidation temperature ensures the integrity of the substrate, preventing temperatures exceeding the phase transition point from destroying the original structure of the substrate and seriously reducing the mechanical properties of the material. At the same time, it can also ensure that the residual Al-Si liquid phase in the coating continues to undergo internal diffusion reaction, thereby forming a stable multiphase layer structure. The above-mentioned long-term high-temperature pre-oxidation time ensures that the diffusion reaction in the coating is complete, forming a stable multiphase layer structure, and at the same time ensures that the TGO layer in the coating is stable and continuous. The above-mentioned long-term high-temperature pre-oxidation time ensures the sufficient formation of the Al2O3 / Ni(Al,Si) / Al2O3 composite coating.

[0018] Compared with the patent application number CN201410687157.6 "A Si-modified β-(Ni, Pt)Al coating and its preparation method", the Al2O3 / Ni(Al, Si) / Al2O3 composite coating and its preparation method of the present invention have the following advantages:

[0019] 1. The present invention first hot-dip-plates pure aluminum on the surface of a nickel-based high-temperature alloy. After the nickel and aluminum fully react, a NiAl3 intermediate phase is first generated. Al-Si is then hot-dip-plated to introduce Si atoms to obtain a Ni(Al,Si)3 phase. A long-term high-temperature pre-oxidation treatment is then performed to form a multi-phase layer structure. From the substrate outward, there are a thermally grown oxide layer Al2O3 layer, a Ni(Al,Si) phase layer, and an Al2O3 protective film layer. The presence of a thermally grown oxide layer in the coating ensures the high-temperature oxidation resistance of the Al2O3 / Ni(Al,Si) / Al2O3 composite coating. At the same time, the present invention uses a two-step hot-dip plating method combined with a long-term high-temperature pre-oxidation method to greatly reduce process costs, making it more economically suitable for industrial production applications.

[0020] 2. The method of the present invention is simple and easy to implement, and can be effectively promoted and applied to fields with high requirements for comprehensive performance of nickel-based high-temperature corrosion resistance, high-temperature thermal corrosion resistance, etc.

[0021] Zang et al. (Corrosion Science 2016) demonstrated that aluminide coatings modified with Si added to the surface of nickel-based superalloys can effectively improve their high-temperature oxidation resistance. The coating exhibits a multiphase structure, consisting of a Ni-Al interphase layer and an Al2O3 protective film from the substrate outward. The Al2O3 / Ni(Al,Si) / Al2O3 composite coating of the present invention maintains a multiphase structure while ensuring the economical preparation process. Furthermore, a TGO layer appears at the junction of the coating and the substrate, effectively improving the coating's high-temperature oxidation resistance.

[0022] The Al2O3 / Ni(Al,Si) / Al2O3 composite coating of the present invention and the coating in the patent application number CN202411486632.3 "A method for preparing a thermal barrier coating" both have a TGO layer in their structure, which ensures the coating's resistance to high-temperature oxidation.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and implementation examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the technical principle of the method for preparing the Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of the nickel-based high-temperature alloy of the present invention.

[0025] Figure 2 This is a microstructural morphology of the protective coating obtained by two-step hot-dip plating of the nickel-based high-temperature alloy in Example 2.

[0026] Figure 3 This is a microstructural morphology of the Al2O3 / Ni(Al,Si) / Al2O3 composite coating obtained after long-term high-temperature pre-oxidation of the nickel-based high-temperature alloy in Example 2. DETAILED DESCRIPTION

[0027] The Al2O3 / Ni(Al,Si) / Al2O3 composite coating prepared on the surface of the nickel-based superalloy can be variously designed according to actual use requirements. The Si concentration gradient in the Al-Si alloy solution and the content of the Ni-Al compound phase can be controlled by controlling the two-step hot-dip plating temperature and the two-step hot-dip plating time. The thickness of the Ni(Al,Si) phase layer can also be controlled by controlling the high-temperature pre-oxidation time and temperature. Therefore, the Al2O3 / Ni(Al,Si) / Al2O3 composite coating prepared on the nickel-based superalloy has good controllability.

[0028] Implementation Example 1

[0029] like Figure 1 As shown, the preparation method of this embodiment includes the following steps:

[0030] Step 1: Use a metal cleaning agent to clean and degrease the surface of the pretreated K447A nickel-based high-temperature alloy sample, then immerse it in a 90°C plating flux of NaF:KF:KCl:deionized water = 1:2:2:15 (mass ratio) for 3 minutes, take it out and place it in a drying oven for drying;

[0031] Step 2: Place two independently temperature-controlled melt pools in an argon-filled hot-dip plating chamber. Melt pool 1 contains pure aluminum liquid, and melt pool 2 contains an Al-Si alloy liquid with a Si content of 10 wt%. The temperature of both melt pools is set at 700°C.

[0032] Step 3: Immerse the K447A nickel-based superalloy sample coated with the flux in Step 1 in pure aluminum molten metal for hot-dip plating. After holding the sample for 60 seconds, remove the sample from the pure aluminum molten metal and then quickly immerse it in molten Al-Si alloy for hot-dip plating. After holding the sample for 60 seconds, remove the sample from the Al-Si alloy molten metal and remove excess hot-dip plating solution from the surface of the K447A nickel-based superalloy. The sample is then water-quenched and dried. The protective coating composed of the aforementioned dendritic Ni(Al,Si)3 phase and residual Al-Si liquid phase is formed to a thickness of 35 microns.

[0033] Step 4: The K447A nickel-based superalloy, which has undergone two hot-dip plating steps in Step 3, is placed in a box-type furnace for a long, high-temperature pre-oxidation treatment. This treatment ultimately forms a stable multiphase structure on the surface of the K447A nickel-based superalloy, consisting of a thermally grown Al2O3 layer, a Ni(Al,Si) layer, and an Al2O3 oxide film, extending from the substrate. The long, high-temperature pre-oxidation treatment is performed at 950°C for 15 hours. The resulting Al2O3 / Ni(Al,Si) / Al2O3 composite coating has a thickness of 50 microns.

[0034] Implementation Example 2

[0035] like Figure 1 As shown, the preparation method of this embodiment includes the following steps:

[0036] Step 1: Use a metal cleaning agent to clean and degrease the surface of the pretreated K447A nickel-based high-temperature alloy sample, then immerse it in a 90°C plating flux of NaF:KF:KCl:deionized water = 1:2:2:15 (mass ratio) for 3 minutes, take it out and place it in a drying oven for drying;

[0037] Step 2: Place two independently temperature-controlled melt pools in an argon-filled hot-dip plating chamber. Melt pool 1 contains pure aluminum liquid, and melt pool 2 contains an Al-Si alloy liquid with a Si content of 10 wt%. The temperatures of both melt pools are set at 750°C.

[0038] Step 3: Immerse the K447A nickel-based superalloy sample, coated with flux in Step 1, in pure aluminum molten metal for hot-dip plating. After holding the sample for 90 seconds, remove the sample from the pure aluminum molten metal and then quickly immerse it in molten Al-Si alloy for hot-dip plating. After holding the sample for 60 seconds, remove the sample from the Al-Si alloy molten metal, remove excess hot-dip plating solution from the surface of the K447A nickel-based superalloy, and quench the sample in water before drying. The protective coating composed of the aforementioned dendritic Ni(Al,Si)3 phase and residual Al-Si liquid phase is formed to a thickness of 40 microns.

[0039] Step 4: The K447A nickel-based superalloy, which had undergone two hot-dip plating steps in Step 3, was placed in a box-type furnace for a long, high-temperature pre-oxidation treatment. This treatment ultimately resulted in a stable multiphase structure on the surface of the K447A nickel-based superalloy, consisting of a thermally grown Al2O3 layer, a Ni(Al,Si) layer, and an Al2O3 oxide film, extending from the substrate outward. The long, high-temperature pre-oxidation treatment was performed at 1000°C for 20 hours. The resulting Al2O3 / Ni(Al,Si) / Al2O3 composite coating had a thickness of 68 microns.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment according to the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on a nickel-based high-temperature alloy surface, characterized in that: The following steps are involved: Step 1: Degrease and clean the surface of the nickel-based high-temperature alloy with a metal cleaning agent, then immerse it in a plating flux of NaF:KF:KCl:deionized water (mass ratio) heated in a 90°C water bath for 3 minutes, remove it and place it in a drying oven to dry; Step 2: Two independently temperature-controlled melt pools are placed in a hot-dip plating box filled with argon protection. Melt pool 1 contains pure aluminum liquid, and melt pool 2 contains Al-Si alloy liquid with a Si content of 10-20wt.%; Step 3: immerse the nickel-based superalloy with the flux coated on the surface in step 1 into pure aluminum liquid for hot dip plating. After holding the nickel-based superalloy for a certain period of time, quickly extract the nickel-based superalloy from the pure aluminum liquid and then quickly immerse the nickel-based superalloy in Al-Si alloy liquid for hot dip plating. After holding the nickel-based superalloy for a certain period of time, extract the nickel-based superalloy from the Al-Si alloy liquid, remove excess hot dip plating liquid from the surface of the nickel-based superalloy, quench with water, and then dry. Step 4: Place the nickel-based high-temperature alloy that has undergone two-step hot-dip plating in step 3 in a box furnace for long-term high-temperature pre-oxidation treatment, and finally obtain an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of the nickel-based high-temperature alloy.

2. The method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on a nickel-based high-temperature alloy surface according to claim 1, characterized in that: The coating after the two-step hot-dip plating described in step 3 is mainly composed of a dendritic Ni(Al,Si)3 phase and a residual Al-Si liquid phase.

3. The method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on a nickel-based high-temperature alloy surface according to claim 1, characterized in that: In step three, the first step of immersing the substrate in pure aluminum liquid for hot-dip plating is at a temperature of 700-800°C and a time of 60-150 seconds; and then immersing the substrate in Al-Si alloy liquid for hot-dip plating is at a temperature of 700-800°C and a time of 60-150 seconds.

4. The method for preparing an Al2O3 / Ni(Al,Si) / Al2O3 composite coating on a nickel-based high-temperature alloy surface according to claim 1, characterized in that: After the long-term high-temperature pre-oxidation treatment described in step 4, the coating forms a stable multi-phase layer structure, which includes a thermally grown oxide layer Al2O3 layer, a Ni(Al,Si) layer and an Al2O3 oxide film layer from the substrate to the outside.

5. The method for preparing Al2O3 / Ni(Al,Si) / Al2O3 composite coating on the surface of nickel-based high-temperature alloy according to claim 1, characterized in that: The process parameters of the long-term high-temperature pre-oxidation treatment described in step 4 are: time 15-20 hours, temperature 950°C-1000°C.

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