Nickel-based alloy surface composite coating as well as preparation method and application thereof

Abstract

The invention discloses a nickel-based alloy surface composite coating and a preparation method and application thereof, and belongs to the technical field of material science and surface engineering. The coating comprises a CoCrY layer and a Ni-coated Al layer, wherein the CoCrY layer is positioned between the Ni-coated Al layer and a nickel-based alloy. The coating material and the coating structure are optimally designed, so that the protection effects such as oxidation resistance of the coating are effectively improved, the high-temperature stability of the coating is improved, the protection aging of the coating is effectively prolonged, and the long-acting, excellent-effect and stable protection of the coating is realized.

Description

Technical Field

[0001] The invention belongs to the fields of material science and surface engineering, and relates to a nickel-based alloy surface composite coating, a preparation method and an application thereof. Background Art

[0002] Nickel-based alloys, due to their excellent high-temperature strength, creep resistance, and corrosion resistance, have become the material of choice for high-temperature components such as aircraft engine turbine blades, gas turbine hot end components, and chemical equipment. These components often need to operate under extremely high-temperature conditions. For example, the gas temperature in aircraft engines often exceeds 1200°C. As a result, nickel-based alloys need to withstand the combined effects of high temperatures, oxidation, and corrosive atmospheres. Under long-term extreme operating conditions, oxidation reactions occur on the surface of nickel-based alloys, generating nickel oxide (NiO) and other oxides. These oxides initially form a protective layer that prevents oxygen penetration. However, as service time increases, the oxide layer gradually thickens and cracks or peels due to thermal expansion and stress concentration, thus losing its protective effect. Once the oxide layer fails and falls off locally, the oxide layer becomes uneven, which may form a micro-battery effect of electrochemical corrosion, accelerating oxidation of exposed areas and further deteriorating the material's oxidation resistance. Therefore, the formation and failure of the oxide layer not only affects the mechanical properties of nickel-based alloys, but also significantly reduces the service life and operational reliability of related components.

[0003] In high-temperature environments, the aluminum (Al) and chromium (Cr) elements in nickel-based alloys diffuse to the alloy surface and react with oxygen to form a stable protective layer of aluminum oxide (Al2O3) or chromium oxide (Cr2O3). The protective layer formed by these oxides is dense and thermodynamically stable, which can effectively prevent oxygen from further diffusing into the matrix and is the main source of the alloy matrix's protective effect. However, due to the rapid high-temperature diffusion rate of aluminum and chromium, the elements will gradually be depleted, causing the protective layer to become thinner and the protective ability to decrease significantly. At the same time, in a high-temperature thermal cycling environment, the repeated generation and failure of the oxide layer will aggravate the cracking or peeling of the interface between the coating and the substrate, thereby further weakening the nickel-based alloy's own protective performance.

[0004] To provide superior protection for nickel-based alloys, surface coating technology is currently being widely used for high-temperature protection of nickel-based alloys. By coating the surface of nickel-based alloys with one or more layers of protective coating, nickel-based alloys can be protected, giving them better resistance to oxidation and corrosion.

[0005] Currently commonly used protective coatings include MCrAlY coatings (where M represents a nickel or cobalt matrix) and CoCrY coatings. These coatings form a dense protective layer (such as Al2O3 or Cr2O3) in a high-temperature environment by providing elements such as aluminum (Al) and chromium (Cr), thereby preventing the penetration of oxygen and corrosive media. However, the currently commonly used coatings still have many problems. For example, the aluminum in the coating is a key element in the formation of the protective layer, but its diffusion rate at high temperatures is relatively fast, and it is easy to migrate quickly to the surface of the coating and participate in the oxidation reaction, resulting in a rapid decrease in the aluminum content on the coating surface, thereby weakening the long-term protective ability of the coating. In addition, the temperature gradient change in the high-temperature thermal cycle environment will lead to a thermal expansion mismatch between the coating and the substrate interface, which can easily cause interface cracking or even peeling. In addition, the excessive growth of the oxide layer will cause internal stress concentration, further aggravating the failure process of the coating.

[0006] Although composite coating technology can provide more complete protection for nickel-based alloys by introducing a functional multilayer structure on the basis of a single-layer coating, composite coating technology (such as thermal barrier coatings and functional gradient coatings) still faces certain challenges in practical applications. First, the preparation process of composite coatings is relatively complex and costly, making them unsuitable for large-scale industrial applications. Second, the bonding strength between multilayer coatings is insufficient, especially under high temperature and thermal cycle conditions, which can easily lead to interface separation and peeling problems. In addition, existing composite coating technologies still have the problem of low control over the aluminum diffusion rate, and cannot effectively solve the problem of poor long-term protective performance of the coating.

[0007] Therefore, it is necessary to provide a nickel-based alloy surface composite coating and its preparation method and application, so that the coating can fully exert its long-term protective performance under extreme working conditions, while improving the bonding strength between the composite coatings and between the composite coatings and the nickel-based alloy, and further improving the long-term and stable protective performance of the coating. Summary of the Invention

[0008] In order to overcome the problems in the background technology, the present invention is to prepare Ni coated Al layer by using Ni coated Al powder particles as raw material, the raw material of this Ni coated Al, can give full play to the diffusion barrier effect of Ni, limit Al outward diffusion rate, extend aluminum oxide layer (Al2O3) generation speed, so as to avoid coating performance due to aluminum consumption too fast and rapid decline, so that Al's oxidation resistance is fully utilized. At the same time, Ni generates dense NiO oxide layer at high temperature, which is conducive to further enhancing the coating oxidation resistance. In addition, the present invention can form chromium oxide (Cr2O3) protective layer by spraying CoCrY layer between Ni coated Al layer and nickel-based alloy, provide excellent primary oxidation resistance, and strengthen the bonding strength between coating and nickel-based alloy, finally, by the synergistic effect of double-layer coating, significantly slow down the oxide layer growth rate, improve coating oxidation resistance and high temperature stability, extend coating protection effect, so as to achieve long-term, excellent and stable protection of coating, in the parts such as aero-engine, gas turbine, chemical high temperature equipment under extreme working conditions for a long time, give full play to its role.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0010] On one hand, the present invention provides a composite coating on the surface of a nickel-based alloy, the coating comprising a CoCrY layer and a Ni-coated Al layer, wherein the CoCrY layer is located between the Ni-coated Al layer and the nickel-based alloy.

[0011] Preferably, the composition of the CoCrY layer comprises, by mass fraction, Co: 60% to 70%, Cr: 25% to 35%, and Y: 0.5% to 1.5%; the sum of the mass fractions of all the components is 100%.

[0012] Preferably, the thickness of the CoCrY layer is 50-80 μm, and the thickness of the Ni-coated Al layer is 30-50 μm, so as to ensure the functionality of the coating while avoiding material waste and stress concentration caused by excessive coating thickness.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned coating, the preparation method comprising the following steps:

[0014] (1) Treat the surface of nickel-based alloy to remove surface oxides and impurities and increase surface roughness.

[0015] (2) Using a mixed powder of Co, Cr, and Y as raw material, plasma spraying is used to spray a CoCrY layer on the surface of the nickel-based alloy. The mixed powder is obtained by mechanically mixing Co powder, Cr powder, and Y powder, which can be achieved using existing mixers and other equipment.

[0016] (3) Using Ni-coated Al powder as raw material, cold spraying is used to spray a Ni-coated Al layer on the surface of the CoCrY layer in step (1).

[0017] (4) Sintering the nickel-based alloy sprayed in step (3) to obtain a coating nickel-based alloy.

[0018] Preferably, in step (1), the surface of the nickel-based alloy is sequentially sandblasted, cleaned, and dried.

[0019] Preferably, in step (2), the plasma jet temperature is 6000-7000K, the spraying speed is 30-50m / s, and the spraying distance is 100-150mm.

[0020] Preferably, in step (3), the cold spraying pressure is 3-5 MPa, the spraying temperature is 60-80° C., and the spraying distance is 30-50 mm.

[0021] Preferably, in step (4), the sintering temperature is 950-1000° C., and the holding time is 2-4 hours.

[0022] Preferably, the Ni coating layer of the Ni-coated Al powder has a thickness of 2 to 5 μm and an Al particle size of 20 to 50 μm, so as to achieve uniform coating thickness.

[0023] The present invention also proposes a specific application of the above-mentioned coating, which is to apply the composite coating to aircraft engine turbine blades, gas turbine hot end components, and pipelines or reactors of chemical high-temperature equipment for protection.

[0024] Beneficial effects of the present invention:

[0025] 1. The present invention uses Ni-coated Al powder as a raw material for spraying to obtain a Ni-coated Al coating, which effectively controls the Al diffusion rate and prolongs the protective effect of the coating. In addition, Ni forms a dense NiO oxide layer at high temperatures, further enhancing the coating's antioxidant capacity, thereby significantly improving the coating's high-temperature antioxidant capacity, allowing nickel-based alloys to obtain more long-lasting, stable, and high-quality protection under extreme working conditions.

[0026] 2. The present invention sprays a CoCrY layer between the Ni-coated Al layer and the nickel-based alloy substrate, utilizing the high-temperature strength and plastic deformation ability of Co to alleviate stress accumulation during thermal cycling, thereby enhancing the thermal fatigue resistance of the coating and helping to improve the long-term protective capability of the coating. Y is utilized to inhibit the grain growth of the Cr2O3 oxide layer, thereby improving the density and strengthening the protective effect of the CoCrY layer. At the same time, the "pinning effect" is utilized to enhance the bonding strength between the coating and the nickel-based alloy substrate, and between the coating and the layer. Cr is utilized to form a Cr2O3 oxide layer, thereby preventing further oxygen penetration through the Ni-coated Al layer, forming a rapid barrier, and forming a gradient protective effect together with the slow-release protection of the Ni-coated Al layer, thereby enhancing the overall protective performance of the coating.

[0027] 3. The coating structure of the present invention is two-layer, which can effectively reduce the mutual influence of powder particles in the coating after the coating is formed. When Cr, Co, Y, and Ni-coated Al powder particles exist in a layer of coating at the same time, the surface of the Cr or Ni-coated Al particles may be covered with other substances, hindering their contact with oxygen, thereby hindering the formation of the oxide layer, causing Al to migrate through the grain boundaries to the nickel-based alloy substrate under high temperature, seriously affecting the protective effect of the coating, and failing to form a gradient protection effect.

[0028] 4. High-temperature plasma spraying helps to improve the density of the CoCrY layer, and can partially melt the raw material particle powder of the CoCrY layer and diffuse it with the surface of the nickel-based alloy substrate to form a metallurgical bond, thereby enhancing the bonding strength between the coating and the nickel-based alloy substrate. At the same time, it can also make Cr diffuse preferentially to the surface, quickly forming a continuous and dense Cr2O3 protective layer, thereby forming a rapid barrier. However, during the high-temperature plasma spraying process, Ni-coated Al powder particles will cause Ni to melt or partially evaporate, causing the Al core to be directly exposed to a high-temperature oxidizing environment, resulting in premature oxidation and loss of control over diffusion. The present invention designs a double-layer coating structure, and the two-layer structure can be prepared by different spraying methods, effectively avoiding premature oxidation of the Al element, which leads to a rapid decline in the subsequent coating protection effect.

[0029] 5. The present invention facilitates simplifying the coating preparation method by placing the CoCrY layer between the Ni-coated Al layer and the nickel-based alloy substrate, thereby enabling a smooth connection between the two coating layers. Otherwise, if the Ni-coated Al layer is sprayed first, the Al will still undergo premature oxidation during the subsequent high-temperature plasma spraying process, thereby affecting the protective effect of the coating.

[0030] 6. The preparation method of the present invention is relatively simple and low in cost. The prepared coating has high density, strong bonding force, good long-term protective effect, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1Schematic diagram of the coating structure of the present invention;

[0032] Figure 2 This is a cross-sectional SEM image of the coating of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0034] Example 1

[0035] In this embodiment, IN718 nickel-based alloy is used as the nickel-based alloy substrate, and the dimensions are 50 mm×50 mm×5 mm.

[0036] This embodiment uses the following method to prepare the coating:

[0037] (1) The surface of the nickel-based alloy substrate was sandblasted with corundum particles with a particle size of 60 μm to remove surface oxides and impurities and increase surface roughness. The nickel-based alloy substrate was immersed in an ethanol solution for ultrasonic cleaning for 10 minutes and then dried at 80°C for use.

[0038] (2) Using plasma spraying equipment, spray CoCrY coating on the surface of nickel-based alloy substrate, the coating powder composition is cobalt (Co) 65%, chromium (Cr) 33.5%, yttrium (Y) 1.5%;

[0039] Spraying parameter settings: plasma jet temperature 7000K, spraying speed 40m / s, spraying distance 120mm, coating thickness controlled at 60μm, and naturally cooled to room temperature after spraying.

[0040] (3) nickel-coated aluminum powder was selected, the Al particle size was 30 μm, the nickel coating layer thickness was 3 μm, and the nickel-coated aluminum powder was evenly sprayed on the surface of the CoCrY layer using cold spraying equipment;

[0041] Spraying parameter settings: spraying pressure 4MPa, spraying temperature 60℃, spraying distance 40mm.

[0042] The coating thickness is controlled at 40 μm and is cooled naturally after spraying.

[0043] (4) The sprayed nickel-based alloy is placed in a vacuum sintering furnace for vacuum sintering at 950°C for 3 hours, and then cooled to room temperature to obtain a coated nickel-based alloy product.

[0044] The coated nickel-based alloy product was placed in a static air environment at 1000°C for a long-term oxidation test. The test time was 100 hours. After the test, the coating oxide layer thickness was 5μm and the weight gain was 0.4mg / cm 2 .

[0045] Example 2:

[0046] In this embodiment, IN625 nickel-based alloy is used as the nickel-based alloy substrate, and the dimensions are 100 mm×50 mm×5 mm.

[0047] This embodiment uses the following method to prepare the coating:

[0048] (1) The surface of the nickel-based alloy substrate was sandblasted with corundum particles with a particle size of 80 μm to remove surface oxides and impurities and increase surface roughness. The nickel-based alloy substrate was immersed in an ethanol solution for ultrasonic cleaning and then dried for use.

[0049] (2) Using plasma spraying equipment, spray CoCrY coating on the surface of nickel-based alloy substrate, the coating powder composition is cobalt (Co) 64.5%, chromium (Cr) 35%, yttrium (Y) 0.5%;

[0050] Spraying parameter settings: plasma jet temperature 6800K, spraying speed 35m / s, spraying distance 100mm, coating thickness controlled at 70μm, and naturally cooled to room temperature after spraying.

[0051] (3) nickel-coated aluminum powder was selected, the Al particle size was 25 μm, the nickel coating layer thickness was 2 μm, and the nickel-coated aluminum powder was evenly sprayed on the surface of the CoCrY layer using cold spraying equipment;

[0052] Spraying parameter settings: spraying pressure 3.5MPa, spraying temperature 70℃, spraying distance 50mm.

[0053] The coating thickness is controlled at 30 μm and is cooled naturally after spraying.

[0054] (4) The sprayed nickel-based alloy is placed in an inert gas (argon) atmosphere at 1000°C for 4 hours, and then cooled to room temperature to obtain a coated nickel-based alloy product.

[0055] The coated nickel-based alloy product was placed in a static air environment at 1050°C for a long-term oxidation test for 50 hours. After the test, the coating oxide layer thickness was 6μm and the weight gain was 0.5mg / cm 2 .

[0056] Example 3

[0057] This embodiment uses a gas turbine blade with a complex geometry as the nickel-based alloy substrate.

[0058] This embodiment uses the following method to prepare the coating:

[0059] (1) The blade surface was sandblasted with corundum particles with a particle size of 50 μm, and then steam cleaned to remove surface oxides and impurities, increase surface roughness, and then dried for use.

[0060] (2) Using plasma spraying equipment, spray CoCrY coating on the blade surface. The coating powder composition is cobalt (Co) 70%, chromium (Cr) 28.5%, and yttrium (Y) 1.5%;

[0061] Spraying parameter settings: plasma jet temperature 7000K, spraying speed 30m / s, spraying distance 120mm, coating thickness controlled at 55μm, and naturally cooled to room temperature after spraying.

[0062] (3) nickel-coated aluminum powder was selected, the Al particle size was 50 μm, the nickel coating layer thickness was 5 μm, and the nickel-coated aluminum powder was evenly sprayed on the surface of the CoCrY layer using cold spraying equipment;

[0063] Spraying parameter settings: spraying pressure 4.5MPa, spraying temperature 80℃, spraying distance 40mm.

[0064] The coating thickness is controlled at 35 μm and cooled naturally after spraying.

[0065] (4) The sprayed blade is placed in a vacuum sintering furnace for vacuum sintering at 950°C for 3 hours, and then cooled to room temperature to obtain a coated blade product.

[0066] The blades were subjected to thermal cycle tests under actual operating conditions (cooling from 1100°C to room temperature, 200 cycles). After the test, there was no obvious cracking or peeling of the coating, the antioxidant layer remained stable, and the coating showed excellent adhesion and high-temperature stability.

[0067] Comparative Example 1

[0068] In this comparative example, a coated nickel-based alloy product was prepared by the same method as in Example 1, except that a single-layer CoCrY coating was sprayed in this comparative example.

[0069] The nickel-based alloy coating obtained in this comparative example was tested under the same conditions as in Example 1. After the test, the coating oxide layer thickness was 10 μm and the weight gain was 0.8 mg / cm 2 .

[0070] According to the test results of the coated nickel-based alloy product in Example 1 and the coated nickel-based alloy product in Comparative Example 1, it can be seen that the smaller the weight gain, the less oxide will be generated, that is, the oxide layer is thinner, indicating that oxidation is suppressed. Therefore, the coated nickel-based alloy product in Example 1 has better oxidation resistance than the coated nickel-based alloy product in Comparative Example 1.

[0071] Comparative Example 2

[0072] In this comparative example, a coated nickel-based alloy product was prepared using the same method as in Example 2, except that a single-layer MCrAlY coating was sprayed in this comparative example.

[0073] The nickel-based alloy coating obtained in this comparative example was tested under the same conditions as in Example 2. After the test, the coating oxide layer thickness was 12 μm and the weight gain was 1.2 mg / cm 2 .

[0074] By comparing Example 2 with Comparative Example 2, it can be seen that the thickness of the coating oxide layer of Example 2 is only 5 μm, and the weight increase is only 0.48 mg / cm 2 The oxidation resistance of the coated nickel-based alloy product in Example 2 is significantly improved.

[0075] Comparative Example 3

[0076] In this comparative example, a coated nickel-based alloy product was prepared using the same method as in Example 1, except that the ratio of Cr powder, Co powder, and Y powder used in this comparative example was 59% cobalt (Co), 40% chromium (Cr), and 1% yttrium (Y).

[0077] The nickel-based alloy coating obtained in this comparative example was tested under the same conditions as in Example 1. After the test, the coating oxide layer thickness was 16 μm and the weight gain was 1.4 mg / cm 2 Excessive Cr leads to uneven distribution of components, discontinuous oxide layer in local areas during the oxidation process, and aggravates the oxidation reaction.

[0078] By comparing Example 1 with Comparative Example 2, it can be seen that the thickness of the coating oxide layer of Example 1 is only 10 μm, and the weight increase is only 0.8 mg / cm 2 The oxidation resistance of the coated nickel-based alloy product of Example 1 is significantly improved.

[0079] Comparative Example 4

[0080] In this comparative example, a coated nickel-based alloy product was prepared using the same method as in Example 1, except that the ratio of Cr powder, Co powder, and Y powder used in this comparative example was 75% cobalt (Co), 24% chromium (Cr), and 1% yttrium (Y).

[0081] The nickel-based alloy coating obtained in this comparative example was tested under the same conditions as in Example 1. After the test, the coating oxide layer thickness was 13 μm and the weight gain was 1.3 mg / cm 2 Excessive Co causes Cr to be diluted, making it difficult for the oxide layer to form continuously, resulting in the oxide layer being unable to play a protective role.

[0082] By comparing Example 1 with Comparative Example 2, it can be seen that the thickness of the coating oxide layer of Example 1 is only 10 μm, and the weight increase is only 0.8 mg / cm 2 The oxidation resistance of the coated nickel-based alloy product of Example 1 is significantly improved.

[0083] Comparative Example 5

[0084] This comparative example uses the same method as Example 1 to prepare a coated nickel-based alloy product. The difference is that this comparative example uses Cr powder, Co powder, and Y powder in a ratio of cobalt (Co) 65%, chromium (Cr) 32%, and yttrium (Y) 3%.

[0085] The nickel-based alloy coating obtained in this comparative example was tested under the same conditions as in Example 1. After the test, the coating oxide layer thickness was 15 μm and the weight gain was 1.5 mg / cm 2 Excessive Y will generate larger particles of Y2O3 embedded in the oxide layer, increasing the stress within the oxide layer and causing the oxide layer to fail.

[0086] By comparing Example 1 with Comparative Example 2, it can be seen that the thickness of the coating oxide layer of Example 1 is only 10 μm, and the weight increase is only 0.8 mg / cm 2 The oxidation resistance of the coated nickel-based alloy product of Example 1 is significantly improved.

[0087] pass Figure 2 It can be seen that after spraying the CoCrY layer and the Ni-coated Al layer, a dense oxide protective layer will be generated to fill the gaps when undergoing high-temperature oxidation, which greatly improves the oxidation resistance of the nickel-based alloy.

Claims

1. A composite coating on the surface of a nickel-based alloy, characterized in that: The coating comprises a CoCrY layer and a Ni-coated Al layer, wherein the CoCrY layer is located between the Ni-coated Al layer and the nickel-based alloy.

2. The nickel-based alloy surface composite coating according to claim 1, characterized in that: The components of the CoCrY layer include, by mass fraction, Co: 60% to 70%, Cr: 25% to 35%, and Y: 0.5% to 1.5%, and the sum of the mass fractions of all the components is 100%.

3. The nickel-based alloy surface composite coating according to claim 1, characterized in that: The thickness of the CoCrY layer is 50 to 80 μm, and the thickness of the Ni-coated Al layer is 30 to 50 μm.

4. The method for preparing a composite coating on a nickel-based alloy surface according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) Treat the surface of nickel-based alloy to remove surface oxides and impurities and increase surface roughness; (2) Using a mixed powder of Co, Cr, and Y as raw material, plasma spraying is used to spray a CoCrY layer on the surface of the nickel-based alloy; (3) using Ni-coated Al powder as raw material, cold spraying is used to spray a Ni-coated Al layer on the surface of the CoCrY layer in step (1); (4) Sintering the nickel-based alloy sprayed in step (3) in a vacuum or inert gas protection environment to obtain a coated nickel-based alloy.

5. The preparation method according to claim 4, characterized in that: In the step (1), the surface of the nickel-based alloy is sequentially sandblasted, cleaned, and dried.

6. The preparation method according to claim 4, wherein: In the step (2), the plasma jet temperature is 6000-7000K, the spraying speed is 30-50m / s, and the spraying distance is 100-150mm.

7. The preparation method according to claim 4, characterized in that: In the step (3), the cold spraying pressure is 3-5 MPa, the spraying temperature is 60-80° C., and the spraying distance is 30-50 mm.

8. The preparation method according to claim 4, characterized in that: In the step (4), the sintering temperature is 950-1000° C., and the holding time is 2-4 hours.

9. The preparation method according to claim 4, characterized in that: The Ni coating layer of the Ni-coated Al powder has a thickness of 2 to 5 μm, and the Al particle size is 20 to 50 μm.

10. Use of a composite coating on a nickel-based alloy surface according to any one of claims 1 to 3, characterized in that: The composite coating is applied to aviation engine turbine blades, gas turbine hot end components, and pipelines or reactors of chemical high-temperature equipment for protection.

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