Preparation method of (Ni, Pt) Al / Ni composite coating of single-crystal high-temperature alloy

Abstract

The invention discloses a (Ni, Pt) Al / Ni composite coating of a single-crystal high-temperature alloy, the composite coating takes the single-crystal high-temperature alloy as a matrix, the composite coating is a single-layer coating formed by single-phase beta-(Ni, Pt) Al, and no mutual diffusion zone exists between the composite coating and the matrix. The preparation method comprises the following steps: firstly, pre-electroplating Ni on the surface of the substrate as a transition layer, then electroplating a Pt layer, carrying out hydrogen removal and diffusion vacuum annealing treatment and high-temperature low-activity gas phase aluminizing treatment, and finally, forming the composite coating on the surface of the substrate. The composite coating and the pre-plated Ni layer are introduced as a diffusion barrier layer, so that direct contact between the Pt layer and the matrix is effectively blocked, mutual diffusion between the Pt layer and the matrix is inhibited, damage to a coherent phase structure in the matrix and formation of a TCP precipitated phase caused by mutual diffusion of Ni and Al are delayed, formation of a secondary reaction zone is delayed, and the material stability is ensured. The composite coating provided by the invention is a high-temperature protective coating with slow oxidation weight gain at high temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of single crystal superalloys, in particular to a surface composite coating of single crystal superalloy and a preparation method thereof. BACKGROUND

[0002] Single crystal superalloys are the core materials of turbine blades of aero-engines, and the component design thereof aims at high temperature strength, oxidation resistance and creep resistance. For example, a nickel-based single crystal superalloy mainly comprises base elements, solid solution strengthening elements, γ' phase forming elements, oxidation / corrosion resistance elements and some trace elements with specific functions. The base element nickel accounts for about 50% to 70%, which forms a γ phase as a base to provide a solid solution strengthening basis at high temperature; the γ' phase forming elements such as aluminum and titanium form an ordered γ' phase (Ni3Al or Ni3(Al, Ti)) with nickel, which accounts for 60% to 70% of the total volume, and is the main strengthening phase. A PtAl coating is usually formed on the surface of a single crystal superalloy as an oxidation protection layer thereof. Under the condition of high temperature service, the PtAl coating on the surface generates a continuous Al2O3 film through high temperature oxidation to prevent the inward diffusion of oxygen and protect the base alloy. The PtAl coating usually exists in the forms of ζ-PtAl2 single phase, β-(Ni, Pt)Al single phase and ζ-PtAl2+β-(Ni, Pt)Al two phases. Relevant researches show that the ζ-PtAl2 phase is a brittle phase, which is easy to peel off from the base under a high temperature stress state and cannot play a good protection role. The β-(Ni, Pt)Al phase coating is a phase that is relatively stable in combination with the nickel-based single crystal superalloy. Researches show that the β-(Ni, Pt)Al phase as a surface protection coating of the single crystal superalloy will not lose the protection effect on the base due to peeling off.

[0003] However, at the same time, the interdiffusion of elements between the PtAl coating and the high temperature single crystal alloy base reduces the Al content in the coating. The interdiffusion mainly refers to the inward diffusion of Al from the surface coating to the high temperature single crystal alloy base and the outward diffusion of Ni in the high temperature single crystal alloy base to the coating. The interdiffusion of elements between the coating and the high temperature single crystal alloy base during the long-term high temperature oxidation process will destroy the coherent γ / γ' two-phase structure. Since the solubility of refractory elements in the β phase and the γ' phase is much lower than that in the γ phase, these elements inevitably precipitate and form TCP phases. The appearance of TCP phases is usually related to the discontinuous precipitation of refractory elements, in which the migration of large-angle grain boundaries leads to the formation of a secondary reaction zone. Generally, the needle-like TCP precipitated phase is harmful to the high temperature mechanical properties (such as creep rupture and fatigue life) of the single crystal superalloy, because the precipitation of strengthening elements in the alloy solid solution will cause intergranular embrittlement. The interdiffusion of elements between the (Ni, Pt)Al coating and the single crystal superalloy base plays a crucial role in the performance and life of the alloy component. Therefore, it is of great significance to inhibit or delay the interdiffusion of elements. SUMMARY

[0004] Based on the above problems in the prior art, the purpose of the present application is to provide a composite coating for single-crystal superalloys and a preparation method thereof, by pre-plating a Ni layer before forming a (Ni, Pt) Al coating, forming a (Ni, Pt) Al / Ni composite coating composed of a single-phase β-(Ni, Pt) Al on the surface of a single-crystal superalloy substrate, reducing TCP phase precipitation of the substrate while having good oxidation resistance and stable substrate protection.

[0005] To achieve the above-mentioned purpose of the application, the following technical solutions are adopted.

[0006] The present application provides a preparation method of a composite coating for single-crystal superalloys, comprising the following steps: (1) Substrate surface treatment. Specifically, the substrate is continuously ground by sandpaper, and after wet sandblasting, it is placed in acetone and ethanol solutions respectively for ultrasonic cleaning.

[0007] The substrate is a single-crystal superalloy, including but not limited to second or third generation nickel-based single-crystal or single-crystal intermetallic compounds.

[0008] (2) Pre-electroplating Ni on the substrate surface; the thickness of the Ni layer obtained by pre-electroplating is 20-30 μm. More specifically, the electroplating solution for pre-electroplating Ni is composed of NiSO4·6H2O, NaCl, H2BO3, Na2SO4 and C 12 H 25 NaSO4, the pH value of the electroplating solution is controlled at 5.5-6.5, the electroplating is carried out at 50 ℃-60 ℃ water bath conditions, the current density is 5-6 mA / cm 2 , and the deposition rate is about 2-3 μm / h.

[0009] (3) Electroplating Pt on the Ni layer. More specifically, the main salt used for electroplating Pt is Pt(NH3)2(NO2)2, and the auxiliary salt is NaNO2 and Na3C6H5O7. The main salt and auxiliary salt are dissolved in 60 ℃ deionized water to form a salt solution, and the pH value of the salt solution is adjusted to 9 with ammonia water; the electroplating is carried out at 70 ℃ water bath conditions, the current density is 5 mA / cm 2 , and the deposition rate is about 2.5 μm / h. The thickness of the Pt plating layer is 3-8 μm.

[0010] (4) Vacuum annealing treatment: vacuum annealing is performed on the substrate with completed Ni layer and Pt layer electroplating for hydrogen removal treatment. Specifically, the annealing conditions are as follows: the vacuum degree is kept below 6×10 -3Pa, the heating rate is less than 10 ℃ / min; the treatment temperature is 600-700 ℃, and the holding time is 2-3 h, in the annealing process, as much hydrogen as possible is removed, and then the temperature is kept at 1150-1200 ℃ for 3-5 h, and then the furnace is cooled to room temperature.

[0011] (5) high-temperature low-activity gas phase aluminizing treatment: after vacuum annealing, high-temperature low-activity gas phase aluminizing treatment is carried out in a vertical furnace filled with argon, when aluminizing, the heating rate is about 10-12 ℃ / min, the aluminizing temperature is 1700-1750 ℃, and the holding time is 4-5 h, and thus a (Ni, Pt) Al / Ni composite coating is obtained.

[0012] According to test analysis, the (Ni, Pt) Al / Ni composite coating prepared by the preparation method is a single-layer coating composed of single-phase β-(Ni, Pt) Al; the thickness of the single-layer coating is 55-65 μm, and there is no interdiffusion zone between the single-layer coating and the substrate.

[0013] In the prior art, the steps for forming a PtAl coating on the surface of a single-crystal high-temperature alloy are as follows: first, a Pt layer is electroplated on the surface of a cleaned substrate single-crystal high-temperature alloy, then vacuum annealing is carried out for hydrogen removal and diffusion treatment, and then aluminizing treatment is carried out to obtain a PtAl coating, and finally, the obtained PtAl coating is a double-layer structure composed of an outer layer and an interdiffusion zone. For example, the above steps 1), 3), 4) and 5) in the present application Comparative Example 1 are used to prepare a PtAl coating, the coating includes an outer layer (OZ zone: Outer Zone) and an interdiffusion zone (IDZ zone: Interdiffusion Zone) between the outer layer and the substrate, the interdiffusion zone is formed in the high-temperature aluminizing process, in which Ni in the substrate diffuses outwardly, Al in the coating diffuses into the substrate, and the mutual diffusion of the two elements destroys the coherent γ / γ' two-phase structure, and forms an interdiffusion zone containing TCP precipitates on the surface layer of the coating and the substrate, and it is more likely to form a SRZ zone containing a large amount of needle-like TCP precipitates in the substrate in the subsequent high-temperature oxidation process.

[0014] In the technical scheme of the present application, a layer of Ni is first pre-electroplated on the surface of the substrate as a transition layer, then a Pt layer is electroplated on the surface, and finally vacuum annealing treatment and high-temperature low-activity vapor phase aluminizing are performed. Compared with the traditional PtAl coating process, the introduction of the pre-plated Ni layer plays a key role in the vacuum annealing process, and the element interdiffusion between the (Ni, Pt) Al / Ni composite coating prepared by pre-electroplating Ni and the high-temperature alloy substrate can be greatly alleviated. Firstly, the pre-plated Ni layer acts as a diffusion barrier layer, effectively blocking the direct contact between the Pt layer and the substrate, and significantly inhibiting the interdiffusion phenomenon between the two; secondly, in the subsequent high-temperature low-activity vapor phase aluminizing process, the Ni transition layer can effectively hinder the outward diffusion of Ni elements in the substrate, thereby avoiding the contact between the Ni in the substrate and the inward diffusing Al during aluminizing to form phases such as beta-(Ni, Pt) Al, delaying the destruction of the coherent gamma / gamma' two-phase structure in the substrate and the formation of TCP precipitated phases caused by the interdiffusion of Ni and Al in the substrate, and delaying the formation of the secondary reaction zone. Therefore, this innovative multi-layer structure design not only effectively prevents the formation of the interdiffusion zone, but more importantly, the coherent structure of the substrate is completely retained, ensuring the stability of the material performance. Therefore, the technical scheme of the present application obtains an advanced high-temperature protective coating that inhibits interdiffusion with the substrate and has a slower oxidation weight gain at high temperatures.

[0015] Moreover, the thickness of the pre-electroplated Ni layer and the electroplated Pt layer is matched, and the key parameters such as the temperature and time of vacuum annealing, the aluminizing temperature and time are within the appropriate range, so that in the process of high-temperature aluminizing, the Ni in the pre-electroplated Ni layer diffuses outward to form a coating of a single beta-(Ni, Pt) Al phase with the inward diffusing Al, and the single beta-(Ni, Pt) Al phase is a relatively stable phase combined with nickel-based single crystal high-temperature alloy, which serves as a protective coating and will not lose its protective effect on the substrate due to peeling.

[0016] The present application has the following advantages and beneficial effects: 1. The preparation process is simple and controllable. The present application uses electroplating and vapor deposition methods, which can be used for depositing complex-shaped parts at low cost.

[0017] 2. Compared with the traditional PtAl coating process, the introduction of the pre-plated Ni layer greatly alleviates the element interdiffusion between the coating and the high-temperature alloy substrate, effectively prevents the formation of the interdiffusion zone, and more importantly, the coherent structure of the substrate is completely retained, ensuring the stability of the material performance.

[0018] 3. The present application performs pre-electroplating of Ni, electroplating of Pt, and vapor deposition of aluminizing, and the content in the coating is controllable, the thickness of the plating layer is controllable, and through reasonable control, a coating of a single beta-(Ni, Pt) Al phase is formed, obtaining a more stable protective layer. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Cross-sectional morphology of the PtAl coating, i.e. (Ni, Pt)Al / Ni composite coating, prepared in Example 1 and after isothermal oxidation at 1100 ℃ for 1000 h.

[0020] Figure 2 Cross-sectional morphology of the PtAl coating, i.e. (Ni, Pt)Al coating, prepared in Comparative Example 1 and after isothermal oxidation at 1100 ℃ for 1000 h.

[0021] Figure 3 XRD diffractograms of the (Ni, Pt)Al coating prepared in Comparative Example 1 and the (Ni, Pt)Al / Ni composite coating prepared in Example 1. In the figure, the horizontal axis 2theta represents the diffraction angle (deg.), and the vertical axis Intensity represents the relative intensity (a.u.).

[0022] Figure 4 XRD diffractograms of the (Ni, Pt)Al coating prepared in Comparative Example 1 and the (Ni, Pt)Al / Ni composite coating prepared in Example 1 after isothermal oxidation at 1100 ℃ for 1000 h.

[0023] Figure 5 Changes in the thickness of the SRZ of the (Ni, Pt)Al coating prepared in Comparative Example 1 and the (Ni, Pt)Al / Ni composite coating prepared in Example 1 during isothermal oxidation. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be described in more detail below in combination with the drawings and specific examples.

[0025] In the following examples and comparative examples, the single crystal superalloy substrate selected is a nickel-based single crystal superalloy.

[0026] The present application will be further described below in combination with examples. Example 1

[0027] In this example, the substrate used is a second-generation nickel-based single crystal superalloy N5, and the substrate size is Φ15×2 mm. Before electroplating, the substrate is polished with 240# and 400# SiC sandpaper in turn, and then wet sandblasted with 300-mesh alumina grit at 0.2 MPa, and cleaned in an ultrasonic bath in acetone and ethanol solutions, respectively.

[0028] Pre-electroplated Ni layer: the electroplating solution is prepared by dissolving NiSO4·6H2O, NaCl, H2BO3, Na2SO4 and C 12 H 25Na2SO4, pH of the solution is 5.5. The electroplating is carried out in a water bath at 50°C, the current density is 5 mA / cm 2 , and the deposition rate is about 2 μm / h. In this embodiment, the thickness of the pre-plated Ni layer is 25 μm.

[0029] Electroplating of Pt layer: Pt is electroplated on the prepared Ni plating layer. The main salt used in the electroplating solution for electroplating pure Pt is Pt(NH3)2(NO2)2, and the auxiliary salt is NaNO2 and Na3C6H5O7. The three are dissolved in deionized water at 60°C, and the pH of the solution is adjusted to 9 by using ammonia water. The electroplating is carried out in a water bath at 70°C, the current density is 5 mA / cm 2 , and the deposition rate is about 2.5 μm / h. Finally, the thickness of the Pt plating layer is 5 μm.

[0030] The substrate sample containing the pre-plated Ni layer and the electroplated Pt layer is vacuum annealed, aiming to reduce residual stress, hydrogen removal treatment, and dilute the Pt content on the surface, diffuse Pt to the pre-plated Ni layer, and diffuse Ni in the pre-plated Ni layer to the Pt layer. The vacuum degree is kept below 6 x 10 -3 Pa, the heating rate is less than 10°C / min, the temperature is raised to 600-700°C, and the temperature is kept for 2-3 h. As much hydrogen as possible remaining in the electroplating process can be removed in this annealing process. Then, the temperature is kept at 1150°C for 4 h. After the vacuum annealing treatment is completed, the sample is cooled to room temperature in the furnace.

[0031] The sample after annealing is subjected to high-temperature low-activity vapor aluminizing, which is carried out in an argon-filled vertical furnace. The aluminizing agent used in the aluminizing is a mixture of iron-aluminum alloy powder (49 wt.% Fe) and 4 wt.% NH4Cl. The heating rate during aluminizing is about 10°C / min, and the aluminizing is carried out at 1750°C for 5 h. After the aluminizing process is completed, the sample is cooled to below 100°C in the furnace, and finally the sample is taken out of the furnace. A PtAl coating is prepared on the surface of the substrate, which is denoted as: (Ni, Pt)Al / Ni composite coating. Example 2

[0032] In this embodiment, the substrate used is the second-generation nickel-based single crystal superalloy N5, and the size of the substrate is Φ15 x 2 mm. The substrate treatment before electroplating is the same as that in Example 1.

[0033] Pre-plated Ni layer: The electroplating solution is composed of NiSO4·6H2O, NaCl, H2BO3, Na2SO4 and C 12 H 25 NaSO4, and the pH of the solution is 6.5. The electroplating is carried out in a water bath at 60°C, and the current density is 6 mA / cm 2, the deposition rate is about 3 μm / h, in this example, the thickness of the pre-plated Ni layer is 30 μm.

[0034] Plating Pt layer: using the same plating parameters as in Example 1, increasing the deposition time, the thickness of the final Pt layer is 8 μm.

[0035] Vacuum annealing the substrate sample containing the pre-plated Ni layer and the plated Pt layer, the purpose is to reduce residual stress, hydrogen removal treatment, and at the same time dilute the surface Pt content, Pt diffuses to the pre-plated Ni layer, and at the same time, the Ni in the pre-plated Ni layer diffuses to the Pt layer. The vacuum degree is kept below 6 x 10 -3 Pa, the heating rate is less than 10 ℃ / min, to 600-700 ℃, holding for 2-3 h, as much as possible to remove the residual hydrogen in the plating process during the annealing process; then holding at 1200 ℃ for 3 h, after the vacuum annealing treatment, the sample is cooled to room temperature in the furnace.

[0036] High-temperature low-activity vapor aluminizing is carried out on the annealed sample, in an argon-filled vertical furnace, the aluminizing agent used during aluminizing is a mixture of iron-aluminum alloy powder (49 wt.% Fe) and 4 wt.% NH4Cl powder. The heating rate during aluminizing is about 10 ℃ / min, aluminizing at 1700 ℃ for 5 h, after the aluminizing process is completed, the sample is cooled to below 100 ℃ in the furnace, and finally the sample is taken out of the furnace, and a PtAl coating is prepared on the surface of the substrate. Example 3

[0037] In this example, the substrate used is a second-generation nickel-based single crystal superalloy N5, the substrate size is Φ15 x 2 mm, and the substrate treatment before plating is consistent with Example 1.

[0038] Pre-plated Ni layer: the plating solution is composed of NiSO4·6H2O, NaCl, H2BO3, Na2SO4 and C 12 H 25 NaSO4, the pH value of the solution is 6. The plating is carried out in a 60 ℃ water bath, the current density is 5.5 mA / cm 2 , the deposition rate is about 2.5 μm / h, in this example, the thickness of the pre-plated Ni layer is 20 μm.

[0039] Plating Pt layer: using the same plating parameters as in Example 1, adjusting the deposition time, the thickness of the final Pt layer is 3 μm.

[0040] Vacuum annealing the substrate sample containing the pre-plated Ni layer and the plated Pt layer, the purpose is to reduce residual stress, hydrogen removal treatment, and at the same time dilute the surface Pt content, Pt diffuses to the pre-plated Ni layer, and at the same time, the Ni in the pre-plated Ni layer diffuses to the Pt layer. The vacuum degree is kept below 6 x 10-3 Pa, the heating rate is less than 10 ℃ / min, to 600-700 ℃, and the holding time is 2-3 h, so as to remove as much as possible the hydrogen gas remaining in the plating process. Then, the holding time is 5 h at 1150 ℃, and after the vacuum annealing treatment is completed, the sample is cooled to room temperature in the furnace.

[0041] The sample after annealing is subjected to high-temperature low-activity vapor aluminum infiltration, which is carried out in an argon-filled vertical furnace. The infiltrant used in the aluminum infiltration is a mixture of iron-aluminum alloy powder (49 wt.% Fe) and 4 wt.% NH4Cl. During the aluminum infiltration, the heating rate is about 12 ℃ / min, and the aluminum infiltration is carried out at 1750 ℃ for 4 h. After the aluminum infiltration is completed, the sample is cooled to below 100 ℃ in the furnace, and finally the sample is taken out of the furnace, and a PtAl coating is prepared on the surface of the substrate.

[0042] Comparative Example 1 In this comparative example, the substrate used is the same second-generation nickel-based single crystal superalloy N5 as in Example 1, and the substrate size is Φ15x2mm. Before plating Pt, the substrate is polished with 240# and 400# SiC sandpaper in turn, and then subjected to wet sandblasting treatment with 300-mesh alumina grit at 0.2 MPa. The substrate is then subjected to ultrasonic cleaning in acetone and ethanol solutions, respectively. After that, PtAl coating is prepared on the surface of the substrate, and the steps are as follows.

[0043] Plating of Pt layer: A pure Pt layer is plated on the second-generation nickel-based single crystal superalloy substrate after the above surface treatment. The main salt used in the plating of pure Pt is Pt(NH3)2(NO2)2, and the auxiliary salt is NaNO2 and Na3C6H5O7. The three are dissolved in deionized water at 60 ℃, and the pH value of the solution is adjusted to 9 with ammonia water. The plating is carried out in a water bath at 70 ℃, and the current density is 5 mA / cm 2 , and the deposition rate is about 2.5 μm / h. Finally, the thickness of the plated Pt layer is 5 μm.

[0044] The sample with the Pt-containing plated layer after plating Pt is subjected to vacuum annealing, which aims to reduce residual stress, hydrogen removal treatment, and dilution of the Pt content on the surface, i.e. diffusion of Pt from the plated Pt layer into the substrate, and diffusion of Ni from the substrate to the outside. The vacuum degree is maintained below 6x10 -3 Pa, the heating rate is less than 10 ℃ / min, to 600-700 ℃, and the holding time is 2-3 h, so as to remove as much as possible the hydrogen gas remaining in the plating process. Then, the holding time is 5 h at 1150 ℃, and after the vacuum annealing treatment is completed, the sample is cooled to room temperature in the furnace.

[0045] The annealed samples were subjected to high-temperature low-activity vapor phase aluminizing. The aluminizing agent used was a mixture of iron-aluminum alloy powder (49 wt.% Fe) and 4 wt.% NH4CI. The heating rate during aluminizing was about 10 °C / min. The holding time and aluminizing temperature were determined according to the desired thickness of the aluminized layer. Aluminizing was performed at 1750 °C for 5 h. After aluminizing, the sample was cooled to below 100 °C in the furnace, and then removed from the furnace. A PtAl coating was prepared on the surface of the substrate, which is denoted as: (Ni, Pt)Al coating.

[0046] The PtAl coatings prepared in each of the above examples and comparative examples were tested and analyzed.

[0047] 1) Analysis of the cross-sectional morphology of the prepared coating First, the cross-sectional morphology of the PtAl coatings prepared in each of the examples and comparative examples was analyzed by SEM. It was found that the PtAl coatings prepared in each of the examples were single-layer coatings composed of a single phase of β-(Ni, Pt)Al. The thickness of the single-layer coating was 55-65 μm, and there was no interdiffusion zone between the single-layer coating and the substrate. For example, Figure 1 Figure a in the middle is a cross-sectional morphology diagram of the PtAl coating prepared in Example 1, i.e., the (Ni, Pt)Al / Ni composite coating, Figure 1 The structure of the (Ni, Pt)Al / Ni coating in Figure (a) is composed only of an outer layer (the "Outer Zone" region in the figure) with a thickness of about 60 μm, and there is no interdiffusion zone between the outer layer and the single-crystal superalloy substrate (the "Substrate" in the figure). Some dark particles observed at the interface between the outer layer and the substrate in the figure are alumina sand particles remaining from sandblasting during surface treatment of the substrate.

[0048] In contrast, the cross-sectional morphology of the PtAl coating prepared in the comparative example was analyzed by SEM. It can be seen that the PtAl coating prepared in the comparative example is a very obvious double-layer structure, including an outer layer and an interdiffusion zone containing TCP phases. For example, Figure 2 Figure a in the middle is a cross-sectional morphology diagram of the PtAl coating prepared in Comparative Example 1. In this figure, a typical double-layer structure of the β-(Ni, Pt)Al coating can be observed: an outer layer (the "Outer Zone" region in the figure) with a thickness of about 28 μm, and an interdiffusion zone (the "IDZ" region in the figure) containing white TCP phases with a thickness of about 17 μm. The dark particles at the interface between the outer layer and the IDZ in the figure are alumina sand particles remaining from sandblasting during surface treatment of the substrate.

[0049] 2) Analysis of the cross-sectional morphology of the coating after high-temperature oxidation simulation experiment The PtAl coatings prepared in each of the examples and comparative examples were subjected to a high-temperature oxidation simulation experiment, and the cross-sectional morphology of the PtAl coating was observed. The high-temperature oxidation condition was 1100 °C constant temperature oxidation for 1000 h. For example,Figure 1 Figure (b) of the present application shows the cross-sectional morphology of the PtAl coating, i.e. the (Ni, Pt)Al / Ni composite coating prepared in Example 1, after oxidation at 1100 °C for 1000 h. It can be seen from the figure that the oxide film (alumina film) formed on the surface of the (Ni, Pt)Al / Ni composite coating is continuous and dense. In the high magnification image (in the enlarged view in the lower left corner of Figure (b) of the present application), it can be clearly seen that the oxide film is free of cracks. The average thickness of the oxide film formed on the surface of the (Ni, Pt)Al / Ni composite coating is about 3.1 μm. After oxidation at 1100 °C for 1000 h, the outer layer (the "OZ" region in the figure) of the (Ni, Pt)Al / Ni composite coating has a thickness of about 55 μm. After high-temperature oxidation for a long time, an IDZ region with a thickness of about 20 μm is formed in the coating and the substrate. In addition, a SRZ region composed of a large number of needle-like TCP precipitated phases is formed in the substrate, and the thickness of the SRZ region is about 55 μm. Figure 1

[0050] In contrast, Figure (b) of the present application shows the cross-sectional morphology of the PtAl coating, i.e. the (Ni, Pt)Al coating prepared in Comparative Example 1, after oxidation at 1100 °C for 1000 h. As can be seen from the figure, the oxide film (alumina film) formed on the surface of the conventional (Ni, Pt)Al coating prepared in the comparative example is basically continuous, and the thickness of the oxide film is about 5.5 μm, which is much thicker than the oxide film (3.1 μm) of the (Ni, Pt)Al / Ni composite coating in Example 1 under the same high-temperature oxidation conditions. Figure 2 Figure 2 As can be seen from Figure (b), after high-temperature oxidation, the (Ni, Pt)Al coating in Comparative Example 1 forms a SRZ region composed of a large number of needle-like TCP precipitated phases in the substrate (below the IDZ), and the thickness of the SRZ region is about 96 μm. In comparison, the thickness of the SRZ region formed under the same conditions in Example 1 is only about 55 μm, which is about 43% less than that of the SRZ region in Comparative Example 1. Figure 2

[0051] 3) Analysis of the phases of the prepared coating The PtAl coatings prepared in each of the examples and the comparative example were analyzed by XRD for the composition of the phases, and it was found that the PtAl coatings prepared in each of the examples and the comparative example were all composed of a single phase of β-(Ni, Pt)Al. For example, as can be seen from Figure (a) of the present application, the PtAl coating prepared in Example 1 is composed of a single phase of β-(Ni, Pt)Al. Figure 3 ​​​The XRD patterns of the (Ni, Pt) Al / Ni composite coating prepared in Example 1 and the (Ni, Pt) Al coating prepared in Comparative Example 1 are shown in the figure, and it can be seen that both the coatings are single β-(Ni, Pt) Al phase (identified as "β-NiAl" in the figure), which indicates that the pre-plated Ni layer does not change the phase composition of the (Ni, Pt) Al coating.

[0052] 4) Analysis of coating phase after high-temperature oxidation simulation experiment The PtAl coatings prepared in each example and comparative example were subjected to high-temperature oxidation simulation experiment, and the XRD patterns of the changes of the PtAl coatings were observed and compared, and the changes of the phase composition were analyzed; the high-temperature oxidation condition was 1100 ℃ oxidation for 1000 h. As shown in the figure, Figure 4 The XRD patterns of the (Ni, Pt) Al / Ni composite coating prepared in Example 1 and the (Ni, Pt) Al coating prepared in Comparative Example 1 after being subjected to 1100 ℃ constant temperature oxidation for 1000 h, from the XRD results, it can be seen that the diffraction peaks of the (Ni, Pt) Al of Comparative Example 1 and the (Ni, Pt) Al / Ni composite coating of Example 1 after being subjected to 1100 ℃ constant temperature oxidation for 1000 h are basically the same, and the oxidation film is single α-Al2O3 phase, the coating is γ / γ' phase and contains a small amount of β-(Ni, Pt) Al phase (identified as "β-NiAl" in the figure).

[0053] 5) Analysis of SRZ zone of coating after constant temperature oxidation After high-temperature oxidation, an SRZ zone composed of a large number of needle-like TCP precipitated phases will be formed in the substrate, and different coatings will have different protection effects on the substrate, and the thickness of the formed SRZ zone will be significantly different. As shown in the figure, Figure 5 The thickness of the SRZ zone formed in the substrate of the (Ni, Pt) Al coating prepared in Comparative Example 1 and the (Ni, Pt) Al / Ni composite coating prepared in Example 1 after being subjected to 1100 ℃ constant temperature oxidation for 20 h, 100 h, 300 h, 500 h and 1000 h. Overall, the SRZ thickness of the substrate of the (Ni, Pt) Al / Ni composite coating of Example 1 is smaller than that of the (Ni, Pt) Al coating of Comparative Example 1. The (Ni, Pt) Al coating of Comparative Example 1 can observe the formation of SRZ after oxidation for 20 h, and the SRZ thickness increases significantly as the oxidation time increases to 1000 h; while for the (Ni, Pt) Al / Ni composite coating of Example 1, no SRZ formation is observed after oxidation for 20 h, and the increase of the SRZ thickness is also relatively low from 100 h to 1000 h, which proves that the (Ni, Pt) Al coating with pre-coated Ni layer on the surface of the high-temperature alloy can delay the formation and growth of SRZ.

[0054] The results of the various embodiments demonstrate that this invention provides a simple and economical electroplating method for preparing a (Ni,Pt)Al / Ni composite coating composed of a single-phase β-(Ni,Pt)Al phase. A continuous and highly adhesive α-Al₂O₃ oxide film is formed on the coating surface, reducing its oxidation and degradation rates and exhibiting good oxidation performance. Furthermore, the interdiffusion of elements between the (Ni,Pt)Al / Ni composite coating and the high-temperature alloy substrate is significantly mitigated, with a substantial reduction in the thickness of the SRZ (Solar Surface Zone) and the amount of TCP phase precipitated in the alloy substrate. The (Ni,Pt)Al / Ni composite coating can effectively extend the service life of nickel-based single-crystal alloy components, which is of great significance for promoting the development of aerospace and gas turbine engines.

Claims

1. A (Ni, Pt)Al / Ni composite coating of single crystal superalloy, characterized in that: the composite coating is formed on the surface of a single crystal superalloy substrate; the composite coating is a single-layer coating composed of a single phase of β-(Ni, Pt)Al, and there is no interdiffusion zone between the coating and the substrate; the composite coating is formed on the surface of the substrate by pre-electroplating a Ni layer, electroplating a Pt layer, and then annealing and high-temperature low-activity vapor phase aluminizing. The thickness of the single-layer coating is 55-65 μm. The thickness of the pre-electroplated Ni layer and the electroplated Pt layer is 20-30 μm and 3-8 μm, respectively. The substrate is a second or third generation nickel-based single crystal superalloy or a nickel-based single crystal intermetallic compound.

2. The (Ni, Pt)AI / Ni composite coating of a single crystal superalloy according to claim 1, characterized in that: The method comprises the following steps:

3. The (Ni, Pt)AI / Ni composite coating of a single crystal superalloy according to claim 1, characterized in that: 1) surface treatment of the substrate; 4. The (Ni, Pt)AI / Ni composite coating of a single crystal superalloy according to claim 1, characterized in that: 2) pre-electroplating a Ni layer on the surface of the substrate; 5. A method of producing a (Ni, Pt)Al / Ni composite coating of a single crystal superalloy according to any one of claims 1 to 4, characterized in that 3) electroplating a Pt layer on the Ni layer; 4) vacuum annealing; 5) high-temperature low-activity vapor phase aluminizing. The high-temperature low-activity vapor phase aluminizing in step 5) is performed in a vertical furnace filled with argon, and the heating rate during aluminizing is about 10-12 ℃ / min, and the aluminizing is performed at 1700-1750 ℃ for 4-5 h. The surface treatment of the substrate in step 1) is performed by grinding and sandblasting the surface of the substrate, and then ultrasonic cleaning in acetone and ethanol solutions, respectively. ​ 6. A method of producing a (Ni, Pt)Al / Ni composite coating of a single-crystal high-temperature alloy according to claim 5, characterized in that: The electroplating solution for pre-plating Ni in step 2) includes NiSO4-6H2O, NaCl, H2BO3, Na2SO4 and C 12 H 25 NaSO4, the pH value of the electroplating solution is controlled at 5.5-6.5, the electroplating is carried out under the condition of 50-60℃ water bath, the current density is 5-6 mA / cm 2 , and the deposition rate is about 2-3 μm / h.

7. The method for preparing a (Ni,Pt)Al / Ni composite coating of a single-crystal superalloy according to claim 5, characterized in that, In step 3), Pt is electroplated: the main salt of the electroplating solution is Pt(NH3)2(NO2)2, and the auxiliary salt is NaNO2 and Na3C6H5O7. The main salt and the auxiliary salt are dissolved in 60 °C deionized water to form a salt solution, and the pH value of the salt solution is adjusted to 9 by using ammonia water; the electroplating is carried out in a 70 °C water bath, and the current density is 5 mA / cm 2 , and the deposition rate is about 2.5 μm / h.

8. A method for preparing a (Ni,Pt)Al / Ni composite coating of a single-crystal superalloy according to claim 5, characterized in that, The conditions for vacuum annealing in step 4) are: maintaining the vacuum degree below 6 x 10 -3 Pa, the heating rate is less than 10 °C / min; the treatment temperature is 600-700 °C, the holding time is 2-3 h, then holding at 1150 °C-1200 °C for 3-5 h, and then cooling to room temperature with the furnace.

9. A method for preparing a (Ni,Pt)Al / Ni composite coating of a single-crystal superalloy according to claim 5, characterized in that, ​ 10. The method for preparing a (Ni,Pt)Al / Ni composite coating of a single-crystal superalloy according to claim 5, characterized in that, ​

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