A platinum-aluminum protective coating on a surface of a dd6 single crystal superalloy and a method of making the same

Abstract

This invention discloses a platinum-aluminum protective coating on the surface of DD6 single-crystal superalloy and its preparation method, belonging to the field of high-temperature protective coating technology. The platinum-aluminum coating is formed on the surface of a DD6 nickel-based single-crystal superalloy substrate, consisting of an interdiffusion layer and an aluminized layer from the inside out. The preparation process includes: pretreating the DD6 alloy substrate; preparing a platinum layer with a thickness of 3-4 μm on the substrate surface using electroplating; performing a first vacuum heat treatment under a protective atmosphere to allow the platinum layer to interdiffused with the substrate to form a platinum-modified layer; then preparing an aluminized layer on the surface of the platinum-modified layer using a vapor-phase aluminizing method; and finally performing a second vacuum diffusion treatment under a protective atmosphere to obtain a dense coating. The platinum-aluminum coating prepared by this invention has strong adhesion to the substrate and a controllable microstructure, significantly improving the oxidation resistance of DD6 alloy under high-temperature oxidizing environments, and is suitable for the protection of high-temperature hot-end components such as turbine blades of aero-engines.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, specifically to a platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy and its preparation method. Background Technology

[0002] DD6 alloy is a second-generation nickel-based single-crystal superalloy independently developed in my country. Due to its excellent high-temperature creep properties and fatigue strength, it is widely used in the manufacture of key hot-end components such as turbine blades for aero-engines and ground gas turbines. However, with the continuous improvement of the thrust-to-weight ratio of modern aero-engines, the turbine inlet temperature has risen sharply. DD6 alloy itself is difficult to resist the severe oxidation and corrosion in the high-temperature gas environment, and a protective coating must be applied to its surface.

[0003] Aluminide coatings are among the most widely used high-temperature protective coatings, forming a continuous, dense Al₂O₃ oxide film to block the inward diffusion of oxygen. However, during long-term high-temperature service, the interdiffusion between the coating and the substrate intensifies in a single aluminized coating, leading to accelerated coating degradation and a limited protective lifespan. To further improve the oxidation resistance of coatings, platinum-modified aluminide coatings have emerged. The addition of platinum can significantly improve the adhesion of the Al₂O₃ film, delay the consumption of beneficial aluminum in the coating, and inhibit the precipitation of harmful phases, thereby greatly enhancing the overall protective performance of the coating.

[0004] Existing platinum-aluminum coating preparation processes typically involve platinum electroplating followed by aluminizing. However, precisely controlling the thickness, microstructure, and phase composition of each layer, avoiding the acquisition of excessive PtAl2 phase, and ensuring a strong bond and dense microstructure between the coating and the DD6 alloy substrate remain key technical challenges in current process optimization. Improper process control can easily lead to excessive internal stress, uneven composition distribution, or defects in the coating, thereby affecting its long-term service reliability under high-temperature oxidizing environments.

[0005] Therefore, developing a platinum-aluminum coating with controllable microstructure, strong adhesion, and significantly improved high-temperature oxidation resistance of DD6 alloy, and its preparation process, is of great significance for extending the service life of hot-end components. Summary of the Invention

[0006] To overcome the shortcomings of existing single aluminized coatings, such as poor adhesion, insufficient oxidation resistance, and difficulty in controlling the coating microstructure, the present invention aims to provide a platinum-aluminum protective coating for the surface of DD6 single-crystal superalloy and its preparation method. The prepared protective coating significantly improves the service performance of DD6 nickel-based single-crystal superalloy in extreme high-temperature oxidation environments, meeting the urgent need for long-life and high-reliability protective coatings for hot-end components such as turbine blades of aero-engines.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a platinum-aluminum protective coating on the surface of a DD6 single-crystal superalloy, comprising the following steps: (1) Pretreatment of DD6 nickel-based single crystal superalloy matrix; (2) Electroplating a platinum layer on the pretreated substrate surface, wherein the thickness of the platinum layer is 3 to 4 μm; (3) The sample after electroplating in step (2) is subjected to a first vacuum heat treatment to allow the platinum layer to interdiffused with the substrate to form a platinum modified layer (interdiffusion layer). (4) After heat treatment in step (3), an aluminized layer is prepared on the surface of the platinum modified layer by vapor phase aluminizing method, and the thickness of the aluminized layer is 25-35 μm. (5) After a second vacuum heat treatment under a protective atmosphere, a platinum-aluminum protective coating resistant to high-temperature oxidation is obtained on the surface of DD6 single crystal high-temperature alloy.

[0008] Further, in step (1), the pretreatment includes sequential electrolytic degreasing and acid pickling activation treatment of the substrate.

[0009] Furthermore, the degreasing solution used comprises: sodium carbonate 30–50 g / L, sodium metasilicate pentahydrate 8–15 g / L, surfactant TX-10 (nonylphenol polyoxyethylene ether) 1–2.5 g / L, disodium EDTA 0.5–1.5 g / L, and the balance being deionized water; the degreasing temperature of the electrolytic degreasing is 35–45℃, the degreasing time is 240–360 s, the degreasing current is 0.5 A, and the degreasing voltage is 2 V; in the acid pickling activation process, the activation solution used is a 20 wt.% hydrochloric acid solution, and the activation time is 240–360 s.

[0010] Furthermore, in step (2) of the electroplating process, the electroplating solution used is an alkaline platinum plating system with tetraammineplatinium hydrogen phosphate as the main salt. The concentration of tetraammineplatinium hydrogen phosphate in the electroplating solution is 3.5-5.0 g / L, and the pH of the electroplating solution is 10.2-10.5. DC electroplating is adopted, and the electroplating process parameters are: current density 2~6 A / dm², electroplating time 25-35 min. The deposition thickness of the platinum layer is precisely controlled to ensure that the platinum layer is uniform, continuous and dense.

[0011] Furthermore, in step (3), the first vacuum heat treatment is carried out in a vacuum heat treatment furnace at a temperature of 1040°C. ~ 1060℃, heat preservation time is 1.5-2.5 hours.

[0012] Further, in step (4), the process of the vapor phase aluminizing method is as follows: the sample is placed in a aluminizing tank containing aluminizing agent; then, under a protective atmosphere (such as argon) or vacuum conditions, it is heated to 1060°C. ~ 1080℃, heat preservation 3.5 ~ 4.5 hours; the aluminizing agent is composed of CrAl bulk and activator AlF3, and the activator content in the aluminizing agent is 0.15~0.25 wt.%.

[0013] Furthermore, in step (5), the second vacuum heat treatment is carried out in a vacuum heat treatment furnace at a temperature of 860-880°C and a holding time of 30-35 hours.

[0014] Furthermore, the heat treatment processes in steps (3) and (5) are carried out under vacuum conditions or an inert atmosphere.

[0015] Furthermore, the prepared protective coating is a multi-layer composite structure, consisting of an interdiffusion layer and an aluminizing layer from the substrate surface outwards. The Pt content in the interdiffusion layer increases gradually from the inside out, and the aluminizing layer is mainly composed of NiAl phase, exhibiting good high-temperature stability and oxidation resistance.

[0016] Compared with the prior art, the present invention has the following significant advantages: 1. Excellent high-temperature oxidation resistance: The Pt-Al coating prepared by this invention has a unique PtAl2 / NiAl multilayer structure. During high-temperature service, the aluminum in the coating preferentially forms a dense and slowly growing α-Al2O3 protective film, which effectively hinders the inward diffusion of harmful elements such as S and O and the outward diffusion of the base metal, thereby greatly improving the service life of DD6 alloy in high-temperature oxidation environments above 1050℃.

[0017] 2. Strong adhesion between coating and substrate: Through the “electroplated platinum + first vacuum diffusion” process, a metallurgically bonded interdiffusion layer is first formed, eliminating the physical interface; the subsequent vapor phase aluminizing and second vacuum diffusion treatment further strengthen this metallurgical bond, so that there is no sharp interface between the coating and the substrate, which greatly improves the coating’s resistance to peeling and thermal cycling stability.

[0018] 3. Strong controllability of the structure: By independently controlling the thickness of the electroplated platinum layer, the parameters of the first diffusion treatment, the parameters of the vapor phase aluminizing process, and the parameters of the second diffusion treatment, this invention can achieve precise control over the thickness, phase composition, and microstructure of each layer (aluminizing layer and interdiffusion layer) of the final coating. This allows for the "tailoring" and optimization of the coating performance according to different service conditions.

[0019] 4. The process is stable and reliable, and suitable for industrial production: The electroplating, vacuum heat treatment, and vapor phase aluminizing methods used in this invention are all relatively mature processes in the field of aerospace material surface treatment. The equipment is highly versatile, the process window is wide, and it is easy to achieve mass production and quality control, and has good engineering application prospects.

[0020] In summary, the DD6 alloy platinum-aluminum coating and its preparation process provided by this invention, through multi-layer structure design and precise process control, successfully solve the problems of poor adhesion and insufficient oxidation resistance of traditional coatings, providing a long-life and highly reliable high-temperature protection solution for key hot-end components such as aero-engine turbine blades. Attached Figure Description

[0021] Figure 1 The image shows the cross-sectional scanning electron microscope microstructure of the platinum-aluminum protective coating prepared in Example 1.

[0022] Figure 2 This is a schematic diagram of the detection points on the surface microstructure of the platinum-aluminum protective coating of the test piece in Example 1.

[0023] Figure 3 The image shows the microstructure of the platinum-aluminum protective coating prepared in Example 1 after static oxidation at 1100°C for 200 hours.

[0024] Figure 4 This is a schematic diagram of the detection points on the surface microstructure of the oxidized sample in Example 1.

[0025] Figure 5 The image shows the cross-sectional scanning electron microscope microstructure of the platinum-aluminum protective coating (platinum layer thickness 4.5 μm) prepared for Comparative Example 1.

[0026] Figure 6 The image shows the cross-sectional scanning electron microscope microstructure of the platinum-aluminum protective coating (platinum layer thickness 5.5 μm) prepared for Comparative Example 1.

[0027] Figure 7 The image shows the cross-sectional scanning electron microscope microstructure of the platinum-aluminum protective coating (aluminized layer thickness 50 μm) prepared for Comparative Example 2.

[0028] Figure 8 This is a schematic diagram of the detection points on the surface microstructure of the test pieces for Comparative Example 2.

[0029] Figure 9 The image shows the microstructure of the coating prepared for Comparative Example 3 after static oxidation at 1100℃ for 200 h.

[0030] Figure 10 This is a schematic diagram of the detection points on the surface microstructure of the oxidized sample in Comparative Example 3. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0032] The organic binder used in the following examples was prepared by uniformly mixing polyvinyl alcohol powder (PVA2488 or PVA088-50) with deionized water at a volume ratio of 1:3. Example 1:

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] Example 1: This embodiment provides a platinum-aluminum protective coating on the surface of a DD6 single-crystal superalloy that resists high-temperature oxidation, and its preparation process. The specific preparation process is as follows: 1. Matrix pretreatment: Using DD6 nickel-based single-crystal superalloy as the substrate, it was first wire-cut into square specimens measuring 1cm × 2cm × 2mm. A 1cm diameter hole was made in the top of each specimen. Then, the specimens were polished sequentially with 240-grit, 600-grit, and 1200-grit sandpaper to remove the wire-cutting marks. Subsequently, the specimens were sandblasted to remove the natural oxide film on the surface. Finally, they were rinsed with deionized water and dried to obtain a clean surface.

[0035] The test specimens were degreased using a degreasing solution composed of: sodium carbonate 40 g / L, sodium metasilicate pentahydrate 10 g / L, surfactant TX-10 (nonylphenol polyoxyethylene ether) 2.0 g / L, disodium EDTA 1.2 g / L, and the balance being deionized water. The degreasing temperature was 40°C. o C, degreasing time 300s, degreasing current 0.5A, degreasing voltage 2V.

[0036] After degreasing, the test piece was placed in 20wt.% hydrochloric acid for activation treatment for 300s.

[0037] 2. Electroplated platinum layer: A platinum layer was prepared on the surface of a pretreated DD6 alloy sample using direct current electroplating. The electroplating solution consisted of tetraammineplatinum hydrogen phosphate, NaOH, and deionized water, with a tetraammineplatinum hydrogen phosphate concentration of 4.0 g / L (based on Pt) and a pH of 10.3. The electroplating process parameters were: current density of 4 A / dm³. 2 The electroplating temperature was 92℃, and the electroplating time was 30 minutes. In this step, the platinum layer deposition thickness was precisely controlled to 3.5 μm by controlling the process parameters, ensuring that the platinum layer was uniform, continuous, and dense.

[0038] 3. First vacuum heat treatment (platinum diffusion treatment): The platinum-plated sample was placed in a vacuum heat treatment furnace, with the vacuum level controlled at 10.-3 The temperature is increased to 1050℃ at a rate of 10℃ / min, held for 2 hours, and then cooled in the furnace. This step allows for sufficient interdiffusion between the platinum layer and the DD6 substrate, forming a platinum-modified layer (interdiffusion layer). This process promotes sufficient solid-state interdiffusion between the electroplated platinum layer and elements such as Ni and Co in the DD6 alloy substrate, forming a platinum-modified layer (i.e., interdiffusion layer) with a compositional gradient at the interface. This provides a platinum-rich surface layer for subsequent aluminizing and initially achieves metallurgical bonding of the coating.

[0039] 4. Vapor phase aluminizing: A metallized layer was prepared on the surface of a platinum-modified substrate using a vapor-phase aluminizing method. The process involved placing the substrate with the platinum-modified layer in a vapor-phase aluminizing furnace. The aluminizing agent consisted of chromium-aluminum blocks and an activator, aluminum fluoride (AlF3), with a weight ratio of 500:1 (40 wt.% Cr and 60 wt.% Al in the chromium-aluminum blocks). Under argon protection, the temperature was raised to 1070℃ and held for 4 hours, allowing active aluminum atoms to deposit and diffuse onto the substrate surface, forming a 30 μm metallized layer. During this process, aluminum was deposited onto the platinum-modified layer surface via chemical vapor transport or diffusion, reacting with elements such as Ni and Pt in the matrix to form a metallized layer dominated by the β-NiAl phase, while the outer surface was enriched with the PtAl2 phase. By precisely controlling the aluminizing temperature, time, and aluminum activity, the thickness and phase composition of the metallized layer could be controlled.

[0040] 5. Second vacuum diffusion treatment: The aluminized specimen was placed back into the vacuum heat treatment furnace, with the vacuum level controlled at 10. -3 The temperature is raised to 870℃ above Pa and held for 32 hours, then cooled in the furnace. This ultimately forms a platinum-aluminum protective coating on the DD6 alloy substrate, consisting of an interdiffusion layer and an aluminizing layer, arranged sequentially from the inside out. This process eliminates potential component segregation and micro-stress that may occur during vapor-phase aluminizing, resulting in a more uniform elemental distribution within the coating and at the coating / substrate interface. Furthermore, it promotes further densification and phase stabilization of the coating's internal structure, optimizing the thickness ratio and microstructure of the PtAl2 phase, the aluminizing layer, and the interdiffusion layer, ultimately yielding a platinum-aluminum coating with controllable microstructure and excellent performance. The aluminizing layer, formed on top of the interdiffusion layer, is predominantly NiAl phase and serves as the main load-bearing layer of the coating, exhibiting good high-temperature stability and oxidation resistance.

[0041] Figure 1 The cross-sectional scanning electron microscope (SEM) microstructure of the platinum-aluminum protective coating with a 3.5 μm platinum layer and a 30 μm aluminized layer prepared in this embodiment is shown. Figure 2 The diagram shown is a schematic of the detection points for the microstructure of the sample surface in this embodiment. Figure 2 Different positions (spectral) of the pilot sample Figure 1-3The elemental composition distribution is shown in Table 1. Figure 3 The microstructure diagram of the protective coating prepared in this embodiment after static high-temperature oxidation at 1100℃ for 200h. Figure 4 The diagram shown is a schematic diagram of the detection points on the surface microstructure of the sample after high-temperature oxidation in this embodiment. Figure 4 Different positions (spectral) of the pilot sample Figure 1-3 The elemental composition distribution is shown in Table 2.

[0042] Table 1 Figure 2 Different positions (spectral) of the pilot sample Figure 1-3 Elemental composition distribution element Spectrum Figure 1 Spectrum Figure 2 Spectrum Figure 3 Al 14.88 wt.% 15.88 wt.% 15.06 wt.% Pt 25.08 wt.% 25.57 wt.% 26.59 wt.% Table 2 Figure 4 Different positions (spectral) of the pilot sample Figure 1-3 Elemental composition distribution element Spectrum Figure 1 Spectrum Figure 2 Spectrum Figure 3 Al 18.16 wt.% 18.54wt.% 18.00wt.% Pt 10.82 wt.% 11.16wt.% 10.44 wt.% Tables 1 and 2 show the changes in Al content: After high-temperature oxidation, the Al content of the platinum-aluminum protective coating with a 30μm aluminized layer increased from 14.88-15.88% to 18.00-18.54%. This indicates that the alumina film formed in the early stage of oxidation is very dense, effectively preventing Al from diffusing outwards. Simultaneously, Al diffusion and enrichment occurred within the coating. The increase in Al content instead of a decrease indicates minimal coating loss and excellent oxidation resistance. The Pt content of the coating decreased even more, from 25.08-26.59% to 10.44-11.16%, suggesting that the Pt dilution may originate from Al enrichment. In the platinum-aluminum coating, one of the key roles of Pt is to inhibit the precipitation of harmful second phases (such as the TCP phase) and promote the formation of a pure Al2O3 film. The significant decrease in Pt content means that it fully participates in the establishment of the protective mechanism, representing an "effective consumption."

[0043] The protective coating exhibits a clear structure after high-temperature oxidation, with a continuous and dense surface layer of alumina (Al2O3). The diffusion layer is uniform, and secondary reaction zones appear, ranging from 30 to 40 μm in size.

[0044] Example 2: The difference from Example 1 is that the test piece is replaced with a DD6 alloy cylindrical standard test bar (total length 60mm, gauge length diameter Φ5mm). Other processes are the same as in Example 1.

[0045] The test bars prepared with the platinum-aluminum protective coating in this embodiment were subjected to high-temperature tensile testing (standard GB / T 228.2-2015) and creep rupture testing (HB 5150-1996). The test results are shown in Tables 3-4.

[0046] Table 3 High Temperature Tensile Properties Sample number Temperature detection <![CDATA[Tensile strength (N / mm 2 )]]> <![CDATA[Yield strength (N / mm 2 )]]> Elongation after fracture (%) Reduction of area (%) L250223-201 760℃ 1095 948 7.5 12 L250223-202 760℃ 1079 939 5.5 8 L250223-203 760℃ 1090 945 8.0 11 L250223-204 760℃ 1077 944 7.5 11 L250223-205 760℃ 1045 924 9.5 15 Table 4 High Temperature Duration Performance

[0047] Based on the above results, it is demonstrated that the test bar prepared using the aforementioned platinum-aluminum coating process exhibits good adaptability. High-temperature tensile testing shows that it maintains high strength even under oxidation at 760℃. Creep performance results indicate good long-term service stability.

[0048] Comparative Example 1: The difference between this example and Example 1 is that in step 2, platinum layers with thicknesses of 4.5 μm and 5.5 μm were prepared on the substrate surface. Two platinum-aluminum protective coatings were ultimately prepared.

[0049] The microstructure of the coating was characterized using scanning electron microscopy (SEM), such as... Figure 5-6 As shown in the figure. It is clear from the figure that when the electroplating thickness is 4.5 μm ( Figure 5 A small amount of PtAl2 phase began to appear inside the coating; when the electroplating thickness increased to 5.5 μm ( Figure 6 The content of the PtAl2 phase in the coating increased significantly and was distributed in an aggregated manner. Compared with the dense single-phase coating prepared in Example 1 (3.5 μm platinum layer), the coating in this comparative example showed decreased adhesion to the substrate and increased brittleness due to the presence of excessive PtAl2 phase. This indicates that when the electroplating thickness exceeds the range of 3-4 μm, the coating quality will be severely degraded due to the formation of excessive PtAl2 phase, failing to achieve the excellent protective performance expected by this invention.

[0050] Comparative Example 2: The difference between this example and Example 1 is that the thickness of the aluminized layer prepared in step 4 is 50 μm.

[0051] Figure 7 The cross-sectional scanning electron microscope image shows the microstructure of the platinum-aluminum protective coating prepared for this comparative example. Figure 8 The diagram shows the detection points on the surface microstructure of the comparative sample. Figure 8 The elemental composition distribution at different locations in the pilot sample is shown in Table 5. Figure 9 The microstructure of the protective coating prepared for this comparative example after static oxidation at 1100℃ for 200h is shown in the figure. Figure 10 The diagram shows the detection points of the surface microstructure of the oxidized specimen in this comparative example. Figure 10 The elemental composition distribution at different locations in the pilot sample is shown in Table 6.

[0052] Table 5 Figure 8 Different positions (spectral) of the pilot sample Figure 1-3 Elemental composition distribution element Spectrum Figure 1 Spectrum Figure 2 Spectrum Figure 3 Al 21.76wt.% 22.07wt.% 21.48wt.% Pt 25.36wt.% 26.02 wt.% 24.19wt.% Table 6 Figure 10 Different positions (spectral) of the pilot sample Figure 1-3 Elemental composition distribution element Spectrum Figure 1 Spectrum Figure 2 Spectrum Figure 3 Al 16.54wt.% 16.45wt.% 16.02wt.% Pt 14.16wt.% 14.05wt.% 13.34wt.% The test results above show that after oxidation of the protective coating with an aluminized layer thickness of 50 μm, the Al content significantly decreased from 21.48-22.07% to 16.02-16.54%, which is a typical Al loss. Although the final content is similar to that of the protective coating with an aluminized layer thickness of 30 μm, the consumption is large, indicating that the formation efficiency or density of its protective oxide film is not as good as that of the protective coating with a 30 μm aluminized layer thickness.

[0053] After high-temperature oxidation, the Pt content of the protective coating with an aluminized layer thickness of 50 μm decreased from 24.19~26.02% to 13.34~14.16%. However, considering the severe Al loss, the Pt distribution may be uneven, and the optimization effect was not fully realized.

[0054] Although the initial aluminized layer was thicker, the structure degraded significantly after oxidation. Secondary reaction diffusion zones appeared internally, ranging from 80 to 100 μm. This indicates that the effective load-bearing thickness of the coating was drastically reduced, and mechanical properties such as fatigue resistance may decline even faster.

[0055] In summary, the advantages of this invention are as follows: 1. Excellent anti-oxidation properties: The protective coating of the present invention with a specific thickness (platinum layer and aluminized layer) shows that the aluminum content increases rather than decreases after high-temperature oxidation, proving that a dense and highly protective oxide film is formed on the surface, which can effectively prevent the inward diffusion of oxygen.

[0056] 2. Good structural stability: After high-temperature oxidation treatment, the secondary reaction diffusion zone between the coating and the substrate is small, indicating that the coating of this thickness has excellent structural stability as a barrier layer, which can significantly suppress the interdiffusion of elements between the coating and the substrate, thereby better protecting the DD6 single crystal substrate.

[0057] 3. High utilization rate and comprehensive performance: Compared with thicker coatings, the platinum-aluminum coating with a 30±5μm aluminized layer in this invention has a higher effective thickness utilization rate. Most of its thickness is used to form the surface protective layer (aluminized layer) and the intermediate barrier layer (interdiffusion layer), avoiding the degradation of some tissues into harmful diffusion zones due to excessive coating thickness, thus achieving a balance between protective performance and economy.

[0058] Therefore, the preparation method provided by the present invention significantly improves the overall protective performance of the coating and extends the service life of DD6 single crystal high-temperature alloy components by precisely controlling the platinum layer thickness within the range of 3-4 μm and the aluminized layer thickness within the range of 30±5 μm.

[0059] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a platinum-aluminum protective coating on the surface of a DD6 single-crystal high-temperature alloy, characterized in that: This method involves preparing a protective coating on the surface of a DD6 nickel-based single-crystal superalloy substrate, specifically including the following steps: (1) Pretreatment of DD6 nickel-based single crystal superalloy matrix; (2) Electroplating a platinum layer on the pretreated substrate surface, wherein the thickness of the platinum layer is 3 to 4 μm; (3) The sample after electroplating in step (2) is subjected to a first vacuum heat treatment to allow the platinum layer to interdiffused with the substrate to form a platinum modified layer (interdiffusion layer). (4) After heat treatment in step (3), an aluminized layer is prepared on the surface of the platinum modified layer by vapor phase aluminizing method, and the thickness of the aluminized layer is 25-35 μm. (5) After a second vacuum heat treatment under a protective atmosphere, a platinum-aluminum protective coating resistant to high-temperature oxidation is obtained on the surface of DD6 single crystal high-temperature alloy.

2. The method for preparing the platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 1, characterized in that: In step (1), the pretreatment includes electrolytic degreasing and acid pickling activation treatment of the substrate in sequence.

3. The method for preparing the platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 2, characterized in that: The degreasing temperature of the electrolytic degreasing is 35-45℃, the degreasing time is 240-360s, the degreasing current is 0.5A, and the degreasing voltage is 2V. During the pickling and activation process, the activation solution used is a 20wt.% hydrochloric acid solution, and the activation time is 240-360s.

4. The method for preparing a platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 2, characterized in that: In step (2) of the electroplating process, the electroplating solution used is an alkaline platinum plating system with tetraammineplatin hydrogen phosphate as the main salt. The concentration of tetraammineplatin hydrogen phosphate in the electroplating solution is 3.5-5.0 g / L, and the pH of the electroplating solution is 10.2-10.

5. Direct current electroplating is used, and the electroplating process parameters are: current density 2~6 A / dm³. 2 The electroplating time is 25-35 minutes, and the deposition thickness of the platinum layer is precisely controlled to ensure that the platinum layer is uniform, continuous and dense.

5. The method for preparing a platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 1, characterized in that: In step (3), the first vacuum heat treatment is carried out in a vacuum heat treatment furnace at a temperature of 1040~1060℃ and a holding time of 1.5-2.5 hours.

6. The method for preparing the platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 1, characterized in that: In step (4), the process of the vapor phase aluminizing method is as follows: the sample is placed in a aluminizing tank containing aluminizing agent; then, under a protective atmosphere or vacuum, it is heated to 1060~1080℃ and kept at that temperature for 3.5~4.5 hours; the aluminizing agent is composed of CrAl bulk and activator AlF3, with an activator content of 0.15~0.25wt.%.

7. The method for preparing a platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 1, characterized in that: In step (5), the second vacuum heat treatment is carried out in a vacuum heat treatment furnace at a temperature of 860-880℃ and a holding time of 30-35 hours.

8. The method for preparing a platinum-aluminum protective coating on the surface of DD6 single-crystal high-temperature alloy according to claim 1, characterized in that: The heat treatment processes in steps (3) and (5) are carried out under vacuum or inert atmosphere.

9. A platinum-aluminum protective coating on the surface of a DD6 single-crystal superalloy prepared by the method of claim 1, characterized in that: The protective coating is a multi-layer composite structure, consisting of an interdiffusion layer and an aluminizing layer from the substrate surface outwards. The Pt content in the interdiffusion layer increases gradually from the inside out, and the aluminizing layer is mainly composed of NiAl phase, exhibiting good high-temperature stability and oxidation resistance.

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