Cr-Al coating with both high-temperature oxidation resistance and hot corrosion resistance and its vapor infiltration preparation process

Abstract

This invention discloses a Cr-Al coating with both high-temperature oxidation and hot corrosion resistance and its vapor phase infiltration preparation process, belonging to the technical field of high-temperature protective coatings. The coating consists of a β-NiAl phase and an α-Cr phase, with Al and Ni elements evenly distributed throughout the coating. The Cr element, in the form of an α-Cr phase, is dispersed throughout the coating's outer layer and interdiffusion zone, effectively reducing the diffusion of aluminum from the coating into the substrate, thereby improving its hot corrosion resistance and high-temperature oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature protective coatings, and in particular to a Cr-Al coating having both high-temperature oxidation resistance and thermal corrosion resistance and a vapor phase infiltration preparation process thereof. Background Art

[0002] The higher the inlet temperature of hollow turbine blades in aircraft engines and gas turbines, the more efficient they are. Turbine blades operate in harsh environments of high temperature and pressure. Nickel-based high-temperature single-crystal alloys, with their excellent high-temperature mechanical properties, are the material of choice for turbine blades in advanced fighter aircraft and gas turbines. In practice, alloys are often required to possess both excellent mechanical properties and high-temperature corrosion resistance, but these requirements are difficult to achieve in the same material. The best solution is typically to apply a protective coating to the surface of the alloy substrate, which already possesses excellent mechanical properties, to enhance its resistance to high-temperature oxidation and corrosion.

[0003] While coatings can be deposited on the outer surface of blades using a variety of methods, including PVD, CVD, and thermal spray, depositing coatings within the blade cavity is limited to slurry deposition, embedding, and chemical vapor deposition. Currently, advanced fighter aircraft turbine blades have complex structures, intricately curved surfaces, and winding gaps within them. Traditional slurry and embedding methods are no longer suitable for preparing coatings within the blade cavity.

[0004] Chinese invention patent application 202011071362.1 discloses a method and apparatus for fluoride ion cleaning and aluminide coating preparation for blades with complex inner cavities. This method first uses fluoride ions to clean the inner cavities of the blades, and then uses chemical vapor deposition to prepare the aluminide coating. Chinese invention patent application 201510812234.0 discloses a process for aluminizing the inner cavities and outer surfaces of cobalt-based alloy blades. These two technologies use large amounts of highly dangerous hydrogen fluoride and hydrogen in the preparation of aluminide coatings, placing high demands on the experimental equipment. Therefore, there is a domestic gap in the development of a method that requires low equipment requirements and can prepare complex inner cavity coatings without the use of complex equipment and highly dangerous gases. Summary of the Invention

[0005] The purpose of the present invention is to provide a vapor-phase infiltrated Cr-Al coating with both high-temperature oxidation resistance and thermal corrosion resistance and a preparation process thereof. The method can prepare the coating in the complex blade cavity and irregular surface of the workpiece. The coating contains α-Cr and β-NiAl phases, and provides sufficient content of Cr and Al elements while ensuring the thermal stability of the coating, which can improve the high-temperature oxidation resistance and thermal corrosion resistance of the coating.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A Cr-Al coating with both high-temperature oxidation resistance and hot corrosion resistance consists of a β-NiAl phase and an α-Cr phase.

[0008] Furthermore, the Al and Ni elements are evenly distributed in the coating; the Cr element is dispersed in the outer layer of the coating and the interdiffusion zone in the form of an α-Cr phase, which can effectively reduce the diffusion of aluminum elements in the coating into the substrate and improve the heat corrosion resistance and high-temperature oxidation resistance.

[0009] Furthermore, the average contents of Al, Ni and Cr elements on the surface of the Cr-Al coating are: Al is 40-60at.%, Ni is 30-50at.%, and Cr is 2-8at.%; the contents of Al, Ni and Cr elements at the precipitation phase (α-Cr phase) position on the surface of the Cr-Al coating are: Al is 30-40at.%, Ni is 25-35at.%, and Cr is 25-35at.%.

[0010] Furthermore, the Cr-Al coating is prepared on a nickel-based high-temperature alloy substrate, for example, the nickel-based high-temperature alloy substrate is a complex blade cavity or an irregular alloy part surface.

[0011] The Cr-Al coating having both high-temperature oxidation resistance and hot corrosion resistance is prepared by a vapor phase infiltration process, which comprises the following steps:

[0012] (1) vapor deposition of Cr element on the substrate to form a chromized base layer;

[0013] (2) Al element is vapor-deposited on the Cr-infiltrated base layer, and finally a Cr-Al coating with both high-temperature oxidation resistance and hot corrosion resistance is obtained.

[0014] In the above-mentioned step (1) vapor deposition, the vapor-phase Cr infiltrant consists of a Cr infiltrating source, an activator and a filler, wherein the Cr infiltrating source is Cr powder, the activator is ammonium chloride, and the filler is alumina powder; the chromium powder content in the vapor-phase Cr infiltrant is 1-50wt.%, the activator content is 0.5-10wt.%, and the rest is filler; the particle size of the Cr powder is 60 mesh-1000 mesh, and the particle size of the filler is 60 mesh-600 mesh.

[0015] In the above step (1), the substrate is suspended above the chromizing agent. During the deposition of the Cr element, the temperature is 850-1200°C, the time is 0.5-6 hours, argon is passed for protection, and the ventilation volume is 3-20L / min. After chromizing, a Cr-rich coating, namely a chromized base layer, is formed.

[0016] In the above step (1), the thickness of the chromized base layer is 3-20 μm.

[0017] In the above-mentioned step (2) of vapor deposition of Al element, the Al-infiltrating agent used is composed of an Al-infiltrating source and an activator, wherein the Al-infiltrating source is a chromium-aluminum block and the activator is aluminum fluoride trihydrate powder; the activator content in the Al-infiltrating agent is 0.5-10wt.%, and the rest is the chromium-aluminum block.

[0018] The process of vapor deposition of Al element in step (2) is as follows: placing the sample treated in step (1) (the substrate with the chromized base layer) in acetone, anhydrous ethanol and deionized water in turn and ultrasonically cleaning them for 5 minutes respectively, and then blowing them dry; hanging the sample above the aluminizing agent, during the deposition process of the aluminum element, the temperature is 950-1100°C, the time is 1-8 hours, argon is passed for protection, and the ventilation volume is 3-20L / min. After aluminizing, a Cr-Al coating composed of β-NiAl phase and α-Cr phase is formed.

[0019] The present invention adopts a two-step vapor deposition method for Cr-Al coating, which has the following advantages compared with the traditional Cr-Al coating preparation method:

[0020] 1. This invention utilizes a two-step vapor deposition coating process, enabling precise control of the thickness of each layer. A Cr layer is first deposited on the substrate, followed by an Al layer. This results in the presence of α-Cr precipitates in the interdiffusion zone and outer layer of the coating. The outer layer of the coating is primarily composed of a β-NiAl phase with a small amount of α-Cr precipitates dispersed therein. The chromium and aluminum contents can be adjusted based on actual usage.

[0021] 2. In high-temperature corrosion protection applications, the presence of Cr can significantly improve the corrosion resistance of the coating. The deposited Cr in the present invention can reduce the critical Al content for selective oxidation of Al, improving the "self-repair" ability of the oxide film. In addition, in the coating of the present invention, most of the Cr forms a diffusion barrier in the interdiffusion zone (at the interface between the substrate and the coating), which can reduce the diffusion of Al elements in the coating into the substrate. A small portion is dispersed in the outer layer of the coating. In a hot corrosion environment, the Cr in the outer layer of the coating can fix S and improve the hot corrosion resistance of the coating.

[0022] 3. The coating preparation method of the present invention can deposit coatings on the outer surface and inner cavity surface of parts with complex shapes, with good coating properties and uniform coating thickness and structure.

[0023] 4. The Cr content in the coating of the present invention can be adjusted within a wide range, breaking through the Cr content in traditional Cr-modified aluminide coatings, and having excellent hot corrosion resistance.

[0024] 5. The thickness of the Cr-infiltrated layer of the present invention is easy to control, and the thickness can be adjusted to about 3-20 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1This is the surface morphology of the vapor-phase chromized coating in Example 1.

[0026] Figure 2 This is a cross-sectional morphology of the vapor-phase chromized coating in Example 1.

[0027] Figure 3 Surface morphology of the Cr-Al coating in Example 1; wherein: (a) is the surface morphology under a large field of view; (b) is the magnified surface morphology under a large field of view.

[0028] Figure 4 The cross-sectional morphology and Cr element distribution surface scan of the aluminized coating in Example 1; wherein: (a) is the cross-sectional morphology; (b) is the Cr element distribution surface scan.

[0029] Figure 5 This is the XRD pattern of the Cr-Al coating in Example 1.

[0030] Figure 6 The surface morphology and cross-sectional morphology of the Cr-Al coating and the NiAl coating in Example 1 after constant temperature oxidation at 1100°C for 300h and the corresponding cross-sectional surface scans are shown.

[0031] Figure 7 The oxidation kinetic curves of the Cr-Al coating and the NiAl coating in Example 1 were obtained by constant temperature oxidation at 1100°C for 300 hours.

[0032] Figure 8 This is the surface morphology of the vapor-phase chromizing coating in Example 2.

[0033] Figure 9 This is a cross-sectional morphology of the vapor-phase chromized coating in Example 2.

[0034] Figure 10 These are the surface morphologies of the vapor-diffused Cr-Al coating in Example 2; wherein: (a) is the surface morphology under a large field of view; and (b) is the magnified surface morphology under a large field of view.

[0035] Figure 11 These are the cross-sectional morphology and Cr element distribution surface scan of the vapor-diffused Cr-Al coating in Example 2; wherein: (a) is the cross-sectional morphology; (b) is the Cr element distribution surface scan.

[0036] Figure 12 This is the XRD pattern of the Cr-Al coating in Example 2.

[0037] Figure 13 This is the corrosion weight gain curve of the Cr-Al coating and the NiAl coating in Example 2 when corroded at 900°C in a mixed salt of 75 Na2SO4 wt.% + 25 NaCl wt.% for 100 h.

[0038] Figure 14 These are the surface morphologies and cross-sectional morphologies of the Cr-Al coating and NiAl coating in Example 2 after being corroded at 900°C in a mixed salt of 75 wt.% Na2SO4 + 25 wt.% NaCl for 100 h.

[0039] Figure 15 This is the surface morphology of the vapor-phase chromizing coating in Example 3.

[0040] Figure 16 This is a cross-sectional morphology of the vapor-phase chromized coating in Example 3.

[0041] Figure 17 Surface morphology of the vapor-diffused Cr-Al coating in Example 3; wherein: (a) is the surface morphology under a large field of view; (b) is the magnified surface morphology under a large field of view.

[0042] Figure 18 This is the cross-sectional morphology of the vapor-diffused Cr-Al coating in Example 3. DETAILED DESCRIPTION

[0043] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0044] The invention provides a process for preparing a Cr-Al coating for the inner cavity of a hollow turbine blade of an aero-engine or a gas turbine.

[0045] High-temperature oxidation and thermal corrosion are common failure modes of gas turbine blades. As the operating temperature of gas turbine blades increases, the requirements for the performance of protective coatings also increase. Simple aluminide coatings have good resistance to high-temperature oxidation, but poor resistance to thermal corrosion. The main idea to improve the thermal corrosion resistance and high-temperature oxidation resistance of simple aluminide coatings is to ensure a high Al content in the coating. The consumption of Al elements is inevitable at high temperatures. Generally, the consumption of Al elements in the coating is reduced from two aspects. On the one hand, the adhesion of the protective oxide film formed on the surface of the coating is improved, and on the other hand, the diffusion rate of Al elements in the coating into the substrate is reduced. The current method is to add third elements such as Pt, Cr, Si, and Y for modification to improve the high-temperature oxidation resistance and thermal corrosion resistance of the coating.

[0046] Increasing the thrust of an aircraft engine can effectively improve the engine's operating efficiency, but it also increases the air inlet temperature of the turbine blades. In order to adapt to high temperatures, turbine blades, on the one hand, use single-crystal high-temperature alloys with excellent high-temperature mechanical properties, and on the other hand, change the blades from a solid structure to a hollow structure to improve heat dissipation conditions. The main advantage of single-crystal high-temperature alloys is their excellent mechanical properties, but their disadvantage is their low Al and Cr content, which makes them less resistant to high-temperature oxidation and thermal corrosion. In addition, improvements in the casting process have resulted in the thinnest wall thickness of hollow turbine blades being only about 0.5 mm. If the coating is not applied, the service life and working stability of the blades will be greatly reduced.

[0047] Traditional methods for preparing blade inner cavity coatings include slurry and embedding methods. However, the inner cavities of turbine blades in advanced fighter aircraft are complex in shape, and slurry and embedding methods are prone to leakage, resulting in uneven coatings. After the coating is applied, cleaning the inner cavity is difficult, labor-intensive, and prone to pore blockage. The present invention utilizes vapor deposition, introducing a reactive atmosphere into the blade inner cavity to deposit the coating. This results in a uniform coating, a dense surface, and no cleaning required, offering significant advantages in the preparation of inner cavity coatings.

[0048] Example 1:

[0049] The substrate is a nickel-based single crystal high-temperature alloy with the following chemical composition (mass percentage wt.%): Cr: 4.3%, Co: 8.0%, W: 7.7%, Mo: 0.8%, Al: 5.6%, Nb: 1.4%, Ta: 3.5%, Re: 3.5%, Ni: balance. A high-temperature alloy rod with a diameter of 15 mm is processed into a 1.5 mm thick disc by wire cutting. The center of the disc is 1.5 mm from the edge of the disc. The circular hole of mm is convenient for suspension during vapor deposition.

[0050] The substrate was polished using SiC180#, 400#, and 800# sandpaper, and the corners were rounded. Then, the substrate was sandblasted using 300# corundum sand at a pressure of 0.5 MPa. Finally, the substrate was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 15 minutes, followed by drying.

[0051] Normal pressure vapor chromizing is adopted, and the vapor chromizing agent consists of a chromizing source, an activator and a filler; the chromizing source is chromium powder, the activator is ammonium chloride, and the filler is aluminum oxide powder; the chromium powder content is 10wt.%, the activator content is 1wt.%, and the rest is filler; the chromium powder particle size is 300 mesh, and the filler particle size is 80 mesh.

[0052] The process of vapor phase chromization is as follows: hang the sample above the chromizing agent, pass argon protection, the flow rate is 5L / min, the temperature is 1020℃, the heating rate is 8℃ / min, and the temperature is kept for 1 hour. The surface morphology of the coating obtained after chromization is as follows Figure 1 As shown, the cross-sectional morphology is Figure 2 As shown in FIG. 1 , EDS analysis shows that the average content of each element in the coating after chromizing is 54.41Cr-34.00Ni-5.95Co-5.56W (at.%).

[0053] Subsequently, atmospheric pressure vapor phase Al infiltration is adopted, and the vapor phase aluminizing agent consists of an aluminizing source and an activator; the aluminizing source is a chromium-aluminum block (the aluminum and chromium contents in the chromium-aluminum block are both 50wt.%), and the activator is aluminum fluoride trihydrate powder; the activator content is 3wt.%, and the rest is the chromium-aluminum block.

[0054] The vapor phase Al infiltration process is as follows: hang the sample above the aluminizing agent, pass argon gas protection at normal pressure, the flow rate is 5L / min, the aluminizing temperature is 1060℃, the heating rate is 8℃ / min, and the temperature is kept for 3 hours. The surface morphology of the coating obtained after aluminizing is as follows Figure 3 As shown, the cross-sectional morphology is Figure 4 As shown. EDS analysis shows that the average element content of the prepared Cr-Al coating surface is: 49.27Al-42.28Ni-3.96Cr-3.49Co (at.%), and the element content of the precipitated phase position on the coating surface is: 34.58Al-32.59Ni-29.72Cr-3.11Co (at.%). XRD results show that the coating is composed of β-NiAl phase and α-Cr phase. Figure 5 As shown in the figure, the outer layer of the coating that is directly Al-infiltrated on the substrate surface without Cr-infiltration is composed of a single β-NiAl phase.

[0055] The NiAl coating obtained by vapor phase infiltration of Al alone and the Cr-Al coating obtained by two-step infiltration of Cr and Al were subjected to constant temperature oxidation experiments in a muffle furnace at a temperature of 1100°C for 300 hours. The oxidation results showed that after 300 hours of oxidation, the Cr-Al coating had less oxide film peeling than the NiAl coating, and the Cr-Al coating had more β-NiAl phase, such as Figure 6 As shown in the figure. EDS analysis shows that the average element content of the Cr-Al coating after oxidation treatment is 44.81Ni-45.16Al-5.03Co-5.01Cr (at.%), and the average element content of the NiAl coating is 56.47Ni-33.35Al-6.87Co-3.30Cr (at.%). The oxidation kinetic curve shows that after 10 hours of oxidation, the oxidation weight increase of the NiAl coating is greater than that of the Cr-Al coating. Figure 7 shown.

[0056] The NiAl coating obtained by vapor-phase infiltration of Al only and the Cr-Al coating obtained by two-step infiltration of Cr and Al were subjected to corrosion tests. The process is as follows: first prepare a saturated salt solution, put 75g of anhydrous Na2SO4 salt and 25g of anhydrous NaCl salt in the same container, and use deionized water to make an approximately saturated solution. Place the sample on a heating device and preheat it for 1-3 minutes. Use a spray pen to evenly spray the mixed salt solution onto the coating surface. The required spraying amount is 1mg / cm2, and both sides are sprayed. The sprayed sample is hung in a muffle furnace for corrosion testing. The muffle furnace temperature is 900℃. After the sample is taken out of the muffle furnace and cooled, the surface salt is washed off in boiling water, blown dry and weighed, and the change in sample weight is recorded. Then, the salt solution is sprayed again for thermal corrosion.

[0057] After 100 hours of corrosion, a large amount of corrosion products were generated on the surface of the NiAl coating, the oxide film of the coating was severely cracked and peeled off, and the coating was completely corroded and failed. The average element content in the coating was 68.74Ni-12.03Al-10.79Co-4.91W-1.84Cr-1.69S (at.%); since Cr can lower the threshold of Al selective oxidation, a new oxide film can be generated at the place where the oxide film peels off. The oxide film of the Cr-Al coating is relatively complete, and the coating corrosion is lighter than that of the NiAl coating. The average element content in the coating is 54.71Ni-35.16Al-5.45Co-4.67Cr (at.%).

[0058] Example 2:

[0059] The substrate is a nickel-based single crystal high-temperature alloy with the following chemical composition (mass percentage): Cr: 4.3%, Co: 8.0%, W: 7.7%, Mo: 0.8%, Al: 5.6%, Nb: 1.4%, Ta: 3.5%, Re: 3.5%, Ni: balance. A high-temperature alloy rod with a diameter of 15 mm is processed into a 1.5 mm thick disc by wire cutting. The center of the disc is 1.5 mm from the edge of the disc. The circular hole of mm is convenient for suspension during vapor deposition.

[0060] The substrate was polished using SiC 180#, 400#, and 800# sandpaper, and the corners were rounded. It was then sandblasted using 300# steel sand at a pressure of 0.5 MPa. The substrate was then ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 15 minutes before being dried.

[0061] Atmospheric pressure vapor chromizing is adopted, and the vapor chromizing agent consists of a chromizing source, an activator and a filler; the chromizing source is chromium powder, the activator is ammonium chloride, and the filler is aluminum oxide powder; the chromium powder content is 20wt.%, the activator content is 2wt.%, and the rest is filler; the chromium powder particle size is 300 mesh, and the filler particle size is 80 mesh.

[0062] The process of vapor phase chromization is as follows: the sample is suspended above the chromizing agent, and argon gas is passed through at normal pressure for protection, with a flow rate of 5L / min, aluminizing temperature of 1060℃, heating rate of 8℃ / min, and holding temperature for 2 hours. The surface morphology of the coating obtained after chromization is as follows Figure 8 As shown, the cross-sectional morphology is Figure 9 As shown in FIG. 1 , EDS analysis shows that the content of each element in the coating after chromizing is 61.43Cr-28.30Ni-5.98Co-4.29W (at.%).

[0063] Subsequently, atmospheric pressure vapor phase Al infiltration is adopted, and the vapor phase aluminizing agent is composed of an aluminizing source and an activator; the aluminizing source is a chromium-aluminum block (the aluminum and chromium contents in the chromium-aluminum block are both 50wt.%), and the activator is aluminum fluoride trihydrate powder; the activator content is 3wt.%, and the rest is the chromium-aluminum block.

[0064] The vapor phase Al infiltration process is as follows: the sample is suspended above the aluminizing agent, argon gas is passed through at atmospheric pressure, the flow rate is 5L / min, the aluminizing temperature is 1060℃, the heating rate is 8℃ / min, and the temperature is kept at this temperature for 4 hours. The surface morphology of the coating obtained after chromization is as follows Figure 10 As shown, the cross-sectional morphology is Figure 11 As shown. EDS analysis shows that the average element content of the Cr-Al coating surface is 49.32Al-45.46Ni-5.22Cr (at.%), and the element content of the precipitated phase is 31.35Al-32.41Ni-28.11Cr-4.13Co (at.%). XRD results show that the internal structure of the coating is β-NiAl and α-Cr, as shown in Figure 2. Figure 12 shown.

[0065] The NiAl coating obtained by vapor phase infiltration of Al and the CrAl coating obtained by two-step infiltration of Cr and Al were subjected to corrosion experiments (same as in Example 1). The cross-sectional and surface morphology images ( Figure 13) It can be found that after 100 hours of corrosion, a large amount of corrosion products are generated on the surface of the NiAl coating, and the coating is corroded to failure. The average element content of the outer layer of the coating is 68.74Ni-12.03Al-1079Co-1.84Cr-1.69S-10.79Co (at.%). Compared with the NiAl coating, the surface corrosion damage of the Cr-Al coating is smaller, the Cr content in the coating is higher, and the surface state is better. After corrosion, the average element content of the outer layer of the coating is 54.23Ni-36.43Al-5.03Co-4.31Cr (at.%). This is because Cr can reduce the intrusion of "S" and "Cl" ions in the corrosive salt into the coating, and Cr can generate stable CrS with S, fix the corrosive elements that invade the coating, hinder the corrosion of the coating, and keep the structure intact. During the entire corrosion process, the weight gain of the NiAl coating is higher than that of the Cr-Al coating. The corrosion weight gain curve is shown as follows. Figure 14 As shown in Figure 3, it also shows that the Cr-Al coating has a lower corrosion rate than the simple NiAl coating.

[0066] After 200 hours of constant-temperature oxidation, the oxide film on the surface of the simple NiAl coating peeled off extensively, with no new oxide film forming at the peeled areas. The cross-section of the coating showed significant Al depletion, with the Ni3Al phase dominating the coating, while the NiAl phase made up a small fraction. The oxide film of the Cr-Al coating also cracked and peeled, but the peeling occurred in a limited number of locations and over a small area. The cross-section of the coating was dominated by the NiAl phase, and the coating structure was intact.

[0067] Example 3:

[0068] The substrate is a nickel-based single crystal high-temperature alloy with the following chemical composition (mass percentage): Cr: 4.3%, Co: 8.0%, W: 7.7%, Mo: 0.8%, Al: 5.6%, Nb: 1.4%, Ta: 3.5%, Re: 3.5%, Ni: balance. A high-temperature alloy rod with a diameter of 15 mm is processed into a 1.5 mm thick disc by wire cutting. The center of the disc is 1.5 mm from the edge of the disc. The circular hole of mm is convenient for suspension during vapor deposition.

[0069] The substrate was polished using SiC180#, 400#, and 800# sandpaper, and the corners were rounded. It was then sandblasted using 300# corundum sand at a pressure of 0.5 MPa. The sample substrate was then ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 15 minutes before being dried.

[0070] Atmospheric pressure vapor chromizing is adopted, and the vapor chromizing agent consists of a chromizing source, an activator and a filler; the chromizing source is chromium powder, the activator is ammonium chloride, and the filler is aluminum oxide powder; the chromium powder content is 30wt.%, the activator content is 5wt.%, and the rest is filler; the chromium powder particle size is 300 mesh, and the filler particle size is 80 mesh.

[0071] The process of vapor phase chromization is as follows: the sample is suspended above the chromizing agent, and argon gas is passed through the sample at normal pressure for protection, with a flow rate of 5L / min, a temperature of 1080℃, a heating rate of 8℃ / min, and a holding time of 1.5 hours. The surface morphology of the coating obtained after chromization is as follows: Figure 15 As shown, the cross-sectional morphology is Figure 16 As shown, EDS analysis shows that the element content of the coating after chromizing is 64.17Cr-26.66Ni-4.43Co-4.74W (at.%).

[0072] Subsequently, atmospheric pressure vapor phase Al infiltration is adopted, and the vapor phase aluminizing agent is composed of an aluminizing source and an activator; the aluminizing source is a chromium-aluminum block (the aluminum and chromium contents in the chromium-aluminum block are both 50wt.%), and the activator is aluminum fluoride trihydrate powder; the activator content is 3wt.%, and the rest is the chromium-aluminum block.

[0073] The process of vapor phase Al infiltration is as follows: hang the sample above the aluminizing agent, pass argon protection at normal pressure, flow rate of 5L / min, temperature of 1060℃, heating rate of 8℃ / min, and keep warm for 4 hours. The surface morphology of the coating obtained after Al infiltration is as follows Figure 17 As shown, the cross-sectional morphology is Figure 18 EDS analysis shows that the average element content of the Cr-Al coating surface is 54.67Al-36.74Ni-4.66Cr-2.93Co (at.%), and the element content of the precipitated phase is 34.58Al-32.27Ni-29.97Cr-2.30Co-0.88Fe (at.%). XRD results show that the internal structure of the coating is β-NiAl and α-Cr phases.

[0074] A NiAl coating obtained by vapor-phase infiltration of Al alone and a CrAl coating obtained by a two-step Cr-in-Al infiltration process were subjected to constant-temperature oxidation experiments in a muffle furnace at 1100°C for 200 hours. The oxidation results showed that after 200 hours of oxidation, the NiAl coating exhibited significant formation of mixed oxides, severe cracking and spalling, and significant Al depletion in the coating. Compared to the NiAl coating, the Cr-Al coating exhibited less spalling and less Al depletion in the coating.

[0075] A NiAl coating obtained by vapor-phase infiltration of Al and a Cr-Al coating obtained by infiltration of Cr and Al in a two-step process were subjected to corrosion tests (same as in Example 1): After 100 hours of corrosion, the NiAl coating oxide film suffered severe corrosion, with a large amount of corrosion products appearing. The protective effect of the oxide film on the coating was essentially lost, and the interior of the coating was completely corroded, losing its protective effect on the substrate. The Cr-Al coating oxide film had a higher integrity, fewer corrosion products, and a lighter degree of corrosion within the coating. The average element content within the coating was 52.62Ni-36.30Al-6.12Co-4.97Cr (at.%), indicating that a new oxide film protective coating could be generated.

Claims

1. A Cr-Al coating having both high-temperature oxidation resistance and hot corrosion resistance, characterized in that: The coating consists of β-NiAl phase and α-Cr phase, and the Al and Ni elements are evenly distributed in the coating. The Cr element is dispersed in the outer layer of the coating and the interdiffusion zone in the form of the α-Cr phase, which can effectively reduce the diffusion of aluminum elements in the coating into the substrate, thereby improving the heat corrosion resistance and high-temperature oxidation resistance. The Cr-Al coating is prepared by a vapor infiltration process, which includes the following steps: (1) vapor deposition of Cr element on the substrate to form a chromized base layer; (2) vapor deposition of Al elements on the Cr-infiltrated substrate to ultimately obtain a Cr-Al coating with both high-temperature oxidation resistance and hot corrosion resistance; In step (1) vapor deposition, the vapor-phase Cr infiltrant is composed of a Cr source, an activator, and a filler, wherein the Cr source is Cr powder, the activator is ammonium chloride, and the filler is alumina powder; the chromium powder content in the vapor-phase Cr infiltrant is 1-50 wt.%, the activator content is 0.5-10 wt.%, and the rest is filler; the Cr powder particle size is 60 mesh to 1000 mesh, and the filler particle size is 60 mesh to 600 mesh; In the process of vapor deposition of Al element in step (2), the Al infiltration agent used is composed of an Al infiltration source and an activator, wherein the Al infiltration source is a chromium aluminum block and the activator is aluminum fluoride trihydrate powder; the activator content in the Al infiltration agent is 0.5-10wt.%, and the rest is the chromium aluminum block.

2. The Cr-Al coating having both high-temperature oxidation resistance and hot corrosion resistance according to claim 1, characterized in that: The average contents of Al, Ni and Cr elements on the surface of the Cr-Al coating are: Al is 40-60at.%, Ni is 30-50at.%, and Cr is 2-8at.%; the contents of Al, Ni and Cr elements at the precipitation phase position on the surface of the Cr-Al coating are: Al is 30-40at.%, Ni is 25-35at.%, and Cr is 25-35at.%; the precipitation phase on the surface of the Cr-Al coating is an α-Cr phase.

3. The Cr-Al coating having both high temperature oxidation resistance and hot corrosion resistance according to claim 1, characterized in that: The Cr-Al coating is prepared on a nickel-based high-temperature alloy substrate.

4. The Cr-Al coating having both high-temperature oxidation resistance and hot corrosion resistance according to claim 1, characterized in that: In step (1), the substrate is suspended above the chromizing agent. During the deposition of the Cr element, the temperature is 850-1200°C, the time is 0.5-6 hours, argon is passed for protection, and the ventilation volume is 3-20L / min. After chromizing, a Cr-rich coating, i.e., a chromized base layer, is formed.

5. The Cr-Al coating having both high temperature oxidation resistance and hot corrosion resistance according to claim 1, characterized in that: In step (1), the thickness of the chromized base layer is 3-20 μm.

6. The Cr-Al coating having both high-temperature oxidation resistance and hot corrosion resistance according to claim 1, characterized in that: The process of vapor deposition of Al element in step (2) is as follows: placing the substrate with the chromized base layer treated in step (1) in acetone, anhydrous ethanol and deionized water in turn for ultrasonic cleaning for 5 minutes respectively, and then drying; hanging the sample above the aluminizing agent, during the deposition process of the aluminum element, the temperature is 950-1100°C, the time is 1-8 hours, argon is passed for protection, and the ventilation volume is 3-20L / min. After aluminizing, a Cr-Al coating composed of β-NiAl phase and α-Cr phase is formed.

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