Si element modified coating for improving high-temperature oxidation resistance of gamma-TiAl alloy and preparation method thereof

Abstract

The present application relates to a preparation technique of high-temperature protective coating of gamma-TiAl alloy, in particular to a Si element modified coating for improving high-temperature oxidation resistance of gamma-TiAl alloy and a preparation method thereof. Al-Si alloy powder, polyvinyl alcohol aqueous solution and ethanol aqueous solution are mixed in a mass ratio of 12:10:3, and then ball-milled for 2 hours to configure Al-Si slurry. Then, the Al-Si slurry is sprayed on the sand-blasted gamma-TiAl base alloy by air spraying, and the coating is obtained after solidification. Then, vacuum or argon gas heat treatment is carried out at 600-750 DEG C for 2-8 hours, and the furnace is cooled down. During the heat treatment process, Al and Si penetrate into the surface of the TiAl alloy base together to prepare the Si element modified coating. The coating is mainly composed of Ti(Al,Si)3 phase, and Si is uniformly distributed in the coating. The preparation method is simple, the thermal diffusion temperature is low, the composition is easy to control, the obtained coating has good compatibility and bonding force with the base, and can significantly improve the high-temperature oxidation resistance of TiAl alloy.

Description

Technical Field

[0001] This invention relates to the preparation technology of high-temperature protective coating for γ-TiAl alloy, specifically a Si element modified coating for improving the high-temperature oxidation resistance of γ-TiAl alloy and its preparation method. The Si element modified coating with Ti(Al,Si)3 as the main phase is prepared on the surface of TiAl alloy by spraying Al-Si slurry and thermal diffusion treatment. Background Technology

[0002] Weight reduction and efficiency improvement are inevitable trends in the development of advanced aero-engines. In recent years, the development of high-performance, high thrust-to-weight ratio aero-engines has promoted the development and application of intermetallic compounds. γ-TiAl-based alloys, with their low density, high elastic modulus, good high-temperature strength, creep resistance, oxidation resistance, and flame retardancy, have become ideal lightweight and high-strength materials to replace nickel-based high-temperature alloys. Currently, γ-TiAl alloys have been successfully applied to key parts of aero-engines, such as high-pressure compressors and low-pressure turbine blades. However, γ-TiAl alloys have insufficient resistance to high-temperature oxidation, especially when the operating temperature exceeds 800℃. A non-protective TiO2 oxide film forms on the surface, and oxygen penetrates into the matrix to form a solid solution with the titanium matrix, reducing the alloy's plasticity and severely affecting its performance. Therefore, a protective coating is necessary to protect it in high-temperature environments.

[0003] Al compound coatings exhibit excellent compatibility with the base alloy and have been extensively studied. Preparation methods mainly include: powder embedding Al diffusion, hot-dip Al diffusion, electroplating Al followed by thermal diffusion, sputtering Al followed by thermal diffusion, and thermal spraying Al followed by thermal diffusion. Al compound coatings can improve the high-temperature oxidation resistance of the base alloy to a certain extent. However, they still have shortcomings. On the one hand, the coating is relatively brittle and prone to cracking; on the other hand, interdiffusion between the coating and the substrate during high-temperature oxidation leads to rapid coating degradation. Simple Al diffusion coatings can no longer meet the increasingly demanding requirements of engine hot-end components. However, Al compound coatings still have two problems: first, the oxide film formed on the surface usually contains TiO2, resulting in poor adhesion and easy peeling; second, at high temperatures, Al elements in the Al diffusion coating rapidly diffuse into the TiAl matrix, causing TiAl3 phase degradation and reducing the coating's high-temperature oxidation resistance.

[0004] To improve the high-temperature oxidation resistance of Al-infiltrated coatings, adding modifying elements to prepare composite co-infiltrated coatings is an effective method. Si is an element that can effectively improve the performance of Al-infiltrated coatings. On the one hand, the SiO2 oxide film formed by Si has excellent oxidation resistance; on the other hand, according to thermodynamic analysis, Si can stabilize Ti elements within the oxide film and coating, thereby increasing the diffusion coefficient of Al and promoting the formation of the Al2O3 phase.

[0005] Powder embedding and slurry methods are widely used for preparing Si-modified coatings. Existing technologies typically use mechanically mixed Al and Si elemental powders as the infiltrator, requiring diffusion temperatures exceeding 1000℃ to activate Al and Si, far exceeding the application temperature range of γ-TiAl alloys, severely damaging the mechanical properties of the substrate. Furthermore, mechanically mixed Al and Si elemental powders suffer from uneven dispersion, making it difficult to ensure uniformity of the diffused coating. Therefore, obtaining a uniform, dense, and high-performance coating within a lower diffusion temperature range is crucial, while ensuring the mechanical properties of the substrate remain unaffected. Generally, higher melting points correspond to lower diffusion coefficients. Compared to Al and Si elemental powders, Al-Si alloy powders have a lower melting point, allowing for Al and Si activation within the normal operating temperature range of the alloy. Therefore, this invention proposes using Al-Si alloy powders to replace traditional Al and Si elemental powders, thereby significantly reducing the heat treatment temperature for preparing Si-modified coatings on TiAl alloy surfaces. Summary of the Invention

[0006] The purpose of this invention is to provide a Si element modified coating and its preparation method for improving the high-temperature oxidation resistance of γ-TiAl alloy. The preparation method is simple to operate, has a low thermal diffusion temperature, and the composition is easy to control. The obtained coating has good compatibility and adhesion with the substrate, and can effectively improve the high-temperature oxidation resistance of TiAl alloy.

[0007] The technical solution of this invention is:

[0008] A Si-modified coating for improving the high-temperature oxidation resistance of γ-TiAl alloy is prepared by spraying Al-Si slurry and thermal diffusion treatment on the surface of TiAl alloy substrate. The coating exhibits metallurgical bonding with the TiAl alloy substrate. The coating is composed of Ti(Al,Si)3 single phase, with an average Al content of 60-72 at.%, an average Si content of 3-15 at.%, and the remainder being Ti.

[0009] The Si-modified coating that improves the high-temperature oxidation resistance of γ-TiAl alloy has Si uniformly distributed in the coating, and the atomic ratio of Al to Si ranges from 12:1 to 5:1.

[0010] The Si element modified coating that improves the high-temperature oxidation resistance of γ-TiAl alloy has a coating thickness of more than 30 μm.

[0011] A method for preparing a Si-modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy involves first sandblasting the surface of a TiAl alloy substrate; then spraying a ball-milled Al-Si slurry onto the sandblasted γ-TiAl alloy substrate; after natural drying at room temperature, drying at 60–100℃ for 20–40 min, and then curing at 230–250℃ for 20–40 min; repeating the above steps 2–3 times to obtain a workpiece with a coating thickness of 50–100 μm.

[0012] The method for preparing the Si element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy is described above. The Al-Si slurry uses Al-Si alloy powder as a penetrant, polyvinyl alcohol aqueous solution as a binder, and ethanol aqueous solution as a diluent. The Si content in the Al-Si alloy powder is 6wt.% to 40wt.%, and the mass ratio of Al-Si alloy powder, polyvinyl alcohol aqueous solution, and ethanol aqueous solution is 12:10:3.

[0013] The method for preparing the Si element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy involves mixing the penetrant, binder, and diluent according to the specified proportions and then ball milling for 1.5–2.5 hours to ensure uniform mixing of the slurry. The penetrant, Al-Si alloy powder, has a particle size of 1–3 μm; the binder, polyvinyl alcohol aqueous solution, has a mass concentration of 5–10 wt.%; and the diluent, ethanol aqueous solution, has a mass concentration of 65–75 wt.%.

[0014] The method for preparing the Si element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy involves an Al-Si slurry spraying method using an air carrier spraying pressure of 0.5–0.6 MPa.

[0015] The method for preparing the Si element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy involves subjecting the sprayed coating to heat diffusion treatment at 600–750℃ for 2–8 hours in an Ar protective atmosphere or vacuum. During the heat treatment, Al and Si co-permeate into the surface of the TiAl alloy substrate. After cooling in the furnace, the resulting Si element modified coating is an intermetallic compound layer of Ti(Al,Si)3.

[0016] The method for preparing the Si element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy involves ultrasonic cleaning and polishing of the workpiece coating surface after the thermal diffusion treatment is completed and the workpiece is taken out of the furnace to remove impurities bonded by the slurry.

[0017] The design concept of this invention is:

[0018] Si-modified coatings can significantly improve the high-temperature oxidation performance of TiAl alloys and are less expensive than Pt-modified Al compound coatings. This invention uses Al-Si alloy powder, prepares a slurry by controlling the ratio of binder to diluent, and then air-sprays it followed by thermal diffusion treatment at a lower temperature to prepare a uniform and dense coating.

[0019] The advantages and beneficial effects of this invention are:

[0020] 1. The coating designed in this invention can significantly improve the high-temperature oxidation resistance of γ-TiAl alloys.

[0021] 2. The coating of this invention is prepared by a slurry method. Compared with other coating manufacturing methods such as thermal spraying, physical vapor deposition, and powder embedding, its process equipment is simple, which minimizes costs and saves raw materials. It can be applied to the local repair of workpieces with complex shapes and infiltration layers.

[0022] 3. The raw material is Al-Si alloy powder, which can reduce the temperature of subsequent vacuum or argon thermal diffusion, further reducing costs, and does not impair the mechanical properties of the matrix.

[0023] 4. The coating prepared by diffusion of Al-Si alloy powder has a uniform composition and is easy to control. Attached Figure Description

[0024] Figure 1 Cross-sectional morphology of Si-modified coatings prepared by air spraying and thermal diffusion treatment.

[0025] Figure 2 XRD patterns of Si-modified coatings prepared by air spraying and thermal diffusion treatment. In the figure, the horizontal axis 2Theta represents the diffraction angle (degree), and the vertical axis Intensity represents the relative intensity (arb.units).

[0026] Figure 3 The figure shows the oxidation kinetics curves of the Si-modified coating at 900℃ for 500 h. In the figure, Time at 900℃ represents the oxidation time (h) at 900℃, and Mass Change on the ordinate represents the mass change (mg / cm³). 2 ). Detailed Implementation

[0027] In its specific implementation, this invention relates to a Si-modified coating for improving the high-temperature oxidation resistance of γ-TiAl alloys and its preparation method. Al-Si alloy powder is used to prepare an Al-Si slurry, which is then air-sprayed onto a sandblasted and cleaned workpiece at a pressure of 0.5–0.6 MPa. After drying at room temperature, it is cured at 80°C and 230–250°C, respectively. Repeated spraying is performed to prepare a coating with a thickness of 50–100 μm. Subsequently, it undergoes vacuum or argon-fluxed heat diffusion treatment at 600–750°C for 2–8 hours, followed by furnace cooling. During the heat treatment, Al and Si co-diffused into the TiAl alloy matrix, preparing a Si-modified coating with Ti(Al,Si)3 as the main component. Si is uniformly distributed in the coating, with an Al to Si atomic ratio ranging from 12:1 to 5:1. This coating exhibits low porosity, good compatibility with the matrix, and strong adhesion, effectively improving the high-temperature oxidation resistance of γ-TiAl alloys.

[0028] In this invention, the Si-modified coating on the surface of the γ-TiAl alloy mainly consists of the Ti(Al,Si)3 phase, with Si uniformly distributed throughout the coating. The coating thickness is above 30 μm (preferably 50–80 μm). Additionally, the coating may contain trace amounts of the tertiary component Mn or Nb introduced through interdiffusion. When preparing the Si-modified coating on the γ-TiAl alloy surface, Al-Si alloy powder, polyvinyl alcohol aqueous solution, and ethanol aqueous solution are mixed in a mass ratio of 12:10:3 and ball-milled for 2 hours to prepare an Al-Si slurry. The particle size range of the raw material Al-Si alloy powder is 1–3 μm, the mass concentration of the binder polyvinyl alcohol aqueous solution is 7 wt.%, and the mass concentration of the diluent ethanol aqueous solution is 70 wt.%.

[0029] To make the technical solution and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0030] Example 1

[0031] Al-12Si alloy powder with a particle size of 1-3 μm, a 7 wt.% aqueous solution of polyvinyl alcohol, and a 70 wt.% aqueous solution of ethanol were mixed in a mass ratio of 12:10:3 and ball-milled for 2 h to prepare an Al-Si slurry. The Al-Si slurry was then sprayed onto the sandblasted γ-TiAl matrix alloy using an air spraying method. After curing at room temperature, 80℃ for 30 min, and 230℃ for 30 min, a coating was obtained. Subsequently, the coating was vacuum heat-treated at 650℃ for 4 h and then cooled in the furnace to prepare a Ti(Al,Si)3 coating with a thickness of 60 μm and uniform Si distribution in the coating.

[0032] like Figure 1 and Figure 2As shown, the coating consists of a single phase of Ti(Al,Si)3, with an average Al content of 63 at.% and an average Si content of 12 at.%. The coating exhibits a metallurgical bond with the substrate. Figure 3 As shown, the TiAl matrix alloy exhibits very rapid weight gain during oxidation, indicating that a non-protective oxide film is formed during high-temperature oxidation. In contrast, the coating shows slow weight gain, significantly reducing the oxidation rate of the matrix alloy and demonstrating excellent high-temperature oxidation resistance. The performance indicator for this embodiment is: the coating's weight gain after isothermal oxidation at 900℃ for 500 hours is less than 1.5 mg / cm³. 2 .

[0033] Example 2

[0034] Al-20Si alloy powder with a particle size of 1-3 μm, a 7 wt.% aqueous solution of polyvinyl alcohol, and a 70 wt.% aqueous solution of ethanol were mixed in a mass ratio of 12:10:3 and ball-milled for 2 hours to prepare an Al-Si slurry. The Al-Si slurry was then sprayed onto the sandblasted γ-TiAl matrix alloy using an air spraying method. After curing at room temperature, 80℃ for 30 min, and 230℃ for 30 min, a coating was obtained. Subsequently, the coating was vacuum heat-treated at 700℃ for 4 hours and then cooled in the furnace to prepare a coating with a thickness of 50 μm. Si was uniformly distributed in the coating.

[0035] In this embodiment, the coating is composed of a single phase of Ti(Al,Si)3, with an average Al content of 61 at.% and an average Si content of 14 at.%. The coating exhibits a metallurgical bond with the substrate. The performance indicators of this embodiment are: the coating's weight gain after 300 cycles of oxidation at 900℃ is less than 3.0 mg / cm³. 2 .

[0036] Example 3

[0037] Al-6Si alloy powder with a particle size of 1-3 μm, a polyvinyl alcohol aqueous solution with a mass concentration of 7 wt.%, and an ethanol aqueous solution with a mass concentration of 70 wt.% were mixed at a mass ratio of 12:10:3 and ball-milled for 2 hours to prepare an Al-Si slurry. The Al-Si slurry was then sprayed onto the sandblasted γ-TiAl matrix alloy using an air spraying method. After curing at room temperature, 80℃ for 30 min, and 230℃ for 30 min, a coating was obtained. Subsequently, the coating was vacuum heat-treated at 700℃ for 4 hours and cooled in the furnace to prepare a coating with a thickness of 50 μm. Si was uniformly distributed in the coating.

[0038] In this embodiment, the coating is composed of a single phase Ti(Al,Si)3, with an average Al content of 71 at.% and an average Si content of 4 at.%. The coating exhibits a metallurgical bond with the substrate. The performance indicator of this embodiment is: the oxide film shows no peeling after 100 cycles of cyclic oxidation at 900°C.

[0039] The results of the examples show that the coating produced by the present invention, which uses air spraying and thermal diffusion treatment, is mainly composed of the Ti(Al,Si)3 phase, with Si uniformly distributed in the coating and a coating thickness of over 30 μm. Compared with traditional slurry processes, the preparation method of the Si element modified coating of the present invention is simple to operate, has a low thermal diffusion temperature, and is easy to control in terms of composition. The obtained coating has good compatibility and adhesion with the substrate, and can significantly improve the high-temperature oxidation resistance of TiAl alloys.

Claims

1. A method for preparing a Si-modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloys, characterized in that, A Si-modified coating was prepared on the surface of a TiAl alloy substrate by spraying Al-Si slurry and thermal diffusion treatment. The coating and the TiAl alloy substrate exhibited a metallurgical bond. The coating was composed of a single phase Ti(Al,Si)3 with an average Al content of 60-72 at.%, an average Si content of 3-15 at.%, and the remainder being Ti. The Al-Si slurry spraying method uses air carrier spraying at a pressure of 0.5–0.6 MPa. The Al-Si slurry uses Al-Si alloy powder as a penetrant, polyvinyl alcohol aqueous solution as a binder, and ethanol aqueous solution as a diluent. The Si content in the Al-Si alloy powder is 6 wt.%–40 wt.%, and the mass ratio of Al-Si alloy powder, polyvinyl alcohol aqueous solution, and ethanol aqueous solution is 12:10:

3. The sprayed coating is then subjected to heat diffusion treatment at 600–750℃ for 2–8 hours in an Ar protective atmosphere or vacuum. During the heat treatment, Al and Si co-permeate the surface of the TiAl alloy substrate. After furnace cooling, the resulting Si-modified coating is an intermetallic compound layer of Ti(Al,Si)3.

2. The method for preparing a Si-element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 1, characterized in that, Si is uniformly distributed in the coating, and the atomic ratio of Al to Si ranges from 12:1 to 5:

1.

3. The method for preparing a Si-element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 1, characterized in that, The coating thickness is above 30µm.

4. The method for preparing a Si-element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 1, characterized in that, First, the surface of the TiAl alloy substrate is sandblasted; then, the ball-milled Al-Si slurry is sprayed onto the sandblasted γ-TiAl alloy substrate; after natural drying at room temperature, it is dried at 60-100℃ for 20-40 minutes, and then cured at 230-250℃ for 20-40 minutes; repeat the above steps 2-3 times to obtain a workpiece with a coating thickness of 50-100μm.

5. The method for preparing a Si-element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 4, characterized in that, Al-Si slurry uses Al-Si alloy powder as a penetrant, polyvinyl alcohol aqueous solution as a binder, and ethanol aqueous solution as a diluent. The Si content in the Al-Si alloy powder is 6 wt.% to 40 wt.%, and the mass ratio of Al-Si alloy powder, polyvinyl alcohol aqueous solution, and ethanol aqueous solution is 12:10:

3.

6. The method for preparing a Si-element modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 5, characterized in that, When preparing Al-Si slurry, the infiltrator, binder, and diluent are mixed according to the required proportions and then ball-milled for 1.5 to 2.5 hours to ensure uniform mixing of the slurry. The particle size of the infiltrator Al-Si alloy powder is 1 to 3 μm, the mass concentration of the binder polyvinyl alcohol aqueous solution is 5 to 10 wt.%, and the mass concentration of the diluent ethanol aqueous solution is 65 to 75 wt.

7. The method for preparing a Si-modified coating to improve the high-temperature oxidation resistance of γ-TiAl alloy according to claim 1, characterized in that, After the thermal diffusion treatment is completed and the workpiece is taken out of the furnace, the coating surface of the workpiece is ultrasonically cleaned and polished to remove impurities that are bound to the slurry.

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