A method for preparing γ / γ' phase platinum aluminum coating on the surface of high temperature alloy substrate

Abstract

The present invention relates to the field of high-temperature protective coatings, and in particular to a method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate. The method comprises the following steps: (1) surface treatment such as pre-grinding, sandblasting and degreasing of the high-temperature alloy substrate; (2) electroplating platinum; (3) pre-diffusion treatment; (4) depositing a layer of pure Al by magnetron sputtering or multi-arc ion plating; (5) diffusion annealing treatment to obtain a high-temperature protective γ / γ' phase platinum aluminum coating. Compared with the common β phase platinum aluminum coating, the γ / γ' phase platinum aluminum coating obtained by the present invention has a significantly lower Al content, which fundamentally reduces the diffusion chemical potential of Al between the coating and the substrate, and avoids the precipitation of needle-like TCP phase, so the coating has excellent low diffusion performance. In addition, the coating also has good long-term oxidation resistance and can be used as a new type of metal bonding layer for turbine blade thermal barrier coating system.

Description

Technical Field

[0001] The invention relates to the field of high-temperature protective coatings, and in particular to a method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate. Background Art

[0002] As aircraft engines develop towards high thrust-to-weight ratio and high-efficiency propulsion, thermal barrier coating technology has become one of the "three key technologies" of high-performance aircraft turbine engines, along with high-temperature alloy material technology and high-efficiency film cooling technology. The thermal barrier coating system is mainly composed of a double-layer structure of a surface ceramic layer and a metal bonding layer. β-phase platinum aluminum coating has a high melting point, low density and good high-temperature oxidation resistance, so it is widely used as a bonding layer in thermal barrier coating systems. However, compared with the high-temperature alloy substrate, the Al content in the β-phase platinum aluminum coating is too high, and severe interdiffusion will occur between the coating and the substrate during service. The consumption of Al in the coating caused by this interdiffusion will not only cause the initial β phase in the coating to degenerate into the γ′ phase, shortening the service life of the coating, but also cause the precipitation of the TCP phase in the alloy substrate below the coating, resulting in a secondary reaction zone and reducing the mechanical properties of the high-temperature alloy.

[0003] In order to alleviate the serious element interdiffusion between the β-phase platinum aluminum coating and the substrate, a γ / γ′ phase platinum aluminum coating can be designed to achieve this goal by reducing the Al content in the coating. However, due to the low Al content in the coating, the long-term high-temperature oxidation resistance is insufficient. At present, the Al content in the coating is generally increased by aluminizing. However, there are many influencing factors in the aluminizing process, and it is not easy to accurately control the Al content of the coating, which easily generates a β phase with too high Al content. Therefore, it is of great significance to develop a preparation method for a γ / γ′ phase platinum aluminum coating that can accurately control the Al content in the coating. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, which has good high-temperature oxidation resistance while ensuring low diffusion performance. After serving for 1000 hours at 1100°C, no needle-like TCP phase is precipitated under the coating, and the oxide film formed on the surface of the coating is a continuous, dense and pure α-Al2O3 film.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, which is used as a coating for engine turbine blades, wherein the long-term service temperature of the coating is above 1100°C, comprising the following steps:

[0007] (1) Surface treatment: The high-temperature alloy substrate is pre-grinded and sandblasted, and then ultrasonically treated with a mixed solution of acetone and alcohol in a volume ratio of 1:1 to remove surface oil stains;

[0008] (2) Platinum electroplating: electroplating 2 to 5 μm thick metal platinum on the treated substrate surface;

[0009] In this step, the electroplated platinum layer is required to be free of defects such as peeling, cracking, flaking, and pinholes visible to the naked eye;

[0010] (3) Pre-diffusion treatment: The platinum-plated sample is placed in a vacuum annealing furnace for pre-diffusion treatment. The pressure in the furnace should be less than 1×10 -3 Pa, keep warm at 1000-1100℃ for 4-6h;

[0011] In this step, the role of the pre-diffusion treatment is to allow the platinum-plated layer to diffuse with the substrate and dilute the platinum content on the surface. The vacuum degree of the pre-diffusion treatment requires a high degree of vacuum. When the vacuum degree is insufficient, the surface will be slightly oxidized, which seriously affects the final coating quality.

[0012] (4) Depositing pure Al: A layer of pure Al with a thickness of 1 to 3 μm is deposited on the surface of the sample after pre-diffusion treatment by magnetron sputtering or multi-arc ion plating. The purity of the Al target used for deposition is greater than 99.99 wt%;

[0013] In this step, the deposited pure Al layer is required to be free of defects such as peeling, cracking, flaking, and pinholes visible to the naked eye;

[0014] (5) Diffusion annealing treatment: After depositing the Al layer, the sample is placed in a vacuum annealing furnace for diffusion treatment. The pressure in the furnace should be less than 1×10 -3 Pa, keep the temperature at 900-1000℃ for 1-3h, and after diffusion annealing, a sample with γ / γ' phase platinum aluminum coating can be obtained.

[0015] In this step, the role of diffusion annealing treatment is to diffuse the surface Al into the coating, dilute the surface Al content, and increase the Al content in the coating; the vacuum degree of diffusion annealing treatment is relatively high. When the vacuum degree is insufficient, oxide inclusions will exist in the formed γ / γ' phase platinum aluminum coating, which seriously affects the final coating quality;

[0016] The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate comprises, in step (1), using white corundum sand with a particle size less than or equal to 220 mesh, and wet sand blowing at a pressure of 0.2 to 0.4 MPa to make the substrate surface have a certain roughness (preferably in the range of Ra = 0.2 to 0.8 μm) to prepare for subsequent platinum electroplating.

[0017] In the method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, in step (2), an alkaline platinum electroplating process is used.

[0018] In the method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, in step (3), the heating rate of the vacuum annealing furnace during the pre-diffusion treatment is below 10°C / min (preferably in the range of 6-10°C / min), and the furnace needs to be cooled to room temperature.

[0019] In the method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, in step (5), the heating rate of the vacuum annealing furnace during diffusion annealing is below 6°C / min (preferably in the range of 4 to 6°C / min), and the furnace needs to be cooled to room temperature.

[0020] The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, the thickness of the γ / γ' phase platinum aluminum coating ranges from 10 to 25 μm, the Al content in the coating does not exceed 25 at.% (preferably in the range of 20 to 25 at.%), the main phase component is the γ / γ' phase, and does not contain the β phase.

[0021] The design concept of the present invention is:

[0022] The present invention develops a protective coating that has a low degree of mutual diffusion with the base alloy, has no needle-like flake TCP phase precipitation during long-term service, and has good resistance to high-temperature oxidation. The common β-phase platinum aluminum coating has very excellent resistance to high-temperature oxidation, but the Al content in the coating is too high, and the mutual diffusion with the base is serious. The β-phase platinum aluminum coating is mainly prepared by electroplating platinum and vapor phase aluminizing. The content of deposited Al during the vapor phase aluminizing process is too much, and it is difficult to reduce the deposited Al content by adjusting the aluminizing process parameters. The present invention deposits the Al layer by magnetron sputtering or multi-arc ion plating, and can accurately control the deposited Al content, so that the Al content in the coating remains moderate, and neither serious mutual diffusion with the base alloy occurs, but also good resistance to high-temperature oxidation is maintained.

[0023] The present invention has the following advantages and beneficial effects:

[0024] 1. The preparation process of the γ / γ' phase platinum aluminum coating of the present invention is simple and highly controllable. The present invention deposits an Al layer on the surface of the sample by magnetron sputtering or multi-arc ion plating, and the thickness of the deposited Al layer can be accurately controlled.

[0025] 2. The γ / γ' phase platinum aluminum coating of the present invention has good high-temperature oxidation resistance. After cyclic oxidation at 1100°C for 1000 hours, the coating surface is still a continuous, dense and pure α-Al2O3 oxide film, and its high-temperature oxidation resistance is equivalent to that of the β-phase platinum aluminum coating.

[0026] 3. The γ / γ' phase platinum aluminum coating of the present invention has excellent low diffusion performance, avoids the precipitation of needle-like TCP phase during service, and basically does not damage the mechanical properties of the base alloy.

[0027] 4. The γ / γ' phase platinum aluminum coating of the present invention solves the problem of oxide film wrinkling. The common β phase platinum aluminum coating will have serious wrinkles in the oxide film during service, which is mainly due to the volume shrinkage caused by the degenerative phase transformation of β→γ' phase in the platinum aluminum coating. The γ / γ' phase platinum aluminum coating does not have β phase, thus avoiding the occurrence of the above problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The cross-sectional morphology (a) and corresponding XRD pattern (b) of the deposited 2μm thick Pt-γ / γ' coating. In the figure (b), the horizontal axis 2theta represents the diffraction angle (deg.), and the vertical axis Intensity represents the relative intensity (au).

[0029] Figure 2 Cross-sectional morphologies of 2 μm thick Pt-γ / γ' coating (a) and β-phase Pt-Al coating (b) after cyclic oxidation at 1100°C for 1000 h.

[0030] Figure 3 The cross-sectional morphology (a) and corresponding XRD pattern (b) of the deposited 5μm thick Pt-γ / γ' coating. In (b), the horizontal axis 2theta represents the diffraction angle (deg.), and the vertical axis Intensity represents the relative intensity (au).

[0031] Figure 4 This is the cross-sectional morphology of a 5 μm thick Pt-γ / γ' coating after cyclic oxidation at 1100°C for 1000 h. DETAILED DESCRIPTION

[0032] In a specific implementation process, the present invention proposes a method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, the method comprising the following steps: (1) pre-grinding, sandblasting and degreasing the high-temperature alloy substrate; (2) electroplating platinum; (3) pre-diffusion treatment; (4) depositing a layer of pure Al by magnetron sputtering or multi-arc ion plating; (5) diffusion annealing treatment to obtain a high-temperature protective γ / γ' phase platinum aluminum coating.

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

[0034] Example 1

[0035] In this embodiment, the substrate used is a nickel-based second-generation single-crystal high-temperature alloy DD5, and the substrate size is Φ16×2mm. The substrate is polished with 240# and 400# sandpaper in turn, and then wet sandblasted with white corundum sand with a particle size less than or equal to 220 mesh at a pressure of 0.3MPa to make the substrate surface have a certain roughness Ra of 0.58μm. Subsequently, an acetone and alcohol mixed solution with a volume ratio of 1:1 is used for ultrasonic treatment to remove surface oil stains, and the substrate is blown dry for use.

[0036] The surface of the treated DD5 substrate is plated with platinum to a thickness of 2 μm using an alkaline electroplating platinum process, and the electroplated platinum layer is required to be free of defects such as peeling, cracking, flaking, and pinholes visible to the naked eye.

[0037] The platinum-plated sample was placed in a vacuum annealing furnace for pre-diffusion treatment. The pressure in the furnace was less than 1×10 -3 Heating was started at 0.0547°C / min with a heating rate of 8°C / min. When the temperature reached 1000°C, it was kept at that temperature for 6 hours and then cooled to room temperature with the furnace to allow better mutual diffusion between the platinum-plated layer and the substrate and dilute the platinum content on the surface.

[0038] A 1 μm thick pure Al layer is deposited on the surface of the pre-diffusion treated sample by magnetron sputtering. The Al target used for deposition is vacuum melted and cast, with a purity greater than 99.99wt%, and a flat plate with a size of 380×128×8mm. The deposited pure Al layer is required to have no defects such as peeling, cracking, flaking, and pinholes visible to the naked eye.

[0039] After the Al layer is deposited, the sample is placed in a vacuum annealing furnace for diffusion treatment. The pressure in the furnace is less than 1×10 -3 Pa, the heating rate is 5℃ / min, and when the temperature reaches 900℃, it is kept for 3h, cooled to room temperature with the furnace, and after diffusion annealing, a sample with γ / γ' phase platinum aluminum coating can be obtained. Figure 1 As shown in the figure, the thickness of the γ / γ' phase platinum aluminum coating is 13.3μm, and the XRD results show that the main phase component of the coating is the γ / γ' phase, without the β phase. The Al content in the coating is 20.7at.%, the Pt content is 10.4at.%, and the rest is the matrix component diffused into the coating.

[0040] The precise control of the Al content in the coating ensures the stable formation of the α-Al2O3 film on the coating surface and avoids severe interdiffusion between the coating and the substrate. Figure 2 The cross-sectional morphologies of the γ / γ' phase platinum aluminum coating of this embodiment and the common β phase platinum aluminum coating after cyclic oxidation at 1100°C for 1000h are shown. It can be seen that the γ / γ' phase platinum aluminum coating has equivalent high-temperature oxidation resistance to the β phase platinum aluminum coating, and only a single layer of α-Al2O3 film is formed on the surface without obvious cracking and peeling. There is no needle-like TCP phase precipitation under the γ / γ' phase platinum aluminum coating, and it has excellent low diffusion performance, while an obvious secondary reaction zone composed of a large number of needle-like TCP phases is formed under the interdiffusion zone of the β phase platinum aluminum coating, and the thickness is relatively large, which seriously affects the high-temperature mechanical properties of the substrate.

[0041] Example 2

[0042] In this embodiment, the substrate used is a nickel-based second-generation single-crystal high-temperature alloy DD5, and the substrate size is Φ16×2mm. The substrate is polished with 240# and 400# sandpaper in turn, and then wet sandblasted with white corundum sand with a particle size less than or equal to 220 mesh at a pressure of 0.2MPa to make the substrate surface have a certain roughness Ra of 0.41μm, and then ultrasonically treated with a mixed solution of acetone and alcohol in a volume ratio of 1:1 to remove surface oil stains, and then blown dry for use.

[0043] The surface of the treated DD5 substrate is plated with platinum to a thickness of 5 μm using an alkaline electroplating platinum process, and the electroplated platinum layer is required to be free of defects such as peeling, cracking, flaking, and pinholes visible to the naked eye.

[0044] The platinum-plated sample was placed in a vacuum annealing furnace for pre-diffusion treatment. The pressure in the furnace was less than 1×10 -3 Heating was started at 0.05 Pa with a heating rate of 8°C / min. When the temperature reached 1100°C, it was kept for 4 hours and then cooled to room temperature with the furnace to allow good mutual diffusion between the platinum-plated layer and the substrate to dilute the platinum content on the surface.

[0045] A 2 μm thick pure Al layer is deposited on the surface of the sample after pre-diffusion treatment by multi-arc ion plating. The Al target used for deposition is a vacuum melting and casting cylindrical target with a purity greater than 99.99wt% and a size of Φ100×40mm. The deposited pure Al layer is required to have no defects such as peeling, cracking, flaking, and pinholes visible to the naked eye.

[0046] After the Al layer is deposited, the sample is placed in a vacuum annealing furnace for diffusion treatment. The pressure in the furnace is less than 1×10 -3 Pa, the heating rate is 5℃ / min, and when the temperature reaches 1000℃, it is kept for 2h, cooled to room temperature with the furnace, and after diffusion annealing, a sample with γ / γ' phase platinum aluminum coating can be obtained. Figure 3 As shown in the figure, the thickness of the γ / γ' phase platinum aluminum coating is 23.1μm, and the XRD results show that the main phase component of the coating is the γ / γ' phase, without the β phase. The Al content in the coating is 22.3at.%, the Pt content is 17.8at.%, and the rest is the matrix component diffused into the coating.

[0047] Figure 4 The cross-sectional morphology of the γ / γ' phase platinum aluminum coating of this embodiment after cyclic oxidation at 1100°C for 1000h is shown. It can be seen that the coating has excellent low diffusion performance and good high temperature oxidation resistance.

[0048] The implementation results show that the γ / γ' phase platinum aluminum coating obtained by the present invention has a significantly lower Al content than the common β phase platinum aluminum coating, which fundamentally reduces the diffusion chemical potential of Al between the coating and the substrate and avoids the precipitation of needle-like TCP phase. Therefore, the coating has excellent low diffusion performance. In addition, the coating also has good long-term oxidation resistance and can be used as a new type of metal bonding layer for turbine blade thermal barrier coating system, which is suitable for the first to fourth generation nickel-based single crystal high-temperature alloys.

[0049] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made based on the spirit and substance of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate, which is used as a coating for engine turbine blades, and the long-term service temperature of the coating is above 1100°C, characterized in that: The following steps are involved: (1) Surface treatment: The high-temperature alloy substrate is pre-grinded and sandblasted, and then ultrasonically treated with a mixed solution of acetone and alcohol in a volume ratio of 1:1 to remove surface oil stains; (2) Platinum electroplating: electroplating 2 to 5 μm thick metal platinum on the treated substrate surface; (3) Pre-diffusion treatment: The platinum-plated sample is placed in a vacuum annealing furnace for pre-diffusion treatment. The pressure in the furnace should be less than 1×10 −3 Pa, keep warm at 1000 ~ 1100 ℃ for 4 ~ 6h; (4) Deposition of pure Al: A layer of pure Al with a thickness of 1 to 3 μm is deposited on the surface of the sample after pre-diffusion treatment by magnetron sputtering or multi-arc ion plating. The purity of the Al target used for deposition is greater than 99.99wt%; (5) Diffusion annealing treatment: After depositing the Al layer, the sample is placed in a vacuum annealing furnace for diffusion treatment. The pressure in the furnace should be less than 1×10 −3 Pa, and keep the temperature at 900 ~ 1000 ℃ for 1 ~ 3h. After diffusion annealing, a sample of γ / γ' phase platinum aluminum coating with the main phase component of γ / γ' phase and no β phase can be obtained.

2. The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate according to claim 1, characterized in that: In step (1), white corundum sand with a particle size less than or equal to 220 mesh is used for wet sand blowing under a pressure of 0.2 to 0.4 MPa to give the substrate surface a certain degree of roughness in preparation for subsequent platinum electroplating.

3. The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate according to claim 1, characterized in that: In step (2), an alkaline platinum electroplating process is used.

4. The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high-temperature alloy substrate according to claim 1, characterized in that: In step (3), the heating rate of the vacuum annealing furnace during the pre-diffusion treatment is less than 10 °C / min, and the furnace needs to be cooled to room temperature.

5. The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high temperature alloy substrate according to claim 1, characterized in that: In step (5), the heating rate of the vacuum annealing furnace during the diffusion annealing treatment is less than 6°C / min, and the furnace needs to be cooled to room temperature.

6. The method for preparing a γ / γ' phase platinum aluminum coating on the surface of a high temperature alloy substrate according to claim 1, characterized in that: The thickness of the γ / γ' phase Pt-Al coating ranges from 10 to 25 μm, and the Al content in the coating does not exceed 25 at.%.

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