Environmental barrier coating with gradient structure and long service life and suspension plasma spraying preparation method thereof

Abstract

The invention relates to the field of high-temperature protective ceramic coatings for aero-engines, and particularly discloses an environmental barrier coating with a gradient structure and a long service life and a suspension plasma spraying preparation method thereof. The specific method comprises the following steps: by taking silicon powder as a raw material, preparing a bonding layer on a silicon carbide ceramic or SiCf / SiC ceramic-based composite material by utilizing an axial powder feeding three-electrode atmosphere plasma spraying system, preparing suspension liquid by taking rare earth silicate RE2Si2O7 and the like as raw materials, and respectively spraying a compact structure RE2Si2O7 middle layer and a columnar crystal-like structure RE2Si2O7 surface layer; and the prepared state coating is placed in Ar atmosphere and subjected to high-temperature annealing treatment, and the environment barrier coating with the high crystallinity and the gradient structure is obtained. The coating prepared by the invention has gradient transition structural characteristics, has excellent thermal shock resistance in actual tests, and has important application significance in prolonging the service life of silicon carbide ceramic or SiCf / SiC ceramic-based composite materials.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protective ceramic coatings for aero-engines, specifically relating to a gradient structure, long-life environmental barrier coating and its preparation method by plasma spraying of a suspension. Background Technology

[0002] Aero engines are the culmination of complex manufacturing processes and precision mechanics, with thrust being a core performance indicator in their iteration. It is well known that the gas turbine temperature directly determines the core power output, and for every 100°C increase, the gas turbine's thermal efficiency can improve by 2-3%. Therefore, the turbine inlet temperature requirement for next-generation advanced aero engines is soaring to over 1700°C. Facing this ultra-high temperature service environment, silicon carbide ceramics and SiC... f / SiC ceramic matrix composites stand out due to their advantages such as high strength, low density and high toughness.

[0003] However, silicon carbide ceramics and SiC f SiC ceramic matrix composites used in aero-engine components face threats such as high-temperature water vapor, CMAS corrosion, and mechanical damage from foreign objects. Applying specific environmental barrier coatings is therefore a crucial measure to combat these threats. After decades of exploration and development, rare-earth silicate materials have demonstrated significant advantages. Among them, rare-earth silicates not only possess excellent high-temperature stability and corrosion resistance, but also exhibit good compatibility with silicon carbide ceramics and SiC. f / SiC ceramic matrix composites achieve excellent matching of thermal expansion coefficients and chemical compatibility. Compared with previous environmental barrier coating systems, these materials show greater application potential and have a very broad prospect.

[0004] It is worth noting that aero-engines need to maintain long-term durability and reliability under harsh service conditions. High-temperature components often need to undergo thousands of cycles of start-up, heating, isothermal, and cooling, during which there are extreme service environments where temperatures can drop from over a thousand degrees Celsius to room temperature. Coatings are not only prone to significant internal stress but may also undergo crystal transformations. This necessitates consideration of the bonding performance of each layer of material. Rare earth silicates RE2Si2O7 (RE stands for rare earth element) have a good coefficient of thermal expansion that matches the substrate. Some rare earth silicates maintain a single crystal form in high and low temperature environments, which can reduce volume changes and mitigate the destructive effects of stress.

[0005] Among various thermal spraying technologies, axial powder feeding suspension plasma spraying combines the advantages of plasma spraying and physical vapor deposition, offering both strong controllability of structural morphology and low spraying cost. The suspension often uses submicron or nano-sized particles with excellent fluidity. After melting and deposition, the coating contains numerous nanoscale voids, exhibiting a small-grained, high-strength microstructure that significantly improves thermal insulation performance. Furthermore, by controlling the spraying parameters through the axial powder feeding suspension plasma spraying process, controllable preparation of both columnar crystalline and dense crystalline coatings can be achieved simultaneously. By constructing a gradient transition structure within the coating—a columnar crystalline layer followed by a dense crystalline layer—the coating's strain tolerance is significantly improved while maintaining effective protection against corrosive media. This allows it to better adapt to substrate deformation and thermal expansion mismatch caused by thermal shock during service, thus preventing harmful cracking and peeling. In summary, the gradient structure coating prepared using this process can significantly improve the structural stability and service life of environmental barrier coatings for aero-engines. Summary of the Invention

[0006] This invention provides a gradient structure, long-life rare-earth silicate environmental barrier coating. The coating has a clear three-layer structure, specifically as follows: the substrate is silicon carbide ceramic or SiC. f The SiC ceramic matrix composite material consists of a substrate coated with a silicon binder layer, a dense rare-earth silicate RE2Si2O7 intermediate layer, and a columnar-crystalline RE2Si2O7 topcoat layer. This coating exhibits a gradient structure, with a high-density intermediate layer and a clearly defined columnar-crystalline topcoat. The overall coating demonstrates higher strain tolerance and excellent thermal shock resistance, and is expected to significantly improve the structural stability and service life of environmental barrier coatings for aero-engines during actual service.

[0007] The present invention provides a gradient structure and long-life environmental barrier coating, wherein the coating comprises, from the substrate upwards, a dense silicon bonding layer, a dense RE2Si2O7 intermediate layer, and a columnar RE2Si2O7 surface layer; the thickness of the dense silicon bonding layer is 50μm to 250μm, the thickness of the dense RE2Si2O7 intermediate layer is 50μm to 300μm, and the thickness of the columnar RE2Si2O7 surface layer is 100μm to 500μm.

[0008] Furthermore, the substrate is silicon carbide ceramic or SiC. f / SiC ceramic matrix composites.

[0009] Furthermore, the rare earth element RE in the dense RE2Si2O7 intermediate layer is one of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

[0010] This invention provides a method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating. The specific operation steps are as follows:

[0011] (1) Using silicon powder as raw material, an axial powder feeding three-electrode atmospheric plasma spraying system is used to coat silicon carbide ceramics or SiC. f A silicon bonding layer is sprayed onto a SiC ceramic matrix composite material to obtain a deposited silicon bonding layer.

[0012] (2) A rare earth silicate suspension was prepared by ball milling rare earth silicate RE2Si2O7 powder raw material with solvent and dispersant added;

[0013] (3) The rare earth silicate suspension A is first sprayed onto the deposited silicon bonding layer with RE2Si2O7 intermediate layer using an axial powder feeding suspension plasma spraying system, and then the rare earth silicate suspension B is sprayed onto the RE2Si2O7 intermediate layer with RE2Si2O7 top layer using an axial powder feeding suspension plasma spraying system to obtain the prepared environmental barrier coating.

[0014] (4) The prepared environmental barrier coating is annealed to obtain a rare earth silicate environmental barrier coating with a gradient structure and long life.

[0015] Furthermore, the particle size range of the silicon powder in step (1) is 10 μm ~ 100 μm.

[0016] Further, the spraying parameters for the silicon adhesive layer in step (1) are as follows: plasma gas Ar: 0~100L / min; plasma gas N2: 20L / min~100L / min; plasma gas H2: 10L / min~100L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; powder feeding rate: 2g / min~100g / min; carrier gas Ar: 2L / min~20L / min; spraying distance: 60mm~280mm.

[0017] Further, in step (2), the RE2Si2O7 powder is a single pure target rare earth silicate, and the solvent is selected from deionized water, pure water, ethanol or any combination thereof; the dispersant is selected according to the solvent type, using hydrophilic or alcoholic dispersants such as polyacrylate, polyvinyl ester, polyacrylamide, polyvinyl alcohol or dibutyl phosphate; the total solid content of RE2Si2O7 powder in the prepared rare earth silicate suspension is 10% to 40%, and the ball milling time is 0.5h to 72h.

[0018] Further, the spraying parameters for the RE2Si2O7 intermediate layer in step (3) are as follows: plasma gas Ar content: 30%~90%; plasma gas N2 content: 0~50%; plasma gas H2 content: 0~30%; total gas volume: 120L / min~300L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; feeding rate: 10mL / min~90mL / min; spraying distance: 80mm~160mm.

[0019] Further, the spraying parameters for the RE2Si2O7 surface layer in step (3) are as follows: plasma gas Ar content: 40%~90%; plasma gas N2 content: 0~40%; plasma gas H2 content: 0~30%; total gas volume: 200L / min -280L / min; spraying current: 170A ~250A; spraying power: 60kW~120kW; feeding rate: 30mL / min~70mL / min; spraying distance: 60mm ~150mm.

[0020] Further, the parameters for the annealing treatment in step (4) are: Ar is selected as the protective atmosphere, the heating rate is 2℃ / min ~ 10℃ / min, the target temperature is 1100℃ ~ 1600℃, and the holding time is 2h ~ 36h.

[0021] The design concept of this invention is:

[0022] This invention selects rare earth silicates as the dense intermediate layer and columnar crystal surface layer material, and RE2Si2O7 as the actual spraying material. This selection is based on a thorough consideration of the excellent corrosion resistance of rare earth elements, the matching coefficient of thermal expansion, and the requirement that RE2Si2O7 maintains a single crystal form at high and low temperatures. This helps the coating resist corrosion threats during practical applications and meets the design requirements for long service life.

[0023] This invention employs a design consisting of an adhesive layer, a dense intermediate layer, and a columnar crystalline surface layer. The preferred material for the adhesive layer, Si, is chosen based on the optimal matching of its thermal expansion coefficients with the substrate and intermediate layer materials, as well as its good chemical compatibility. This approach improves the bonding state between interfaces and the adhesion between layers. The surface layer is designed with columnar crystalline structures, while the intermediate layer is designed as a dense layer. This layered approach provides resistance to corrosion and thermal shock, enhancing strain tolerance while offering excellent protective performance.

[0024] This invention employs an axial powder feeding suspension plasma spraying process, which offers the following advantages: The structure of the deposited coating is highly controllable through adjustment of the suspension and spraying parameters; the high-energy three-electrode provides high power, ensuring thorough breakup, evaporation, and melting of the suspended droplets during flight, resulting in a uniform phase distribution; axial powder feeding directly delivers the suspension to the high-temperature zone of the plasma torch, accelerating melting and deposition efficiency. This process can highly achieve pre-defined coating structures, laying the foundation for gradient structures and long-life environmental barrier coatings.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0026] (1) In view of the characteristics of different coatings, the present invention uses a single pure RE2Si2O7 powder as raw material, combined with dispersant and solvent, and designs and uses ball milling process to prepare rare earth silicate suspension. The final suspension is stable and has excellent fluidity.

[0027] (2) The present invention uses an axial powder feeding suspension plasma spraying system, which has low spraying process cost and deposited coating with both small grain size and high strength; the high-energy three-electrode has high power, the spraying process is not only fast, but also has good melting degree; the axial powder feeding method directly delivers the suspension to the high temperature area of ​​the plasma torch, and the melting is sufficient during flight, and the deposition efficiency is higher than that of the radial powder feeding method.

[0028] (3) This invention designs a gradient structure environmental barrier coating. By controlling the characteristics of the suspension, a columnar crystal structure surface layer and a dense structure intermediate layer are sprayed using suspension plasma spraying technology. The columnar crystal structure surface layer improves the coating's strain tolerance and thermal shock resistance, while the dense structure intermediate layer enhances its corrosion resistance. An axially fed atmospheric plasma spraying silicon binder layer is used to increase the binder layer's density and simultaneously strengthen the interfacial bonding strength between the binder layer and the intermediate layer. Each layer of the gradient structure environmental barrier coating performs its specific function, resulting in a strong bond and significantly improving the structural stability and service life of the environmental barrier coating for aero-engines. Attached Figure Description

[0029] Figure 1 A schematic diagram of the axial powder feeding suspension plasma spraying equipment used in this invention;

[0030] Figure 2 This is a schematic diagram of a gradient structure and long-life environmental barrier coating according to the present invention;

[0031] Figure 3 This is a photograph of the annealed sample prepared by the axial powder feeding suspension plasma spraying process in Example 1 of the present invention.

[0032] Figure 4 This is a surface X-ray diffraction pattern of an annealed sample prepared by axial powder feeding suspension plasma spraying process in Example 1 of the present invention;

[0033] Figure 5 The images show (a) and (b) enlarged views of the surface morphology of the annealed sample prepared by axial powder feeding suspension plasma spraying process in Example 1 of this invention.

[0034] Figure 6 This is a cross-sectional morphology diagram of the annealed sample prepared by axial powder feeding suspension plasma spraying process in Example 1 of the present invention;

[0035] Figure 7 Images of the intermediate layer and silicon bonding layer after air-cooled thermal shock cycling in Embodiment 1 of the present invention (a for 500 cycles, b for 1000 cycles, c for 1500 cycles, d for 2000 cycles), and a statistical chart of the thickness of the thermally grown oxide (TGO) layer (e).

[0036] Figure 8 This is a cross-sectional morphology diagram of the annealed sample prepared by axial powder feeding suspension plasma spraying process in Example 2 of the present invention;

[0037] Figure 9 This is a cross-sectional morphology diagram of the annealed sample prepared by axial powder feeding suspension plasma spraying process in Example 3 of the present invention;

[0038] Figure 10 This is a surface X-ray diffraction pattern of an annealed sample prepared by axial powder feeding suspension plasma spraying process in the comparative example of this invention.

[0039] In the figure, 1. High-energy plasma torch A; 2. High-energy plasma torch B; 3. High-energy plasma torch C; 4. Suspension feed pipe; 5. Outer wall; 6. Converging nozzle; 7. Plasma flame. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. The reagents mentioned in the following embodiments are not limited to specific manufacturers, and commercially available products well known in the art can be selected; the equipment mentioned in the embodiments is also not limited to specific manufacturers and models, and equipment well known in the art can be selected.

[0041] The equipment used to test various properties of the coatings in the following examples is as follows:

[0042] (1) Phase identification

[0043] The phase composition and phase ratio of the coating surface were identified using an X-ray diffractometer (Bruker, D8 Advance, Germany).

[0044] (2) Morphological observation

[0045] The surface and cross-sectional morphology of the coating were photographed using a scanning electron microscope (FEI, Apreo 2s, USA), and energy dispersive spectroscopy analysis was performed on specific areas.

[0046] (3) Image analysis

[0047] The thickness of each coating layer and the thickness of the TGO layer before and after air cooling thermal shock were statistically analyzed using image analysis software (Mipar, Mipar Software LLC, USA).

[0048] The present invention will be further illustrated below through examples.

[0049] This invention provides a long-life rare-earth silicate environmental barrier coating with a gradient structure. The coating consists of a dense silicon bonding layer, a dense RE2Si2O7 intermediate layer, and a columnar RE2Si2O7 surface layer, arranged sequentially from the substrate upwards. The thickness of the dense silicon bonding layer is 50μm to 250μm, the thickness of the dense RE2Si2O7 intermediate layer is 50μm to 300μm, and the thickness of the columnar RE2Si2O7 surface layer is 100μm to 500μm.

[0050] Furthermore, the substrate is silicon carbide ceramic or SiC. f / SiC ceramic matrix composites.

[0051] Furthermore, the rare earth element RE in the dense RE2Si2O7 intermediate layer is one of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

[0052] This invention provides a method for preparing a suspension plasma spray coating with a gradient structure and long lifespan rare earth silicate environmental barrier coating. The specific operation steps are as follows:

[0053] (1) Using silicon powder as raw material, an axial powder feeding three-electrode atmospheric plasma spraying system is used to coat silicon carbide ceramics or SiC. f A silicon bonding layer is sprayed onto a SiC ceramic matrix composite material to obtain a deposited silicon bonding layer.

[0054] (2) A rare earth silicate suspension was prepared by ball milling rare earth silicate RE2Si2O7 powder raw material with solvent and dispersant added;

[0055] (3) The rare earth silicate suspension A is first sprayed onto the deposited silicon bonding layer with RE2Si2O7 intermediate layer using an axial powder feeding suspension plasma spraying system, and then the rare earth silicate suspension B is sprayed onto the RE2Si2O7 intermediate layer with RE2Si2O7 top layer using an axial powder feeding suspension plasma spraying system to obtain the prepared environmental barrier coating.

[0056] (4) The prepared environmental barrier coating is annealed to obtain a rare earth silicate environmental barrier coating with a gradient structure and long lifespan. Figure 2 This is a schematic diagram of a gradient structure and long-life environmental barrier coating prepared according to the present invention.

[0057] Furthermore, the particle size range of the silicon powder in step (1) is 10μm to 100μm, and the silicon powder is prepared by mechanical ball milling, vapor deposition, solution method or melt crushing.

[0058] Further, the spraying parameters for the silicon adhesive layer in step (1) are as follows: plasma gas Ar: 0~100L / min; plasma gas N2: 20L / min~100L / min; plasma gas H2: 10L / min~100L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; powder feeding rate: 2g / min~100g / min; carrier gas Ar: 2L / min~20L / min; spraying distance: 60mm~280mm.

[0059] Further, in step (2), the RE2Si2O7 powder is a single pure target rare earth silicate, which can be prepared by solid-state reaction synthesis or chemical methods (including but not limited to sol-gel method, co-precipitation method or hydrothermal reaction method); it is recommended to use RE2Si2O7 powder synthesized by solid-state reaction; the solvent is selected from deionized water, pure water, ethanol or any combination thereof; the dispersant is selected according to the solvent type, and hydrophilic or alcoholic dispersants are selected, such as polyacrylate, polyvinyl ester, polyacrylamide, polyvinyl alcohol or dibutyl phosphate, etc.; the total solid content of RE2Si2O7 powder in the prepared rare earth silicate suspension is 10%~40%, and the ball milling time is 0.5h~72h.

[0060] Further, the spraying parameters for the RE2Si2O7 intermediate layer in step (3) are as follows: plasma gas Ar content: 30%~90%; plasma gas N2 content: 0~50%; plasma gas H2 content: 0~30%; total gas volume: 120L / min~300L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; feeding rate: 10mL / min~90mL / min; spraying distance: 80mm~160mm.

[0061] Further, the spraying parameters for the RE2Si2O7 surface layer in step (3) are as follows: plasma gas Ar content: 40%~90%; plasma gas N2 content: 0~40%; plasma gas H2 content: 0~30%; total gas volume: 200L / min~280L / min; spraying current: 170A~250A; spraying power: 60kW~120kW; feeding rate: 30mL / min~70mL / min; spraying distance: 60mm~150mm.

[0062] Further, the parameters for the annealing treatment in step (4) are: Ar is selected as the protective atmosphere, the heating rate is 2℃ / min ~ 10℃ / min, the target temperature is 1100℃ ~ 1600℃, and the holding time is 2h ~ 36h.

[0063] A schematic diagram of the axial powder feeding suspension plasma spraying equipment used in this invention is shown below. Figure 1 The device includes a high-energy plasma torch A1, a high-energy plasma torch B2, a high-energy plasma torch C3, a suspension feed pipe 4, an outer wall 5, and a converging nozzle 6. The plasma gases Ar, N2, and H2 are generated into jets through the high-energy plasma torches A1, B2, and C3, respectively. The rare earth silicate suspension is injected from the suspension feed pipe 4. Under the drive of the carrier gas, the rare earth silicate suspension finally forms a plasma flame 7 at the converging nozzle 6 to spray out the RE2Si2O7 intermediate layer and the RE2Si2O7 surface layer.

[0064] Example 1

[0065] A method for preparing a long-life environmental barrier coating with a gradient structure, comprising the following steps:

[0066] (1) Silicon powder was selected as the raw material with a particle size range of 10μm~100μm. A silicon bonding layer was sprayed on silicon carbide ceramic using an axial powder feeding three-electrode atmospheric plasma spraying system. The substrate material was sandblasted and roughened before spraying. The specific process parameters are as follows: plasma gas Ar: 50L / min; plasma gas N2: 30L / min; plasma gas H2: 20L / min; spraying current: 180A; spraying power: 90kW; powder feeding rate: 50g / min; carrier gas Ar: 8L / min; spraying distance: 170mm.

[0067] (2) Using a self-made Yb2Si2O7 suspension with a solid content of 10%, a rare earth silicate dense structure intermediate layer was sprayed onto the silicon bonding layer deposited in (1) using an axial powder feeding suspension plasma spraying system; the specific process parameters are as follows: plasma gas Ar content: 80%; plasma gas N2 content: 10%; plasma gas H2 content: 10%; total gas volume: 245L / min; spraying current: 220A; spraying power: 88kW; feeding rate: 45mL / min; spraying distance: 95mm.

[0068] (3) A self-made Yb2Si2O7 suspension with a solid content of 20% was used. A rare earth silicate surface layer was sprayed onto the silicon bonding layer and intermediate layer substrate deposited in (2) using an axial powder feeding suspension plasma spraying system to obtain a pre-prepared environmental barrier coating. The specific process parameters are as follows: plasma gas Ar content: 80%; plasma gas N2 content: 10%; plasma gas H2 content: 10%; total gas volume: 245L / min; spraying current: 220A; spraying power: 87kW; feeding rate: 45mL / min; spraying distance: 65mm.

[0069] (4) The prepared environmental barrier coating after spraying in step (3) is subjected to high-temperature annealing. The specific annealing parameters are as follows: Ar is selected as the protective atmosphere, heating rate: 10℃ / min; target temperature: 1300℃; holding time: 20h; then cooled to room temperature.

[0070] Figure 3 The image shows the annealed coating. The coating surface exhibits small granules without obvious warping or macroscopic cracks. The coating surface is intact and initially shows the morphology of cauliflower (small granules), indicating that the process of this invention has initially achieved the expected results.

[0071] Figure 4The XRD diffraction results for the annealed coating surface are shown. The straight baseline of the diffraction pattern indicates good crystallinity of the coating after annealing. The distinct diffraction peaks correspond to the β-Yb₂Si₂O₇ and X₂-Yb₂SiO₅ phases. The X₂-Yb₂SiO₅ phase diffraction peak intensity is significantly higher than that of the β-Yb₂Si₂O₇ phase, indicating that the suspended particles melted sufficiently during flight in the plasma torch, resulting in SiO₂ volatilization. Based on existing data, the X₂ phase rare-earth monosilicate exhibits better corrosion resistance, which is beneficial for enhancing the overall performance of the coating.

[0072] Figure 5 The image shows a scanning electron microscope image of the annealed coating surface. The annealed coating surface has a cauliflower-like appearance. The magnified image shows round submicron-sized particles, which are speculated to be spherical particles formed by surface tension after complete melting. The coating has an overall columnar crystalline structure (cauliflower) and obvious grooves, with no obvious cracks, indicating that the surface structure has reached the expected level.

[0073] Figure 6 The images show scanning electron microscope (SEM) images of the cross-section of the annealed coating. The annealed coating cross-section exhibits a clear gradient structure, with a complete columnar crystal structure in the surface layer; the intermediate layer has high density and no obvious cracks; and the silicon binder layer has good deposition. This indicates that axial suspension plasma spraying is effective for both the intermediate and surface layers. Using Mipar software, the thickness of each coating layer was statistically analyzed: the silicon binder layer thickness ranged from 96 μm to 108 μm, the intermediate layer thickness from 86 μm to 95 μm, and the surface layer thickness from 179 μm to 191 μm.

[0074] The specific steps for air-cooled thermal shock cycling testing of the long-life environmental barrier coating with a gradient structure prepared in this embodiment are as follows:

[0075] The sample was placed in an air-cooled thermal shock test furnace, the temperature was set to 1350℃, the heating rate was set to the fastest possible reach of the target temperature, the holding time was 5 minutes, and the cooling time was 5 minutes. A single thermal shock cycle included a heating phase, a holding phase, and a cooling phase. The heating and cooling of the sample were achieved by a mechanically raised and lowered sample stage.

[0076] Figure 7Images of the interlayer and silicon bond layer after different cycles of air-cooling thermal shock are shown, along with statistical data on the TGO layer thickness. After 2000 cycles of air-cooling thermal shock, the silicon bond layer showed no obvious cracking and remained well bonded to the dense interlayer without peeling. The TGO layer thickness was identified and statistically analyzed using Mipar software. The results showed that the TGO layer thickness increased from 1.22 μm after 500 cycles to 2.05 μm after 2000 cycles, indicating that the TGO layer thickness increased slowly after long-cycle air-cooling thermal shock. Linear fitting revealed a parabolic curve in the TGO layer thickness with increasing cycle count, suggesting that TGO layer growth is diffusion-controlled.

[0077] Example 2

[0078] A method for preparing a long-life environmental barrier coating with a gradient structure, comprising the following steps:

[0079] (1) Silicon powder was selected as the raw material with a particle size range of 10μm~100μm. A silicon bonding layer was sprayed on silicon carbide ceramic using an axial powder feeding three-electrode atmospheric plasma spraying system. The substrate material was sandblasted and roughened before spraying. The specific process parameters are as follows: plasma gas Ar: 50L / min; plasma gas N2: 30L / min; plasma gas H2: 20L / min; spraying current: 180A; spraying power: 90kW; powder feeding rate: 50g / min; carrier gas Ar: 8L / min; spraying distance: 170mm.

[0080] (2) Using a self-made Yb2Si2O7 suspension with a solid content of 40%, a rare earth silicate dense structure intermediate layer was sprayed onto the silicon bonding layer deposited in (1) using an axial powder feeding suspension plasma spraying system; the specific process parameters are as follows: plasma gas Ar content: 50%; plasma gas N2 content: 40%; plasma gas H2 content: 10%; total gas volume: 300L / min; spraying current: 240A; spraying power: 98kW; feeding rate: 90mL / min; spraying distance: 155mm.

[0081] (3) Using a self-made Yb2Si2O7 suspension with a solid content of 10%, a rare earth silicate surface layer was sprayed onto the silicon bonding layer and intermediate layer substrate deposited in (2) using an axial powder feeding suspension plasma spraying system to obtain a pre-prepared environmental barrier coating. The specific process parameters are as follows: plasma gas Ar content: 50%; plasma gas N2 content: 40%; plasma gas H2 content: 10%; total gas volume: 200L / min; spraying current: 200A; spraying power: 79kW; feeding rate: 50mL / min; spraying distance: 100mm.

[0082] (4) The prepared environmental barrier coating after spraying in step (3) is subjected to high-temperature annealing. The specific annealing parameters are as follows: Ar is selected as the protective atmosphere, heating rate: 10℃ / min; target temperature: 1500℃; holding time: 6h; then cooled to room temperature.

[0083] Figure 8 The image shows a cross-sectional scanning electron microscope image of the annealed coating. The surface layer shows a columnar crystal structure; the intermediate layer is not dense, but there are no obvious cracks; the silicon binder layer has a good deposition state.

[0084] Example 3

[0085] A method for preparing a long-life environmental barrier coating with a gradient structure, comprising the following steps:

[0086] (1) Silicon powder was selected as the raw material with a particle size range of 10μm~100μm. A silicon bonding layer was sprayed on silicon carbide ceramic using an axial powder feeding three-electrode atmospheric plasma spraying system. The substrate material was sandblasted and roughened before spraying. The specific process parameters are as follows: plasma gas Ar: 50L / min; plasma gas N2: 30L / min; plasma gas H2: 20L / min; spraying current: 180A; spraying power: 90kW; powder feeding rate: 50g / min; carrier gas Ar: 8L / min; spraying distance: 170mm.

[0087] (2) Using a self-made Yb2Si2O7 suspension with a solid content of 10%, a rare earth silicate dense structure intermediate layer was sprayed onto the silicon bonding layer deposited in (1) using an axial powder feeding suspension plasma spraying system; the specific process parameters are as follows: plasma gas Ar content: 90%; plasma gas N2 content: 10%; plasma gas H2 content: 0%; total gas volume: 120L / min; spraying current: 160A; spraying power: 52kW; feeding rate: 40mL / min; spraying distance: 80mm.

[0088] (3) A self-made Yb2Si2O7 suspension with a solid content of 40% was used. A rare earth silicate surface layer was sprayed onto the silicon bonding layer and intermediate layer substrate deposited in (2) using an axial powder feeding suspension plasma spraying system to obtain a pre-prepared environmental barrier coating. The specific process parameters are as follows: plasma gas Ar content: 90%; plasma gas N2 content: 10%; plasma gas H2 content: 0%; total gas volume: 280L / min; spraying current: 248A; spraying power: 98kW; feeding rate: 45mLmin; spraying distance: 110mm.

[0089] (4) The prepared environmental barrier coating after spraying in step (3) is subjected to high-temperature annealing. The specific annealing parameters are as follows: Ar is selected as the protective atmosphere, heating rate: 10℃ / min; target temperature: 1400℃; holding time: 12h; then cooled to room temperature.

[0090] Figure 9 The images show a cross-sectional scanning electron microscope image of the annealed coating. The annealed coating cross-section reveals a gradient structure, with a relatively complete columnar crystal structure in the surface layer; the intermediate layer is less dense but without obvious cracks; and the silicon binder layer has a good deposition state.

[0091] Comparative Example

[0092] A method for preparing a long-life environmental barrier coating with a gradient structure, comprising the following steps:

[0093] (1) Silicon powder was selected as the raw material with a particle size range of 10μm~100μm. A silicon bonding layer was sprayed on silicon carbide ceramic using an axial powder feeding three-electrode atmospheric plasma spraying system. The substrate material was sandblasted and roughened before spraying. The specific process parameters are as follows: plasma gas Ar: 50L / min; plasma gas N2: 30L / min; plasma gas H2: 20L / min; spraying current: 180A; spraying power: 90kW; powder feeding rate: 50g / min; carrier gas Ar: 8L / min; spraying distance: 170mm.

[0094] (2) Using a self-made Yb2Si2O7 suspension with a solid content of 10%, a rare earth silicate dense structure intermediate layer was sprayed onto the silicon bonding layer deposited in (1) using an axial powder feeding suspension plasma spraying system; the specific process parameters are as follows: plasma gas Ar content: 80%; plasma gas N2 content: 10%; plasma gas H2 content: 10%; total gas volume: 245L / min; spraying current: 220A; spraying power: 88kW; feeding rate: 45mL / min; spraying distance: 95mm.

[0095] (3) A self-made Yb2Si2O7 suspension with a solid content of 20% was used. A rare earth silicate surface layer was sprayed onto the silicon bonding layer and intermediate layer substrate deposited in (2) using an axial powder feeding suspension plasma spraying system to obtain a pre-prepared environmental barrier coating. The specific process parameters are as follows: plasma gas Ar content: 80%; plasma gas N2 content: 10%; plasma gas H2 content: 10%; total gas volume: 245L / min; spraying current: 220A; spraying power: 87kW; feeding rate: 45mL / min; spraying distance: 65mm.

[0096] (4) The prepared environmental barrier coating after spraying in step (3) is subjected to high-temperature annealing. The specific annealing parameters are as follows: Ar is selected as the protective atmosphere, heating rate: 10℃ / min; target temperature: 1200℃; holding time: 1.5h; then cooled to room temperature.

[0097] Figure 10 The XRD diffraction results of the coating surface after annealing show significant broadening of peaks in the diffraction pattern, indicating that a large number of amorphous phases still exist in the coating, and the annealing operation failed.

[0098] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A long-life environmental barrier coating with a gradient structure, characterized in that, The coating consists of, from the substrate upwards, a dense silicon bonding layer, a dense RE2Si2O7 intermediate layer, and a columnar RE2Si2O7 surface layer; the thickness of the dense silicon bonding layer is 50μm to 250μm, the thickness of the dense RE2Si2O7 intermediate layer is 50μm to 300μm, and the thickness of the columnar RE2Si2O7 surface layer is 100μm to 500μm.

2. The long-life environmental barrier coating with a gradient structure according to claim 1, characterized in that, The substrate is silicon carbide ceramic or SiC. f / SiC ceramic matrix composites.

3. The long-life environmental barrier coating with a gradient structure according to claim 1, characterized in that, The rare earth element RE in the dense RE2Si2O7 intermediate layer is one of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

4. A method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating as described in any one of claims 1-3, characterized in that, The specific operating steps are as follows: (1) Using silicon powder as raw material, an axial powder feeding three-electrode atmospheric plasma spraying system is used to coat silicon carbide ceramics or SiC. f A silicon bonding layer is sprayed onto a SiC ceramic matrix composite material to obtain a deposited silicon bonding layer. (2) A rare earth silicate suspension was prepared by ball milling rare earth silicate RE2Si2O7 powder raw material with solvent and dispersant added; (3) The rare earth silicate suspension A is first sprayed onto the deposited silicon bonding layer with RE2Si2O7 intermediate layer using an axial powder feeding suspension plasma spraying system, and then the rare earth silicate suspension B is sprayed onto the RE2Si2O7 intermediate layer with RE2Si2O7 top layer using an axial powder feeding suspension plasma spraying system to obtain the prepared environmental barrier coating. (4) The prepared environmental barrier coating is annealed to obtain a rare earth silicate environmental barrier coating with a gradient structure and long life.

5. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, The particle size range of the silicon powder in step (1) is 10 μm ~ 100 μm.

6. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, The spraying parameters for the silicon adhesive layer in step (1) are as follows: plasma gas Ar: 0~100L / min; plasma gas N2: 20L / min~100L / min; plasma gas H2: 10L / min~100L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; powder feeding rate: 2g / min~100g / min; carrier gas Ar: 2L / min~20L / min; spraying distance: 60mm~280mm.

7. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, In step (2), the RE2Si2O7 powder is a single pure target rare earth silicate. The solvent is selected from deionized water, pure water, ethanol or any combination thereof. The dispersant is selected according to the solvent type, using hydrophilic or alcoholic dispersants such as polyacrylate, polyvinyl ester, polyvinyl alcohol, polyvinyl alcohol or dibutyl phosphate. The total solid content of RE2Si2O7 powder in the prepared rare earth silicate suspension is 10% to 40%, and the ball milling time is 0.5h to 72h.

8. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, The spraying parameters for the RE2Si2O7 intermediate layer in step (3) are as follows: plasma gas Ar content: 30%~90%; plasma gas N2 content: 0~50%; plasma gas H2 content: 0~30%; total gas volume: 120L / min~300L / min; spraying current: 80A~240A; spraying power: 40kW~120kW; feeding rate: 10mL / min~90mL / min; spraying distance: 80mm~160mm.

9. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, The spraying parameters for the RE2Si2O7 surface layer in step (3) are as follows: plasma gas Ar content: 40%~90%; plasma gas N2 content: 0~40%; plasma gas H2 content: 0~30%; total gas volume: 200L / min-280L / min; spraying current: 170A~250A; spraying power: 60kW~120kW; feeding rate: 30mL / min~70mL / min; spraying distance: 60mm~150mm.

10. The method for preparing a suspension plasma spray coating with a gradient structure and long lifespan environmental barrier coating according to claim 4, characterized in that, The parameters for the annealing process in step (4) are: Ar is selected as the protective atmosphere, the heating rate is 2℃ / min ~ 10℃ / min, the target temperature is 1100℃ ~ 1600℃, and the holding time is 2h ~ 36h.

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