An ultrahigh-temperature functionally graded composite coating and a method of making the same

Abstract

The application discloses an ultrahigh-temperature functional gradient composite coating and a preparation method thereof, and belongs to the technical field of high-temperature protective coatings. The coating comprises, from the substrate outward, a metal bonding bottom layer, a gradient transition layer, a ceramic main functional layer and a rare earth modified self-repairing surface layer. The interface thermal stress is eliminated by the continuous gradient design of the composition and the thermal expansion coefficient, and the self-healing of micro-cracks at ultrahigh temperature is realized by combining the rare earth modified self-repairing surface layer. The preparation method adopts supersonic plasma spraying combined with pulsed laser in-situ cladding and vacuum diffusion heat treatment to realize semi-metallurgical bonding of the coating interface. The coating can serve at an ultrahigh temperature of 1200-1600 DEG C for a long time, the interface bonding strength is greater than or equal to 80 MPa, the water cooling thermal shock cycle number at 1400 DEG C is more than 3 times that of a traditional double-layer coating, the coating has excellent thermal shock resistance, oxidation resistance and erosion resistance, and is suitable for the protection of high-temperature components in the fields of aerospace, energy and power, metallurgy and the like.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protective coating technology, and particularly relates to an ultra-high temperature functional gradient composite coating and its preparation method. Background Technology

[0002] With the technological advancements in aerospace, gas turbines, metallurgy, and other fields, the service temperatures of hot-section components in equipment are continuously increasing, placing increasingly stringent demands on the performance of high-temperature protective coatings. Currently, the most widely used high-temperature protective coating is the traditional double-layer thermal barrier coating, composed of a metal bonding layer and a ceramic top layer. However, it has significant drawbacks in ultra-high-temperature service: The double-layer structure has a large difference in thermal expansion coefficient, and thermal stress is concentrated at the interface. During the hot and cold cycle, it is prone to interface delamination and flaking, resulting in poor thermal shock resistance and difficulty in meeting the requirements for long-term service above 1400℃. Ceramic surfaces are prone to microcracks under ultra-high temperature thermal cycling and particle erosion. Oxygen diffuses rapidly along the cracks to the adhesive layer, forming a brittle thermally grown oxide layer, which accelerates coating failure.

[0003] Therefore, it is necessary to provide a new ultra-high temperature functional gradient composite coating and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0004] The technical problem solved by this invention is to provide an ultra-high temperature functionally graded composite coating and its preparation method, which solves the technical problems of traditional high temperature coatings such as interface thermal stress concentration, lack of self-healing ability, and short high temperature life, and realizes a long-term stable ultra-high temperature functionally graded composite coating and its preparation method in an ultra-high temperature environment of 1200~1600℃.

[0005] To solve the above-mentioned technical problems, the ultra-high temperature functional gradient composite coating provided by the present invention includes: a metal bonding underlayer, a gradient transition layer, a ceramic main functional layer and a rare earth modified self-healing surface layer arranged sequentially from the surface of the substrate outward; The metal bonding underlayer is an alloy layer with a thickness of 80~150; the gradient transition layer is a metal-ceramic composite gradient layer, with the ceramic phase volume fraction increasing linearly from 15% to 65% from the inside to the outside, and a thickness of 200~350. The main functional ceramic layer is a rare earth-doped lanthanum zirconate-yttrium oxide stabilized zirconium oxide composite ceramic layer with a thickness of 150~250; the rare earth-modified self-healing surface layer is a rare earth oxide modified ceramic layer containing borosilicate glass phase precursor with a thickness of 50~100. The overall coefficient of thermal expansion of the coating decreases in a continuous gradient from the inside to the outside, with the rate of decrease being per 100 mm thickness.

[0006] As a further aspect of the present invention, the composition of the metal bonding underlayer is an alloy, with the following mass fractions of each element: Co20 28%, Cr18 24%, Al10 14%, Y0.5 1.2%, and the balance being Ni.

[0007] As a further embodiment of the present invention, the metallic phase of the gradient transition layer is an alloy, and the ceramic phase is 3 mol% yttrium oxide-stabilized zirconium oxide. The volume fraction of the ceramic phase along the coating thickness direction from the inside to the outside is 15%, 30%, 45%, and 65%, forming a four-level gradient sublayer with equal thickness for each sublayer.

[0008] As a further aspect of the present invention, the mass ratio of lanthanum zirconate to yttrium oxide-stabilized zirconium oxide in the main ceramic functional layer is 1:1.2 / 1:2, and the doped rare earth oxide is gadolinium oxide, with a doping amount of 2 / 5% of the total mass of the coating.

[0009] As a further aspect of the present invention, the raw materials of the rare earth modified self-healing surface layer include, by mass fraction: 60-75% yttrium oxide stabilized zirconia ceramic powder, 10-20% borosilicate glass powder, 5-12% cerium oxide, and 3-8% ytterbium oxide.

[0010] This invention also provides a method for preparing an ultra-high temperature functionally graded composite coating, comprising the following steps: S1. Substrate pretreatment: The substrate surface is roughened by sandblasting, followed by ultrasonic cleaning with acetone and anhydrous ethanol in sequence, and then dried for later use. S2, Gradient Layer Supersonic Plasma Spraying: Using powder-feeding supersonic plasma spraying equipment, the metal bonding base layer, gradient transition layer, and ceramic main functional layer are sprayed sequentially from the inside out. Compressed air is used to cool the substrate during the spraying process to control the substrate temperature to not exceed 180℃. S3. Surface laser in-situ cladding: The mixed powder of rare earth modified self-healing surface layer is clad onto the surface of the main functional layer of ceramic by pulsed laser cladding process, and a dense self-healing surface layer containing rare earth phase is generated in situ. S4. Vacuum diffusion heat treatment: The coated sample is placed in a vacuum heat treatment furnace for gradient heating diffusion treatment to eliminate residual stress in the coating and promote interdiffusion of interfacial elements.

[0011] As a further aspect of the present invention, in step S2, the process parameters for supersonic plasma spraying are: spraying power 35 / 45kW, main gas argon flow rate 80 / 100L / min, auxiliary gas hydrogen flow rate 10 / 15L / min, powder feeding rate 25 / 35g / min, spraying distance 100 / 120mm, and spray gun moving speed 300 / 500mm / s.

[0012] As a further embodiment of the present invention, in step S3, the process parameters of pulsed laser cladding are: laser power 800 / 1200W, scanning speed 8 / 12mm / s, spot diameter 2 / 3mm, overlap rate 30 / 40%, and argon protective gas flow rate 15~20L / min.

[0013] As a further aspect of the present invention, in step S4, the specific process of gradient heating diffusion treatment is as follows: heating to 600°C at a rate of 5°C / min and holding for 2 hours, then heating to 950°C at a rate of 3°C / min and holding for 4 hours, and then cooling to room temperature with the furnace, with the vacuum degree inside the furnace not lower than 1.

[0014] As a further embodiment of the present invention, the substrate is a nickel-based high-temperature alloy, a ceramic matrix composite material, or a graphite material, and the coating is suitable for ultra-high temperature service environments of 1200℃~1600℃, and is used for the protection of hot-end components of aero-engines, gas turbine blades, and metallurgical furnace rollers.

[0015] Compared with related technologies, the ultra-high temperature functionally graded composite coating and its preparation method provided by the present invention have the following beneficial effects: This invention utilizes gradient stress relief to significantly improve thermal shock resistance. Through a four-level composition gradient design, the coefficient of thermal expansion of the coating is reduced from approximately 13 × 10⁻⁶ to approximately 13 × 10⁻⁶. -6 / ℃ continuously decreases to ~8×10 at the surface. -6 / ℃, eliminating the sudden change in interfacial stress in traditional double-layer coatings. Finite element simulation and experimental verification show that the maximum thermal stress at the coating interface is reduced by more than 45%, and the number of water-cooled thermal shock cycles at 1400℃ is more than 3 times that of traditional YSZ double-layer coatings, effectively avoiding interfacial delamination failure.

[0016] In high-temperature environments above 1200℃, the borosilicate glass precursor reacts in situ with rare earth oxides to generate a low-viscosity rare earth borosilicate glass phase. This phase spontaneously fills surface microcracks and pores through capillary action, blocking oxygen diffusion channels. Oxidation weight gain after 100 hours of isothermal oxidation at 1400℃ is reduced by more than 60% compared to traditional coatings, significantly extending long-term service life.

[0017] The ceramic main functional layer adopts a multiphase doping design of lanthanum zirconate and YSZ. The low thermal conductivity of lanthanum zirconate and the high toughness of YSZ complement each other. Combined with the grain boundary strengthening effect of rare earth elements, the coating achieves a high-temperature hardness of ≥12GPa at 1200℃ and excellent fracture toughness. It improves the resistance to high-speed particle erosion by more than 40%; at the same time, the multi-layer interface enhances phonon scattering, and the thermal conductivity at 1200℃ is as low as 0.8~1.0W / (m・K), improving the heat insulation effect by more than 30%.

[0018] The composite process of supersonic plasma spraying as a base coat, laser in-situ cladding as a surface coat, and vacuum diffusion heat treatment is adopted. The metal base coat and the substrate form an element diffusion zone with a thickness of 5~10μm, achieving semi-metallurgical bonding. The coating bonding strength is ≥80MPa. The process parameters can be precisely controlled, and the coating thickness and composition uniformity deviation is ≤5%, which is suitable for large-scale industrial applications. Attached Figure Description

[0019] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 A schematic diagram of the ultra-high temperature functional gradient composite coating provided by the present invention; Figure 2 This is a schematic flowchart illustrating the preparation method of the ultra-high temperature functionally graded composite coating provided by the present invention. Detailed Implementation

[0021] Please refer to the following: Figure 1 and Figure 2 ,in, Figure 1 A schematic diagram of the ultra-high temperature functional gradient composite coating provided by the present invention; Figure 2 This is a schematic flowchart illustrating the preparation method of the ultra-high temperature functionally graded composite coating provided by the present invention. The ultra-high temperature functionally graded composite coating includes, from the surface of the substrate outwards, a metal bonding underlayer, a gradient transition layer, a ceramic main functional layer, and a rare earth modified self-healing surface layer; The metal bonding underlayer is an alloy layer with a thickness of 80~150; the gradient transition layer is a metal-ceramic composite gradient layer, with the ceramic phase volume fraction increasing linearly from 15% to 65% from the inside to the outside, and a thickness of 200~350. The main functional ceramic layer is a rare earth-doped lanthanum zirconate-yttrium oxide stabilized zirconium oxide composite ceramic layer with a thickness of 150~250; the rare earth-modified self-healing surface layer is a rare earth oxide modified ceramic layer containing borosilicate glass phase precursor with a thickness of 50~100. The overall coefficient of thermal expansion of the coating decreases in a continuous gradient from the inside to the outside, with the rate of decrease being per 100 mm thickness.

[0022] The composition of the metal bonding underlayer is an alloy, with the following mass fractions of each element: Co 20 28%, Cr 18 24%, Al 10 14%, Y 0.5 1.2%, and the balance being Ni.

[0023] The metallic phase of the gradient transition layer is an alloy, and the ceramic phase is 3 mol% yttrium oxide stabilized zirconium oxide. The volume fraction of the ceramic phase along the coating thickness direction from the inside to the outside is 15%, 30%, 45%, and 65%, forming a four-level gradient sublayer with equal thickness for each sublayer.

[0024] The mass ratio of lanthanum zirconate to yttrium oxide-stabilized zirconium oxide in the main ceramic functional layer is 1:1.2 / 1:2, and the doped rare earth oxide is gadolinium oxide, with a doping amount of 2 / 5% of the total coating mass.

[0025] The raw materials of the rare earth modified self-healing surface layer include, by mass fraction: 60-75% yttrium oxide stabilized zirconia ceramic powder, 10-20% borosilicate glass powder, 5-12% cerium oxide, and 3-8% ytterbium oxide.

[0026] This invention provides a method for preparing an ultra-high temperature functionally graded composite coating, comprising the following steps: S1. Substrate pretreatment: The substrate surface is roughened by sandblasting, then ultrasonically cleaned with acetone and anhydrous ethanol in sequence, and dried for later use. S2, Gradient Layer Supersonic Plasma Spraying: Using powder-feeding supersonic plasma spraying equipment, the metal bonding base layer, gradient transition layer, and ceramic main functional layer are sprayed sequentially from the inside out. Compressed air is used to cool the substrate during the spraying process to control the substrate temperature to not exceed 180℃. S3. Surface laser in-situ cladding: The mixed powder of rare earth modified self-healing surface layer is clad onto the surface of the main functional layer of ceramic by pulsed laser cladding process, and a dense self-healing surface layer containing rare earth phase is generated in situ. S4. Vacuum diffusion heat treatment: The coated sample is placed in a vacuum heat treatment furnace for gradient heating diffusion treatment to eliminate residual stress in the coating and promote interdiffusion of interfacial elements.

[0027] In step S2, the process parameters for supersonic plasma spraying are: spraying power 35 / 45kW, main gas argon flow rate 80 / 100L / min, auxiliary gas hydrogen flow rate 10 / 15L / min, powder feeding rate 25 / 35g / min, spraying distance 100 / 120mm, and spray gun moving speed 300 / 500mm / s.

[0028] In step S3, the process parameters for pulsed laser cladding are: laser power 800 / 1200W, scanning speed 8 / 12mm / s, spot diameter 2 / 3mm, overlap rate 30 / 40%, and argon protective gas flow rate 15~20L / min.

[0029] In step S4, the specific process of gradient heating diffusion treatment is as follows: the temperature is increased to 600℃ at a rate of 5℃ / min and held for 2 hours, then increased to 950℃ at a rate of 3℃ / min and held for 4 hours, and then cooled to room temperature with the furnace, with the vacuum degree inside the furnace not lower than 100℃.

[0030] The substrate is a nickel-based superalloy, ceramic matrix composite material, or graphite material. The coating is suitable for ultra-high temperature service environments of 1200℃~1600℃ and is used for the protection of hot-end components of aero-engines, gas turbine blades, and metallurgical furnace rollers. Example 1 The ultra-high temperature functionally graded composite coating in this embodiment uses K417G nickel-based high-temperature alloy as the substrate, and the coating structure and parameters are as follows: Metal bonding underlayer: Alloy, 100mm thick The elemental mass fractions are Co 25%, Cr 20%, Al 12%, Y 0.8%, with the balance being Ni; Gradient transition layer: a fourth-order gradient sublayer, with the metallic phase being... The alloy has a ceramic phase of 3YSZ, with the volume fractions of the ceramic phase from the inside out being 15%, 30%, 45%, and 65%, respectively. The thickness of each sublayer is 75 mm. Total thickness 300 ; The main functional ceramic layer consists of La₂Zr₂O₇ and 3YSZ in a mass ratio of 1:1.5. Doping amount 3wt%, thickness 200 ; Rare earth modified self-healing surface layer: raw material mass fraction is 70% 3YSZ, 15% borosilicate glass powder, 8% CeO2, 7%... Thickness 80 .

[0031] The preparation steps are as follows: S1 Matrix Pretreatment: The matrix was roughened by sandblasting with 46# white corundum abrasive at a pressure of 0.5 MPa, resulting in a roughness Ra≈6. Then, ultrasonic cleaning with acetone for 10 minutes, ultrasonic cleaning with anhydrous ethanol for 5 minutes, and drying at 100°C for later use. S2 supersonic plasma spraying: power 40kW, argon flow rate 90L / min, hydrogen flow rate 12L / min, powder feeding rate 30g / min, spraying distance 110mm, spray gun moving speed 400mm / s, sequentially spraying metal bonding base layer, four-level gradient transition layer, ceramic main functional layer, substrate temperature controlled within 150℃. S3 pulsed laser cladding: laser power 1000W, scanning speed 10mm / s, spot diameter 2.5mm, overlap rate 35%, argon protection flow rate 18L / min, cladding rare earth modified self-healing surface. S4 vacuum diffusion heat treatment: vacuum degree 3×10 -3Pa was heated to 600℃ at a rate of 5℃ / min and held for 2 hours, then heated to 950℃ at a rate of 3℃ / min and held for 4 hours, followed by furnace cooling. Performance test results: interfacial bonding strength 86MPa, failure after 42 water-cooled thermal shock cycles at 1400℃, and oxidation weight gain of 0.82mg / cm³ after 100 hours at 1400℃. 2 Thermal conductivity at 1200℃ is 0.92 W / (m・K).

[0032] Example 2 The ultra-high temperature functionally graded composite coating in this embodiment uses a C / SiC ceramic matrix composite material as the substrate. The coating structure and parameters are as follows: Metal bonding underlayer: NiCoCrAlY alloy, 80 mm thick The elemental mass fractions are Co 22%, Cr 22%, Al 11%, Y 1.0%, with the balance being Ni; Gradient transition layer: a four-level gradient sublayer, with ceramic phase volume fractions of 15%, 30%, 45%, and 65% from the inside out, and a total thickness of 200 mm. ; Ceramic main functional layer: The mass ratio of 3YSZ is 1:1.2. Doping amount 4wt%, thickness 150 ; Rare earth modified self-healing surface layer: raw material mass fraction is 65% 3YSZ, 18% borosilicate glass powder, 10% CeO2, 7%... Thickness 50 .

[0033] Preparation process parameters were adjusted as follows: spraying power 36kW, spraying distance 100mm; laser power 850W, scanning speed 12mm / s; heat treatment process was the same as in Example 1.

[0034] Performance test results: interfacial bonding strength 72MPa, failure after 36 cycles of water-cooled thermal shock at 1400℃, and weight gain of 0.75mg / cm³ after 100h oxidation at 1400℃. 2 .

[0035] Example 3 The ultra-high temperature functionally graded composite coating in this embodiment uses GH4169 high-temperature alloy as the substrate, and the coating structure and parameters are as follows: Metal bonding underlayer: NiCoCrAlY alloy, 150 mm thick The elemental mass fractions are Co 28%, Cr 18%, Al 14%, Y 0.6%, with the balance being Ni; Gradient transition layer: four-level gradient sublayers, total thickness 350. ; Ceramic main functional layer The mass ratio of 3YSZ is 1:2. Doping amount 2wt%, thickness 250 ; Rare earth modified self-healing surface layer: raw material mass fraction is 75% 3YSZ, 12% borosilicate glass powder, 8% CeO2, 5%... Thickness 100 Preparation process parameters were adjusted as follows: spraying power 45kW, powder feeding rate 35g / min; laser power 1200W, scanning speed 8mm / s; heat treatment process was the same as in Example 1.

[0036] Performance test results: interfacial bonding strength 91 MPa, failure after 48 water-cooled thermal shock cycles at 1400℃, and oxidation weight gain of 0.91 mg / cm³ after 100 hours at 1400℃. 2 .

[0037] Working Principle: The ultra-high temperature functionally graded composite coating of this invention achieves stable ultra-high temperature service based on four synergistic mechanisms: gradient stress relief, multi-phase thermal barrier insulation, high-temperature self-healing, and interfacial diffusion bonding. The detailed principles of each mechanism are as follows: The gradient thermal stress relief mechanism in traditional double-layer coatings is caused by abrupt changes in the coefficient of thermal expansion. The formula for calculating thermal stress is:

[0038] in, For interfacial thermal stress, For the elastic modulus of the coating, Poisson's ratio, This represents the difference in the thermal expansion coefficients of adjacent layers. This refers to the change in service temperature. This invention employs a four-level composition gradient design to ensure that the coating's coefficient of thermal expansion α decreases continuously and linearly along the thickness direction, with adjacent sublayers... Controlled

[0039] Within this range, abrupt stress changes are avoided. The stress is distributed continuously and gently along the thickness direction, with the maximum stress transferred from the interface to the interior of the coating. This eliminates the driving force for interface delamination at its source and significantly improves thermal shock resistance.

[0040] In the multiphase thermal barrier insulation mechanism, the thermal conduction of ceramic coatings is mainly phonon conduction, and the total thermal conductivity λ satisfies the following relationship:

[0041] in, The intrinsic thermal conductivity of the ceramic phase, This represents the equivalent thermal resistance of phonon scattering at grain boundaries and layer interfaces.

[0042] In this invention, lanthanum zirconate has an extremely low intrinsic thermal conductivity (approximately 1.1 W / (m·K) at 1200 °C). After multiplying with YSZ, it forms a large number of grain boundaries, which enhances phonon scattering. At the same time, the gradient structure introduces multilayer interfaces, further increasing the phonon scattering probability. This reduces the overall thermal conductivity of the coating to 0.8~1.0 W / (m·K) at 1200 °C, resulting in a significantly better thermal insulation effect than a single YSZ coating.

[0043] High-temperature self-healing mechanism: When the service temperature exceeds 1200℃, the borosilicate glass powder in the self-healing surface softens and melts, and simultaneously undergoes an in-situ solid-phase reaction with rare earth oxides such as CeO2 and Yb2O3.

[0044] The generated rare earth borosilicate glass phase has low viscosity and good fluidity. Driven by capillary force, it spontaneously fills the microcracks and pores on the coating surface, forming a dense oxide barrier layer that prevents oxygen from diffusing inward. At the same time, rare earth elements can inhibit the formation of adhesive layers. Phase transformation and growth reduce the brittleness of thermally grown oxide layers and improve the long-term high-temperature stability of coatings.

[0045] In the interface diffusion bonding mechanism of supersonic plasma spraying, high-speed molten particles impact the substrate surface, causing plastic deformation and forming mechanical interlocking. During subsequent vacuum diffusion heat treatment, Al and Cr elements from the underlying metal diffuse towards the substrate, while Ni and Fe elements from the substrate diffuse towards the coating, forming a coating with a thickness of 5-10 mm. The element interdiffusion region achieves semi-metallurgical bonding, increasing the interfacial bonding strength from 30-50MPa in traditional mechanical bonding to over 80MPa, thus avoiding interfacial delamination under high-temperature service conditions.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments, or they can be used directly or indirectly, without departing from the principles and spirit of the invention. In other related technical fields, the scope of the invention is defined by the appended claims and their equivalents, and they are similarly included within the scope of patent protection of the invention.

Claims

1. A high-temperature functional gradient composite coating, characterized in that, include: From the surface of the substrate outwards, the substrate consists of a metal bonding underlayer, a gradient transition layer, a ceramic main functional layer, and a rare earth modified self-healing surface layer. The metal bonding underlayer is Alloy layer, thickness 80~150 The gradient transition layer is a metal-ceramic composite gradient layer, in which the volume fraction of the ceramic phase linearly increases from 15% to 65% from the inside out, and the thickness is 200~350 mm. ; The main functional ceramic layer is a rare-earth-doped lanthanum zirconate-yttrium oxide stabilized zirconium oxide composite ceramic layer with a thickness of 150~250 mm. The rare earth-modified self-healing surface layer is a rare earth oxide-modified ceramic layer with a borosilicate glass phase precursor and a thickness of 50-100 mm. ; The overall coefficient of thermal expansion of the coating decreases continuously from the inside to the outside, with a decreasing rate of... per 100 thickness.

2. The ultra-high temperature functionally graded composite coating according to claim 1, characterized in that: The composition of the metal bonding underlayer is The alloy has the following mass fractions of elements: Co 20% 28%, Cr 18% 24%, Al 10% 14%, Y 0.5% 1.2%, with the balance being Ni.

3. The ultra-high temperature functionally graded composite coating according to claim 1, characterized in that: The metallic phase of the gradient transition layer is The alloy has a ceramic phase of 3 mol% yttrium oxide-stabilized zirconium oxide. The volume fraction of the ceramic phase along the coating thickness direction is 15%, 30%, 45%, and 65% from the inside to the outside, forming a four-level gradient sublayer with equal thickness for each sublayer.

4. The ultra-high temperature functionally graded composite coating according to claim 1, characterized in that: The mass ratio of lanthanum zirconate to yttrium oxide-stabilized zirconium oxide in the main ceramic functional layer is 1:1.2 / 1:2, and the doped rare earth oxide is gadolinium oxide, with a doping amount of 2 / 5% of the total coating mass.

5. The ultra-high temperature functionally graded composite coating according to claim 1, characterized in that: The raw materials of the rare earth modified self-healing surface layer include, by mass fraction: 60-75% yttrium oxide stabilized zirconia ceramic powder, 10-20% borosilicate glass powder, 5-12% cerium oxide, and 3-8% ytterbium oxide.

6. A method for preparing an ultra-high temperature functionally graded composite coating according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Substrate pretreatment: The substrate surface is roughened by sandblasting, followed by ultrasonic cleaning with acetone and anhydrous ethanol in sequence, and then dried for later use. S2, Gradient Layer Supersonic Plasma Spraying: Using powder-feeding supersonic plasma spraying equipment, the metal bonding base layer, gradient transition layer, and ceramic main functional layer are sprayed sequentially from the inside out. Compressed air is used to cool the substrate during the spraying process to control the substrate temperature to not exceed 180℃. S3. Surface laser in-situ cladding: The mixed powder of rare earth modified self-healing surface layer is clad onto the surface of the main functional layer of ceramic by pulsed laser cladding process, and a dense self-healing surface layer containing rare earth phase is generated in situ. S4. Vacuum diffusion heat treatment: The coated sample is placed in a vacuum heat treatment furnace for gradient heating diffusion treatment to eliminate residual stress in the coating and promote interdiffusion of interfacial elements.

7. The method for preparing the ultra-high temperature functionally graded composite coating according to claim 6, characterized in that: In step S2, the process parameters for supersonic plasma spraying are: spraying power 35 / 45kW, main gas argon flow rate 80 / 100L / min, auxiliary gas hydrogen flow rate 10 / 15L / min, powder feeding rate 25 / 35g / min, spraying distance 100 / 120mm, and spray gun moving speed 300 / 500mm / s.

8. The method for preparing the ultra-high temperature functionally graded composite coating according to claim 6, characterized in that: In step S3, the process parameters for pulsed laser cladding are: laser power 800 / 1200W, scanning speed 8 / 12mm / s, spot diameter 2 / 3mm, overlap rate 30 / 40%, and argon protective gas flow rate 15~20L / min.

9. The method for preparing the ultra-high temperature functionally graded composite coating according to claim 6, characterized in that: In step S4, the specific process of gradient temperature diffusion treatment is as follows: the temperature is increased to 600℃ at a rate of 5℃ / min and held for 2 hours, then increased to 950℃ at a rate of 3℃ / min and held for 4 hours, followed by cooling to room temperature in the furnace, with the vacuum degree inside the furnace not lower than [missing information]. .

10. The method for preparing the ultra-high temperature functionally graded composite coating according to claim 6, characterized in that: The substrate is a nickel-based high-temperature alloy, a ceramic matrix composite material, or a graphite material. The coating is suitable for ultra-high temperature service environments of 1200℃~1600℃ and is used for the protection of hot-end components of aero-engines, gas turbine blades, and metallurgical furnace rollers.

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