A multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions and a preparation method thereof

Abstract

The present invention relates to a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions and a preparation method thereof. The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation resistance layer, a self-lubricating transition layer and an abradable surface layer from the substrate to the surface. It integrates high-temperature oxidation resistance, abradable and self-lubricating functions, breaks through the performance contradictions of different coating materials through the collaborative optimization of the material system, and improves the interfacial bonding strength to avoid peeling failure.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal spraying, and in particular, to a multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions, and a preparation method thereof. Background Art

[0002] At present, the following bottlenecks exist in high-temperature seal coating technology: there is a contradiction between high-temperature oxidation resistance and abradability. Traditional abradable coatings (such as porous NiCrAlY) have a high porosity (>20%), and a fast oxidation rate at high temperatures (weight gain >10 mg / cm² at 1000°C / 100h), resulting in seal failure. The self-lubricating performance is insufficient. Graphite or MoS₂-based lubricating coatings have poor heat resistance (<500°C decomposition), while high-temperature solid lubricants (such as CaF₂) have a low bonding strength with the metal matrix (<30 MPa). The interlayer thermal mismatch is serious. Multi-layer coatings are prone to interface cracks (stress >300 MPa) due to differences in thermal expansion coefficients (such as ceramics and metals), and are prone to spalling under dynamic conditions.

[0003] CN104278226A discloses a preparation technology for a wide-temperature-range self-lubricating coating. The coating is prepared by atmospheric plasma spraying technology, and its spraying powder consists of four powders: NiCrAlY, Cr₂O₃, Ag, and CaF₂ / BaF₂ eutectic. The prepared NiCrAlY-Cr₂O₃-Ag-CaF₂ / BaF₂ wide-temperature-range self-lubricating coating has a low friction coefficient and wear rate in the temperature range of 20°C to 1000°C. CN115287592A discloses a high-temperature wear-resistant self-lubricating coating for fingertip seals and a preparation method thereof. The high-temperature wear-resistant self-lubricating coating includes, in sequence along the thickness direction: a metal Me bonding layer, a composition gradient transition layer, and a high-temperature wear-resistant self-lubricating surface layer; the composition gradient transition layer is a Me-MeN-MeN / MoS₂ transition layer; the high-temperature wear-resistant self-lubricating surface layer is a MeN / MoS₂ composite layer, and the internal stress is reduced by setting the gradient content. However, the prior art still focuses on the improvement of single functions and does not overcome the performance contradictions of single materials.

[0004] Therefore, there is an urgent need to develop a gradient coating integrating the functions of "anti-oxidation-abradability-self-lubrication", and break through the performance contradictions through the collaborative optimization of the material system and process. Summary of the Invention

[0005] To solve the above technical problems, the present invention successfully combines the functions of high-temperature oxidation resistance, abradability and self-lubrication by setting a multi-layer gradient coating, and at the same time maintains good interlayer bonding to avoid spalling failure under dynamic conditions caused by differences in thermal expansion coefficients.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions. The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation resistance layer, a self-lubricating transition layer and an abradable surface layer from the substrate to the surface.

[0008] The present invention realizes the integration of multiple functions by setting a multi-layer gradient coating. The bonding layer and the composition transition layer can improve the bonding strength between the coating and the substrate; the high-temperature oxidation resistance layer improves the high-temperature oxidation resistance of the coating, the self-lubricating transition layer can release a lubricating phase at high temperature to reduce the friction coefficient, and the abradable surface layer reduces the overall hardness and brittleness of the coating to achieve controllable wear.

[0009] As a preferred technical solution of the present invention, the bonding layer is a first alloy powder; the composition transition layer includes a first alloy powder and a second alloy powder; the high-temperature oxidation resistance layer includes a second alloy powder and Al2O3 nanoparticles; the self-lubricating transition layer includes a first alloy powder and a first lubricating phase powder; the abradable surface layer includes porous first alloy powder and a second lubricating phase powder.

[0010] The present invention introduces alumina nanoparticles into the high-temperature oxidation resistance layer, which can form a dense alumina film on the surface, thereby improving the high-temperature oxidation resistance of the coating.

[0011] As a preferred technical solution of the present invention, the volume content of the second alloy powder in the composition transition layer increases from 0% to 100% in the direction from the bonding layer to the high-temperature oxidation resistance layer.

[0012] Preferably, the thickness of the composition transition layer is 50 - 80 μm, for example, it can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm, etc.

[0013] Preferably, the first alloy powder in the bonding layer includes NiCrAlY powder.

[0014] Preferably, the particle size of the first alloy powder is 15 - 45 μm, for example, it can be 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm, etc.

[0015] Preferably, the NiCrAlY powder includes Ni-22Cr-10Al-1Y powder.

[0016] Preferably, the thickness of the bonding layer is 50 - 80 μm, for example, it can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm, etc.

[0017] As a preferred technical solution of the present invention, the mass fraction of Al2O3 nanoparticles in the high-temperature oxidation-resistant layer is 3-10%, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0018] By preferably setting the mass fraction of Al2O3 nanoparticles in the high-temperature oxidation-resistant layer within the above range, a dense alumina film can be formed while ensuring good interfacial bonding force between layers.

[0019] Preferably, the particle size of the Al2O3 nanoparticles is 10-60 nm, for example, it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm or 60 nm, etc.

[0020] Preferably, the second alloy powder includes CoNiCrAlY powder.

[0021] Preferably, the particle size of the second alloy powder is 15-45 μm, for example, it can be 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm, etc.

[0022] Preferably, the CoNiCrAlY powder includes Co-32Ni-21Cr-8Al-0.5Y.

[0023] In the present invention, Co metal is introduced into the second alloy powder. The addition of Co reduces the diffusion activation energy of Al, accelerates the diffusion of Al element to the coating surface, preferentially promotes the formation of a continuous and dense α-Al2O3 oxidation film layer, reduces the generation of porous mixed oxides of Ni, thereby further improving the density of the high-temperature oxidation-resistant layer, enhancing the antioxidant ability, and significantly improving the comprehensive performance of the coating.

[0024] Preferably, the coating thickness of the high-temperature oxidation-resistant layer is 100-150 μm, for example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm, etc.

[0025] As a preferred technical solution of the present invention, the mass fraction of the first lubricating phase powder in the self-lubricating transition layer is 20-40%, for example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 38% or 40%, etc.

[0026] Preferably, the first lubricating phase powder in the self-lubricating transition layer includes Ag powder and CaF2 powder.

[0027] Preferably, the particle sizes of the Ag powder and the CaF₂ powder are 10 - 38 μm, and can be, for example, 10 μm, 12 μm, 14 μm, 16 μm, 20 μm, 22 μm, 26 μm, 30 μm, 34 μm, or 38 μm, etc.

[0028] Preferably, the particle size of the first alloy powder in the self-lubricating transition layer is 15 - 45 μm, and can be, for example, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 45 μm, etc.

[0029] As a preferred technical solution of the present invention, the mass ratio of the Ag powder to the CaF₂ powder is 2:1 - 4:1, and can be, for example, 2:1, 2.2:1, 2.4:1, 2.6:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, or 4:1, etc.

[0030] Preferably, the Ag powder is enriched on the surface layer of the self-lubricating transition layer, and the CaF₂ powder is enriched on the inner layer of the self-lubricating transition layer.

[0031] Preferably, the coating thickness of the self-lubricating transition layer is 50 - 80 μm, and can be, for example, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, or 80 μm, etc.

[0032] In the present invention, Ag and CaF₂ are used as the first lubricating phase in the self-lubricating transition layer. The ductility of Ag enables it to form a continuous lubricating film through plastic deformation at low temperatures. The underlying CaF₂ enhances high-temperature lubrication and effectively inhibits high-temperature adhesive wear. The gradient transition has no lubrication blind spots, achieving a reduction in the friction coefficient across the entire temperature range. The enrichment of Ag on the surface layer can block the diffusion of oxygen to the bottom layer, while the underlying CaF₂ layer inhibits the upward migration of elements such as Co and Cr, avoiding the formation of brittle phases.

[0033] As a preferred technical solution of the present invention, the mass fraction of the second lubricating phase powder in the abradable surface layer is 3% - 5%, and can be, for example, 3%, 3.2%, 3.8%, 4%, 4.2%, 4.8%, or 5%, etc.

[0034] Preferably, the second lubricating phase powder includes h-BN powder.

[0035] Preferably, the thickness of the abradable surface layer is 80 - 120 μm, and can be, for example, 80 μm, 90 μm, 100 μm, 110 μm, or 120 μm, etc.

[0036] As a preferred technical solution of the present invention, the average porosity of the porous first alloy powder is 20-40%, for example, it can be 20%, 25%, 30%, 35% or 40%, etc.; the porosity of the abradable surface layer is 15-30%, for example, it can be 15%, 18%, 21%, 24%, 27% or 30%, etc.

[0037] Preferably, the particle size of the porous first alloy powder is 25-53μm, for example, it can be 25μm, 27μm, 30μm, 34μm, 38μm, 40μm, 44μm, 48μm, 50μm or 53μm, etc.

[0038] In a second aspect, the present invention provides a method for preparing a multi-layer gradient coating as described in the first aspect. The preparation method includes: successively spraying a bonding layer, a composition transition layer and a high-temperature oxidation-resistant layer on the pretreated substrate by supersonic plasma spraying, magnetically assisted supersonic plasma spraying a self-lubricating transition layer, and air plasma spraying an abradable surface layer.

[0039] The present invention prepares a bonding layer, a composition transition layer and a high-temperature oxidation-resistant layer with low porosity by supersonic plasma spraying. While fully melting the first alloy powder by plasma spraying, a part of alumina is formed in the coating by plasma high-temperature oxidation. An abradable surface layer with a higher porosity is prepared by air plasma spraying.

[0040] Preferably, the pretreatment includes sandblasting the surface of the substrate.

[0041] Preferably, the abrasive material for sandblasting includes white fused alumina of 120 mesh.

[0042] Preferably, sand blowing is carried out after sandblasting, and the surface roughness of the substrate after sand blowing is 4-6μm, for example, it can be 4μm, 4.4μm, 4.8μm, 5μm, 5.4μm, 5.8μm or 6μm, etc.

[0043] Preferably, ultrasonic cleaning is carried out with a mixed solution of acetone and ethanol after sand blowing.

[0044] Preferably, the spraying power of the supersonic plasma spraying is 40-45KW, for example, it can be 40KW, 41KW, 42KW, 43KW, 44KW or 45KW, etc.

[0045] Preferably, the working gas for the supersonic plasma spraying is propane and oxygen. The flow rate of the propane is 250 - 350 SLPM, for example, it can be 250 SLPM, 280 SLPM, 300 SLPM, 320 SLPM, or 350 SLPM, etc. The flow rate of the oxygen is 750 - 850 SLPM, for example, it can be 750 SLPM, 780 SLPM, 800 SLPM, 820 SLPM, or 850 SLPM, etc.

[0046] Preferably, the powder feeding rate for the supersonic plasma spraying is 30 - 40 g / min, for example, it can be 30 g / min, 32 g / min, 34 g / min, 36 g / min, 38 g / min, or 40 g / min, etc.

[0047] Preferably, the spraying distance for the supersonic plasma spraying is 120 - 150 mm, for example, it can be 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, or 150 mm, etc.

[0048] In the present invention, the spraying distance is preferably within the above range to avoid overheating of the substrate caused by too short a spraying distance, and too long a spraying distance may lead to incomplete solidification of particles, too large a porosity, and excessive oxidation of the coating.

[0049] Preferably, the cooling gas for the supersonic plasma spraying is nitrogen. The flow rate of the nitrogen is 10 - 20 SLPM, for example, it can be 10 SLPM, 11 SLPM, 12 SLPM, 15 SLPM, or 20 SLPM, etc.

[0050] Preferably, the moving speed of the spray gun for the supersonic plasma spraying is 500 - 1000 mm / s, for example, it can be 500 mm / s, 600 mm / s, 700 mm / s, 800 mm / s, 900 mm / s, or 1000 mm / s, etc.

[0051] Preferably, the overlapping rate for the supersonic plasma spraying is 40 - 50%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, or 50%, etc.

[0052] In the present invention, the moving speed of the spray gun and the overlapping rate are preferably within the above range to ensure the uniformity of the coating spraying and make the thickness fluctuation within 5 μm.

[0053] Preferably, the spraying of the composition transition layer adopts double-barrel powder feeding.

[0054] In the present invention, by adjusting the powder feeding ratio through double-barrel powder feeding, the gradient composition adjustment of the composition transition layer is realized, and the thermal expansion coefficient is changed from 14.5×10 -6 / K gradient transition to 13.8×10 -6 / K to improve the interlayer bonding force of the coating.

[0055] Preferably, the magnetic field strength of the magnetic field-assisted supersonic plasma spraying is 0.4 - 0.5 T, and for example, it can be 0.4 T, 0.42 T, 0.44 T, 0.46 T, 0.48 T or 0.5 T, etc.

[0056] Preferably, the direction of the magnetic field is perpendicular to the axis direction of the plasma jet.

[0057] Preferably, the magnetic field frequency is 50 - 1000 Hz, and for example, it can be 50 Hz, 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, 700 Hz, 800 Hz or 1000 Hz, etc.

[0058] The present invention can adjust and match the spraying particle velocity through the magnetic field frequency to improve the coating uniformity.

[0059] Preferably, the spraying power of the abradable surface layer by atmospheric plasma spraying is 20 - 40 KW, and for example, it can be 20 KW, 24 KW, 28 KW, 30 KW, 34 KW, 38 KW or 40 KW, etc.

[0060] Preferably, the powder feeding rate of the abradable surface layer by atmospheric plasma spraying is 25 - 35 g / min, and for example, it can be 25 g / min, 26 g / min, 30 g / min, 32 g / min, 34 g / min or 35 g / min, etc.

[0061] Preferably, the scanning speed of the abradable surface layer by atmospheric plasma spraying is 600 - 800 mm / s, and for example, it can be 600 mm / s, 640 mm / s, 680 mm / s, 700 mm / s, 740 mm / s, 780 mm / s or 800 mm / s, etc.

[0062] Preferably, the spraying distance of the abradable surface layer by atmospheric plasma spraying is 100 - 120 mm, and for example, it can be 100 mm, 104 mm, 108 mm, 110 mm, 112 mm, 114 mm, 118 mm or 120 mm, etc.

[0063] The present invention controls the spraying power and scanning speed within the above ranges to prepare an abradable surface layer with a suitable porosity, which can reduce the friction coefficient of the surface layer and control the wear rate. Part of h - BN is oxidized to B2O3 during spraying and forms a liquid lubricating film at high temperature, further reducing the friction coefficient.

[0064] As a preferred technical solution of the present invention, after the spraying of the bonding layer, the composition transition layer and the high-temperature oxidation-resistant layer are completed, the surface of the coating is micro-melted by pulsed laser respectively.

[0065] Preferably, the scanning rate of the pulsed laser is 8-10 mm / s, and for example, it can be 8 mm / s, 8.2 mm / s, 8.4 mm / s, 8.6 mm / s, 9 mm / s, 9.4 mm / s, 9.8 mm / s or 10 mm / s, etc.

[0066] Preferably, the power density of the pulsed laser is 5-8 J / mm 2 , and for example, it can be 5 J / mm 2 , 5.5 J / mm 2 , 6 J / mm 2 , 6.5 J / mm 2 , 7 J / mm 2 , 7.5 J / mm 2 or 8 J / mm 2 etc.

[0067] The present invention adopts laser remelting-assisted spraying: after spraying, the surface is micro-melted with a pulsed laser with a power density of 5-8 J / mm² to eliminate interlayer pores and form a metallurgical bonding layer, improving the bonding strength between the bonding layer, the composition transition layer, the high-temperature oxidation-resistant layer and the self-lubricating transition layer. Laser micro-melting is not used between the self-lubricating transition layer and the abradable surface layer to maintain its porosity and abradable performance.

[0068] Preferably, the preparation method further includes the preparation of spraying powder. The preparation of the spraying powder includes: ball-milling and mixing the second alloy powder with Al2O3 nanoparticles to obtain the high-temperature oxidation-resistant layer powder; mechanically mixing the first lubricating phase powder with the first alloy powder to obtain the self-lubricating transition layer powder; preparing porous first alloy powder by using a pore-forming agent, and mechanically mixing the second lubricating phase powder with the porous first alloy powder to obtain the abradable surface layer powder.

[0069] Preferably, the pore-forming agent includes NH4HCO3.

[0070] Preferably, the preparation of the porous first alloy powder includes: mixing the pore-forming agent with the initial first alloy powder, dispersing it in water, spray-drying and granulating to obtain the porous first alloy powder.

[0071] Preferably, the porous first alloy powder is spherical.

[0072] Preferably, the particle size of the initial first alloy powder is 1-3 μm, and for example, it can be 1 μm, 1.4 μm, 1.8 μm, 2 μm, 2.4 μm, 2.8 μm or 3 μm, etc.

[0073] Preferably, the mass ratio of the pore former to the initial first alloy powder is 1:(8 - 9.5), for example, it can be 1:8, 1:8.2, 1:8.4, 1:8.6, 1:8.8, 1:9 or 1:9.5, etc.

[0074] Preferably, the particle size of the h-BN powder is 1 - 3 μm, for example, it can be 1 μm, 1.4 μm, 1.8 μm, 2 μm, 2.4 μm, 2.8 μm or 3 μm, etc.

[0075] As a preferred technical solution of the present invention, the post-annealing treatment includes heating under vacuum conditions, the heating temperature is 650 - 900 °C, for example, it can be 650 °C, 690 °C, 730 °C, 770 °C, 810 °C, 850 °C or 900 °C, etc.; after the heating is completed, the furnace is cooled to 100 - 300 °C, for example, it can be 100 °C, 140 °C, 180 °C, 200 °C, 240 °C, 280 °C or 300 °C, etc.; after furnace cooling, it is air-cooled to room temperature.

[0076] Preferably, the heating rate of the heating is 4 - 6 °C / min, for example, it can be 4 °C / min, 4.2 °C / min, 4.4 °C / min, 4.8 °C / min, 5 °C / min, 5.2 °C / min, 5.8 °C / min or 6 °C / min, etc.

[0077] Preferably, the vacuum degree of the vacuum condition is 5×10 -4 -1×10 -3 Pa, for example, it can be 0.5×10 -3 Pa, 0.6×10 -3 Pa, 0.7×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa, etc.

[0078] The present invention heats the sprayed coating under vacuum conditions. Preferably, the heating temperature and vacuum degree are within the above ranges. The Al element in the NiCrAlY matrix reacts with the residual oxygen in the spraying process and in the furnace to generate a dense Al2O3 film in cooperation with the alumina nanoparticles in the coating, further inhibiting the oxidation of the matrix.

[0079] Compared with the prior art, the present invention has at least the following beneficial effects:

[0080] (1) The multi-layer gradient coating provided by the present invention realizes the integration of high-temperature oxidation resistance, abradable and self-lubricating functions by sequentially arranging multi-layers of coatings with different functions, and the multi-layers of coatings cooperate with each other. The friction coefficient is reduced by 50% compared with the traditional coating, and the wear rate of the abradable surface layer ≤ 5×10 -6 mm 3 / N•m, oxidation weight gain at 1000℃ / 200h ≤ 3 mg / cm 2 Reduced by 30%, leakage ≤ 3% (far lower than the industry standard ≤ 5%);

[0081] (2) The multi-layer gradient coating provided by the present invention reduces the difference in thermal expansion coefficients between layers through the cooperation of the compositions of each layer, avoiding the phenomenon of thermal mismatch between layers. The synergistic effect of each layer and the matching of the thermal expansion coefficient of the coating are improved, increasing the thermal shock cycle life of the coating by 50%. It solves the problem of performance fragmentation of a single coating and the thermal stress problem of a multi-layer composite coating, providing a long-term and reliable high-temperature sealing coating. Detailed implementation manners

[0082] For the convenience of understanding the present invention, the following examples are listed. Those skilled in the art should understand that the said examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0083] Example 1:

[0084] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions. The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation resistance layer, a self-lubricating transition layer, and an abradable surface layer from the substrate to the surface; the bonding layer is Ni-22Cr-10Al-1Y powder; the composition transition layer includes Ni-22Cr-10Al-1Y powder and Co-32Ni-21Cr-8Al-0.5Y powder; the high-temperature oxidation resistance layer includes Co-32Ni-21Cr-8Al-0.5Y powder and 5% Al2O3 nanoparticles; the self-lubricating transition layer includes Ni-22Cr-10Al-1Y powder and 30% Ag and CaF2 mixed powder, and the mass ratio of Ag to CaF2 in the mixed powder is 3:1; the abradable surface layer includes porous Ni-22Cr-10Al-1Y powder and 4% h-BN powder. The particle size of the Ni-22Cr-10Al-1Y powder is 15 - 45μm, the particle size of the Al2O3 nanoparticles is 50nm, the particle size of the Co-32Ni-21Cr-8Al-0.5Y powder is 15 - 45μm, the particle size of the Ag and CaF2 mixed powder is 10 - 38μm, and the particle size of the porous Ni-22Cr-10Al-1Y powder is 25 - 53μm.

[0085] The multi-layer gradient coating is prepared by the following method:

[0086] (1) Powder preparation:

[0087] Mix Co-32Ni-21Cr-8Al-0.5Y powder and Al2O3 nanoparticles in a mass ratio and mix them for 8 h at 300 RPM by high-energy ball milling to obtain the powder for the high-temperature oxidation-resistant layer;

[0088] Mix Ag powder and CaF2 powder in a mass ratio of 3:1, and mechanically mix the mixed powder of Ag and CaF2 with Ni-22Cr-10Al-1Y powder in a mass ratio of 3:7 in a V-type mixer for 2 h to obtain the powder for the self-lubricating transition layer;

[0089] Mix NH4HCO3 and the initial Ni-22Cr-10Al-1Y powder with a particle size of 1-3 μm in a mass ratio of 1:9, disperse them in water, and granulate them by spray drying to prepare spherical porous Ni-22Cr-10Al-1Y powder. The average porosity of the porous Ni-22Cr-10Al-1Y powder is 30%. Mechanically mix 4 wt% h-BN powder and the porous Ni-22Cr-10Al-1Y powder in a V-type mixer for 2 h to obtain the powder for the abradable surface layer;

[0090] (2)Coating spraying:

[0091] Sandblast the Inconel 718 substrate with 120-mesh white corundum. After sandblasting, the surface roughness of the substrate is 5 μm, and ultrasonically clean it with a mixed solution of acetone and ethanol for 5 min;

[0092] Spray the bonding layer by supersonic plasma spraying. The spraying power is 42 KW, the oxygen flow rate is 800 L / h, the propane flow rate is 280 SLPM, the spraying distance is 130 mm, the powder feeding rate is 35 g / min, and the total spraying thickness is 60 μm;

[0093] Micro-melt the surface of the bonding layer by pulsed laser. The scanning rate of the pulsed laser is 9 mm / s, and the power density of the pulsed laser is 7 J / mm²;

[0094] Spray the composition transition layer by supersonic plasma spraying. Use a double-barrel powder feeding method to adjust the content of Co-32Ni-21Cr-8Al-0.5Y powder to gradually transition from 0% to 100%. The spraying power is 42 KW, the oxygen flow rate is 800 L / h, the propane flow rate is 280 SLPM, the spraying distance is 130 mm, the powder feeding rate is 35 g / min, and the total spraying thickness is 60 μm;

[0095] Micro-melt the surface of the composition transition layer by pulsed laser. The scanning rate of the pulsed laser is 9 mm / s, and the power density of the pulsed laser is 7 J / mm 2 ;

[0096] Spray the high-temperature oxidation-resistant layer by supersonic plasma spraying method, with a spraying power of 42 KW, an oxygen flow rate of 800 L / h, a propane flow rate of 280 SLPM, a spraying distance of 130 mm, a powder feeding rate of 35 g / min, and a total spraying thickness of 120 μm;

[0097] Use pulsed laser to micro-melt the surface of the high-temperature oxidation-resistant layer. The scanning rate of the pulsed laser is 9 mm / s, and the power density of the pulsed laser is 7 J / mm 2 ;

[0098] Magnetic field-assisted supersonic plasma spraying of self-lubricating transition layer. The magnetic field direction is perpendicular to the plasma jet direction, the magnetic field intensity is 0.45 T, the spraying power is 42 KW, the oxygen flow rate is 800 L / h, the propane flow rate is 280 SLPM, the spraying distance is 130 mm, the powder feeding rate is 35 g / min, and the total spraying thickness is 60 μm;

[0099] Atmospheric plasma spraying of abradable surface layer, with a spraying power of 35 kW, a powder feeding rate of 25 g / min, a spraying distance of 110 mm, a scanning speed of 750 mm / s, a total spraying thickness of 100 μm, and a coating porosity of 22%;

[0100] (3)Annealing post-treatment:

[0101] Heat the sprayed substrate in a furnace with a vacuum degree of 1×10 -3 Pa to 700 °C, keep it warm for 3 hours, then cool it in the furnace to 300 °C, and then air-cool it to room temperature. Obtain the multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions.

[0102] Example 2:

[0103] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions. The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation resistance layer, a self-lubricating transition layer and an abradable surface layer from the substrate to the surface; the bonding layer is Ni-22Cr-10Al-1Y powder; the composition transition layer includes Ni-22Cr-10Al-1Y powder and Co-32Ni-21Cr-8Al-0.5Y powder; the high-temperature oxidation resistance layer includes Co-32Ni-21Cr-8Al-0.5Y powder and 3% Al2O3 nanoparticles; the self-lubricating transition layer includes Ni-22Cr-10Al-1Y powder and 20% Ag-CaF2 mixed powder, and the mass ratio of Ag to CaF2 in the mixed powder is 2:1; the abradable surface layer includes porous Ni-22Cr-10Al-1Y powder and 3% h-BN powder. The particle size of the Ni-22Cr-10Al-1Y powder is 15-45 μm, the particle size of the Al2O3 nanoparticles is 10 nm, the particle size of the Co-32Ni-21Cr-8Al-0.5Y powder is 15-45 μm, the particle size of the Ag and CaF2 mixed powder is 10-38 μm, and the particle size of the porous Ni-22Cr-10Al-1Y powder is 25-53 μm.

[0104] The multi-layer gradient coating is prepared by the following method:

[0105] (1) Powder preparation:

[0106] Mix Co-32Ni-21Cr-8Al-0.5Y powder with Al2O3 nanoparticles by high-energy ball milling at 300 RPM for 8 h according to the mass ratio to obtain the high-temperature oxidation resistance layer powder;

[0107] Mix Ag and CaF2 according to the mass ratio of 2:1 to obtain the Ag and CaF2 mixed powder. Mix the Ag and CaF2 mixed powder with Ni-22Cr-10Al-1Y powder in a V-type mixer according to the mass ratio of 2:8 for 2 h to obtain the self-lubricating transition layer powder;

[0108] Mix NH4HCO3 with the initial Ni-22Cr-10Al-1Y powder with a particle size of 1-3 μm according to the mass ratio of 1:8.5, disperse it in water, spray dry and granulate to prepare spherical porous Ni-22Cr-10Al-1Y powder, and the average porosity of the porous Ni-22Cr-10Al-1Y powder is 40%. Mix 3 wt% h-BN powder with the porous Ni-22Cr-10Al-1Y powder in a V-type mixer for 2 h to obtain the abradable surface layer powder;

[0109] (2) Coating spraying:

[0110] The Inconel 718 substrate was sandblasted with 120-mesh white fused alumina. After sandblasting, the surface roughness of the substrate was 4 μm, and it was ultrasonically cleaned with a mixed solution of acetone and ethanol for 5 min;

[0111] The bonding layer was sprayed by supersonic plasma spraying. The spraying power was 40 KW, the oxygen flow rate was 750 L / h, the propane flow rate was 250 SLPM, the spraying distance was 120 mm, the powder feeding rate was 30 g / min, and the total spraying thickness was 50 μm;

[0112] The surface of the bonding layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 8 mm / s, and the power density of the pulsed laser was 5 J / mm 2 ;

[0113] The composition transition layer was sprayed by supersonic plasma spraying. Double-barrel powder feeding was used to adjust the content of Co-32Ni-21Cr-8Al-0.5Y powder to gradually transition from 0% to 100%. The spraying power was 40 KW, the oxygen flow rate was 750 L / h, the propane flow rate was 250 SLPM, the spraying distance was 120 mm, the powder feeding rate was 30 g / min, and the total spraying thickness was 50 μm;

[0114] The surface of the composition transition layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 8 mm / s, and the power density of the pulsed laser was 5 J / mm 2 ;

[0115] The high-temperature oxidation-resistant layer was sprayed by supersonic plasma spraying. The spraying power was 40 KW, the oxygen flow rate was 750 L / h, the propane flow rate was 250 SLPM, the spraying distance was 120 mm, the powder feeding rate was 30 g / min, and the total spraying thickness was 100 μm;

[0116] The surface of the high-temperature oxidation-resistant layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 8 mm / s, and the power density of the pulsed laser was 5 J / mm 2 ;

[0117] The self-lubricating transition layer was sprayed by magnetic field-assisted supersonic plasma spraying. The magnetic field direction was perpendicular to the plasma jet direction, the magnetic field intensity was 0.4 T, the spraying power was 40 KW, the oxygen flow rate was 750 L / h, the propane flow rate was 250 SLPM, the spraying distance was 120 mm, the powder feeding rate was 30 g / min, and the total spraying thickness was 50 μm;

[0118] The abradable surface layer was sprayed by atmospheric plasma spraying. The spraying power was 35 kW, the powder feeding rate was 35 g / min, the spraying distance was 100 mm, the scanning speed was 750 mm / s, the total spraying thickness was 80 μm, and the coating porosity was 15%;

[0119] (3) Post-annealing treatment:

[0120] The substrate after spraying is heated to 650 °C in a furnace with a vacuum of 0.8×10 -3 Pa, held for 3 hours, then cooled in the furnace to 100 °C, and then air-cooled to room temperature. The multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions is obtained.

[0121] Example 3:

[0122] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubricating functions. The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation resistance layer, a self-lubricating transition layer and an abradable surface layer from the substrate to the surface; the bonding layer is Ni-22Cr-10Al-1Y powder; the composition transition layer includes Ni-22Cr-10Al-1Y powder and Co-32Ni-21Cr-8Al-0.5Y powder; the high-temperature oxidation resistance layer includes Co-32Ni-21Cr-8Al-0.5Y powder and 10% Al2O3 nanoparticles; the self-lubricating transition layer includes Ni-22Cr-10Al-1Y powder and 40% Ag-CaF2 mixed powder, and the mass ratio of Ag to CaF2 in the mixed powder is 4:1; the abradable surface layer includes porous Ni-22Cr-10Al-1Y powder and 5% h-BN powder. The particle size of the Ni-22Cr-10Al-1Y powder is 15 - 45 μm, the particle size of the Al2O3 nanoparticles is 60 nm, the particle size of the Co-32Ni-21Cr-8Al-0.5Y powder is 15 - 45 μm, the particle size of the Ag and CaF2 mixed powder is 10 - 38 μm, and the particle size of the porous Ni-22Cr-10Al-1Y powder is 25 - 53 μm.

[0123] The multi-layer gradient coating is prepared by the following method:

[0124] (1) Powder preparation:

[0125] The Co-32Ni-21Cr-8Al-0.5Y powder is mixed with Al2O3 nanoparticles by high-energy ball milling at 300 RPM for 8 h to obtain the high-temperature oxidation resistance layer powder;

[0126] Ag and CaF2 are mixed in a mass ratio of 4:1 to obtain the Ag and CaF2 mixed powder. The Ag and CaF2 mixed powder and Ni-22Cr-10Al-1Y powder are mechanically mixed in a V-type mixer at a mass ratio of 4:6 for 2 h to obtain the self-lubricating transition layer powder;

[0127] NH4HCO3 was mixed with the initial Ni-22Cr-10Al-1Y powder with a particle size of 1-3 μm at a mass ratio of 1:9.5, and then dispersed in water. After spray drying and granulation, spherical porous Ni-22Cr-10Al-1Y powder was prepared, and the average porosity of the porous Ni-22Cr-10Al-1Y powder was 20%. 5wt% h-BN powder was mechanically mixed with the porous Ni-22Cr-10Al-1Y powder in a V-type mixer for 2 h to obtain the abradable surface layer powder;

[0128] (2)Coating spraying:

[0129] The Inconel 718 substrate was sandblasted with 120-mesh white corundum, and the surface roughness of the substrate after sandblasting was 6 μm. Then it was ultrasonically cleaned with a mixed solution of acetone and ethanol for 5 min;

[0130] The bonding layer was sprayed by supersonic plasma spraying. The spraying power was 45 KW, the oxygen flow rate was 850 L / h, the propane flow rate was 350 SLPM, the spraying distance was 150 mm, the powder feeding rate was 40 g / min, and the total spraying thickness was 80 μm;

[0131] The surface of the bonding layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 10 mm / s, and the power density of the pulsed laser was 8 J / mm 2 ;

[0132] The composition transition layer was sprayed by supersonic plasma spraying. Double-barrel powder feeding was used to adjust the content of Co-32Ni-21Cr-8Al-0.5Y powder to gradually transition from 0% to 100%. The spraying power was 45 KW, the oxygen flow rate was 850 L / h, the propane flow rate was 350 SLPM, the spraying distance was 150 mm, the powder feeding rate was 40 g / min, and the total spraying thickness was 80 μm;

[0133] The surface of the composition transition layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 10 mm / s, and the power density of the pulsed laser was 8 J / mm 2 ;

[0134] The high-temperature oxidation-resistant layer was sprayed by supersonic plasma spraying. The spraying power was 45 KW, the oxygen flow rate was 850 L / h, the propane flow rate was 350 SLPM, the spraying distance was 150 mm, the powder feeding rate was 40 g / min, and the total spraying thickness was 150 μm;

[0135] The surface of the high-temperature oxidation-resistant layer was micro-melted by pulsed laser. The scanning rate of the pulsed laser was 10 mm / s, and the power density of the pulsed laser was 8 J / mm 2 ;

[0136] Magnetic field-assisted supersonic plasma spraying of self-lubricating transition layer, with the magnetic field direction perpendicular to the plasma jet direction, magnetic field intensity of 0.5 T, spraying power of 45 KW, oxygen flow rate of 850 L / h, propane flow rate of 350 SLPM, spraying distance of 150 mm, powder feeding rate of 40 g / min, and total spraying thickness of 80 μm;

[0137] Atmospheric plasma spraying of abradable surface layer, with spraying power of 40 kW, powder feeding rate of 35 g / min, spraying distance of 120 mm, scanning speed of 800 mm / s, spraying thickness of 120 μm, and coating porosity of 30%;

[0138] (3)Annealing post-treatment:

[0139] The sprayed substrate is heated to 900 °C in a furnace with a vacuum of 0.5×10 -3 Pa, held for 3 hours, then cooled in the furnace to 200 °C, and then air-cooled to room temperature. The multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions is obtained.

[0140] Example 4:

[0141] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions. Except that the mass fraction of Al2O3 nanoparticles in the high-temperature oxidation resistance layer is 1%, the rest are the same as in Example 1.

[0142] Example 5:

[0143] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions. Except that the mass fraction of Al2O3 nanoparticles in the high-temperature oxidation resistance layer is 15%, the rest are the same as in Example 1.

[0144] Example 6:

[0145] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions. Except that the mass fraction of the Ag and CaF2 mixed powder in the self-lubricating transition layer is 15%, the rest are the same as in Example 1.

[0146] Example 7:

[0147] This example provides a multi-layer gradient coating with high-temperature oxidation resistance, abradable and self-lubricating functions. Except that the mass fraction of the Ag and CaF2 mixed powder in the self-lubricating transition layer is 45%, the rest are the same as in Example 1.

[0148] Example 8:

[0149] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the mass ratio of Ag to CaF₂ in the Ag and CaF₂ mixed powder is 1:1, the rest are the same as in Embodiment 1.

[0150] Embodiment 9:

[0151] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the mass ratio of Ag to CaF₂ in the Ag and CaF₂ mixed powder is 5:1, the rest are the same as in Embodiment 1.

[0152] Embodiment 10:

[0153] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the mass fraction of h-BN powder in the abradable surface layer is 1%, the rest are the same as in Embodiment 1.

[0154] Embodiment 11:

[0155] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the mass fraction of h-BN powder in the abradable surface layer is 10%, the rest are the same as in Embodiment 1.

[0156] Embodiment 12:

[0157] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the porosity of the abradable surface layer is 10%, the rest are the same as in Embodiment 1.

[0158] Embodiment 13:

[0159] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that the porosity of the abradable surface layer is 40%, the rest are the same as in Embodiment 1.

[0160] Embodiment 14:

[0161] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubrication functions. Except that no post-annealing treatment is carried out during the preparation process, the rest are the same as in Embodiment 1.

[0162] Embodiment 15:

[0163] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for the high-temperature oxidation resistance layer where no Al2O3 nanoparticles are added, the rest are the same as in Embodiment 1.

[0164] Embodiment 16:

[0165] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for the high-temperature oxidation resistance layer where the Co-32Ni-21Cr-8Al-0.5Y powder is replaced with Ni-22Cr-10Al-1Y powder, the rest are the same as in Embodiment 1.

[0166] Embodiment 17:

[0167] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for the abradable surface layer where the porous Ni-22Cr-10Al-1Y powder is replaced with non-porous Ni-22Cr-10Al-1Y powder, the rest are the same as in Embodiment 1.

[0168] Embodiment 18:

[0169] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for the high-temperature oxidation resistance layer where the particle size of the Al2O3 nanoparticles is 5 nm, the rest are the same as in Embodiment 1.

[0170] Embodiment 19:

[0171] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for the high-temperature oxidation resistance layer where the particle size of the Al2O3 nanoparticles is 65 nm, the rest are the same as in Embodiment 1.

[0172] Embodiment 20:

[0173] This embodiment provides a multi-layer gradient coating with high-temperature oxidation resistance, abradability, and self-lubricating functions. Except for not using pulsed laser to micro-melt the coating surface, the rest are the same as in Embodiment 1.

[0174] Comparative Example 1:

[0175] This comparative example provides a coating. Except for not including a high-temperature oxidation resistance layer, the rest are the same as in Embodiment 1.

[0176] Comparative Example 2:

[0177] This comparative example provides a coating. Except for not including a self-lubricating transition layer, the rest are the same as in Embodiment 1.

[0178] Comparative Example 3:

[0179] This comparative example provides a coating. Except that it does not include an abradable surface layer and the self-lubricating transition layer directly contacts the abrading part as the surface layer, the rest are the same as those in Example 1.

[0180] Comparative Example 4:

[0181] This comparative example provides a coating. Except that it does not include a composition transition layer, the rest are the same as those in Example 1.

[0182] Testing method:

[0183] Perform coating performance tests on the coatings of Examples 1 - 13 and Comparative Examples 1 - 6 for the gas turbine labyrinth seal ring coating. According to ASTM G99 (Standard for Pin-on-Disk or Ring-on-Disk Wear Tests), the test temperature is 900°C, the rotational speed is 12,000 RPM, the abrading part is made of Inconel 718 hard alloy, the load is 50 N, the contact between the abrading part and the coating is line contact, the test time is 2 - 5 h, and evaluate the volumetric wear rate of the surface layer of the test sample. According to ASTM G54 (Standard for High-Temperature Oxidation Tests of Materials), the test temperature is 900°C, the test atmosphere is static air or simulated gas (containing O2, H2O, CO2), the test time is 100 - 500 hours (simulating long-term service), and evaluate the oxidation weight gain of the test sample. According to API 617 (Seal Performance Specification for the Gas Turbine Industry), test the seal performance of the test sample, the test temperature is 900°C, the pressure difference is 0.5 - 1.5 MPa (simulating the pressure difference between the compressor / turbine section of the gas turbine), the medium is nitrogen or air, dynamically adjust the abrading gap (the initial gap is 50 - 100 μm, simulating the sealing performance after labyrinth wear), and evaluate the leakage amount. ASTM C633 tests the bonding strength between the high-temperature oxidation-resistant layer and the self-lubricating transition layer of the coating.

[0184] Test results:

[0185] The test results are shown in Table 1.

[0186] Table 1

[0187]

[0188] It can be seen from the test results that:

[0189] (1) It can be seen from Examples 1 to 3 that through the synergistic effect of the bonding layer, the high-temperature oxidation-resistant layer, the self-lubricating transition layer and the abradable surface layer of the present invention, it is possible to achieve a reduction in the friction coefficient, a controllable surface layer wear rate, good oxidation resistance and excellent sealing performance. The friction coefficient in the steady state stage is between 0.18 and 0.22, a 50% reduction compared to traditional coatings, and the wear rate of the abradable surface layer ≤ 5×10-6 mm 3 / N•m, oxidation weight gain ≤ 3 mg / cm at 1000 °C for 200 h 2 , leakage rate ≤ 3% (far lower than the industry standard of ≤ 5%);

[0190] (2) It can be seen from Examples 1 and 4 - 11 that by further optimizing the component content of each layer, the present invention can better balance the functions of high-temperature oxidation resistance, abradability, and self-lubrication, so as to achieve a lower friction coefficient, a smaller wear rate, and a smaller interlayer thermal stress. When the content of Al2O3 nanoparticles in the high-temperature oxidation-resistant layer of Example 4 is too low, the oxidation weight gain increases by 50% and the high-temperature oxidation resistance decreases; when the content of Al2O3 nanoparticles in the high-temperature oxidation-resistant layer of Example 5 is too high, the bonding force between the high-temperature oxidation-resistant layer and the self-lubricating transition layer drops from 57 MPa to 38 MPa. When the content of the Ag and CaF2 mixed powder in the self-lubricating transition layer of Example 6 is too low, the friction coefficient rises and the surface wear rate increases. When the content of the Ag and CaF2 mixed powder in the self-lubricating transition layer of Example 7 is too high, the bonding force between the high-temperature oxidation-resistant layer and the self-lubricating transition layer drops from 57 MPa to 28 MPa. When the mass ratio of Ag and CaF2 in the self-lubricating transition layer of Examples 8 and 9 is too high or too low, the friction coefficient of the coating rises and the surface wear rate increases. When the content of h-BN powder in the abradable surface layer of Examples 10, 11 is too low or too high, the friction coefficient of the coating rises and the surface wear rate increases;

[0191] (3) It can be seen from Example 1 and Examples 12 - 13 and 17 that by optimizing the pore structure of the abradable surface layer, the present invention improves the lubricity of the abradable surface layer and reduces the surface wear rate. When the porosity of the surface layer is too low, the wear rate decreases but the friction coefficient rises significantly. When the surface porosity is too high, the wear rate increases significantly. When porous powder is not used, the friction coefficient of the coating rises and the surface wear rate increases. It can be seen from Example 1 and Examples 15 - 16 that by introducing alumina particles and Co into the high-temperature oxidation-resistant layer, the present invention greatly improves the high-temperature oxidation resistance. It can be seen from Example 1 and Examples 18 - 19 that by optimizing the particle size of the alumina particles, the present invention further improves the high-temperature oxidation resistance. It can be seen from Example 1 and Example 20 that by means of laser micromelting technology, the present invention further improves the interlayer bonding force;

[0192] (4) It can be seen from Example 1 and Comparative Examples 1 - 4 that through the synergistic effect of the multi-functional coating, the present invention realizes the functions of high-temperature oxidation resistance, abradability, and self-lubrication, and can obtain a lower friction coefficient, high-temperature oxidation resistance, and sealing effect. When any one of the layers is missing, the technical effects of this application cannot be achieved.

[0193] In summary, through the setting of the multi-layer gradient composite structure, the present invention realizes the integration of high-temperature oxidation resistance, self-lubrication and abradable functions into the coating, breaks through the performance contradiction problem of traditional single coatings, overcomes the spalling failure problem caused by the difference in thermal expansion coefficients of multi-layer coatings, and provides a multi-functional and highly stable coating through the synergistic effect of various types of coatings and the optimization of materials and processes.

[0194] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A multi-layer gradient coating with high-temperature oxidation resistance, abradability and self-lubrication functions, characterized in that, The multi-layer gradient coating sequentially includes a bonding layer, a composition transition layer, a high-temperature oxidation-resistant layer, a self-lubricating transition layer, and an abradable surface layer from the substrate to the surface; The bonding layer is a first alloy powder; the composition transition layer includes the first alloy powder and a second alloy powder; the high-temperature oxidation-resistant layer includes the second alloy powder and Al2O3 nanoparticles; the self-lubricating transition layer includes the first alloy powder and a first lubricating phase powder; the abradable surface layer includes porous first alloy powder and a second lubricating phase powder; The first alloy powder includes NiCrAlY powder; the first lubricating phase powder in the self-lubricating transition layer includes Ag powder and CaF2 powder; the second alloy powder includes CoNiCrAlY powder; the second lubricating phase powder includes h-BN powder; In the composition transition layer, the volume content of the second alloy powder increases from 0% to 100% in the direction from the bonding layer to the high-temperature oxidation-resistant layer.

2. The multi-layer gradient coating according to claim 1, characterized in that, In the high-temperature oxidation-resistant layer, the mass fraction of the Al2O3 nanoparticles is 3-10%.

3. The multi-layer gradient coating according to claim 1, wherein In the self-lubricating transition layer, the mass fraction of the first lubricating phase powder is 20-40%.

4. The multi-layer gradient coating according to claim 1, wherein, In the abradable surface layer, the mass fraction of the second lubricating phase powder is 3%-5%.

5. The multi-layer gradient coating according to claim 1, characterized in that The average porosity of the porous first alloy powder is 20-40%, and the porosity of the abradable surface layer is 15-30%.

6. A method for preparing a multi-layer gradient coating according to any one of claims 1-5, characterized in that, The preparation method includes: sequentially spraying the bonding layer, the composition transition layer, and the high-temperature oxidation-resistant layer on the pretreated substrate by supersonic plasma spraying, spraying the self-lubricating transition layer by magnetic field-assisted supersonic plasma spraying, and spraying the abradable surface layer by atmospheric plasma spraying.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes micro-melting the surface of the coating by pulsed laser respectively after the spraying of the bonding layer, the composition transition layer, and the high-temperature oxidation-resistant layer is completed.

8. The preparation method according to claim 7, characterized in that, The preparation method further includes post-annealing treatment, and the post-annealing treatment includes heating under vacuum conditions, and the heating temperature is 650-900 °C.

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