La2Zr2O7-NiCoCrAlTaY composite gradient multilayer coating and preparation method thereof

Abstract

The invention belongs to the technical field of high-temperature protective coatings, and particularly discloses a La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating suitable for surface protection of high-temperature parts such as gas turbines of ocean vessels and a preparation method of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating. According to the composite gradient multilayer coating, a bonding layer, a gradient transition layer and an outer layer are sequentially arranged on the surface of a base body. Wherein the bonding layer is a NiCoCrAlY alloy layer, the gradient transition layer is a multi-layer composite coating formed by gradient change of NiCoCrAlTaY alloy and La2Zr2O7 components, and the outer layer is a La2Zr2O7 ceramic layer. Due to gradient change of NiCoCrAlTaY alloy and La2Zr2O7 components of the gradient transition layer, slow transition of the coefficient of thermal expansion in the whole coating from a metal base material to a ceramic layer can be achieved, and therefore thermal stress between the coating and a base body and thermal stress between all layers in the coating are remarkably reduced. Meanwhile, the coating is prepared through laser cladding, metallurgical bonding is formed among the base body, the bonding layer, the gradient transition layer and the ceramic layer, and the bonding force of the metal base body and the ceramic coating can be enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature protective coatings, and specifically relates to a La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating and a preparation method thereof, which are applicable to the surface protection of high-temperature components such as gas turbines of ocean-going ships. Background Art

[0002] The power systems of ocean-going ships are mainly divided into several types such as steam power, diesel-steam alternate power (CODOS), diesel power, gas-gas power (COGAG), and all-electric propulsion systems. Among them, gas turbines are the most common and excellent power systems for ocean-going ships nowadays. With the advantages of small volume, light weight, large power, fast start-up response, convenient maintenance, and high reliability, gas turbines have become the most favored power systems for modern ships. As the requirements for the power and performance of gas turbines of ocean-going ships are getting higher and higher, the ultimate service temperature of gas turbines has exceeded the melting point of superalloys. Therefore, it is necessary to protect the hot-end components such as the blades of gas turbines. The traditional yttria-stabilized zirconia material (YSZ) is currently a widely used surface ceramic layer material, but its ultimate service temperature is lower than 1250°C, and it has poor anti-sintering ability, poor phase stability, and poor anti-CMAS (environmental deposit) corrosion performance, and it can no longer meet the higher usage requirements of engines.

[0003] Compared with traditional materials, rare-earth doped zirconates have the advantages of high melting point, low thermal conductivity, low density, low thermal expansion coefficient, no phase change between room temperature and melting point, oxygen impermeability, and no sintering below 1400°C. Due to the mismatch of thermal expansion coefficients between rare-earth doped zirconates and metals, the interfacial thermal stress is relatively large, and the coating is prone to peeling. Therefore, solving the problem of the mismatch of thermal expansion coefficients between rare-earth doped zirconates and substrate metals is of great significance for the development of surface engineering technology and meeting the high-temperature performance requirements of metal components. Summary of the Invention

[0004] The purpose of the present invention is to provide a La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating and a preparation method thereof, which solve the problem of the mismatch of thermal expansion coefficients between ceramics and metals and have excellent high-temperature protection performance.

[0005] To achieve the above purpose, the specific technical solutions adopted by the present invention are as follows:

[0006] In a first aspect, the present invention provides a La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating. The composite gradient coating on the substrate surface successively includes a bonding layer, a gradient transition layer, and an outer layer. The material of the bonding layer is a first alloy, and the first alloy is MCrAlY or MCrAlTaY (M is Ni, Co, or NiCo). The gradient transition layer is a rare earth modified cermet layer, specifically a composite coating formed by slow compositional gradient change of a second alloy and a rare earth doped ceramic. The outer layer is a ceramic layer, and the material is the rare earth doped ceramic.

[0007] Preferably, the substrate is a superalloy (GH4169).

[0008] Preferably, the first alloy is NiCoCrAlY, and the composition range (in mass percentage) is: Ni 45%-65%, Co 20%-25%, Cr 15%-25%, Al 7%-12%, Y 0.3%-0.6%. More preferably: Ni 45%-55%, Co 22%-25%, Cr 20%-25%, Al 9%-12%, Y 0.4%-0.6%.

[0009] Preferably, the second alloy is NiCoCrAlTaY, and the composition range (in mass percentage) is: Ni 40%-45%, Co 20%-24%, Cr 20%-25%, Al 9%-12%, Ta 2%-6%, Y 0.1%-0.4%. The rare earth doped ceramic is a rare earth doped zirconate, specifically La2Zr2O7. That is, the gradient transition layer is a multi-layer composite coating formed by the compositional gradient change of NiCoCrAlTaY alloy and La2Zr2O7. Among them, NiCoCrAlTaY can enhance the oxidation resistance and corrosion resistance of the gradient transition layer, and the outer layer is a La2Zr2O7 ceramic layer.

[0010] Preferably, the compositional gradient of the gradient transition layer is: from the bonding layer to the ceramic layer, the content of the second alloy decreases, and the content of the rare earth doped ceramic increases.

[0011] Preferably, the thickness of the bonding layer is 50-500 μm, the thickness of the gradient transition layer is 100-300 μm, and the thickness of the outer layer is 50-100 μm. More preferably, the thickness of the bonding layer is 100-500 μm, the thickness of the gradient transition layer is 100-200 μm, and the thickness of the outer layer is 50-80 μm.

[0012] In a second aspect, the present invention provides a preparation method for the above La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating, including the following steps:

[0013] (1) Substrate pretreatment: The substrate is polished with sandpaper and cleaned with absolute ethanol to obtain a pretreated substrate;

[0014] (2) Cladding the bonding layer: A first alloy powder is pre-placed on the surface of the substrate, and multi-pass laser cladding is carried out to obtain a bonding layer with a certain thickness;

[0015] (3) Pre-placing the gradient transition layer:

[0016] Mix the rare earth-doped ceramic powder and the second alloy powder according to the mass ratio A, add an aqueous solution of 2-6 wt% polyvinyl alcohol (PVA), ball mill for 1-4 h to obtain a transition powder, pre-place it on the surface of the bonding layer to obtain the first transition layer, with a pre-placed thickness of 100-300 μm, and dry for 5-10 h;

[0017] Mix the rare earth-doped ceramic powder and the second alloy powder according to the mass ratio B, add an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h to obtain a transition powder, pre-place it on the surface of the first transition layer to obtain the second transition layer, with a pre-placed thickness of 100-300 μm, and dry for 5-10 h;

[0018] Mix the rare earth-doped ceramic powder and the second alloy powder according to the mass ratio C, add an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h to obtain a transition powder, pre-place it on the surface of the second transition layer to obtain the third transition layer, with a pre-placed thickness of 100-300 μm, and dry for 5-10 h;

[0019] Among them, A < B < C, and A = 1:(1 - 5), B = 1:(1 - 3), C = (1 - 5):1;

[0020] (4) Pre-placing the outer layer powder: Add the rare earth-doped ceramic powder to an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h, pre-place it on the surface of the third transition layer to obtain a ceramic layer, with a pre-placed thickness of 100-300 μm, and dry for 2-10 h;

[0021] (5) Laser cladding: Using a laser, the multi-layer pre-placed layers are cladded on the surface of the bonding layer to obtain a composite gradient multi-layer coating.

[0022] Preferably, in step (2), the parameters of the laser cladding are: the laser power is 1000-2000 W, the protective gas is argon, the flow rate is 20-40 L / min, and the cladding speed is 8-14 mm / s.

[0023] Preferably, in step (3), A = 1:(2 - 3), B = 1:(1 - 2), C = (2 - 3):1.

[0024] Preferably, in steps (3) and (4), the concentration of PVA is 3-5 wt%, the ball milling time is 2-3 h, and the drying time is 8-10 h.

[0025] Preferably, in step (5), the parameters of the laser cladding are as follows: the laser power is 2000-5000 W, the shielding gas is argon, the flow rate is 20-60 L / min, and the cladding speed is 5-15 mm / s.

[0026] In the present invention, first, a bonding layer is cladded on the surface of the substrate. On the one hand, the bonding layer can reduce the difference in the coefficient of thermal expansion between some ceramic materials and metals, improve the coating bonding strength, enable the ceramic layer to be tightly attached to the surface of the substrate, and is not prone to cracking and peeling; on the other hand, the bonding layer is made of NiCoCrAlY alloy powder, which improves the oxidation resistance and corrosion resistance of the substrate and extends the service life of the substrate material. There is a metal-ceramic layer with a gradual change in composition on the bonding layer. The composite material containing both the bonding layer and the ceramic layer can make the outer layer tightly combined with the bonding layer without cracking and peeling between the metal and ceramic materials.

[0027] Through the design of the bonding layer + gradient transition layer, a gradual transition of the coefficient of thermal expansion from the metal substrate to the rare-earth doped zirconate ceramic layer can be achieved, thereby significantly reducing the interfacial thermal stress. The rare-earth elements react with impurities such as oxygen and sulfur to form stable oxides (such as La2O3), which can enhance the oxidation resistance and corrosion resistance of the substrate.

[0028] Preparing the coating by laser cladding can enhance the bonding force between the metal substrate and the ceramic coating, and enable the elements between the substrate, the bonding layer, the gradient transition layer, and the ceramic layer to form a metallurgical bond.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) Through the collaborative design of the bonding layer and the gradient transition layer, the present invention effectively reduces the gap in the coefficient of thermal expansion between the rare-earth doped zirconate and the metal substrate, increases the bonding force between the metal and the ceramic, and improves the service life of the coating.

[0031] (2) The present invention uses the method of synchronously regulating the gradient composition by laser cladding, and uses rare-earth doped zirconate as the ceramic layer to form a metallurgical bond with the substrate. The obtained composite coating has excellent high-temperature protection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 : Schematic diagram of the structure of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating of the present invention.

[0033] Figure 2: Cross-sectional morphology diagram of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating of the present invention. Specific embodiments

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] The composite gradient multi-layer coating structure of the following embodiments is as Figure 1 shown. The composite gradient multi-layer coating includes a bonding layer, a gradient transition layer, and an outer layer in sequence on the substrate surface. The bonding layer is a NiCoCrAlY alloy layer, the gradient transition layer is a multi-layer composite coating formed by the compositional gradient change of NiCoCrAlTaY alloy and La2Zr2O7, and the outer layer is a La2Zr2O7 ceramic layer.

[0036] Example 1

[0037] This example provides a composite gradient multi-layer coating, and its preparation method includes the following steps:

[0038] (1) Substrate pretreatment: A 1 cm thick GH4169 substrate is polished with 400-mesh sandpaper for 10 minutes and washed twice with anhydrous ethanol to obtain a pretreated GH4169 substrate;

[0039] (2) Cladding the bonding layer: A 1000 μm thick NiCoCrAlY powder with specific components of Ni 51.4%, Co 20%, Cr 18%, Al 10%, and Y 0.6% is pre-placed on the substrate surface, and multi-pass laser cladding is carried out to obtain the bonding layer; the parameters of laser cladding are a laser power of 1500 W, a protective gas of argon, a flow rate of 40 L / min, and a cladding speed of 10 mm / s;

[0040] (3) Pre-place the gradient transition layer:

[0041] La2Zr2O7 powder with a particle size of 40 μm and NiCoCrAlTaY powder with a particle size of 15 μm, with specific components of Ni 43.9%, Co 23%, Cr 20%, Al 9%, Ta 4%, and Y 0.1%; the powders are mixed at a mass ratio of 1:3, added with an aqueous solution of 4 wt% PVA, ball-milled for 2 hours to obtain transition powder, pre-placed on the surface of the bonding layer to obtain the first transition layer, with a pre-placed thickness of 200 μm, and dried for 10 hours;

[0042] Mix 40-μm La2Zr2O7 powder and 15-μm NiCoCrAlTaY powder in a mass ratio of 1:1, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the first transition layer to obtain a second transition layer with a pre-placed thickness of 200 μm, and dry for 10 h;

[0043] Mix 40-μm La2Zr2O7 powder and 15-μm NiCoCrAlTaY powder in a mass ratio of 3:1, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the second transition layer to obtain a third transition layer with a pre-placed thickness of 200 μm, and dry for 10 h;

[0044] (4) Pre-place the outer layer powder: Add 40-μm La2Zr2O7 powder to an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the transition layer to obtain a ceramic layer with a pre-placed thickness of 200 μm, and dry for 10 h;

[0045] (5) Laser cladding: Use a laser to clad multiple pre-placed layers on the surface of the bonding layer to obtain a composite gradient multi-layer coating with a thickness of 660 μm, where the outer layer thickness is 60 μm, the transition layer thickness is 300 μm, and the bonding layer thickness is 300 μm; Laser cladding parameters: Laser power is 3000 W, the shielding gas is argon, the flow rate is 40 L / min, and the cladding speed is 10 mm / s.

[0046] Example 2

[0047] This example provides a composite gradient multi-layer coating, and its preparation method includes the following steps:

[0048] (1) Substrate pretreatment: Polish a 1-cm thick GH4169 substrate with 400-mesh sandpaper for 10 min and wash it twice with absolute ethanol to obtain a pretreated GH4169 substrate;

[0049] (2) Clad the bonding layer: Pre-place 1000-μm thick NiCoCrAlY powder on the substrate surface, with the specific composition the same as in Example 1, and perform multi-pass laser cladding to obtain a bonding layer; The laser cladding parameters are laser power of 1500 W, the shielding gas is argon, the flow rate is 40 L / min, and the cladding speed is 10 mm / s;

[0050] (3) Pre-place the gradient transition layer:

[0051] Mix La2Zr2O7 powder with a particle size of 40 μm and NiCoCrAlTaY powder with a particle size of 15 μm, with the specific composition being the same as in Example 1; mix them in a mass ratio of 1:4, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the bonding layer to obtain the first transition layer, with a pre-placed thickness of 200 μm, and dry it for 10 h;

[0052] Mix 40 μm La2Zr2O7 powder and 15 μm NiCoCrAlTaY powder in a mass ratio of 1:1, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the first transition layer to obtain the second transition layer, with a pre-placed thickness of 200 μm, and dry it for 10 h;

[0053] Mix 40 μm La2Zr2O7 powder and 15 μm NiCoCrAlTaY powder in a mass ratio of 4:1, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the second transition layer to obtain the third transition layer, with a pre-placed thickness of 200 μm, and dry it for 10 h;

[0054] (4) Pre-place the outer layer powder: Add 40 μm La2Zr2O7 powder to an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain a transition powder, pre-place it on the surface of the transition layer to obtain a ceramic layer, with a pre-placed thickness of 200 μm, and dry it for 10 h;

[0055] (5) Laser cladding: Use a laser to clad multiple pre-placed layers on the surface of the bonding layer to obtain a composite gradient multi-layer coating with a thickness of 660 μm, where the outer layer thickness is 60 μm, the transition layer thickness is 300 μm, and the bonding layer thickness is 300 μm; Laser cladding parameters: Laser power is 3000 W, the protective gas is argon, the flow rate is 40 L / min, and the cladding speed is 10 mm / s.

[0056] Example 3

[0057] This example provides a composite gradient multi-layer coating, and its preparation method includes the following steps:

[0058] (1) Substrate pretreatment: Polish a 1 cm thick GH4169 substrate with 400-mesh sandpaper for 10 min, and wash it twice with anhydrous ethanol to obtain a pretreated GH4169 substrate;

[0059] (2) Clad the bonding layer: Pre-place 1000 μm thick NiCoCrAlY powder on the substrate surface, with the specific composition being the same as in Example 1, and perform multi-pass laser cladding to obtain the bonding layer; The laser cladding parameters are laser power of 1500 W, the protective gas is argon, the flow rate is 40 L / min, and the cladding speed is 10 mm / s;

[0060] (3) Preset gradient transition layer:

[0061] Mix La2Zr2O7 powder with a particle size of 40 μm and NiCoCrAlTaY powder with a particle size of 15 μm, with the specific composition being the same as in Example 1; mix them in a mass ratio of 1:4, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain transition powder, pre-place it on the surface of the bonding layer to obtain the first transition layer, with a preset thickness of 200 μm, and dry it for 10 h;

[0062] Mix La2Zr2O7 powder with a particle size of 40 μm and NiCoCrAlTaY powder with a particle size of 15 μm in a mass ratio of 1:2, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain transition powder, pre-place it on the surface of the first transition layer to obtain the second transition layer, with a preset thickness of 200 μm, and dry it for 10 h;

[0063] Mix La2Zr2O7 powder with a particle size of 40 μm and NiCoCrAlTaY powder with a particle size of 15 μm in a mass ratio of 2:1, add an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain transition powder, pre-place it on the surface of the second transition layer to obtain the third transition layer, with a preset thickness of 200 μm, and dry it for 10 h;

[0064] (4) Preset outer layer powder: Add La2Zr2O7 powder with a particle size of 40 μm to an aqueous solution of 4 wt% PVA, ball mill for 2 h to obtain transition powder, pre-place it on the surface of the transition layer to obtain a ceramic layer, with a preset thickness of 200 μm, and dry it for 10 h;

[0065] (5) Laser cladding: Use a laser to clad multiple preset layers on the surface of the bonding layer to obtain a composite gradient multi-layer coating with a thickness of 660 μm, where the outer layer thickness is 60 μm, the transition layer thickness is 300 μm, and the bonding layer thickness is 300 μm; Laser cladding parameters: Laser power is 3000 W, the protective gas is argon, the flow rate is 40 L / min, and the cladding speed is 10 mm / s.

[0066] Comparative Example 1

[0067] This comparative example provides a composite gradient multi-layer coating. For details, refer to Example 1. The difference is that the gradient transition layer is 1 layer, that is, the first transition layer in Example 1.

[0068] Comparative Example 2

[0069] This comparative example provides a composite gradient multi-layer coating. For details, refer to Example 1. The difference is that the gradient transition layer is 2 layers, that is, the first and second transition layers in Example 2.

[0070] Comparative Example 3

[0071] This comparative example provides a composite gradient multi-layer coating. For details, refer to Example 1, with the difference that the gradient transition layer is not cladded.

[0072] Cross-sectional metallographic observation was carried out on the samples prepared in Example 1, and Figure 2 the morphology shown was obtained. It can be observed that the gradient transition is uniform.

[0073] Thermal shock performance: The coatings of Examples 1-3 and Comparative Examples 1-3 were tested for thermal shock performance. The muffle furnace was heated to 1100 °C, the samples were put in, kept warm for 50 min, taken out and water-cooled, which was recorded as one cycle. The duration of one cycle was 1 h. The results are shown in Table 1.

[0074] Table 1 Test results of thermal shock times

[0075] Sample Number of thermal shocks Sample Number of thermal shocks Example 1 232 Comparative Example 1 164 Example 2 198 Comparative Example 2 182 Example 3 209 Comparative Example 3 120

[0076] Taking the shedding of 10% of the top ceramic layer as the standard, the thermal shock times of Example 1 can reach more than 200 times, showing excellent thermal shock resistance. However, after reducing the gradient transition layer therein, it has a great negative impact on the thermal shock performance of the coating. The reduction of the gradient transition layer results in a poor match of the thermal expansion coefficient of the coating, reducing the service life of the coating.

[0077] This specific embodiment is only an interpretation of the present invention and not a limitation thereto. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating, characterized in that, The composite gradient coating on the substrate surface successively includes a bonding layer, a gradient transition layer, and an outer layer; The material of the bonding layer is a first alloy, and the first alloy is MCrAlY or MCrAlTaY, where M is Ni, Co, or NiCo; The gradient transition layer is a rare-earth modified cermet layer, specifically a composite coating formed by the slow gradual change of composition of a second alloy and a rare-earth doped ceramic; The outer layer is a ceramic layer, and the material is the rare-earth doped ceramic.

2. The La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 1, wherein The substrate is a superalloy.

3. The La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 1, characterized in that, The first alloy is NiCoCrAlY, and the composition range by mass percentage is: Ni 45%-65%, Co 20%-25%, Cr 15%-25%, Al 7%-12%, Y 0.3%-0.6%.

4. The La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 1, characterized in that, The second alloy is NiCoCrAlTaY, and the composition range by mass percentage is: Ni 40%-45%, Co 20%-24%, Cr 20%-25%, Al 9%-12%, Ta 2%-6%, Y 0.1%-0.4%; The rare-earth doped ceramic is a rare-earth doped zirconate, specifically La2Zr2O7.

5. The La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 1, wherein The composition of the gradient transition layer gradually changes as follows: from the bonding layer to the ceramic layer, the content of the second alloy decreases, and the content of the rare-earth doped ceramic increases.

6. The La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 1, characterized in that, The thickness of the bonding layer is 50-500 μm, the thickness of the gradient transition layer is 100-300 μm, and the thickness of the outer layer is 50-100 μm.

7. The preparation method of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to any one of claims 1 to 6, characterized in that, It includes the following steps: (1) Substrate pretreatment: The substrate is polished with sandpaper and cleaned with anhydrous ethanol to obtain a pretreated substrate; (2) Cladding the bonding layer: The first alloy powder is pre-placed on the substrate surface, and multi-pass laser cladding is carried out to obtain a bonding layer with a certain thickness; (3) Pre-setting the gradient transition layer: Mix the rare-earth doped ceramic powder and the second alloy powder according to mass ratio A, add an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h to obtain transition powder, pre-place it on the surface of the bonding layer to obtain the first transition layer, with a pre-set thickness of 100-300 μm, and dry for 5-10 h; Mix the rare-earth doped ceramic powder and the second alloy powder according to mass ratio B, add an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h to obtain transition powder, pre-place it on the surface of the first transition layer to obtain the second transition layer, with a pre-set thickness of 100-300 μm, and dry for 5-10 h; Mix the rare-earth doped ceramic powder and the second alloy powder according to mass ratio C, add an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h to obtain transition powder, pre-place it on the surface of the second transition layer to obtain the third transition layer, with a pre-set thickness of 100-300 μm, and dry for 5-10 h; Among them, A < B < C, and A = 1:(1-5), B = 1:(1-3), C = (1-5):1; (4) Pre-setting the outer layer powder: Add the rare-earth doped ceramic powder to an aqueous solution of 2-6 wt% PVA, ball mill for 1-4 h, pre-place it on the surface of the third transition layer to obtain a ceramic layer, with a pre-set thickness of 100-300 μm, and dry for 2-10 h; (5) Laser cladding: Using a laser, multiple pre-placed layers are cladded on the surface of the bonding layer to obtain a composite gradient multi-layer coating.

8. The preparation method of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 7, characterized in that, In step (2), the parameters of the laser cladding are as follows: the laser power is 1000 - 2000 W, the shielding gas is argon, the flow rate is 20 - 40 L / min, and the cladding speed is 8 - 14 mm / s.

9. The preparation method of the La2Zr2O7-NiCoCrAlTaY composite gradient multi-layer coating according to claim 7, characterized in that, In step (5), the parameters of the laser cladding are: the laser power is 2000 - 5000 W, the shielding gas is argon, the flow rate is 20 - 60 L / min, and the cladding speed is 5 - 15 mm / s.

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