Preparation method of interface self-reaction strong chemical bonding radiant heat protection multilayer gradient coating

Abstract

The invention discloses a preparation method of an interface self-reaction strong chemical bonding radiant heat protection multilayer gradient coating, and belongs to the technical field of coating surface modification. The invention aims to solve the problems that the existing coating is high in preparation temperature, long in period, high in cost and not suitable for industrial batch production, the interface bonding between the coating and a nickel-based high-temperature alloy matrix is poor, the coating is easy to crack and even lose efficacy due to mismatching of thermal expansion under high-temperature service, and the thermal protection performance of the traditional coating is insufficient. The interface self-reaction strong-chemical-bonding radiant heat protection multilayer gradient coating and a nickel-based high-temperature substrate are subjected to self-reaction at the interface to form strong chemical bonding, the bonding strength of the coating reaches 15 MPa or above, the emissivity value of the coating reaches up to 0.9, the structure of the coating is kept complete and does not fall off after the coating is oxidized in 1250 DEG C high-temperature static air for 30 h, and the coating has the advantages of being simple in preparation process, low in cost and the like. The method has application potential in a nickel-based high-temperature alloy anti-oxidation radiation thermal protection multifunctional integrated metal thermal protection system for a high-speed aircraft.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating surface modification, and particularly relates to a preparation method of a radiation heat protection multi-layer gradient coating with strong chemical bonding of interfacial self-reaction. Background Art

[0002] With the rapid development of aerospace technology, the flight range and speed of high-speed aircraft have been significantly improved, which puts more stringent requirements on the high-temperature resistance and oxidation resistance of key components of the aircraft. The thermal protection of high-speed aircraft is a complex issue involving various disciplines, but thermal protection materials are currently a bottleneck problem faced by the generally accepted thermal protection of aircraft. Research shows that nickel-based superalloys have high chemical stability at room temperature, but they will undergo severe oxidation in an oxygen-containing environment, which limits their application in high-temperature environments. So far, designing and preparing high-temperature resistant and oxidation-resistant coatings is still a way with a short R & D cycle, high economic benefits and remarkable effects, which can prevent the strength and stiffness of the substrate from being greatly lost under high-temperature conditions, ensure that the working temperature of structural components does not exceed the allowable range, and ensure service reliability.

[0003] The published patent (CN 117626057 A) prepared a modified MCrAlY coating on a nickel-based single-crystal superalloy by arc ion plating deposition technology. This coating considered the problem of thermal expansion mismatch between the coating and the high-temperature alloy substrate, and improved the high-temperature oxidation resistance and interfacial stability of the coating by regulating the contents of Si, Al, Cr, and Co. However, the synergistic effect of multi-layer coatings was not considered in the coating design, and the antioxidant improvement effect of only a single-layer MCrAlY coating was limited and could not meet the high-temperature thermal protection above 1200 °C; moreover, the preparation temperature of this coating reached 1000 °C, and the coating preparation temperature was relatively high and the process was complicated. The published patent (CN 117186729 A) disclosed a long-life, high-temperature resistant and high-emissivity temperature control coating and its preparation process. The coating is composed of an organic film-forming substance and fillers, and the fillers include enamel powders with different softening points. This coating also considered reducing the coating preparation temperature, and the one-time film-forming temperature was relatively low, and the coating preparation process was simple, and the emissivity of the coating reached 0.85. The disadvantage is that in the process of preparing this coating, all fillers were directly dispersed in the organic film-forming substance, and the coating was obtained by air spraying and drying, without considering the thermal expansion matching problem between the substrate and the coating. The high-temperature oxidation temperature of the coating was only 400 °C, the temperature resistance was relatively low, and the bonding performance was poor. Its antioxidant performance under ultra-high temperature conditions remains to be discussed. Therefore, the comprehensive thermal protection performance of the high-temperature resistant, oxidation-resistant and high-emissivity coating on the surface of superalloys still needs to be further improved to meet the further requirements of the high-temperature resistant and oxidation-resistant performance of the thermal protection coating for key components of high-speed aircraft. Summary of the Invention

[0004] The object of the present invention is to solve the problems of high preparation temperature, long cycle and high cost of existing coatings, which are not suitable for industrial mass production, poor interfacial bonding between the coating and the nickel-based superalloy matrix, easy cracking and even failure of the coating due to thermal expansion mismatch under high-temperature service, and insufficient thermal protection performance of traditional coatings, and to provide a preparation method for a radiation thermal protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding.

[0005] A preparation method for a radiation thermal protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding, wherein the multi-layer gradient coating includes an interfacial strong chemical bonding reaction layer, a high-bonding / oxidation-resistant / thermal expansion matching gradient transition layer, and a high-emissivity / oxidation-resistant / erosion-resistant / ablation-resistant multi-functional outer layer;

[0006] The specific preparation method is completed according to the following steps:

[0007] I. Pretreatment of the substrate:

[0008] First, use SiC sandpaper to polish the surface of the superalloy matrix until it is flat, and then remove the oil stain on the surface of the superalloy matrix to obtain a pretreated superalloy matrix;

[0009] II. Construction of the interfacial strong chemical bonding reaction layer:

[0010] Spray a low-temperature polymerized inorganic precursor binder onto one or two surfaces of the superalloy matrix to obtain a matrix with an interfacial strong chemical bonding reaction layer to be formed on the surface;

[0011] III. Construction of the high-bonding / oxidation-resistant / thermal expansion matching gradient transition layer:

[0012] Weigh and mix the thermal expansion matching metal component powders and the high-temperature oxidation-resistant component powders according to different gradient ratios to obtain multiple groups of transition layer powders; then add the multiple groups of transition layer powders into multiple groups of low-temperature polymerized inorganic precursor binders to make gradient slurries; then spray the gradient slurries layer by layer onto the matrix with an interfacial strong chemical bonding reaction layer to be formed on the surface to construct a gradient transition layer, wherein the proportion of the thermal expansion matching metal component powders in the layer close to the matrix is the highest and gradually decreases layer by layer outward;

[0013] IV. Construction of the high-emissivity / oxidation-resistant / erosion-resistant / ablation-resistant multi-functional outer layer:

[0014] Mix the high-emissivity component powders and the high-temperature oxidation-resistant component powders to obtain multi-functional outer layer powders; add the multi-functional outer layer powders into a low-temperature polymerized inorganic precursor binder to make a slurry, and then spray it on the surface of the gradient transition layer to construct a multi-functional outer layer, obtaining a superalloy matrix with a multi-layer coating to be formed;

[0015] V. Low-temperature curing of the coating:

[0016] The superalloy substrate to be formed with a multi-layer coating is placed in a specific humidity environment, left to dry to the surface dry state at room temperature, and then heated and cured. After the curing of the multi-layer coating is completed, it is cooled to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding.

[0017] Principle of the present invention:

[0018] The present invention proposes a preparation method for a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding. By means of the room-temperature spraying - inorganic precursor low-temperature polymerization conversion method, a strongly chemically bonded reaction layer at the interface, a high-bonding / anti-oxidation / thermal expansion matching gradient transition layer, and a multi-functional outer layer with high emissivity / anti-oxidation / erosion resistance / ablation resistance are respectively prepared on the surface of a nickel-based superalloy, strengthening the interfacial bonding between the substrate and the coating, and realizing the integration of multiple functions such as high temperature resistance, anti-oxidation, thermal expansion matching, and high emissivity; the co-design strategy of this composite coating for strengthening the heat protection mechanism of the nickel-based superalloy substrate is mainly reflected in:

[0019] (1) Strong interfacial self-reactive chemical bonding design:

[0020] In order to enhance the interfacial bonding strength between the coating and the nickel-based superalloy substrate, a strongly chemically bonded reaction layer is pre-introduced at the substrate-coating interface. A phosphate binder is selected as the low-temperature polymerization inorganic precursor binder, and the pH value of the binder is 2 to 6. It can undergo low-temperature curing with the nickel-based superalloy at 100°C to 300°C. The binder and the substrate undergo a self-reaction through the mutual diffusion of atoms such as P, Fe, and Cr at the interface to form a strongly chemically bonded layer with a thickness of hundreds of nanometers; this design of the strongly chemically bonded layer is different from the traditional mechanically bonded interface and can significantly improve the bonding strength between the coating and the substrate.

[0021] (2) Multi-layer synergistic effect:

[0022] The strongly chemically bonded reaction layer, the gradient transition layer, and the multi-functional outer layer use the same low-temperature polymerization inorganic precursor binder, ensuring good interfacial matching between the multi-layer coatings; in a high-temperature environment, the multi-functional outer layer serves as the first radiation heat protection barrier, playing the role of radiative cooling and resisting oxygen erosion; the gradient transition layer serves as the second anti-oxidation heat protection barrier, resisting oxygen erosion and maintaining thermal expansion matching at high temperatures; the strongly chemically bonded reaction layer ensures high bonding between the coating and the substrate; the multi-layer coating structure plays a synergistic role, effectively improving the high-temperature heat protection effect of the coating.

[0023] (3) Multi-component synergistic effect:

[0024] In a high-temperature environment, the high-emissivity component in the multi-functional outer layer takes the lead in playing a role, reducing the surface heat load of the coating through the high-emissivity radiative heat dissipation effect; the high-temperature and anti-oxidation component MoSi 2 、SiB4 etc. as additional oxygen-consuming phases can generate SiO after high-temperature oxidation 2 , B 2 O 3 , Mo 5 Si 3 , MoO 3 etc. Among them, the fluid SiO 2 , B 2 O 3 etc. can quickly fill the pores left by the volatilization of some gas-phase products, heal the defects such as holes and cracks in the coating, ensure the continuity of the oxide layer, and greatly improve the strain tolerance and thermal stability of the coating. Moreover, at high temperature, the P-O-Al skeleton anchors the SiO 2 oxide layer to form a dense and stable oxygen diffusion barrier layer, which can slow down the further diffusion of the oxidation atmosphere into the coating, thereby delaying the oxidation rate of the coating. As the service time prolongs, when heat is transferred to the gradient transition layer, the high-temperature oxidation-resistant components such as Al and SiC far from the substrate in the coating act as oxygen-consuming phases to play an antioxidant role, and continuous and dense Al 2 O 3 , SiO 2 are generated after high-temperature oxidation. As an oxygen shielding layer, it has excellent thermodynamic stability, can block the further inward diffusion of oxygen, and provides effective thermal protection for the nickel-based superalloy substrate; the gradient transition layer always plays a role in regulating the thermal matching between the nickel-based superalloy substrate and the multi-functional ceramic outer layer, solving the problem of coating cracking or even failure under high-temperature service.

[0025] The present invention has the following beneficial effects:

[0026] First, a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared by the present invention forms strong chemical bonding through the mutual diffusion of atoms at the interface with the nickel-based superalloy substrate, breaking through the problem of poor interface bonding between traditional coatings and substrates; the synergistic effect of the multi-layer coating structure realizes the integration of multiple functions such as high temperature resistance, oxidation resistance, thermal expansion matching, and high emissivity. Compared with the existing multi-layer structure coatings, it solves the problems of interfacial thermal mismatch and insufficient thermal protection performance.

[0027] Second, the present invention realizes the preparation of the coating through the room-temperature spraying-low-temperature polymerization inorganic precursor chemical conversion method. The inorganic precursor binder used has a low curing temperature, and the low-temperature preparation of high-temperature-resistant coatings can be realized; the coating preparation process is simple, suitable for the surface of workpieces with complex shapes, and has good application prospects; the binder and filler components do not contain harmful components to the human body and the environment, and are safe and environmentally friendly.

[0028] III. The bonding strength of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared by the present invention reaches over 15 MPa; the emissivity value of the coating is as high as 0.9, having excellent radiation heat protection performance; the coating thickness is controllable, being 60 - 300 μm; the coating structure remains intact without peeling after oxidizing in static air at 1250 °C for 30 h, and has application potential in the antioxidant radiation heat protection multi-functional integrated metal thermal protection system of high-speed aircraft. Description of the Drawings

[0029] Figure 1 XRD pattern of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention;

[0030] Figure 2 Surface microscopic morphology photo of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention;

[0031] Figure 3 Cross-sectional microscopic morphology photo of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention;

[0032] Figure 4 Cross-sectional morphology photo of the interface strong chemical bond reaction layer in a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention;

[0033] Figure 5 Bonding strength of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention;

[0034] Figure 6 Macroscopic morphology comparison photos of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Examples 1 - 3 of the present invention and nickel-based superalloy GH4061 in Comparative Example 1 before / after oxidizing at 1250 °C in static air for 30 h;

[0035] Figure 7 XRD patterns of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Examples 1 - 3 of the present invention and nickel-based superalloy GH4061 in Comparative Example 1 after oxidizing at 1250 °C in static air for 30 h;

[0036] Figure 8 Oxidation weight gain curves of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonds prepared in Example 1 of the present invention and nickel-based superalloy GH4061 in Comparative Example 1;

[0037] Figure 9Emissivity spectra of a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Example 1 of the present invention and the nickel-based superalloy GH4061 in Comparative Example 1;

[0038] Figure 10 Schematic diagram of the structure of a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared on one surface of a superalloy substrate in the present invention. Specific embodiments

[0039] Specific Embodiment 1: A preparation method of a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding. The multi-layer gradient coating includes an interfacial strong chemical bonding reaction layer, a high-bonding / oxidation-resistant / thermal expansion matching gradient transition layer, and a high-emissivity / oxidation-resistant / erosion-resistant / ablation-resistant multi-functional outer layer;

[0040] The preparation method is specifically completed according to the following steps:

[0041] I. Pretreatment of the substrate:

[0042] First, use SiC sandpaper to polish the surface of the superalloy substrate until it is flat, and then remove the oil on the surface of the superalloy substrate to obtain a pretreated superalloy substrate;

[0043] II. Construction of the interfacial strong chemical bonding reaction layer:

[0044] Spray a low-temperature polymerized inorganic precursor binder onto one or two surfaces of the superalloy substrate to obtain a substrate with a surface to form an interfacial strong chemical bonding reaction layer;

[0045] III. Construction of the high-bonding / oxidation-resistant / thermal expansion matching gradient transition layer:

[0046] Weigh and mix the thermal expansion matching metal component powders and high-temperature oxidation-resistant component powders according to different gradient ratios to obtain multiple groups of transition layer powders; then add the multiple groups of transition layer powders into multiple groups of low-temperature polymerized inorganic precursor binders to make gradient slurries; then spray the gradient slurries layer by layer onto the substrate with a surface to form an interfacial strong chemical bonding reaction layer to construct a gradient transition layer, where the proportion of the thermal expansion matching metal component powder in the layer closest to the substrate is the highest and decreases layer by layer outward;

[0047] IV. Construction of the high-emissivity / oxidation-resistant / erosion-resistant / ablation-resistant multi-functional outer layer:

[0048] Mix the high-emissivity component powder and the high-temperature oxidation-resistant component powder to obtain a multi-functional outer layer powder; add the multi-functional outer layer powder into a low-temperature polymerized inorganic precursor binder to make a slurry, and then spray it onto the surface of the gradient transition layer to construct a multi-functional outer layer, obtaining a superalloy substrate to form a multi-layer coating;

[0049] V. Low-temperature curing of the coating:

[0050] Place the superalloy substrate to be formed with a multi-layer coating in a specific humidity environment, air-dry it at room temperature until the surface is dry, and then heat and cure it. After the multi-layer coating is cured, cool it to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction.

[0051] In the fourth step of this embodiment, a multi-functional outer layer with high emissivity / oxidation resistance / erosion resistance / ablation resistance is designed and prepared. On the one hand, the heat is radiated to the outer space by strengthening the radiation heat dissipation effect, effectively reducing the surface heat load of the substrate; on the other hand, the comprehensive properties of the coating such as high temperature resistance, oxidation resistance, erosion resistance, and ablation resistance are improved. The multi-functional outer layer includes a high emissivity component and a high temperature oxidation resistance component.

[0052] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: in Step 1, the superalloy substrate is a nickel-based superalloy; in Step 1, the surface of the superalloy substrate is polished smoothly with 400#, 600#, 800#, and 1000# sandpapers in sequence, and then the oil stain on the surface of the superalloy substrate is removed with anhydrous ethanol to obtain a pretreated superalloy substrate. Other steps are the same as those in Specific Embodiment 1.

[0053] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that: the low-temperature polymerized inorganic precursor binder in Step 2, Step 3, and Step 4 is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps:

[0054] Weigh and mix the phosphoric acid solution with a mass fraction of 85% and deionized water according to a volume ratio of (1-2):1, and then heat it in a water bath at 60°C - 100°C and continuously stir for 20 min - 60 min; then weigh and add aluminum hydroxide powder according to the ratio of P:Al of 3:(1-2), keep the temperature of the water bath heating at 60°C - 100°C, heat and stir for 1 h - 3 h to obtain a mixed solution; add a curing agent to the mixed solution, the mass ratio of the curing agent to the volume of the mixed solution is (1 g - 10 g):100 mL, heat and stir at 60°C - 100°C for 1 h - 3 h, and then adjust the pH value of the solution to 2 - 6 to obtain a phosphate binder; the curing agent is one or a mixture of several of MgO, ZnO, CuO, CrO 3 in one or a mixture of several of them. Other steps are the same as those in Specific Embodiment 1 or 2.

[0055] In this embodiment, the low-temperature polymerized inorganic precursor binder and the nickel-based superalloy undergo a self-reaction at the interface through the mutual diffusion of atoms such as P, Fe, and Cr to form a strong chemical bond bonding layer with a thickness of hundreds of nanometers; the same low-temperature polymerized inorganic precursor binder is selected in Steps 3 and 4, ensuring the interface matching between the high bonding / oxidation resistance / thermal expansion matching gradient transition layer and the high emissivity / oxidation resistance / erosion resistance / ablation resistance multi-functional outer layer.

[0056] Specific Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is as follows: the thermal expansion matching metal component powder in Step 3 is metal powder; the metal powder is one or a mixture of several of MCrAlY, NiCrBSi, Ni, and W powder; the high-temperature oxidation resistance component powder in Step 3 is one or a mixture of several of Al, SiC, B 4 C, BN, and WSi 2 powder. Other steps are the same as those in Embodiments 1 to 3.

[0057] In this embodiment, the basis for selecting the thermal expansion matching metal component powder is: metal powder with a thermal expansion coefficient close to that of the nickel-based superalloy matrix;

[0058] In this embodiment, the basis for selecting the high-temperature oxidation resistance component powder is: powder with oxygen-consuming ability and a thermal expansion coefficient close to that of the multi-functional ceramic outer layer.

[0059] Specific Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is as follows: in the formation of the multi-layer gradient structure in Step 3, from the matrix outwards, the mass ratio of the thermal expansion matching metal component powder to the high-temperature oxidation resistance component powder decreases in a gradient, changing from (1:0) to (1:X), and the value range of X is: 1 ≤ X ≤ 10. Other steps are the same as those in Embodiments 1 to 4.

[0060] In this embodiment, the mass ratio of the thermal expansion matching metal component powder to the high-temperature oxidation resistance component powder decreases in a gradient, using the gradually decreasing thermal expansion coefficient to relieve thermal stress and realizing the multi-layer interface thermal expansion matching between the superalloy matrix and the multi-functional ceramic outer layer.

[0061] Specific Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is as follows: the preparation method of the slurry in Step 3 is: putting the transition layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill tank, adding zirconia balls, and ball milling for 12 h to 24 h under the condition of a ball milling speed of 60 r / min to 100 r / min to obtain a uniform slurry; the mass ratio of the transition layer powder to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4); the mass ratio of the zirconia balls to the transition layer powder is (2 to 4):1. Other steps are the same as those in Embodiments 1 to 5.

[0062] Embodiment 7 in detail: The difference between this embodiment and any one of Embodiments 1 to 6 is that: in Step 4, the mass ratio of the high emissivity component powder to the high temperature resistant and oxidation resistant component powder in the multifunctional outer layer powder is (1 to 3):(1 to 3); the high emissivity component powder described in Step 4 is MoSi 2 , SiB 4 , SiB 6 and SiC, or a mixture of several of them, with a particle size of 1 μm to 10 μm; the high temperature resistant and oxidation resistant component powder described in Step 4 is MoSi 2 , SiB 4 , SiB 6 , ZrSi 2 , B 4 C, SiC, BN and Si powder, or a mixture of several of them, with a particle size of 1 μm to 10 μm. Other steps are the same as those in Embodiments 1 to 6.

[0063] In this embodiment, the selection basis of the high emissivity component powder is: select ceramic powders with higher emissivity values; in MoSi 2 , SiB 4 , SiB 6 and SiC, there are strong Si-M (M = Mo, C, B) covalent bonds in the crystal structure. Utilizing the synergistic effect of the lattice vibration absorption matching of multi-phase and multi-chemical bondings can effectively improve the emissivity of the multifunctional outer layer.

[0064] In this embodiment, the selection basis of the high temperature resistant and oxidation resistant component powder is: ceramic powders with oxygen consumption ability. MoSi 2 , SiB 4 , SiB 6 , ZrSi 2 , B 4 C, SiC, BN and Si powder can achieve high temperature oxidation protection of the substrate in a wide temperature range. Among them, MoSi 2 etc. play an antioxidant role by forming a SiO 2 passivation layer at ultra-high temperatures of 1500 to 1700 °C. SiC and ZrSi 2 form a dense ZrO 2 , SiO 2 protective film in the temperature range of 1100 to 1500 °C to block the penetration of oxygen. SiB 4 , SiB 6 form a flowing B 2 O 3 protective film in the temperature range of 800 to 1100 °C to block the penetration of oxygen into the interior of the coating. B 4 C, BN, and Si form a stable oxide protective film at 800 °C without the escape of gas-phase products;

[0065] In this embodiment, the particle size of the powder is 1 - 10 μm. The small particle size of the powder ensures the overall continuity and density of the coating.

[0066] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 - 7 is as follows: The preparation method of the slurry described in Step 4 is: Put the multifunctional outer layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill tank, add zirconia balls, and ball mill for 12 - 24 hours under the condition of a ball mill speed of 60 r / min - 100 r / min to obtain a homogeneous slurry; the mass ratio of the multifunctional outer layer powder to the low-temperature polymerized inorganic precursor binder is 1:(1 - 4); the mass ratio of zirconia balls to the multifunctional outer layer powder is (2 - 4):1; the spraying methods described in Steps 3 and 4 are: spraying at room temperature, with an air pump pressure of 30 MPa - 90 MPa, a spraying distance of 60 mm - 150 mm, and a spraying speed of 10 mm / min - 50 mm / min; the number of spraying times is one or more. Other steps are the same as those in Specific Embodiments 1 - 7.

[0067] Specific Embodiment 9: The difference between this embodiment and any one of Specific Embodiments 1 - 8 is as follows: The specific humidity environment described in Step 5 is a constant humidity environment of 20% - 60%; the heating and curing process in Step 5 is: heating from room temperature to 100 °C at a heating rate of 2 °C / min - 5 °C / min, holding for 12 - 24 hours, then heating from 100 °C to 300 °C at a heating rate of 5 °C / min - 10 °C / min, holding for 1 - 5 hours, and cooling to room temperature. Other steps are the same as those in Specific Embodiments 1 - 8.

[0068] Specific Embodiment 10: The difference between this embodiment and any one of Specific Embodiments 1 - 9 is as follows: In the radiation heat protection multi-layer gradient coating with interfacial self-reactive strong chemical bonding described in Step 5, the thickness of the interfacial strong chemical bonding reaction layer is 100 nm - 500 nm; the total thickness of the high bonding / oxidation resistance / thermal expansion matching gradient transition layer is 10 - 100 μm, and the thickness of each sub-layer is 3 μm - 20 μm; the thickness of the high emissivity / oxidation resistance / erosion resistance / ablation resistance multifunctional outer layer is 50 μm - 200 μm; the bonding strength of the radiation heat protection multi-layer gradient coating with interfacial self-reactive strong chemical bonding described in Step 5 reaches above 15 MPa, the emissivity is as high as 0.9, and the coating does not break after being oxidized in static air at 1250 °C for 30 hours. Other steps are the same as those in Specific Embodiments 1 - 9.

[0069] The following examples are used to verify the beneficial effects of the present invention:

[0070] Example 1: A preparation method of a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding. The multi-layer gradient coating includes an interfacial strong chemical bonding reaction layer, a high-bonding / anti-oxidation / thermal expansion matching gradient transition layer, and a high-emissivity / anti-oxidation / erosion-resistant / ablation-resistant multi-functional outer layer;

[0071] The specific preparation method is completed according to the following steps:

[0072] I. Pretreatment of the substrate:

[0073] The surface of the superalloy substrate is polished smoothly in sequence with 400#, 600#, 800#, and 1000# sandpapers, and then the oil stain on the surface of the superalloy substrate is removed with absolute ethanol to obtain the pretreated superalloy substrate;

[0074] The superalloy substrate described in step I is nickel-based superalloy GH4061;

[0075] II. Construction of the interfacial strong chemical bonding reaction layer:

[0076] The low-temperature polymerization inorganic precursor binder is sprayed onto the two surfaces of the superalloy substrate to obtain the substrate with the interfacial strong chemical bonding reaction layer to be formed on the surface;

[0077] In step II, during the subsequent thermal curing process, the low-temperature polymerization inorganic precursor binder undergoes an interfacial chemical reaction with Fe and Cr in the nickel-based superalloy substrate, forming a Fe(H 2 PO 4 ) 3 and CrP x strong chemical bonding interface layer with a thickness of about one hundred nanometers between the coating and the substrate;

[0078] III. Construction of the high-bonding / anti-oxidation / thermal expansion matching gradient transition layer:

[0079] The thermal expansion matching metal component powder and the high-temperature oxidation resistance component powder are weighed and mixed according to different gradient ratios to obtain multiple groups of transition layer powders; then the multiple groups of transition layer powders are respectively added to multiple groups of low-temperature polymerization inorganic precursor binders to make gradient slurries; then the gradient slurries are sprayed layer by layer onto the substrate with the interfacial strong chemical bonding reaction layer to be formed on the surface to construct the gradient transition layer, where the proportion of the thermal expansion matching metal component powder in the layer close to the substrate is the highest and decreases layer by layer outward;

[0080] The thermal expansion matching metal component powder described in step III is MCrAlY, purchased from Hebei Guifa Alloy Wear-Resistant Materials Co., Ltd., with the composition of Cr: 21.57%, Al: 4.35%, Y 2 O 3 : 0.58%, Fe: 0.32%, Ni: the balance;

[0081] The high-temperature oxidation-resistant component powder described in Step 3 is Al;

[0082] In the formation of the multi-layer gradient structure described in Step 3, from the substrate outwards, the mass ratio of the thermal expansion matching metal component powder to the high-temperature oxidation-resistant component powder decreases in a gradient, which are 1:0, 1:1, 1:2, and 1:3 in sequence;

[0083] The preparation method of the slurry described in Step 3 is: put the transition layer powder and the low-temperature polymerizable inorganic precursor binder into a ball milling tank, add zirconia balls, and ball mill for 12 h under the condition of a ball milling speed of 80 r / min to obtain a uniform slurry; the mass ratio of the transition layer powder to the low-temperature polymerizable inorganic precursor binder is 1:2; the mass ratio of the zirconia balls to the transition layer powder is 4:1;

[0084] IV. Construct a multi-functional outer layer with high emissivity / oxidation resistance / erosion resistance / ablation resistance:

[0085] Mix the high emissivity component powder and the high temperature oxidation resistant component powder to obtain the multi-functional outer layer powder; add the multi-functional outer layer powder into the low-temperature polymerizable inorganic precursor binder to make a slurry, and then spray it on the surface of the gradient transition layer to construct the multi-functional outer layer, obtaining a superalloy substrate to be formed with a multi-layer coating;

[0086] In the multi-functional outer layer powder described in Step 4, the mass ratio of the high emissivity component powder to the high temperature oxidation resistant component powder is 1:1;

[0087] The high emissivity component powder described in Step 4 is MoSi 2 , with a particle size of 1 μm to 10 μm;

[0088] The high temperature oxidation resistant component powder described in Step 4 is SiB 4 , with a particle size of 1 μm to 10 μm;

[0089] The preparation method of the slurry described in Step 4 is: put the multi-functional outer layer powder and the low-temperature polymerizable inorganic precursor binder into a ball milling tank, add zirconia balls, and ball mill for 12 h under the condition of a ball milling speed of 80 r / min to obtain a uniform slurry; the mass ratio of the multi-functional outer layer powder to the low-temperature polymerizable inorganic precursor binder is 1:2; the mass ratio of the zirconia balls to the multi-functional outer layer powder is 4:1;

[0090] The spraying methods described in Step 3 and Step 4 are: spraying at room temperature, with an air pump pressure of 70 MPa, a spraying distance of 100 mm, and a spraying speed of 40 mm / min; the number of spraying times is multiple;

[0091] V. Low-temperature curing of the coating:

[0092] Place the superalloy substrate to be formed with a multi-layer coating in a specific humidity environment, air-dry it at room temperature until the surface is dry, and then heat and cure it. After the multi-layer coating is cured, cool it to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction;

[0093] The specific humidity environment described in step five is a constant humidity environment of 30%;

[0094] The process of heating and curing in step five is: heat from room temperature to 100°C at a heating rate of 4°C / min, hold for 12 h, then heat from 100°C to 300°C at a heating rate of 8°C / min, hold for 2 h, and cool to room temperature;

[0095] The low-temperature polymerized inorganic precursor binder described in step two, step three, and step four is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps:

[0096] Weigh and mix the phosphoric acid solution with a mass fraction of 85% and deionized water in a volume ratio of 2:1, then heat in a water bath at 80°C and continuously stir for 30 min; then weigh and add aluminum hydroxide powder according to the ratio of P:Al of 3:1, keep the temperature of the water bath heating at 80°C, heat and stir for 2 h to obtain a mixed solution; add a curing agent to the mixed solution, and the mass ratio of the curing agent to the volume of the mixed solution is 10 g:100 mL, heat and stir at 80°C for 3 h, and then adjust the pH value of the solution to 2 to obtain the phosphate binder; the curing agent is ZnO.

[0097] Figure 1 This is the XRD pattern of a radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction prepared in Example 1 of the present invention;

[0098] From Figure 1 It can be seen that the radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction obtained after curing mainly includes the matrix γ-Ni phase, the binder AlPO 4 phase, the multi-functional outer layer filler MoSi 2 , SiB 4 phase, and the gradient transition layer fillers Ni, Cr, Al phases. After low-temperature curing, the phase composition of the coating is stable.

[0099] Figure 2 This is the surface microtopography photo of a radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction prepared in Example 1 of the present invention;

[0100] Figure 3 This is the cross-section microtopography photo of a radiation heat protection multi-layer gradient coating with strong chemical bonds formed by interfacial self-reaction prepared in Example 1 of the present invention;

[0101] Figure 4 This is a cross-sectional morphology photo of the interface strong chemical bonding reaction layer in a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonding at the interface prepared in Example 1 of the present invention;

[0102] From Figures 2 to 4 it can be seen that: After curing, a continuous and complete coating is formed. The surface of the coating is flat, without cracks or other defects. The interface morphology of the coating shows that the total thickness of the finally prepared radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonding at the interface is about 100 μm, including an interface strong chemical bonding reaction layer with a thickness of about 100 nm, a gradient transition layer with a thickness of 50 μm, and a multi-functional outer layer with a thickness of about 50 μm. Among them, the gradient transition layer is composed of four sub-layers, and the thickness of each layer is about 10 μm.

[0103] Figure 5 This is the bonding strength of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonding at the interface prepared in Example 1 of the present invention;

[0104] From Figure 5 it can be seen that: The bonding strength of the radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonding at the interface prepared in Example 1 of the present invention reaches more than 15 MPa, which is significantly higher than the bonding strength of traditional mechanically bonded interface coatings.

[0105] Example 2: A preparation method of a radiation heat protection multi-layer gradient coating with self-reactive strong chemical bonding at the interface. The multi-layer gradient coating includes an interface strong chemical bonding reaction layer, a high bonding / oxidation resistance / thermal expansion matching gradient transition layer, and a high emissivity / oxidation resistance / erosion resistance / ablation resistance multi-functional outer layer;

[0106] The specific preparation method is completed according to the following steps:

[0107] I. Pretreatment of the substrate:

[0108] The surface of the superalloy substrate is polished flat in sequence with 400#, 600#, 800#, and 1000# sandpapers, and then the oil on the surface of the superalloy substrate is removed with anhydrous ethanol to obtain a pretreated superalloy substrate;

[0109] The superalloy substrate described in step I is a nickel-based superalloy GH4061;

[0110] II. Construction of the interface strong chemical bonding reaction layer:

[0111] The low-temperature polymerized inorganic precursor binder is sprayed onto the two surfaces of the superalloy substrate to obtain a substrate with an interface strong chemical bonding reaction layer to be formed on the surface;

[0112] In Step 2, during the thermal curing process, the binder undergoes an interfacial chemical reaction with Fe and Cr in the nickel-based superalloy matrix, forming an interfacial layer with a thickness of about a hundred nanometers between the coating and the matrix, which is composed of Fe(H 2 PO 4 ) 3 strongly chemically bonded to CrP x interface layer;

[0113] III. Construct a high-bonding / oxidation-resistant / thermal expansion-matching gradient transition layer:

[0114] Weigh and mix the thermal expansion-matching metal component powders and high-temperature oxidation-resistant component powders according to different gradient ratios to obtain multiple groups of transition layer powders; then add the multiple groups of transition layer powders into multiple groups of low-temperature polymerizable inorganic precursor binders to make gradient slurries; then spray the gradient slurries layer by layer onto the substrate whose surface is to form an interfacial strong chemical bonding reaction layer to construct a gradient transition layer, where the proportion of the thermal expansion-matching metal component powder is the highest in the layer closest to the substrate and decreases layer by layer outward;

[0115] The thermal expansion-matching metal component powder described in Step 3 is MCrAlY, purchased from Hebei Guifa Alloy Wear-Resistant Materials Co., Ltd., with the composition: Cr: 21.57%, Al: 4.35%, Y 2 O 3 : 0.58%, Fe: 0.32%, Ni: the balance;

[0116] The high-temperature oxidation-resistant component powder described in Step 3 is SiC;

[0117] In the formation of the multi-layer gradient gradual change structure described in Step 3, from the substrate outward, the mass ratio of the thermal expansion-matching metal component powder to the high-temperature oxidation-resistant component powder decreases in a gradient, being 1:0, 1:1, 1:2, 1:3 in sequence;

[0118] The preparation method of the slurry described in Step 3 is: put the transition layer powder and the low-temperature polymerizable inorganic precursor binder into a ball milling tank, add zirconia balls, and ball mill for 18 h under the condition of a ball milling speed of 60 r / min to obtain a uniform slurry; the mass ratio of the transition layer powder to the low-temperature polymerizable inorganic precursor binder is 1:3; the mass ratio of the zirconia balls to the transition layer powder is 3:1;

[0119] IV. Construct a high-emissivity / oxidation-resistant / erosion-resistant / ablation-resistant multi-functional outer layer:

[0120] Mix the high-emissivity component powder and the high-temperature oxidation-resistant component powder to obtain the multi-functional outer layer powder; add the multi-functional outer layer powder into the low-temperature polymerizable inorganic precursor binder to make a slurry, and then spray it on the surface of the gradient transition layer to construct the multi-functional outer layer, obtaining the superalloy substrate to form a multi-layer coating;

[0121] The mass ratio of the high emissivity component powder to the high temperature resistant and oxidation resistant component powder in the multi-functional outer layer powder described in Step 4 is 3:1;

[0122] The high emissivity component powder described in Step 4 is MoSi 2 , with a particle size of 1 μm to 10 μm;

[0123] The high temperature resistant and oxidation resistant component powder described in Step 4 is SiB 4 , with a particle size of 1 μm to 10 μm;

[0124] The preparation method of the slurry described in Step 4 is: put the multi-functional outer layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill tank, add zirconia balls, and ball mill for 18 h under the condition of a ball mill speed of 60 r / min to obtain a homogeneous slurry; the mass ratio of the multi-functional outer layer powder to the low-temperature polymerized inorganic precursor binder is 1:3; the mass ratio of zirconia balls to the multi-functional outer layer powder is 3:1;

[0125] The spraying methods described in Step 3 and Step 4 are: spraying at room temperature, with an air pump pressure of 50 MPa, a spraying distance of 60 mm, and a spraying speed of 50 mm / min; the number of sprayings is multiple times to achieve the control of the coating thickness;

[0126] V. Low-temperature curing of the coating:

[0127] Place the superalloy substrate to be formed with a multi-layer coating in a specific humidity environment, air-dry it at room temperature until the surface is dry and then heat and cure it. After the multi-layer coating is cured, cool it to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonds;

[0128] The specific humidity environment described in Step 5 is a constant humidity environment of 20%;

[0129] The heating and curing process in Step 5 is: heat from room temperature to 100 °C at a heating rate of 2 °C / min, hold for 24 h, then heat from 100 °C to 300 °C at a heating rate of 5 °C / min, hold for 5 h, and cool to room temperature;

[0130] The low-temperature polymerized inorganic precursor binder described in Step 2, Step 3, and Step 4 is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps:

[0131] Weigh and mix 85% phosphoric acid solution and deionized water in a volume ratio of 3:2 evenly, then heat them in a water bath at 90 °C and continuously stir for 20 min; then weigh and add aluminum hydroxide powder according to the ratio of P:Al of 2:1, keep the temperature of the water bath heating at 90 °C, heat and stir for 1 h to obtain a mixed solution; add a curing agent to the mixed solution, and the mass-to-volume ratio of the curing agent to the mixed solution is 5 g:100 mL, heat and stir at 90 °C for 2 h, and then adjust the pH value of the solution to 4 to obtain a phosphate binder; the curing agent is CuO.

[0132] After testing, the total thickness of a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in this example is about 200 μm, including an interfacial strong chemical bonding reaction layer with a thickness of about 100 nm, a gradient transition layer with a thickness of 100 μm, and a multi-functional outer layer with a thickness of about 100 μm. The gradient transition layer consists of four sub-layers, and the thickness of each layer is about 25 μm.

[0133] Example 3: A preparation method of a radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding, the multi-layer gradient coating includes an interfacial strong chemical bonding reaction layer, a high-bonding / anti-oxidation / thermal expansion matching gradient transition layer, and a high-emissivity / anti-oxidation / erosion-resistant / ablation-resistant multi-functional outer layer;

[0134] The specific preparation method is completed according to the following steps:

[0135] I. Pretreatment of the substrate:

[0136] Use 400#, 600#, 800#, and 1000# sandpapers to polish the surface of the superalloy substrate in turn, and then use anhydrous ethanol to remove the oil stains on the surface of the superalloy substrate to obtain a pretreated superalloy substrate;

[0137] The superalloy substrate described in step I is a nickel-based superalloy GH4061;

[0138] II. Construction of the interfacial strong chemical bonding reaction layer:

[0139] Spray a low-temperature polymerized inorganic precursor binder onto the two surfaces of the superalloy substrate to obtain a substrate with an interfacial strong chemical bonding reaction layer to be formed on the surface;

[0140] In step II, during the thermal curing process, the binder reacts with Fe and Cr in the nickel-based superalloy substrate to form an interfacial chemical reaction, and a Fe(H 2 PO 4 ) 3 and CrP x strong chemical bonding interface layer with a thickness of about a hundred nanometers is formed between the coating and the substrate;

[0141] III. Constructing a high-bonding / antioxidant / thermal expansion matching gradient transition layer:

[0142] Weigh and mix the powder of the metal component with thermal expansion matching and the powder of the high-temperature antioxidant component according to different gradient ratios to obtain multiple groups of transition layer powders; then add the multiple groups of transition layer powders into multiple groups of low-temperature polymerized inorganic precursor binders to make gradient slurries; then spray the gradient slurries layer by layer onto the substrate whose surface is to form an interfacial strong chemical bonding reaction layer to construct a gradient transition layer, where the proportion of the powder of the metal component with thermal expansion matching in the layer close to the substrate is the highest and gradually decreases layer by layer outward.

[0143] The powder of the metal component with thermal expansion matching described in step III is MCrAlY, purchased from Hebei Guifa Alloy Wear-Resistant Materials Co., Ltd., with the composition of Cr: 21.57%, Al: 4.35%, Y 2 O 3 : 0.58%, Fe: 0.32%, Ni: the balance;

[0144] The powder of the high-temperature antioxidant component described in step III is B 4 C;

[0145] In the formation of the multi-layer gradient gradual change structure described in step III, from the substrate outward, the mass ratio of the powder of the metal component with thermal expansion matching to the powder of the high-temperature antioxidant component decreases in a gradient, which are 1:0, 1:1, 1:2, and 1:3 in sequence.

[0146] The preparation method of the slurry described in step III is: put the transition layer powder and the low-temperature polymerized inorganic precursor binder into a ball milling tank, add zirconia balls, and ball mill for 24 h under the condition of a ball milling speed of 100 r / min to obtain a uniform slurry; the mass ratio of the transition layer powder to the low-temperature polymerized inorganic precursor binder is 1:4; the mass ratio of the zirconia balls to the transition layer powder is 2:1;

[0147] IV. Constructing a multi-functional outer layer with high emissivity / antioxidant / erosion resistance / ablation resistance:

[0148] Mix the powder of the high emissivity component and the powder of the high-temperature antioxidant component to obtain the multi-functional outer layer powder; add the multi-functional outer layer powder into the low-temperature polymerized inorganic precursor binder to make a slurry, and then spray it on the surface of the gradient transition layer to construct the multi-functional outer layer, obtaining a superalloy substrate to form a multi-layer coating.

[0149] In the multi-functional outer layer powder described in step IV, the mass ratio of the powder of the high emissivity component to the powder of the high-temperature antioxidant component is 1:3;

[0150] The powder of the high emissivity component described in step IV is MoSi 2 , with a particle size of 1 μm to 10 μm;

[0151] The high-temperature resistant and oxidation-resistant component powder described in Step 4 is SiB 4 , with a particle size of 1 μm to 10 μm;

[0152] The preparation method of the slurry described in Step 4 is as follows: Put the multi-functional outer layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill tank, add zirconia balls, and ball mill for 24 h under the condition of a ball mill speed of 100 r / min to obtain a homogeneous slurry; the mass ratio of the multi-functional outer layer powder to the low-temperature polymerized inorganic precursor binder is 1:4; the mass ratio of zirconia balls to the multi-functional outer layer powder is 2:1;

[0153] The spraying method described in Step 3 and Step 4 is: spraying at room temperature, with an air pump pressure of 90 MPa, a spraying distance of 150 mm, and a spraying speed of 30 mm / min; the number of spraying times is multiple times to achieve the regulation of the coating thickness;

[0154] V. Low-temperature curing of the coating:

[0155] Place the superalloy substrate to be formed with a multi-layer coating in a specific humidity environment, air-dry it at room temperature until the surface is dry and then heat and cure it. After the multi-layer coating is cured, cool it to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonds;

[0156] The specific humidity environment described in Step 5 is a constant humidity environment of 50%;

[0157] The heating and curing process in Step 5 is: heat up from room temperature to 100 °C at a heating rate of 5 °C / min, keep warm for 12 h, then heat up from 100 °C to 300 °C at a heating rate of 10 °C / min, keep warm for 1 h, and cool to room temperature;

[0158] The low-temperature polymerized inorganic precursor binder described in Step 2, Step 3 and Step 4 is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps:

[0159] Weigh and mix the phosphoric acid solution with a mass fraction of 85% and deionized water in a volume ratio of 1:1, and then heat it in a water bath at 60 °C and continuously stir for 60 min; then weigh and add aluminum hydroxide powder according to the ratio of P:Al of 3:2, keep the temperature of the water bath heating at 60 °C, heat and stir for 3 h to obtain a mixed solution; add a curing agent to the mixed solution, the mass ratio of the curing agent to the volume of the mixed solution is 2 g:100 mL, heat and stir at 60 °C for 1 h, and then adjust the pH value of the solution to 6 to obtain a phosphate binder; the curing agent is MgO.

[0160] After detection, the total thickness of a radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding prepared in this embodiment is about 70 μm, including an interfacial strong chemical bonding reaction layer with a thickness of about 100 nm, a gradient transition layer with a thickness of 20 μm, and a multi-functional outer layer with a thickness of about 50 μm. The gradient transition layer is composed of four sub-layers, and the thickness of each layer is about 5 μm.

[0161] Comparative Example 1:

[0162] In this comparative example, the nickel-based superalloy GH4061 was selected.

[0163] Test Example:

[0164] The radiation heat protection multi-layer gradient coatings with strong interfacial self-reactive chemical bonding prepared in Examples 1 to 3 and the nickel-based superalloy GH4061 of the comparative example were respectively subjected to static high-temperature oxidation tests at 1250 °C and emissivity performance tests. The detection methods are as follows:

[0165] (1) The high-temperature oxidation resistance of the radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding and the nickel-based superalloy GH4061 was measured using a high-temperature muffle furnace;

[0166] (2) The emissivity of the radiation heat protection multi-layer gradient coating with strong interfacial self-reactive chemical bonding and the nickel-based superalloy GH4061 was measured using an emissivity test device.

[0167] The comparative photos of the macroscopic morphologies of Examples 1 to 3 and Comparative Example 1 before / after static high-temperature oxidation at 1250 °C for 30 h are as Figure 6 shown, and the XRD patterns of the surfaces of the specimens after oxidation are as Figure 7 shown.

[0168] The comparative photos of the macroscopic morphologies of Examples 1 to 3 and Comparative Example 1 before / after static high-temperature oxidation at 1250 °C for 30 h are as Figure 6 shown. Figure 6 Among them, (a1), (a2), (a3), and (a4) respectively represent the surface morphologies of the specimens of the comparative example and Examples 1 to 3 before oxidation; (b1), (b2), (b3), and (b4) respectively represent the surface morphologies of the specimens of the comparative example and Examples 1 to 3 after oxidation. From Figure 6It can be seen that before oxidation, the surface of the nickel-based superalloy GH4061 in the comparative example is bright and flat, and the surface of the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Examples 1 to 3 is dark brown, flat and uniform; after high-temperature oxidation, the surface of the nickel-based superalloy GH4061 in the comparative example undergoes severe oxidation, and a large amount of oxide scale is generated on the surface. The surface of the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Examples 1 to 3 changes from dark brown to grayish white, and the coating remains intact after high-temperature oxidation, without peeling and falling off phenomena, indicating that the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared by the present invention has good high-temperature oxidation resistance and can significantly improve the high-temperature heat protection ability of the substrate.

[0169] The XRD patterns of the specimens before and after static oxidation at 1250 °C for 30 h in Examples 1 to 3 and Comparative Example 1 are as Figure 7 shown. It can be Figure 7 seen that after oxidation, the surface of the nickel-based superalloy GH4061 in the comparative example mainly includes the γ-Ni phase and oxidation products NiO, Cr 2 O 3 , NiCr 2 O 4 , TiO 2 phases; after oxidation, the surface of the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Examples 1 to 3 mainly includes SiO 2 and Al 2 O 3 phases, indicating that the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared by the present invention reacts with oxygen at high temperature to form SiO 2 and Al 2 O 3 oxygen diffusion barrier layers, delaying the oxidation rate of the substrate.

[0170] The weight gain curves of high-temperature oxidation with time for Example 1 and Comparative Example 1 are plotted as Figure 8 shown. It can be Figure 8 seen that the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Example 1 of the present invention and the nickel-based superalloy GH4061 in the comparative example both show segmented oxidation behavior during the entire oxidation process, but there are obvious differences in the oxidation rate and oxidation weight gain. The radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Example 1 of the present invention has a relatively fast weight gain during 0 - 2 h, and the weight gain significantly slows down during 5 - 30 h. The total weight gain of the specimen after 30 h of oxidation is 2.567 mg / cm 2, indicating that in the early stage of oxidation (0 - 2 h), the high-temperature oxidation-resistant components in the coating play a role, and the components with oxygen-consuming effects react with oxygen, resulting in obvious oxidation weight gain; as oxidation proceeds (5 - 30 h), the dense and stable oxidation products SiO 2 and Al 2 O 3 etc. act as oxygen diffusion barrier layers, which can slow down the further diffusion of the oxidation atmosphere into the coating, thus delaying the oxidation rate of the coating; while for the comparative nickel-based superalloy GH4061, the oxidation rate is relatively high in the ranges of 0 - 2 h and 5 - 30 h, with obvious oxidation weight gain, and the total weight gain of the sample after 30 h of oxidation is 4.025 mg / cm 2 , indicating that the comparative example undergoes a severe oxidation reaction at high temperature. In the early stage of oxidation (0 - 2 h), the oxide layer does not form a dense layer and cannot effectively prevent the diffusion of ions, resulting in a high oxidation rate; in the later stage of oxidation, the oxide film becomes dense, so the oxidation rate decreases. However, at high temperature, the oxidation products NiO, Cr 2 O 3 , NiCr 2 O 4 , TiO 2 etc. have large crystal grains and are easy to spall, unable to provide effective protection. Therefore, the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared by the present invention has excellent high-temperature oxidation resistance and can provide effective thermal protection for the nickel-based superalloy GH4061.

[0171] Figure 9 is the emissivity spectrum of the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Example 1 of the present invention and the nickel-based superalloy GH4061 of Comparative Example 1.

[0172] From Figure 9 it can be seen that the emissivity of the nickel-based superalloy GH4061 of Comparative Example 1 is about 0.2, while the emissivity of the radiation heat protection multi-layer gradient coating with strong interfacial self-reaction chemical bonding prepared in Example 1 of the present invention is as high as 0.9, and the emissivity value has increased by 3.5 times, indicating that the radiation heat protection multi-layer gradient coating designed and prepared by the present invention has a good radiation heat protection effect.

Claims

1. A method for preparing a radiation heat protection multilayer gradient coating with strong chemical bonding through self-reaction at the interface, characterized in that The multi-layer gradient coating comprises an interface strong chemical bonding reaction layer, a high bonding / oxidation resistance / thermal expansion matching gradient transition layer and a high emissivity / oxidation resistance / erosion resistance / ablation resistance multifunctional outer layer; The preparation method is specifically completed according to the following steps:

1. Pretreatment of substrate: Firstly, SiC sandpaper is used to grind the surface of the high-temperature alloy substrate flat, and then oil stains on the surface of the high-temperature alloy substrate are removed to obtain a pretreated high-temperature alloy substrate; 2. Constructing a strong chemical bonding reaction layer on the interface: Spraying a low-temperature polymerized inorganic precursor binder onto one or two surfaces of a high-temperature alloy substrate to obtain a substrate with an interface strong chemical bonding reaction layer to be formed on the surface; 3. Constructing a high bonding / anti-oxidation / thermal expansion matching gradient transition layer: The thermal expansion matching metal component powder and the high temperature anti-oxidation component powder are weighed and mixed in different gradient proportions to obtain multiple groups of transition layer powders; the multiple groups of transition layer powders are respectively added into multiple groups of low temperature polymerized inorganic precursor binders to prepare gradient slurries; the gradient slurries are then sprayed layer by layer onto a substrate whose surface is to form an interfacial strong chemical bonding reaction layer to construct a gradient transition layer, wherein the proportion of the thermal expansion matching metal component powder is the highest in the layer close to the substrate and decreases layer by layer outward; 4. Constructing a multifunctional outer layer with high emissivity / anti-oxidation / erosion resistance / anti-ablation: The high-emissivity component powder is mixed with the high-temperature resistant and anti-oxidation component powder to obtain a multifunctional outer layer powder; the multifunctional outer layer powder is added to a low-temperature polymerized inorganic precursor binder to prepare a slurry, and then sprayed on the surface of the gradient transition layer to construct a multifunctional outer layer, thereby obtaining a high-temperature alloy substrate to be formed with a multi-layer coating; 5. Low temperature curing of coating: The high-temperature alloy substrate on which the multi-layer coating is to be formed is placed in a specific humidity environment, left to dry at room temperature and then heated for curing. After the multi-layer coating is cured, it is cooled to room temperature to obtain a radiation heat protection multi-layer gradient coating with strong chemical bonding and self-reaction on the interface.

2. The method for preparing a multi-layer gradient coating for radiation heat protection with strong chemical bonding through interface self-reaction according to claim 1, characterized in that The high-temperature alloy substrate described in step one is a nickel-based high-temperature alloy; in step one, 400#, 600#, 800#, and 1000# sandpapers are used in sequence to polish the surface of the high-temperature alloy substrate, and then anhydrous ethanol is used to remove oil stains on the surface of the high-temperature alloy substrate to obtain a pretreated high-temperature alloy substrate.

3. The method for preparing a multi-layer gradient coating for radiation heat protection with strong chemical bonding and self-reaction at the interface according to claim 1, characterized in that The low-temperature polymerized inorganic precursor binder described in step 2, step 3 and step 4 is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps: A phosphoric acid solution with a mass fraction of 85% and deionized water are weighed and mixed uniformly in a volume ratio of (1-2):1, and then heated in a water bath at 60°C-100°C and continuously stirred for 20min-60min; aluminum hydroxide powder is weighed and added in a ratio of P:Al of 3:(1-2), the water bath heating temperature is maintained at 60°C-100°C, and heated and stirred for 1h-3h to obtain a mixed solution; a curing agent is added to the mixed solution, the mass ratio of the curing agent to the volume ratio of the mixed solution is (1g-10g):100mL, heated and stirred at 60°C-100°C for 1h-3h, and then the pH value of the solution is adjusted to 2-6 to obtain a phosphate binder; the curing agent is one of MgO, ZnO, CuO, CrO3 or a mixture of several thereof.

4. The method for preparing a multi-layer gradient coating for radiation heat protection with strong chemical bonding through interface self-reaction according to claim 1, characterized in that The thermal expansion matching metal component powder described in step three is metal powder; the metal powder is one of MCrAlY, NiCrBSi, Ni and W powder or a mixture of several of them; the high temperature antioxidant component powder described in step three is one of Al, SiC, B4C, BN and WSi2 powder or a mixture of several of them.

5. The method for preparing a radiation heat protection multilayer gradient coating with strong chemical bonding through interface self-reaction according to claim 1, characterized in that In the formation of the multi-layer gradient structure described in step three, the mass ratio of the thermal expansion matching metal component powder to the high temperature antioxidant component powder decreases gradually from the substrate to the outside, varying from (1:0) to (1:X), and the value range of X is: 1≤X≤10.

6. The method for preparing a radiation heat protection multilayer gradient coating with strong chemical bonding through interface self-reaction according to claim 1, characterized in that The preparation method of the slurry described in step three is: put the transition layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill, add zirconium oxide balls, and ball mill for 12h to 24h at a ball milling speed of 60r / min to 100r / min to obtain a uniform slurry; the mass ratio of the transition layer powder to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4); the mass ratio of zirconium oxide balls to the transition layer powder is (2 to 4):

1.

7. The method for preparing a multi-layer gradient coating for radiation heat protection with strong chemical bonding through self-reaction at the interface according to claim 1, characterized in that The mass ratio of the high-emissivity component powder to the high-temperature resistant and antioxidant component powder in the multifunctional outer layer powder described in step four is (1 to 3): (1 to 3); the high-emissivity component powder described in step four is one of MoSi2, SiB4, SiB6 and SiC or a mixture of several of them, and the particle size is 1μm to 10μm; the high-temperature resistant and antioxidant component powder described in step four is one of MoSi2, SiB4, SiB6, ZrSi2, B4C, SiC, BN and Si powder or a mixture of several of them, and the particle size is 1μm to 10μm.

8. The method for preparing a radiation heat protection multilayer gradient coating with strong chemical bonding through interface self-reaction according to claim 1, characterized in that The preparation method of the slurry described in step 4 is: put the multifunctional outer layer powder and the low-temperature polymerized inorganic precursor binder into a ball mill, add zirconium oxide balls, and ball mill for 12h to 24h at a ball milling speed of 60r / min to 100r / min to obtain a uniform slurry; the mass ratio of the multifunctional outer layer powder to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4); the mass ratio of zirconium oxide balls to the multifunctional outer layer powder is (2 to 4):1; the spraying method described in steps 3 and 4 is: room temperature spraying, the air pump pressure is 30MPa to 90MPa, the spray distance is 60mm to 150mm, and the spraying speed is 10mm / min to 50mm / min; the number of spraying is one or more times.

9. The method for preparing a radiation heat protection multilayer gradient coating with interfacial self-reaction strong chemical bonding according to claim 1, characterized in that The specific humidity environment described in step five is a constant humidity environment of 20% to 60%; the heating and curing process in step five is: heating from room temperature to 100°C at a heating rate of 2°C / min to 5°C / min, keeping warm for 12h to 24h, then heating from 100°C to 300°C at a heating rate of 5°C / min to 10°C / min, keeping warm for 1h to 5h, and cooling to room temperature.

10. The method for preparing a radiation heat protection multilayer gradient coating with strong chemical bonding through interface self-reaction according to claim 1, characterized in that The thickness of the interface strong chemical bonding reaction layer in the interface self-reactive strong chemical bonding radiation heat protection multilayer gradient coating described in step five is 100nm~500nm; the total thickness of the high bonding / anti-oxidation / thermal expansion matching gradient transition layer is 10~100μm, and the thickness of each sublayer is 3μm~20μm; the thickness of the high emissivity / anti-oxidation / erosion resistance / anti-ablation multifunctional outer layer is 50μm~200μm; the bonding strength of the interface self-reactive strong chemical bonding radiation heat protection multilayer gradient coating described in step five reaches more than 15MPa, the emissivity is as high as 0.9, and the coating is not damaged when oxidized in high temperature static air at 1250℃ for 30h.

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