A Sr-doped LaFeO3 high-emissivity coating and its preparation method

Abstract

The present invention discloses an Sr-doped LaFeO3 high-emissivity coating and a preparation method thereof. The Sr-doped LaFeO3 high-emissivity coating is a double-layer structure, wherein the coating structure comprises a metal substrate, a metal bonding layer and a high-emissivity layer from bottom to top; the metal substrate is a high-temperature Ni-based alloy, the metal bonding layer is a NiCrAlY alloy bonding layer or a CoNiCrAlY alloy bonding layer, and the high-emissivity layer is LaFeO3 with different Sr doping amounts. 1‑x Sr x FeO3 layer (0< x ≤0.6). The present invention selects LaFeO3 as the matrix material, Sr 2+ are impurity ions with similar radii, Sr 2+ The doping of La increases the impurity absorption and free carrier absorption in the crystal, making La 1‑x Sr x The emissivity of the FeO3 coating was improved, and a high emissivity coating with an emissivity above 0.8 was prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature thermal protective coating preparation, and in particular relates to an Sr-doped LaFeO3 high-emissivity coating and a preparation method thereof. Background Art

[0002] When an aircraft flies at high speed in the atmosphere, severe aerodynamic heating causes the surface temperature to rise sharply. This leads to problems such as thermal stress concentration, high-temperature creep, and material ablation, significantly shortening the aircraft's service life. Therefore, reducing the surface temperature of the aircraft and extending its service life are particularly important.

[0003] The three basic modes of heat transfer at high temperatures are conduction, convection, and radiation. Conduction occurs within an object or between contacting surfaces, convection occurs in liquids or gases, and radiation is generated by all objects with temperatures above absolute zero. For aircraft operating in high-temperature environments, radiation is the primary method of dissipating heat. However, traditional thermal radiation materials have low service temperatures (for example, SiC coatings are susceptible to oxidation at high temperatures, resulting in a decrease in the coating's infrared emissivity during service), resulting in poor heat dissipation and failing to meet high-temperature service requirements. Oxide-based thermal radiation materials generally offer high-temperature resistance but low emissivity in the near- and mid-infrared bands. Above 1000°C, the amount of heat transferred by radiation in the near-infrared band (3μm to 5μm) accounts for over 76% of the total energy in the band. Therefore, developing infrared radiation coatings with high emissivity and high service reliability in the 3μm to 5μm band is of great significance.

[0004] LaFeO3 is a perovskite-based material with a stable crystal structure. It can be substituted by a variety of ions with similar radii without changing the overall crystal form. It has a melting point of 1900°C and exhibits excellent oxidation resistance at high temperatures, making it a good p-type semiconductor. According to semiconductor light absorption theory, doping with metal ions with similar radii is an effective way to increase the emissivity of LaFeO3 in the near-infrared band. Introducing appropriate impurities into the matrix to form impurity energy levels corresponding to the near-infrared band can enhance the semiconductor's absorptivity in the corresponding band, thereby improving the infrared radiation performance of LaFeO3. Plasma spraying is a well-established coating preparation method. This method is stable, can spray a wide range of materials, and can produce a wide variety of coatings with excellent performance. It can be applied to the preparation of high-emissivity coatings.

[0005] In summary, preparing a coating with high emissivity, high service temperature and stable performance is a difficult problem that technicians in this field need to overcome. Summary of the Invention

[0006] In response to the problem in the prior art of lacking coatings with high emissivity, high service temperature and stable performance, the present invention provides an Sr-doped LaFeO3 high-emissivity coating and a preparation method thereof, which is also a high-temperature Ni-based alloy surface high-emissivity coating and a preparation method thereof. The preparation method is environmentally friendly, has a simple preparation process, and low energy consumption. The prepared coating has an emissivity of above 0.8 at high temperatures.

[0007] The technical solutions of the present invention are as follows:

[0008] A Sr-doped LaFeO3 high emissivity coating is constructed by selecting LaFeO3 as the matrix material and Sr 2+ For impurity ions with similar radii, a high emissivity coating with an emissivity of more than 0.8 was prepared; according to the relevant theories of semiconductor physics, electron transitions and band gaps are closely related; the band gap of LaFeO3 is 2.46 eV, and when doped with Sr 2+ The decrease of band gap is beneficial to electron transition, thus improving the emission rate of the sample; In addition, Sr 2+ The doping of La increases the impurity absorption and free carrier absorption in the crystal, making La 1-x Sr x The emissivity of FeO3 coating is improved.

[0009] The Sr-doped LaFeO3 high emissivity coating is a double-layer structure, and the coating structure is composed of a metal substrate, a metal bonding layer and a high emissivity layer from bottom to top; the metal substrate is a high-temperature Ni-based alloy, the metal bonding layer is a NiCrAlY alloy bonding layer or a CoNiCrAlY alloy bonding layer, and the high emissivity layer is LaFeO3 with different Sr doping amounts. 1- x Sr x FeO3 layer (0< x ≤0.6).

[0010] The method for preparing the coated metal composite material comprises the following steps:

[0011] (1) Synthesis of La with different Sr doping amounts by sol-gel method 1-x Sr x FeO3 ceramic powder was used to prepare spherical La 1-x Sr x FeO3 powder to be sprayed;

[0012] (2) placing the high-temperature Ni-based alloy substrate in a sandblasting machine for sandblasting roughening treatment, and coating the roughened substrate surface with a metal bonding layer using an atmospheric plasma spraying process;

[0013] (3) The spherical La obtained in step (1)1-x Sr x FeO3 powder to be sprayed is coated on the surface of the metal bonding layer obtained in step (2) by atmospheric plasma spraying technology to obtain La 1-x Sr x FeO3 high emissivity layer.

[0014] The purpose of the present invention is achieved through the following technical solutions:

[0015] A Sr-doped LaFeO3 high-emissivity coating having a double-layer structure, comprising, from bottom to top, a metal substrate, a metal bonding layer, and a high-emissivity layer;

[0016] The metal substrate is a high-temperature Ni-based alloy, the metal bonding layer is a NiCrAlY alloy bonding layer or a CoNiCrAlY alloy bonding layer, and the high-emissivity layer is a La-based alloy with different Sr doping amounts. 1-x Sr x FeO3 layer (0< x ≤0.6);

[0017] The thickness of the metal bonding layer is 80 μm to 100 μm, and the thickness of the high emissivity layer is 800 μm to 1000 μm;

[0018] The high emissivity layer is made of the following raw materials in the following mass percentages:

[0019]

[0020] The Sr-doped LaFeO3 high-emissivity coating has the following performance indicators:

[0021] The emissivity in the 3 μm to 5 μm band is ≥0.8. By adjusting the doping content of the Sr element, the emissivity of the coating can be controlled in the 3 μm to 5 μm band, which is more conducive to improving the heat dissipation performance of the coating. The Sr-doped LaFeO3 high-emissivity coating prepared by the present invention has high bonding strength, high fracture toughness and excellent thermal shock resistance. The shock resistance at 1100°C is ≥60 times, and the bonding strength at room temperature is 7.22 MPa~11.40 MPa. The infrared emissivity at 900°C (3 μm~5 μm) is 0.84~0.89, and the infrared emissivity at 1100°C (3 μm~5 μm) is 0.84~0.86, meeting the service requirements at high temperatures.

[0022] The present invention also relates to a method for preparing the above-mentioned Sr-doped LaFeO3 high-emissivity coating, comprising the following steps:

[0023] (1) Using the sol-gel method, La(NO3)3·6H2O, Sr(NO3)2, and Fe(NO3)3·9H2O were dissolved in a deionized water-ethanol mixed solvent to form a uniform solution. Acetic acid was used as a hydrolysis catalyst and chelating agent, and added to a round-bottom flask in stoichiometric order. After sealing, the solution was stirred in a water bath at a constant temperature until the reaction was complete. The solution was allowed to stand, dried, heat-treated, and ground to obtain La(NO3)3·6H2O with controllable composition. 1- x Sr x FeO3 nano ceramic powder (i.e. La 1-x Sr x FeO3 dry gel powder) as raw material powder;

[0024] The composition of the raw material powder is according to the chemical formula La 1-x Sr x Weigh the FeO3 element mass percentage, x Take 0 to 0.6, according to the following mass percentage:

[0025]

[0026] The volume ratio of deionized water to ethanol is (1-3):(3-1), the molar ratio of acetic acid to metal ions is (0.5-4):1, the reaction temperature is 70-80°C, the reaction time is 8-24 hours, the reaction is allowed to stand for 24-48 hours, the heat treatment temperature is 600-1200°C, the drying temperature is 80-150°C, and the heat treatment time is 1-9 hours.

[0027] (2) Weigh triammonium citrate, gum arabic and the La 1-x Sr x FeO3 nano-ceramic powder was placed in a mixing tank and ball-milled in a mass ratio of 1.5:0.03:0.012 to obtain a slurry. The obtained slurry was spray-granulated to obtain spherical particles with uniform particle size and excellent fluidity. The spherical particles were sieved with a 60-100 mesh sieve to obtain a powder to be sprayed with a designed particle size;

[0028] (3) Using atmospheric plasma spraying process to prepare metal bonding layer on Ni-based alloy after sandblasting roughening;

[0029] The process parameters of sandblasting roughening treatment are: pressure of 0.3 MPa to 0.5 MPa, sandblasting distance of 80 mm to 150 mm, sand size of 12 mesh to 36 mesh, and sandblasting time of 1 min to 5 min;

[0030] The atmospheric plasma spraying process parameters for the metal bonding layer are as follows: main gas flow rate of 30L / min to 50L / min, carrier gas flow rate of 1L / min to 3L / min; current size control of 500A to 550A, power of 25kW to 40kW, powder feeding amount of 10g / min to 20g / min; coating distance of 80mm to 120mm; the thickness of the metal bonding layer on the Ni-based alloy is 80μm to 100μm;

[0031] (4) spraying the powder to be sprayed with the designed particle size obtained in step (2) onto the bonding layer using an atmospheric plasma spraying process;

[0032] The process parameters of atmospheric plasma spraying are as follows: main gas flow rate is 30 L / min~50 L / min, carrier gas flow rate is 1 L / min~3 L / min; current size is controlled at 500 A~550 A, power is 25 kW~35 kW; powder feeding argon flow rate is 2.0 L / min~5.0 L / min, powder feeding amount is 15 g / min~30 g / min; spraying distance is 80 mm~120 mm, and La doped with different Sr is obtained. 1-x Sr x FeO3 high emissivity coating.

[0033] Furthermore, in step (2), the ratio of deionized water to raw material powder during ball milling is 2:(1.5-2), and the ball milling time is 24 h;

[0034] Furthermore, in step (2), the spray granulation is performed by treating the slurry with a spray drying device, the drying tower temperature is 120°C to 250°C, and the powder screening range after granulation is 38 μm to 150 μm.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention discloses a method for preparing a Sr-doped LaFeO3 high-emissivity coating. The sol-gel method and atmospheric plasma spraying technology employed in this invention are environmentally friendly. The powder synthesis process produces no toxic or harmful substances, resulting in no environmental pollution. The coating preparation process also produces no harmful gases, only splashed dust and a small amount of exhaust gas. These are collected through necessary dust removal and filtration, resulting in minimal environmental pollution.

[0037] 2. The Sr-doped LaFeO3 high emissivity coating of the present invention, wherein the lower valence state of Sr 2+Doping into the La position, on the one hand, reduces the band gap width of LaFeO3, reduces the energy required for electron transition, and enhances carrier ion absorption; on the other hand, it can promote the formation of abundant oxygen vacancies on the LaFeO3 surface, thereby improving the emissivity of the material.

[0038] 3. The Sr-doped LaFeO3 high-emissivity coating described in the present invention has an emissivity of more than 0.8 in the 3 μm to 5 μm band. By adjusting the doping content of the Sr element, the emissivity of the coating can be controlled in the 3 μm to 5 μm band, which is more conducive to improving the heat dissipation performance of the coating.

[0039] 4. The Sr-doped LaFeO3 high-emissivity coating described in the present invention has the characteristics of good sintering resistance, high-temperature stability and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the Sr-doped LaFeO3 high-emissivity coating on the surface of the high-temperature Ni-based alloy in Example 1 of the present invention;

[0041] Figure 2 This is a microscopic morphology of Sr-doped LaFeO3 nanopowder in Example 1 of the present invention;

[0042] Figure 3 This is a microscopic morphology of the surface of the Sr-doped LaFeO3 high-emissivity coating in Example 1 of the present invention;

[0043] Figure 4 This is a diagram of a flat plate sample of Sr-doped LaFeO3 high-emissivity coating in Example 1 of the present invention;

[0044] Figure 5 This is a graph of the infrared emissivity of the Sr-doped LaFeO3 high emissivity coating under different temperature conditions in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and examples. It should be noted that the embodiments and drawings are only used to exemplify the present invention and do not limit the scope of protection of the present invention.

[0046] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0047] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0048] Example 1:

[0049] A Sr-doped LaFeO3 high emissivity coating, comprising a CoNiCrAlY metal bonding layer and a La 0.8 Sr 0.2 FeO3 high emissivity layer, wherein the Sr content of the high emissivity layer is 20 mol%;

[0050] In Example 1, the thickness of the CoNiCrAlY metal bonding layer is 100 μm, the thickness of the high emissivity layer is 1000 μm, and the total thickness of the coating is 1100 μm;

[0051] Example 1 provides a metal composite material coated with the above-mentioned high-emissivity coating, comprising a high-temperature Ni-based alloy substrate and a high-emissivity coating coated on the surface of the substrate. The preparation method of the above-mentioned coated metal composite material comprises the following steps:

[0052] (1) Preparation of Sr-doped LaFeO3 nanopowder: La(NO3)3·6H2O, Sr(NO3)2, and Fe(NO3)3·9H2O were mixed in a molar ratio of 4:1:5, with water and ethanol as the mixed solvent and acetic acid as the hydrolysis catalyst and chelating agent. The mixture was stirred in a water bath at 80°C for 8 h to form a transparent sol. The obtained sol was allowed to stand for 36 h and then dried at 150°C to obtain a dry gel. The dry gel was ground and pulverized, and then heat-treated at 1200°C for 2 h to obtain LaFeO3 nanopowder. 0.8 Sr 0.2 FeO3 nanopowder;

[0053] (2) La 0.8 Sr 0.2 Preparation of FeO3 ceramic spray powder: La prepared in step (1) 0.8 Sr 0.2 FeO3 nanopowder was mixed with deionized water, gum arabic, and ammonium citrate in a mass ratio of 1.5:2:0.03:0.012. A uniform and fine ceramic slurry was obtained by wet ball milling. The ceramic slurry was prepared into spherical particles with a certain fluidity by spray drying equipment. La particles with uniform particle size were obtained by sieving. 0.8 Sr 0.2 FeO3 nano ceramic powder (such as Figure 2As shown); wherein, the wet ball milling process is mixing on a horizontal ball mill, and the ball milling process control parameters are: the mass ratio of deionized water: ceramic powder: zirconia balls is 1.5:2:4, the rotation speed of the horizontal ball mill is 400 r / min, and the stirring time is 24 h; the inlet temperature of the centrifugal spray drying is 250°C, the outlet temperature is 120°C, and the atomizer frequency is 24 Hz;

[0054] (3) Roughening of high-temperature Ni-based alloy substrate: The surface of the high-temperature Ni-based alloy substrate was roughened by sandblasting. The process parameters were: sandblasting pressure of 0.3 MPa, 24-mesh white corundum sand, sandblasting distance of 100 mm, and sandblasting time of 3 min.

[0055] (4) Preparation of metal bonding layer: The CoNiCrAlY metal bonding layer was sprayed on the substrate surface after treatment in step (3) by atmospheric plasma spraying process. The bonding layer thickness was 100 μm. The spraying process parameters were: main gas flow rate of 46 L / min, carrier gas flow rate of 2.6 L / min, current of 550 A, power of 38 kW, powder feed rate of 25%, and spraying distance of 120 mm.

[0056] (5) La 0.8 Sr 0.2 Preparation of FeO3 high emissivity layer: La is sprayed on the surface of the metal bonding layer after step (4) using atmospheric plasma spraying process. 0.8 Sr 0.2 FeO3 ceramic powder, high emissivity layer thickness is 1000 μm, spraying process parameters are: main gas flow rate is 36 L / min, carrier gas flow rate is 2 L / min, current size is 520 A, power size is 35 kW, powder feed rate is 19 g / min, and spraying distance is 120 mm.

[0057] The surface micromorphology of the high emissivity layer is as follows Figure 3 As shown;

[0058] The coated flat plate sample prepared in Example 1 is as follows Figure 4 As shown, the bonding strength of the coating at room temperature is 11.40 MPa, the total coating thickness is 1100 μm, and the thermal cycle life is 117 times;

[0059] like Figure 5 As shown in the figure, the measured infrared emissivity (3-5 μm) of the coating at 900°C, 1000°C, and 1100°C is 0.89, 0.88, and 0.84, respectively. The above results show that the Sr-doped LaFeO3 high-emissivity coating prepared in Example 1 has high infrared emissivity characteristics, good mechanical properties, and thermal shock resistance.

[0060] Example 2:

[0061] A Sr-doped LaFeO3 high emissivity coating structure includes a CoNiCrAlY metal bonding layer and a La 0.7 Sr 0.3 FeO3 high emissivity layer, wherein the Sr content of the high emissivity layer is 30 mol%.

[0062] In Example 2, the thickness of the CoNiCrAlY metal bonding layer is 100 μm, the thickness of the high emissivity layer is 1000 μm, and the total thickness of the coating is 1100 μm.

[0063] Example 2 provides a metal composite material coated with the above-mentioned high-emissivity coating, comprising a high-temperature Ni-based alloy substrate and a high-emissivity coating coated on the surface of the substrate. The preparation method and related steps of the above-mentioned coated metal composite material are consistent with those of Example 1, except that the Sr doping content in step (1) is different. The raw material powder ratio: La(NO3)3·6H2O, Sr(NO3)2, Fe(NO3)3·9H2O molar ratio is 3.5:1.5:5.

[0064] The total thickness of the coating prepared in Example 2 is 1100 μm, the bonding strength at room temperature is 9.14 MPa, the thermal cycle life is 66 times, and the measured infrared emissivity (3-5 μm) of the coating at 900°C, 1000°C and 1100°C are 0.86, 0.85 and 0.84, respectively.

[0065] The above results show that the Sr-doped LaFeO3 high-emissivity coating prepared in Example 2 has excellent infrared radiation characteristics and good thermal shock resistance.

[0066] Comparative Example 1:

[0067] The difference between Comparative Example 1 and Example 1 is that the lower valence Sr 2+ Doping to the La position, the parameters and preparation method of steps (2), (3), (4) and (5) are the same as those in Example 1. When preparing Sr-doped LaFeO3 nanopowder in step (1), no Sr(NO3)2 is added. La(NO3)3·6H2O and Fe(NO3)3·9H2O are mixed in a molar ratio of 1:1. The other parameters and preparation method are the same as those in Example 1.

[0068] The coating obtained in Comparative Example 1 had a total thickness of 1083 μm and a bonding strength of 12.33 MPa at room temperature. This coating thickness was slightly less than that of Example 1, and its thermal shock life at 1100°C was 17 cycles. The measured infrared emissivity (3 μm to 5 μm) of the coating at 900°C, 1000°C, and 1100°C was 0.89, 0.88, and 0.83, respectively.

[0069] The coating thickness obtained in Comparative Example 1 exhibited some deviation. Compared to Example 1, the thermal cycle life of Comparative Example 1 was only 17 cycles. This was due to a mismatch between the thermal expansion coefficient of the coating in Comparative Example 1 and that of the substrate, which in turn generated thermal mismatch stress and led to coating failure. Although Comparative Example 1 exhibited excellent infrared radiation performance and mechanical properties, the thermal shock resistance of the high-temperature infrared high-emissivity coating prepared in Comparative Example 1 was poor, failing to meet application requirements.

[0070] Comparative Example 2:

[0071] The difference between Comparative Example 2 and Example 1 is that the excess Sr 2+ Doping to the La position, the parameters and preparation method of step (2), step (3), step (4) and step (5) are the same as those in Example 1. When preparing Sr-doped LaFeO3 nanopowder in step (1), La(NO3)3·6H2O, Sr(NO3)2, and Fe(NO3)3·9H2O are mixed in a molar ratio of 1.5:3.5:5. The other parameters and preparation method are the same as those in Example 1.

[0072] The total thickness of the coating obtained in Comparative Example 2 is 1130 μm, the bonding strength at room temperature is 6.52 MPa, the thermal cycle life at 1100°C is 1 time, and the measured infrared emissivity (3 μm to 5 μm) of the coating at 900°C, 1000°C and 1100°C are 0.84, 0.83 and 0.82, respectively.

[0073] The coating obtained in Comparative Example 2 has an Sr content of 70 mol%, which is much higher than that in Example 1. The total thickness of the coating is higher than that in Example 1, and its infrared emissivity is not much different from that in Example 1. However, the thermal cycle life of Comparative Example 2 at 1100°C is only 1 time, and the bonding strength is only 7.16 MPa. The reason for this phenomenon is that the Sr doping of the coating prepared in Comparative Example 2 reaches 70 mol%, which is much higher than that in Example 1. As the Sr content increases, the porosity increases, which reduces the effective bearing area of ​​the coating and causes a significant decrease in bonding strength. At the same time, the thermal expansion coefficient of Comparative Example 2 is too high and does not match the substrate, generating thermal adaptation stress that causes the coating to peel off and fail. Although Comparative Example 2 has good infrared radiation performance, the thermal shock resistance and mechanical properties of the high-temperature infrared high-emissivity coating prepared in Comparative Example 2 cannot meet application requirements.

[0074] The foregoing is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the foregoing embodiments. Any technical solution that falls within the scope of protection of the present invention is within the scope of protection of the present invention. It should be noted that improvements and modifications made by persons of ordinary skill in the art without departing from the principles of the present invention are also considered within the scope of protection of the present invention.

Claims

1. A Sr-doped LaFeO3 high-emissivity coating, characterized by: It is a double-layer structure, consisting of a metal base, a metal bonding layer and a high emissivity layer from bottom to top; The metal substrate is a high-temperature Ni-based alloy, the metal bonding layer is a NiCrAlY alloy bonding layer or a CoNiCrAlY alloy bonding layer, and the high-emissivity layer is a La-based alloy with different Sr doping amounts. 1-x Sr x FeO3 layer, 0< x ≤0.6; The thickness of the metal bonding layer is 80 μm to 100 μm, and the thickness of the high emissivity layer is 800 μm to 1000 μm; The high emissivity layer is made of the following raw materials in the following mass percentages: The Sr-doped LaFeO3 high-emissivity coating has the following performance indicators: The emissivity in the 3 μm to 5 μm band is ≥0.8, and the emissivity of the coating can be controlled in the 3 μm to 5 μm band by adjusting the doping content of the Sr element; the Sr-doped LaFeO3 high-emissivity coating has a seismic performance of ≥60 times at 1100°C, and a bonding strength of 7.22 MPa to 11.40 MPa at room temperature; the infrared emissivity at 900°C is 0.84 to 0.89 for 3 μm to 5 μm, and the infrared emissivity at 1100°C is 0.84 to 0.86 for 3 μm to 5 μm, meeting service requirements.

2. The method for preparing a Sr-doped LaFeO3 high-emissivity coating according to claim 1, characterized in that: The following steps are involved: (1) Using the sol-gel method, La(NO3)3·6H2O, Sr(NO3)2, and Fe(NO3)3·9H2O were dissolved in a deionized water-ethanol mixed solvent to form a uniform solution. Acetic acid was used as a hydrolysis catalyst and chelating agent, and added to a round-bottom flask in stoichiometric order. After sealing, the solution was stirred in a water bath at a constant temperature until the reaction was complete. The solution was allowed to stand, dried, heat-treated, and ground to obtain La(NO3)3·6H2O with controllable composition. 1- x Sr x FeO3 nano-ceramic powder is used as raw material powder, namely La 1-x Sr x FeO3 xerogel powder; The composition of the raw material powder is according to the chemical formula La 1-x Sr x Weigh the FeO3 element mass percentage, x Take 0 to 0.6, according to the following mass percentage: The volume ratio of deionized water to ethanol is (1-3):(3-1), the molar ratio of acetic acid to metal ions is (0.5-4):1, the reaction temperature is 70-80°C, the reaction time is 8-24 hours, the reaction is allowed to stand for 24-48 hours, the heat treatment temperature is 600-1200°C, the drying temperature is 80-150°C, and the heat treatment time is 1-9 hours. (2) Weigh triammonium citrate, gum arabic and the La 1-x Sr x FeO3 nano-ceramic powder was placed in a mixing tank and ball-milled in a mass ratio of 1.5:0.03:0.012 to obtain a slurry. The obtained slurry was spray-granulated to obtain spherical particles with uniform particle size. The spherical particles were sieved with a 60-100 mesh sieve to obtain a powder to be sprayed with a designed particle size; (3) Using atmospheric plasma spraying process to prepare metal bonding layer on Ni-based alloy after sandblasting roughening; The process parameters of sandblasting roughening treatment are: pressure of 0.3 MPa to 0.5 MPa, sandblasting distance of 80 mm to 150 mm, sand size of 12 mesh to 36 mesh, and sandblasting time of 1 min to 5 min; The atmospheric plasma spraying process parameters for the metal bonding layer are as follows: main gas flow rate of 30L / min to 50L / min, carrier gas flow rate of 1L / min to 3L / min; current size control of 500A to 550A, power of 25kW to 40kW, powder feeding amount of 10g / min to 20g / min; coating distance of 80mm to 120mm; the thickness of the metal bonding layer on the Ni-based alloy is 80μm to 100μm; (4) spraying the powder to be sprayed with the designed particle size obtained in step (2) onto the bonding layer using an atmospheric plasma spraying process; The process parameters of atmospheric plasma spraying are as follows: main gas flow rate is 30 L / min~50 L / min, carrier gas flow rate is 1 L / min~3 L / min; current size is controlled at 500 A~550 A, power is 25 kW~35 kW; powder feeding argon flow rate is 2.0 L / min~5.0 L / min, powder feeding amount is 15 g / min~30 g / min; spraying distance is 80 mm~120 mm, and La doped with different Sr is obtained. 1-x Sr x FeO3 high emissivity coating.

3. The method for preparing a Sr-doped LaFeO3 high-emissivity coating according to claim 2, characterized in that: In step (2), the ratio of deionized water to raw material powder during ball milling is 2:(1.5-2), and the ball milling time is 24 h.

4. The method for preparing a Sr-doped LaFeO3 high-emissivity coating according to claim 2, characterized in that: In step (2), the spray granulation is to process the slurry through a spray drying device, the drying tower temperature is 120°C to 250°C, and the powder screening range after granulation is 38 μm to 150 μm.

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