Highly reflective absorbing double-layer radiation shielding barrier coating design, preparation method and coating

Abstract

The application belongs to the field of turbine blade thermal barrier coating of an aero-engine. Specifically, it is a structure design, a preparation method and a prepared coating of a double-layer radiation-resistant thermal barrier coating with a high-reflection layer and a high-absorption layer. The coating comprises a high-absorption layer and a high-reflection layer. The high-absorption layer can absorb part of the energy of photon radiation and re-emit it into the environment, while relying on a cooling gas film to quickly remove heat. Part of the energy of the photon radiation is reflected by the high-reflection layer again to the high-absorption layer after passing through the high-absorption layer, and the process of absorption-emission-cooling gas film heat dissipation is repeated. Within a set temperature range, the absorption rate of the high-absorption layer is determined based on the temperature difference requirement between the inner and outer surfaces of the thermal barrier coating, and the high-absorption layer material is determined based on the absorption rate. The application greatly reduces the radiation heat flow penetrating the coating, avoids the direct heating of the high-temperature alloy by infrared radiation, and significantly improves the heat insulation capacity of the thermal barrier coating and the service life of the turbine blade.

Description

Technical Field

[0001] This invention belongs to the field of thermal barrier coatings for aero-engine turbine blades. Specifically, this invention relates to the structural design, preparation method, and prepared coating of a double-layer radiation-blocking thermal barrier coating consisting of a high-reflectivity layer and a high-absorption layer. Background Technology

[0002] Currently, thermal barrier coatings are widely used in aerospace turbine engines and marine gas turbine engines. Traditional thermal barrier coating materials are mainly yttrium-stabilized zirconium oxide (YSZ) and zirconate oxide (Gd₂Zr₂O₇), generally containing a double-layer structure. The top layer is a ceramic thermal barrier coating, and an adhesive layer is prepared between the coating and the substrate to bridge the large difference in thermal expansion coefficients between the ceramic coating and the metal substrate. Compared with the single ceramic layer of traditional thermal barrier coatings, double or triple ceramic layer coatings introduce additional interfaces, increasing interfacial thermal resistance. In addition, the refractive index difference of each layer of the double ceramic coating can effectively improve the overall reflectivity of the coating and enhance its radiation blocking capability.

[0003] The main methods for preparing thermal barrier coatings include air plasma spraying (APS), plasma spraying-physical vapor deposition (PS-PVD), and electron beam physical vapor deposition (EB-PVD), with coating thicknesses typically ranging from 150 to 300 micrometers. As the inlet temperature of turbines in high thrust-to-weight ratio aero-engines continues to increase, according to the Stefan-Boltzmann law, the power radiated from a blackbody surface is proportional to the fourth power of its thermodynamic temperature. With increasing temperature, the heating method of the thermal barrier coating by the high-temperature exhaust gas will gradually shift from phonon conduction to photon radiation heating. According to Planck's blackbody radiation law, when the temperature exceeds 1000℃, more than 90% of the radiant energy is concentrated in the near-infrared band of 0.5-5 μm. Traditional thermal barrier coatings, such as YSZ and Gd₂Zr₂O₇, achieve thermal insulation by blocking phonon heat conduction through low thermal conductivity. However, recent studies have found that these traditional thermal barrier coatings exhibit semi-transparency in the 0.5-4.5 micrometer wavelength range. This means that high-temperature combustion gas heat radiation can penetrate the coating and directly heat the underlying metal substrate, leading to a decrease in the coating's thermal insulation performance. Furthermore, the coating's thermal insulation effect deteriorates further with increasing temperature (as the proportion of photon radiation continues to increase). Therefore, there is an urgent need to develop a coating with low thermal conductivity that can effectively block infrared radiation.

[0004] Tsinghua University designed a high-absorption material (Gd₂Zr₂O₇+GdMnO₃) with an infrared absorptivity of 0.74 and a transmittance of only 0.06 in the short-wavelength band. However, the research was limited to bulk materials, and no coating was designed. Harbin Institute of Technology prepared a high-absorption material (La₂Hf₂O₇+NiFe₂O₄) with an absorptivity of 0.85 and a transmittance of only 0.001 in the short-wavelength band. However, the thermal conductivity of the material increased significantly at 800℃, and its mechanical properties deteriorated significantly compared to the substrate material La₂Hf₂O₇. Harbin Institute of Technology also studied a multilayer ceramic thin film (Y₃NbO₇ / GdTaO₄) with a transmittance of around 0.005 in the short-wavelength band, but the overall coating thickness reached 400 micrometers, which does not meet the requirements for thermal barrier coatings. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a coating structure design and preparation method for a high infrared reflectivity layer + high infrared absorption layer. The coating prepared according to this structure has a thin thickness, good radiation blocking effect, low thermal conductivity, and long thermal cycling life, significantly improving the coating's heat insulation and thermal protection capabilities in ultra-high temperature service environments.

[0006] The complete technical solution of this invention includes: A design method for a high-reflectivity absorption double-layer radiation-blocking thermal barrier coating, comprising a high-absorption layer and a high-reflectivity layer, wherein the high-reflectivity layer is connected to a substrate or adhesive layer, and the high-absorption layer is located outside the high-reflectivity layer; the high-absorption layer can absorb part of the energy of photon radiation and re-emit it into the environment, while simultaneously relying on a cooling gas film to rapidly remove heat; part of the energy of photon radiation passes through the high-absorption layer and is reflected back to the high-absorption layer by the high-reflectivity layer, repeating the absorption-emission-cooling gas film heat dissipation process; the design method includes the following steps: (1) Within the set temperature range, the absorption rate of the high absorption layer is determined based on the temperature difference requirement between the inner and outer surfaces of the thermal barrier coating; (2) Determine the composition of the high-absorption layer material based on the absorption rate.

[0007] Furthermore, in step (1), the set temperature range is not lower than 1000℃.

[0008] Furthermore, the temperature difference between the inner and outer surfaces is required to be: within the set temperature range, the temperature difference between the inner and outer surfaces based on the thermal barrier coating is not less than 100°C, and the temperature difference between the inner and outer surfaces is more than 40°C higher than that of the YSZ coating of the same thickness.

[0009] Furthermore, in step (2), the absorption rate is not less than 0.5.

[0010] Furthermore, the high-absorption layer material is a gadolinium iron oxide doped zirconium oxide rolled biphase composite material.

[0011] Furthermore, a method for preparing a high-reflection absorption double-layer radiation-blocking thermal barrier coating is provided, wherein the high-absorption layer material obtained by the design method is used to prepare a high-reflection absorption double-layer radiation-blocking thermal barrier coating by electron beam physical vapor deposition (EB-PVD).

[0012] Furthermore, the evaporation current during deposition was 1.0 A, the substrate temperature was 900 °C, and the sample rotation speed was 20 rpm / min.

[0013] Furthermore, during the preparation of the high-absorption layer, the particle size and feed rate of the zirconate-impregnated matrix and the gadolinium ferrite powder of the second phase material are synergistically controlled for deposition.

[0014] The beneficial effects of this invention are as follows: 1. The use of a high-reflectivity and high-absorption dual ceramic layer structure can significantly reduce the radiative heat flow that penetrates the coating, prevent the high-temperature alloy from being directly heated by infrared radiation, and significantly improve the heat insulation capability of the thermal barrier coating and the service life of the turbine blades.

[0015] 2. The thermal barrier coating with a double ceramic layer structure significantly improves its overall thermal insulation performance due to the interfacial thermal resistance between the two layers and the different refractive indices between them. Therefore, it can achieve efficient thermal insulation with a thinner thickness, reducing the cost of coating preparation. With the same thermal insulation performance, thinner coatings have a longer service life.

[0016] 3. To meet the different service temperatures, different heat insulation gradients, and specific coating thickness requirements of various engine models, by changing the near-infrared optical properties of the high-reflection and high-emission layers, the ratio of high absorption to high reflection layer thickness, and other parameters in the finite element model, a wide-temperature-range, long-life, and highly efficient heat-insulating dual-ceramic radiation-blocking coating can be designed.

[0017] 4. The main component of the high-absorption material (GZO+GFO) and high-reflectivity material (GYbZ) selected in this invention, zirconium oxide (Gd2Zr2O7), is itself a thermal barrier coating material with low thermal conductivity and high melting point. Experiments have shown that GZO+GFO and GYbZ both have lower thermal conductivity and mechanical properties similar to Gd2Zr2O7, making them one of the most promising candidate materials for the next generation of ultra-high temperature thermal barrier coatings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the geometric model of the high-absorption + high-reflection dual ceramic thermal barrier coating used in the finite element simulation of this invention.

[0019] Figure 2 The trend of temperature variation of the upper and lower surfaces of the coating with the absorption rate is shown.

[0020] Figure 3 The trend of thermal radiation flux on the upper and lower surfaces of the coating as absorptivity is shown.

[0021] Figure 4 A comparison of the temperature field and thermal insulation performance of YSZ, GYbZ, and GZO / GFO+GYbZ coatings of the same thickness.

[0022] Figure 5 The microstructure of the cross-section of the GZO / GFO + GYbZ double ceramic radiation-blocking coating is shown.

[0023] In the figure: 1-top surface of the coating, 2-bottom surface of the coating, 3-high absorption layer (Gd2Zr2O7+GdFeO3, GZO / GFO), 4-high reflectivity layer (Gd 0.9 Yb 0.1 )2Zr2O7, GYbZ), 5-metal bonding layer, 6-metal matrix. Detailed Implementation

[0024] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0025] This invention relates to a high-reflectivity layer + double-layer radiation-blocking thermal barrier coating structure design and its preparation method. The high-absorption layer on the surface can rapidly absorb the energy of photon radiation and re-emit it into the environment, with heat being rapidly carried away by a cooling gas film. Some thermal radiation passes through the high-absorption layer and is reflected back to the high-absorption layer by the high-reflectivity layer, repeating the absorption-emission-cooling gas film rapid heat dissipation process again. Under the synergistic effect of the above mechanisms, the high-reflectivity layer + high-absorption double-layer radiation-blocking coating can effectively block infrared radiation energy in high-temperature combustion gases, preventing the internal metal substrate from being directly exposed to strong radiative heat flow, thereby significantly improving the coating's heat insulation and thermal protection capabilities in ultra-high temperature service environments.

[0026] The design and preparation method of the double-layer radiation-blocking thermal barrier coating structure of the present invention, consisting of a high-reflectivity layer and a high-absorption layer, includes the following steps: (1) Within the set temperature range, the absorption rate of the high absorption layer is determined based on the temperature difference requirement between the inner and outer surfaces of the thermal barrier coating; specifically, the influence of boundary conditions with different absorption rates on the coating temperature field and the temperature of the upper and lower surfaces of the coating is simulated using the finite element method. This invention first verifies the influence of absorptivity on the overall temperature field and thermal radiation flux of a thermal barrier coating. Assuming an ideal material has a reflectivity of 0.1 and a sum of transmittance and absorptivity of 0.9, a series of absorptivity gradients were designed with a step size of 0.1, such as absorptivity = 0.1, transmittance = 0.8; absorptivity = 0.2, transmittance = 0.7; absorptivity = 0.9, transmittance = 0.0, etc. With a total coating thickness of 300 micrometers, the trend of the overall temperature field of the coating with thickness and absorptivity was calculated as follows: Figure 2 As shown, this illustrates the temperature trends of the upper and lower surfaces of the coating as absorptivity changes. It can be seen that as the absorptivity gradually increases, the upper surface temperature gradually increases, while the lower surface temperature first increases and then decreases, with the inflection point near the absorptivity level of 0.3. As the absorptivity continues to increase, the lower surface temperature continues to decrease.

[0027] The trends of thermal radiation flux on the upper and lower surfaces of the coating with absorptivity were further calculated as follows: Figure 3 As shown, the incident radiation flux on the upper surface increases with increasing absorptivity, while the transmitted radiation flux on the lower surface gradually decreases with increasing absorptivity. This further proves that a high absorptivity coating can effectively block thermal radiation from penetrating the coating.

[0028] According to the design requirements, the thermal insulation effect of the high absorption layer + high reflection layer needs to be 40°C higher than that of the YSZ coating of the same thickness, and the thermal insulation temperature of the coating should be above 100°C. According to the finite element simulation results, the above requirements can be met when the absorption rate is above 0.5.

[0029] (2) Based on the design requirements and for different insulation temperature requirements, a suitable high-absorption layer (Gd2Zr2O7+GdFeO3, GZO / GFO) and a high-reflection layer (Gd2Zr2O7+GdFeO3, GZO / GFO) were selected. 0.9 Yb 0.1 Infrared absorptivity, transmittance, and reflectivity data of YSZ coating, GYbZ coating, and GYbZ+GZO / GFO coating of the same thickness were input into a finite element model to compare their heat insulation effects.

[0030] In this invention, the high-absorption layer is a two-phase composite material (Gd₂Zr₂O₇+GdFeO₃, GZO / GFO) prepared by adding a small amount of gadolinium ferrite to zirconate oxide. Experiments showed that this material has an integrated emissivity of 0.73, an integrated reflectivity of 0.23, and an integrated transmittance of 0.04 in the 0.6-4.5 micrometer short-wavelength band. The high-reflectivity layer material used in this invention is ytterbium-doped zirconate oxide (Gd₂Zr₂O₇+GdFeO₃, GZO / GFO). 0.9 Yb 0.1(2Zr₂O₇, GYbZ) Experimentally measured the material's integrated emissivity in the 0.6-4.5 micrometer short-wavelength band as 0.17, integrated reflectivity as 0.59, and integrated transmittance as 0.23. The geometric model of the finite element model is as follows: Figure 1 As shown in the figure. This invention calculated the temperature field distribution of three coatings of the same thickness: a traditional thermal barrier coating YSZ, a single high-reflectivity coating GYbZ, and a high-absorption + high-reflectivity dual-ceramic coating GZO / GFO+GYbZ. The total coating thickness was set at 150 micrometers. For the GZO / GFO+GYbZ dual-ceramic coating, this thickness satisfies the coating's thermal insulation requirements while ensuring a long thermal cycling life. The temperature field distribution of the three coatings is shown in the figure. Figure 4 As shown in the figure on the right, the thermal insulation effect of the coating is calculated by subtracting the lower surface temperature from the upper surface temperature of the three coatings.

[0031] from Figure 4 As can be seen, the top and bottom surfaces of YSZ have the highest temperatures and the worst heat insulation effect. The top surface temperature of the high-reflectivity coating GYbZ is slightly lower than that of the GZO / GFO+GYbZ dual-ceramic coating, while the bottom surface temperature is significantly higher. In terms of heat insulation performance, the GZO / GFO+GYbZ coating achieves 120.05℃, while the GYbZ coating reaches 99.62℃ and the YSZ coating only 75.18℃. The GZO / GFO+GYbZ coating has a heat insulation temperature approximately 45℃ higher than YSZ of the same thickness. Under the same thickness conditions, the GZO / GFO+GYbZ coating improves the heat insulation effect by 20.51% compared to the GYbZ coating and by 59.68% compared to the YSZ coating, demonstrating that this new generation of radiation-blocking coatings achieves highly efficient heat insulation.

[0032] (3) A high-absorption + high-reflection double-layer radiation-blocking thermal barrier coating was prepared by electron beam physical vapor deposition (EB-PVD).

[0033] In step (1) of this invention, by controlling variables and assuming that the sum of absorptivity and transmittance is constant, this invention only studies the influence of changes in material emissivity and transmittance on the overall temperature field of the coating, and calculates the temperature changes of the upper and lower surfaces based on the changes in the temperature field. Further calculations are made of the changes in the incident flux and transmitted radiation flux of the coating with emissivity, demonstrating that the determined absorptivity improves the radiation blocking and heat insulation effects of the coating.

[0034] In step (2) of this invention, a complete finite element model of the double ceramic coating is constructed based on step (1). According to the design requirements, the novel thermal barrier coating needs to achieve a thermal insulation temperature 40°C higher than that of the YSZ coating under the same thickness conditions, and the thermal insulation temperature of the coating should be above 100°C. By inputting the intrinsic infrared optical properties of YSZ, GYbZ, and GZO / GFO+GYbZ into the finite element model of the double ceramic coating and calculating the thermal insulation effects of the three coatings of the same thickness, YSZ, GYbZ, and GZO / GFO+GYbZ, the three materials correspond to the traditional thermal barrier single-layer coating, single-layer high-reflection coating, and high-absorption + high-reflection double-layer thermal barrier coating, respectively, demonstrating the excellent thermal insulation performance of the high-absorption + high-reflection double ceramic coating at the same thickness obtained by the design method of this invention.

[0035] In step (3) of the present invention, the present invention designs coatings with different total thicknesses and high absorption and high reflection layer thickness ratios to meet the requirements of heat insulation effect under different environments, and uses electron beam physical vapor deposition (EB-PVD) and other technologies to prepare double ceramic radiation blocking coatings.

[0036] Based on the above structural design, this invention uses electron beam physical vapor deposition (EB-PVD) to prepare a dual ceramic coating of GZO / GFO+GYbZ. Since both the GZO / GFO and GYbZ layers are mainly composed of zirconium oxide, and the amounts of GdFeO3 and Yb2O3 added to both materials are small, they do not significantly alter the melting point, coefficient of thermal expansion, or other properties of the zirconium oxide material. Therefore, similar deposition parameters were used, including an evaporation current of 1.0 A, a substrate temperature of 900 °C, and a sample rotation speed of 20 rpm / min. The microstructure of the prepared coating is shown below. Figure 5 As shown in the figure, the columnar crystals are well-developed, large, dense, and uniform, with clear and tight grain boundaries. This is a typical, high-quality EB-PVD columnar crystal structure.

[0037] Optionally, during the preparation of the high-absorption layer, the particle size and feed rate of the zirconate-impregnated matrix and the gadolinium ferrite powder of the second phase are synergistically controlled for deposition. By controlling the particle size and feed rate of the matrix and second phase powders, the matrix powder is deposited in the gas phase during deposition, while the second phase powder retains at least partially in a solid particle state, preventing complete melting and forming a solid-particle interface in the coating. After deposition, the mass ratio of the matrix material to the second phase material in the coating is 1~1.5. Lower particle size facilitates sufficient heat transfer during the powder's movement within the high-temperature beam. Since the heat transfer required for vaporization is higher than that for liquefaction, a smaller particle size is required for the matrix material Gd₂Zr₂O₇. For the second phase GdFeO₃ material introduced as solid particles, its particle size is required to be larger than that of Gd₂Zr₂O₇ to ensure it remains solid particles during beam heating without complete melting. The feed rate also affects the ratio of gas and solid phases in the coating system, as well as the powder's ability to withstand heat. If the GdFeO3 feed rate is too high, the coating system will primarily consist of a solid GdFeO3 phase, impairing its thermal expansion properties. Conversely, if the GdFeO3 feed rate is too low, the powder particles will liquefy or vaporize, failing to form a solid-particle interface and thus failing to achieve the goal of creating a micro-interface. Therefore, synergistically controlling the feed rate and particle size is a key parameter in the coating preparation process.

[0038] Specifically, during the deposition process, the particle size of Gd₂Zr₂O₇ is 5-15 micrometers, and the particle size of GdFeO₃ is 50-90 micrometers. The feed rate of Gd₂Zr₂O₇ powder from the gas phase feed port is 10-12 g / min, and the feed rate of GdFeO₃ powder from the liquid-solid phase feed port is 8-10 g / min. After preparation, the GdFeO₃ solid particles are uniformly dispersed throughout the entire high-absorption layer, with a particle size of 0.5-2 micrometers. Micrometer-sized air gaps exist between the solid particles and between the solid particles and the columnar crystals.

[0039] The resulting high-absorption layer has excellent infrared radiation penetration resistance. The infrared transmittance of the 250-micron thick coating is as low as 20%, the thermal cycle life at 1100℃ is 900 cycles, and the thermal conductivity at 1300℃ is 0.8 W / mK.

[0040] The foregoing detailed description only illustrates preferred embodiments of the present invention and is not intended to limit the invention. Those skilled in the art, upon considering the disclosure in the specification and embodiments, will readily conceive of other embodiments of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

Claims

1. A design method for a high-reflection absorption double-layer radiation-blocking thermal barrier coating, characterized in that... , The high-reflectivity absorption double-layer radiation-blocking thermal barrier coating comprises a high-absorption layer and a high-reflectivity layer. The high-reflectivity layer is connected to the substrate or adhesive layer, and the high-absorption layer is located outside the high-reflectivity layer. The high-absorption layer can absorb part of the energy of photon radiation and re-emit it into the environment. Simultaneously, it relies on a cooling gas film to quickly remove heat. Part of the energy of photon radiation passes through the high-absorption layer and is reflected back to the high-absorption layer by the high-reflectivity layer, repeating the absorption-emission-cooling gas film heat dissipation process. The design method includes the following steps: (1) Within the set temperature range, the absorption rate of the high absorption layer is determined based on the temperature difference requirement between the inner and outer surfaces of the thermal barrier coating; (2) Determine the composition of the high-absorption layer material based on the absorption rate.

2. The thermal barrier coating design method according to claim 1, characterized in that, In step (1), the set temperature range is not lower than 1000℃.

3. The thermal barrier coating design method according to claim 2, characterized in that, The required temperature difference between the inner and outer surfaces is as follows: within the set temperature range, the temperature difference between the inner and outer surfaces based on the thermal barrier coating is not less than 100°C, and the temperature difference between the inner and outer surfaces is more than 40°C higher than that of the YSZ coating of the same thickness.

4. The thermal barrier coating design method according to claim 2, characterized in that, In step (2), the absorption rate shall not be less than 0.

5.

5. The thermal barrier coating design method according to claim 2, characterized in that, The high-absorption layer material is a gadolinium iron oxide doped zirconium oxide rolled biphase composite material.

6. A method for preparing a high-reflectance absorption double-layer radiation-blocking thermal barrier coating, characterized in that, Based on the high-absorption layer material obtained by the design method described in claim 5, a high-reflection absorption double-layer radiation-blocking thermal barrier coating is prepared by electron beam physical vapor deposition (EB-PVD).

7. The method for preparing a high-reflectance absorption double-layer radiation-blocking thermal barrier coating according to claim 6, characterized in that, The evaporation current during deposition was 1.0 A, the substrate temperature was 900 °C, and the sample rotation speed was 20 rpm / min.

8. The method for preparing a high-reflectance absorption double-layer radiation-blocking thermal barrier coating according to claim 6, characterized in that, During the preparation of the high-absorption layer, the particle size and feed rate of the zirconate-impregnated matrix and the gadolinium ferrite powder of the second phase material are synergistically controlled for deposition.

9. A high-reflectivity absorption double-layer radiation-blocking thermal barrier coating prepared by the method of any one of claims 6-8.

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