Environmental barrier coating and coating method thereof

Abstract

The invention provides an environmental barrier coating and a coating method thereof. The environmental barrier coating at least comprises a functional layer, wherein the porosity of the functional layer is sequentially increased or decreased along the thickness direction of the functional layer. The thermal conductivity of the coating is reduced by limiting the change of the porosity of the coating, the thermal resistance of a functional layer in the environmental barrier coating is improved, the thermal expansion coefficient of the coating is highly matched with a silicon-based base material, and when the environmental barrier coating is applied to surface service of the silicon-based base material, the thermal resistance of the functional layer is improved. And the problem of coating stripping caused by thermal expansion mismatch can be avoided, so that the service life of the coating is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic surface treatment, and in particular relates to an environmental barrier coating and a coating method thereof. Background Art

[0002] Continuous silicon carbide fiber reinforced silicon carbide ceramic matrix composites (SiC f The combination of / SiC composite material) + EBC coating can meet the requirements of serving in a gas environment below 1350℃. However, with the increase of thrust-to-weight ratio, the inlet temperature of the turbine front end reaches or even exceeds the gas temperature of 2000K, forcing the current SiC f The service temperature of the surface of SiC components ranges from 1350°C to 1500°C. Especially when serving in a gas environment at 1500°C or above, the existing EBC coating system (Si / rare earth silicate) is difficult to meet the needs of the new generation of high-performance engines due to the insufficient temperature resistance of the internal Si bonding layer and the fiber in the composite.

[0003] At present, the temperature resistance of the composite material is improved by adding HfO2 to the Si layer to form a Si-HfO2 bonding layer. However, during the service process, Si-HfO2 is difficult to form a continuous phase and cannot protect the composite material. In addition, there is currently a T / EBC system formed by adding a thermal blocking layer (TBC) on the surface of the EBC, which uses TBC to reduce the conduction of temperature and protect the Si layer and the composite material from thermal damage, which solves the high temperature resistance problem of the composite material in service to a certain extent.

[0004] However, in the above T / EBC structure, due to the mismatch in thermal expansion coefficients between the TBC layer and the EBC layer, the volume change of the coating is different under thermal cycling conditions, resulting in coating peeling failure. Although the subsequent multi-layer gradient coating structure design is used to reduce the difference in thermal expansion coefficients, the increase in interfaces in the coating structure makes the interlayer stress more complicated, which increases the risk of coating peeling and reduces the service reliability of the coating. In addition, the design of this multi-layer structure also increases the manufacturing cost and difficulty.

[0005] Therefore, how to design an environmental barrier coating structure with low thermal conductivity and a thermal expansion coefficient that is highly matched with a silicon-based matrix material is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] The present invention provides an environmental barrier coating, which reduces the thermal conductivity of the coating by limiting the porosity change of the coating, thereby reducing the heat transfer of the coating and preventing the Si layer and SiC f / SiC composite materials are not subject to thermal damage. In addition, providing each layer of coating material as a homogeneous EBC material can avoid the problem of coating peeling due to thermal expansion mismatch, thereby improving the service life of the coating.

[0007] The present invention also provides a method for coating an environmental barrier coating, which can coat an environmental barrier coating with a porosity gradient change on the surface of a substrate material, especially on a silicon-based substrate material, and can significantly protect the substrate from heat loss and improve the service performance and life of the substrate material.

[0008] In a first aspect of the present invention, there is provided an environmental barrier coating, which at least includes a functional layer; wherein,

[0009] Along the thickness direction of the functional layer, the porosity of the functional layer increases or decreases in sequence.

[0010] The environmental barrier coating as described above, wherein the functional layer includes a first functional layer and a second functional layer stacked in sequence, and the porosity of the second functional layer is greater than that of the first functional layer.

[0011] The environmental barrier coating as described above, wherein the porosity of the first functional layer is less than 10%; and / or,

[0012] The porosity of the second functional layer is 10-20%.

[0013] The environmental barrier coating as described above, wherein the thickness of the first functional layer is 50-100 μm; and / or,

[0014] The thickness of the second functional layer is 50-100 μm.

[0015] The environmental barrier coating as described above, wherein the material of the functional layer includes rare earth silicate.

[0016] The environmental barrier coating as described above, wherein the rare earth silicate powder in the functional layer has a porous spherical structure;

[0017] The size of the rare earth silicate powder is 200-400 mesh,

[0018] The tap density of the rare earth silicate powder is 1.2-1.4 g / cm 3 , and the fluidity is (50-60) s / 50 g.

[0019] In a second aspect of the present invention, there is provided a method for coating the environmental barrier coating according to the first aspect, including the following steps:

[0020] Spray the rare earth silicate powder on the surface of a support to form a rare earth silicate coating with a porosity increasing or decreasing in sequence along the thickness direction, and perform heat treatment on the rare earth silicate coating to form a functional layer.

[0021] The coating method as described above, wherein a first coating is sprayed on the surface of the support, and then a second coating is sprayed on the surface of the first coating away from the support; the porosity of the second coating is greater than that of the first coating;

[0022] The first coating and the second coating are heat-treated to form a first functional layer and a second functional layer.

[0023] The coating method as described above, wherein during the process of spraying the first coating on the surface of the support, the distance between the spray gun and the support is 100 - 120 mm, the moving speed of the spray gun is 300 - 800 mm / s, the power of the spray gun is 38 - 40 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 6 - 9 liters per minute; and / or,

[0024] During the process of spraying the second coating on the surface of the first coating away from the support, the distance between the spray gun and the support is 120 - 150 mm, the moving speed of the spray gun is 300 - 800 mm / s, the power of the spray gun is 35 - 38 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 6 - 9 liters per minute.

[0025] The coating method as described above, wherein the support comprises a base material and a silicon layer located on the surface of the base material;

[0026] The silicon layer is located between the base material and the functional layer;

[0027] The thickness of the silicon layer is 30 - 100 μm.

[0028] The implementation of the present invention has at least the following beneficial effects:

[0029] The environmental barrier coating provided by the present invention uses the part with relatively large pores to reduce the heat transfer of the coating, and uses the highly dense part with relatively low porosity to block the diffusion of water and oxygen in the environment. By defining the gradient change of the porosity of the functional layer, it helps to reduce the thermal conductivity of the coating while improving the high-temperature resistance of the coating, so that the coating has both the effects of cooling and heat insulation and corrosion resistance. In addition, applying the environmental barrier coating of the present invention on the surface of the support can also avoid the problem of coating peeling failure caused by thermal expansion mismatch. Description of the Drawings

[0030] Figure 1 It is the SEM image of the environmental barrier coating with a pore gradient in Example 1;

[0031] Figure 2 It is the SEM image of the environmental barrier coating with a pore gradient in Example 2;

[0032] Figure 3 It is the SEM image of the environmental barrier coating with the same porosity in Example 6;

[0033] Figure 4 It is the SEM image of the environmental barrier coating with the same porosity in Comparative Example 1;

[0034] Figure 5 It is the XRD pattern of the functional layer with a pore gradient in Example 1;

[0035] Figure 6 It is the SEM image of the rare earth silicate powder used when coating the environmental barrier coating in Example 1;

[0036] Figure 7 It is the particle size distribution diagram of the rare earth silicate powder used when coating the environmental barrier coating in Example 1;

[0037] Figure 8 It is the thermal conductivity diagram of the pore gradient environmental barrier coating in each example;

[0038] Figure 9 It is the thermal expansion coefficient diagram of the novel pore gradient environmental barrier coating in Example 1. Detailed implementation manners

[0039] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0040] In the first aspect of the present invention, an environmental barrier coating is provided, and the environmental barrier coating at least includes a functional layer; wherein, along the thickness direction of the functional layer, the porosity of the functional layer increases or decreases in sequence.

[0041] The environmental barrier coating of the present invention mainly serves as a protective coating and is applied to the surface of a silicon-based matrix material, such as the surface of a hot-end component of an engine made of a silicon-based ceramic material. This coating can establish a barrier between the matrix material and the operating environment to prevent or reduce the influence of the engine operating environment on the performance of the matrix material.

[0042] In the specific application process of the environmental barrier coating, the environmental barrier coating can be directly set on the surface of the matrix material, and the matrix material is the material to be protected. Alternatively, an adhesive layer can be set on the surface of the matrix material, and then the environmental barrier coating is set on the surface of the adhesive layer away from the matrix material. Among them, the adhesive layer can be a silicon layer. At this time, the silicon layer serves as the adhesive layer and can further enhance the adhesion between the environmental barrier coating and the matrix material.

[0043] In the environmental barrier coating of the present invention, one side of the functional layer is in contact with the matrix material, and the other side is exposed to contact with the outside.

[0044] Along the thickness direction of the functional layer, the porosity of the functional layer increases or decreases, that is, the porosity of the functional layer changes gradiently in the thickness direction. At this time, the side with relatively low porosity can be fitted with the matrix material, and the side with relatively high porosity faces the external environment.

[0045] In the prior art, the porosity of the environmental barrier coating remains unchanged in the thickness direction. Although increasing the coating thickness alone can increase the heat resistance to a certain extent, it greatly increases the risk of coating peeling and failure. The present invention limits the porosity of the functional layer on the side close to the substrate material to be smaller and the density to be higher, which is beneficial to blocking the diffusion of corrosive atmospheres such as water vapor and oxygen in the external environment, so that the environmental barrier coating has excellent corrosion resistance, hinders the contact between the corrosive atmosphere and the substrate material, and avoids the oxidation of the silicon layer and the substrate material by water vapor and oxygen in the external environment, thereby helping to ensure the service life of the environmental barrier coating and the surface stability of the substrate material; at the same time, the porosity of the functional layer on the side away from the substrate material is larger, that is, the porosity of the functional layer on the side close to the external environment is larger, containing a large number of closed-cell voids, and the thermal conductivity of the gas in the voids is much lower than the thermal conductivity of the material. Therefore, the increase in porosity will further reduce the thermal conductivity and heat transfer capacity, thereby helping to further reduce the thermal conductivity of the environmental barrier coating, so that the environmental barrier coating has excellent high temperature resistance and reduces the thermal impact of the external high temperature environment on the substrate material. Therefore, applying the environmental barrier coating to the surface of the substrate material can significantly improve the performance and life of the substrate material in terms of high temperature resistance and corrosion resistance.

[0046] The present invention does not limit the number of functional layers, as long as the porosity of the functional layers varies. In one embodiment, the functional layers include a first functional layer and a second functional layer stacked in sequence, and the porosity of the second functional layer is greater than that of the first functional layer.

[0047] In the above embodiment, the functional layer is two layers, and the first functional layer is closer to the base material relative to the second functional layer. When the porosity of the second functional layer is greater than that of the first functional layer, the first functional layer is ensured to be a relatively dense structure, which can block the diffusion of water vapor and oxygen in the external environment, so that the environmental barrier coating has excellent corrosion resistance and hinders the oxidative corrosion of the silicon layer and the base material by water vapor and oxygen in the external environment. At the same time, the second functional layer has a relatively loose structure and a reduced heat transfer capacity, which is beneficial to reducing the thermal conductivity of the environmental barrier coating, so that the environmental barrier coating has a lower thermal conductivity and avoids the thermal influence of the external high temperature environment on the base material.

[0048] The present invention does not limit the porosity of the first functional layer and the second functional layer, which can be specifically adjusted according to actual needs. In some embodiments, the porosity of the first functional layer is less than 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 9.5% or the range composed of any two of them; and / or, the porosity of the second functional layer is 10-20%, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or the range composed of any two of them.

[0049] The present invention does not limit the thickness of the silicon layer, the first functional layer and the second functional layer, which can be adjusted according to actual needs. In some embodiments, the thickness of the first functional layer is 50-100 μm, such as 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or the range composed of any two of them; and / or, the thickness of the second functional layer is 50-100 μm, such as 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or the range composed of any two of them.

[0050] The present invention does not limit the material of the functional layer, which can be conventional silicates in the art. For example, the material of the functional layer includes rare earth silicates. At this time, the functional layer and the matrix material can have the same silicon element, so that the functional layer and the matrix material have excellent chemical compatibility and matching thermal expansion coefficients, avoiding the peeling of the functional layer from the matrix material and improving the structural stability of the environmental barrier coating itself. In addition, the functional layer has excellent surface stability and can protect the matrix material at high temperatures.

[0051] It should be emphasized that the environmental barrier coating of the present invention is particularly suitable for matrix materials made of silicon-based ceramics. At this time, the matrix material and the functional layer have the same silicon element, so that there is good chemical compatibility and matching thermal expansion coefficients between the matrix material and the functional layer, which not only ensures the structural stability of the environmental barrier coating, but also can avoid the environmental barrier coating from falling off the surface of the matrix material, thereby improving the service life of the environmental barrier coating.

[0052] In addition, when the above environmental barrier coating is applied to the surface of the matrix material, the functional layer is close to the external environment. When the external environment is a high-temperature environment, due to the low thermal conductivity of rare earth silicates themselves, the thermal conductivity of the functional layer is low, which plays a role in heat insulation to a certain extent and prevents the high-temperature environment from deteriorating the matrix material.

[0053] The present invention does not limit the specific type of rare earth silicate. For example, in some embodiments, the chemical formula of rare earth silicate can be, for example, (Y 0.2 Yb 0.2 Sc 0.2 Gd 0.2 Lu0.2 )2Si2O7. By using the above rare earth disilicate as the material of the functional layer, it helps to further improve the high temperature resistance and corrosion resistance of the environmental barrier coating.

[0054] The present invention does not limit the specific preparation process of the above functional layer, as long as the functional layer with the above material and structure can be obtained. For example, in some embodiments, the functional layer is formed by atmospheric plasma spraying technology using rare earth silicate powder; the rare earth silicate powder has a porous spherical structure; the size of the rare earth silicate powder is 200 - 400 mesh, and the tapped density of the rare earth silicate powder is 1.2 - 1.4 g / cm 3 , and the fluidity is (50 - 60) s / 50 g.

[0055] In the present invention, the atmospheric plasma spraying technology can be used to spray the functional layer. Specifically, the rare earth silicate powder is loaded into the powder tank of the plasma sprayer as the spraying feedstock. The powder is ejected under the drive of a high-speed gas flow, heated, melted, and accelerated under the high temperature and high pressure conditions of the plasma to generate a particle stream guided towards the surface of the substrate material, thereby forming a coating when contacting the substrate material, and then forming a functional layer through high-temperature crystallization.

[0056] The rare earth silicate powder mainly presents a spherical morphology and has good fluidity, which helps to form a particle stream; and the surface of the rare earth silicate powder has a porous and loose structure, which helps to obtain a functional layer with an increasing porosity subsequently.

[0057] The present invention does not limit the specific preparation process of the above rare earth silicate powder. For example, in some embodiments, the rare earth silicate powder is obtained by a method including the following process: Y2O3, Sc2O3, Yb2O3, Lu2O3, Gd2O3, and SiO2 are mixed evenly and then calcined to obtain a first material; the first material is subjected to ball milling treatment to obtain a second material; wherein, the rotation speed of the ball milling treatment is 200 - 300 r / min and the time is 12 - 36 h; the second material, polyvinyl alcohol, and water are mixed to obtain a slurry; the slurry is sent to a spray granulator for granulation treatment to obtain a spherical product; wherein, the feeding speed of the spray dryer is 20 - 40 mL / min, the inlet temperature is 200 - 240 °C, the outlet temperature is 100 - 150 °C, and the rotation speed is 4000 - 5000 r / s; the spherical product is subjected to drying treatment and roasting treatment, and then sieved through a 200 - 400 mesh sieve to obtain the rare earth silicate powder.

[0058] In the second aspect of the present invention, there is provided a coating method for the environmental barrier coating provided in the first aspect, including the following steps: spraying the rare earth silicate powder on the surface of a support to form a coating with a porosity increasing or decreasing sequentially along the thickness direction, and performing heat treatment on the coating to form a functional layer.

[0059] In some embodiments, a first coating is sprayed on the surface of the support, and then a second coating is sprayed on the surface of the first coating away from the support; the porosity of the second coating is greater than that of the first coating; the first coating and the second coating are heat-treated to form a first functional layer and a second functional layer.

[0060] In the present invention, during the spraying process, by adjusting the process parameters, it is beneficial to obtain a functional layer with increasing porosity. For example, in some embodiments, during the process of spraying the first coating on the surface of the support, the distance between the spray gun and the support is 100 - 120 mm, the moving speed of the spray gun is 300 - 800 mm / s, the power of the spray gun is 38 - 40 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 6 - 9 liters per minute; and / or, during the process of spraying the second coating on the surface of the first coating away from the support, the distance between the spray gun and the support is 120 - 150 mm, the moving speed of the spray gun is 300 - 800 mm / s, the power of the spray gun is 35 - 38 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 6 - 9 liters per minute.

[0061] Among them, the support includes a matrix material and a silicon layer located on the surface of the matrix material; the silicon layer is located between the matrix material and the functional layer. At this time, the silicon layer can be used as an adhesive layer between the matrix material and the functional layer, which can play an adhesive role. In addition, the matrix material, the silicon layer, and the functional layer have the same silicon element, so that there are good chemical compatibility and matching thermal expansion coefficients between the matrix material and the silicon layer, and between the silicon layer and the functional layer, which not only ensures the structural stability of the environmental barrier coating, but also can prevent the environmental barrier coating from peeling off the surface of the matrix material, thereby improving the service life of the environmental barrier coating.

[0062] In some embodiments, the thickness of the silicon layer is 30 - 100 μm, such as 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or the range composed of any two of them.

[0063] In the specific implementation process of the present invention, spherical Si powder can be first loaded into the APS powder tank and sprayed on the surface of the matrix material to obtain a silicon layer and thus obtain a support.

[0064] Among them, the working power of the plasma spheroidization device used during the above spraying is 30 - 40 kW, the pressure is 2 - 2.5 Pa, the sheath gas is argon, the gas flow rate is 40 - 55 slpm, the central gas is argon, the gas flow rate is 20 - 35 liters per minute, and the carrier gas is argon, the gas flow rate is 5 - 8 liters per minute.

[0065] During the spraying process, the distance between the spray gun and the substrate is set to be 100 - 120 cm, the moving speed of the spray gun is independently 300 - 800 mm / s, the power is 30 - 40 kW, the argon gas flow rate is 40 - 45 liters per minute, and the hydrogen gas flow rate is 5 - 10 liters per minute.

[0066] The present invention will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, conventional materials, and conventional instruments, which can be obtained commercially, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0067] The following is the test method for the tapped density: The experiment of using a tapped density tester (BT - 311) refers to the national standard GB / T21354 - 2008. Set the vibration amplitude to 3 mm, the vibration frequency to 250 times / min, the number of vibrations to 3000 times, and each group is tested three times. The result is the average value. Divide the mass of the powder by the volume occupied by the powder after vibration, which is the tapped density of the powder. Divide the mass of the powder by the volume before vibration, which is the loose bulk density.

[0068] The test method for the powder flowability: Use a powder flowability tester (BT - 200) to measure the powder flowability. According to the national standard GBT1482 - 2010, each time weigh 50 g of powder and put it into a standard funnel with a pore diameter of 5 mm, and record the time for the powder to completely flow out of the funnel. Divide the time for the powder to flow out by the mass of the powder, which is the powder flowability, with the unit s / 50 g. Each sample is repeated three times and the average value is taken.

[0069] The test method for the porosity: Use image analysis to detect the porosity of the coating. After polishing and cleaning the cross - section of the sample, test it in the SEM - BSE mode. Randomly select more than 5 backscattered images as the test area. Use ImageJ software to black - and - white process the BSE coating at the selected gray level, and use the analysis program of the software to calculate the porosity. The average value is the porosity of the coating.

[0070] The following SiC f / SiC substrate is purchased from Northwestern Polytechnical University.

[0071] Example 1

[0072] This example provides an environmental barrier coating, which at least includes a functional layer; among them, the functional layer includes a first functional layer and a second functional layer stacked in sequence. The porosity of the second functional layer is greater than that of the first functional layer. The porosity of the first functional layer is 5%, and the thickness is 100 μm.

[0073] The porosity of the second functional layer is 15%, and the thickness is 100 μm.

[0074] The preparation method comprises the following steps:

[0075] I. Preparation of the spraying feedstock:

[0076] Preparation of the rare earth silicate spraying feedstock: Mix the powders of Y2O3, Sc2O3, Yb2O3, Lu2O3, Gd2O3, and SiO2 evenly according to the molar ratio of (Y 0.2 Yb 0.2 Sc 0.2 Gd 0.2 Lu 0.2 )2Si2O7, calcine at 1500 °C for 10 h to obtain the first material; ball-mill the above first material, adjust the ball-milling speed to 250 r / min, and run for 24 h to obtain the second material; mix the second material with deionized water to form a slurry with a solid-liquid ratio of 50 wt%, add a polyvinyl alcohol (PVA) thickener accounting for 0.8 wt% of the total slurry, and stir for 5 h to form a uniform total slurry; send the slurry to a spray granulator, set the feeding speed at 30 mL / min, the inlet temperature of the spraying drying tower at 220 °C, the outlet temperature at 120 °C, and the rotation speed at 4500 r / s to obtain spherical products; dry the spherical products in an oven at 120 °C for 12 h, put them into a crucible, keep them at 500 °C for 2 h to remove PVA, continuously heat up to 1500 °C and keep it for 2 h to compact the powder by calcination, and sieve through a 400 - 200 mesh sieve to obtain the rare earth silicate spraying feedstock. Among them, the apparent density of the rare earth silicate spraying feedstock is 1.13 g / cm 3 , and the tapped density is 1.31 g / cm 3 , and the fluidity is 62 s / 50 g.

[0077] II. Coating of the environmental barrier coating:

[0078] S1. Preparation of the silicon layer:

[0079] Load Si powder into the APS powder tank, set the distance between the spray gun and the SiC f / SiC substrate at 100 mm, the moving speed of the spray gun at 600 mm / s, the power at 37 kW, the flow rate of argon at 40 L / min, and the flow rate of hydrogen at 10 L / min to form a 50 - μm silicon layer on the surface of the substrate.

[0080] S2. Preparation of the first coating:

[0081] Load the rare earth silicate spraying feedstock into the APS powder tank, set the distance between the spray gun and the substrate at 120 mm, the moving speed of the spray gun at 600 mm / s, the power at 38 kW, the flow rate of argon at 45 L / min, and the flow rate of hydrogen at 9 L / min to form a 100 - μm first coating with a porosity of 5% on the surface of the silicon layer away from the substrate.

[0082] S3. Preparation of the second coating:

[0083] Adjust the parameters as follows: the distance between the spray gun and the substrate is 150 mm, the moving speed of the spray gun is 600 mm / s, the power is 40 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 6 liters per minute. Continue spraying on the surface of the first coating away from the silicon layer to form a second coating with a thickness of 100 μm and a porosity of 15%.

[0084] S4. Heat treatment is carried out at 1300 °C in an Ar protective atmosphere for 5 h to transform the first coating and the second coating from amorphous state to crystallization, forming the first functional layer and the second functional layer.

[0085] The above environmental barrier coating is observed by scanning electron microscopy, as Figure 1 shown, where the Si bonding layer is the silicon layer, the low-porosity layer is the first functional layer, and the high-porosity layer is the second functional layer.

[0086] Example 2

[0087] This example provides an environmental barrier coating, which at least includes a functional layer; wherein, the functional layer includes a first functional layer and a second functional layer stacked in sequence, the porosity of the second functional layer is greater than that of the first functional layer, the porosity of the first functional layer is 5%, and the thickness is 100 μm.

[0088] The porosity of the second functional layer is 10%, and the thickness is 100 μm.

[0089] Its preparation method includes the following steps

[0090] S1. Preparation of the silicon layer:

[0091] Refer to Example 1.

[0092] S2. Preparation of the first coating:

[0093] Refer to Example 1 to form a first coating with a thickness of 100 μm and a porosity of 5%.

[0094] S3. Preparation of the second coating:

[0095] Adjust the parameters as follows: the distance between the spray gun and the substrate is 130 mm, the moving speed of the spray gun is 600 mm / s, the power is 40 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 7 liters per minute. Continue spraying on the surface of the first coating away from the silicon layer to form a second coating with a thickness of 100 μm and a porosity of 10%.

[0096] S4. Heat treatment is carried out at 1300 °C in an Ar protective atmosphere for 5 h to transform the first coating and the second coating from amorphous state to crystallization, forming the first functional layer and the second functional layer.

[0097] The above environmental barrier coating was observed by scanning electron microscopy, as Figure 2 shown. Among them, the Si bonding layer is the silicon layer, the low-porosity layer is the first functional layer, and the high-porosity layer is the second functional layer.

[0098] Example 3

[0099] This example provides an environmental barrier coating, which at least includes a functional layer; among them, the functional layer includes a first functional layer and a second functional layer stacked in sequence, the porosity of the second functional layer is greater than that of the first functional layer, the porosity of the first functional layer is 8%, and the thickness is 100 μm.

[0100] The porosity of the second functional layer is 18%, and the thickness is 100 μm.

[0101] Its preparation method includes the following steps

[0102] S1. Preparation of the silicon layer:

[0103] Refer to Example 1.

[0104] S2. Preparation of the first coating:

[0105] Load the rare earth silicate spraying feed into the APS powder tank, set the distance between the spray gun and the substrate to 120 mm, the moving speed of the spray gun to 600 mm / s, the power to 38 kW, the flow rate of argon to 45 liters per minute, and the flow rate of hydrogen to 6 liters per minute, and form a first coating with a thickness of 100 μm and a porosity of 8% on the surface of the silicon layer away from the substrate.

[0106] S3. Preparation of the second coating:

[0107] Adjust the parameters as follows: the distance between the spray gun and the substrate is 150 mm, the moving speed of the spray gun is 600 mm / s, the power is 40 kW, the flow rate of argon is 45 liters per minute, and the flow rate of hydrogen is 3 liters per minute, and continue spraying on the surface of the first coating away from the silicon layer to form a second coating with a thickness of 100 μm and a porosity of 18%.

[0108] S4. Heat treatment is carried out at 1300 °C under an Ar protective atmosphere for 20 h to transform the first coating and the second coating from amorphous state to crystallization state, forming the first functional layer and the second functional layer.

[0109] The above environmental barrier coating was observed by scanning electron microscopy, as Figure 3 shown. Among them, the Si bonding layer is the silicon layer, the low-porosity layer is the first functional layer, and the high-porosity layer is the second functional layer.

[0110] Example 4

[0111] Same as Example 1, with the only difference being that the porosity of the first functional layer is 10% and the porosity of the second functional layer is 20%.

[0112] The preparation method is different from that of Example 1 in that the flow rate of the He functional gas during spraying is reduced to increase the porosity inside the coating.

[0113] Example 5

[0114] Same as Example 1, with the only difference being that the porosity of the first functional layer is 10% and the porosity of the second functional layer is 22%.

[0115] The preparation method is different from that of Example 1 in that the flow rate of the He functional gas during spraying is reduced to increase the porosity inside the coating.

[0116] Example 6

[0117] Same as Example 1, with the only difference being that the thickness of the first functional layer is 80 μm and the thickness of the second functional layer is 80 μm.

[0118] Example 7

[0119] Same as Example 1, with the only difference being that the thickness of the first functional layer is 120 μm and the thickness of the second functional layer is 120 μm.

[0120] Comparative Example 1

[0121] Same as Example 1, with the only difference being that the porosity of both the first functional layer and the second functional layer is 5%.

[0122] The preparation method is different from that of Example 1 in that the flow rate of the He functional gas during spraying is changed to change the porosity inside the coating.

[0123] Comparative Example 2

[0124] Same as Example 1, with the only difference being that the porosity of the first functional layer is 15% and the porosity of the second functional layer is 8%.

[0125] The preparation method is different from that of Example 1 in that the flow rate of the He functional gas during spraying is changed to change the porosity inside the coating.

[0126] Test Example

[0127] 1. Testing of thermal conductivity:

[0128] The thermal diffusivity of the coating was tested using a (LFA 427) type laser thermal conductivity analyzer produced by NETZSCH Germany. The test temperature range was 30 - 1350 °C. The EBC sample was sprayed on a graphite sheet, and the sample was separated from the graphite by wire cutting. The sample size of Φ12.7 mm × 1 mm was prepared by grinding and polishing. The thermal conductivity of the coating was calculated by Equation (1):

[0129] k = C p × α × ρ (1),

[0130] where k is the thermal conductivity (W·mK -1 ); α is the thermal diffusivity (cm 2 ·s -1 ); ρ is the density (g·cm -3 ); C p is the heat capacity (J·kg -1 ·K -1 ).

[0131] 2. Test of thermal expansion coefficient

[0132] A coating with a certain thickness was sprayed on the graphite surface. The coating was separated from the graphite using a diamond wire cutting machine and cut into samples of 10 mm × 4 mm × 4 mm. A thermal dilatometer (NETZSCH, DIL 402C, Germany) was used to measure the thermal expansion coefficient of the samples. The temperature range was RT - 1400 °C, and the heating rate was 5 °C / min. The linear expansion coefficient α l obtained needed to satisfy the following Equation (2):

[0133]

[0134] where α l is the linear expansion coefficient (×10 -6 ·K -1 );

[0135] l0 is the original size of the specimen (cm);

[0136] Δl is the increased length of the specimen (cm);

[0137] Δt is the temperature change (K).

[0138] 3. High temperature resistance test

[0139] A coating with a certain thickness was sprayed on the graphite surface. The coating was separated from the graphite using a diamond wire cutting machine. The prepared coating was kept in a box furnace at 1600 °C for 5 h, and XRD characterization was performed after cooling.

[0140] The test results are shown in Table 1.

[0141] Table 1

[0142] Number Thermal conductivity Coefficient of thermal expansion High temperature resistance performance Example 1 0.79 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 2 1.10 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 3 0.63 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 4 0.60 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 5 0.55 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 6 0.97 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Example 7 0.67 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Comparative example 1 1.93 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃ Comparative example 2 0.73 W / mK <![CDATA[3.5×10 -6 / °C]]> 1600℃

[0143] As can be seen from Table 1, compared with the coating without pore gradient (Comparative Example 1), the thermal conductivity in Example 1 decreased by ~54%, and that in Example 2 decreased by ~36%, demonstrating that the increase in porosity reduces the thermal conductivity of the coating. The three coatings are made of the same material, and the coefficient of thermal expansion remains unchanged at ~3.5×10 -6 / K, which is matched with the SiC f / SiC substrate.

[0144] The preferred specific embodiments of the present invention and experimental verifications have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should be within the protection scope of the present invention.

Claims

1. An environmental barrier coating, characterized in that, The environmental barrier coating at least includes a functional layer; wherein, along the thickness direction of the functional layer, the porosity of the functional layer increases or decreases successively.

2. The environmental barrier coating according to claim 1, wherein The functional layer includes a first functional layer and a second functional layer stacked in sequence, and the porosity of the second functional layer is greater than that of the first functional layer.

3. The environmental barrier coating according to claim 2, wherein, The porosity of the first functional layer is less than 10%; and / or, The porosity of the second functional layer is 10-20%.

4. The environmental barrier coating according to claim 3, wherein The thickness of the first functional layer is 50-100 μm; and / or, The thickness of the second functional layer is 50-100 μm.

5. The environmental barrier coating according to any one of claims 1-4, characterized in that, The material of the functional layer includes rare earth silicate.

6. The environmental barrier coating according to claim 5, wherein The rare earth silicate powder in the functional layer has a porous spherical structure; The size of the rare earth silicate powder is 200-400 mesh, The tap density of the rare earth silicate powder is 1.2 to 1.4 g / cm 3 , and the fluidity is (50 - 60) s / 50 g.

7. A method for applying an environmental barrier coating according to any one of claims 1-6, characterized in that, including the following steps: Spray the rare earth silicate powder on the surface of the support to form a coating with the porosity increasing or decreasing successively along the thickness direction, and heat-treat the coating to form a functional layer.

8. The coating method according to claim 7, characterized in that, Spray a first coating on the surface of the support, and then spray a second coating on the surface of the first coating away from the support; the porosity of the second coating is greater than that of the first coating; Heat-treat the first coating and the second coating to form a first functional layer and a second functional layer.

9. The coating method according to claim 8, characterized in that, During the process of spraying the first coating on the surface of the support, the distance between the spray gun and the support is 100-120 mm, the moving speed of the spray gun is 300-800 mm / s, the power of the spray gun is 38-40 kW, the flow rate of argon is 35-50 liters per minute, and the flow rate of hydrogen is 6-9 liters per minute; and / or, During the process of spraying the second coating on the surface of the first coating away from the support, the distance between the spray gun and the support is 120-150 mm, the moving speed of the spray gun is 300-800 mm / s, the power of the spray gun is 35-38 kW, the flow rate of argon is 35-50 liters per minute, and the flow rate of hydrogen is 6-9 liters per minute.

10. The coating method according to claim 8 or 9, characterized in that, The support includes a matrix material and a silicon layer located on the surface of the matrix material; The silicon layer is located between the matrix material and the functional layer; The thickness of the silicon layer is 30-100 μm.

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