A high-temperature water-oxygen corrosion resistant environmental barrier coating for SiC-based ceramics or composites thereof and a method for preparing the same

Abstract

The present application belongs to the technical field of thermal protection coating of aero-engine and gas turbine, and relates to an environmental barrier coating for resisting high-temperature water-oxygen corrosion of SiC-based ceramic or composite material and a preparation method thereof. With SiC or SiC-based composite material as a substrate, MoSi2 powder is first sprayed on the surface of the substrate by atmospheric plasma spraying, so that the Si element in MoSi2 is selectively volatilized to form a composite coating mainly composed of MoSi2 and Mo5Si3; then HfO2 powder is sprayed on the surface of the composite coating by atmospheric plasma spraying to form an HfO2 layer; and then the substrate after spraying the HfO2 layer is placed in an oxygen-containing gas atmosphere, heated to 1200-1500 DEG C for high-temperature oxygen-containing heat treatment to obtain a coating structure with three-layer structure of sacrificial layer, oxygen barrier layer and water barrier layer. The environmental barrier coating prepared by the present application has higher stability in high-temperature water-oxygen environment and higher comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection coating technology for aero-engines and gas turbines, and relates to an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Improving the thrust-to-weight ratio of aero-engines and further enhancing gas turbine efficiency both require increasing the inlet temperature of the turbine inlet. Traditional nickel-based alloys, limited by their melting points, cannot meet these higher processing requirements. Higher-temperature-resistant ceramic matrix composites are important candidate materials for the hot-end components of next-generation aero-engines and gas turbines, and are expected to further improve their operating temperature and thermal efficiency. However, non-oxide ceramic matrix composites, represented by SiC, rapidly oxidize in high-temperature water-oxygen environments to form gaseous Si(OH)4, leading to a sharp decline in performance. Applying an environmental barrier coating (EBC) to the surface of SiC ceramic matrix composites can effectively improve their service performance and extend their service life.

[0004] Currently, environmental barrier coatings (EBCs) mainly have a three-layer structure: an adhesive layer, an intermediate layer, and a topcoat. Si is a commonly used adhesive layer material. However, Si softens at around 1350℃ and melts at 1414℃, limiting the maximum operating temperature of EBCs to below 1400℃. Furthermore, the SiO2 generated from Si oxidation exhibits significant thermal expansion mismatch with the SiC ceramic matrix composite substrate, resulting in a phase transition with a volume change of approximately 5% at low temperatures. This volume change easily leads to coating peeling, limiting the service life and overall performance of the environmental barrier coating system. Adding hafnium oxide (HfO2) to the Si adhesive layer to consume the SiO2 generated from Si oxidation and form HfSiO4 can alleviate the thermal mismatch problem with the SiC substrate. However, the addition of HfO2 does not increase the operating temperature of either the Si adhesive layer or the environmental barrier coating. Moreover, HfO2 does not consume oxygen and has a high oxygen diffusion coefficient, thus its addition reduces the oxidation resistance of the adhesive layer. The intermediate layer is generally made of mullite, but mullite is not stable enough at high temperatures and the activity of Si is relatively high, which makes it easy to react with water vapor and cause Si volatilization. The outer layer is generally made of rare earth silicates, but rare earth silicates are very easy to decompose and volatilize Si components during plasma spraying, resulting in unstable phase composition. This leads to thermal mismatch stress and defects such as pores and cracks, and makes it difficult to prevent oxygen and water vapor from entering the coating and damaging the SiC substrate.

[0005] HfO2 is a high-performance refractory material with a very stable structure that does not react with high-temperature steam. However, its coefficient of thermal expansion differs significantly from that of the SiC matrix, and it exhibits considerable anisotropy, making it prone to cracking during thermal cycling. Currently, there is a lack of methods for using HfO2 alone as an environmental barrier coating. HfSiO4, formed by the reaction of HfO2 and SiO2, has a coefficient of thermal expansion very close to that of the SiC matrix and is nearly isotropic, making it a promising environmental barrier coating material. However, the preparation of HfSiO4 using atmospheric plasma spraying also faces serious decomposition problems, and its structure is relatively less stable than that of HfO2 in high-temperature water and oxygen environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion, and a method for preparing the same. The environmental barrier coating prepared by the present invention exhibits higher stability and superior overall performance in high-temperature water and oxygen environments.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] On one hand, a method for preparing an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion involves using SiC or SiC-based composites as a substrate. First, MoSi2 powder is sprayed onto the substrate surface using atmospheric plasma spraying, causing the Si element in MoSi2 to selectively volatilize and form a composite coating whose main components are MoSi2 and Mo5Si3. Then, HfO2 powder is sprayed onto the surface of the composite coating using atmospheric plasma spraying to form an HfO2 layer. Finally, the substrate after the HfO2 layer is sprayed is placed in an oxygen-containing atmosphere and heated to 1200–1500°C for high-temperature oxygen heat treatment to obtain a coating structure with a three-layer structure of a sacrificial layer, an oxygen barrier layer, and a water barrier layer, which is the environmental barrier coating.

[0009] The main phases of the sacrificial layer are MoSi2, Mo5Si3 and SiO2 glass, the main phase of the oxygen barrier layer is SiO2, and the main phases of the water barrier layer are HfO2 and HfSiO4.

[0010] In the preparation process of this invention, firstly, MoSi2 powder is sprayed onto the substrate surface using atmospheric plasma spraying, causing Si to selectively volatilize and form a composite coating mainly composed of MoSi2 and Mo5Si3. This composite coating can stably provide the required Si for subsequent high-temperature heat treatment and service processes, causing the Si element to be continuously consumed to protect the SiC substrate from corrosion, thus becoming a sacrificial layer. Secondly, in a high-temperature oxygen-containing environment, oxygen rapidly enters the internal pores of the sacrificial layer, generating SiO2 glass. The low coefficient of thermal expansion of SiO2 glass further reduces the thermal expansion rate of the MoSi2 and Mo5Si3 composite coating, making it closer to the SiC substrate and preventing coating cracking. At the same time, it can rapidly generate a slowly growing and dense SiO2 layer (i.e., an oxygen barrier layer) on the surface of the sacrificial layer, which can prevent oxygen from further penetrating the coating and the substrate. Furthermore, in a high-temperature and oxygen-rich environment, the oxygen barrier layer SiO2 and the outer layer HfO2 undergo a solid-phase reaction at high temperature to generate HfSiO4. HfSiO4 grows along the pores and cracks in the HfO2 coating to form a water-blocking layer. The formed water-blocking layer makes the structure of the outer HfO2 layer more compact and hinders the propagation of cracks in the coating, promoting crack self-healing. The outer layer, whose main components are HfO2 and HfSiO4 and whose structure is dense, can effectively block the intrusion of most water vapor.

[0011] On the other hand, an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion is obtained by the above preparation method.

[0012] Thirdly, a workpiece includes a substrate and the above-mentioned environmental barrier coating for resisting high-temperature water and oxygen corrosion of SiC-based ceramics or their composites, wherein the substrate is made of SiC or a SiC-based composite material.

[0013] Fourthly, the application of the aforementioned environmental barrier coating or workpiece in aerospace or gas turbines.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. The environmental barrier coating prepared by the present invention has a significantly improved operating temperature. Existing coatings contain elemental Si, and are limited by the melting point of Si (1414℃), so the operating temperature of the coating cannot exceed 1400℃. The environmental barrier coating provided by the present invention can theoretically be used normally below 1700℃. In particular, the present invention has completed long-term service testing at 1450℃.

[0016] 2. The outer layer (water barrier layer) of the environmental barrier coating provided by this invention uses HfO2 as the main phase and HfSiO4 is used to modify the thermal properties of HfO2. Compared with the rare earth silicate outer layer commonly used now, HfO2 has significantly better structural stability in high-temperature water and oxygen environment. During long-term use, HfSiO4 may decompose, and its decomposition products are HfO2 and SiO2. SiO2 reacts with water vapor to generate Si(OH)4 gas, and HfO2 will react with the SiO2 continuously provided by the inner layer to generate HfSiO4 until the Si in the sacrificial layer and oxygen barrier layer is consumed. This reaction mechanism greatly improves the service life of the coating in high-temperature water and oxygen environment.

[0017] 3. The atmospheric plasma spraying preparation method used in this invention has the advantages of high reliability, fast preparation speed and good adhesion. It can also be prepared using other spraying technologies such as electron beam physical vapor deposition, flame spraying, low-pressure plasma spraying, and plasma spraying physical vapor deposition, all of which are within the scope of this patent protection.

[0018] 4. This invention generates low-expansion SiO2 glass through heat treatment in a high-temperature oxygen environment, which fills the internal pores of the coating and reduces the overall thermal expansion performance of the sacrificial layer; it generates a SiO2 oxygen barrier layer, which reduces the rate of oxygen diffusion into the sacrificial layer and slows down the consumption of the sacrificial layer; it generates HfSiO4 at the interface between the oxygen barrier layer SiO2 and HfO2 and at the internal pores of HfO2, which adjusts the thermal expansion coefficient of the HfO2 layer, promotes the self-healing of the original crack, forms a dense water barrier layer, and slows down the rate of water vapor intrusion into the inner layer. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 The microstructures of the sprayed powders MoSi2(a) and HfO2(b) in the embodiments of the present invention are shown.

[0021] Figure 2 The particle size distribution diagrams of the sprayed powders MoSi2(a) and HfO2(b) in the embodiments of the present invention are shown.

[0022] Figure 3 The following are the surface microstructures of the SiC substrate after MoSi2 and HfO2 were sprayed on it in the embodiments of the present invention: (a) is the surface microstructure at low magnification, and (b) is the surface microstructure at high magnification.

[0023] Figure 4The following are X-ray diffraction analysis diagrams of the sprayed powder and the sample surface after spraying in the embodiments of the present invention: (a) MoSi2, (b) MoSi2+HfO2;

[0024] Figure 5 This is a backscattering image of the cross section of the sample after MoSi2 and HfO2 were sprayed onto the SiC substrate in an embodiment of the present invention.

[0025] Figure 6 The following are the surface micromorphologies of the sprayed samples after high-temperature heat treatment in the embodiments of the present invention: (a) surface micromorphology at low magnification before high-temperature heat treatment, (b) surface micromorphology at low magnification after high-temperature heat treatment in Example 1, (c) surface micromorphology at high magnification before high-temperature heat treatment, and (d) surface micromorphology at high magnification after high-temperature heat treatment in Example 1.

[0026] Figure 7 The XRD patterns of the sample after spraying in this embodiment of the invention are shown before and after high-temperature heat treatment.

[0027] Figure 8 This is a cross-sectional backscattering image of the sample after high-temperature heat treatment in an embodiment of the present invention;

[0028] Figure 9 The macroscopic morphology of the heat-treated sample in the embodiments of the present invention before and after high-temperature heat treatment and high-temperature water-oxygen corrosion at 1450℃ is shown in the following figures: (a) sprayed state, (b) after heat treatment for 2 hours, (c) after water-oxygen corrosion for 20 hours, (d) after water-oxygen corrosion for 50 hours, (e) after water-oxygen corrosion for 100 hours, and (f) after water-oxygen corrosion for 50 hours on the uncoated substrate surface. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] The high-temperature water-oxygen corrosion described in this invention refers to the corrosion of SiC-based ceramics and their composites in an atmosphere containing water vapor at temperatures above 1200°C. The environmental barrier coating can withstand corrosion in a water-oxygen environment at temperatures above 1450°C for at least 100 hours.

[0032] Given the poor stability of current environmental barrier coatings in high-temperature water and oxygen environments, this invention proposes an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion, and its preparation method.

[0033] A typical embodiment of the present invention provides a method for preparing an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion. Using SiC or SiC-based composites as a substrate, MoSi2 powder is first sprayed onto the substrate surface using atmospheric plasma spraying, causing the Si element in MoSi2 to selectively volatilize and form a composite coating whose main components are MoSi2 and Mo5Si3. Then, HfO2 powder is sprayed onto the surface of the composite coating using atmospheric plasma spraying to form an HfO2 layer. Finally, the substrate with the HfO2 layer sprayed is placed in an oxygen-containing atmosphere and heated to 1400–1450°C for high-temperature aerobic heat treatment, obtaining a coating structure with a sacrificial layer, an oxygen barrier layer, and a water barrier layer, which is the environmental barrier coating.

[0034] The main phases of the sacrificial layer are MoSi2, Mo5Si3 and SiO2 glass, the main phase of the oxygen barrier layer is SiO2, and the main phases of the water barrier layer are HfO2 and HfSiO4.

[0035] In some embodiments, atmospheric plasma spraying has a power of 20–40 kW, a spray distance of 70–150 mm, and a spraying speed of 90–120 mm / min.

[0036] In some embodiments, the spraying current for atmospheric plasma spraying of MoSi2 powder is 700–840 A and the voltage is 35–40 V.

[0037] In some embodiments, the powder feed rate for atmospheric plasma spraying of MoSi2 powder is 0.5 to 4.0 rpm.

[0038] In some embodiments, the main gas pressure, auxiliary gas pressure, and carrier gas pressure for atmospheric plasma spraying of MoSi2 powder are 53–57 psig, 28–32 psig, and 33–37 psig, respectively.

[0039] In some embodiments, when atmospheric plasma spraying is used to coat MoSi2 powder, the spray distance is set to 80-100 mm and the spraying speed is set to 100-120 mm / min.

[0040] Studies have shown that when using atmospheric plasma spraying to coat MoSi2 powder, any of the above conditions can better enable the selective volatilization of Si in MoSi2; when all of the above conditions are used in combination, the resulting environmental barrier coating has better resistance to high-temperature water and oxygen corrosion.

[0041] In some embodiments, the spraying current for atmospheric plasma spraying of HfO2 powder is 800–840 A.

[0042] In some embodiments, the powder feeding rate for atmospheric plasma spraying of HfO2 powder is 1.0 to 2.0 rpm.

[0043] In some embodiments, the main gas pressure, auxiliary gas pressure, and carrier gas pressure for atmospheric plasma spraying of HfO2 powder are 53–57 psig, 28–32 psig, and 33–37 psig, respectively.

[0044] In some embodiments, when atmospheric plasma spraying is used to coat HfO2 powder, the spray distance is set to 78-82 mm and the spraying speed is set to 108-112 mm / min.

[0045] Studies have shown that when using atmospheric plasma spraying of HfO2 powder, adopting any of the above conditions can better control the thickness of the HfO2 layer, thereby better producing a three-layer coating structure of sacrificial layer, oxygen barrier layer and water barrier layer in combination with subsequent high temperature and oxygen heat treatment; when all the above conditions are adopted, the environmental barrier coating obtained has better resistance to high temperature water and oxygen corrosion.

[0046] In some embodiments, the temperature of the high-temperature aerobic heat treatment is 1400–1450°C.

[0047] In some embodiments, the atmosphere for high-temperature oxygen-containing heat treatment is air.

[0048] In some embodiments, the atmosphere for high-temperature oxygen-containing heat treatment is a mixture of Ar and O2.

[0049] In some embodiments, the atmosphere for high-temperature oxygen-containing heat treatment is a mixture of O2 and water vapor.

[0050] In some embodiments, the high-temperature aerobic heat treatment time is 1 to 50 hours, preferably 1 to 10 hours.

[0051] In some embodiments, the particle size distribution of MoSi2 powder is between 30 and 125 μm, and the average particle size of MoSi2 powder is 75 to 80 μm.

[0052] In some embodiments, the particle size distribution of HfO2 powder is between 30 and 125 μm, and the average particle size of HfO2 powder is 65 to 70 μm.

[0053] In some embodiments, before spraying the substrate, the substrate is first sandblasted, then cleaned and dried. Specifically, the sandblasting process uses a mixture of corundum powder and diamond micron powder. More specifically, the particle size of the corundum powder is 150–250 mesh. More specifically, the particle size of the diamond micron powder is 0.2–0.4 mm. Specifically, the sandblasting pressure is 0.35–0.45 MPa.

[0054] Another embodiment of the present invention provides an environmental barrier coating for SiC-based ceramics or their composites that resists high-temperature water and oxygen corrosion, obtained by the above preparation method.

[0055] In some embodiments, the total thickness of the environmental barrier coating is 50–150 μm.

[0056] In some embodiments, the thickness of the sacrificial layer is 30–80 μm, the thickness of the oxygen barrier layer is 0.5–30 μm, and the thickness of the water barrier layer is 5–50 μm.

[0057] A third embodiment of the present invention provides a workpiece comprising a substrate and the above-mentioned environmental barrier coating for resisting high-temperature water and oxygen corrosion of SiC-based ceramics or their composites, wherein the substrate is made of SiC or a SiC-based composite material.

[0058] A fourth embodiment of the present invention provides an application of the above-mentioned environmental barrier coating or workpiece in aerospace or gas turbines.

[0059] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0060] Example 1

[0061] A method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites, comprising the following steps:

[0062] (1) Using SiC as the substrate, the substrate was treated with a mixture of 200-mesh corundum powder and 0.3mm diamond micro powder before spraying. The substrate was sandblasted with a sandblasting pressure of 0.4MPa to make the surface of each area of ​​the substrate reach a roughness visible to the naked eye. After sandblasting, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 15min, and then dried at 80℃ for 6h.

[0063] (2) The substrate treated in step (1) was sequentially subjected to atmospheric plasma spraying of MoSi2 powder and HfO2 powder using a 3710 plasma spraying system manufactured by Praxair, USA. For MoSi2 spraying, a spraying current of 830A was used, the powder feed rate was set to 2.5 rpm, the pressures of the main gas, auxiliary gas, and carrier gas were set to 55, 30, and 35 psig, respectively, the spray distance was set to 90 mm, and the spraying speed was set to 110 mm / min. For HfO2 spraying, the process settings were: spraying current of 830A, powder feed rate of 1.5 rpm, pressures of the main gas, auxiliary gas, and carrier gas of 55, 30, and 35 psig, respectively, the spray distance of 80 mm, and the spraying speed of 110 mm / min.

[0064] (3) Heat the temperature inside the high-temperature tube furnace to 1450℃, then put in the specimen after spraying in step (2), heat treat for 10 hours, and then cool to room temperature.

[0065] The microstructures of the MoSi2 powder and HfO2 powder used in step (2) are as follows: Figure 1 As shown, its shape is irregular. The particle size distribution of MoSi2 powder and HfO2 powder is between 30 and 125 μm, with an average particle size of 77.7 μm for MoSi2 and 67.3 μm for HfO2. Figure 2 As shown. The powder was dried at 80℃ for 12 hours to ensure good flowability.

[0066] After step (2), the coating surface spreads well, but there are a few unmelted particles, pores, and microcracks, such as Figure 3 As shown. After X-ray diffraction analysis, after step (2) of spraying MoSi2 powder, the coating mainly contains two structures: MoSi2 phase and Mo5Si3 phase, forming Mo5Si3 phase. After spraying HfO2, only HfO2 phase is visible on the coating surface, indicating that the HfO2 phase is stable during plasma spraying. Figure 4 As shown. Step (2) The coating after spraying is divided into two layers. The inner layer is mainly composed of loosely structured MoSi2 with a thickness of about 50 μm, and the outer layer is an HfO2 layer with a thickness of about 15 μm, as shown. Figure 5 As shown.

[0067] After the high-temperature heat treatment in step (3), a two-phase structure appears on the coating surface, and cracks and pores are filled, resulting in effective densification of the structure, such as... Figure 6 As shown. X-ray diffraction analysis revealed that the two-phase microstructure of the coating surface after high-temperature heat treatment was HfO2 and HfSiO4, respectively. Figure 7 As shown. Figure 8As shown, after the high-temperature heat treatment in step (3), the coating cross section becomes a three-layer structure, which consists of a water barrier layer, an oxygen barrier layer and a sacrificial layer from top to bottom. The water barrier layer is mainly composed of HfO2 and HfSiO4, the oxygen barrier layer is mainly composed of SiO2, and the sacrificial layer is composed of MoSi2, Mo5Si3 and SiO2 glass.

[0068] The coating after high-temperature heat treatment in step (3) is placed in a high-temperature furnace at 1450℃. A fluid water-oxygen atmosphere of 90% H2O + 10% O2 is introduced. Ar and O2 mixed gas is introduced into water at 80℃. The collected gas is introduced into a tube furnace. The flow rate of Ar gas is 800 mL / min and the flow rate of O2 gas is 100 mL / min.

[0069] like Figure 9 As shown, after high-temperature heat treatment, the surface color of the coating turns white. After water and oxygen corrosion, the surface changes little, and the coating maintains good adhesion. Compared with the SiC substrate surface without an environmental barrier coating, the coating is effectively protected.

[0070] Example 2

[0071] A method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites, comprising the following steps:

[0072] (1) Using SiC as the substrate, the substrate was treated with a mixture of 200-mesh corundum powder and 0.3mm diamond micro powder before spraying. The substrate was sandblasted with a sandblasting pressure of 0.4MPa to make the surface of each area of ​​the substrate reach a roughness visible to the naked eye. After sandblasting, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 15min, and then dried at 80℃ for 6h.

[0073] (2) The substrate treated in step (1) was sequentially coated with MoSi2 powder and HfO2 powder using a 3710 plasma spraying system manufactured by Praxair, USA. For MoSi2 spraying, a spraying current of 830A was used, the powder feed rate was set to 2.5 rpm, the pressures of the main gas, auxiliary gas, and carrier gas were set to 55, 30, and 35 psig, respectively, the spray distance was set to 80 mm, and the spraying speed was set to 110 mm / min. For HfO2 spraying, the process settings were: spraying current of 830A, powder feed rate of 1.5 rpm, pressures of the main gas, auxiliary gas, and carrier gas of 55, 30, and 35 psig, respectively, the spray distance of 80 mm, and the spraying speed of 110 mm / min.

[0074] (3) Heat the temperature inside the high-temperature tube furnace to 1450℃, then put in the specimen after spraying in step (2), heat treat for 10 hours, and then cool to room temperature.

[0075] Depend on Figure 4The results show that when the spraying distance of the MoSi2 powder in step (2) is smaller, the peak height of the Mo5Si3 phase is significantly higher, indicating that the energy of the plasma torch is more concentrated at this time, the volatilization of Si in MoSi2 is more intense, and more Mo5Si3 phase is generated. Therefore, the content of Mo5Si3 phase in the final coating structure can be changed by adjusting the spraying distance or adjusting the spraying power, thereby adjusting the coating performance.

[0076] Example 3

[0077] A method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites, comprising the following steps:

[0078] (1) Using SiC as the substrate, the substrate was treated with a mixture of 200-mesh corundum powder and 0.3mm diamond micro powder before spraying. The substrate was sandblasted with a sandblasting pressure of 0.4MPa to make the surface of each area of ​​the substrate reach a roughness visible to the naked eye. After sandblasting, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 15min, and then dried at 80℃ for 6h.

[0079] (2) The substrate treated in step (1) was sequentially subjected to atmospheric plasma spraying of MoSi2 powder and HfO2 powder using a 3710 plasma spraying system manufactured by Praxair, USA. For MoSi2 spraying, a spraying current of 830A was used, the powder feed rate was set to 2.5 rpm, the pressures of the main gas, auxiliary gas, and carrier gas were set to 55, 30, and 35 psig, respectively, the spray distance was set to 90 mm, and the spraying speed was set to 110 mm / min. For HfO2 spraying, the process settings were: spraying current of 830A, powder feed rate of 1.5 rpm, pressures of the main gas, auxiliary gas, and carrier gas of 55, 30, and 35 psig, respectively, the spray distance of 80 mm, and the spraying speed of 110 mm / min.

[0080] (3) The temperature inside the high-temperature tube furnace is raised to 1400℃, and a mixture of 70% Ar + 30% O2 gas is introduced. Then the specimen after spraying in step (2) is placed in the furnace and heat-treated for 50 hours. Then the specimen is taken out and cooled to room temperature.

[0081] Example 4

[0082] A method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites, comprising the following steps:

[0083] (1) Using SiC as the substrate, the substrate was treated with a mixture of 200-mesh corundum powder and 0.3mm diamond micro powder before spraying. The substrate was sandblasted with a sandblasting pressure of 0.4MPa to make the surface of each area of ​​the substrate reach a roughness visible to the naked eye. After sandblasting, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 15min, and then dried at 80℃ for 6h.

[0084] (2) The substrate treated in step (1) was sequentially coated with MoSi2 powder and HfO2 powder using a 3710 plasma spraying system manufactured by Praxair, USA. For MoSi2 spraying, a spraying current of 830A was used, the powder feed rate was set to 2.5 rpm, the pressures of the main gas, auxiliary gas, and carrier gas were set to 55, 30, and 35 psig, respectively, the spray distance was set to 90 mm, and the spraying speed was set to 110 mm / min. For HfO2 spraying, the process settings were: spraying current of 830A, powder feed rate of 1.0 rpm, pressures of the main gas, auxiliary gas, and carrier gas of 55, 30, and 35 psig, respectively, the spray distance of 80 mm, and the spraying speed of 110 mm / min.

[0085] (3) Raise the temperature inside the high-temperature tube furnace to 1450℃, introduce a mixed gas of 90% H2O + 10% O2, and then place the specimen after spraying in step (2) into the furnace. Heat treat for 1 hour and then cool to room temperature.

[0086] Example 5

[0087] A method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites, comprising the following steps:

[0088] (1) Using SiC as the substrate, the substrate was treated with a mixture of 200-mesh corundum powder and 0.3mm diamond micro powder before spraying. The substrate was sandblasted with a sandblasting pressure of 0.4MPa to make the surface of each area of ​​the substrate reach a roughness visible to the naked eye. After sandblasting, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 15min, and then dried at 80℃ for 6h.

[0089] (2) The substrate treated in step (1) was sequentially subjected to atmospheric plasma spraying of MoSi2 powder and HfO2 powder using a 3710 plasma spraying system manufactured by Praxair, USA. For MoSi2 spraying, a spraying current of 830A was used, the powder feed rate was set to 2.5 rpm, the pressures of the main gas, auxiliary gas, and carrier gas were set to 55, 30, and 35 psig, respectively, the spray distance was set to 90 mm, and the spraying speed was set to 110 mm / min. For HfO2 spraying, the process settings were: spraying current of 830A, powder feed rate of 1.5 rpm, pressures of the main gas, auxiliary gas, and carrier gas of 55, 30, and 35 psig, respectively, the spray distance of 80 mm, and the spraying speed of 110 mm / min.

[0090] (3) Heat the temperature inside the high-temperature tube furnace to 1450℃, then put in the specimen after spraying in step (2), heat treat for 20 hours, and then cool to room temperature.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing an environmental barrier coating for high-temperature water-oxygen corrosion resistance of SiC-based ceramics or composites thereof, characterized by, Using SiC or SiC-based composite materials as the substrate, MoSi2 powder is first sprayed onto the substrate surface using atmospheric plasma spraying, causing the Si element in MoSi2 to selectively volatilize and form a composite coating with MoSi2 and Mo5Si3 as the main components. Then, HfO2 powder is sprayed onto the surface of the composite coating using atmospheric plasma spraying to form an HfO2 layer. The substrate after the HfO2 layer is sprayed is then placed in an oxygen-enriched gas atmosphere and heated to 1400-1450°C for high-temperature oxygen-enriched heat treatment to obtain a coating structure with a three-layer structure of sacrificial layer, oxygen barrier layer, and water barrier layer, which is the environmental barrier coating. The main phases of the sacrificial layer are MoSi2, Mo5Si3 and SiO2 glass, the main phase of the oxygen barrier layer is SiO2, and the main phases of the water barrier layer are HfO2 and HfSiO4.

2. The method for producing an environmental barrier coating against high-temperature water-oxygen corrosion of SiC-based ceramics or composites thereof according to Claim 1, characterized by, The spraying current for atmospheric plasma spraying of MoSi2 powder is 700–840 A. Alternatively, the powder feeding rate for atmospheric plasma spraying of MoSi2 powder is 0.5–4.0 rpm; Alternatively, the main gas pressure, auxiliary gas pressure, and carrier gas pressure of atmospheric plasma spraying MoSi2 powder are 53-57 psig, 28-32 psig, and 33-37 psig, respectively. Alternatively, atmospheric plasma spraying can be used to coat MoSi2 powder, with the spray distance set to 80–100 mm and the spraying speed set to 100–120 mm / min.

3. The method for producing an environmental barrier coating against high-temperature water-oxygen corrosion of SiC-based ceramics or composites thereof according to Claim 1, characterized by, The spraying current for atmospheric plasma spraying of HfO2 powder is 700–840 A; Alternatively, the powder feeding rate for atmospheric plasma spraying of HfO2 powder is 1.0–2.0 rpm; Alternatively, the main gas pressure, auxiliary gas pressure, and carrier gas pressure of HfO2 powder can be 53–57 psig, 28–32 psig, and 33–37 psig, respectively, when using atmospheric plasma spraying. Alternatively, atmospheric plasma spraying can be used to coat HfO2 powder, with the spray distance set to 78–82 mm and the spraying speed set to 108–112 mm / min.

4. The method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites as described in claim 1, characterized in that, The atmosphere for high-temperature aerobic heat treatment is air, a mixture of Ar and O2, or a mixture of water vapor and oxygen, and the temperature is 1400-1450℃. Alternatively, the high-temperature aerobic heat treatment time is 1 to 50 hours.

5. The method for producing an environmental barrier coating against high-temperature water-oxygen corrosion of SiC-based ceramics or composites thereof according to Claim 1, characterized by, The particle size distribution of MoSi2 powder is between 30 and 125 μm, and the average particle size of MoSi2 powder is 75 to 80 μm. Alternatively, the particle size distribution of HfO2 powder is between 30 and 125 μm, and the average particle size of HfO2 powder is 65 to 70 μm.

6. The method for preparing an environmental barrier coating resistant to high-temperature water and oxygen corrosion for SiC-based ceramics or their composites as described in claim 1, characterized in that, Before spraying the substrate, the substrate is first sandblasted, then cleaned and dried.

7. An environmental barrier coating for SiC-based ceramics or composites thereof, which is resistant to high-temperature water-oxygen corrosion, characterized in that, Obtained by the preparation method described in any one of claims 1 to 6.

8. The environmental barrier coating for SiC-based ceramics or composites thereof against high temperature water vapor corrosion according to claim 7, characterized in that The total thickness of the environmental barrier coating is 50–150 μm; Alternatively, the sacrificial layer thickness is 30–80 μm, the oxygen barrier layer thickness is 0.5–30 μm, and the water barrier layer thickness is 5–50 μm.

9. A workpiece characterized by, It includes a substrate and an environmental barrier coating for resisting high-temperature water and oxygen corrosion for SiC-based ceramics or their composites as described in claim 7 or 8, wherein the substrate is made of SiC or a SiC-based composite material.

10. Use of an environmental barrier coating according to claim 7 or 8 or a workpiece according to claim 9 in aerospace or gas turbine.

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