A mullite / rare earth silicate integrated environmental barrier coating and a preparation method and application thereof

Abstract

This invention discloses an integrated mullite / rare earth silicate environmental barrier coating, its preparation method, and its application, belonging to the field of coating preparation technology. The environmental barrier coating is deposited on a C / C composite substrate, and from the surface of the C / C composite substrate outwards, consists of a SiC bonding layer, a mullite intermediate layer, and a rare earth silicate composite surface layer; the rare earth silicate composite surface layer is RE2SiO5-RE2Si2O7-RE3Al5O 12 RE can be Yb, Y, or Lu. The mullite intermediate layer and rare earth silicate composite surface layer are prepared by mixing SiC oxide powder with Al2O3 powder and RE2SiO5 powder with Al2O3 powder, respectively, into two slurries. These slurries are then applied layer by layer to the surface of the SiC bonding layer and dried, followed by in-situ heat treatment to form the composite layer. An in-situ reaction at the interface between the mullite intermediate layer and the rare earth silicate composite surface layer creates a component transition zone, exhibiting a multiphase structure where rare earth dual silicate phases are dispersed within the mullite framework. This environmental barrier coating addresses the technical problem of weak interlayer bonding and easy cracking during thermal cycling in existing coatings.

Description

Technical Field

[0001] This invention belongs to the field of coating preparation technology, specifically relating to an integrated mullite / rare earth silicate environmental barrier coating, its preparation method, and its application. Background Technology

[0002] Ceramic matrix composites (such as C / C, C / SiC, and SiC / SiC) have become ideal materials for hot-end components of next-generation aero-engines and gas turbines due to their low density, high specific strength, and excellent high-temperature stability. However, in high-temperature gas environments (especially those containing water vapor and molten salt), these materials are prone to oxidation and volatilization corrosion, leading to a sharp degradation in performance. To address this issue, environmental barrier coatings (EBCs) are typically applied to their surfaces to isolate them from corrosive media.

[0003] Currently, mainstream environmental barrier coating systems include a Si binder layer, a mullite intermediate layer, and a rare earth silicate top layer (such as Yb₂Si₂O₇, Y₂Si₂O₇, etc.). For example, Chinese invention patent application CN106435443A discloses the preparation of Si / mullite / Yb₂SiO₅ coatings using plasma spraying-physical vapor deposition, but this process requires multiple depositions and has poor thermal matching between coatings; Chinese invention patent application CN110983233A proposes a Si / mullite / rare earth silicate multilayer environmental barrier coating. Although this patent improves the matching of thermal expansion coefficients by adjusting the rare earth double silicate content in the top layer of the environmental barrier, the atmospheric plasma spraying technology it uses results in significant thermal stress within the coating due to the excessively fast cooling rate, which easily leads to microcrack propagation during thermal cycling. For example, Chinese invention patent application CN106747670A discloses an environmental barrier coating for multi-component carbon and ceramic matrix composite materials and its preparation method. However, the functional layers are physically stacked at the interface, lacking chemical and metallurgical bonding. This leads to significant abrupt changes in the coefficient of thermal expansion at the interface, making it highly susceptible to interlayer delamination failure due to thermal mismatch stress concentration during high-temperature thermal cycling. Therefore, developing an integrated environmental barrier coating structure with strong interfacial bonding and excellent thermal shock resistance is crucial. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide an integrated mullite / rare earth silicate environmental barrier coating, its preparation method and application, to solve the technical problem of weak interlayer bonding and easy cracking during thermal cycling of existing coatings.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention provides an integrated mullite / rare earth silicate environmental barrier coating, wherein the environmental barrier coating is disposed on a C / C composite substrate, and from the surface of the C / C composite substrate outwards, it consists of a SiC adhesive layer, a mullite intermediate layer, and a rare earth silicate composite surface layer; the rare earth silicate composite surface layer is RE2SiO5-RE2Si2O7-RE3Al5O 12 RE can be Yb, Y, or Lu; Among them, the mullite intermediate layer and rare earth silicate composite surface layer are prepared by two slurries, namely SiC oxide powder and Al2O3 powder, and RE2SiO5 powder and Al2O3 powder, respectively. They are then coated layer by layer on the surface of SiC bonding layer and dried, and then generated in situ through integrated heat treatment. An in-situ reaction forms a compositional transition zone at the interface between the mullite intermediate layer and the rare earth silicate composite surface layer. The compositional transition zone exhibits a multiphase structure in which rare earth dual silicate phases are dispersed in the mullite framework.

[0006] In one embodiment, the thickness of the SiC adhesive layer is 50-100 μm, the thickness of the mullite intermediate layer is 50-100 μm, and the thickness of the rare earth silicate composite surface layer is 150-200 μm.

[0007] This invention also provides a method for preparing an integrated mullite / rare earth silicate environmental barrier coating, comprising the following steps: S1, SiC powder is oxidized, and then the oxidized SiC powder, Al2O3 powder, silica sol binder, and deionized water solvent are magnetically stirred and mixed to prepare slurry 1; RE2SiO5 powder, Al2O3 powder, silica sol binder, and deionized water solvent are magnetically stirred and mixed to prepare slurry 2. S2, slurry 1 and slurry 2 are sequentially applied to the surface of the SiC bonding layer, and then dried to form a multi-layer environmental barrier pre-coating layer; S3. In an argon atmosphere, the multi-layer environmental barrier pre-coating is subjected to integrated heat treatment to obtain a mullite / rare earth silicate integrated environmental barrier coating.

[0008] In one embodiment, the SiC powder has an average particle size of 3 μm, the RE2SiO5 powder has an average particle size of 10 μm, and the Al2O3 powder has an average particle size of 300 nm.

[0009] In one embodiment, the weight ratio of SiC oxide powder, Al2O3 powder, silica sol binder and deionized water solvent in the slurry 1 is (5~6):1:(2~4):(8~11).

[0010] In one embodiment, the weight ratio of RE2SiO5 powder, Al2O3 powder, silica sol binder and deionized water solvent in the slurry 2 is (20~30):1:(8~12):(30~40).

[0011] In one embodiment, the ratio of the number of coating layers of slurry 1 to slurry 2 is (8-13):(15-20).

[0012] In one embodiment, the drying process is carried out at a temperature of 60-80 °C for 12-24 h.

[0013] In one embodiment, the integrated heat treatment temperature is 1500-1530℃, and the holding time is 2 hours.

[0014] This invention also provides an application of an integrated mullite / rare earth silicate environmental barrier coating in hot-end components of aero engines or gas turbines.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an integrated mullite / rare earth silicate environmental barrier coating system. This coating system features a gradient interface, achieving a seamless transition of the coating structure from the substrate to the surface. By sequentially coating a SiO2-Al2O3 intermediate pre-coating and a RE2SiO5-Al2O3 environmental barrier pre-coating onto the surface of the SiC binder layer, and then undergoing an integrated heat treatment process, the coating system is transformed in situ from the inside out into a SiC binder layer, a mullite intermediate layer, and a RE2Si2O7-RE2SiO5-RE3AlO3 layer. 12 Environmental barrier layer. This process avoids the porosity and microcrack defects generated during traditional thermal spraying, significantly improving the bonding strength and density between the coating and the substrate, and between the coatings themselves, allowing the coating to maintain good integrity even in a high-temperature water-oxygen corrosion environment of 1400℃. Secondly, the intermediate layer design of this invention effectively balances thermal compatibility and chemical stability. In this invention, SiC powder is pre-oxidized to generate SiO2 glass in the intermediate layer slurry, and then reacted with Al2O3 to generate mullite phase. This not only ensures good thermal expansion compatibility of the intermediate layer, preventing structural failure at high temperatures, but also allows the residual SiO2 to form a stable chemical bond with RE2SiO5 generated in the surface layer during high-temperature service, effectively mitigating the risk of interface cracking and delamination caused by differences in thermal expansion coefficients. Thirdly, the environmental barrier layer of this invention achieves synergistic optimization of corrosion resistance and thermal insulation performance. This surface layer uses RE2SiO5 and Al2O3 as raw materials, and RE2SiO5 and RE3Al5O3 are generated in situ through argon heat treatment. 12 Multiphase. Among them, RE3Al5O 12The phase has low thermal conductivity and excellent resistance to water and oxygen corrosion, which can significantly reduce the operating temperature of hot-end components and extend the protection life; the RE2SiO5 phase further improves the coating's resistance to CMAS (calcium magnesium aluminum silicate) and water vapor erosion, solving the technical problem of the single protective function of traditional single coatings.

[0016] The preparation method of this invention is simple and efficient, possessing significant economic and technical advantages. This integrated intermediate and top-layer preparation process eliminates the steps of stepwise deposition and multiple high-temperature treatments, reducing the damage to the coating's microstructure caused by process thermal history. Simultaneously, due to the compositional transition at the interface, thermal stress can be gradually released during thermal cycling, achieving a certain degree of self-healing effect. This significantly improves the service reliability and lifespan of C / C composite materials in hot-end components of aero-engines and gas turbines. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing an integrated mullite / rare earth silicate environmental barrier coating provided by the present invention; Figure 2 Here are the SEM images of the coating prepared in Example 3 of this invention: (a) XRD pattern of the coating; (b) coating surface; (c) coating cross section; (d) energy dispersive spectroscopy (EDS) results; Figure 3 This is a SEM image of the coating surface of SiC powder 1 in slurry 1 after oxidation at 1100 ℃ for 6 h, which is Comparative Example 1. Figure 4 This is a SEM image of the coating after SiC powder was oxidized at 1100 ℃ for 4 h and then subjected to an integrated heat treatment at 1550 ℃ (Comparative Example 2). Figure 5 This is a SEM image of the coating after SiC powder was oxidized at 1100 ℃ for 1 h and then subjected to an integrated heat treatment at 1480 ℃ (Comparative Example 2). Detailed Implementation

[0018] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0019] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0020] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0021] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0022] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0023] This invention provides an integrated mullite / rare earth silicate environmental barrier coating and its preparation method. It innovatively proposes an integrated design for preparing a mullite intermediate layer and a rare earth silicate composite top layer: by optimizing the slurry composition and heat treatment process, the intermediate layer and the top layer achieve a component transition during the formation process, effectively relieving thermal stress; this integrated structure avoids the interface defects of traditional multilayer coatings, and significantly enhances the thermal shock resistance life of the coating while ensuring resistance to water and oxygen corrosion.

[0024] This invention provides an integrated mullite / rare earth silicate environmental barrier coating. The environmental barrier coating is disposed on a C / C composite substrate and includes, from the inside out, a SiC bonding layer, a mullite intermediate layer, and a rare earth silicate composite surface layer. The mullite intermediate layer and the rare earth silicate composite surface layer are prepared by a slurry coating combined with an integrated heat treatment process. There is a component transition zone at the interface, which presents a multiphase structure in which rare earth dual silicate phases are dispersed in the mullite framework.

[0025] The thickness of the embedded SiC bonding layer is 50-100 μm, the thickness of the mullite intermediate layer is 50-100 μm, and the rare earth silicate surface layer is RE2SiO5-RE2Si2O7-RE3Al5O 12 The thickness of the rare earth silicate composite surface layer is 150-200 μm.

[0026] like Figure 1 As shown, this invention provides a method for preparing an integrated mullite / rare earth silicate environmental barrier coating. The aforementioned integrated mullite / rare earth silicate environmental barrier coating is prepared using a slurry coating combined with integrated heat treatment technology. The preparation method includes the following steps: (1) The SiC powder is oxidized, and then the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent are magnetically stirred and mixed to prepare slurry 1; and RE2SiO5 powder, Al2O3 powder, silica sol binder and deionized water solvent are magnetically stirred and mixed to prepare slurry 2. (2) Apply slurry 1 and slurry 2 sequentially to the surface of the embedded SiC bonding layer, and then dry it to form a multi-layer environmental barrier pre-coating layer; (3) In an argon atmosphere, the coated sample is subjected to integrated heat treatment, so that the SiO2 glass in slurry 1 reacts with Al2O3 to form a mullite intermediate layer, and the RE2SiO5 in slurry 2 reacts with Al2O3 to form RE2Si2O7-RE2SiO5-RE3Al5O 12 Composite surface layer.

[0027] In step (1), the average particle size of the SiC powder is 3 μm, the average particle size of the RE2SiO5 powder is 10 μm, and the average particle size of the Al2O3 is 300 nm.

[0028] In step (1), the SiC powder is oxidized to form SiO2 glass at an oxidation temperature of 1100 ℃ for 2-5 h in an air atmosphere.

[0029] In step (1), the weight ratio of SiC oxide powder, Al2O3 powder, silica sol binder and deionized water solvent in slurry 1 is (5~6):1:(2~4):(8~11); the weight ratio of RE2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in slurry 2 is (20~30):1:(8~12):(30~40).

[0030] In step (1), the magnetic stirring time of slurry 1 and slurry 2 is 2-6 h.

[0031] In step (2), the number of coating layers of slurry 1 and slurry 2 are 8-13 and 15-20 respectively, and the ratio of the number of coating layers of slurry 1 to slurry 2 is (8-13):(15-20). The drying temperature is 60-80 ℃ and the drying time is 12-24 h.

[0032] In step (3), the integrated heat treatment temperature of the mullite intermediate layer and the rare earth silicate surface layer is 1500-1530℃, and the heat treatment time is 2 h.

[0033] like Figure 1As shown, this invention employs a slurry coating combined with integrated heat treatment technology to prepare an integrated environmental barrier coating of mullite / rare earth silicate on the surface of a C / C composite material with an embedded SiC binder layer. First, oxidized SiC powder and Al2O3 powder, as well as RE2SiO5 and Al2O3, are prepared into slurry 1 and slurry 2, respectively. Then, slurry 1 and slurry 2 are sequentially coated onto the surface of the embedded SiC binder layer and dried to form an environmental barrier pre-coating. Subsequently, by adjusting the integrated heat treatment process, the oxidized SiC reacts with Al2O3 to form a mullite intermediate layer, while RE2SiO5 reacts with Al2O3 to form RE2SiO7-RE2SiO5-RE3Al5O7. 12 Composite surface layer. At the interface between the mullite intermediate layer and the rare earth silicate composite surface layer, an in-situ reaction forms a compositional transition zone, which exhibits a multiphase structure in which rare earth bisilicate phases are dispersed in the mullite framework.

[0034] In one specific implementation, the specific steps are as follows: Step 1: Oxidize SiC powder in air at 1100 ℃ for 2-5 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of (5~6):1:(2~4):(8~11), and prepare slurry 1 by magnetic stirring for 2-6 h. Step 2: Weigh RE2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of (20~30):1:(8~12):(30~40), and prepare slurry 2 by magnetic stirring for 2-6 h. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 to be 8-13 layers and 15-20 layers respectively, and then dry in an oven at 60-80 ℃ for 12-24 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC binder C / C composite material with environmental barrier pre-coating is heat-treated in an argon atmosphere at 1500-1530 ℃ for 2 h to obtain a mullite interlayer with a thickness of 50-100 μm and a RE2Si2O7-RE2SiO5-RE3Al5O3 layer with a thickness of 150-200 μm. 12 Rare earth silicate composite surface layer.

[0035] The C / C composite material with an embedded SiC binder layer is prepared by the following method: First, the C / C composite material was polished with 400-grit sandpaper, ultrasonically cleaned with alcohol-free ethanol for 0.5 h, and dried at 70℃ for later use. Second, the embedding powder was mixed: Si powder and C powder were weighed at a weight ratio of 80:20 and mixed in a horizontal ball mill for 7 h to obtain the embedding powder. Finally, the C / C composite material was embedded in the mixed embedding powder and kept at 2100℃ in an argon atmosphere for 2 h. During the heat preservation process, the Si in the embedding powder reacted with the C matrix on the surface of the C / C composite material to prepare the SiC bonding layer.

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] Example 1: Step 1: Oxidize SiC powder in air at 1100 °C for 2 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 5:1:4:8, and stir magnetically for 2 h to prepare slurry 1. Step 2: Weigh Y2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 20:1:8:30, and prepare slurry 2 by magnetic stirring for 2 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 8 and 20 layers respectively, and then dry in an oven at 60 ℃ for 24 h to obtain an environmental barrier pre-coating. Step 4: The embedded SiC binder C / C composite material with an environmental barrier pre-coating was heat-treated in an argon atmosphere at 1500 ℃ for 2 h to obtain a mullite interlayer with a thickness of approximately 50 μm and a Y2Si2O7-Y2SiO5-Y3Al5O3 layer with a thickness of approximately 200 μm. 12 Rare earth silicate composite surface layer.

[0039] Example 2: Step 1: Oxidize SiC powder in air at 1100 °C for 5 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 6:1:2:11, and stir magnetically for 6 h to prepare slurry 1. Step 2: Weigh Lu2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 30:1:12:40, and prepare slurry 2 by magnetic stirring for 6 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 13 and 15 layers respectively, and then dry in an oven at 80 ℃ for 12 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC binder C / C composite material with environmental barrier pre-coating was heat-treated in an argon atmosphere at 1530 ℃ for 2 h to obtain a 100 μm thick mullite interlayer and a 150 μm thick Lu2Si2O7-Lu2SiO5-Lu3Al5O3 interlayer. 12 Rare earth silicate composite surface layer.

[0040] Example 3: Step 1: Oxidize SiC powder in air at 1100 °C for 4 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 5.5:1:3:10, and stir magnetically for 4 h to prepare slurry 1. Step 2: Weigh Yb2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 25:1:10:35, and prepare slurry 2 by magnetic stirring for 4 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 10 and 18 layers respectively, and then dry in an oven at 70 ℃ for 18 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC binder C / C composite material with an environmental barrier pre-coating was heat-treated in an argon atmosphere at 1520 ℃ for 2 h to obtain a 75 μm thick mullite interlayer and a 175 μm thick Yb2Si2O7-Yb2SiO5-Yb3Al5O3 layer. 12 Rare earth silicate composite surface layer.

[0041] Comparative Example 1: Step 1: Oxidize SiC powder in air at 1100 °C for 6 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 5.5:1:3:10, and stir magnetically for 4 h to prepare slurry 1. Step 2: Weigh Yb2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 25:1:10:35, and prepare slurry 2 by magnetic stirring for 4 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 10 and 18 layers respectively, and then dry in an oven at 70 ℃ for 18 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC adhesive layer C / C composite material with environmental barrier pre-coating is heat-treated in an argon atmosphere at 1520 ℃ for 2 h to obtain a mullite intermediate layer with a thickness of 75 μm and a rare earth silicate composite surface layer with a thickness of 175 μm and through cracks.

[0042] Comparative Example 2: Step 1: Oxidize SiC powder in air at 1100 °C for 4 h. Then weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 5.5:1:3:10, and stir magnetically for 4 h to prepare slurry 1. Step 2: Weigh Yb2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 25:1:10:35, and prepare slurry 2 by magnetic stirring for 4 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 10 and 18 layers respectively, and then dry in an oven at 70 ℃ for 18 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC adhesive layer C / C composite material with environmental barrier pre-coating is heat-treated in an argon atmosphere at 1550 ℃ for 2 h to obtain a mullite intermediate layer with a thickness of 75 μm and a rare earth silicate composite surface layer with penetrating cracks with a thickness of 175 μm.

[0043] Comparative Example 3: Step 1: Oxidize SiC powder in air at 1100 °C for 1 h. Then, weigh the oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in a weight ratio of 5.5:1:3:10, and stir magnetically for 4 h to prepare slurry 1. Step 2: Weigh Yb2SiO5 powder, Al2O3 powder, silica sol binder and deionized water in a weight ratio of 25:1:10:35, and prepare slurry 2 by magnetic stirring for 4 hours. Step 3: Apply slurry 1 and slurry 2 sequentially to the surface of the C / C composite material with embedded SiC bonding layer, controlling the number of slurry 1 and slurry 2 applied to be 10 and 18 layers respectively, and then dry in an oven at 70 ℃ for 18 h to obtain the environmental barrier pre-coating. Step 4: The embedded SiC adhesive layer C / C composite material with environmental barrier pre-coating is heat-treated in an argon atmosphere at 1480 ℃ for 2 h to obtain a mullite intermediate layer and a rare earth silicate composite surface layer with a large number of pores on the surface and cross-section, respectively.

[0044] Depend on Figure 2 As can be seen from (a), (b), (c) and (d), the coating prepared in Example 3 has high density and tight bonding between the SiC adhesive layer, the mullite intermediate layer and the rare earth silicate composite surface layer.

[0045] Depend on Figure 3 It can be seen that, due to the excessive oxidation time of SiC powder in slurry 1, the SiO2 in the mullite intermediate layer and the rare earth silicate composite surface layer prepared in Comparative Example 1 consumed too much Al2O3 in the rare earth silicate composite surface layer during the integrated heat treatment process of the coating. Consequently, the Al2O3 in the rare earth silicate surface layer was severely insufficient, resulting in the inability to detect Yb3Al5O3 by XRD. 12 The presence of this phase does not meet the design requirements for the coating composition in rare earth silicate composite layers.

[0046] Depend on Figure 4 It can be seen that the mullite intermediate layer and rare earth silicate composite surface layer prepared in Comparative Example 1 both developed through-cracks due to excessively high integrated heat treatment temperature.

[0047] Depend on Figure 5 It can be seen that the mullite intermediate layer and rare earth silicate composite surface layer prepared in Comparative Example 2 both produced a large number of undensified pores due to the low integrated heat treatment temperature. At the same time, the interface bonding between the mullite intermediate layer and the rare earth silicate composite surface layer was poor due to insufficient oxidation time of the SiC powder in slurry 1.

[0048] See Figure 2 and Figure 3 The difference between Comparative Example 1 and Example 3 lies in the excessively long oxidation time of the SiC powder in slurry 1. As shown in Comparative Example 1, the excessively long oxidation time of the SiC powder in slurry 1 leads to excessive consumption of Al2O3 in the rare earth silicate composite surface layer by the SiO2 in the mullite intermediate layer during the integrated coating heat treatment process. Consequently, the Al2O3 in the rare earth silicate surface layer is severely insufficient, preventing the formation of Yb3Al5O3 during the heat treatment process. 12 High-temperature stable phase.

[0049] See Figure 2 and Figure 4 The difference between Comparative Example 2 and Example 3 is that the integrated heat treatment temperature is too high. As can be seen from Comparative Example 2, when the heat treatment temperature is high (over-densification), each ceramic particle sinters rapidly due to the difference in its thermal expansion coefficient, resulting in the formation of through cracks in the coating and bulging on the coating surface due to rapid volume expansion.

[0050] See Figure 2 and Figure 5 The difference between Comparative Example 3 and Example 3 lies in the shorter oxidation time of SiC powder in slurry 1 and the lower integrated heat treatment temperature. As can be seen from Comparative Example 3, when the heat treatment temperature is low, the reaction rate and diffusion rate between the phases in the intermediate layer and the surface layer are slower, resulting in a large number of undensified pores in both the intermediate layer and the rare earth silicate composite surface layer. At the same time, the shorter oxidation time of SiC powder in slurry 1 results in a weaker bond between the mullite intermediate layer and the rare earth silicate composite surface layer due to insufficient interfacial reaction.

[0051] In summary, this invention provides an integrated mullite / rare earth silicate environmental barrier coating and its preparation method. The environmental barrier coating is disposed on a C / C composite substrate and, from the inside out, comprises a SiC binder layer, a mullite intermediate layer, and a rare earth silicate composite surface layer. The mullite intermediate layer and the rare earth silicate composite surface layer are prepared by a slurry coating combined with an integrated heat treatment process, resulting in a compositional transition structure at their interface. The preparation method includes: sequentially coating the surface of the embedded SiC binder layer with a slurry 1 containing SiO2-Al2O3 and a slurry 2 containing RE2SiO5-Al2O3 (RE = Yb, Y, Lu). After integrated heat treatment, the SiO2 in slurry 1 reacts with Al2O3 to form the mullite intermediate layer, and the RE2SiO5 in slurry 2 reacts with Al2O3 to form RE2Si2O7-RE2SiO5-RE3Al5O3. 12 Composite Top Layer. The interface between the intermediate layer and the top layer is also tightly bonded due to the chemical reaction between SiO2 in slurry 1 and RE2SiO5 in slurry 2. This invention achieves optimized chemical compatibility and thermal matching between the intermediate layer and the top layer through integrated preparation, avoiding cracking problems caused by mismatched coefficients of thermal expansion in multilayer coatings. The coating can serve for extended periods in a high-temperature water-oxygen corrosion environment at 1400℃, significantly improving the service reliability of C / C composite materials in hot-end components of aero-engines and gas turbines.

[0052] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A mullite / rare earth silicate integrated environmental barrier coating, characterized in that, The environmental barrier coating is disposed on a C / C composite substrate, and from the surface of the C / C composite substrate outwards, it consists of a SiC bonding layer, a mullite intermediate layer, and a rare earth silicate composite surface layer; the rare earth silicate composite surface layer is RE2SiO5-RE2Si2O7-RE3Al5O 12 RE can be Yb, Y, or Lu; Among them, the mullite intermediate layer and rare earth silicate composite surface layer are prepared by two slurries, namely SiC oxide powder and Al2O3 powder, and RE2SiO5 powder and Al2O3 powder, respectively. They are then coated layer by layer on the surface of SiC bonding layer and dried, and then generated in situ through integrated heat treatment. An in-situ reaction forms a compositional transition zone at the interface between the mullite intermediate layer and the rare earth silicate composite surface layer. The compositional transition zone exhibits a multiphase structure in which rare earth dual silicate phases are dispersed in the mullite framework.

2. The mullite / rare earth silicate integrated environmental barrier coating according to claim 1, characterized in that, The thickness of the SiC bonding layer is 50-100 μm, the thickness of the mullite intermediate layer is 50-100 μm, and the thickness of the rare earth silicate composite surface layer is 150-200 μm.

3. A method for preparing an integrated mullite / rare earth silicate environmental barrier coating as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1, SiC powder is oxidized, and then the oxidized SiC powder, Al2O3 powder, silica sol binder, and deionized water solvent are magnetically stirred and mixed to prepare slurry 1; RE2SiO5 powder, Al2O3 powder, silica sol binder, and deionized water solvent are magnetically stirred and mixed to prepare slurry 2. S2, slurry 1 and slurry 2 are sequentially applied to the surface of the SiC bonding layer, and then dried to form a multi-layer environmental barrier pre-coating layer; S3. In an argon atmosphere, the multi-layer environmental barrier pre-coating is subjected to integrated heat treatment to obtain a mullite / rare earth silicate integrated environmental barrier coating.

4. The method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The average particle size of the SiC powder is 3 μm, the average particle size of the RE2SiO5 powder is 10 μm, and the average particle size of the Al2O3 powder is 300 nm.

5. The method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The weight ratio of the medium-oxidized SiC powder, Al2O3 powder, silica sol binder and deionized water solvent in the slurry 1 is (5~6):1:(2~4):(8~11).

6. The method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The weight ratio of RE2SiO5 powder, Al2O3 powder, silica sol binder and deionized water solvent in the slurry 2 is (20~30):1:(8~12):(30~40).

7. The method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The ratio of the number of coating layers of slurry 1 to slurry 2 is (8-13):(15-20).

8. The method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The drying process is carried out at a temperature of 60-80 ℃ for 12-24 h.

9. A method for preparing an integrated mullite / rare earth silicate environmental barrier coating according to claim 3, characterized in that, The integrated heat treatment temperature is 1500-1530℃, and the holding time is 2 hours.

10. The application of a mullite / rare earth silicate integrated environmental barrier coating in hot-end components of aero-engines or gas turbines, characterized in that, The mullite / rare earth silicate integrated environmental barrier coating described in any one of claims 1 to 2 is used.

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