Method for implementing integrated ultrahigh temperature environmental barrier composite coating

Abstract

The application discloses a method for realizing an integrated ultrahigh-temperature environmental barrier composite coating. After a high-entropy alloy or boride layer and a molybdenum metal pre-coating layer are pre-coated on the surface of a substrate, a silicon-boron co-embedding deposition is carried out through a pre-oxidation process to form an ordered Mo-Si-B multilayer structure in the molybdenum metal layer. A composite coating formed by a metal silicide and silicon dioxide is cold sprayed on the Mo-Si-B multilayer structure to form a three-dimensional network structure composite self-healing layer through high-temperature sintering. An alloy oxide is cold sprayed or magnetron sputtered outside the composite self-healing layer to form a water vapor resistant layer. Through the integrated coating preparation process, the advantages of different components are complementary, and the effective protection of various refractory alloys in a wide temperature range (room temperature-1700 DEG C) can be realized.

Description

Technical Field

[0001] This invention relates to a new material coating technology, specifically a method for implementing an integrated ultra-high temperature environment barrier composite coating. Background Technology

[0002] The key factor for novel multi-principal-element refractory alloys (RMPEA or RHEA) to function in oxidizing environments is the formation of a protective oxide layer. However, in high-temperature oxidizing environments, most refractory alloys struggle to form a dense oxide layer, or the formed oxide layer often fails to provide adequate protection due to excessively high oxygen diffusion rates. During thermal cycling and under thermal loads, stress-induced severe cracking within the coating can lead to coating damage and failure. Substrate-compatible protective coatings can provide protection to the substrate with minimal impact on its overall performance. Existing high-temperature ablation-resistant coatings are prone to cracking and peeling due to the difference in thermal expansion coefficients between the coating and the substrate under rapid heating and cooling cycles. Furthermore, these coatings cannot withstand working environments with complex gas compositions; for example, high-temperature water vapor (H2O) in the working gas will react with the SiO2 component in the coating, rapidly consuming SiO2 and reducing coating life. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes an integrated method for achieving an ultra-high temperature environmental barrier composite coating. Through an integrated coating preparation process, the advantages of different components are complemented, enabling effective protection of various refractory alloys over a wide temperature range.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for realizing an integrated ultra-high temperature environmental barrier composite coating. The method involves pre-coating a high-entropy alloy or its boride layer onto a substrate surface, followed by pre-coating a pure molybdenum metal pre-coating layer, and then vacuum high-temperature sintering. Silicon-boron co-embedding deposition is then performed, forming an ordered Mo-Si-B multilayer structure within the molybdenum metal layer through a pre-oxidation process. A composite coating consisting of metal silicide and silicon dioxide is cold-sprayed onto the Mo-Si-B multilayer surface, and after high-temperature air sintering, a three-dimensional network structure composite self-healing layer is formed. Finally, an alloy oxide is cold-sprayed or magnetron sputtered onto the composite self-healing layer to form a water vapor-resistant layer, followed by sintering.

[0006] The high-entropy alloy or its boride refers to: W-Mo-Ta-Nb, W-Mo-Ta-Nb-Zr, W-Mo-Ta-Nb-Hf, W-Mo-Ta-Nb-V or its borides (W-Mo-Ta-Nb)B, (W-Mo-Ta-Nb-Zr)B, (W-Mo-Ta-Nb-Hf)B or (W-Mo-Ta-Nb-V)B.

[0007] The metal silicides and silicon dioxide mentioned refer to MoSi2, WSi2, and SiO2.

[0008] The alloy oxides are: HfO2, ZrO2, MgO or CrTaO4.

[0009] The present invention relates to an integrated composite coating for ultra-high temperature environmental barriers prepared by the above method, comprising: a reinforced diffusion barrier layer composed of a high-entropy alloy or its boride, a Mo-Si-B antioxidant diffusion barrier layer, a composite self-healing layer and a water vapor resistant layer, which are sequentially located on a substrate.

[0010] Technical effect

[0011] This invention utilizes an integrated composite coating design method, through spraying, hot sintering, embedding co-deposition, and pre-oxidation treatment, to add a diffusion-resistant refractory high-entropy alloy or its boride, a controllable three-dimensional network self-healing layer, and a high-temperature water vapor resistant layer to the original Mo-Si-B coating. Compared with the prior art, this invention achieves multiple functions of the coating in one, greatly improving the coating's integrity, high-temperature oxidation resistance, and durability in complex environments. Attached Figure Description

[0012] Figure 1 This is a flowchart of the present invention;

[0013] Figure 2 This is a simplified diagram of the coating structure of the present invention;

[0014] Figure 3 The images shown are cross-sectional backscattered electron images and elemental distribution diagrams of silicon and molybdenum after the two-step method for preparing Mo pre-coating and Mo-Si-B coating samples in the example were exposed to air at 1300°C for 10 hours.

[0015] Figure 4 (a) shows the mass change curves of the uncoated and coated samples in the examples during the isothermal oxidation test at 1300°C; (b) is a schematic diagram of the cross-sectional backscattered electron image of the coated sample after 50 hours of isothermal testing.

[0016] Figure 5 (a) shows the weight change curve during the thermal cycling test in the example, with an inset showing the coated sample after 750 hours of cycling; (b) shows the backscattered electron cross-sectional image of the coated sample after 100 cycles; (c)-(d) are schematic diagrams of the backscattered electron cross-sectional images of the coated sample after 750 cycles.

[0017] Figure 6 This is a photograph of the integrated composite coating applied to a TZM disk.

[0018] Figure 7The graph shows the relationship between the weight change of the integrated composite coating sample and the exposure time in an oxidizing environment at 1600°C for 100 hours.

[0019] Figure 8 This is a cross-sectional view of the composite coating after undergoing a thermal cycle of 1600℃ for 4×25 hours in the example.

[0020] Figure 9 The image shows a cross-sectional view of the composite coating after the Mo-Si-B coating (B layer) was pretreated with air oxidation at 1300°C for 75 hours, followed by thermal cycling at 1600°C for 4×25 hours.

[0021] Figure 10 This is a schematic diagram illustrating the mechanism of thermal expansion coefficient adjustment in self-healing composite layers. Detailed Implementation

[0022] This embodiment relates to a method for implementing a diffusion-blocking layer, a Mo pre-coating layer and Si-B embedded co-deposition, a self-healing layer, and a water vapor-resistant layer on a high-entropy alloy substrate, verifying that the coating system can be applied to conventional refractory alloy systems, including:

[0023] Step 1: Prepare W-Mo-Ta-Nb-V multi-principal-element refractory alloy substrate (RMPEA) with equal atomic ratio by arc melting;

[0024] Preferably, in this embodiment, the ingot is flipped five times to achieve homogenization.

[0025] The electric arc melting process, after annealing at 1800°C for 50 hours, completely removed the dendritic structure in the original as-cast sample, and the composition was fully homogenized.

[0026] Step 2: Apply the Mo-Si-B coating to the RMPEA refractory alloy substrate in two steps, specifically including:

[0027] 2.1 After preparing a refractory high-entropy alloy diffusion barrier layer and a Mo pre-coating layer by spraying a slurry onto the substrate, the coating is dried in air and the temperature is less than 1×10⁻⁶. -5 Slowly heat up and cool down in a high vacuum of mBar (rate < 200 ℃ / h), and sinter at 1300-1800℃ for 2-10 hours.

[0028] The slurry is prepared by mixing 99.9% pure, 1-5 micron metal powder and 2.0% by weight of 1000-4000 [unclear - possibly a specific ingredient or ingredient] in ethanol. Hydroxypropyl cellulose is used as a binding agent to obtain the following:

[0029] i. Prepare refractory high-entropy alloy or its boride slurry by mixing refractory high-entropy alloy powder with cellulose in a certain proportion, dissolving it in alcohol and mixing it thoroughly to form a uniform slurry;

[0030] ii. Prepare Mo slurry by dissolving Mo powder and cellulose powder in alcohol in a certain proportion and mixing them thoroughly to form a uniform slurry.

[0031] Preferably, in this embodiment, the substrate is ground to remove sharp edges before spraying, and then sandblasted to increase surface roughness.

[0032] The spraying process involves using a compressed air spray gun to uniformly spray refractory high-entropy alloy / boride and Mo metal slurry onto the substrate surface.

[0033] The sintering process is preferably carried out at a heating / cooling rate of 15°C / min to reach 1750°C and sintering for 2 hours.

[0034] 2.2 Si-B Packaging Atmosphere Infiltration Process: After mixing and grinding Si, B and activator powders for 30 minutes to obtain a homogeneous mixture, Al2O3 filler is added, and the Mo pre-coated sample is embedded in a sealed alumina crucible. Then, it is placed in a sealed alumina tube in a furnace filled with argon gas for deposition treatment.

[0035] The mass ratio of Si powder to B powder is 35:1.

[0036] Preferably, Al2O3 is used as an inert filler, while NaF is used as an activator.

[0037] The deposition process is carried out at a temperature of 1000°C for 50-100 hours, preferably at 1000°C with an argon flow of approximately 15 ml / min for 50 hours.

[0038] Preferably, a protective multilayer structure is generated by exposure to air at 1300°C for 10-30 hours.

[0039] The powder coating comprises: 34.03% by weight of Si (99.5% purity, 44 micrometers), 0.97% by weight of B (99% purity, 44 micrometers), 2.5% by weight of NaF activator (99.99% purity), and 62.5% by weight of Al2O3 filler (99.7% purity, 180 micrometers).

[0040] The samples obtained in multiple steps 2 were subjected to isothermal oxidation analysis and thermal cycling oxidation analysis, respectively. First, the coating samples were removed, rinsed with pure water to remove surface-adhering powder, and then ultrasonically cleaned in alcohol or acetone for 10 minutes to obtain clean, smooth coating samples. Then, ① a spherical coating sample with a diameter of 2.5 mm was placed in a crucible and kept in a protective argon atmosphere during heating and cooling. When the sample reached 1300°C, an oxidation atmosphere of 20 vol% O2 and 80 vol% Ar was introduced to obtain the isothermal oxidation analysis sample. Alternatively, ② an irregular rectangular coating sample with dimensions of approximately 6×2×2 mm was placed in a tube furnace with both ends partially open to outdoor air for thermal cycling testing. The furnace hot zone temperature was 1300°C. For each cycle, the sample was placed on an alumina plate and placed in the furnace for 60 minutes, then removed and cooled in air for 10 minutes to room temperature (23°C) to obtain the rapid heating and cooling cycle test sample.

[0041] Preferably, in this embodiment, the flow rate of the isothermal oxidizing gas is 100 mL / min.

[0042] like Figure 4 As shown in b. Elemental analysis results show clear boundaries between the Mo-Si-B / Mo pre-coating and the Mo pre-coating / MPEA substrate, indicating that the interdiffusion between the Mo pre-coating and the MPEA substrate is very slow during sintering and infiltration into the bag atmosphere.

[0043] like Figure 3 The image shows a cross-sectional BSE (backscattered scanning electron) image of the coating after initial oxidation testing in air at 1300°C. The multilayer structure formed in the coating is a result of phase sequencing along a multi-component diffusion path. From the outermost to the innermost layer, the sequence is alumina borosilicate, MoSi2, Mo5Si3 (T1), Mo5SiB2 (T2), and a Mo pre-coating. Some pores were introduced in the first spraying step of the Mo pre-coating; most of these pores were filled by Al2O3 in the polishing agent during the embedding co-deposition penetration and polishing processes. However, considering the stress introduced by the difference in the coefficient of thermal expansion (CTE) in the multilayer structure, these pores do not adversely affect the coating. In fact, these pores can accommodate stress in the coating and help suppress cracking during thermal cycling. Similarly, the elemental distribution test demonstrates a clear boundary between the coating and the substrate.

[0044] Isothermal and thermal cycling tests were conducted on uncoated and two-step coated RMPEA samples at 1300°C. The mass change curves of the samples are shown below. Figure 4 As shown in figure a, the uncoated bare RMPEA sample experienced a rapid weight gain in the first two hours, followed by a rapid weight loss for the remainder of the time. In contrast, the two-step coating provided strong protection to the substrate, with a weight change of only -3.4 mg / cm³.2 . Figure 5 To obtain the mass change curve and cross-sectional morphology of the thermally cycled samples, the coated samples underwent up to 750 cycles of thermal cycling at 1300°C, with a mass change of only -1.4 mg / cm². 2 .

[0045] Isothermal oxidation experiments at 1300°C demonstrated that the coating exhibits parabolic oxidation kinetics. Thermal cycling tests were conducted on the coated samples from 1300°C to room temperature for 750 hours (with each cycle involving a 1-hour stay in the hot zone). After this period, the samples maintained their integrity, with a mass change of only 1.4 mg / cm³. 2 The coating's durability is attributed to its self-healing ability. The coating can accommodate internal stresses caused by thermal shock, and any cracks that form will be filled by borosilicate glass to prevent further oxidative damage. The initially formed Mo-based T2 layer acts as the first diffusion barrier, preventing elemental diffusion into the matrix and maintaining the coating's integrity and function. After prolonged use, due to boron trapping, a solid solution T2 layer and a (RMPEA)-B layer form at the RMPEA-matrix interface, acting as a second diffusion barrier and boron reservoir in the coating system. These diffusion-blocking layers significantly improve the coating's integrity and service life.

[0046] Step 3: Prepare the composite self-healing layer and water vapor resistant layer, specifically including:

[0047] 3.1 Preparation of refractory alloy silicide and SiO2 powder slurry: Mix the two powders with cellulose in alcohol in a certain proportion and stir thoroughly to form a uniform slurry;

[0048] 3.2 Use a compressed air spray gun to evenly spray the mud onto the sample surface;

[0049] 3.3 Preparation of refractory alloy oxide powder slurry: The oxide powder and cellulose are mixed evenly in proportion and dissolved in alcohol to form slurry;

[0050] 3.4. Spray the refractory alloy oxide slurry evenly onto the sample surface;

[0051] 3.5. The sample is placed in air and sintered at 1500-1600 ℃ for 2 hours to form a composite self-healing layer and a water vapor-resistant layer. (Example:) Figure 6 The image shows the morphology of the coated sample; as shown... Figures 7-9 The figure shows the oxidation test results of the integrated composite coating.

[0052] Preferably, the thermal compatibility control method of the three-dimensional mesh self-healing layer is as follows: Figure 10As shown, by controlling the volume fraction of metal silicides (such as the volume fraction of MoSi2) in the composite coating, the overall coefficient of thermal expansion (CTE) of the composite coating can be calculated. By adjusting the proportion of silicides such as MoSi2, the coefficient of thermal expansion of the composite coating and the substrate can be made similar, which can reduce the thermal stress caused by the difference in the coefficient of thermal expansion during service and achieve thermomechanical compatibility between the composite coating and the substrate.

[0053] Compared with existing technologies, this method, by employing a composite self-healing layer with an adjustable coefficient of thermal expansion, can achieve a matching coefficient of thermal expansion with the substrate material, enhance the thermomechanical compatibility between the coating system and the substrate, reduce or avoid cracks within the coating during service, and improve the coating's durability and service life. By integrating an outermost water vapor-resistant layer composed of refractory alloy oxides, the coating's interior can be protected from contact with complex environmental atmospheres such as water vapor, effectively slowing down the consumption of coating components and improving coating integrity and service life.

[0054] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for preparing an integrated composite coating for ultra-high temperature environment barriers, characterized in that, A high-entropy alloy layer is pre-coated on the substrate surface, followed by a pure molybdenum metal pre-coating layer, and then vacuum high-temperature sintering is performed. Silicon-boron co-embedding deposition is performed, and an ordered Mo-Si-B multilayer structure is formed in the molybdenum metal layer through a pre-oxidation process. A composite self-healing layer and a water vapor resistant layer are prepared by cold spraying on the surface of the Mo-Si-B multilayer structure. After high-temperature hot sintering, the composite self-healing layer forms a three-dimensional network structure. The pure molybdenum metal pre-coating is prepared by spraying a slurry onto a substrate. This slurry is obtained by mixing 99.9% pure, 1-5 micrometer Mo powder and 2.0% by weight of 1000-4000... Hydroxypropyl cellulose was used as a binder to obtain the product; The aforementioned composite self-healing layer and water vapor resistant layer are prepared by the following method: a) Prepare refractory alloy silicide and SiO2 powder slurry by mixing the two powders with cellulose in alcohol in a certain proportion and stirring thoroughly to form a uniform slurry. b) Use a compressed air spray gun to evenly spray the mud onto the sample surface; c) Prepare refractory alloy oxide powder slurry by uniformly mixing oxide powder and cellulose in a certain proportion and dissolving them in alcohol to form slurry; d) Spray the refractory alloy oxide slurry evenly onto the sample surface; e) The sample is placed in air and heated to 1500-1600 ℃ for 2 hours to form a composite self-healing layer and a water vapor resistant layer; The ultra-high temperature environment barrier integrated composite coating specifically consists of a high-entropy alloy reinforced diffusion barrier layer, a Mo-Si-B diffusion barrier layer, a composite self-healing layer, and a water vapor resistant layer, which are sequentially located on the substrate. The high-entropy alloy mentioned refers to: W-Mo-Ta-Nb-V; The refractory alloy silicide mentioned refers to MoSi2; The refractory alloy oxide mentioned is HfO2.

2. The method for preparing the integrated composite coating for ultra-high temperature environment barriers according to claim 1, characterized in that, The vacuum high-temperature sintering process involves reaching 1750°C at a heating / cooling rate of 15°C / min and sintering for 2 hours.

3. The method for preparing the integrated composite coating for ultra-high temperature environment barriers according to claim 1, characterized in that, The silicon-boron co-embedded deposition refers to: mixing and grinding Si, B and activator powder for 30 minutes to obtain a uniform mixture, then adding Al2O3 filler, embedding the Mo pre-coated sample into a sealed alumina crucible, and then loading it into a sealed alumina tube in a furnace filled with argon gas for deposition treatment. The mass ratio of Si to B is 35:

1.

4. An integrated composite coating for ultra-high temperature environment protection, characterized in that, Prepared according to any one of the methods described in claims 1-3.

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