A tantalum-based high-entropy silicide oxidation-resistant coating and a method for preparing the same using a slurry method

Abstract

The application discloses a tantalum-based coating prepared by a slurry method, and the coating is composed of an outer layer, an intermediate layer and an inner layer, wherein the outer layer is composed of high-entropy silicide MeSi2, the intermediate layer is composed of TaSi2, and the inner layer is composed of a low silicide of Ta; the Me is an alloy composed of at least three metal elements selected from W, Mo, Nb, Ta and Cr. The application further provides a preparation method of the coating, which comprises the following steps: firstly, the surface of a tantalum plate is polished smooth by sandpaper, and then is subjected to weak acid washing, weak alkali washing, water washing and drying; precursor powder is prepared by ball milling, and then a slurry is configured; the slurry is uniformly coated on the surface of the tantalum plate by an immersion or brushing method; after the sample is dried and solidified in a vacuum drying box, vacuum sintering is performed, and then the sample is cooled to room temperature, so that the preparation of the high-entropy silicide coating is completed. The coating preparation process is simple and controllable, and the low and high temperature oxidation resistance of the tantalum-based alloy can be improved.

Description

Technical Field

[0001] This invention relates to the field of coating structure design and preparation, and in particular to a tantalum-based high-entropy silicide anti-oxidation coating and a method for preparing it using a slurry method. Background Technology

[0002] Tantalum and tantalum alloys possess excellent high-temperature mechanical properties, but their high-temperature oxidation resistance is poor. Metallic tantalum undergoes accelerated oxidation to form Ta2O5 above 500℃, which severely restricts the application of tantalum and tantalum alloys. Improving the high-temperature oxidation resistance of tantalum and tantalum alloys is very important for expanding their application range. When common MoSi2 coatings operate under high-temperature and oxygen-containing conditions (800–1700℃), the MoO3 generated inside the coating rapidly volatilizes, while the SiO2 glass film formed on the coating surface effectively blocks oxygen from entering. SiO2 has fluidity at high temperatures, which can heal defects such as cracks and pores generated during coating oxidation, extending the service life of the silicide coating and providing better protection for the substrate. Simultaneously, the formation of Mo5Si3 in the outermost layer of the coating balances the difference in thermal expansion coefficients between the SiO2 glass film and the main coating layer, exhibiting excellent high-temperature oxidation resistance. However, MoSi2 has poor low-temperature oxidation resistance, exhibiting a "pesting" phenomenon at 400–800℃. At these temperatures, the diffusion coefficient of Si in MoSi2 is low, preventing the formation of a continuous SiO2 glass film. Oxygen enters and reacts with molybdenum and silicon, causing MoSi2 to pulverize and generate powder products mainly composed of MoO3 whiskers (flakes), SiO2 clusters, and residual MoSi2. This pulverization leads to coating failure and oxidation.

[0003] In the prior art, Han Jiesheng et al. disclosed the preparation and anti-oxidation mechanism of silicide coatings on the surface of MoNbTaTiW refractory high-entropy alloys. However, the coatings they obtained were mixtures of several silicides, and their anti-oxidation performance was still poor. Therefore, developing a low-cost, high-bonding-strength, and excellent anti-oxidation thermal barrier coating has become an urgent technical problem to be solved in this field.

[0004] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0005] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide a tantalum-based high-entropy silicide anti-oxidation coating and a method for preparing it using a slurry method, so as to solve or at least partially solve the above-mentioned technical defects existing in the prior art.

[0006] To achieve the first objective of this invention, the technical solution adopted by this invention is as follows:

[0007] A tantalum-based high-entropy silicide anti-oxidation coating, the coating comprising an outer layer, an intermediate layer and an inner layer, wherein: the outer layer material composition is high-entropy silicide MeSi2, the intermediate layer material composition is TaSi2, and the inner layer material composition is low-silicide Ta; the Me is an alloy composed of at least three metallic elements selected from W, Mo, Nb, Ta and Cr, for example, it may be three metallic elements, four metallic elements or five metallic elements.

[0008] Furthermore, in the above technical solution, the thickness of the tantalum-based high-entropy silicide anti-oxidation coating is 30–200 μm.

[0009] Preferably, in the above technical solution, the outer layer of the tantalum-based high-entropy silicide anti-oxidation coating has a thickness of 15–120 μm, the middle layer has a thickness of 8–50 μm, and the inner layer has a thickness of 5–25 μm.

[0010] Furthermore, in a preferred embodiment of the present invention, the above technical solution is provided, wherein Me is composed of four or five metallic elements selected from W, Mo, Nb, Ta, and Cr.

[0011] Specifically, when Me is composed of five metallic elements—W, Mo, Nb, Ta, and Cr—the outer layer material composition of the tantalum-based high-entropy silicide anti-oxidation coating can be (Mo... 0.2 W 0.2 Cr 0.2 Ta 0.2 Nb 0.2 )Si2.

[0012] The second objective of this invention is to provide a method for preparing the aforementioned tantalum-based high-entropy silicide antioxidant coating, the method specifically comprising the following four steps:

[0013] High-entropy silicide precursor powder was prepared; slurry was prepared; coating green body was prepared; and sintering was performed to finally obtain the tantalum-based high-entropy silicide antioxidant coating.

[0014] Furthermore, in the above technical solution, the specific steps for preparing the high-entropy silicide precursor powder are as follows:

[0015] Based on the MeSi2 molar ratio, Si powder and at least three metal powders selected from W, Mo, Nb, Ta, and Cr were weighed and then ball-milled under an inert atmosphere to obtain the high-entropy silicide precursor powder.

[0016] Alternatively, based on the MeSi2 molar ratio, at least three of the following powders—WSi2, MoSi2, NbSi2, TaSi2, and CrSi2—are weighed and ball-milled under an inert atmosphere to obtain the high-entropy silicide precursor powder.

[0017] Preferably, in the above technical solution, the mass ratio of each metal element in the alloy Me is between 5% and 35%. Specifically, the present invention first determines the molar ratio of each metal element in the alloy Me, and then calculates the mass ratio of each powder in 100g of powder based on the molar ratio.

[0018] Preferably, in the above technical solution, the ball mill rotation speed is 350-400 r / min and the ball milling time is 48-72 h.

[0019] Preferably, in the above technical solution, the ball-to-material mass ratio is controlled at 10:1 to 15:1 during the ball milling process.

[0020] Furthermore, in the above technical solution, the specific steps for preparing the slurry are as follows:

[0021] Solvent, sintering aid and binder are added to the high-entropy silicide precursor powder and mixed in a mass ratio of 40-50:45-55:2-6:1-4. The mixture is then ball-milled for 5-10 hours until a slurry with uniform viscosity is obtained.

[0022] Preferably, in the above technical solution, the solvent is either anhydrous ethanol or deionized water.

[0023] Preferably, in the preferred embodiment of the present invention, the sintering aid is Si powder with a particle size of 200-400 mesh.

[0024] Preferably, in the preferred embodiment of the present invention, the adhesive is at least one of PVB or polyethylene glycol.

[0025] Furthermore, in the above technical solution, the specific steps for preparing the coated green blank are as follows:

[0026] The slurry is coated onto a clean, dry tantalum plate surface and then dried to obtain the coated green blank.

[0027] Preferably, in the above technical solution, the clean and dry tantalum plate is obtained by polishing the surface of the tantalum plate with sandpaper, followed by weak acid washing, weak alkali washing, water washing, and drying.

[0028] Preferably, in the above technical solution, the coating method mainly includes brush coating, spray coating, dip coating, etc.

[0029] Preferably, in the above technical solution, the dip coating specifically involves immersing the tantalum plate in the slurry for 2-4 minutes, and then slowly and uniformly pulling the tantalum plate out of the slurry so that the surface of the substrate is uniformly covered by the slurry.

[0030] Furthermore, in the above technical solution, the specific steps of sintering are as follows:

[0031] The coated green body is placed in a vacuum sintering furnace, which is heated from room temperature to 350-600℃ and held for 1-2 hours to remove the added binder; then the temperature is raised to 1600-1700℃ and held for 1-3 hours, and finally cooled to room temperature to obtain the tantalum-based high-entropy silicide anti-oxidation coating.

[0032] Preferably, in the above technical solution, the heating rate of the sintering furnace is 5-15℃ / min, and the cooling rate of the sintering furnace is 1-5℃ / min.

[0033] More preferably, in a preferred embodiment of the present invention, the heating rate of the sintering furnace is 10°C / min, and the cooling rate of the sintering furnace is 2°C / min.

[0034] Preferably, in a preferred embodiment of the present invention, the heat preservation time is 2 hours.

[0035] The tantalum-based high-entropy silicide anti-oxidation coating of this invention comprises three layers, with the outermost layer being a high-entropy silicide, which is a single phase, and this high-entropy silicide exhibits better anti-oxidation performance. The design of this invention is based on the following two aspects:

[0036] 1) This invention proposes to prepare a high-entropy silicide anti-oxidation coating on a tantalum base and to prepare a high-entropy alloy silicide layer by a slurry sintering method, thereby achieving the goal of preparing a tantalum-based high-entropy silicide coating.

[0037] 2) This invention utilizes the "high entropy effect" of high-entropy silicides to eliminate the pulverization phenomenon of refractory metal silicides and prepares an inner layer to reduce the internal diffusion of Si elements.

[0038] The roles of the various raw materials used in this invention and the principles of this invention are as follows:

[0039] In this invention, the metal element occupies the cation lattice and the silicon element occupies the anion lattice, forming a high-entropy silicide. The slow diffusion effect of the high-entropy silicide improves the oxidation resistance of the coating. Furthermore, the linear expansion coefficient of the high-entropy silicide solid solution of this invention is close to that of the tantalum substrate. The tantalum substrate has a coefficient of 6.5 × 10⁻⁶. -6 K -1 The coefficient of linear expansion of the coating is 6 × 10⁻⁶. -6 K -1 This can reduce stress changes caused by temperature increases.

[0040] The PVB or polyethylene glycol added during the preparation of the slurry in this invention acts as a binder, achieving good particle dispersibility in the solvent, dispersing the coating, making the slurry uniform, and improving the density of the coating by dispersing the particles.

[0041] The high-entropy ceramics of this invention utilize the high-entropy effect, lattice distortion effect, slow diffusion effect, and cocktail effect to endow high-entropy silicides (HERMS) with high hardness, oxidation resistance, thermal stability, and high melting point. In high-entropy silicides, metal elements are randomly distributed at cation sites. The difference in cation atomic radii leads to severe lattice distortion and introduces a large number of stable vacancies with high migration energy barriers, forming high entropy. The slow diffusion effect hinders cation diffusion. When the SiO2 formation rate is higher than that of metal oxides, the material can be protected from further oxidation. Therefore, high-entropy silicides, characterized by high entropy, slow diffusion, and the cocktail effect, inhibit the formation of metal oxides, promoting the formation of a complete and dense SiO2 layer before surface cations begin to form metal oxides. The outer high-entropy silicide layer eliminates pulverization, while the middle and inner layers act as transition layers to match the thermal expansion coefficient of the tantalum substrate.

[0042] The three-layer structure of the tantalum-based high-entropy silicide anti-oxidation coating of the present invention consists of an outermost layer composed of high-entropy silicide, a middle layer of tantalum silicide, and an inner layer of low-silicide tantalum. The reason for this structure is that silicon diffuses during the coating sintering process, gradually diffusing from the surface to the interior, thus forming a three-layer coating structure consisting of low-silicide tantalum, TaSi2, and MeSi2 from the inside out.

[0043] The beneficial effects of this invention are as follows:

[0044] 1) This invention proposes to prepare a composite coating on a tantalum substrate, which combines an inner layer and a high-entropy silicide coating. The inner layer inhibits the diffusion of interfacial elements and enhances interfacial bonding, while the high-entropy silicide layer serves as an antioxidant layer.

[0045] 2) This invention obtains high-entropy silicide precursor powder through high-energy ball milling, thereby reducing the powder sintering temperature. The reasons are as follows:

[0046] During high-energy ball milling, the powder particles undergo prolonged and intense impacts and collisions with the grinding balls, causing repeated cold welding and fractures in the powder particles. This leads to atomic diffusion within the powder particles, resulting in alloying between the powder particles. Local alloying occurs in the powder after high-energy ball milling, which can lower the sintering temperature. Furthermore, after high-energy ball milling, the powder particle size decreases, the powder activity increases, and the sintering temperature decreases.

[0047] 3) This invention utilizes the antioxidant and thermal stability properties of high-entropy silicides to remove the "pesting" phenomenon of refractory metal silicides based on the high-entropy effect. The dense SiO2 film formed at high temperature effectively inhibits the diffusion of O atoms to the tantalum substrate, providing better protection for the substrate. At the same time, the thermal expansion coefficient of the coating can be controlled by adjusting the proportion of elements in the high-entropy silicide.

[0048] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is the XRD pattern of the high-entropy silicide coating surface in Example 1 of the present invention.

[0051] Figure 2 This is a cross-sectional morphology diagram of the high-entropy silicide coating in Embodiment 2 of the present invention. Detailed Implementation

[0052] High-entropy silicides (HERMS), as a novel type of high-entropy ceramic, have a structure similar to intermetallic compounds, and their performance is close to or even superior to that of single intermetallic compounds. HERMS possesses high hardness, oxidation resistance, thermal stability, and a high melting point. The high-entropy effect of HERMS causes Si to oxidize preferentially during oxidation, meaning the formation rate of SiO2 is higher than that of metal oxides. Before the cation sites begin to form metal oxides, a complete and dense SiO2 layer is formed on the surface, preventing cation oxidation and effectively avoiding the "pesting" phenomenon, thus solving the low-temperature oxidation problem of MoSi2 coating materials. Therefore, this invention selects high-entropy silicides as a novel anti-oxidation coating. This invention achieves superior performance compared to ordinary single-phase silicide coatings by rationally designing the elemental composition and preparation process, and controlling the preparation cost. Currently, the preparation of high-entropy silicide coatings mainly employs processes such as magnetron sputtering, plasma spraying, electron beam physical vapor deposition, chemical vapor deposition, and thermal spraying. However, the slurry method has advantages over these processes, including simple equipment, convenient operation, and the ability to artificially control the coating structure, significantly reducing the cost of coating preparation.

[0053] This invention provides a tantalum-based coating prepared using a slurry method. The coating consists of three layers from the inside out: a low-silicide tantalum layer, a TaSi2 layer, and a MeSi2 layer. The invention also provides a method for preparing the aforementioned coating, comprising the following steps: First, the surface of a tantalum plate is smoothed by sanding, followed by weak acid washing, weak alkali washing, water washing, and drying. Then, a precursor powder is prepared by ball milling, and a slurry is prepared. Next, the slurry is uniformly coated onto the surface of the tantalum plate using methods such as impregnation or brushing. Finally, the specimen is dried and cured in a vacuum drying oven, then vacuum sintered and cooled to room temperature to complete the preparation of the high-entropy silicide coating. The coating preparation process of this invention is simple and controllable, and can improve the low- and high-temperature oxidation resistance of tantalum-based alloys.

[0054] The present invention will be further described in detail below through implementation examples. These implementation examples are carried out based on the technology of the present invention. Detailed implementation methods and specific operating procedures are provided to illustrate the inventiveness of the present invention, but the scope of protection of the present invention is not limited to the following implementation examples.

[0055] Based on the information contained in this application, various modifications to the precise description of the invention can be readily made by those skilled in the art. It should be understood that the scope of the invention is not limited to the defined processes, properties, or components, as these embodiments and other descriptions are merely illustrative of specific aspects of the invention.

[0056] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless otherwise stated, the numerical parameters listed in the specification are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0057] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0058] The low-temperature oxidation performance tests involved in the following embodiments of the present invention were conducted in a muffle furnace, and the specific test methods are as follows:

[0059] A muffle furnace was heated to 600℃ and kept at a constant temperature. Five parallel samples were tested. The original samples were weighed using an analytical balance with a sensitivity of 0.1 mg. Simultaneously, the sample surface area was measured. Samples were removed from the muffle furnace at regular intervals and weighed, and the rate of weight change was recorded. The test duration was 100-200 hours. The weight gain rate was obtained by dividing the weight change by the surface area and time. The unit is (mg / cm³). 2 *h).

[0060] The high-temperature oxidation performance involved in the following embodiments of the present invention was tested in a high-temperature tube furnace, and the specific test methods are as follows:

[0061] The original sample was weighed using an analytical balance. The sample was placed in a corundum boat at room temperature. The tube furnace was heated to 1600℃ and held for 5–10 hours. The sample was then cooled with the furnace. The original sample was weighed using an analytical balance, with the weight controlled to be within 0.0001g. The surface area of ​​the sample was measured at the same time, and the mass gain rate was calculated.

[0062] The low-temperature oxidation test in this invention is carried out in a muffle furnace at a test temperature of 600℃ for a test duration of 100-200h, and the high-temperature oxidation test is carried out at a temperature of 1600℃ for a holding time of 5-10h.

[0063] Example 1

[0064] This embodiment describes a method for preparing a tantalum-based high-entropy silicide antioxidant coating, the method specifically including the following steps:

[0065] The raw material powders were placed in a ball mill jar according to the following mass percentages: WSi2 27.07%, MoSi2 17.16%, NbSi2 16.82%, TaSi2 26.75%, CrSi2 12.20%. The particle size of all powders was 30–40 μm, and the purity was 99.9%. The ball milling speed was 400 r / min, and the milling time was 60 h. The milled powder, anhydrous ethanol, silicon powder, and PVB (mass ratio 45:50:4:1) were then ball milled again at 250 r / min for 4 h to obtain a coating slurry of suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy. The surface of the tantalum substrate was then shot-peened to improve its roughness. After treatment, acid pickling was performed to remove surface oxide impurities. After rinsing with deionized water, the substrate was ultrasonically cleaned with anhydrous ethanol for 30 min to obtain the pretreated tantalum substrate. The obtained tantalum substrate was coated with a slurry, and the sample was immediately dried at 70°C for 30 min. After four cycles, the sample was dried at 70°C for 12 h. The resulting sample was then placed in a vacuum sintering furnace with a vacuum degree of 1×10⁻⁶. -3 Pa, heating rate of 10℃ / min, holding at 550℃ for 2h, holding at 1600℃ for 2h, then furnace cooled to room temperature to obtain sintered sample.

[0066] The sides of the sintered samples were ground to 240 mesh, -400 mesh, -800 mesh, -100 mesh, -1200 mesh, -1500 mesh, and -2000 mesh, and then polished with diamond polishing paste. The material composition of the cross-section of the treated samples was analyzed by SEM and EDS. The surface phase of the material was analyzed by XRD. The outer layer thickness was 80μm±5μm, the middle layer thickness was 35μm±3μm, and the inner layer thickness was 20μm±2μm.

[0067] Based on XRD and energy dispersive spectroscopy results, the composition from the inside out is inferred to be tantalum low-silicide, TaSi2, (W 0.2 Mo 0.2 Ta 0.2 Cr 0.2 Nb 0.2 The weight gain of the Si2 sample in the low-temperature oxidation experiment at 600℃ for 100h was 0.0040 (mg / cm³). 2 *h), far lower than common disilicide single-coating materials, preventing low-temperature oxidation and eliminating the pest phenomenon. The weight gain after high-temperature oxidation at 1600℃ / 10h was 0.213 (mg / cm³). 2 *h), a dense SiO2 oxide film is formed on the surface of the high-temperature oxide coating, which can effectively prevent further oxidation.

[0068] Example 2

[0069] This embodiment describes a method for preparing a tantalum-based high-entropy silicide antioxidant coating, the method specifically including the following steps:

[0070] The raw material powders were placed in a ball mill jar according to the following mass percentages: W 20.76%, Mo 10.84%, Ta 20.43%, Cr 5.87%, Nb 10.49%, Si 31.62%. The particle size of all powders was 325 mesh (30–40 μm), and the purity was 99.9%. The ball mill jar rotated at 350 r / min for 60 h. The milled powder, anhydrous ethanol, silicon powder, and PVB (mass ratio 43:50:4:3) were then ball milled at 250 r / min for 6 h to obtain a coating slurry with suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy. The surface of the tantalum substrate was then shot-peened to improve its roughness. After treatment, acid pickling was performed to remove surface oxide impurities. After rinsing with deionized water, the substrate was ultrasonically cleaned with anhydrous ethanol for 30 min to obtain the pretreated tantalum substrate. The tantalum substrate was immersed in the slurry and allowed to stand for 2 minutes. Then, the sample was slowly pulled out and immediately dried at 70°C for 30 minutes. After five cycles, the sample was dried at 70°C for 12 hours. The resulting sample was placed in a vacuum sintering furnace at a vacuum degree of 1×10⁻⁶. - 3 Pa, heating rate of 10℃ / min, holding at 600℃ for 2h, holding at 1600℃ for 2h, then furnace cooled to room temperature to obtain sintered sample.

[0071] The sides of the obtained sintered samples were ground. The material composition of the cross-section of the treated samples was analyzed by SEM and EDS. XRD analysis was used to analyze the surface phases of the material; the outer layer thickness was 100 μm ± 5 μm, the middle layer thickness was 40 μm ± 3 μm, and the inner layer thickness was 20 μm ± 2 μm. From the inside out, the phases are tantalum low-silicide, TaSi2, (W... 0.2 Mo 0.2 Ta 0.2 Cr 0.2 Nb 0.2 The weight gain of the Si2 sample in the low-temperature oxidation experiment at 600℃ for 100h was 0.0044 (mg / cm³). 2 *h), completely avoiding low-temperature oxidation and eliminating the pest phenomenon. High-temperature oxidation at 1600℃ / 10h resulted in a weight gain of 0.333 (mg / cm³). 2 *h), a dense SiO2 oxide film is formed on the coating surface, which provides a protective effect.

[0072] Example 3

[0073] This embodiment describes a method for preparing a tantalum-based high-entropy silicide antioxidant coating, the method specifically including the following steps:

[0074] The raw material powders were placed in a ball mill jar according to the following mass percentages (W 10.92%, Mo 17.10%, Ta 21.50%, Cr 6.18%, Nb 11.04%, Si 33.26%). All powders had a particle size of 400 mesh and a purity of 99.9%. The ball mill jar rotated at 350 r / min for 60 h. The milled powder, anhydrous ethanol, silicon powder, and polyethylene glycol (mass ratio 45:50:3:2) were then ball milled at 200 r / min for 10 h to obtain a coating slurry with suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy. The surface of the tantalum substrate was then shot-peened to improve its roughness. After treatment, acid pickling was performed to remove surface oxide impurities. After rinsing with deionized water, the substrate was ultrasonically cleaned with anhydrous ethanol for 30 min to obtain the pretreated tantalum substrate. The tantalum substrate was immersed in the slurry and allowed to stand for 3 minutes. Then, the sample was slowly pulled out and immediately dried at 70°C for 30 minutes. After five cycles, the sample was dried at 70°C for 12 hours. The resulting sample was placed in a vacuum sintering furnace at a vacuum degree of 1×10⁻⁶. -3 Pa, heating rate of 10℃ / min, held at 550℃ for 2h, held at 1700℃ for 60min, then furnace cooled to room temperature to obtain sintered sample.

[0075] The sides of the sintered samples were ground. The material composition of the cross-sections of the treated samples was analyzed by SEM and EDS. XRD analysis was used to analyze the surface phases, revealing an outer layer thickness of 60 μm ± 4 μm, a middle layer thickness of 20 μm ± 3 μm, and an inner layer thickness of 15 μm. From the inside out, the phases are tantalum low-silicide, TaSi2, (W... 0.1 Mo 0.3 Ta 0.2 Cr 0.2 Nb 0.2 The weight gain of the Si2 sample in the low-temperature oxidation experiment at 600℃ for 100h was 0.0063 mg / cm³. 2 *h), the weight gain rate after high-temperature oxidation at 1600℃ / 10h was 0.854 (mg / cm³). 2 *h).

[0076] Example 4

[0077] This embodiment describes a method for preparing a tantalum-based high-entropy silicide antioxidant coating, the method specifically including the following steps:

[0078] Raw materials were placed in a ball mill jar according to the following mass percentages (W 20.22%, Mo 15.83%, Ta 24.88%, Cr 5.72%, Nb 2.56%, Si 30.8%). The particle size of all powders was 400 mesh, and the purity was 99.9%. The ball mill jar rotated at 350 r / min for 60 h. The milled powder, anhydrous ethanol, Si powder, and polyethylene glycol (mass ratio 40:53:5:2) were then ball milled at 200 r / min for 10 h to obtain a coating slurry with suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy. The surface of the tantalum substrate was then shot-peened to improve its roughness. After treatment, acid pickling was performed to remove surface oxide impurities. After rinsing with deionized water, the substrate was ultrasonically cleaned with anhydrous ethanol for 30 min to obtain the pretreated tantalum substrate. The tantalum-based sample was impregnated in the slurry and allowed to stand for 3 minutes. Then, the sample was slowly pulled out and immediately dried at 70°C for 30 minutes. After five cycles, the sample was dried at 70°C for 12 hours. The resulting sample was then placed in a vacuum sintering furnace at a vacuum degree of 1×10⁻⁶. -3 Pa, heating rate of 10℃ / min, held at 600℃ for 2h, held at 1650℃ for 2h, then furnace cooled to room temperature to obtain sintered sample.

[0079] The sides of the obtained sintered samples were ground. The material composition of the cross-section of the treated samples was analyzed by SEM and EDS. XRD analysis was used to analyze the surface phases of the material; the outer layer thickness was 90 μm ± 3 μm, the middle layer thickness was 30 μm ± 2 μm, and the inner layer thickness was 15 μm. From the inside out, the phases are tantalum low-silicide, TaSi2, (W... 0.2 Mo0.3 Ta 0.25 Cr 0.2 Nb 0.05 The weight gain of the Si2 sample in the low-temperature oxidation experiment at 600℃ for 100h was 0.0083 mg / cm³. 2 *h), the weight gain rate after high-temperature oxidation at 1600℃ / 10h was 1.013 (mg / cm³). 2 *h).

[0080] Figure 1 The image shows the XRD pattern of the high-entropy silicide coating surface prepared in Example 1 of the present invention. It can be seen from the figure that a single-phase MeSi2 solid solution is formed on the coating surface.

[0081] Figure 2 This is a cross-sectional morphology diagram of the coating prepared in Example 2 of the present invention. As can be seen from the diagram, the coating comprises a three-layer structure. EDS elemental analysis was performed on the cross-sections of each layer of the coating, and point scan elemental analysis was performed as shown in the diagram. Based on the elemental composition of the middle layer, it is inferred that the coating composition from the inside out is tantalum low-silicide, TaSi2, (W... 0.2 Mo 0.2 Ta 0.2 Cr 0.2 Nb 0.2 )Si2.

[0082] Table 1. EDS results of the outer coating prepared in Example 1 (W 0.2 Mo 0.2 Ta 0.2 Cr 0.2 Nb 0.2 Si2

[0083] element Wt% Atomic% O 1.08 4.01 Si 29.47 62.52 Cr 4.84 5.54 Nb 10.49 6.73 Mo 11.92 7.40 Ta 23.26 7.66 W 18.95 6.14 Total 100.00 100.00

[0084] Table 2. EDS results of the intermediate layer of the coating prepared in Example 1, TiSi2

[0085] element wt% At% O 0.74 3.39 Si 25.36 66.28 Cr 0.2 0.28 Nb 0.05 0.04 Mo 0.38 0.29 Ta 73.28 29.73 W 0 0 Total 100 100

[0086] Table 3 shows the EDS results of the inner coating layer prepared in Example 1, with low silicide content of tantalum.

[0087] element wt% At% O 0.79 5.31 Si 10.79 41.43 Cr 0.25 0.53 Nb 0.02 0.02 Mo 0.34 0.39 Ta 87.48 52.14 W 0.33 0 Total 100.00 100.00

[0088] Comparative Example 1

[0089] This comparative example describes a method for preparing a tantalum-based coating, the method specifically comprising the following steps:

[0090] The raw material powders were weighed according to the following mass percentages (WSi2 27.07%, MoSi2 17.16%, NbSi2 16.82%, TaSi2 26.75%, CrSi2 12.20%) to reduce the number of ball milling steps. The silicide powder, anhydrous ethanol, silicon powder, and PVB (mass ratio 45:50:4:1) were mixed and ball-milled at 250 r / min for 4 h to obtain a coating slurry of suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy, and the surface of the tantalum substrate was shot-peened to improve roughness. After treatment, acid washing was performed to remove surface oxide impurities, followed by rinsing with deionized water and ultrasonic cleaning with anhydrous ethanol for 30 min to obtain a pretreated tantalum substrate. The obtained tantalum substrate was coated with the slurry, and the sample was immediately dried at 70℃ for 30 min. After four cycles, the sample was dried at 70℃ for 12 h. The obtained sample was placed in a vacuum sintering furnace with a vacuum degree of 1×10⁻⁶. -3 The sample was heated at 10℃ / min, held at 550℃ for 2 hours, and then held at 1600℃ for 1 hour before being furnace cooled to room temperature to obtain the sintered sample. XRD analysis of the treated sample showed no high-entropy silicide phase formed on the coating surface.

[0091] Comparative Example 2

[0092] This comparative example describes a method for preparing a tantalum-based coating, the method specifically comprising the following steps:

[0093] The raw material powder selected was a single silicide powder, MoSi2, with a particle size of 325 μm and a purity of 99.9%. The ball milling jar speed was 400 r / min, and the milling time was 60 h. The silicide powder, anhydrous ethanol, silicon powder, and PVB (mass ratio 45:50:4:1) were mixed and ball milled again at 250 r / min for 4 h to obtain a coating slurry with suitable viscosity. The tantalum substrate was successively polished with 80-mesh, 240-mesh, and 400-mesh sandpaper until smooth and glossy. The surface of the tantalum substrate was then shot-peened to improve roughness. After treatment, acid washing was performed to remove surface oxide impurities. After rinsing with deionized water, the substrate was cleaned with anhydrous ethanol using an ultrasonic cleaner for 30 min to obtain a pretreated tantalum substrate. The obtained tantalum substrate was coated with the slurry, and the sample was immediately dried at 70℃ for 30 min. After four cycles, the sample was dried at 70℃ for 12 h. The resulting sample was placed in a vacuum sintering furnace with a vacuum degree of 1×10⁻⁶. -3 The sample was heated at 10℃ / min, held at 550℃ for 2 hours, and then held at 1600℃ for 2 hours before being furnace cooled to room temperature to obtain a sintered sample. The cross-section of the coating formed on the surface of the sintered sample is shown in the figure. After sintering, the powder forms a two-layer coating structure, with the coating composed of MoSi2 and TaSi2 from the outside to the inside. An oxidation experiment was conducted on the sample at 600℃, and after 10 hours, the sample showed powdering, indicating coating failure.

Claims

1. A tantalum-based high-entropy silicide anti-oxidation coating, said coating comprising an outer layer, an intermediate layer, and an inner layer, characterized in that: The outer layer material is composed of high-entropy silicide MeSi2, the middle layer material is composed of TaSi2, and the inner layer material is composed of low-silicide Ta; the Me is an alloy composed of at least three metallic elements selected from W, Mo, Nb, Ta, and Cr. The method for preparing the tantalum-based high-entropy silicide antioxidant coating includes the following four steps: preparing high-entropy silicide precursor powder; preparing slurry; preparing coating green body; sintering, and finally obtaining the coating. The specific steps for preparing the slurry are as follows: Solvent, sintering aid and binder are added to the high-entropy silicide precursor powder. The high-entropy silicide precursor powder, solvent, sintering aid and binder are mixed in a mass ratio of 40-50:45-55:2-6:1-4 and ball milling is continued for 5-10 hours until a slurry with uniform viscosity is obtained. The specific steps of the sintering are as follows: The coated green body is placed in a vacuum sintering furnace, which is heated from room temperature to 350-600℃ and held for 1-2 hours to remove the added binder; then the temperature is raised to 1600-1700℃ and held for 1-3 hours, and finally cooled to room temperature to obtain the tantalum-based high-entropy silicide anti-oxidation coating.

2. The tantalum-based high-entropy silicide anti-oxidation coating according to claim 1, characterized in that: The thickness of the tantalum-based high-entropy silicide anti-oxidation coating is 30–200 μm.

3. The tantalum-based high-entropy silicide anti-oxidation coating according to claim 1 or 2, characterized in that: In the tantalum-based high-entropy silicide anti-oxidation coating, the outer layer has a thickness of 15–120 μm, the middle layer has a thickness of 8–50 μm, and the inner layer has a thickness of 5–25 μm.

4. The tantalum-based high-entropy silicide anti-oxidation coating according to claim 1, characterized in that: The Me is composed of four or five metallic elements selected from W, Mo, Nb, Ta, and Cr.

5. The method for preparing the tantalum-based high-entropy silicide antioxidant coating according to any one of claims 1-4, characterized in that: The method specifically includes the following four steps: preparing high-entropy silicide precursor powder; preparing slurry; preparing coating green body; sintering, and finally obtaining the coating; The specific steps for preparing the slurry are as follows: Solvent, sintering aid and binder are added to the high-entropy silicide precursor powder. The high-entropy silicide precursor powder, solvent, sintering aid and binder are mixed in a mass ratio of 40-50:45-55:2-6:1-4 and ball milling is continued for 5-10 hours until a slurry with uniform viscosity is obtained. The specific steps of the sintering are as follows: The coated green body is placed in a vacuum sintering furnace, which is heated from room temperature to 350-600℃ and held for 1-2 hours to remove the added binder; then the temperature is raised to 1600-1700℃ and held for 1-3 hours, and finally cooled to room temperature to obtain the tantalum-based high-entropy silicide anti-oxidation coating.

6. The method according to claim 5, characterized in that: The specific steps for preparing the high-entropy silicide precursor powder are as follows: Based on the MeSi2 molar ratio, Si powder and at least three metal powders selected from W, Mo, Nb, Ta, and Cr were weighed and then ball-milled under an inert atmosphere to obtain the high-entropy silicide precursor powder. Alternatively, based on the MeSi2 molar ratio, at least three of the following powders—WSi2, MoSi2, NbSi2, TaSi2, and CrSi2—are weighed and ball-milled under an inert atmosphere to obtain the high-entropy silicide precursor powder.

7. The method according to claim 6, characterized in that: The mass ratio of each element in the alloy Me is between 5% and 35%.

8. The method according to claim 5, characterized in that: The sintering aid is Si powder with a particle size of 200-400 mesh.

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