Method for preparing ultrahigh-temperature carbide high-entropy ceramic coating at low temperature in situ

Abstract

The invention discloses a method for low-temperature in-situ preparation of an ultrahigh-temperature carbide high-entropy ceramic coating, which comprises the following steps: uniformly mixing medium salt, five or more than five refractory metal simple substances and ionic salt or reactive salt corresponding to each refractory metal simple substance in proportion to obtain mixed powder; and in an inert atmosphere, heating to melt the refractory metal elementary substances and the ionic salt or the reactive salt in the mixed powder into the medium salt, then dipping the carbon preform into the obtained molten salt, and heating to carry out a thermal disproportionation reaction to obtain the ultrahigh-temperature carbide high-entropy ceramic coating. The method disclosed by the invention has the advantages of rapidness, strong designability, near-net forming, low cost, simple process and the like; and the prepared ultrahigh-temperature carbide high-entropy ceramic coating has the advantages of excellent oxidation ablation resistance, good uniformity and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of high entropy ceramic coating preparation, and relates to a method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating, and specifically relates to a method for low-temperature in-situ preparation of refractory metal carbide high entropy ceramic coating by molten salt thermal disproportionation reaction. Background Art

[0002] Ultrahigh-temperature, high-entropy ceramics (UHTHCs) are single-phase solid solution ceramics composed of five or more metal cations. Due to the random substitution of cations and their severely distorted lattice structure, they exhibit superior oxidation and ablation resistance and mechanical properties compared to conventional UHT ceramics. High-temperature components such as aerospace engine components, guidance systems, and combustion chambers typically require excellent high-temperature resistance to ensure safe and reliable operation. The high-temperature strength, corrosion resistance, and oxidation and ablation resistance of HECs make them an ideal material choice. The application of HECs can effectively extend the service life of aircraft components, reduce maintenance costs, and improve overall performance. However, because the cations in UHTHCs are mostly Group IVB-VIB metals, the bulk UHTHCs are dense, which is not conducive to lightweight applications in engineering. Therefore, coating HECs is an important strategy for advancing their engineering applications.

[0003] At present, the main methods for preparing ultra-high temperature high entropy ceramic coatings include thermal spraying, solid-phase reaction, magnetron sputtering, chemical vapor deposition, etc. However, these methods all have obvious defects: the process temperature of the thermal spraying method is too high, and the obtained coating has poor uniformity, low density, and low bonding strength with the substrate; the solid-phase reaction method requires melting the alloy and then reacting with carbon to form carbide high entropy ceramics. The temperature required for this process is extremely high, and after cooling, the coating will have obvious crack defects; the magnetron sputtering method has significant defects such as high cost, low efficiency, and difficulty in near-net forming; the chemical vapor deposition method has defects such as long preparation cycle and high cost. In summary, the above methods have significant problems such as high cost, long cycle, high process temperature, and poor designability. In addition, due to the obvious defects, the obtained coatings fail to achieve the ideal level of anti-ultra-high temperature ablation performance, and the corresponding linear ablation rate is higher than 1 micron / second.

[0004] In order to promote the engineering application of ultra-high temperature high entropy ceramics, there is an urgent need for a faster, more efficient, highly designable, near-net-shape, and low-cost preparation method for ultra-high temperature carbide high entropy ceramic coatings, so as to improve the ultra-high temperature oxidation and ablation resistance of ultra-high temperature high entropy ceramic coatings and reduce the process cost of ultra-high temperature high entropy ceramic coatings. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology, especially the technical defects such as high cost, long cycle, high process temperature and poor designability in the current preparation of high-entropy ceramic coatings, and provide a method for low-temperature in-situ preparation of ultra-high temperature carbide high-entropy ceramic coatings that is fast, efficient, highly designable, near-net shaping, low cost and simple process. The obtained ultra-high temperature carbide high-entropy ceramic coating has the advantages of excellent anti-oxidation and ablation performance and good uniformity.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0007] A method for low-temperature in-situ preparation of an ultra-high-temperature carbide high-entropy ceramic coating comprises the following steps: A dielectric salt, five or more refractory metal elements, and ionic salts corresponding to each of the refractory metal elements are uniformly mixed to obtain a mixed powder; in an inert atmosphere, the temperature is increased to melt the refractory metal elements and ionic salts in the mixed powder into the dielectric salt to form a molten salt, and then a carbon preform is immersed in the obtained molten salt, and the temperature is increased to 1000°C to 1300°C for a thermal disproportionation reaction to obtain an ultra-high temperature carbide high-entropy ceramic coating.

[0008] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high-entropy ceramic coating at low temperature, preferably, the five or more refractory metal elements include five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten; the ionic salts corresponding to the refractory metal elements include chloride salts containing the refractory metal elements, fluoride salts containing the refractory metal elements or fluorides containing the refractory metal elements.

[0009] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high-entropy ceramic coating at low temperature, preferably, the refractory metal element is five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten, and the molar ratio of the total mole of the refractory metal element to titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1:0~0.1:0.25~0.5:0.25~0.5:0~0.1:0~0.1:0~0.1:0~0.1 (that is, the total molar amount of the refractory metal element is 1, then the sum of the molar fractions of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1), and each refractory metal element and the corresponding ionic salt are in an equal molar ratio; the total mass of the refractory metal element and the ionic salt is 2% to 50% of the mass of the dielectric salt.

[0010] The above-mentioned method for low-temperature in-situ preparation of ultra-high temperature carbide high-entropy ceramic coating, preferably, the heating is carried out to 700°C to 800°C and kept warm for 30min to 60min to melt the refractory metal elements and ionic salts in the medium salt; the time of the thermal disproportionation reaction is 30min to 300min, and the rate of heating to the thermal disproportionation reaction temperature is 10°C / min to 20°C / min.

[0011] As a general technical concept, the present invention also provides a method for low-temperature in-situ preparation of an ultra-high temperature carbide high-entropy ceramic coating, comprising the following steps: A dielectric salt, a refractory metal element with five or more components, and a reactive salt are uniformly mixed to obtain a mixed powder; in an inert atmosphere, the temperature is increased to melt the refractory metal elements and the reactive salt in the mixed powder in the dielectric salt to form a molten salt; a carbon preform is immersed in the obtained molten salt, and the temperature is increased to 1000°C to 1300°C for a thermal disproportionation reaction to obtain an ultra-high temperature carbide high-entropy ceramic coating.

[0012] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high entropy ceramic coating at low temperature, preferably, the five or more refractory metal elements include five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten; the reactive salt is a reactive salt that causes the refractory metal element to form high-valent metal ions in a thermal disproportionation reaction, and the reactive salt includes ammonium fluoride or ammonium chloride.

[0013] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high-entropy ceramic coating at low temperature, preferably, the refractory metal element is five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten, and the molar ratio of the total mole of the refractory metal element to titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1:0~0.1:0.25~0.5:0.25~0.5:0~0.1:0~0.1:0~0.1:0~0.1 (that is, the total molar amount of the refractory metal element is 1, then the sum of the molar fractions of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1), the mass of the reactive salt is 0.8~1.2 of the total mass of the refractory metal element; the sum of the mass of the refractory metal element and the reactive salt is 2%~50% of the mass of the dielectric salt.

[0014] The above-mentioned method for preparing ultra-high temperature carbide high-entropy ceramic coating in situ at low temperature is preferably, wherein the temperature is raised to 700°C to 800°C and kept warm for 30min to 120min to melt the refractory metal elements and reactive salts in the medium salt; the time of the thermal disproportionation reaction is 30min to 300min, and the rate of heating to the thermal disproportionation reaction temperature is 10°C / min to 20°C / min.

[0015] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high entropy ceramic coating at low temperature, preferably, the medium salt is a binary or higher metal compound molten salt, the binary or higher metal compound molten salt includes a binary or higher metal chloride salt or a binary or higher metal fluoride salt, and the binary or higher metal chloride salt includes NaCl-KCl eutectic salt, NaCl-CaCl2 eutectic salt, KF-KCl eutectic salt, LiF-KF eutectic salt, KCl-LiCl-NaCl eutectic salt or KCl-LiCl-CaCl2 eutectic salt.

[0016] In the above-mentioned method for in-situ preparation of ultra-high temperature carbide high-entropy ceramic coating at low temperature, preferably, the mixed powder is laid in a crucible and placed in a sintering furnace; the carbon preform is suspended above the crucible by a lifting rod before impregnation; after the reaction is completed, the component with the ultra-high temperature carbide high-entropy ceramic coating is taken out by the lifting rod, the component is cooled to room temperature with the furnace, and then washed with water or heat treated to remove residual medium molten salt; the carbon preform includes a carbon / carbon preform or a graphite preform.

[0017] In the present invention, the refractory metal element having five or more components may preferably be a refractory metal element having 5 to 9 components.

[0018] The method of the present invention may specifically preferably include the following steps, but is not limited thereto: (1) A uniform mixture of refractory metal elements (five or more components) and their corresponding ionic salts (or reactive salts) and dielectric salts is placed in an alumina crucible and placed in a high-temperature sintering furnace. A carbon preform (carbon / carbon or graphite preform, either dense or porous) is suspended above the crucible by a lifting rod. (2) In an inert atmosphere, the high-temperature sintering furnace is heated to melt the refractory metal and ionic salt (or reactive salt) in the mixed powder into the medium salt; the pulling rod is lowered to immerse the carbon preform in the molten salt to undergo a thermal disproportionation reaction, and then the carbon preform is removed from the molten salt by the pulling rod and cooled to room temperature in the furnace to obtain a component with an ultra-high temperature carbide high entropy ceramic coating; (3) The obtained component is washed with deionized water or subjected to high-temperature heat treatment to remove the residual medium molten salt in the sample.

[0019] In the present invention, there are two sources of high-valent reactive metal salts. One is to directly add high-valent metal salts (ionic salts) during mixing. The other is to react the reactive salt with the metal element to obtain the high-valent salt in situ in the reaction material.

[0020] In the present invention, the refractory metal element M (5-9 components) and the corresponding refractory metal chloride salt, fluoride salt, fluoride salt (M i+) or reactive salts (e.g., ammonium fluoride or ammonium chloride, which can corrode M elemental metal to form metal ions M i+ ) reacts to form M j + (Formula 1), and then the refractory metal M formed in the molten salt j+ Reacts with carbon to form MC high entropy ceramic coating (Formula 2). That is, the refractory metal element is M, and the ion salt corresponding to the refractory metal element is M-containing i+ Ionic salts, reactive salts are those that can corrode M element to form metal ions M i+ salt (such as ammonium fluoride or ammonium chloride), as shown in formula (1), the M element and the metal ion M i+ Thermal disproportionation reaction is carried out in molten medium salt to form M j+ , then as shown in formula (2), the refractory metal ions M formed in the molten salt j+ Reacts with carbon to form MC high entropy ceramic coating.

[0021] The reaction formula is as follows: M+M i+ →M j+ Formula (1) M j+ +C→M i+ +MC formula (2) Among them, M i+ It is a high-valence ion of the refractory metal element M. j+ It is the intermediate valence ion of the refractory metal element M, and i is greater than j. MC is a carbide ceramic.

[0022] In the present technical field, refractory metals refer to elements in subgroups 4 to 6 of the periodic table.

[0023] In this field, ultrahigh temperature carbide high entropy ceramics refer to carbide high entropy ceramics with a melting point above 3000°C.

[0024] Compared with the prior art, the advantages of the present invention are: 1. In the prior art, methods for preparing ultrahigh-temperature carbide high-entropy ceramic coatings include thermal spraying, reactive infiltration, and chemical vapor deposition. Thermal spraying and reactive infiltration require extremely high temperatures (above 2000°C), and most other conventional methods also require heating to temperatures above 1850°C. Chemical vapor deposition processes suffer from drawbacks such as poor coating designability, particularly significant limitations in gaseous raw materials. The present invention utilizes a low-temperature, in-situ thermal disproportionation reaction with a reaction temperature below 1300°C, and the raw materials can be pre-blended. Rather than using conventional formulations with equimolar ratios of refractory metals, an ultrahigh-temperature, high-entropy ceramic formulation tailored to the desired service environment is developed. For example, the ultrahigh-temperature carbide high-entropy ceramic coating of the present invention exhibits excellent ultrahigh-temperature ablation resistance and can be used in erosive, aerobic environments exceeding 2000°C. Furthermore, the thermal disproportionation reaction ensures uniformity of the ultrahigh-temperature, high-entropy ceramic coating and allows for low-temperature, in-situ preparation, achieving stable ablation resistance and low-cost production of the ultrahigh-temperature, high-entropy ceramic coating. Furthermore, after the reaction is complete, only the residual molten salt needs to be removed to obtain the ultra-high temperature carbide high-entropy ceramic coating. In summary, the method of the present invention can quickly and easily prepare an ultra-high temperature carbide high-entropy ceramic coating with excellent ablation resistance, stability, and good uniformity. It has the advantages of rapidity, strong designability, near-net shape, low cost, and simple process.

[0025] 2. The method of the present invention can achieve high-entropy ceramic coatings in various structural states by manipulating the carbon preform structure. For example, when the preform is porous carbon, the coating can be embedded in the carbon pores to form an embedded, highly stable high-entropy ceramic coating. Furthermore, by preforming the carbon material's external structure, the high-entropy ceramic coating can be formed into a near-net shape on the component surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a microscopic morphology of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 1 of the present invention.

[0027] Figure 2 This is the XRD pattern of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 1 of the present invention.

[0028] Figure 3 This is a microscopic morphology of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 2 of the present invention.

[0029] Figure 4 This is the XRD pattern of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 2 of the present invention.

[0030] Figure 5This is a microscopic morphology of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 3 of the present invention.

[0031] Figure 6 This is the XRD pattern of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 3 of the present invention.

[0032] Figure 7 This is a microscopic morphology of the (TiMoHfNbTaW)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 4 of the present invention.

[0033] Figure 8 This is the XRD pattern of the (TiMoHfNbTaW)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 4 of the present invention.

[0034] Figure 9 This is a microscopic morphology of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 5 of the present invention.

[0035] Figure 10 This is the XRD pattern of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0037] The method of the present invention for preparing an ultra-high temperature carbide high entropy ceramic coating at low temperature in situ comprises the following steps: (1) Raw material mixing The refractory metal elements of five or more components, the ionic salts or reactive salts corresponding to the refractory metal elements, and the medium salt are uniformly mixed to obtain a mixed powder; the refractory metal element M participating in the thermal disproportionation reaction can be selected from titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), molybdenum (Mo) and tungsten (W), etc., but not limited thereto; the ionic salt containing M participating in the thermal disproportionation reaction includes a chloride salt containing M, a fluoride salt containing M or a fluoride salt containing M, and the reactive salt participating in the thermal disproportionation reaction includes a fluoride salt containing M. The salt includes ammonium fluoride or ammonium chloride, and the medium salt is a molten salt of a binary or higher metal compound, including a binary or higher metal chloride salt or fluoride salt, such as NaCl-KCl, NaCl-CaCl2, KF-KCl, LiF-KF, KCl-LiCl-NaCl, KCl-LiCl-CaCl2, etc. However, the present invention is not limited to the aforementioned chloride or fluoride medium salts. Any salt that can provide a molten liquid environment for the thermal disproportionation reaction in the present invention can be used as the medium salt.

[0038] (2) Reaction and reaction conditions In an inert atmosphere, heating is performed to melt the refractory metal element and ionic salt or reactive salt in the mixed powder into a medium salt, preferably at a temperature of 700°C to 800°C. The carbon preform is then immersed in the molten salt and heated to 1000°C to 1300°C for a thermal disproportionation reaction to produce an ultra-high-temperature carbide high-entropy ceramic coating. This method allows for the preparation of a high-entropy ceramic coating on a component surface at relatively low temperatures, reducing energy consumption, equipment requirements, and costs. Furthermore, the mass ratio of the combined mass of the refractory metal element M and the M salt (or reactive salt) to the medium salt can range from 2% to 50% of the mass of the medium salt. After the medium salt is melted, the carbon preform is immersed in the molten medium salt using a lifting rod and held in the molten salt for a period of time before removal. The holding time in the molten salt can be adjusted based on the desired thickness of the high-entropy ceramic coating, for example, from 30 minutes to 300 minutes, which can serve as the thermal disproportionation reaction time.

[0039] The thermal disproportionation reaction process of the present invention is shown in formula (1) and formula (2): M+M i+ →M j+ Formula (1) M j+ +C→M i+ +MC formula (2).

[0040] (3) Removal of residual salts in carbon components After the carbon component reacts in a molten dielectric salt to form a high-entropy ceramic coating, a small amount of residual salt remains. This residual salt must be removed to improve the coating's performance. Specifically, removal methods include ultrasonic immersion cleaning in deionized water and thermal decomposition in a high-temperature furnace. However, these methods are not limited to these. Any method that can remove the dielectric salt without damaging the coating can be used to remove the residual salt. For example, immersion in deionized water followed by thermal decomposition of the residual salt in a high-temperature furnace can ultimately yield a carbon preform component with a high-entropy ceramic coating free of residual salt.

[0041] The operation process of the present invention is further described below with reference to specific embodiments.

[0042] Example 1 A method for preparing an ultra-high temperature carbide high entropy ceramic coating in situ at low temperature according to the present invention comprises the following steps: Weigh 100 g of a eutectic salt (medium salt) with an equal molar ratio of NaCl-KCl, 10 g of five metal powders of Ti, Zr, Hf, Nb, and Ta with a molar ratio of 0.1:0.35:0.35:0.1:0.1 (i.e., the molar ratio of the total molar amount of the five metal powders to Ti, Zr, Hf, Nb, and Ta is 1:0.1:0.35:0.35:0.1:0.1, and the metal powder is about 400 mesh), and 20 g of TiF4, ZrF4, HfF4, NbF5, and TaF5 with a molar ratio of 0.1:0.35:0.35:0.1:0.1 are mixed to obtain a mixed powder. The mixed powder was placed in an alumina crucible, which was then placed in a high-temperature sintering furnace. The graphite block was placed on a pull rod installed in the furnace. The atmosphere was evacuated to 0.5 Pa and filled with argon. This process was repeated three times, followed by a continuous argon flow through the furnace to maintain a high-purity inert atmosphere. The sintering furnace was heated to 700°C at a rate of 10°C / min and held at this temperature for 30 minutes to ensure that the refractory metal and ionic salt melted into the NaCl-KCl medium. The graphite block was then immersed in the molten salt using a pull rod. The temperature was then increased to 1200°C at a rate of 10°C / min and held at this temperature for 180 minutes. After the reaction was complete, the component was removed from the furnace using the pull rod and cooled to obtain a carbon component with a (TiZrHfNbTa)C ultrahigh-temperature carbide high-entropy ceramic coating on its surface. The resulting component was ultrasonically treated in deionized water at 80°C for 120 minutes to produce a carbon component free of residual salt.

[0043] The cross-sectional micromorphology and X-ray diffraction (XRD) spectrum of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating obtained in this embodiment are shown in FIG. Figure 1 and Figure 2 As shown. The XRD spectrum shows that the obtained ceramic is a single-phase solid solution with a face-centered structure, that is, the formed phase is a high-entropy ceramic, and the melting point of the ceramic coating is higher than 3000°C. In this embodiment, the salts participating in the thermal disproportionation reaction are TiF4, ZrF4, HfF4, NbF5, and TaF5, and the obtained (TiZrHfNbTa)C ultra-high temperature carbide high-entropy ceramic coating has a thickness of about 150μm and good uniformity. The prepared ultra-high temperature carbide high-entropy ceramic coating was ablated in an oxyacetylene flame at 2000°C for 300 seconds, and the measured linear ablation rate was less than 0.4 microns / second, which has very excellent ablation resistance and has reached the advanced level of ultra-high temperature ablation resistance.

[0044] Example 2 A method for preparing an ultra-high temperature carbide high entropy ceramic coating in situ at low temperature according to the present invention comprises the following steps: Weigh 100g of a eutectic salt of NaCl and KCl in an equal molar ratio, 10g of five metal powders (approximately 400 mesh) (Ti, Zr, Hf, Nb, and Ta) in a molar ratio of 0.1:0.35:0.35:0.1:0.1, and 30g of K₂TiF₆, K₂ZrF₆, K₂HfF₆, K₂NbF₇, and K₂TaF₇ in a molar ratio of 0.1:0.35:0.35:0.1:0.1. Mix them to obtain a mixed powder. Place the mixed powder in an alumina crucible. Place the crucible in a high-temperature sintering furnace, place the graphite block on the lifting rod in the furnace, evacuate the furnace (0.5 Pa), and fill it with argon. Repeat this process three times, then circulate argon gas through the sintering furnace to ensure a high-purity inert atmosphere. The sintering furnace was heated to 700°C at a rate of 10°C / min and held for 30 minutes to ensure that the ionic salt and refractory metal were dissolved in the NaCl-KCl medium salt. The graphite block was then immersed in the molten salt using a lifting rod, and the temperature was raised to 1200°C at a rate of 10°C / min and held for 180 minutes. After the reaction was complete, the component was removed using a lifting rod and cooled in the furnace to obtain a carbon component with a (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating on the surface. The obtained component was placed in 80°C deionized water for ultrasonic treatment for 120 minutes to obtain a carbon component without residual salt.

[0045] The cross-sectional micromorphology and XRD spectrum of the (TiZrHfNbTa)C high entropy ceramic coating obtained in this embodiment are shown in FIG. Figure 3 and Figure 4 As shown. The XRD spectrum shows that the obtained ceramic is a single-phase solid solution with a face-centered structure, that is, the formed phase is a high-entropy ceramic, and the melting point of the ceramic coating is higher than 3000°C. In this case, the salts involved in the thermal disproportionation reaction are K2TiF6, K2ZrF6, K2HfF6, K2NbF7, and K2TaF7. The obtained (TiZrHfNbTa)C high-entropy ceramic coating is about 150μm and has good uniformity. The prepared ultra-high temperature carbide high-entropy ceramic coating was ablated in an oxyacetylene flame at 2000°C for 300 seconds, and the measured linear ablation rate was less than 0.3 microns / second, which has very excellent anti-ablation performance.

[0046] Example 3 A method for preparing an ultra-high temperature carbide high entropy ceramic coating in situ at low temperature according to the present invention comprises the following steps: Weigh 100g of a eutectic salt of NaCl-KCl in an equal molar ratio, 10g of five metal powders (approximately 400 mesh) of Ti, Zr, Hf, Nb, and Ta in a molar ratio of 0.1:0.35:0.35:0.1:0.1, and 20g of TiF4, ZrF4, HfF4, NbF5, and TaF5 in a molar ratio of 0.1:0.35:0.35:0.1:0.1, and mix to obtain a mixed powder. Place the mixed powder in an alumina crucible, place the crucible in a high-temperature sintering furnace, and place the graphite block on a lifting rod in the furnace. Vacuum the crucible (0.5 Pa) and fill it with argon. Repeat this process three times, then circulate argon in the sintering furnace to ensure a high-purity inert atmosphere. The sintering furnace was heated to 700°C at a rate of 10°C / min and held for 30 minutes to ensure that the ionic salt and refractory metal were dissolved in the NaCl-KCl medium salt. The graphite block was then immersed in the molten salt using a lifting rod, and the temperature was raised to 1000°C at a rate of 10°C / min and held for 60 minutes. After the reaction was complete, the component was removed using a lifting rod and cooled in the furnace to obtain a carbon component with a (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating on the surface. The obtained component was placed in 80°C deionized water for ultrasonic treatment for 120 minutes to obtain a carbon component without residual salt.

[0047] The cross-sectional micromorphology and XRD spectrum of the (TiZrHfNbTa)C high entropy ceramic coating obtained in this embodiment are shown in FIG. Figure 5 and Figure 6 As shown. The XRD spectrum shows that the obtained ceramic is a single-phase solid solution with a face-centered structure, that is, the formed phase is a high-entropy ceramic, and the melting point of the ceramic coating is higher than 3000°C. In this embodiment, a disproportionation reaction temperature of 1000°C and a shorter holding time of 60 minutes are used to obtain a thinner (TiZrHfNbTa)C high-entropy ceramic coating of about 100μm with good uniformity. The prepared ultra-high temperature carbide high-entropy ceramic coating was ablated at 2000°C in an oxyacetylene flame for 300 seconds, and the measured linear ablation rate was less than 0.5 microns / second, showing very excellent anti-ablation performance.

[0048] Example 4 A method for preparing an ultra-high temperature carbide high entropy ceramic coating in situ at low temperature according to the present invention comprises the following steps: Weigh 100g of a eutectic salt of NaCl-KCl in an equal molar ratio, 10g of six metal powders (approximately 400 mesh) of Ti, Mo, Hf, Nb, Ta, and W in a molar ratio of 0.1:0.1:0.5:0.1:0.1:0.1, and 20g of TiF4, MoF5, HfF4, NbF5, TaF5, and WF5 in a molar ratio of 0.1:0.1:0.5:0.1:0.1:0.1 to obtain a mixed powder. Place the mixed powder in an alumina crucible, place the crucible in a high-temperature sintering furnace, and place the graphite block on a lifting rod in the furnace. Evacuate the crucible (0.5 Pa) and fill it with argon. Repeat this process three times, then circulate argon in the sintering furnace to ensure a high-purity inert atmosphere. The sintering furnace was heated to 700°C at a rate of 10°C / min and held for 30 minutes to ensure that the ionic salt and refractory metal were dissolved in the NaCl-KCl medium salt. The graphite block was then immersed in the molten salt using a lifting rod, and the temperature was raised to 1200°C at a rate of 10°C / min and held for 180 minutes. After the reaction was complete, the component was removed using a lifting rod and cooled in the furnace to obtain a carbon component with a (TiMoHfNbTaW)C ultra-high temperature carbide high-entropy ceramic coating on the surface. The obtained component was placed in 80°C deionized water for ultrasonic treatment for 120 minutes to obtain a carbon component without residual salt.

[0049] The cross-sectional micromorphology and XRD spectrum of the (TiMoHfNbTaW)C ultrahigh temperature carbide high entropy ceramic coating obtained in this embodiment are as follows: Figure 7 and Figure 8 As shown. The XRD spectrum shows that the obtained ceramic is a single-phase solid solution with a face-centered structure, that is, the formed phase is a high-entropy ceramic, and the melting point of the ceramic coating is higher than 3000°C. This embodiment uses six components of Ti, Mo, Hf, Nb, Ta, W and TiF5, MoF5, HfF4, NbF5, TaF5, WF5 as reactants. The formed (TiMoHfNbTaW)C high-entropy ceramic coating has a thickness of about 120μm and good uniformity. The prepared ultra-high temperature carbide high-entropy ceramic coating was ablated in an oxyacetylene flame at 2000°C for 300 seconds, and the measured linear ablation rate was less than 0.3 microns / second, which has very excellent anti-ablation performance.

[0050] Example 5 A method for preparing an ultra-high temperature carbide high entropy ceramic coating in situ at low temperature according to the present invention comprises the following steps: Weigh 100g of a eutectic salt of NaCl and KCl in an equimolar ratio and mix it with 20g of approximately 400-mesh metal powders (Ti, Zr, Hf, Nb, and Ta) in a molar ratio of 0.1:0.35:0.35:0.1:0.1, along with 20g of NH₄Cl. Place the mixture in an alumina crucible. Place the crucible in a high-temperature sintering furnace, place the graphite block on the furnace's lifting rod, evacuate the crucible (0.5 Pa), and then fill it with argon. Repeat this process three times, then continue circulating argon gas through the furnace to maintain a high-purity inert atmosphere. Heat the furnace to 700°C at a rate of 10°C / min and maintain this temperature for 30 minutes to ensure that the reaction salts and refractory metals dissolve in the NaCl-KCl medium. Then, the graphite block was immersed in molten salt by a lifting rod, and the temperature was raised to 1200℃ at a rate of 10℃ / min and kept at this temperature for 180min. After the reaction was completed, the component was taken out by the lifting rod and cooled in the furnace to obtain a carbon component with a (TiZrHfNbTa)C high entropy ceramic coating on the surface. The obtained component was placed in 80℃ deionized water for ultrasonic treatment for 120min to obtain a carbon component without residual salt. The cross-sectional micromorphology and XRD spectrum of the (TiZrHfNbTa)C ultrahigh temperature carbide high entropy ceramic coating obtained in this embodiment are shown in FIG. Figure 9 and Figure 10 As shown. The XRD spectrum shows that the obtained ceramic is a single-phase solid solution with a face-centered structure, that is, the formed phase is a high-entropy ceramic, and the melting point of the ceramic coating is higher than 3000°C. In this embodiment, the reactive salt NH4Cl is used as a reactant for oxidizing the metal element. Since the HCl formed by the decomposition of NH4Cl at high temperature volatilizes, the metal ions formed are relatively small, and the corresponding (TiZrHfNbTa)C coating formed is relatively thin, about 90μm. The prepared ultra-high temperature carbide high-entropy ceramic coating was ablated in an oxyacetylene flame at 2000°C for 300 seconds, and the measured linear ablation rate was less than 0.7 microns / second, which has very excellent anti-ablation performance.

[0051] Comparative Example 1 A method for preparing a high-entropy ceramic coating is substantially the same as that of Example 1, differing only in that the five metal powders of Ti, Zr, Hf, Nb, and Ta are present in an equimolar ratio, and in an equimolar ratio with TiF4, ZrF4, HfF4, NbF5, and TaF5. Because the metal elements in this comparative example are present in equimolar ratios, the ZrC and HfC contents in the prepared coating are relatively low. The melting points of the oxides formed during the ablation of TiC, NbC, and TaC are all below 2000°C, resulting in relatively poor ablation resistance of the prepared coating. A linear ablation rate of 5.1 μm / s was measured after ablation at 2000°C for 300 seconds using an oxyacetylene flame.

[0052] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing ultra-high temperature carbide high entropy ceramic coating in situ at low temperature, characterized in that: The following steps are involved: A dielectric salt, five or more refractory metal elements, and ionic salts corresponding to each of the refractory metal elements are uniformly mixed to obtain a mixed powder; in an inert atmosphere, the temperature is increased to melt the refractory metal elements and ionic salts in the mixed powder into the dielectric salt to form a molten salt, and then a carbon preform is immersed in the obtained molten salt, and the temperature is increased to 1000°C to 1300°C for a thermal disproportionation reaction to obtain an ultra-high temperature carbide high-entropy ceramic coating.

2. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 1, characterized in that: The five or more refractory metal elements include five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten; the ionic salts corresponding to the refractory metal elements include chloride salts containing the refractory metal elements, fluoride salts containing the refractory metal elements or fluorates containing the refractory metal elements.

3. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 2, characterized in that: The refractory metal elements are five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten, and the molar ratio of the total mole of the refractory metal elements to titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1:0~0.1:0.25~0.5:0.25~0.5:0~0.1:0~0.1:0~0.1:0~0.1, and each refractory metal element and the corresponding ionic salt are in an equal molar ratio; the total mass of the refractory metal elements and the ionic salt is 2%~50% of the mass of the medium salt.

4. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 1, characterized in that: The temperature is raised to 700°C to 800°C and kept warm for 30min to 60min to melt the refractory metal elements and ionic salts into the medium salt; the time for the thermal disproportionation reaction is 30min to 300min, and the rate of heating to the thermal disproportionation reaction temperature is 10°C / min to 20°C / min.

5. A method for preparing ultra-high temperature carbide high entropy ceramic coating in situ at low temperature, characterized in that: The following steps are involved: A dielectric salt, a refractory metal element with five or more components, and a reactive salt are uniformly mixed to obtain a mixed powder; in an inert atmosphere, the temperature is increased to melt the refractory metal elements and the reactive salt in the mixed powder in the dielectric salt to form a molten salt; a carbon preform is immersed in the obtained molten salt, and the temperature is increased to 1000°C to 1300°C for a thermal disproportionation reaction to obtain an ultra-high temperature carbide high-entropy ceramic coating.

6. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 5, characterized in that: The five or more refractory metal elements include five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten; the reactive salt is a reactive salt that causes the refractory metal elements to form high-valent metal ions in a thermal disproportionation reaction, and the reactive salt includes ammonium fluoride or ammonium chloride.

7. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 6, characterized in that: The refractory metal elements are five or more of titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten, and the molar ratio of the total mole of the refractory metal elements to titanium, zirconium, hafnium, niobium, tantalum, molybdenum and tungsten is 1:0-0.1:0.25-0.5:0.25-0.5:0-0.1:0-0.1:0-0.1:0-0.1:0-0.1, the mass of the reactive salt is 0.8-1.2 of the total mass of the refractory metal elements; the sum of the mass of the refractory metal elements and the reactive salt is 2%-50% of the mass of the medium salt.

8. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to claim 5, characterized in that: The temperature is raised to 700°C to 800°C and kept warm for 30min to 120min to melt the refractory metal elements and reactive salts into the medium salt; the thermal disproportionation reaction time is 30min to 300min, and the rate of heating to the thermal disproportionation reaction temperature is 10°C / min to 20°C / min.

9. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to any one of claims 1 to 8, characterized in that: The medium salt is a binary or higher metal compound molten salt, the binary or higher metal compound molten salt includes a binary or higher metal chloride salt or a binary or higher metal fluoride salt, the binary or higher metal chloride salt includes a NaCl-KCl eutectic salt, a NaCl-CaCl2 eutectic salt, a KF-KCl eutectic salt, a LiF-KF eutectic salt, a KCl-LiCl-NaCl eutectic salt or a KCl-LiCl-CaCl2 eutectic salt.

10. The method for low-temperature in-situ preparation of ultra-high temperature carbide high entropy ceramic coating according to any one of claims 1 to 8, characterized in that: The mixed powder is laid in a crucible and placed in a sintering furnace; before impregnation, the carbon preform is suspended above the crucible by a lifting rod; after the reaction is completed, the component with the ultra-high temperature carbide high-entropy ceramic coating is taken out by the lifting rod, and the component is cooled to room temperature with the furnace, and then washed with water or heat treated to remove residual medium molten salt; the carbon preform includes a carbon / carbon preform or a graphite preform.

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