Multi-component alloy capsule, preparation method thereof and preparation method of ultrahigh-temperature ceramic-based composite material

Abstract

The invention discloses a multi-component alloy capsule, a preparation method thereof and a preparation method of an ultra-high-temperature ceramic-based composite material, and solves the problems that a continuous carbon fiber toughened ultra-high-temperature ceramic-based composite material prepared by an existing process method is poor in compactness and uniformity; a large-area alloy block is easily formed when the alloy melt is cooled, and surface fibers are easily damaged in the machining process. In the preparation method of the multi-component alloy capsule, the carbon powder and the silicon carbide powder are uniformly and dispersively coated on the surfaces of the alloy particles by utilizing the good viscosity and wettability of the polyvinyl alcohol aqueous solution. In the preparation and sintering process of the ultra-high-temperature ceramic matrix composite material, stress is applied to a thin shell through the volume expansion effect by heating, and a small amount of silicon particles with the surfaces wrapped with a polyvinyl alcohol solution preferentially seep out of micro-nano pores, so that the temperature field distribution of the embedded particles tends to be synchronous; and the silicon is controlled to more uniformly permeate into the porous intermediate at a higher temperature and a lower viscosity, so that the infiltration uniformity of the material is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a preparation process of a dense material, and in particular to a multi-element alloy capsule and a preparation method thereof, and a preparation method of an ultra-high temperature ceramic-based composite material. Background Art

[0002] Ultra-high temperature ceramic-based composites toughened with continuous carbon fibers overcome the intrinsic brittleness of ultra-high temperature ceramics while possessing the high temperature resistance (>2000°C) and oxidation resistance of ultra-high temperature ceramics. In particular, their structural strength increases rather than decreases under high enthalpy non-chemical equilibrium gas dynamic pressure. This makes them widely used in hot-end components such as the nose cover, leading edge, control rudder, and thermal protection cover system of hypersonic vehicles.

[0003] At present, the manufacturing processes of continuous carbon fiber toughened ultra-high temperature ceramic matrix composites mainly include chemical vapor deposition (CVI), polymer impregnation pyrolysis (PIP), slurry impregnation (SI), sol-gel (Sol-Gel) and reactive melt infiltration (RMI) methods. Except for the RMI method, it is difficult for the composite materials to achieve complete density using the other manufacturing processes mentioned above, and usually 10-15% porosity is left, resulting in low thermal conductivity and insufficient ablation resistance of the material. The technical advantages of the RMI method are short preparation cycle, much lower alloy raw material cost compared to ultra-high temperature ceramic precursors, ultra-high temperature ceramic powders, etc., and it is not restricted by the shape of the component, and the porosity of the material is low (<5%).

[0004] Alloys formed by silicon and refractory metals typically have high melting points, which leads to two consequences: First, very high reaction temperatures are required to completely melt the alloy. The melt viscosity is a function of temperature, making it difficult to balance the permeation driving force with the degree of fiber damage. Second, the traditional alloy powder embedding method creates a larger temperature gradient from the outer surface of the embedding to the product surface at a higher melting temperature. This temperature difference further leads to uneven melting of the alloy, resulting in rapid and uneven penetration of the liquid alloy directly in contact with the product surface. Due to a lack of effective control, the volume expansion caused by the reaction between carbon and the alloy can quickly close the pores on the product surface. This phenomenon further eliminates the permeation path for the peripheral liquid alloy, limiting the smooth progress of the subsequent RMI process. Furthermore, improper alloy ratio design can significantly affect material properties. For example, an excessively high silicon content will result in insufficient ultra-high-temperature ceramic content, while an excessively high refractory metal content will increase the melting point of the alloy melt.

[0005] Numerous studies have attempted to improve the uniformity of alloy RMI infiltration into porous ceramic intermediates. For example, patent publication number CN106882976A discloses a method for preparing a C / HfC-ZrC-SiC composite material. A resin-based slurry is prepared using phenolic resin, an organic solvent, and silicon-zirconium alloy powder. Subsequently, ZrC and SiC ceramics are obtained within the preform through an in-situ high-temperature reaction, thereby increasing the wettability of the subsequent silicon-zirconium alloy melt with the porous intermediate. This method improves the effect of subsequent alloy infiltration by increasing the reaction wetting dynamics. Although this method is helpful, it still cannot control the asynchronous melting of the alloy, and the pre-obtained ZrC and SiC ceramics are discontinuous, which cannot fundamentally solve the problem. Patent publication number CN110803942A discloses a method for modifying Si-Zr powder using a K2ZrF6 molten salt. By partially replacing Si or a Si-rich melt with a reactive molten salt, the Zr component is infiltrated into the C / C matrix at low temperatures. The high-valence Zr component undergoes a multi-step reaction to form a low-valence state, which reacts with C to precipitate a high-content ZrC. This method addresses the problems of excessive SiC content and high infiltration temperatures in the material after Si-based alloy infiltration, but it still fails to address the asynchrony of melting inside and outside the embedded powder. Although the overall ZrC ceramic content formed by the reaction is significantly increased, the molten salt generally has low melting and boiling points and limited solubility in the alloy. Although some alloy can be carried into the porous C / C at low temperatures, improving reactive wettability, the temperature gradient between the inside and outside of the embedded alloy powder quickly increases with temperature, making it impossible to control the RMI infiltration rate and resulting in uneven distribution of ZrC and SiC ceramics. The patent with publication number CN113773094B discloses a method for processing melt-infiltrated silicon powder, which includes chemical vapor deposition of carbon on the surface of the silicon powder, and mixing phenolic resin or other types of resin with the silicon powder, and pre-treating at around 900-1100°C to form a core-shell structure of the silicon powder. The purpose is to form a thin shell on its surface, and to utilize the volume change effect during its melting and heating process to enable silicon to break the shell and quickly enter the porous body, avoiding problems such as reaction clogging. Although the uniformity of melt infiltration is effectively improved, the invention has the following problems: first, the pretreatment steps are too complicated, which invisibly increases the manufacturing cost and production cycle. Second, whether the silicon is coated by chemical vapor deposition carbon or phenolic resin conversion carbon, its surface microstructure is a hard glassy carbon layer, which reacts with silicon at high temperature to form a thin SiC layer. Due to the presence of the hard carbon layer on the outside of the silicon powder, the thermal stress management of this thin layer is difficult, which will lead to poor quality of the thin layer and premature rupture. Third, chemical vapor deposition (CVD) of carbon-coated silicon powder is affected by the flow field, making deposition uniformity and yield difficult to guarantee. Phenolic resin-coated carbon can leave residue in the silicon powder, forming large SiC blocks within the powder, hindering subsequent liquid silicon infiltration. Fourth, both CVI and PIP methods can cause adhesion between silicon particles. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems of poor density and uniformity of continuous carbon fiber toughened ultra-high temperature ceramic-based composite materials prepared by existing process methods, and the problem that the alloy melt is prone to form large-area alloy blocks when cooling and the surface fibers are easily damaged during processing. A multi-element alloy capsule and a preparation method thereof and a preparation method of ultra-high temperature ceramic-based composite materials are provided.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a multi-element alloy capsule is characterized in that it comprises the following steps:

[0009] Step 1, weighing silicon powder and metal powder in a mass ratio of 11-12:8-9, mixing them evenly and placing them in a high-temperature furnace for melting, cooling them to room temperature, and crushing them to obtain alloy particles with a particle size of 1 μm to 5 μm;

[0010] Step 2: adding polyvinyl alcohol to deionized water, stirring and dissolving the water with a magnetic rotor and a magnetic stirrer to prepare a polyvinyl alcohol solution with a concentration of 2% to 8%;

[0011] Step 3, weighing alloy particles and pouring them into a ball mill, adding a polyvinyl alcohol solution with a concentration of 2% to 8% until the alloy particles are completely immersed, ball milling, and filtering to obtain alloy particles with polyvinyl alcohol coated on the surface;

[0012] Step 4: Weigh silicon carbide powder, alloy particles coated with polyvinyl alcohol, and carbon powder and add them into a ball mill. After multiple ball milling and sieving, multi-element alloy capsules are obtained.

[0013] Furthermore, the mass proportion of the silicon carbide powder is 10%-20%, the mass proportion of the alloy particles coated with polyvinyl alcohol is 70%-80%, the mass proportion of the carbon powder is 5%-10%, and the sum of the mass percentages of the above components is 100%.

[0014] Furthermore, in step 1, the metal powder is one of zirconium, hafnium and titanium.

[0015] Furthermore, in step 1, the melting temperature in the high-temperature furnace is 1600° C. to 1700° C., until the silicon powder and the metal powder are completely melted.

[0016] Furthermore, step 3 is specifically as follows:

[0017] Pour alloy particles with a particle size of 0.5μm to 10μm into a ball mill, add a polyvinyl alcohol solution with a concentration of 2% to 8% to completely immerse the alloy particles, ball mill for 4h to 6h, and pass through a 5000-10000 mesh sieve to obtain alloy particles with polyvinyl alcohol coated on the surface.

[0018] Furthermore, step 4 is specifically as follows:

[0019] Step 4.1, weighing silicon carbide powder with a particle size of 5 μm to 25 μm, alloy particles coated with polyvinyl alcohol, and carbon powder, adding them to a ball mill, ball milling for 2 h to 4 h, passing through a 10-mesh sieve, and adding them to the ball mill again;

[0020] Step 4.2: ball mill for 2 h to 4 h, and pass through a 10-mesh sieve to obtain multi-element alloy capsules.

[0021] A multi-element alloy capsule is special in that it is prepared based on the above-mentioned preparation method of the multi-element alloy capsule.

[0022] A method for preparing an ultra-high temperature ceramic-based composite material, which is special in that it comprises the following steps:

[0023] Step A: placing the porous intermediate into a graphite crucible or a graphite paper box, and evenly embedding the multi-element alloy capsules on the surface of the porous intermediate;

[0024] Step B: placing the graphite crucible in a vacuum sintering furnace, sintering, and cooling to room temperature to obtain an ultrahigh temperature ceramic-based composite material.

[0025] Furthermore, in step A, the porous intermediate is one of a porous carbon fiber, a porous silicon carbide fiber preform, a porous ceramic whisker preform, a porous tape-cast ceramic embryo, and a porous gel-injection molded ceramic embryo prepared by one of the CVI, PIP, SI, and So-Gel methods.

[0026] Furthermore, step B is specifically as follows: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to between 1600 and 1800° C., and keeping the temperature for 2 to 3 hours to obtain an ultrahigh temperature ceramic-based composite material.

[0027] When the temperature rises to between 300 and 600°C, polyvinyl alcohol, with its excellent film-forming properties, is mixed with carbon powder and spread on the surface of silicon particles. When the temperature rises to 800°C, due to the low residual carbon rate of the polyvinyl alcohol film, the dense carbon layer on the surface will be transformed into a porous carbon film, alleviating the thermal stress mismatch between silicon and carbon caused by the difference in thermal expansion coefficient. At the same time, the porous carbon film reacts with silicon to obtain a relatively dense XC-SiC thin layer, where X is one of zirconium, hafnium, and titanium.

[0028] The alloy particle ratio set in the present invention can control the physical phase composition of the capsule surface shell. When the metal powder content is appropriate, a composite shell will be preferentially generated on the surface, which can better manage the expansion coefficient of the shell to match that of the alloy at high temperature and will not cause premature rupture of the shell.

[0029] When the temperature rises to above 1600℃, the alloy particles melt in the composite shell. Due to the wrapping effect of the porous thin shell, the alloy particles will not escape at low temperatures, which prevents premature reaction with the carbon matrix in the porous intermediate and avoids the premature closure of the alloy liquid infiltration channel; when the temperature is further increased, the alloy particles with polyvinyl alcohol coated on the surface exert stress on the thin shell through the volume expansion effect, and a small amount of polyvinyl alcohol preferentially seeps out from the micro-nano pores, making the temperature field distribution of the embedded alloy particles close to synchronization, thereby controlling the alloy particles with polyvinyl alcohol coated on the surface to infiltrate the porous intermediate at higher temperature, lower viscosity and more uniformly, thereby significantly improving the material's infiltration uniformity.

[0030] Beneficial effects of the present invention:

[0031] (1) The present invention provides a method for preparing a multi-component alloy capsule and the resulting multi-component alloy capsule. The capsule utilizes the excellent viscosity and wettability of a polyvinyl alcohol aqueous solution to uniformly disperse carbon powder and silicon carbide powder onto the surface of alloy particles, avoiding the uneven coating and inter-particle adhesion associated with CVI and PIP methods. Water-soluble polyvinyl alcohol serves as a binder and a dispersion medium for the silicon carbide and carbon powders. Compared to ethanol and acetone solvents, water has a moderate saturated vapor pressure, making it easy to store for long periods of time and non-toxic and green.

[0032] (2) The present invention provides a method for preparing an ultra-high temperature ceramic-based composite material. During the sintering process, stress is applied to the thin shell through the volume expansion effect by increasing the temperature, and a small amount of silicon particles with a polyvinyl alcohol solution coated on the surface preferentially seep out from the micro-nano pores, so that the temperature field distribution of the embedded particles approaches synchronization, thereby controlling the silicon to penetrate into the porous intermediate at a higher temperature, lower viscosity, and more uniformly, thereby significantly improving the melt infiltration uniformity of the material.

[0033] (3) The present invention provides a method for preparing an ultra-high temperature ceramic-based composite material. After infiltration, the surface of the product is free of residual silicon-metal alloy blocks, and the surface fibers are intact and undamaged. Only light polishing is required, avoiding damage to the product surface caused by using tools to break off silicon blocks. The ultra-high temperature ceramic-based composite material prepared by the present invention has high density, high strength, low porosity, and low residual silicon, which significantly improves the consistency of the product.

[0034] (4) The present invention provides a method for preparing an ultra-high temperature ceramic-based composite material, which can avoid the "black core" phenomenon and improve the density of the product. The density of the C / SiC-XC composite material prepared by the present invention can reach 3.3g / cm 3 density, porosity is less than 5%, wherein X is one of zirconium, hafnium and titanium.

[0035] (5) The present invention provides a method for preparing an ultra-high temperature ceramic-based composite material, which can complete the preparation of multi-element alloy capsules in an oven, has low equipment requirements, and can be manufactured on a large scale at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is an appearance morphology diagram of the ultra-high temperature ceramic-based composite material prepared in Example 3 of the present invention;

[0037] Figure 2 This is an X-ray image of the ultra-high temperature ceramic-based composite material prepared in Example 3 of the present invention;

[0038] Figure 3 This is a SEM photograph of the fracture surface of the ultra-high temperature ceramic-based composite material prepared in Example 3 of the present invention;

[0039] Among them, (a) is a 30.4 mm × 50 SE magnification SEM photo, (b) is a 5.6 mm × 600 BSE magnification SEM photo;

[0040] Figure 4 A comparison of the morphology of the surface of the RMI after being embedded with conventional silicon powder and after being broken and processed, and the morphology of the surface of the ultra-high temperature ceramic-based composite material prepared in Example 3 of the present invention after being broken and processed;

[0041] Among them, (a) is a morphology photograph of the surface of the RMI after being embedded with traditional silicon powder and processed; (b) is a morphology photograph of the surface of the ultra-high temperature ceramic-based composite material prepared in Example 3 of the present invention after being processed. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Example 1

[0044] A method for preparing a multi-element alloy capsule comprises the following steps:

[0045] Step 1: Weigh 110 g of silicon powder and 90 g of titanium powder, the purity of which is not less than 99%, mix them evenly, and place them in a high-temperature furnace for melting at a temperature of 1600° C. until the silicon powder and titanium powder are completely melted. Cool them to room temperature, and crush them to obtain alloy particles with a particle size of 1 μm to 5 μm.

[0046] Step 2: adding polyvinyl alcohol to deionized water and stirring and dissolving the water with a magnetic rotor and a magnetic stirrer to prepare a polyvinyl alcohol solution with a concentration of 2%;

[0047] Step 3: Pour alloy particles with a particle size of 0.5 μm to 10 μm into a ball mill, add a 2% polyvinyl alcohol solution until the alloy particles are completely immersed, ball mill for 4 hours, and pass through a 5000 mesh sieve to obtain alloy particles with polyvinyl alcohol coated on the surface.

[0048] Step 4: Weigh 10 g of silicon carbide powder with a particle size of 5 μm to 25 μm, 80 g of alloy particles coated with polyvinyl alcohol, and 10 g of carbon powder, add them to a ball mill, ball mill for 2 h, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 2 h, pass through a 10-mesh sieve, and obtain multi-element alloy capsules.

[0049] This embodiment also provides a method for preparing an ultra-high temperature ceramic-based composite material, comprising the following steps:

[0050] Step A: placing a porous intermediate into a graphite crucible or a graphite paper box, and uniformly embedding the multi-element alloy capsules on the surface of the porous intermediate; the porous intermediate is a porous carbon fiber prepared by the CVI method.

[0051] Step B: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to 1600° C., and keeping the temperature for 2 hours to obtain an ultrahigh temperature ceramic-based composite material.

[0052] Example 2

[0053] A method for preparing a multi-element alloy capsule comprises the following steps:

[0054] Step 1, weighing 120g of silicon powder and 80g of hafnium powder, the purity of the silicon powder and hafnium powder being not less than 99%, mixing them evenly and placing them in a high-temperature furnace for melting at a melting temperature of 1700°C until the silicon powder and hafnium powder are completely melted, cooling to room temperature, and crushing to obtain alloy particles with a particle size of 1μm to 5μm;

[0055] Step 2: adding polyvinyl alcohol to deionized water and stirring and dissolving the polyvinyl alcohol with a magnetic rotor and a magnetic stirrer to prepare a polyvinyl alcohol solution with a concentration of 8%;

[0056] Step 3: Pour alloy particles with a particle size of 0.5 μm to 10 μm into a ball mill, add 8% polyvinyl alcohol solution until the alloy particles are completely immersed, ball mill for 6 hours, and pass through a 10,000 mesh sieve to obtain alloy particles with polyvinyl alcohol coated on the surface.

[0057] Step 4: Weigh 20 g of silicon carbide powder with a particle size of 5 μm to 25 μm, 70 g of alloy particles coated with polyvinyl alcohol, and 10 g of carbon powder, add them to a ball mill, ball mill for 4 h, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 4 h, pass through a 10-mesh sieve, and obtain multi-element alloy capsules.

[0058] This embodiment also provides a method for preparing an ultra-high temperature ceramic-based composite material, comprising the following steps:

[0059] Step A: placing a porous intermediate into a graphite crucible or a graphite paper box, and uniformly embedding the multi-element alloy capsules on the surface of the porous intermediate; the porous intermediate is a porous ceramic whisker preform prepared by the So-Gel method.

[0060] Step B: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to 1700° C., and keeping the temperature for 3 hours to obtain an ultrahigh temperature ceramic-based composite material.

[0061] Example 3

[0062] A method for preparing a multi-element alloy capsule comprises the following steps:

[0063] Step 1, weighing 115g of silicon powder and 85g of zirconium powder, the purity of the silicon powder and zirconium powder being not less than 99%, mixing them evenly and placing them in a high-temperature furnace for melting at a melting temperature of 1650°C until the silicon powder and zirconium powder are completely melted, cooling to room temperature, and crushing to obtain alloy particles with a particle size of 1μm to 5μm;

[0064] Step 2: adding polyvinyl alcohol to deionized water and stirring and dissolving the polyvinyl alcohol with a magnetic rotor and a magnetic stirrer to prepare a polyvinyl alcohol solution with a concentration of 5%;

[0065] Step 3: Pour alloy particles with a particle size of 0.5 μm to 10 μm into a ball mill, add a 5% polyvinyl alcohol solution until the alloy particles are completely immersed, ball mill for 5 hours, and pass through an 8000 mesh sieve to obtain alloy particles with polyvinyl alcohol coated on the surface.

[0066] Step 4: Weigh 15 g of silicon carbide powder with a particle size of 5 μm to 25 μm, 80 g of alloy particles coated with polyvinyl alcohol, and 5 g of carbon powder, add them to a ball mill, ball mill for 3 h, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 3 h, pass through a 10-mesh sieve, and obtain multi-element alloy capsules.

[0067] This embodiment also provides a method for preparing an ultra-high temperature ceramic-based composite material, comprising the following steps:

[0068] Step A: placing a porous intermediate into a graphite crucible or a graphite paper box, and uniformly embedding the multi-element alloy capsules on the surface of the porous intermediate; the porous intermediate is a porous gel-casting ceramic embryo prepared by a PIP method.

[0069] Step B: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to 1650° C., and keeping the temperature for 3 hours to obtain an ultrahigh temperature ceramic-based composite material.

[0070] Figure 1 This is the appearance morphology of the ultra-high temperature ceramic-based composite material prepared in Example 3. Figure 1 It can be seen that there is no residual silicon-zirconium alloy block on the surface; only slight grinding is required to obtain a product with net size.

[0071] The X-ray images of the ultra-high temperature ceramic matrix composite material prepared in Example 3 are as follows: Figure 2 As shown, according to Figure 2 It can be seen that the overall density of the sample is high and the infiltration is uniform.

[0072] The SEM photo of the fracture of the ultra-high temperature ceramic matrix composite material prepared in Example 3 is as follows: Figure 3 As shown in the figure, (a) is a 30.4 mm × 50 SE magnification SEM photo, and (b) is a 5.6 mm × 600 BSE magnification SEM photo. According to (a) and (b), it can be seen that the high-temperature ceramic matrix composite material is dense inside, with extremely small pore size and low porosity. The ultra-high temperature ceramic, SiC ceramic and residual alloy components are evenly distributed. The density of C / SiC after RMI alloying can reach 3.3 g / cm 3 , the porosity is 1.9%.

[0073] Figure 4 (a) is a morphological photograph of the surface of the RMI after the traditional silicon powder embedding process. It can be seen that due to the adhesion of large areas of alloy melt, alloy blocks are formed during cooling and are combined with ZrC and SiC on the surface through chemical reactions. The strong bonding force causes large areas of fibers to be peeled off after the blocks are broken, and the surface of the product is seriously damaged. The morphological photograph of the surface of the continuous fiber toughened ceramic matrix composite prepared in Example 3 after the surface is broken is shown in the figure. Figure 4 As shown in (b), according to Figure (b), after surface polishing, the surface fibers of the continuous fiber reinforced ceramic matrix composite are well preserved.

[0074] The above description is merely a specific embodiment of the present invention, and a comparison of the effects of the specific embodiment with the relevant comparative examples. However, the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a multi-element alloy capsule, characterized in that: The following steps are involved: Step 1, weighing silicon powder and metal powder in a mass ratio of 11-12:8-9, mixing them evenly and placing them in a high-temperature furnace for melting, cooling them to room temperature, and crushing them to obtain alloy particles with a particle size of 1 μm to 5 μm; Step 2: adding polyvinyl alcohol to deionized water, stirring and dissolving the water with a magnetic rotor and a magnetic stirrer to prepare a polyvinyl alcohol solution with a concentration of 2% to 8%; Step 3, weighing alloy particles and pouring them into a ball mill, adding a polyvinyl alcohol solution with a concentration of 2% to 8% until the alloy particles are completely immersed, ball milling, and filtering to obtain alloy particles with polyvinyl alcohol coated on the surface; Step 4: Weigh silicon carbide powder, alloy particles coated with polyvinyl alcohol, and carbon powder and add them into a ball mill. After multiple ball milling and sieving, multi-element alloy capsules are obtained.

2. The method for preparing a multi-element alloy capsule according to claim 1, wherein: In step 4, the mass proportion of the silicon carbide powder is 10%-20%, the mass proportion of the alloy particles coated with polyvinyl alcohol is 70%-80%, and the mass proportion of carbon powder is 5%-10%. The sum of the mass percentages of the above components is 100%.

3. The method for preparing a multi-element alloy capsule according to claim 1, characterized in that: In step 1, the metal powder is one of zirconium, hafnium and titanium.

4. The method for preparing a multi-element alloy capsule according to claim 1, characterized in that: In step 1, the melting temperature in the high-temperature furnace is 1600° C. to 1700° C., until the silicon powder and the metal powder are completely melted.

5. The method for preparing a multi-element alloy capsule according to claim 1, characterized in that: Step 3 is as follows: Pour alloy particles with a particle size of 0.5μm to 10μm into a ball mill, add a polyvinyl alcohol solution with a concentration of 2% to 8% to completely immerse the alloy particles, ball mill for 4h to 6h, and pass through a 5000-10000 mesh sieve to obtain alloy particles with polyvinyl alcohol coated on the surface.

6. The method for preparing a multi-element alloy capsule according to claim 1 or 2, characterized in that: Step 4 is as follows: Step 4.1, weighing silicon carbide powder with a particle size of 5 μm to 25 μm, alloy particles coated with polyvinyl alcohol, and carbon powder, adding them to a ball mill, ball milling for 2 h to 4 h, passing through a 10-mesh sieve, and adding them to the ball mill again; Step 4.2: ball mill for 2 h to 4 h, and pass through a 10-mesh sieve to obtain multi-element alloy capsules.

7. A multi-element alloy capsule, characterized in that: The multi-element alloy capsule is prepared using the preparation method of any one of claims 1-6.

8. A method for preparing an ultra-high temperature ceramic-based composite material, characterized in that: The following steps are involved: Step A, placing the porous intermediate into a graphite crucible or a graphite paper box, and uniformly embedding the multi-element alloy capsules prepared by the method for preparing the multi-element alloy capsules according to any one of claims 1 to 6 on the surface of the porous intermediate; Step B: placing the graphite crucible in a vacuum sintering furnace, sintering, and cooling to room temperature to obtain an ultrahigh temperature ceramic-based composite material.

9. The method for preparing an ultrahigh temperature ceramic matrix composite material according to claim 8, characterized in that: In step A, the porous intermediate is one of a porous carbon fiber, a porous silicon carbide fiber preform, a porous ceramic whisker preform, a porous tape-cast ceramic embryo, and a porous gel-injection-molded ceramic embryo prepared by one of the CVI, PIP, SI, and So-Gel methods.

10. The method for preparing an ultra-high temperature ceramic-based composite material according to claim 8, characterized in that: Step B is specifically as follows: placing a graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to between 1600 and 1800° C., and keeping the temperature for 2 to 3 hours to obtain an ultrahigh temperature ceramic-based composite material.

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