A high-temperature resistant high-entropy metal ceramic microwave absorbing filler and its preparation method

Abstract

The present invention discloses a high-temperature resistant high-entropy metal ceramic microwave absorbing filler and a preparation method thereof. The high-temperature resistant high-entropy metal ceramic microwave absorbing filler has a composite phase of a metal phase and a ceramic phase in-situ precipitated in a ceramic phase matrix, wherein the metal phase is a high-entropy alloy or a transition metal-based alloy, and the ceramic phase is a high-entropy oxide; calculated by mole percentage, the content of the metal phase of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler is 30-90%, and the content of the ceramic phase is 10-70%.

Description

Technical Field

[0001] The present invention belongs to the field of radar electromagnetic wave absorbing materials, and particularly relates to a high-temperature resistant high-entropy metal ceramic wave-absorbing filler and a preparation method thereof. Background Art

[0002] In modern warfare, all-round stealth is one of the core technologies for achieving rapid offense and defense conversion, and has become an important research goal of major military powers around the world. As the main radar scattering source, the engine and its afterbody structure are restricted by power conditions on the one hand, with limited room for structural stealth design, and on the other hand, restricted by high-temperature conditions, and room-temperature wave-absorbing materials can no longer meet the requirements. High-entropy materials have excellent properties such as oxidation resistance, high temperature resistance, and corrosion resistance, providing a good solution for high-temperature wave-absorbing materials.

[0003] At present, the research and development of domestic high-temperature wave-absorbing materials is in its infancy, and more reports are on continuous silicon carbide fiber-reinforced silicon carbide-based (SiC f / SiC) high-temperature resistant wave-absorbing composites. Chinese Patent CN 106220211A discloses a high-temperature wave-absorbing metamaterial based on a silicon carbide composite material, which consists of a continuous silicon carbide fiber layer, an antioxidant connection layer, and a metamaterial layer. By designing the periodic structure of the metamaterial and adjusting the resistivity of the silicon carbide composite material, a high-temperature resistant wave-absorbing composite material with excellent wave-absorbing performance is prepared, especially having excellent wave-absorbing performance in the low-frequency band of radar waves. However, there are still problems such as low bonding strength between layers, complex processes, and high costs. In addition, Chinese Patent CN 108998689A discloses a composite material of a nickel-based superalloy, silicon carbide, and conductive carbon black, with a reflectivity less than -6 dB within the frequency range of 12.5 - 18 GHz, effectively reducing the preparation cost of previous high-temperature wave-absorbing materials, but sacrificing certain performance and design space at the same time.

[0004] Since the advent of high-entropy alloys in 2004, major science and engineering universities and research institutes around the world have carried out research on them. In 2015, entropy-stabilized oxides were further confirmed, and high-entropy materials have become a hot research direction. The multi-component system of high-entropy materials not only endows the materials with an entropy-stable structure, making them have the performance advantage of high temperature resistance, but also endows the materials with a wide design space and broad application prospects. However, existing high-entropy materials are generally in a single-phase structure. Among them, high-entropy alloys are difficult to be applied to microwave absorption materials due to their inevitable skin effect, and high-entropy oxides have problems such as insufficient microwave loss ability and single loss mode. Summary of the Invention

[0005] In view of the above problems, the present invention provides a high-temperature resistant high-entropy metal ceramic microwave absorption filler and a preparation method thereof, which has excellent microwave absorption performance, a broad design space, integrated multiple properties, a stable structure, easy control of parameters, and is convenient for engineering production.

[0006] In the first aspect, the present invention provides a high-temperature resistant high-entropy metal ceramic microwave absorption filler. The high-temperature resistant high-entropy metal ceramic microwave absorption filler has a composite phase of a metal phase and a ceramic phase precipitated in-situ in a ceramic phase matrix, wherein the metal phase is a high-entropy alloy or a transition metal-based alloy, and the ceramic phase is a high-entropy oxide; calculated by mole percentage, the metal phase content of the high-temperature resistant high-entropy metal ceramic microwave absorption filler is 30-90%, and the ceramic phase content is 10-70%.

[0007] Preferably, the metal components of the high-temperature resistant high-entropy metal ceramic microwave absorption filler are at least five of Fe, Co, Ni, Cr, Mn, Al, Ti, Cu, Mg, Y, Zn, Sn, and preferably Fe, Co, Ni, Cr, Mn.

[0008] Preferably, the ceramic phase has a spinel structure, a rock salt structure or a perovskite structure.

[0009] Preferably, the metal phase forms a conductive network in the microscopic region without forming large-area aggregates.

[0010] Preferably, the composite phase is an ohmic phase composite dielectric phase.

[0011] In the second aspect, the present invention also provides a preparation method of the high-temperature resistant high-entropy metal ceramic microwave absorption filler described in any one of the above. The preparation method includes: using oxides containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; subjecting the precursor mixture to high-temperature sintering in an air atmosphere and then rapidly cooling in air to obtain an entropy-stable ceramic phase, and then reducing the entropy-stable ceramic phase at a high temperature in a reducing atmosphere to in-situ precipitate a metal phase in the ceramic phase matrix to obtain the high-temperature resistant high-entropy metal ceramic microwave absorption filler. Alternatively, the preparation method includes: using oxides containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; performing high-temperature sintering in a reducing atmosphere to directly prepare the high-temperature resistant high-entropy metal ceramic microwave absorption filler.

[0012] Preferably, the molar content of the metal components in the oxides is 5-35%.

[0013] Preferably, the sintering temperature is 1000-1400 °C, and the sintering time is 1-5 h.

[0014] Preferably, the reduction temperature is 800-1400 °C, the reduction time is 1-10 h, and preferably 3-10 h.

[0015] Beneficial effects:

[0016] 1. The design space of the high-temperature resistant cermet microwave absorbing filler of the present invention is broad. By selecting different components and changing their contents, the two-phase structure, distribution state, and microwave absorbing performance of the final cermet can be adjusted, and multi-functional integration such as high temperature resistance, corrosion resistance, and mechanical properties can be achieved.

[0017] 2. When the thickness of the high-temperature resistant cermet microwave absorbing filler of the present invention is 1.8 mm, the effective absorption of electromagnetic waves can reach more than 90% within the frequency range of 11.6 - 18 GHz.

[0018] 3. The high-temperature resistant cermet microwave absorbing filler of the present invention in-situ precipitates metal phases on the matrix of high-entropy ceramics, which rapidly increases the carrier concentration and introduces the Ohmic loss mechanism; a large number of hetero-interfaces are formed at the junction of the two phases of the cermet, effectively enhancing the dielectric polarization loss ability; in addition, the metal phase can also have excellent soft magnetic properties to enhance the magnetic loss and improve the impedance matching.

[0019] 4. The high-temperature resistant cermet microwave absorbing filler of the present invention has a two-phase structure uniformly dispersed at the micron scale, making the carrier concentration at an appropriate scale and endowing the material with excellent impedance matching performance.

[0020] 5. The high-temperature resistant cermet microwave absorbing filler of the present invention has severe lattice distortion due to the difference in atomic (ionic) radii between different elements, which simultaneously intensifies the scattering of carriers and phonons, further enhancing the loss ability of electromagnetic waves, as well as high temperature resistance and low thermal diffusion ability. Brief Description of the Drawings

[0021] Figure 1 XRD pattern of the high-temperature resistant high-entropy cermet microwave absorbing filler (x = 1, 2, 3, 4, 5, 6) prepared in Example 1 provided by the present invention;

[0022] Figure 2 SEM pattern of the high-temperature resistant high-entropy cermet microwave absorbing filler (x = 1) prepared in Example 1 provided by the present invention;

[0023] Figure 3 Electromagnetic wave absorption pattern of the high-temperature resistant high-entropy cermet microwave absorbing filler (x = 1, 2, 6) prepared in Example 1 provided by the present invention;

[0024] Figure 4 Electromagnetic wave absorption pattern of the high-temperature resistant high-entropy cermet microwave absorbing filler (x = 5) prepared in Example 1 provided by the present invention;

[0025] Figure 5 Thermogravimetric analysis diagram of the high-temperature resistant high-entropy cermet microwave absorbing filler (x = 1) prepared in Example 1 provided by the present invention;

[0026] Figure 6 XRD patterns of the high-temperature resistant high-entropy metal ceramic microwave absorbing fillers (x = 1, 2, 3, 4, 5, 6) prepared in Example 2 provided by the present invention;

[0027] Figure 7 SEM pattern of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler (x = 1) prepared in Example 2 provided by the present invention;

[0028] Figure 8 XRD patterns of the high-temperature resistant high-entropy metal ceramic microwave absorbing fillers (x = 1, 2, 3, 4, 5, 6) prepared in Example 3 provided by the present invention. Detailed implementation manners

[0029] The present invention is further illustrated by the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention, rather than limiting the present invention. Without special instructions, the percentage contents refer to mass percentage contents.

[0030] Most of the existing high-entropy materials are single-phase structures. High-entropy alloys are difficult to be applied to microwave absorbing materials due to the inevitable skin effect. High-entropy oxides have problems such as insufficient microwave loss ability and single loss mode. The present invention provides a high-temperature resistant high-entropy metal ceramic microwave absorbing filler, which comprises a two-phase structure of a metal phase and a ceramic phase.

[0031] The metal phase is a high-entropy alloy or a transition metal-based alloy. The high-entropy alloy is an alloy formed by more than five metal components, which may include transition metals, but is not limited to only transition metals. The alloys of the high-entropy alloy include but are not limited to FeCoNiCrMn, FeCoNiCrAl, FeCoNiAlMn, FeCoNiCrMnAl, etc. As an example, the high-entropy alloy is a {Fe, Co, Ni}-based high-entropy alloy. The number of metal components of the transition metal-based alloy is usually less than five, and may also include non-transition metals. As an example, the transition metal-based alloy can also be a {Fe, Co, Ni}-based alloy. The alloy range can be relatively wide, and the precipitated ones are not only transition metals, but relatively active metal elements.

[0032] The ceramic phase is a high-entropy oxide. The high-entropy oxides include but are not limited to {Mn, Cr}-based spinels, {Zn, Cr}-based spinels, {Zn, Mn, Cr}-based spinels, etc. As an example, the high-entropy oxide is a {Mn, Cr}-based spinel. The structure of the ceramic phase can be a spinel structure, a rock salt structure, a perovskite structure, etc.

[0033] Preferably, in terms of molar percentage, the metal phase content of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler is 30-90%, and the ceramic phase content is 10-70%. If the content of the metal phase is less than 30%, the carrier concentration will be too low, the ohmic loss ability will be insufficient, and the microwave absorbing performance will decline; if the content of the metal phase is higher than 90%, the carrier concentration will be too high, and the reflection of the material will be too strong, which is not conducive to achieving excellent microwave absorbing performance. In some technical solutions, the metal phase content of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler is 50-90%, and the ceramic phase content is 10-50%.

[0034] The two-phase structure of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler has significantly different diffraction peaks on the XRD pattern, and both the metal phase and the ceramic phase are relatively evenly distributed. The two-phase structure is obvious in the SEM pattern and the secondary electron image, and the distribution of the two phases is further confirmed in the backscattered electron diffraction. Among them, the average atomic number in the metal phase is higher, and the corresponding backscattered electron pattern is brighter, while the backscattered electron pattern of the ceramic phase is darker.

[0035] The two-phase structure of the existing high-temperature resistant transition metal high-entropy oxide microwave absorbing filler is a two-phase structure of spinel structure and corundum type structure, belonging to the composite dielectric phase. It attempts to increase the heterointerface to form more dipole polarizations and improve the microwave absorbing performance by enhancing the dielectric loss. However, the present invention is a composite of high-entropy alloy phase and spinel ceramic phase, belonging to the ohmic phase composite dielectric phase, and mainly improves the microwave absorbing performance by enhancing the ohmic loss; the introduction of the metal phase not only forms more heterointerfaces, but also greatly increases the carrier concentration and conductivity, which significantly improves the loss ability and microwave absorbing performance of the material system.

[0036] The high-temperature resistant high-entropy metal ceramic microwave absorbing filler of the present invention precipitates the metal phase in-situ in the ceramic phase matrix. Preferably, the precipitated metal phase forms a regional conductive network instead of a large-scale conductive block, which can avoid the strong electromagnetic wave reflection caused by excessive conductivity.

[0037] The following exemplarily illustrates the preparation method of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler of the present invention.

[0038] As an example, the preparation method includes: using oxides containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; sintering the precursor mixture at high temperature to form an entropy-stable ceramic phase, and then reducing it to precipitate the metal phase in-situ in the ceramic phase matrix. Through the control of the reduction process, the selection of components and the regulation of the molar ratio of components, the regulation of the type, content and distribution of the conductive second phase (conductive phase) is realized, aiming to introduce ohmic loss and suitable impedance matching to achieve excellent microwave absorbing performance, as well as to realize the integration of multiple functions such as heat insulation, corrosion resistance and high temperature resistance.

[0039] Mixing of metal oxide raw materials. The oxides containing metal components serve to introduce cation components. The oxides containing metal components include more than three of Fe-based oxides, Ni-based oxides, Co-based oxides, Cr-based oxides, Mn-based oxides, Al-based oxides, Mg-based oxides, Ti-based oxides, Cu-based oxides, and Y-based oxides. Preferably, there are three. Preferably, the molar content of the metal components in the oxides is between 5% and 35%. This can enable the material to have sufficient configurational entropy to form an entropy-stable structure.

[0040] The number of metal components is greater than five, which can enable the material to have sufficient configurational entropy to form an entropy-stable structure. Correspondingly, the metal components of the high-entropy alloy are at least five of Fe, Co, Ni, Cr, Mn, Al, Ti, Cu, Mg, Y, Zn, and Sn, preferably Fe, Co, Ni, Cr, and Mn. When using Fe, Co, Ni, Cr, and Mn as metal components, the molar ratio of Fe, Co, Ni, Cr, and Mn is 0.05 - 0.35:0.05 - 0.35:0.05 - 0.35:0.05 - 0.35:0.05 - 0.35. The proportion of metal components will affect the formation of the two-phase structure. When the proportion of metal components deviates from the equimolar ratio, the configurational entropy of the system decreases. At this time, the precursor sintered in an air atmosphere is not a high-entropy ceramic phase, and the subsequently in-situ precipitated metal phase is not a high-entropy alloy either, but mostly a transition metal-based alloy.

[0041] The particle size of the oxides is independently selected from 1 - 20 μm. This is beneficial for uniform ball milling mixing and subsequent pressing and sintering forming.

[0042] The mixing method can be ball milling. For example, ball mill the oxides containing metal components, and then dry the ball-milled sample to obtain a precursor mixture. For example, select appropriate types and contents of metal oxides for Wet ball ball milling. After ball milling, pour it out of the beaker, stir and dry it to make a uniformly mixed composite powder. The ball milling parameters are the conventional choices of those skilled in the art. As an example, the ball milling medium is selected as ethanol; the ball milling time is 2 - 10 h; the mass ratio of the ball milling beads to the raw materials to be ball milled is 4:1 - 20:1; the ball milling speed is 200 - 400 revolutions per minute. After ball milling, dry it. The drying temperature can be 60 - 100 °C.

[0043] Form the precursor mixture into a green body. The blank sample can be prepared by pressing. For example, pour the precursor mixture powder into a pre-prepared mold and press it into a block. The pressing pressure is 5 - 40 MPa, and the pressure holding time is 3 - 30 min. The block can be ground and sieved before sintering.

[0044] Sintering. After sintering the precursor mixture in an air atmosphere and rapidly cooling it in air, a high-entropy oxide ceramic phase (also referred to as "high-entropy ceramic" or "entropy-stabilized ceramic phase") is obtained. Preferably, the sintering temperature is 1000 - 1400 °C, and the sintering time is 1 - 5 h. The heating rate can be 2 - 10 °C / min to raise the temperature to the sintering temperature. For example, the pressed block is subjected to high-temperature sintering in an air atmosphere; after sintering is completed, the sample is quickly taken out and rapidly cooled in air; after cooling is completed, the high-entropy ceramic is obtained.

[0045] High-temperature reduction. The cooled high-entropy ceramic is subjected to high-temperature reduction in a reducing atmosphere. After the reduction is completed, it is cooled with the furnace to obtain the high-temperature-resistant cermet microwave absorbing filler with a dual-phase structure. The reducing atmosphere can be hydrogen. Preferably, the reduction temperature is 800 - 1400 °C, and the reduction time is 1 - 10 h. The reduction time affects the precipitation content of the metal phase. For example, the temperature is raised to the reduction temperature at a heating rate of 2 - 10 °C / min.

[0046] The preparation method and process of the high-temperature-resistant cermet microwave absorbing filler described in the present invention are non-toxic and harmless, and the raw materials are widely sourced and relatively inexpensive. By adjusting the reduction time, reduction temperature, component types and their contents, a high-temperature-resistant high-entropy cermet microwave absorbing filler with coexistence of metal and ceramic phases is formed, thereby improving the electromagnetic wave absorption ability.

[0047] As a second example, the preparation method includes: using the oxide containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; performing high-temperature sintering in a reducing atmosphere to directly prepare the high-temperature-resistant high-entropy cermet microwave absorbing filler. The metal components and reduction conditions refer to the foregoing method and will not be described herein again.

[0048] In some technical solutions, the thickness of the high-temperature-resistant cermet microwave absorbing material obtained by the method is 1 - 5 mm, and the density is 2.0 - 6.0 g / cm 3 。

[0049] Chinese Patent CN 111168057A mentions a nano-ceramic reinforced high-entropy alloy composite powder for additive manufacturing, its preparation method and application. Using high-entropy alloy as the matrix powder and nano-ceramic particles as the reinforcing phase particles, a high-entropy alloy powder with nano-ceramic particles uniformly adhered to its surface is obtained by means of ultrasonic dispersion and metal stirring. There are significant differences between the present invention and this solution in terms of preparation method, phase structure, phase content, usage, etc. In terms of the preparation method, this solution selects a specific high-entropy alloy and modifies selected nano-ceramic particles on its surface. It is a modified preparation in the way of additive manufacturing, and the final product is still particles. While the present invention directly prepares the wave absorber from the raw materials by in-situ precipitating a conductive second phase in the high-entropy ceramic phase, aiming to pursue the formation of the heterogeneous interface at the junction of the two phases and the content and distribution of the conductive phase. Its product is a bulk (which can also be ground into wave absorber particles). In terms of the phase structure, the two-phase material system of this solution depends on the specific high-entropy alloy and nano-ceramic particles it selects. While the present invention has a very wide design space for the two phases. The metal phase is not limited to high-entropy alloys and can also be transition metal-based alloys. Similarly, the ceramic phase is not only limited to nano-particles with enhanced performance and can be high-entropy ceramics. In terms of the phase content, the content of the two phases in this solution is mainly high-entropy alloy with nano-particle modification. While the proportion of the two phases in the present invention has no primary or secondary relationship and can be designed according to the needs of wave absorption performance and other performances and can be effectively adjusted. In terms of usage, this solution pursues the performance in the mechanical field, focusing on the uniform distribution of nano-ceramic powder on the surface of high-entropy alloy to improve its ductility. While the present invention is pursuing the directional design of the content and distribution of the two phases, aiming at high loss and impedance matching of electromagnetic waves. Therefore, CN 111168057A is completely different from the present invention. It pursues enhanced mechanical properties, pays attention to the uniform distribution on the surface of alloy particles, presents in the form of a spherical shell structure, cannot meet the regulation design of the content of the two phases, and has a narrower selection space for the two phases, which is not conducive to electromagnetic regulation.

[0050] The following further gives examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0051] Example 1

[0052] Using Fe2O3 powder, Co3O4 powder, NiO powder, Cr2O3 powder and MnO2 powder as raw materials (all reagent pure, >99%, 300 mesh), where the molar concentration ratio of metal cations in the raw materials (Fe element: Co element: Ni element: Cr element: Mn element) is x:1:1:1:1 (x = 1, 2, 3, 4, 5, 6). Place the raw materials in a nylon ball milling jar and wet ball mill at a speed of 360 revolutions per minute for 6 hours, changing the rotation direction every half hour. The mass ratio of the ball milling beads to the raw materials is 15:1, and the ball milling medium is industrial ethanol. After ball milling, pour the mixture into a beaker, add a stir bar, and stir and dry on a heating stirrer table at a drying temperature of 80°C. After drying, pour the mixed powder into a pre-prepared mold, hold the pressure at 20 MPa for 10 minutes, release the pressure, take out the pressed block and place it in a platinum crucible, and put it into a muffle furnace together, and sinter at a high temperature of 1100°C for 3 hours, with a heating rate of 2°C / min. After sintering, take out the crucible, and quickly cool the sample and the crucible in the air. Cool to room temperature to obtain a high-entropy ceramic sample. Put the high-entropy ceramic sample into a tube furnace and carry out high-temperature reduction in a hydrogen atmosphere, with a heating rate of 2°C / min, a hydrogen flow rate of 200 mL / min, a reduction temperature of 1100°C, and a reduction time of 3 hours. After the high-temperature reduction is completed, the sample is cooled with the furnace to obtain a high-temperature resistant high-entropy metal ceramic microwave absorption filler.

[0053] As Figure 1 shown, the XRD pattern of the high-temperature resistant high-entropy metal ceramic microwave absorption filler prepared in this example shows that when x = 1, 2, 3, 4, 5, 6, the samples all exhibit a two-phase structure of ceramic and metal. Among them, the ceramic phase is a high-entropy oxide with a spinel structure; while the metal phase presents a high-entropy alloy phase and / or an iron-based alloy phase. When x = 1, the metal phase is a face-centered cubic high-entropy alloy phase; when x = 3, 4, 5, 6, the metal phase is an iron-based alloy phase; when x = 2, the metal phase is a two-phase structure of face-centered cubic high-entropy alloy and iron-based alloy. The experimental results show that with the increase of the content of the component iron element, the metal phase gradually changes from a high-entropy alloy phase to an iron-based alloy phase. The main reason may be that the ratio between the precipitated metal elements is no longer a near molar ratio, and it cannot provide enough configurational entropy to maintain the entropy-stable structure.

[0054] As Figure 2 shown, the SEM (backscattered electron diffraction) pattern (x = 1) of the high-temperature resistant high-entropy metal ceramic microwave absorption filler prepared in this example presents the micro-morphology of the sample. According to the imaging principle of the backscattered electron diffraction pattern, the region with a higher atomic number is brighter, and the region with a lower atomic number is relatively darker. Therefore, Figure 2The bright regions are metal phases, while the dark regions are ceramic phases. The metal phases precipitate in-situ in the ceramic phase matrix, forming a conductive network (conductive micro-regions) in the microscopic regions, and without forming large-area metal phase agglomerations macroscopically, effectively introducing ohmic losses, enhancing the dielectric polarization ability, and endowing the material with excellent impedance matching.

[0055] As Figure 3 shown, the electromagnetic wave absorption properties of the high-temperature resistant high-entropy metal ceramic microwave absorbing fillers prepared in this example (x = 1, 2, 6) are as follows. When x = 1, the sample can achieve more than 90% effective absorption within the frequency range of 10.5 - 14.2 GHz at a thickness of 2.5 mm; when x = 2, the sample can achieve more than 90% effective absorption within the frequency range of 11.6 - 16.3 GHz at a thickness of 2.0 mm; when x = 6, the sample can achieve more than 90% effective absorption within the frequency range of 11.6 - 18 GHz at a thickness of 1.8 mm.

[0056] As Figure 4 shown, the electromagnetic wave absorption properties of the high-temperature resistant high-entropy metal ceramic microwave absorbing fillers prepared in this example. It can be seen from the figure that when x = 5, the sample can achieve more than 90% effective absorption within the frequency range of 12.9 - 17.8 GHz at a thickness of 1.6 mm, achieving quite excellent electromagnetic wave absorption performance at a very thin thickness.

[0057] As Figure 5 shown, the thermal analysis (x = 1) results of the high-temperature resistant high-entropy metal ceramic microwave absorbing fillers prepared in this example show that the powder sample maintains good thermal stability below 400 °C, while the powder sample begins to oxidize above 400 °C.

[0058] The results show that for the high-temperature resistant metal ceramic microwave absorbing material prepared by the present invention, the metal phase and the ceramic phase are evenly distributed, the phase structure and content are adjustable, and it has excellent high-temperature resistance and electromagnetic wave absorption performance. The preparation method has a rich adjustment mechanism, strong designability, low raw material cost, no pollution, and is environmentally friendly.

[0059] Example 2

[0060] Using Fe2O3 powder, Co2O3 powder, NiO powder, Cr2O3 powder and MnO2 powder as raw materials (all are reagent pure, >99%, 300 mesh), where the molar concentration ratio of metal cations in the raw materials (Fe element: Co element: Ni element: Cr element: Mn element) is x:1:1:1:1 (x = 1, 2, 3, 4, 5, 6). Place the raw materials in a nylon ball milling tank and wet ball mill at a speed of 360 revolutions per minute for 6 hours, changing the rotation direction every half hour. The mass ratio of the ball milling beads to the raw materials is 15:1, and the ball milling medium is industrial ethanol. After ball milling, pour the mixture into a beaker, add a magnetic stirrer, and stir and dry on a heating stirrer table at a drying temperature of 80°C. After drying, pour the mixed powder into a pre-prepared mold, keep the pressure at 20 MPa for 10 min, release the pressure, take out the pressed block and place it in a platinum crucible, and put it into a muffle furnace together. Sinter at a high temperature of 1100°C for 3 hours, and the heating rate is 2°C / min. After sintering, take out the crucible, and quickly cool the sample and the crucible in the air. After cooling to room temperature, a high-entropy ceramic sample is obtained. Put the high-entropy ceramic sample into a tube furnace and perform high-temperature reduction in a hydrogen atmosphere. The heating rate is 2°C / min, the hydrogen flow rate is 200 mL / min, the reduction temperature is 1100°C, and the reduction time is 2 hours. After the high-temperature reduction is completed, the sample is cooled with the furnace to obtain a high-temperature resistant high-entropy metal ceramic microwave absorbing filler.

[0061] As Figure 6 shown, the XRD pattern of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler prepared in this example shows that when x = 1, 2, 3, 4, 5, 6, the samples all exhibit a two-phase structure of ceramic and metal. Among them, the ceramic phase is a high-entropy oxide, and the structure presents a spinel structure; while the metal phase presents a high-entropy alloy phase or an iron-based alloy phase. When x = 1, the metal phase is a face-centered cubic high-entropy alloy phase; when x = 2, 3, 4, 5, 6, the metal phase is an iron-based alloy phase.

[0062] As Figure 7 shown, the SEM (backscattered electron diffraction) pattern (x = 1) of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler prepared in this example presents the microscopic morphology of the sample. According to the imaging principle of the backscattered electron diffraction pattern, the region with a higher atomic number is brighter, and the region with a lower atomic number is relatively darker. Therefore, Figure 6 the bright particles in

[0063] The results show that for the high-temperature resistant cermet microwave absorbing material prepared by the present invention, the metal phase first precipitates in the form of particles on the ceramic phase matrix. As the reduction time prolongs, the metal particles gradually connect to form a regional conductive network, thereby effectively enhancing the ohmic loss and improving the electromagnetic wave loss performance of the material. In addition, as the reduction time prolongs, more active metal elements precipitate, the configurational entropy of the material further decreases, and the high-entropy alloy phase gradually transforms into the iron-based alloy phase. This preparation method has a rich adjustment mechanism, strong designability, low raw material cost, no pollution and is environmentally friendly.

[0064] Example 3

[0065] Using Fe2O3 powder, Co2O3 powder, NiO powder, Cr2O3 powder and MnO2 powder as raw materials (all are reagent grade, >99%, 300 mesh), wherein the molar concentration ratio of metal cations (Fe element: Co element: Ni element: Cr element: Mn element) in the raw materials is x:1:0.5:1:0.5 (x = 1, 2, 3, 4, 5, 6). Place the raw materials in a nylon ball milling jar, wet ball mill at a speed of 360 revolutions per minute for 6 hours, change the rotation direction every half hour, where the mass ratio of the ball milling beads to the raw materials is 15:1, and the ball milling medium is industrial ethanol. After ball milling, pour the mixture into a beaker, add a magnetic stirrer, stir and dry on a heating stirrer table, and the drying temperature is 80 °C. After drying, pour the mixed powder into a pre-prepared mold, keep the pressure at 20 MPa for 10 min, release the pressure, take out the pressed block and place it in a platinum crucible, and put it into a muffle furnace together, sinter at a high temperature of 1100 °C for 3 hours, and the heating rate is 2 °C / min. After sintering, take out the crucible, and quickly cool the sample and the crucible together in the air. After cooling to room temperature, a high-entropy ceramic sample is obtained. Put the high-entropy ceramic sample into a tubular furnace, carry out high-temperature reduction in a hydrogen atmosphere, the heating rate is 2 °C / min, the hydrogen flow rate is 200 mL / min, the reduction temperature is 1100 °C, and the reduction time is 2 hours. After the high-temperature reduction is completed, the sample is cooled with the furnace to obtain the high-temperature resistant high-entropy cermet microwave absorbing filler.

[0066] As Figure 8 shown, the XRD pattern of the high-temperature resistant high-entropy cermet microwave absorbing filler prepared in this example shows that when x = 1, 2, 3, 4, 5, 6, the samples all exhibit a two-phase structure of ceramic and metal. Among them, the ceramic phase is a high-entropy oxide, and the structure presents a spinel structure; while the metal phase presents a high-entropy alloy phase or an iron-based alloy phase. When x = 1, the metal phase is a face-centered cubic high-entropy alloy phase; when x = 2, 3, 4, 5, 6, the metal phase is an iron-based alloy phase.

[0067] The results show that with the change of the component content, the configurational entropy of the material will change accordingly. When deviating from the equimolar ratio, the metal phase tends to present in the form of an alloy phase. The structures and contents of the metal and ceramic phases can still be adjusted, thereby obtaining adjustable electromagnetic wave absorption performance. This preparation method has a rich adjustment mechanism, strong designability, low raw material cost, no pollution and is environmentally friendly.

[0068] The above are only the preferred embodiments listed in the present invention. It should be pointed out that for all those skilled in the art of this technology, without departing from the spirit of the appended claims and the principles shown in the present invention, changes or alterations can still be made to the illustrated examples, and these changes should also be regarded as the scope of the right protection of the present invention.

Claims

1. A high-temperature resistant high-entropy metal ceramic microwave absorbing filler, characterized in that, The high-temperature resistant high-entropy metal-ceramic microwave absorbing filler has a composite phase of a ceramic phase and a metal phase in-situ precipitated in the ceramic phase matrix, wherein the metal phase is a high-entropy alloy or a transition metal-based alloy, and the ceramic phase is a high-entropy oxide; calculated by mole percentage, the content of the metal phase in the high-temperature resistant high-entropy metal-ceramic microwave absorbing filler is 30-90%, and the content of the ceramic phase is 10-70%.

2. The high-temperature resistant high-entropy metal ceramic wave-absorbing filler according to claim 1, wherein The metal components of the high-temperature resistant high-entropy metal-ceramic microwave absorbing filler are at least five of Fe, Co, Ni, Cr, Mn, Al, Ti, Cu, Mg, Y, Zn, and Sn.

3. The high-temperature resistant high-entropy metal ceramic microwave absorbing filler according to claim 2, wherein The metal components of the high-temperature resistant high-entropy metal-ceramic microwave absorbing filler are Fe, Co, Ni, Cr, and Mn.

4. The high-temperature resistant high-entropy metal ceramic microwave absorbing filler according to claim 1, wherein The ceramic phase is a spinel structure, a rock-salt structure, or a perovskite structure.

5. The high-temperature resistant high-entropy metal ceramic wave-absorbing filler according to claim 1, characterized in that, The metal phase forms a conductive network in the microscopic region without forming large-area aggregates.

6. The high-temperature resistant high-entropy metal ceramic wave-absorbing filler according to claim 1, wherein The composite phase is an ohmic phase composite dielectric phase.

7. The preparation method of the high-temperature resistant high-entropy metal ceramic wave-absorbing filler according to any one of claims 1 to 6, characterized in that, The preparation method includes: using oxides containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; subjecting the precursor mixture to high-temperature sintering in an air atmosphere and then rapidly cooling in air to obtain an entropy-stable ceramic phase, and then reducing the entropy-stable ceramic phase at high temperature in a reducing atmosphere to in-situ precipitate a metal phase in the ceramic phase matrix, so as to obtain the high-temperature resistant high-entropy metal-ceramic microwave absorbing filler.

8. The preparation method of the high-temperature resistant high-entropy metal ceramic microwave absorbing filler according to any one of claims 1 to 6, characterized in that, The preparation method includes: using oxides containing metal components as raw materials, and mixing the raw materials evenly to obtain a precursor mixture; performing high-temperature sintering in a reducing atmosphere to directly prepare the high-temperature resistant high-entropy metal-ceramic microwave absorbing filler.

9. The preparation method according to claim 7 or 8, characterized in that The mole content of the metal components in the oxide is 5-35%.

10. The preparation method according to claim 7, characterized in that, The sintering temperature is 1000-1400 °C, and the sintering time is 1-5 h.

11. The preparation method according to claim 7, characterized in that, The reduction temperature is 800-1400 °C, and the reduction time is 1-10 h.

12. The preparation method according to claim 11, wherein, The reduction time is 3-10 h.

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