High-entropy carbide ceramic and preparation method and application thereof

Abstract

The application discloses high-entropy carbide ceramic and a preparation method and application thereof. The preparation method of the high-entropy carbide ceramic comprises the following steps: 1) mixing metal oxide powder and carbon powder to carry out wet ball milling, and then drying to obtain mixed powder; 2) pressing the mixed powder into a green body, and then carrying out flash sintering, and then taking out the obtained clinker to carry out crushing and screening to obtain core-shell structure clinker powder; and 3) pressing the core-shell structure clinker powder into a green body, and then carrying out discharge plasma sintering to obtain the high-entropy carbide ceramic. The high-entropy carbide ceramic has high fracture toughness, and the preparation method has the advantages of simple operation and process flow, short reaction time, low synthesis cost and the like, is suitable for microstructure regulation and large-scale industrial production, and has a very wide application prospect in the fields of high-temperature thermal structure components, nuclear fuel cladding, high-speed cutting tools and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-entropy ceramics, and in particular to a high-entropy carbide ceramic, a preparation method and applications thereof. BACKGROUND

[0002] High-entropy carbide ceramics have excellent properties such as high hardness, high melting point, low thermal conductivity, excellent corrosion resistance and excellent oxidation resistance, and have shown a very broad application prospect in extreme fields such as high-temperature thermal structural components, nuclear fuel cladding and high-speed cutting tools. However, high-entropy carbide ceramics also have inherent defects such as high brittleness and low fracture toughness, which greatly limit their practical application in extreme fields.

[0003] Beilin Ye et al. disclosed a method for toughening high-entropy carbide ceramics by using nanosheets to induce crack deflection and nanosheet pull-out and bridging toughening mechanisms, which increased the fracture toughness of high-entropy carbide ceramics from 3.0MPa·m 1 / 2 ±0.2MPa·m 1 / 2 to 4.7MPa·m 1 / 2 ±0.5MPa·m 1 / 2 However, the fracture toughness of high-entropy carbide ceramics is still low and cannot meet the service requirements in extreme environments (Beilin Ye, Tongqi Wen, Manh Cuong Nguyen, Luyao Hao, Cai-Zhuang Wang, Yanhui Chu. First-principles study, fabrication and characterization of (Zr 0.25 Nb 0.25 Ti 0.25 V 0.25 )Chigh-entropy ceramics, Acta Materialia, 2019, 170: 15-23; Beilin Ye, Tongqi Wen, Kehan Huang, Cai-Zhuang Wang, Yanhui Chu. First-principles study, fabrication, and characterization of (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )C high-entropy ceramic, J. Am. Ceram. Soc. 2019, 102: 4344-4352).

[0004] Therefore, it is of great significance to develop a high-entropy carbide ceramic with high fracture toughness. SUMMARY

[0005] The application aims to provide a high-entropy carbide ceramic and a preparation method and application thereof.

[0006] The technical scheme adopted by the application is as follows:

[0007] The preparation method of the high-entropy carbide ceramic comprises the following steps:

[0008] 1) mixing metal oxide powders and carbon powder for wet ball milling, wherein the metal oxide powders are composed of HfO2 powder, ZrO2 powder, Ta2O5 powder, Nb2O5 powder, TiO2 powder and Cr2O3 powder, and then drying to obtain mixed powders;

[0009] 2) pressing the mixed powders into a green body, embedding the green body into graphite felt after covering the upper and lower surfaces of the green body with graphite paper coated with boron nitride on the upper surface, connecting the graphite felt to alternating current in a protective atmosphere to perform flash sintering on the green body, taking out the obtained clinker for crushing and screening to obtain clinker powder with a core-shell structure;

[0010] 3) embedding the graphite paper coated with boron nitride into a graphite mold, loading the clinker powder with the core-shell structure into the graphite mold and pressing into a green body, connecting the graphite mold to pulse current in a protective atmosphere to perform discharge plasma sintering on the green body, thereby obtaining the high-entropy carbide ceramic.

[0011] Preferably, the ratio of the total molar amount of metal atoms in the metal oxide powders to the molar amount of the carbon powder in step 1) is 1:1.

[0012] Preferably, the particle size of the HfO2 powder, ZrO2 powder, Ta2O5 powder, Nb2O5 powder, TiO2 powder and Cr2O3 powder in step 1) is 1-3 μm, and the purity of each is ≥99.9%.

[0013] Preferably, the particle size of the carbon powder in step 1) is ≤2 μm, and the purity is ≥99.95%.

[0014] Preferably, the process parameters of the wet ball milling in step 1) include: the ball milling medium is anhydrous ethanol, the ball milling equipment is a planetary ball mill, the weight ratio of the powder raw material, ZrO2 balls and anhydrous ethanol is 1:1.8-2.2:1.0-1.5, and the ball milling time is 15-25 h.

[0015] Preferably, the pressing in step 2) is performed under a pressure of 8-12 MPa, and the pressure holding time is 8-12 min.

[0016] Preferably, the blank in step 2) is in a cylindrical shape with a diameter ≤ 16 mm and a thickness ≤ 3.5 mm.

[0017] Preferably, the graphite felt in step 2) has a length of 100 mm to 120 mm, a width of 15 mm to 20 mm, and a thickness of 4.5 mm to 5.5 mm.

[0018] Preferably, the protective atmosphere in step 2) is an argon atmosphere.

[0019] Preferably, the flash sintering in step 2) specifically includes the following operations: connecting alternating current to both ends of the graphite felt, increasing the current from 0 to 60 A to 75 A at a rate of 2 A / s to 4 A / s, and then maintaining for 55 s to 65 s, disconnecting the power, and naturally cooling. The ultrafast carbon thermal reduction reaction brought by flash sintering can make the high-melting-point components completely react to form a high-entropy main phase, and the low-melting-point components melt to perform liquid-phase sintering and rapidly cool down, which can ensure obtaining high-entropy carbide ceramic powder without oxide impurities and with fine grains, and can also ensure obtaining high-entropy carbide ceramic powder with a core-shell structure in which the low-melting-point components wrap the high-melting-point components.

[0020] Preferably, the grinding method in step 2) is used for the pulverization.

[0021] Preferably, the screen mesh used in the sieving in step 2) has a mesh size of 180 mesh to 230 mesh.

[0022] Preferably, the pressing in step 3) is performed under a pressure of 25 MPa to 35 MPa.

[0023] Preferably, the blank in step 3) is in a cylindrical shape with a diameter ≤ 15 mm.

[0024] Preferably, the protective atmosphere in step 3) is an argon atmosphere.

[0025] Preferably, the spark plasma sintering in step 3) specifically includes the following operations: connecting a pulsed current to the graphite mold, increasing the current from 0 A to 950 A to 1050 A at a rate of 95 A / min to 105 A / min, then continuously increasing the current to 1350 A to 1500 A at a rate of 75 A / min to 85 A / min, maintaining for 8 min to 12 min, disconnecting the power, and naturally cooling. The pulsed current with low voltage and high current and the generated plasma in the spark plasma sintering process promote the rapid sintering and densification of the blank, while reducing the temperature required for densification and reducing the volatilization of the low-melting-point components, which can ultimately better form a high-entropy carbide ceramic with a biomimetic structure.

[0026] Preferably, the spark plasma sintering in step 3) is performed under a pressure holding state, and the pressure applied to the blank is 25 MPa to 35 MPa.

[0027] A high-entropy carbide ceramic prepared by the above preparation method.

[0028] Use of the high-entropy carbide ceramic as described above in the preparation of a high-temperature structural component of a spacecraft, a wear-resistant cutting tool, a wear-resistant coating, an electromagnetic shielding material or a military armor.

[0029] The high-entropy carbide ceramic of the present application has high fracture toughness, and the preparation method thereof has the advantages of simple operation and process flow, short reaction time, low synthesis cost, etc., is suitable for microstructure regulation and large-scale industrial production, and has very broad application prospects in the fields of high-temperature thermal structural components, nuclear fuel cladding, high-speed cutting tools, etc.

[0030] Specifically:

[0031] 1) The present application is inspired by the "soft / hard" alternating structure of the nacre layer of nature and the honeycomb "grid" structure, uses transition metal oxides and carbon powder as raw materials, utilizes carbon thermal reduction reaction, and prepares a high-entropy carbide ceramic containing six metal elements of Hf, Zr, Ta, Nb, Ti and Cr and having a biomimetic "soft / hard" phase structure by a two-step method of flash sintering and spark plasma sintering, overcoming the pain points of low fracture toughness and high brittleness of traditional high-entropy carbide ceramics;

[0032] 2) The present application forms a core-shell structure powder having an outer "soft phase" and an inner "hard phase" by flash sintering technology, and then densifies by spark plasma sintering, so that the "soft phase" is uniformly distributed at the grain boundaries of the "hard phase", overcoming the problem of uneven distribution of toughening phases existing in general toughening methods;

[0033] 3) The fracture toughness of the high-entropy carbide ceramic of the present application can reach 12.5MPa·m 1 / 2 ±1.5MPa·m 1 / 2 , which is about 2 times higher than that of the high-entropy carbide ceramic (4.7MPa·m 1 / 2 ±0.5MPa·m 1 / 2 ) reported in the literature, and can fully meet the high requirements for the toughness of high-entropy carbide ceramics in actual application, and has very broad application prospects in the fields of high-temperature structural materials of spacecraft, nuclear fuel cladding, cutting and wear-resistant tools, etc. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 XRD patterns of the core-shell structure clinker powder and the high-entropy carbide ceramic in Example 2.

[0035] Figure 2 SEM image of the high-entropy carbide ceramic after acid etching in Example 2.

[0036] Figure 3 SEM image and EDS element mapping of high-entropy carbide ceramic in Example 2.

[0037] Figure 4 SEM image of high-entropy carbide ceramic in Comparative Example 1.

[0038] Figure 5 SEM image and EDS element mapping of high-entropy carbide ceramic in Comparative Example 2. DETAILED DESCRIPTION

[0039] The application will be further explained and described with reference to specific examples.

[0040] The particle size of HfO2 powder, ZrO2 powder, Ta2O5 powder, Nb2O5 powder, TiO2 powder and Cr2O3 powder in Examples 1-5 and Comparative Examples 1-3 is 1-3 μm, and the purity is ≥99.9%.

[0041] The particle size of carbon powder in Examples 1-5 and Comparative Examples 1-3 is ≤2 μm, and the purity is ≥99.95%.

[0042] Example 1:

[0043] A high-entropy carbide ceramic is prepared by the following method:

[0044] 1) 8.4 g of HfO2 powder, 4.9 g of ZrO2 powder, 8.8 g of Ta2O5 powder, 5.3 g of Nb2O5 powder, 3.2 g of TiO2 powder, 3.0 g of Cr2O3 powder and 8.9 g of carbon powder are added into a nylon ball mill jar, and anhydrous ethanol and zirconia milling beads are added, the weight ratio of the powder raw material, zirconia milling beads and anhydrous ethanol being 1:1.8:1, the nylon ball mill jar is then loaded into a planetary ball mill, and ball milling is carried out for 20 h, and then anhydrous ethanol is evaporated by a rotary evaporator to obtain a mixed powder;

[0045] 2) 2.0 g of the mixed powder is loaded into a mold (the mold cavity is cylindrical with a diameter of 16 mm), and slowly pressurized to 8 MPa to keep pressure for 10 min to form a green body (thickness about 3 mm), then a graphite felt (AvCarb Company, model G475) with a length of 100 mm, a width of 20 mm and a thickness of 4.75 mm is cut to form three through holes with a length of about 18 mm in the middle of the side surface, the through holes are spaced about 3 mm apart, then the upper and lower surfaces of the green body are covered with boron nitride coated graphite paper and embedded into the graphite felt, then the graphite felt is clamped at both ends along the length direction by electrodes, and placed in a reaction kettle, the reaction kettle is closed, a mechanical pump and a side extraction valve are opened to perform vacuum extraction on the reaction kettle cavity to make the vacuum pressure gauge count value reach 10 Pa, then a molecular pump and a plug valve are opened to continue vacuum extraction until the vacuum pressure gauge count value is less than 1.2×10-2 Pa, slowly purging argon into the cavity again to make it semi-vacuum, connecting the two ends of the graphite felt with alternating current by turning on the power switch, increasing the current from 0 to 65 A at a rate of 2 A / s, keeping the temperature at about 1800℃ for 55 s (measured by an infrared thermometer), turning off the power switch, cooling down with the furnace, taking out the clinker and grinding it, sieving it through a 200-mesh sieve to obtain the core-shell structure clinker powder;

[0046] 3) The graphite paper coated with boron nitride was embedded in a graphite mold, which was in the shape of a cylinder with an inner diameter of 15.4 mm, and the actual inner diameter of the graphite mold was 15.0 mm after embedding the graphite paper coated with boron nitride. Then 3.5 g of the core-shell structure clinker powder was loaded into the graphite mold, and the core-shell structure clinker powder was clamped in the middle of the graphite mold by using the upper and lower pressing columns. The graphite mold was placed in the spark plasma sintering reaction cavity, and the pressure head pressure was adjusted to 5.3 kN (30 MPa) to press the core-shell structure clinker powder into a green body. Then argon was purged, and the upper and lower pressing columns of the graphite mold were connected to the pulse current by turning on the power switch. The current was increased from 0 to 1000 A at a rate of 100 A / min, and then the current was further increased to 1350 A at a rate of 80 A / min. The temperature was kept at about 1550℃ for 10 min (measured by an infrared thermometer), the power switch was turned off, and the furnace was cooled down to obtain the high-entropy carbide ceramic (denoted as 6HEC-1).

[0047] It was tested that the density of the high-entropy carbide ceramic (6HEC-1) in this embodiment was 99.2%, and the fracture toughness was 10.5 MPa·m 1 / 2 ±1.8 MPa·m 1 / 2 .

[0048] Note:

[0049] Density: tested by using the Archimedes principle, and the calculation formula was: density (%) = (ρ 实际 / ρ 理论 ) x 100%, ρ 实际 = (m1 x ρ 水 ) / (m0 - m2), ρ 理论 = (N x M) / (V x N A ), wherein ρ 实际 was the actual density of the sample, ρ 理论 was the theoretical density of the sample, m1 was the mass of the dried sample in air, m0 was the mass of the sample containing saturated deionized water in air, m2 was the mass of the sample in deionized water, N was the number of atoms contained in a single unit cell, M was the molar mass, V was the volume of a single unit cell, and N A was the Avogadro constant.

[0050] Fracture toughness: tested according to "GB / T 23806-2009 Fine Ceramics Fracture Toughness Test Method Single Edge Pre-cracked Beam (SEPB) Method".

[0051] Example 2:

[0052] A high-entropy carbide ceramic is prepared by the following method:

[0053] 1) 8.4 g of HfO2 powder, 4.9 g of ZrO2 powder, 8.8 g of Ta2O5 powder, 5.3 g of Nb2O5 powder, 3.2 g of TiO2 powder, 5.1 g of Cr2O3 powder, and 9.7 g of carbon powder are added to a nylon ball mill jar, and anhydrous ethanol and zirconia milling beads are added, with the weight ratio of the powder raw materials, zirconia milling beads, and anhydrous ethanol being 1:2:1.2. The nylon ball mill jar is then loaded into a planetary ball mill, and ball milling is performed for 20 h. Anhydrous ethanol is then evaporated using a rotary evaporator to obtain a mixed powder;

[0054] 2) 2.0 g of the mixed powder is loaded into a mold (the mold cavity is cylindrical, with a diameter of 16 mm), and slowly pressurized to 9 MPa, and held for 10 min to form a green body (about 3 mm thick). A graphite felt (AvCarb Company, model G475) with a length of 100 mm, a width of 20 mm, and a thickness of 4.75 mm is then used, and three through-holes about 18 mm long are drawn in the middle of the side surface, with the through-holes spaced about 3 mm apart. The upper and lower surfaces of the green body are then covered with boron nitride-coated graphite paper, and the green body is then embedded in the graphite felt. The graphite felt is then clamped at both ends along the length direction using electrodes, and placed in a reaction kettle. The reaction kettle is closed, the mechanical pump and the side extraction valve are opened to perform vacuum extraction on the reaction kettle cavity, and the vacuum pressure gauge count value reaches 10 Pa. The molecular pump and the plug valve are then opened to continue vacuum extraction until the vacuum pressure gauge count value is less than 1.2 x 10 -2 Pa, argon gas is slowly introduced into the cavity to create a semi-vacuum, the power switch is turned on to connect the two ends of the graphite felt with alternating current, the current is increased from 0 to 70 A at a rate of 3 A / s, and the temperature is maintained at about 1850°C for 60 s (measured using an infrared temperature meter), the power switch is turned off, the furnace is cooled, and the clinker is removed and ground, and then passed through a 200 mesh sieve to obtain a core-shell structure clinker powder;

[0055] 3) The boron nitride coated graphite paper is inserted into a graphite mold, which is in a cylindrical shape with an inner diameter of 15.4 mm. After the insertion of the boron nitride coated graphite paper, the actual inner diameter of the graphite mold is 15.0 mm. Then, 3.5 g of core-shell structure sintered powder is loaded into the graphite mold. The upper and lower pressing columns are used to clamp the core-shell structure sintered powder in the middle of the graphite mold. The graphite mold is placed in a spark plasma sintering reaction chamber. The pressure of the pressing head is adjusted to 5.3 kN (30 MPa) to press the core-shell structure sintered powder into a green body. Argon gas is introduced, and the power switch is turned on to connect the upper and lower pressing columns of the graphite mold to the pulse current. The current is increased from 0 to 1000 A at a rate of 100 A / min, and then increased to 1400 A at a rate of 80 A / min. The temperature is maintained at about 1600℃ for 10 min (measured by an infrared thermometer). The power switch is turned off, and the furnace is cooled down to obtain a high-entropy carbide ceramic (denoted as 6HEC-2).

[0056] Performance test:

[0057] 1) The X-ray diffraction (XRD) patterns of the core-shell structure sintered powder and the high-entropy carbide ceramic (6HEC-2) in this example are shown in Figure 1 (Powder represents the core-shell structure sintered powder, and bulk represents the high-entropy carbide ceramic).

[0058] From Figure 1 it can be seen that 6HEC-2 contains a high-entropy main phase and a honeycomb structure secondary phase, indicating that it indeed has a biomimetic "soft / hard" phase structure.

[0059] 2) The scanning electron microscope (SEM) image of the high-entropy carbide ceramic (6HEC-2) in this example after acid etching (the acid etching process is as follows: the sample to be tested is polished to a mirror surface with 6000 mesh diamond grinding paste, and then a mixed acid solution of hydrofluoric acid, nitric acid and deionized water with a volume ratio of 1:1:3 is used for surface etching, the acid etching time is 1 min, and then ultrasonic cleaning is performed in anhydrous ethanol) is shown in Figure 2 .

[0060] From Figure 2 it can be seen that 6HEC-2 has a honeycomb-like biomimetic structure (since Cr has better corrosion resistance to acid, the grains with low Cr content are significantly corroded during the etching process of the polished surface, and the grains with high Cr content are not significantly corroded, thus the morphology contrast can better reflect the content, distribution and morphology of the honeycomb-like biomimetic structure).

[0061] 3) The SEM image and EDS element area distribution map of the high-entropy carbide ceramic (6HEC-2) in this example are shown in Figure 3 .

[0062] From Figure 3It can be seen that Hf, Zr, Ta, Nb and Ti in 6HEC-2 are uniformly distributed in the grain, and Cr element is mainly distributed at the grain boundary, which indicates that the structure design of soft phase wrapping hard phase and low melting point component wrapping high melting point component is realized.

[0063] 4) After testing (the testing method is the same as that in Example 1), the density of the high-entropy carbide ceramic (6HEC-2) in the present example is 99.5%, and the fracture toughness is 12.5 MPa·m 1 / 2 ±1.5 MPa·m 1 / 2 .

[0064] Example 3:

[0065] A high-entropy carbide ceramic is prepared by the following method:

[0066] 1) 8.4 g of HfO2 powder, 4.9 g of ZrO2 powder, 8.8 g of Ta2O5 powder, 5.3 g of Nb2O5 powder, 3.2 g of TiO2 powder, 7.6 g of Cr2O3 powder and 10.7 g of carbon powder are added into a nylon ball mill jar, and anhydrous ethanol and zirconia ball milling beads are added, and the weight ratio of the powder raw material, zirconia ball milling beads and anhydrous ethanol is 1:2.2:1.5, then the nylon ball mill jar is loaded into a planetary ball mill, and ball milling is performed for 20 h, and then the anhydrous ethanol is evaporated by a rotary evaporator to obtain a mixed powder;

[0067] 2) 2.0 g of the mixed powder is loaded into a mold (the mold cavity is in a cylindrical shape with a diameter of 16 mm), and slowly pressurized to 10 MPa, and kept for 10 min to form a green body (about 3 mm thick), then a graphite felt (AvCarb company, model G475) with a length of 100 mm, a width of 20 mm and a thickness of 4.75 mm is cut to form three through holes with a length of about 18 mm in the middle of the side surface, and the through holes are spaced about 3 mm apart, then the upper and lower surfaces of the green body are covered with boron nitride coated graphite paper and then embedded into the graphite felt, and then the graphite felt at both ends is clamped with electrodes along the length direction and placed in a reaction kettle, the reaction kettle is closed, the mechanical pump and the side extraction valve are opened to perform vacuum extraction on the cavity of the reaction kettle until the vacuum pressure gauge value reaches 10 Pa, then the molecular pump and the plug valve are opened to continue vacuum extraction until the vacuum pressure gauge value is less than 1.2×10 -2 Pa, then argon is slowly introduced into the cavity to form a semi-vacuum, then the power switch is turned on to connect the two ends of the graphite felt with alternating current, the current is increased from 0 to 75 A at a rate of 4 A / s, and then kept for 65 s (the temperature is kept at about 1900 ℃ measured by an infrared temperature measuring instrument), the power switch is turned off, and the furnace is cooled down, then the clinker is taken out and ground, and then sieved through a 200 mesh sieve to obtain a core-shell structure clinker powder;

[0068] 3) embed the surface boron nitride coated graphite paper into a graphite mold, the graphite mold is in a cylindrical shape, the inner diameter is 15.4 mm, after embedding the surface boron nitride coated graphite paper, the actual inner diameter of the graphite mold is 15.0 mm, then load 3.5 g of core-shell structure sintered powder into the graphite mold, and use the upper and lower pressing columns to clamp the core-shell structure sintered powder in the middle of the graphite mold, then place the graphite mold in the spark plasma sintering reaction cavity, adjust the pressure head pressure to 5.3 kN (30 MPa) to press the core-shell structure sintered powder into a green body, then introduce argon, turn on the power switch to connect the upper and lower pressing columns of the graphite mold to the pulse current, increase the current from 0 to 1000 A at a rate of 100 A / min, then continue to increase the current to 1450 A at a rate of 80 A / min, keep the temperature at about 1650 ℃ for 10 min (use an infrared thermometer to measure the temperature), turn off the power switch, and cool in the furnace to obtain a high-entropy carbide ceramic (denoted as 6HEC-3).

[0069] After testing (the testing method is the same as that in Example 1), the density of the high-entropy carbide ceramic (6HEC-3) in this example is 99.0%, the fracture toughness is 11.4 MPa·m 1 / 2 ±2.1 MPa·m 1 / 2 .

[0070] Example 4:

[0071] A high-entropy carbide ceramic is prepared by the following method:

[0072] 1) add 8.4 g of HfO2 powder, 4.9 g of ZrO2 powder, 8.8 g of Ta2O5 powder, 5.3 g of Nb2O5 powder, 3.2 g of TiO2 powder, 5.1 g of Cr2O3 powder and 9.7 g of carbon powder into a nylon ball mill jar, and add anhydrous ethanol and zirconia ball milling beads, the weight ratio of the powder raw material, zirconia ball milling beads and anhydrous ethanol is 1:2:1.2, then load the nylon ball mill jar into a planetary ball mill, ball mill for 20 h, and then evaporate the anhydrous ethanol with a rotary evaporator to obtain a mixed powder;

[0073] 2) 2.0 g of the mixed powder was loaded into a mold (the mold cavity was cylindrical with a diameter of 16 mm), slowly pressurized to 9 MPa, and held for 10 min to form a green body (about 3 mm thick). A graphite felt (AvCarb, model G475) with a length of 100 mm, a width of 20 mm, and a thickness of 4.75 mm was used, and three through-holes with a length of about 18 mm were drawn in the middle of the side surface, with a spacing of about 3 mm between the through-holes. The upper and lower surfaces of the green body were then covered with boron nitride-coated graphite paper, and the green body was then embedded in the graphite felt. The graphite felt was then clamped at both ends along the length direction with electrodes, and then placed in a reaction kettle. The reaction kettle was closed, the mechanical pump and the side extraction valve were opened to perform vacuum extraction on the reaction kettle cavity, and the vacuum pressure gauge count value reached 10 Pa. The molecular pump and the plug valve were then opened to continue the vacuum extraction until the vacuum pressure gauge count value was less than 1.2 x 10 -2 Pa. Argon was then slowly introduced into the cavity to create a semi-vacuum. The power switch was then turned on to connect the two ends of the graphite felt with alternating current. The current was increased from 0 to 60 A at a rate of 3 A / s, and then maintained for 60 s (the temperature was maintained at about 1750°C as measured by an infrared temperature meter). The power switch was then turned off, and the graphite felt was cooled in the furnace. The clinker was then removed and ground, and then passed through a 200-mesh sieve to obtain a core-shell structure clinker powder;

[0074] 3) The boron nitride-coated graphite paper was embedded in a graphite mold, which was cylindrical with an inner diameter of 15.4 mm. After embedding the boron nitride-coated graphite paper, the actual inner diameter of the graphite mold was 15.0 mm. 3.5 g of the core-shell structure clinker powder was then loaded into the graphite mold, and the core-shell structure clinker powder was clamped in the middle of the graphite mold using upper and lower pressing columns. The graphite mold was then placed in a spark plasma sintering reaction cavity, and the pressure head pressure was adjusted to 5.3 kN (30 MPa) to press the core-shell structure clinker powder into a green body. Argon was then introduced, and the power switch was turned on to connect the upper and lower pressing columns of the graphite mold with a pulse current. The current was increased from 0 to 1000 A at a rate of 100 A / min, and then increased to 1400 A at a rate of 80 A / min. The temperature was maintained at about 1600°C for 10 min (as measured by an infrared temperature meter). The power switch was then turned off, and the graphite mold was cooled in the furnace to obtain a high-entropy carbide ceramic (denoted as 6HEC-4).

[0075] After testing (the testing method was the same as in Example 1), the density of the high-entropy carbide ceramic (6HEC-4) in this example was 99.0%, and the fracture toughness was 10.5 MPa·m 1 / 2 ±1.8 MPa·m 1 / 2 .

[0076] Example 5:

[0077] A high-entropy carbide ceramic was prepared by the following method:

[0078] 1) 8.4 g of HfO2 powder, 4.9 g of ZrO2 powder, 8.8 g of Ta2O5 powder, 5.3 g of Nb2O5 powder, 3.2 g of TiO2 powder, 5.1 g of Cr2O3 powder and 9.7 g of carbon powder were added into a nylon ball mill jar, and anhydrous ethanol and zirconia milling beads were added, the weight ratio of the powder raw materials, zirconia milling beads and anhydrous ethanol was 1:2:1.2, the nylon ball mill jar was then loaded into a planetary ball mill, ball milling was performed for 20 h, and the anhydrous ethanol was evaporated by a rotary evaporator to obtain a mixed powder;

[0079] 2) 2.0 g of the mixed powder was loaded into a mold (the mold cavity was in a cylindrical shape with a diameter of 16 mm), and was slowly pressurized to 9 MPa to form a green body (about 3 mm in thickness) by maintaining the pressure for 10 min, then a graphite felt (AvCarb Company, model G475) with a length of 100 mm, a width of 20 mm and a thickness of 4.75 mm was cut to form three through holes with a length of about 18 mm in the middle of the side surface, and the through holes were spaced about 3 mm apart from each other, then the upper and lower surfaces of the green body were covered with boron nitride coated graphite paper and then embedded into the graphite felt, and then the graphite felt was clamped at both ends along the length direction by electrodes and placed in a reaction kettle, the reaction kettle was closed, a mechanical pump and a side extraction valve were opened to perform vacuum extraction treatment on the cavity of the reaction kettle until the vacuum pressure gauge count value reached 10 Pa, then a molecular pump and a plug valve were opened to continue vacuum extraction treatment until the vacuum pressure gauge count value was less than 1.2 × 10 -2 Pa, then argon was slowly introduced into the cavity to make it semi-vacuum, then the power switch was turned on to connect the two ends of the graphite felt with alternating current, the current was increased from 0 to 70 A at a rate of 3 A / s, and the temperature was maintained at about 1850℃ for 60 s (measured by an infrared temperature measuring instrument), then the power switch was turned off, the furnace was cooled down, then the clinker was taken out and ground, and then passed through a 200 mesh sieve to obtain a core-shell structure clinker powder;

[0080] 3) The boron nitride coated graphite paper was embedded into a graphite mold, the graphite mold was in a cylindrical shape with an inner diameter of 15.4 mm, and after embedding the boron nitride coated graphite paper, the actual inner diameter of the graphite mold was 15.0 mm, then 3.5 g of the core-shell structure clinker powder was loaded, and the core-shell structure clinker powder was clamped in the middle of the graphite mold by upper and lower pressing columns, then the graphite mold was placed in a spark plasma sintering reaction cavity, the pressure head pressure was adjusted to 5.3 kN (30 MPa) to press the core-shell structure clinker powder into a green body, then argon was introduced, the power switch was turned on to connect the upper and lower pressing columns of the graphite mold with pulse current, the current was increased from 0 to 1000 A at a rate of 100 A / min, and then the current was further increased to 1500 A at a rate of 80 A / min, and the temperature was maintained at about 1700℃ for 10 min (measured by an infrared temperature measuring instrument), then the power switch was turned off, the furnace was cooled down, and a high-entropy carbide ceramic (denoted as 6HEC-5) was obtained.

[0081] The high-entropy carbide ceramic (6HEC-5) in this embodiment has a density of 99.4% and a fracture toughness of 9.6 MPa·m 1 / 2 ±1.5 MPa·m 1 / 2 .

[0082] Comparative Example 1:

[0083] A high-entropy carbide ceramic (denoted as 6HEC-6) is prepared in the same way as in Example 2, except that the current in step 2) is adjusted from “70 A” to “55 A” and the size of the graphite felt in step 2) is adjusted to “100 mm in length, 25 mm in width, and 4.75 mm in thickness”.

[0084] Performance test:

[0085] 1) The SEM image and EDS element mapping of the high-entropy carbide ceramic (6HEC-6) in this comparative example are shown in Figure 4 .

[0086] It can be seen from Figure 4 that the density of 6HEC-6 is low, because the current in step 2) is too low and the graphite felt is too wide, resulting in that the actual reaction temperature cannot make the carbothermal reduction reaction proceed completely, and the continuous generation of gas in the subsequent experimental steps leads to the formation of a large number of micro-pore structures inside the ceramic, thereby reducing the density of the ceramic.

[0087] 2) The high-entropy carbide ceramic (6HEC-6) in this comparative example has a density of 91.2% and a fracture toughness of 2.7 MPa·m 1 / 2 ±0.5 MPa·m 1 / 2 .

[0088] Comparative Example 2:

[0089] A high-entropy carbide ceramic (denoted as 6HEC-7) is prepared in the same way as in Example 2, except that the current in step 3) is adjusted from “1400 A” to “1550 A (temperature maintained at about 1750°C)”.

[0090] Performance test:

[0091] 1) The SEM image and EDS element mapping of the high-entropy carbide ceramic (6HEC-7) in this comparative example are shown in Figure 5 .

[0092] It can be seen from Figure 5 that 6HEC-7 does not contain a honeycomb-like biomimetic structure, because the current in step 3) is too large, and the discharge plasma sintering reaction temperature is too high, resulting in that the low-melting-point components volatilize and react with the graphite mold under high temperature.

[0093] 2) The high-entropy carbide ceramic (6HEC-7) in this comparative example has a relative density of 99.0% and a fracture toughness of 2.5 MPa·m 1 / 2 ± 0.6 MPa·m 1 / 2 .

[0094] Comparative Example 3:

[0095] A high-entropy carbide ceramic (denoted as 6HEC-8) was prepared in the same way as in Example 2, except that in step 3), the operation was adjusted to "1.2 g of core-shell structure clinker powder was loaded into a mold (the mold cavity was cylindrical with a diameter of 10 mm), slowly pressurized to 8 MPa for 5 min to form a clinker green body, a graphite felt (AvCarb Company, model G475) with a length of 100 mm, a width of 12 mm, and a thickness of 4.75 mm was cut to have a through hole about 12 mm long in the middle of the side, the clinker green body was embedded in the graphite felt after covering the upper and lower surfaces with boron nitride coated graphite paper, the graphite felt was clamped at both ends along the length direction with electrodes, and then placed in a reaction kettle, the reaction kettle was closed, the mechanical pump and the side extraction valve were opened to vacuumize the reaction kettle cavity to make the vacuum pressure gauge count value reach 10 Pa, the molecular pump and the plug valve were then opened to continue vacuumizing until the vacuum pressure gauge count value was less than 1.2 x 10 -2 Pa, argon was slowly introduced into the cavity to make it semi-vacuum, the power switch was then turned on to connect the two ends of the graphite felt with alternating current, the current was increased from 0 to 60 A at a rate of 2 A / s, and then maintained for 60 s (the temperature was maintained at about 1900°C as measured by an infrared temperature meter), the power switch was turned off, and the furnace was cooled down".

[0096] The 6HEC-8 has a lower relative density, which is because the flash sintering method used in step 3) is pressureless sintering, which cannot completely densify the sample in a short time, thereby reducing the relative density of the ceramic.

[0097] 2) The high-entropy carbide ceramic (6HEC-8) in this comparative example has a relative density of 95.0% and a fracture toughness of 6.7 MPa·m 1 / 2 ± 0.9 MPa·m 1 / 2 .

[0098] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be within the scope of protection of the present application.

Claims

1. A method for preparing high-entropy carbide ceramics, characterized in that, Includes the following steps: 1) The metal oxide powder and carbon powder are mixed and wet ball milled. The metal oxide powder consists of HfO2 powder, ZrO2 powder, Ta2O5 powder, Nb2O5 powder, TiO2 powder and Cr2O3 powder. The mixture is then dried to obtain the mixed powder. 2) Press the mixed powder into a green body, then cover the upper and lower surfaces of the green body with graphite paper coated with boron nitride on the upper surface and embed graphite felt, then place it in a protective atmosphere and connect the graphite felt to AC power to flash sinter the green body, then take out the clinker and crush and sieve it to obtain core-shell structured clinker powder. 3) Graphite paper coated with boron nitride is embedded into a graphite mold, then core-shell structured clinker powder is loaded and pressed into a green body. The green body is then placed in a protective atmosphere and a pulse current is applied to the graphite mold to perform discharge plasma sintering, thus obtaining high-entropy carbide ceramics. Step 2) The pressing is carried out under a pressure of 8MPa to 12MPa, and the holding time is 8min to 12min; Step 2) The flash sintering specifically includes the following operations: connecting both ends of the graphite felt to AC power, increasing the current from 0 to 60A to 75A at a rate of 2A / s to 4A / s, maintaining it for 55s to 65s, then turning off the power and allowing it to cool naturally; Step 3) The pressing is carried out under a pressure of 25MPa to 35MPa. Step 3) The discharge plasma sintering specifically includes the following operations: connect the graphite mold to a pulsed current, increase the current from 0A to 950A to 1050A at a rate of 95A / min to 105A / min, then continue to increase the current to 1350A to 1500A at a rate of 75A / min to 85A / min, hold for 8min to 12min, then turn off the power and allow it to cool naturally; Step 3) The discharge plasma sintering is carried out under pressure holding conditions, and the pressure applied to the green body is 25MPa to 35MPa.

2. The method for preparing high-entropy carbide ceramics according to claim 1, characterized in that: Step 1) The ratio of the total molar amount of metal atoms in the metal oxide powder to the molar amount of carbon powder is 1:

1.

3. The method for preparing high-entropy carbide ceramics according to claim 1 or 2, characterized in that: The particle size of the HfO2 powder, ZrO2 powder, Ta2O5 powder, Nb2O5 powder, TiO2 powder and Cr2O3 powder mentioned in step 1) is 1μm to 3μm, and the purity is ≥99.9%; the particle size of the carbon powder mentioned in step 1) is ≤2μm, and the purity is ≥99.95%.

4. The method for preparing high-entropy carbide ceramics according to claim 1 or 2, characterized in that: The process parameters for wet ball milling in step 1) include: the ball milling medium is anhydrous ethanol, the ball milling equipment is a planetary ball mill, the weight ratio of powder raw material, ZrO2 balls and anhydrous ethanol is 1:1.8~2.2:1.0~1.5, and the ball milling time is 15h~25h.

5. The method for preparing high-entropy carbide ceramics according to claim 1, characterized in that: The blank in step 2) is cylindrical with a diameter ≤16mm and a thickness ≤3.5mm; the graphite felt in step 2) has a length of 100mm~120mm, a width of 15mm~20mm, and a thickness of 4.5mm~5.5mm.

6. The method for preparing high-entropy carbide ceramics according to claim 1, characterized in that: Step 3) The blank is cylindrical with a diameter ≤15mm.

7. A high-entropy carbide ceramic, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the high-entropy carbide ceramic as described in claim 7 in the preparation of high-temperature structural components for spacecraft, wear-resistant cutting tools, wear-resistant coatings, electromagnetic shielding materials, or military armor.

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