High-entropy carbonitride ceramic with high toughness and oxidation resistance and method of making same

Abstract

The application discloses a high-entropy carbonitride ceramic with high toughness and oxidation resistance and a preparation method thereof. The high-entropy carbonitride ceramic is composed of a high-entropy carbonitride matrix phase, a high-entropy boride second phase and a hexagonal boron nitride third phase which are uniformly distributed. The high-entropy carbonitride ceramic is obtained by ball milling high-entropy carbonitride powder and high-entropy boride powder to obtain high-entropy mixed powder and then performing spark plasma sintering on the high-entropy mixed powder. The high-entropy carbonitride ceramic provided by the application has good uniformity, high density, excellent high toughness and oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy carbonitride ceramic preparation technology, specifically relating to a high-toughness, oxidation-resistant high-entropy carbonitride ceramic and its preparation method. Background Technology

[0002] The successful development of high-entropy alloys has extended the high-entropy design concept to the field of ceramic materials. Compared with traditional ceramics, high-entropy ceramics exhibit superior mechanical and high-temperature properties. Furthermore, the diversification of main components allows for broader control over performance, bringing new opportunities for the functional applications of ceramic materials. Numerous studies have successfully prepared novel ceramic materials such as single-phase high-entropy carbides, high-entropy nitrides, high-entropy borides, and high-entropy oxides. Currently, researchers have demonstrated through first-principles calculations that multi-type anionic high-entropy ceramic systems exhibit better performance than ordinary single-anionic systems, and high-entropy carbonitride ceramics have been prepared. Further adjustments to the carbon-nitrogen ratio can improve the mechanical properties of ceramics to some extent, but the inherent strong covalent bonding of high-entropy ceramics limits the improvement in toughness. Moreover, high-entropy carbonitride ceramics suffer from a significant drawback at high temperatures: the inability to form a continuous and dense oxide layer to protect the matrix, leading to continuous oxidation reactions. All of these factors severely restrict the subsequent engineering applications of high-entropy carbonitride ceramics.

[0003] To address the poor oxidation resistance and low toughness of high-entropy carbonitride ceramics, researchers are currently focusing on the following approaches: First, by controlling the carbon-nitrogen ratio in the ceramic. Increasing the nitrogen content results in a higher oxidation initiation temperature, fewer cracks, and a more complete structure after oxidation, while also producing greater lattice distortion, thus achieving a toughening effect. Second, by altering the types and proportions of metallic elements in the high-entropy ceramic; for example, high-entropy ceramics containing chromium form a more dense and continuous oxide layer.

[0004] The aforementioned methods for improving the oxidation resistance and toughness of high-entropy carbonitrides still have some problems that need to be solved: although changing the carbon-nitrogen ratio and the types of metal elements can promote the integrity and continuity of the oxide layer to a certain extent, the gases generated by oxidation make these oxide layers macroscopically complete and continuous, but microscopically loose and porous, providing channels for oxygen diffusion; in addition, the deformation of ceramics is dominated by brittle fracture, and high-entropy design can strengthen the lattice and improve strength, but cannot fundamentally change its bonding properties, and relies more on the introduction of a second phase or phase transformation design. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a high-entropy carbonitride ceramic with high toughness and oxidation resistance. The high-entropy carbonitride ceramic provided by this invention has good uniformity, high density, and excellent high toughness and oxidation resistance.

[0006] The second objective of this invention is to provide a method for preparing high-entropy carbonitride ceramics with high toughness and oxidation resistance. The method involves first preparing pre-solidified high-entropy carbonitride and high-entropy boride powders using carbothermic reduction nitridation and boronothermic reduction methods, respectively. Then, a second phase is introduced and completely homogenized through a secondary ball milling process. Finally, the high pressure, high temperature, and pulsed current generated during spark plasma sintering enable the in-situ generation of a hexagonal boron nitride third phase during the sintering process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a high-entropy carbonitride ceramic with high toughness and oxidation resistance, wherein the high-entropy carbonitride ceramic is composed of a uniformly distributed high-entropy carbonitride matrix phase, a high-entropy boride second phase, and a hexagonal boron nitride third phase.

[0009] The high-entropy carbonitride ceramic with high toughness and oxidation resistance provided by this invention is composed of a high-entropy carbonitride matrix phase, a high-entropy boride second phase, and a hexagonal boron nitride third phase. The three phases are evenly distributed and the overall structure is dense. The lamellar structure of the hexagonal boron nitride can effectively deflect cracks, bridge cracks, and dissipate stress, significantly extending the crack propagation path and improving the fracture toughness of the material. When the high-entropy boride and hexagonal boron nitride are oxidized at high temperatures, both will produce B2O3. At high temperatures, this B2O3 is in a liquid phase that wets and binds oxide particles, effectively sealing pores and blocking oxygen diffusion channels, thereby improving the oxidation resistance of the material. Thus, the high-entropy carbonitride ceramic provided by this invention has both excellent toughness and oxidation resistance.

[0010] In a preferred embodiment, the mass ratio of the high-entropy carbonitride matrix phase to the high-entropy boride second phase in the high-entropy carbonitride ceramic is 6~9:1~4, more preferably 6~8:2~4, and even more preferably 6~7:3~4.

[0011] The optimal performance is achieved by controlling the amount of high-entropy borides within the range of this invention. If too much high-entropy borides are added, although the antioxidant properties of the material will be further enhanced, the density of the composite material will decrease, resulting in a decline in the increase in its toughness.

[0012] In a preferred embodiment, the high-entropy carbonitride ceramic matrix phase is composed of a first group of transition metal elements, carbon, and nitrogen, wherein the first group of transition metal elements is composed of at least five elements selected from Ti, Zr, Hf, V, Nb, and Ta; and the high-entropy boride second phase is composed of a second group of transition metal elements and boron, wherein the second group of transition metal elements is composed of at least five elements selected from Ti, Zr, Hf, V, Nb, and Ta.

[0013] Further optimization involves ensuring that the first group of transition metal elements has the same composition as the second group of transition metal elements. Experiments have shown that having the same composition as the second group of transition metal elements is more conducive to the uniformity of the material's composition.

[0014] In a preferred embodiment, the hexagonal boron nitride third phase is generated in situ.

[0015] This invention discloses a method for preparing high-toughness, oxidation-resistant high-entropy carbonitride ceramics, which involves ball milling high-entropy carbonitride powder and high-entropy boride powder to obtain a high-entropy mixed powder, and then subjecting the high-entropy mixed powder to spark plasma sintering.

[0016] The preparation method of the present invention involves ball milling high-entropy carbonitride powder and high-entropy boride powder to ensure that the two high-entropy pre-solidified powders are uniformly distributed at the microscale, preventing the agglomeration of the second phase in the matrix. Then, under the conditions of high temperature, high pressure and pulsed current during spark plasma sintering, hexagonal boron nitride can be generated in situ during the sintering process, resulting in a high-entropy carbonitride-based ceramic with a three-phase structure.

[0017] In a preferred embodiment, the high-entropy carbonitride powder has a particle size of 75-200 μm, preferably 75-125 μm, and the high-entropy boride powder has a particle size of 75-200 μm, preferably 75-125 μm. Experiments have shown that controlling the particle size of both powders within the above ranges can eliminate particle agglomeration and effectively prevent component segregation in the product, resulting in a more uniform three-phase distribution in the final product.

[0018] In a preferred embodiment, the process of obtaining the high-entropy carbonitride powder is as follows: oxide powder and carbon powder corresponding to the first group of transition metal elements are prepared according to the design ratio, mixed to obtain a mixed powder, and the mixed powder is subjected to an in-situ carbothermic reduction nitridation reaction under a nitrogen atmosphere. The resulting reactant is then crushed and sieved to obtain the powder.

[0019] For equicomponent high-entropy carbonitride ceramics, the composition is designed based on the equiatomic ratio of the material system, that is, each metal atom in the carbonitride corresponds to one carbon atom and one nitrogen atom.

[0020] Further preferred, the purity of the oxide powder and carbon powder corresponding to the first group of transition metal elements is ≥99.5wt%.

[0021] In a further preferred embodiment, the particle size of the oxide powder corresponding to the first group of transition metal elements is 0.5~2μm.

[0022] In a further preferred embodiment, the mixing method is wet ball milling, using anhydrous ethanol as the milling medium, with a ball-to-material ratio of 3–10:1, preferably 3–5:1. The milling speed is 200–300 r / min, with continuous forward and reverse rotation cycles. Each forward rotation cycle lasts 30–60 min, and each reverse rotation cycle lasts 30–60 min, for a total milling time of 12–36 h. This ball milling method ensures thorough and uniform mixing of transition metal oxides and provides a higher energy level to the mixed system, which is beneficial for subsequent carbothermic reduction nitridation reactions.

[0023] In actual operation, after wet ball milling, the resulting wet powder is dried. The preferred conditions for the wet mixed powder drying process are: drying time of 8~12h in a normal drying oven and drying temperature of 60℃~90℃. Under the preferred drying conditions, the anhydrous ethanol in the ball milling media during the wet mixing process can be completely evaporated, reducing the impurity content and improving the purity of the product.

[0024] In a further preferred embodiment, during the in-situ carbothermic reduction nitriding reaction, a graphite tube is placed in the reactor.

[0025] In a further preferred embodiment, during the in-situ carbothermic reduction nitriding reaction, the flow rate of nitrogen gas introduced is 20-200 sccm, preferably 120-200 sccm.

[0026] In a further preferred embodiment, the in-situ carbothermic reduction nitriding reaction process is as follows: heating to 1100℃~1600℃, preferably 1300~1600℃, at a heating rate of 5~20℃ / min, and holding at that temperature for 1h~4h, preferably 2~3h.

[0027] In a further preferred embodiment, the in-situ carbothermic reduction nitriding reaction process is as follows: first, the temperature is raised to 1400-1450℃ at a heating rate of 8-12℃ / min, and then raised to 1600-1650℃ at a heating rate of 4-6℃ / min and held for 2-3 hours.

[0028] The in-situ carbothermic reduction nitriding reaction of the present invention involves placing a graphite tube in a tube furnace beforehand to maintain the carbon atmosphere required for reduction. At the same time, it is necessary to ensure the good airtightness of the tube furnace, and to introduce high-purity nitrogen into the furnace while ensuring that the gas can be discharged normally. Then, the temperature is raised to carry out the in-situ carbothermic reduction nitriding reaction. After the reaction is completed, the temperature is lowered to room temperature.

[0029] In actual operation, the product after in-situ carbothermic reduction nitriding reaction is crushed using an agate mortar and then passed through a 60-200 mesh sieve, preferably a 120-200 mesh sieve.

[0030] In a preferred embodiment, the process for obtaining the high-entropy boride powder is as follows: Take oxide powders corresponding to the second group of transition metal elements, graphite powder, and boron carbide powder, controlling the amount of boron carbide powder added to be 25-35 wt% excess of the theoretical amount, mix to obtain a mixed powder, and subject the mixed powder to a boronothermic reduction reaction under a nitrogen atmosphere. The resulting reactant is then crushed and sieved to obtain the final product.

[0031] For high-entropy boride ceramics, the composition is designed based on the atomic ratio of the material system. In the boride, each metal atom corresponds to two boron atoms. Then, based on the theoretical amount, oxide powder is prepared. In order to avoid the loss of boron during the reduction reaction, an excess of boron carbide is added. Experiments have shown that adding an appropriate amount of boron carbide can not only avoid the loss of boron, but also achieve grain refinement and improve the performance of the product.

[0032] Further preferred, the purity of the oxide powder, carbon powder, and boron carbide powder corresponding to the second group of transition metal elements is ≥99.5wt%.

[0033] In a further preferred embodiment, the particle size of the oxide powder corresponding to the second group of transition metal elements is 0.5~2μm.

[0034] In a further preferred embodiment, the mixing method is wet ball milling, using anhydrous ethanol as the milling medium, with a ball-to-material ratio of 3-10:1, preferably 3-5:1. The milling speed is 200-300 r / min, with continuous forward-reverse rotation. Each forward rotation lasts 30-60 min, and each reverse rotation lasts 30-60 min, for a total milling time of 12-36 h. This ball milling method ensures thorough and uniform mixing of transition metal oxides and provides a higher energy level to the mixed system, which is beneficial for subsequent carbothermic reduction nitridation reactions.

[0035] In actual operation, after wet ball milling, the resulting wet powder is dried. The preferred conditions for the wet mixed powder drying process are: drying time of 8~12h in a normal drying oven and drying temperature of 60℃~90℃. Under the preferred drying conditions, the anhydrous ethanol in the ball milling media during the wet mixing process can be completely evaporated, reducing the impurity content and improving the purity of the product.

[0036] In a further preferred embodiment, during the boronothermal reduction reaction, a graphite tube is placed in the reactor.

[0037] In a further preferred embodiment, during the boronothermal reduction reaction, the flow rate of nitrogen gas introduced is 20-200 sccm, preferably 120-200 sccm.

[0038] In a further preferred embodiment, the borothermic reduction reaction process is as follows: the temperature is increased to 1100℃~1600℃ at a heating rate of 5~20℃ / min, preferably 1300~1600℃, and held for 1h~4h, preferably 2~3h.

[0039] In a further preferred embodiment, the borothermic reduction reaction process is as follows: first, the temperature is raised to 1400-1450℃ at a heating rate of 8-12℃ / min, and then raised to 1600-1650℃ at a rate of 4-6℃ / min and held for 2-3 hours.

[0040] In the boronothermal reduction reaction of the present invention, a graphite tube is placed in a tube furnace beforehand to maintain the carbon atmosphere required for reduction. At the same time, it is necessary to ensure that the tube furnace is airtight and to introduce high-purity nitrogen into the furnace while ensuring that the gas can be discharged normally. Then, the temperature is raised to carry out the boronothermal reduction reaction. After the reaction is completed, the temperature is lowered to room temperature.

[0041] In actual operation, the product after the borothermic reduction reaction is crushed using an agate mortar and then passed through a 60-200 mesh sieve, preferably a 120-200 mesh sieve.

[0042] In a preferred embodiment, the ball milling is carried out under an argon atmosphere, the ball milling speed is 200~400 r / min, preferably 200~300 r / min, the ball milling time is 8~15 h, preferably 9~12 h, and the ball-to-material ratio is 3~10:1, preferably 3~5:1.

[0043] In a further preferred embodiment, the ball milling is performed in a cycle of forward rotation-pause-reverse rotation-pause, with each forward rotation lasting 5-30 minutes, preferably 5-15 minutes, each reverse rotation lasting 5-30 minutes, preferably 5-15 minutes, and each pause lasting 3-10 minutes, preferably 3-5 minutes. Experiments have shown that this preferred ball milling method allows for complete and uniform mixing and full activation of the high-entropy carbonitride powder and high-entropy boride powder. This promotes the uniform distribution of the second phase in the matrix during subsequent spark plasma sintering and, synergistically with the spark plasma sintering process of this invention, the formation of in-situ hexagonal boron nitride.

[0044] In a preferred embodiment, the temperature of the discharge plasma sintering is 1600℃~2100℃, preferably 1800℃~2100℃, the holding time is 3min~20min, preferably 5min~15min, and the pressure is 10~50MPa.

[0045] In a further preferred embodiment, the discharge plasma sintering process is as follows: first, the temperature is raised to 1500~1700℃ and held for 2~5 minutes, then the temperature is raised to 1900~2100℃ and held for 7~10 minutes, while controlling the pressure to be 30~50MPa.

[0046] Experiments have shown that raising the temperature to 1500~1700℃ and holding it at this temperature for 2~5 minutes helps to achieve uniform densification during sintering, resulting in a dense bulk material free of impurities. More importantly, under these optimal conditions, the sintering process during spark plasma sintering, combined with high temperature and high pressure and the pulsed current during spark plasma sintering, not only can the ceramic be completely densified during sintering, but also more hexagonal boron nitride can be generated in situ in the ceramic under these sintering conditions.

[0047] Principles and advantages

[0048] One of the key aspects of the technical solution of this invention is that a certain proportion of high-entropy boride presolution powder is introduced into the high-entropy carbonitride presolution powder through secondary ball milling, which can make the two high-entropy presolution powders uniformly distributed at the microscale and prevent the agglomeration of the second phase in the matrix.

[0049] The second key aspect of the technical solution of this invention lies in the environment during spark plasma sintering. The conditions of high temperature, high pressure, and pulsed current can generate hexagonal boron nitride in situ during the sintering process, thereby obtaining a high-entropy carbonitride-based ceramic with a three-phase structure.

[0050] Therefore, the high-entropy carbonitride bulk material prepared by the above method according to the present invention has the following significant advantages compared with existing high-entropy carbonitride materials:

[0051] (1). The process steps include carbothermic reduction nitriding technology and boronothermic reduction technology. In the boronothermic reduction, an additional 30ω% excess boron carbide is added, which can reduce the presence of oxygen and replenish the boron lost through volatilization so that it can be fully reduced, resulting in high-entropy carbonitride ceramics and high-entropy borides with fine particle size and high purity.

[0052] (2). The two-phase presolidified powders of HEB and HECN, which are achieved by secondary ball milling, are tightly and uniformly mixed, which effectively expands the reaction interface and shortens the atomic diffusion path.

[0053] (3) The third phase BN was prepared by spark plasma sintering technology. The synergistic effect of instantaneous high temperature, axial pressure and pulse current during sintering provided conditions for the formation of BN. Attached Figure Description

[0054] Figure 1 SEM and EDS images of the bulk product after spark plasma sintering in Embodiment 3 of the present invention.

[0055] Figure 2 SEM and EDS images of the bulk product after spark plasma sintering in Comparative Example 1 of this invention. Detailed Implementation

[0056] To enable those skilled in the art to fully understand the technical solution and innovative points of the present invention, the implementation methods, technical features, and operational effects of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments. It should be particularly noted that the scope of protection of the present invention should be determined by the claims, and should not be limited to the specific technical details listed in the embodiments.

[0057] Unless otherwise expressly defined, the technical terms used in this specification shall be interpreted as having the normative meaning as understood by one of ordinary qualifications in the art to which this invention pertains. These terms are used only to precisely describe the technical solutions of specific embodiments, and their use does not constitute any limitation on the scope of protection of this invention.

[0058] The raw materials, reagents, experimental equipment, and testing devices involved in the embodiments of this invention can all be obtained commercially or prepared using processes known in the art. Unless otherwise specified, the process parameters such as temperature and pressure in the relevant operating steps are achieved using conventional experimental conditions in this technical field.

[0059] Example 1

[0060] A simple method for preparing high-entropy carbonitride ceramics with high oxidation resistance and high toughness includes the following steps:

[0061] (1) TiO2 (99.9% purity), Nb2O5 (99.5% purity), Ta2O5 (99.5% purity), ZrO2 (99.5% purity), HfO2 (99.5% purity), V2O5 (99.5% purity), 1~2μm graphite and 1~2μm boron carbide with particle sizes of 500nm~2μm, except for a small amount of unavoidable impurity elements, do not contain other metallic impurity elements in the raw materials; for the preparation of high-entropy carbonitrides, the anions and cations are weighed according to the equiatomic ratio: first weigh 7.56g of TiO2 powder and 12.58g of Nb2O5 powder, The following ingredients were used to prepare high-entropy borides: 20.91g Ta₂O₅ powder, 11.66g ZrO₂ powder, 19.92g HfO₂ powder, 8.61g V₂O₅ powder, and 18.76g graphite. To prevent boron loss during the reduction reaction, an additional 30ω% excess boron carbide was added, and the mass of the graphite powder was adjusted: 6.94g TiO₂ powder and 11.55g Nb₂O₅ powder were weighed. 19.21g of Ta2O5 powder, 10.71g of ZrO2 powder, 18.3g of HfO2 powder, 7.91g of V2O5 powder, 10.02g of graphite, and 18.73g of boron carbide were weighed and placed separately in a cemented carbide ball mill jar for wet mixing. The wet mixing conditions were as follows: ball-to-powder ratio of 4:1, ball milling medium of 100ml anhydrous ethanol, ball milling speed of 250r / min, forward rotation for 60min, reverse rotation for 60min, with no interruption between forward and reverse rotation, for a total ball milling time of 24h. The mixed powder after ball milling needed to be dried at 90℃ for 10h.

[0062] (2) The two mixed powders dried in step (1) are crushed and sieved through a 100-mesh sieve to control the particle size to below 150 μm; the two powders are reduced by the following method: 15g of the sieved powder is weighed and placed in a graphite boat, and then the graphite boat is placed in the middle of the carbon tube of the tube furnace to ensure accurate temperature; first, the tube furnace is purged. For the preparation of high-entropy carbonitrides, high-purity nitrogen is continuously introduced into the tube at a flow rate of 160 sccm. The heating rate in the tube furnace before reaching 1400℃ is 10℃ / m. In the tube furnace, the heating rate was 5℃ / min after reaching 1400℃, and then held at 1600℃ for 2 hours before cooling to room temperature to obtain high-entropy carbonitride pre-solidified powder. For the preparation of high-entropy borides, high-purity argon gas was continuously introduced into the tube at a flow rate of 80 sccm. The heating rate in the tube furnace was 10℃ / min before reaching 1400℃, and then 5℃ / min after reaching 1400℃. After holding at 1600℃ for 2 hours, the temperature was then lowered to room temperature to obtain high-entropy boride pre-solidified powder. After repeated reduction to obtain sufficient powder, it was crushed and sieved through a 120-mesh sieve to control the particle size below 125 μm.

[0063] (3) The two high-entropy presolution powders obtained by reduction in step (2) are weighed according to the mass ratio and then ball-milled and mixed for a second time. The mass ratio is high-entropy carbonitride presolution powder: high-entropy boride presolution powder = 9:1. Weigh 22.5g of high-entropy carbonitride presolution powder and 2.5g of high-entropy boride presolution powder obtained by reduction in (2), a total of 25g of powder, and place them in a cemented carbide ball mill jar for dry grinding and mixing. The ball-to-material ratio is 4:1. High-purity argon gas is introduced into the ball mill jar to prevent oxidation. The ball milling speed is 250r / min, 10min forward rotation, 10min reverse rotation, and 3min interval between forward and reverse rotation. The total ball milling time is 10h. The mixed powder after ball milling is taken out and vacuum-sealed.

[0064] (4) The two-phase presolidified mixed powder obtained by ball milling in step (3) is subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)(CN)9B1 high-entropy ceramic. The discharge plasma sintering temperature is first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature is raised to 2000℃ and held for 7 min. The sintering pressure is controlled at 40MPa.

[0065] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic blocks. High-entropy carbonitride and high-entropy boride phases were observed in the high-entropy bulk ceramic after ultra-high temperature discharge plasma sintering (UHTPS). SEM and EDS analysis of the UHTPS product of this embodiment revealed light gray high-entropy carbonitride, dark gray high-entropy boride, and black hexagonal boron nitride. The three phases were uniformly distributed and the overall microstructure was dense. Notably, the hexagonal boron nitride was generated in situ during the discharge plasma sintering process and its crystallinity was inferior to the high-entropy phase, thus it could not be observed in the XRD pattern. Relevant mechanical tests showed that the product had a Vickers hardness of HV. 0.5 The value is 2046, and the fracture toughness is 3.36 MPa•m. 1 / 2 Oxidation experiments were conducted at 800℃, 1000℃, and 1200℃ for 2 hours, with oxidative weight increases of 13.51 mg / cm³. 2 38.72 mg / cm 2 and 32.99 mg / cm 2 .

[0066] Example 2

[0067] A simple method for preparing high-entropy carbonitride ceramics with high oxidation resistance and high toughness includes the following steps:

[0068] (1) The ball milling mixing step is the same as step (1) in Example 1, and will not be repeated here.

[0069] (2) The carbothermic reduction nitriding step after crushing is the same as step (2) in Example 1, and will not be repeated here.

[0070] (3) The two high-entropy presolution powders obtained by reduction in step (2) are weighed according to the mass ratio and then ball-milled and mixed for a second time. The mass ratio is high-entropy carbonitride presolution powder: high-entropy boride presolution powder = 8:2. Weigh 20g of high-entropy carbonitride presolution powder and 5g of high-entropy boride presolution powder obtained by reduction in (2), and place a total of 25g of powder in a cemented carbide ball milling jar for dry grinding and mixing. The ball-to-material ratio is 4:1. High-purity argon gas is introduced into the ball milling jar to prevent oxidation. The ball milling speed is 250r / min, with 10min of forward rotation, 10min of reverse rotation, and a 3min interval between forward and reverse rotation. The total ball milling time is 10h. The mixed powder after ball milling is taken out and vacuum-sealed.

[0071] (4) The two-phase presolidified mixed powder obtained by ball milling in step (3) is subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)(CN)8B2 high-entropy ceramic. The discharge plasma sintering temperature is first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature is raised to 2000℃ and held for 7 min. The sintering pressure is controlled at 40 MPa.

[0072] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic blocks. High-entropy carbonitride and high-entropy boride phases were observed in the high-entropy bulk ceramic after ultra-high temperature discharge plasma sintering (UHTPS). SEM and EDS analysis of the UHTPS product of this embodiment revealed light gray high-entropy carbonitride, dark gray high-entropy boride, and black hexagonal boron nitride. The three phases were uniformly distributed and the overall microstructure was dense. Relevant mechanical tests showed that the product had a Vickers hardness of HV. 0.5 The value is 1953, and the fracture toughness is 3.71 MPa•m. 1 / 2 Oxidation experiments were conducted at 800℃, 1000℃, and 1200℃ for 2 hours, with oxidative weight gains of 7.36 mg / cm³. 2 15.07 mg / cm 2 and 23.48 mg / cm 2 .

[0073] Example 3

[0074] A simple method for preparing high-entropy carbonitride ceramics with high oxidation resistance and high toughness includes the following steps:

[0075] (1) The ball milling mixing step is the same as step (1) in Example 1, and will not be repeated here.

[0076] (2) The carbothermic reduction nitriding step after crushing is the same as step (2) in Example 1, and will not be repeated here.

[0077] (3) The two high-entropy presolution powders obtained by reduction in step (2) are weighed according to the mass ratio and then ball-milled and mixed for a second time. The mass ratio is high-entropy carbonitride presolution powder: high-entropy boride presolution powder = 7:3. Weigh 17.5g of high-entropy carbonitride presolution powder and 7.5g of high-entropy boride presolution powder obtained by reduction in (2), a total of 25g of powder, and place them in a cemented carbide ball mill jar for dry grinding and mixing. The ball-to-material ratio is 4:1. High-purity argon gas is introduced into the ball mill jar to prevent oxidation. The ball milling speed is 250r / min, 10min for forward rotation, 10min for reverse rotation, and 3min interval between forward and reverse rotation. The total ball milling time is 10h. The mixed powder after ball milling is taken out and vacuum-sealed.

[0078] (4) The two-phase presolidified mixed powder obtained by ball milling in step (3) is subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)(CN)7B3 high-entropy ceramic. The discharge plasma sintering temperature is first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature is raised to 2000℃ and held for 7 min. The sintering pressure is controlled at 40MPa.

[0079] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic bulk bodies. High-entropy carbonitride and high-entropy boride phases were observed in the bulk ceramic after ultra-high temperature discharge plasma sintering (UHTPS). SEM and EDS analyses of the UHTPS bulk product of this embodiment further support this assessment. Figure 1 The product exhibits light gray high-entropy carbonitrides, dark gray high-entropy borides, and black hexagonal boron nitride. The three phases are uniformly distributed and the overall microstructure is dense. Relevant mechanical tests show that the product has a Vickers hardness of HV. 0.5 The value is 1865, and the fracture toughness is 4.07 MPa•m. 1 / 2 Oxidation experiments were conducted at 800℃, 1000℃, and 1200℃ for 2 hours, with oxidative weight gains of 4.96 mg / cm³. 2 10.49 mg / cm 2 and 19.61 mg / cm2 .

[0080] Example 4

[0081] A simple method for preparing high-entropy carbonitride ceramics with high oxidation resistance and high toughness includes the following steps:

[0082] (1) The ball milling mixing step is the same as step (1) in Example 1, and will not be repeated here.

[0083] (2) The carbothermic reduction nitriding step after crushing is the same as step (2) in Example 1, and will not be repeated here.

[0084] (3) The two high-entropy presolution powders obtained by reduction in step (2) are weighed according to the mass ratio and then ball-milled and mixed for a second time. The mass ratio is high-entropy carbonitride presolution powder: high-entropy boride presolution powder = 6:4. Weigh 15g of high-entropy carbonitride presolution powder and 10g of high-entropy boride presolution powder obtained by reduction in (2), a total of 25g of powder is placed in a cemented carbide ball mill jar for dry grinding and mixing. The ball-to-material ratio is 4:1. High-purity argon gas is introduced into the ball mill jar to prevent oxidation. The ball milling speed is 250r / min, 10min for forward rotation, 10min for reverse rotation, and 3min interval between forward and reverse rotation. The total ball milling time is 10h. The mixed powder after ball milling is taken out and vacuum-sealed.

[0085] (4) The two-phase presolidified mixed powder obtained by ball milling in step (3) is subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)(CN)6B4 high-entropy ceramic. The discharge plasma sintering temperature is first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature is raised to 2000℃ and held for 7 min. The sintering pressure is controlled at 40MPa.

[0086] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic blocks. After ultra-high temperature discharge plasma sintering (UHTPS), high-entropy carbonitride and high-entropy boride phases were observed in the high-entropy ceramic block. SEM and EDS analysis of the UHTPS block product of this embodiment revealed light gray high-entropy carbonitride, dark gray high-entropy boride, and black hexagonal boron nitride, with uniform three-phase distribution and a dense overall microstructure. Subsequent TEM analysis confirmed that the black phase was indeed hexagonal boron nitride. After relevant mechanical testing, the product achieved a Vickers hardness of HV. 0.5 The value is 1893, and the fracture toughness is 4.71 MPa•m. 1 / 2Oxidation experiments were conducted at 800℃, 1000℃, and 1200℃ for 2 hours, with oxidized weight increases of 2.42 mg / cm³. 2 5.19 mg / cm 2 and 12.40 mg / cm 2 .

[0087] Comparative Example 1

[0088] A simple method for preparing high-entropy carbonitride ceramics includes the following steps:

[0089] (1) TiO2 (99.9% purity), Nb2O5 (99.5% purity), Ta2O5 (99.5% purity), ZrO2 (99.5% purity), HfO2 (99.5% purity), V2O5 (99.5% purity) with particle sizes of 500nm~2μm, and graphite with particle sizes of 1~2μm, except for a small amount of unavoidable impurity elements, do not contain other metallic impurity elements in the raw materials; the anions and cations are weighed according to the equiatomic ratio: first weigh 7.56g of TiO2 powder and 12.58g of Nb2O5 powder, 20.91g of Ta2O5 powder, 11.66g of ZrO2 powder, 19.92g of HfO2 powder, 8.61g of V2O5 powder, and 18.76g of graphite were weighed and placed separately in a cemented carbide ball mill jar for wet mixing. The ball-to-powder ratio was 4:1, the ball milling medium was 100ml of anhydrous ethanol, the ball milling speed was 250r / min, the clockwise rotation was 60min, the counterclockwise rotation was 60min, and the clockwise and counterclockwise rotations were continuous. The total ball milling time was 24h. The mixed powder after ball milling needed to be dried at 90℃ for 10h.

[0090] (2) After crushing the dried mixed powder in step (1), sieve it through a 100-mesh sieve to control the particle size below 150 μm. The powder is reduced using the following method: Weigh 15 g of the sieved powder and place it in a graphite boat, then place the graphite boat in the middle of the carbon tube of the tube furnace to ensure accurate temperature. Wash the tube furnace and keep high-purity nitrogen gas continuously flowing into the tube at a flow rate of 160 sccm. The heating rate in the tube furnace is 10 °C / min before reaching 1400 °C and 5 °C / min after reaching 1400 °C. After heating to the target temperature of 1600 °C, hold for 2 h, and then cool to room temperature to obtain high-entropy carbonitride presolution powder. Repeat the reduction to obtain sufficient powder, then crush it and sieve it through a 120-mesh sieve to control the particle size below 125 μm.

[0091] (3) The presolution mixed powder obtained by the tube furnace reduction in step (2) is subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)CN high entropy ceramic. The discharge plasma sintering temperature is first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature is raised to 2000℃ and held for 7 min. The sintering pressure is controlled at 40MPa.

[0092] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic bulk bodies. Uniform high-entropy carbonitride phases were observed in the bulk ceramic bodies after ultra-high temperature discharge plasma sintering (UHTPS) of this embodiment. SEM and EDS analyses of the UHTPS bulk products of this embodiment further support this assessment. Figure 2 Light gray high-entropy carbonitrides were observed in the sample, with uniform phase structure, uniform grain size, no obvious elemental segregation, and overall density. Relevant mechanical tests showed that the product had a Vickers hardness of HV. 0.5 The value is 2133, and the fracture toughness is 2.09 MPa•m. 1 / 2 Oxidation experiments showed that after 2 hours of oxidation at 800℃, the weight gain was 82.49 mg / cm³. 2 After oxidation at 1000℃ and 1200℃ for 1 hour, the samples were completely oxidized, with an oxidation weight gain of 75.46 mg / cm³. 2 and 83.89 mg / cm 2

[0093] Comparative Example 2

[0094] A simple method for preparing high-entropy carbonitride ceramics with high oxidation resistance and high toughness includes the following steps:

[0095] (5) TiO2 (99.9% purity), Nb2O5 (99.5% purity), Ta2O5 (99.5% purity), ZrO2 (99.5% purity), HfO2 (99.5% purity), V2O5 (99.5% purity), 1~2μm graphite and 1~2μm boron carbide with particle sizes of 500nm~2μm, except for a small amount of unavoidable impurity elements, do not contain other metallic impurity elements in the raw materials; for the preparation of high-entropy carbonitrides, the anions and cations are weighed according to the equiatomic ratio: first weigh 7.56g of TiO2 powder and 12.58g of Nb2O5 powder, The following ingredients were used to prepare high-entropy borides: 20.91g Ta₂O₅ powder, 11.66g ZrO₂ powder, 19.92g HfO₂ powder, 8.61g V₂O₅ powder, and 18.76g graphite. To prevent boron loss during the reduction reaction, an additional 30ω% excess boron carbide was added, and the mass of the graphite powder was adjusted: 6.94g TiO₂ powder and 11.55g Nb₂O₅ powder were weighed. 19.21g of Ta2O5 powder, 10.71g of ZrO2 powder, 18.3g of HfO2 powder, 7.91g of V2O5 powder, 10.02g of graphite, and 18.73g of boron carbide were weighed and placed separately into a cemented carbide ball mill jar for wet mixing. The ball-to-powder ratio was 4:1, the ball milling medium was 100ml of anhydrous ethanol, the ball milling speed was 250r / min, the clockwise rotation was 60min, the counterclockwise rotation was 60min, and the clockwise and counterclockwise rotations were continuous. The total ball milling time was 24h. The mixed powder after ball milling needed to be dried at 90℃ for 10h.

[0096] (6) After crushing the two mixed powders dried in step (1), sieve them through a 100-mesh sieve to control the particle size to below 150 μm; the two powders are reduced by the following method: weigh 15 g of the sieved powder and place it in a graphite boat, then place the graphite boat in the middle of the carbon tube of the tube furnace to ensure accurate temperature; first, the tube furnace is purged. For the preparation of high-entropy carbonitrides, high-purity nitrogen is continuously introduced into the tube at a flow rate of 160 sccm. The heating rate in the tube furnace before reaching 1400℃ is 10℃ / min. For the preparation of high-entropy borides, high-purity argon gas was continuously introduced into the tube at a flow rate of 80 sccm. The heating rate before reaching 1400℃ was 10℃ / min, and the heating rate after reaching 1400℃ was 5℃ / min. The target temperature of 1600℃ was reached and held for 2 hours, followed by cooling to room temperature to obtain high-entropy boride pre-solidified powder. After repeated reduction to obtain sufficient powder, it was crushed and sieved through a 120-mesh sieve to control the particle size below 125 μm.

[0097] (7) The two high-entropy presolidified powders obtained by reduction in step (2) are weighed according to the mass ratio and then ball-milled and mixed for a second time. The mass ratio is high-entropy carbonitride presolidified powder: high-entropy boride presolidified powder = 5:5. Weigh 12.5g of high-entropy carbonitride presolidified powder and 12.5g of high-entropy boride presolidified powder obtained by reduction in (2), a total of 25g of powder, and place them in a cemented carbide ball mill jar for dry grinding and mixing. The ball-to-material ratio is 4:1. High-purity argon gas is introduced into the ball mill jar to prevent oxidation. The ball milling speed is 250r / min, 10min of forward rotation, 10min of reverse rotation, and 3min of interval between forward and reverse rotation. The total ball milling time is 10h. The mixed powder after ball milling is taken out and vacuum-sealed.

[0098] (8) The two-phase presolidified mixed powder obtained by the second ball milling in step (3) was subjected to discharge plasma sintering to prepare (TiNbTaZrHfV)(CN)5B5 high-entropy ceramic. The discharge plasma sintering temperature was first controlled at 1600℃ and held at 1600℃ for 3 min. Then the temperature was raised to 2000℃ and held for 7 min. The sintering pressure was controlled at 40 MPa.

[0099] The product of this embodiment was characterized by phase analysis, microstructure observation, and elemental analysis. Performance tests were conducted on the product through mechanical and oxidation experiments. This invention can produce dense, uniformly distributed high-entropy ceramic blocks. High-entropy carbonitride and high-entropy boride phases were observed in the high-entropy bulk ceramic after ultra-high temperature discharge plasma sintering (UHTPS). SEM and EDS analysis of the UHTPS product of this embodiment revealed light gray high-entropy carbonitride, dark gray high-entropy boride, and black hexagonal boron nitride, all uniformly distributed. Notably, the hexagonal boron nitride was generated in situ during the discharge plasma sintering process and, due to its lower crystallinity compared to the high-entropy phase, could not be observed in the XRD pattern. Relevant mechanical tests showed that the product had a Vickers hardness of HV. 0.5 The value is 1796, and the fracture toughness is 3.21 MPa•m. 1 / 2 Oxidation experiments were conducted at 800℃, 1000℃, and 1200℃ for 2 hours, with oxidative weight gains of 1.49 mg / cm³. 2 3.68 mg / cm 2 and 12.0 mg / cm 2 .

Claims

1. A high-toughness, oxidation-resistant, high-entropy carbonitride ceramic, characterized in that: The high-entropy carbonitride ceramic is composed of a uniformly distributed high-entropy carbonitride matrix phase, a high-entropy boride second phase, and a hexagonal boron nitride third phase.

2. A high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 1, characterized in that: In the high-entropy carbonitride ceramic, the mass ratio of the high-entropy carbonitride matrix phase to the high-entropy boride second phase is 6~9:1~4.

3. A high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 1 or 2, characterized in that: The high-entropy carbonitride ceramic matrix phase is composed of a first group of transition metal elements, carbon, and nitrogen. The first group of transition metal elements is composed of at least five elements selected from Ti, Zr, Hf, V, Nb, and Ta. The high-entropy boride second phase is composed of a second group of transition metal elements and B. The second group of transition metal elements is composed of at least five elements selected from Ti, Zr, Hf, V, Nb, and Ta. The hexagonal boron nitride third phase is generated in situ.

4. A method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to any one of claims 1-3, characterized in that: High-entropy mixed powder is obtained by ball milling high-entropy carbonitride powder and high-entropy boride powder, and then obtained by spark plasma sintering of the high-entropy mixed powder.

5. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 4, characterized in that: The high-entropy carbonitride powder has a particle size of 75~200μm, and the high-entropy boride powder has a particle size of 75~200μm.

6. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 4, characterized in that: The process of obtaining the high-entropy carbonitride powder is as follows: the oxide powder and carbon powder corresponding to the first group of transition metal elements are prepared according to the design ratio, and mixed to obtain a mixed powder. The mixed powder is subjected to an in-situ carbothermic reduction nitridation reaction under a nitrogen atmosphere, and the resulting reactant is crushed and sieved to obtain the powder. The purity of the oxide powder and carbon powder corresponding to the first group of transition metal elements is ≥99.5wt%; The particle size of the oxide powder corresponding to the first group of transition metal elements is 0.5~2μm; the mixing method is wet ball milling, the ball milling medium is anhydrous ethanol, the ball-to-material ratio is 3~10:1, the ball milling speed is 200~300r / min, and the forward-reverse rotation is continuously cyclically performed, the single forward rotation time is 30min~60min, the single reverse rotation time is 30min~60min, and the total ball milling time is 12~36h; During the in-situ carbothermic reduction nitriding reaction, a graphite tube is placed in the reactor. During the in-situ carbothermic reduction nitriding reaction, the flow rate of nitrogen gas introduced is 20-200 sccm; The in-situ carbothermic reduction nitriding reaction process is as follows: the temperature is increased to 1100℃~1600℃ at a heating rate of 5~20℃ / min, and held for 1h~4h.

7. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 4, characterized in that: The process of obtaining the high-entropy boride powder is as follows: Take oxide powder, graphite powder, and boron carbide powder corresponding to the second group of transition metal elements, control the amount of boron carbide powder added to be 25-35 wt% excess of the theoretical amount, mix to obtain mixed powder, carry out boron thermal reduction reaction of the mixed powder under nitrogen atmosphere, and crush and sieve the resulting reactant. The purity of the oxide powder, carbon powder, and boron carbide powder corresponding to the second group of transition metal elements is ≥99.5 wt%. The particle size of the oxide powders corresponding to the second group of transition metal elements is 0.5~2μm; The mixing method is wet ball milling, the ball milling medium is anhydrous ethanol, the ball-to-material ratio is 3~10:1, the ball milling speed is 200~300 r / min, and the forward-reverse rotation is continuously cyclical, the single forward rotation time is 30min~60min, the single reverse rotation time is 30min~60min, and the total ball milling time is 12~36h. During the borothermal reduction reaction, a graphite tube is placed in the reactor. During the borothermal reduction reaction, the flow rate of nitrogen gas introduced is 20-200 sccm; The process of the boronothermal reduction reaction is as follows: the temperature is increased to 1100℃~1600℃ at a heating rate of 5~20℃ / min, and held for 1h~4h.

8. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 4, characterized in that: The ball milling is carried out under an argon atmosphere, with a milling speed of 200~400 r / min, a milling time of 8~15 h, and a ball-to-material ratio of 3~10:

1. During the ball milling process, the cycle of forward rotation-stop-reverse rotation-stop is followed. The time for a single forward rotation is 5-30 minutes, the time for a single reverse rotation is 5-30 minutes, and the time for a stop is 3-10 minutes.

9. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 4, characterized in that: The temperature of the discharge plasma sintering is 1600℃~2100℃, the holding time is 3min~20min, and the pressure is 10~50MPa.

10. The method for preparing a high-toughness, oxidation-resistant, high-entropy carbonitride ceramic according to claim 9, characterized in that: The discharge plasma sintering process is as follows: first, the temperature is raised to 1500~1700℃ and held for 2~5 minutes, then the temperature is raised to 1900~2100℃ and held for 7~10 minutes, while controlling the pressure to 30~50MPa.

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