A multiphase high-entropy ceramic and a preparation method and application thereof

Abstract

The application belongs to the technical field of ceramic materials, and relates to a complex-phase high-entropy ceramic as well as a preparation method and application thereof. In view of the technical problem that high-entropy ceramics cannot simultaneously have high hardness and fracture toughness in the prior art, the application provides a complex-phase high-entropy ceramic, which comprises a carbonitride phase and a monoboride phase; both contain transition metal elements, and the transition metal elements are titanium, zirconium, niobium, tantalum and hafnium; in the complex-phase high-entropy ceramic, 93Vol% <= carbonitride phase < 100Vol%, 0Vol% < monoboride phase <= 7Vol% according to volume content. The complex-phase high-entropy ceramic has uniform two-phase distribution, small grain size, high density and simultaneously has high hardness and high fracture toughness. The application further provides a preparation method of the complex-phase high-entropy ceramic, which adopts a liquid-phase precursor method combined with an in-situ hot-pressing sintering method, and has simple process and short production cycle. Meanwhile, the application further provides application of the complex-phase high-entropy ceramic in material preparation in the fields of aerospace and mechanical engineering.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ceramic materials, and in particular relates to a multiphase high-entropy ceramic as well as a preparation method and application thereof. BACKGROUND

[0002] High-entropy ceramics are single-phase solid solution ceramic materials composed of multiple main elements (usually five or more), which have high-entropy effect, sluggish diffusion effect, lattice distortion effect and cocktail effect. These effects endow the material with excellent properties such as high hardness, high elastic modulus, good oxidation resistance and thermal stability. Among them, high-entropy carbides, nitrides and borides are usually considered as the most promising thermal protection materials in the field of aerospace vehicles due to their extremely high melting points. However, since aerospace vehicles need to withstand severe airflow scouring during high-speed flight, the thermal protection materials also need to have extremely high mechanical strength, usually including high hardness and high fracture toughness, so as to maintain their structural integrity. Although high-entropy ceramics have more excellent hardness than single-main-element ceramics, their fracture toughness has not been improved, and even has been reduced. This is because the hardness and fracture toughness of high-entropy ceramics are mutually restrictive. High-entropy ceramics usually have extremely high hardness due to their multiple main element composition and complex crystal structure. These characteristics make the material exhibit excellent deformation resistance and wear resistance at the microscale, but this high hardness is often accompanied by low fracture toughness, because the increase in hardness usually requires the material to have a denser microstructure and fewer defects, which limits the propagation of cracks and makes the material more prone to brittle fracture when subjected to external force. Therefore, achieving the strengthening and toughening of high-entropy ceramics, and simultaneously enhancing the hardness and fracture toughness of high-entropy ceramics, is an urgent need for the development of aerospace vehicle materials.

[0003] The existing technology for the toughening of high-entropy ceramics mainly introduces a second phase to form a multiphase ceramic in the ceramic matrix, including particle dispersion toughening, phase transformation toughening, whisker or fiber toughening. These toughening methods can enhance the fracture toughness of high-entropy ceramics to some extent, but they cannot positively affect the hardness, and even sacrifice some hardness. For example, Wang et al. doped 19.2Vol% Co particles in (Nb, Ta, Ti, V, W)C [Metals, 2021, 11, 1-12], which increased the fracture toughness from 3.8MPa·m 1 / 2 to 6.7MPa·m 1 / 2 , but the hardness decreased from 18.4Gpa to 14.0Gpa; Luo et al. doped 10Vol% TiC in (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C with 20 Vol% SiCw whiskers [J. Mater. Sci. Technol., 2021, 94, 99-103] to 3.0 MPa·m 1 / 2 4.3 MPa·m 1 / 2 , while the hardness is basically unchanged, 24.5 Gpa; Hu et al. introduced ZrO2 in (WTaNbZrTi)C [Natl Commun., 2023, 14, 5717], and the fracture toughness of high-entropy ceramics was enhanced to 5.0 MPa·m 1 / 2 , while its hardness is only 18.1 Gpa.

[0004] In summary, it is still difficult to simultaneously enhance the hardness and fracture toughness of high-entropy ceramics at present, therefore, it is urgent to explore the preparation method of high-entropy ceramics to simultaneously achieve high hardness and high fracture toughness. SUMMARY

[0005] 1. Problem to be solved

[0006] In view of the technical problem that the high-entropy ceramics in the prior art cannot have high hardness and fracture toughness at the same time, the present application provides a complex high-entropy ceramic with high hardness and fracture toughness, and wide application range. The present application also provides a preparation method of the complex high-entropy ceramic. Meanwhile, the present application also provides an application of the complex high-entropy ceramic.

[0007] 2. Technical solution

[0008] To achieve the above-mentioned purpose, the technical solution provided is as follows:

[0009] A complex high-entropy ceramic, which comprises a carbonitride phase and a monoboride phase; the carbonitride phase and the monoboride phase both contain transition metal elements, and the transition metal elements are titanium, zirconium, niobium, tantalum and hafnium; in the complex high-entropy ceramic, the volume content of the carbonitride phase is 93 Vol% to 100 Vol%, and the volume content of the monoboride phase is 0 Vol% to 7 Vol%.

[0010] The carbonitride phase refers to carbonitride ceramic, and the monoboride phase refers to monoboride ceramic.

[0011] Further, the hardness of the complex high-entropy ceramic is 22 GPa to 27 GPa; and the fracture toughness of the complex high-entropy ceramic is 3 MPa·m 1 / 2 6 MPa·m 1 / 2 .

[0012] Further, the grain size of the complex high-entropy ceramic is 0.5 μm to 1.3 μm, and the density of the complex high-entropy ceramic is ≥ 99%.

[0013] Further, the ratio of the amount of substance of the transition metal element, the carbon element, the boron element and the nitrogen element in the complex phase high-entropy ceramic is X:Y:Z:W, wherein X=1, 0Y<1, 0Z≤0.5, and 0<W<1.

[0014] Preferably, the raw material of the transition metal element is ZrCl4, HfCl4, TiCl4, NbCl5, or TaCl5; the raw material of the boron element is boric acid; the raw material of the carbon element is sorbitol; and the raw material of the nitrogen element is nitrogen.

[0015] Preferably, the ratio of the amount of substance of ZrCl4, HfCl4, TiCl4, NbCl5, and TaCl5 is 1:1:1:1:1.

[0016] A complex phase high-entropy ceramic is prepared by a liquid precursor method combined with an in-situ hot sintering method.

[0017] A preparation method of a complex phase high-entropy ceramic includes the following steps:

[0018] ZrCl4, HfCl4, TiCl4, NbCl5, and TaCl5 with equal amount of substance are mixed and dissolved in acetic acid to obtain a transition metal solution;

[0019] Boric acid and sorbitol are mixed and added to acetic acid, and constant temperature heating and stirring are performed until complete dissolution to obtain a boron and carbon solution;

[0020] The transition metal solution and the boron and carbon solution are thoroughly mixed and continuously stirred to obtain a precursor precipitate mixture;

[0021] The precursor precipitate mixture is dried and calcined in a nitrogen atmosphere to obtain a powder;

[0022] The powder is ground, sieved, and in-situ hot-pressed and sintered to obtain the complex phase high-entropy ceramic;

[0023] The ratio of the amount of substance of the transition metal element, the carbon element, and the boron element in the raw material of the complex phase high-entropy ceramic is A:B:C, wherein A=1, 3<B<5, and 0<C≤0.5.

[0024] In the prepared complex phase high-entropy ceramic, the volume content of the carbonitride phase is 93Vol%≤carbonitride phase<100Vol%, and the volume content of the monoboride phase is 0Vol%<monoboride phase≤7Vol%.

[0025] Preferably, the ratio of the amount of substance of the transition metal element, the carbon element, the boron element and the nitrogen element in the prepared complex phase high-entropy ceramic is X:Y:Z:W, wherein X=1, 0Y<1, 0Z≤0.5, and 0<W<1.

[0026] During the reaction, some of the carbon elements in the raw materials will generate CO gas, rather than all of them being converted into carbon elements in the prepared multiphase high-entropy ceramic. Therefore, the carbon content added to the raw materials is higher than the carbon content in the prepared multiphase high-entropy ceramic.

[0027] Preferably, the mesh size of the sieve is 100 to 200 mesh.

[0028] Furthermore, the temperature of the constant temperature heating is 60℃~80℃.

[0029] Furthermore, the calcination is carried out in a nitrogen atmosphere at a temperature of 1500℃~1600℃ for 1h~2h, with a nitrogen flow rate of 100mL / min~300mL / min.

[0030] Furthermore, the specific parameters for the in-situ hot pressing sintering are as follows: the vacuum degree in the hot press furnace is maintained at less than 10. -2 Pa, heat to 1000℃ at a rate of 10℃ / min to 15℃ / min and hold for 5 min; heat to 1800℃ at a rate of 5℃ / min to 10℃ / min and hold for 60 min; heat to 2100℃ at a rate of 2℃ / min to 3℃ / min and hold for 120 min.

[0031] Preferably, the vacuum level is maintained at less than 10. -2 When Pa, apply a pressure of 30MPa to 50MPa.

[0032] An application of a multiphase high-entropy ceramic, specifically its application in material preparation in the aerospace or mechanical engineering fields; or the application of the multiphase high-entropy ceramic prepared by the method in material preparation in the aerospace or mechanical engineering fields.

[0033] 3. Beneficial effects

[0034] Compared with existing known technologies, the technical solution provided by this invention has the following beneficial effects:

[0035] (1) A multiphase high-entropy ceramic of the present invention comprises a carbonitride phase and a monoboride phase; both the carbonitride phase and the monoboride phase contain transition metal elements, namely titanium, zirconium, niobium, tantalum and hafnium, i.e. (Ti,Zr,Nb,Ta,Hf)(C,N)-(Ti,Zr,Nb,Ta,Hf)B multiphase high-entropy ceramic, which has high purity, shows a two-phase solid solution in XRD, has no other impurity peaks, and the two phases are evenly distributed; it has high density, reaching more than 99%; the grain size is controllable, and the smallest grain can reach 0.57μm, thus giving it better performance; at the same time, it has higher hardness and fracture toughness, which is more conducive to the structural stability of the material;

[0036] (2) The application discloses a preparation method of a multiphase high-entropy ceramic, and the multiphase high-entropy ceramic is prepared by using a liquid precursor method and an in-situ hot-pressing sintering method, and has high hardness and fracture toughness. Transition metal chloride, boric acid, sorbitol and acetic acid are used as raw materials to form a precursor precipitation mixed solution, and ceramic powder is obtained by calcining the precursor precipitation mixed solution after drying in a nitrogen atmosphere; and the multiphase high-entropy ceramic is obtained by in-situ hot-pressing sintering of the ceramic powder. The liquid precursor method is used to synthesize high-entropy carbonitride powder containing boron, i.e., (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder, so that the boron element is distributed at a molecular level in the high-entropy carbonitride, the monoboride generated by in-situ sintering is more uniformly dispersed in the carbonitride, and the sintered ceramic grains are very small and can reach the nanometer level. The liquid precursor method has more uniform two-phase distribution, higher purity and smaller grains than the mechanical ball milling method, and the powder prepared by the mechanical ball milling method is prone to introduce oxygen or other impurities, and the grain size is large. The in-situ hot-pressing sintering occurs in the ceramic sintering process, the sintering reaction rate is faster, the two-phase distribution is more uniform, and the ceramic bulk density is higher. The preparation method has the advantages of simple process, short production cycle, uniform two-phase distribution, small grain size and high density, and the obtained (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramic has high hardness and fracture toughness.

[0037] (3) The application discloses the application of the multiphase high-entropy ceramic, and the (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramic has high hardness and fracture toughness, can withstand extreme high temperature and mechanical stress, and can be applied to the preparation of materials in the fields of aerospace and mechanical engineering, such as thermal protection materials of spaceflight vehicles, thermal structure parts and high-temperature wear-resistant parts of aircraft engines, and mechanical parts working in harsh environments. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 XRD patterns of the multiphase high-entropy ceramics prepared in the examples and the comparative examples;

[0039] Figure 2 SEM images of polished surfaces of the multiphase high-entropy ceramics prepared in the examples and the comparative examples. DETAILED DESCRIPTION

[0040] In order to further understand the content of the application, the application will be described in detail in combination with the examples.

[0041] Example 1

[0042] A preparation method of a multiphase high-entropy ceramic of the embodiment includes the following steps:

[0043] S1. 4.66 g of ZrCl4, 6.41 g of HfCl4, 3.80 g of TiCl4, 5.41 g of NbCl5, and 7.16 g of TaCl5 are mixed, 100 mL of acetic acid (analytical pure) is added, and stirring is performed until complete dissolution to obtain a yellow clear transition metal solution;

[0044] S2. 10.29 g of sorbitol and 0.618 g of boric acid are mixed, 70 mL of acetic acid (analytical pure) is added, and stirring is performed at 70°C until complete dissolution to obtain a colorless clear transparent boron and carbon solution;

[0045] S3. The transition metal solution and the boron and carbon solution are mixed thoroughly, and stirring is continued to obtain a precursor precipitate mixture, i.e., a white precipitate and a precursor solution;

[0046] S4. The precursor precipitate mixture is dried and calcined at 1600°C for 2 h in a nitrogen atmosphere, and the nitrogen flow rate is 100 mL / min to 300 mL / min to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0047] S5. The (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder is ground and sieved through a 200-mesh sieve to obtain a sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0048] S6. The sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder is poured into a graphite mold with a diameter of 20 mm, and sintering is performed in a hot-pressing furnace, in which the vacuum degree is extracted to less than 10 -2 Pa, a pressure of 40 MPa is applied, the temperature is raised to 1000°C at a rate of 10°C / min, the temperature is kept at 1000°C for 5 min, the temperature is raised to 1800°C at a rate of 7°C / min, the temperature is kept at 1800°C / min for 60 min, the temperature is raised to 2100°C at a rate of 2°C / min, and the temperature is kept at 2100°C for 120 min, the pressure is removed after the end of the holding, and the temperature is reduced to room temperature by water cooling to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramic.

[0049] The carbonitride phase accounts for 96.4 Vol% and the monoboride phase accounts for 3.6 Vol% in the multiphase high-entropy ceramic, which is measured by electron backscatter diffraction (EBSD).

[0050] The liquid precursor method is a method for preparing a target product by using a liquid precursor material. The method can realize uniform dispersion of various elements in a solution, so that a material with uniform composition and controllable structure can be obtained in a subsequent sintering process. In the S1 step and the S2 step, transition metal chloride, boric acid, sorbitol and acetic acid are used as raw materials to form a precursor precipitate mixture. In the S3 step, the precipitate is dried and calcined in a nitrogen atmosphere to obtain ceramic powder. In other words, the high-entropy carbonitride powder containing boron is first synthesized by the liquid precursor method to realize the molecular-level distribution of boron in the high-entropy carbonitride. In the S4 step, the larger particles of the powder can be broken into smaller particles by grinding, and the uniformity of the particle size of the powder can be ensured by sieving. The fine and uniformly distributed powder can more easily form a dense structure in the sintering process, thereby improving the mechanical properties of the material. In the S5 step, the monoboride generated by in-situ hot-pressing sintering can be more uniformly dispersed in the carbonitride without aggregation, and the sintered ceramic grains can be very small, reaching the size of nanometers, thereby improving the hardness and fracture toughness of the multiphase high-entropy ceramic.

[0051] Example 2

[0052] The preparation method of the multiphase high-entropy ceramic of the present embodiment comprises the following steps:

[0053] S1. 4.66g of ZrCl4, 6.41g of HfCl4, 3.80g of TiCl4, 5.41g of NbCl5 and 7.16g of TaCl5 are mixed, 100mL of acetic acid (analytical pure) is added, and the mixture is stirred until completely dissolved to obtain a yellow clear transition metal solution;

[0054] S2. 10.745g of sorbitol and 1.236g of boric acid are mixed, 70mL of acetic acid (analytical pure) is added, and the mixture is stirred at 70℃ until completely dissolved to obtain a colorless clear transparent boron and carbon solution;

[0055] S3. The transition metal solution and the boron and carbon solution are thoroughly mixed, and the mixture is continuously stirred to obtain a precursor precipitate mixture, i.e., a white precipitate and a precursor solution;

[0056] S4. The precursor precipitate mixture is dried and calcined in a nitrogen atmosphere at 1600℃ for 2h, and the nitrogen flow rate is 100mL / min-300mL / min to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0057] S5. The (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder is ground and sieved through a 200-mesh sieve to obtain a sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0058] S6. The sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder was poured into a graphite mold with a diameter of 20 mm and sintered in a hot-pressing furnace, in which the vacuum degree was extracted to less than 10 -2 Pa, a pressure of 40 MPa was applied, the temperature was raised to 1000°C at a rate of 10°C / min, and the temperature was kept at 1000°C for 5 min; the temperature was raised to 1800°C at a rate of 7°C / min, and the temperature was kept at 1800°C / min for 60 min; the temperature was raised to 2100°C at a rate of 2°C / min, and the temperature was kept at 2100°C for 120 min; the pressure was removed after the end of the holding, and the temperature was lowered to room temperature by water cooling, to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramic.

[0059] The content of the carbonitride phase in the multiphase high-entropy ceramic was measured by electron backscatter diffraction (EBSD) to be 94.8 Vol%, and the content of the monoboride phase was 5.2 Vol%.

[0060] Example 3

[0061] A method for preparing a multiphase high-entropy ceramic according to the present embodiment includes the following steps:

[0062] S1. 4.66 g of ZrCl4, 6.41 g of HfCl4, 3.80 g of TiCl4, 5.41 g of NbCl5, and 7.16 g of TaCl5 were mixed, 100 mL of acetic acid (analytical pure) was added, and the mixture was stirred until completely dissolved to obtain a yellow transparent transition metal solution;

[0063] S2. 11.207 g of sorbitol and 1.854 g of boric acid were mixed, 70 mL of acetic acid (analytical pure) was added, and the mixture was stirred at 70°C until completely dissolved to obtain a colorless transparent boron and carbon solution;

[0064] S3. The transition metal solution and the boron and carbon solution were mixed thoroughly, and the mixture was continuously stirred to obtain a precursor precipitate mixture, i.e., a white precipitate and a precursor solution;

[0065] S4. The precursor precipitate mixture was dried and calcined at 1600°C for 2 h in a nitrogen atmosphere, and the nitrogen flow rate was 100 mL / min to 300 mL / min, to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0066] S5. The (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder was ground and sieved through a 200-mesh sieve to obtain a sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder;

[0067] S6. The sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high-entropy ceramic powder was poured into a graphite mold with a diameter of 20 mm, and sintering was performed in a hot-pressing furnace, in which the vacuum degree was extracted to less than 10 -2 Pa, a pressure of 40 MPa was applied, and the temperature was raised to 1000°C at a rate of 10°C / min, and the temperature was kept at 1000°C for 5 min; the temperature was raised to 1800°C at a rate of 7°C / min, and the temperature was kept at 1800°C / min for 60 min; the temperature was raised to 2100°C at a rate of 2°C / min, and the temperature was kept at 2100°C for 120 min; the pressure was removed after the end of the holding, and the temperature was lowered to room temperature by water cooling, to obtain a (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramic.

[0068] The carbonitride phase in the multiphase high-entropy ceramic accounted for 93.9 Vol%, and the monoboride phase accounted for 6.1 Vol%, as measured by electron backscatter diffraction (EBSD).

[0069] Comparative Example 1

[0070] A method for preparing a multiphase high-entropy ceramic of the present comparative example comprises the following steps:

[0071] S1. 4.66 g of ZrCl4, 6.41 g of HfCl4, 3.80 g of TiCl4, 5.41 g of NbCl5, and 7.16 g of TaCl5 were mixed, 100 mL of acetic acid (analytical pure) was added, and the mixture was stirred until completely dissolved to obtain a yellow clear transition metal solution;

[0072] S2. 9.84 g of sorbitol was added to 70 mL of acetic acid (analytical pure), and the mixture was stirred at 70°C until completely dissolved to obtain a colorless clear transparent solution;

[0073] S3. The transition metal solution and the colorless clear transparent solution were thoroughly mixed, and the mixture was continuously stirred to obtain a precursor precipitate mixture, i.e., a white precipitate and a precursor solution;

[0074] S4. The precursor precipitate mixture was dried and calcined at 1600°C for 2 h in a nitrogen atmosphere, with a nitrogen flow rate of 100 mL / min to 300 mL / min, to obtain a ceramic powder;

[0075] S5. The ceramic powder was ground and sieved through a 200-mesh sieve to obtain a sieved ceramic powder;

[0076] S6. The sieved ceramic powder was poured into a graphite mold with a diameter of 20 mm, and sintering was performed in a hot-pressing furnace, in which the vacuum degree was extracted to less than 10 -2Pa, a pressure of 40 MPa was applied, the temperature was raised to 1000°C at a rate of 10°C / min, the temperature was kept at 1000°C for 5 min, the temperature was raised to 1800°C at a rate of 7°C / min, the temperature was kept at 1800°C for 60 min, the temperature was raised to 2100°C at a rate of 2°C / min, and the temperature was kept at 2100°C for 120 min, the pressure was removed at the end of the keeping, and the temperature was lowered to room temperature by water cooling, to obtain a ceramic block.

[0077] The proportion of the carbonitride phase in the ceramic block was 100 Vol% as measured by electron backscatter diffraction (EBSD).

[0078] In the multiphase high-entropy ceramic prepared in the above embodiments of the application, the molar ratio of the transition metal element, the carbon element, the boron element and the nitrogen element is X:Y:Z:W, wherein X = 1, 0 < Y < 1, 0 < Z ≤ 0.5, and 0 < W < 1. The ceramic prepared in the embodiments and the comparative examples of the application was tested for phase, morphology, density, hardness and fracture toughness, and the following results were obtained.

[0079] (1) The high-entropy ceramics prepared in the embodiments 1-3 and the comparative example 1 of the application were tested for purity by X-ray diffraction analysis, as shown in Figure 1 (a)-(d) are the XRD patterns of the embodiments 1-3 and the comparative example 1, respectively. It can be seen that the powders formed in the embodiments 1-3 and the comparative example 1 at 1600°C are all (Ti, Zr, Nb, Ta, Hf)(C, N) single-phase solid solutions. After the heat pressing sintering at 2100°C, the second phase (Ti, Zr, Nb, Ta, Hf)B is generated in the block of the embodiments 1-3, without any other impurity peaks, indicating that a reaction occurs during the heat pressing sintering, and a multiphase ceramic is formed in situ, and the multiphase ceramic does not contain any other impurities. After the heat pressing sintering at 2100°C, the comparative example 1 does not generate the second phase, and does not form the multiphase ceramic.

[0080] (2) The high-entropy ceramic blocks prepared in the embodiments 1-3 and the comparative example 1 of the application were tested for morphology by scanning electron microscopy, as shown in Figure 2 (a)-(d) are the scanning electron micrographs of the polished surfaces of the ceramics of the embodiments 1-3 and the comparative example 1, respectively. It can be seen that the (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B multiphase high-entropy ceramics prepared in the embodiments 1-3 of the application are very uniform in two-phase distribution, without aggregation phenomenon, and there are almost no pores on the surface, and the multiphase ceramic grains are small, with the average grain size of 1.26 μm, 0.79 μm and 0.57 μm, respectively. The grain size of the single-phase ceramic block prepared in the comparative example 1 is 7.8 μm, which is much larger than the grain size of the multiphase ceramic prepared.

[0081] (3) The actual density of the high-entropy ceramic bulk prepared by the application examples 1-3 and the comparative example 1 was tested by Archimedes drainage method, and the density was 99.3%, 99.1%, 99.1%, 99.9%, respectively, all with an extremely high density of more than 99%.

[0082] (4) The hardness of the high-entropy ceramic bulk prepared by the application examples 1-3 and the comparative example 1 was tested by Vickers hardness tester, and the fracture toughness was calculated by the indentation crack length. The hardness of the application examples 1-3 and the comparative example 1 was 22.4 GPa, 24.3 GPa, 26.5 GPa, 19.9 GPa, respectively, and the fracture toughness was 3.7 MPa·m 1 / 2 , 4.2 MPa·m 1 / 2 , 5.8 MPa·m 1 / 2 , 2.8 MPa·m 1 / 2 It can be seen that the high-entropy ceramic bulk prepared by the application examples 1-3 has higher hardness and fracture toughness than the comparative example 1, and realizes the strengthening and toughening of high-entropy ceramics. The method of preparing the composite high-entropy ceramic bulk by in-situ hot-pressing sintering can effectively prepare the composite high-entropy ceramic with high mechanical properties, which will expand the application prospect of high-entropy ceramics in the fields of aerospace and mechanical engineering, such as thermal protection materials of aerospace vehicles, thermal structure parts and high-temperature wear-resistant parts of aircraft engines, and mechanical parts working in harsh environments.

[0083] In summary, the application samples the liquid precursor method combined with the in-situ hot-pressing sintering method to prepare the carbonitride-monoboride composite high-entropy ceramic with high hardness and high fracture toughness, i.e. (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite high-entropy ceramic, which has the advantages of simple process, short production cycle, high purity, uniform distribution of two phases, small grain size, high density and wide application range.

[0084] The above examples only express the preferred embodiments of the application, which are described in detail and specifically, but cannot be understood as the limitation of the patent scope of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications, improvements and substitutions can be made, which all belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A method for preparing a multiphase high-entropy ceramic, characterized in that: The method comprises the following steps: mixing ZrCl4, HfCl4, TiCl4, NbCl5 and TaCl5 in equal molar ratio, and dissolving them in acetic acid to obtain a transition metal solution; mixing boric acid and sorbitol, and then adding acetic acid to obtain a boron-carbon solution; mixing the transition metal solution and the boron-carbon solution, and continuously stirring to obtain a precursor precipitate mixture; drying the precursor precipitate mixture and calcining it in a nitrogen atmosphere to obtain a powder; grinding and sieving the powder, and in-situ hot-pressing and sintering to obtain the complex high-entropy ceramic; the molar ratio of transition metal elements, carbon elements and boron elements in the raw material of the complex high-entropy ceramic is A:B:C, wherein A=1, 3<B<5, and 0<C≤0.5; in the prepared complex high-entropy ceramic, 93 Vol% ≤ carbonitride phase < 100 Vol%, and 0 Vol% < monoboride phase ≤ 7 Vol% according to the volume content.

2. The method of claim 1, wherein the method comprises: The temperature of the constant temperature heating is 60 ℃~80 ℃.

3. The method of claim 1, wherein the method further comprises: The calcination in the nitrogen atmosphere is performed at a temperature of 1500 ℃~1600 ℃ for 1 h~2 h, and the nitrogen flow rate is 100 mL / min~300 mL / min.

4. The method of claim 1, wherein the method further comprises: The specific parameters of the in-situ hot-pressing sintering are: the vacuum degree in the hot-pressing furnace is kept less than 10 -2 Pa, the temperature is raised to 1000 ℃ at a rate of 10 ℃ / min~15 ℃ / min, and kept for 5 min; the temperature is raised to 1800 ℃ at a rate of 5 ℃ / min~10 ℃ / min, and kept for 60 min; the temperature is raised to 2100 ℃ at a rate of 2 ℃ / min~3 ℃ / min, and kept for 120 min.

5. A multiphasic high-entropy ceramic, characterized by: The complex high-entropy ceramic prepared by the method of any one of claims 1-4 comprises a carbonitride phase and a monoboride phase; the carbonitride phase and the monoboride phase both contain transition metal elements, and the transition metal elements are titanium, zirconium, niobium, tantalum and hafnium.

6. The multiphase high-entropy ceramic of claim 5, wherein: The hardness of the multiphase high-entropy ceramic is 22 GPa to 27 GPa; the fracture toughness of the multiphase high-entropy ceramic is 3 MPa·m 1 / 2 to 6 MPa·m 1 / 2 .

7. The multiphase high-entropy ceramic of claim 5, wherein: The grain size of the complex high-entropy ceramic is 0.5 μm~1.3 μm, and the density of the complex high-entropy ceramic is ≥99%.

8. The multiphase high-entropy ceramic according to any one of claims 5-7, wherein: The molar ratio of transition metal elements, carbon elements, boron elements and nitrogen elements in the complex high-entropy ceramic is X:Y:Z:W, wherein X=1, 0<Y<1, 0<Z≤0.5, and 0<W<1.

9. Use of a multiphase high-entropy ceramic, characterized in that The complex high-entropy ceramic of any one of claims 5-8 is used in the preparation of materials in the fields of aerospace or mechanical engineering.

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