Complex-phase high-entropy ceramic as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramic materials, and relates to complex-phase high-entropy ceramic as well as a preparation method and application thereof. The technical problem that in the prior art, high-entropy ceramic cannot synchronously have high hardness and fracture toughness is solved. The invention provides a complex-phase high-entropy ceramic. The complex-phase high-entropy ceramic comprises a carbonitride phase and a single boride phase, the transition metal elements comprise titanium, zirconium, niobium, tantalum and hafnium; in the complex-phase high-entropy ceramic, calculated according to the volume content, 93Vol% is smaller than or equal to the carbonitride phase lt; 100 Vol%, 0 Vol% lt; and the single boride phase is less than or equal to 7Vol%. The complex-phase high-entropy ceramic has the advantages of uniform two-phase distribution, small grain size, high density, high hardness and high fracture toughness. The invention further provides a preparation method of the complex-phase high-entropy ceramic, a liquid-phase precursor method is combined with an in-situ hot pressing sintering method, the process is simple, and the production period is short. Meanwhile, the invention 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 invention belongs to the technical field of ceramic materials, and in particular, relates to a composite high-entropy ceramic and a preparation method and application thereof. Background Art

[0002] High entropy ceramics are a type of single-phase solid solution ceramic material composed of multiple main elements (usually five or more), which have high entropy effect, hysteresis diffusion effect, lattice distortion effect and cocktail effect. These effects give the material excellent properties, such as high hardness, high elastic modulus, good oxidation resistance and thermal stability. Among them, high entropy carbides, nitrides and borides are generally regarded 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 violent airflow scouring during high-speed flight, thermal protection materials are also required 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 better hardness than single-principal-element ceramics, their fracture toughness has not been improved, and has even been reduced. This is because the hardness and fracture toughness of high-entropy ceramics are mutually constrained. High-entropy ceramics usually have extremely high hardness due to their multi-principal component 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 will limit the expansion of cracks and make the material more prone to brittle fracture when subjected to external forces. Therefore, achieving the strengthening and toughness 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 toughening methods for high entropy ceramics are mainly to introduce a second phase into the ceramic matrix to form a multiphase ceramic, including particle dispersion toughening, phase change toughening, whisker or fiber toughening. These toughening methods can enhance the fracture toughness of high entropy ceramics to a certain extent, but they cannot play a positive role in its hardness and may even sacrifice a certain degree of hardness. For example, et al. added 19.2 Vol% Co particles into (Nb, Ta, Ti, V, W) C [Metals, 2021, 11, 1-12], which increased its fracture toughness by 3.8 MPa·m 1 / 2 Increased to 6.7MPa·m 1 / 2 , but the hardness decreased from 18.4Gpa to 14.0Gpa; Luo et al. (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C was added with 20Vol% SiCw whiskers [J.Mater.Sci.Technol.,2021,94,99-103], which increased its fracture toughness from 3.0MPa·m 1 / 2 Increased to 4.3MPa·m 1 / 2 , while the hardness remained basically unchanged at 24.5Gpa; Hu et al. introduced ZrO2 into (WTaNbZrTi)C [Nat. Commun., 2023, 14, 5717] and used the phase transformation of ZrO2 to enhance the fracture toughness of high entropy ceramics to 5.0MPa·m 1 / 2 , and its hardness is only 18.1Gpa.

[0004] In summary, it is still difficult to simultaneously enhance the hardness and fracture toughness of high-entropy ceramics. Therefore, it is urgent to explore the preparation methods of high-entropy ceramics to simultaneously achieve high hardness and high fracture toughness. Summary of the invention

[0005] 1. Problems to be solved

[0006] Aiming at the technical problem that high entropy ceramics in the prior art cannot have both high hardness and fracture toughness. The present application provides a composite high entropy ceramic, which has high hardness and fracture toughness and a wide range of applications. The present application also provides a method for preparing the composite high entropy ceramic. At the same time, the present application also provides an application of the composite high entropy ceramic.

[0007] 2. Technical solution

[0008] In order to achieve the above purpose, the technical solution provided is:

[0009] A multiphase high-entropy ceramic, comprising a carbonitride phase and a monoboride phase; both the carbonitride phase and the monoboride phase contain transition metal elements, the transition metal elements are titanium, zirconium, niobium, tantalum and hafnium; in the multiphase high-entropy ceramic, calculated by volume content, 93Vol%≤carbonitride phase<100Vol%, 0Vol%<monoboride phase≤7Vol%.

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

[0011] Furthermore, the hardness of the composite high entropy ceramic is 22 GPa to 27 GPa; the fracture toughness of the composite high entropy ceramic is 3 MPa·m 1 / 2 ~6MPa·m 1 / 2 .

[0012] Furthermore, the grain size of the composite high-entropy ceramic is in the range of 0.5 μm to 1.3 μm, and the density of the composite high-entropy ceramic is ≥99%.

[0013] Furthermore, the molar ratio of the transition metal element, carbon element, boron element and nitrogen element in the composite high entropy ceramic is X:Y:Z:W, wherein X=1, 0 <Y<1,0<Z≤0.5,0<W<1。

[0014] Preferably, the raw material of the transition metal element is ZrCl4, HfCl4, TiCl4, NbCl5, 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 molar ratio of ZrCl4, HfCl4, TiCl4, NbCl5, and TaCl5 is 1:1:1:1:1.

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

[0017] A method for preparing a composite high entropy ceramic comprises the following steps:

[0018] Mixing ZrCl4, HfCl4, TiCl4, NbCl5 and TaCl5 in equal molar ratios and dissolving them in acetic acid to obtain a transition metal solution;

[0019] After mixing boric acid and sorbitol, add acetic acid, heat and stir at a constant temperature until they are completely dissolved to obtain a boron and carbon solution;

[0020] Fully mixing the transition metal solution and the boron and carbon solutions, and continuously stirring to obtain a precursor precipitation mixed solution;

[0021] Drying the precursor precipitation mixed liquid and calcining it in a nitrogen atmosphere to obtain a powder;

[0022] Grinding the powder, sieving, and in-situ hot pressing and sintering to obtain the composite high entropy ceramic;

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

[0024] In the prepared multiphase high entropy ceramic, calculated by volume content, 93 Vol%≤carbonitride phase<100 Vol%, 0 Vol%<single boride phase≤7 Vol%.

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

[0026] During the reaction, part of the carbon element in the raw materials will generate CO gas, rather than being completely converted into the carbon element in the prepared composite high-entropy ceramics. Therefore, the carbon element content added to the raw materials is higher than the carbon element content in the prepared composite high-entropy ceramics.

[0027] Preferably, the mesh size of the sieving is 100-200 mesh.

[0028] Furthermore, the temperature of the constant temperature heating is 60°C to 80°C.

[0029] Furthermore, the calcination in the nitrogen atmosphere is carried out at a temperature of 1500° C. to 1600° C., for a time of 1 h to 2 h, and a nitrogen flow rate of 100 mL / min to 300 mL / min.

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

[0031] Preferably, the vacuum degree is maintained at less than 10 -2 When the pressure is 30MPa~50MPa, the applied pressure is 30MPa~50MPa.

[0032] An application of a composite high-entropy ceramic, the application of the composite high-entropy ceramic in the preparation of materials in the aerospace field or the mechanical engineering field; or the application of the composite high-entropy ceramic prepared by the method in the preparation of materials in the aerospace field or the mechanical engineering field.

[0033] 3. Beneficial effects

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

[0035] (1) A composite 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, the transition metal elements are titanium, zirconium, niobium, tantalum and hafnium, i.e. (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite high entropy ceramic, which has high purity, shows a two-phase solid solution in XRD, has no other impurity peaks, and has a uniform distribution of the two phases; has a high density of more than 99%; has a controllable grain size, with the smallest grain reaching 0.57 μm, so that it has more excellent performance; and has higher hardness and fracture toughness, which is more conducive to the structural stability of the material;

[0036] (2) A method for preparing a composite high-entropy ceramic of the present invention uses a liquid-phase precursor method combined with an in-situ hot pressing sintering method to prepare a composite high-entropy ceramic having both high hardness and fracture toughness. A transition metal chloride, boric acid, sorbitol and acetic acid are mixed as raw materials to form a precursor precipitation mixture, which is dried and calcined in a nitrogen atmosphere to obtain a ceramic powder, and the ceramic powder is subjected to in-situ hot pressing sintering to obtain a composite high-entropy ceramic. A high-entropy carbonitride powder containing boron elements, i.e., (Ti, Zr, Nb, Ta, Hf) (C, N) high-entropy ceramic powder, is first synthesized by a liquid-phase precursor method to achieve a molecular-level distribution of boron elements in the high-entropy carbonitride, so that the single boride generated by the final in-situ sintering can be more evenly dispersed in the carbonitride without aggregation, and the sintered ceramic grains can also be made very fine, reaching the size of nanometers. The liquid phase precursor method used is more uniform in the two-phase distribution, higher in purity, and finer in grains than the mechanical ball milling method for preparing the composite ceramics. The powder prepared by mechanical ball milling is often easy to introduce oxygen or other impurities, and the grain size is large. In-situ hot pressing sintering occurs during the ceramic sintering process. This sintering reaction rate is faster, the two-phase distribution is more uniform, and the density of the ceramic block can be higher. The preparation method of the present application has a simple process, a short production cycle, a uniform distribution of the two phases, fine grains, and a high density. The obtained (Ti, Zr, Nb, Ta, Hf) (C, N)-(Ti, Zr, Nb, Ta, Hf) B composite high entropy ceramics have both high hardness and fracture toughness.

[0037] (3) Application of a composite high-entropy ceramic of the present invention, the (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite high-entropy ceramic has both high hardness and fracture toughness, enabling it to withstand extreme high temperatures and mechanical stresses. It can be used in the preparation of materials in the aerospace field or mechanical engineering field, such as thermal protection materials for aerospace vehicles, thermal structural components and high-temperature wear-resistant components of aircraft engines; mechanical components working in harsh environments, etc. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2 SEM images of polished surfaces of composite high entropy ceramics prepared in Examples and Comparative Examples. DETAILED DESCRIPTION

[0040] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with embodiments.

[0041] Example 1

[0042] A method for preparing a composite high entropy ceramic of this embodiment comprises the following steps:

[0043] S1. 4.66 g ZrCl4, 6.41 g HfCl4, 3.80 g TiCl4, 5.41 g NbCl5, and 7.16 g TaCl5 were mixed, 100 mL acetic acid (analytical grade) was added, and the mixture was stirred until completely dissolved to obtain a yellow clear transition metal solution;

[0044] S2. 10.29 g of sorbitol and 0.618 g of boric acid were mixed, 70 mL of acetic acid (analytical grade) was added, and the mixture was stirred at 70 ° C until completely dissolved to obtain a colorless, clear and transparent boron and carbon solution;

[0045] S3. The transition metal solution and the boron and carbon solutions are fully mixed and stirred continuously to obtain a precursor precipitate mixture, namely 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 with a nitrogen flow rate of 100 mL / min to 300 mL / min to obtain (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder;

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

[0048] S6. Pour the sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder into a graphite mold with a diameter of 20 mm and sinter it in a hot press furnace. The vacuum degree in the hot press furnace is drawn to less than 10 -2 Pa, apply a pressure of 40 MPa, heat up to 1000 ° C at a rate of 10 ° C / min, and keep at 1000 ° C for 5 min; heat up to 1800 ° C at a rate of 7 ° C / min, and keep at 1800 ° C / min for 60 min; heat up to 2100 ° C at a rate of 2 ° C / min, and keep at 120 min. After the insulation, release the pressure and cool to room temperature with water to obtain (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite phase high entropy ceramics.

[0049] Electron backscatter diffraction (EBSD) measured that the carbonitride phase accounted for 96.4 Vol%, and the single boride phase accounted for 3.6 Vol% in the complex phase high entropy ceramic.

[0050] The liquid phase precursor method is a method for preparing the target product through liquid precursor materials. This method can achieve uniform dispersion of multiple elements in the solution, thereby obtaining a material with uniform composition and controllable structure in the subsequent sintering process. In step S1 and step S2, transition metal chloride, boric acid, sorbitol and acetic acid are mixed as raw materials to form a precursor precipitation mixture. In step S3, the precipitate is dried and then calcined in a nitrogen atmosphere to obtain a ceramic powder, that is, a high-entropy carbonitride powder containing boron elements is first synthesized by a liquid-phase precursor method to achieve molecular-level distribution of boron elements in the high-entropy carbonitride. The grinding in step S4 can break larger particles of powder into finer particles, and screening can ensure the consistency of the powder particle size. Powders with fine particles and uniform distribution are more likely to form a dense structure during the sintering process, thereby improving the mechanical properties of the material. The single boride generated by the in-situ hot-pressing sintering in the last step S5 can be more evenly dispersed in the carbonitride without aggregation, and the sintered ceramic grains can also be made very fine, reaching the size of nanometers, thereby improving the hardness and fracture toughness of the complex phase high-entropy ceramic.

[0051] Example 2

[0052] A method for preparing a composite high entropy ceramic of this embodiment comprises the following steps:

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

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

[0055] S3. The transition metal solution and the boron and carbon solutions are fully mixed and stirred continuously to obtain a precursor precipitate mixture, namely a white precipitate and a precursor solution;

[0056] S4. The precursor precipitate mixture is 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 (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder;

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

[0058] S6. Pour the sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder into a graphite mold with a diameter of 20 mm and sinter it in a hot press furnace. The vacuum degree in the hot press furnace is drawn to less than 10 -2 Pa, apply a pressure of 40 MPa, heat up to 1000 ° C at a rate of 10 ° C / min, and keep at 1000 ° C for 5 min; heat up to 1800 ° C at a rate of 7 ° C / min, and keep at 1800 ° C / min for 60 min; heat up to 2100 ° C at a rate of 2 ° C / min, and keep at 120 min. After the insulation, release the pressure and cool to room temperature with water to obtain (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite phase high entropy ceramics.

[0059] Electron backscatter diffraction (EBSD) analysis revealed that the carbonitride phase accounted for 94.8 Vol%, and the monoboride phase accounted for 5.2 Vol% in the composite high entropy ceramic.

[0060] Example 3

[0061] A method for preparing a composite high entropy ceramic of this embodiment comprises the following steps:

[0062] S1. 4.66 g ZrCl4, 6.41 g HfCl4, 3.80 g TiCl4, 5.41 g NbCl5, and 7.16 g TaCl5 were mixed, 100 mL acetic acid (analytical grade) was added, and the mixture was stirred until completely dissolved to obtain a yellow clear 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 grade) was added, and the mixture was stirred at a constant temperature of 70°C until completely dissolved to obtain a colorless, clear and transparent boron and carbon solution;

[0064] S3. The transition metal solution and the boron and carbon solutions are fully mixed and stirred continuously to obtain a precursor precipitate mixture, namely a white precipitate and a precursor solution;

[0065] S4. The precursor precipitate mixture is 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 (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder;

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

[0067] S6. Pour the sieved (Ti, Zr, Nb, Ta, Hf)(C, N) high entropy ceramic powder into a graphite mold with a diameter of 20 mm and sinter it in a hot press furnace. The vacuum degree in the hot press furnace is drawn to less than 10 -2 Pa, apply a pressure of 40 MPa, heat up to 1000 ° C at a rate of 10 ° C / min, and keep at 1000 ° C for 5 min; heat up to 1800 ° C at a rate of 7 ° C / min, and keep at 1800 ° C / min for 60 min; heat up to 2100 ° C at a rate of 2 ° C / min, and keep at 120 min. After the insulation, release the pressure and cool to room temperature with water to obtain (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite phase high entropy ceramics.

[0068] Electron backscatter diffraction (EBSD) analysis revealed that the carbonitride phase accounted for 93.9 Vol%, and the monoboride phase accounted for 6.1 Vol% in the composite high entropy ceramic.

[0069] Comparative Example 1

[0070] A method for preparing a composite high entropy ceramic in this comparative example comprises the following steps:

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

[0072] S2. Add 9.84 g of sorbitol to 70 mL of acetic acid (analytical grade), and stir at 70 ° C until completely dissolved to obtain a colorless, clear and transparent solution;

[0073] S3. The transition metal solution and the colorless clear transparent solution are fully mixed and stirred continuously to obtain a precursor precipitate mixture, ie, a white precipitate and a precursor solution;

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

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

[0076] S6. Pour the sieved ceramic powder into a graphite mold with a diameter of 20 mm and sinter it in a hot press furnace. The vacuum degree in the hot press furnace is drawn to less than 10 -2Apply a pressure of 40 MPa to Pa, heat it up to 1000 °C at a rate of 10 °C / min, hold it at 1000 °C for 5 min; heat it up to 1800 °C at a rate of 7 °C / min, hold it at 1800 °C / min for 60 min; heat it up to 2100 °C at a rate of 2 °C / min, and hold it for 120 min. After the holding is completed, release the pressure and cool it to room temperature with water cooling to obtain a ceramic block.

[0077] It is measured by electron backscatter diffraction (EBSD) that the proportion of carbonitride phase in the ceramic block is 100 Vol%.

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

[0079] (1) Use an X-ray diffractometer to detect the material purity of the high-entropy ceramics prepared in Examples 1-3 and Comparative Example 1 of the present invention, as Figure 1 (a)-(d) are the XRD patterns of Examples 1-3 and Comparative Example 1 respectively. It can be seen that the powders formed at 1600 °C in Examples 1-3 and Comparative Example 1 are all (Ti,Zr,Nb,Ta,Hf)(C,N) single-phase solid solutions. After hot pressing and sintering at 2100 °C in Examples 1-3, a second phase of (Ti,Zr,Nb,Ta,Hf)B is formed in the block, and there are no any other impurity peaks, indicating that a reaction occurs during the hot pressing and sintering process, and a multiphase ceramic is formed in-situ, and there are no any other impurities in the multiphase ceramic. After hot pressing and sintering at 2100 °C in Comparative Example 1, no second phase is generated and no multiphase ceramic is formed.

[0080] (2) Use a scanning electron microscope to detect the morphology of the high-entropy ceramic blocks prepared in Examples 1-3 and Comparative Example 1 of the present invention respectively, as Figure 2 (a)-(d) are the scanning electron microscope images of the polished surfaces of the ceramics in Examples 1-3 and Comparative Example 1 respectively. It can be seen that the two phases of the (Ti,Zr,Nb,Ta,Hf)(C,N)-(Ti,Zr,Nb,Ta,Hf)B multiphase high-entropy ceramic prepared in Examples 1-3 of the present invention are very evenly distributed, no aggregation phenomenon occurs, there are almost no pores on the surface, and the grains of the multiphase ceramic are fine. The average grain sizes are statistically obtained as 1.26 μm, 0.79 μm, and 0.57 μm respectively, while the grains of the single-phase ceramic block prepared in Comparative Example 1 reach 7.8 μm, which is much larger than the grain size of the prepared multiphase ceramic.

[0081] (3) The actual density of the high entropy ceramic blocks prepared in Examples 1-3 of the present invention and Comparative Example 1 was tested by the Archimedean drainage method, and the density was found to be 99.3%, 99.1%, 99.1%, and 99.9%, respectively, all of which have extremely high densities greater than 99%.

[0082] (4) The hardness of the high entropy ceramic blocks prepared in Examples 1-3 and Comparative Example 1 of the present invention was tested using a Vickers hardness tester, and the fracture toughness was calculated by indenting the crack length. The hardness of Examples 1-3 and Comparative Example 1 was 22.4 GPa, 24.3 GPa, 26.5 GPa, and 19.9 GPa, respectively, and the fracture toughness was 3.7 MPa·m 1 / 2 , 4.2MPa·m 1 / 2 , 5.8MPa·m 1 / 2 , 2.8MPa·m 1 / 2 . It can be seen that the high-entropy ceramic blocks prepared in Examples 1-3 have higher hardness and fracture toughness than those prepared in Comparative Example 1, achieving the strengthening and toughening of high-entropy ceramics. This method of preparing a complex high-entropy ceramic block by in-situ hot pressing and sintering can effectively prepare complex high-entropy ceramics with high mechanical properties, which will expand the application prospects of high-entropy ceramics in the aerospace field or mechanical engineering field, such as thermal protection materials for aerospace vehicles, thermal structural components and high-temperature wear-resistant components of aircraft engines; mechanical components working in harsh environments, etc.

[0083] In summary, the present application adopts a liquid phase precursor method combined with an in-situ hot pressing sintering method to prepare a carbonitride-monoboride composite high-entropy ceramic with both high hardness and high fracture toughness, namely, (Ti, Zr, Nb, Ta, Hf)(C, N)-(Ti, Zr, Nb, Ta, Hf)B composite high-entropy ceramic, which has a simple process, short production cycle, high purity, uniform distribution of the two phases, fine grains, high density and a wide range of applications.

[0084] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A composite high entropy ceramic, characterized in that: The multiphase high entropy ceramic 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 multiphase high entropy ceramic, calculated by volume content, 93Vol%≤carbonitride phase<100Vol%, 0Vol%<monoboride phase≤7Vol%.

2. A multiphase high entropy ceramic according to claim 1, characterized in that: The hardness of the composite high entropy ceramic is 22 GPa to 27 GPa; the fracture toughness of the composite high entropy ceramic is 3 MPa·m 1 / 2 ~6MPa·m 1 / 2 .

3. The multiphase high entropy ceramic according to claim 1, characterized in that: The grain size of the composite high entropy ceramic is in the range of 0.5 μm to 1.3 μm, and the density of the composite high entropy ceramic is ≥99%.

4. A multiphase high entropy ceramic according to any one of claims 1 to 3, characterized in that: The molar ratio of the transition metal element, carbon element, boron element and nitrogen element in the composite high entropy ceramic is X:Y:Z:W, wherein X=1, 0 <Y<1,0<Z≤0.5,0<W<1。 5. A multiphase high entropy ceramic according to any one of claims 1 to 4, characterized in that: The composite high entropy ceramic is prepared by a liquid phase precursor method combined with an in-situ hot pressing sintering method.

6. A method for preparing a composite high entropy ceramic, characterized in that: The following steps are involved: Mixing ZrCl4, HfCl4, TiCl4, NbCl5 and TaCl5 in equal molar ratios and dissolving them in acetic acid to obtain a transition metal solution; After mixing boric acid and sorbitol, add acetic acid, heat and stir at a constant temperature until they are completely dissolved to obtain a boron and carbon solution; Fully mixing the transition metal solution and the boron and carbon solutions, and continuously stirring to obtain a precursor precipitation mixed solution; Drying the precursor precipitation mixed liquid and calcining it in a nitrogen atmosphere to obtain a powder; Grinding the powder, sieving, and in-situ hot pressing and sintering to obtain the composite high entropy ceramic; The ratio of the amount of transition metal element, carbon element and boron element in the raw material of the composite high entropy ceramic is A:B:C, wherein A=1,3 <B<5,0<C≤0.5; In the prepared multiphase high entropy ceramic, calculated by volume content, 93 Vol%≤carbonitride phase<100 Vol%, 0 Vol%<single boride phase≤7 Vol%.

7. The method for preparing a composite high entropy ceramic according to claim 6, characterized in that: The temperature of the constant temperature heating is 60°C to 80°C.

8. The method for preparing a composite high entropy ceramic according to claim 6, characterized in that: The calcination in the nitrogen atmosphere is carried out at a temperature of 1500° C. to 1600° C., for a time of 1 h to 2 h, and at a nitrogen flow rate of 100 mL / min to 300 mL / min.

9. The method for preparing a composite high entropy ceramic according to claim 6, characterized in that: 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, heat to 1000℃ at a rate of 10℃ / min~15℃ / min, and keep warm for 5min; heat to 1800℃ at a rate of 5℃ / min~10℃ / min, and keep warm for 60min; heat to 2100℃ at a rate of 2℃ / min~3℃ / min, and keep warm for 120min.

10. An application of a multiphase high entropy ceramic, characterized in that: Application of the composite high entropy ceramics described in any one of claims 1 to 5 in the preparation of materials in the aerospace field or mechanical engineering field; or application of the composite high entropy ceramics prepared by the method described in any one of claims 6 to 9 in the preparation of materials in the aerospace field or mechanical engineering field.

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