A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering

Abstract

A method for preparing high-strength and tough ultra-high temperature composite high-entropy ceramics by two-step powder mixing combined with reaction sintering belongs to the technical field of ceramic materials. The purpose of the present invention is to overcome the technical difficulty of uniform mixing of transition metal and ceramic powders. Method: 1. Prepare composite powder; 2. Place the fully mixed composite powder in a mold, and then place it in a spark plasma sintering furnace for sintering to obtain high-strength and tough ultra-high temperature composite high-entropy ceramics. The high-strength and toughness composite high-entropy ceramics prepared by the present invention have a finer grain size, and at the same time, the strength and toughness are significantly improved. The hardness of the material at room temperature can reach 28 to 35 GPa, the elastic modulus can reach 560 GPa, the three-point bending strength can reach 600 to 800 MPa, and the fracture toughness can reach 6 to 7 MPa·m 1 / 2 The present invention can obtain a high-strength, high-toughness, ultra-high-temperature multiphase high-entropy ceramic.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials, and in particular relates to a method for preparing high-strength and toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing combined with reaction sintering. Background Art

[0002] With the further expansion of the concept of high-entropy materials in the field of ceramics, high-entropy ceramics have gradually become a global research hotspot over the past five years. High-entropy ceramics of various systems, such as oxides, carbides, borides, silicides, and nitrides, have been extensively studied. Compared with single-component ceramics, high-entropy ceramics possess superior high-temperature mechanical properties, thermal stability, and oxidation resistance. In particular, high-entropy diborides (HEBs) and carbides (HECs) ceramics, due to their high melting points and excellent high-temperature performance, are expected to become ultra-high-temperature materials for service in extreme environments.

[0003] It is well known that HEB and HEC ceramics are difficult to densify by sintering due to their strong covalent bonds and low self-diffusion coefficients. Research results show that HEB-HEC composite high-entropy ceramics are easier to sinter than single-phase high-entropy ceramics, with significantly reduced grain size and improved mechanical properties. Current research methods for preparing HEB-HEC composite high-entropy ceramics typically involve direct mixing of diboride and carbide powders followed by sintering, or by carbon / boron thermal reduction of corresponding transition metal oxide powders followed by sintering.

[0004] Compared to the above methods, directly mixing transition metals with ceramic powders is a simpler process, improving sintering activity while also allowing for easier composition control. However, due to the significant differences in the properties of transition metals and ceramic powders, uniform mixing of the two is difficult, which in turn affects the subsequent reaction and sintering process. The present invention aims to overcome these technical difficulties and produce high-strength and tough HEB-HEC composite high-entropy ceramics with a uniform microstructure. Summary of the Invention

[0005] The purpose of the present invention is to overcome the technical difficulty of uniformly mixing transition metal and ceramic powders. The present invention provides a method for greatly improving the uniformity of transition metal and ceramic mixed powders by combining low-speed swing vibration with high-energy ball milling, and preparing high-strength and tough ultra-high temperature composite phase high entropy ceramics by reaction sintering.

[0006] A method for preparing high-strength and high-toughness ultrahigh-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering is completed in the following steps:

[0007] 1. Preparation of composite powder:

[0008] ①, weighing 3 to 6 metal powders selected from the group consisting of titanium powder, zirconium powder, hafnium powder, vanadium powder, niobium powder, tantalum powder, molybdenum powder, tungsten powder, and chromium powder in equal molar ratios to obtain a metal mixed powder I;

[0009] ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is (3-4):1;

[0010] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0011] ④. The preliminarily mixed composite powder is subjected to high-energy ball milling to obtain a fully mixed composite powder;

[0012] Second, the fully mixed composite powder is placed in a mold and then placed in a spark plasma sintering furnace for sintering to obtain high-strength and toughness ultra-high temperature composite phase high entropy ceramics.

[0013] The present invention has the following beneficial effects:

[0014] First, the present invention uses a two-step method of low-speed swing vibration combined with high-energy ball milling to directly mix transition metal and boron carbide powders. The uniformity of the mixed powders is greatly improved. During the subsequent sintering process, the transition metal and boron carbide can fully react to prepare a HEB-HEC composite high-entropy ceramic with uniform microstructure.

[0015] Second, the present invention utilizes the reaction of transition metals with boron carbide to generate corresponding transition metal carbides and diborides, and selects a spark plasma furnace to carry out reaction sintering under the protection of an inert atmosphere to obtain high-strength and tough HEB-HEC composite high-entropy ceramics; multiple transition metal powders and boron carbide react in situ during the sintering process, and solid solution coupling occurs at the same time, which greatly promotes the mass transfer process. The density of the prepared composite ceramics is greater than 97%; in addition, the composite high-entropy ceramics have more complex interface relationships and multi-component effects, which makes grain growth more difficult than that of single-phase high-entropy ceramics;

[0016] The high-strength and toughness composite high-entropy ceramics prepared by the present invention have finer grain sizes, and their strength and toughness are significantly improved. At room temperature, the hardness of the material can reach 28-35 GPa, the elastic modulus can reach 560 GPa, the three-point bending strength can reach 600-800 MPa, and the fracture toughness can reach 6-7 MPa·m 1 / 2 .

[0017] The present invention can obtain a high-strength and high-toughness ultra-high-temperature multiphase high-entropy ceramic. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The XRD pattern of the high-strength and tough multiphase high-entropy ceramic with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3;

[0019] Figure 2This is a SEM microstructure photograph of the high-strength and toughness multiphase high-entropy ceramic with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3;

[0020] Figure 3 This is a fracture photograph of the high-strength and toughness multiphase high-entropy ceramic with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3;

[0021] Figure 4 This is a SEM microstructure photograph of the composite high entropy ceramic with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 1;

[0022] Figure 5 This is the SEM microstructure photograph of the composite high entropy ceramic with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 2. DETAILED DESCRIPTION

[0023] Specific embodiment 1: This embodiment is a method for preparing high-strength and high-toughness ultra-high temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is completed by the following steps:

[0024] 1. Preparation of composite powder:

[0025] ①, weighing 3 to 6 metal powders selected from the group consisting of titanium powder, zirconium powder, hafnium powder, vanadium powder, niobium powder, tantalum powder, molybdenum powder, tungsten powder, and chromium powder in equal molar ratios to obtain a metal mixed powder I;

[0026] ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is (3-4):1;

[0027] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0028] ④. The preliminarily mixed composite powder is subjected to high-energy ball milling to obtain a fully mixed composite powder;

[0029] Second, the fully mixed composite powder is placed in a mold and then placed in a spark plasma sintering furnace for sintering to obtain high-strength and toughness ultra-high temperature composite phase high entropy ceramics.

[0030] Specific Embodiment 2: This embodiment differs from Specific Embodiment 1 in that the purity of the titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, and chromium powders described in step 1 (1) above is greater than 99.0 wt.%, and the particle size of the powders is between 10 and 90 μm. Other steps are the same as those in Specific Embodiment 1.

[0031] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the purity of the boron carbide powder in step 1② is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm. The other steps are the same as those in specific embodiment 1 or 2.

[0032] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the molar ratio of the metal mixed powder I to the boron carbide powder in step 1 ② is (3 to 3.4): 1. The other steps are the same as those of specific embodiments 1 to 3.

[0033] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the molar ratio of the metal mixed powder I to the boron carbide powder in step 1 ② is (3.4-3.5):1. The other steps are the same as specific embodiments 1 to 4.

[0034] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 100-500 r / min, the reverse rotation speed is 100-500 r / min, the forward rotation time in each cycle is 5-300 minutes, the reverse rotation time in each cycle is 5-300 minutes, and the pause time in each cycle is 5-30 minutes; the total number of cycles is 1 to 10. Other steps are the same as specific embodiments 1 to 5.

[0035] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the specific parameters of the high-energy ball milling described in step 1 (4) are: the ball-to-material ratio of the ball milling is (10-50):1, the ball mill speed is 100-400 rpm for the main disc and 400-800 rpm for the planetary disc, the total ball milling time is 10-40 hours, the running time during each cycle is 20-80 minutes, the rest time is 10-40 minutes, the number of cycles is 8-40, and the ball mill jar and grinding ball media are all cemented carbide. The other steps are the same as specific embodiments 1 to 6.

[0036] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that, in step 2, under inert atmosphere, the spark plasma sintering furnace is heated from room temperature to 1900-2300°C at a heating rate of 50-200°C / min, ensuring that the applied pressure reaches 25-50 MPa at 800-1500°C and then maintained at 25-50 MPa until the end of the cooling phase. The temperature is then maintained at 1900-2300°C for 5-30 minutes, then cooled to room temperature at a cooling rate of 50-250°C / min, and demolded to obtain a high-strength, tough, ultra-high-temperature composite high-entropy ceramic. The other steps are the same as specific embodiments 1 to 7.

[0037] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the inert atmosphere is argon, helium or neon. The other steps are the same as those of specific embodiments 1 to 8.

[0038] Specific embodiment 10: The difference between this embodiment and specific embodiments 1 to 9 is that the high-strength and toughness ultra-high temperature composite high entropy ceramic described in step 2 has a relative density of >97%, a room temperature hardness of 28-35 GPa, a three-point bending strength of 600-800 MPa, and a fracture toughness of 6-7 MPa·m 1 / 2 The other steps are the same as those in Specific Embodiments 1 to 9.

[0039] The following examples are used to verify the beneficial effects of the present invention:

[0040] Example 1: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is specifically completed in the following steps:

[0041] 1. Preparation of composite powder:

[0042] ①, weighing metal titanium powder, metal niobium powder and metal zirconium powder in equal molar ratios to obtain metal mixed powder I;

[0043] The purity of the titanium powder, niobium powder and zirconium powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm;

[0044] ② Weigh boron carbide powder, with the molar ratio of the metal mixed powder I and boron carbide powder being 3:1;

[0045] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0046] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0047] The parameters of the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 500 r / min, the reverse rotation speed is 500 r / min, the forward rotation time in each cycle is 60 minutes, the reverse rotation time in each cycle is 60 minutes, and the pause time in each cycle is 20 minutes; the number of cycles is 5;

[0048] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0049] The ball-to-material ratio of the ball mill described in step 1 (4) is 20:1, the ball mill speed is 300 rpm for the main disc and 500 rpm for the planetary disc, the total ball milling time is 30 h, the running time during each cycle is 40 min, the rest time is 20 min, the number of cycles is 30, and the ball mill jar and the grinding ball media are all cemented carbide;

[0050] 2. Place the fully mixed composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of an argon atmosphere, heat the spark plasma sintering furnace from room temperature to 2000°C at a heating rate of 100°C / min, ensuring that the applied pressure reaches 50MPa when the temperature reaches 1500°C, and then maintain the pressure of 50MPa until the end of the cooling stage; during the sintering process, argon is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2000°C, keep the temperature for 20 minutes, and then cool to room temperature at a cooling rate of 100°C / min. Demolding to obtain a high-strength and toughness ultra-high-temperature composite high-entropy ceramic with a chemical formula of (Ti,Zr,Nb)B2-(Ti,Zr,Nb)C.

[0051] The mechanical properties of the high-strength and tough ultra-high-temperature composite high-entropy ceramic with the chemical formula (Ti, Zr, Nb) B2-(Ti, Zr, Nb) C prepared in Example 1 were tested. The results showed that the relative density of the composite ceramic at room temperature was 99%, the hardness of the material was 28.4 GPa, the elastic modulus was 550 GPa, the three-point bending strength was 621 MPa, and the fracture toughness was 6.1 MPa·m 1 / 2 .

[0052] Example 2: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is specifically completed in the following steps:

[0053] 1. Preparation of composite powder:

[0054] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder and metal tantalum powder in equal molar ratios to obtain metal mixed powder I;

[0055] The purity of the titanium powder, niobium powder, zirconium powder and tantalum powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0056] ② Weigh boron carbide powder, with the molar ratio of the metal mixed powder I and boron carbide powder being 3:1;

[0057] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0058] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0059] The parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 400 r / min, the reverse rotation speed is 400 r / min, the forward rotation time in each cycle is 50 minutes, the reverse rotation time in each cycle is 50 minutes, and the pause time in each cycle is 20 minutes; the total number of cycles is 6;

[0060] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0061] The ball-to-material ratio of the ball mill described in step 1 (4) is 30:1, the ball mill speed is 200 r / min for the main disc and 600 r / min for the planetary disc, the total ball milling time is 20 h, the running time in each cycle is 30 min, the rest time is 30 min, the number of cycles is 20, and the ball mill jar and the grinding ball media are all cemented carbide;

[0062] 2. Place the composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of an argon atmosphere, heat the spark plasma sintering furnace from room temperature to 2100°C at a heating rate of 150°C / min, ensuring that the applied pressure reaches 40MPa when the temperature reaches 1500°C, and then maintain the pressure of 40MPa until the end of the cooling stage; during the sintering process, argon is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2100°C, keep warm for 20 minutes, and then cool to room temperature at a cooling rate of 150°C / min. Demolding to obtain a high-strength and tough composite high-entropy ceramic with a chemical formula of (Ti,Zr,Nb,Ta)B2-(Ti,Zr,Nb,Ta)C.

[0063] The mechanical properties of the high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Example 2 were tested. The results showed that the relative density of the composite ceramic at room temperature was 97%, the hardness of the material was 29.6 GPa, the elastic modulus was 560 GPa, the three-point bending strength was 635 MPa, and the fracture toughness was 6.3 MPa·m 1 / 2 .

[0064] Example 3: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is specifically completed in the following steps:

[0065] 1. Preparation of composite powder:

[0066] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder and metal vanadium powder in equal molar ratios to obtain metal mixed powder I;

[0067] The purity of the titanium powder, niobium powder, zirconium powder and vanadium powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size of the powder is 20 to 50 μm;

[0068] ② Weigh boron carbide powder, with the molar ratio of the metal mixed powder I and boron carbide powder being 3:1;

[0069] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0070] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0071] The parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 450 r / min, the reverse rotation speed is 450 r / min, the forward rotation time in each cycle is 80 minutes, the reverse rotation time in each cycle is 80 minutes, and the pause time in each cycle is 15 minutes; the total number of cycles is 5;

[0072] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0073] The ball-to-material ratio of the ball mill described in step 1 (4) is 10:1, the ball mill speed is 400 rpm for the main disc and 800 rpm for the planetary disc, the total ball milling time is 15 h, the running time during each cycle is 60 min, the rest time is 30 min, the number of cycles is 10, and the ball mill jar and the grinding ball media are all cemented carbide;

[0074] Second, the fully mixed composite powder is placed in a mold and then placed in a spark plasma sintering furnace. Under the protection of an argon atmosphere, the spark plasma sintering furnace is heated from room temperature to 1900°C at a heating rate of 75°C / min. The applied pressure is ensured to reach 30MPa at 1200°C and then maintained at 30MPa until the end of the cooling stage. During the sintering process, argon gas is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber at a dynamic equilibrium. After heating to 1900°C, the temperature is maintained for 15 minutes, and then the temperature is cooled to room temperature at a cooling rate of 200°C / min. The mold is then removed to obtain a high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti,Zr,V,Nb)B2-(Ti,Zr,V,Nb)C.

[0075] The high strength and toughness composite high entropy ceramics with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3 were subjected to XRD testing. The test results are as follows: Figure 1 As shown in the figure, "*" is the diffraction peak corresponding to (Ti, Zr, V, Nb) C, and "◆" is the diffraction peak corresponding to (Ti, Zr, V, Nb) B2. As can be seen from the figure, during the spark plasma sintering process, the transition metal powder reacts with boron carbide to form corresponding diborides and carbides. Various borides and carbides undergo mutual solid solution, ultimately forming two solid solution phases; the diffraction peaks show that the sintered material is a complex phase. Calibration of the diffraction peaks reveals that the main phases are a carbide phase with a face-centered cubic structure and a boride phase with a close-packed hexagonal structure, respectively. This proves that the technical solution of Example 3 can be used to obtain a high-strength, tough, complex-phase, high-entropy ceramic with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C.

[0076] The high strength and toughness composite high entropy ceramics with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3 were subjected to SEM testing. The test results are shown in Figure 2. Figure 2 shown by Figure 2 It can be seen that the high-strength and toughness composite high-entropy ceramics are composed of a black diboride phase and a white carbide phase; the material contains almost no pores and is basically densified; the material structure is evenly distributed and the grain size is small.

[0077] The high strength and toughness composite high entropy ceramics with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3 were subjected to fracture analysis. The test results are as follows: Figure 3 As shown in the figure, it can be seen that the sintering of high-strength and toughness multiphase high-entropy ceramics is basically dense, and river patterns and the extraction of boride plate crystals are observed, that is, the fracture mode of high-strength and toughness multiphase high-entropy ceramics is a mixed fracture of intergranular and transgranular fracture.

[0078] The mechanical properties of the high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti, Zr, V, Nb) B2-(Ti, Zr, V, Nb) C prepared in Example 3 were tested. The results showed that the relative density of the composite ceramic at room temperature was 99%, the hardness of the material was 34.8 GPa, the elastic modulus was 560 GPa, the three-point bending strength was 774 MPa, and the fracture toughness was 7 MPa·m 1 / 2 .

[0079] Example 4: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, specifically completed in the following steps:

[0080] 1. Preparation of composite powder:

[0081] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder and metal tungsten powder in equal molar ratios to obtain metal mixed powder I;

[0082] The purity of the titanium powder, niobium powder, zirconium powder and tungsten powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0083] ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is 3.25:1;

[0084] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0085] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0086] The parameters of the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 100 r / min, the reverse rotation speed is 100 r / min, the forward rotation time in each cycle is 200 minutes, the reverse rotation time in each cycle is 200 minutes, and the pause time in each cycle is 30 minutes; the total number of cycles is 2;

[0087] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0088] The ball-to-material ratio of the ball mill described in step 1 (4) is 50:1, the ball mill speed is 100 rpm for the main disc and 400 rpm for the planetary disc, the total ball milling time is 25 h, the running time during each cycle is 50 min, the rest time is 10 min, the number of cycles is 25, and the ball mill jar and the grinding ball media are all cemented carbide;

[0089] 2. Place the composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of an argon atmosphere, heat the spark plasma sintering furnace from room temperature to 2200°C at a heating rate of 100°C / min, ensuring that the applied pressure reaches 45MPa when the temperature reaches 1400°C, and then maintain the pressure of 45MPa until the end of the cooling stage; during the sintering process, argon is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2200°C, keep warm for 10 minutes, and then cool to room temperature at a cooling rate of 150°C / min. Demolding to obtain a high-strength and tough composite high-entropy ceramic with a chemical formula of (Ti,Zr,Nb,W)B2-(Ti,Zr,Nb,W)C.

[0090] The mechanical properties of the high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti, Zr, Nb, W) B2-(Ti, Zr, Nb, W) C prepared in Example 4 were tested. The results showed that the relative density of the composite ceramic at room temperature was 98%, the hardness of the material was 34 GPa, the elastic modulus was 535 GPa, the three-point bending strength was 702 MPa, and the fracture toughness was 6.2 MPa·m 1 / 2 .

[0091] Example 5: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is specifically completed in the following steps:

[0092] 1. Preparation of composite powder:

[0093] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder, metal hafnium powder, metal tantalum powder and metal vanadium powder in equal molar ratios to obtain a metal mixed powder I;

[0094] The purity of the titanium powder, niobium powder, zirconium powder, hafnium powder, tantalum powder and vanadium powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0095] ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is 3.25:1;

[0096] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0097] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0098] The parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 450 r / min, the reverse rotation speed is 450 r / min, the forward rotation time in each cycle is 50 minutes, the reverse rotation time in each cycle is 50 minutes, and the pause time in each cycle is 20 minutes; the total number of cycles is 5;

[0099] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0100] The ball-to-material ratio of the ball mill described in step 1 (4) is 20:1, the ball mill speed is 300 rpm for the main disc and 700 rpm for the planetary disc, the total ball milling time is 30 h, the running time during each cycle is 45 min, the rest time is 15 min, the number of cycles is 30, and the ball mill jar and the grinding ball media are all cemented carbide;

[0101] 2. Place the composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of a helium atmosphere, heat the spark plasma sintering furnace from room temperature to 2100°C at a heating rate of 200°C / min, ensuring that the applied pressure reaches 35 MPa when the temperature reaches 1000°C, and then maintain the pressure of 35 MPa until the end of the cooling stage; during the sintering process, helium is continuously introduced and discharged into the spark plasma sintering furnace to maintain the helium pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2100°C, keep the temperature for 20 minutes, and then cool to room temperature at a cooling rate of 200°C / min. Demolding to obtain a high-strength and tough composite high-entropy ceramic with a chemical formula of (Ti, Zr, Hf, V, Nb, Ta)B2-(Ti, Zr, Hf, V, Nb, Ta)C.

[0102] The mechanical properties of the high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti, Zr, Hf, V, Nb, Ta) B2-(Ti, Zr, Hf, V, Nb, Ta) C prepared in Example 5 were tested. The results showed that the relative density of the composite ceramic at room temperature was 98%, the hardness of the material was 29.2 GPa, the elastic modulus was 526 GPa, the three-point bending strength was 678 MPa, and the fracture toughness was 6.9 MPa·m 1 / 2 .

[0103] Example 6: A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, which is specifically completed in the following steps:

[0104] 1. Preparation of composite powder:

[0105] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder, metal vanadium powder and metal tantalum powder in equal molar ratios to obtain metal mixed powder I;

[0106] The purity of the titanium powder, niobium powder, zirconium powder, vanadium powder and tantalum powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0107] ② Weigh boron carbide powder, with the molar ratio of the metal mixed powder I to the boron carbide powder being 3.5:1;

[0108] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0109] ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder;

[0110] The parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 350 r / min, the reverse rotation speed is 350 r / min, the forward rotation time in each cycle is 30 minutes, the reverse rotation time in each cycle is 30 minutes, and the pause time in each cycle is 15 minutes; the total number of cycles is 10;

[0111] ④. High-energy ball milling is performed on the composite powder that has been preliminarily mixed by low-speed vibration to obtain a fully mixed composite powder;

[0112] The ball-to-material ratio of the ball mill described in step 1④ is 40:1, the ball mill speed is 150r / min for the main disc and 600r / min for the planetary disc, the total ball milling time is 30h, the running time during each cycle is 60min, the intermittent time is 30min, the number of cycles is 20 times, and the ball mill jar and grinding ball media are all cemented carbide.

[0113] 2. Place the composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of an argon atmosphere, heat the spark plasma sintering furnace from room temperature to 2300°C at a heating rate of 50°C / min, ensuring that the applied pressure reaches 35MPa when the temperature reaches 800°C, and then maintain the pressure of 35MPa until the end of the cooling stage; during the sintering process, argon gas is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2300°C, keep warm for 10 minutes, and then cool to room temperature at a cooling rate of 150°C / min. Demolding to obtain a high-strength and tough composite high-entropy ceramic with a chemical formula of (Ti,Zr,Nb,V,Ta)B2-(Ti,Zr,Nb,V,Ta)C.

[0114] The mechanical properties of the high-strength and toughness composite high-entropy ceramic with the chemical formula (Ti, Zr, Nb, V, Ta) B2-(Ti, Zr, Nb, V, Ta) C prepared in Example 6 were tested. The results showed that the relative density of the composite ceramic at room temperature was 99%, the hardness of the material was 32.1 GPa, the elastic modulus was 524 GPa, the three-point bending strength was 724 MPa, and the fracture toughness was 6.4 MPa·m 1 / 2 .

[0115] Comparative Example 1: A method for preparing a composite high-entropy ceramic is specifically completed by the following steps:

[0116] 1. Preparation of composite powder:

[0117] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder and metal tantalum powder in equal molar ratios to obtain metal mixed powder I;

[0118] The purity of the titanium powder, niobium powder, zirconium powder and tantalum powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0119] ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is 3:1 to obtain a composite powder;

[0120] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0121] ③. Perform high-energy ball milling on the composite powder to obtain ball-milled composite powder;

[0122] The ball-to-material ratio of the ball mill described in step 1 (3) is 30:1, the ball mill speed is 200 rpm for the main disc and 600 rpm for the planetary disc, the total ball milling time is 20 h, the running time in each cycle is 30 min, the rest time is 30 min, the number of cycles is 20, and the ball mill jar and the grinding ball media are all cemented carbide;

[0123] 2. The ball-milled composite powder is placed in a mold and then placed in a spark plasma sintering furnace. Under the protection of an argon atmosphere, the spark plasma sintering furnace is heated from room temperature to 2100°C at a heating rate of 150°C / min, ensuring that the applied pressure reaches 40 MPa when the temperature reaches 1500°C, and then the pressure of 40 MPa is maintained until the end of the cooling stage; during the sintering process, argon gas is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium, and after heating to 2100°C, the temperature is kept at 20 minutes, and then the temperature is cooled to room temperature at a cooling rate of 150°C / min, and the mold is demolded to obtain a composite high-entropy ceramic with a chemical formula of (Ti, Zr, Nb, Ta)B2-(Ti, Zr, Nb, Ta)C.

[0124] The composite high entropy ceramics with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 1 were subjected to SEM testing. The test results are shown in Figure 2. Figure 4 shown by Figure 4 It can be seen that the one-step ball milling mixing effect of the composite powder using high-energy ball milling alone is not good. The porosity of the material is high, the densification process is incomplete, the material structure is uneven, and the grain size is also large.

[0125] The mechanical properties of the composite high entropy ceramic with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 1 were tested. The results showed that the relative density of the composite ceramic at room temperature was 95%, the hardness of the material was 22.1 GPa, the elastic modulus was 477 GPa, the three-point bending strength was 489 MPa, and the fracture toughness was 4.2 MPa·m 1 / 2 Through comparative example 1, it can be found that the technical solution of the present invention has significant advantages in improving the toughness of ceramic materials.

[0126] Comparative Example 2: A method for preparing a composite high-entropy ceramic is specifically completed by the following steps:

[0127] 1. Preparation of composite powder:

[0128] ①, weighing metal titanium powder, metal niobium powder, metal zirconium powder and metal tantalum powder in equal molar ratios to obtain metal mixed powder I;

[0129] The purity of the titanium powder, niobium powder, zirconium powder and tantalum powder described in step 1 (1) is greater than 99.0 wt.%, and the particle size is 20 to 50 μm.

[0130] ② Weigh boron carbide powder, with the molar ratio of the metal mixed powder I and boron carbide powder being 3:1;

[0131] The purity of the boron carbide powder described in step 1 (2) is greater than 99.0 wt.%, and the particle size of the powder is 1 to 20 μm;

[0132] ③. Mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a mixed composite powder;

[0133] The parameters during the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, a pause, and one reverse rotation; the forward rotation speed is 400 r / min, the reverse rotation speed is 400 r / min, the forward rotation time in each cycle is 50 minutes, the reverse rotation time in each cycle is 50 minutes, and the pause time in each cycle is 20 minutes; the total number of cycles is 6;

[0134] 2. Place the mixed composite powder in a mold and then place it in a spark plasma sintering furnace. Under the protection of an argon atmosphere, heat the spark plasma sintering furnace from room temperature to 2100°C at a heating rate of 150°C / min, ensuring that the applied pressure reaches 40 MPa when the temperature reaches 1500°C, and then maintain the pressure of 40 MPa until the end of the cooling stage; during the sintering process, argon gas is continuously introduced and discharged into the spark plasma sintering furnace to maintain the argon pressure in the furnace chamber to reach a dynamic equilibrium. After heating to 2100°C, keep warm for 20 minutes, and then cool to room temperature at a cooling rate of 150°C / min. Demolding to obtain a composite high-entropy ceramic with a chemical formula of (Ti, Zr, Nb, Ta)B2-(Ti, Zr, Nb, Ta)C.

[0135] The composite high entropy ceramics with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 2 were subjected to SEM testing. The test results are shown in Figure 2. Figure 5 shown by Figure 5 It can be seen that the effect of mixing composite powders using vibration alone is poor. The one-step vibration mixing method leads to insufficient system energy and obvious incomplete and uneven diffusion of transition metal elements. The material has low density, poor microstructure uniformity, and large grain size.

[0136] The mechanical properties of the composite high entropy ceramic with the chemical formula (Ti, Zr, Nb, Ta) B2-(Ti, Zr, Nb, Ta) C prepared in Comparative Example 2 were tested. The results showed that the relative density of the composite ceramic at room temperature was 96.2%, the hardness of the material was 21.4 GPa, the elastic modulus was 464 GPa, the three-point bending strength was 495 MPa, and the fracture toughness was 4.1 MPa·m 1 / 2 Through comparative example 2, it can be found that the technical solution of the present invention has significant advantages in improving the toughness of ceramic materials.

Claims

1. A method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering, characterized in that The method is completed in the following steps:

1. Preparation of composite powder: ①, weighing 3 to 6 metal powders selected from the group consisting of titanium powder, zirconium powder, hafnium powder, vanadium powder, niobium powder, tantalum powder, molybdenum powder, tungsten powder, and chromium powder in equal molar ratios to obtain a metal mixed powder I; ② Weigh boron carbide powder, the molar ratio of the metal mixed powder I and the boron carbide powder is (3-4):1; ③. Preliminarily mixing the metal mixed powder I and the boron carbide powder by low-speed pendulum vibration to obtain a preliminarily mixed composite powder; The parameters of the oscillation process described in step 1 (3) are set as follows: clockwise rotation is forward rotation, counterclockwise rotation is reverse rotation, and a complete cycle process includes one forward rotation, an interval, and one reverse rotation; the forward rotation speed is 100-500 r / min, the reverse rotation speed is 100-500 r / min, the forward rotation time in each cycle is 5-300 min, the reverse rotation time in each cycle is 5-300 min, and the interval time in each cycle is 5-30 min; the total number of cycles is 1-10 times; ④. The preliminarily mixed composite powder is subjected to high-energy ball milling to obtain a fully mixed composite powder; 2. Place the fully mixed composite powder in a mold. Under the protection of an inert atmosphere, heat the spark plasma sintering furnace from room temperature to 1900-2300°C at a heating rate of 50-200°C / min, ensuring that the applied pressure reaches 25-50 MPa when the temperature reaches 800-1500°C, and then maintain the pressure of 25-50 MPa until the end of the cooling stage; keep warm at 1900-2300°C for 5-30 minutes, then cool to room temperature at a cooling rate of 50-250°C / min, demold, and obtain high-strength and toughness ultra-high-temperature composite high-entropy ceramics.

2. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that The purity of the metal titanium powder, metal zirconium powder, metal hafnium powder, metal vanadium powder, metal niobium powder, metal tantalum powder, metal molybdenum powder, metal tungsten powder and metal chromium powder described in step 1① is >99.0wt.%, and the particle size of the powder is 10-90μm.

3. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that The purity of the boron carbide powder described in step 1② is greater than 99.0wt.%, and the particle size of the powder is 1 to 20μm.

4. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that In step 1②, the molar ratio of the metal mixed powder I and the boron carbide powder is (3-3.4):

1.

5. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that In step 1②, the molar ratio of metal mixed powder I and boron carbide powder is (3.4-3.5):

1.

6. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that The specific parameters of the high-energy ball milling described in step 1④ are: the ball-to-material ratio of the ball milling is (10-50):1, the ball mill speed is 100-400 r / min for the main disk, 400-800 r / min for the planetary disk, the total ball milling time is 10-40 h, the running time during each cycle is 20-80 min, the intermittent time is 10-40 min, the number of cycles is 8-40 times, and the ball mill jar and grinding ball media are all cemented carbide.

7. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that The inert atmosphere is argon, helium or neon.

8. The method for preparing high-strength and high-toughness ultra-high-temperature composite high-entropy ceramics by two-step powder mixing and reaction sintering according to claim 1, characterized in that The high-strength and toughness ultra-high temperature composite high-entropy ceramics described in step 2 have a relative density of >97%, a room temperature hardness of 28-35 GPa, a three-point bending strength of 600-800 MPa, and a fracture toughness of 6-7 MPa·m 1 / 2 .

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