A method for rapid preparation of fully dense refractory metal carbide high-entropy ceramics

Abstract

This invention discloses a rapid method for preparing high-density, refractory metal carbide high-entropy ceramics, belonging to the fields of high-entropy ceramic materials and powder metallurgy technology. The method involves thoroughly mixing high-purity refractory metal carbide powders with small particle size variations under an argon atmosphere. The mixed powder is then placed in a graphite mold for pre-pressing. The pressed compact is then placed in a high-vacuum rapid hot press furnace. Through a process involving high pressure, instantaneous high temperature, cooling, and short-term holding at a lower temperature and pressure, a fully dense, small-grained, single-phase, and uniformly structured refractory metal carbide high-entropy ceramic is obtained.

Description

Technical Field

[0001] This invention relates to a method for rapidly preparing high-density, refractory metal carbide high-entropy ceramics, belonging to the fields of high-entropy ceramic materials and powder metallurgy technology. Background Technology

[0002] High-entropy carbide ceramics are typically single-phase solid solution materials with a simple face-centered cubic structure, obtained by the solid solution diffusion of five or more metal carbides at high temperatures. Refractory metal carbide high-entropy ceramics possess high hardness and strength, low thermal conductivity, strong resistance to high-temperature creep and radiation, and excellent electromagnetic wave absorption capabilities. Refractory metal carbide high-entropy ceramics have significant application potential in hypersonic vehicles, machining, and nuclear energy.

[0003] Currently, refractory metal carbide high-entropy ceramics are generally prepared using powder metallurgy methods such as spark plasma sintering, hot pressing, and hot isostatic pressing. These techniques typically have limited sintering pressure (generally below 50 MPa), while refractory metal carbides have very high melting points, and their solid solution diffusion and densification usually require temperatures above 2000 °C to be fully completed. These factors all contribute to the coarse grain size of the prepared refractory metal carbide high-entropy ceramics, which are prone to abnormal grain growth, severely degrading the material's properties.

[0004] This invention addresses the problems encountered in the preparation of refractory metal carbide high-entropy ceramics, such as high sintering temperatures, coarse grains, poor microstructure uniformity, difficulty in densification, and low mechanical properties. It proposes a rapid hot-pressing sintering method, combining a comprehensive design of sintering pressure and temperature-time, to achieve high densification and even full densification at lower sintering temperatures. The proposed sintering process involves initial densification of the refractory metal carbide powder at a specific higher temperature under higher pressure, followed by a temperature reduction and holding at a lower temperature for a certain period of time under pressure. This achieves complete densification and full solid solution of elements in the refractory metal carbide high-entropy ceramic, forming a homogeneous single-phase solid solution. This method ensures full densification of the refractory metal carbide high-entropy ceramic while simultaneously guaranteeing grain refinement and uniform solid solution of multiple elements, without abnormal grain growth. Consequently, the prepared refractory metal carbide high-entropy ceramic exhibits superior mechanical properties. Summary of the Invention

[0005] The preparation method and process provided by this invention are as follows: high-purity refractory metal carbide powder with small particle size differences is thoroughly mixed uniformly under an argon atmosphere, the mixed powder is placed into a graphite mold for pre-pressing, and then the pressed blank is placed in a high-vacuum rapid hot press furnace. Through the process steps of high pressure-instantaneous high temperature-cooling-low temperature short-time heat holding and pressure holding, a fully dense, small-grain-size, single-phase, and uniformly structured refractory metal carbide high-entropy ceramic is prepared.

[0006] The present invention provides a method for rapidly preparing high-density, refractory metal carbide high-entropy ceramics, characterized by comprising the following steps:

[0007] (1) Using commercially available refractory metal carbide powders of TiC, NbC, VC, TaC, Mo2C, and WC with a purity of ≥99.9 wt.%, an average particle size of 1-3 μm, and a relatively uniform particle size distribution as raw materials, five or six of these powders are selected as initial materials. The powders are weighed, loaded, and sieved in a glove box protected by high-purity argon gas (99.999 vol.%). The five or six refractory metal carbide powders are weighed according to an equimolar or near-equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders are mixed and ground at a mass ratio of 15-20:1 (milling balls to powder). The milling speed is 500-600 r / min, and the milling time is 3-6 h. The mill is stopped for 15 min after every 30 min of continuous milling to prevent overheating of the milling system and potential phase changes or other reactions. The ground mixed powder is then sieved through a 200-mesh sieve in the glove box.

[0008] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 10-20 MPa for 1-2 min.

[0009] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace to sinter, densify, and perform solid solution diffusion on the pre-pressed powder. Axial pressure is applied through the upper and lower electrodes, with an initial pressure of 40 MPa. The temperature is first raised to 1600℃ at a heating rate of 80-100℃ / min, while the applied pressure is increased to 100 MPa. Then, the temperature is raised to 1700-1850℃ at a heating rate of 50-70℃ / min and held for 1 min. Subsequently, the temperature is lowered to 1550-1600℃ at a rate of 100-150℃ / min and held for 10-20 min, while the applied pressure is maintained at 100 MPa. After the holding period, the temperature is lowered to 800℃ at a rate of 100-110℃ and then cooled to room temperature with the furnace. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process, and the vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0010] In this invention, near equimolar ratio refers to a molar ratio of one or more types that does not exceed 20% of the equimolar ratio; generally, near equimolar ratio refers to a molar ratio of one or more types that does not exceed 10% of the equimolar ratio.

[0011] The unique advantages of this invention are:

[0012] (1) This invention develops a new high-entropy refractory metal carbide ceramic material with unique compositional components, achieving full density, uniform structure, and fine grain size, exhibiting high hardness and excellent toughness. (2) This invention combines mechanical ball milling for pretreatment of refractory metal carbide powder with a staged rapid hot-pressing sintering process. Under high sintering pressure, the initial densification of the refractory metal carbide powder is achieved through a first sintering at a specific high temperature for an instantaneous period. Then, a heat-holding and pressure-holding treatment is performed at a specific lower temperature for a certain period of time to achieve complete densification of the refractory metal carbide and full solid solution of the elements. (3) This invention solves the difficulty of obtaining high-density high-entropy refractory metal carbide ceramics only under high temperature and long-term heat-holding conditions in previous methods. At the same time, it avoids the coarsening of the structure and abnormal grain growth caused by continuous heat-holding at high temperature, and obtains a high-entropy refractory metal carbide bulk material with fine and uniform grain structure, complete density, and uniform solid solution forming a single phase. Attached Figure Description

[0013] Figure 1 (Nb,V,Ta,Mo,W)C high-entropy ceramics prepared in Example 1: (a) X-ray diffraction pattern of the high-entropy ceramics; (b) microstructure of the high-entropy ceramics; (c) grain size statistics of the high-entropy ceramics.

[0014] Figure 2 The (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 2: (a) X-ray diffraction pattern of the high-entropy ceramic; (b) microstructure of the high-entropy ceramic; (c) grain size statistics of the high-entropy ceramic.

[0015] Figure 3 (Nb,V,Ta,Mo,W)C high-entropy ceramics prepared in Example 3: (a) X-ray diffraction pattern of the high-entropy ceramics; (b) microstructure of the high-entropy ceramics; (c) statistical diagram of grain size of the high-entropy ceramics.

[0016] Figure 4 (Ti,Nb,V,Ta,Mo,W)C high-entropy ceramics prepared in Example 4: (a) X-ray diffraction pattern of the high-entropy ceramics; (b) microstructure of the high-entropy ceramics; (c) statistical diagram of grain size of the high-entropy ceramics.

[0017] Figure 5(Nb,V,Ta,Mo,W)C high-entropy ceramics prepared in Comparative Example 1: (a) X-ray diffraction pattern of the high-entropy ceramics; (b) microstructure of the high-entropy ceramics; (c) statistical diagram of grain size of the high-entropy ceramics.

[0018] Figure 6 (Nb,V,Ta,Mo,W)C high-entropy ceramics prepared in Comparative Example 2: (a) X-ray diffraction pattern of high-entropy ceramics; (b) microstructure of high-entropy ceramics; (c) statistical diagram of grain size of high-entropy ceramics.

[0019] Table 1 shows the properties of the refractory metal carbide high-entropy ceramics prepared in Examples 1-4 and Comparative Examples 1-2. Detailed Implementation

[0020] The following embodiments further illustrate the present invention, but the present invention is not limited to the following embodiments.

[0021] Example 1

[0022] (1) Using commercially available refractory metal carbide powders of NbC, VC, TaC, Mo2C, and WC with a purity of over 99.9 wt.%, an average particle size of 2.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The five refractory metal carbide powders were weighed according to the equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of 15:1 (grinding balls to powder), at a milling speed of 500 r / min, for a milling time of 3 h, with a 15 min stop after every 30 min of continuous milling to avoid overheating of the milling system and causing phase changes or other reactions in the material. The ground mixed powder was sieved through a 200-mesh sieve in the glove box.

[0023] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 10 MPa for 1 min.

[0024] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace to sinter, densify, and perform solid solution diffusion on the pre-pressed powder. Axial pressure is applied through the upper and lower electrodes. The initial pressure is 40 MPa. The temperature is first raised to 1600℃ at a heating rate of 80℃ / min, while the applied pressure is increased to 100 MPa. Then, the temperature is raised to 1800℃ at a heating rate of 70℃ / min and held for 1 min. Subsequently, the temperature is lowered to 1550℃ at a rate of 125℃ / min and held for 10 min. During this process, the applied pressure is maintained at 100 MPa. After the holding period, the temperature is lowered to 800℃ at a rate of 110℃. Then, the furnace is cooled to room temperature. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process. The vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0025] Phase analysis of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 1 is shown in [reference needed]. Figure 1 (a) shows a single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 1 (b) and Figure 1 (c) It can be seen that the average grain size of the prepared (Nb,V,Ta,Mo,W)C high-entropy ceramic is 2.83 μm. The properties of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 1 are shown in Table 1.

[0026] Example 2

[0027] (1) Using commercially available refractory metal carbide powders of NbC, VC, TaC, Mo2C, and WC with a purity of over 99.9 wt.%, an average particle size of 2.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The five refractory metal carbide powders were weighed according to a near equimolar ratio of metal atoms (1:1.1:1:0.9:1). In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of grinding balls to powder of 18:1. The ball milling speed was 560 r / min, and the milling time was 5 h. The mill was stopped for 15 min after every 30 min of continuous milling to avoid overheating of the ball milling system, which could cause phase transformation or other reactions in the material. The ground mixed powder was sieved through a 200-mesh sieve in the glove box.

[0028] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 15 MPa for 1.5 min.

[0029] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace to sinter, densify, and perform solid solution diffusion on the pre-pressed powder. Axial pressure is applied through the upper and lower electrodes, with an initial pressure of 40 MPa. The temperature is first raised to 1600°C at a heating rate of 90°C / min, while the applied pressure is increased to 100 MPa. Then, the temperature is raised to 1750°C at a heating rate of 60°C / min and held for 1 min. Subsequently, the temperature is lowered to 1550°C at a rate of 100°C / min and held for 10 min, while the applied pressure remains at 100 MPa. After the holding period, the temperature is lowered to 800°C at a rate of 110°C and then cooled to room temperature with the furnace. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process, and the vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0030] Phase analysis of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 2 is shown in [reference needed]. Figure 2 (a) shows a single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 2 (b) and Figure 2 (c) The average grain size of the prepared (Nb,V,Ta,Mo,W)C high-entropy ceramic is 2.50 μm. The properties of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 2 are shown in Table 1.

[0031] Example 3

[0032] (1) Using commercially available refractory metal carbide powders of NbC, VC, TaC, Mo2C, and WC with a purity of ≥99.9 wt.%, an average particle size of 1.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The five refractory metal carbide powders were weighed according to the equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of 20:1 (grinding balls to powder), at a milling speed of 600 r / min, for a milling time of 6 h, with a 15-min stop after every 30 min of continuous milling to avoid overheating of the milling system and causing phase transformation or other reactions in the material. The ground mixed powder was then sieved through a 200-mesh sieve in the glove box.

[0033] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 20 MPa for 2 min.

[0034] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace to sinter, densify, and perform solid solution diffusion on the pre-pressed powder. Axial pressure is applied through the upper and lower electrodes. The initial pressure is 40 MPa. The temperature is first raised to 1600°C at a heating rate of 100°C / min, while the applied pressure is increased to 100 MPa. Then, the temperature is raised to 1700°C at a heating rate of 50°C / min and held for 1 min. Subsequently, the temperature is lowered to 1550°C at a rate of 150°C / min and held for 15 min. During this process, the applied pressure is maintained at 100 MPa. After the holding period, the temperature is lowered to 800°C at a rate of 110°C and then cooled to room temperature with the furnace. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process. The vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0035] Phase analysis of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 3 is shown in [reference needed]. Figure 3 (a) shows a single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 3 (b) and Figure 3 (c) The average grain size of the prepared (Nb,V,Ta,Mo,W)C high-entropy ceramic was 2.21 μm. The properties of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 3 are shown in Table 1.

[0036] Example 4

[0037] (1) Using commercially available refractory metal carbide powders of TiC, NbC, VC, TaC, Mo2C, and WC with a purity of ≥99.9 wt.%, an average particle size of 3.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The six refractory metal carbide powders were weighed according to the equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of 20:1 (grinding balls to powder), at a milling speed of 600 r / min, for a milling time of 6 h, with a 15-min stop after every 30 min of continuous milling to avoid overheating of the milling system and causing phase transformation or other reactions in the material. The ground mixed powder was sieved through a 200-mesh sieve in the glove box.

[0038] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 20 MPa for 2 min.

[0039] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace to sinter, densify, and perform solid solution diffusion on the pre-pressed powder. Axial pressure is applied through the upper and lower electrodes. The initial pressure is 40 MPa. The temperature is first raised to 1600°C at a heating rate of 100°C / min, while the applied pressure is increased to 100 MPa. Then, the temperature is raised to 1850°C at a heating rate of 70°C / min and held for 1 min. Subsequently, the temperature is lowered to 1600°C at a rate of 100°C / min and held for 15 min. During this process, the applied pressure is maintained at 100 MPa. After the holding period, the temperature is lowered to 800°C at a rate of 100°C and then cooled to room temperature with the furnace. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process. The vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0040] Phase analysis of the (Ti,Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 4 is shown in [reference needed]. Figure 4 (a) shows a single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 4 (b) and Figure 4 (c) It can be seen that the average grain size of the prepared (Ti,Nb,V,Ta,Mo,W)C high-entropy ceramic is 3.95μm. The properties of the (Ti,Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Example 4 are shown in Table 1.

[0041] Comparative Example 1

[0042] (1) Using commercially available refractory metal carbide powders of NbC, VC, TaC, Mo2C, and WC with a purity of ≥99.9 wt.%, an average particle size of 1.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The five refractory metal carbide powders were weighed according to the equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of 20:1 (grinding balls to powder), at a milling speed of 600 r / min, for a milling time of 6 h, with a 15-min stop after every 30 min of continuous milling to avoid overheating of the milling system and causing phase changes or other reactions in the material. The ground mixed powder was sieved through a 200-mesh sieve in the glove box.

[0043] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 20 MPa for 2 min.

[0044] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace. Axial pressure is applied through the upper and lower electrodes. The initial applied pressure is 40 MPa. The temperature is first raised to 1700℃ at a heating rate of 80℃ / min, while the applied pressure is increased to 100 MPa. The temperature is held for 1 min, during which the applied pressure is maintained at 100 MPa. After the holding period, the temperature is lowered to 800℃ at a rate of 100℃. Then, the furnace is cooled to room temperature. The applied pressure is reduced from 100 MPa to 30 MPa during the cooling process. The vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0045] Phase analysis of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 1 is shown in [reference needed]. Figure 5 (a) A single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 5 (b) and Figure 5 (c) The average grain size of the prepared (Nb,V,Ta,Mo,W)C high-entropy ceramic was 1.80 μm. The properties of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 1 are shown in Table 1. From the density detection, microstructure observation, and performance test results, it can be seen that the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 1 did not achieve full density and had relatively low mechanical properties.

[0046] Comparative Example 2

[0047] (1) Using commercially available refractory metal carbide powders of NbC, VC, TaC, Mo2C, and WC with a purity of over 99.9 wt.%, an average particle size of 3.0 μm, and a relatively uniform particle size distribution as raw materials, the powders were weighed, loaded, and sieved in a glove box protected by high-purity argon gas (purity 99.999 vol.%). The five refractory metal carbide powders were weighed according to the equimolar ratio of metal atoms. In a cemented carbide ball mill jar, the powders were mixed and ground at a mass ratio of 15:1 (grinding balls to powder), at a milling speed of 500 r / min, for a milling time of 3 h, with a 15 min stop after every 30 min of continuous milling to avoid overheating of the milling system and causing phase changes or other reactions in the material. The ground mixed powder was then sieved through a 200-mesh sieve in the glove box.

[0048] (2) The mixed powder prepared in step (1) is loaded into a custom graphite mold, and carbon paper is used to separate the mixed powder from the inner wall of the mold. The mixture is pre-pressed with a pressure of 10 MPa for 1 min.

[0049] (3) The mold containing the pre-pressed powder from step (2) is placed into a rapid hot press furnace. Axial pressure is applied through the upper and lower electrodes. The temperature is first raised to 1800℃ at a heating rate of 100℃ / min, while the pressure is increased to 100MPa. The temperature is held for 10 minutes, during which the pressure is maintained at 100MPa. After the holding period, the temperature is lowered to 800℃ at a rate of 100℃. Then, the furnace is cooled to room temperature. The applied pressure is reduced from 100MPa to 30MPa during the cooling process. The vacuum degree of the furnace is maintained at 10 throughout the process. -1 Below Pa.

[0050] Phase analysis of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 2 is shown in [reference needed]. Figure 6 (a) shows a single-phase solid solution with only a face-centered cubic structure. Statistical analysis of the microstructure and grain size is shown in [reference needed]. Figure 6 (b) and Figure 6 (c) The average grain size of the prepared (Nb,V,Ta,Mo,W)C high-entropy ceramic was 8.29 μm. The properties of the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 2 are shown in Table 1. From the microstructure observation and performance test results, it can be seen that the (Nb,V,Ta,Mo,W)C high-entropy ceramic prepared in Comparative Example 2 has a coarse microstructure, poor grain size uniformity, and low mechanical properties.

[0051] Table 1. Properties of refractory metal carbide high-entropy ceramics prepared in each example and comparative example

[0052]

Claims

1. A method for rapid fabrication of fully dense refractory metal carbide high entropy ceramic characterized in that, The method comprises the following steps: (1) using commercially pure TiC, NbC, VC, TaC, Mo2C, WC refractory metal carbide powder with a purity of 99.9 wt.% or above and an average particle size of 1-3 μm as raw materials, selecting five or six kinds of powder as initial materials, and weighing, loading and sieving the powder in an argon-protected glove box; the five or six kinds of refractory metal carbide powder are weighed according to an equimolar ratio or a near equimolar ratio of metal atoms; the near equimolar ratio refers to that the molar ratio of one or several kinds is not more than 10% of the equimolar ratio; the mixed powder is mixed and ground in a hard alloy ball mill jar at a mass ratio of grinding ball to powder of 15-20:1, a ball milling speed of 500-600 r / min, and a ball milling time of 3-6 h, and the ball milling is stopped for 15 min every 30 min of continuous ball milling; the ground mixed powder is sieved with a 200-mesh sieve in the glove box; (2) loading the mixed powder prepared in step (1) into a customized graphite mold, separating the mixed powder from the inner wall of the mold by using carbon paper, and pre-pressing at a pressure of 10-20 MPa for 1-2 min; (3) Put the mold containing the pre-pressed powder in step (2) into a rapid hot-pressing furnace, and sinter and densify the pre-pressed powder, and apply axial pressure through the upper and lower electrodes, with an initial pressure of 40 MPa, first increase the temperature to 1600°C at a heating rate of 80-100°C / min, while increasing the pressure to 100 MPa, then increase the temperature to 1700-1850°C at a heating rate of 50-70°C / min, and keep the temperature for 1 min, then decrease the temperature to 1550-1600°C at a rate of 100-150°C / min, and keep the temperature for 10-20 min, while keeping the pressure at 100 MPa, then decrease the temperature to 800°C at a rate of 100-110°C / min, and then cool to room temperature in the furnace, the pressure decreases from 100 MPa to 30 MPa during the temperature decreasing process, and the vacuum degree of the furnace is kept below 10 Pa throughout the process. -1 Pa throughout the process.

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