Method for preparing high-entropy diboride ceramic through ultrahigh pressure-strong electric field coupling sintering

Abstract

The invention discloses a method for preparing high-entropy diboride ceramic through ultrahigh pressure-strong electric field coupling sintering. The preparation method of the high-entropy diboride ceramic comprises the following steps: mixing at least five kinds of transition metal powder with boron powder to obtain mixed powder, and carrying out vacuum sintering on the mixed powder at 1200-2000 DEG C to obtain high-entropy diboride powder; and the high-entropy diboride powder is pre-pressed into a green body, the green body is gradually pressurized to 5-20 GPa under the vacuum condition, pressure maintaining is conducted, an electric field of 300-1000 V / cm is applied while pressure maintaining is conducted, and cooling is conducted after 1-2 min. The high-entropy diboride ceramic prepared by the preparation method disclosed by the invention has higher density, and the hardness is up to 30 GPa or above. Compared with a traditional SPS sintering method, the sintering temperature is reduced by 300-500 DEG C, the whole sintering process can be completed within 5 min, and the sintering time is shortened by about 90% compared with the traditional method.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, and in particular relates to a method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering. Background Technology

[0002] High-entropy boride ceramics (HEBs), as an important branch of high-entropy materials (HEMs), combine the excellent properties of traditional boride ceramics with the unique design concept of high-entropy alloys, exhibiting groundbreaking comprehensive performance and becoming one of the ideal candidates for materials used in ultra-high temperature and extreme environments. They possess high melting points, high hardness, excellent oxidation resistance, good thermal shock resistance, and high radiation resistance, showing broad application prospects in ultra-high temperature structural materials, wear-resistant coatings, the nuclear industry, and thermoelectric materials. However, in the preparation of high-entropy ceramics, the sintering process directly determines the performance of the finished product. Typically, the sintering of high-entropy ceramics requires extremely high temperatures, while the diffusion of multi-component components often requires long periods of heat treatment, which may lead to coarsening of ceramic grains, thereby weakening material properties. Therefore, controlling grain growth during the sintering process is crucial to ensuring the excellent performance of ceramics.

[0003] Ultra-high pressure sintering technology overcomes the limitations of traditional sintering, which relies solely on heat-driven processes. It directly compresses powder particles through "high pressure drive," promoting atomic diffusion and eliminating voids. This method simultaneously suppresses grain boundary migration and grain growth, maintaining fine grains, and at a sintering temperature 300-500°C lower than that under ambient pressure. Flash sintering is an electric field-assisted sintering technology that has gained attention in recent years. Compared to traditional solid-state sintering, flash sintering utilizes an electric field to drive a low-temperature, high-speed densification process. The electric field drives the directional migration of charged particles (such as oxygen vacancies and metal ions), accelerating grain boundary diffusion and pore closure. This method significantly shortens the sintering time, allowing the entire process to be completed within minutes. Because the grains only experience a brief high-temperature process, the kinetics of grain growth are "frozen."

[0004] In summary, how to combine ultra-high pressure sintering with flash sintering technology to overcome the problems of grain coarsening, high sintering temperature and densification difficulties in existing technologies, and thus prepare high-entropy boride ceramics with excellent performance, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, which solves problems such as grain coarsening, high sintering temperature, and difficulty in densification in existing technologies.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering includes the following steps: At least five transition metal powders are mixed with boron powder to obtain a mixed powder, and the mixed powder is sintered under vacuum at 1200~2000℃ to obtain high-entropy diboride powder; the ratio of the total molar amount of the transition metal powder to the molar amount of the boron powder is 1:2. The high-entropy diboride powder was pre-pressed into a green body, and then gradually pressurized to 5~20 GPa under vacuum and held at that pressure. While holding the pressure, an electric field of 300~1000 V / cm was applied and held for 1~2 minutes. The green body was then cooled to room temperature in the furnace to obtain high-entropy diboride ceramic.

[0007] In this invention, firstly, mixed metal powder and boron powder are pre-calcined at 1200-2000°C, undergoing a thorough solid-state reaction to form a stable and homogeneous high-entropy compound powder. Secondly, a large electric field drives current to flow through the material, generating Joule heating. Simultaneously, this electric field accelerates the directional migration of charged particles (such as ions and vacancies), thereby promoting material diffusion and grain boundary activation. The application of high pressure forces rapid atomic / grain boundary diffusion, which can eliminate porosity and inhibit grain growth.

[0008] Preferably, the transition metal powder is selected from at least five of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W.

[0009] In this invention, the particle size of the transition metal powder should be as uniform as possible. The selection of transition metal is based on the difference in lattice size (<5.2%) and electronegativity (<5.5%), which directly affects the uniform sintering, composition control and final performance of high-entropy ceramics. Since boron powder is easily volatilized at high temperatures, an excess of 2-5% should be used to compensate for volatilization loss.

[0010] Preferably, the transition metal powder and boron powder are wet ball-milled, dried, ground, and sieved to obtain a mixed powder.

[0011] Preferably, the operating parameters of the wet ball mill are as follows: the milling media are agate balls or zirconia balls with a diameter of 2~5mm, and the mass ratio of material to ball is 1:10; the liquid medium is anhydrous ethanol, and the mass ratio of powder to anhydrous ethanol is 1:3; the milling speed is controlled at 100~150rpm, and the milling time is 24~72h.

[0012] Preferably, the sieving refers to passing through a 200-mesh sieve.

[0013] Preferably, the mixed powder is placed at 1200~2000℃, at 1×10 -2 ~1×10 -5High-entropy diboride powder was obtained by sintering under vacuum conditions of Pa for 2 hours.

[0014] Preferably, the pre-compression pressure is 40~50MPa, and the pressure holding time is 60~120s.

[0015] Preferably, in 1×10 -2 ~1×10 -5 Under a vacuum of 30-40 MPa / min, the pressure is gradually increased to 5-20 GPa and held.

[0016] Preferably, the pressure is gradually increased to 15 GPa at a rate of 30 MPa / min and then maintained.

[0017] Preferably, the strength of the electric field is 500~600V / cm.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) Samples prepared by conventional spark plasma sintering (SPS) typically have a relative density of 92% to 95%, an average grain size greater than 1 μm, and a hardness range of 20 to 30 GPa. In contrast, the samples prepared by this invention have a higher density (relative density exceeding 99%), the grain size can be maintained close to the original powder particle size (approximately 50 nm), and the hardness is increased to over 30 GPa.

[0019] (2) In traditional spark plasma sintering (SPS), the electric field strength is typically in the range of 10~50V / cm, the heating rate is about 100℃ / min, and the sintering process usually takes 30 minutes. Especially for high-entropy ceramics, the sintering temperature often needs to reach above 1800℃. This invention introduces a strong electric field of 300~1000V / cm, which enables the heating rate to reach above 1000℃ / min, while reducing the sintering temperature by 300~500℃. The entire sintering process can be completed within 5 minutes, which is about 90% shorter than the traditional method, thereby significantly reducing energy consumption and improving process efficiency. Attached Figure Description

[0020] Figure 1 SEM micrograph of the high-entropy diboride ceramic prepared in Example 1.

[0021] Figure 2 The images show a comparison of the SEM microstructures of the high-entropy diboride ceramic prepared in Example 1 and the ceramic prepared in Comparative Example 1. The left image corresponds to Example 1, and the right image corresponds to Comparative Example 1.

[0022] Figure 3 The XRD diffraction pattern of the high-entropy diboride ceramic prepared in Example 1.

[0023] Figure 4 SEM micrograph and EDS elemental analysis diagram of the high-entropy diboride ceramic prepared in Example 1.

[0024] Figure 5 The images show the SEM microstructures of the high-entropy diboride ceramics prepared in Examples 2 and 3, with the left image corresponding to Example 2 and the right image corresponding to Example 3. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] The ultra-high pressure sintering equipment used in the embodiments is a six-sided top press, which uses an octahedral structure to fill the sample.

[0027] The relative density was determined according to Archimedes' method of displacement, and the hardness was measured using a Vickers hardness tester.

[0028] Example 1 A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, the specific steps of which are as follows: (1) Select five metal powders, Ti, Zr, Hf, Nb and Ta, and boron powder, according to (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 B2 was stoichiometrically prepared into a mixed powder with a total mass of 20g. The mixed powder, 60g of alcohol, and 200g of agate balls were sequentially added to a plastic ball mill jar and ball-milled for 48 hours at 100-150 rpm. The milled slurry was transferred to a rotary evaporator and distilled under reduced pressure at 30 rpm to remove the alcohol, followed by drying in a 65°C water bath for 30 minutes. The dried product was ground and passed through a 200-mesh sieve to obtain the precursor powder. The precursor powder was then heated in a muffle furnace (vacuum degree 1×10⁻⁶). -2 ~1×10 -5 The mixture was heated to 1200℃ and kept at that temperature for 2 hours to obtain high-entropy diboride powder. (2) Take 0.05g of high-entropy diboride powder, wrap it with platinum foil and put it into a cylindrical mold. Pre-press it at 40MPa (hold pressure for 120s) to obtain a green body. Assemble the green body with MgO pad, Re heater, LaCrO3 insulation sleeve and Al2O3 sleeve into an octahedral structure, place it in an ultra-high pressure sintering equipment, and use W-Re thermocouple to monitor the temperature under high pressure in real time. (3) Ultra-high pressure sintering equipment at 1×10-2 ~1×10 -5 Under vacuum conditions of Pa, the pressure was increased to 15 GPa at a rate of 30 MPa / min and held. Then, an electric field of 500 V / cm was applied to allow current to pass through the sample. The temperature was rapidly increased to 1300 °C within 30 s, and the sample was sintered at this temperature for 60 s. After sintering, the sample was cooled to room temperature in the furnace to obtain a high-entropy diboride ceramic bulk.

[0029] The high-entropy diboride ceramic prepared in Example 1 was tested and found to have a relative density of 99.5% and a hardness of 35.6 GPa.

[0030] Comparative Example 1 A method for preparing high-entropy diboride ceramics by SPS sintering, the specific steps of which are as follows: (1) Select five metal powders, Ti, Zr, Hf, Nb and Ta, and boron powder, according to (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 B2 was stoichiometrically prepared into a mixed powder with a total mass of 20g. The mixed powder, 60g of alcohol, and 200g of agate balls were sequentially added to a plastic ball mill jar and ball-milled for 48 hours at 100-150 rpm. The milled slurry was transferred to a rotary evaporator and distilled under reduced pressure at 30 rpm to remove the alcohol, followed by drying in a 65°C water bath for 30 minutes. The dried product was ground and passed through a 200-mesh sieve to obtain the precursor powder. The precursor powder was then heated in a muffle furnace (vacuum degree 1×10⁻⁶). -2 ~1×10 -5 The mixture was heated to 1200℃ and kept at that temperature for 2 hours to obtain high-entropy diboride powder. (2) Take 0.5g of high-entropy diboride powder and put it into a cylindrical graphite mold with an inner diameter of 10mm. Separate the inner wall of the mold sleeve and the powder with carbon paper with a thickness of 0.15mm.

[0031] (3) Pressure sintering was performed on the sample using a discharge plasma sintering apparatus under vacuum conditions. The temperature was increased to 1800℃ at a heating rate of 100℃ / min, and a pressure of 50MPa was applied to the sample. The sample was held at this temperature and pressure for 5min. After the heat and pressure holding was completed, the sample was then cooled to room temperature in the furnace to obtain a high-entropy diboride ceramic bulk.

[0032] The high-entropy diboride ceramic prepared in Comparative Example 1 was tested and found to have a relative density of 95.8% and a hardness of 27 GPa.

[0033] Example 2 A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, the specific steps of which are as follows: (1) Select five metal powders, W, Mo, Ta, Nb and Cr, and boron powder, according to (W 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Cr 0.2 B2 was stoichiometrically prepared into a mixed powder with a total mass of 20g. The mixed powder, 60g of alcohol, and 200g of agate balls were sequentially added to a plastic ball mill jar and ball-milled for 48 hours at 100-150 rpm. The milled slurry was transferred to a rotary evaporator and distilled under reduced pressure at 30 rpm to remove the alcohol, followed by drying in a 65°C water bath for 30 minutes. The dried product was ground and passed through a 200-mesh sieve to obtain the precursor powder. The precursor powder was then heated in a muffle furnace (vacuum degree 1×10⁻⁶). -2 ~1×10 -5 The mixture was heated to 1200℃ and kept at that temperature for 2 hours to obtain high-entropy diboride powder. (2) Take 0.05g of high-entropy diboride powder, wrap it with platinum foil and put it into a cylindrical mold. Pre-press it at 40MPa (hold pressure for 120s) to obtain a green body. Assemble the green body with MgO pad, Re heater, LaCrO3 insulation sleeve and Al2O3 sleeve into an octahedral structure, place it in an ultra-high pressure sintering equipment, and use W-Re thermocouple to monitor the temperature under high pressure in real time. (3) Ultra-high pressure sintering equipment at 1×10 -2 ~1×10 -5 Under vacuum conditions of Pa, the pressure was increased to 15 GPa at a rate of 30 MPa / min and held. Then, an electric field of 500 V / cm was applied to allow current to pass through the sample. The temperature was rapidly increased to 1200 °C within 30 s, and the sample was sintered at that temperature for 60 s. After sintering, the sample was cooled to room temperature in the furnace to obtain a high-entropy diboride ceramic bulk.

[0034] The high-entropy diboride ceramic prepared in Example 2 was tested and found to have a relative density of 99.4% and a hardness of 38.1 GPa.

[0035] Example 3 A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, the specific steps of which are as follows: (1) Select five metal powders, Ti, Hf, Ta, Nb and Mo, and boron powder, according to (Ti 0.2 Hf 0.2 Nb 0.2 Ta 0.2 Mo 0.2B2 was stoichiometrically prepared into a mixed powder with a total mass of 20g. The mixed powder, 60g of alcohol, and 200g of agate balls were sequentially added to a plastic ball mill jar and ball-milled for 48 hours at 100-150 rpm. The milled slurry was transferred to a rotary evaporator and distilled under reduced pressure at 30 rpm to remove the alcohol, followed by drying in a 65°C water bath for 30 minutes. The dried product was ground and passed through a 200-mesh sieve to obtain the precursor powder. The precursor powder was then heated in a muffle furnace (vacuum degree 1×10⁻⁶). -2 ~1×10 -5 The mixture was heated to 1200℃ and kept at that temperature for 2 hours to obtain high-entropy diboride powder. (2) Take 0.05g of high-entropy diboride powder, wrap it with platinum foil and put it into a cylindrical mold. Pre-press it at 40MPa (hold pressure for 120s) to obtain a green body. Assemble the green body with MgO pad, Re heater, LaCrO3 insulation sleeve and Al2O3 sleeve into an octahedral structure, place it in an ultra-high pressure sintering equipment, and use W-Re thermocouple to monitor the temperature under high pressure in real time. (3) Ultra-high pressure sintering equipment at 1×10 -2 ~1×10 -5 Under vacuum conditions of Pa, the pressure was increased to 15 GPa at a rate of 30 MPa / min and held. Then, an electric field of 500 V / cm was applied to allow current to pass through the sample. The temperature was rapidly increased to 1200 °C within 30 s, and the sample was sintered at that temperature for 60 s. After sintering, the sample was cooled to room temperature in the furnace to obtain a high-entropy diboride ceramic bulk.

[0036] The high-entropy diboride ceramic prepared in Example 3 was tested and found to have a relative density of 99.2% and a hardness of 39.3 GPa.

[0037] Example 4 A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, the specific steps of which are as follows: (1) Select five metal powders, Ti, Zr, Nb, Mo and Hf, and boron powder, according to (Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Hf 0.2 B2 was stoichiometrically prepared into a mixed powder with a total mass of 20g. The mixed powder, 60g of alcohol, and 200g of agate balls were sequentially added to a plastic ball mill jar and ball-milled for 48 hours at 100-150 rpm. The milled slurry was transferred to a rotary evaporator and distilled under reduced pressure at 30 rpm to remove the alcohol, followed by drying in a 65°C water bath for 30 minutes. The dried product was ground and passed through a 200-mesh sieve to obtain the precursor powder. The precursor powder was then heated in a muffle furnace (vacuum degree 1×10⁻⁶).-2 ~1×10 -5 The mixture was heated to 1200℃ and kept at that temperature for 2 hours to obtain high-entropy diboride powder. (2) Take 0.05g of high-entropy diboride powder, wrap it with platinum foil and put it into a cylindrical mold. Pre-press it at 40MPa (hold pressure for 120s) to obtain a green body. Assemble the green body with MgO pad, Re heater, LaCrO3 insulation sleeve and Al2O3 sleeve into an octahedral structure, place it in an ultra-high pressure sintering equipment, and use W-Re thermocouple to monitor the temperature under high pressure in real time. (3) Ultra-high pressure sintering equipment at 1×10 -2 ~1×10 -5 Under vacuum conditions of Pa, the pressure was increased to 15 GPa at a rate of 30 MPa / min and held. Then, an electric field of 600 V / cm was applied to allow current to pass through the sample. The temperature was rapidly increased to 1400 °C within 30 s, and the sample was sintered at this temperature for 60 s. After sintering, the sample was cooled to room temperature in the furnace to obtain a high-entropy diboride ceramic bulk.

[0038] The high-entropy diboride ceramic prepared in Example 4 was tested and found to have a relative density of 99.8% and a hardness of 39.8 GPa.

[0039] Figure 1 The image shows the SEM microstructure of the high-entropy diboride ceramic prepared in Example 1. Figure 1 As can be seen, the ceramic material has a dense microstructure with relatively uniform grain distribution; the grain boundaries are clear, and no obvious pores or cracks are observed, indicating that the sample has achieved good densification during the ultra-high pressure-strong electric field coupled sintering process.

[0040] Figure 2 The images show a comparison of the SEM microstructures of the high-entropy diboride ceramic prepared in Example 1 and the ceramic prepared in Comparative Example 1. The left image corresponds to Example 1, and the right image corresponds to Comparative Example 1. Figure 2 It can be seen that the ultra-high pressure sintered sample has a more uniform and finer grain size, and the overall structure is extremely dense with clear grain boundaries and no obvious pores or cracks. In contrast, the SPS sintered sample has a relatively larger grain size and is accompanied by a small number of micropores.

[0041] Figure 3 The XRD diffraction pattern of the high-entropy diboride ceramic prepared in Example 1 is shown below. Figure 3 It can be seen that after the high-temperature solid-state reaction (Ti) 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Hf 0.2 B2 is a single-phase material.

[0042] Figure 4 The SEM micrograph and EDS elemental analysis diagram of the high-entropy diboride ceramic prepared in Example 1 are shown below. Figure 4 It can be seen that the five elements Ti, Zr, Hf, Nb and Ta are evenly distributed.

[0043] Figure 5 SEM images of the high-entropy diboride ceramics prepared in Examples 2 and 3 are shown, with the left image corresponding to Example 2 and the right image corresponding to Example 3. Figure 4 It can be seen that the ceramic materials prepared in Examples 2 and 3 also have a dense microstructure with relatively uniform grain distribution; the grain boundaries are clear and no obvious pores or cracks are observed.

[0044] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering, characterized in that, Includes the following steps: At least five transition metal powders are mixed with boron powder to obtain a mixed powder, and the mixed powder is sintered under vacuum at 1200~2000℃ to obtain high-entropy diboride powder; the ratio of the total molar amount of the transition metal powder to the molar amount of the boron powder is 1:

2. The high-entropy diboride powder was pre-pressed into a green body, and then gradually pressurized to 5~20 GPa under vacuum and held at that pressure. While holding the pressure, an electric field of 300~1000 V / cm was applied and held for 1~2 minutes. The green body was then cooled to room temperature in the furnace to obtain high-entropy diboride ceramic.

2. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, The transition metal powder is selected from at least five of the following: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W.

3. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, The transition metal powder and boron powder are wet ball-milled, dried, ground, and sieved to obtain a mixed powder.

4. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 3, characterized in that, The operating parameters of the wet ball mill are as follows: the milling media are agate balls or zirconia balls with a diameter of 2~5mm, and the mass ratio of material to ball is 1:10; the liquid medium is anhydrous ethanol, and the mass ratio of powder to anhydrous ethanol is 1:3; the milling speed is controlled at 100~150rpm, and the milling time is 24~72h.

5. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 3, characterized in that, The sieving process refers to passing through a 200-mesh sieve.

6. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, The mixed powder is placed at 1200~2000℃ and subjected to a 1×10⁻⁶ ppm temperature. -2 ~1×10 -5 High-entropy diboride powder was obtained by sintering under vacuum conditions of Pa for 2 hours.

7. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, The pre-compression pressure is 40~50MPa, and the pressure is held for 60~120s.

8. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, In 1×10 -2 ~1×10 -5 Under a vacuum of 30-40 MPa / min, the pressure is gradually increased to 5-20 GPa and held.

9. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 8, characterized in that, The pressure was gradually increased to 15 GPa at a rate of 30 MPa / min and held.

10. The method for preparing high-entropy diboride ceramics by ultra-high pressure-strong electric field coupled sintering according to claim 1, characterized in that, The strength of the electric field is 500~600V / cm.

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