A multi-element transition metal borocarbide ceramic and a low-cost method of making the same

Abstract

This invention discloses a multi-element transition metal boron carbide ceramic and its low-cost preparation method, belonging to the field of ceramic materials technology. The ceramic has the molecular formula (M)₂BC, where M represents at least four different transition metal elements, each with a mole fraction greater than 0 and less than 0.9, and the sum of the mole fractions of all elements is 1. This invention uses at least four transition metal oxide powders, boron carbide powder, and carbon powder as raw materials. After ball milling and mixing, pressing, and molding, high-purity multi-element boron carbide powder is synthesized under vacuum conditions through a boronothermal-carbothermal reduction reaction, followed by sintering to obtain a dense ceramic. This invention achieves the preparation of multi-element high-entropy boron carbide ceramics for the first time, with low raw material costs, a simple process, and the resulting ceramic having a single-phase structure, a grain size of 10-30 μm, a relative density ≥97%, a Vickers hardness of 28-38 GPa, and a fracture toughness of 3.2-3.8 MPa·m. 1 / 2 It combines high hardness with moderate toughness and has broad application prospects in the field of high-temperature structural materials.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a multi-component transition metal boron carbide ceramic and its low-cost preparation method. Background Technology

[0002] Transition metal boron carbides, due to their unique electronic structure and chemical bonding characteristics, combine the high melting point and excellent chemical stability of borides with the high hardness and high wear resistance of carbides, making them a promising new type of high-temperature structural ceramic material. The reported material systems can be mainly classified into three categories: (1) Carbide solid solutions represented by Zr-Ti-BC and Zr-Ta-BC. These materials usually do not form independent ternary ordered compound crystals. Essentially, boron atoms are dissolved in the interstitial spaces of transition metal carbide lattices or replace some carbon sites. Although the hardness can be further improved through solid solution strengthening, the overall performance of the material is still based on the performance of carbides. (2) Rare earth boron carbides with typical layered characteristics, REB2C2, RE = Sc, Y and lanthanides. These compounds belong to the tetragonal crystal system. Their crystal structure is formed by alternating stacking of rare earth metal atom layers and two-dimensional boron carbon atom grid layers. They mainly exhibit special magnetic, electrical and other physical properties and are often studied as functional materials. (3) M2BC (M is a transition metal). Currently, only Mo2BC has been reported in detail. Mo₂BC exhibits an orthorhombic structure at room temperature and pressure, with space group Cmcm (No. 63) and lattice parameters a = 0.3086 nm, b = 1.350 nm, and c = 0.3047 nm. The crystal structure of Mo₂BC can be described as an alternating sequence of Mo₆B triangular prisms and Mo₆C octahedrons. This unique crystal structure allows for an excellent combination of high stiffness, high hardness, high elastic modulus, and moderate ductility.

[0003] This excellent mechanical property quickly attracted the attention of researchers. Z'abransk'y predicted the elastic properties of Mo2BC based on first-principles calculations, obtaining Young's modulus, bulk modulus, and shear modulus as high as 470 GPa, 324 GPa, and 187 GPa, respectively. The B / G ratio (1.74) and Cauchy pressure (+43 GPa) both indicate that it has appropriate ductility. Subsequently, Emmerlich measured the hardness of the Mo2BC coating with a thickness greater than 600 nm on the alumina substrate under a 5 mN load using nanoindentation, and found it to be 29±2 GPa and Young's modulus 460±21 GPa, consistent with the first-principles calculation results. No crack initiation or propagation was found around the residual indentation, and material accumulation was observed. This result confirms that the Mo2BC coating has high hardness and stiffness while maintaining appropriate ductility (Journal of Physics D: Applied Physics, 2009 (42), 185406).

[0004] While traditional Mo2BC materials exhibit excellent performance, research on multi-component boron carbides remains largely unexplored. More importantly, although Mo2BC-based materials possess superior theoretical properties, significant technical bottlenecks exist in their bulk fabrication processes. Currently, two reported methods for preparing Mo2BC-based materials exist. One method utilizes electric arc melting: Jeitschko employs electric arc melting of appropriate proportions of molybdenum, boron, and carbon (graphite) in an argon atmosphere at a melting temperature of 2500°C. By repeatedly melting the billet, a uniformly composed Mo2BC bulk material can be obtained (Monatshefte Für Chemie Und Verwandte TeileAnderer Wissenschaften, 1963, 94(3): 565-568.). Another method is hot pressing sintering, which can prepare Mo2BC bulk materials at temperatures lower than those of electric arc melting. Existing research has shown that either Mo, B, and C powders are hot-pressed at 1900 °C for 2 hours (Journal of the Less Common Metals, 1967, 13(1): 129-131.), or Mo2BC powders are prepared by proportionally mixing Mo, B, and C powders at 1300 °C to obtain Mo2BC bulk materials, and then Mo2BC bulk materials are obtained at 1600 °C (Journal of the European Ceramic Society, 2021, 41(10): 5109-5114.). In related studies, the synthesis of Mo2BC-based materials mainly relies on the direct reaction between metal powder and boron powder, but this method has many problems: 1) Boron powder is expensive, and the reaction is highly dependent on the purity of the boron powder. 2) Metal powder raw materials are ductile and tend to stretch during ball milling, which is not conducive to thorough mixing; at the same time, metal powder is also at risk of oxidation during grinding. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-temperature, simple, and low-cost multi-element transition metal boron carbide ceramic and its preparation method. This ceramic has the advantages of high density, low temperature, small grain size, moderate fracture toughness, and high Vickers hardness.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a multi-element transition metal boron carbide ceramic, wherein the molecular formula of the ceramic is (M)2BC, wherein M is at least four different transition metal elements, the mole fraction of each transition metal element is greater than 0 and less than 0.9, and the sum of the mole fractions of all transition metal elements is 1.

[0007] As a preferred embodiment of the present invention, M is at least four of the following: Mo, W, Cr, Ta, V, Nb, Ni, and Fe.

[0008] As a preferred embodiment of the present invention, the ceramic has a single-phase structure, a grain size of 10-30 μm, a relative density ≥97%, a Vickers hardness of 28-38 GPa, and a fracture toughness of 3.2-3.8 MPa·m. 1 / 2 .

[0009] Secondly, the present invention provides a low-cost preparation method for the aforementioned multi-element transition metal boron carbide ceramic, comprising the following steps: (1) At least four transition metal oxides MO x The powder, boron carbide (B4C) powder, and carbon (C) powder are mixed, ball-milled, dried, and sieved to obtain a mixed powder. (2) The mixed powder is pressed into a blank and heat-treated under vacuum conditions. During the reaction, gas replacement is carried out to obtain multi-element transition metal boron carbide powder. (3) The powder is sintered to obtain a dense multi-element transition metal boron carbide ceramic.

[0010] As a preferred technical solution of the present invention, in step (1), the transition metal oxide MO x The molar ratio of powder, boron carbide (B4C) powder, and carbon (C) powder is 7.6. <MO x / B4C<8.8, 0.36 <MO x / C<0.42; the purity of the transition metal oxide powder is ≥99wt%, and the particle size is 1-3μm.

[0011] As a preferred technical solution of the present invention, the heat treatment temperature in step (2) is 1500-1750℃, the holding time is 30-90min, and the heating rate is 20-300℃ / min.

[0012] As a preferred technical solution of the present invention, the gas replacement process in step (2) is as follows: during the vacuum heat treatment process, when the vacuum degree is restored to below 50Pa, argon gas is introduced to normal pressure and then vacuum is drawn again, and this process is repeated 2-3 times.

[0013] As a preferred technical solution of the present invention, the sintering method in step (3) is any one of pressureless sintering, spark plasma sintering, hot pressing sintering or selective laser sintering.

[0014] As a preferred technical solution of the present invention, the sintering temperature in step (3) is 1750-1950℃, the holding time is 10-90min, the heating rate is 20-400℃ / min, and the axial pressure is 0-100MPa.

[0015] As a preferred technical solution of the present invention, the particle size of the multi-element transition metal boron carbide powder obtained in step (2) is 0.9-1.7 μm.

[0016] Compared with the prior art, the specific beneficial effects of the present invention are summarized as follows: 1. This invention successfully synthesizes for the first time a novel multi-component transition metal boron carbide (M)₂BC ceramic material system. The M-site contains at least four different transition metal elements, overcoming the limitations of existing technologies that focus solely on a single Mo₂BC system. This fills a research gap in the field of multi-component / high-entropy boron carbide materials and expands the material spectrum of transition metal boron carbides. Based on multi-principal high-entropy design, this invention achieves targeted optimization and synergistic improvement of material properties, breaking through the performance bottlenecks of traditional binary / ternary boron carbides and providing a novel design approach for the development of new ultra-hard, high-temperature resistant ceramic materials.

[0017] 2. The ceramic prepared by this invention has a single-phase homogeneous structure with no obvious second-phase formation. The grain size can be controlled within 10-30 μm, and the relative density is ≥97%, achieving near-complete densification. This avoids the degradation of material properties by porosity and impurities, and exhibits excellent batch-to-batch performance stability. The ceramic material prepared by this invention achieves an excellent balance between high hardness and moderate fracture toughness, with a Vickers hardness of 28-38 GPa and a fracture toughness stable at 3.2-3.8 MPa·m. 1 / 2 It retains the inherent high melting point, high wear resistance, excellent chemical stability and high temperature resistance of transition metal boron carbides, while solving the defects of high brittleness and poor impact resistance that are common in traditional superhard ceramics. It can be widely adapted to the application needs of structural components under extreme working conditions.

[0018] 3. This invention abandons the reliance on expensive, high-purity boron powder and easily oxidized elemental metal powders in traditional processes. It innovatively uses readily available transition metal oxides, boron carbide, and carbon powder as core raw materials. These raw materials are widely available and inexpensive, significantly reducing procurement costs and offering substantial economies of scale. It addresses the inherent defects of traditional elemental metal powder raw materials from the source: avoiding the problem of metal powder spreading during ball milling and resulting in uneven mixing, while also eliminating the risk of oxidation during grinding. This significantly improves the uniformity of raw material mixing and reduces the difficulty of quality control in the production process. The material composition design of this invention is highly flexible. The M-position can flexibly select four or more elements from transition metals such as Mo, W, Cr, Ta, V, Nb, Ni, and Fe. The molar ratio of each element can be precisely controlled within the range of 0-0.9. The mechanical, high-temperature resistance, and corrosion resistance properties of the material can be optimized through elemental ratio design, adapting to the personalized application needs of different scenarios.

[0019] 4. This invention pioneers a boronothermic-carbothermic reduction reaction pathway, achieving low-temperature and efficient synthesis of multi-element transition metal boron carbide powders: the powder synthesis heat treatment temperature is only 1500-1750℃, far lower than the ultra-high temperature process of 2500℃ in traditional electric arc melting, and also significantly lower than the temperature requirements of traditional hot pressing synthesis, greatly reducing production energy consumption and equipment entry barriers. The process flow is simple and controllable, requiring only three core steps: ball milling, vacuum heat treatment, and sintering. It eliminates the need for complex operations such as repeated melting in traditional processes, resulting in a short process step, low operational threshold, and suitability for large-scale continuous production. This invention innovatively designs an argon gas replacement process during vacuum heat treatment, which effectively removes reaction byproduct gases, inhibits impurity phase formation, and significantly improves the purity of the powder product; simultaneously, the prepared powder particle size is uniformly controllable at 0.9-1.7μm, providing an excellent raw material basis for subsequent sintering densification. The sintering process of this invention is highly versatile, compatible with various mainstream sintering methods such as pressureless sintering, spark plasma sintering, hot pressing sintering, and selective laser sintering. The process parameters can be flexibly adjusted according to the product form and performance requirements, adapting to the needs of all scenarios from laboratory research and development to industrial mass production. Attached Figure Description

[0020] Figure 1 The (Mo) obtained in Example 1 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25 XRD pattern of 2BC powder.

[0021] Figure 2 The (Mo) obtained in Example 1 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25SEM and elemental distribution diagram of 2BC powder.

[0022] Figure 3 The (Mo) obtained in Example 1 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25 XRD pattern of 2BC ceramic.

[0023] Figure 4 The (Mo) obtained in Example 1 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25 SEM and elemental distribution diagram of 2BC ceramics.

[0024] Figure 5 The (Mo) obtained in Example 2 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25 XRD pattern of 2BC ceramic.

[0025] Figure 6 The (Mo) obtained in Example 2 of this invention 0.25 W 0.25 Cr 0.25 Ta 0.25 SEM and elemental distribution diagram of 2BC ceramics. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0027] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0028] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available chemical raw materials that are known in the market.

[0029] This invention provides a high-purity, low-cost powder preparation method to replace the traditional boronothermal reduction method. Traditional methods rely on expensive boron powder, and the metal powder raw materials used are prone to oxidation during grinding. The method for preparing a micron-sized multi-element transition metal boron carbide ceramic according to this invention specifically includes the following steps: Step 1: Raw Material Mixing. Select 4-8 commercially available micron-sized transition metal oxide powders, B4C, and C powders as raw materials, ensuring that all powders have a particle size of 1-3 μm and a purity of not less than 99 wt%. Use anhydrous ethanol as the solvent and zirconia balls as the grinding media to ball-mill the raw materials for 12 hours. The resulting slurry is dried by rotary evaporation at 60°C. The dried material is then crushed and sieved to obtain a uniform mixed powder.

[0030] Step 2, Vacuum Heat Treatment: The uniformly mixed powder obtained after sieving in Step 1 is pressed into a green body (or block) under a pressure range of 3-20 MPa. Then, the block material is placed in a graphite crucible lined with graphite paper and transferred into a graphite carbon tube furnace for vacuum heat treatment. To improve the purity of boron carbides, during the vacuum holding process, the reaction is degassed. When the vacuum level returns to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated. This process is repeated 2-3 times, which helps to improve the purity of the boron carbide powder.

[0031] Step 3: After crushing and grinding the obtained powder, place it in a graphite mold; calcine the powder using pressureless sintering / discharge plasma sintering / hot pressing sintering / selective laser sintering to obtain high-entropy boron carbide ceramics.

[0032] Preferably, the vacuum heat treatment temperature range in step 2 is 1500-1750℃, the holding time range is 30-90 min, and the heating rate range is 20-300℃ / min. To avoid the formation of other borides or carbides during the reaction, the upper limit of B4C addition is strictly limited during the ingredient preparation process. (7.6) <MO x / B4C<8.8). And the heating rate is increased to more than 20℃ / min. The sintering temperature in step 3 is 1750-1950℃, the axial pressure is 0-100MPa, the holding time is 10-90min, and the heating rate is 20-400℃ / min.

[0033] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0034] Example 1 Step 1: Select and weigh commercially available raw materials: 3.46g MoO3 powder, 5.58g WO3 powder, 1.83g Cr2O3 powder, 5.31g Ta2O5 powder, 0.66g B4C powder, and 3.15g C powder. Combine 20g of the above raw material powders with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0035] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground for subsequent pressureless sintering.

[0036] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. The powder is then calcined using pressureless sintering to obtain high-entropy boron carbide ceramics. The sintering temperature is 1900℃, the holding time is 90 min, and the heating rate is 20℃ / min.

[0037] (Mo) prepared according to the above method 0.25 W 0.25 Cr 0.25 Ta 0.25 For XRD, SEM, elemental distribution, and XRD patterns of 2BC powder and ceramics, please refer to [reference needed]. Figures 1-4 The results showed that no obvious second phase was detected in the sample. The ceramic grains exhibited a strip-like crystal structure and were fine, with a grain size of 23.61 μm and a relative density of 98.61%. Subsequent mechanical testing revealed a high hardness of 34.86 ± 0.93 GPa and a fracture toughness of 3.26 ± 0.37 MPa. 1 / 2 .

[0038] Example 2 Step 1: Select and weigh commercially available raw materials: 3.46g MoO3 powder, 5.58g WO3 powder, 1.83g Cr2O3 powder, 5.31g Ta2O5 powder, 0.66g B4C powder, and 3.15g C powder. Combine 20g of the above raw material powders with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0039] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent spark plasma sintering.

[0040] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. The powder is then calcined using spark plasma sintering to obtain high-entropy boron carbide ceramics. The sintering temperature is 1750℃, the axial pressure is 60MPa, the holding time is 10min, and the heating rate is 100℃ / min.

[0041] (Mo) prepared according to the above method 0.25 W 0.25 Cr 0.25 Ta 0.25 For XRD, SEM, elemental distribution, and XRD patterns of 2BC powder and ceramics, please refer to [reference needed]. Figures 5-6 The results showed that no obvious second phase was detected in the sample. The ceramic grains exhibited a strip-like crystal structure and were fine, with a grain size of 14.53 μm and a relative density of 98.95%. Subsequent mechanical testing revealed a high hardness of 37.89 ± 0.76 GPa and a fracture toughness of 3.63 ± 0.32 MPa. 1 / 2 .

[0042] Example 3 Step 1: Select and weigh commercially available raw materials: 3.46g MoO3 powder, 5.58g WO3 powder, 1.83g Cr2O3 powder, 5.31g Ta2O5 powder, 0.66g B4C powder, and 3.15g C powder. Combine 20g of the above raw material powders with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0043] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent hot pressing sintering.

[0044] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. The powder is then calcined using hot pressing to obtain high-entropy boron carbide ceramics. The sintering temperature is 1750℃, the axial pressure is 60MPa, the holding time is 30min, and the heating rate is 20℃ / min.

[0045] The ceramics prepared in the above steps were characterized by XRD. XRD testing confirmed that the ceramics prepared through the above steps were (Mo) 0.25 W 0.25 Cr 0.25 Ta 0.25 The ceramic consisted of 2BC grains with no second phase detected, a grain size of 16.19 μm, and a relative density of 98.32%. Mechanical testing revealed a high hardness of 37.08 ± 1.14 GPa and a fracture toughness of 3.53 ± 0.29 MPa. 1 / 2 .

[0046] Example 4 Step 1: Select and weigh commercially available raw materials: 3.46g MoO3 powder, 5.58g WO3 powder, 1.83g Cr2O3 powder, 5.31g Ta2O5 powder, 0.66g B4C powder, and 3.15g C powder. Combine 20g of the raw material powder with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0047] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent selective laser sintering.

[0048] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. High-entropy boron carbide ceramics are obtained by selective laser sintering (SLS). The sintering temperature is 1750℃, the axial pressure is 60MPa, the holding time is 30min, and the heating rate is 20℃ / min.

[0049] The ceramics prepared in the above steps were characterized by XRD. The results showed that no obvious second phase was detected in the sample, the grain size was 15.04 μm, and the relative density was 97.72%. Subsequently, mechanical testing revealed that the ceramics had a hardness of 37.38 ± 0.81 GPa and a fracture toughness of 3.48 ± 0.27 MPa. 1 / 2 .

[0050] Example 5 Step 1: Select and weigh commercially available raw materials: 2.99g MoO3 powder, 4.82g WO3 powder, 1.58g Cr2O3 powder, 4.59g Ta2O5 powder, 1.89g V2O5 powder, 0.72g B4C powder, and 3.41g C powder. Combine 20g of the raw material powder with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0051] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent spark plasma sintering.

[0052] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. The powder is then calcined using spark plasma sintering to obtain high-entropy boron carbide ceramics. The sintering temperature is 1750℃, the axial pressure is 60MPa, the holding time is 10min, and the heating rate is 100℃ / min.

[0053] XRD testing confirmed that the ceramic prepared through the above steps was (Mo). 0.2 W 0.2 Cr 0.2 Ta 0.2 V 0.2 The ceramic consisted of 2BC grains, with no second phase detected. The grain size was 18.34 μm, and the relative density was 97.63%. Mechanical testing revealed a high hardness of 33.96 ± 0.54 GPa and a fracture toughness of 3.35 ± 0.29 MPa. 1 / 2 .

[0054] Example 6 Step 1: Select and weigh the following commercially available raw materials: 2.54g MoO3 powder, 4.09g WO3 powder, 1.34g Cr2O3 powder, 3.89g Ta2O5 powder, 1.60g V2O5 powder, 2.34g Nb2O5 powder, 0.73g B4C powder, and 3.47g C powder. Combine 20g of the raw material powder with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder. (The ingredient ratios must be provided, regardless of whether they are equimolar or not.) Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent spark plasma sintering.

[0055] Step 3: The obtained powder is crushed and ground, then placed in a graphite mold. The powder is then calcined using spark plasma sintering to obtain high-entropy boron carbide ceramics. The sintering temperature is 1750℃, the axial pressure is 60MPa, the holding time is 10min, and the heating rate is 100℃ / min.

[0056] XRD testing confirmed that the ceramic prepared through the above steps was (Mo). 0.167 W 0.167 Cr 0.167 Ta 0.167 V 0.167 Nb 0.1 67 The ceramic consisted of 2BC grains, with no second phase detected. The grain size was 15.84 μm, and the relative density was 99.07%. Mechanical testing revealed a high hardness of 34.33 ± 1.47 GPa and a fracture toughness of 3.28 ± 0.24 MPa. 1 / 2 .

[0057] Example 7 Step 1: Weigh the commercially available raw materials: 2.34g MoO3 powder, 3.76g WO3 powder, 1.23g Cr2O3 powder, 3.59g Ta2O5 powder, 1.48g V2O5 powder, 1.21g NiO powder, 2.16g Nb2O5 powder, 0.78g B4C powder, and 3.45g C powder. Combine the total 20g of raw material powder with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0058] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent spark plasma sintering.

[0059] The obtained powder was crushed and ground, then placed in a graphite mold. High-entropy boron carbide ceramics were prepared by spark plasma sintering. The sintering temperature was 1750℃, the axial pressure was 60MPa, the holding time was 10min, and the heating rate was 100℃ / min.

[0060] XRD testing confirmed that the ceramic prepared through the above steps was (Mo). 0.14 W 0.14 Cr 0.14 Ta 0.14 V 0.14 Ni 0.14 Nb 0.14 The ceramic consisted of 2BC grains with no second phase detected, a grain size of 20.37 μm, and a relative density of 98.62%. Mechanical testing revealed a high hardness of 30.09 ± 2.17 GPa and a fracture toughness of 3.58 ± 0.32 MPa. 1 / 2 .

[0061] Example 8 Step 1: Weigh the commercially available raw materials: 2.16g MoO3 powder, 3.47g WO3 powder, 1.14g Cr2O3 powder, 3.31g Ta2O5 powder, 1.36g V2O5 powder, 1.12g NiO powder, 1.16g Fe3O4 powder, 1.99g Nb2O5 powder, 0.83g B4C powder, and 3.47g C powder. Combine 20g of the raw material powder with 50g anhydrous ethanol and 40g yttrium-stabilized zirconia balls (material-to-ball mass ratio controlled at approximately 1:2) in a ball mill jar and ball mill for 12 hours. After ball milling, dry the resulting slurry using a rotary evaporator at 60°C for 1 hour. Then, pass the dried material through a 200-mesh sieve to obtain a uniform dry-mixed powder.

[0062] Step 2: Take the dry-mixed powder obtained above and dry-press it under a pressure of 3-20 MPa for 1 min to form a mixed powder block. Place the block in a graphite crucible lined with graphite paper and transfer it to a graphite carbon tube furnace for vacuum heat treatment. During the vacuum holding process, the reaction is released. When the vacuum degree recovers to below 50 Pa, high-purity Ar is introduced for gas replacement. After reaching 1 atmosphere, the vacuum is re-evacuated, and this process is repeated 3 times. The heat treatment process parameters are set as follows: heating rate 20℃ / min, heat treatment temperature 1650℃, and holding time 90 min. The obtained powder is crushed and ground before being used for subsequent spark plasma sintering.

[0063] The obtained powder was crushed and ground, then placed in a graphite mold. High-entropy boron carbide ceramics were prepared by spark plasma sintering. The sintering temperature was 1750℃, the axial pressure was 60MPa, the holding time was 10min, and the heating rate was 100℃ / min.

[0064] XRD testing confirmed that the ceramic prepared through the above steps was (Mo). 0.13 W 0.13 Cr 0.13 Ta 0.13 V 0.13 Ni 0.13 Nb 0.13 Fe 0.13 The ceramic consisted of 2BC grains with no second phase detected, a grain size of 26.89 μm, and a relative density of 99.44%. Mechanical testing revealed a high hardness of 28.73 ± 1.86 GPa and a fracture toughness of 3.77 ± 0.29 MPa. 1 / 2 .

[0065] In summary, this invention successfully prepared single-phase multi-element transition metal boron carbide ceramics, and the synthesized ceramic samples were confirmed by XRD combined with SEM characterization techniques to have fine grain size, high Vickers hardness, and moderate fracture toughness.

[0066] It should be noted that the above embodiments are merely preferred examples of the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications, substitutions, or variations can be made to the technical solutions of the present invention without departing from the core concept of the present invention, and none of these require creative effort.

[0067] Therefore, any modifications, equivalent substitutions, and improvements made based on the inventive concept should fall within the scope of protection defined by the claims of this invention. In other words, any technical solution that can be readily obtained by a person skilled in the art through conventional logical analysis, reasoning, or a limited number of experiments based on the technical solution disclosed in this invention should be considered within the scope of protection defined by the claims of this invention.

Claims

1. A multi-element transition metal boron carbide ceramic, characterized in that, The ceramic has the molecular formula (M)2BC, where M is at least four different transition metal elements, each with a mole fraction greater than 0 and less than 0.9, and the sum of the mole fractions of all transition metal elements is 1.

2. The multi-element transition metal boron carbide ceramic according to claim 1, characterized in that, M is at least four of the following: Mo, W, Cr, Ta, V, Nb, Ni, and Fe.

3. The multi-element transition metal boron carbide ceramic according to claim 1, characterized in that, The ceramic has a single-phase structure with a grain size of 10-30 μm, a relative density of ≥97%, a Vickers hardness of 28-38 GPa, and a fracture toughness of 3.2-3.8 MPa·m. 1 / 2 .

4. A low-cost preparation method for multi-component transition metal boron carbide ceramics as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) At least four transition metal oxides MO x The powder, boron carbide (B4C) powder, and carbon (C) powder are mixed, ball-milled, dried, and sieved to obtain a mixed powder. (2) The mixed powder is pressed into a blank and heat-treated under vacuum conditions. During the reaction, gas replacement is carried out to obtain multi-element transition metal boron carbide powder. (3) The powder is sintered to obtain a dense multi-element transition metal boron carbide ceramic.

5. The preparation method according to claim 4, characterized in that, In step (1), the transition metal oxide MO x The molar ratio of powder, boron carbide (B4C) powder, and carbon (C) powder is 7.

6. <MO x / B4C<8.8, 0.36 <MO x / C<0.42; the purity of the transition metal oxide powder is ≥99wt%, and the particle size is 1-3μm.

6. The preparation method according to claim 4, characterized in that, The heat treatment temperature in step (2) is 1500-1750℃, the holding time is 30-90min, and the heating rate is 20-300℃ / min.

7. The preparation method according to claim 4, characterized in that, The gas replacement process described in step (2) is as follows: during the vacuum heat treatment process, when the vacuum degree is restored to below 50 Pa, argon gas is introduced to atmospheric pressure and then the vacuum is evacuated again, and this process is repeated 2-3 times.

8. The preparation method according to claim 4, characterized in that, The sintering method mentioned in step (3) is any one of pressureless sintering, spark plasma sintering, hot pressing sintering or selective laser sintering.

9. The preparation method according to claim 4 or 8, characterized in that, The sintering temperature in step (3) is 1750-1950℃, the holding time is 10-90min, the heating rate is 20-400℃ / min, and the axial pressure is 0-100MPa.

10. The preparation method according to claim 4, characterized in that, The particle size of the multi-element transition metal boron carbide powder obtained in step (2) is 0.9-1.7 μm.

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