Boron carbide bulletproof ceramic material and preparation method thereof

Abstract

The invention belongs to the technical field of bulletproof ceramic preparation, and provides a boron carbide bulletproof ceramic material and a preparation method thereof. The method comprises the following steps: firstly, carrying out reduction treatment on molybdenum trioxide in a hydrogen atmosphere to prepare reduced molybdenum dioxide; secondly, mixing boron carbide, reduced molybdenum dioxide and an auxiliary agent with a specific proportion with a solvent, uniformly mixing through a ball milling process, then carrying out vacuum drying and sieving treatment to prepare uniform mixed powder, carrying out one-way pressurization cold pressing preforming on the mixed powder, and further improving the compactness of a green body through cold isostatic pressing; a green body is subjected to gradient heating sintering and sequentially subjected to a reduction activation stage and a densification stage, a high-densification structure of the ceramic material is achieved, finally, a sintered body is subjected to hot isostatic pressing treatment, the internal structure of the material is further optimized, the compactness and the mechanical property are improved, and the ceramic material is suitable for the field of bulletproof materials.

Description

Technical Field

[0001] This invention belongs to the field of bulletproof ceramic preparation technology, and relates to a boron carbide bulletproof ceramic material and its preparation method. Background Technology

[0002] Boron carbide is a highly promising functional ceramic material, widely used in defense, aerospace, nuclear energy, and abrasive industries due to its excellent physical and chemical properties. Its low density, high hardness, high melting point, and strong chemical stability give it irreplaceable advantages, particularly in bulletproof armor materials. The high hardness and thermal stability of boron carbide ceramics stem from its unique crystal structure and strong covalent bonds. However, this characteristic also results in extremely high sintering activation energy, requiring very high temperatures for complete densification using traditional additive-free sintering methods. Since the sintering temperature of boron carbide is close to its intrinsic melting point, this not only places stringent demands on equipment but also easily leads to residual porosity formation during sintering, thus weakening its mechanical properties. Furthermore, traditional additives may undergo complex interfacial reactions with boron carbide or other system components during sintering, generating high-melting-point metallic or brittle phases. This not only reduces the fluidity of the additives and weakens the effect of liquid-phase sintering but also exacerbates the conflict between strength and toughness.

[0003] Chinese patent CN106631028A discloses a preparation process for metal-composite magnesium silicon carbide bulletproof ceramics. The production steps are as follows: Pre-mix metallic aluminum, nano-alumina, and cerium oxide; using silicon carbide and high-purity sintered magnesium oxide as main raw materials, add an appropriate amount of phenolic resin, and then add the pre-mixed metallic aluminum, nano-alumina, and cerium oxide powder to prepare metal-composite magnesium silicon carbide bulletproof ceramic powder; pack the prepared metal-composite magnesium silicon carbide bulletproof ceramic powder into a low-carbon steel casing, use nitrogen as a medium, and heat the casing through electromagnetic or resistance heating; apply pressure and maintain the temperature using hot isostatic pressing to obtain a green body of the corresponding shape; then obtain the desired shape of bulletproof ceramic by wire cutting. In this technical solution, the ceramic uses metal powder composite ceramic raw materials, which improves impact strength but degrades toughness. Therefore, how to effectively avoid the formation of high-melting-point metal phases or weak interface phases while achieving a balance between ceramic strength and toughness is a significant challenge in current boron carbide sintering technology research. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a boron carbide bulletproof ceramic material and its preparation method. First, molybdenum trioxide is partially reduced in a hydrogen atmosphere to convert it into reduced molybdenum dioxide. Then, boron carbide, reduced molybdenum dioxide, and additives (composed of ferric oxide, silicon nitride, and boron nitride) are mixed. The components are fully dispersed and uniformly mixed using wet ball milling. The resulting mixed powder is then subjected to unidirectional pressure preforming and cold isostatic pressing to obtain a green body. The green body is sintered in an inert atmosphere. The sintering process is divided into a reduction activation stage and a densification stage to optimize the microstructure of the ceramic material. Finally, high-temperature and high-pressure hot isostatic pressing further eliminates internal defects and improves the material's density and mechanical properties, thereby meeting the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing boron carbide bulletproof ceramic material, the method comprising:

[0007] S1, molybdenum trioxide is placed in a hydrogen atmosphere and kept at a constant temperature to obtain reduced molybdenum dioxide;

[0008] S2, Boron carbide, reduced molybdenum dioxide, additives and ethanol are mixed and then ball-milled to obtain a mixed powder;

[0009] S3. The mixed powder is cold-pressed under unidirectional pressure to obtain a preliminary green body, which is then transferred to a cold isostatic press for holding pressure to obtain a green body. The green body is placed in an argon atmosphere for gradient heating sintering, which consists of a reduction activation stage and a densification stage. After the densification stage is completed, the body is cooled and removed to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing to obtain a boron carbide bulletproof ceramic material.

[0010] Specifically, it includes:

[0011] S1, Molybdenum trioxide is placed in a hydrogen atmosphere and the temperature is adjusted to the first temperature and held to obtain reduced molybdenum dioxide;

[0012] S2, Boron carbide, reduced molybdenum dioxide, additives and ethanol are mixed and ball-milled, then vacuum dried and sieved to obtain a mixed powder;

[0013] S3, the mixed powder is cold-pressed under unidirectional pressure to obtain a preliminary green body, which is then transferred to a cold isostatic press for holding pressure to obtain a green body. The green body is placed in an argon atmosphere for gradient heating sintering, which consists of a reduction activation stage and a densification stage. After the densification stage, it is cooled to a second temperature and removed to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing to obtain a boron carbide bulletproof ceramic material.

[0014] Molybdenum oxide is often used as a sintering aid or a precursor for reinforcing phases in the preparation of high-temperature ceramics. However, directly using molybdenum trioxide (MoO3) presents two major problems. First, it is unstable at high temperatures; MoO3 is prone to volatilization above 700°C, leading to component loss and increased material porosity. Second, there is a risk of over-reduction. During sintering, if MoO3 comes into direct contact with boron carbide, it may be over-reduced to metallic molybdenum. Metallic molybdenum has an extremely high melting point, making it difficult to form a liquid phase and hindering particle rearrangement and densification. Therefore, the core significance of the pre-reduction step lies in converting the volatile MoO3 into the more thermally stable molybdenum dioxide (MoO2). By controlling the degree of reduction in advance, the direct formation of metallic molybdenum or other undesirable phases is prevented, thereby achieving in-situ synthesis and uniform distribution of the reinforcing phase. In a hydrogen atmosphere, hydrogen initially contacts and adsorbs onto the MoO3 surface. Hydrogen molecules dissociate into active hydrogen atoms on the molybdenum oxide surface. These hydrogen atoms gradually attack the lattice oxygen of MoO3, combining with the oxygen in MoO3 to form water molecules. Simultaneously, the oxidation state of molybdenum decreases from +6 (MoO3) to +4 (MoO2). This stage is dominated by surface reactions, and the reaction rate is limited by hydrogen diffusion and lattice oxygen migration. The generated MoO2 retains some oxygen vacancies in its lattice; these defect sites enhance the subsequent reactivity with boron carbide (B4C), promoting the diffusion and bonding of boron and carbon atoms. Furthermore, the layered crystal structure of MoO2 guides the directional growth of the reinforcing phase during sintering, forming an anisotropic microstructure beneficial to mechanical properties. Compared to pristine molybdenum trioxide, the pre-reduced material exhibits superior interfacial wettability, which is crucial for particle rearrangement and densification during the liquid-phase sintering stage. The core role of the pre-reduced product MoO2 in the sintering stage is reflected in two aspects: staged reaction control. In the early stage of sintering, MoO2 undergoes a solid-solid reaction with B4C to gradually generate the molybdenum diboride (MoB2) reinforcing phase. Compared with the direct use of MoO3, this stepwise reaction can avoid micro-cracks caused by violent exothermic reactions. Secondly, it controls the liquid phase formation. By controlling the content of MoO2 through pre-reduction, the liquid phase formation temperature and viscosity of the Fe2O3-B4C system can be indirectly affected, thereby optimizing the "soft matrix-hard particle" composite structure.

[0015] During the sintering process of boron carbide bulletproof ceramics, molybdenum atoms, due to their high electronegativity, attract boron atoms from boron carbide, forming localized electron-rich regions. This charge polarization weakens the stability of the original chemical bonds. After detaching from the boron carbide lattice, boron atoms diffuse along the grain boundaries towards molybdenum dioxide. Oxygen atoms in the molybdenum dioxide lattice combine with the carbon atoms released from boron carbide to generate gaseous carbon monoxide. The escape of this gas forms a microscopic channel network within the material. These channels not only provide pathways for material transport but also guide the direction of liquid phase penetration through capillary action. Simultaneously, the valence state of molybdenum continuously decreases, gradually transitioning from tetravalent to zero-valent metallic state. The newly formed metallic molybdenum particles have high surface energy and tend to aggregate to form nanoclusters, becoming active sites for boron atom adsorption, forming molybdenum diboride. The interaction between iron oxide and boron carbide triggers selective melting, with the boron-rich phase preferentially dissolving to form a eutectic liquid phase. Iron ions in the melt combine with free boron atoms through coordination bonds to form a network-like metallic boride framework. Silicon nitride nanoparticles form covalent bonds with boron atoms of boron carbide through surface hydroxyl groups, constructing a three-dimensional pinning network at grain boundaries. During high-temperature grain boundary migration, silicon atoms generated from the partial decomposition of silicon nitride infiltrate into the boron carbide lattice, inducing lattice distortion. The incorporation of silicon atoms enhances the intrinsic hardness of the material. The layered structure of boron nitride nanosheets undergoes orientation rearrangement during sintering, with its basal plane ultimately parallel to the hot-pressing direction. When cracks propagate, they first encounter the weak bonding interfaces between the nanosheet layers. The interface debonding process consumes fracture energy, and the plastic deformation capability provided by interlayer shear slip allows the material to slow crack propagation through energy dissipation when subjected to impact.

[0016] In the initial stage of sintering, the core objective is to clean the surface of powder particles and stimulate their reactivity through pyrolysis and chemical reactions. Since the powder is typically prepared using processes like ball milling, impurities, including oxides, residual organic matter, or moisture, may be adsorbed on the particle surface. These surface impurities significantly reduce the bonding ability between particles, necessitating removal through chemical reactions at low temperatures. For example, the reduction and decomposition reactions of oxides transform the particle surface into lower-energy substances, while the generated volatile products are carried away by the atmospheric gas. Furthermore, organic residues introduced during ball milling undergo pyrolysis at low temperatures, generating small molecule gases that are also expelled. This process strengthens the direct contact between powder particles, providing favorable interfacial conditions for subsequent high-temperature densification. As the temperature gradually increases, sintering enters the intermediate-temperature stage, where significant interfacial reactions and grain growth begin to occur. Additives play a crucial role in this stage; they are typically highly reactive compounds that can react with the main components of the sintering system within the intermediate-temperature range, generating low-melting-point mesophases. This intermediate phase exists as a liquid phase at certain temperatures, which wets the surface of powder particles, thereby reducing the interfacial energy between particles and promoting particle rearrangement and bonding. The presence of the liquid phase can also significantly reduce the sintering temperature, reducing the potential problem of excessive grain growth during sintering. Simultaneously, the diffusion process within the particles also manifests at this stage. Due to the increase in temperature, atoms within the particles begin to migrate through bulk diffusion and grain boundary diffusion, driving the gradual formation and growth of particles. At the high-temperature stage, sintering enters the densification stage, and the powder system undergoes significant pore closure and grain growth, ultimately forming a highly dense ceramic material structure. Due to the significantly increased diffusion coefficient at high temperatures, the mass migration efficiency between particles is further enhanced, and the bonding between particles becomes tighter. Driven by surface energy, the porosity between particles gradually decreases, and residual gases inside are discharged through diffusion or liquid phase flow. With the elimination of porosity, the bulk density of the material continuously increases, ultimately forming a dense ceramic structure. Liquid phase additives can further reduce the activation energy of grain boundary migration, making the bonding between grains even tighter, while also inhibiting excessive grain growth and preventing material performance degradation. The densification process at high temperatures is accompanied by grain rearrangement and optimization. This rearrangement is achieved through grain boundary migration and interface energy reduction, ultimately resulting in ceramic materials with a uniform microstructure. Gradient heating sintering achieves material densification and performance optimization through chemical and physical processes. At low temperatures, removing surface impurities and activating particle activity provides favorable interfacial conditions for sintering. At medium temperatures, initial particle bonding and rearrangement are achieved through interfacial reactions, diffusion mechanisms, and the action of liquid-phase additives. At high temperatures, final densification is achieved through pore closure and grain optimization, optimizing the microstructure and mechanical properties of boron carbide ceramics.

[0017] As a preferred embodiment of the present invention, in S1, the flow rate of hydrogen is 4-5 L / min, for example, it can be 4.0 L / min, 4.1 L / min, 4.2 L / min, 4.3 L / min, 4.4 L / min, 4.5 L / min, 4.6 L / min, 4.7 L / min, 4.8 L / min, 4.9 L / min or 5.0 L / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In some alternative instances, the first temperature is 580-600°C, for example, it can be 580°C, 582°C, 584°C, 586°C, 588°C, 590°C, 592°C, 594°C, 596°C, 598°C, or 600°C, and the heating rate is 5-8°C / min, for example, it can be 5.0°C / min, 5.3°C / min, 5.6°C / min, 5.9°C / min, 6.2°C / min, 6.5°C / min, 6.8°C / min, 7.1°C / min, 7.4°C / min, 7.7°C / min, or 8.0°C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some optional instances, the heat preservation time is 1-2 hours, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] As a preferred embodiment of the present invention, in S2, the boron carbide D 50 ≤5μm.

[0021] In some alternative examples, the mass ratio of boron carbide, reduced molybdenum dioxide, and auxiliaries is (95-97):(0.8-1.2):(3.5-6), for example, (95.0, 95.2, 95.4, 95.6, 95.8, 96.0, 96.2, 96.4, 96.6, 96.8, or 97.0):(0.80, 0.84, 0.88, 0.92, 0.96, 1.00, 1.04, 1.08, 1.12, 1.16, or 1.20):(3.50, 3.75, 4.00, 4.25, 4.50, 4.75, 5.00, 5.25, 5.50, 5.75, or 6.00), but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0022] In some alternative examples, the additive is ferric oxide, silicon nitride, and boron nitride in a mass ratio of (2-3):(1-2):(0.5-1), for example, (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0):(1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0):(0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 1.00), but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] In some optional instances, the silicon nitride's D 50 ≤10μm.

[0024] In some alternative instances, the boron nitride has a sheet diameter of 1-2 μm, for example, it may be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2.0 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In some optional instances, the ball-to-material ratio of the ball mill is 5:1, and the milling time is 6-7 hours, for example, 6.0 hours, 6.1 hours, 6.2 hours, 6.3 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.7 hours, 6.8 hours, 6.9 hours, or 7.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0026] In some optional instances, the vacuum drying temperature is 80-90°C, for example, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] In some optional instances, the sieve mesh size is 200 mesh.

[0028] As a preferred technical solution of the present invention, in S3, the pressure of the unidirectional pressurization is 100-110 MPa, for example, it can be 100 MPa, 101 MPa, 102 MPa, 103 MPa, 104 MPa, 105 MPa, 106 MPa, 107 MPa, 108 MPa, 109 MPa or 110 MPa, and the pressurization time is 2-3 min, for example, it can be 2.0 min, 2.1 min, 2.2 min, 2.3 min, 2.4 min, 2.5 min, 2.6 min, 2.7 min, 2.8 min, 2.9 min or 3.0 min, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] In some optional instances, the pressure of the cold isostatic press is 200-210 MPa, for example, 200 MPa, 201 MPa, 202 MPa, 203 MPa, 204 MPa, 205 MPa, 206 MPa, 207 MPa, 208 MPa, 209 MPa or 210 MPa, and the holding time is 10-12 min, for example, 10.0 min, 10.2 min, 10.4 min, 10.6 min, 10.8 min, 11.0 min, 11.2 min, 11.4 min, 11.6 min, 11.8 min or 12.0 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In some optional examples, during the reduction and activation stage, the temperature is raised from room temperature to 800-810°C, for example, 800°C, 801°C, 802°C, 803°C, 804°C, 805°C, 806°C, 807°C, 808°C, 809°C, or 810°C, at a heating rate of 5°C / min, and held for 30-40 min, for example, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, or 40 min. After holding, the gas is vented and argon gas is maintained. Continue heating the atmosphere to 1400-1420℃, for example, 1400℃, 1402℃, 1404℃, 1406℃, 1408℃, 1410℃, 1412℃, 1414℃, 1416℃, 1418℃ or 1420℃, at a heating rate of 2℃ / min, and holding for 5-6 hours, for example, 5.0h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h or 6.0h, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] In some optional instances, the densification stage continues to be heated to 1850-1870℃, for example, 1850℃, 1852℃, 1854℃, 1856℃, 1858℃, 1860℃, 1862℃, 1864℃, 1866℃, 1868℃ or 1870℃, at a heating rate of 10℃ / min, and the holding time is 2-3h, for example, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0032] In some alternative instances, the second temperature is 200-210°C, for example, it can be 200°C, 201°C, 202°C, 203°C, 204°C, 205°C, 206°C, 207°C, 208°C, 209°C or 210°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional examples, the temperature of the hot isostatic pressing is 1800-1820°C, for example, 1800°C, 1802°C, 1804°C, 1806°C, 1808°C, 1810°C, 1812°C, 1814°C, 1816°C, 1818°C, or 1820°C, and the pressure is 150-160 MPa, for example, 150 MPa, 151 MPa, 152 MPa, 153 MPa, or 150 MPa. The holding time is 2-3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] In a second aspect, the present invention provides a boron carbide bulletproof ceramic material prepared by the preparation method described in the first aspect.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The volatile MoO3 is converted into the more thermally stable MoO2 by hydrogen reduction. By controlling the degree of reduction in advance, the generation of metallic molybdenum or other unfavorable phases in subsequent processes is prevented, and the in-situ synthesis and uniform distribution of the reinforcing phase are achieved. The generated MoO2 retains some oxygen vacancies in its lattice, which can enhance the subsequent reaction activity with B4C and promote the diffusion and bonding of boron and carbon atoms. Compared with the original molybdenum trioxide, the material after pre-reduction treatment exhibits better interfacial wettability; (2) Fe2O3 forms a liquid phase during sintering, which promotes particle rearrangement and densification through capillary force. The pinning effect of silicon nitride Si3N4 nanoparticles at the grain boundaries inhibits abnormal grain growth through local stress field distortion. The silicon carbide SiC transition layer generated by decomposition further strengthens the interfacial bonding. Boron nitride (BN) nanosheets, with their unique layered structure, dissipate energy through mechanisms such as interfaces during crack propagation. The liquid phase generated by the additive can fill the pores between particles through fluidity during sintering, while promoting the closure of pores and improving the volume density and uniformity of ceramic materials. (3) By introducing a unique composite additive system, rapid densification sintering of boron carbide ceramics can be achieved under extreme high temperature conditions far lower than those required by traditional processes. This eliminates the microscopic pores and defects inside the material that easily lead to stress concentration and early failure, resulting in a highly homogeneous and dense ceramic matrix. This reduces energy consumption during the production process and lowers the cost of large-scale manufacturing of key components such as ceramic valves and pump valve liners. Attached Figure Description

[0036] Figure 1 The flowchart shows a method for preparing boron carbide bulletproof ceramic material according to Embodiments 1-4 of the present invention. Detailed Implementation

[0037] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0038] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0039] Example 1

[0040] This embodiment provides a boron carbide bulletproof ceramic material and its preparation method. See [link to documentation]. Figure 1The preparation method specifically includes the following steps:

[0041] S1. Molybdenum trioxide was placed in a hydrogen atmosphere with a hydrogen flow rate of 4 L / min and a heating rate of 5 °C / min. The temperature was adjusted to 580 °C and held for 1 h to obtain reduced molybdenum dioxide.

[0042] S2, 950g of boron carbide, 9g of reduced molybdenum dioxide, 35g of additives and ethanol are mixed and ball-milled. The additives are ferric oxide, silicon nitride and boron nitride in a mass ratio of 2:1:0.5. After ball milling, the mixture is vacuum dried at 88°C and sieved through a 200-mesh sieve to obtain a mixed powder.

[0043] S3. The mixed powder is pre-formed by cold pressing under unidirectional pressure of 100 MPa for 2.0 min to obtain a preliminary blank. This blank is then transferred to a cold isostatic press for holding at 200 MPa for 10 min to obtain a green blank. The green blank is then placed in an argon atmosphere for gradient heating sintering, consisting of a reduction activation stage and a densification stage. In the reduction activation stage, the temperature is raised from room temperature to 800℃ at a rate of 5℃ / min, and held for 3 minutes. After holding at 0 min, the gas is discharged while maintaining an argon atmosphere. The temperature is then increased to 1400℃ at a rate of 2℃ / min and held for 5 h. During the densification stage, the temperature is further increased to 1850℃ at a rate of 10℃ / min and held for 2 h. After the densification stage, the temperature is cooled to 200℃ and the sintered body is obtained. The sintered body is then subjected to hot isostatic pressing (HIP) at 1800℃ and 150 MPa for 2 h to obtain a boron carbide bulletproof ceramic material.

[0044] Example 2

[0045] This embodiment provides a boron carbide bulletproof ceramic material and its preparation method, the preparation method specifically including the following steps:

[0046] S1. Molybdenum trioxide was placed in a hydrogen atmosphere with a hydrogen flow rate of 5 L / min and a heating rate of 8 °C / min. The temperature was adjusted to 600 °C and held for 1.6 h to obtain reduced molybdenum dioxide.

[0047] S2, 960g of boron carbide, 8g of reduced molybdenum dioxide, 40g of additives and ethanol are mixed and ball-milled. The additives are ferric oxide, silicon nitride and boron nitride in a mass ratio of 2.2:1.2:0.6. After ball milling, the mixture is vacuum dried at 80°C and sieved through a 200-mesh sieve to obtain a mixed powder.

[0048] S3. The mixed powder is pre-formed by cold pressing under unidirectional pressure of 110 MPa for 2.5 min to obtain a preliminary blank. This blank is then transferred to a cold isostatic press for holding at 210 MPa for 12 min to obtain a green blank. The green blank is then subjected to gradient heating sintering in an argon atmosphere, consisting of a reduction activation stage and a densification stage. In the reduction activation stage, the temperature is raised from room temperature to 803°C at a rate of 5°C / min and held for 33 min. After holding at a certain temperature, the gas is discharged while maintaining an argon atmosphere. The temperature is then increased to 1410℃ at a rate of 2℃ / min and held for 5.7 hours. During the densification stage, the temperature is further increased to 1870℃ at a rate of 10℃ / min and held for 2.3 hours. After the densification stage, the temperature is cooled to 202℃ to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing (HIP) at a temperature of 1810℃, a pressure of 155 MPa, and a holding time of 2.3 hours to obtain a boron carbide bulletproof ceramic material.

[0049] Example 3

[0050] This embodiment provides a boron carbide bulletproof ceramic material and its preparation method, the preparation method specifically including the following steps:

[0051] S1, molybdenum trioxide was placed in a hydrogen atmosphere with a hydrogen flow rate of 4.2 L / min and a heating rate of 7 °C / min. The temperature was adjusted to 590 °C and held for 2.0 h to obtain reduced molybdenum dioxide.

[0052] S2, 970g boron carbide, 12g reduced molybdenum dioxide, 60g additives and ethanol are mixed and ball-milled. The additives are ferric oxide, silicon nitride and boron nitride in a mass ratio of 3:2:1. After ball milling, the mixture is vacuum dried at 90℃ and sieved through a 200-mesh sieve to obtain a mixed powder.

[0053] S3. The mixed powder is pre-formed by cold pressing under unidirectional pressure at a pressure of 103 MPa for 3.0 min to obtain a preliminary blank. This blank is then transferred to a cold isostatic press at a pressure of 203 MPa for 11 min to obtain a green blank. The green blank is then subjected to gradient heating sintering in an argon atmosphere, consisting of a reduction activation stage and a densification stage. In the reduction activation stage, the temperature is raised from room temperature to 810°C at a rate of 5°C / min and held for 40 min. After holding at a certain temperature, the gas is discharged while maintaining an argon atmosphere. The temperature is then increased to 1405℃ at a rate of 2℃ / min and held for 6.0h. During the densification stage, the temperature is further increased to 1860℃ at a rate of 10℃ / min and held for 3.0h. After the densification stage, the temperature is cooled to 210℃ to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing (HIP) at a temperature of 1820℃, a pressure of 160MPa, and a holding time of 3h to obtain a boron carbide bulletproof ceramic material.

[0054] Example 4

[0055] This embodiment provides a boron carbide bulletproof ceramic material and its preparation method, the preparation method specifically including the following steps:

[0056] S1, molybdenum trioxide was placed in a hydrogen atmosphere with a hydrogen flow rate of 4.7 L / min and a heating rate of 6 °C / min. The temperature was adjusted to 585 °C and held for 1.2 h to obtain reduced molybdenum dioxide.

[0057] S2, 950g of boron carbide, 10g of reduced molybdenum dioxide, 50g of additives and ethanol are mixed and ball-milled. The additives are ferric oxide, silicon nitride and boron nitride in a mass ratio of 2.8:1.5:0.7. After ball milling, the mixture is vacuum dried at 84℃ and sieved through a 200-mesh sieve to obtain a mixed powder.

[0058] S3. The mixed powder is pre-formed by cold pressing under unidirectional pressure of 108 MPa for 2.8 min to obtain a preliminary blank. This blank is then transferred to a cold isostatic press for holding at 206 MPa for 10.8 min to obtain a green blank. The green blank is then subjected to gradient heating sintering in an argon atmosphere, consisting of a reduction activation stage and a densification stage. In the reduction activation stage, the temperature is raised from room temperature to 807°C at a rate of 5°C / min, and held for 37 min. After holding at a certain temperature, the gas is discharged while maintaining an argon atmosphere. The temperature is then increased to 1420℃ at a rate of 2℃ / min and held for 5.4 hours. During the densification stage, the temperature is further increased to 1855℃ at a rate of 10℃ / min and held for 2.8 hours. After the densification stage, the temperature is cooled to 207℃ to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing (HIP) at a temperature of 1805℃, a pressure of 158 MPa, and a holding time of 2.9 hours to obtain a boron carbide bulletproof ceramic material.

[0059] Comparative Example 1

[0060] This comparative example provides a boron carbide bulletproof ceramic material and its preparation method. The difference between this example and Example 1 is that reduced molybdenum dioxide is not added in S2, while other process parameters and operating conditions are exactly the same as in Example 1.

[0061] Comparative Example 2

[0062] This comparative example provides a boron carbide bulletproof ceramic material and its preparation method. The difference between this example and Example 1 is that no additives are added in S2, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0063] The testing standards for flexural strength and compressive strength are GB / T 4740-2024; the testing standard for hardness is GB / T16534-2009. The test results are shown in Table 1.

[0064] Table 1. Test results of a boron carbide bulletproof ceramic material in Examples 1-4 and Comparative Examples 1-2.

[0065]

[0066]

[0067] As shown in Table 1, compared to Example 1, the flexural strength, compressive strength, and hardness of Comparative Example 1 all decreased; the flexural strength, compressive strength, and hardness of Comparative Example 2 also decreased. This is because in Comparative Example 1, the mass fraction of reduced molybdenum dioxide was 0, and the absence of MoO2 caused the system to lose its ability to generate the MoB2 reinforcing phase in situ. At the same time, the high modulus of MoB2 disappeared its contribution to the load-bearing capacity of the matrix. Therefore, the flexural strength, compressive strength, and hardness of Comparative Example 1 all decreased. In Comparative Example 2, the mass fraction of the additive was 0, and the absence of the Fe2O3 liquid phase resulted in a lack of capillary force-driven densification between particles, leading to increased porosity. The disappearance of the Si3N4 pinning effect caused abnormal grain growth, and the interparticle bonding strength decreased. Therefore, the flexural strength, compressive strength, and hardness of Comparative Example 2 all decreased.

[0068] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing boron carbide bulletproof ceramic material, characterized in that, The preparation method includes: S1, molybdenum trioxide is placed in a hydrogen atmosphere and kept at a constant temperature to obtain reduced molybdenum dioxide; S2, Boron carbide, reduced molybdenum dioxide, additives and ethanol are mixed and then ball-milled to obtain a mixed powder; S3. The mixed powder is cold-pressed under unidirectional pressure to obtain a preliminary green body, which is then transferred to a cold isostatic press for holding pressure to obtain a green body. The green body is placed in an argon atmosphere for gradient heating sintering, which consists of a reduction activation stage and a densification stage. After the densification stage is completed, the body is cooled and removed to obtain a sintered body. The sintered body is then subjected to hot isostatic pressing to obtain a boron carbide bulletproof ceramic material.

2. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S1, The flow rate of the hydrogen gas is 4-5 L / min.

3. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S2, The boron carbide D 50 ≤5μm; The mass ratio of boron carbide, reduced molybdenum dioxide, and auxiliaries is (95-97):(0.8-1.2):(3.5-6).

4. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S2, The additives are ferric oxide, silicon nitride, and boron nitride, in a mass ratio of (2-3):(1-2):(0.5-1); The D of the silicon nitride 50 ≤10μm; The boron nitride has a sheet diameter of 1-2 μm.

5. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S3, The unidirectional pressurization pressure is 100-110 MPa, and the pressurization time is 2-3 minutes.

6. The method for preparing a boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S3, The pressure of the cold isostatic press is 200-210 MPa, and the pressure holding time is 10-12 min.

7. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S3, During the reduction and activation stage, the room temperature is raised to 800-810℃ at a rate of 5℃ / min and held for 30-40min. After holding, the gas is discharged and the argon atmosphere is maintained. The temperature is then raised to 1400-1420℃ at a rate of 2℃ / min and held for 5-6h.

8. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S3, During the densification stage, the temperature is further increased to 1850-1870℃ at a rate of 10℃ / min, and the holding time is 2-3h.

9. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S3, The hot isostatic pressing is performed at a temperature of 1800-1820℃, a pressure of 150-160 MPa, and a holding time of 2-3 hours.

10. A boron carbide bulletproof ceramic material is obtained by the preparation method according to any one of claims 1-9.

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