A boron carbide ballistic-resistant ceramic material and a method of making the same

Abstract

The application belongs to the technical field of bulletproof ceramic preparation, and provides a boron carbide bulletproof ceramic material and a preparation method thereof; first, molybdenum trioxide is subjected to reduction treatment in a hydrogen atmosphere to prepare reduced molybdenum dioxide; second, boron carbide, the reduced molybdenum dioxide and an additive in a specific proportion are mixed with a solvent, uniformly mixed through a ball milling process, and then subjected to vacuum drying and sieving treatment to prepare a uniform mixed powder; the mixed powder is subjected to unidirectional pressure cold pressing preforming, and the green body is further improved in density through cold isostatic pressing; the green body is subjected to gradient temperature sintering, sequentially experiences a reduction activation stage and a densification stage, realizes a high densification structure of the ceramic material, and finally, the sintered body is subjected to hot isostatic pressing treatment, further optimizes the internal structure of the material, improves the density and mechanical properties, and is suitable for the field of bulletproof materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bulletproof ceramic preparation and relates to a boron carbide bulletproof ceramic material and a preparation method thereof. BACKGROUND

[0002] Boron carbide is a functional ceramic material with great potential, which is widely used in the fields of national defense, aerospace, nuclear energy and abrasive industry due to its excellent physical and chemical properties. Boron carbide has low density, high hardness, high melting point and strong chemical stability, and has irreplaceable advantages in bulletproof armor materials and the like. The high hardness and high thermal stability of boron carbide ceramic are derived from its unique crystal structure and strong covalent bond characteristics. However, this characteristic also makes boron carbide exhibit extremely high sintering activation energy in the sintering process, resulting in that traditional sintering methods without additives need extremely high temperature to achieve complete densification. The sintering temperature of boron carbide is close to its intrinsic melting point, which not only puts forward strict requirements on the equipment, but also easily causes problems such as residual pore formation in the sintering process, thereby weakening the mechanical properties. However, the traditional additives may have complex interfacial reactions with boron carbide or other system components in the sintering process, generating high-melting-point metal phases or brittle phases, which not only reduces the fluidity of the additives and weakens the effect of liquid-phase sintering, but also intensifies the contradiction between strength and toughness.

[0003] A Chinese patent with the publication number CN106631028A discloses a preparation process of a metal composite magnesium silicon carbide bulletproof ceramic, and the production steps are as follows: aluminum, nano-alumina and cerium oxide are pre-mixed for standby; silicon carbide and high-purity sintered magnesium oxide are used as main raw materials, a proper amount of phenolic resin is added, and the pre-mixed aluminum, nano-alumina and cerium oxide mixed powder is added to prepare a metal composite magnesium silicon carbide bulletproof ceramic powder; the prepared metal composite magnesium silicon carbide bulletproof ceramic powder is loaded into a low-carbon steel package, nitrogen is used as a medium, the package is heated by electromagnetic or resistance heating, hot isostatic pressing is used for pressing and heat preservation to obtain a corresponding shape of a green body, and a wire cutting is used to obtain a bulletproof ceramic with a required shape. In the technical solution, the ceramic uses metal powder composite ceramic raw materials, and the impact strength can be improved, but the toughness performance is poor. Therefore, how to effectively avoid the generation of high-melting-point metal phases or weak interface phases, while realizing the balance between the strength and toughness of the ceramic, is an important challenge in the current sintering technology research of boron carbide. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a boron carbide bulletproof ceramic material and a preparation method thereof, which comprises the following steps: firstly, partially reducing molybdenum trioxide in a hydrogen atmosphere to convert the molybdenum trioxide into reduced molybdenum dioxide; then mixing boron carbide, the reduced molybdenum dioxide and an additive, wherein the additive is composed of ferrous oxide, silicon nitride and boron nitride; fully dispersing and uniformly mixing the components through wet ball milling; performing unidirectional pressing preforming and cold isostatic pressing forming on the obtained mixed powder to obtain a green body; and performing sintering treatment on the green body in an inert atmosphere, wherein the sintering process is divided into a reduction activation stage and a densification stage to realize microstructure optimization of the ceramic material, and finally performing hot isostatic pressing treatment at high temperature and high pressure to further eliminate internal defects and improve the density and mechanical properties of the material, thereby meeting the needs of actual production.

[0005] To achieve the above object, the present application adopts the following technical scheme:

[0006] In a first aspect, the present application provides a preparation method of a boron carbide bulletproof ceramic material, which comprises the following steps:

[0007] S1, placing molybdenum trioxide in a hydrogen atmosphere and adjusting the temperature to a first temperature for heat preservation to obtain reduced molybdenum dioxide;

[0008] S2, mixing boron carbide, the reduced molybdenum dioxide and an additive with ethanol and then ball milling to obtain a mixed powder;

[0009] S3, performing cold pressing preforming on the mixed powder through unidirectional pressing to obtain a preliminary body, then transferring the preliminary body into a cold isostatic pressing machine for pressure preservation to obtain a green body, placing the green body in an argon atmosphere for gradient temperature rising sintering, sequentially performing a reduction activation stage and a densification stage, taking out the sintered body after the densification stage is completed, and performing hot isostatic pressing treatment on the sintered body to obtain a boron carbide bulletproof ceramic material.

[0010] Specifically, the present application comprises the following steps:

[0011] S1, placing molybdenum trioxide in a hydrogen atmosphere and adjusting the temperature to a first temperature for heat preservation to obtain reduced molybdenum dioxide;

[0012] S2, mixing boron carbide, the reduced molybdenum dioxide and an additive with ethanol and then ball milling, vacuum drying and sieving after ball milling to obtain a mixed powder;

[0013] S3, performing cold pressing preforming on the mixed powder through unidirectional pressing to obtain a preliminary body, then transferring the preliminary body into a cold isostatic pressing machine for pressure preservation to obtain a green body, placing the green body in an argon atmosphere for gradient temperature rising sintering, sequentially performing a reduction activation stage and a densification stage, taking out the sintered body after the densification stage is completed, and performing hot isostatic pressing treatment on the sintered body to obtain a boron carbide bulletproof ceramic material.

[0014] Molybdenum oxide is often used as a sintering aid or precursor of reinforcing phase in the preparation of high-temperature ceramics. However, there are two major problems in the direct use of molybdenum trioxide MoO3. First, high-temperature instability, MoO3 is easy to volatilize when the temperature exceeds 700℃, resulting in composition loss and increased material porosity. Second, the risk of excessive reduction, if MoO3 directly contacts boron carbide during sintering, it may be excessively reduced to metallic molybdenum. The melting point of metallic molybdenum is extremely high, making it difficult to form a liquid phase, hindering particle rearrangement and densification. Therefore, the core significance of the pre-reduction step is to convert volatile MoO3 into MoO2 with higher thermal stability. By pre-controlling the degree of reduction, the direct generation of metallic molybdenum or other adverse phases is prevented, thereby realizing the in-situ synthesis and uniform distribution of the reinforcing phase. In a hydrogen atmosphere, hydrogen begins to contact the surface of MoO3 and adsorb. Hydrogen molecules dissociate into active hydrogen atoms on the surface of molybdenum oxide. These hydrogen atoms gradually attack the lattice oxygen of MoO3. Hydrogen atoms combine with oxygen in MoO3 to generate water molecules, while the oxidation state of molybdenum decreases from +6(MoO3) to +4(MoO2). This stage is mainly surface reaction, and the reaction rate is limited by hydrogen diffusion and lattice oxygen migration ability. The generated MoO2 retains part of the oxygen vacancies in its lattice, which can enhance the reactivity with boron carbide B4C and promote the diffusion and bonding of boron and carbon atoms. At the same time, the layered crystal structure of MoO2 can guide the directional growth of the reinforcing phase during sintering, forming an anisotropic microstructure that is beneficial to mechanical properties. Compared with the original molybdenum trioxide, the pre-reduced material exhibits better interface wettability, which is crucial for particle rearrangement and densification during liquid phase sintering. The core role of the pre-reduction product MoO2 in the sintering stage lies in two aspects. First, the MoO2 reacts with B4C in a solid-solid reaction during the initial stage of sintering, gradually generating MoB2 reinforcing phase. Compared with the direct use of MoO3, this step-by-step reaction can avoid micro-cracks caused by intense heat release. Second, liquid phase formation regulation, 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, realizing the optimization of "soft matrix-hard particle" composite structure.

[0015] During the sintering process of boron carbide ballistic-resistant ceramics, molybdenum atoms attract boron atoms in boron carbide due to their higher electronegativity, forming a local electron-rich region. This charge polarization weakens the stability of the original chemical bond. After the boron atoms are released from the boron carbide lattice, they diffuse along the grain boundaries towards the direction of molybdenum dioxide. The oxygen atoms in the molybdenum dioxide lattice combine with the carbon atoms released from boron carbide to form gaseous carbon monoxide. The escape of gas forms a network of micro-channels in the material. These channels not only provide a path for material transport, but also guide the direction of liquid phase penetration through capillary action. At the same time, the valence state of molybdenum continues to decrease from four-valence to zero-valence metal state. The newly generated metal molybdenum particles have high surface energy and tend to aggregate to form nanoclusters, which become active sites for boron atom adsorption to form molybdenum diboride. The interaction between iron oxide and boron carbide triggers the selective melting phenomenon, and the boron-rich phase preferentially dissolves to form a eutectic liquid phase. Iron ions in the melt combine with free boron atoms through coordination bonds to form a network-like metal boride skeleton. Silicon nitride nanoparticles form covalent bonds with boron atoms in boron carbide through surface hydroxyl groups, constructing a three-dimensional pinning network at the grain boundaries. When the grain boundaries migrate at high temperatures, silicon atoms produced by the partial decomposition of silicon nitride infiltrate the boron carbide lattice, causing 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 the sintering process, with their basal planes eventually parallel to the hot pressing direction. When cracks propagate, they first encounter the weakly bonded interfaces between the nanosheet layers. The interface debonding process consumes fracture energy, and the plastic deformation ability provided by interlayer shear sliding allows the material to slow down crack propagation by energy dissipation when subjected to impact.

[0016] In the initial stage of sintering, the core is cleaned by pyrolysis and chemical reaction of the powder particle surface, and the reactivity of the particles is stimulated. Since the powder before sintering is usually prepared by ball milling and other processes, the particle surface may adsorb some impurities, including oxides, residual organic matter or moisture, which will significantly reduce the binding ability between particles. Therefore, it is necessary to remove them at low temperature stage through chemical reaction. For example, the reduction and decomposition reaction of oxides can convert the particle surface to a lower energy state, and the volatile products generated will be carried away by the atmosphere gas. In addition, organic residues introduced during the ball milling process will pyrolyze at low temperature stage, generating small molecule gases which are also discharged. In this way, the direct contact between powder particles is strengthened, providing good interface conditions for subsequent high-temperature densification. As the temperature gradually rises, the sintering enters the medium temperature stage, at which point the powder particles begin to undergo significant interfacial reactions and grain growth. The role of additives is particularly important at this stage. Additives are usually some highly reactive compounds that can react with the main components of the sintering system at medium temperature to form low-melting intermediate phases. This intermediate phase will exhibit a liquid phase state at a certain temperature, which can wet the surface of the powder particles, thereby reducing the interfacial energy between particles and promoting the rearrangement and bonding of particles. The presence of a liquid phase can also significantly reduce the sintering temperature and reduce the problem of excessive grain growth that may occur during sintering. At the same time, the diffusion process within the particles also occurs at this stage. As the temperature rises, atoms within the particles begin to migrate through bulk diffusion and grain boundary diffusion, which drives the formation and growth of particles. In the high-temperature stage, sintering enters the densification stage, and the powder system undergoes significant pore closure and grain growth, ultimately forming a high-density ceramic material structure. Due to the significant increase in diffusion coefficient at high temperature, the efficiency of material migration between particles is further improved, and the bonding between particles becomes more compact. Due to the driving force of surface energy, the pores between particles gradually decrease, and the internal residual gas is discharged through diffusion or liquid flow. As the pores are eliminated, the bulk density of the material increases, and finally a dense ceramic structure is formed. Liquid-phase additives can further reduce the activation energy of grain boundary migration, making the bonding between grains more compact, while inhibiting the excessive growth of grains and avoiding the degradation of material performance. The densification process at high temperature is also accompanied by grain rearrangement and optimization, which is achieved through grain boundary migration and interfacial energy reduction, ultimately generating a ceramic material with uniform microstructure. Gradient temperature sintering achieves material densification and performance optimization through chemical and physical processes. In the low-temperature stage, surface impurities are removed and particle activity is stimulated, providing good interface conditions for sintering. In the medium temperature stage, through interfacial reactions, diffusion mechanisms and the role of liquid-phase additives, the preliminary bonding and rearrangement of particles are completed. In the high-temperature stage, through pore closure and grain optimization, the final densification of the material is achieved, optimizing the microstructure and mechanical properties of boron carbide ceramics.

[0017] As a preferred technical solution of the present application, 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 not limited to the listed values, other values not listed in this range are also applicable.

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

[0019] In some optional examples, the holding time is 1-2h, 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 not limited to the listed values, other values not listed in this range are also applicable.

[0020] As a preferred technical solution of the present application, in S2, the D50 of boron carbide is ≤5μm. 50 ≤5μm.

[0021] In some optional examples, the mass ratio of boron carbide, reduced molybdenum dioxide and auxiliary agent is (95-97):(0.8-1.2):(3.5-6), for example, it can be (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 not limited to the listed values, other values not listed in this range are also applicable.

[0022] In some alternative examples, the adjuvant is iron trioxide, silicon nitride and boron nitride in a mass ratio of (2-3):(1-2):(0.5-1), such as (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 not limited to the listed values, other unlisted values within the range are also applicable.

[0023] In some alternative examples, the D50 of the silicon nitride is 1-2 pm, such as 1.0 pm, 1.1 pm, 1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm, 1.6 pm, 1.7 pm, 1.8 pm, 1.9 pm or 2.0 pm, but not limited to the listed values, other unlisted values within the range are also applicable. 50 ≤10 pm.

[0024] In some alternative examples, the flake diameter of the boron nitride is 1-2 pm, such as 1.0 pm, 1.1 pm, 1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm, 1.6 pm, 1.7 pm, 1.8 pm, 1.9 pm or 2.0 pm, but not limited to the listed values, other unlisted values within the range are also applicable.

[0025] In some alternative examples, the ball-to-material ratio of the ball milling is 5:1, the ball milling time is 6-7 h, such as 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h, but not limited to the listed values, other unlisted values within the range are also applicable.

[0026] In some alternative examples, the temperature of the vacuum drying is 80-90 °C, such as 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C or 90 °C, but not limited to the listed values, other unlisted values within the range are also applicable.

[0027] In some alternative examples, the mesh size of the sieving is 200 mesh.

[0028] As a preferred technical solution of the present application, in S3, the pressure of the one-way pressing 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 pressing 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 not limited to the listed values, other values not listed in the range are also applicable.

[0029] In some optional examples, the pressure of the cold isostatic pressing machine is 200-210 Mpa, for example, it can be 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, it can be 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 not limited to the listed values, other values not listed in the range are also applicable.

[0030] In some optional examples, in the reduction activation stage, the room temperature is raised to 800-810℃, for example, it can be 800℃, 801℃, 802℃, 803℃, 804℃, 805℃, 806℃, 807℃, 808℃, 809℃ or 810℃, the heating rate is 5℃ / min, the holding time is 30-40 min, for example, it can be 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 discharged and the argon atmosphere is continued, and then the temperature is continuously raised to 1400-1420℃, for example, it can be 1400℃, 1402℃, 1404℃, 1406℃, 1408℃, 1410℃, 1412℃, 1414℃, 1416℃, 1418℃ or 1420℃, the heating rate is 2℃ / min, and the holding time is 5-6 h, for example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h, but not limited to the listed values, other values not listed in the range are also applicable.

[0031] In some optional examples, the densification stage continues to heat to 1850-1870℃, for example, it can be 1850℃, 1852℃, 1854℃, 1856℃, 1858℃, 1860℃, 1862℃, 1864℃, 1866℃, 1868℃ or 1870℃, the heating rate is 10℃ / min, the holding time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but not only limited to the listed values, other values not listed in the range are also applicable.

[0032] In some optional examples, the second temperature is 200-210℃, for example, it can be 200℃, 201℃, 202℃, 203℃, 204℃, 205℃, 206℃, 207℃, 208℃, 209℃ or 210℃, but not only limited to the listed values, other values not listed in the range are also applicable.

[0033] In some optional examples, the temperature of the hot isostatic pressing is 1800-1820℃, for example, it can be 1800℃, 1802℃, 1804℃, 1806℃, 1808℃, 1810℃, 1812℃, 1814℃, 1816℃, 1818℃ or 1820℃, the pressure is 150-160Mpa, for example, it can be 150MPa, 151MPa, 152MPa, 153MPa, 154MPa, 155MPa, 156MPa, 157MPa, 158MPa, 159MPa or 160MPa, the holding time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but not only limited to the listed values, other values not listed in the range are also applicable.

[0034] In a second aspect, the present application provides a boron carbide bulletproof ceramic material prepared by the method of the first aspect.

[0035] Compared with the prior art, the application has the following beneficial effects: (1) volatile MoO3 is converted into MoO2 with higher thermal stability by hydrogen reduction, the reduction degree is controlled in advance to prevent the generation of metallic molybdenum or other adverse phases in the subsequent process, the in-situ synthesis and uniform distribution of the reinforcing phase are realized, part of the oxygen vacancies in the crystal lattice of the generated MoO2 can enhance the reactivity with B4C, promote the diffusion and bonding of boron and carbon atoms, and the material after the pre-reduction treatment exhibits better interface wettability than the original molybdenum trioxide; (2) Fe2O3 forms a liquid phase during sintering, the particles are rearranged and densified by capillary force, the pinning effect of the silicon nitride Si3N4 nanoparticles at the grain boundaries can inhibit the abnormal grain growth through local stress field distortion, and the transition layer of silicon carbide SiC generated by the partial decomposition of the liquid phase further strengthens the interface bonding, the unique layered structure of the boron nitride BN nanosheet can dissipate energy through the interface mechanism when the crack propagates, and the liquid phase generated by the additives can fill the pores between the particles and promote the closure of the pores during sintering, thereby improving the bulk density and uniformity of the ceramic material; (3) by introducing a unique composite additive system, the boron carbide ceramic can be rapidly densified and sintered at a temperature much lower than that required by the traditional process, the micro-pores and defects in the material that are prone to cause stress concentration and early failure are eliminated, a highly homogeneous and dense ceramic matrix is obtained, the energy consumption in the production process is reduced, and the cost of large-scale manufacturing of key components such as ceramic valves and pump valve liners is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A flow chart of a boron carbide bulletproof ceramic material preparation method provided for embodiments 1-4 of the application. DETAILED DESCRIPTION

[0037] The technical solutions of the application will be described in detail below with reference to specific embodiments and drawings. The embodiments described herein are specific specific embodiments of the application, which are used to illustrate the concept of the application; these descriptions are all explanatory and exemplary, and should not be understood as limiting the embodiments of the application and the protection scope of the application. In addition to the embodiments described herein, those skilled in the art can also employ other technical solutions that are obvious based on the content disclosed in the claims and the description of the application, which include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0038] The chemical reagents used in the embodiments and comparative examples of the application are all commercially available products and are not subjected to any further purification treatment.

[0039] Embodiment 1

[0040] This embodiment provides a boron carbide bulletproof ceramic material and a preparation method thereof, which is described with reference to Figure 1, the preparation method specifically comprising the following steps:

[0041] S1, the molybdenum trioxide is placed in a hydrogen atmosphere, the flow rate of hydrogen is 4L / min, the temperature is adjusted to 580℃ for 1h, and reduced molybdenum dioxide is obtained;

[0042] S2, 950g of boron carbide, 9g of reduced molybdenum dioxide, 35g of an auxiliary agent, and ethanol are mixed and ball milled, the auxiliary agent is ferroferric oxide, silicon nitride, and boron nitride, the mass ratio is 2:1:0.5, after ball milling, vacuum drying at 88℃ and sieving through a 200 mesh screen are performed, and a mixed powder is obtained;

[0043] S3, the mixed powder is cold-pressed and pre-formed by unidirectional pressing, the pressure of the unidirectional pressing is 100Mpa, the pressing time is 2.0min, a preliminary green body is obtained, and the green body is placed in a cold isostatic pressing machine for pressure holding, the pressure of the cold isostatic pressing machine is 200Mpa, the pressure holding time is 10min, a green body is obtained, the green body is placed in an argon atmosphere for gradient temperature sintering, and the gradient temperature sintering comprises a reduction activation stage and a densification stage in sequence, in the reduction activation stage, the temperature is increased from room temperature to 800℃ at a rate of 5℃ / min, the temperature holding time is 30min, after temperature holding, the gas is discharged and the argon atmosphere is continuously maintained, the temperature is continuously increased to 1400℃ at a rate of 2℃ / min, the temperature holding time is 5h, in the densification stage, the temperature is continuously increased to 1850℃ at a rate of 10℃ / min, the temperature holding time is 2h, after the densification stage is completed, the sintered body is obtained by cooling to 200℃, and the sintered body is subjected to hot isostatic pressing treatment, the temperature of the hot isostatic pressing is 1800℃, the pressure is 150Mpa, and the temperature holding time is 2h, thereby obtaining a boron carbide bulletproof ceramic material.

[0044] Example 2

[0045] The embodiment provides a boron carbide bulletproof ceramic material and a preparation method thereof, and the preparation method specifically comprises the following steps:

[0046] S1, the molybdenum trioxide is placed in a hydrogen atmosphere, the flow rate of hydrogen is 4L / min, the temperature is adjusted to 580℃ for 1h, and reduced molybdenum dioxide is obtained;

[0047] S2, 950g of boron carbide, 9g of reduced molybdenum dioxide, 35g of an auxiliary agent, and ethanol are mixed and ball milled, the auxiliary agent is ferroferric oxide, silicon nitride, and boron nitride, the mass ratio is 2:1:0.5, after ball milling, vacuum drying at 88℃ and sieving through a 200 mesh screen are performed, and a mixed powder is obtained;

[0048] S3, the mixed powder is cold-pressed preformed by one-way pressing, the pressure of the one-way pressing is 110 Mpa, the pressing time is 2.5 min, a preliminary blank is obtained, and the preliminary blank is transferred into a cold isostatic pressing machine for pressure keeping, the pressure of the cold isostatic pressing machine is 210 Mpa, and the pressure keeping time is 12 min, a green body is obtained, the green body is placed in an argon atmosphere for gradient temperature sintering, and the gradient temperature sintering includes a reduction activation stage and a densification stage in sequence; in the reduction activation stage, the temperature is increased from room temperature to 803 ℃ at a speed of 5 ℃ / min, the temperature keeping time is 33 min, the gas is discharged after temperature keeping and the argon atmosphere is continuously kept, the temperature is continuously increased to 1410 ℃ at a speed of 2 ℃ / min, and the temperature keeping time is 5.7 h; in the densification stage, the temperature is continuously increased to 1870 ℃ at a speed of 10 ℃ / min, and the temperature keeping time is 2.3 h, the sintered body is obtained by cooling to 202 ℃ after the densification stage ends, and the sintered body is subjected to hot isostatic pressing treatment, the temperature of the hot isostatic pressing is 1810 ℃, the pressure is 155 Mpa, and the temperature keeping time is 2.3 h, thereby a boron carbide bulletproof ceramic material is obtained.

[0049] Example 3

[0050] The embodiment provides a boron carbide bulletproof ceramic material and a preparation method thereof, and the preparation method specifically includes the following steps.

[0051] S1, the molybdenum trioxide is placed in a hydrogen atmosphere, the flow rate of the hydrogen is 4.2 L / min, the temperature is increased at a speed of 7 ℃ / min, the temperature is adjusted to 590 ℃ and kept for 2.0 h, and reduced molybdenum dioxide is obtained;

[0052] S2, 970 g of boron carbide, 12 g of reduced molybdenum dioxide and 60 g of an additive are mixed with ethanol and then ball milled, the additive is ferrous oxide, silicon nitride and boron nitride, and the mass ratio is 3:2:1, the mixture is vacuum dried at 90 ℃ after ball milling and sieved by using a 200 mesh screen, and a mixed powder is obtained;

[0053] S3, the mixed powder is cold-pressed preformed by one-way pressing, the pressure of the one-way pressing is 103 Mpa, the pressing time is 3.0 min, a preliminary blank is obtained, and the preliminary blank is transferred into a cold isostatic pressing machine for pressure keeping, the pressure of the cold isostatic pressing machine is 203 Mpa, and the pressure keeping time is 11 min, a green body is obtained, the green body is placed in an argon atmosphere for gradient temperature sintering, and the gradient temperature sintering includes a reduction activation stage and a densification stage in sequence; in the reduction activation stage, the temperature is increased from room temperature to 810 ℃ at a speed of 5 ℃ / min, the temperature keeping time is 40 min, the gas is discharged after temperature keeping, the argon atmosphere is continuously kept, the temperature is continuously increased to 1405 ℃ at a speed of 2 ℃ / min, and the temperature keeping time is 6.0 h; in the densification stage, the temperature is continuously increased to 1860 ℃ at a speed of 10 ℃ / min, the temperature keeping time is 3.0 h, the densification stage is ended, the sintered body is obtained by cooling to 210 ℃, and the sintered body is subjected to hot isostatic pressing treatment, the temperature of the hot isostatic pressing is 1820 ℃, the pressure is 160 Mpa, and the temperature keeping time is 3 h, so as to obtain a boron carbide bulletproof ceramic material.

[0054] Example 4

[0055] The embodiment provides a boron carbide bulletproof ceramic material and a preparation method thereof, and the preparation method specifically includes the following steps.

[0056] S1, the molybdenum trioxide is placed in a hydrogen atmosphere, the flow rate of the hydrogen is 4.7 L / min, the temperature is increased at a speed of 6 ℃ / min, the temperature is adjusted to 585 ℃ and kept for 1.2 h, and reduced molybdenum dioxide is obtained;

[0057] S2, 950 g of boron carbide, 10 g of reduced molybdenum dioxide and 50 g of an additive are mixed with ethanol and then ball milled, the additive is ferrous oxide, silicon nitride and boron nitride, the mass ratio is 2.8:1.5:0.7, the ball milled mixture is vacuum dried at 84 ℃ and sieved by using a 200 mesh sieve, and a mixed powder is obtained;

[0058] S3, the mixed powder is cold-pressed preformed by one-way pressing, the pressure of the one-way pressing is 108 Mpa, the pressing time is 2.8 min, a preliminary blank is obtained, and the preliminary blank is transferred into a cold isostatic pressing machine for pressure keeping, the pressure of the cold isostatic pressing machine is 206 Mpa, and the pressure keeping time is 10.8 min, a green body is obtained, the green body is placed in an argon atmosphere for gradient temperature sintering, and the gradient temperature sintering includes a reduction activation stage and a densification stage in sequence; in the reduction activation stage, the temperature is increased from room temperature to 807 ℃ at a speed of 5 ℃ / min, the temperature keeping time is 37 min, the gas is discharged after temperature keeping, the temperature is continuously increased to 1420 ℃ at a speed of 2 ℃ / min, and the temperature keeping time is 5.4 h; in the densification stage, the temperature is continuously increased to 1855 ℃ at a speed of 10 ℃ / min, and the temperature keeping time is 2.8 h, the sintered body is obtained by cooling to 207 ℃ after the densification stage ends, and the sintered body is subjected to hot isostatic pressing treatment, the temperature of the hot isostatic pressing is 1805 ℃, the pressure is 158 Mpa, and the temperature keeping time is 2.9 h, thereby a boron carbide bulletproof ceramic material is obtained.

[0059] Comparative Example 1

[0060] The present comparative example provides a boron carbide bulletproof ceramic material and a preparation method thereof, and the difference between the present comparative example and Example 1 is that no reduced molybdenum dioxide is added in S2, and other process parameters and operation conditions are completely same as those in Example 1.

[0061] Comparative Example 2

[0062] The present comparative example provides a boron carbide bulletproof ceramic material and a preparation method thereof, and the difference between the present comparative example and Example 1 is that no additive is added in S2, and other process parameters and operation conditions are completely same as those in Example 1.

[0063] The test standard of the bending strength and the compressive strength is GB / T 4740-2024, and the test standard of the hardness is GB / T 16534-2009. The test results are shown in Table 1.

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

[0065]

[0066]

[0067] As shown in Table 1, compared with Example 1, the bending strength, compressive strength and hardness of Comparative Example 1 all decrease; the bending strength, compressive strength and hardness of Comparative Example 2 all decrease. This is because in Comparative Example 1, the mass fraction of reduced molybdenum dioxide is 0, the absence of MoO2 causes the system to lose the ability to generate MoB2 reinforcing phase in situ, and at the same time, the high modulus of MoB2 disappears, so the bending strength, compressive strength and hardness of Comparative Example 1 all decrease. In Comparative Example 2, the mass fraction of the additive is 0, and the absence of Fe2O3 liquid phase makes the particles lack the densification driven by capillary force, the porosity increases, the disappearance of Si3N4 pinning effect causes the abnormal grain growth, and the intergranular bonding strength decreases, so the bending strength, compressive strength and hardness of Comparative Example 2 all decrease.

[0068] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A method of making a boron carbide ballistic-resistant ceramic material, comprising: The preparation method comprises: S1, placing molybdenum trioxide in a hydrogen atmosphere for heat preservation to obtain reduced molybdenum dioxide; S2, mixing boron carbide, reduced molybdenum dioxide, an additive and ethanol, and then ball milling to obtain a mixed powder; S3, cold pressing preforming the mixed powder by one-way pressing to obtain a preliminary blank, and then transferring the preliminary blank into a cold isostatic pressing machine for pressure preservation to obtain a green body, placing the green body in an argon atmosphere for gradient temperature sintering, sequentially including a reduction activation stage and a densification stage, cooling and taking out the sintered body after the densification stage to obtain a sintered body, and performing hot isostatic pressing treatment on the sintered body to obtain a boron carbide bulletproof ceramic material; The mass ratio of the boron carbide, the reduced molybdenum dioxide and the additive is (95-97):(0.8-1.2):(3.5-6); The additive is diiron trioxide, silicon nitride and boron nitride, and the mass ratio is (2-3):(1-2):(0.5-1).

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 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 has a D 50 ≤ 5 μm.

4. The method for preparing boron carbide bulletproof ceramic material according to claim 1, characterized in that, In S2, The silicon nitride has a D 50 ≤ 10 μm; The flake diameter of the boron nitride is 1-2 μm.

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

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 pressing machine is 200-210 MPa, and the pressure preservation time is 10-12 min.

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

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

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

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

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