Low-temperature rapid sintering high-performance boron carbide ceramic and preparation method thereof

Abstract

The application discloses a kind of low-temperature rapid sintering high-performance boron carbide ceramic and its preparation method.The preparation method of boron carbide ceramic of the present application comprises the following steps:S1, the raw material including boron carbide raw material powder, organic binder, dispersing agent and solid-phase sintering aid is mixed by wet ball milling, and granulation treatment is carried out by spraying, to obtain boron carbide granulation powder;S2, the boron carbide granulation powder is loaded into a mold, and pressure forming is carried out by applying pressure, to obtain a ceramic green body;S3, the ceramic green body is placed in an electric field assisted sintering device, under vacuum or inert atmosphere, pressure is applied, and a direct current electric field is applied, first heated to 400-800 DEG C, then continue to apply a direct current electric field, and make the current only pass through the ceramic green body, and then heated to 1500-1700 DEG C for sintering, to obtain boron carbide ceramic material.The present application can realize low-temperature, high-densification sintering of boron carbide ceramic at a sintering temperature of 1650 DEG C, and excellent mechanical properties are obtained.

Description

Technical Field

[0001] This invention relates to a high-performance boron carbide ceramic that can be rapidly sintered at low temperatures to achieve density and has high strength and high hardness, and its preparation method, belonging to the field of advanced ceramic material preparation technology. Background Technology

[0002] Boron carbide (B4C) ceramics are a new type of special ceramics that have attracted widespread attention in recent years. They have the characteristics of low density, high hardness, high strength, high chemical stability, and high neutron absorption rate, making them key ceramic materials for ceramic armor, aerospace, nuclear energy protection and other fields.

[0003] However, when carbon and boron atoms combine, they form stable covalent bonds with a high degree of covalent bonding and a low self-diffusion coefficient, making sintering difficult and hindering the densification of ceramics. Traditional techniques typically employ hot pressing sintering, with maximum sintering temperatures between 2000℃ and 2100℃. This requires sophisticated and energy-intensive sintering equipment, and the high-temperature environment can easily induce abnormal grain growth, affecting the performance and practical applications of ceramic products. Newer sintering technologies developed in recent years, such as spark plasma sintering (SPS) and flash sintering, apply electric fields to the upper and lower surfaces of the sample, ensuring the presence of conductive pathways formed by the matrix or conductive phase. The Joule heating effect induced by the current can assist sintering and lower the sintering temperature. However, this method also struggles to reduce the sintering temperature of boron carbide ceramics below 1900℃ and makes it difficult to ensure a uniform distribution of the conductive phase in the matrix, thus affecting the microstructure uniformity of the ceramic and reducing its performance. Furthermore, excessive conductive second phases can further impact the mechanical properties of the ceramic. Furthermore, researchers have further reduced the sintering temperature by applying special techniques to boron carbide powder. For example, patent CN104402441B synthesized boron carbide powder with a high specific surface area using a hard template method, resulting in higher sintering activity. However, SPS sintering is still required at a maximum temperature of 1900℃, resulting in only a slight temperature reduction and introducing a complex powder preparation process. Patent CN120157482A synthesized rare-earth silicon carbide compounds as sintering aids and mixed them with boron carbide powder. Although this reduced the SPS sintering temperature to 1700℃, the resulting boron carbide ceramics had low density and numerous pores, and also introduced a complex sintering aid synthesis process. Other techniques, by introducing a liquid-phase reaction sintering process, can obtain dense boron carbide ceramics in the range of 1600–1800℃, but this significantly reduces ceramic purity, results in an uneven microstructure, and leads to poor mechanical properties.

[0004] In summary, current technologies for the preparation of high-performance boron carbide ceramics still face numerous challenges, mainly including the following three points: 1) The sintering temperature of B4C ceramics is too high, resulting in harsh production conditions and extremely high energy consumption; 2) The processes for refining B4C ceramic powder and synthesizing novel sintering aids are complex and have limited impact on sintering performance; 3) Although reaction sintering and liquid-phase sintering of B4C can lower the sintering temperature, they significantly affect the microstructure of B4C ceramics and reduce the mechanical properties of the ceramic materials. Therefore, reducing the sintering temperature and improving material properties in the B4C solid-state sintering system remains a key issue in current technologies. Summary of the Invention

[0005] To address the technical problems of excessively high sintering temperatures and complex powder modification in current B4C ceramics, this invention proposes a high-performance boron carbide ceramic capable of low-temperature rapid sintering and its preparation method. By granulating and modifying the B4C raw material powder, adding a solid-phase sintering aid to promote sintering and an organic binder to form a uniform conductive network at low sintering temperatures, and comprehensively utilizing pressure and electric fields for multi-field assisted sintering, the overly complex powder processing and refining processes are avoided. This allows for a significant reduction in sintering temperature, ultimately achieving rapid low-temperature, high-density sintering of boron carbide ceramics at 1650℃, resulting in excellent mechanical properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing boron carbide ceramics, comprising the following steps: S1. The raw materials containing boron carbide raw material powder, organic binder, dispersant and solid phase sintering aid are mixed by wet ball milling and then spray granulation to obtain boron carbide granulated powder. The organic binder includes one or more of polyvinyl alcohol, phenolic resin, methylcellulose, polyethylene glycol, and polyvinylpyrrolidone; S2. The boron carbide granulated powder is loaded into a mold and pressure is applied to press and shape it to obtain a ceramic green body. S3. The ceramic green body is placed in an electric field-assisted sintering device. Under vacuum or inert atmosphere, pressure is applied and a DC electric field is applied. The temperature is first raised to 400-800°C to decompose the organic binder on the surface of the granulated powder to form a carbon layer, so as to form a uniform conductive network inside the ceramic green body. Then, the DC electric field is continued to be applied and the current is made to pass only through the ceramic green body. The temperature is then raised to 1500-1700°C for sintering. After sintering, the electric field and heating power supply are turned off and the pressure is released to obtain boron carbide ceramic material.

[0007] Furthermore, the particle size of the boron carbide raw material powder is 0.5–10 μm; And / or, based on the total amount of the boron carbide raw material powder, the organic binder, and the dispersant, the amount of the organic binder added is 5-10 wt%; And / or, the dispersant is selected from one or more of ammonium polyacrylate, tetramethylammonium hydroxide, polymethacrylate, polyvinylpyrrolidone, ethylene glycol, and propylene glycol; And / or, based on the total amount of the boron carbide raw material powder, the organic binder and the dispersant, the amount of the dispersant added is 0.1 to 3 wt%.

[0008] Furthermore, the solid-state sintering aid is selected from one or more of SiC, TiC, TiB2, and C; And / or, the amount of the solid-phase sintering aid added is 1 to 10 wt% of the boron carbide raw material powder, preferably 5 to 10 wt%.

[0009] Furthermore, the wet ball milling adopts a planetary ball mill, and the ball milling parameters include: the ball milling medium is anhydrous ethanol, the ratio of ball milling medium to mixed powder is (2-5):1; the ball-to-material ratio is (2-5):1; the ball milling speed is 200-400 r / min, and the ball milling time is 4-12 h.

[0010] Furthermore, the spray granulation process employs a centrifugal spray dryer, with process parameters including: controlling the inlet air temperature to be 100–200°C, the outlet air temperature to be 60–100°C, the feed rate to be 40–80 kg / h, the atomizing disc rotation speed to be 14000–26000 r / min, and preferably using compressed air as the granulation atmosphere.

[0011] Furthermore, in step S2, the mold is a cylindrical mold, the pressure is axial pressure, the pressure magnitude is 30-100MPa, and the pressure holding time is 2-10min.

[0012] Furthermore, the electric field-assisted sintering device includes a first pressure head, a second pressure head, an annular inner liner, and insulating paper. The first and second pressure heads are spaced apart along a first direction. The annular inner liner at least partially surrounds the first and second pressure heads. The insulating paper is located between the annular inner liner and the first and second pressure heads, forming a sintering cavity between the insulating paper, the first pressure head, and the second pressure head. The insulating paper includes a first surface and a second surface facing each other. The first surface faces and abuts against the annular inner liner, and the second surface faces and abuts against the first and second pressure heads. Further, the thickness of the insulating paper is 0.1–4 mm. The device also includes an annular sleeve located on the side of the annular inner liner away from the sintering cavity, at least partially surrounding the annular inner liner. The first pressure head, the second pressure head, the annular sleeve, and the annular inner liner are all made of graphite or composite graphite material.

[0013] Furthermore, in step S3, the pressure is axial pressure, the pressure magnitude is 30-100 MPa, and the pressure holding time is 2-10 min; And / or, the electric field strength of the DC electric field is 50–200 V / cm, and the upper limit of the current density is controlled to be 30–50 mA / mm. 2 ; And / or, the heating rate in the step of heating to 400-800°C is 10-40°C / min, and the heating rate in the step of continuing to heat to 1500-1700°C is 5-15°C / min.

[0014] In a second aspect, the present invention provides boron carbide ceramics prepared by the method described in any of the preceding claims.

[0015] The above-described technical solution of the present invention has the following advantages: (1) The powder processing technology is simple and the cost is low: The B4C raw material powder in the B4C granulation powder described in this invention has a common particle size and has been commercialized. Furthermore, there is no need to further refine the particle size in subsequent steps, which reduces the cost of industrial application. At the same time, the granulation modification process of B4C raw material powder is a mature process with a wide range of raw material sources and a simple process, which can achieve low-cost mass production.

[0016] (2) High-density sintering of boron carbide under low-temperature conditions can be achieved, significantly reducing energy consumption and providing mild sintering conditions: This invention utilizes the conductive carbon network formed by the decomposition of organic matter on the surface of granulated powder at low temperature (~500℃) and the added solid-phase sintering aids, which causes the green body to conduct current as the temperature rises, resulting in a significant decrease in resistance and a significant increase in current, generating a Joule heating effect. At the same time, the carbon network layer on the particle surface and the sintering aids promote the particle rearrangement and atomic migration process of boron carbide under pressure, accelerating densification. Thus, high-density boron carbide ceramics can be obtained under the conditions of 1650℃, 40MPa axial pressure, and a total sintering time of 2-3h, with a density >99%, which is far lower than the sintering temperature required by the traditional boron carbide manufacturing process, greatly reducing production energy consumption and avoiding the process requirements of high-temperature sintering furnaces.

[0017] (3) Excellent mechanical properties of boron carbide ceramic products: In this invention, the uniform organic matter coated on the surface of B4C granulated powder forms a carbon network layer with uniform thickness and distribution during the in-situ pyrolysis process under the assistance of the electric field. Under the combined action of solid phase sintering aid and auxiliary pressure, the sintering activity of B4C powder is significantly improved. As a result, the prepared boron carbide ceramic can still achieve high density at a low temperature of 1650℃ and can maintain the excellent mechanical properties of traditional high-temperature sintered boron carbide ceramics. The bending strength reaches 550-680MPa and the Vickers hardness reaches 25-31GPa, which is significantly better than boron carbide ceramics prepared by traditional sintering methods at the same temperature.

[0018] (4) Synergistic effect of in-situ electric field-assisted pyrolysis carbon network and pressure-assisted sintering: This invention utilizes the synergistic effect of in-situ pyrolysis carbon network with pressure and electric field to promote the rearrangement of B4C particles and the diffusion of B4C atoms during sintering, which greatly improves the low-temperature sintering activity of boron carbide powder. This mechanism significantly improves the density and mechanical properties of boron carbide ceramics under low-temperature sintering, and is the key to reducing the sintering temperature of strongly covalent carbide ceramics.

[0019] Meanwhile, the novel synthesis method for B4C ceramics involved in this invention is simple in process, easy to operate and master, highly practical, low in cost, and significantly shortens the cycle time, which is beneficial for industrial production. This invention greatly improves the feasibility of stable preparation of high-performance boron carbide ceramics, effectively reduces the sintering temperature of the material, and maintains the intrinsic mechanical properties of the material, which helps to realize the development and application of high-performance boron carbide ceramics in fields such as ceramic armor, aerospace, and nuclear protection. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope (SEM) image of the polished surface morphology of B4C ceramic prepared in Example 1 of this invention. Detailed Implementation

[0021] As described in the background section, how to reduce the sintering temperature and improve the material properties in the B4C solid-state sintering system remains a pressing technical challenge. Although SPS can reduce the sintering temperature to some extent, it is still difficult to meet the low-temperature and performance requirements of B4C solid-state sintering in this field.

[0022] In view of this, in the first part, the present invention provides a method for preparing boron carbide ceramics, comprising the following steps: S1. The raw materials containing boron carbide raw material powder, organic binder, dispersant and solid phase sintering aid are mixed by wet ball milling and then spray granulation to obtain boron carbide granulated powder. The organic binder includes one or more of polyvinyl alcohol, phenolic resin, methylcellulose, polyethylene glycol, and polyvinylpyrrolidone; S2. The boron carbide granulated powder is loaded into a mold and pressure is applied to press and shape it to obtain a ceramic green body. S3. The ceramic green body is placed in an electric field-assisted sintering device. Under vacuum or inert atmosphere, pressure is applied and a DC electric field is applied. The temperature is first raised to 400-800°C to decompose the organic binder on the surface of the granulated powder to form a carbon layer, so as to form a uniform conductive network inside the ceramic green body. Then, the DC electric field is continued to be applied and the current is made to pass only through the ceramic green body. The temperature is then raised to 1500-1700°C for sintering. After sintering, the electric field and heating power supply are turned off to obtain boron carbide ceramic material.

[0023] Based on the above technical solutions, this invention modifies raw materials containing B4C raw material powder, organic binder, and solid-phase sintering aid by granulation, and designs sintering process parameters. This allows the uniform organic matter coated on the surface of the B4C granulated powder to form a carbon network layer during the in-situ pyrolysis process under subsequent electric field assistance. This significantly reduces the conductivity network on-off temperature and sintering temperature. Moreover, the process is simple, has a short preparation cycle, and is low in cost, thereby greatly lowering the threshold for electric field-assisted sintering. Ultimately, this achieves low-temperature, rapid, and highly dense sintering of B4C ceramics, resulting in excellent mechanical properties.

[0024] In some embodiments of the present invention, the particle size of the boron carbide raw material powder is 0.5 to 10 μm, including but not limited to 1 μm.

[0025] In some embodiments of the present invention, in the organic binder, the polyvinyl alcohol is selected from any one of PVA-1788, PVA-1799, and PVA-2488; the phenolic resin is a water-soluble methyl phenolic resin with a weight-average molecular weight of 500–3000 g / mol, such as Mw ≈ 1000 g / mol; the methylcellulose is selected from any one of M15, M50, M100, and M450; the polyethylene glycol is selected from any one of PEG4000, PEG6000, and PEG10000; and the polyvinylpyrrolidone is selected from any one of PVP K15, PVP K30, and PVP K60. As an example, the organic binder is a mixture of polyvinyl alcohol and phenolic resin in a mass ratio of 5:4.5 or 3:2.5.

[0026] In some embodiments of the present invention, based on the total amount of the boron carbide raw material powder, the organic binder, and the dispersant, the amount of the organic binder added is 5-10 wt%, including but not limited to 9.5% and 5.5%. The inventors have found that too low an amount of organic binder will result in incomplete formation of the carbon network during pyrolysis, thereby reducing the density and mechanical properties of the boron carbide ceramic; while too high an amount of organic binder will lead to more residual carbon during pyrolysis, resulting in uneven carbon distribution in the ceramic and affecting the mechanical properties of the boron carbide ceramic.

[0027] In some embodiments of the present invention, the dispersant is selected from one or more of ammonium polyacrylate, tetramethylammonium hydroxide, polymethylammonium methacrylate (NH4PMAA, such as Mw≈2400g / mol), polyvinylpyrrolidone, ethylene glycol, and propylene glycol; based on the total amount of the boron carbide raw material powder, the organic binder, and the dispersant, the amount of the dispersant added is 0.1-3wt%, such as 0.5%.

[0028] In some embodiments of the present invention, the solid-state sintering aid is selected from one or more of SiC, TiC, Ti2B, and C; the amount of the solid-state sintering aid added is 1-10 wt% of the boron carbide raw material powder, preferably 5-10 wt%, such as 5%. The addition of the solid-state sintering aid helps to promote grain boundary diffusion and eliminate residual porosity, thereby improving density and mechanical properties. If the content of the solid-state sintering aid is too low, it will reduce the density and mechanical properties of the boron carbide ceramic; if it is too high, it will reduce the purity of the boron carbide ceramic, increase the density, and affect the specific strength of the ceramic.

[0029] In some embodiments of the present invention, the wet ball milling employs a planetary ball mill, and the milling parameters include: anhydrous ethanol as the milling medium; a milling medium to mixed powder ratio of (2-5):1 (mass ratio); a ball-to-powder ratio of (2-5):1 (mass ratio); a milling speed of 200-400 r / min; and a milling time of 4-12 h. Under these milling parameters, the raw materials can achieve uniform mixing at the microscopic level through ball milling. As an example, the anhydrous ethanol to mixed powder ratio is 2:1, the ball-to-powder ratio is 3:1, the milling speed is 300 r / min, and the milling time is 4 h.

[0030] In some embodiments of the present invention, the spray granulation process employs a centrifugal spray dryer, with process parameters including: controlling the inlet air temperature to be 100–200°C, the outlet air temperature to be 60–100°C, the feed rate to be 40–80 kg / h, and the atomizing disc rotation speed to be 14,000–26,000 r / min. The preferred granulation atmosphere is compressed air. Materials not treated by spray granulation cannot form a uniform organic coating layer on the surface of spherical particles, resulting in an uneven microstructure within the ceramic. Furthermore, by controlling these process parameters, the particle size and conductive network density of the boron carbide granulated powder can be adjusted within a suitable range. As an example, during spray granulation, the inlet temperature is 120°C, the outlet temperature is 80°C, the feed rate is 50 kg / h, the atomizing disc rotation speed is 15,000 r / min, and the granulation atmosphere is compressed air.

[0031] In some embodiments of the present invention, in step S2, the mold is a cylindrical mold, the pressure is an axial pressure of 30–100 MPa, and the holding time is 2–10 min, such as applying an axial pressure of 30 MPa and holding for 3 min. It is understood that, based on the apparatus used in step S3, the mold can directly be a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity, wherein a boron nitride (BN) insulating layer is used to isolate the sample from contact with the inner liner wall and to prevent current from passing through the mold, for example, with a thickness of 0.2 mm.

[0032] Unlike traditional sintering processes, especially discharge plasma sintering, this invention employs an electric field-assisted sintering device. On one hand, the conductive network formed by pyrolysis creates a circuit path, which can significantly reduce the conduction temperature of the conductive network and the sintering temperature. The sintering temperature can be reduced to 1650℃. On the other hand, this device allows the current to pass only through the ceramic green body, resulting in uniform sintering and a uniform internal structure, thus obtaining boron carbide ceramic materials with excellent mechanical properties.

[0033] In some embodiments of the present invention, the electric field-assisted sintering apparatus can be any device capable of allowing current to pass only through the ceramic green body. Exemplarily, the electric field-assisted sintering apparatus includes a first pressure head, a second pressure head, an annular liner, and insulating paper. The first and second pressure heads are spaced apart along a first direction. The annular liner at least partially surrounds the first and second pressure heads. The insulating paper is located between the annular liner and the first and second pressure heads, forming a sintering cavity between the insulating paper, the first pressure head, and the second pressure head. The insulating paper includes opposing first and second surfaces. The first surface faces and abuts against the annular liner, and the second surface faces and abuts against the first and second pressure heads. By providing insulating paper between the annular liner and the first and second pressure heads, insulation is achieved between the annular liner and the first and second pressure heads, thereby allowing the first and second pressure heads to conduct only through the material within the sintering cavity.

[0034] Furthermore, the roughness of the first surface is greater than that of the second surface. By making the roughness of the first surface greater than that of the second surface, the connection stability between the annular inner liner and the insulating paper is improved when the first pressure head, the second pressure head and the insulating paper move relative to each other, and the probability of the insulating paper falling off the annular inner liner and causing insulation failure is reduced.

[0035] Furthermore, the thickness of the insulating paper is 0.1–4 mm. The insulating paper can be boron nitride fiber paper, alumina fiber paper, or fiber paper made of other insulating materials.

[0036] Furthermore, the device also includes an annular sleeve located on the side of the annular liner facing away from the sintering cavity, the annular sleeve at least partially surrounding the annular liner.

[0037] Furthermore, the first pressure head, the second pressure head, the annular sleeve, and the annular liner are all made of graphite or composite graphite materials.

[0038] As an example, the present invention uses the electric field-assisted sintering apparatus disclosed in CN 221717308 U.

[0039] In some embodiments of the present invention, in step S3, the pressure is an axial pressure, with a magnitude of 30–100 MPa, such as 30 MPa. The inventors have found that it is difficult to achieve complete densification of boron carbide ceramics at low temperatures when the pressure is too low. The sintering atmosphere can be a vacuum or an inert atmosphere, such as argon, nitrogen, or a mixture thereof. Applying a DC electric field can induce a flash burning effect. The electric field strength of the DC electric field is 50–200 V / cm, including but not limited to 100–150 V / cm, 100 V / cm, or 150 V / cm, and the upper limit of the current density is controlled to be 30–50 mA / mm². 2 , such as 40 mA / mm 2 The setting of the electric field strength and current density of the DC electric field is crucial for the stable triggering of the flash burning effect and the distribution of Joule heat. The electric field strength provides the driving force to overcome the grain boundary barrier. A suitable electric field not only provides the impetus for atomic diffusion but also induces non-thermal effects such as changes in grain boundary structure. The upper limit of the current density is used to achieve quantitative control of energy consumption and stabilize the internal heat generation rate. The synergistic effect of the two ensures the generation of uniform local hot spots inside the green body. While promoting grain boundary diffusion and accelerating densification, it avoids local melting or abnormal grain growth caused by current overload, thereby endowing the ceramic with a fine microstructure, high density, and excellent mechanical properties.

[0040] In some embodiments of the present invention, the heating rate in the step of heating to 400-800°C is 10-40°C / min, such as heating to 800°C at a rate of 30°C / min; the heating rate in the step of continuing to heat to 1500-1700°C is 5-15°C / min, such as heating to 1650°C at a rate of 10°C / min. During the organic matter decomposition stage, the green body is heated above the decomposition temperature of the granulating agent, and the organic layer on the surface of the granulating powder decomposes to form a continuous or quasi-continuous carbon layer, constituting a conductive network. During the sintering stage, as the temperature continues to rise, under the synergistic effect of the conductive network and the sintering aid, the green body resistance decreases sharply, the current increases rapidly, and a significant Joule heating effect is generated. Simultaneously, under pressure, the B4C powder particles rearrange, accelerating the atomic migration process and achieving low-temperature densification. It is understood that the method also includes a step of furnace cooling to room temperature after depressurization.

[0041] In the second part, this invention provides boron carbide ceramics prepared by the method described in any of the preceding claims. The boron carbide ceramics of this invention not only have high density but also outstanding mechanical properties, with a flexural strength of 550–680 MPa and a Vickers hardness of 25–31 GPa.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. The embodiments given below are only for illustrating this invention and not for limiting its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on this invention in any way.

[0043] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0044] The following examples use conventional testing methods in the industry to test the performance of the obtained products: In this example, the bulk density is tested according to Archimedes' method of water displacement (refer to GB / T 1966-2024); the bending strength is tested by the three-point bending method (refer to ASTM C1161-18); and the hardness is determined by the Vickers hardness test (refer to GB / T 16534-2009).

[0045] In the following examples, the polyvinyl alcohol (PVA) is model PVA-1788, the phenolic resin (PF) is a water-soluble first-stage phenolic resin, model phenolic resin 2402, molecular weight Mw≈1000g / mol, and the polymethyl methacrylate is manufactured by Dow Chemical Company of the United States, catalog number D3005, with a molecular weight of Mw≈2400g / mol.

[0046] Example 1 High-performance boron carbide ceramic materials were prepared according to the following steps: (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC of the B4C powder mass were added as sintering aids. The mixture was ball-milled using a planetary ball mill. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then spray-granulated. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0047] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0048] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 100 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, the DC electric field is continued to be applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min (this current intensity and current density upper limit are maintained throughout the sintering process). After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0049] The measured bulk density of the boron carbide ceramic material was 2.587 g / cm³. 3 The flexural strength was measured to be 559±61MPa, and the Vickers hardness was measured to be 30.6±2.4GPa. Figure 1 SEM images show that the sintered body has a dense microstructure and no obvious pores are observed.

[0050] Example 2 The difference from Example 1 is that the mass ratio of B4C raw material powder, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate ammonium is adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0051] High-performance boron carbide ceramic materials were prepared according to the following steps: (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:3:2.5:0.5, and 1% TiC and 4% SiC of the B4C powder mass were added as sintering aids. The mixture was ball-milled using a planetary ball mill. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then spray-granulated. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0052] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0053] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 100 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, the DC electric field is continued to be applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0054] The measured bulk density of the boron carbide ceramic material was 2.555 g / cm³. 3 The flexural strength was measured to be 652±58MPa, and the Vickers hardness was measured to be 25.7±1.5GPa.

[0055] Example 3 The difference from Example 1 is that the axial pressure in steps (2) and (3) is adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0056] High-performance boron carbide ceramic materials were prepared according to the following steps: (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0057] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 30 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0058] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 30 MPa and a DC electric field of 100 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, the DC electric field is continued to be applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0059] The measured bulk density of the boron carbide ceramic material was 2.534 g / cm³. 3 The flexural strength was measured to be 592±74MPa, and the Vickers hardness was measured to be 28.5±2.2GPa.

[0060] Example 4 The difference from Example 1 is that the electric field strength of the DC electric field in step (3) is adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0061] High-performance boron carbide ceramic materials were prepared according to the following steps: (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0062] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0063] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 150 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, a DC electric field is applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0064] The measured bulk density of the boron carbide ceramic material was 2.596 g / cm³. 3 The flexural strength was measured to be 674±41MPa, and the Vickers hardness was measured to be 29.7±0.6GPa.

[0065] Example 5 The difference from Example 1 is that the temperature and DC electric field strength of the organic matter pyrolysis stage in step (3) are adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0066] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0067] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0068] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 150 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is raised to 500℃ at a rate of 30℃ / min, then a DC electric field is applied, and the temperature is raised to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0069] The measured bulk density of the boron carbide ceramic material was 2.585 g / cm³. 3 The flexural strength was measured to be 593±26MPa, and the Vickers hardness was measured to be 29.8±0.9GPa.

[0070] Comparative Example 1 The difference from Example 1 is that the binder polyvinyl alcohol (PVA), phenolic resin (PF) and dispersant polymethyl methacrylate in step (1) are omitted, as well as the spray granulation step. The remaining steps and process parameters are the same as in Example 1.

[0071] (1) Pure B4C raw material powder with a particle size of 1μm was mixed with 1% TiC by mass of B4C powder and 4% SiC by mass of boron carbide powder by ball milling in a planetary ball mill. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-material ratio was 3:1, the ball milling speed was 300r / min, and the ball milling time was 4h.

[0072] (2) The mixed powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer was used to isolate the sample from the inner wall and had a thickness of 0.2 mm. An axial pressure of 40 MPa was applied and held for 3 min to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0073] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 100 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is raised to 800℃ at a rate of 30℃ / min, then the DC electric field is continued to be applied, and the temperature is raised to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0074] The process parameters for Comparative Example 1, including raw material particle size, type and amount of sintering aid, ball milling and green pressing process, heating program, sintering temperature, pressure, and electric field strength, were exactly the same as those for Example 1. However, Comparative Example 1 used B4C powder without binder granulation. The bulk density of the boron carbide ceramic material was measured to be 1.63 g / cm³. 3 Its structure is loose, making it impossible to conduct effective mechanical performance tests.

[0075] Comparative Example 2 The difference from Example 1 is that the electric field-assisted sintering device in step (3) is replaced with a conventional hot press furnace (without electric field), while the remaining steps and process parameters are the same as in Example 1.

[0076] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0077] (2) The granulated B4C powder is then loaded into a graphite hot press mold (lined with 0.2mm graphite paper). An axial pressure of 40MPa is applied and held for 3 minutes to ensure that the powder is pressed and formed, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0078] (3) After pressing and molding, the product is placed in a conventional hot press furnace. Under vacuum atmosphere and axial pressure of 40MPa, the temperature is increased to 800℃ at 30℃ / min and to 1650℃ at 10℃ / min. After the heating process is completed, the pressure is released and the product is cooled to room temperature with the furnace.

[0079] The raw material formulation, granulation process, maximum sintering temperature (1650℃), and pressure parameters used in Comparative Example 2 were exactly the same as those in Example 1, but no DC electric field was applied throughout the entire process. The measured bulk density was only 1.78 g / cm³. 3 This indicates that under the sintering regime in Example 1, the powder formulation cannot be densified at low temperatures without the assistance of an electric field.

[0080] Comparative Example 3 The difference from Example 1 is that the electric field-assisted sintering device in step (3) is replaced with a conventional hot press furnace (without electric field), and the mold in step (2) is replaced accordingly. The remaining steps and process parameters are the same as in Example 1.

[0081] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0082] (2) The granulated B4C powder is then loaded into a graphite hot press mold (lined with 0.2mm graphite paper). An axial pressure of 40MPa is applied and held for 3 minutes to ensure that the powder is pressed and formed, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0083] (3) After pressing and molding, the product is placed in a traditional hot press furnace. Under vacuum atmosphere and 40MPa axial pressure, the temperature is increased to 800℃ at 30℃ / min, to 1650℃ at 10℃ / min, and to 2000℃ at 5℃ / min. After holding the temperature for 2 hours, the pressure is released and the product is cooled to room temperature in the furnace.

[0084] The raw material formulation, granulation process, and pressure parameters used in Comparative Example 3 were the same as those in Example 1. However, Comparative Example 3 employed a traditional high-temperature hot-pressing sintering process without an applied electric field, and its highest sintering temperature reached 2000℃ (far higher than the 1650℃ in Example 1). The bulk density of the boron carbide ceramic material was measured to be 2.47 g / cm³. 3 The bending strength was 360±23MPa, and the Vickers hardness was 25±1.3GPa. This comparative example demonstrates that the traditional hot-pressing sintering method requires sintering at a high temperature of 2000℃ to achieve mechanical properties similar to those of Example 1. Furthermore, Example 1 exhibits higher bending strength than hot-pressed boron carbide and has broader application prospects.

[0085] Comparative Example 4 The difference from Example 1 is that the electric field-assisted sintering device in step (3) is replaced with a discharge plasma sintering furnace, and the mold in step (2) is replaced accordingly. The remaining steps and process parameters are the same as in Example 1.

[0086] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0087] (2) The granulated B4C powder is then loaded into a graphite mold (lined with 0.2 mm graphite paper). An axial pressure of 40 MPa is applied and held for 3 minutes to ensure that the powder is pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0088] (3) After pressing and forming, the furnace is placed in a discharge plasma sintering furnace. Under vacuum atmosphere and 40MPa axial pressure, the temperature is raised to 1650℃ at a heating rate of 100℃ / min and held for 5min. After sintering, the pressure is released and the furnace is cooled to room temperature.

[0089] The raw material formulation, granulation process, and maximum sintering temperature used in Comparative Example 4 were the same as in Example 1, but Comparative Example 4 employed the SPS sintering process. The bulk density of the boron carbide ceramic material was measured to be 2.21 g / cm³. 3 The flexural strength was 213±32 MPa, and the Vickers hardness was 22±2.3 GPa. This comparative example demonstrates that in the SPS sintering process, because the current does not completely pass through the sample, the granulated organic matter cannot effectively form a carbon network, significantly reducing the sintering-promoting effect. This prevents the complete densification of conventional boron carbide powder at low temperatures, resulting in a decrease in mechanical properties.

[0090] Comparative Example 5 The difference from Example 1 is that the axial pressure in step (3) is adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0091] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0092] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 10 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0093] (3) The green blank is then placed in an electric field-assisted sintering apparatus. Under a vacuum atmosphere, only an axial pressure of 10 MPa is applied, and a DC electric field of 100 V / cm is applied. The upper limit of the current density is set to 40 mA / mm. 2 First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, a DC electric field is applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0094] The raw material formulation, granulation process, maximum sintering temperature (1650℃), and electric field parameters used in Comparative Example 5 were exactly the same as those in Example 1, but Comparative Example 5 applied a lower pressure than Example 1 throughout the sintering process. The measured bulk density of the boron carbide ceramic material was only 2.03 g / cm³. 3 The flexural strength is 103±42 MPa, and the Vickers hardness is 12±1.1 GPa. This comparative example illustrates that the Joule heating effect induced by the applied electric field and the formation of the in-situ carbon network can promote the low-temperature sintering densification of boron carbide. However, it is difficult to achieve complete densification of boron carbide ceramics at low temperatures without pressure assistance, which confirms the synergistic effect of pressure, electric field, and in-situ carbon network.

[0095] Comparative Example 6 The difference from Example 1 is that the content of solid sintering agent in step (1) is adjusted, while the remaining steps and process parameters are the same as in Example 1.

[0096] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 90:5:4.5:0.5, and 0.1% TiC and 0.4% SiC (by mass of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0097] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0098] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 150 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, a DC electric field is applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0099] The measured bulk density of the boron carbide ceramic material was 2.28 g / cm³. 3 The flexural strength was 310±25MPa, and the Vickers hardness was 23±1.6GPa. This comparative example illustrates that an excessively low content of solid-phase sintering aids reduces the density and mechanical properties of boron carbide ceramics, confirming the necessity of sintering aids for the low-temperature sintering of boron carbide.

[0100] Comparative Example 7 The difference from Example 1 is that the content of binder polyvinyl alcohol (PVA), phenolic resin (PF) and dispersant polymethyl methacrylate in step (1) is reduced, while the remaining steps and process parameters are the same as in Example 1.

[0101] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 97:1.5:1.35:0.15, and 1% TiC and 4% SiC of the B4C powder were added as sintering aids. The mixture was ball-milled using a planetary ball mill. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then spray-granulated. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0102] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0103] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 150 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, a DC electric field is applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0104] The measured bulk density of the boron carbide ceramic material was 2.36 g / cm³. 3 The flexural strength was 287±29 MPa, and the Vickers hardness was 19±2.3 GPa. This comparative example illustrates that an excessively low content of organic granulating agent will result in incomplete formation of the carbonization network during the pyrolysis process, thereby reducing the density and mechanical properties of boron carbide ceramics. This further confirms the importance of the carbonization network for the low-temperature sintering of boron carbide ceramics.

[0105] Comparative Example 8 The difference from Example 1 is that the content of the binder polyvinyl alcohol (PVA), phenolic resin (PF) and dispersant polymethyl methacrylate in step (1) is increased. The remaining steps and process parameters are the same as in Example 1.

[0106] (1) B4C raw material powder with a particle size of 1 μm, binder polyvinyl alcohol (PVA), phenolic resin (PF), and dispersant polymethyl methacrylate were mixed in a mass ratio of 80:10:9:1, and 1% TiC and 4% SiC (by weight of B4C powder) were added as sintering aids. A planetary ball mill was used for ball milling and mixing. The ratio of anhydrous ethanol to mixed powder was 2:1, the ball-to-powder ratio was 3:1, the ball milling speed was 300 r / min, and the ball milling time was 4 h. The mixed slurry was then subjected to spray granulation treatment. The inlet temperature was 120 ℃, the outlet temperature was 80 ℃, the feed rate was 50 kg / h, the atomizing disc speed was 15000 r / min, and the granulation atmosphere was compressed air, thereby obtaining granulated modified B4C granulated powder.

[0107] (2) The granulated B4C powder was then loaded into a graphite electric field-assisted hot pressing sintering mold with a cylindrical inner cavity. The BN insulating layer, with a thickness of 0.2 mm, was used to isolate the sample from the inner lining wall. An axial pressure of 40 MPa was applied and held for 3 minutes to ensure that the powder was pressed into shape, thereby obtaining a cylindrical ceramic green body with a diameter of 30 mm and a thickness of about 5 mm.

[0108] (3) The green blank is then placed in an electric field-assisted sintering apparatus, under vacuum atmosphere, with an axial pressure of 40 MPa and a DC electric field of 100 V / cm, and the upper limit of the current density is set to 40 mA / mm. 2First, the temperature is increased to 800℃ at a rate of 30℃ / min to ensure that the organic binder on the surface of the granulated powder is fully decomposed. Then, the DC electric field is continued to be applied, and the temperature is increased to 1650℃ at a rate of 10℃ / min. After sintering, the electric field and heating power supply are turned off, the pressure is released, and the furnace is cooled to room temperature to obtain boron carbide ceramic material.

[0109] The bulk density of the boron carbide ceramic material was measured to be 2.52 g / cm³. 3 The flexural strength was 412±17 MPa, and the Vickers hardness was 20±3.1 GPa. This comparative example illustrates that while a high content of organic granulating agent can achieve densification of boron carbide ceramics, excessive residual carbon will affect the mechanical properties of the ceramics.

[0110] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing boron carbide ceramics, characterized in that, The steps include the following: S1. The raw materials containing boron carbide raw material powder, organic binder, dispersant and solid phase sintering aid are mixed by wet ball milling and then spray granulation to obtain boron carbide granulated powder. The organic binder includes one or more of polyvinyl alcohol, phenolic resin, methylcellulose, polyethylene glycol, and polyvinylpyrrolidone; S2. The boron carbide granulated powder is loaded into a mold and pressure is applied to press and shape it to obtain a ceramic green body. S3. The ceramic green body is placed in an electric field-assisted sintering device. Under vacuum or inert atmosphere, pressure is applied and a DC electric field is applied. The temperature is first raised to 400-800°C to decompose the organic binder on the surface of the granulated powder to form a carbon layer, so as to form a uniform conductive network inside the ceramic green body. Then, the DC electric field is continued to be applied and the current is made to pass only through the ceramic green body. The temperature is then raised to 1500-1700°C for sintering. After sintering, the electric field and heating power supply are turned off and the pressure is released to obtain boron carbide ceramic material.

2. The method for preparing boron carbide ceramics according to claim 1, characterized in that: The boron carbide raw material powder has a particle size of 0.5–10 μm; And / or, based on the total amount of the boron carbide raw material powder, the organic binder, and the dispersant, the amount of the organic binder added is 5-10 wt%; And / or, the dispersant is selected from one or more of ammonium polyacrylate, tetramethylammonium hydroxide, polymethacrylate, polyvinylpyrrolidone, ethylene glycol, and propylene glycol; And / or, based on the total amount of the boron carbide raw material powder, the organic binder and the dispersant, the amount of the dispersant added is 0.1 to 3 wt%.

3. The method for preparing boron carbide ceramics according to any one of claims 1-2, characterized in that: The solid-state sintering aid is selected from one or more of SiC, TiC, Ti2B, and C; And / or, the amount of the solid-phase sintering aid added is 1 to 10 wt% of the boron carbide raw material powder, preferably 5 to 10 wt%.

4. The method for preparing boron carbide ceramics according to any one of claims 1-3, characterized in that: The wet ball milling adopts a planetary ball mill, and the ball milling parameters include: the ball milling medium is anhydrous ethanol, the ratio of ball milling medium to mixed powder is (2-5):1; the ball-to-material ratio is (2-5):1; the ball milling speed is 200-400 r / min, and the ball milling time is 4-12 h.

5. The method for preparing boron carbide ceramics according to any one of claims 1-4, characterized in that: The spray granulation process uses a centrifugal spray dryer, and the process parameters include: controlling the inlet air temperature to be 100-200℃, the outlet air temperature to be 60-100℃, the feed rate to be 40-80 kg / h, the atomizing disc rotation speed to be 14000-26000 r / min, and the preferred granulation atmosphere to be compressed air.

6. The method for preparing boron carbide ceramics according to any one of claims 1-5, characterized in that: In step S2, the mold is a cylindrical mold, the pressure is axial pressure, the pressure magnitude is 30-100MPa, and the pressure holding time is 2-10min.

7. The method for preparing boron carbide ceramics according to any one of claims 1-6, characterized in that: The electric field-assisted sintering device includes a first pressure head, a second pressure head, an annular liner, and insulating paper. The first pressure head and the second pressure head are spaced apart along a first direction. The annular liner at least partially surrounds the first pressure head and the second pressure head. The insulating paper is located between the annular liner and the first pressure head and the second pressure head. A sintering cavity is formed between the insulating paper, the first pressure head, and the second pressure head. The insulating paper includes a first surface and a second surface facing each other. The first surface faces the annular liner and abuts against the annular liner. The second surface faces the first pressure head and the second pressure head and abuts against the first pressure head and the second pressure head.

8. The method for preparing boron carbide ceramics according to claim 7, characterized in that: The thickness of the insulating paper is 0.1–4 mm; The device further includes an annular sleeve located on the side of the annular liner facing away from the sintering cavity, and the annular sleeve at least partially surrounds the annular liner. The first pressure head, the second pressure head, the annular sleeve, and the annular liner are all made of graphite or composite graphite materials.

9. The method for preparing boron carbide ceramics according to any one of claims 1-8, characterized in that: In step S3, the pressure is axial pressure, the pressure magnitude is 30-100 MPa, and the pressure holding time is 2-10 min; And / or, the electric field strength of the DC electric field is 50–200 V / cm, and the upper limit of the current density is controlled to be 30–50 mA / mm. 2 ; And / or, the heating rate in the step of heating to 400-800°C is 10-40°C / min, and the heating rate in the step of continuing to heat to 1500-1700°C is 5-15°C / min.

10. Boron carbide ceramics prepared by the method of any one of claims 1-9.

Images