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

Abstract

The application provides a boron carbide ceramic material and a preparation method thereof, and relates to the technical field of bulletproof materials.The preparation method is as follows: boron carbide powder is mixed with a gelatin solution to form a slurry; the slurry is subjected to directional freeze-drying treatment to obtain a green body with a hollow lamellar structure; and the green body is subjected to hot-press sintering in a vacuum or inert atmosphere to obtain the boron carbide ceramic material.The application controls directional freeze-drying and hot-press sintering, optimizes the interlayer interface, and effectively improves the fracture toughness and bending strength of the boron carbide ceramic material; the preparation method is simple and low in cost, does not need to introduce second-phase hard particles, and avoids the problem that the coarse particle size of the second-phase particles affects the mechanical properties; the boron carbide ceramic material prepared by the application has high strength, high toughness, high energy absorption capacity and impact resistance, and has a wide application prospect in the field of bulletproof armor.

Description

Technical Field

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

[0002] Bulletproof ceramics have developed rapidly and come in many varieties, including alumina, silicon carbide, boron carbide, silicon nitride, and titanium boride. Among them, alumina ceramics (Al2O3), silicon carbide ceramics (SiC), and boron carbide ceramics (B4C) are the most widely used. Comparing these three common bulletproof ceramic materials, alumina bulletproof ceramics are far inferior to silicon carbide and boron carbide in terms of bulletproof performance, especially boron carbide. With the development of sintering technology, the superior performance of boron carbide ceramics is becoming increasingly prominent, and its application in the field of bulletproofing will be further developed.

[0003] Boron carbide is the second hardest known material after diamond and cubic boron nitride. It has a high elastic modulus, a low coefficient of thermal expansion, and relatively high thermal conductivity. B4C has the lowest density among several commonly used armor ceramics, and its high elastic modulus makes it a good choice for military armor and space applications.

[0004] However, the existing method of toughening boron carbide ceramic materials by using second-phase hard particles has the problem of large particle size affecting mechanical properties. The method of assembling small ceramic pieces has the defects of increased weight and weak areas. The prepared boron carbide ceramic materials have the defects of low fracture toughness and bending strength.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a boron carbide ceramic material and its preparation method. By controlling the directional freeze-drying process to design a layered structure, and then optimizing the interlayer interface through staged hot pressing sintering, the fracture toughness and flexural strength of the boron carbide ceramic material are effectively improved. The preparation method is simple and low-cost, and does not require the introduction of second-phase hard particles, thus avoiding the problem of large particle size of the second phase affecting the mechanical properties.

[0007] 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 ceramic materials, comprising the following steps: Boron carbide powder is mixed with a gelling agent solution to form a slurry; The slurry is subjected to directional freeze-drying to obtain a blank with a hollow lamellar structure. The blank has fine pores with an average pore size of 10-40 μm and a porosity of 40-80%.

[0008] The blank is hot-pressed and sintered in a vacuum or inert atmosphere to obtain the boron carbide ceramic material.

[0009] Optionally, the gelling agent solution includes one or more of gellan gum, gelatin, agar, polyvinyl alcohol, polyacrylamide, or polylactic acid gel.

[0010] Furthermore, the concentration of the gelling agent solution is 0.05-0.3%, which is within the range that can inhibit ice crystal growth and form fine pores.

[0011] Furthermore, the mass ratio of the boron carbide powder to the gelling agent solution is 1:0.5-1.5.

[0012] Preferably, the boron carbide powder has a particle size of 2-5 μm.

[0013] Optionally, the mixed powder slurry is ball-milled for 10-20 minutes to ensure thorough dispersion.

[0014] Furthermore, the freezing temperature of the directional freeze-drying is -30 to -50°C; preferably, the freezing rate of the directional freeze-drying is 60-90 μm / s.

[0015] Preferably, the directional freeze-drying involves controlling the temperature at different points from one end to the other in the container containing the slurry, which can form a more regularly oriented crystal structure.

[0016] Furthermore, the hot pressing sintering temperature is 2000-2300℃, and the hot pressing sintering pressure is 20-55MPa.

[0017] Optionally, when the hot pressing sintering is carried out under vacuum, the vacuum degree is <0.001MPa.

[0018] Preferably, the hot-pressing sintering process involves first heating to 450-550℃ at a rate of 2-5℃ / min and holding at that temperature for 0.5-1h; pressurization is then applied during the holding period, followed by heating to 1900-1980℃ at a rate of 2-5℃ / min and holding at that temperature for 0.5-1h. At this temperature, the grain growth process is controlled, allowing the grains to grow at the interlayer junctions, resulting in layered crystal formation and the diffusion of large grains engulfing small grains to form grain boundaries; finally, the temperature is raised to the hot-pressing sintering temperature and held for 0.5-5h.

[0019] Secondly, the present invention also provides a boron carbide ceramic material, prepared by the aforementioned method. The resulting boron carbide ceramic material has a density of 2.3-2.4 g / cm³. 3 With a density of over 95%, it has uniformly distributed grain boundaries, forming layered crystals for toughening. The fracture mode changes from transgranular fracture to a mixed transgranular-intergranular fracture mode, greatly improving bending strength and toughness.

[0020] This invention designs a layered structure by controlling the directional freeze-drying process, and then optimizes the interlayer interface through staged hot-pressing sintering, effectively improving the fracture toughness and flexural strength of boron carbide ceramic materials. Simultaneously, the preparation method of this invention is simple and low-cost, eliminating the need to introduce second-phase hard particles and avoiding the problem of large second-phase particles affecting mechanical properties. The boron carbide ceramic material prepared by this invention exhibits high strength, high toughness, high energy absorption capacity, and impact resistance, with a flexural strength reaching 480-550 MPa and a fracture toughness reaching 5.3-6.7 MPa·m. 1 / 2 It has broad application prospects in the field of bulletproof armor. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] If there are no special limitations on the amount of each substance added in this invention, any ratio can be used; if there are no special limitations on indicators such as concentration, any concentration can be used.

[0023] Example 1 A method for preparing boron carbide ceramic material: Prepare 250g of a 0.3% gellan gum solution, then weigh 250g of boron carbide powder with a particle size of approximately 2μm and mix them evenly. Ball mill the uniformly mixed powder slurry for 20 minutes to ensure thorough dispersion. Pour the resulting uniformly mixed slurry into a freezing container, place the container on a low-temperature cooling platform, use liquid nitrogen as the cold source, freeze at -50℃, and at a freezing rate of 90μm / s (i.e., the liquid nitrogen is introduced at a relatively fast rate, thus creating different temperatures from one end to the other in the initial stage, enabling the formation of a more regularly oriented crystal structure, and finally achieving a uniform and consistent temperature to complete the freezing process). After the slurry is completely frozen, remove the freezing container and freeze-dry it in a freeze-drying oven to obtain a green body with an oriented structure. The green body was placed in a hot-press sintering furnace, which was then evacuated to a vacuum level <0.001 MPa. The temperature was increased to 500℃ at a rate of 5℃ / min. Argon gas was introduced into the furnace, and pressurization was initiated to a pressure of 55 MPa. Sintering was performed under an argon atmosphere, with the temperature increased to 1950℃ at a rate of 5℃ / min and held for 1 hour. The temperature was then increased to 2300℃ and held for 3 hours. Finally, the material was cooled to room temperature and removed to obtain boron carbide ceramic material with a density of 2.38 g / cm³. 3The density reaches over 95%, the flexural strength is 550 MPa, and the fracture toughness is 6.7 MPa·m. 1 / 2 .

[0024] Example 2 A method for preparing boron carbide ceramic material: Prepare 300g of a 0.05% gelatin and agar mixed solution (1:1 ratio). Weigh 200g of boron carbide powder with a particle size of approximately 5μm and mix thoroughly. Ball mill the uniformly mixed powder slurry for 10 minutes to ensure complete dispersion. Pour the resulting uniformly mixed slurry into a freezing container and place it on a low-temperature cooling platform. Use liquid nitrogen as the cold source, freeze at -40℃, and at a freezing rate of 60μm / s. After the slurry is completely frozen, remove the freezing container and freeze-dry it in a freeze-drying oven to obtain a green body with an oriented structure. The green body was placed in a hot-press sintering furnace, which was then evacuated to a vacuum level <0.001 MPa. The temperature was increased to 500℃ at a rate of 5℃ / min. Argon gas was introduced into the sintering furnace, and pressurization was initiated to a pressure of 20 MPa. Sintering was performed under an argon atmosphere, with the temperature increased to 1950℃ at a rate of 5℃ / min and held for 0.5 hours. The temperature was then increased to 2100℃ and held for 0.5 hours. Finally, the material was cooled to room temperature and removed to obtain boron carbide ceramic material with a density of 2.32 g / cm³. 3 The density reaches over 95%, the flexural strength is 480 MPa, and the fracture toughness is 5.3 MPa·m. 1 / 2 .

[0025] Example 3 A method for preparing boron carbide ceramic material: 250g of a mixed solution of 0.1% gellan gum, polyvinyl alcohol, and polylactic acid gel (mixed in a ratio of 2:1:1) is prepared. Then, 250g of boron carbide powder with a particle size of approximately 4μm is weighed and mixed evenly. The uniformly mixed powder slurry is ball-milled for 15 minutes to ensure thorough dispersion. The resulting uniformly mixed slurry is poured into a freezing container and placed on a low-temperature cooling platform. Liquid nitrogen is used as the cold source, the freezing temperature is -45℃, and the freezing rate is 70μm / s. After the slurry is completely frozen, the freezing container is removed and placed in a freeze-drying oven to freeze-dry, obtaining a green body with an oriented structure. The green body was placed in a hot-pressing sintering furnace, which was then evacuated to a vacuum level <0.001 MPa. The temperature was increased to 500℃ at a rate of 5℃ / min. Argon gas was introduced into the sintering furnace, and pressurization was initiated to a pressure of 40 MPa. Sintering was performed under an argon atmosphere, with the temperature increased to 1950℃ at a rate of 5℃ / min and held for 0.5 hours. The temperature was then increased to 2200℃ and held for 1 hour. Finally, the material was cooled to room temperature and removed to obtain boron carbide ceramic material with a density of 2.4 g / cm³. 3 The density reaches over 95%, the flexural strength is 500 MPa, and the fracture toughness is 6.0 MPa·m.1 / 2 .

[0026] Comparative Example 1 The difference from Example 1 is that the freezing rate was 40 μm / s (to allow for slower liquid nitrogen filling, thus ensuring a more uniform temperature from one end of the container to the other). This slow freezing rate resulted in poorer crystal orientation of the boron carbide ceramic material green body, larger pore sizes in the layered structure, and a decrease in density after sintering, with a density below 92% and a density of 2.22 g / cm³. 3 The flexural strength is 400 MPa, and the fracture toughness is 4.7 MPa·m. 1 / 2 .

[0027] Comparative Example 2 The difference from Example 1 is that an aqueous solution was used instead of the 0.3% gellan gum solution. Using an aqueous solution as the solvent resulted in uneven ice crystal growth, leading to an uneven layered structure in the obtained boron carbide ceramic material, increased defects, a compaction density of 93%, and a density of 2.18 g / cm³. 3 The flexural strength is 380 MPa, and the fracture toughness is 4.4 MPa·m. 1 / 2 .

[0028] Comparative Example 3 The difference from Example 1 is that the temperature was directly raised to 2300℃ at a rate of 5℃ / min, held for 3 hours, and not stopped at 1950℃. This resulted in uncontrolled grain size, leading to a reduction in the number of layered crystals in the prepared boron carbide ceramic material, and consequently, decreased strength and toughness. The flexural strength was 350 MPa, and the fracture toughness was 4 MPa·m. 1 / 2 .

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0030] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing boron carbide ceramic material, characterized in that, Includes the following steps: Boron carbide powder is mixed with a gelling agent solution to form a slurry; The slurry is subjected to directional freeze-drying to obtain a blank with a hollow lamellar structure. The blank is hot-pressed and sintered in a vacuum or inert atmosphere to obtain the boron carbide ceramic material; The freezing temperature for the directional freeze-drying is -30 to -50°C; the freezing rate for the directional freeze-drying is 60-90 μm / s. The directional freeze-drying process involves controlling the temperature at different points from one end of the container containing the slurry to the other. The hot pressing sintering temperature is 2000-2300℃, and the hot pressing sintering pressure is 20-55MPa; The hot pressing sintering process involves first heating the temperature to 450-550℃ at a rate of 2-5℃ / min and holding it at that temperature for 0.5-1h. Pressurization is completed during the heat preservation process, followed by heating at a rate of 2-5℃ / min to 1900-1980℃ and holding for 0.5-1h, and finally heating to the temperature of the hot pressing sintering and holding for 0.5-5h.

2. The method for preparing boron carbide ceramic material according to claim 1, characterized in that, The gelling agent solution includes one or more of gellan gum, gelatin, agar, polyvinyl alcohol, polyacrylamide, or polylactic acid gel.

3. The method for preparing boron carbide ceramic material according to claim 1, characterized in that, The concentration of the gelling agent solution is 0.05-0.3%.

4. The method for preparing boron carbide ceramic material according to claim 1, characterized in that, The mass ratio of boron carbide powder to gelling agent solution is 1:0.5-1.

5.

5. The method for preparing boron carbide ceramic material according to claim 1, characterized in that, The boron carbide powder has a particle size of 2-5 μm.

6. A boron carbide ceramic material, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.