Preparation method of boron carbide bulletproof ceramic with hard outside and tough inside and gradient structure

Abstract

The invention discloses a preparation method of a hard-outside tough-inside gradient structure boron carbide bulletproof ceramic, which comprises the following steps: firstly, carrying out ball milling treatment on boron carbide powder to obtain powder with smaller particle size, carrying out oxidation treatment on a dry metal net of which the surface oxide is removed through solution cleaning, and placing the metal net at a fixed position according to a sample design schematic diagram; by utilizing the characteristic that a low-melting-point second phase is diffused in boron carbide, the boron carbide bulletproof ceramic with high surface hardness and high core fracture toughness is prepared through sintering. The content of the second phase of Al2O3 is dispersed and distributed in the boron carbide ceramic in a gradient manner, the content of the second phase in an original metal net area is relatively high, the toughening effect of Al2O3 is obvious, the content of the second phase in a surface area far away from a metal net is relatively low, the mechanical property of the surface of boron carbide is not influenced, and the characteristic of high hardness of the surface of boron carbide is kept. The high surface hardness of the boron carbide bulletproof ceramic with the hard-outside and tough-inside structure is used for crushing bullets, and the high core fracture toughness can consume more energy.

Description

Technical Field

[0001] The invention relates to the technical field of bulletproof ceramic preparation, in particular to a method for preparing boron carbide bulletproof ceramic with a gradient structure that is hard outside and tough inside. Background Art

[0002] Boron carbide ceramic materials have low density (2.52g / cm 3 ), high hardness and high elastic modulus, etc., and it performs well among many bulletproof ceramic materials and is currently the most promising bulletproof ceramic material. However, boron carbide ceramic materials have a more prominent disadvantage, which is that their fracture toughness is relatively low (1.5-2MPa·m 1 / 2 , indentation test results), after the boron carbide ceramic material is impacted, its fracture mode is mainly transgranular fracture, which is not conducive to absorbing the impact energy. This makes it very easy to break as a whole when impacted. This shortcoming seriously restricts the improvement of its resistance to multiple impacts in the field of bulletproof ceramics.

[0003] In the study of boron carbide, compared with pure boron carbide, adding a toughening second phase inside it helps to improve its fracture toughness. Therefore, the sintering preparation of second-phase toughened boron carbide ceramics is a hot topic of research at home and abroad. The second-phase toughened boron carbide ceramics mainly include the following types, such as oxide second phase (Al 2 O 3 ,Y 2 O 3 etc.), carbides (SiC, TiC, etc.), borides (TiB 2 ,CrB 2 etc.), metals (Ti, Cu, etc.), etc. Traditionally, the addition of a second phase to toughen the material is mostly done by using a ball mill to evenly mix boron carbide and the second phase, and then sintering the mixed powder. However, since boron carbide is the third hardest material in the world and has a relatively light density, according to the mixing law of composite materials, the hardness of boron carbide ceramics with the addition of a second phase will decrease and the density will increase. Since the high surface hardness of boron carbide ceramics is used to crush bullets, a decrease in surface hardness will lead to a decrease in the ability to crush bullets. Therefore, the traditional method of adding a toughening second phase to the mixed powder in ball milling has certain limitations in maintaining the high surface hardness of boron carbide ceramics.

[0004] In the field of low-end protection, alumina is usually used instead of boron carbide to achieve the purpose of bulletproofing because of its relatively cheap price. Alumina has a lower hardness than boron carbide and a relatively high density, but it has a relatively high fracture toughness (4-5MPa·m 1 / 2 ). Moreover, alumina itself can also be used as a sintering aid, and Al2O3 may be formed during the sintering process. 5 O 6 BO 3phase, promoting the sintering of boron carbide.

[0005] Adding aluminum oxide to boron carbide can help improve fracture toughness, but how to reduce the impact on hardness is a difficult point. Therefore, how to add aluminum oxide to boron carbide ceramics in a more appropriate way to achieve toughening effect and minimize the impact on surface hardness is an area where boron carbide composite ceramics need to be improved. Summary of the invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0007] Therefore, the purpose of the present invention is to provide a method for preparing boron carbide bulletproof ceramics with an outer hard and inner tough gradient structure, which overcomes the problem that the surface hardness of boron carbide ceramics decreases due to the addition of a second phase during the toughening process, and prepares boron carbide bulletproof ceramics with both high surface hardness and high core fracture toughness by adding a grid-like low-melting-point phase inside the boron carbide and utilizing the diffusion sintering of the low-melting-point phase inside the boron carbide. And the comprehensive regulation of the density, fracture toughness and protective performance of the boron carbide bulletproof ceramics can be achieved by flexibly adjusting the grid structure.

[0008] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0009] A method for preparing boron carbide bulletproof ceramics with a gradient structure of hard outside and tough inside, the steps are as follows:

[0010] S1. Design the schematic diagram, surface size and thickness of the sample to be pressed, and calculate the raw material mass required for each part according to the schematic diagram and the density of boron carbide. Cut the metal mesh into the same surface size as the sample to be pressed, and then put the cut metal mesh into the oxide film cleaning solution for cleaning for 3-5 minutes to remove the surface oxide, then wash it with deionized water for 5 times, and then dry it in a vacuum drying oven at 80°C for 10-12 hours;

[0011] S2, oxidizing the metal mesh in step S1 to form an oxide film with a thickness of 0.3-50 μm on its surface, then washing it with deionized water for 5 times, and then drying it in a vacuum drying oven at 70° C. for 10-12 hours;

[0012] S3, taking boron carbide powder, grinding beads and alcohol, mixing them, putting them into a high-energy ball mill, ball milling for 10-12 hours to grind the boron carbide raw material into a particle size of 600-800 nm, and then drying them in a vacuum drying oven at 80° C. for 18-24 hours;

[0013] S4, loading the metal mesh finally obtained in step S2 and the boron carbide powder finally obtained in step S3 into the graphite mold layer by layer according to the design, and each layer of powder needs to be pressed flat with a pressing head;

[0014] S5. Put the powder prepared in step S4 into a sintering furnace for sintering. The sintering temperature is controlled to be 1800-2300° C., the holding time is 3-90 min, and the sintering pressure is 20-60 MPa to obtain a boron carbide composite ceramic that is hard on the outside and tough on the inside.

[0015] As a preferred embodiment of the method for preparing a boron carbide bulletproof ceramic with a gradient structure that is hard on the outside and tough on the inside described in the present invention, a method for preparing a boron carbide bulletproof ceramic with a gradient structure that is hard on the outside and tough on the inside is characterized in that in step S1, the sample schematic diagram includes the surface size, thickness, metal mesh size, number of metal mesh layers and position of the metal mesh of the sample.

[0016] As a preferred embodiment of the method for preparing the externally hard and internally tough gradient structure boron carbide bulletproof ceramics described in the present invention, in step S1, the surface dimensions of the samples include samples of different sizes and shapes as well as flat samples and samples with different curvatures.

[0017] As a preferred embodiment of the method for preparing the externally hard and internally tough gradient structure boron carbide bulletproof ceramics described in the present invention, in step S1, the metal mesh is an Al mesh.

[0018] As a preferred embodiment of the method for preparing the externally hard and internally tough gradient structure boron carbide bulletproof ceramics of the present invention, in step S1, the oxide film cleaning solution is a sodium hydroxide solution and a nitric acid solution.

[0019] As a preferred embodiment of the method for preparing the externally hard and internally tough gradient structure boron carbide bulletproof ceramics described in the present invention, in step S2, the oxidation process of the metal mesh can be thermal oxidation, anodic oxidation or micro-arc oxidation, and the thickness of the oxide film is 0.3-50 μm.

[0020] As a preferred embodiment of the method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside described in the present invention, in step S4, when the boron carbide powder and the metal mesh are loaded into the mold layer by layer according to the design, each layer of powder is required to be pressed flat with a pressing head before subsequent operations are performed.

[0021] As a preferred embodiment of the method for preparing a boron carbide bulletproof ceramic with a gradient structure that is hard on the outside and tough on the inside described in the present invention, in step S5, the sintering furnace can be a hot pressing sintering furnace, a spark plasma sintering furnace, or a microwave sintering furnace. When a hot pressing sintering furnace is used, the sintering and heat preservation time is long, and when a spark plasma sintering furnace or a microwave sintering furnace is used, the sintering and heat preservation time is short.

[0022] As a preferred embodiment of the method for preparing the externally hard and internally tough gradient structure boron carbide bulletproof ceramics of the present invention, in step S5, the sintering atmosphere can be a vacuum atmosphere or an argon atmosphere.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. First, by ball-milling the boron carbide powder into a powder with a smaller particle size, it will be more conducive to the sintering of the boron carbide powder. The metal mesh is cleaned to remove the surface oxide, and then it is oxidized to generate a purer and thicker oxide film. The metal mesh is placed in a fixed position according to the sample design diagram. The metal mesh has a low melting point and will diffuse preferentially during the sintering process of the boron carbide powder. The second phase Al with a gradient dispersion distribution is prepared by sintering inside the boron carbide ceramic. 2 O 3 .

[0025] 2. Gradient dispersed distribution of the second phase Al 2 O 3 Added inside boron carbide ceramics, it makes full use of Al 2 O 3 The toughening characteristics of the second phase and the advantages of gradient distribution, the second phase content of the original metal mesh is relatively high, Al 2 O 3 The presence of the toughening phase can deflect cracks and improve the toughness of the core of boron carbide. The second phase content in the surface area away from the metal mesh is relatively low, which does not affect the performance of the boron carbide surface and maintains the high hardness of the boron carbide surface, thereby obtaining a boron carbide composite ceramic with external hardness and internal toughness.

[0026] 3. The boron carbide composite ceramics prepared by this method have the effect of hard outside and tough inside, ensuring high surface hardness. The micron indentation hardness value is 29.8GPa. At the same time, the fracture toughness is significantly improved. The fracture toughness calculated by the indentation method can reach 3.8MPa·m 1 / 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0028] Figure 1 The present invention is a flow chart of a method for preparing a boron carbide bulletproof ceramic with a gradient structure that is hard on the outside and tough on the inside.

[0029] Figure 2 This is an electron microscope image of the microstructure of the externally hard and internally tough gradient structure of alumina toughened boron carbide ceramics. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] The present invention provides a method for preparing a boron carbide bulletproof ceramic with an outer hardness and inner toughness gradient structure, which overcomes the problem that the surface hardness of the boron carbide ceramic decreases due to the addition of a second phase during the toughening process, and prepares a boron carbide bulletproof ceramic with both high surface hardness and high core fracture toughness by adding a grid-shaped low-melting-point phase inside the boron carbide and utilizing the diffusion hot pressing sintering of the low-melting-point phase inside the boron carbide. In addition, the density, fracture toughness and protective performance of the boron carbide bulletproof ceramic can be comprehensively regulated by flexibly adjusting the grid structure.

[0032] Example 1

[0033] S1. Design a schematic diagram of the sample to be pressed, with a diameter of 32mm and a thickness of 6mm, and lay a layer of metal mesh (wire diameter is 0.25mm, aperture is 2mm×3mm) at the position of 3mm thickness, and calculate the mass of boron carbide required for every 3mm thickness according to the schematic diagram and the density of boron carbide, which is 6.077g; cut a layer of metal mesh into the same surface size as the sample to be pressed; put the cut metal mesh into sodium hydroxide solution and nitric acid solution for cleaning for 5min to remove surface oxides, then wash it with deionized water 5 times, and then dry it in a vacuum drying oven at 80℃ for 12h;

[0034] S2, anodizing the metal mesh in step S1 in a sulfuric acid solution to form an oxide film with a thickness of 10 μm on its surface, then washing it with deionized water for 5 times, and then drying it in a vacuum drying oven at 70° C. for 10-12 hours;

[0035] S3. Take a certain amount of boron carbide powder, grinding beads and alcohol (mass ratio 1:1:1.5), mix them, put them into a high-energy ball mill, and grind them for 10 hours to grind the boron carbide raw material into a particle size of 800nm; then dry it in a vacuum drying oven at 80℃ for 24 hours, and pass it through a 100-mesh sieve to prevent agglomeration;

[0036] S4, the metal mesh finally obtained in step S2 and the boron carbide powder finally obtained in step S3 are loaded into the graphite mold layer by layer according to the design, first loading 6.077g of boron carbide powder, followed by the metal mesh that has been acid-washed and dried, and then 6.077g of boron carbide powder. Each layer of powder needs to be pressed flat with a pressure head at a pressure of 10MPa. This helps to achieve uniform powder spreading and obtain consistent density, while making the position of the metal mesh more accurate and in line with our design schematic;

[0037] S5. Put the powder prepared in step S4 into a hot pressing furnace, and perform hot pressing sintering in an argon atmosphere. The sintering temperature is controlled to be 2000°C, the holding time is 60min, and the sintering pressure is 50MPa, so as to obtain a boron carbide composite ceramic with gradient structural toughening. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-2000°C heating rate is 5°C / min, and during the cooling process, the cooling rate at 2000°C-1500°C is 5°C / min, and then the ceramic is cooled with the furnace. Sintering in an argon atmosphere prevents the formation of oxidation products. The heating and cooling rates from 1500℃ to 2000℃ are slow, all to prevent sintering too quickly and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300℃, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300℃ to 800℃, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500℃, and then the pressure gradually decreases to 0MPa. Applying pressure during the sintering process helps to promote the sintering process and obtain a higher density sample.

[0038] Example 2

[0039] S1. Design a schematic diagram of the sample to be pressed, with a diameter of 32mm and a thickness of 6mm, and lay a layer of metal mesh (wire diameter is 0.25mm, aperture is 2mm×3mm) at the position of 3mm thickness, and calculate the mass of boron carbide required for every 3mm thickness according to the schematic diagram and the density of boron carbide, which is 6.077g; cut a layer of metal mesh into the same surface size as the sample to be pressed; put the cut metal mesh into sodium hydroxide solution and nitric acid solution for cleaning for 5min to remove surface oxides, then wash it with deionized water 5 times, and then dry it in a vacuum drying oven at 80℃ for 12h;

[0040] S2, the metal mesh in step S1 is placed in a 2 SiO 3、 KOH and (NaPO 3 ) 6 The micro-arc oxidation was carried out in an electrolyte of , and an oxide film with a thickness of 20 μm was formed on the surface, which was then washed with deionized water for 5 times and then dried in a vacuum drying oven at 70°C for 10-12h;

[0041] S3. Take a certain amount of boron carbide powder, grinding beads and alcohol (mass ratio 1:1:1.5), mix them, put them into a high-energy ball mill, and grind them for 10 hours to grind the boron carbide raw material into a particle size of 800nm; then dry it in a vacuum drying oven at 80℃ for 24 hours, and pass it through a 100-mesh sieve to prevent agglomeration;

[0042] S4, the metal mesh finally obtained in step S2 and the boron carbide powder finally obtained in step S3 are loaded into the graphite mold layer by layer according to the design, first loading 6.077g of boron carbide powder, followed by the metal mesh that has been acid-washed and dried, and then 6.077g of boron carbide powder. Each layer of powder needs to be pressed flat with a pressure head at a pressure of 10MPa. This helps to achieve uniform powder spreading and obtain consistent density, while making the position of the metal mesh more accurate and in line with our design schematic;

[0043] S5. Put the powder prepared in step S4 into a hot pressing furnace, and perform hot pressing sintering in an argon atmosphere. The sintering temperature is controlled to be 2000°C, the holding time is 60min, and the sintering pressure is 50MPa, so as to obtain a boron carbide composite ceramic with gradient structural toughening. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-2000°C heating rate is 5°C / min, and during the cooling process, the cooling rate at 2000°C-1500°C is 5°C / min, and then the ceramic is cooled with the furnace. Sintering in an argon atmosphere prevents the formation of oxidation products. The heating and cooling rates from 1500℃ to 2000℃ are slow, all to prevent sintering too quickly and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300℃, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300℃ to 800℃, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500℃, and then the pressure gradually decreases to 0MPa. Applying pressure during the sintering process helps to promote the sintering process and obtain a higher density sample.

[0044] Example 3

[0045] S1. Design a schematic diagram of the sample to be pressed, with a diameter of 32mm and a thickness of 6mm, and lay a layer of metal mesh (wire diameter is 0.5mm, aperture is 2mm×3mm) at the position of 3mm thickness, and calculate the mass of boron carbide required for every 3mm thickness according to the schematic diagram and the density of boron carbide, which is 6.077g; cut a layer of metal mesh into the same surface size as the sample to be pressed; put the cut metal mesh into sodium hydroxide solution and nitric acid solution for cleaning for 5min to remove surface oxides, then wash it with deionized water 5 times, and then dry it in a vacuum drying oven at 80℃ for 12h;

[0046] S2, anodizing the metal mesh in step S1 in a sulfuric acid solution to form an oxide film with a thickness of 10 μm on its surface, then washing it with deionized water for 5 times, and then drying it in a vacuum drying oven at 70° C. for 10-12 hours;

[0047] S3. Take a certain amount of boron carbide powder, grinding beads and alcohol (mass ratio 1:1:1.5), mix them, put them into a high-energy ball mill, and grind them for 10 hours to grind the boron carbide raw material into a particle size of 800nm; then dry it in a vacuum drying oven at 80℃ for 24 hours, and pass it through a 100-mesh sieve to prevent agglomeration;

[0048] S4, the metal mesh finally obtained in step S2 and the boron carbide powder finally obtained in step S3 are loaded into the graphite mold layer by layer according to the design, first loading 6.077g of boron carbide powder, followed by the metal mesh that has been acid-washed and dried, and then 6.077g of boron carbide powder. Each layer of powder needs to be pressed flat with a pressure head at a pressure of 10MPa. This helps to achieve uniform powder spreading and obtain consistent density, while making the position of the metal mesh more accurate and in line with our design schematic;

[0049] S5. Put the powder prepared in step S4 into a hot pressing furnace, and perform hot pressing sintering in an argon atmosphere. The sintering temperature is controlled to be 2000°C, the holding time is 60min, and the sintering pressure is 50MPa, so as to obtain a boron carbide composite ceramic with gradient structural toughening. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-2000°C heating rate is 5°C / min, and during the cooling process, the cooling rate at 2000°C-1500°C is 5°C / min, and then the ceramic is cooled with the furnace. Sintering in an argon atmosphere prevents the formation of oxidation products. The heating and cooling rates from 1500℃ to 2000℃ are slow, all to prevent sintering too quickly and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300℃, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300℃ to 800℃, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500℃, and then the pressure gradually decreases to 0MPa. Applying pressure during the sintering process helps to promote the sintering process and obtain a higher density sample.

[0050] Although the present invention has been described above with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing boron carbide bulletproof ceramics with a gradient structure of hard outside and tough inside, characterized in that: Here are the steps: S1. Design the schematic diagram, surface size and thickness of the sample to be pressed, and calculate the raw material mass required for each part according to the schematic diagram and the density of boron carbide. Cut the metal mesh into the same surface size as the sample to be pressed, and then put the cut metal mesh into the oxide film cleaning solution for cleaning for 3-5 minutes to remove the surface oxide, then wash it with deionized water for 5 times, and then dry it in a vacuum drying oven at 80°C for 10-12 hours; S2, oxidizing the metal mesh in step S1 to form an oxide film with a thickness of 0.3-50 μm on its surface, then washing it with deionized water for 5 times, and then drying it in a vacuum drying oven at 70° C. for 10-12 hours; S3, taking boron carbide powder, grinding beads and alcohol, mixing them, putting them into a high-energy ball mill, ball milling for 10-12 hours to grind the boron carbide raw material into a particle size of 600-800 nm, and then drying them in a vacuum drying oven at 80° C. for 18-24 hours; S4, loading the metal mesh finally obtained in step S2 and the boron carbide powder finally obtained in step S3 into the graphite mold layer by layer according to the design, and each layer of powder needs to be pressed flat with a pressing head; S5. Put the powder prepared in step S4 into a sintering furnace for sintering. The sintering temperature is controlled to be 1800-2300° C., the holding time is 3-90 min, and the sintering pressure is 20-60 MPa to obtain a boron carbide composite ceramic that is hard on the outside and tough on the inside.

2. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S1, the sample schematic diagram includes the surface size, thickness, metal mesh size, number of metal mesh layers and position of the metal mesh of the sample.

3. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S1, the surface dimensions of the samples include different sizes and different shapes as well as flat samples and samples with different curvatures.

4. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S1, the metal mesh is an Al mesh.

5. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S1, the oxide film cleaning solution is a sodium hydroxide solution and a nitric acid solution.

6. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S2, the oxidation process of the metal mesh can be thermal oxidation, anodic oxidation or micro-arc oxidation, and the thickness of the oxide film is 0.3-50 μm.

7. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S4, when the boron carbide powder and the metal mesh are loaded into the mold layer by layer according to the design, each layer of powder is required to be pressed flat with a pressing head before subsequent operations are performed.

8. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S5, the sintering furnace is a hot pressing sintering furnace or a spark plasma sintering furnace or a microwave sintering furnace. When the hot pressing sintering furnace is used, the sintering heat preservation time is long, and when the spark plasma sintering furnace or a microwave sintering furnace is used, the sintering heat preservation time is short.

9. The method for preparing a boron carbide bulletproof ceramic with a gradient structure of hard outside and tough inside according to claim 1, characterized in that: In step S5, the sintering atmosphere is a vacuum atmosphere or an argon atmosphere.

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