Preparation method of boron carbide ceramic composite material

Abstract

The invention relates to the technical field of composite materials, in particular to a preparation method of a boron carbide ceramic composite material, which comprises the following steps: S1, preparing modified magnesium borate nanowires; s2, diamond powder, boron carbide powder, graphite powder, phenolic resin and the modified magnesium borate nanowires are taken. S3, diamond, boron carbide, graphite and the modified magnesium borate nanowire are added into absolute ethyl alcohol, and ball milling and mixing are conducted; and adding phenolic resin, continuously carrying out ball milling to form uniform slurry, and carrying out ultralow-temperature liquid nitrogen spray granulation. And S4, staged vacuum hot press molding is conducted, specifically, low-pressure pre-curing treatment is conducted in the first stage, and high-pressure densification treatment is conducted in the second stage. And S5, degreasing treatment, gradient boriding and electromagnetic field coupling, magnesium borate nanowires are added into a system to serve as a reinforcing phase and a boriding channel at the same time, a pulse electromagnetic field is superposed to solve the problem of uneven boriding, a densification path is optimized through staged hot pressing, and finally comprehensive improvement of the performance of the boron carbide ceramic composite material is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly relates to a preparation method of a boron carbide ceramic composite material. Background Art

[0002] Diamond-boron carbide composite ceramics have important application values in the fields of bulletproof armor, precision cutting tools, and extreme environment protection due to their extremely high hardness, low density, and excellent wear resistance. However, the existing preparation technologies still have the following key problems, which seriously restrict the further improvement of material properties. One is weak grain boundary bonding and frequent occurrence of interfacial microcracks: The physical and chemical properties of boron carbide (B4C) and diamond are significantly different, and the interfacial bonding force between the two is weak. In traditional preparation processes, due to the lack of effective interfacial regulation means, microcracks are easily formed at the interface between boron carbide and diamond. These microcracks rapidly expand under the action of stress, resulting in the difficulty of breaking through the overall hardness (usually ≤ 35 GPa) and density (porosity ≥ 2%) of the material, and severely weakening its impact resistance. The second is uneven boron penetration depth and poor process controllability: Most of the existing boron penetration processes adopt single high-temperature sintering (such as constant temperature at 2200 °C), but due to the temperature gradient effect, a brittle boron carbide layer is formed in the surface area due to excessive reaction, while the internal penetration is insufficient (the boron penetration depth is usually ≤ 1.5 mm). Although the boron penetration methods disclosed in the existing technologies can reduce silicon-based impurities, the problem of uneven boron penetration depth has not been solved, resulting in significantly lower performance of the core part of the material than that of the surface layer, restricting its application in large-sized components. The third is that the porosity is difficult to control and the nano-reinforcing phase is prone to agglomeration: In order to improve the densification of the material, the existing technologies attempt to introduce nano-reinforcing phases (such as nano-silicon carbide). However, due to van der Waals forces, nano-particles are prone to agglomeration and cannot effectively fill the gaps between micron-sized diamond and boron carbide particles. This phenomenon results in a high porosity of the composite material (generally ≥ 3%) and limited improvement in mechanical properties (three-point bending strength ≤ 400 MPa). In addition, the single pressure of the traditional hot pressing process (such as a constant 150 MPa) further exacerbates the problem of incomplete pore closure.

[0003] In summary, although the existing diamond-boron carbide composite ceramics reduce silicon-based impurities through the boron penetration process, their hardness and density are still restricted by grain coarsening, high porosity, and unevenness of the boron penetration reaction. The above problems seriously restrict the application of composite ceramics in high-protection and high-precision scenarios. Therefore, there is an urgent need for an innovative preparation method to comprehensively improve the comprehensive performance of the material by optimizing the interfacial bonding, boron penetration process, and dispersion of the nano-reinforcing phase. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, magnesium borate nanowires are added to the system to act as both a reinforcing phase and a boron penetration channel, a superimposed pulsed electromagnetic field is used to solve the problem of uneven boron penetration, and staged hot pressing is used to optimize the densification path, finally achieving a comprehensive improvement in the performance of the boron carbide ceramic composite material.

[0005] To solve the above problems, the present invention provides a method for preparing a boron carbide ceramic composite material, which is characterized by comprising the following steps:

[0006] Step S1: Take magnesium nitrate, boric acid, and citric acid, stir in a water bath at 80 °C for 6 h to form a transparent sol; after drying at 120 °C, calcine to obtain nanowires; immerse the nanowires in a 2 wt% modifier and ultrasonically treat for 30 min, and dry at 60 °C to obtain modified magnesium borate nanowires.

[0007] Step S2: Take diamond powder, boron carbide powder, graphite powder, phenolic resin, and modified magnesium borate nanowires.

[0008] Step S3: Add diamond, boron carbide, graphite, and modified magnesium borate nanowires into absolute ethanol, ball mill and mix; add phenolic resin, continue to ball mill for 1 h to form a uniform slurry, and use ultra-low temperature liquid nitrogen spray granulation.

[0009] Step S4: Vacuum hot press molding in stages: the first stage is low-pressure pre-curing treatment, and the second stage is high-pressure densification treatment.

[0010] Step S5: Degreasing treatment, gradient boron infiltration and electromagnetic field coupling, pulse electromagnetic field parameters: frequency 30 kHz, magnetic field strength 1 T, pulse period 0.1 s on / 0.05 s off; holding time: 30 min; furnace cooling to room temperature.

[0011] The present invention uses a pulsed electromagnetic field to induce an eddy current effect in molten boron, increasing the penetration depth to 2.5 - 3 mm. The intermittent power-off treatment can inhibit the graphitization of the diamond surface, making the thickness of the surface graphite layer ≤ 50 nm.

[0012] Further, in step S1, the molar ratio of magnesium nitrate, boric acid, and citric acid is 1:2:1.5; the specific calcination conditions are: calcine at 600 °C for 2 h; the modifier is a carboxylated PVP ethanol solution.

[0013] The magnesium borate nanowires of the present invention are synthesized by the sol-gel method and are surface-coated with carboxylated polyvinylpyrrolidone (PVP), which can enhance the compatibility with phenolic resin.

[0014] Further, in step S1, the diameter of the nanowires is 10 - 50 nm and the aspect ratio > 50.

[0015] Further, in step S2, by volume percentage, the content of each component is: diamond powder: 40 - 65%; boron carbide powder: 20 - 35%; graphite powder: 5 - 8%; phenolic resin: 15 - 20%; modified magnesium borate nanowires: 0.3 - 1.5%.

[0016] Further, in step S2, the particle size of the diamond powder is 50 - 150 μm, and the purity is ≥99.9%; the particle size of the boron carbide powder is 10 - 50 μm, and the purity is ≥99.5%; the particle size of the graphite powder is 20 - 50 μm, and the purity is ≥99.9%; the solid content of the phenolic resin is ≥85%.

[0017] Further, the specific parameters for ball milling and mixing in step S3 are: the ball-to-material ratio is 5:1, the rotation speed is 200 rpm, and the time is 4 h; the spray granulation parameters are: the liquid nitrogen temperature is -196°C; the nozzle diameter is 0.5 mm; the spray rate is 8 mL / min; the droplet particle size is 50 - 100 μm.

[0018] Further, the specific parameters for the first-stage low-pressure pre-curing in step S4 are: the temperature is 130 - 140°C; the pressure is 50 MPa; the pressure holding time is 5 min; the vacuum degree is 10 -2 Pa.

[0019] Further, the specific parameters for the second-stage high-pressure densification in step S4 are: the temperature is 150 - 160°C; the pressure is stepped pressurization: 50 MPa - 100 MPa - 200 MPa, the pressurization rate for each stage is 20 MPa / min, and the pressure holding time in the final pressure state is 15 min.

[0020] Further, in step S5, the temperature for degreasing treatment is 1000 - 1100°C; the heating rate is 2°C / min; the heat preservation time is 120 min; the atmosphere is argon protection.

[0021] Further, the specific process parameters for gradient boronizing in step S5 are: the boronizing agent is high-purity boron powder, the purity is ≥99.99%, and the particle size is 1 - 5 μm; the temperature in the first stage is from room temperature to 1800°C, the heating rate is 10°C / min; the axial pressure is 5 MPa; the vacuum degree is 10 -1 Pa; the temperature in the second stage is 1800°C to 2200°C, the heating rate is 5°C / min; the axial pressure is 10 MPa.

[0022] The positive and beneficial effects of the present invention are as follows:

[0023] The present invention introduces nanowires into the system, which can form a "pinning effect" at the interface between diamond and boron carbide to inhibit crack propagation; in addition, the PVP coated on the surface of the modified nanowires in the present invention forms nanopores after thermal decomposition, guiding the directional penetration of boron atoms along the nanowires, thereby improving the uniformity of boronizing.

[0024] In the boronizing stage of the present invention, a pulsed electromagnetic field is introduced. The high-frequency magnetic field will induce an eddy current effect in the molten boron, enhance the fluidity of the liquid boron, and enable it to penetrate deep into the preform, resulting in a 30% comprehensive increase in the penetration depth. In addition, the pulsed power-off interval avoids excessive graphitization on the diamond surface and maintains the intrinsic hardness of the material.

[0025] The present invention adopts a densification mechanism of staged hot pressing: in the first stage, the resin is cured under low pressure to avoid the fracture of nanowires due to high pressure; in the second stage, high pressure promotes the directional arrangement of nanowires along the pressure direction, fills the grain boundary pores, and makes the porosity ≤ 0.5%, thereby significantly improving the comprehensive performance of the composite ceramic. Specific embodiments

[0026] In order to more clearly elaborate the technical solutions and implementation effects of the present invention, the methods of the present invention will be further described in detail below in conjunction with specific embodiments. However, the protection scope of the present invention is not limited to these embodiments.

[0027] Example 1

[0028] Magnesium nitrate, boric acid, and citric acid are taken in a molar ratio of 1:2:1.5, stirred in a water bath at 80°C for 6 hours to form a transparent sol; after drying at 120°C, it is calcined at 600°C for 2 hours to obtain nanowires with a diameter of 10 - 50 nm and an aspect ratio > 50; the nanowires are immersed in a 2 wt% carboxylated PVP ethanol solution and ultrasonically treated for 30 minutes, and then dried at 60°C.

[0029] By volume, diamond powder (particle size 50 - 150 μm, purity ≥ 99.9%): 40%; boron carbide powder (particle size 10 - 50 μm, purity ≥ 99.5%): 20%; graphite powder (particle size 20 - 50 μm, purity ≥ 99.9%): 5%; phenolic resin (solid content ≥ 85%): 15%; modified magnesium borate nanowires: 0.3%

[0030] Freeze spray granulation and mixing: Diamond, boron carbide, graphite, and nanowires are added to anhydrous ethanol, ball milled and mixed with a ball-to-material ratio of 5:1, a rotation speed of 200 rpm, and a time of 4 hours; phenolic resin is added and ball milling is continued for 1 hour to form a uniform slurry. Ultra-low temperature liquid nitrogen spray granulation is used, and the spray parameters are: liquid nitrogen temperature: -196°C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet particle size: 50 - 100 μm.

[0031] Staged vacuum hot pressing forming: In the first stage, low-pressure pre-curing, temperature: 140°C; pressure: 50 MPa; holding pressure time: 5 minutes; vacuum degree: 10 -2Pa. In the second stage of high-pressure densification, temperature: 150°C; pressure: stepped pressure: 50 MPa - 100 MPa - 200 MPa, pressure increase rate of 20 MPa / min for each stage; holding time at the final pressure of 200 MPa: 15 min;

[0032] Pulse electromagnetic field-assisted boronizing sintering: degreasing treatment, degreasing temperature: 1050°C; heating rate: 2°C / min; holding time: 120 min; atmosphere: argon protection.

[0033] Gradient boronizing coupled with electromagnetic field,

[0034] Boronizing agent: high-purity boron powder (purity ≥ 99.99%, particle size 1 - 5 μm); in the first stage, from room temperature to 1800°C, heating rate: 10°C / min; axial pressure: 5 MPa; vacuum degree: 10 -1 Pa. In the second stage, from 1800°C to 2200°C: heating rate: 5°C / min; axial pressure: 10 MPa;

[0035] Pulse electromagnetic field parameters: frequency 30 kHz, magnetic field intensity 1 T, pulse period 0.1 s on / 0.05 s off; holding time: 30 min, cooled to room temperature with the furnace, cut and processed into standard specimens.

[0036] Example 2

[0037] Take magnesium nitrate, boric acid, and citric acid according to the molar ratio of 1:2:1.5, stir in a water bath at 80°C for 6 h to form a transparent sol; after drying at 120°C, calcine at 600°C for 2 h to obtain nanowires with a diameter of 10 - 50 nm and an aspect ratio > 50; immerse the nanowires in a 2 wt% carboxylated PVP ethanol solution and ultrasonically treat for 30 min, then dry at 60°C.

[0038] By volume, take diamond powder (particle size 50 - 150 μm, purity ≥ 99.9%): 48%; boron carbide powder (particle size 10 - 50 μm, purity ≥ 99.5%): 28%; graphite powder (particle size 20 - 50 μm, purity ≥ 99.9%): 6%; phenolic resin (solid content ≥ 85%): 16%; modified magnesium borate nanowires: 0.5%,

[0039] Freeze spray granulation and mixing: Add diamond, boron carbide, graphite, and nanowires to anhydrous ethanol, ball mill and mix, ball-to-material ratio 5:1, rotation speed 200 rpm, time 4 h; add phenolic resin and continue ball milling for 1 h to form a uniform slurry. Use ultra-low temperature liquid nitrogen spray granulation, spray parameters: liquid nitrogen temperature: -196°C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet particle size: 50 - 100 μm.

[0040] Staged vacuum hot pressing and forming: In the first stage, low-pressure pre-curing is carried out at a temperature of 130 - 140 °C, a pressure of 50 MPa, a holding time of 5 min, and a vacuum degree of 10 -2 Pa. In the second stage, high-pressure densification is carried out at a temperature of 150 - 160 °C, with stepwise pressure increase: 50 MPa - 100 MPa - 200 MPa, and the pressure increase rate for each stage is 20 MPa / min. The holding time at the final pressure of 200 MPa is 15 min;

[0041] Pulse electromagnetic field-assisted boronizing sintering: Degreasing treatment is carried out at a degreasing temperature of 1100 °C, a heating rate of 2 °C / min, a holding time of 120 min, and an argon gas protection atmosphere.

[0042] Gradient boronizing is coupled with the electromagnetic field,

[0043] Boronizing agent: High-purity boron powder (purity ≥ 99.99%, particle size 1 - 5 μm); In the first stage, from room temperature to 1800 °C, the heating rate is 10 °C / min; the axial pressure is 5 MPa; the vacuum degree is 10 -1 Pa. In the second stage, from 1800 °C to 2200 °C: the heating rate is 5 °C / min; the axial pressure is 10 MPa;

[0044] Pulse electromagnetic field parameters: frequency 30 kHz, magnetic field intensity 1 T, pulse period 0.1 s on / 0.05 s off; the holding time is 30 min, and it is cooled to room temperature with the furnace, and then cut and processed into standard specimens.

[0045] Example 3

[0046] Magnesium nitrate, boric acid, and citric acid are taken in a molar ratio of 1:2:1.5, and stirred in a water bath at 80 °C for 6 h to form a transparent sol; after drying at 120 °C, it is calcined at 600 °C for 2 h to obtain nanowires with a diameter of 10 - 50 nm and an aspect ratio > 50; the nanowires are immersed in a 2 wt% carboxylated PVP ethanol solution and ultrasonically treated for 30 min, and then dried at 60 °C.

[0047] By volume, diamond powder (particle size 50 - 150 μm, purity ≥ 99.9%): 65%; boron carbide powder (particle size 10 - 50 μm, purity ≥ 99.5%): 35%; graphite powder (particle size 20 - 50 μm, purity ≥ 99.9%): 8%; phenolic resin (solid content ≥ 85%): 20%; modified magnesium borate nanowires: 1.5%,

[0048] Freezing Spray Granulation and Mixing: Add diamond, boron carbide, graphite, and nanowires into absolute ethanol, ball mill and mix them with a ball-to-material ratio of 5:1, a rotation speed of 200 rpm, and a time of 4 h; add phenolic resin and continue ball milling for 1 h to form a uniform slurry. Use ultra-low temperature liquid nitrogen spray granulation, and the spray parameters are as follows: liquid nitrogen temperature: -196 °C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet particle size: 50 - 100 μm.

[0049] Staged Vacuum Hot Pressing and Forming: The first stage is low-pressure pre-curing, with a temperature of 140 °C, a pressure of 50 MPa, a holding time of 5 min, and a vacuum degree of 10 -2 Pa. The second stage is high-pressure densification, with a temperature of 155 °C, a stepwise pressure increase: 50 MPa - 100 MPa - 200 MPa, and the pressure increase rate for each stage is 20 MPa / min; the holding time at the final pressure of 200 MPa is 15 min;

[0050] Pulsed Electromagnetic Field Assisted Boronizing Sintering: Degreasing treatment, with a degreasing temperature of 1100 °C, a heating rate of 2 °C / min, a holding time of 120 min, and an atmosphere of argon protection.

[0051] Gradient Boronizing and Electromagnetic Field Coupling

[0052] Boronizing Agent: High-purity boron powder (purity ≥ 99.99%, particle size 1 - 5 μm); in the first stage, from room temperature to 1800 °C, the heating rate is 10 °C / min; the axial pressure is 5 MPa; the vacuum degree is 10 -1 Pa. In the second stage, from 1800 °C to 2200 °C: the heating rate is 5 °C / min; the axial pressure is 10 MPa;

[0053] Pulsed Electromagnetic Field Parameters: frequency 30 kHz, magnetic field intensity 1 T, pulse period 0.1 s on / 0.05 s off; holding time: 30 min, cool to room temperature with the furnace, and cut and process into standard specimens.

[0054] Example 4

[0055] Take magnesium nitrate, boric acid, and citric acid according to a molar ratio of 1:2:1.5, stir in a water bath at 80 °C for 6 h to form a transparent sol; after drying at 120 °C, calcine at 600 °C for 2 h to obtain nanowires with a diameter of 10 - 50 nm and an aspect ratio > 50; immerse the nanowires in a 2 wt% carboxylated PVP ethanol solution and ultrasonically treat for 30 min, then dry at 60 °C.

[0056] By volume, take diamond powder (particle size 50 - 150 μm, purity ≥ 99.9%): 55%; boron carbide powder (particle size 10 - 50 μm, purity ≥ 99.5%): 30%; graphite powder (particle size 20 - 50 μm, purity ≥ 99.9%): 6%; phenolic resin (solid content ≥ 85%): 18%; modified magnesium borate nanowires: 1.2%,

[0057] Freeze - spray granulation and mixing: Add diamond, boron carbide, graphite, and nanowires into absolute ethanol, ball - mill and mix them with a ball - to - material ratio of 5:1, a rotation speed of 200 rpm, and a time of 4 h; then add phenolic resin and continue ball - milling for 1 h to form a uniform slurry. Use ultra - low - temperature liquid nitrogen spray granulation, and the spray parameters are: liquid nitrogen temperature: - 196 °C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet particle size: 50 - 100 μm.

[0058] Staged vacuum hot - pressing forming: The first stage is low - pressure pre - curing, with a temperature of 130 °C, a pressure of 50 MPa, a holding pressure time of 5 min, and a vacuum degree of 10 -2 Pa. The second stage is high - pressure densification, with a temperature of 160 °C, and a step - wise pressure increase: 50 MPa - 100 MPa - 200 MPa, with a pressure increase rate of 20 MPa / min for each stage; the holding pressure time at the final pressure of 200 MPa is 15 min;

[0059] Pulsed electromagnetic field - assisted boronizing sintering: Degreasing treatment, with a degreasing temperature of 1100 °C, a heating rate of 2 °C / min, a holding time of 120 min, and an argon - protected atmosphere.

[0060] Gradient boronizing and electromagnetic field coupling,

[0061] Boronizing agent: High - purity boron powder (purity ≥ 99.99%, particle size 1 - 5 μm); in the first stage, from room temperature to 1800 °C, the heating rate is 10 °C / min; the axial pressure is 5 MPa; the vacuum degree is 10 -1 Pa. In the second stage, from 1800 °C to 2200 °C: the heating rate is 5 °C / min; the axial pressure is 10 MPa;

[0062] Pulsed electromagnetic field parameters: frequency 30 kHz, magnetic field strength 1 T, pulse period 0.1 s on / 0.05 s off; holding time: 30 min, and then cool to room temperature with the furnace, and cut and process into standard specimens.

[0063] Control example

[0064] By volume, take diamond powder (particle size 50 - 150 μm, purity ≥ 99.9%): 55%; boron carbide powder (particle size 10 - 50 μm, purity ≥ 99.5%): 30%; graphite powder (particle size 20 - 50 μm, purity ≥ 99.9%): 6%; phenolic resin (solid content ≥ 85%): 18%; Add diamond, boron carbide, graphite, and nanowires to absolute ethanol, ball mill and mix them, with a ball-to-material ratio of 5:1, a rotation speed of 200 rpm, and a time of 4 h; Add phenolic resin and continue ball milling for 1 h to form a uniform slurry.

[0065] Use ultra-low temperature liquid nitrogen spray granulation, spray parameters: liquid nitrogen temperature: -196 °C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet particle size: 50 - 100 μm.

[0066] The first stage is low-pressure pre-curing, temperature: 130 °C; pressure: 50 MPa; pressure holding time: 5 min; vacuum degree: 10 -2 Pa. The second stage is high-pressure densification, temperature: 160 °C; pressure: stepped pressure: 50 MPa - 100 MPa - 200 MPa, with a pressure increase rate of 20 MPa / min for each stage; at the final pressure of 200 MPa, the pressure holding time: 15 min;

[0067] Carry out degreasing treatment on the pressed sample, with a heating rate of 2 °C / min, a maximum temperature of 1100 °C, and an insulation time of 120 min;

[0068] Boronizing treatment, boronizing agent: high-purity boron powder (purity ≥ 99.99%, particle size 1 - 5 μm); The first stage, from room temperature to 1800 °C, heating rate: 10 °C / min; axial pressure: 5 MPa; vacuum degree: 10 -1 Pa. The second stage, from 1800 °C to 2200 °C: heating rate: 5 °C / min; axial pressure: 10 MPa; cool to room temperature with the furnace, and cut and process into standard specimens.

[0069] Performance characterization of the composite materials obtained in the examples and comparative examples:

[0070] The Vickers hardness test standard is ISO 6507, with a load of 10 kg; the three-point bending strength test standard is ASTM C1161 standard, with a span of 30 mm; the porosity is measured by the Archimedes drainage method; the boronizing depth is measured by the thickness of the boronized layer using a metallographic microscope.

[0071] The relevant test results are shown in the following table:

[0072] Example Vickers hardness GPa Three-point bending strength MPa Porosity (%) Boronizing depth (mm) Example 1 46 579 0.38 2.77 Example 2 47 572 0.35 2.82 Example 3 47 581 0.39 2.79 Example 4 48 580 0.41 2.81 Comparative Example 1 36 465 2.21 1.30

[0073] Comparing the above relevant data, it can be seen that the present invention introduces nanowires into the system, which can form a "pinning effect" at the interface between diamond and boron carbide, inhibiting crack propagation; in addition, the PVP coated on the surface of the modified nanowires in the present invention forms nanopores after high-temperature decomposition, guiding the directional penetration of boron atoms along the nanowires, thereby improving the boronizing uniformity.

[0074] The present invention introduces a pulsed electromagnetic field in the boronizing stage. The high-frequency magnetic field will induce an eddy current effect in the molten boron, enhancing the fluidity of the liquid boron and enabling it to penetrate deep into the preform, comprehensively increasing the penetration depth by 30%; in addition, the pulsed power-off interval avoids excessive graphitization on the surface of the diamond and maintains the intrinsic hardness of the material.

[0075] The present invention adopts a densification mechanism of staged hot pressing: in the first stage, the resin is cured at low pressure to avoid the fracture of nanowires due to high pressure; in the second stage, high pressure promotes the directional arrangement of nanowires along the pressure direction, filling the grain boundary pores, making the porosity ≤ 0.5%, and thereby significantly improving the comprehensive performance of the composite ceramic.

[0076] The above makes an exemplary description of the present invention. It should be noted that without departing from the core of the present invention, any simple deformation, modification or equivalent substitution that can be made by those skilled in the art without creative labor falls within the protection scope of the present invention.

Claims

1. A preparation method of a boron carbide ceramic composite material, characterized in that, The steps include: Step S1: taking magnesium nitrate, boric acid and citric acid, stirring in a water bath at 80°C for 6 hours to form a transparent sol; drying at 120°C, calcining to obtain nanowires; immersing the nanowires in a 2wt% modifier, ultrasonically treating for 30 minutes, and drying at 60°C to obtain modified magnesium borate nanowires; Step S2: taking diamond powder, boron carbide powder, graphite powder, phenolic resin and modified magnesium borate nanowires; Step S3: adding diamond, boron carbide, graphite, and modified magnesium borate nanowires into anhydrous ethanol, and mixing by ball milling; adding phenolic resin, and continuing ball milling for 1 hour to form a uniform slurry, and granulating by ultra-low temperature liquid nitrogen spray; Step S4: vacuum hot pressing in stages: low-pressure pre-curing treatment in the first stage and high-pressure densification treatment in the second stage; Step S5: degreasing treatment, gradient boronizing and electromagnetic field coupling, pulse electromagnetic field parameters: frequency 30kHz, magnetic field intensity 1T, pulse period 0.1s power on / 0.05s power off; heat preservation time: 30min; cooling to room temperature with the furnace.

2. The preparation method of a boron carbide ceramic composite material as described in claim 1, characterized in that, In step S1, the molar ratio of magnesium nitrate, boric acid and citric acid is 1:2:1.5; the specific conditions of calcination are: calcination at 600° C. for 2 h; and the modifier is a carboxylated PVP ethanol solution.

3. The preparation method of a boron carbide ceramic composite material as described in claim 1, wherein, The nanowires in step S1 have a diameter of 10-50 nm and an aspect ratio of >50.

4. The preparation method of a boron carbide ceramic composite material according to claim 1, characterized in that, In step S2, the content of each component is, by volume percentage, diamond powder: 40-65%; boron carbide powder: 20-35%; graphite powder: 5-8%; Phenolic resin: 15-20%; Modified magnesium borate nanowires: 0.3-1.5%.

5. The preparation method of a boron carbide ceramic composite material as described in claim 1, characterized in that, In step S2, the particle size of the diamond powder is 50-150 μm, and the purity is ≥99.9%; the particle size of the boron carbide powder is 10-50 μm, and the purity is ≥99.5%; the particle size of the graphite powder is 20-50 μm, and the purity is ≥99.9%; and the solid content of the phenolic resin is ≥85%.

6. The preparation method of a boron carbide ceramic composite material according to claim 1, characterized in that, The specific parameters of ball milling mixing in step S3 are: ball-to-material ratio 5:1, rotation speed 200 rpm, time 4 h; spray granulation parameters: liquid nitrogen temperature: -196°C; nozzle diameter: 0.5 mm; spray rate: 8 mL / min; droplet size: 50-100 μm.

7. The preparation method of a boron carbide ceramic composite material according to claim 1, characterized in that, The specific parameters of the first stage low-pressure pre-curing in step S4 are: temperature: 130-140°C; pressure: 50MPa; holding time: 5min; vacuum degree: 10-2Pa.

8. The preparation method of a boron carbide ceramic composite material according to claim 1, wherein, The specific parameters of the second stage high pressure densification in step S4 are: temperature: 150-160°C; pressure: step pressurization: 50MPa→100MPa→200MPa, pressurization rate of each stage 20MPa / min, holding time at the final pressure state: 15min.

9. The preparation method of a boron carbide ceramic composite material as described in claim 1, characterized in that, In step S5, the degreasing treatment temperature is 1000-1100°C; the heating rate is 2°C / min; the holding time is 120min; Atmosphere: argon protection.

10. The preparation method of a boron carbide ceramic composite material according to claim 1, characterized in that, The specific process parameters of gradient boronizing in step S5 are as follows: the boronizing agent is high-purity boron powder with a purity of ≥99.99% and a particle size of 1-5 μm; the temperature in the first stage ranges from room temperature to 1800 °C, and the heating rate is 10 °C / min; the axial pressure is 5 MPa; the vacuum degree is 10-1 Pa; the temperature in the second stage ranges from 1800 °C to 2200 °C, and the heating rate is 5 °C / min; the axial pressure is 10 MPa.