High fatigue strength b4c / al composite material and preparation method thereof

Abstract

This invention belongs to the field of high-content ceramic / metal composite material preparation technology, specifically relating to a high-fatigue-strength B4C / Al composite material and its preparation method. This invention employs chemical vapor deposition to generate CNTs in situ on the surface of micro / nano-scale B4C particles. These CNTs are then thoroughly mixed with aluminum alloy powder, and a billet is prepared using SPS plasma discharge sintering equipment. After grinding and polishing, the billet is processed using a high-frequency current rolling test bench to obtain a high-fatigue-strength B4C / Al composite material. This invention aims to improve the interfacial bonding quality of ceramic / metal composite materials and inhibit harmful reaction products through the modification effect of CNTs; the addition of high-frequency current-assisted rolling enhances the fatigue resistance of the composite material, resulting in a B4C / Al composite material with excellent comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a high fatigue strength B4C / Al composite material and its preparation method. Background Technology

[0002] With the increasing demands for high-performance materials in extreme environments within the nuclear industry, boron carbide (B4C) ceramics have become a key component in high-performance composite materials due to their ultra-hardness, low density, high temperature resistance, neutron absorption capacity, and chemical inertness. However, pure boron carbide ceramics suffer from inherent brittleness, difficulty in sintering and densification, and weak interfacial bonding, limiting their application under high-stress cyclic conditions. Aluminum-based composite materials, prepared by adding a certain amount of boron carbide ceramic particles to an aluminum matrix with excellent plasticity and toughness, are considered excellent neutron shielding materials. However, the physical and chemical properties of ceramics and aluminum matrices differ significantly, such as density and coefficient of thermal expansion. Adding a high content of ceramic particles to the aluminum matrix inevitably leads to uneven particle distribution, uncontrolled interfacial reactions, and insufficient fatigue strength, making it difficult to meet the stringent requirements of long life and high reliability for nuclear reactor shielding structural components.

[0003] In existing technologies, the preparation of B4C / Al composite materials mostly employs powder metallurgy processes, such as hot pressing sintering or spark plasma sintering (SPS). However, this inevitably presents the following key technical challenges: 1) The wettability between the ceramic and the aluminum matrix is ​​poor, and since powder metallurgy is a solid-state forming technology, the quality of the heterogeneous interface between the ceramic and aluminum matrix is ​​difficult to guarantee. During subsequent sheet rolling deformation, micro-gaps easily appear at the heterogeneous interface, thus affecting its overall mechanical properties; 2) Traditional rolling processes typically involve heating the furnace before rolling, and the plastic deformation energy between the ceramic and aluminum matrix is ​​limited. The large difference in stress will further exacerbate the occurrence of microcracks in the matrix and microgap at the heterogeneous interface, and easily lead to coarsening of the matrix structure; 3) The large difference in the coefficient of thermal expansion between the ceramic and the aluminum matrix will inevitably cause stress concentration at the heterogeneous interface of the ceramic / aluminum matrix during the heating-cooling process, which will further exacerbate the occurrence of microgap at the heterogeneous interface during the rolling process, and at the same time have an adverse effect on the flatness of the composite material sheet; 4) The composite material will inevitably be subjected to fatigue alternating loads during the processing, preparation and transportation process, and the weak interfacial bonding quality is very likely to become the initiation site of cracks. Summary of the Invention

[0004] To address the problems existing in current technologies, this invention provides a high-fatigue-strength B4C / Al composite material and its preparation method. This invention utilizes chemical vapor deposition to grow CNTs in situ on the surface of B4C. The modification effect of CNTs reduces the generation of harmful substances at the heterogeneous interface and improves the interfacial bonding quality. Furthermore, current rolling technology enhances the comprehensive mechanical properties of the high-content B4C / Al composite material, thereby improving its fatigue strength.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing a high fatigue strength B4C / Al composite material includes the following steps:

[0007] Step 1, Surface treatment of ceramic (B4C) particles: Take B4C ceramic particles and perform ultrasonic cleaning, then wash with deionized water, filter, and dry to obtain surface-treated B4C ceramic particles.

[0008] Step 2, Preparation of surface catalyst for B4C particles: Ni(NO3)2·6H2O was dissolved in deionized water and then added to the surface-treated B4C ceramic particles and magnetically stirred; NaOH solution was then added until the required pH value was reached, and precipitation was carried out at room temperature; subsequently, the particles were filtered and dried, and finally calcined in air to obtain calcined B4C ceramic particles.

[0009] Step 3, in-situ growth of CNTs from B4C particles: The calcined B4C ceramic particles are placed in a reducing atmosphere tube furnace, and a protective gas is introduced. The temperature is raised to 350~450℃ in the protective gas atmosphere. At this time, hydrogen is introduced and the protective gas is stopped. Then the temperature is raised to 700~800℃. Methane and the protective gas are introduced again, and the hydrogen is stopped. After reacting for 0.6~1.2h, the methane is stopped. The mixture is cooled to room temperature under the action of the protective gas to obtain ceramic particles B4C@CNTs with in-situ CNT coating.

[0010] Step 4: Select 6061Al alloy powder with appropriate particle size and mix it with B4C@CNTs using a planetary ball mill. Then, use a vacuum glove box to pre-press the mixed powder to obtain powder blocks.

[0011] Step 5, Preparation of high-content B4C@CNTs / Al composite material samples: The powder block is placed in an SPS discharge plasma sintering furnace to prepare the sample. After obtaining the blank, it is ground and polished to obtain high-content B4C@CNTs / Al composite material samples.

[0012] Step 6: Current rolling of high-content B4C@CNTs / Al composite material specimens: The high-content B4C@CNTs / Al composite material specimens are clamped onto the high-frequency current rolling test bench using a fixture. Thermocouples and infrared thermal imagers are adjusted, and the pulse current is adjusted based on the temperature measurement results of the thermocouples and infrared thermal imagers. High-frequency current rolling is then performed.

[0013] Step 7, Post-treatment of B4C@CNTs / Al composite material current rolling specimens: The specimens after high-frequency current rolling are ground and polished to obtain high-content B4C@CNTs / Al composite materials.

[0014] Furthermore, in step 1, the B4C ceramic particles have a particle size of 5~8µm and a purity ≥99.99%; during ultrasonic cleaning, deionized water + 0.1~0.5% nonionic surfactant is used as the cleaning agent, and cleaning is performed for 7~10 minutes at 30~40℃, 110~130Hz, and 0.7~0.9W / cm²; during drying, the drying temperature is 120℃~130℃, and the drying time is 6~12 hours.

[0015] Furthermore, in step 2, the mass ratio of Ni(NO3)2·6H2O to B4C is 1:30~1:60; the mass fraction of NaOH solution is 3%~10%; the required pH value is between 7 and 8; the drying temperature for drying is 100~150℃, and the drying time is 6~12h; the calcination treatment is carried out at 350℃~450℃ for 2~3h.

[0016] Furthermore, in step 3, the protective gas is argon; the purity of the protective gas, hydrogen, and methane is ≥99%; when methane and protective gas are introduced, the volume ratio of methane to protective gas is 1:3 to 1:6.

[0017] Further, in step 4, the 6061Al alloy powder has a particle size of 5~25µm and a purity of ≥99.99%. When mixing the powder using a planetary ball mill, the mass ratio of B4C@CNTs to 6061Al alloy powder is 30~33:67~70, the mass ratio of ball:material:solvent is 4:1:1, the ball is zirconia ball, the solvent is anhydrous ethanol, the ball milling speed is 150~300rad / min, and the ball milling time is 8~10h, including 4~5h of forward rotation and 4~5h of reverse rotation. The pre-compression treatment is carried out using a press with a pressure of 40~60MPa for 3~5min, so that the density of the mixed powder reaches ≥65%.

[0018] Furthermore, in step 5, the spark plasma sintering is carried out using an SPS sintering device. During sintering, a pressure of 35~55MPa is applied, the sintering temperature is 550~650℃, the heating rate is 50~70℃ / min, and the graphite mold is kept warm with carbon felt for 25~35min. During grinding and polishing, 120# to 1500# sandpaper is used to grind in sequence, and then the surface of the blank after grinding is cleaned with a 75% alcohol solution.

[0019] Further, step 6 specifically involves attaching a thermocouple to the surface of the high-content B4C@CNTs / Al composite material sample to obtain the surface temperature; observing the overall temperature distribution of the high-content B4C@CNTs / Al composite material sample using an infrared thermal imager; adjusting the pulse current based on the temperature measurement results of the thermocouple and the infrared thermal imager, and performing high-frequency current rolling treatment. Specifically, the pulse frequency of the pulse current is 5 kHz to 25 kHz, the pulse width is 15 to 35 ms, and the temperature is 230 to 280℃; controlling the amount of downward pressure in each rolling pass, rolling multiple times in the same direction, with a rolling speed of 5 to 10 mm / min; and rapidly water-cooling the sample after the high-frequency current rolling treatment is completed.

[0020] Furthermore, the polishing in step 7 specifically involves: using sandpaper ranging from 120# to 1500# to polish the sample in sequence, and then cleaning the polished sample surface with a 75% alcohol solution.

[0021] A high fatigue strength B4C / Al composite material prepared by the above method.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention uses B4C particles with in-situ grown CNTs as a reinforcing phase. Through the modification effect of CNTs, the interfacial bonding quality of ceramic / metal composite materials can be effectively improved and harmful reaction products can be inhibited.

[0024] 2. The skin effect of high-frequency pulsed current induces more high-density pulsed current to concentrate in the sub-millimeter layer on the surface of the board. On the one hand, this causes the surface temperature of the board to rise rapidly, thus softening it and facilitating deformation, while effectively ensuring the surface forming quality of the board; on the other hand, the lower current density in the core region of the board can effectively prevent coarsening of the internal structure.

[0025] 3. Under the condition of rolling stress generated during rolling, the Ampere force generated by the magnetic field generated by the proximity effect of high-frequency pulsed current and the thermocompression stress are assisted. The three forces work together on the micro gaps at the heterogeneous interface of the composite material and the microcracks in the matrix, which can significantly improve the coordinated plastic deformation ability of the heterogeneous interface, thereby obtaining a high-content B4C@CNTs / Al composite material with excellent fatigue performance.

[0026] 4. The synergistic effect of CNTs network and Al matrix can form a highly efficient conductive path. At the same time, the CNTs generated in situ on the surface of B4C particles allow high-frequency pulse current to accumulate further at the micro gaps of the heterogeneous interface, effectively enhancing the proximity effect and improving the bonding quality of the heterogeneous interface. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Microscopic morphology of B4C particles;

[0029] Figure 2 Microscopic morphology of B4C@CNTs particles;

[0030] Figure 3 This is an optical microstructure diagram of Example 1;

[0031] Figure 4 This is an optical microstructure diagram of Example 2;

[0032] Figure 5 This is a comparison chart of the nanoindentation experiment results of Example 1 and Example 2;

[0033] Figure 6 This is a comparison chart of the axial constant amplitude low-cycle fatigue test results of Example 1 and Example 2;

[0034] Figure 7 This is a comparison chart of the conductivity results for Example 1 and Example 2;

[0035] Figure 8 This is a hardness diagram of nanoindentation at the interface of Example 1;

[0036] Figure 9 This is a hardness diagram of nanoindentation at the interface of Example 2;

[0037] Figure 10 This is a schematic diagram of the healing of microcracks and microgap at the interface of B4C@CNTs / Al composite material. Detailed Implementation

[0038] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0039] Example 1 (High-frequency current assisted rolling of high-content B4C / Al composite material)

[0040] Step 1, B4C particle surface treatment: Weigh a certain mass of B4C ceramic particles with a purity ≥99.99% and a particle size of 5~8µm, place them in an ultrasonic cleaner for cleaning, use deionized water + 0.1% nonionic surfactant as the cleaning agent, clean for 8 minutes at 35℃, 120Hz, 0.8W / cm², after cleaning, wash with deionized water, then filter the treated B4C particles, and finally put them into a drying oven for drying at 120℃ for 6 hours;

[0041] Step 2, ball milling and powder mixing: Select 6061Al alloy powder with a purity ≥99.99% and a particle size of 5~25µm. Place B4C particles and 6061Al alloy powder in a ball mill jar at a mass ratio of 30:70 and mix them using a planetary ball mill with anhydrous ethanol as the solvent. The mass ratio of ball:material:solvent is 4:1:1. The ball milling speed is 200 rad / min, and the milling is carried out for a total of 10 hours, including 5 hours of forward rotation and 5 hours of reverse rotation. Place the mixed B4C / Al metal powder into a graphite mold with graphite paper on the top and bottom in a vacuum glove box. Pre-press the mixed powder in the graphite mold at a pressure of 50 MPa for 4 minutes to make the density of the mixed powder reach more than 65% to obtain powder blocks.

[0042] Step 3: The mixed and compacted powder block is subjected to discharge plasma sintering. During sintering, a pressure of 50 MPa is applied, the sintering temperature is 550℃, the heating rate is 70℃ / min, and the mold is kept warm with carbon felt for 25 min to obtain a high-content B4C / Al composite material sample. The sample is then polished by using sandpaper ranging from 120# to 1500#. Finally, the surface is cleaned with a 75% alcohol solution.

[0043] Step 5, High-frequency current rolling treatment: The polished high-content B4C / Al composite material specimens are clamped onto the high-frequency current rolling test bench using fixtures. Thermocouple temperature measurement and infrared thermal imaging temperature measurement are adjusted. The temperature of the specimens is measured using contact thermocouples to ensure good contact between the thermocouples and the specimens. The thermocouples are calibrated before high-frequency current treatment. The overall temperature of the specimens is tested using an infrared thermal imager. Based on the temperature measurement results, the pulse current magnitude is adjusted and high-frequency current rolling treatment is performed. From the perspective of pulse energy, after optimization and adjustment, the optimal parameters for this treatment are: pulse frequency of 15 kHz, pulse width of 30 ms, pulse current treatment temperature of 250℃, control of the reduction in pressure for each rolling is 3% (i.e., 0.15 mm), rolling 10 times in the same direction, with a total reduction of 30%, a sample thickness reduction of 1.5 mm, a rolling speed of 10 mm / min, and a treatment time of 6 min. After the current treatment is completed, the specimens are rapidly water-cooled.

[0044] Step 6, Sample treatment after current rolling: Use sandpaper from 120# to 1500# to polish the sample in sequence, and then clean the surface of the polished sample with a 75% alcohol solution.

[0045] Example 2 (High-frequency current assisted rolling of high-content B4C@CNTs / Al composite material)

[0046] Step 1, B4C particle surface treatment: Weigh a certain mass of B4C particles with a purity ≥99.99% and a particle size of 5~8µm, place them in an ultrasonic cleaner for cleaning, use deionized water + 0.1% nonionic surfactant as the cleaning agent, and clean for 8 minutes at 15℃, 120Hz, and 0.8W / cm². After cleaning, wash with deionized water, then filter the treated B4C particles, and finally put them in a drying oven for drying at 120℃ for 6 hours.

[0047] Step 2, Preparation of B4C particle surface catalyst: Ni(NO3)2·6H2O particles were weighed according to the ratio of Ni(NO3)2·6H2O to B4C of 1:40 and dissolved in 500mL of deionized water. The mixture was magnetically stirred for 1h, and 6% NaOH solution was added dropwise until the pH of the solution became 7-8. The mixture was allowed to precipitate at room temperature for 12h, then filtered. The filtered product was dried in a vacuum drying oven at 120℃ for 6h. The dried powder was placed in a quartz boat and put into a tube furnace and calcined at 400℃ for 2h in an air atmosphere.

[0048] Step 3, in-situ growth of CNTs from B4C particles: The calcined B4C particles were spread evenly in a quartz boat and placed in a reducing atmosphere tube furnace. The temperature was raised to 400°C under Ar protection, then Ar was turned off and H2 was introduced and maintained for 3 hours. Then the temperature was raised to 700°C, then H2 was turned off and CH4 and Ar were introduced, with the ratio of Ar:CH4:H2 being 6:1:1. The reaction was carried out at this temperature for 1 hour, then CH4 was turned off and the mixture was cooled to room temperature under the action of Ar to obtain ceramic particles (B4C@CNTs).

[0049] Step 4: Select 6061Al alloy powder with appropriate particle size and mix it with B4C@CNTs: Weigh a certain amount of 6061Al powder according to the mass ratio of B4C@CNTs:6061Al of 30:70. The particle size of the 6061Al alloy powder is 5~25µm and the purity is ≥99.99%. Ball milling is performed using a planetary ball mill with a ball:material:solvent mass ratio of 4:1:1. Zirconia balls are used as the balls and anhydrous ethanol is used as the solvent. The ball milling speed is 200 rad / min and the ball milling time is 10h, including 5h of forward rotation and 5h of reverse rotation. Then, the mixed B4C@CNTs / Al metal powder is placed in a graphite mold with graphite paper on the top and bottom in a vacuum glove box. The mixed powder in the graphite mold is pre-compressed at a pressure of 50 MPa for 4 min to make the density of the mixed powder reach more than 65% to obtain powder blocks.

[0050] Step 5, Preparation of high-content B4C@CNTs / Al composite material samples: The powder block was placed in an SPS discharge plasma sintering furnace for sintering. The pressure was 50MPa, the sintering temperature was 550℃, and the heating rate was 70℃ / min. The graphite mold was kept warm with carbon felt for 25min. After obtaining the high-content B4C@CNTs / Al composite material samples, they were polished with sandpaper from 120# to 1500# in sequence. Then, the surface of the polished blank was cleaned with a 75% alcohol solution.

[0051] Step 6: Current rolling treatment of high-content B4C@CNTs / Al composite specimens: The polished high-content B4C@CNTs / Al composite specimens were clamped onto a high-frequency current rolling test bench. Thermocouple temperature measurement and infrared thermal imaging temperature measurement were adjusted. Contact thermocouples were used to measure the temperature of the specimens, ensuring good contact between the thermocouples and the specimens. Thermocouples were calibrated before high-frequency current treatment. The overall temperature of the specimens was tested using an infrared thermal imager. Based on the temperature measurement results, the pulse current was adjusted and high-frequency current rolling treatment was performed. From the perspective of pulse energy, after optimization, the optimal parameters for this treatment were: pulse frequency of 20 kHz, pulse width of 35 ms, pulse current treatment temperature of 250 ℃, control of the reduction in pressure for each rolling pass of 3% (i.e., 0.15 mm), 10 reciprocating rolling passes in the same direction, a total reduction in pressure of 30%, a sample thickness reduction of 1.5 mm, a rolling speed of 10 mm / min, and a treatment time of 6 minutes. min, after the current processing is completed, rapid water cooling;

[0052] Step 7, Sample treatment after current rolling: Use sandpaper of 120# to 1500# to polish the sample in sequence, and then clean the surface of the polished sample with a 75% alcohol solution.

[0053] Depend on Figure 1 It can be seen that B4C particles have distinct edges and corners, are uniform in size, have clean surfaces, and are irregularly shaped lumps; Figure 2 It can be seen that the exterior of B4C@CNTs consists of uniform and slender CNTs, and the B4C particles are completely coated; Figure 3 and Figure 4 It can be seen that the sample of Example 1 has more defects, and the bonding between B4C and Al is poor. However, the sample of Example 2 has fewer defects than that of Example 1, and the bonding between B4C@CNTs and Al is relatively better. Figure 5 It can be seen that the hardness of Example 1 is 2.106 GPa, and the hardness of Example 2 is 2.486 GPa, representing an increase of 15.29% in hardness; Figure 6 It can be seen that in 1×10 7 Under cyclic loading, the fatigue strength of Example 1 was 126 MPa, and the fatigue strength of Example 2 was 131 MPa. Figure 7 It can be seen that the conductivity of the sample in Example 1 was 15.6 MS / m, and the conductivity of the sample in Example 2 was 24.3 MS / m. Based on the addition of CNTs to the ceramic particles, the conductivity of the composite material increased by 55.77%. Figure 8 It can be seen that the hardness of nano-indentation dots 1, 2, 3, 4, and 5 in Example 1 are 2.401 GPa, 2.323 GPa, 2.194 GPa, 2.056 GPa, and 1.842 GPa, respectively; Figure 9 It can be seen that the hardness of nano-indentation points 1, 2, 3, 4, and 5 in Example 2 are 3.283 GPa, 2.711 GPa, 2.586 GPa, 2.257 GPa, and 1.896 GPa, respectively; the hardness of points 1, 2, 3, 4, and 5 at the ceramic particle / aluminum-based material interface is increased by 36.73%, 16.70%, 17.87%, 9.78%, and 2.93%, respectively.

[0054] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for preparing a high fatigue strength B4C / Al composite material, characterized in that, Includes the following steps: Step 1: Take B4C ceramic particles and perform ultrasonic cleaning, then wash with deionized water, filter, and dry to obtain surface-treated B4C ceramic particles. Step 2: Ni(NO3)2·6H2O is dissolved in deionized water and then surface-treated B4C ceramic particles are added and magnetically stirred; NaOH solution is then added until the required pH value is reached, and precipitation occurs at room temperature; subsequently, filtration and drying are performed, and finally calcination is performed to obtain calcined B4C ceramic particles. Step 3: Place the calcined B4C ceramic particles in a reducing atmosphere tube furnace, introduce a protective gas, and heat to 350~450℃ in the protective gas atmosphere. At this time, introduce hydrogen gas and stop the introduction of the protective gas. Then heat to 700~800℃. At this time, introduce methane and protective gas again and stop the introduction of hydrogen gas. After reacting for 0.6~1.2h, stop the introduction of methane and cool to room temperature under the action of the protective gas to obtain in-situ CNT-coated ceramic particles B4C@CNTs. Step 4: Select 6061Al alloy powder with appropriate particle size and mix it with B4C@CNTs using a planetary ball mill. Then, use a vacuum glove box to pre-press the mixed powder to obtain powder blocks. Step 5: Place the powder block into an SPS discharge plasma sintering furnace to prepare the sample. After obtaining the blank, grind and polish it to obtain a high-content B4C@CNTs / Al composite material sample. Step 6: The high-content B4C@CNTs / Al composite material sample is clamped onto the high-frequency current rolling test bench using a fixture. The thermocouple and infrared thermal imager are adjusted. Based on the temperature measurement results of the thermocouple and infrared thermal imager, the pulse current is adjusted and high-frequency current rolling is performed. Step 7: Grind and polish the sample after high-frequency current rolling to obtain a high-content B4C@CNTs / Al composite material; In step 2, the mass ratio of Ni(NO3)2·6H2O to B4C is 1:30~1:60; In step 3, when methane and protective gas are introduced, the volume ratio of methane to protective gas is 1:3 to 1:

6. In step 3, the ratio of CH4 to H2 is 1:

1.

2. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, In step 1, the B4C ceramic particles have a particle size of 5~8µm and a purity of ≥99.99%. For ultrasonic cleaning, deionized water with 0.1~0.5% nonionic surfactant is used as the cleaning agent, and the cleaning is performed at 30~40℃, 110~130Hz, and 0.7~0.9W / cm² for 7~10 minutes. For drying, the drying temperature is 120℃~130℃, and the drying time is 6~12 hours.

3. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, In step 2, the mass fraction of the NaOH solution is 3% to 10%; the required pH value is between 7 and 8; the drying temperature for the drying treatment is 100 to 150°C, and the drying time is 6 to 12 hours; the calcination treatment is carried out at 350°C to 450°C for 2 to 3 hours.

4. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, In step 3, the protective gas is argon; the purity of the protective gas, hydrogen, and methane is ≥99%.

5. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, In step 4, the 6061Al alloy powder has a particle size of 5~25µm and a purity of ≥99.99%. When mixing the powder using a planetary ball mill, the mass ratio of B4C@CNTs to 6061Al alloy powder is 30~33:67~70, the mass ratio of ball:material:solvent is 4:1:1, the ball is zirconia ball, the solvent is anhydrous ethanol, the ball milling speed is 150~300rad / min, and the ball milling time is 8~10h, including 4~5h of forward rotation and 4~5h of reverse rotation. The pre-compression treatment is carried out using a press with a pressure of 40~60MPa for 3~5min, so that the density of the mixed powder reaches ≥65%.

6. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, In step 5, the spark plasma sintering is carried out using an SPS sintering equipment. During sintering, a pressure of 35~55MPa is applied, the sintering temperature is 550~650℃, the heating rate is 50~70℃ / min, and the graphite mold is kept warm with carbon felt for 25~35min. During grinding and polishing, 120# to 1500# sandpaper is used to grind in sequence, and then the surface of the blank after grinding is cleaned with a 75% alcohol solution.

7. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, Step 6 specifically involves attaching a thermocouple to the surface of the high-content B4C@CNTs / Al composite material sample to obtain the surface temperature; observing the overall temperature distribution of the high-content B4C@CNTs / Al composite material sample using an infrared thermal imager; adjusting the pulse current based on the temperature measurement results of the thermocouple and the infrared thermal imager, and performing high-frequency current rolling treatment. Specifically, the pulse frequency of the pulse current is 5 kHz to 25 kHz, the pulse width is 15 to 35 ms, and the temperature is 230 to 280℃; controlling the amount of downward pressure in each rolling pass, rolling multiple times in the same direction, and the rolling speed is 5 to 10 mm / min. After the high-frequency current rolling treatment is completed, the sample is rapidly water-cooled.

8. The method for preparing a high fatigue strength B4C / Al composite material according to claim 1, characterized in that, The polishing in step 7 specifically involves: using sandpaper ranging from 120# to 1500# to polish the sample in sequence, and then cleaning the surface of the polished sample with a 75% alcohol solution.

9. A high fatigue strength B4C / Al composite material prepared by the preparation method according to any one of claims 1 to 8.

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