Multi-stage synergistically-reinforced nano covalently-linked graphene preform and application thereof in metal-based composite material

Abstract

The invention discloses a multi-stage synergistically reinforced nano covalently linked graphene preform and application of the multi-stage synergistically reinforced nano covalently linked graphene preform in a metal-based composite material. Firstly, transition metal modified silica sol is introduced into graphene ink, and an oriented porous structure is constructed through electromagnetic field assisted freeze drying; then growing a vertical nano graphene array on the surface of the graphene sheet layer in situ in a double-carbon-source gradient gas supply mode by adopting a plasma activation-chemical vapor deposition (PACVD) process in a rotary deposition furnace; and finally, carbon-silicon covalent bonding is triggered through microwave irradiation. A transition metal catalysis-plasma activation-gradient deposition-microwave bonding quadruple synergistic mechanism is creatively fused, so that the compression strength of the preform is improved by 35-60%, and meanwhile, directional regulation and control of nanopores are realized. When the preform is used as a metal matrix composite reinforcement, the tensile strength of the composite is improved by more than 40% through the design of an interface transition layer.

Description

Technical Field

[0001] This invention belongs to the field of nano-carbon material reinforcement technology, specifically relating to a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites. Background Technology

[0002] Graphene is a type of sp 2 Hybrid two-dimensional materials possess high specific surface area, excellent thermal conductivity, electromagnetic shielding performance, and optical properties, making them promising candidates for applications in aerospace, military, and electronics. If graphene is used as a reinforcement in metal matrix composites, the composite material can combine the excellent thermal and electrical conductivity of both graphene and metals, resulting in a high-performance metal matrix composite. Solid-state and liquid-state methods are commonly used to prepare graphene-reinforced metal matrix composites. The liquid-state method is more widely used in the preparation of metal matrix composites due to its advantages of low cost, simple operation, and high efficiency. However, in liquid-state preforms, the graphene sheets tend to agglomerate due to the large van der Waals forces. These graphene agglomerates not only fail to effectively transfer loads, heat, and electrons but can also become defects in the matrix, leading to a decline in the composite material's performance.

[0003] Existing technologies face three major bottlenecks: insufficient compressive strength of physically overlapping structures; graphene lattice defects caused by high-temperature deposition; and collapse of nanostructures during metal infiltration. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and provide a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites.

[0005] A method for preparing a multi-level reinforced nanocovalently linked graphene preform, characterized by comprising the following steps:

[0006] Step 1. Preparation of modified sol: Fe / Co / Ni transition metal salts are blended with nano-silica sol and then subjected to hydrothermal reaction to obtain metal-doped silica sol, wherein the molar ratio of transition metal elements to Si is 1:(5-20).

[0007] Step 2. Directional cryo-molding: The modified sol is added to the graphene ink and oriented hydrogel is formed under alternating magnetic field and liquid nitrogen gradient freezing. The mass ratio of sol to graphene is 1:(10-30).

[0008] Step 3. Plasma-activated deposition: The freeze-dried preform is placed in a rotary deposition furnace. First, hydrogen-argon plasma is introduced to activate the surface, and then gradient deposition is performed using a methane / alcohol dual carbon source: First stage: deposition of nano-graphene nuclei at 800-1000℃; Second stage: growth of vertical nanoarrays at 1000-1300℃; Deposition pressure 1-8 kPa, time 30-180 min;

[0009] Step 4. Microwave covalent bonding: Microwave irradiation is performed under nitrogen protection to trigger covalent bonding between nano-silicon and carbon, forming a Si-C interface layer.

[0010] In step 1, the molar concentration of the Fe / Co / Ni transition metal salt is 0.1-1 mol / L.

[0011] The concentration of graphene ink in step 2 is 5-30 mg / ml;

[0012] The magnitude of the alternating magnetic field is 0.5-2T;

[0013] The liquid nitrogen gradient freezing rate is 5-20℃ / min.

[0014] In step 3, the rotary deposition furnace rotates at a speed of 1-10 rpm.

[0015] The power of the hydrogen-argon plasma is 300-1000W;

[0016] In step 4, the microwave irradiation is 2.45 GHz, 500-1500 W.

[0017] In step 3, gradient deposition uses a dual-channel independent gas supply system, with gaseous carbon source accounting for 70-90% in the first stage and liquid carbon source accounting for 60-80% in the second stage.

[0018] The rotary deposition furnace is equipped with multi-stage baffles to create a vortex field with a turbulence intensity of 1.5-3.0.

[0019] In step 4, after microwave irradiation, pulsed laser treatment is performed at a wavelength of 1064 nm and an energy density of 5-15 J / cm² to generate carbon quantum dots on the top of the nanoarray to strengthen the end connections.

[0020] A method for preparing a metal matrix composite material, characterized in that: a multi-level reinforced nano-covalently linked graphene preform prepared above is immersed in a metal melt containing 0.5-5wt% nano-TiB2, and formed in a vacuum pressure infiltration furnace at 600-900℃ and 10-50MPa; the metal melt is any one of Al, Cu, and Mg alloys.

[0021] A multi-level reinforced nanocovalently linked graphene preform prepared according to claim 1, characterized in that it has a tertiary porous structure:

[0022] Primary vias: Frozen to form 50-200μm oriented through-holes;

[0023] Secondary pores: 1-10μm interlayer pores;

[0024] Tertiary pores: 50-300nm nanometer array gap pores;

[0025] At 50% strain, the compressive strength is 15-50 MPa, and the conductivity is >1000 S / m.

[0026] The main innovative points of this invention are as follows:

[0027] 1. Transition metal-silicon synergistic modification mechanism: In hydrothermally synthesized Fe-Si sol, Fe... 3+ Embedded SiO2 network forms ≡Si-O-Fe≡ structure (XPS verification); Fe catalyzes the cracking of carbon source during deposition, reducing activation energy by 40% (DSC test); residual Fe nanoparticles become heterogeneous nucleation sites in the metal matrix.

[0028] 2. Magnetic field-gradient freezing orientation technology: An alternating magnetic field causes graphene sheets to magnetically align, thereby forming a vertical through-hole structure; at the same time, gradient freezing technology causes ice crystals to grow in an oriented manner, thereby forming a vertical through-hole structure.

[0029] 3. Plasma activation-rotation deposition system: The rotating stage combined with the baffle design significantly improves the uniformity of deposition; hydrogen plasma pretreatment reduces the oxygen content.

[0030] 4. Microwave-laser secondary bonding: Microwave selective heating of the Si-C interface initiates a reaction: ≡Si-OH reacts with C to generate ≡Si-C and H2O (which can be confirmed by in-situ Raman); Pulsed laser generates carbon quantum dots at the top of the nanoarray, forming a "pinning effect".

[0031] 5. Metal infiltration interface regulation: Nano-TiB2 reacts with the preform to generate a TiC interface layer: TiB2 reacts with C to generate TiC and 2B (inhibiting the Al4C3 brittle phase).

[0032] Beneficial technical effects of the present invention:

[0033] This invention achieves a breakthrough improvement in the structure and performance of graphene preforms through a five-level synergistic mechanism of transition metal catalysis, magnetic field orientation, plasma deposition, microwave bonding, and laser enhancement.

[0034] 1. Mechanical properties: Under 50% compressive strain, the compressive strength reaches 15-50MPa, which is due to: (1) the vertical through holes (first-order holes) constructed by magnetic field directional freezing make the stress uniformly distributed along the axis; (2) the nano-graphene array (tertiary holes) deposited by plasma activation expands the sheet contact area and achieves atomic-level connection through microwave-triggered Si-C covalent interface layer; (3) the carbon quantum dots generated by laser form a "pinning effect" at the top of the array, which inhibits interlayer slip.

[0035] 2. Functional characteristics: conductivity >1000S / m, which is attributed to: (1) transition metal salt doping reduces the activation energy of carbon source cracking, making the defect rate of deposited graphene significantly lower than that of conventional CVD process; (2) the three-level pore structure (first-level oriented pores, second-level interlayer pores and third-level nano-array pores work together to form a continuous electronic pathway.

[0036] 3. Impregnation compatibility: When used in metal matrix composites: (1) The nano-TiB2 additive reacts at the interface to generate a TiC barrier layer, which completely suppresses the Al4C3 brittle phase; (2) The high structural integrity of the preform allows the molten metal (Al / Cu / Mg alloy) to achieve an impregnation integrity rate of over 95% under low pressure of 10-50MPa, which is a significant improvement over traditional processes, and the tensile strength of the composite material is also greatly improved.

[0037] 4. Industrial value: The collaborative process reduces the high-pressure impregnation requirement from 50MPa to 15MPa, while avoiding complex pretreatment such as carbon nanotube bridging, thus reducing mass production costs. Attached Figure Description

[0038] Figure 1 This invention discloses a method for preparing a multi-level synergistically reinforced nano-covalently linked graphene preform, with a multi-level reinforcement process flow diagram.

[0039] Figure 2 The electron microscope (EM) schematic diagram of a multi-level synergistically reinforced covalently linked graphene preform nanostructure prepared by this invention is compared with the EEM schematic diagram of a traditional graphene preform nanostructure.

[0040] Figure 3 This invention provides a schematic diagram illustrating the correlation mechanism between the properties of a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites and the properties of transition metals.

[0041] Figure 4 A schematic diagram of the five-level synergistic mechanism applied in a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention.

[0042] Figure 5A schematic diagram of the five-level synergistic mechanism applied in a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention.

[0043] Figure 6 A schematic diagram of the traditional physical tower structure of graphene nanotubes prepared by a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites.

[0044] Figure 7 A schematic diagram of a vertical nanoarray structure of graphene nanotubes (labeled Si-C interface layer) prepared by a multi-level synergistically reinforced nanocovalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention.

[0045] Figure 8 A schematic diagram of the carbon quantum dot pinning effect in a graphene nanotube prepared by a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites. Detailed Implementation

[0046] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0047] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0048] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0049] Example 1

[0050] A method for preparing a multi-level reinforced nanocovalently linked graphene preform, characterized by comprising the following steps:

[0051] Step 1. Preparation of modified sol: Fe transition metal nitrate or chloride is mixed with nano-silica sol and then subjected to hydrothermal reaction to obtain metal-doped silica sol, wherein the molar ratio of transition metal element to Si is 1:10;

[0052] Step 2. Directional cryo-molding: The modified sol is added to the graphene ink and oriented hydrogel is formed under alternating magnetic field and liquid nitrogen gradient freezing. The mass ratio of sol to graphene is 1:20.

[0053] Step 3. Plasma-activated deposition: The freeze-dried preform is placed in a rotary deposition furnace. First, hydrogen-argon plasma is introduced to activate the surface, and then gradient deposition is performed using a methane / alcohol dual carbon source: First stage: Deposition of nano-graphene nuclei at 900℃, pressure 4 kPa, time 40 min; Second stage: Growth of vertical nanoarrays at 1200℃; deposition pressure 4 kPa, time 80 min;

[0054] Step 4. Microwave covalent bonding: Microwave irradiation is performed under nitrogen protection to trigger covalent bonding between nano-silicon and carbon, forming a Si-C interface layer;

[0055] The Fe transition metal nitrate or chloride is Fe(NO3)3·9H2O; the hydrothermal reaction conditions are hydrothermal reaction at 180℃ for 12h; the thickness of the Si-C interface layer is 5nm.

[0056] The nano-silica sol has a SiO2 content of 20 wt%;

[0057] In step 1, the concentration of the Fe transition metal salt solution is 0.5 mol / L; the purity of the transition metal salt is ≥99.9%.

[0058] In step 2, the concentration of graphene ink is 30 mg / ml; the magnitude of the alternating magnetic field is 1.5 T; and the liquid nitrogen gradient freezing rate is 50 °C / min.

[0059] In step 3, the rotary deposition furnace rotates at 5 rpm; the hydrogen-argon plasma has a power of 600 W and an activation time of 10 minutes; and the methane / alcohol dual carbon source has a weight ratio of 7:1.

[0060] In step 4, the microwave frequency is 2.45 GHz and the power density is 10 W / cm².

[0061] In step 3, gradient deposition employs a dual-channel independent gas supply system. In the first stage, gaseous carbon source accounts for 90% of the total carbon source; in the second stage, liquid carbon source cracking gas accounts for 70% of the total carbon source.

[0062] The rotary deposition furnace is equipped with multi-stage baffles to create a vortex field with a Reynolds number of 6000.

[0063] Step 4 involves microwave irradiation followed by pulsed laser treatment with a wavelength of 1064 nm, an energy density of 10 J / cm², a pulse width of 50 ns, and a repetition frequency of 5 Hz, to generate carbon quantum dots on the top of the nanoarray to strengthen the end connections; the diameter of the laser-generated carbon quantum dots is 10 ± 2 nm.

[0064] This invention also discloses a method for preparing a metal matrix composite material, characterized in that: a multi-level reinforced nano-covalently linked graphene preform prepared by the present invention is immersed in a metal melt containing 2wt% nano-TiB2, and formed in a vacuum pressure infiltration furnace at 750℃ and 30MPa; the metal melt is Al.

[0065] The present invention provides a multi-level reinforced nano-covalently linked graphene preform, characterized by having a tertiary porous structure:

[0066] Primary vias: 120μm oriented through-holes formed by freezing;

[0067] Secondary pores: 5.2μm interlayer pores;

[0068] Tertiary pores: 350nm nanometer array gap pores;

[0069] At 50% strain, the compressive strength is 42.7 MPa, the conductivity is >1000 S / m, the porosity is 92%, and the specific surface area is 650 m² / g.

[0070] Figure 1 This invention discloses a method for preparing a multi-level synergistically reinforced nano-covalently linked graphene preform, with a multi-level reinforcement process flow diagram.

[0071] Figure 2 The electron microscope (EM) schematic diagram of a multi-level synergistically reinforced covalently linked graphene preform nanostructure prepared by this invention is compared with the EEM schematic diagram of a traditional graphene preform nanostructure.

[0072] Figure 3 This invention provides a schematic diagram illustrating the correlation mechanism between the properties of a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites and the properties of transition metals.

[0073] Figure 4 A schematic diagram of the five-level synergistic mechanism applied in a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention.

[0074] Figure 5 A schematic diagram of the five-level synergistic mechanism applied in a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention.

[0075] Figure 6 A schematic diagram of the traditional physical tower structure of graphene nanotubes prepared by a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites (a bright wavy line in the figure represents the rough surface).

[0076] Figure 7 A schematic diagram of a vertical nanoarray structure of graphene nanotubes (labeled Si-C interface layer) prepared by a multi-level synergistically reinforced nanocovalently linked graphene preform and its application in metal matrix composites (the bottom square is the base, the column-like structure above is the nanopillar, and the top of the nanopillar is the Si-C interface layer).

[0077] Figure 8 A schematic diagram of the carbon quantum dot pinning effect of a multi-level synergistically reinforced nano-covalently linked graphene preform and its application in metal matrix composites is shown in one embodiment of the present invention (the square at the bottom represents the material surface, and the dots on top represent carbon quantum dots pinned to the surface).

[0078] Example 2

[0079] A method for preparing a multi-level reinforced nanocovalently linked graphene preform, characterized by comprising the following steps:

[0080] Step 1. Preparation of modified sol: Co transition metal nitrate or chloride is mixed with nano-silica sol and then subjected to hydrothermal reaction to obtain metal-doped silica sol, wherein the molar ratio of transition metal element to Si is 1:10;

[0081] Step 2. Directional cryo-molding: The modified sol is added to the graphene ink and oriented hydrogel is formed under alternating magnetic field and liquid nitrogen gradient freezing. The mass ratio of sol to graphene is 1:20.

[0082] Step 3. Plasma-activated deposition: The freeze-dried preform is placed in a rotary deposition furnace. First, hydrogen-argon plasma is introduced to activate the surface, and then gradient deposition is performed using a methane / alcohol dual carbon source: First stage: deposition of nano-graphene nuclei at 900℃; Second stage: growth of vertical nanoarrays at 1250℃; Deposition pressure 4 kPa, time 60 min;

[0083] Step 4. Microwave covalent bonding: Microwave irradiation is performed under nitrogen protection to trigger covalent bonding between nano-silicon and carbon, forming a Si-C interface layer;

[0084] The Co transition metal nitrate or chloride is CoCl2·6H2O; the hydrothermal reaction conditions are hydrothermal reaction at 180℃ for 12h; the Si-C interface layer thickness is 5nm.

[0085] In step 1, the concentration of the Co transition metal salt solution is 0.5 mol / L; the purity of the transition metal salt is ≥99.9%.

[0086] In step 2, the concentration of graphene ink is 30 mg / ml; the magnitude of the alternating magnetic field is 1.5 T; and the liquid nitrogen gradient freezing rate is 50 °C / min.

[0087] In step 3, the rotary deposition furnace rotates at 5 rpm; the hydrogen-argon plasma has a power of 600 W; and the methane / alcohol dual carbon source has a weight ratio of 7:1.

[0088] In step 4, the microwave frequency is 2.45 GHz and the power density is 12 W / cm².

[0089] In step 3, gradient deposition employs a dual-channel independent gas supply system. In the first stage, gaseous carbon source accounts for 90% of the total carbon source; in the second stage, liquid carbon source cracking gas accounts for 70% of the total carbon source.

[0090] The rotary deposition furnace is equipped with multi-stage baffles to create a vortex field with a Reynolds number of 6000.

[0091] Step 4 involves microwave irradiation followed by pulsed laser treatment with a wavelength of 1064 nm, an energy density of 10 J / cm², a pulse width of 50 ns, and a repetition frequency of 5 Hz, to generate carbon quantum dots on the top of the nanoarray to strengthen the end connections; the diameter of the laser-generated carbon quantum dots is 10 nm.

[0092] This invention also discloses a method for preparing a metal matrix composite material, characterized in that: a multi-level reinforced nano-covalently linked graphene preform prepared by the present invention is immersed in a metal melt containing 2wt% nano-TiB2, and formed in a vacuum pressure infiltration furnace at 750℃ and 30MPa; the metal melt is Al.

[0093] The present invention provides a multi-level reinforced nano-covalently linked graphene preform, characterized by having a tertiary porous structure:

[0094] Primary vias: 110μm oriented vias formed by freezing;

[0095] Secondary pores: 4.8μm interlayer pores;

[0096] Tertiary pores: 420nm nanometer array gap pores;

[0097] At 50% strain, the compressive strength is 32.2 MPa, the conductivity is >1000 S / m, the porosity is 90%, and the specific surface area is 580 m² / g.

[0098] The low catalytic efficiency of Co leads to a decrease in the growth density of nanoarrays, which in turn leads to a decrease in specific surface area.

[0099] Example 3

[0100] A method for preparing a multi-level reinforced nanocovalently linked graphene preform, characterized by comprising the following steps:

[0101] Step 1. Preparation of modified sol: Ni transition metal nitrate or chloride is blended with nano-silica sol and then subjected to hydrothermal reaction to obtain metal-doped silica sol, wherein the molar ratio of transition metal element to Si is 1:10;

[0102] Step 2. Directional cryo-molding: The modified sol is added to the graphene ink and oriented hydrogel is formed under alternating magnetic field and liquid nitrogen gradient freezing. The mass ratio of sol to graphene is 1:20.

[0103] Step 3. Plasma-activated deposition: The freeze-dried preform is placed in a rotary deposition furnace. First, hydrogen-argon plasma is introduced to activate the surface, and then gradient deposition is performed using methane / alcohol dual carbon sources: First stage: deposition of nano-graphene nuclei at 900℃; Second stage: growth of vertical nanoarrays at 1200℃; Deposition pressure 4 kPa, time 60 min;

[0104] Step 4. Microwave covalent bonding: Microwave irradiation is performed under nitrogen protection to trigger covalent bonding between nano-silicon and carbon, forming a Si-C interface layer;

[0105] The Fe transition metal nitrate or chloride is Ni(NO3)2·6H2O; the hydrothermal reaction conditions are hydrothermal reaction at 180℃ for 12h; the thickness of the Si-C interface layer is 5nm.

[0106] In step 1, the concentration of the Ni transition metal salt solution is 0.5 mol / L; the purity of the transition metal salt is ≥99.9%.

[0107] In step 2, the concentration of graphene ink is 40 mg / ml; the magnitude of the alternating magnetic field is 1.5 T; and the liquid nitrogen gradient freezing rate is 50 °C / min.

[0108] In step 3, the rotary deposition furnace rotates at 5 rpm; the hydrogen-argon plasma has a power of 600 W; and the methane / alcohol dual carbon source has a weight ratio of 7:1.

[0109] In step 4, the microwave frequency is 2.45 GHz and the power density is 12 W / cm².

[0110] In step 3, gradient deposition employs a dual-channel independent gas supply system. In the first stage, gaseous carbon source accounts for 90% of the total carbon source; in the second stage, liquid carbon source cracking gas accounts for 70% of the total carbon source.

[0111] The rotary deposition furnace is equipped with multi-stage baffles to create a vortex field with a Reynolds number of 6000.

[0112] Step 4 involves microwave irradiation followed by pulsed laser treatment with a wavelength of 1064 nm, an energy density of 10 J / cm², a pulse width of 50 ns, and a repetition frequency of 5 Hz, to generate carbon quantum dots on the top of the nanoarray to strengthen the end connections; the diameter of the laser-generated carbon quantum dots is 10 nm.

[0113] This invention also discloses a method for preparing a metal matrix composite material, characterized in that: a multi-level reinforced nano-covalently linked graphene preform prepared by the present invention is immersed in a metal melt containing 2wt% nano-TiB2, and formed in a vacuum pressure infiltration furnace at 750℃ and 30MPa; the metal melt is Al.

[0114] The present invention provides a multi-level reinforced nano-covalently linked graphene preform, characterized by having a tertiary porous structure:

[0115] Primary vias: 130μm oriented vias formed by freezing;

[0116] Secondary pores: 5.5μm interlayer pores;

[0117] Tertiary pores: 380nm nanometer array gap pores;

[0118] At 50% strain, the compressive strength is 34.8 MPa, the conductivity is >1000 S / m, the porosity is 91%, and the specific surface area is 620 m² / g.

[0119] Comparative Example 1

[0120] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 has no magnetic field orientation.

[0121] Comparative Example 2

[0122] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not involve microwave bonding.

[0123] Comparative Example 3

[0124] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses Al2O3 instead of TiB2.

[0125] Comparative Example 4

[0126] Traditional precast concrete, publication number CN112876201A.

[0127] Test Items

[0128] The testing standards are as follows:

[0129] Compressive strength: GB / T 1041-2018 @ 0.5 mm / min;

[0130] Conductivity: GB / T 1551-2021 Four-probe method (25℃ isothermal conditions);

[0131] Infiltration integrity: metallographic sectioning method (ISO 4499-4:2016);

[0132] Strength of Al-based composite materials: GB / T 228.1-2010 (tensile rate 1 mm / min);

[0133] Pore ​​structure: ISO 15901-2 Mercury porosimetry;

[0134] Interface components: ISO 15472 XPS test;

[0135] Test Example 1: Compressive strength (MPa), electrical conductivity (S / m), and impregnation integrity (%) of graphene preforms prepared in the examples and comparative examples; strength test of Al-based composite materials.

[0136] Table 1. Compressive strength (MPa), electrical conductivity (S / m), impregnation integrity (%), and strength test results of Al-based composite materials prepared in the examples and comparative examples.

[0137] Group Compressive strength (MPa) Conductivity (S / m) Infiltration integrity rate (%) Al-based composite material strength (MPa) Example 1 42.7±1.8 1380±90 99.1 503±15 Example 2 32.2±1.5 1005±80 91.3 429±12 Example 3 34.8±1.2 1100±85 92.6 433±10 Comparative Example 1 14.5±0.9 320±25 61.5 312±20 Comparative Example 2 18.7±1.1 680±50 78.2 348±18 Comparative Example 3 33.6±1.4 1210±75 76.4 285±25* Comparative Example 4 12.0±1.5 350±39 82.5 375±20

[0138] As can be seen from Table 1 above, the strength of the graphene preform material prepared in Comparative Example 3 suddenly becomes relatively small. The possible reason is that the strength of the composite material in Comparative Example 3 decreased significantly due to the formation of the Al4C3 brittle phase.

[0139] Comparing Examples 1-3, the possible reasons for the differences in test results are mainly the following three aspects: 1. Differences in catalytic cracking efficiency: Fe 3+ d 5 High-spin states possess optimal electron-accepting ability, resulting in the lowest CH bond breaking energy during CH4 cleavage; Fe-based deposited graphene exhibits the highest crystallinity, leading to increased conductivity. 2. Stability of silica sol doping: Fe 3+ The formation of strong covalent bonds with the SiO2 network and the more complete Si-C reaction during microwave bonding increase the compressive strength of the Fe-based composite material. 3. Role of metal residues: Fe nanoparticles act as a highly efficient nucleation substrate in the aluminum melt, thus increasing the strength of the Fe-based composite material.

[0140] In summary: the performance ranking of the three transition metals is Fe > Co ≈ Ni. This is based on the fact that Fe... 3+ Unique electronic structure (high spin d) 5 It imparts optimal catalytic activity and interfacial stability; the size effect (20-50nm) of residual Fe particles significantly refines the aluminum matrix grains; the catalytic side reactions of Co / Ni (such as the formation of carbonyl compounds from Co) slightly reduce the deposition efficiency.

[0141] By comparing Example 1 with the comparative example, the technical effects of the present invention can be seen.

[0142] 1. The core role of magnetic field orientation: In Comparative Example 1, the absence of a magnetic field led to disordered stacking of graphene sheets, resulting in decreased compressive strength; the infiltration integrity rate was only 61.5% (significantly increased porosity defects). 2. The irreplaceable nature of microwave bonding: In Comparative Example 2, the lack of Si-C covalent bonds resulted in decreased compressive strength; conductivity decreased by 51% (discontinuous electron transport paths). 3. The crucial role of TiB2 interface control (Comparative Example 3): In Comparative Example 3, the inability of Al2O3 to form a TiC barrier layer led to the extensive formation of the brittle Al4C3 phase.

[0143] The inventiveness of this invention can be seen by comparing Example 1 with Comparative Example 4. The five-stage synergistic process of this invention (transition metal catalysis-magnetic field orientation-plasma deposition-microwave bonding-laser strengthening) enables the graphene preform prepared by this invention to have good compressive strength, conductivity, etc.

[0144] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a multi-level reinforced nano-covalently linked graphene preform, characterized in that, Includes the following steps: Step 1. Preparation of modified sol: Fe / Co / Ni transition metal nitrates or chlorides are blended with nano-silica sol and then subjected to hydrothermal reaction to obtain metal-doped silica sol, wherein the molar ratio of transition metal elements to Si is 1:(5-20). Step 2. Directional cryo-molding: The modified sol is added to the graphene ink and oriented hydrogel is formed under alternating magnetic field and liquid nitrogen gradient freezing. The mass ratio of sol to graphene is 1:(10-30). Step 3. Plasma-activated deposition: The freeze-dried preform is placed in a rotary deposition furnace. First, hydrogen-argon plasma is introduced to activate the surface, and then gradient deposition is performed using a methane / alcohol dual carbon source: First stage: deposition of nano-graphene nuclei at 800-1000℃; Second stage: growth of vertical nanoarrays at 1000-1300℃; Deposition pressure 1-8 kPa, time 30-180 min; Step 4. Microwave covalent bonding: Microwave irradiation is performed under nitrogen protection to trigger covalent bonding between nano-silicon and carbon, forming a Si-C interface layer; The Fe / Co / Ni transition metal nitrate or chloride is Fe(NO3)3·9H2O, CoCl2·6H2O, or Ni(NO3)2·6H2O; the hydrothermal reaction conditions are 120-220℃ for 6-24h; and the Si-C interface layer thickness is 2-10nm.

2. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: In step 1, the concentration of the Fe / Co / Ni transition metal salt solution is 0.1-1 mol / L; the purity of the transition metal salt is ≥99.9%.

3. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: In step 2, the concentration of graphene ink is 10-50 mg / ml; the magnitude of the alternating magnetic field is 0.5-2 T; and the liquid nitrogen gradient freezing rate is 20-100 °C / min.

4. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: In step 3, the rotary deposition furnace rotates at 1-10 rpm; the hydrogen-argon plasma has a power of 300-1000W; and the methane / alcohol dual carbon source has a weight ratio of (3-10):

1.

5. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: In step 4, the microwave frequency is 2.45 GHz and the power density is 5-15 W / cm².

6. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: In step 3, gradient deposition employs a dual-channel independent gas supply system. In the first stage, gaseous carbon source accounts for 70-90% of the total carbon source; in the second stage, liquid carbon source cracking gas accounts for 60-80% of the total carbon source.

7. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: The rotary deposition furnace is equipped with multi-stage baffles to create a vortex field with a Reynolds number of 3000-10000.

8. The method for preparing a multi-level reinforced nano-covalently linked graphene preform according to claim 1, characterized in that: Step 4 involves microwave irradiation followed by pulsed laser treatment with a wavelength of 1064±10nm, an energy density of 5-15J / cm², a pulse width of 10-100ns, and a repetition frequency of 1-10Hz, to generate carbon quantum dots on the top of the nanoarray to strengthen the end connections; the diameter of the laser-generated carbon quantum dots is 5-20nm.

9. A method for preparing a metal matrix composite material, characterized in that: A multi-level reinforced nano-covalently linked graphene preform prepared according to any one of claims 1-8 is immersed in a metal melt containing 0.5-5 wt% nano-TiB2 and formed in a vacuum pressure infiltration furnace at 600-900℃ and 10-50 MPa; the metal melt is any one of Al, Cu, and Mg alloys.

10. A multi-level reinforced nano-covalently linked graphene preform prepared according to claim 1, characterized in that, It has a three-level pore structure: Primary vias: Frozen to form 50-200μm oriented through-holes; Secondary pores: 1-10μm interlayer pores; Tertiary pores: 200-800nm ​​nanometer array gap pores; At 50% strain, the compressive strength is 15-50 MPa, the conductivity is >1000 S / m, the porosity is 85-95%, and the specific surface area is 400-800 m² / g.

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