A high-hardness and high-strength graphene / molybdenum metal composite material, a preparation method and application thereof

Abstract

The application discloses a kind of high hardness, high strength graphene / molybdenum metal composite material and its preparation method and application.Firstly, graphene oxide is mixed with ammonium molybdate tetrahydrate in aqueous solution and dried to obtain precursor powder;Using joule heating technology, in-situ generated Mo2C composite powder loaded on graphene;Subsequently, the composite powder is mixed with molybdenum powder in proportion, and prepared into a dense block composite material by spark plasma sintering technology.The method realizes the uniform dispersion of graphene in the molybdenum matrix through the in-situ formation of Mo2C interface layer, effectively inhibits the agglomeration problem of graphene, strengthens the interface bonding, and improves the overall hardness and strength of the composite material.The prepared material shows significant high hardness, high strength and good toughness, and is suitable for aerospace structural parts, wear-resistant tools and high-reliability mechanical components.

Description

Technical Field

[0001] This invention belongs to the field of transition metals and carbon materials technology, and particularly relates to a high-hardness, high-strength graphene / molybdenum metal composite material, its preparation method and application. Background Technology

[0002] Metal matrix composites are renowned for their comprehensive properties, including high strength, high hardness, high temperature resistance, and low coefficient of thermal expansion, and have been widely used in aerospace structural components, wear-resistant tools, precision machinery, and high-reliability parts. Molybdenum, as a typical high-melting-point metal (melting point approximately 2623℃), possesses excellent stiffness, strength, and creep resistance, making it an ideal matrix material for extreme environments. However, pure molybdenum still suffers from insufficient toughness, susceptibility to wear, and fatigue crack propagation under high loads or cyclic stress conditions, limiting its application in even more demanding environments.

[0003] Graphene, a two-dimensional material known for its extremely high strength, low density, and excellent mechanical toughness, is an ideal reinforcing phase for strengthening metal matrices. Theoretically, graphene can significantly improve the hardness, strength, and wear resistance of molybdenum-based composites while maintaining or improving overall toughness. However, in actual preparation, graphene is prone to agglomeration, stacking, or wrinkling, resulting in uneven dispersion within the molybdenum matrix. Simultaneously, the weak interfacial bonding between graphene and molybdenum (poor wettability) easily leads to the formation of micropores, crack initiation sites, and stress concentration zones, ultimately limiting the improvement in the mechanical properties of the composite material and even causing localized defects that reduce overall strength.

[0004] In existing technologies, the preparation of graphene / molybdenum or molybdenum alloy composites often employs mechanical mixing, ball milling, or hot pressing, but agglomeration and interface problems are prominent. For example, Chinese patent document CN114540661B discloses a graphene-reinforced copper-molybdenum composite material, which forms a three-dimensional network structure through electrostatic self-assembly and in-situ reduction, improving strength and conductivity. However, the process involves multiple steps of surface modification and is dependent on the copper matrix, making it impossible to directly transfer to a pure molybdenum system, and agglomeration control still depends on subsequent sintering. Chinese patent document CN109371304B discloses an in-situ generated molybdenum carbide-reinforced molybdenum-based composite material, in which molybdenum powder and graphene are directly ball-milled and then hot-pressed and sintered, generating a small amount of Mo2C in-situ to strengthen the interface. This method directly mixes graphene and molybdenum powder and then sintersects, but the initial uneven dispersion of graphene and agglomeration lead to large fluctuations in local hardness of the composite material, resulting in insufficient improvement in overall strength and wear resistance. Chinese patent document CN104835945A discloses a graphene / molybdenum carbide composite anode material, which uses graphene oxide and ammonium molybdate precursor to prepare Mo2C-supported graphene through reduction. However, this method is designed for lithium battery applications and does not involve the composite with metallic molybdenum powder. None of the above-mentioned prior technologies employ a strategy of pre-generating Mo2C in situ on the graphene surface, resulting in limited improvement in the hardness, strength, and uniformity of the composite material, failing to meet the stringent requirements of high-load, high-reliability applications such as aerospace and wear-resistant tools. Summary of the Invention

[0005] The primary objective of this invention is to overcome the problem of insufficient improvement in mechanical properties caused by the easy agglomeration of graphene and weak interfacial bonding in existing graphene / molybdenum composite materials. An improved method is proposed to achieve uniform dispersion of graphene in a molybdenum matrix, strong interfacial bonding, and a significant improvement in overall hardness and strength.

[0006] To achieve the above objectives, this invention provides a high-hardness, high-strength graphene / molybdenum metal composite material and its preparation method. The composite material uses molybdenum powder as the matrix and in-situ generated graphene supported on molybdenum carbide (Mo2C) as the reinforcing phase. Through molecular-level interfacial bridging and uniform dispersion mechanisms, the material acquires superior mechanical properties. The prepared material exhibits significant high hardness, high strength, and good toughness, making it suitable for applications such as aerospace structural components, wear-resistant tools, and high-reliability mechanical parts.

[0007] A method for preparing a high-hardness, high-strength graphene / molybdenum metal composite material, the main raw materials of which include: graphene oxide, ammonium molybdate tetrahydrate, and molybdenum powder. The method specifically includes the following steps: S1: Mix the graphene oxide dispersion with ammonium molybdate tetrahydrate in an aqueous solution, and stir the resulting mixture thoroughly to form a homogeneous dispersion; S2: The above uniform dispersion is freeze-dried to form a precursor powder. The precursor powder is placed in a Joule furnace and thermally reacted under the protection of inert argon gas to obtain a composite powder of molybdenum carbide supported on graphene. S3: Mix the composite powder with molybdenum powder evenly to obtain a mixed powder; S4: The above mixed powder is prepared into a graphene / molybdenum metal composite material by spark plasma sintering.

[0008] Further, in step S1, the dry basis mass ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:(0.3-1.0).

[0009] Furthermore, in step S1, the stirring is carried out at room temperature, the stirring speed is 300-600 rpm, and the stirring time is 0.5-2 hours.

[0010] Furthermore, in step S2, the Joule heating reaction is carried out in a Joule furnace under inert gas protection, with a heating temperature of 900-1100℃ and a heating time of 5-20 minutes.

[0011] More preferably, the Joule heating reaction adopts a segmented control mode, achieving stepwise heating through segmented current control, including at least three stages: a first heating stage with a current of 30-50 A and a holding time of 0.5-3 minutes; a second heating stage with a current of 50-100 A and a holding time of 3-10 minutes; and a third heating stage with a current of 100-200 A and a holding time of 3-10 minutes; the total heating temperature is 900-1100℃, and the total heating time is 5-20 minutes. This rapid heating process not only promotes the uniform formation of Mo2C but also repairs defects generated in graphene during ball milling dispersion, improving its crystallinity and structural integrity.

[0012] Further, in step S3, the composite powder and molybdenum powder are mixed by ball milling, wherein the composite powder accounts for 0.4-1.5 wt% and the molybdenum powder accounts for 98.5-99.6 wt%. The composite powder and molybdenum powder are placed in a ball mill jar, and zirconia balls are added as the grinding medium, with a ball-to-powder ratio of 10-20:1. Preferably, the ball milling speed is controlled at 150-400 rpm, and the milling time is 0.5-2 hours. This step ensures uniform pre-dispersion of the composite powder in the molybdenum matrix, further reducing the risk of agglomeration and improving the microstructure uniformity and mechanical property consistency of the subsequent sintered material. After uniform mixing, the powder to be sintered is obtained.

[0013] Further optimized, in step S3, the composite powder accounts for 0.5%-1.0% of the mixture of composite powder and metallic molybdenum powder.

[0014] Further, in step S4, the mixed powder is loaded into a graphite mold, placed in a spark plasma sintering (SPS) furnace and evacuated. Under inert gas protection, a unidirectional axial pressure of 40-60 MPa is applied, and a pulsed current is simultaneously applied for sintering. The heating rate is 80-150℃ / min, the sintering temperature is 1400-1600℃, the sintering holding time is 3-10 minutes, and the furnace is cooled to room temperature to obtain a high-density bulk graphene / molybdenum composite material.

[0015] More preferably, the graphene oxide in step S1 is prepared using a modified Hummers method, and the preparation process includes the following steps: Concentrated H₂SO₄ was added to a container, followed by KMnO₄ with stirring. Stirring continued until completely dissolved. The container was then placed in an ice-water bath, and graphite powder was added, with continued stirring. The mixture was then transferred to room temperature. After stirring, the mixture was poured into ice water, and H₂O₂ solution was added dropwise until no bubbles were generated. After standing and separating into layers, the supernatant was discarded. The precipitate was washed with hydrochloric acid solution, followed by repeated washing with deionized water until the supernatant showed no precipitate when tested with BaCl₂ and was neutral (6-7) according to pH paper. Finally, centrifugation was performed to obtain a graphene oxide dispersion. The concentration of the graphene oxide dispersion was 7-10 mg / mL, the number of graphene oxide layers was 1-3, and the layer size was 10-60 μm.

[0016] The graphene / molybdenum composite material obtained by the above preparation method uses metallic molybdenum as a continuous matrix and uniformly disperses a graphene reinforcing phase supported by Mo2C inside. The Mo2C is generated by the pre-reaction of graphene oxide and ammonium molybdate (not by direct reaction with molybdenum powder). The Mo2C particles serve as an interfacial bridge layer and are grown in situ on the surface of graphene oxide, achieving strong chemical bonding and molecular-level bonding between the molybdenum matrix and graphene, thus avoiding interfacial micropores or cracks.

[0017] The graphene / molybdenum composite material of this invention features enhanced interfacial bonding between graphene and the molybdenum matrix, resulting in high overall hardness and strength. It is suitable for applications such as aerospace structural components, wear-resistant tools, and high-reliability mechanical parts. Specific applications include processing the composite material into blocks or components to withstand high-load environments, achieving excellent mechanical support and durability.

[0018] The advantages and beneficial effects of this invention are as follows: 1. By pre-generating a Mo2C layer in situ on the surface of graphene, agglomeration is suppressed from the source, achieving highly uniform dispersion of graphene in the molybdenum matrix and improving the overall density and micro-uniformity of the material.

[0019] 2. Mo2C serves as an ideal interfacial bridge, with one end bonded to the graphene carbon network by strong covalent bonds and the other end tightly connected to the molybdenum matrix by metallic bonds, achieving molecular-level interfacial bonding, significantly eliminating interfacial micropores and stress concentration, and improving the hardness and strength of the composite material.

[0020] 3. By fully utilizing the high melting point, high rigidity, and high temperature resistance of the molybdenum matrix and combining it with the ultra-high strength of graphene, the resulting material exhibits excellent mechanical properties and is suitable for structural components subjected to high loads, wear resistance, and extreme environments.

[0021] 4. The flash Joule heating technology and SPS rapid low-temperature process are adopted. This programmed temperature control mode can not only promote the uniform formation of Mo2C, but also repair the defects generated in graphene during ball milling and dispersion, and improve its crystallinity and structural integrity.

[0022] 5. The entire preparation process is short and energy-efficient, avoiding damage to the graphene structure caused by prolonged high temperatures, and meeting the requirements of green and efficient manufacturing. Attached Figure Description

[0023] Figure 1 The image shows an electron microscope image of Mo2C@rGO prepared in Example 2.

[0024] Figure 2 Electron micrograph of Mo2C@rGO prepared for Comparative Example 3.

[0025] Figure 3 XRD patterns of Mo2C@rGO standard, Mo2C@rGO prepared in Example 2, and Mo2C@rGO material prepared in Comparative Example 2.

[0026] Figure 4 Raman spectra of the precursor powder prepared in Example 2 and Mo2C@rGO.

[0027] Figure 5 Raman spectra of Mo2C@rGO prepared in Examples 3 and 4. Detailed Implementation

[0028] To better understand the present invention, further description is provided below with reference to the accompanying drawings and specific embodiments. However, the implementation of the present invention is not limited thereto. The described embodiments are some, but not all, embodiments of the present invention, and are for illustrative purposes only and not for limitation. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort, such as adjusting relevant process parameters according to the experimental scale, are within the scope of protection of the present invention.

[0029] The graphene oxide in the following examples can be prepared using the modified Hummers method, and the specific preparation process includes the following steps: Add 90 mL of 98% concentrated H₂SO₄ to a beaker and stir at 300 rpm on a magnetic stirrer. Add 8.5 g of KMnO₄ and continue stirring until completely dissolved. Transfer the beaker to an ice-water bath at 0°C and slowly add 2 g of 100-mesh graphite powder, continuing to stir for 10 minutes. Then, transfer the mixture to room temperature and stir at 150 rpm for 24 hours. After the reaction is complete, pour the mixture into ice water and slowly add 30 wt% H₂O₂ solution until no bubbles are generated. After standing and separating the layers, discard the supernatant. Wash the precipitate with 1 L of hydrochloric acid aqueous solution (1:10), and then wash repeatedly with deionized water until the supernatant shows no precipitate when tested with BaCl₂ and is neutral (6-7) when tested with pH paper. Finally, centrifuge at 5000 rpm to obtain a graphene oxide dispersion. The concentration of the graphene oxide dispersion is 7-10 mg / mL, the number of graphene oxide sheets is 1-3, and the sheet size is 10-60 μm.

[0030] Example 1 S1: Take the equivalent of 0.4 g of graphene oxide dispersion (graphene oxide dispersed in water, concentration approximately 8 mg / mL), add it to 0.20 g of ammonium molybdate tetrahydrate and deionized water to a final volume of 100 mL. Stir at 500 rpm for 1 hour on a magnetic stirrer to form a uniform dispersion. (At this point, the dry weight ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:0.5.) S2: The above dispersion was dried in a freeze dryer for 36 hours to obtain the precursor powder. The precursor powder was then placed in a flash Joule furnace. After evacuation, high-purity argon was introduced as a protective gas. A stepped temperature increase was achieved by controlling the current in stages using a programmed temperature control mode: the current was held at 30 A for 1 minute, then increased to 50 A and held for 1 minute, then increased to 80 A and held for 1 minute, then increased to 100 A and held for 5 minutes, and finally increased to 200 A and held for 5 minutes. After the reaction was completed, the mixture was cooled to room temperature under an argon atmosphere. The programmed temperature control mode was repeated twice to obtain a composite powder of molybdenum carbide supported on graphene, named Mo2C@rGO.

[0031] S3: Take 0.025 g of the above composite powder and place it in a ball mill jar with 4.975 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (composite powder accounts for 0.5 wt%).

[0032] S4: Take 2g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a dense blocky graphene / molybdenum composite material.

[0033] Example 2 S1: Take the equivalent of 0.4 g of graphene oxide dispersion (graphene oxide dispersed in water, concentration approximately 8 mg / mL), add it to 0.20 g of ammonium molybdate tetrahydrate and deionized water to a final volume of 100 mL. Stir at 500 rpm for 1 hour on a magnetic stirrer to form a uniform dispersion. (At this point, the dry weight ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:0.5.) S2: The above dispersion was dried in a freeze dryer for 36 hours to obtain the precursor powder. The precursor powder was then placed in a flash Joule furnace. After evacuation, high-purity argon was introduced as a protective gas. A stepped temperature increase was achieved by controlling the current in stages using a programmed temperature control mode: the current was held at 30 A for 1 minute, then increased to 50 A and held for 1 minute, then increased to 80 A and held for 1 minute, then increased to 100 A and held for 5 minutes, and finally increased to 200 A and held for 5 minutes. After the reaction was completed, the mixture was cooled to room temperature under an argon atmosphere. The programmed temperature control mode was repeated twice to obtain a composite powder of molybdenum carbide supported on graphene, named Mo2C@rGO.

[0034] S3: Take 0.05 g of the above composite powder and place it in a ball mill jar with 4.95 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), with a ball-to-powder ratio of 10:1, and ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (composite powder accounts for 1 wt%).

[0035] S4: Take 2g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a dense blocky graphene / molybdenum composite material.

[0036] Example 3 S1: Take the equivalent of 0.4 g of graphene oxide dispersion (graphene oxide dispersed in water, concentration approximately 8 mg / mL), add it to 0.12 g of ammonium molybdate tetrahydrate and deionized water to a final volume of 100 mL. Stir at 500 rpm for 1 hour on a magnetic stirrer to form a uniform dispersion. (At this point, the dry weight ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:0.3.) S2: The above dispersion was dried in a freeze dryer for 36 hours to obtain the precursor powder. The precursor powder was then placed in a flash Joule furnace. After evacuation, high-purity argon was introduced as a protective gas. A stepped temperature increase was achieved by controlling the current in stages using a programmed temperature control mode: the current was held at 30 A for 1 minute, then increased to 50 A and held for 1 minute, then increased to 80 A and held for 1 minute, then increased to 100 A and held for 5 minutes, and finally increased to 200 A and held for 5 minutes. After the reaction was completed, the mixture was cooled to room temperature under an argon atmosphere. The programmed temperature control mode was repeated twice to obtain a composite powder of molybdenum carbide supported on graphene, named Mo2C@rGO.

[0037] S3: Take 0.05 g of the above composite powder and place it in a ball mill jar with 4.95 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), with a ball-to-powder ratio of 10:1, and ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (composite powder accounts for 1 wt%).

[0038] S4: Take 2g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a dense blocky graphene / molybdenum composite material.

[0039] Example 4 S1: Take the equivalent of 0.4 g of graphene oxide dispersion (graphene oxide dispersed in water, concentration approximately 8 mg / mL), add it to 0.40 g of ammonium molybdate tetrahydrate and deionized water to a final volume of 100 mL. Stir at 500 rpm for 1 hour on a magnetic stirrer to form a uniform dispersion. (At this point, the dry weight ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:1.0.) S2: The above dispersion was dried in a freeze dryer for 36 hours to obtain the precursor powder. The precursor powder was then placed in a flash Joule furnace. After evacuation, high-purity argon was introduced as a protective gas. A stepped temperature increase was achieved by controlling the current in stages using a programmed temperature control mode: the current was held at 30 A for 1 minute, then increased to 50 A and held for 1 minute, then increased to 80 A and held for 1 minute, then increased to 100 A and held for 5 minutes, and finally increased to 200 A and held for 5 minutes. After the reaction was completed, the mixture was cooled to room temperature under an argon atmosphere. The programmed temperature control mode was repeated twice to obtain a composite powder of molybdenum carbide supported on graphene, named Mo2C@rGO.

[0040] S3: Take 0.05 g of the above composite powder and place it in a ball mill jar with 4.95 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), with a ball-to-powder ratio of 10:1, and ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (composite powder accounts for 1 wt%).

[0041] S4: Take 2g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a dense blocky graphene / molybdenum composite material.

[0042] Comparative Example 1 S1: Take 0.025 g of pure graphene powder (commercially available or prepared by reducing graphene oxide, sheet size 10-60 μm) and place it in a ball mill jar with 4.975 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (graphene content 0.5wt%).

[0043] S2: Take 2 g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a blocky graphene / molybdenum composite material.

[0044] Comparative Example 2 S1: Take 0.05 g of pure graphene powder (commercially available or prepared by reducing graphene oxide, sheet size 10-60 μm) and 4.95 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm) and place them in a ball mill jar. The ball-to-powder ratio is 10:1. Ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (graphene content 1 wt%).

[0045] S2: Take 2 g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a blocky graphene / molybdenum composite material.

[0046] Comparative Example 3 S1: Take a dispersion equivalent to 0.4 g of graphene oxide (graphene oxide dispersed in water at a concentration of about 8 mg / mL), add it to 0.20 g of ammonium molybdate tetrahydrate and deionized water to a final volume of 100 mL, and stir on a magnetic stirrer at 500 rpm for 1 hour to form a uniform dispersion.

[0047] S2: The above dispersion was dried in a freeze dryer for 36 hours to obtain precursor powder. The precursor powder was then loaded into a tube furnace. After evacuation, high-purity argon was introduced as a protective gas. The temperature was increased to 1000℃ at a rate of 10℃ / min and held for 40 minutes. After the reaction was completed, the furnace was allowed to cool naturally to room temperature to obtain molybdenum carbide / graphene composite powder under conventional heat treatment in a tube furnace (control group Mo2C@rGO).

[0048] S3: Take 0.05 g of the above composite powder and place it in a ball mill jar with 4.95 g of metallic molybdenum powder (purity ≥99.9%, particle size 100 nm), with a ball-to-powder ratio of 10:1, and ball mill at 150 rpm for 1 hour to obtain a uniformly mixed powder (composite powder accounts for 1 wt%).

[0049] S4: Take 2g of mixed powder, put the mixed powder into a graphite mold with a diameter of 10 mm, place it in a spark plasma sintering (SPS) furnace and evacuate it. Apply 50 MPa unidirectional axial pressure under argon protection, heat it to 1500℃ at a heating rate of 100℃ / min, hold it for 5 minutes, and cool it to room temperature with the furnace to obtain a blocky graphene / molybdenum composite material.

[0050] The experimental samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, and the results are as follows: Figure 1 This is a scanning electron microscope (SEM) image of the Mo2C@rGO composite material prepared in Example 2. Mo2C particles, approximately 10-50 nm in size, are uniformly distributed on the surface of the reduced graphene oxide (rGO), exhibiting spherical or near-spherical morphology and a highly uniform dispersion. The Mo2C particles are tightly attached to the wrinkles and edges of the graphene sheets, forming a continuous loading structure. This indicates that Mo2C was successfully grown through in-situ reaction and achieved good interfacial bonding with graphene, providing an ideal interfacial bridge for subsequent composite with the molybdenum matrix.

[0051] Figure 2 The image shows a scanning electron microscope (SEM) image of the Mo2C@rGO composite material prepared in Comparative Example 3, compared with... Figure 1 The states of medium and high dispersion are quite different. Figure 2The Mo2C particles on the surface of reduced graphene oxide (rGO) exhibit uneven sizes, displaying irregular, coarse lumps of approximately 200-500 nm, with some agglomerated lumps exceeding 800 nm, and exhibiting extremely pronounced agglomeration. This morphological degradation is primarily due to the slow heating rate of the tube furnace, leading to long-range diffusion and grain growth of Mo2C nanoparticles on the graphene surface under high temperature and prolonged driving conditions. Locally, large particles even detach from the substrate, disrupting the ideal interfacial bonding. In contrast, the flash Joule heating technology used in Example 2 enables the reaction system to rapidly heat up to the required reaction temperature within a short time, thereby driving the precursor to achieve rapid in-situ nucleation and growth of Mo2C at multiple sites on the graphene surface. Simultaneously, the water-cooling system attached to the Joule furnace cools the Mo2C particles in a short time before they diffuse, preventing further surface growth and diffusion.

[0052] Figure 3 XRD patterns of Mo2C@rGO standard, Mo2C@rGO prepared in Example 2, and Mo2C@rGO material prepared in Comparative Example 2. Pretreatment of graphene oxide and ammonium molybdate tetrahydrate successfully generated Mo2C, and characteristic peaks of the β-Mo2C hexagonal phase (100), (002), (101), (102), (110), (103), (211), and (112) were successfully observed in the figures. The main peak (101) of Mo2C in the Example 2 was stronger than that in the Comparative Example. This is because the Mo2C in the Example 2 was generated in situ, while the Comparative Example relied solely on passive diffusion during sintering, resulting in a smaller and discontinuous amount of carbides. Furthermore, the graphene peak in Example 2 was significantly lower than that in Comparative Example 2, indicating that the graphene surface was encapsulated by in-situ generated carbides and chemically bonded, and that the in-situ generated carbides blocked the van der Waals attraction between graphene layers.

[0053] Figure 4 The Raman spectra of the precursor powder prepared in Example 2 and Mo2C@rGO are shown. In the spectrum of the precursor powder, I can be observed. D / I G The value is as high as 2.07. This indicates that in the precursor stage, due to the large number of oxygen-containing functional groups on the surface of graphene oxide, the sp2 hybrid structure of the carbon network is severely disrupted, exhibiting high defect density and disorder. After flash Joule heating treatment, the Raman spectrum of the composite powder changed significantly, I D / I G The value reached 0.18 because the instantaneous release of high heat during Joule heating rapidly removed oxygen-containing groups from the graphene surface, achieving the reduction of graphene oxide. On the other hand, the high-temperature process provided sufficient kinetic energy for carbon atoms to rearrange their lattice, repairing structural defects introduced by earlier processes and inducing them to rebuild into highly ordered sp...2 Hybrid network. Furthermore, the sharp 2D peaks observed in Mo2C@rGO further confirm its extremely high crystallinity and excellent interlayer arrangement. Raman results quantitatively demonstrate that the pre-reaction not only completed the phase loading but also repaired defects in the graphene-reinforcing phase, thereby improving the overall strength of the material and ensuring that the embodiments can exert the ideal mechanical strengthening effect in subsequent composite processes.

[0054] Figure 5 The Raman spectra of Mo2C@rGO prepared in Examples 3 and 4 were used to investigate the effect of the addition ratio of graphene oxide to ammonium molybdate tetrahydrate on the effect. For Example 3 (ammonium molybdate ratio was relatively low), I D / I G The value decreased to 0.13, slightly lower than 0.18 in Example 2, due to a reduction in the number of carbon atoms involved in the in-situ formation of Mo2C, resulting in more complete Joule heating for defect repair and graphitization of graphene oxide. In Example 4, the ammonium molybdate ratio was too high, I D / I G The value increased to 0.47, which was due to the increased production of more Mo2C from the addition of ammonium molybdate, but also led to increased consumption of the carbon skeleton, thus introducing more defects.

[0055] The Vickers hardness test was performed on the samples of the above embodiments and comparative examples using a Vickers hardness tester under a load of 1.961 N Hv0.2, and the results are shown in Table 1.

[0056] Table 1

[0057] As shown in Table 1, the Vickers hardness value of Example 1 is 1354 HV, Example 2 is 1848.5 HV, Comparative Example 1 is 1022 HV, and Comparative Example 2 is 1385 HV. Compared to Comparative Example 1, the hardness of Example 1 of the present invention is increased by approximately 32.5%; compared to Comparative Example 2, the hardness of Example 2 is increased by approximately 33.5%. This indicates that by generating Mo2C in situ and loading it onto the graphene surface, the present invention significantly improves the hardness of the composite material, demonstrating the superiority of this method in suppressing graphene agglomeration and strengthening interfacial bonding, thereby achieving improved mechanical properties. Example 3 is a composite metal material formed with a lower ammonium molybdate content, with a Vickers hardness of 1255 HV. Figure 5Raman spectroscopy revealed that due to less carbon skeleton consumption, graphene structural repair was more complete; however, due to less Mo2C formation, the improvement in material hardness was limited. Example 4, a composite metal material formed with a higher ammonium molybdate content, showed a decrease in hardness to 1605 HV. The excessive Mo2C formation process consumed more of the graphene structure, introducing more structural defects, thus negatively impacting the strengthening effect. Comparative Example 3, Mo2C obtained through conventional tube furnace heating, had a hardness of only 1418 HV, lower than Example 2 using flash Joule heating technology. This further illustrates that slow heating leads to particle agglomeration and growth diffusion, resulting in a decrease in material performance. The rapid heating of flash Joule heating technology can effectively suppress particle coarsening, thereby improving material performance.

[0058] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a graphene / molybdenum metal composite material, characterized in that, Includes the following steps: S1: Mix the graphene oxide dispersion with ammonium molybdate tetrahydrate in an aqueous solution and stir to form a uniform dispersion; S2: The above uniform dispersion is freeze-dried to form a precursor powder, and the precursor powder is subjected to Joule heating reaction to obtain a composite powder of molybdenum carbide supported on graphene. S3: Mix the above composite powder with metallic molybdenum powder to obtain a mixed powder; S4: The above mixed powder is prepared into a graphene / molybdenum metal composite material by spark plasma sintering.

2. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S1, the concentration of the graphene oxide dispersion is 7-10 mg / mL.

3. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S1, the dry basis mass ratio of graphene oxide to ammonium molybdate tetrahydrate is 1:(0.3-1.0).

4. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S2, the Joule heating reaction is carried out in a Joule furnace under inert gas protection, at a heating temperature of 900-1100℃, for a heating time of 5-20 minutes.

5. The method for preparing the graphene / molybdenum metal composite material according to claim 4, characterized in that, The Joule heating reaction adopts a segmented control mode, including at least three stages: the first heating stage, with a current of 30-50 A and a holding time of 0.5-3 minutes; During the second heating stage, the current is 50-100 A, and the holding time is 3-10 minutes. In the third heating stage, the current is 100-200 A, and the holding time is 3-10 minutes.

6. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S3, the composite powder accounts for 0.4%-1.5% of the total mass, and the molybdenum metal powder accounts for 98.5%-99.6% of the total mass.

7. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S3, the mixing is carried out by ball milling, with a ball milling speed of 150-400 rpm and a ball milling time of 0.5-2 hours.

8. The method for preparing the graphene / molybdenum metal composite material according to claim 1, characterized in that, In step S4, the discharge plasma sintering process is as follows: a unidirectional axial pressure of 40-60 MPa is applied under inert gas protection, and a pulsed current is simultaneously applied for sintering. The sintering heating rate is 80-150℃ / min, the sintering temperature is 1400-1600℃, and the sintering holding time is 3-10 minutes.

9. A graphene / molybdenum metal composite material obtained by the preparation method according to any one of claims 1-8.

10. The application of the graphene / molybdenum metal composite material of claim 9 in the preparation of aerospace structural components or wear-resistant tools.

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