Molecular model construction and simulation method of graphene reinforced copper-chromium alloy contact material

Abstract

The application belongs to the technical field of electrical contact material design and molecular simulation, and discloses a molecular model construction and simulation method of graphene reinforced copper-chromium alloy contact material. The method comprises the steps of model construction, potential function selection and simulation parameter setting, etc. The application initiates a method of constructing a three-dimensional continuous graphene network topology along a polycrystalline grain boundary, and accurately maps the in-situ coating and network interweaving characteristics of graphene on the surface of metal powder in a high-end powder metallurgy preparation process. The model reconstruction with high physical fidelity completely overcomes the disadvantages of traditional two-dimensional isolated models that cannot transmit overall stress and space heat.

Description

Technical Field

[0001] This invention relates to the field of electrical contact material design and molecular simulation technology, and more specifically to a method for constructing and simulating molecular models of graphene-reinforced copper-chromium alloy contact materials based on a three-dimensional continuous grain boundary network configuration. Background Technology

[0002] As a key functional component in high-voltage switchgear and electromagnetic launch systems, electrical contacts are subjected to a multi-field coupling of electricity, heat, and force during high-current switching and high-frequency opening and closing processes. Their service performance directly affects the operational reliability and service life of the system. Especially under conditions of high current carrying capacity and frequent operation, the contact interface is prone to significant temperature rise and localized arcing, leading to material degradation.

[0003] Under the aforementioned complex operating conditions, copper-chromium alloy contact materials are prone to various degradation behaviors, including mechanical wear, arc ablation, molten adhesion, and microstructural evolution, leading to increased contact resistance, deteriorated frictional performance, and reduced service life. Existing research indicates that introducing reinforcing phases such as graphene can improve the wear resistance and ablation resistance of materials to some extent. However, the mechanism involves atomic-scale interfacial interactions and structural evolution processes, making it difficult to achieve precise characterization and mechanism revelation solely through macroscopic experimental methods.

[0004] Currently, molecular dynamics studies on graphene-modified copper-chromium alloy contact materials face significant limitations in model construction. Existing techniques typically employ random matrix atom substitution or two-dimensional rigid planar layer insertion to introduce carbon atoms. However, in actual high-performance copper-chromium alloy preparation (such as powder metallurgy and in-situ coating processes), graphene does not exist randomly and in isolation, but rather segregates along the grain boundaries of copper / chromium polycrystalline particles, forming a highly continuous and three-dimensional curved surface-like encapsulated or network-like spatial topology. Existing coarse two-dimensional, discrete graphene doping models disrupt the three-dimensional connectivity within the composite material, failing to accurately reflect the core physical mechanisms of rapid local heat conduction and omnidirectional dislocation slip blocking of the graphene three-dimensional network under extreme conditions such as high-speed sliding and high-current switching. The lack of precise construction and quantitative analysis methods for the true spatial topological configuration of graphene leads to distorted tribological results from existing simulations, making them unreliable selection criteria for macroscopic-scale powder metallurgy alloy composition and microstructure design.

[0005] Therefore, developing a molecular model and simulation method for graphene-reinforced copper-chromium alloy contact materials based on a three-dimensional continuous grain boundary network configuration is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for constructing and simulating a molecular model of graphene-reinforced copper-chromium alloy contact materials. Existing molecular simulation techniques mostly employ random atomic substitution or two-dimensional rigid plane insertion methods, which disrupt the spatial continuity of the nano-reinforcing phase within the matrix. This invention pioneers a method for constructing a three-dimensional continuous graphene network topology along polycrystalline grain boundaries, accurately mapping the in-situ coating and network interweaving characteristics of graphene on the surface of metal powders in advanced powder metallurgy preparation processes. This high-fidelity model reconstruction completely overcomes the shortcomings of traditional two-dimensional isolated models that cannot transmit overall stress and spatial heat.

[0007] To achieve the above objectives, this invention provides a method for constructing and simulating a molecular model of graphene-reinforced copper-chromium alloy contact materials based on a three-dimensional continuous grain boundary network configuration. The method includes steps such as model construction, potential function selection, and simulation parameter setting, as detailed below:

[0008] Step 1: Construction of the multiphase polycrystalline matrix model and extraction of grain boundary coordinates: A nanocrystalline copper-chromium system with a specified number of grains was constructed using the Voronoi polyhedral method, in which chromium grains were distributed in a specific proportion within a copper matrix. Subsequently, the set of atomic coordinates of the three-dimensional grain boundary surfaces at the copper-copper, chromium-chromium, and copper-chromium polycrystalline boundaries was accurately identified and extracted using the centrosymmetry parameter method and common nearest neighbor analysis.

[0009] Step 2: Conformal construction of graphene along a three-dimensional continuous network topology at grain boundaries: Based on the preset graphene mass fraction, a three-dimensional continuous graphene network topology, meandering and undulating along the grain boundaries, is constructed using surface mapping and structure reconstruction algorithms on the three-dimensional grain boundary surface coordinate set extracted in step one. This three-dimensional continuous graphene network is then embedded in a pure copper-chromium matrix, replacing the original grain boundary transition region atoms, ultimately constructing a high-fidelity composite molecular model with a realistic microstructure of a metal matrix-three-dimensional graphene grain boundary encapsulation network.

[0010] Step 3: Selection and allocation of multi-scale combined potential functions: The EAM potential function is used to describe the interactions between metal atoms (Cu-Cu, Cr-Cr, Cu-Cr); the AIREBO potential function is used to describe the strong covalent interactions (CC) between carbon atoms inside the graphene three-dimensional network; and the Lennard-Jones (LJ) potential function is used to describe the interfacial van der Waals interactions (C-Cu, C-Cr) between the three-dimensional graphene network and the encapsulated metal grains.

[0011] Step 4: System energy minimization and geometry optimization: Overlapping atoms during network reconstruction were removed using the distance threshold method in LAMMPS software. Geometric optimization was performed using the conjugate gradient method, with a time interval of 1 fs, room temperature, an NPT ensemble, and 20,000 equilibrium relaxation steps to eliminate high residual stress at grain boundaries, thus ensuring stable interface lattice matching between the three-dimensional graphene network and the polycrystalline metal matrix.

[0012] Step 5: Decoupling Transient Thermo-Coupling Friction Simulation from Physical Mechanisms: Using the optimized composite material molecular model from step four, the effect of different graphene contents on tribological properties under extremely demanding contact / electromagnetic emission conditions was simulated and calculated. This included the following sub-steps: (1) Thermal boundary setting: The Z direction is set as a non-periodic boundary condition, and the X and Y directions are periodic boundaries. From bottom to top, it is divided into a rigid fixed layer, a Langevin isothermal layer and a free Newton layer.

[0013] (2) High-speed / transient thermo-mechanical coupling loading: The radius of the spherical indenter was set to 8 Å in LAMMPS using the fix indent command. To simulate the transient harsh conditions of actual high-speed contacts or electromagnetic launch rails, the indenter was controlled to rub at a uniform speed of 10 m / s along the Y-axis; at the same time, a dynamic local heat bath was introduced to simulate the friction flash temperature effect at the interface during the rubbing.

[0014] (3) Microscopic property extraction and quantitative selection criteria output: Output the displacement and force magnitude of the indenter in the model, and plot the friction coefficient-displacement curve. Focus on extracting and calculating the transient conduction efficiency of the three-dimensional graphene network for frictional heat during the scratching process, as well as the cage effect of the three-dimensional network interwoven structure on the nucleation and expansion of dislocations in the matrix. Finally, the atomic-level data of the comprehensive mechanical response and the evolution of dislocation defects will be used as the quantitative selection criteria for designing the optimal powder metallurgy wear-resistant CuCr alloy in macroscopic experiments.

[0015] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention include at least the following: 1) This invention constructs a graphene-reinforced copper-chromium alloy contact material model based on molecular dynamics methods, and realizes atomic-level dynamic observation of the friction process through nano-scratching simulation. Compared with traditional macroscopic experimental methods, it can directly reveal microscopic mechanisms such as interface slip, atomic rearrangement and dislocation evolution.

[0016] 2) This invention constructs a composite model that includes a metal matrix and a graphene-reinforced phase, and uses the EAM, AIREBO and LJ combined potential functions to achieve a unified description of metallic bonds, covalent bonds and weak interfacial interactions, thereby accurately reflecting the multi-physical coupling behavior of materials under friction and current-carrying conditions. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a flowchart of the molecular modeling and selection method based on three-dimensional continuous grain boundary network configuration of the present invention; Figure 2 This is a schematic diagram illustrating the construction of the nano-polycrystalline copper-chromium matrix in an embodiment of the present invention; Figure 3 This is a molecular model diagram of a composite material with a three-dimensional continuous graphene grain boundary encapsulation network configuration in an embodiment of the present invention; Figure 4 This is a comparison chart of friction coefficient-displacement curves with different graphene contents under transient thermo-mechanical coupling conditions in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A molecular model construction and simulation method for graphene-reinforced copper-chromium alloy contact materials includes steps such as model construction, potential function selection, and simulation parameter setting, as detailed below: Step 1: Construction of the multiphase polycrystalline matrix model and extraction of grain boundary coordinates: In the open-source molecular dynamics software LAMMPS, a three-dimensional orthogonal simulation domain with dimensions of 200 Å × 200 Å × 150 Å was defined, employing periodic boundary conditions. Using the Voronoi polyhedron method, 50 randomly oriented grains were generated within the simulation domain. Based on the macroscopic compositional requirements of the copper-chromium alloy (Cu-25Cr), the corresponding volumetric grains were designated as body-centered cubic chromium, and the remainder as face-centered cubic copper, thus constructing a nanocrystalline polycrystalline copper-chromium matrix model containing pure metallic phases and phase interfaces.

[0021] Preliminary energy minimization was performed on the constructed matrix model. Subsequently, the atomic topology in the model was identified using the centrosymmetric parameter method and the common nearest neighbor analysis algorithm, and atoms in imperfect lattice regions were screened out. The three-dimensional grain boundary surface atomic coordinate sets at copper-copper, chromium-chromium, and copper-chromium polycrystalline boundaries were accurately extracted.

[0022] Step 2: Conformal construction of graphene along a three-dimensional continuous network topology at grain boundaries: Based on the graphene mass fraction variables required for the experimental design (set to 0.25wt%, 0.5wt%, 0.75wt%, and 1wt%, respectively), the total number of carbon atoms required in the molecular system was calculated. Using a spatial surface mapping algorithm, the two-dimensional hexagonal honeycomb graphene lattice was projected onto the three-dimensional grain boundary surface atomic coordinate set extracted in step one, generating a continuous three-dimensional graphene network undulating along polycrystalline grain boundaries. This three-dimensional graphene network was embedded in a polycrystalline copper-chromium matrix, and overlapping metal atoms with a distance less than 1.2 Å around the network were removed, completing the construction of a composite molecular model with a metal matrix-three-dimensional graphene grain boundary encapsulated network microstructure.

[0023] Step 3: Selection and allocation of multi-scale combined potential functions: To accurately describe the complex underlying physical mechanisms within multiphase composite systems, the following combination of potential functions is used: Metallic bonds: The interatomic interaction force fields of Cu-Cu, Cr-Cr and Cu-Cr metal atoms are represented by the embedded atom method (EAM) potential function to accurately describe the plastic deformation and stacking fault energy of the metal.

[0024] Covalent bonds: The interaction between carbon atoms in the three-dimensional graphene network adopts the adaptive intermolecular reaction empirical bond sequence (AIREBO) potential function to ensure high fidelity of the bond breaking and recombination behavior of the carbon skeleton under load.

[0025] Interfacial van der Waals forces: The nonbonded interaction between carbon atoms and metal atoms at the heterostructure interface is described using the Lennard-Jones (LJ) potential function, with a cutoff radius set to 8.5 Å.

[0026] Step 4: System energy minimization and geometry optimization: In LAMMPS, the `delete_atoms` command was executed with a distance threshold of 1.5 Å to completely eliminate high-potential overlapping atoms locally present in the system after network reconstruction and potential function loading. The conjugate gradient method was used to iteratively minimize the total system energy, eliminating residual stress at the interface. The time step was set to 1 fs. The system was placed under an isothermal-isobaric ensemble (NPT) with an ambient temperature of 300 K and a pressure of 0 Pa, and 20,000 steps of thermodynamic equilibrium relaxation were performed to allow atomic-level reconstruction and adaptive matching between the three-dimensional graphene network and the polycrystalline grain boundaries of the metal, achieving thermodynamic steady state.

[0027] Step 5: Decoupling Transient Thermo-Coupling Friction Simulation from Physical Mechanisms: Simulation tests were conducted using the relaxed model to reveal the physical mechanisms under extreme sliding friction conditions and to output quantitative indicators: (1) Thermal boundary setting: Modify the Z-axis direction of the simulation box to a non-periodic boundary. Divide the physical layers from bottom to top along the Z-axis: the bottom 15Å is set as a rigid fixed layer; the upper 20Å is set as a Langevin isothermal layer, and the temperature is controlled at 300 K to simulate the heat dissipation of the bulk material; the rest of the upper structure is set as a free Newton layer that follows Newton's laws of motion.

[0028] (2) High-speed transient loading: A spherical repulsive indenter with a radius of 8 Å was introduced above the upper surface of the model using the fix indent command. After the indenter was pressed into the free surface to a maximum indentation depth of 12 Å, it was scratched at a high strain rate of 10 m / s along the Y-axis. At the same time, the local temperature calculation output was enabled to record the transient thermal field distribution induced by the scratch.

[0029] (3) Decoupling of underlying mechanisms and data extraction: The force feedback of the indenter, the displacement coordinates of atoms, and the CNA structural parameters are output in real time using the dump command. Two core physical mechanism data are extracted: one is the blocking effect of the three-dimensional graphene network on dislocation line slip; the other is the conduction efficiency of the three-dimensional carbon network on the local friction flash temperature in the scratched area.

[0030] (4) Establish macroscopic experimental selection criteria: extract normal force and tangential friction force data in the steady-state stage of scratch. Simulation results show that when the mass fraction of the three-dimensional continuous graphene network is 0.25wt%, 0.5wt%, 0.75wt%, and 1wt%, the maximum values ​​of the normal force reach 61.69 nN, 82.19 nN, 92.04 nN, and 105.12 nN, respectively, and the corresponding calculated friction coefficients are 0.825, 0.731, 0.507, and 0.443, respectively.

[0031] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for constructing and simulating a molecular model of a graphene-reinforced copper-chromium alloy contact material, characterized in that, Includes the following steps: Step 1: Construction of the multiphase polycrystalline matrix model and extraction of grain boundary coordinates: Randomly oriented grains were generated using the Voronoi polyhedral method to construct a nanocrystalline copper-chromium matrix model containing pure metallic phases and phase interfaces; wherein, according to the macroscopic composition ratio of the copper-chromium alloy, chromium grains were distributed in the copper matrix. Using the central symmetry parameter method and common nearest neighbor analysis algorithm, the three-dimensional grain boundary surface atomic coordinate set at the copper-copper, chromium-chromium, and copper-chromium polycrystalline grain boundaries of the nano-polycrystalline copper-chromium matrix model was accurately identified and extracted; Step 2: Conformal construction of graphene along a three-dimensional continuous network topology at grain boundaries: Based on the required total number of carbon atoms, a three-dimensional continuous graphene network topology that is connected along the grain boundary undulations is constructed on the three-dimensional grain boundary surface atomic coordinate set using surface mapping and structure reconstruction algorithms. The three-dimensional continuous graphene network topology is embedded into the three-dimensional grain boundary surface atomic coordinate set, replacing the original grain boundary transition region atoms, and finally constructing a composite material molecular model with a metal matrix-three-dimensional graphene grain boundary encapsulation network microstructure. Step 3: Selection and allocation of multi-scale combined potential functions: The EAM potential function is used to describe the interaction between metal atoms; the AIREBO potential function is used to describe the interaction between carbon atoms inside the three-dimensional graphene network; and the Lennard-Jones potential function is used to describe the van der Waals interaction between the three-dimensional graphene network and the encapsulated metal grains. Step 4: System energy minimization and geometry optimization: The overlapping atoms after network reconstruction and potential function loading were removed using the distance threshold method in LAMMPS software; the geometric structure of the composite material molecular model was optimized using the conjugate gradient method. Step 5: Decoupling Transient Thermo-Coupling Friction Simulation from Physical Mechanism: Using the optimized composite material molecular model, the effect of different graphene contents on friction performance under extremely harsh conditions of contact / electromagnetic emission is simulated and calculated.

2. The molecular model construction and simulation method according to claim 1, characterized in that, Step one also includes performing preliminary energy minimization on the nanocrystalline copper-chromium matrix model.

3. The molecular model construction and simulation method according to claim 1, characterized in that, In step one, the centrosymmetric parameter method and common nearest neighbor analysis include: identifying the atomic topology in the nanocrystalline copper-chromium matrix model and screening out atoms in imperfect lattice regions.

4. The molecular model construction and simulation method according to claim 1, characterized in that, In step two, the required total number of carbon atoms is calculated from the graphene mass fraction.

5. The molecular model construction and simulation method according to claim 1, characterized in that, In step two, replacing the original grain boundary transition region atoms includes deleting overlapping metal atoms with a distance of less than 1.2 Å around the three-dimensional continuous graphene network.

6. The molecular model construction and simulation method according to claim 1, characterized in that, In step three, the Lennard-Jones potential function includes a cutoff radius set to 8.5 Å.

7. The molecular model construction and simulation method according to claim 1, characterized in that, In step four, the distance threshold method includes using 1.5 Å as the distance threshold.

8. The molecular model construction and simulation method according to claim 1, characterized in that, In step four, the conjugate gradient method includes: setting the time interval to 1 fs, the temperature to room temperature, the ensemble to the NPT ensemble, and the number of equilibrium relaxation steps to 20,000.

9. The molecular model construction and simulation method according to claim 1, characterized in that, Step five includes the following sub-steps: (1) Thermal boundary setting: The Z direction is set as a non-periodic boundary condition, and the X and Y directions are periodic boundaries; along the Z direction from bottom to top, it is divided into a rigid fixed layer, a Langevin isothermal layer and a free Newton layer. (2) High-speed / transient thermo-mechanical coupling loading: In LAMMPS, the radius of the spherical indenter is set to 8 Å using the fix indent command. After the indenter is pressed into the free surface at a maximum indentation depth of 12 Å, the indenter is controlled to scratch along the Y-axis at a uniform speed of 10 m / s. At the same time, a dynamic local heat bath is introduced to record the transient thermal field distribution induced by the scratch. (3) Microscopic characteristics extraction and quantitative selection criteria output: output the displacement and force of the indenter of the model, plot the friction coefficient-displacement curve, focus on extracting and calculating the transient conduction efficiency of the three-dimensional graphene network for frictional heat during the scratching process, and the cage effect of the three-dimensional network interwoven structure on the nucleation and expansion of the matrix; finally, the atomic-level data of the comprehensive mechanical response and dislocation defect evolution will be used as the quantitative selection criteria for designing the optimal powder metallurgy wear-resistant copper-chromium alloy in macroscopic experiments.

10. The molecular model construction and simulation method according to claim 1, characterized in that, In step (1), the structure is divided into a rigid fixed layer, a Langevin isothermal layer and a free Newton layer from bottom to top along the Z direction, including: the bottom 15 Å is set as a rigid fixed layer; the top 20 Å is set as a Langevin isothermal layer; and the remaining upper structure is set as a free Newton layer.

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