A Modeling and Simulation Method for Aluminum-Magnesium Polycrystalline Layered Composite Materials Based on Molecular Dynamics

Abstract

This invention provides a molecular dynamics-based modeling and simulation method for aluminum-magnesium polycrystalline layered composite materials, comprising: establishing aluminum and magnesium atomic cells separately using Atomsk; generating polycrystalline structures using the Voronoi mosaic method with the Atomsk polycrystalline command – polycrystal, and expanding the cells to polycrystalline models of specified size and number of grains; ensuring that the atom type in the source files of the polycrystalline models is 1 for all atoms; modifying the source file data of the two polycrystalline models by changing Atomstypes from 1 to 2, consistently setting Al as type 1 and Mg as type 2; adding corresponding atomic mass information; writing a Lammps script and using the set command to replace the magnesium atom type with 2; using the Atomsk merge command – merge – to merge the models after the Lammps substitution along the z-axis into the desired composite system; and using Ovito to observe whether the established model is reasonable. This method simplifies the modeling process using only the Lammps script, increasing the efficiency and accuracy of modeling aluminum-magnesium nanocrystalline polycrystalline composite materials.

Description

Technical Field

[0001] This invention provides a molecular dynamics-based modeling and simulation method for aluminum-magnesium polycrystalline layered composite materials, belonging to the field of nanomaterials technology. Background Technology

[0002] Nanoscale aluminum-magnesium materials have a wide range of applications. Not only can nano-polycrystalline aluminum-magnesium layered composites be used to prepare protective films for optical instruments due to their good stability, refractive index and unique comprehensive mechanical properties of ultrafine grains, but nano-polycrystalline aluminum-magnesium alloys can also be used as protective films for molds and hydrophobic films for superhydrophobic surfaces.

[0003] However, in experimental studies, the preparation and deformation behavior testing of polycrystalline aluminum-magnesium layered composite materials are easily limited by experimental setups, testing instruments, and experimental costs. For example, studies on the plastic deformation of polycrystalline Au nanowires in the literature use electron beam evaporation to prepare tensile film samples. Not only is it difficult to guarantee the grain size, but there are also difficulties in clamping, stretching, and observing the samples. Extensive attempts are time-consuming, labor-intensive, and uneconomical. Molecular dynamics (MD) simulation can study the mechanisms of various macroscopic properties of materials at the microscopic molecular level, and then determine physical parameters from a theoretical perspective. The conclusions have good universality, and numerous studies have confirmed its applicability to the study of the deformation behavior of nanocrystalline polycrystalline materials.

[0004] LAMMPS (Large-scale Atomic / Molecular Massively Parallel Simulator) is one of the mainstream software programs for molecular dynamics simulations. Developed by Sandia National Laboratories in the United States, LAMMPS is released under a GPL license, meaning its open-source code is freely available and can be modified according to user needs. LAMMPS supports systems with millions of atoms and molecules in various ensembles, including gaseous, liquid, and solid phases, and provides support for multiple potential functions. LAMMPS also boasts excellent parallel scalability. ATOMSK (The Swiss-armyknife of atomic simulations) is an excellent molecular modeling software that can be used as an alternative to MS and LAMMPS command-line modeling. It is available on Linux, Mac, and Windows systems.

[0005] The Lammps script is used to directly model and simulate composite systems. A simulation box is created, divided into aluminum and magnesium regions, filled with aluminum and magnesium atoms respectively. The `orient` command specifies the crystal orientation of each part, and the model is exported for subsequent simulations. However, the Lammps script cannot quickly create polycrystalline structures. While it can create boxes of corresponding shapes and fill them with atoms for complex grain boundary shapes, this is overly cumbersome. Generally, single-crystal or bicrystalline composite systems can be created, but using only single-crystal or bicrystalline systems cannot accurately describe the macroscopic plastic deformation behavior of isotropic polycrystalline structures, such as macroscopic stress-strain behavior, macroscopic crack initiation and propagation, dislocation nucleation and propagation, and the influence of heterogeneous interfaces in polycrystalline layered composites. (It is difficult or almost impossible to create polycrystalline structures).

[0006] Using the Voronoi mosaicking method in Atomsk to build a polycrystalline model allows for the random generation of a specified number and orientation of grains within a simulation box of a set size. The data can then be exported, read using Lammps, and used for subsequent simulations. However, Atomsk's research on polycrystalline systems is generally applied to single-atom polycrystalline systems. If multiple atom types are created separately and then merged, the program will automatically classify all atom types into one, making it impossible to directly build multi-atom polycrystalline systems. (Directly generated polycrystalline structures contain only one type of atom, and merging different atom types still results in a single atom type). Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a molecular dynamics-based polycrystalline modeling and simulation method for aluminum-magnesium composite materials. This method provides an ideal model for studying the mechanical properties and plastic deformation mechanisms of nanocrystalline aluminum-magnesium layered composite materials under specific conditions. Experimental conditions often struggle to prepare aluminum-magnesium composite materials with grain sizes of only a few nanometers, and the clamping, stretching, and observation of nanoscale samples also present challenges. This method facilitates molecular dynamics simulation studies of aluminum-magnesium nanocrystalline layered composite materials, thereby providing a theoretical basis for their development.

[0008] This invention uses Atomsk to establish aluminum polycrystalline and magnesium polycrystalline models respectively. The parameters of the model source file are changed to be readable by Atomsk. A script is written using Lammps to replace aluminum atoms in the magnesium polycrystalline model with magnesium atoms. After exporting, Atomsk is used to merge the aluminum polycrystalline and magnesium polycrystalline models, and finally a model that can be used to study the plastic deformation mechanism of aluminum-magnesium nanopolycrystalline materials is obtained.

[0009] The purpose of this invention is to solve the following problems:

[0010] 1. Since open-source MD simulation modeling software such as Lammps and Atomsk are only packages with limited functions and can only be called via command line, it is difficult to accurately build multi-atom polycrystalline composite system models using only a single program. This method uses the unique functions of these two packages in combination to achieve rapid and accurate model building for such models.

[0011] 2. The preparation and experimental study of the mechanical properties of aluminum-magnesium nanocrystalline layered composite materials are quite challenging. This method can provide an ideal model for the simulation of aluminum-magnesium nanocrystalline layered composite materials, support the study of the mechanical properties and deformation mechanisms of aluminum-magnesium nanocrystalline layered composite materials, and thus expand their application in various industries.

[0012] A molecular dynamics-based modeling and simulation method for polycrystalline layered aluminum-magnesium composite materials includes the following steps:

[0013] S1. Use Atomsk to construct atomic unit cells for aluminum and magnesium respectively;

[0014] S2. Use the Atomsk polycrystalline command -- polycrystal -- to generate polycrystalline models using the Voronoi mosaic method, expanding the cell to a polycrystalline model of specified size and number of grains. At this point, the atom type in the source files of both the aluminum and magnesium polycrystalline models is 1;

[0015] S3. Modify the source file data of the two polycrystalline models, change Atomstype from 1 to 2, and consistently set Al to type 1 and Mg to type 2; add the corresponding atomic mass information. At this time, all atomic types in the magnesium polycrystalline model source file are still 1.

[0016] S4. Write a Lammps script and use the set command to replace the magnesium atom type with 2.

[0017] S5. Use Atomsk's merge command --merge to merge the models after running the Lammps script along the z-axis into the desired composite system;

[0018] S6. Use Ovito to observe whether the established model is reasonable.

[0019] Compared with the prior art, the technical effects of the present invention are as follows:

[0020] This method can greatly simplify the modeling process using only Lammps scripts or only Atomsk, increasing the efficiency and accuracy of modeling aluminum-magnesium nanocrystalline layered composites and making it easier to study the deformation mechanism and mechanical properties of aluminum-magnesium nanocrystalline layered composites. Furthermore, this method is not limited to aluminum and magnesium; it can also be used to model multi-atom layered composites with other atomic types. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention;

[0022] Figure 2 In this embodiment, an Al unit cell is created;

[0023] Figure 3 The example demonstrates the creation of Mg unit cells;

[0024] Figure 4 It is the Al unit cell in the embodiment;

[0025] Figure 5 The Mg unit cell in the example;

[0026] Figure 6 This is the polycrystalline file code in the embodiment;

[0027] Figure 7 In this embodiment, the polycrystal command generates a polycrystalline model.

[0028] Figure 8 This is the Al polycrystalline model in the embodiment;

[0029] Figure 9 This is the Mg polycrystalline model in the embodiments;

[0030] Figure 10 In this example, the initial atom types for the Mg and Al model files are 1;

[0031] Figure 11 Change the initial atom species in the Mg and Al model files to 2;

[0032] Figure 12 This is the Lammps atomic substitution script in the embodiment;

[0033] Figure 13 In this example, the Lammps script is run to replace all Mg atom types with 2;

[0034] Figure 14 This embodiment combines aluminum and magnesium polycrystalline models in the Z direction;

[0035] Figure 15 This is the merged layered composite material model in the embodiment. Detailed Implementation

[0036] The specific technical solutions of the present invention will be described with reference to the embodiments. For example... Figure 1 The process shown in this embodiment establishes a 20×10×20nm aluminum-magnesium layered composite material model with a grain size of 6.29nm, including the following steps:

[0037] 1. Invoke the command line, such as Figure 2 and Figure 3 Use the `--create` command in Atomsk to create aluminum and magnesium unit cells respectively, such as... Figure 4 and Figure 5 .

[0038] 2. Create an Atomsk polycrystalline file, expanding the model dimensions and grain size to the set values. For example... Figure 6 As shown.

[0039] Where box represents the dimensions of the model in the x, y, and z directions, and random represents the number of grains randomly generated within the model using the Voronoi method, such as... Figure 7 Eight grains were randomly generated within a 20×10×10nm model, with an average grain size of 6.29nm. The `--polycrystal` command in Atmospheric was run to generate polycrystalline Al and Mg models, respectively. Figure 8 and Figure 9 .

[0040] At this point, the LMP files for the aluminum and magnesium models show that both models have an atom type of 1. If these are merged into a composite material model, the atom types cannot be distinguished, and the potential function will not be correctly applied to the aluminum and magnesium atoms during subsequent simulations, causing the program to malfunction.

[0041] Therefore, at this point, the source file data is modified, changing the atom type to 2, setting the Al atom type to 1, and the Mg atom type to 2. This only changes the initial atom type; the type of each magnesium atom in the subsequent atomic coordinates remains 1. Manually changing this would require modifying the type of each atom tens of thousands of times. Therefore, a Lammps script is now needed to replace the type of magnesium atoms. Figure 10 and Figure 11 .

[0042] 3. Use the Lammps script to replace the magnesium atom type.

[0043] Use the `set` command in Lammps to replace all magnesium atom types from 1 to 2, such as... Figure 12 .

[0044] The script uses the `set` command to replace the atom types. `type1` is the initial atom type, and `type / ratio21` represents the percentage of atoms of type 2 that comprise 100% of the original type 1 atoms. For example... Figure 13 .

[0045] Run the script in the command line to read the original magnesium polycrystalline model file and replace it with the required magnesium polycrystalline model file. At this point, the model can be directly merged into a composite material model.

[0046] 4. Merge the polycrystalline aluminum and magnesium models into a layered composite material model.

[0047] like Figure 14 Use Atomsk's `--merge` command to merge the aluminum and magnesium polycrystalline models into an aluminum-magnesium layered composite material model, such as... Figure 15 .

[0048] This method is not limited to aluminum-magnesium diatomic systems, but can also be applied to multi-atomic layered composite material models with other atomic types. The same method applied to layered composite materials with other atomic types is also within the scope of this patent.

Claims

1. A molecular dynamics-based modeling and simulation method for polycrystalline layered aluminum-magnesium composite materials, characterized in that, Includes the following steps: S1. Use Atomsk to construct atomic unit cells for aluminum and magnesium respectively; S2. Use the Atomsk polycrystalline command -- polycrystal to generate polycrystalline structures using the Voronoi mosaic method, and expand the cells to polycrystalline models of specified size and number of grains. At this time, the atom type in the source files of the aluminum polycrystalline model and the magnesium polycrystalline model is 1. S3. Modify the source file data of the two polycrystalline models, change Atomstype from 1 to 2, and consistently set Al to type 1 and Mg to type 2; add the corresponding atomic mass information. At this time, all atomic types in the magnesium polycrystalline model source file are still 1. S4. Write a Lammps script and use the set command to replace the magnesium atom type with 2. S5. Use the Atomsk merge command --merge to merge the Lammps-permuted models along the z-axis into the desired composite system; S6. Use Ovito to observe whether the established model is reasonable.

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