A molecular dynamics method for constructing magnesium dislocations

Abstract

The present invention is applicable to the field of molecular dynamics simulation technology and provides a molecular dynamics method for constructing magnesium dislocations.<c+a> Dislocations, the method includes the following steps: Step 1, establishing a molecular dynamics simulation model; Step 2, processing the data file output from Step 1 using Lammps; Step 2.1, selecting a potential function; Step 2.2, selecting boundary conditions; Step 2.3, relaxing the system; Step 3, outputting the data file and using Ovito for visualization and model processing. This method can quickly construct various complex dislocations in any direction and position within a crystal. The dislocation construction is accurate, saving a significant amount of time for studying magnesium alloy plasticity and having practical significance for the practical application of molecular dynamics research on magnesium alloy plasticity.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular dynamics simulation, and in particular relates to a molecular dynamics method for constructing magnesium dislocations. Background Art

[0002] Since its discovery in the 19th century, pure magnesium has been widely integrated into our lives, even being called the "21st century green engineering material." Lightweighting in automobiles is gaining increasing attention, and magnesium alloys are well-suited for use in automotive parts, significantly contributing to weight reduction and energy efficiency. However, magnesium alloys also have significant drawbacks, including low strength, poor mechanical properties at high temperatures, poor room-temperature plasticity, and poor corrosion resistance, all of which hinder their widespread application.

[0003] Based on the Von Mises criterion, magnesium must have five independent slip systems per grain in order to have good plasticity, but magnesium can only provide four independent slip systems. Basal slip and prism slip are the two most common slip systems in HCP metals, which can provide four slip systems.<c+a> When the slip system of the dislocation is activated, it can provide 5 independent slip systems to satisfy the Von Mises law.<c+a> Dislocations are constructed primarily by deleting half-atomic planes using Lammps software, or by using complex programming languages. These methods suffer from inaccurate dislocation formation and are unable to construct complex dislocation structures. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a molecular dynamics method for constructing magnesium dislocations, aiming to solve the problems raised in the above background technology.

[0005] The embodiment of the present invention is achieved by a molecular dynamics method for constructing magnesium dislocations, wherein the dislocations are<c+a> Dislocation, including the following steps:

[0006] Step 1: Establishment of molecular dynamics simulation model:

[0007] Use Atomsk to build a single crystal magnesium model, with the crystal directions [1, 1, -2, 0], [1, 0, -1, 0] and [0, 0, 0, 1] as the x, y and z coordinate axes respectively. Use the inverse trigonometric function calculation method to calculate the angle of rotation of the initial model, and then use the command in Atomsk to turn the initial model to<c+a> The slip plane and direction of the dislocation (for (10-11)<c+a> Dislocation We rotate the initial model twice. The first time, we rotate the model along the [1 1 -2 0] direction by θ1 (θ1 is the angle between the (10-11) plane and the (10-10) plane, θ1 = 28.06970482°) to the (1 0 -1 1) plane. Then, we rotate the model along the [0 00 1] direction by θ2 (θ2 is the angle between the (10-10) plane and the [11-23] direction, θ2 = 15.19848206°).<c+a> Directions. For (11-22)<c+a> Dislocation We rotate the initial model once, rotating it along the [1 0 -1 0] direction by θ (θ is the angle between the [11-23] direction and the

[0001] direction, θ = 31.62344340°) and directly rotating the model to the (11-22) plane.<c+a> direction) and then use the elastic modulus file and the dislocation command in Atomsk to insert it directly<c+a> Dislocation, and output data file;

[0008] The close-packed hexagonal crystal system has five independent matrix elements (C11, C12, C13, C33, C44).

[0009] The elastic modulus of Mg is as follows:

[0010]

[0011] Atomsk insertion dislocations are based on the theory proposed by JPHirth and J.Lothe in Theory of dislocations:

[0012]

[0013] b e =ξ×(b×ξ)b s =(b·ξ)ξ

[0014] Step 2: Use Lammps to process the data file output in step 1:

[0015] Step 2.1, selection of potential function:

[0016] The potential function type adopts MEAM (improved embedded atomic potential function) because it can accurately reflect the interaction between microscopic particles of metal materials and can accurately insert<c+a> dislocation.

[0017] Step 2.2, boundary condition selection:

[0018] Select the wrapping boundary condition in the stretching direction, that is, the boundary will change with the size of the model and always wrap around the atoms in the model;

[0019] Step 2.3, system relaxation: Select the microcanonical ensemble (NVE) for equilibrium constraint, use the conjugate gradient method to minimize energy, select the temperature as 300K, and then relax to allow the initial model of the system to reach equilibrium.

[0020] Step 3: Output the data file and use Ovito for visualization and model processing.

[0021] According to a further technical solution, the model constructed in step 1 has a size of 100 nm × 170 nm × 160 nm, with a total of 108,000 atoms.

[0022] A further technical solution is to construct two models in step 1, corresponding to the two cone surfaces (10-11) and (11-22).

[0023] An embodiment of the present invention provides a molecular dynamics method for constructing magnesium dislocations. This method can quickly construct various complex dislocations in any direction and at any position within a crystal. The dislocation construction is accurate, which saves a lot of time for studying the plasticity of magnesium alloys and has practical significance for the practical application of molecular dynamics research on the plasticity of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a model construction method for constructing a molecular dynamics method for magnesium dislocations provided in an embodiment of the present invention;

[0025] Figure 2 An Hcp structure and a corresponding angle calculation diagram in a molecular dynamics method for constructing magnesium dislocations provided in an embodiment of the present invention;

[0026] Figure 3 Another Hcp structure and corresponding angle calculation diagram in a molecular dynamics method for constructing magnesium dislocations provided in an embodiment of the present invention.

[0027] Figure 4 The (10-11) screw dislocation diagram constructed before relaxation and after Lammps relaxation is provided in an embodiment of the present invention.

[0028] Figure 5 The (11-22) edge dislocation diagram constructed before relaxation and after Lammps relaxation is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0031] like Figure 1-3 As shown in FIG. 1 , a molecular dynamics method for constructing magnesium dislocations is provided in one embodiment of the present invention. The dislocations are<c+a> Dislocation, including the following steps:

[0032] Step 1: Establishment of molecular dynamics simulation model:

[0033] A single crystal magnesium model was created using Atomsk, with the directions [1, 1, -2, 0], [1, 0, -1, 0], and [0, 0, 0, 1] as the x, y, and z coordinate axes. The model size was 100nm × 170nm × 160nm, with a total of 108,000 atoms. The required rotation angle was calculated using the inverse trigonometric function method, and then the model was rotated using the command in Atomsk.<c+a> The slip plane and direction of the dislocation (for (10-11)<c+a> Dislocation We rotate the initial model twice. The first time, we rotate the model along the [1 1 -2 0] direction by θ1 (θ1 is the angle between the (10-11) plane and the (10-10) plane, θ1 = 28.06970482°) to the (1 0 -1 1) plane. Then, we rotate the model along the [0 0 0 1] direction by θ2 (θ2 is the angle between the (10-10) plane and the [11-23] direction, θ2 = 15.19848206°).<c+a> Directions. For (11-22)<c+a> Dislocation We rotate the initial model once, rotating it along the [1 0 -1 0] direction by θ (θ is the angle between the [11-23] direction and the

[0001] direction, θ = 31.62344340°) and directly rotating the model to the (11-22) plane.<c+a> direction) and then use the elastic modulus file and the dislocation command in Atomsk to insert it directly<c+a> Dislocation, and output data file;

[0034] The close-packed hexagonal crystal system has five independent matrix elements (C11, C12, C13, C33, C44).

[0035] The elastic modulus of Mg is as follows:

[0036]

[0037] Atomsk insertion dislocations are based on the theory proposed by JPHirth and J.Lothe in Theory of dislocations:

[0038]

[0039] b e =ξ×(b×ξ) b s =(b·ξ)ξ

[0040] Step 2: Use Lammps to process the data file output in step 1:

[0041] Step 2.1, selection of potential function:

[0042] The potential function type adopts MEAM (improved embedded atomic potential function) because it can accurately reflect the interaction between microscopic particles of metal materials and can accurately insert<c+a> dislocation.

[0043] Step 2.2, boundary condition selection:

[0044] Select the wrapping boundary condition in the stretching direction, that is, the boundary will change with the size of the model and always wrap around the atoms in the model;

[0045] Step 2.3, system relaxation: Select the microcanonical ensemble (NVE) for equilibrium constraint, use the conjugate gradient method to minimize energy, select the temperature as 300K, and then relax to allow the initial model of the system to reach equilibrium.

[0046] Step 3: Output the data file and use Ovito for visualization and model processing.

[0047] As a preferred embodiment of the present invention, in step 1, two models are constructed respectively, corresponding to the two cone surfaces (10-11) and (11-22).

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A molecular dynamics method for constructing magnesium dislocations, characterized in that: The dislocation is in magnesium<c+a> dislocation, the method comprising the steps of: Step 1: Establishment of molecular dynamics simulation model: Use Atomsk to build a single crystal magnesium model, with the crystal directions [1, 1, -2, 0], [1, 0, -1, 0] and [0, 0, 0, 1] as the x, y and z coordinate axes respectively. Use the inverse trigonometric function calculation method to calculate the angle of rotation of the initial model, and then use the rotate command in Atomsk to rotate the initial model to the original position.<c+a> The slip plane and direction of the dislocation are then inserted directly using the elastic modulus file and the dislocation command in Atomsk<c+a> Dislocation, and output data file; The close-packed hexagonal system has five independent matrix elements: C11, C12, C13, C33, and C44; The elastic modulus of Mg is as follows: Atomsk insertion dislocations are based on the theory proposed in Theory of dislocations: b e =ξ×(b×ξ)b s =(b·ξ)ξ; Step 2: Use Lammps to process the data file output in step 1: Step 2.1, selection of potential function: Improved embedded atomic potential function is used as the potential function type to accurately insert<c+a> dislocation; Step 2.2, boundary condition selection: Select the wrapping boundary condition in the stretching direction, that is, the boundary will change with the size of the model and always wrap around the atoms in the model; Step 2.3, system relaxation: Select the microcanonical ensemble for equilibrium constraint, use the conjugate gradient method to minimize energy, select the temperature as 300K, and then relax to allow the initial model of the system to reach equilibrium; Step 3: Output the data file and use Ovito for visualization and model processing.

2. The molecular dynamics method for constructing magnesium dislocations according to claim 1, characterized in that: The model constructed in step 1 has a size of 100 nm × 170 nm × 160 nm, with a total of 108,000 atoms.

3. The molecular dynamics method for constructing magnesium dislocations according to claim 2, characterized in that: In step 1, two models are constructed, corresponding to the two cone surfaces (10-11) and (11-22) respectively.

4. The molecular dynamics method for constructing magnesium dislocations according to claim 1, characterized in that: In step 1, for (10-11)<c+a> Dislocation, by rotating the initial model twice, the first time along the [1 1-2 0] direction by θ1, where θ1 is the angle between the (10-11) plane and the (10-10) plane, θ1 = 28.06970482°, the model is rotated to the (1 0-1 1) plane, and then along the [0 0 0 1] direction by θ2, where θ2 is the angle between the (10-10) plane and the [11-23] direction, θ2 = 15.19848206°, the model is rotated to<c+a> direction.

5. The molecular dynamics method for constructing magnesium dislocations according to claim 4, characterized in that: In step 1, for (11-22)<c+a> Dislocation, by rotating the initial model once, rotating along the [1 0-1 0] direction by θ, where θ is the angle between the [11-23] direction and the [0001] direction, θ = 31.62344340°, directly rotating the model to the (11-22) plane<c+a> direction.

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