Molecular dynamics method for simulating mechanical properties of high-entropy alloy

Abstract

The invention provides a molecular dynamics method for simulating mechanical properties of a high-entropy alloy. By exploring the mechanical property response and plastic deformation mechanism of the high-entropy alloy through the method, not only can the atomic structure transformation, stress-strain change and dislocation evolution process of the high-entropy alloy in the nanoindentation process be deeply analyzed to realize real-time observation of the internal deformation behavior of the material, but also the calculation tasks can be processed in batches, so that the calculation efficiency is improved. And the calculation efficiency is greatly improved, so that an important theoretical support is provided for engineering application of the high-entropy alloy and design and development of excellent performance.

Description

Technical Field

[0001] The invention relates to the technical field of nano alloy materials, in particular to a molecular dynamics method for simulating the mechanical properties of high entropy alloys. Background Art

[0002] High entropy alloys usually refer to alloy systems composed of three or more metal elements as the main elements. The biggest difference between them and traditional alloy systems is that there is no distinction between the main elements in terms of primary and secondary or solvent solutes. Due to their unique composition, high entropy alloys have excellent performance, such as high tensile strength and yield strength, good plasticity and elongation, excellent corrosion resistance and friction and wear resistance. These properties make high entropy alloys very attractive in the fields of hydrogen storage materials, radiation-resistant materials, high-temperature resistant materials, corrosion-resistant coating materials and antibacterial materials. However, because the development history of high entropy alloys is relatively short compared to traditional alloys, the preparation and processing of high entropy alloys are still in the exploratory stage. Therefore, it is relatively difficult to prepare high entropy alloys and measure their mechanical properties by traditional experimental methods.

[0003] Nanoindentation is a method used to measure the mechanical properties of nanomaterials at a microscopic scale. Since the loss of materials during nanoindentation is very small, nanoindentation has been widely used to measure the mechanical properties of various nanomaterials. However, it is difficult to observe the stress and strain conditions inside the material and the formation and evolution of dislocations in nanoindentation experiments. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a molecular dynamics method for simulating the mechanical properties of high entropy alloys, simulate the mechanical properties response of high entropy alloys during nanoindentation, and analyze the dislocation evolution process inside the high entropy alloy material, so as to provide theoretical support for exploring the changing laws of the mechanical properties of high entropy alloys.

[0005] To achieve the above object, the present invention adopts the following technical solution: a molecular dynamics method for simulating the mechanical properties of high entropy alloys, comprising the following steps: Step 1: construct a three-dimensional high entropy alloy model, determine the sizes of the three-dimensional high entropy alloy model in three dimensions, and determine the proportion of each component in the three-dimensional high entropy alloy model; Step 2: Use the embedded interatomic potential in the three-dimensional high entropy alloy model to set the boundary conditions of the three-dimensional high entropy alloy model in the three-dimensional directions; Step 3: Fix the atoms at the bottom of the three-dimensional high entropy alloy model and stabilize the three-dimensional high entropy alloy model through energy minimization and relaxation processes; Step 4: Change the boundary conditions and apply loads to the three-dimensional high entropy alloy model to simulate the nanoindentation process and set the corresponding nanoindentation parameters; Step 5: Obtain the mechanical data of the three-dimensional high entropy alloy model under nanoindentation, and draw a load-displacement curve based on the mechanical data. At the same time, obtain the stress-strain cloud map and dislocation evolution of the high entropy alloy during the nanoindentation process.

[0006] In a preferred embodiment, in the step 1, the sizes of the three-dimensional high entropy alloy model in the x-axis, y-axis and z-axis directions are 30 nm, 20 nm and 1.76 nm respectively. First, atoms with a lattice constant of 0.354 nm and a lattice structure of FCC are used for modeling, and then the atoms are randomly replaced with Fe atoms, Ni atoms and Cr atoms according to an equiatomic proportion distribution to obtain a FeNiCr high entropy alloy model with an equimolar ratio.

[0007] In a preferred embodiment, in step 2, the embedded interatomic potential used is the EAM potential, and the boundary conditions of the three-dimensional high entropy alloy model in three dimensions are all set as periodic boundary conditions.

[0008] In a preferred embodiment, in step 3, the bottom atoms of the three-dimensional high entropy alloy model need to be fixed to ensure the stability of the high entropy alloy model during the nanoindentation simulation.

[0009] In a preferred embodiment, in step 3, the conjugate gradient algorithm is first used to minimize the energy of the three-dimensional high entropy alloy model, and then the NPT ensemble and the NVT ensemble are used to relax the three-dimensional high entropy alloy model for 100 ps respectively to obtain a three-dimensional high entropy alloy model with a stable state.

[0010] In a preferred embodiment, in step 4, the boundary conditions of the three-dimensional high entropy alloy model in the z-axis direction are modified to free boundary conditions.

[0011] In a preferred embodiment, in step 4, the virtual indenter radius used in the nanoindentation simulation process is 30 Å, the indentation direction is the z-axis direction, and the indentation speed is 1 m / s.

[0012] In a preferred embodiment, in step 5, the load and indentation depth at each sampling point during the nanoindentation simulation are collected, and a load-displacement curve of the three-dimensional high entropy alloy model during the nanoindentation process is drawn. At the same time, according to the atomic trajectory motion file at each collection point, the corresponding stress-strain cloud map is drawn using OVITO software.

[0013] In a preferred embodiment, in step 5, the dislocation analysis algorithm in the OVITO software is used to obtain the dislocation generation, movement and mutual reaction of the three-dimensional high entropy alloy model during the nanoindentation process.

[0014] Compared with the prior art, the present invention has the following beneficial effects: the present invention takes into account the influence of the interaction between the nanoindenter and the atoms of the high entropy alloy model during the nanoindentation process, applies a virtual indenter, effectively avoids the interaction between the two, and ensures the accuracy of the simulation process. At the same time, the technical solution of the present invention reduces the energy of the high entropy alloy model to the minimum through the energy minimization and relaxation methods, which is consistent with the actual situation and fully eliminates the influence of the structural instability of the model. The technical solution of the present invention performs real-time tracking and detection of the deformation process inside the high entropy alloy material from the atomic level, which helps to further understand the mechanical response of the high entropy alloy during the nanoindentation process, and can provide theoretical guidance for some phenomena in the nanoindentation experiment to a certain extent. Compared with the traditional characterization test method, the technical solution of the present invention can realize the observation and study of the dislocation evolution behavior inside the high entropy alloy material, thereby helping to understand the mechanical property response and corresponding plastic deformation mechanism of the high entropy alloy, so as to guide the performance regulation and optimization of the high entropy alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A high entropy alloy modeling diagram of a preferred embodiment of the present invention; Figure 2 A load-displacement curve diagram outputted by the nanoindentation process of a preferred embodiment of the present invention; Figure 3 A stress-strain cloud diagram during the nanoindentation process of a preferred embodiment of the present invention; Figure 4 This is a diagram of dislocation distribution inside a crystal during the nanoindentation process in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0017] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0018] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0019] refer to Figure 1-4 In this embodiment, a molecular dynamics method for simulating the mechanical properties of high entropy alloys is implemented by the following steps: Step 1: Construct a three-dimensional high entropy alloy model, determine the sizes of the high entropy alloy model in three dimensions, and determine the proportion of each component in the high entropy alloy model.

[0020] First, the crystallographic directions of the high entropy alloy model in the x-axis, y-axis, and z-axis directions are determined to be [-110], [-1-12], and

[111] , respectively, and the corresponding sizes are 30 nm, 20 nm, and 1.76 nm, respectively. Then, atoms with a lattice constant of 0.354 nm and a lattice structure of FCC are used for modeling, and the atoms are randomly replaced with Fe atoms, Ni atoms, and Cr atoms according to an equiatomic ratio distribution to obtain a FeNiCr high entropy alloy model with an equimolar ratio. Figure 1 Shown is the modeling diagram of FeNiCr high entropy alloy. The three types of atoms are represented by three different colors, where Fe atoms are red, Ni atoms are blue, and Cr atoms are yellow. The three types of atoms are randomly distributed in equal proportions in the model.

[0021] Step 2: Use the embedded interatomic potential in the high entropy alloy model to set the boundary conditions of the high entropy alloy model in three directions.

[0022] The embedded interatomic potential is selected as the EAM potential, which can accurately describe the interaction between the three elements contained in the FeNiCr high entropy alloy model and is widely used in molecular dynamics simulation of metal materials. The boundary conditions of the high entropy alloy model in three dimensions are set as periodic boundary conditions. Under this condition, when an atom runs out of one end of the simulation unit, a particle with the same motion state will enter the simulation unit at the boundary of the other end in the opposite direction of the simulation unit, thereby ensuring that the number of atoms in the system remains unchanged. This is equivalent to the model being infinite in the direction of the periodic boundary, which effectively reduces the impact of the size effect on the results during the simulation process.

[0023] Step 3: Fix the atoms at the bottom of the high entropy alloy model and stabilize the high entropy alloy model through energy minimization and relaxation processes.

[0024] Firstly, the atoms in the high entropy alloy model are divided into a fixed group and a nanoindentation group. The atoms within 1 nm from the bottom of the model are the fixed group, and the rest are the nanoindentation group. The atoms in the fixed group remain fixed throughout the nanoindentation process to prevent the high entropy alloy model from moving during the nanoindentation process and affecting the simulation results. The atoms in the nanoindentation group undergo transformations according to the real-time state during the simulation and undergo corresponding plastic deformation. The energy of the high entropy alloy model is minimized by the conjugate gradient algorithm, and the NPT ensemble and NVT ensemble are used to relax the high entropy alloy model for 100 ps respectively, which eventually makes the energy in the high entropy alloy model tend to be stable.

[0025] Step 4: Change the boundary conditions and apply loads to the high entropy alloy model to simulate the nanoindentation process and set the corresponding nanoindentation parameters; For the nanoindentation process, the periodic boundary conditions of the high entropy alloy model in the z-axis direction are modified to free boundary conditions to ensure that the high entropy alloy model can produce the corresponding plastic deformation process, thereby ensuring the correctness of the simulation. The virtual indenter radius used in the nanoindentation simulation process is 30 Å, the indentation direction is the z-axis direction, the indentation speed is 1m / s, and the action time is set to 1500 ps.

[0026] Step 5: Obtain the mechanical data of the high entropy alloy model under nanoindentation, and draw a load-displacement curve based on the mechanical data. At the same time, obtain the stress-strain cloud map and dislocation evolution of the high entropy alloy during nanoindentation.

[0027] Firstly, the simulation steps, applied load and indentation depth data of the high entropy alloy model at each acquisition point in the nanoindentation simulation process are output through the command in molecular dynamics and converted into the corresponding mechanical parameter units to obtain the load and indentation depth of the high entropy alloy model in the nanoindentation direction. Then, the load-displacement curve is drawn through this series of data. Figure 2 The load-displacement curve is drawn by the corresponding data. At the same time, the atomic trajectory motion information of the high entropy alloy model at each acquisition point in the nanoindentation simulation process is output through the command in molecular dynamics, and the data at each acquisition point is subjected to atomic force analysis, staining and slicing using OVITO visualization software to draw the corresponding stress-strain cloud map. Figure 3 is the stress-strain cloud diagram obtained at a data point during the nanoindentation process. At the same time, the dislocation evolution behavior during the entire nanoindentation process can also be observed through lattice analysis, common neighbor analysis, and dislocation analysis, such as Figure 4 This is the dislocation state distribution diagram obtained at a data point during the nanoindentation process. Finally, the mechanical properties and plastic deformation mechanism of the FeNiCr high entropy alloy model under nanoindentation are analyzed from multiple perspectives.

[0028] In summary, a molecular dynamics method for simulating the mechanical properties of a high entropy alloy of the present invention relates to a nanoindentation simulation method for a high entropy alloy. Through this method, the interference of various factors in the nanoindentation experiment can be well avoided, thereby further highlighting the mechanical properties response of the high entropy alloy during the nanoindentation process. At the same time, the technical solution of the present invention can track and detect the deformation process inside the high entropy alloy material in real time from the atomic level, and effectively simulate its atomic structure transformation, stress-strain changes and dislocation evolution during the nanoindentation process, which not only helps to provide theoretical guidance for some phenomena in the nanoindentation experiment, but also helps to have a deeper understanding of the mechanical properties response and plastic deformation mechanism of the high entropy alloy, and provides theoretical guidance for the performance regulation and optimization of the high entropy alloy.

[0029] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

Claims

1. A molecular dynamics method for simulating the mechanical properties of high entropy alloys, characterized in that: The following steps are involved: Step 1: construct a three-dimensional high entropy alloy model, determine the sizes of the three-dimensional high entropy alloy model in three dimensions, and determine the proportion of each component in the three-dimensional high entropy alloy model; Step 2: Use the embedded interatomic potential in the three-dimensional high entropy alloy model to set the boundary conditions of the three-dimensional high entropy alloy model in the three-dimensional directions; Step 3: Fix the atoms at the bottom of the three-dimensional high entropy alloy model and stabilize the three-dimensional high entropy alloy model through energy minimization and relaxation processes; Step 4: Change the boundary conditions and apply loads to the three-dimensional high entropy alloy model to simulate the nanoindentation process and set the corresponding nanoindentation parameters; Step 5: Obtain the mechanical data of the three-dimensional high entropy alloy model under nanoindentation, and draw a load-displacement curve based on the mechanical data. At the same time, obtain the stress-strain cloud map and dislocation evolution of the high entropy alloy during the nanoindentation process.

2. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In the step 1, the sizes of the three-dimensional high entropy alloy model in the x-axis, y-axis and z-axis directions are 30 nm, 20 nm and 1.76 nm respectively. First, atoms with a lattice constant of 0.354 nm and a lattice structure of FCC are used for modeling, and then the atoms are randomly replaced with Fe atoms, Ni atoms and Cr atoms according to an equiatomic ratio distribution to obtain a FeNiCr high entropy alloy model with an equimolar ratio.

3. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 2, the embedded interatomic potential used is the EAM potential, and the boundary conditions of the three-dimensional high entropy alloy model in three dimensions are all set as periodic boundary conditions.

4. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 3, the bottom atoms of the three-dimensional high entropy alloy model need to be fixed to ensure the stability of the high entropy alloy model during the nanoindentation simulation.

5. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 3, the conjugate gradient algorithm is first used to minimize the energy of the three-dimensional high entropy alloy model, and then the three-dimensional high entropy alloy model is relaxed for 100 ps using the NPT ensemble and the NVT ensemble respectively to obtain a three-dimensional high entropy alloy model with a stable state.

6. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 4, the boundary conditions of the three-dimensional high entropy alloy model in the z-axis direction are modified to free boundary conditions.

7. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 4, the virtual indenter radius used in the nanoindentation simulation process is 30 Å, the indentation direction is the z-axis direction, and the indentation speed is 1 m / s.

8. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 5, the load and indentation depth at each sampling point during the nanoindentation simulation are collected, and a load-displacement curve of the three-dimensional high entropy alloy model during the nanoindentation process is drawn. At the same time, according to the atomic trajectory motion file at each collection point, the corresponding stress-strain cloud map is drawn using OVITO software.

9. A molecular dynamics method for simulating mechanical properties of high entropy alloys according to claim 1, characterized in that: In step 5, the dislocation analysis algorithm in the OVITO software is used to obtain the dislocation generation, movement and mutual reaction of the three-dimensional high entropy alloy model during the nanoindentation process.

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