A simulation method for controlling the thickness of a crystal layer in a hole state to improve material strength

Abstract

The present invention discloses a simulation method for controlling the thickness of a crystal layer and improving the material strength in a hole state, which prepares four groups of amorphous high-entropy alloy models; relaxes the four groups of amorphous high-entropy alloy models for 200 ps respectively; digs holes with different radii respectively to obtain four groups of amorphous material models with different hole sizes; stretches the 4 kinds of porous amorphous models along the y-axis under the NVT condition, with a stretching rate of 1×10<supgt;9< / supgt; s<supgt;‑1< / supgt> and the temperature controlled at 300 K to obtain stress-strain curves, and determines the subsequent simulation processing of the porous amorphous model with the optimal strength and plasticity according to the stress-strain curves; prepares four groups of composite material models with different crystal layer thicknesses according to the porous amorphous model with the optimal strength and plasticity and conducts stretching respectively to obtain the stress-strain curves obtained by stretching; solves the technical problems that it is difficult to observe the deformation mechanism of the microstructure during the shear process of crystalline and amorphous composite materials with different crystal layer thicknesses at the atomic scale in experiments.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and particularly relates to a simulation method for controlling the thickness of a crystal layer in a hole state to improve the strength of a material. Background Art

[0002] High-entropy alloys are alloys formed by equimolar mixing of five or more elements. Compared with traditional alloys, they have excellent properties such as high strength, high hardness, high wear resistance, and high-temperature stability, which have attracted great interest both theoretically and experimentally. High-entropy metallic glasses can be obtained by rapid solidification methods, but the poor plasticity of high-entropy metallic glasses limits their industrial applications. To improve the mechanical properties of high-entropy metallic glasses, a method of using magnetron sputtering to deposit different metal alternating layers is used to prepare amorphous / crystalline composites, and the obtained composites exhibit excellent properties. However, in the manufacturing process of multiphase composites, defects such as holes and cracks will inevitably be introduced. The presence of volume defects such as holes in the composite material will affect its mechanical properties, especially when the hole size is close to the size of the representative microstructures in the nanomaterial. It has been found that by adjusting the size, number, shape, position, etc. of the holes, the heterogeneity of the material can be effectively improved, thereby improving the plasticity and strength of the material; due to the difficulty in experimentally controlling the relative sizes of the crystal layer and the amorphous layer in the crystal and amorphous composite material, and the addition of holes makes the production of this composite material more challenging, thus limiting our understanding of the influence of different crystal layer thicknesses on the mechanical properties of the crystal and amorphous composite material in the hole state. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a simulation method for controlling the thickness of a crystal layer in a hole state to improve the strength of a material, so as to solve problems such as the wrong understanding of the influence of the crystal layer thickness on the mechanical properties of the hole-containing composite material by researchers due to insufficient experimental conditions.

[0004] The technical solution of the present invention:

[0005] A simulation method for controlling the thickness of a crystal layer in a hole state to improve the strength of a material, the method comprising:

[0006] Step 1, preparing four groups of amorphous high-entropy alloy models;

[0007] Step 2, relaxing the four groups of amorphous high-entropy alloy models for 200 ps respectively; then respectively digging holes with different radii in the four groups of models, and the radii of the holes are respectively set to multiples of the lattice constant of CoNiCrFeMn: 0 nm, and obtaining four groups of amorphous material models with different hole sizes;

[0008] Step 3: Stretch the 4 porous amorphous models along the y-axis under the NVT condition at a stretching rate of 1×10 9 s -1 , control the temperature at 300K, and set the periodic boundary conditions in the x, y, and z directions to obtain the stress-strain curve. Determine the porous amorphous model with the optimal strength and plasticity from the stress-strain curve for subsequent simulation processing;

[0009] Step 4: Prepare a porous crystal and amorphous composite model according to the porous amorphous model with the most suitable strength and plasticity; obtain four groups of composite models with crystal layer thicknesses of and respectively;

[0010] Step 5: Stretch the four groups of composite models respectively, apply periodic boundary conditions in the x, y, and z directions during the stretching process, and the stretching rate is 1×10 9 s -1 , and the stretching direction is the y-axis; obtain the stress-strain curve of the stretching.

[0011] The method for preparing four groups of amorphous high-entropy alloy models is as follows: First, construct an FCC-phase crystalline CoNiCrFeMn model through lammps, with the model size of 24a×24a×24a, The lattice constant is The interaction between CoNiCrFeMn atoms is calculated using the modified embedded atom method MEAM; secondly, melt it at 3000K for 300ps under the NPT ensemble condition, and use the Nose and Hoover methods for temperature and pressure control; finally, solidify it to 300K at a cooling rate of 10 13 K / S to obtain an amorphous CoNiCrFeMn model; repeat the preparation 4 times to obtain four groups of amorphous high-entropy alloy models.

[0012] The method for calculating the modified embedded atom method MEAM is as follows:

[0013] In the MEAM potential, the total energy of atoms in the system is calculated as follows:

[0014]

[0015] where F is the embedding energy, which is a function of the atomic electron density ρ; represents a pair-potential interaction; the pair-potential interaction is the sum of the interactions of atom i with all neighboring atoms j within the cut-off distance; the content ratio of each type of atom in the CoNiCrFeMn high-entropy alloy is 1:1:1:1:1, and each type of atom is randomly distributed in space.

[0016] Prepare a porous crystal and amorphous composite model and the crystal layer thickness is and The preparation method of four groups of composite material models including:

[0017] Step 4.1: Delete the atoms in the middle layer of the amorphous model;

[0018] Step 4.2: Construct a crystal model corresponding to the size of the deleted area;

[0019] Step 4.3: Minimize the energy of the composite material model and relax it for 20 ps under the NPT ensemble. The Polak-Ribiere version of the conjugate gradient algorithm is used for energy minimization, and the set energy tolerance and force tolerance are

[0020] Step 4.4: Finally, delete the atoms in the spherical region with an internal pore diameter of in the composite material model; By controlling the deleted amorphous atoms and the added crystal atoms, four groups of composite material models with crystal layer thicknesses of and are obtained.

[0021] The beneficial effects of the present invention are:

[0022] The present invention proposes a simulation method for improving the strength of materials by controlling the crystal layer thickness. This simulation method can output the internal stress and strain data of the material in real time, thus facilitating the monitoring of the strength change of the material. In addition, through this simulation method, the improvement of the material strength under different crystal layer thicknesses is understood, which is convenient for experimental personnel to determine the production direction of the actual material, avoiding unnecessary material consumption during the production process, and greatly saving manpower, time and material costs.

[0023] The present invention can effectively simulate the enhancement of the material performance by the crystal layer thickness under the condition of pre-existing holes, thereby simulating the formation process and microstructural mechanism of shear bands in the composite material, contributing to predicting the strength enhancement mechanism of the composite material, and can be used to improve the plasticity of high-entropy composite materials. At the same time, it also provides a theoretical reference for the design, research and development and structural optimization of new composite materials, shortening the research and development cycle.

[0024] It solves the technical problems that it is difficult to observe the deformation mechanism of the microstructure during the shear process of crystalline and amorphous composite materials with different crystal layer thicknesses at the atomic scale experimentally, and the presence of holes makes the evolution process more complex. Brief Description of the Drawings

[0025] Figure 1 is the flow schematic diagram of the present invention;

[0026] Figure 2 is the amorphous model with different holes in the embodiment of the present invention;

[0027] Figure 3 It is the tensile stress-strain curve of different pore amorphous models in the embodiments of the present invention;

[0028] Figure 4 It is a porous composite material model with different crystal layer thicknesses in the embodiments of the present invention;

[0029] Figure 5 It is the tensile stress-strain curve of the porous crystal and amorphous composite material model in the embodiments of the present invention. Specific embodiments

[0030] The present invention will be further described below in conjunction with the drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0031] Embodiment. A simulation method for controlling the strength of materials by increasing the crystal layer thickness in a hole state, as Figure 1 shown, includes the following steps:

[0032] Obtain an amorphous high-entropy alloy model. First, construct an FCC-phase crystalline CoNiCrFeMn model through lammps. The size of the model is The lattice constant is The interaction between CoNiCrFeMn atoms is calculated using the MEAM potential. Secondly, melt it at a high temperature of 3000K for 300ps. The ensemble conditions set are NPT (i.e., the total number of atoms N, the total pressure P, and the temperature T remain constant). The Nose-Hoover method (by adding some dynamic variables that couple the particle velocity and the simulation domain size to achieve temperature and pressure control) is used for temperature and pressure control. Finally, solidify it to 300K at a cooling rate of 10 13 K / S to obtain an amorphous CoNiCrFeMn model.

[0033] ② Repeat step ① four times to obtain four groups of amorphous CoNiCrFeMn models. Relax each of the four groups of models for 200ps to make them reach a stable state. Then, dig holes with different radii inside the four groups of models to obtain four groups of amorphous material models with different hole sizes. The holes are located at the center of the material. Since the mechanical properties of the material will be severely affected when the hole size is close to the representative microstructure size in the material, the radii of the holes are respectively set as multiples of the CoNiCrFeMn lattice constant: 0nm, and The setting command for a hole with an aperture of a is: region hole sphere 0 0 0 3.53units box, delete_atomsregionhole, so as to obtain the four groups of amorphous models as shown in Figure 2 shown, and use the aperture to distinguish the four groups of amorphous models.

[0034] ③ Stretch the 4 porous amorphous models obtained in step ② along the y-axis under the NVT condition, with a stretching rate of 1×10 9 s -1 , the temperature is controlled at 300K, and periodic boundary conditions are set in all three xyz directions. The execution commands in LAMMPS for the above operations are: boundary p pp, fix 1 all nvt temp 300 300 0.1, fix 2 all deform1000yerate 0.001 units box remap x. The stress-strain curve obtained is as Figure 3 shown, where the horizontal axis represents strain and the vertical axis represents stress. The stress change △σ = σ over -σ flow . The larger the stress change △σ, the poorer the plasticity of the material. The peak stress σ over can reflect the strength of the material. The model with a pore size of a has a higher strength, but a larger △σ, indicating lower plasticity, while the model with a pore size of 3a has higher plasticity but lower strength. Since the amorphous model with a pore size of 2a has both excellent strength and plasticity compared to the models with pore sizes of a and 3a, the subsequent invention continues the simulation and processing based on this.

[0035] ④ Based on step ③, select the holes with a radius of 2a as the possible hole or crack sizes during the experiment. Immediately insert crystal materials with different thicknesses into the amorphous material model with a pore size of 2a to prepare porous crystal and amorphous composite models.

[0036] The construction method of the porous crystal and amorphous composite models is as follows:

[0037] First, delete the atoms in the middle layer of the amorphous model. The corresponding LAMMPS command is region middle block -42.36 42.36 -20 20 -42.36 42.36 units box (where -20 20 represents the thickness of the deleted middle layer as ), delete_atoms region middle;

[0038] Second, construct a crystal model corresponding to the size of the deleted region, and use the LAMMPS command (read_data crystal_model.lmp add append) to composite the crystal model into the amorphous model to obtain the crystal and amorphous composite model;

[0039] Subsequently, the energy of the composite material model was minimized and relaxed for 20 ps in the NPT (constant number of total atoms N, total pressure P, and temperature T) ensemble. The Polak-Ribiere version of the conjugate gradient algorithm was used for energy minimization, and the set energy tolerance and force tolerance were The implementation command was: min_style cg, minimize 1e-15 1e-15 10000 10000. In each iteration of this conjugate gradient algorithm, the force gradient is combined with the information from the previous iteration to calculate a new search direction perpendicular (conjugate) to the previous search direction. The PR (Polak-Ribiere) variable affects the direction selection and how the algorithm restarts when it stops advancing. The PR variable is considered the most effective conjugate gradient selection;

[0040] Finally, atoms within the spherical region with an internal pore diameter of 2a in the composite material model were deleted (region hole sphere 0 0 0 7.06 units box, delete_atoms region hole); by controlling the deleted amorphous atoms and the added crystalline atoms, four groups of composite material models with crystalline layer thicknesses of and were obtained, as shown in Figure 4 shown.

[0041] ⑤ The four groups of composite material models obtained in step ④ were respectively stretched. Periodic boundary conditions were applied in the xyz directions during the stretching process, and the stretching rate was 1×10 9 s -1 , and the stretching direction was the y-axis.

[0042] Figure 5 shows the stress-strain curves obtained from the stretching. The results show that the thicker the crystalline layer thickness in the composite material model, the higher the peak stress of the composite material model, and the more obvious the strength enhancement. The composite material model with a crystalline layer thickness of has the highest strength among the test models. This result helps researchers understand the influence of the crystalline layer thickness on the crystal / amorphous composite material in the presence of pores, thus providing a theoretical reference for the fabrication and design of high-strength high-entropy materials.

[0043] The modified embedded atom method (MEAM) was used for the interaction between atoms. This atomic potential can accurately reflect the interaction between atoms. In the MEAM potential, the total energy of the atoms in the system is calculated as follows:

[0044]

[0045] where F is the embedding energy, which is a function of the atomic electron density ρ; represents a pair potential interaction, where the pair potential interaction is the sum of the interactions of atom i with all neighboring atoms j within the cut-off distance, r ij represents the distance between atom i and atom j.

[0046] In addition, in the above steps, the content ratio of each type of atom in the CoNiCrFeMn high-entropy alloy is 1:1:1:1:1, and each type of atom is randomly distributed in space.

[0047] All of the above calculation results are achieved based on the LAMMPS software.

Claims

1. A simulation method for controlling the thickness of a crystal layer and enhancing the material strength in a hole state, characterized in that: The method includes: Step 1, preparing four groups of amorphous high-entropy alloy models; Step 2: Relax each of the four amorphous high-entropy alloy models for 200 ps; then, within each of the four models, dig holes with different radii, and the radii of the holes are set to multiples of the lattice constant of CoNiCrFeMn: 0 nm, and to obtain four amorphous material models with different hole sizes; Step 3: Stretch the 4 porous amorphous models along the y-axis under the NVT condition, with a stretching rate of 1×10 9 s -1 , control the temperature at 300 K, and set the periodic boundary conditions in all three xyz directions to obtain the stress-strain curve. Determine the porous amorphous model with the optimal strength and plasticity according to the stress-strain curve for subsequent simulation processing; Step 4: Prepare a porous crystal and amorphous composite model according to the porous amorphous model with the most suitable strength and plasticity; obtain four groups of composite models with crystal layer thicknesses of and respectively; Step 5: Tensile tests were performed on the four groups of composite material models respectively. During the tensile process, periodic boundary conditions were applied in the xyz directions, and the tensile rate was 1×10 9 s -1 , and the tensile direction was the y-axis; the stress-strain curves obtained from the tensile tests were obtained.

2. The simulation method for controlling the thickness of the crystal layer and enhancing the material strength in a hole state according to claim 1, wherein: The method for preparing four groups of amorphous high-entropy alloy models is as follows: First, a crystalline CoNiCrFeMn model with an FCC phase is constructed by LAMMPS, and the model size is 24a×24a×24a. The lattice constant is The interaction between CoNiCrFeMn atoms is calculated using the modified embedded atom method (MEAM); the method for calculating the modified embedded atom method (MEAM) is as follows: In the MEAM potential, the calculation method of the total energy of atoms in the system is as follows: Among them, F is the embedding energy, which is a function of the atomic electron density ρ; represents a pair-potential interaction; the pair-potential interaction is the sum of the interactions of atom i with all neighboring atoms j within the cut-off distance; r ij represents the distance between atom i and atom j; the content ratio of each type of atom in the CoNiCrFeMn high-entropy alloy is 1:1:1:1:1, and each type of atom is randomly distributed in space; secondly, it is melted at 3000 K for 300 ps, the ensemble condition set is NPT, and the Nose and Hoover methods are used for temperature and pressure control; finally, it is solidified to 300 K at a cooling rate of 10 13 K / S to obtain an amorphous CoNiCrFeMn model; repeat the preparation 4 times to obtain four groups of amorphous high-entropy alloy models.

3. A simulation method for controlling the thickness of a crystal layer and enhancing the material strength in a hole state according to claim 1, characterized in that: Preparation method of a porous crystal and amorphous composite material model and four groups of composite material models with a crystal layer thickness of and comprises: Step 4.1, deleting the atoms in the middle layer of the amorphous model; Step 4.2, constructing a crystal model corresponding to the size of the deleted area; Step 4.3: Minimize the energy of the composite material model and relax it for 20 ps under the NPT ensemble. The Polak-Ribiere version of the conjugate gradient algorithm is used for energy minimization, and the set energy tolerance and force tolerance are Step 4.

4. Finally, delete the atoms within the spherical region with an internal pore diameter of in the composite material model; by controlling the deleted amorphous atoms and the added crystalline atoms, four groups of composite material models with crystalline layer thicknesses of and are obtained respectively.

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