Modeling method of columnar nanotwins and friction and wear research method based on this

Abstract

The present invention belongs to the field of material simulation, and specifically relates to a modeling method for columnar nanotwins and a friction and wear research method based on the modeling method. First, a molecular dynamics simulation model of columnar nanotwin nickel is constructed; then the indenter is pressed vertically downward along the y direction at a speed into the matrix, and then a horizontal speed is applied to the indenter in the matrix to perform uniform friction motion under a microcanonical ensemble; finally, a simulation calculation is performed to obtain the friction curve of the indenter when rubbing on the matrix over time. The change in dislocation density during the friction process can be obtained through post-processing, and the change in the microstructure of the material during the friction process can be directly observed. Compared with traditional molecular dynamics friction simulation experiments, the model of the present invention can more carefully and clearly observe the changes in the microstructure of columnar nanotwin nickel during the friction process, and can be used to guide experiments on the influence of the microstructure of columnar nanotwin materials on friction performance, so as to develop more wear-resistant materials.

Description

Technical Field

[0001] The present invention belongs to the field of material simulation, and in particular relates to a modeling method of columnar nanotwins and friction and wear research based on the modeling method. Background Art

[0002] Nanotwinned materials are composed of nanoscale twinned lamellae. By introducing a high density of twin planes, the material's mechanical and electrical properties, including strength, hardness, toughness, and conductivity, are significantly improved without sacrificing ductility or thermal stability. Because twin boundaries can both hinder dislocation slip and allow dislocations to pass through, and dislocations can also slip across twin boundaries, this leads to three mechanisms for plastic deformation in nanotwins: dislocation pileup and passage through twin boundaries, Shockley partial dislocation-induced twin boundary migration, and restricted slip of through-dislocations within the twin lamellae.

[0003] There have been extensive studies on the plastic deformation of nanotwin materials, but there is currently no in-depth study of the deformation mechanism of the micro-friction properties of nanotwin materials, and there is no simple method for constructing columnar nanotwin materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a modeling method for columnar nanotwins and a friction and wear research method based on the modeling method.

[0005] The technical solution for achieving the purpose of the present invention is: a modeling method for columnar nanotwins, comprising the following steps:

[0006] Step (1) establishing a matrix unit cell: selecting the lattice constant of the material and the crystal directions corresponding to the x, y, and z directions, establishing a unit cell file, mirroring the unit cell file to obtain a mirror file, and then stacking and obtaining a matrix unit cell file;

[0007] Step (2) establishing a polycrystal: establishing a matrix text file, which contains the parameters of the polycrystal structure, wherein the matrix height direction is set to 0, i.e. establishing a two-dimensional polycrystal, using the matrix unit cell file obtained in step (1) as a unit and the matrix text file as a condition to obtain an ideal model of columnar nanotwins;

[0008] Step (3) Moving the twin boundary: translating the twin boundary in the ideal model of the columnar twin material, ensuring that the model is within the peripheral box that matches the twin during modeling, and translating the twin boundary by different distances to obtain a columnar nanotwin translation model with the same twin layer thickness but different twin boundary positions;

[0009] Step (4) Multiphase combination: Use the method of establishing multiphase alloys to perform multiphase combination on nanotwin materials with different twin thicknesses but different positions - that is, delete the grain with ID 1 in the twin model of the first position, then keep the grain with ID 1 in the twin model of the second position, delete the remaining grains, and stack these two models to obtain a practical model of columnar nanotwins.

[0010] Furthermore, the number of “stacking” steps in step (1) depends on the actual height of the nanotwins.

[0011] A method for studying the friction and wear of columnar nano-twinned nickel based on the above method comprises the following steps:

[0012] Step (1): constructing a columnar nano-twinned nickel model based on the method described in any one of claims 1 to 2, establishing an indenter model, and stacking the columnar nano-twinned nickel model and the indenter model to obtain a friction model;

[0013] Step (2): Read the friction model, set the X-direction, Y-direction and Z-direction of the model area as periodic boundary conditions; define variables and calculate the required physical quantities;

[0014] Step (3): Select a potential function that can describe the interaction force between atoms in the nanoscale nickel system;

[0015] Step (4): Energy minimization using the conjugate gradient method;

[0016] Step (5): relax the system to obtain a relaxed model;

[0017] Step (6): limiting simulation parameters and performing simulation: the indenter is pressed into the columnar nano-twinned nickel at a constant speed, and then rubbed at a constant speed, and outputting information after the friction;

[0018] Step (7): Data processing and visualization analysis.

[0019] Furthermore, the variables defined in step (2) include: the force and position coordinates of the indenter in the x and y directions, and the physical quantities required for calculation include temperature, kinetic energy, and potential energy.

[0020] Furthermore, in step (3), the potential function uses a mixed potential, selects the EAM potential to describe the interaction between Ni-Ni, selects the LJ potential to describe the interaction potential between Ni-N and Ni-Si, and ignores the interaction between NN, Si-Si and N-Si.

[0021] Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) The modeling method of columnar nanotwins of the present invention avoids the alignment of coherent twin boundaries in two grains on the same plane by translating the twin boundaries and using a multiphase composite method of selective deletion and stacking during modeling. In other words, it is possible to construct more practical nanotwin materials more simply and quickly.

[0023] (2) The twin modeling method of the present invention is suitable for experimental verification of various nano-twin materials.

[0024] (3) The wear research method of the present invention is based on the modeling method of columnar nanotwins to establish columnar nanotwin nickel, which is in line with the actual situation and can clearly and accurately observe and analyze the changes in the microstructure during the friction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the nanotwin unit cell seed model.

[0026] Figure 2 Twin alignment model for columnar nanotwinned nickel.

[0027] Figure 3 This is the actual model of columnar nanotwinned nickel.

[0028] Figure 4 This is the actual friction and wear model of columnar nanotwinned nickel.

[0029] Figure 5 It is the nano-gradient twin unit cell seed model.

[0030] Figure 6 This is the actual model of columnar gradient nanotwinned nickel. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings.

[0032] A research method for simulating friction and wear of nano-twinned nickel based on molecular dynamics includes the following steps:

[0033] (1) Establishment of molecular dynamics simulation model:

[0034] Step 1: Establishment of base model

[0035] ① Establishment of matrix unit cell: Select the lattice constant of the material and the crystal directions corresponding to the x, y, and z directions, establish the unit cell file, mirror it, obtain the mirror file, and then stack it to obtain the matrix unit cell file. It can also be stacked multiple times to form a matrix unit cell file. The height of the matrix depends on the length of the matrix unit cell file;

[0036] ② Establishment of polycrystal: First, create a text file containing the parameters of the polycrystal structure, in which the height direction of the substrate is set to 0, that is, to establish a two-dimensional polycrystal. Then, use the command to establish the polycrystal to obtain the ideal model of columnar nanotwins.

[0037] ③ Movement of twin boundaries: To avoid the coherent twin boundaries in two grains being aligned on the same plane, the established twins need to be translated. Use the translation command and place the translated model within the box. By translating the twin boundaries by different distances, a columnar nanotwin translation model with the same twin layer thickness but different twin boundary positions can be obtained.

[0038] ④ Multiphase combination: Using the method of establishing multiphase alloys, nano-twin materials with different twin thicknesses but different positions are combined into a multiphase combination. That is, the grain with ID 1 in the twin material at the first position is deleted, and then the grain with ID 1 in the twin material at the second position is retained (the rest of the grains are deleted). By stacking these two models, a realistic model of columnar nano-twins can be obtained.

[0039] Step 2: Build the indenter model - Create a unit cell model, use visual analysis software to construct a silicon box, and then cut out a silicon ball as the indenter;

[0040] Step 3: Place the indenter model directly above the base model and stack them together, with the whole model serving as the friction model.

[0041] (2) Read the matrix model file in molecular dynamics and divide the matrix into a fixed layer, a constant temperature layer and a Newton layer. The atoms in the range a at the bottom of the matrix and in the Y direction are set as fixed layer atoms to prevent the system from drifting up and down and left and right. The atoms in the range b above the bottom fixed layer are set as constant temperature layer atoms to absorb the heat generated during friction. The remaining atoms in the matrix are set as Newton layer atoms to simulate the interaction with other atoms. The atoms in the constant temperature layer and the Newton layer follow Newton's second law of motion.

[0042] (3) Model initialization: The simulation unit is metal, periodic boundary conditions are applied, and the system only contains atoms, without considering other contents such as bond angles. A neighborhood list is also constructed to save time in determining the distance between atoms.

[0043] (4) Define variables: force and position coordinates of the indenter in the x and y directions;

[0044] (5) Selection of potential function: In this friction simulation, three elements, Ni, N, and Si, are involved. Therefore, a mixed potential is used. The EAM potential is selected to describe the interaction between Ni and Ni, and the LJ potential is selected to describe the interaction potential between Ni and N, and Ni and Si. The interaction between NN, Si and Si, and N and Si is ignored.

[0045] (6) Energy minimization: Use minimize to minimize energy, keep the potential energy of the initial configuration optimized, and output the kinetic energy and potential energy of each step;

[0046] (7) System relaxation: The isothermal and isobaric ensemble (NPT) was selected for equilibrium constraint. The system was relaxed for 10,000 steps at 300 K using the Nose-Hoover thermal bath method to allow the initial model of the system to reach equilibrium.

[0047] (8) Setting and simulation related parameters: The initial temperature of the simulation system was set to 300K, the head speed was set to Cutting depth is The friction length is The integration step size is chosen to be 1fs;

[0048] (9) Data processing and visualization: Use molecular dynamics simulation software to perform molecular dynamics simulation calculations on self-written program files, statistically calculate the calculation results, and obtain output files of relevant data of the simulation process and calculation results. The output files contain information on changes in variable parameters and atomic coordinates. Select drawing and data analysis software for data processing, and use visualization analysis software for visualization and structural analysis.

[0049] Example 1

[0050] (1) Establishment of molecular dynamics simulation model:

[0051] Use visual analysis software to construct a matrix model of nano-twinned nickel:

[0052] ① Establishment of matrix unit cell: Select the lattice constant of Ni as Crystal orientation

[111] and As the corresponding crystal directions in the x, y and z directions, a unit cell file of Ni is created, which is then mirrored to obtain a mirror file, which is then stacked and created into a matrix unit cell file. The stacked files are stacked four times to obtain a matrix unit cell file (e.g. Figure 1 shown);

[0053] ② Establishment of polycrystal: First, create a text file with the base size as The two-dimensional columnar crystal contains 4 grains, and then the ideal model of columnar nanotwins can be obtained using the polycrystal command (such as Figure 2 shown);

[0054] ③ Movement of twin boundaries: To avoid the coherent twin boundaries in two grains being aligned on the same plane, the established twins need to be translated. Use the translation command and place the translated model within the box. By translating the twin boundaries by different distances, a columnar nanotwin translation model with the same twin layer thickness but different twin boundary positions can be obtained.

[0055] ④ Multiphase combination: Using the method of establishing multiphase alloys, nano-twin nickel with different twin thicknesses but different positions is multiphase combined - that is, the grain with ID 1 in the twin material at one position is deleted, and then the grain with ID 1 in the twin material at the second position is left (the rest of the grains are deleted). By stacking these two models, a nano-twin model that conforms to reality can be obtained (such as Figure 3 shown);

[0056] Establishment of the indenter: Select silicon with a diamond structure of lattice constant of 5.431, and use the visual analysis software to first establish a Then cut out a box with a radius of The indenter contains 5651 silicon atoms. The friction ball is placed on the upper left of the substrate and is 100 nm away from the substrate in the X direction. The distance from the substrate in the Y direction The Z direction is placed in the middle of the substrate, and the constructed model is as follows Figure 4 As shown;

[0057] (2) Read the matrix model file in the molecular dynamics simulation software and divide the matrix into a fixed layer, a constant temperature layer and a Newton layer. The atoms within the range are set as fixed layer atoms to prevent the system from drifting up and down and left and right; the atoms above the bottom fixed layer are set as fixed layer atoms. The atoms within the range are set as isothermal layer atoms to absorb the heat generated during friction; the remaining atoms in the matrix are set as Newtonian layer atoms to simulate the interaction with other atoms; the atoms in the isothermal layer and Newtonian layer follow Newton's second law of motion;

[0058] (3) Model initialization: The simulation unit is metal, periodic boundary conditions are applied, and the system only contains atoms, without considering other contents such as bond angles. A neighborhood list is also constructed to save time in determining the distance between atoms.

[0059] (4) Define variables: force and position coordinates of the indenter in the x and y directions;

[0060] (5) Selection of potential function: In this friction simulation, three elements, Ni, N, and Si, are involved. Therefore, a mixed potential is used. The classical embedded atom potential (EAM potential) is selected to describe the interaction between Ni-Ni, and the LJ potential is selected to describe the interaction potential between Ni-N and Ni-Si. The interaction between NN, Si-Si, and N-Si is ignored.

[0061] (6) Energy minimization: Use minimize to minimize energy, keep the potential energy of the initial configuration optimized, and output the kinetic energy and potential energy of each step;

[0062] (7) System relaxation: The isothermal and isobaric ensemble (NPT) was selected for equilibrium constraint. The system was relaxed for 10,000 steps at 300 K using the Nose-Hoover thermal bath method to allow the initial model of the system to reach equilibrium.

[0063] (8) Setting and simulation related parameters: The initial temperature of the simulation system is set to 300K, the friction ball speed is set to Cutting depth is The friction length is The integration step size is chosen to be 1fs;

[0064] (9) Data processing and visualization: molecular dynamics simulation calculations are performed on the self-written program files through molecular dynamics software, and the calculation results are statistically calculated to obtain the force of the indenter and the position information during the friction process. The data can be processed using drawing and data analysis software to obtain the changes in friction force and friction coefficient with the change of position or time; visualization analysis software is selected for visualization: ① The calculated atomic configuration model file is subjected to dislocation analysis (DXA), and the time, position of the friction direction and the total length of the dislocation line are output. Calculations can produce an image of how dislocation density changes with time or position; ② Counting the number of atoms deposited during friction and calculating the volume of each atom can yield the wear volume; ③ Performing a common-neighbor analysis on the friction model and cutting it in the middle along the Z direction allows for observation of changes in the microstructure during friction; ④ Viewing the friction from the Y direction reveals the accumulation pattern, which can be more intuitively observed by coloring and adding a ruler.

[0065] Example 2

[0066] The difference between this embodiment and embodiment 1 is that: the establishment of the matrix unit cell file

[0067] The lattice constant of Ni is selected as The crystal directions are Crystal orientation

[111] and As the corresponding crystal directions in the x, y and z directions, establish a Ni layer with a thickness of 2 unit cell file 1, then mirror it to obtain the mirror file 2, and then stack and establish a matrix unit cell file 3; stack file 1 on file 3 to obtain unit cell file 4; then establish file 3 with a layer thickness of 8 and stack it with file 4, and repeat the above process in sequence to obtain the seed file of gradient nanotwins, such as Figure 5 The columnar gradient nanotwin model is shown in Figure 6 shown.

Claims

1. A modeling method for columnar nanotwins, characterized in that: The steps include: Step (1) establishing a matrix unit cell: selecting the lattice constant of the material and the crystal directions corresponding to the x, y, and z directions, establishing a unit cell file, mirroring the unit cell file to obtain a mirror file, and then stacking and obtaining a matrix unit cell file; Step (2) establishing a polycrystal: establishing a matrix text file, which contains the parameters of the polycrystal structure, wherein the matrix height direction is set to 0, i.e. establishing a two-dimensional polycrystal, using the matrix unit cell file obtained in step (1) as a unit and the matrix text file as a condition to obtain an ideal model of columnar nanotwins; Step (3) Moving the twin boundary: translating the twin boundary in the ideal model of the columnar nanotwins, ensuring that the model matches the model at the time of modeling, and translating the twin boundary by different distances within the peripheral box to obtain a columnar nanotwin translation model with the same twin layer thickness but different twin boundary positions; Step (4) Multiphase combination: Use the method of establishing multiphase alloys to perform multiphase combination on nanotwin materials with different twin thicknesses but different positions - that is, delete the grain with ID 1 in the twin model of the first position, then keep the grain with ID 1 in the twin model of the second position, delete the remaining grains, and stack these two models to obtain a practical model of columnar nanotwins.

2. The method according to claim 1, characterized in that The number of "stacking" steps in step (1) depends on the actual height of the columnar nanotwin material.

3. A method for studying friction and wear of columnar nano-twinned nickel based on the method according to any one of claims 1-2, characterized in that: The steps include: Step (1): constructing a columnar nano-twinned nickel model based on the method described in any one of claims 1 to 2, establishing an indenter model, and stacking the columnar nano-twinned nickel model and the indenter model to obtain a friction model; Step (2): Read the friction model and set the X, Y, and Z directions of the model area as periodic boundary conditions; Define variables and calculate required physical quantities; Step (3): Select potential function; Step (4): Energy minimization using the conjugate gradient method; Step (5): relax the system to obtain a relaxed model; Step (6): limiting simulation parameters and performing simulation: the indenter is pressed into the columnar nano-twinned nickel at a constant speed, and then rubbed at a constant speed, and outputting information after the friction; Step (7): Data processing and visualization analysis.

4. The method according to claim 3, characterized in that The variables defined in step (2) include the force and position coordinates of the indenter in the x and y directions, and the physical quantities required for calculation include temperature, kinetic energy, and potential energy.

5. The method according to claim 4, characterized in that Specifically in step (3): the potential function uses a mixed potential, selects the EAM potential to describe the interaction between Ni-Ni, selects the LJ potential to describe the interaction potential between Ni-N and Ni-Si, and ignores the interaction between NN, Si-Si and N-Si.

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