Molecular dynamics simulation method and system for deformation behavior of biphase polycrystalline titanium alloy

Abstract

The invention discloses a molecular dynamics simulation method and a molecular dynamics simulation system for a deformation behavior of a biphase polycrystalline titanium alloy, belongs to the technical field of metal material design, and solves the problems that a traditional test method is difficult to efficiently reveal association between a two-phase structure and performance, and existing molecular dynamics simulation is mostly limited to single-crystal / polycrystalline pure titanium research. And a modeling method for the atomic scale deformation behavior of the double-phase polycrystalline titanium alloy is lacked. The method mainly comprises the following steps: S1, carrying out molecular dynamics modeling on a layered double-phase structure unit; s2, carrying out molecular dynamics modeling on the single-phase / double-phase polycrystalline titanium alloy; s3, energy minimization and system relaxation are carried out; s4, selecting a potential function; s5, setting boundary conditions; s6, temperature and pressure control; s7, deformation load setting; and S8, performing visualization and post-processing analysis. The method is suitable for titanium alloy microstructure design scenes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material design, and particularly relates to a molecular dynamics simulation method for deformation behavior of a dual-phase polycrystalline titanium alloy. BACKGROUND

[0002] Titanium alloys have good mechanical properties, welding performance and high-temperature service performance, and are widely used in the fields of aerospace, automobile manufacturing and biomedical treatment. Due to the characteristics of high deformation resistance and poor machinability of titanium alloys, it is difficult to machine and manufacture complex structures. The additive manufacturing technology produces parts with complex geometries in a flexible, efficient and environmentally friendly manner, effectively realizing the production and manufacturing of titanium alloy complex structures. Due to the rapid cooling rate and large temperature gradient in the additive process, the microstructure of the printed titanium alloy is a supersaturated non-equilibrium alpha '' martensite phase, which has inherent brittleness and low plasticity, severely limiting the application of titanium alloy additive structures. The transformation from the alpha '' martensite phase to the alpha + beta dual-phase structure with better comprehensive performance is a common modification method in industrial production and manufacturing. Previous studies have shown that the beta phase in the dual-phase titanium alloy structure can effectively hinder the crack propagation rate and improve the plasticity / toughness of the alloy. Due to the limitations of characterization techniques, the deformation mechanism and microstructure evolution characteristics of dual-phase titanium alloys during loading are not clear. Moreover, using experimental methods to study the relationship between the two-phase microstructure and performance requires a large amount of experimental data, and obtaining a specific organizational state requires a long experimental period and cost. Molecular dynamics simulation (MD) as a computational simulation method can reveal the dynamic evolution of microstructure at the atomic scale during loading, and is widely used in the study of material deformation behavior and mechanism. Existing researches are limited to the study of deformation mechanism of single-crystal pure titanium or polycrystalline titanium alloy, and there is a lack of modeling methods and atomic-scale deformation behavior researches on dual-phase polycrystalline titanium alloys. SUMMARY

[0003] The application provides a molecular dynamics simulation method and system for deformation behavior of a dual-phase polycrystalline titanium alloy, which aims to solve the problem that traditional experimental methods cannot efficiently reveal the correlation between two-phase microstructure and performance, and existing molecular dynamics simulation methods are mostly limited to the study of single-crystal / pure titanium, lacking modeling methods for atomic-scale deformation behavior of dual-phase polycrystalline titanium alloys.

[0004] In a first aspect, the application aims to provide a molecular dynamics simulation method for deformation behavior of a dual-phase polycrystalline titanium alloy, comprising the following steps: S1, constructing a layered dual-phase structure unit molecular dynamics model: calculating the cell expansion multiple based on the lattice constants of the alpha phase and the beta phase, sequentially establishing an alpha single-crystal model and a beta single-crystal model and stacking them in the z direction to form an alpha / beta layered dual-phase structure unit model, and controlling the thickness ratio of the alpha phase to the beta phase to be 3:1; S2, preparation of polycrystalline titanium alloy molecular dynamics model: generate a polycrystalline node file containing 8 random orientations in a simulation box of 200 Å x 200 Å x 200 Å using the Voronoi method, and fill the titanium single crystal as a seed to construct a single-phase polycrystalline model; the layered dual-phase structure unit molecular dynamics model of S1 is filled as a seed to construct a dual-phase polycrystalline model; replace the Ti atoms in the β phase with alloy element atoms according to the composition ratio of the titanium alloy to construct a dual-phase polycrystalline titanium alloy molecular dynamics model corresponding to the actual material organization; S3: energy minimization is performed using the conjugate gradient method, and the system is relaxed for 50 ps under isothermal-isobaric ensemble to reach an equilibrium state; S4, potential function configuration: embedded atom potential is used to describe the deformation behavior of titanium alloy, and the total potential energy is obtained; S5, boundary condition setting: periodic boundary condition is used to avoid surface effect; S6, temperature and pressure control: control the simulation temperature to be 300K under NPT ensemble and keep the three-way pressure balance; S7: deformation load application: constant strain rate uniaxial tensile load is applied along the z-axis under the environment of 300K, and the lateral pressure is kept at zero; S8: visual processing is performed using OVITO software to analyze the crystal structure and dislocation behavior.

[0005] Further, a preferred scheme is provided: in S1, the cell expansion multiples of the α phase in the x and y directions are 4x4, the cell expansion multiples of the β phase in the x and y directions are 8x5, and the cell expansion multiples of the α phase and the β phase in the z direction are 9 and 3, respectively; Further, a preferred scheme is provided: in S1, the lattice type of the α phase is hexagonal close-packed HCP, and the β phase is body-centered cubic BCC, and the lattice matching of the dual-phase interface is realized by adjusting the x-y plane cell expansion multiple.

[0006] Further, a preferred scheme is provided: in S2, Mo atoms are used to replace titanium atoms in the β phase.

[0007] Further, a preferred scheme is provided: the expression of the total potential energy is: , wherein, is the embedding energy of the embedded i-th atom, is the electronic density of the matrix when there is no atom i, and is a short-range two-body potential function, is the distance between atoms i and j, is the electronic density distribution of atom i. Further, a preferred scheme is provided: in S7, the constant strain rate is set to 109 s -1 .

[0008] Further, the preferred scheme is provided: in the S8, the Common Neighbor Analysis and Dislocation Extraction Algorithm are used to analyze the microstructure evolution and dislocation behavior, and the Centroid Method is used to identify the twin boundaries.

[0009] In a second aspect, the purpose of the present application is to provide a molecular dynamics simulation system for the deformation behavior of dual-phase polycrystalline titanium alloy, which is realized based on the molecular dynamics simulation method for the deformation behavior of dual-phase polycrystalline titanium alloy according to any one or more of the above schemes, and the system comprises: A first modeling module: for constructing a layered dual-phase structure unit molecular dynamics model, calculating the cell expansion multiple based on the lattice constants of the α phase and the β phase, sequentially establishing an α single crystal model and a β single crystal model and stacking them in the z direction to form an α / β layered dual-phase structure unit model, and controlling the thickness ratio of the α phase to the β phase to be 3:1; A second modeling module: for preparing a polycrystalline titanium alloy molecular dynamics model, using the Voronoi method to generate a polycrystalline node file containing 8 randomly oriented polycrystalline nodes in a simulation box of 200Åx200Åx200Å, and filling and constructing a single-phase polycrystalline model with titanium single crystals as seeds; The layered dual-phase structure unit molecular dynamics model of S1 is used as a seed to fill and construct a dual-phase polycrystalline model; Randomly replace Ti atoms in the β phase with alloy element atoms according to the composition ratio of the titanium alloy to construct a dual-phase polycrystalline titanium alloy molecular dynamics model corresponding to the actual material structure; An equilibrium module: the conjugate gradient method is used for energy minimization, and the system is relaxed for 50ps under isothermal-isobaric ensemble to reach an equilibrium state; A potential function configuration module: an embedded atom potential is selected to describe the deformation behavior of titanium alloy, and a total potential energy is obtained; A boundary condition setting module: a periodic boundary condition is used to avoid surface effects; A temperature and pressure control module: for controlling the simulation temperature to be 300K under NPT ensemble and maintaining three-way pressure balance; A deformation load applying module: for applying a constant strain rate uniaxial tensile load along the z-axis under the condition of 300K, and maintaining the lateral pressure to be zero; A crystal analysis module: visual processing is performed using OVITO software to analyze the crystal structure and dislocation behavior.

[0010] In a third aspect, the present application is to provide a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program stored in the memory, the processor executes the molecular dynamics simulation method of the deformation behavior of the dual-phase polycrystalline titanium alloy according to any one or more of the above-mentioned schemes.

[0011] In a fourth aspect, the present application is to provide a computer readable storage medium for storing a computer program, wherein the computer program executes the molecular dynamics simulation method of the deformation behavior of the dual-phase polycrystalline titanium alloy according to any one or more of the above-mentioned schemes.

[0012] The present application has the following beneficial effects: The present application refers to the actual additive titanium alloy microstructure characteristics, establishes a dual-phase polycrystalline titanium alloy model with different organizational features, obtains the deformation stress-strain response curve, compares and analyzes the influence of the organizational features on the mechanical properties of the dual-phase titanium alloy, simplifies the development process of the high-performance titanium alloy, realizes the atomic scale simulation of the α / β dual-phase microstructure and the deformation behavior, and the method adopts the scheme of combining the Voronoi polycrystalline modeling and the EAM potential function, can quickly construct a complex model containing millions of atoms at a scale of 200 Å, and compared with the traditional experimental trial and error method, can shorten the development cycle of the new titanium alloy by more than 80%.

[0013] The present application analyzes the system deformation behavior dynamics characteristics, obtains the dislocation, twinning and phase transformation behavior and mechanism in the plastic deformation process of the dual-phase polycrystalline titanium alloy, reveals the relationship between the microstructure evolution and the mechanical properties of the dual-phase polycrystalline alloy from the atomic scale, and provides theoretical support for the titanium alloy microstructure design. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The α / β lamellar dual-phase structure unit model schematic diagram described in the specific embodiment of the present application is shown in the figure; Figure 2 The single-phase polycrystalline model schematic diagram described in the specific embodiment of the present application is shown in the figure; Figure 3 The dual-phase polycrystalline model schematic diagram described in the specific embodiment of the present application is shown in the figure; Figure 4 The dual-phase polycrystalline titanium alloy element distribution model schematic diagram described in the specific embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0015] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present application with unnecessary detail.

[0016] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present application with unnecessary detail.

[0017] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present application with unnecessary detail.

[0018] Embodiment one A molecular dynamics simulation method of deformation behavior of a two-phase polycrystalline titanium alloy, comprising the following steps: Step 1: According to the two-phase orientation relationship, set {110} β and {0001} α as atomically close-packed surfaces with parallel relationship, parallel to the z coordinate axis. According to the α / β crystal structure and the cell constant, the cell is expanded in the x and y directions respectively to realize the lattice length matching at the two-phase interface, and the two-phase thickness is controlled by the z direction expansion.

[0019] Step 2: Take crystal orientation [11-20], [1-100],

[0001] as x, y and z three coordinate axes, the lattice type is HCP, the size is calculated according to the expansion multiple in step 1, and the filling atom type is Ti, to establish an α single crystal model.

[0020] Step 3: Take crystal orientation [1-11], [1-1-2],

[110] as x, y and z three coordinate axes, the lattice type is BCC, the size is calculated according to the expansion multiple in step 1, and the filling atom type is Ti, to construct a β single crystal model.

[0021] Step 4: Stack the models obtained in steps 2 and 3 in the z direction to construct an α / β layered dual-phase structure unit model.

[0022] Step 5: Generate a certain number of random-orientation polycrystalline node files in a certain size box in the size box using the Voronoi method, fill the titanium single crystal as a seed into the node file, and construct a single-phase polycrystalline model. Fill the α / β lamellar dual-phase structure unit model in step 4 as a seed into the node file, and construct a dual-phase polycrystalline model.

[0023] Step 6: According to the type of titanium alloy and the proportion of each phase element, randomly replace the Ti atoms in the α phase or β phase in the model in equal proportion, and establish a dual-phase polycrystalline titanium alloy model corresponding to the actual material organization characteristics according to the actual titanium alloy organization element distribution characteristics. Step 7: Energy minimization and system relaxation: use the conjugate gradient method for energy minimization, and then relax for 50 ps under isothermal-isobaric ensemble to reach the equilibrium state.

[0024] Step 8: Potential function selection: select a potential function that can accurately describe the deformation behavior of titanium alloy, embedded atom potential (EAM) divides the total potential energy into two parts: the interaction potential between atomic nuclei located on the lattice and the embedding energy of atomic nuclei embedded in the electron cloud background, which can accurately reflect the interaction between metal particles and is suitable for metal or alloy systems. The total potential energy expression is:

[0025] Where is the embedding energy of the embedded i-th atom, is the short-range two-body potential function, is the electron density of the matrix when there is no atom i, is the distance between atoms i and j, is the electron density distribution of atom i. Step 9: Boundary condition setting: in order to avoid the introduction of the surface during relaxation and subsequent deformation behavior simulation, periodic boundary conditions are used.

[0026] Step 10: Temperature and pressure control: use NPT ensemble to control the system temperature and three-way pressure during relaxation and deformation.

[0027] Step 11: Deformation load setting: apply a constant strain rate uniaxial tensile load along the z-axis under certain environmental temperature conditions, and keep the pressure in the direction without applied strain to 0 through NPT ensemble.

[0028] Step 12: Visualization and post-processing analysis: use OVITO software to process the simulation results, display the molecular dynamics simulation process file as image information, present the particle motion trajectory in the entire dynamics process, and analyze the crystal structure and dislocation behavior.

[0029] Based on the molecular dynamics simulation method described in the embodiment, a molecular dynamics model of a dual-phase polycrystalline titanium alloy with a layered beta phase is established, and atomic-scale simulation of the deformation behavior of a single-phase polycrystalline titanium alloy and a dual-phase polycrystalline titanium alloy is carried out. By comparing the microstructure evolution mechanism and micro-dislocation behavior of models with different organizational states, the micro-mechanism of plastic deformation is further revealed, providing a feasible idea for the development and design of high-performance additive manufacturing titanium alloy materials.

[0030] Embodiment two A molecular dynamics simulation system for the deformation behavior of a dual-phase polycrystalline titanium alloy, which is realized based on the molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy described in Embodiment one, and comprises: A first modeling module for constructing a layered dual-phase structure unit molecular dynamics model, calculating the cell expansion multiple based on the lattice constants of the alpha phase and the beta phase, sequentially establishing an alpha single crystal model and a beta single crystal model and stacking them in the z direction to form an alpha / beta layered dual-phase structure unit model, and controlling the thickness ratio of the alpha phase to the beta phase to be 3:1; A second modeling module for preparing a polycrystalline titanium alloy molecular dynamics model, using the Voronoi method to generate a polycrystalline node file containing 8 randomly oriented polycrystalline nodes in a simulation box of 200Åx200Åx200Å, and filling and constructing a single-phase polycrystalline model using titanium single crystals as seeds; filling and constructing a dual-phase polycrystalline model using the layered dual-phase structure unit molecular dynamics model of S1 as seeds; randomly replacing Ti atoms in the beta phase with alloy element atoms according to the composition ratio of the titanium alloy to construct a dual-phase polycrystalline titanium alloy molecular dynamics model corresponding to the actual material organization; An equilibrium module for performing energy minimization using the conjugate gradient method and relaxing the system for 50ps under an isothermal-isobaric ensemble to achieve an equilibrium state; A potential function configuration module for describing the deformation behavior of titanium alloy using embedded atom potentials to obtain the total potential energy; A boundary condition setting module for using a full periodic boundary condition to avoid surface effects; A temperature and pressure control module for controlling the simulation temperature to be 300K under an NPT ensemble and maintaining three-way pressure balance; A deformation load applying module for applying a constant strain rate uniaxial tensile load along the z-axis under a 300K environment and maintaining the lateral pressure to be zero; A crystal analysis module for visualizing and analyzing the crystal structure and dislocation behavior using OVITO software.

Claims

1. A molecular dynamics simulation method for the deformation behavior of a two-phase polycrystalline titanium alloy, characterized in that, Includes the following steps: S1, Constructing a molecular dynamics model of a layered biphase structural unit: Based on Harmony The lattice constant of the phase is used to calculate the cell expansion factor, and then the following steps are taken to establish the lattice constant of the phase. Single crystal model and Single-crystal models are stacked in the z-direction to form Layered two-phase structural unit model, control phase and The phase thickness ratio is 3:1; S2, Preparation of a molecular dynamics model for polycrystalline titanium alloy: A polycrystalline node file with 8 random orientations was generated in a 200Å×200Å×200Å simulation box using the Voronoi method. A single-phase polycrystalline model was constructed using titanium single crystals as seeds. A two-phase polycrystalline model was constructed using the layered two-phase structure molecular dynamics model from S1 as seeds. The titanium alloy composition was then randomly replaced. Ti atoms in the phase are alloying element atoms, and a molecular dynamics model of a two-phase polycrystalline titanium alloy corresponding to the actual material microstructure is constructed. S3: The conjugate gradient method is used to minimize energy, and the system is relaxed for 50 ps under isothermal and isobaric ensemble to reach equilibrium. S4, Potential function configuration: The embedded atomic potential is used to describe the deformation behavior of the titanium alloy and obtain the total potential energy; S5, Boundary condition setting: Use fully periodic boundary conditions to avoid surface effects; S6, Temperature and Pressure Control: Under the NPT ensemble, the simulated temperature is controlled at 300K to maintain triaxial pressure balance; S7: Deformation load application: Apply a constant strain rate uniaxial tensile load along the z-axis at 300K, keeping the transverse pressure zero; S8: Use OVITO software for visualization processing to analyze crystal structure and dislocation behavior.

2. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, In S1, The cell expansion factor in the x and y directions is 4×4. The cell expansion factor in the x and y directions is 8 × 5. Harmony The cell expansion factors in the z-direction are 9 and 3, respectively.

3. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, In S1, The phase lattice type is hexagonal close-packed (HCP). The phase is body-centered cubic (BCC), and the lattice matching of the two-phase interface is achieved by adjusting the cell expansion factor of the xy plane.

4. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, In S2, Mo atoms are substituted. Titanium atoms in the phase.

5. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, The expression for the total potential energy is: ； in, The embedding energy is the energy at which the i-th atom is embedded. for When atom i is absent, the electron density of the matrix is ​​a short-range two-body potential function. The distance between atoms i and j Let i be the electron density distribution of atom i.

6. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, In S7, the constant strain rate is set to .

7. The molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy according to claim 1, characterized in that, In S8, Common Neighbor Analysis and Dislocation Extraction Algorithm are used to analyze the microstructure evolution and dislocation behavior, and twin boundaries are identified by Centroid Method.

8. A molecular dynamics simulation system for the deformation behavior of a two-phase polycrystalline titanium alloy, characterized in that, The system is based on a molecular dynamics simulation method for the deformation behavior of a dual-phase polycrystalline titanium alloy as described in any one of claims 1-7, and the system comprises: The first modeling module is used to construct molecular dynamics models of layered two-phase structural units, based on... Harmony The lattice constant of the phase is used to calculate the cell expansion factor, and then the following steps are taken to establish the lattice constant of the phase. Single crystal model and Single-crystal models are stacked in the z-direction to form Layered two-phase structural unit model, control phase and The phase thickness ratio is 3:1; The second modeling module is used to prepare molecular dynamics models of polycrystalline titanium alloys. The Voronoi method is used to generate polycrystalline node files with 8 random orientations within a 200Å×200Å×200Å simulation box. Titanium single crystals are used as seeds to construct single-phase polycrystalline models; the layered two-phase structure unit molecular dynamics model of S1 is used as a seed to construct two-phase polycrystalline models; and random replacements are made according to the titanium alloy composition ratio. Ti atoms in the phase are alloying element atoms, and a molecular dynamics model of a two-phase polycrystalline titanium alloy corresponding to the actual material microstructure is constructed. Equilibrium module: Energy is minimized using the conjugate gradient method, and the system reaches equilibrium after a 50 ps relaxation under an isothermal and isobaric ensemble. Potential function configuration module: Selects embedded atomic potential to describe the deformation behavior of titanium alloy and obtains the total potential energy; Boundary condition setting module: Employs fully periodic boundary conditions to avoid surface effects; Temperature and pressure control module: used to control the simulated temperature to 300K under the NPT ensemble and maintain triaxial pressure balance; Deformation load application module: used to apply a constant strain rate uniaxial tensile load along the z-axis in a 300K environment, while keeping the transverse pressure zero; Crystal Analysis Module: Utilizes OVITO software for visualization processing to analyze crystal structure and dislocation behavior.

9. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program. When the processor runs the computer program stored in the memory, the processor executes a molecular dynamics simulation method for the deformation behavior of a biphase polycrystalline titanium alloy according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store a computer program that executes a molecular dynamics simulation method for the deformation behavior of a biphase polycrystalline titanium alloy according to any one of claims 1-7.

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