Molecular dynamics-based evolution simulation method for point defects of different atom types under neutron irradiation

Abstract

The invention relates to a molecular dynamics-based evolution simulation method for point defects of different atom types under neutron irradiation, which comprises the following steps of: constructing irradiation simulation models of different research atom contents, and replacing a traditional experimental process with a virtual molecular dynamics simulation test on a neutron irradiation simulation model; according to the method, the defects of experiments in time and space scales are made up, meanwhile, the relation between atom types and defect numbers in the multi-component alloy with different research atom contents is obtained through molecular dynamics simulation tests, the process of generating defects of test points of irradiation damage to the multi-component alloy with different research atom contents is visually displayed, and the defect generation accuracy is improved. The influence of different elements on the radiation resistance of the alloy is known, and powerful support is provided for research on the radiation resistance of the alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular dynamics simulation calculation, and in particular to a method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics. Background Art

[0002] With the development of the fourth generation of nuclear reactors, the requirements for the performance of structural materials in reactors are becoming higher and higher. Among them, radiation resistance is one of the key factors that determine whether a material can become a structural material in a reactor. Irradiation will produce point defects in alloys, and the evolution of these point defects will significantly affect the mechanical properties, thermal properties and radiation tolerance of the material. Therefore, studying the evolution of point defects of different atomic types under neutron irradiation is of great significance for understanding and predicting the behavior of materials under irradiation.

[0003] Since the point defects caused by radiation damage to the alloy are at the nanoscale, it is difficult to observe the specific number of point defects using traditional experimental testing methods. In addition, the process of neutron radiation damage to the alloy is at the picosecond scale on a time scale. It is difficult to observe the process of point defect generation during actual testing, and it is impossible to analyze the alloy's radiation resistance from a mechanistic perspective. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to intuitively show the process of generation of point defects of different atomic types in multi-element alloys damaged by radiation, understand the influence of different elements on the radiation resistance of alloys, and provide strong support for the research on the radiation resistance of alloys.

[0005] The present invention provides a method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics, comprising: S1. According to the crystal structure and lattice constant of the multi-component alloy, multiple microstructure models of the multi-component alloy are established, the research atoms in the alloy are selected, and the content of the research atoms in each microstructure model is adjusted; S2. setting initial parameters of each microstructure model; the initial parameters include the spatial dimension of the microstructure model, the system of the microstructure model, the boundary conditions of the microstructure model, and the potential function between the studied atom and other atoms in the microstructure model; and constructing a neutron irradiation simulation model based on the initial parameters of the microstructure model; S3. Initialize the parameters of each neutron irradiation simulation model and perform relaxation operations under a canonical ensemble with equal particle number, equal volume and equal temperature; S4. Performing irradiation damage simulation on each neutron irradiation simulation model after the relaxation operation based on molecular dynamics, and outputting simulation results of irradiation simulation models with different research atomic contents; the simulation results include irradiation time, irradiation temperature, irradiation energy and coordinate positions of each atom after neutron irradiation; S5. Based on the simulation results of the irradiation simulation model with different research atomic contents, the relationship between the multi-element alloys with different research atomic contents and the number of point defects is obtained.

[0006] Compared with the prior art, the present application has the following advantages: by constructing irradiation simulation models with different research atomic contents, a virtual molecular dynamics simulation test of the neutron irradiation simulation model is used to replace the traditional experimental process to make up for the shortcomings of the experiment in time and space scales. At the same time, the relationship between the atomic type and the number of defects in the multi-component alloys with different research atomic contents is obtained through molecular dynamics simulation tests, and the process of defect generation at the test point of the multi-component alloys with different research atomic contents under irradiation damage is intuitively displayed, so as to understand the influence of different elements on the radiation resistance of the alloy and provide strong support for the research on the radiation resistance of the alloy.

[0007] In a possible implementation, the potential function between the studied atom and other atoms in the microstructure model in S2 uses a potential function of an improved embedded atomic potential to describe the interaction force between atoms, specifically including: first using a MEAM potential function to describe the non-bonded interaction of the multi-element alloy, and then using a ZBL potential function to describe the short-range force between atoms; wherein the MEAM potential function is: ; In the formula, represents the embedding energy, It is expressed as the local electron density; Represents atoms and atoms The distance between represents the energy of the interaction; The ZBL potential function is: ; In the formula, represents the electron charge, Expressed as the dielectric constant of a vacuum; Represents interacting atoms and atoms The atomic number of .

[0008] In a possible implementation manner, the initialization of parameters of each neutron irradiation simulation model in S3 specifically includes: S301. Selecting primary knockout atoms; S302. Setting the initial parameters of the primary ejected atoms, including: setting the initial movement direction of the primary ejected atoms; setting the initial energy of the primary ejected atoms; calculating the initial movement speed of the primary ejected atoms according to the initial energy; , the calculation formula is: , where is the initial energy of the primary knocked-out atom, represents Avogadro's constant, It represents the molar mass of the primary knocked-out atom.

[0009] In a possible implementation, before performing the relaxation operation in the canonical ensemble of equal particle number, equal volume and equal temperature in S3, the step size, relaxation time and relaxation temperature of the relaxation operation are defined to simulate a real reactor environment.

[0010] In a possible implementation, the radiation damage simulation in S4 uses a microcanonical ensemble with equal particle number, equal volume and equal energy.

[0011] In a possible implementation manner, before the radiation damage simulation in S4, the time step of the radiation damage process and the radiation damage simulation time are defined. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 Schematic diagram of Zr-1Nb-xTi model with different Ti contents in a specific embodiment of the present invention; Figure 3 A defect number-time curve diagram obtained for a specific embodiment of the present invention; Figure 4 A schematic diagram of the number of Nb defects in the Zr-1Nb-xTi alloy irradiation damage test in a specific embodiment of the present invention; Figure 5 It is a schematic diagram of the number of Ti defects in the radiation damage test of Zr-1Nb-xTi alloy in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0013] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0014] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0015] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0016] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] See also Figure 1 As shown, the embodiment of the present application discloses a method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics, including: S1. According to the crystal structure and lattice constant of the multi-component alloy, multiple microstructure models of the multi-component alloy are established by Large-scale Atomic Molecular Massively Parallel Simulator (LAMMPS) software, the research atoms in the alloy are selected, and the content of the research atoms in each microstructure model is adjusted; Regarding the method for establishing the microstructure model of the multi-component alloy, this specific embodiment first pre-constructs a model of a single atom type according to the crystal structure and lattice constant of the multi-component alloy, and then adds other atoms in the multi-component alloy to the model by a random replacement method to obtain a microstructure model; then, a control experiment is carried out according to adjusting the content of the research atoms in each microstructure model; after the construction is completed, it is output in the form of a data file for easy calling.

[0018] S2. Set the initial parameters of each microstructure model; the initial parameters include the spatial dimension of the microstructure model, the system of the microstructure model, the boundary conditions of the microstructure model, and the potential function between the studied atom and other atoms in the microstructure model; and construct a neutron irradiation simulation model based on the initial parameters of the microstructure model; wherein, regarding the potential function between the studied atom and other atoms in the microstructure model, the potential function of the improved embedded atomic potential is used to describe the interaction force between atoms, specifically including: first using the MEAM potential function to describe the non-bonded interaction of the multi-element alloy, and then using the ZBL potential function to describe the short-range interaction force between atoms; wherein, the MEAM potential function is: ; In the formula, represents the embedding energy, It is expressed as the local electron density; Represents atoms and atoms The distance between represents the energy of the interaction; The ZBL potential function is: ; In the formula, represents the electron charge, Expressed as the dielectric constant of a vacuum; Represents interacting atoms and atoms The atomic number of .

[0019] S3. Initialize the parameters of each neutron irradiation simulation model and perform relaxation operation under a canonical ensemble with equal particle number, equal volume and equal temperature; wherein the parameters of each neutron irradiation simulation model are initialized including: S301. Selecting primary knockout atoms; S302. Setting the initial parameters of the primary ejected atoms, including: setting the initial movement direction of the primary ejected atoms; setting the initial energy of the primary ejected atoms; calculating the initial movement speed of the primary ejected atoms according to the initial energy; , the calculation formula is: , where is the initial energy of the primary knocked-out atom, represents Avogadro's constant, represents the molar mass of the primary knocked-out atom; In addition, before performing the relaxation operation, the step size, relaxation time and relaxation temperature of the relaxation operation are defined to simulate the real reactor environment.

[0020] S4. Perform radiation damage simulation on each neutron irradiation simulation model after relaxation operation based on molecular dynamics, and output simulation results of radiation simulation models with different research atomic contents; the simulation results include irradiation time, irradiation temperature, irradiation energy and the coordinate position of each atom after neutron irradiation; define the time step of the radiation damage process and the radiation damage simulation time before the radiation damage simulation; and use a microcanonical ensemble with equal particle number, equal volume and equal energy to simulate radiation damage.

[0021] S5. Based on the simulation results of the irradiation simulation model with different research atomic contents, the relationship between the multi-element alloys with different research atomic contents and the number of point defects is obtained.

[0022] The following will use the molecular dynamics simulation calculation example of the Zr-1Nb-xTi alloy irradiation damage test to specifically illustrate the molecular dynamics-based simulation method of point defect evolution of different atomic types under neutron irradiation, including: S1. Use LAMMPS software to construct the microstructure model of Zr-1Nb-xTi, including: The hcp-Zr unit cell was constructed with lattice constants a=3.24 Å and c=5.17 Å. The unit cell was supercelled according to the different Ti contents in the multi-element alloy; then the Nb atoms and Ti atoms were randomly substituted to replace the Zr atoms in the microstructure model after the supercell, and the models of Zr-1Nb, Zr-1Nb-0.3Ti, Zr-1Nb-1.5Ti and Zr-1Nb-3Ti were completed, as shown in Figure 2 As shown; finally, the constructed model is output in the form of a data file.

[0023] S2. Set the initial parameters of the microstructure model in LAMMPS, including: (1) Set the unit of the model system to metal. (2) Set the spatial dimension of the model to 3D; (3) Setting boundary conditions to be periodic boundaries (p boundaries) in the x, y, and z directions; (4) Using the potential function of the improved atomic potential to describe the interaction between atoms includes first using the MEAM potential function to describe the non-bonded interaction of the material, and then using the ZBL potential function to describe the short-range force between atoms; wherein the MEAM potential function is defined as: ; In the formula, represents the embedding energy, It is expressed as the local electron density; Represents atoms and atoms The distance between represents the energy of the interaction; The ZBL potential function is: ; In the formula, represents the electron charge, Expressed as the dielectric constant of a vacuum; Represents interacting atoms and atoms Atomic number; (5) Read in the data file of the radiation damage test model constructed in the first step and generate the neutron irradiation simulation model.

[0024] S3. Initialize the parameters of each neutron irradiation simulation model, including: S301. Define the central atom in the model as the primary knockout atom (PKA); S302. Define the initial energy of PKA as 10 KeV; The initial movement direction of PKA was set to the

[001] direction; The initial energy of PKA is brought into the solution equation to calculate the initial velocity of PKA to be 1858.45Å / ps. The solution equation is: ; In the formula, is the initial energy of the primary knocked-out atom, represents Avogadro's constant, represents the molar mass of the primary knocked-out atom; Then, relaxation operations are performed in a canonical ensemble with equal particle number, equal volume and equal temperature; specifically, the relaxation operations include: The step size during the relaxation process is defined as 0.001ps; The relaxation time is defined as 20,000 steps, and the entire relaxation time is 20 ps according to the relaxation time step; The relaxation temperature is defined as 600K to simulate the real reactor environment; The ensemble used in the relaxation process is defined as a canonical ensemble (NVT) with equal particle numbers, equal volumes, and equal temperatures; Define to output time, temperature, energy and coordinate position of each atom every 1000 steps; After relaxation operation in a canonical ensemble with equal particle number, equal volume and equal temperature, the neutron irradiation simulation model reaches equilibrium; then the irradiation damage simulation is carried out, including: The time step in the irradiation damage process is defined as 0.0001ps to ensure that the atomic information in the simulation process can be fully obtained; The simulation time of radiation damage is defined as 300,000 steps. According to the time step of radiation damage, the whole radiation damage time is 30ps. The ensemble used in the radiation damage process is defined as the microcanonical ensemble (NVE) with equal particle numbers, equal volumes and equal energy; The time scale of the radiation damage test is at the picosecond level. Considering that the atoms move too fast during the collision process, in order to ensure the calculation accuracy of force and energy during the test, the time step needs to be controlled according to the distance of atomic movement. Here, the atomic movement distance in a time step is set to no more than 0.005 times the lattice constant. To ensure the accuracy of the simulation, the same model was simulated 10 times.

[0025] S4. Perform molecular dynamics simulation according to the calculation parameters set in S301, and then output the time, temperature, energy and coordinate position of each atom. The atomic position information obtained by the molecular dynamics simulation is used to dynamically display the entire Zr-1Nb-xTi alloy irradiation damage test process through OVITO software. According to the obtained simulation results, the number of point defects of the Zr-1Nb-xTi alloy with different Ti contents is obtained, specifically including: (1) Use the “Wigner-Seitz defect analysis” module to identify point defects inside the alloy during the radiation damage simulation; (2) Use the "Delete selected" module to delete atoms that are not damaged by irradiation, so as to more intuitively observe the number and distribution of point defects in the alloy; (3) Use the "Expression selection" module to filter the atom types and obtain the number of Nb defects and Ti defects in point defects; (4) The “Expression selection” module is used to distinguish the interstitial atoms and vacancies in point defects. The number of Nb interstitial atoms, Nb vacancies, Ti interstitial atoms, and Ti vacancies in point defects are obtained respectively, which facilitates the analysis of the effect of Ti element on the radiation resistance of the alloy.

[0026] S5. Calculate the average value and error of the 10 simulation data obtained in step 4, import them into Origin software for plotting, and obtain the corresponding defect number-time curve, such as Figure 4 As shown; and the number of Nb defects and the number of Ti defects in point defects (point defects are composed of interstitial atoms and vacancies), as shown Figure 5 shown.

[0027] Finally, according to the defect number-time curve obtained by S5 and the number of Nb defects and Ti defects, a systematic conclusion is put forward on the effect of Ti element on the radiation resistance of Zr-1Nb-xTi alloy, including: (1) At the peak, the number of point defects in Zr-1Nb alloy is the smallest, and the number of point defects increases with the increase of Ti content. Compared with other alloys, Zr-1Nb alloy has the least number of residual point defects after the radiation damage test. The addition of the same Ti element increases the number of residual point defects after the radiation damage test, reducing the radiation resistance of Zr-1Nb-xTi alloy; (2) After the addition of Ti, the number of Nb interstitial atoms remaining after the radiation damage test was significantly reduced, while the number of residual Ti interstitial atoms increased proportionally with the increase of Ti content, indicating that Ti atoms are more likely to generate defects during the radiation damage process than Zr and Nb atoms; (3) After the addition of Ti, the number of Nb vacancies remaining after the radiation damage test increases with the increase of Ti content, while the number of residual Ti vacancies is almost 0, indicating that compared with the interstitial atoms of Zr and Nb, which are easier to recombine with Ti vacancies during the radiation damage process, it is difficult for Ti interstitial atoms to recombine with Zr and Nb vacancies; (4) Based on the above conclusions, it can be concluded that the addition of Ti element reduces the radiation resistance of Zr-1Nb-xTi alloy.

[0028] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms such as "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description, and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present application.

[0029] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0030] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics, characterized in that: include: S1. According to the crystal structure and lattice constant of the multi-component alloy, multiple microstructure models of the multi-component alloy are established, the research atoms in the alloy are selected, and the content of the research atoms in each microstructure model is adjusted; S2. setting initial parameters of each microstructure model; the initial parameters include the spatial dimension of the microstructure model, the system of the microstructure model, the boundary conditions of the microstructure model, and the potential function between the studied atom and other atoms in the microstructure model; and constructing a neutron irradiation simulation model based on the initial parameters of the microstructure model; S3. Initialize the parameters of each neutron irradiation simulation model and perform relaxation operations under a canonical ensemble with equal particle number, equal volume and equal temperature; S4. Performing irradiation damage simulation on each neutron irradiation simulation model after the relaxation operation based on molecular dynamics, and outputting simulation results of irradiation simulation models with different research atomic contents; the simulation results include irradiation time, irradiation temperature, irradiation energy and coordinate positions of each atom after neutron irradiation; S5. Based on the simulation results of the irradiation simulation model with different research atomic contents, the relationship between the multi-element alloys with different research atomic contents and the number of point defects is obtained.

2. The method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics according to claim 1, characterized in that: The potential function between the studied atoms and other atoms in the microstructure model in S2 adopts the potential function of the improved embedded atomic potential to describe the interaction force between atoms, specifically including: first using the MEAM potential function to describe the non-bonded interaction of the multi-element alloy, and then using the ZBL potential function to describe the short-range force between atoms; wherein the MEAM potential function is: ； In the formula, represents the embedding energy, It is expressed as the local electron density; Represents atoms and atoms The distance between represents the energy of the interaction; The ZBL potential function is: ； In the formula, represents the electron charge, Expressed as the dielectric constant of a vacuum; Represents interacting atoms and atoms The atomic number of .

3. The method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics according to claim 1, characterized in that: The parameters of each neutron irradiation simulation model are initialized in S3, specifically including: S301. Selecting primary knockout atoms; S302. Setting the initial parameters of the primary ejected atoms, including: setting the initial movement direction of the primary ejected atoms; setting the initial energy of the primary ejected atoms; calculating the initial movement speed of the primary ejected atoms according to the initial energy; , the calculation formula is: , where is the initial energy of the primary knocked-out atom, represents Avogadro's constant, It represents the molar mass of the primary knocked-out atom.

4. The method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics according to claim 1, characterized in that: In S3, before performing the relaxation operation under the canonical ensemble of equal particle number, equal volume and equal temperature, the step size, relaxation time and relaxation temperature of the relaxation operation are defined to simulate the real reactor environment.

5. The method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics according to claim 1, characterized in that: The radiation damage simulation in S4 adopts a microcanonical ensemble with equal particle number, equal volume and equal energy.

6. The method for simulating the evolution of point defects of different atomic types under neutron irradiation based on molecular dynamics according to claim 1, characterized in that: Before the radiation damage simulation in S4, the time step of the radiation damage process and the radiation damage simulation time are defined.

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