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A Arjhangmehr - One of the best experts on this subject based on the ideXlab platform.

  • atomistic investigation of cr influence on primary radiation damage in fe 12 at cr grain boundaries
    Modelling and Simulation in Materials Science and Engineering, 2016
    Co-Authors: A Esfandiarpour, S A H Feghhi, A Arjhangmehr
    Abstract:

    In this paper, we investigate the influence of Cr on the primary radiation damage in Fe-12 at.% Cr with different atomic grain boundaries (GBs). Four different GB structures, two twists and two symmetric tilt boundaries are selected as the model structures. The primary radiation damage near each GB in α-Fe and Fe-12 at.% Cr is simulated using Molecular Dynamics for 9 keV primary knock-on atoms with velocity vectors perpendicular to the GB plane. In agreement with previous works, the results indicate that the atomic GBs are biased toward interstitials and due to the reduction of 'in-cascade' interstitial-vacancy annihilation rates, vacancies accumulate in the bulk grains. The minimum defect production occurs when the overlap between cascade center and GB plane is maximum; in contrast, the number of residual defects in the bulk (vacancies and interstitials) increases when the overlap decreases. Moreover, we find that the presence of Cr hardly affects the number of residual defects in the grain interiors, and causes a Cr-enrichment in the surviving self-interstitial atoms in bulk during relaxation of the primary cascades—also in agreement with previous studies. Further, in order to study the effect of 12 at.% Cr on the energetic and kinetic properties of vacancies near the atomic GBs, we calculate formation energies and diffusion barriers of defects using Molecular Static and climbing-Nudged Elastic Band methods. The results reveal that the vacancies energetically and kinetically tend to form and cluster around the GB plane due to the substantial reduction of their formation energies and migration barriers in layers close to the GB center and are immobile on the simulated time frame (~ps).

A Esfandiarpour - One of the best experts on this subject based on the ideXlab platform.

  • atomistic investigation of cr influence on primary radiation damage in fe 12 at cr grain boundaries
    Modelling and Simulation in Materials Science and Engineering, 2016
    Co-Authors: A Esfandiarpour, S A H Feghhi, A Arjhangmehr
    Abstract:

    In this paper, we investigate the influence of Cr on the primary radiation damage in Fe-12 at.% Cr with different atomic grain boundaries (GBs). Four different GB structures, two twists and two symmetric tilt boundaries are selected as the model structures. The primary radiation damage near each GB in α-Fe and Fe-12 at.% Cr is simulated using Molecular Dynamics for 9 keV primary knock-on atoms with velocity vectors perpendicular to the GB plane. In agreement with previous works, the results indicate that the atomic GBs are biased toward interstitials and due to the reduction of 'in-cascade' interstitial-vacancy annihilation rates, vacancies accumulate in the bulk grains. The minimum defect production occurs when the overlap between cascade center and GB plane is maximum; in contrast, the number of residual defects in the bulk (vacancies and interstitials) increases when the overlap decreases. Moreover, we find that the presence of Cr hardly affects the number of residual defects in the grain interiors, and causes a Cr-enrichment in the surviving self-interstitial atoms in bulk during relaxation of the primary cascades—also in agreement with previous studies. Further, in order to study the effect of 12 at.% Cr on the energetic and kinetic properties of vacancies near the atomic GBs, we calculate formation energies and diffusion barriers of defects using Molecular Static and climbing-Nudged Elastic Band methods. The results reveal that the vacancies energetically and kinetically tend to form and cluster around the GB plane due to the substantial reduction of their formation energies and migration barriers in layers close to the GB center and are immobile on the simulated time frame (~ps).

  • effects of atomic grain boundary structures on primary radiation damage in α fe
    Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2015
    Co-Authors: A Esfandiarpour, S A H Feghhi, A A Shokri
    Abstract:

    Abstract In this paper, we used five different grain boundary (GB) structures including two twists, two symmetric tilts and one asymmetric tilt for α-Fe, in order to study the influence of different GB structures on the production and time evolution of defects. Energetic behavior of point defects near GBs is investigated and analyzed using Molecular Static (MS) method to calculate and compare the “defect absorbency” of each structure. The primary radiation damage state near each GB structure is simulated using Molecular Dynamic (MD) method for 3 keV and 6 keV primary-knocked on atom (PKA) with velocity vector perpendicular to the GB plane at various distances in 300 K. We found that all five GB structures can decrease the defect number in bulk region, if cascade center locates on the GB plane (prefect overlap) and increase the vacancy number, if the overlap is imperfect. This depends on the energy of PKA and its distance from GB plane. Also, the results proved that the magnitude of the observed variations depends on the atomic structure of GB. Furthermore, the GBs that have stronger “interstitial absorbency” produce an excess concentration of vacancies in the bulk region, while the edge of the cascades overlaps with GB plane. This is the result of bigger “interstitial absorbency” of GBs in comparison with vacancies.

Andrei V. Nazarov - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Static simulation of edge dislocation core in bcc iron
    arXiv: Materials Science, 2020
    Co-Authors: A A Gusev, Andrei V. Nazarov
    Abstract:

    We simulate the dislocation core structure in bcc iron using the modified Molecular Static method. A feature of this method is the application of an iterative procedure in which the atomic structure in the vicinity of the defect and the constants that determine the displacements of atoms immersed in the elastic continuum are calculated in a self-consistent manner. Following the mentioned approach, we develop a model for calculating the atomic structure of edge dislocations, taking into account the anisotropy of the elastic medium surrounding the main calculation cell. Anisotropy is taken into account by introducing an explicit angular dependence for the parameters of the elastic field created by the dislocation: magnitude of Burgers vector and Poisson's ratio. Simulation is carried out for a split dislocation with Burgers vector along [100]. The convergence of the iterative algorithm is shown and the influence of the computational cell size on the results is considered. Calculated results are: atomic structure of dislocation in bcc iron, angular dependence of the parameters describing the elastic dislocation field at large distances from the dislocation line, and the strain tensor components in the entire simulation area.

  • Molecular Static simulation of edge dislocation core in bcc iron
    arXiv: Materials Science, 2020
    Co-Authors: A A Gusev, Andrei V. Nazarov
    Abstract:

    We simulate the dislocation core structure in bcc iron using the modified Molecular Static method. A feature of this method is the application of an iterative procedure in which the atomic structure in the vicinity of the defect and the constants that determine the displacements of atoms immersed in the elastic continuum are calculated in a self-consistent manner. Following the mentioned approach, we develop a model for calculating the atomic structure of edge dislocations, taking into account the anisotropy of the elastic medium surrounding the main calculation cell. Anisotropy is taken into account by introducing an explicit angular dependence for the parameters of the elastic field created by the dislocation: magnitude of Burgers vector and Poisson's ratio. Simulation is carried out for a split dislocation with Burgers vector along [100]. EAM interatomic potential is used. The convergence of the iterative algorithm is shown and the influence of the computational cell size on the results is considered. Calculated results are: atomic structure of dislocation in bcc iron, angular dependence of the parameters describing the elastic dislocation field at large distances from the dislocation line, and the strain tensor components in the entire simulation area.

  • Simulation of Atomic Structure Near Nanovoids in BCC Iron
    KnE Materials Science, 2018
    Co-Authors: Andrei V. Nazarov, I. V. Ershova, Y. S. Volodin
    Abstract:

    Generally, displacement fields near voids are determined by the equations of elasticity theory. Such a description has its disadvantages as it does not take into account the discrete atomic structure of materials. In this work, we use a new variant of Molecular Static method for investigation of the atomic structure near nanovoids. In our model an iterative procedure is employed, in which the atomic structure in the void vicinity and the parameter determining the displacement of atoms embedded into an elastic continuum are obtained in a self-consistent manner.  Results show that the displacements are significantly different for varies crystallographic directions.

S A H Feghhi - One of the best experts on this subject based on the ideXlab platform.

  • atomistic investigation of cr influence on primary radiation damage in fe 12 at cr grain boundaries
    Modelling and Simulation in Materials Science and Engineering, 2016
    Co-Authors: A Esfandiarpour, S A H Feghhi, A Arjhangmehr
    Abstract:

    In this paper, we investigate the influence of Cr on the primary radiation damage in Fe-12 at.% Cr with different atomic grain boundaries (GBs). Four different GB structures, two twists and two symmetric tilt boundaries are selected as the model structures. The primary radiation damage near each GB in α-Fe and Fe-12 at.% Cr is simulated using Molecular Dynamics for 9 keV primary knock-on atoms with velocity vectors perpendicular to the GB plane. In agreement with previous works, the results indicate that the atomic GBs are biased toward interstitials and due to the reduction of 'in-cascade' interstitial-vacancy annihilation rates, vacancies accumulate in the bulk grains. The minimum defect production occurs when the overlap between cascade center and GB plane is maximum; in contrast, the number of residual defects in the bulk (vacancies and interstitials) increases when the overlap decreases. Moreover, we find that the presence of Cr hardly affects the number of residual defects in the grain interiors, and causes a Cr-enrichment in the surviving self-interstitial atoms in bulk during relaxation of the primary cascades—also in agreement with previous studies. Further, in order to study the effect of 12 at.% Cr on the energetic and kinetic properties of vacancies near the atomic GBs, we calculate formation energies and diffusion barriers of defects using Molecular Static and climbing-Nudged Elastic Band methods. The results reveal that the vacancies energetically and kinetically tend to form and cluster around the GB plane due to the substantial reduction of their formation energies and migration barriers in layers close to the GB center and are immobile on the simulated time frame (~ps).

  • effects of atomic grain boundary structures on primary radiation damage in α fe
    Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2015
    Co-Authors: A Esfandiarpour, S A H Feghhi, A A Shokri
    Abstract:

    Abstract In this paper, we used five different grain boundary (GB) structures including two twists, two symmetric tilts and one asymmetric tilt for α-Fe, in order to study the influence of different GB structures on the production and time evolution of defects. Energetic behavior of point defects near GBs is investigated and analyzed using Molecular Static (MS) method to calculate and compare the “defect absorbency” of each structure. The primary radiation damage state near each GB structure is simulated using Molecular Dynamic (MD) method for 3 keV and 6 keV primary-knocked on atom (PKA) with velocity vector perpendicular to the GB plane at various distances in 300 K. We found that all five GB structures can decrease the defect number in bulk region, if cascade center locates on the GB plane (prefect overlap) and increase the vacancy number, if the overlap is imperfect. This depends on the energy of PKA and its distance from GB plane. Also, the results proved that the magnitude of the observed variations depends on the atomic structure of GB. Furthermore, the GBs that have stronger “interstitial absorbency” produce an excess concentration of vacancies in the bulk region, while the edge of the cascades overlaps with GB plane. This is the result of bigger “interstitial absorbency” of GBs in comparison with vacancies.

Nazarov A. - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Static simulation of edge dislocation core in bcc iron
    'IOP Publishing', 2020
    Co-Authors: Gusev A. A., Nazarov A.
    Abstract:

    We simulate the dislocation core structure in bcc iron using the modified Molecular Static method. A feature of this method is the application of an iterative procedure in which the atomic structure in the vicinity of the defect and the constants that determine the displacements of atoms immersed in the elastic continuum are calculated in a self-consistent manner. Following the mentioned approach, we develop a model for calculating the atomic structure of edge dislocations, taking into account the anisotropy of the elastic medium surrounding the main calculation cell. Anisotropy is taken into account by introducing an explicit angular dependence for the parameters of the elastic field created by the dislocation: magnitude of Burgers vector and Poisson's ratio. Simulation is carried out for a split dislocation with Burgers vector along [100]. The convergence of the iterative algorithm is shown and the influence of the computational cell size on the results is considered. Calculated results are: atomic structure of dislocation in bcc iron, angular dependence of the parameters describing the elastic dislocation field at large distances from the dislocation line, and the strain tensor components in the entire simulation area.Comment: 6 pages, 6 figure

  • Kinetics of segregation formation in elastic field of edge dislocation in bcc iron
    2020
    Co-Authors: Gusev A. A., Nazarov A.
    Abstract:

    We study the kinetics of the redistribution of impurity atoms in the elastic fields of dislocations by computer simulation methods. A work consists of several stages. The first is the simulation of a dislocation core structure with a Burgers vector along [100] direction by using the modified Molecular Static method. The second is obtaining the coefficients that determine the influence of the components of the strain tensor on the diagonal elements of the matrix of diffusion coefficients and in the equations for fluxes of carbon atoms in bcc iron. The third stage is associated with modeling the diffusion characteristics of carbon atoms by the method of Molecular dynamics in a crystal without defects. The fourth and final stage uses the data about atomic structure that we obtained at first stage, as well as the characteristics calculated in the second and third, is a simulation of the formation of segregations of interstitial atoms, which is based on solving diffusion equations that take into account the elastic deformations created by the dislocation. The complex of developed models is used to analyze the kinetics of segregation formation. 3D graphs illustrate the distribution of interstitial atoms in the vicinity of a dislocation for different times at certain temperatures.Comment: 7 pages, 2 figure

  • Simulation of the atomic structure near voids and estimation of their growth rate anisotropy
    'Elsevier BV', 2019
    Co-Authors: Nazarov A., Mikheev A. A., Melnikov A. P.
    Abstract:

    We use a new variant of Molecular Static method for simulation of the atomic structure near nanovoids. In our model an iterative procedure is employed, in which the atomic structure in the void vicinity and the parameter determining the displacement of atoms embedded into an elastic continuum are obtained in a self-consistent manner. Results show that the atom displacements near nanovoids are significantly different for varies crystallographic directions in bcc metals. Not long ago we have obtained an equation of vacancy diffusion under strain. Now we use this equation and the atom displacements near nanovoids to evaluate shift of the void surface for varies crystallographic directions. We find the equation for the normal component of the vacancy flux to the surface of the sphere for some crystallographic directions and then calculate shifting rate of the void surface element in mentioned directions for the different supersaturations of the vacancies as a function of temperature.Comment: 11 pages, 7 figure