arXiv subjects

A. V. Nazarov

Publications and source records attributed to A. V. Nazarov.

9 recordsLinked to original sources

arXiv2025

Modeling changes in atomic structure around a vacancy with increasing temperature and calculation of temperature dependences of vacancy characteristics in bcc iron

We have created an innovative natural thermostat algorithm to mimic the direct impact of temperature on interatomic distances in both a perfect crystal and a system containing a vacancy. Unlike previous research, our findings demonstrate that in a system with a defect, the radii of the initial ten coordination spheres increase almost linearly with temperature. However, the coefficients defining these dependencies, unlike those for interatomic distances farther from the vacancy, do not equal the linear thermal expansion coefficient of the perfect crystal. Knowing the atomic coordinates and their temperature evolution, we calculated the temperature dependence of the vacancy formation energy and the vacancy relaxation volume in bcc iron. The significance of these effects for the accurate calculation of atomic diffusion coefficients is analyzed and discussed.

cond-mat.mtrl-sci↗

arXiv2022

Multiscale simulation of atomic structure in the vicinity of nanovoids and evaluation of the shifting rates of the void surface elements in bcc iron and aluminum

We simulate structure in the vicinity of different size nanovoids using a new variant of the Molecular Statics, wherein atomic structure in the vicinity of nanovoids and the parameters that define the displacements of atoms placed in elastic continuum around main computation cell are determined in a self-consistent manner. Then we model structure of the surface of different crystallographic planes. Next, the kinetic equations for shifting rate of void surface elements located normal to the void surface are obtained. These equations take into account the dependence of the vacancy flux on strain and the surface energies of the crystallographic planes. In the next section, we apply the obtained expressions and simulation results to calculate the shifting rates of void surface elements for different crystallographic directions. Rates of displacements in different crystallographic directions for bcc and fcc metals differ significantly, and for the <100> direction they are greatly lower than for other directions.

cond-mat.mtrl-sci↗

arXiv2020

Molecular static simulation of edge dislocation core in bcc iron

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.

cond-mat.mtrl-sci↗

arXiv2020

Kinetics of segregation formation in elastic field of edge dislocation in bcc iron

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.

cond-mat.mtrl-sci↗

arXiv2020

Modeling the atomic structure in the vicinity of the spherical voids and calculation of void growth rate anisotropy in bcc iron and tungsten

We study the influence of the atomic structure in the vicinity of voids on their growth rate anisotropy. In the first part, we model the atomic structure in the vicinity of nanovoids in Fe and W using the advanced Molecular Statics method. In the second part, we use the earlier obtained equations that taking the influence of elastic fields into account to calculate the shifting rate of the void surface elements, and to evaluate the components of the strain tensor we use the atomic structure modeling results from the first part. The calculations are performed for voids of several sizes at certain oversaturation's in a wide temperature range. The simulation results for the mentioned metals with a bcc structure show that displacements of atoms located along the crystallographic directions of the 100, 110, 111 types in the vicinity of the voids are significantly different, and this anisotropy of atom displacements leads to a reduction of spherical symmetry for the shifting rate of the surface elements. As the result, the initially spherical void shape becomes faceted.

cond-mat.mtrl-sci↗

arXiv2019

Simulation of the atomic structure near voids and estimation of their growth rate anisotropy

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.

cond-mat.mtrl-sci↗

arXiv2019

Alternative interdiffusion theory of many component alloys

We examine the interdiffusion in multicomponent systems using the approach analogically to one developed earlier for description of interdiffusion in binary alloys. This approach in opposite to traditional theory, takes into consideration an active role of vacancies, equilibrium distribution of which is not supposed. In this case, in equations for flux components there are contributions conditioned by vacancy concentration gradient. As the vacancy diffusion coefficient is much larger than those for the components, a counteraction to this process will equalize the fluxes of components and, consequently, hinder from increase of deviation of vacancy concentration from the equilibrium one. If we substitute the expressions for fluxes in the equation of a continuity then we have the system of diffusion equations for components and vacancies. This system is solved and we have found a relation between the interdiffusion coefficients and the corresponding tracer diffusion coefficients. Interdiffusion coefficient equations sufficiently differ from traditional one (Darken's approach). The analysis of the possible reasons of sluggish diffusion in multicomponent alloys is carried out on the basis of the derived equations for fluxes.

cond-mat.mtrl-sci↗

arXiv2017

Simulation of atomic structure in the neighbourhood of nanovoids in bcc Fe

Generally displacement fields in the vicinity of voids were determined by the equations of theory of elasticity. Such a description has its disadvantages as it does not take into account the discrete atomic structure of materials and it should be expected that atom displacements in the vicinity of nanovoids should significantly differ from the predictions of mentioned theory. In our recent works a new variant of Molecular Static method was developed. In particular in this model an iterative procedure is used in which the atomic structure in the vicinity of defect and constant, determining the displacement of atoms embedded into an elastic continuum, are obtained in a self-consistent manner. In this work we use our model for investigation of the atomic structure in the vicinity of nanovoids of different sizes. Results show that the displacements are significantly different for variant crystallographic directions and these differences are particularly large in bcc metals.

cond-mat.mtrl-sci↗

arXiv2015

Kinetics of segregation formation in the vicinity of edge dislocation in fcc metals

We use new equations for the interstitial impurity diffusion fluxes under strain to study impurity atom redistribution in the vicinity of dislocations. Two levels of simulation are applied. The first one is evaluation of coefficients that determine the influence of strain tensor components on interstitial diffusion fluxes in FCC structures. For this purpose we have developed a model into the framework of a molecular static method taking into account an atom environment both near the interstitial site and for the saddle-point configuration. The second level is modeling the interstitial segregation formation based on nonlinear diffusion equations that take strains generated by defects into account. The results show that the distributions of the interstitials near the dislocations have quite complicated characters and the vacancy distribution has a qualitatively different character as compared with the carbon distribution.

cond-mat.mtrl-sci↗