Papers by Author: Andrei V. Nazarov

Abstract: Elastic fields, generating by precipitates, cracks, dislocations and other defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic, segregation formation and changes of the alloy properties. However, understanding the effects of strain on diffusion in solids is now limited. One of the chief aims of our approach is to obtain the general equations for the diffusion fluxes under strain that give the possibility of using these equations at low temperatures, as in this case, the strain influence on the diffusion fluxes is manifested in maximal degree. Recently some important generalization of our approach was done and equations for the vacancy fluxes in cubic metals were obtained. Now we have made the next step in the development of approach: general equations for the fluxes in interstitial alloys are obtained for different kinds of jumps in bcc and fcc structures. We are going to discuss the main features of the theory of diffusion under stress, to compare the equations for the fluxes and to present results of theory applications that are obtained with the help of computer simulations.

Abstract: Our recent model has been used to evaluate the point defect characteristics including those determining the effect of pressure on the concentration of vacancies, di-vacancies, interstitials and their diffusion mobility in set of BCC and FCC metals. Our model has been developed to calculate temperature dependences of mentioned features. In contrast to other studies, the vacancy migration volumes have been found for all the metals studied.

Abstract: This work is devoted to simulation of potential barrier spectrum for hydrogen atom and vacancy jumps in fcc- and bcc- metals taking into account the mutual effect of the point defects on the potential barrier spectrum and as a result the effect on complex defect diffusion in bcc- and fccmetals. The molecular static and the Monte Carlo methods are used. The developed model allows us to determine a diffusion coefficient of the impurity atom depending on temperature and other parameters. The simulation of point defect random walk in lattice on the basis MC-method and potential barrier spectrum has gave an impulse toward an understanding of hydrogen motion on the atomic scale in metals, which is required to determine such important parameters as the diffusion coefficient of H. As well it allows us to understand reasons of more complicated behaviour of H in realistic metal in comparison with perfect metal.

Abstract: This work is devoted to the study of the point defect diffusion features in metals. In particular, we propose the model, which allows calculating activation volumes that describe the influence of pressure on the diffusion processes in solids. Our model realizes a new approach that makes it possible to self-consistently determine atomic structure near defect and constants characterizing the displacement of atoms in an elastic matrix around computational cell. Also we take into consideration that the energy of perfect system and system with a defect differently depends on the outer pressure, and this gives an addition to the values of migration and formation volumes. This addition can comprise a considerable part of activation volume. Moreover, we take into account that the atomic jump is a momentary process and so we carry out only partial relaxation of the atomic structure in the vicinity of a defect. The formation and migration energies and formation and migration volumes have been calculated for vacancies, di-vacancies and interstitials in bcc iron and tungsten using pair and many-body potentials.

Abstract: This work is devoted to the simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into consideration these factors. It allows defining the “fine structure” of displacement atoms near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration energies and volumes of defect. Also we take into consideration that the energy of system (in particular the system with defect) depends on the external pressure. This dependence gives an addition to the values of migration and formation volumes.

Abstract: This work is devoted to simulation of the diffusion features of point defects in bcc metals. The properties of point defects have been investigated with the usage of many-body interatomic potentials. This approach, based on the density-functional theory, permitted us to derive more adequate diffusion features of solids. This investigation is carried out within the framework of the Finnis-Sinclair formalism, developed for an assembly of N atoms and represents the secondmoment approximation of the tight-binding theory. We used a new model, based on the molecular static method for simulating the atomic structure near the defect and vacancy migration in pure metals. This approach gives the opportunity to simulate the formation and the migration volumes of the point defects, taking into consideration the influence of pressure on structure and consequently on energy. The diffusion characteristics of bcc α-Fe and anomalous β-Zr have been investigated.

Abstract: This work is devoted to simulation of interstitial atom diffusion in fcc metals with point defects. We used the molecular static and the Monte Carlo methods. An activation barrier set for different configurations of the carbon–vacancy complexes is simulated by the method of the molecular static (MS). Then we calculate atom jump rates for these configurations. The simulation of the carbon and vacancy migration in an fcc metal is realized on the basis of obtained atom jump rates by using the Monte-Carlo (MC) method. In particular, the calculations were made for the system of the nickel-carbon. In the result of that interstitial atom diffusion coefficient has been obtained at different temperatures.