Aleksandr V. Korchuganov

Features of structural changes in the near-surface aluminum layer under various schemes of ion implantation

The molecular dynamics simulation of structural rearrangements in the surface layer of aluminum samples under ion implantation of various intensities was carried out. The features of the internal structure and the crystallographic orientation of the irradiated crystallite were taken into account. To describe the interatomic interaction many-body potentials obtained in the framework of the embedded atom method were used. Irradiation of the {100} surface results in much less number of formed defects than irradiation of the {110} and {111} ones. When irradiating surfaces with beams of relatively low energy grains remain unchanged in the surface region and the formation of stacking faults was not observed. At a high intensity of irradiation, the near-surface layer of the crystallite melts. In the absence of heat removal, the centers of crystallization become grains lying on the boundary of the solid and liquid phases. Those grains increase due to the adjustment of the atoms of the liquid phase to their lattic...

Features of structural response of vanadium crystallite under deformation in different crystallographic directions

In the framework of the molecular dynamics method the features of structural rearrangements in vanadium crystallites under deformation in constrained conditions are investigated. Twins and edge dislocations are nucleated during the deformation of the crystallite. A large twin lamella is formed at stretching along the [112¯] direction. Stretching along [111] and [11¯0] results in the formation of numerous small fragments. These fragments are formed due to the growth and interaction of twins. Some of them have crystal orientations that differ from twin ones.

Role of Localized Non-Equilibrium States in Nucleation of Plastic Deformation in Nanocrystalline Materials

A molecular dynamics simulation of the behavior of nanocrystalline materials in the fields of external influences was carried out. Crystallites of the fcc copper and bcc iron under different schemes of mechanical loading were investigated. Revealed specific localized non-equilibrium states served as the mechanism of formation and evolution of partial dislocations in fcc materials and twin growth in bcc materials. These non-equilibrium states were realized on the basis of local transformation of the martensitic type when the nearest surrounding of atoms – the centers of local rearrangements – changed according to the A-B(C) scheme, where A, B and C are types of crystal lattice. The bcc-fcc-bcc local rearrangements during twin growth were typical for bcc iron. The fcc-bcc-hcp and hcp-bcc-fcc local rearrangements during the partial dislocation movement were typical for fcc copper.

Dynamics of Bicomponent Nanoparticle Formation under Metal Wire Explosion

A molecular dynamics simulation of bi-component nanoparticle formation under synchronous electric explosion of Cu and Ni wires was carried out. The approximation of the embedded atom method for a description of the interatomic interactions was used. The simulated nanowires had a cylindrical shape. Periodic boundary conditions were used along the cylinder axis, while in the other directions a free surface was simulated. Heating of the nanowires was performed by scaling of the atomic velocities following a linear law while maintaining a Maxwell distribution. It was shown that as a result of the synchronous electrical dispersion of metal wires the bi-component nanoparticles having a block structure may be formed. The basic mechanism of particle synthesis was the agglomeration of smaller clusters, and the minor one was the deposition of atoms from the gas phase on the particle surfaces. It was found that the distribution of chemical elements was non-uniform over the cross section of the synthesized particles. The concentration of Cu atoms in the subsurface region was higher than in the particle volume. It was noted that the method of molecular dynamics can effectively be used to select the optimal technological mode of producing nanoparticles with a block structure using electric explosion of metal wires.

Plastic deformation nucleation in elastically loaded CuNi alloy during nanoindentation

The molecular dynamics simulation of the behavior of elastically loaded CuNi alloy at nanoindentation is carried out. It is shown that the stoichiometric composition and the preliminary elastic deformation influence characteristics of the nucleation of plastic deformation. Under tension of specimens with a low concentration of nickel, the nucleation of plastic deformation is determined by the formation of stacking faults. The formation of nanotwins makes a significant contribution to the nucleation of plasticity at high concentrations of nickel. The increase of the degree of preliminary elastic deformation of the crystallites leads to a decrease in the depth of indentation at which structural defects start to form.

Features of structural changes in aluminum specimens with various crystallographic orientation under ion irradiation

Atomic structure changes of surface layers of aluminum crystallites after ion bombardment are studied. The molecular dynamics simulation is used for the investigation of structural changes in irradiated crystallites. The results of calculations show that orientation of the irradiated surface and preliminary elastic deformation has a significant impact on features of formation of the atomic structure in the ion-modified layer. The minimal changes in the surface layer are observed at the irradiation of surfaces with {100} lattice planes. A sufficiently great number of stacking faults was formed under irradiation of {111} and {110} surfaces. On the base of the simulation, it can be expected that the process of the surface structure fragmentation is most favorable for cases when surfaces with the {111} and {110} lattice planes are irradiated. An increase in the degree of preliminary elastic deformation can reduce the energy of incident particles, which is necessary for fragmentation of the surface structure.

Peculiarities of plastic deformation nucleation in copper under nanoindentation

The computer simulation results on the atomic structure of the copper crystallite and its behavior in nanoindentation demonstrate the key role of local structural transformations in nucleation of plasticity. The generation of local structural transformations can be considered as an elementary event during the formation of higher scale defects, including partial dislocations and stacking faults. The cause for local structural transformations, both direct fcc-hcp and reverse hcp-fcc, is an abrupt local increase in atomic volume. A characteristic feature is that the values of local volume jumps in direct and reverse structural transformations are comparable with that in melting and lie in the range 5–7%.

Plastic deformation nucleation in BCC crystallites under nanoindentation

Molecular dynamics investigation of metal crystallite with bcc lattice under nanoindentation was carried out. Potentials of interatomic interactions were calculated on the base of the approximation of the Finnis-Sinclair method. For clarity and simpler indentation data interpretation, an extended cylindrical indenter was used in the investigation. The features of the bcc iron structural response at nanoindentation of surfaces with different crystallographic orientations were revealed. Generation of structural defects in the contact zone always resulted in the decrease in the rate of growth of the reaction force.

Investigation of defect nucleation in titanium under mechanical loading

The paper undertakes a study of plastic deformation in a titanium crystallite under mechanical loading (uniaxial tension and indentation) in terms of atomic mechanisms of its generation and development. The molecular dynamics method with many-body interatomic potentials is employed. It is shown that there is a threshold strain, at which a crystal reveals the generation of local structural transformations associated with changes in atomic configurations of the first and second coordination spheres. The onset of plastic deformation in a crystallite is accompanied by a stepwise decrease in potential energy. The effect of free surfaces and grain boundaries on the generation of local structural transformations in a titanium crystallite is investigated.

Influence of crystallographic orientation on the response of copper crystallites to nanoindentation

Molecular dynamics simulation was performed to study the features of nucleation and development of plastic deformation in copper crystallites in nanoindentation with different crystallographic orientations of their loaded surface: (011), (001), and (111). Atomic interaction was described by a potential constructed in terms of the embedded atom method. It is shown that behavior of the crystallite reaction force correlates well with a change in the fraction of atoms involved in local structural rearrangements. The generation of local structural changes decreases the slope of the crystallite reaction force curve or results in an extremum due to internal stress relaxation. Analysis of structural changes in the material being indented demonstrates that the orientation of its loaded surface greatly affects the features of nucleation and development of plastic deformation.