Konstantin P. Zolnikov

Dynamic vortex defects in deformed material

The paper studies the generation and evolution of dynamic vortex structures in a material on different structural scales. It is shown that the generation of dynamic vortex structures can be the main accommodation mechanism in a material under external mechanical loading. On the microscale, these structures can provide inter-granular sliding and grain boundary migration with anomalously high rates. On higher structural scales, their evolution can be the main process responsible for nucleation and propagation of cracks, fragmentation of material, formation of a “quasiliquid” layer in friction pairs, etc. The data and conclusions derived from the study are confirmed by numerical calculations for different types of materials in the framework of molecular dynamics and movable cellular automaton methods.

MD simulation of plastic deformation nucleation in stressed crystallites under irradiation

The investigation of plastic deformation nucleation in metals and alloys under irradiation and mechanical loading is one of the topical issues of materials science. Specific features of nucleation and evolution of the defect system in stressed and irradiated iron, vanadium, and copper crystallites were studied by molecular dynamics simulation. Mechanical loading was performed in such a way that the modeled crystallite volume remained unchanged. The energy of the primary knock-on atom initiating a cascade of atomic displacements in a stressed crystallite was varied from 0.05 to 50 keV. It was found that atomic displacement cascades might cause global structural transformations in a region far larger than the radiation-damaged area. These changes are similar to the ones occurring in the process of mechanical loading of samples. They are implemented by twinning (in iron and vanadium) or through the formation of partial dislocation loops (in copper).

Local structural transformations in copper crystallites under nanoindentation

A molecular-dynamic simulation of the response of a copper crystallite at the atomic level at local contact interaction has been performed. The calculation results have shown that plastic deformation is nucleated and developed according to the mechanism of generation of local structural transformations, which, in turn, give rise to higher level defects (dislocations, stacking faults, interfaces, etc.). During loading, the formed structural defects pass from the contact region into the crystallite bulk and, when emerging on the free surface, change its shape.

Evolution of atomic collision cascades in vanadium crystal with internal structure

The formation of radiation-damage regions (radiation-damage cascades) in vanadium crystallites with internal structures (intergrain boundary) has been simulated by the molecular-dynamic method. The interatomic interaction is described within the embedded-atom method. A relatively small number of clusters of intrinsic point defects (vacancies and self-interstitial atoms) are formed both in ideal vanadium crystallites and in crystallites with boundaries after the relaxation of atomic-displacement cascades. The evolutionary character of atomic-displacement cascades is determined in many respects by the presence of extended boundaries in materials. The intergrain boundaries hinder the propagation of atomic-displacement cascades and store many radiation-induced defects.

MD simulation of primary radiation damage in metals with internal structure

A review on simulation of the primary radiation damage (PRD) and formation of radiation defects by atomic displacement cascades is conducted. Results of the simulation by the molecular dynamics method of the atomic displacement cascades and peculiarities of their interaction with the defects of the internal crystal structure (point defect, pores, dislocations, grain boundaries (GBs), and free surfaces) are given. It is shown that the defects exert a significant impact on the evolution of the atomic displacement cascades and formation of the PRD in metals.

Structural Response of Metal Crystallite with BCC Lattice on Atomic Level 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 embedded atom method. The potentials chosen make it possible to describe with a high accuracy the elastic and surface properties of the simulated metal and energy parameters of defects, which is important for solution of the task posed in the work. For clarity and simpler indentation data interpretation, an extended cylindrical indenter was used in the investigation and loading was realized by its lateral surface. The simulated crystallite had a parallelepiped shape. The loaded plane of crystallite was modeled as a free surface while the positions of atoms in the opposite plane of crystallite were fixed along the indentation direction. Other planes of crystallite were simulated as free surfaces. The indenter velocity varied from 5 to 25 m/s in different calculations. The loading of the model crystallite was realized at 300 K. Influence of interfaces (free surfaces and grain boundaries) on peculiarities of plastic deformation nucleation and interactions of generated structural defects with interfaces in simulated crystallite under nanoindentation were investigated.

Molecular-dynamics study of crystal structure defect formation by the thermal fluctuation mechanism during high-rate deformation

The possibility of structural defect generation in materials with the ideal crystal lattice under dynamic loading conditions in a broad temperature range has been studied by means of molecular dynamics using the embedded atom method with many-body interatomic interaction potentials. It is shown that thermal fluctuations can lead to a jumplike nucleation of defects in the ideal crystal under high-rate deformation conditions. Features of the defect nucleation via this mechanism are analyzed for various temperatures and loading regimes.

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.

Computer simulation of metal wire explosion under high rate heating

Synchronous electric explosion of metal wires and synthesis of bicomponent nanoparticles were investigated on the base of molecular dynamics method. Copper and nickel nanosized crystallites of cylindrical shape were chosen as conductors for explosion. The embedded atom approximation was used for calculation of the interatomic interactions. The agglomeration process after explosion metal wires was the main mechanism for particle synthesis. The distribution of chemical elements was non-uniform over the cross section of the bicomponent particles. The copper concentration in the surface region was higher than in the bulk of the synthesized particle. By varying the loading parameters (heating temperature, the distance between the wires) one can control the size and internal structure of the synthesized bicomponent nanoparticles. The obtained results showed that the method of molecular dynamics can be effectively used to determine the optimal technological mode of nanoparticle synthesis on the base of electric explosion of metal wires.