Features of structural response of mechanically loaded crystallites to irradiation

A molecular dynamics method is employed to investigate the origin and evolution of plastic deformation in elastically deformed iron and vanadium crystallites due to atomic displacement cascades. Elastic stress states o

Molecular dynamics simulation of nucleation and growth of defects in the alloy fe-cr in the conditions of high-energy loading

Features of primary radiation damages in the near-surface layers of the Fe-Cr crystallite were investigated. The calculations were based on the molecular dynamics method. It was found that the number of surviving defects at the generation of atomic displacement cascades near the free surfaces is almost twice their number than in case of cascade generation far away from the various interfaces. Besides it the cascades can knock out some atoms from the free surfaces and form some specific structural defects: craters, adatom islands, dislocation loops of vacancy type. The crystallographic orientation of the irradiated surfaces has a significant influence on the features of the material damage. Craters are much more frequently formed at the irradiation of the (111) surface. There is a correlation between the size of the vacancy loops and the number of adatoms on the free surface. The size of the vacancy loops formed by the irradiation of the (111) surface is slightly larger than the number of adatoms. The inverse relationship was found at the irradiation of the (110) surface of Fe-Cr crystallite

Computer simulation of surface modification of al crystallite under high energy treatment

The simulation of structural changes in the surface region of Al crystallite during self-ion bombardment was carried out. The calculations were performed on the base of the molecular dynamics method. A many-body potential calculated in the approximation of the embedded atom method was used to describe the interatomic interactions. It is shown that atomic displacement cascades in the near-surface region were generated under ion irradiation. At relatively low energies the impact of the atomic displacement cascades not only lead to the generation of Frenkel pairs, but also to the nucleation of plastic deformation. That is due to the high-rate heating of the grains, causing their expansion and deformation in the stained conditions with the formation of stacking faults. Melting of surface layers takes place at high energies of irradiation. A crystallization process and a formation of a grain structure of the surface layers will be determined by the characteristics of the propagation of the crystallization front, which shape depends on the relative location, size and orientation of grains on the boundary of the liquid and solid phases

Features of nucleation and evolution of defect structure in vanadium under constrained deformation

Atomic mechanisms of structural transformations leading to fragmentation in vanadium under deformation in constrained conditions without changing its volume are investigated on the basis of the molecular dynamics method. The process of formation of a fragmented structure in a deformed specimen can be divided into two stages. At the first stage, twins nucleate and grow in the crystallite. In the second stage, the orientation of lattice in twins may change due to the intersection of twins leading to their anisotropic deformation. In this case, the directions of stretching and compression of the crystal lattice in the deformed twin quite closely lie in the directions of stretching and compression of the whole crystallite

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

Features of particle synthesis at metal wire dispersion

Features of particle synthesis under simultaneous dispersion of copper and nickel wires were investigated using a molecular dynamics method. The dynamics of wire dispersion, the size and phase composition of synthesized particles depend on the internal structure of dispersed metal wires and the distance between them. The main mechanism of particle synthesis was agglomeration of sputtered clusters, which predominated over the atom deposition from the gas phase on the particle surface. Synthesized particles were characterized by a nonuniform distribution of chemical elements along their cross section. The subsurface region had a higher concentration of copper in comparison with the particle volume. The molecular dynamics simulation of the metal wire dispersion allows finding optimal loading parameters for the synthesis of particles with desirable size and internal structure

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

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 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

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