D.S. Kryzhevich

Local structural transformations in the fcc lattice in various contact interaction. Molecular dynamics study

The work is a molecular dynamics study of the peculiarities of local structural transformations in a copper crystallite at the atomic level in contact interaction of various types: shear loading of perfectly conjugate surfaces, local shear loading and nanoindentation. Interatomic interaction is described in the framework of the embedded atom method. It is shown that initial accommodation of the loaded crystallite proceeds through local structural transformations giving rise to higher-rank defects such as dislocations, stacking faults, interfaces, etc. In further plastic deformation, the structural defects propagate from the contact zone to the crystallite bulk. The egress of structural defects to a free surface causes deformation of the model crystallite. The deformation pattern can evolve, depending on the loading conditions, with a change in crystallographic orientation of the crystallite near the contact zone, generation of misoriented nano-sized regions, and eventually formation of a stable nanostructural state. The obtained results allow conceptually new understanding of the nature of defect generation in a crystalline structure during the nucleation and development of plastic deformation in loaded materials.

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.

Protodefect as a Basis of Multilevel Nanoscale Plasticity of Crystal Materials

Atomic mechanisms of plastic deformation initiation in materials with crystal structure are investigated. It is shown that thermal fluctuations can be a reason for structural defect generation and there is a threshold strain value at which zones with local structural changes (protodefects) grow almost abruptly. The calculations illustrate that protodefect formation is induced by a local expansion of atomic volume.

Molecular Dynamic Study of Proto-Faults Generation as an Atomistic Mechanism of Incipient Plasticity during High-Speed Loading in Ideal Crystal

The molecular dynamics investigation of plastic deformation initiation has shown that at the first stage local structural distortions, i.e. protodefects that give rise to conventional lattice defects, are generated. We study in detail the dynamics of atomic displacements that govern protodefect nucleation. The calculations illustrate that protodefect formation is induced by a local expansion of atomic volume. The stage-by-stage generation of protodefects in the conditions of relaxation unambiguously correlates with potential energy variation in the crystallite.