M. D. Starostenkov

Energy localization on the Al sublattice of Pt3Al with L12 order

A three-dimensional molecular-dynamics model of Pt3Al with L12 order was developed and found to support the excitation of discrete breathers (DBs) and energy localization on the Al sublattice. For an initial lattice temperature of 0 K, large-amplitude DBs polarized along [100] are found to be very weakly damped, retaining most of their initial energy for more than 1000 cycles, while DBs polarized along [111] damped out over ∼15 cycles. Because the DBs and their dissipation channels are confined to the Al sublattice, long-lived nonequilibrium states with large energy differences between the Al and Pt sublattices occur. Since collisions during irradiation more efficiently generate lattice vibrations in light atoms than heavy atoms, such nonequilibrium states may occur and alter the relaxation processes occurring during radiation damage.

Localized oscillating modes in two-dimensional model of regulated Pt3Al alloy

By means of molecular-dynamics simulations, it is shown that discrete breathers are excited in two-dimensional model lattice of the regulated Pt3Al alloy by periodic external action of a certain frequency. The energy of Al atoms carrying a non-linear localized mode can more than ten times exceed the mean energy of Pt atoms.

Contributions of different mechanisms of self-diffusion in face-centered cubic metals under equilibrium conditions

The contributions of different mechanisms of self-diffusion in face-centered cubic metals Ni, Cu, and Al at thermodynamic equilibrium have been analyzed using the molecular dynamics method. The vacancy, divacancy, and cyclic mechanisms of self-diffusion, as well as the mechanisms involving the vacancy migration to the second coordination sphere and the formation and recombination of Frenkel pairs, have been considered. It has been shown that the second in contribution to the self-diffusion after the vacancy mechanism in the metals under consideration is the migration of divacancies. The third is the mechanism involving the formation and recombination of dynamic Frenkel pairs. The cyclic mechanisms (with simultaneous atomic displacements) and the vacancy migration directly to the second coordination sphere in face-centered cubic metals are unlikely.

Simulation of the interaction between discrete breathers of various types in a Pt3Al crystal nanofiber

It is known that, in a molecular dynamics model of Pt3Al crystal, a discrete breather (DB) with soft type nonlinearity (DB1) can be excited, which is characterized by a high degree of localization on a light atom (Al), stationarity, as well as a frequency that lies in the gap of the phonon spectrum and decreases with increasing amplitude of the DB. In this paper, it is demonstrated that a DB with hard type nonlinearity (DB2) can be excited in a Pt3Al nanofiber; this DB is localized on several light atoms, can move along the crystal, and has a frequency that lies above the phonon spectrum and increases with the DB amplitude. It is noteworthy that the presence of free surfaces of a nanofiber does not prevent the existence of DB1 and DB2 in it. Collisions of two DBs counterpropagating with equal velocities, as well as a collision of DB2 with a standing DB1, are considered. Two colliding DBs with hard type nonlinearity are repelled almost elastically, losing only insignificant part of their energy during the interaction. DB2 is also reflected from a standing DB1; in this case, the energy of the breathers is partially scattered into the Al sublattice. The results obtained indicate that DBs can transfer energy along a crystal over large distances. During the collision of two or more DBs, the energy localized in space can be as high as a few electron-volts; this allows one to raise the question of the participation of DBs in structural transformations of the crystal.

Structural transformations of stacking fault tetrahedra upon the absorption of point defects

Mechanisms of the structural modification of stacking fault tetrahedra (SFTs) upon the absorption of point defects have been studied by the method of molecular dynamics. The sequential absorption of vacancies by a perfect SFT is accompanied by the following transformations: (i) the formation of a step on one of the SFT faces, (ii) a change in the step sign upon reaching the middle of the face, (iii) the formation of an SFT with truncated vertex, and (iv) the formation of the perfect SFT. Upon the absorption of interstitial atoms, the stages of SFT transformation follow the reverse order.

Molecular dynamics investigation of the diffusion permeability of triple junctions of tilt and mixed-type boundaries in nickel

The diffusion permeability of triple junctions of high-angle tilt boundaries 〈111〉 and 〈100〉 and mixed-type boundaries in nickel has been investigated using the molecular dynamics method. It has been shown that the diffusion permeability of equilibrium triple junctions does not exceed the permeability of the grain boundaries forming them. The effective diffusion radius of the considered triple junctions and the width of the grain boundaries are determined.

Exciting discrete breathers of two types in a computer 3D model of Pt3Al crystal

The possibility of exciting discrete breathers (DBs) with both soft and hard nonlinearity in a threedimensional crystal has been shown for the first time using molecular dynamics simulation by example of an ordered Pt3Al crystal model. The oscillation frequencies of DBs of the first (soft) type fall in the gap of the phonon spectrum and decrease with increasing amplitude. For DBs of the second type, the oscillation frequencies are above the phonon spectrum and increase with the amplitude, i.e., exhibit hard nonlinearity. An example of the transformation of a hard DB into a set of gap (soft) DBs with soft nonlinearity is presented. The influence of various factors on the lifetime of interacting DBs is considered.

Dynamic collective displacements of atoms in metals and their role in the vacancy mechanism of diffusion

The phenomenon of dynamic collective displacements of atoms in face-centered cubic crystals has been revealed using molecular dynamics method. This phenomenon plays an important role in the vacancy mechanism of diffusion. The vacancy mechanism is provided by the collision of two regions of collective atomic displacements that move a migrating atom and a vacancy toward each other. The collective thermal atomic displacements from crystal lattice sites occur as a result of the nonuniform momentum distribution of atoms according to the Maxwellian distribution. Owing to their statistical nature, the degree of correlation of the atomic displacements depends neither on the temperature nor on the interatomic interaction potential.

Thermoactivated structure rearrangements in a binary CuAu3 alloy under deviation from stoichiometric composition

Thermoactivated structure rearrangements at the micro-, meso-, and macroscale levels in a binary Cu3Au alloy are investigated for the case of deviation from stoichiometry.

Mutual diffusion at the interface in a two-dimensional Ni-Al system

Mutual diffusion at the interface in a two-dimensional Ni-Al system has been studied by the method of molecular dynamics. It is established that the main diffusion mechanism consists in correlated jumps of atoms over the vacancies near misfit dislocation cores.