A. Yu. Nikonov

Molecular dynamics study of lattice rearrangement under mechanically activated diffusion

The paper presents a molecular dynamics study to investigate the behavior of materials under loading by friction stir welding (FPW). The loading is simulated by assigning constant angular and forward velocities to a certain group of atoms, being a FPW tool. The joined materials are two defect-free Cu crystallites, Cu and Fe crystallites, and two crystallites of the same solid solution structured as D16 (2024) alloy. It is found that as the tool passes along the weld line, the crystal structure of the materials is rearranged with subsequent mixing of their surface atoms. Under certain loading conditions, the crystal lattice after passage of the tool recovers its regular order. Also analyzed is the influence of vibrations additionally applied to the FPW tool. The simulation results provide a better understanding of the processes involved in mechanically activated diffusion.

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.

Modeling of nanostructuring burnishing on different scales

The operating characteristics of machine parts and units are defined in many respects by the physical and mechanical properties of their surface layers. Unfortunately, it is still not quite clear what parameters and mechanisms are responsible for one or another modification of surface layer properties. In this context, computer modeling techniques can be a useful tool in studying the variation of surface properties in contact interaction and run-in. Of fundamental importance is the possibility to consider the processes occurring on nanoscales and scales of individual atoms. In the work, loading conditions in plastic surface deformation was reproduced on the macroscale (traditional approach), atomic scale, and mesoscale by computer modeling with the finite element method, movable cellular automata method, and molecular dynamics method. The modeling results are in good qualitative agreement with data of experimental measurements.

On the conditions of strain localization and microstructure fragmentation under high-rate loading

The paper reports on research in the deformation and fragmentation mechanisms of coarse- and fine-grained materials under high-rate loading. The study was performed by an experimental procedure based on collapse of thick-walled hollow cylinders and by molecular dynamics simulation. The key issue was to study the formation of plastic strain localization bands. It is found that the pattern of plastic deformation is governed by loading conditions and characteristic grain sizes. For a coarse-grained material, the governing mechanism is dislocation deformation resulting in localization bands. For a fine-grained material, the governing mechanism is grain boundary sliding with attendant fragmentation of the material. A dependence of the strain rate and degree on the critical grain size was disclosed. The computer simulation revealed mechanisms of grain boundary sliding on the scales studied.

Influence of stresses on structure and properties of Ti and Zr- based alloys from first-principles simulations

Computer simulations in the framework of the Density Functional Theory have become an established tool for computer simulations of materials properties. In most cases, however, information is obtained at ambient conditions, preventing design of materials for applications at extreme conditions. In this work we employ ab initio calculations to investigate the influence of stresses on structure and stability of Ti-Mo and Zr-Nb alloys, an important class of construction materials. Calculations reproduce known phase stability trends in these systems, and we resolve the controversy regarding the stability of body-centered cubic solid solution in Mo-rich Ti-Mo alloys against the isostructural decomposition. Calculated results are explained in terms of the electronic structure effects, as well as in terms of physically transparent thermodynamic arguments that relate phase stability to deviations of concentration dependence of atomic volume from the linear behavior.

Simulation of the behavior of a Σ5 grain boundary under combined thermal and external shear loading

The behavior of the grain boundary of a copper bicrystal under shear loading is studied by molecular dynamics simulation. The subject of the research is a high-angle boundary of the Σ = 5(210)[001] special type. The effect of the temperature of the sample on the characteristics of the behavior of the grain boundary under shear deformation is analyzed. It is shown that, in the sample heated above a certain temperature, the previously found mechanism of grain-boundary sliding in fcc crystals, which is accompanied by a simultaneous motion of the boundary in the direction perpendicular to the applied load, gives way to the conventional mechanism of grain-boundary sliding associated with the displacement of the grains relative to each other along the plane of the defect. The features of the change in the structure of the grain boundary upon a change in its response to shear deformation with increasing temperature are studied.

Synthesis of N -[chloro(diorganyl)silyl]anilines

A series of N-[chloro(diorganyl)silyl]anilines RR′Si(NR″Ph)Cl (R, R′ = Me, Ph, CH2=CH, ClCH2, Cl(CH2)3; R″ = H, Me) was prepared via the reaction of diorganyldichlorosilanes with aniline or N-ethylaniline in the presence of triethylamine.

Molecular dynamics simulation of copper bicrystal response to shear loading

The behavior of a large-angle grain boundary of the Σ = 5 (210)[001] special type in a copper bicrystal under shear loading conditions has been computer simulated. It is established that, simultaneously with the relative slippage of grains in the direction of applied load, the grain boundary shifts in the direction perpendicular to that of shear straining. This motion of the grain boundary exhibits a discrete character and leads to a growth of one grain at the expense of another. The mechanism of this displacement is analyzed and the influence of the loading rate and direction on the character of grain boundary motion is studied. The obtained results provide better understanding of the atomic mechanisms of plastic strain development in polycrystalline materials.

Calculation of mechanical properties of BCC Ti-Nb alloys

We have calculated mechanical properties of bcc Ti-Nb alloys in the framework of the first-principles approach using the exact muffin-tin orbital method. The results obtained quantitatively correlate well with known experimental data and can be used in order to design new materials based on of Ti alloys intended for various applications, e.g. for bio-medical applications.

Erratum to: “Numerical Study of Mechanical Properties of Nanoparticles of ß-Type Ti-Nb Alloy under Conditions Identical to Laser Sintering. Multilevel Approach”

A multilevel approach is used to numerically investigate physical and mechanical properties of titanium-based bcc alloys and their behavior under conditions identical to selective laser sintering. Plastic properties of P-Ti-Nb alloy are calculated within the first principles approach. An algorithm is proposed and tested to optimize the calculations and reduce their number by more than 5 times. A molecular dynamics method is employed to study structural changes of titanium and niobium powder particles during sintering and to calculate adhesion characteristics of nanoparticles of the produced alloy depending on the external action. The simulation results are in good agreement with the known experimental data and can be used as input data both for numerical models of a higher spatial scale and for the optimization of production parameters of titanium alloys by additive technologies.