A. G. Sheinerman

Misfit dislocations in wire composite solids

A theoretical model is suggested, which describes generation of misfit dislocations in film/substrate composites of wire form. In the framework of the model, the ranges of the geometric parameters (wire radius, film thickness, misfit parameter) of a wire composite are calculated at which the generation of misfit dislocations is energetically favourable. The specific features of generation of misfit dislocations in wire composites are discussed and compared with those in conventional platelike composites.

Special strain hardening mechanism and nanocrack generation in nanocrystalline materials

A special mechanism of strain hardening in deformed nanocrystalline materials (NCMs) is suggested and theoretically described. The mechanism represents generation of disclination dipoles at grain boundaries (GBs) due to GB sliding. It is shown that special strain hardening can effectively suppress plastic flow instability in metallic and ceramic NCMs and thus enhance their ductility. At the same time, the disclination dipoles formed due to GB sliding serve as dangerous stress sources that can induce nucleation of nanocracks, decreasing ductility of NCMs.

Misfit dislocation loops in composite nanowires

A new mechanism for relaxation of misfit stresses in composite nanowires (quantum wires) is suggested and theoretically examined, namely the formation of misfit dislocation loops. The stress field of a prismatic dislocation loop in a cylinder (nanowire) is calculated. The parameters of two-phase composite nanowires at which the formation of misfit dislocation loops is energetically favourable are estimated. The effect of stress fields of dislocation loops on the formation of compositionally modulated nanowires is discussed.

Misfit dislocations in composites with nanowires

A theoretical model is suggested which describes the generation and evolution of misfit dislocations in composite solids containing nanowires with rectangular cross-section. In the framework of the model, the ranges of the geometric parameters (nanowire sizes, misfit parameter, interspacing between the nanowire and the free surface of the composite) are calculated at which the generation of various misfit dislocation configurations (loops, semi-loops and dipoles) is energetically favourable. Transformations of these dislocation configurations and their specific features are discussed.

Misfit Disclinations and Dislocation Walls in a Two‐Phase Cylindrical Composite

A detailed analysis is given of the conditions for the generation of misfit-induced defects (misfit wedge disclinations and disclination dipoles, periodical arrays of misfit wedge disclinations, and misfit-dislocation walls (MDWs)) in a two-phase cylindrical composite misfitting system. It is shown that the nucleation of the above defects may be favoured in some range of parameters which include substrate and film thicknesses, misfit eigenstrain, and disclination strength or MDW misorientation angle. The limiting case of massive (cylindrical or planar) substrate is specially investigated. The conditions for the misfit defect formation in cylindrical and planar misfitting composites are compared. The peculiarities of misfit defect generation in cylindrical composite systems are briefly discussed.

Misfit dislocations in nanocomposites with quantum dots, nanowires and their ensembles

We review theoretical concepts and experimental results on the physics of misfit dislocations in nanocomposite solids with quantum dots (QDs) and nanowires (quantum wires). Special attention is paid to thermodynamic theoretical models of formation of misfit dislocations in QDs and nanowires, including composite core–shell nanowires. The effects of misfit dislocations on the film growth mode during heteroepitaxy and phase transitions in QD systems are analysed. Experimental results and theoretical models of the ordered spatial arrangement of QDs growing on composite substrates with misfit dislocation networks are discussed. The influence of subsurface dislocations in composite substrates on the nucleation of QDs and nanowires on the substrate surface is considered. Models of misfit strain relaxation and dislocation formation in nanofilms on compliant substrates are also reviewed.

Cracks at disclinated grain boundaries in graphene

A theoretical model is suggested which describes the formation of cracks at grain boundaries (GBs) containing partial (non-topological) disclinations and their dipoles in graphene. Such partial disclinations and their dipoles at GBs are associated with experimentally observed structural irregularities of real GBs in graphene. Within the suggested model, the dependences of the critical stress for crack formation on the parameters of sole disclinations and their dipole configurations at GBs are calculated. The results of the model effectively explain the experimental data (Huang et al 2011 Nature 469 389, Ruiz-Vargas et al 2011 Nano Lett. 11 2259) on crack formation in polycrystalline graphene at comparatively low levels of the applied stress and their discrepancy with the results of computer simulations (presented in the scientific literature) of strength exhibited by graphene bi-crystals with structurally perfect, periodic GBs.

Grain-boundary dislocations and enhanced diffusion in nanocrystalline bulk materials and films

A theoretical model is suggested which describes the transformations of grain-boundary dislocation walls and their influence on diffusion processes in nanocrystalline materials fabricated under highly non-equilibrium conditions. It is shown that the decay of boundary dislocation walls of finite extent, occurring via the climb of boundary dislocations and the corresponding emission of vacancies, is capable of highly enhancing the grain-boundary diffusion in nanocrystalline materials. The enhanced diffusion, in turn, strongly affects the deformation behaviour of nanocrystalline materials. In the case of nanocrystalline films deposited on to substrates, the effects of misfit stresses on the transformations of boundary dislocation walls and the diffusion are analysed. It is demonstrated that the mean diffusion coefficient in a nanocrystalline film may increase by approximately several orders of magnitude owing to misfit stresses.

Elastic Interaction of Micropipes in Crystals

The stress field, strain energy and interaction force are calculated for an isolated pair of straight parallel screw dislocations, one or both of which is (are) associated with (a) micropipe(s). The effect of the attraction of two dislocated micropipes (or a dislocated micropipe and a full-core screw dislocation) with Burgers vectors of the same sign is examined in detail. An analytical expression for the critical distance below which a dislocated micropipe attracts a full-core screw dislocation is found. It is shown that two parallel dislocated micropipes with the same signs of the Burgers vectors may attract each other if the distance between the micropipes is small enough and the ratios of the micropipe radii and the Burgers vector magnitudes are sufficiently different. The stress field and strain energy of a dislocated micropipe near a planar free surface and the force of the interaction between the micropipe and the free surface are also found.

Nanoscale rotational deformation near crack tips in nanocrystalline solids

A special physical micromechanism of plastic flow in pre-cracked nanocrystalline solids is suggested and theoretically described. The micromechanism represents the fast nanoscale rotational deformation (NRD) occurring through collective events of ideal nanoscale shear near crack tips. We calculated the stress and energy characteristics of the NRD. It has been found that such rotational deformation can effectively occur near crack tips and enhance fracture toughness of nanocrystalline materials. Our theoretical model accounts for the in situ experimental observations (Ke et al 1995 Nanostruct. Mater. 5 689, Shan et al 2008 Phys. Rev. Lett. 100 105502, Cheng et al 2010 Phys. Rev. Lett. 104 255501, Liu et al 2011 Scripta Mater. 64 343) of crystal lattice rotations within nanoscale grains and formation of modulated/agglomerated grain structures near crack tips in deformed nanocrystalline solids with finest grains.