Dislocation Dipoles in Nanocrystalline Films

Abstract

A theoretical model is suggested that describes the behavioral features and energetic characteristics of dipoles of grain boundary dislocations in nanocrystalline films. Such dislocation dipoles in nanocrystalline films are shown to play the role of misfit defect configurations that compensate, in part, for misfit stresses that occur due to a mismatch between crystal lattice parameters of films and substrates. Ranges of parameters (misfit parameter, grain size, etc.) are revealed at which the formation of dislocation dipoles is energetically favorable in nanocrystalline films. It is demonstrated that dislocation dipoles are typical structural elements of nanocrystalline films fabricated at highly nonequilibrium conditions.

Plastic Deformation Micromechanism in Nanotwinned Films

“…1b). The most works on the nanotwinned metals are concerned with copper [4,5,[13][14][15][16]. So, in the framework of the model, we will consider widening of twins in fcc metallic films, that is, films with face-centered cubic crystal lattice.…”

“…For example, it was revealed in experimental studies [4,5] that nanotwinned cooper films (ultrafine-grained metallic films with high-density ensembles of nanoscale twins within grains) which were formed by electrical deposition demonstrate high strength with conservation of the functional plastic properties. According to the recent experimental [4,5] and theoretical [13][14][15][16] works, the main micromechanism responsible for the unique combination of high strength and plasticity of nanotwinned materials is viewed to be plastic deformation occurring through widening of nanoscale twins due to migration of twin boundaries. In theoretical models [14][15][16] dislocation reactions resulting in formation of the twinning partial dislocations that move along the twin boundaries and provide widening of twins in bulk nanotwinned materials were considered.…”

“…According to the recent experimental [4,5] and theoretical [13][14][15][16] works, the main micromechanism responsible for the unique combination of high strength and plasticity of nanotwinned materials is viewed to be plastic deformation occurring through widening of nanoscale twins due to migration of twin boundaries. In theoretical models [14][15][16] dislocation reactions resulting in formation of the twinning partial dislocations that move along the twin boundaries and provide widening of twins in bulk nanotwinned materials were considered. The main aim of this paper is to suggest a theoretical model which describes plastic deformation through widening of nanoscale twins in nanotwinned films with ultrafinegrained structure.…”