Disconnections kinks and competing modes in shear-coupled grain boundary migration

Abstract

The response of small-grained metals to mechanical stress is investigated by a theoretical study of the elementary mechanisms occurring during the shear-coupled migration of grain boundaries (GB). Investigating a model 17(410) GB in a copper bicrystal, both 110 and 100 GB migration modes are studied focusing on both the structural and energetic characteristics. The minimum energy paths of these shear-coupled GB migrations are computed using the nudge elastic band method. For both modes, the GB migration occurs through the nucleation and motion of disconnections. However, the atomic mechanisms of both modes qualitatively differ: While the 110 mode presents no metastable state, the 100 mode shows multiple metastable states, some of them evidencing some kinks along the disconnection lines. Disconnection kinks nucleation and motion activation energies are evaluated. Besides, the activation energies of the 100 mode are smaller than those of the 110 one except for very high stresses. These results significantly improve our knowledge of the GB migration mechanisms and the conditions under which they occur.

Shear-coupled grain-boundary migration dependence on normal strain/stress

“…While at T = 0 K, the migration occurs for an applied shear displacement corresponding to the yield shear stress, at finite temperature, the GB migration can be thermally activated for a smaller applied shear displacement 9,24 . In order to investigate the finite temperature migration, the reaction paths of the GB migration between configurations of the system before and after the GB migration are calculated for a given position of the slabs.…”

“…Numerical studies relying on atomistic simulations and corroborating theoretical predictions have investigated GB-based mechanisms concentrating noticeably the efforts on the coupling factor or the mobility 12,[15][16][17][18][19][20] . Interestingly, atomistic simulations have also recently succeeded in uncovering the role of disconnection 21,22 in the migration 9,23,24 . Remarkably, in all of the previous theoretical studies, the shear coupled GB migration is induced by applying a pure shear strain on the GB in absence of any other strain component on the GB.…”

Friction of atomically stepped surfaces

“…In Refs. [29,30], it is explained how local atomic rearrangement leads to step motion from which the migration results. In Ref.…”

“…The contact migration is a consequence of the motion of the step similar to the mechanism for grain boundary migration discussed in Refs. [29][30][31]. In Refs.…”

Reconstruction of α–Iron 〈100〉 Symmetric Tilt Grain Boundaries Σ17(410) and Σ13(510)

“…Close to GB the spatial arrangement of lattice planes, their crystallographic structure as well as dynamics of the constituent atoms may differ from the corresponding features in the grain. From microscopical point of view, the crystal structure along the GBs is mainly responsible for changes in physical properties of polycrystalline as well as nanocrystalline materials [4][5][6]. Consequently, a detailed understanding of the mechanism of formation and development of GBs is an important step in the creation of new structural materials with well-defined parameters and long time stability.…”