Assessment of interatomic potentials for atomistic analysis of static and dynamic properties of screw dislocations in W

Abstract

Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally-activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, non-degenerate core with an associated Peierls stress between 1.7 and 2.8 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we assess the suitability of five different potentials in terms of static properties relevant to screw dislocations in pure W. Moreover, we perform molecular dynamics simulations of stress-assisted glide using all five potentials to study the dynamic behavior of screw dislocations under shear stress. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that one potential predicts a core transformation from compact to dissociated at finite temperature that affects the energetics of kink-pair production and impacts the mechanism of motion. We conclude that a modified embedded-atom potential achieves the best compromise in terms of static and dynamic screw dislocation properties, although at an expense of about ten-fold compared to central potentials.

Linking atomistic, kinetic Monte Carlo and crystal plasticity simulations of single‐crystal tungsten strength

“…The values of the parameters defined in the constitutive model are listed in tables 2 and 3. Most of the parameters of these tables have been obtained directly from kMC simulations [64] or first principle and atomistic calculations [73] with the EAM interatomic potential [74] …”

“…By contrast, edge dislocations display viscous motion (linear with the applied stress) and thus screw motion is the rate-limiting step for plastic shear. Molecular dynamics (MD) is commonly used to simulate dislocation motion [59][60][61], although it is generally not suited to capture rare-event mechanisms (such as nucleation). In bcc crystals, MD simulations naturally include non-Schmid effects as part of the simulated dynamics of screw dislocation motion, but they provide overdriven dynamics and are limited to glide on {1 1 2} planes due to limitations with boundary conditions and said non-Schmid effects [60,61].…”

“…Molecular dynamics (MD) is commonly used to simulate dislocation motion [59][60][61], although it is generally not suited to capture rare-event mechanisms (such as nucleation). In bcc crystals, MD simulations naturally include non-Schmid effects as part of the simulated dynamics of screw dislocation motion, but they provide overdriven dynamics and are limited to glide on {1 1 2} planes due to limitations with boundary conditions and said non-Schmid effects [60,61]. An alternative technique that is not subjected to this limitation is kMC [62][63][64].…”

“…Cereceda et al [73] Stukowski et al [64] Stukowski et al [64] This work Fig. 2 (online colour at: www.gamm-mitteilungen.org) Schematic diagram of the multiscale approach that links atomistic, kinetic Monte Carlo and crystal plasticity simulations.…”

Techniques to accelerate convergence of stress-controlled molecular dynamics simulations of dislocation motion

“…It is not the objective of this paper, however, to investigate the details of that mechanism, which we leave for a future study [13].…”