Thermally-activated Non-Schmid Glide of Screw Dislocations in W using Atomistically-informed Kinetic Monte Carlo Simulations

TL;DR

This study develops a kinetic Monte Carlo model, parameterized with atomistic simulations, to investigate thermally-activated screw dislocation motion in tungsten, revealing the significant impact of non-Schmid effects on dislocation dynamics.

Contribution

The paper introduces a new atomistically-informed kinetic Monte Carlo approach that captures non-Schmid effects in screw dislocation glide in tungsten, extending the understanding of dislocation behavior at low temperatures.

Findings

Non-Schmid effects significantly alter dislocation velocities.

Dislocation velocities depend strongly on stress, temperature, and line length.

Effective mobility laws are derived for use in larger-scale models.

Abstract

Thermally-activated $\small{\nicefrac{1}{2}}<111>$ screw dislocation motion is the controlling plastic mechanism at low temperatures in body-centered cubic (bcc) crystals. Motion proceeds by the nucleation and propagation of atomic-sized kink pairs susceptible of being studied using molecular dynamics (MD). However, MD's natural inability to properly sample thermally-activated processes as well as to capture $\{110\}$ screw dislocation glide calls for the development of other methods capable of overcoming these limitations. Here we develop a kinetic Monte Carlo (kMC) approach to study single screw dislocation dynamics from room temperature to $0.5T_m$ and at stresses $0<\sigma<0.9\sigma_P$, where $T_m$ and $\sigma_P$ are the melting point and the Peierls stress. The method is entirely parameterized with atomistic simulations using an embedded atom potential for tungsten. To increase the physical fidelity of our simulations, we calculate the deviations from Schmid's law prescribed by the interatomic potential used and we study single dislocation kinetics using both projections. We calculate dislocation velocities as a function of stress, temperature, and dislocation line length. We find that considering non-Schmid effects has a strong influence on both the magnitude of the velocities and the trajectories followed by the dislocation. We finish by condensing all the calculated data into effective stress and temperature dependent mobilities to be used in more homogenized numerical methods.