Stochastic behavior of dislocation nucleation from acute and obtuse angles in metallic nanowires

Pristine metallic nanowires yield plastically under tensile load by nucleating dislocations from their surfaces. It was commonly accepted that in nanowires with a rhombic cross-section, dislocations are nucleated from edges with acute angles. Using Molecular Dynamics (MD) simulations we show that dislocation nucleation at the onset of plasticity in Pd nanowires can occur from both acute and obtuse angles, with a temperature-dependent probability; nucleation from the obtuse angle is more probable at higher temperature. We quantify this stochastic behavior by calculating the free energy barrier, using MD simulations and the nudged-elastic band method, in combination with the varying driving-force analysis proposed previously for Mo nanoparticles [1]. The free-energy barriers are then incorporated in a Metropolis Monte-Carlo simulation, to predict the nucleation probabilities from each site. Based on the simulation results, we propose a model for the strength distribution of nanowires when nucleation can occur in two site types.

[1] Chachamovitz D. and Mordehai D., The Stress-Dependent Activation Parameters for Dislocation Nucleation in Molybdenum Nanoparticles, Sci. Rep. 8, 3915 (2018).