Strain rate effects on the plastic flow in submicron copper pillars:Considering the influence of sample size and dislocation nucleation

Three-dimensional discrete dislocation dynamics (DDD) simulations are performed to investigate the plastic flow behaviors of submicron copper pillars under different loading rates, in which both inertial effect of dislocation motion and surface nucleation are taken into account. It is found that: (1) for pillars with a diameter below similar to 400 nm, there is a transition from internal dislocation multiplication to surface dislocation nucleation as the strain rate increases (>= 10(4) s(-1)); (2) for similar to 1 um diameter pillars, stable internal dislocation sources dominate for both low and high strain rates; (3) in general, a larger strain rate, smaller sample size and less internal dislocation sources make it more probable for a surface nucleation process to take the place of dislocation multiplication. Furthermore, a theoretical model is proposed to predict the submicron plastic behavior at different strain rates when internal dislocation sources prevail. (c) 2017 Elsevier Ltd. All rights reserved.