Entropic effects on thermally-activated dislocation cross-slip
Date:
The 10th International Conference on Multiscale Materials Modeling
Abstract
Dislocation cross-slip is one of the main microscale mechanisms involved in the temperature dependence of stage-III strain-hardening of face-cubic centered (fcc) metals. So far, atomistic investigations of cross-slip rate focused on determining the activation enthalpy of cross-slip under stress and the entropic effects were usually neglected. We show that the rate predicted based only on activation enthalpy underestimates the cross-slip rate by 6-orders of magnitude compared to direct molecular dynamics (MD) simulation. Based on harmonic transition state theory (HTST) with corrections of anharmonic soft modes, we develop a fully atomistic model that successfully predicts the cross-slip rate of fcc nickel under a much wider range of stress and temperature conditions. We find that thermal expansion and thermal softening effects contribute significantly to the activation entropy and the rate due to a non-negligible coupling between the activation enthalpy to the hydrostatic component of the stress.