Stress-Dependent activation energy barrier for Cross-Slip in FCC metals

Cross-slip is a mechanism by which screw dislocations can change their glide plane and it is an essential mechanism in understanding dislocation-based process and materials modeling. Cross-slip is a thermally activated mechanism and quantifying the stress-dependent activation barrier for cross-slip is crucial. In this work, we present a line-tension model for cross-slip of screw dislocations in face-centered cubic (FCC) metals, with which we calculate the activation energy barrier when Escaig stresses are applied on the primary and cross-slip planes and Schmid stress is applied on the cross-slip plane. A closed-form expression is obtained for the activation energy for cross-slip in a large range of stresses, without any fitting parameters. The model yields results which are in excellent comparison with previous numerical results. By turning one parameter into a fitting parameter, the model results are also in very good agreement with atomistic simulations. Using the closed-form expression, we show that when only Escaig stresses are applied, cross-slip can be energetically unfavorable for a certain relation between these stress. However, Schmid stresses on the cross-slip plane always lower the values of the activation energy and the constraint on cross-slip is removed, i.e., it can occur for all Escaig stresses. This proposed closed-form expression for the activation energy can be easily implemented in dislocation dynamics simulations, owing to its simplicity and universality.