The linking of atomistic simulations of stress-driven processes to experimentally observed mechanical behaviour via the computation of activation energy barriers was a topic of intense current research. Using dislocation nucleation from a crack tip as the reaction process, long-time multiscale molecular dynamics simulations show that the activation barrier could exhibit significant temperature dependence. Using an analytic model for the nucleation process and computing the relevant material properties (elastic constants and stacking fault energies), the temperature dependence was shown to arise primarily from the temperature dependence of the material parameters for both Al and Ni. After thermally activated emission of the first partial dislocation, there was then a competition between two other thermally activated processes: twinning and full dislocation emission. Because the activation barriers depended on temperature, this transition was more complex than usually envisioned. Simulations in Al revealed that a transition from twinning to full dislocation emission back to twinning occurred with increasing temperature, which was counter to traditional metallurgical wisdom. Temperature-dependent activation energies were thus essential to accurate understanding and prediction of those phenomena that controlled fracture and metal deformation at realistic loading rates.

Origins and Implications of Temperature-Dependent Activation Energy Barriers for Dislocation Nucleation in Face-Centered Cubic Metals. D.H.Warner, W.A.Curtin: Acta Materialia, 2009, 57[14], 4267-77