Mechanisms of Guinier-Preston zone hardening in the athermal limit

The interaction of dislocations with Guinier-Preston (GP) zones is a process that contributes to the yield strength of many underaged precipitate-strengthened alloys. Here we use atomistic modeling to investigate this process in an Al-Cu alloy using a newly developed interatomic potential. The study focuses on edge dislocation interactions in the athermal limit. The critical shear stress and the mechanism by which dislocations overcome GP zones is found to vary significantly depending upon GP zone size, orientation and offset from the dislocation glide plane. Dislocation cutting, looping, leading partial cutting with trailing partial looping, diffusionless climb and defect nucleation at the dislocation-GP zone contact point are all observed. In the majority of cases dislocation looping is the controlling mechanism, challenging the applicability of traditional continuum dislocation cutting models to the underaged Al-Cu system at 0 K.