Transformation of shear loop into prismatic loops during bypass of an array of impenetrable particles by edge dislocations

Particle strengthening resulting from the interaction between edge dislocations and impenetrable particles is investigated by molecular statics in the framework of the (modified-) embedded atoms method for magnesium. The dynamics of the bypassing mechanism have been identified as a function of the number of glide dislocations interacting with the particle. Qualitatively, it was found that the first glide dislocation bypassed the impenetrable particle by an Orowan mechanism. The net result of the first dislocation bypass was a straight dislocation line and a particle encircled by a non-planar Orowan loop. Furthermore, when a second glide dislocation interacted with the particle encircled by a non-planar Orowan loop, the molecular statics calculations revealed a bypassing mechanism occurring through a series of dislocation cross-slips. The net result obtained after the bypass of a particle with diameter between 2 nm and 8 nm by two glide dislocations is two prismatic loops on one side of the particle and a glide dislocation carrying two super jogs and a prismatic loop on the other side of the particle. Quantitatively, the stress required by a first glide dislocation to bypass an impenetrable particle was in good agreement with continuum predictions from the literature. A systematic decrease of the shear stress needed for a second glide dislocation to bypass an impenetrable particle encircled by a non-planar Orowan loop was found. Such a decrease of the bypassing stress is interpreted as the evidence that the bypass of the second dislocation by cross-slip maneuvers is a stress relief mechanism.