[SY-I12] Formation and shrinkage of grain boundary loops in two-dimensional colloidal crystals
Invited
Understanding the dynamics of grain boundaries in polycrystalline metals and alloys is crucial to enable tuning their mechanical properties. From an experimental point of view, grain boundaries in colloidal crystals are convenient model systems since imaging their dynamics requires only simple optical microscopy and they can be manipulated using optical tweezers. The formation and kinetics of grain boundaries are closely related to the topological constraints imposed on their complex dislocation structure. As such, loop-shaped grain boundaries are unique structures to establish such a link because their overall topological “charge” is zero due to their null net Burgers vector.
Here, we study the formation and shrinkage of such grain boundary loops by creating them on demand via a local rotational deformation of a two-dimensional colloidal crystal using an optical vortex. In particular, we observe that a grain boundary loop only forms if the product of its radius and misorientation exceeds a critical value. In this case, the deformation is plastic and the grain boundary loop spontaneously shrinks at a rate that solely depends on this product while otherwise, the deformation is elastically restored. We show that this elastic-to-plastic crossover is a direct consequence of the unique dislocation structure of grain boundary loops. Our results thus reveal a new general limit on the formation of grain boundary loops in two-dimensional crystals and elucidate the central role of defects in both the onset of plasticity and the kinetics of grain boundaries.
Here, we study the formation and shrinkage of such grain boundary loops by creating them on demand via a local rotational deformation of a two-dimensional colloidal crystal using an optical vortex. In particular, we observe that a grain boundary loop only forms if the product of its radius and misorientation exceeds a critical value. In this case, the deformation is plastic and the grain boundary loop spontaneously shrinks at a rate that solely depends on this product while otherwise, the deformation is elastically restored. We show that this elastic-to-plastic crossover is a direct consequence of the unique dislocation structure of grain boundary loops. Our results thus reveal a new general limit on the formation of grain boundary loops in two-dimensional crystals and elucidate the central role of defects in both the onset of plasticity and the kinetics of grain boundaries.