Geometric origin of particle and dislocation dynamics during grain boundary migration

Speaker: Roel Dullens (Institute for Molecules and Materials, Radboud University)

Abstract:

Grain boundary (GB) migration induces significant changes in the structure of polycrystalline solids and has a pronounced effect on the macroscopic properties of these materials [1-3]. On the atomic scale, GB migration is governed a mechanism via which constituent particles are displaced between lattice sites of neighbouring grains. Despite many efforts to characterise such mechanism for GB migration, a comprehensive understanding of the migration mechanism in terms of the dynamics of atoms and dislocations remains largely unclear.

Here, we investigate this link between particle, defect and GB migration experimentally by using holographic optical tweezers [4] to create loop-shaped GBs in a model two-dimensional colloidal crystal. We reveal a clear connection between the dynamics of particles and dislocations where local block rotations observed in the particle dynamics correspond to the reaction and glide of dislocations along the paths of maximum misfit. Hence, the paths taken by the dislocations correspond to regions of largest particle displacement. Moreover, we identify the particle dynamics to be guided by set of equivalence points between both lattices that act as points of transition as particles displace between grains. Using this geometric underpinning, we establish a framework that predicts the microscopic dynamics of particles and dislocations during GB migration in our two-dimensional crystals.

References [1] JM Howe, Interfaces in materials. (John Wiley & Sons, 1997). [2] EO Hall, Proceedings of the Physical Society, Section B 64 (9), 747 (1951). [3] NJ Petch, Journal of the Iron and Steel Institute 174, 25 (1953). [4] FA Lavergne et al., PNAS 115 (27), 6922 (2018).

This seminar will take place in room D1.113