Grain Boundary Migration and Grain Growth: A Multiscale Perspective 

David J Srolovitz*

City University of Hong Kong, Hong Kong SAR, China

ABSTRACT: Grain growth is the coarsening of a polycrystalline microstructure driven by the reduction in the total grain boundary (GB) energy. A description of grain growth should include the geometry and topology of the GB network (GBs, triple-lines, quad-junctions) AND a description of how GBs move. Classically, we assume isotropy; i.e., all GBs have the same energy (independent of GB misorientation and inclination) and the same mobility. We first discuss how to simulate the evolution of the complex GB network/microstructure in this limit. Our approach is based upon front tracking methods and is consistent with the MacPherson-Srolovitz theory for individual grains (an exact extension of the von Neumann theory to 3-dimensions). Next, we repeat these simulations on at atomistic level using semi-empirical interatomic potentials in molecular dynamics (MD). The MD results reveal many phenomena that are not consistent with the isotropic front tracking results that cannot be explained based upon anisotropy. We track the source of these inconsistencies to the fundamental mechanisms by which GBs migrate. GBs migrate by the motion of line defects (disconnections) that are constrained to GB planes; disconnections have both dislocation and step character. The dislocation character couples GB motion to stress, strain, and grain rotation. Using MD simulations and analytical theory, we show how this character leads to much richer GB equation of motion than the classical equation of motion. We illustrate this with several examples from MD, Monte Carlo, and new front tracking simulations.

Keywords:grain boundary migration; grain boundary mobility; grain growth; multiscale modeling