Grain splitting: a novel mechanism for grain coarsening

Grain coarsening, the process by which crystal grains grow and merge, determines the evolution of crystal structure in metals and self-assembled colloidal materials alike, ultimately governing material properties ranging from yield strength to electrical conductivity. We study hard sphere colloidal polycrystals and find that, contrary to the current paradigm in which grains disappear only by shrinking or rotating as a single rigid object to align with a neighbor, grains may split into a pair of counterrotating regions to match the orientations of two adjacent grains. Each of these counterrotating regions is itself composed of smaller, independently rotating granules. This discovery reveals a new route for grain growth, which may provide insight to grain coarsening and aging in a wide range of polycrystalline materials.