Ostwald ripening — larger grains consume smaller ones
Grain growth in polycrystalline materials follows Burke-Turnbull kinetics: R̄²(t) − R̄²(0) = Kt, where K = K₀ exp(−Q/RT). Boundaries migrate toward their center of curvature. Grains with fewer than 6 sides shrink; those with more than 6 sides grow (von Neumann-Mullins rule). This coarsening reduces total grain boundary energy (driving force = γ/R).