text: Abnormal grain growth (AGG) is encountered in metallic or ceramic systems exhibiting one or more of several characteristics:
  # Systems with secondary phase inclusions, precipitates or impurities above a certain threshold concentration.
  # Systems with a highly anisotropic surface energy.
  # Systems far from chemical equilibrium.
  Abnormal grain growth occurs due to very high local rates of interface migration and is enhanced by the localized formation of liquid at grain boundaries. In 2023, Liss et al.  
  have shown that the spontaneous activation of a grain boundary opens diffusion pathways, leading to the activation of one grain in an otherwise inactive microstructure and allowing the grain to rotate and coalesce with a neighbor grain. However, due to competition with the surrounding grains, rotation may proceed erratically. Coupled with spontaneous activation, this makes abnormal grain growth a largely erratic process. While the activation of grain boundaries (leading to rotation and growth) can occur at temperatures well below the temperatures required for partial melting of the grain boundaries, the effect is emphasized when melting occurs.