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Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon through which certain energetically favorable grains (crystallites) grow rapidly in a matrix of finer grains resulting in a bimodal grain size distribution. In ceramic materials this phenomena can result in the formation of elongated prismatic, acicular or needle-like grains in a densified matrix with implications for improved fracture toughness through the impedance of crack propagation. == Mechanisms == Abnormal grain growth (AGG) is encountered in metallic or ceramic systems exhibiting one or more of several characteristics.〔〔 # Secondary phase inclusions, precipitates or impurities above a certain threshold concentration. # High anisotropy in solid/liquid interfacial energy or grain boundary energy (solid/solid) in bulk materials. # Highly anisotropic surface energy in thin film materials. # High chemical inequilibrium. Although many gaps remain in our fundamental understanding of AGG phenomena, in all cases abnormal grain growth occurs as a result of very high local rates of interface migration and is enhanced by the localised formation of liquid at grain boundaries. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Abnormal grain growth」の詳細全文を読む スポンサード リンク
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