Microstructural evolution during sintering of TiO2/SiO2-doped alumina: mechanism of anisotropic abnormal grain growth

Abstract Microstructural changes that occurred during the sintering of alumina doped with TiO 2 and SiO 2 have been investigated. The kinetics of normal grain growth at the initial stage is retarded by the dopant segregation at the grain boundaries. However, due to the accumulation of dopants at the grain boundaries during grain growth, its concentration at the boundaries ultimately exceeds the solubility limit and an intergranular liquid film emerges. The appearance of the liquid and the resulting increase in boundary mobility are confirmed to be the main cause of abnormal grain growth. For the abnormal grains, a liquid phase is observed at the basal surface in most cases, while the edges of these grains were partially wetted. Anisotropic or directional growth of the abnormal grains is explained in terms of the enhanced growth kinetics due to the re-entrant edges formed by grain boundaries at the non-basal planes.