Anisotropic grain growth in TiO₂-doped alumina

Grain growth in TiO₂-doped alumina was studied in a high density, ultrafine matrix (0.4 μm. Normal grain growth, anisotropic grain growth and abnormal grain growth were observed. With 0.15-0.4 wt.% TiO₂, samples initially undergo normal grain growth until a crystal microstructure is attained and anisotropic grain growth in nucleated. Large anisotropic, platelet-shaped grains grow rapidly by a step growth process until impingement of the large grains essentially stops further growth. The volume fraction of anisotropic grains ranged from 20 to 100 vol.% suggesting that physical properties dependent on grain shape and volume fraction can be tailored. Critical requirements are proposed for the in situ growth of anisotropic grains.