Defect formation by order coalescence in vermicular grains during alumina phase transformation

Abstract Vermicular α-Al 2 O 3 grains obtained from γ- to α-phase transformation were investigated. X-ray diffraction patterns showed a left-shifting shoulder in all diffraction peaks of transformed α-Al 2 O 3 . High-resolution transmission electron microscopy results confirmed large amounts of defects inside the vermicular α-Al 2 O 3 single-crystal. Combined with grain-growth discontinuity, the authors proposed that the defects inside vermicular grains resulted from assembly of nanosized α-crystallites by an ordered coalescence mechanism directly after phase transformation, by which the orientation alignment was thermodynamically favored in the solid-state sintering.