Three-dimensional shapes and distributions of long-period stacking ordered structures in Mg₉₇Zn₁Gd₂ cast alloys characterized by electron tomography

Three-dimensional (3D) configurations of 14H long-period stacking ordered (LPSO) structures formed in Mg₉₇Zn₁Gd₂ cast alloys at intermediate stages of the formation process have been studied by single tilt-axis electron tomography using high-angle annular dark-field scanning transmission electron microscopy. Lateral morphology of the 14H LPSO is clearly visualized by reconstructing 3D volumes. An existence of "dent-shaped" area was found in a 3D reconstructed volume for the first time. The edge of LPSO shows a characteristic triangular shape with an angle of 60°, which indicates that the growth front is parallel to {112¯0}_Mg. It is suggested that in-plane irregular or characteristic shapes are related to the lateral growth mechanism of LPSO. Electron tomography has proven to be an indispensable tool to characterize in-plane structural information of LPSO formed in α-Mg matrix.