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 degrees, which indicates that the growth front is parallel to {11 (2) over bar0}(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 alpha-Mg matrix.