Time-resolved tomography (4D-CT) combined with X-ray diffraction (XRD) has allowed us to observe the dendritic structure and measure crystallographic orientation in situ. The observations were performed in a synchrotron radiation facility SPring-8. A specimen (0.6-3 mm in diameter and 5 mm in length) was rotated at 0.25–2 rps. The convolution back-projection using 200-400 projection images was used for reconstruction (voxel edge length 6.5 µm or 2 µm). It was necessary to improve the reconstruction images for evaluating the solid-liquid interface area and the interface curvatures. A phase field model was used as an image processing procedure. The reconstructed images gave the initial phase field and the restraint condition (solid fraction). The 3D image was sufficiently improved for the evaluation. In particular, the interface shape was reconstructed not to contradict the curvature effect because the curvature effect was inherent in the phase field model. Even for the Fe-C system, in which the difference in X-ray absorption coefficient between liquid and solid was low, the interface area and the curvature of dendrites were evaluated. In addition, rather complicated growth directions in hexagonal Mg-Zn alloys were determined by 4D-CT and XRD. This paper discussed applications of 4D-CT+XRD.

Moderated by: Andreas Ludwig / Alain Jacot