Development of a data assimilation system for the investigation of the dendrite solidification process by integrating in situ X-ray imaging and phase-field simulation

The dendrite solidification process has been observed and simulated using state-of-the-art techniques, such as time-resolved X-ray tomography (4D-CT) and high-performance phase-field (PF) simulations. 4D-CT has enabled the direct observation of the 3D dendrite growth in opaque alloys. However, the spatiotemporal resolution is not sufficient for investigating fast phenomena because a 3D solidification structure is obtained using hundreds of transmission images during the 180° rotation of a sample. High-performance PF simulations have enabled the simulation of multiple 3D dendrite growth phenomena. However, the material properties required in PF solutions of alloys are often unavailable. Therefore, integrating in situ X-ray observations with PF simulations using data assimilation is a promising approach for simultaneously solving these issues. In this study, we developed a data assimilation system with an ensemble Kalman filter, in which the solid fraction along the thickness of a sample was used as observation data to enable data assimilation using X-ray transmission images. The performance of the developed data assimilation system was evaluated via twin experiments for columnar dendrite growth during the directional solidification of a binary alloy in a thin film. The results showed that data assimilation using the solid fraction as observation data estimated the material properties and solidification morphologies with reasonable accuracy.