Dynamic evolution of microstructure morphology in thin-sample solidification: Deep learning assisted synchrotron X-ray radiography

The dendrite morphology significantly affects the formation of micro-segregation, intermetallic precipitation, and rheology of the mushy zone during solidification. Among the parameters that describe the morphology of dendrites, the specific interface area is critical since it characterizes the overall morphology of dendrites in a universal and general sense. In this work, a novel radiography-based method has been proposed to achieve in-situ determination of the evolving specific interface area during thin-sample solidification. Employing our proposed deep-learning-based dendrite segmentation model and image processing method, a generally authentic three-dimensional solidification microstructure can be obtained, which underlies the measurement of specific interface area from radiographs with negligible relative error. This method can be employed to study the evolution of 3D microstructure under large cooling rates requiring high temporal resolution. Based on this method, the morphology evolution of the overall solidification microstructure during directional solidification of Al-15 wt% Cu alloy has been studied. The results indicate that the evolution of interfacial area density SV conforms to the relation suggested by Rath with asymmetric law. Besides, the asymmetric evolution of SV concerning solid fraction can be attributed to the concurrent growth and coarsening of the solid phase with uneven change rates under temperature gradient.