Multiscale Simulation of α-Mg Dendrite Growth via 3D Phase Field Modeling and Ab Initio First Principle Calculations

Abstract

Based on synchrotron X-ray tomography and electron backscattered diffraction techniques, recent studies revealed that the α-Mg dendrite exhibited an 18-primary-branch morphology in 3D, of which six grew along $< 11\overline{2}0 >$ on the basal plane, whereas the other twelve along $< 11\overline{2}3 >$ on non-basal planes. To describe this growth behaviour and simulate the morphology of the α-Mg dendrite in 3D, an anisotropy function based on cubic harmonics was developed and coupled into a 3D phase field model previously developed by the current authors. Results showed that this anisotropy function, together with the phase field model could perfectly describe the 18-primary-branch dendrite morphology for the magnesium alloys. The growth tendency or orientation selection of the 18-primary-branch morphology was further investigated by performing ab initio first principle calculations based on the hexagonal symmetry structure. It was showed that those crystallographic planes normal to the preferred growth directions of α-Mg dendrite were characterized by higher surface energy than these of others, i.e. coinciding with the 18-primary-branch dendritic morphology. Apart from agreement with experiment results and providing great insights in understanding dendrite growth behaviour, such multiscale computing scheme could also be employed as a standard tool for studying general pattern formation behaviours in solidification.