The growth direction selection of inclined dendrites induced by solute interaction: A phase-field study

Columnar dendritic patterns are the predominant microstructures of directional solidified alloys, which control the micro-segregation and largely affect the mechanical properties of the material. Herein, the growth direction selection of inclined columnar dendrites during the directional solidification of a Mg-4 wt% Li alloy with the hexagonal close-packed (HCP) crystal structure was investigated by means of phase-field simulations. It is found that the DGP law, which suggests the variation of dendrite growth direction with P é clet number Pe (directly related to the pulling velocity and the primary dendrite spacing), is also applicable to HCP-structured materials. However, results at high pulling velocity show a deviation from the DGP law. To characterize the solute distribution variation around the dendrite tip with changing Pe, we defined a quantitative characteristic of solute concentration field. This quantitative characterization proves that the DGP law is dominated by the solute interaction coming from the solute diffusion layers overlap of neighboring dendrites. That is, increasing the primary spacing or the pulling velocity can weaken the solute interaction and result in the rotation of dendrite growth direction to the preferred crystalline direction. The solute interaction does not work when the solute diffusion layer becomes thin enough under very high pulling velocities. The weakening and failure of solute interaction between neighboring dendrites result in the deviation of dendrite growth direction from the DGP law found in this study and previous study.