Growth competition between columnar dendrite and degenerate seaweed during directional solidification of alloys: Insights from multi-phase field simulations

In this paper, the growth competition between columnar dendrite and degenerate seaweed during directional solidification of a dilute alloy was investigated by using the quantitative multi-phase field model of dilute binary alloys developed by Ofori-Opoku et al. [Acta Materialia, 2010, 58: 2155–2164]. Our recent experiments of degenerate seaweed in directional solidification of an Al-4.5 wt% Cu alloy by employing (100)[011] orientated planar-front seeds motivate this work. We found that the way of symmetrical columnar dendrites impinging is the lateral movement of the grain boundary by adjusting the dendritic primary spacing. The elimination rate of degenerate seaweed at the converging grain boundary increases rapidly as the misorientation angle is increased. This can be explained by the increase of the lateral component of the real tilted dendritic direction with the increase of misorientation angle. This proves the finding from our experiments. Predicted results also show that the degenerate seaweed can overgrow the tilted dendrite at the diverging grain boundary. This is not consistent with experimental results. Moreover, our results show that grain boundary angles at the two grain boundary angles increase with the misorientation angle increasing.