Non-uniplanar competitive growth of columnar dendritic grains during directional solidification in quasi-2D and 3D configurations

The competitive growth of bicrystals during directional solidification in both thin samples and three-dimensions (3D) was investigated by phase-field simulations. Unlike previous studies, which assumed the <001> orientation of the two competing grains to be in the same plane or in two parallel planes which are normal to the contacting plane of two grains, simulations in the present study focused on the more common configurations in which the <001> orientation of the two grains is non-uniplanar. Simulations of competitive growth in thin samples showed that the deviation of the <001> orientation of an unfavorably orientated grain from the sample plane caused difficulty in the generation of new primary arms from the unfavorably orientated grain. Therefore, the grain boundary orientation in thin samples may deviate from that in two-dimensions (2D), even though the bicrystal configuration observed in the thin-sample plane appeared similar to that in the 2D. It was found that in 3D, the new primary arms could develop from the favorably oriented dendrites along two directions to occupy the gap left by the unfavorably orientated grains, which led to a faster overgrowth rate of the unfavorably orientated grains than that in the case of diverging growth in 2D.