Growth directions of microstructures in directional solidification of crystalline materials

Abstract

In directional solidification, as the solidification velocity increases, the growth direction of cells or dendrites rotates from the direction of the thermal gradient to that of a preferred cristalline orientation. Meanwhile, their morphology varies with important implications for microsegregation. Here, we experimentally document the growth directions of these microstructures in a succinonitrile alloy in the whole accessible range of directions, velocities, and spacings. For this, we use a thin sample made of a single crystal on which the direction of the thermal gradient can be changed. This allows a fine monitoring of the misorientation angle between thermal gradient and preferred crystalline orientation. Data analysis shows evidence of an internal symmetry which traces back to a scale invariance of growth directions with respect to a Péclet number. This enables the identification of the relationship between growth directions and relevant variables, in fair agreement with experiment. Noticeable variations of growth directions with misorientation angles are evidenced and linked to a single parameter.

Experimental observation of oscillatory cellular patterns in three-dimensional directional solidification

“…We attribute the origin of these different drifting regions to the 8 µm/s growth stage during which the high pulling rate leads to more dendritic patterns combined to a highly concave front. Those two elements lead to a tilting of the growth direction with respect to the pulling axis, possibly due to the combined effect of crystalline misorientations, as previously discussed [46,47], and thermal gradient misorientation at concave growth front [38,48]. A crystalline misorientation induces translational drift when the thermal gradient is aligned to the pulling axis but combined to the misorientation of the thermal gradient due to concavity, of axial symmetry, a complex variation of tilting of the growth direction throughout the pattern is observed.…”

“…We evidenced the critical influence of pattern drift on oscillation inhibition. Such a drift consists of a component of growth velocity in the plane normal to the pulling axis, which is due to a misalignment between the <100> preferred growth direction and the pulling/thermal axis; the direction and rate of drift depend on the misorientation angle and the pulling velocity [47].…”

“…In practice, the growth direction changes from the thermal gradient direction at low velocity to the closest <100> direction when pulling rate increases [46,47], meaning that the growth direction will be misoriented with respect to the pulling/thermal axis if no <100> direction is perfectly aligned with this axis. Inclined structures are particularly well revealed by the pattern drift that they induce in the lateral direction (i.e.…”

Morphological evolution of the solid-liquid interface near grain boundaries during directional solidification

“…Another interesting feature of the solidification process is the growth direction of a microstructure [16][17][18][19][20]. It is well known that the growth directions of cells are approximately parallel to the thermal gradient direction, deflecting from the crystalline orientation <100> for a SCN-based alloy.…”

Solidification in a Supercomputer: From Crystal Nuclei to Dendrite Assemblages

“…6c and d. Because the inclined dendrites grow in the h100i direction with increasing arm spacing, [99][100][101][102] the UO dendrites move toward the FO dendrites. As a result, the competition between dendrites becomes intense at the GB, and the shape of the GB becomes zigzag as shown in Fig.…”