The trajectory of subboundary grooves during directional solidification of dilute alloys

Due to their strong surface energy anisotropy, subboundaries generally do not intersect solid–melt interfaces at right angles. As a consequence, subboundary surface grooves move laterally during solidification, and thereby interact, in alloys, with the solute concentration gradients created in the liquid. We discuss the consequences of this effect during thin directional solidification at speeds (V) lower than the cellular-instability threshold V c of the system. We show that the lateral drift of the subboundary grooves slows down (or equivalently the tilt angle of the subboundaries relative to the growth direction decreases) as V increases and vanishes as V approaches V c .