EFFECTS OF SHEAR-FLOW AND ANISOTROPIC KINETICS ON THE MORPHOLOGICAL STABILITY OF A BINARY ALLOY

The effect of a parallel shear flow and anisotropic interface kinetics on the onset of instability during the directional solidification of a binary alloy at constant velocity is calculated. The model for aniso tropy is based on the motion of steps. A shear flow (linear Couette fl ow or asymptotic suction profile), parallel to the crystal-melt interf ace in the same direction as the step motion, decreases interface stab ility in that the critical solute concentration decreases. A shear flo w counter to the step motion enhances stability for small shear rates; for larger shear rates, the neutral curve develops a bimodal structur e, and the critical solute concentration slowly decreases with shear r ate.