NONEQUILIBRIUM ANALYSIS OF HIGH-GRADIENT ABSOLUTE STABILITY DURING UNIDIRECTIONAL SOLIDIFICATION

Further analysis of the M-S interface stability theory predicts a new phenomenon, the high gradient absolute stability (HGAS); that is, when temperature gradient exceeds a critical value, the solidification int erface becomes absolutely stable no matter how large solidification ve locity is. The critical temperature gradient for HGAS is explicitly ev aluated by incorporating mathematical deduction with numerical calcula tion. The critical conditions for HGAS of several typical alloys are m odified by inserting a velocity-dependent partition coefficient and a velocity-dependent slope of the ''kinetic liquidus'' into the HGAS ana lysis. These nonequilibrium interface kinetic effects decrease the pre dicted critical temperature gradient for HGAS. (C) 1997 Elsevier Scien ce Ltd.