SATBILITY CRITERION OF NONEQUILIBRIUM PLANAR SOLID/LIQUID INTERFACE.

Effects of the deviation of actual solute distribution from the equilibrium distribution at interface of the undercooling theory, which is especially important in solidification theory, are analysed. It is suggested that the deviation from equilibrium of a solid/liquid interface can be expressed in terms of DELTA Tk plus DELTA Tn, where DELTA Tk is a kinetic undercooling and DELTA Tn an additional interface undercooling resulting from the nonequilibrium solute distribution. A mistaken conception that a planar interface becomes unstable because a constitutionally undercooled zone exists in the melt ahead of the interface, which has been widely accepted by metallurgists and physicists for more than thirty years, is corrected.