Numerical model for nucleation of peritectic alloy during unidirectional solidification

Based on transient nucleation theory, a numerical model has been constructed to describe the nucleation process of a new phase in front of the liquid-solid interface of a prior steady-growth phase in peritectic alloy with the combination of the concentration field calculated by a self-consistent numerical model for cellular/dendritic growth. The results show that the nucleation incubation time of a new phase varies with the solidification rate during unidirectional solidification. During unidirectional solidification of the Zn-4.0 wt.% Cu alloy, the incubation time changes very slightly when the solidification rate increases from 50 to 500 μm/s, but it increases significantly when the solidification rate exceeds 500 μm/s. The calculated results show a reasonable agreement with the experimental ones. This model reveals that nucleation of a new phase is time-dependent and reasonably explains the effect of the solidification velocity on the behaviors of nucleation and growth of ε dendrites in the matrix of the η phase in unidirectional solidification of Zn rich Zn-Cu alloys.