An exact measurement of nucleation incubation times in isothermal crystallizations of liquid metal Al via configuration heredity

Abstract

Nucleation induction time τ∗ is a crucial parameter in the classical nucleation theory, which is intimately associated with the steady-state nucleation rate I0 in the homogenous nucleation. To examine the impact of temperatures T on τ∗(T) in the isothermal crystallizations of liquid metal Al, a series of molecular dynamics simulations are performed at different undercoolings ΔTm. With the help of cluster type index method based on Honeycutt–Anderson bond-type index, a cluster analysis method based on the continuous heredity of crystal clusters is developed to further distinguish nuclei from various embryos. By means of the transient heredity of crystal clusters, a nucleation incubation time τc different from nucleation induction time, i.e., a sum of incubation time of embryo τe and its effective growth time τgeff prior to arriving the critical size, is introduced and exactly measured. For the critical nuclei emerged in the transient nucleation stage, the τc are found to be long compared with the steady-state nucleation stage and mainly depend on an effective growth of incubated embryos, while those in steady-state nucleation stage are mostly decided by a successful incubation of initial embryos. Also, relative to the τ∗(T) derived from I0(T) at different ΔTm, these measured τc(T) are very small, but their average times τ¯c(T) in the whole region are mirror symmetric to I0(T).