Understanding Homogeneous Nucleation in Solidification of Aluminum by Molecular Dynamics Simulations

TL;DR

This study uses large-scale molecular dynamics simulations to investigate the process of homogeneous nucleation in aluminum melt, identifying critical parameters, phases, and effects of cooling rates on solidification behavior.

Contribution

It provides detailed insights into aluminum nucleation mechanisms and phase formation during solidification, using extensive atomistic simulations with new findings on phase fractions and grain growth.

Findings

Identified critical nucleus size and nucleation temperature.

Detected face-centered cubic, hexagonal close-packed, and amorphous phases.

Showed cooling rate influences phase fractions and grain growth.

Abstract

Homogeneous nucleation from aluminum (Al) melt was investigated by million-atom molecular dynamics (MD) simulations utilizing the second nearest neighbor modified embedded atom method (MEAM) potentials. The natural spontaneous homogenous nucleation from the Al melt was produced without any influence of pressure, free surface effects and impurities. Initially isothermal crystal nucleation from undercooled melt was studied at different constant temperatures, and later superheated Al melt was quenched with different cooling rates. The crystal structure of nuclei, critical nucleus size, critical temperature for homogenous nucleation, induction time, and nucleation rate were determined. The quenching simulations clearly revealed three temperature regimes: sub-critical nucleation, super-critical nucleation, and solid-state grain growth regimes. The main crystalline phase was identified as face-centered cubic (fcc), but a hexagonal close-packed (hcp) and an amorphous solid phase were also detected. The hcp phase was created due to the formation of stacking faults during solidification of Al melt. By slowing down the cooling rate, the volume fraction of hcp and amorphous phases decreased. After the box was completely solid, grain growth was simulated and the grain growth exponent was determined for different annealing temperatures.