Asymmetric crystallization during cooling and heating in model glass-forming systems

TL;DR

This study uses molecular dynamics simulations to explore the asymmetric crystallization behavior during heating and cooling in model glass-forming systems, revealing how intrinsic and preparation-rate factors influence crystallization kinetics.

Contribution

It demonstrates that the asymmetry ratio of critical heating and cooling rates depends on glass-forming ability and preparation rate, aligning with classical nucleation theory and experimental data.

Findings

Asymmetry ratio R_h*/R_c* exceeds 1, increasing with GFA.

Classical nucleation theory qualitatively predicts the asymmetry ratio.

Preparation rate R_p significantly influences crystallization behavior.

Abstract

We perform molecular dynamics (MD) simulations of the crystallization process in binary Lennard-Jones systems during heating and cooling to investigate atomic-scale crystallization kinetics in glass-forming materials. For the cooling protocol, we prepared equilibrated liquids above the liquidus temperature $T_l$ and cooled each sample to zero temperature at rate $R_c$. For the heating protocol, we first cooled equilibrated liquids to zero temperature at rate $R_p$ and then heated the samples to temperature $T > T_l$ at rate $R_h$. We measured the critical heating and cooling rates $R_h^*$ and $R_c^*$, below which the systems begin to form a substantial fraction of crystalline clusters during the heating and cooling protocols. We show that $R_h^* > R_c^*$, and that the asymmetry ratio $R_h^*/R_c^*$ includes an intrinsic contribution that increases with the glass-forming ability (GFA) of the system and a preparation-rate dependent contribution that increases strongly as $R_p \rightarrow R_c^*$ from above. We also show that the predictions from classical nucleation theory (CNT) can qualitatively describe the dependence of the asymmetry ratio on the GFA and preparation rate $R_p$ from the MD simulations and results for the asymmetry ratio measured in Zr- and Au-based bulk metallic glasses (BMG). This work emphasizes the need for and benefits of an improved understanding of crystallization processes in BMGs and other glass-forming systems.