Nucleation of stoichiometric compounds from liquid: the role of the kinetic factor

TL;DR

This study uses molecular dynamics simulations to investigate how kinetic factors influence the nucleation of stoichiometric compounds from liquids, highlighting the importance of kinetics over free energy barriers.

Contribution

It provides new insights into the kinetic factors affecting nucleation rates, especially in the context of ordered phases like B2 in metallic alloys.

Findings

Nucleation rate in Ni50Al50 is lower despite a higher free-energy barrier.

Ordered B2 phase's structure influences nucleation kinetics.

Cu50Zr50 B2 phase nucleation is not observed due to minimal anti-site defects.

Abstract

While the role of the free energy barrier during nucleation is a text-book subject the importance of the kinetic factor is frequently underestimated. We obtained both quantities from molecular dynamics (MD) simulations for the pure Ni and B2 phases in the Ni50Al50 and Cu50Zr50 alloys. The free-energy barrier was found to be higher in Ni but the nucleation rate is much lower in the Ni50Al50 alloy which was attributed to the ordered nature of the B2 phase. Since the Cu50Zr50 B2 phase can has even smaller fraction of the anti-site defects its nucleation is never observed in the MD simulation.