# Chemical Ordering and Crystal Nucleation at the Liquid Surface: A Comparison of $\rm{Cu}_{50}\rm{Zr}_{50}$ and $\rm{Ni}_{50}\rm{Al}_{50}$ Alloys

## TL;DR

This study compares how the liquid-vapor surface affects crystallization in two metal alloys, revealing that compositional fluctuations at the surface influence heterogeneous nucleation and glass forming ability.

## Contribution

It demonstrates that compositional ordering at the surface correlates with increased crystallization in certain alloys, providing insight into surface effects on glass formation.

## Key findings

- Ni50Al50 shows surface-enhanced crystallization due to compositional ordering.
- Cu50Zr50 exhibits diffuse adsorption without surface crystallization.
- Surface composition susceptibility influences glass forming ability.

## Abstract

We study the influence of the liquid-vapor surface on the crystallization kinetics of supercooled metal alloys. While a good glass former, $\rm{Cu}_{50}\rm{Zr}_{50}$, shows no evidence of surface enhancement of crystallization, $\rm{Ni}_{50}\rm{Al}_{50}$ exhibits an increased rate of crystallization due to heterogeneous nucleation at the free liquid surface. The difference in the compositional fluctuations at the interface is proposed as the explanation of the distinction between the two alloys. Specifically, we observe compositional ordering at the surface of $\rm{Ni}_{50}\rm{Al}_{50}$ while the $\rm{Cu}_{50}\rm{Zr}_{50}$ alloy only exhibits a diffuse adsorption of the Cu at the interface. We argue that the general difference in composition susceptibilities at planar surfaces represents an important factor in understanding the difference in the glass forming ability of the two alloys.