# Compositional complexity buffers free-volume sensitivity and serrated flow in metallic glasses

## TL;DR

This study shows that increasing compositional complexity in metallic glasses reduces sensitivity to quench rate and improves mechanical performance.

## Contribution

The paper quantifies how compositional complexity buffers free-volume sensitivity and serrated flow in Cu-Zr-based metallic glasses.

## Key findings

- Higher compositional complexity narrows free-volume distributions and reduces quench-rate sensitivity.
- Hardness, modulus, and elastic recovery increase with complexity, while serration density and plastic-zone volume decrease.
- Radial-distribution metrics confirm enhanced short/medium-range stability with increased complexity.

## Abstract

Processing history imprints metallic glasses (MGs), yet whether compositional complexity desensitizes structure and mechanics to quench rate remains unresolved. We use large-scale molecular dynamics along a controlled Cu-Zr complexity ladder, Cu50Zr50, Cu47.5Zr47.5Al5, and Cu45Zr45Al5Ti5, vitrified over 1011–1015 K·s−1 and probed by spherical nanoindentation. Additionally, composition-resolved CuxZr100−x sweep (x = 40–65 at.%) and a microalloying series Cu50-z/2Zr50-z/2Alz, (z = 1–5 at.%) disentangle configurational entropy-driven effects from enthalpic and structural covariates. Atomic free volume is obtained from radical-Voronoi tessellation; non-affine rearrangements are quantified by Falk–Langer \documentclass[12pt]{minimal}
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\begin{document}$${D}_{\min }^{2}$$\end{document}Dmin2 field and clustered in three dimensions. Three quantitative descriptors capture the dispersion of free volume and its quench rate sensitivity as a function of compositional complexity. Increasing compositional complexity narrows free-volume distributions across quench rates and systematically reduces the fast-slow disparity. A two-axis reconciliation emerges: within binary Cu-Zr, configurational entropy peaks near equiatomic and minimizes rate sensitivity, whereas across alloy families (binary→ternary→quaternary), increased species diversity and size/enthalpy mismatch further suppress sensitivity. Structure-property co-variation is consistent: at fixed rate, hardness, modulus and elastic recovery increase, while serration density, STZ number density, and plastic-zone volume decrease. Radial-distribution metrics and indentation-induced icosahedral losses corroborate enhanced short/medium-range stability. Compositional complexity thus provides a quantitative lever for processing-tolerant, high-performance Cu-Zr-based MGs.