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

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, Cu 50 Zr 50 , Cu 47.5 Zr 47.5 Al 5 , and Cu 45 Zr 45 Al 5 Ti 5 , vitrified over 10 11 –10 15 K·s −1 and probed by spherical nanoindentation. Additionally, composition-resolved Cu x Zr 100− x sweep ( x = 40–65 at.%) and a microalloying series Cu 50- z /2 Zr 50- z /2 Al z , ( 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 $${D}_{\min }^{2}$$ D min 2 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.