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

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 Dₘᵢₙ² 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.