Composition-dependent fracture energy in metallic glasses

Abstract

The interplay between metallic glasses (MGs) mechanical properties, fracture energy $(G)$, and glass-forming ability (GFA) and their dependence on alloy composition remain poorly understood. Here, we perform molecular dynamics simulations to investigate the intrinsic composition dependence of $G$ in ${\mathrm{Cu}}_{x}{\mathrm{Zr}}_{100\ensuremath{-}x}\mathrm{MGs}$ $(x=20,30,40,50,64)$. The results indicate that the value of $G$ increases with Cu content. In addition, it is revealed that MGs with higher $G$ values display higher Poisson's ratio (\ensuremath{\nu}) and GFA, suggesting a close correlation between fracture toughness, mechanical properties, and GFA. This correlation between G, \ensuremath{\nu}, and GFA can be understood based on the fragility ($m$) of supercooled liquids, which is directly related to the structural heterogeneity in MGs. Larger $m$ values are related to dynamic slowdown and supercooled liquid stabilization, which enhance GFA and the formation of pronounced structural heterogeneity, comprised of loosely packed regions that favor \ensuremath{\beta} relaxation and the activation of shear transformation zones. Those concurrently promote the expansion of the plastic zone at the crack tip, enhancing the observed value of $G$. These simulation results shed light on the intrinsic relationship between fracture toughness, mechanical properties, and alloy composition in MGs.