Atomistic study of chemical effect on local structure in Mg-based metallic glasses

Abstract

By applying a recently constructed interatomic potential, molecular dynamics (MD) simulations were performed to investigate the structural origin of chemical effects in Mg–Cu–Ni ternary metallic glasses. The detailed evolution of local atomic structure in a series of Mg_x(Cu_42.5Ni_57.5)_100−x (x = 40–80) metallic glasses was tracked and comprehensively characterized by the pair correlation function, Voronoi tessellation, Honeycutt–Andersen bond pair and local chemistry analyses. Remarkable topological short-range orders (SROs) were found in Mg–Cu–Ni metallic glasses, with the characteristic motifs being icosahedra. The degree of icosahedral ordering varies distinctly with the alloy composition and is intimately correlated with the phase stability of metallic glasses. In contrast to the long-term understanding that five-fold bond pairs are a direct indication of icosahedral ordering, it was revealed that bond pairs are actually insensitive to the composition, and whether icosahedral ordering is preferred or not, fragmented pentagonal bipyramids are always populated. Furthermore, it was indicated that multiple chemical interactions among constituent atoms do result in chemical SROs in Mg–Cu–Ni metallic glasses, which are characterized by enriched Mg atoms in neighboring shells than expected from the nominal composition. The atomic-scale topological or chemical heterogeneity helps tune the local environments in Mg–Cu–Ni metallic glasses to achieve efficient packing and energy minimization for various compositions.