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 42.5 Ni 57.5 ) 100Àx (x ¼ 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 shortrange 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. Fig. 2 Total pair correlation functions, g(r), for Mg x (Cu 42.5 Ni 57.5 ) 100Àx (x ¼ 40, 50, 60, 70 and 80) MGs. To further reveal the fine structure, the partial pair correlation functions, g AB (r), that contribute to the total g(r) for MG with x ¼ 80 are also displayed. The blue dashed line is g AB (r) for Mg-Mg, the dashed/dotted line is for Mg-Cu, and the dotted line is for Mg-Ni. The g AB (r) for Cu-Cu, Cu-Ni, and Ni-Ni are not shown here due to their minor contributions.This journal is

Point-Pattern Matching Technique for Local Structural Analysis in Condensed Matter

“…The clusters with Voronoi indices 0 0 12 0 are most geometrically similar to the perfect icosahedron, consistent with the MG literature, as shown by their notably low mean GME. The Voronoi indices that are most often considered quasi-icosahedral include 0 2 8 2 , 0 2 8 1 , and 0 1 10 2 45,[69][70][71][72] , and while many of the clusters with these topologies exhibit a low GME, they display a wide range of distortions. In addition, the mean GME of clusters with Voronoi index 0 3 6 3 is 0.57.…”