Short-range ordering in metallic supercooled liquids and glasses

The structural order in metallic supercooled liquids and glasses is a long-standing issue. Unlike the medium-range order (MRO) which involves at least hundreds of atoms, short-range order (SRO) only concerns the central atom and its neighbors, which can be described more easily. Here, we use the molecular dynamics simulation to investigate the SRO in supercooled liquids and glasses of two pure metals Ta and Ni respectively with the body-centered cubic (BCC) and the face-centered cubic (FCC) crystalline lattice and two binary alloys Cu50Zr50 and Ni50Al50 both with a B2 crystalline phase. To compare, a ternary alloy of Cu47.5Zr47.5Al5 is also investigated. Hexagonal closed-packed (HCP) and icosahedron (ICO) clusters are found to dominate the SRO in both supercooled liquids and glasses. As expected, the glass is found more structurally ordered than the supercooled liquid. The glass transition is found to be linked to the kink of the temperature dependence of SRO. The binary system, as the relatively good glass-former, is less structurally ordered than the monatomic system as a poor glass-former, but it is more structurally ordered than the ternary one. These findings have profound implications for understanding the glass transition and designing new metallic glasses. (C) 2018 Elsevier B.V. All rights reserved.