Comparing short–range and medium–range ordering in Cu[sbnd]Zr and Ni[sbnd]Zr metallic glasses – Correlation between structure and glass form ability

Abstract

According to recent studies, CuZr and NiZr binary alloying systems are very similar based on known glass-forming ability criteria, however, they exhibit significant difference in glass-forming ability in practice. In this work, local atomic structures of CuZr and NiZr metallic glasses are studied by molecular dynamics simulation to explain the source of mentioned difference. The total and partial distribution functions, coordination number and voronoi analysis are utilized to characterize the local atomic structures around Zr, Ni and Cu atoms. It was found that the local environment around Zr atoms is almost similar in both systems. The difference in the atomic structure in these systems mainly arises from topologies of polyhedra around Cu and Ni atoms. In particular, full icosahedron is one of the most popular local structure in CuZr system, while its population is significantly smaller in NiZr system with the same composition. Additionally, networks formed by full icosahedra connections, medium range order, are more robust in CuZr system. Higher percentage of topologically ordered and compact structures and their connectivity could explain why bulk metallic glass formation is possible in CuZr system but not in NiZr system.