The relationship between viscosity and local structure in liquid zirconium via electromagnetic levitation and molecular dynamics simulations

The temperature dependent viscosities of stable and undercooled liquid zirconium (Zr) have been studied by the electromagnetic levitation (EML) experiments on the International Space Station ISS together with molecular dynamics (MD) simulations. Oxygen additions of about 1.2 +/- 0.5 at.% in EML experiments increases the viscosity of undercooled liquid Zr. MD simulations reveal a Vogel-Fulcher-Tammann-type temperature dependent viscosity for pure Zr in the temperature range of 1600-2700 K. The evolution of the internal energy and the nearest neighboring coordination numbers show crossovers at about 2000 K, indicating a local structural change when stable liquid Zr is cooled into undercooled liquid state. This local structural change is reflected by a slight drop of fraction of the <0,3,6,4> cluster, and the nonlinear temperature dependent evolution of icosahedral-like, bcc-like and tetrahedral-like short-range order. The temperature dependent fraction of mobile atoms with high potential energy exhibits a strong anti-correlation with the temperature dependent viscosity. The decrease of these mobile atoms reduces the potential energy and increases the high-coordinated clusters with strong spatial correlations upon cooling, resulting in an increase of the local stability and viscosity of stable and undercooled liquid Zr. All results obtained here will promote the research activities of the thermophysical properties and structural evolution of metallic liquids. (C) 2019 Elsevier B.V. All rights reserved.