Temperature Dependence of Viscosity in Supercooled Liquid of Cu-Zr Bulk Metallic Glass by Molecular Dynamics

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When a cooling rate is fast enough to prevent crystallization, molten metals are solidified into disordered structures so called amorphous metals. During the cooling process, molten metals become supercooled liquid below the melting point, and dynamic factors such as viscosity and relaxation time rapidly increase, while static factors such as density show no significant change. In the present study, we investigated a temperature dependence of viscosity of Cu-Zr bulk metallic glass above the glass transition temperature Tg using both molecular dynamics (MD) technique and a recently developed energetic technique. A limitation of MD time scale prevents us to calculate viscosity at Tg, because a relaxation time of supercooled liquid becomes significantly long at slightly above Tg. On the other hand, a new method developed by Kushima et. al., analyzes transition state pathway trajectory from an energetic viewpoint and provides viscosity of liquid state at wide temperature range from sufficient high temperature to Tg. We discuss a temperature dependence of viscosity of Cu-Zr bulk metallic glass both from atomistic and energetic viewpoints.