Newtonian and non-Newtonian viscosity of supercooled liquid in metallic glasses

We have investigated the viscosity of the supercooled liquids over a wide range of strain rate by constant-strain-rate tensile tests for La55Al25Ni20, Zr65Al10Ni10Cu15 and Pd40Cu40P20 (at.%) metallic glasses. The supercooled liquids exhibited Newtonian viscosity (equilibrium state) that transferred to a non-Newtonian viscosity (non-equilibrium state) with increasing temperature. The critical strain rate of the Newtonian viscosity increased with increasing temperature in accordance with the Arrhenius relation. The strain rate dependence of viscosity was described well with a master curve expressed by a stretched exponential function η/η0=1−exp(C/ε̇β). The Newtonian viscosity was successfully described with the free-volume model of Cohen and Grest. The fragility of the Newtonian viscosity revealed that the supercooled liquids of the metallic glasses were classified into the relatively strong liquids such as Ge10As10Se80, B2O3 and Na2O–2SiO2 glass formers.