The influence of shear rate and temperature on the viscosity and fragility of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 metallic-glass-forming liquid

The shear rate and temperature dependence of the viscosity in the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic-glass-forming liquid has been measured in the liquid and undercooled liquid state between 907 and 1300 K. After quenching the alloy into a glassy state, the reheated material displays very high viscosity values above the liquidus temperature of 1026 K. This liquid alloy is kinetically strong with pronounced shear thinning. With increasing temperature a transition to a more fragile liquid is observed with a drastic drop in viscosity that is associated with the disappearance of shear thinning. This fragile state is attained above 1225 K. When cooled from this state the strong state is only recovered when the liquid is deeply undercooled below the liquidus temperature. The shear thinning and strong to fragile transition is attributed to the destruction of medium- and short-range order in the liquid by mechanical and thermal effects, respectively.