Newtonian viscosity of supercooled liquid in a Pd40Ni40P20 metallic glass

The Newtonian viscosity of the supercooled liquid measured by the continuous-strain-rate tensile test was investigated in the Pd40Ni40P20 metallic glass. It was found that continuous-strain-rate tests were applicable to determine the viscosity over a wide strain-rate region, and that the measured Newtonian viscosity eta(0) corresponded to the equilibrium one. The viscosity eta over the entire strain-rate interval could be well described by one master curve expressed with a stretched exponential function eta/eta(0)=1-exp(C/(epsilon)over dot(beta)) in which beta was 0.82. The free-volume-theory relation proposed by Cohen and Grest reproduced the equilibrium viscosity data over the entire temperature region better than the famous Vogel-Fulcher-Tammann relation. The supercooled liquid of the Pd40Ni40P20 metallic glass was classified into the relatively strong liquids as well as the other metallic glasses. The Pd40Ni40P20 metallic glass that is a metal-metalloid alloy exhibited to be more fragile than metal-metal glasses. (C) 2000 American Institute of Physics. [S0003-6951(00)03034-5].