Anomalous Viscoelastic Behavior of Metallic Glasses of Pd–Si-Based Alloys

Abstract

The temperature and the stress dependence of viscoelastic properties of metallic glasses of three compositions: Pd_0.795Au_0.04Si_0.165, Pd_0.795Ag_0.04Si_0.165 and Pd_0.775Cu_0.06Si_0.165 have been studied near the glass temperature. The total retarded tensile compliance of these alloy glasses, ${\mathrm{J̃}}_d^0$ is small at low temperature (of the order of glass compliance J̃_g) but increases rapidly in a narrow temperature range when the temperature approaches T_a, at which the viscosity of the glass attains 10¹² P, and attains a value as high as 200 times the glass compliance J̃_g for the Pd_0.775Cu_0.06Si_0.165 glassy alloy, at T > T_a + 15°K. Concurrent with an increase in ${\mathrm{J̃}}_d^0$ near T_a, the alloy liquids become non‐Newtonian in the stress range employed (σ varies from 6×10⁶ to 3×10⁸ dyn/cm²). The apparent shear activation volume for the viscous flow deduced from the non‐Newtonian behavior increases with temperature and attains a value as high as 100 times the atomic volume. These results have been compared with viscoelastic behavior of other types of liquids. It is suggested that the strong temperature dependence of the shear compliance of metallic liquids near T_g may be attributed to some sort of macroscopic structural rearrangements taking place as temperature is changed. The large activation volume of viscous flow seems to imply that the flow mechanism involves a large number of simultaneous atomic displacements in the flow direction.