Newtonian to non-Newtonian master flow curves of a bulk glass alloy Pd40Ni10Cu30P20

Abstract

The viscosity and flow stress of a bulk ${\mathrm{Pd}}_{\mathrm{40}}{\mathrm{Ni}}_{\mathrm{10}}{\mathrm{Cu}}_{\mathrm{30}}{\mathrm{P}}_{\mathrm{20}}$ alloy glass near the glass transition were measured as a function of temperature and strain rate under compression. The steady-state viscosity of the glass for a given temperature remains constant at low strain rate, then decreases by many orders of magnitude above a critical strain rate. A master curve in term of the viscosity ratio ${\mathrm{\eta /\eta }}_N$ and the product ${\eta }_N\mathrm{\epsilon ̇}$ has been constructed, where η and ${\eta }_N$ are, respectively, the steady-state viscosity and Newtonian viscosity, and $\mathrm{\epsilon ̇}$ is the strain rate. The flow stress also can be represented in terms of the product ${\eta }_N\mathrm{\epsilon ̇.}$ The master curves are fitted with a simple stress relaxation of the form $\text{1−}\exp \mathrm{[-t/\lambda ]}$ with ${\mathrm{t=\epsilon ̇}}^{\text{−1}}.$