In Situ Observation of Stress-Induced Structural Disorder and Fictive Stress in a Zr55Al10Ni5Cu30 Glassy Alloy

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The heat evolution of stress-induced structural disorder, $\Delta H_{\text{s}}(t)$, in a Zr55Al10Ni5Cu30 glassy alloy during creep deformation under a constant load at the glass transition region ($T_{\text{g}}=680$ K) is investigated by an in situ measurement of temperature change of a deforming sample. For an initial stress, $\sigma_{0}$, greater than a critical stress, $\sigma_{\text{c}}=80$ MPa, all $\Delta H_{\text{s}}(t)$ curves grow gradually attaining a maximum then decrease with further deformation. The peak in $\Delta H_{\text{s}}$ indicates the attainment of an equilibrium flow structure. The $\Delta H_{\text{s}}$ curves plotted against the logarithm of normalized viscosity (ratio of viscosity, $\eta$, to the Newtonian viscosity, $\eta_{\text{N}}$) tend to merge and increase linearly with a slope of $-500$ J/mol, as established previously for the steady-state flow state. The present result implies that the same relationship between the structural disorder and viscosity is applicable in the transient flow state as well as in the steady-state flow state. There exists a fictive stress, or steady-state flow stress, which indirectly represents a glass structure. It is also shown that the fictive stress, $\sigma_{\text{f}}$, can describe the free volume, $v_{\text{f}}$, as well as the $\eta$ and $\Delta H_{\text{s}}$ of a glass experiencing various stress deformations.
2003-10-15