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

The heat evolution of stress-induced structural disorder, ΔH _s(t), in a Zr₅₅Al₁₀Ni₅Cu ₃₀ glassy alloy during creep deformation under a constant load at the glass transition region (T_g = 680 K) is investigated by an in situ measurement of temperature change of a deforming sample. For an initial stress, σ₀, greater than a critical stress, σ _c = 80MPa, all ΔH_s(t) curves grow gradually attaining a maximum then decrease with further deformation. The peak in ΔH_s indicates the attainment of an equilibrium flow structure. The ΔH_s curves plotted against the logarithm of normalized viscosity (ratio of viscosity, η, to the Newtonian viscosity, η _N) tend to merge and increase linearly with a slope of -500J/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, σ_f, can describe the free volume, v _f, as well as the η and ΔH_s of a glass experiencing various stress deformations.