Creep deformation and stress-induced structural disorder near T_g in a Zr₅₅Al₁₀Ni₅Cu₃₀ glassy alloy

Creep deformation under a constant applied load in a Zr₅₅Al₁₀Ni₅Cu₃₀ glassy alloy at the glass transition region is investigated. At an initial stress, σ₀, less than a critical stress, σ_c=80 MPa, the glass shows a Newtonian flow. When σ₀≥σ_c, the flow viscosity, η, initially decreases and attains a minimum. It then increases as the true stress, σ, decreases with further deformation. The initial decrease in η and the attendance of viscosity minimum are due to the stress-induced structural disorder and the structural equilibration with the applied stress, respectively. For stress, σ, less than the viscosity minimum stress, the stress dependence of viscosity, η(σ), curves all tend to merge together, and is fitted well with a master curve, η(σ), established previously for the steady-state flow under constant strain-rate experiments. These results render further support to the hypothesis of stress-induced structural disorder and the concept of fictive stress.