Thermal evidence of stress-induced structural disorder of a Zr₅₅Al₁₀Ni₅Cu₃₀ glassy alloy in the non-Newtonian region

The evolution of specific heat near the glass transition temperature, T_g, of a Zr₅₅Al₁₀Ni₅Cu₃₀ glassy alloy subjected to different degrees of non-Newtonian flow conditions was investigated. At conditions in which non-Newtonian flow begins, a gradual exothermic relaxation near T_g was observed. This is attributed to the change in configuration of the long-range liquid structure of the alloy. At conditions in which a high degree of non-Newtonian flow is favored, the alloy exhibits both high-temperature and low-temperature relaxation due to a change in local short-range order. The enthalpy of relaxation is found to scale as the logarithm of the normalized viscosity and is interpreted in terms of the free volume model of viscous flow. The decrease in viscosity in the non-Newtonian flow region is associated with a highly disordered structure and induced free volume.