STUDY ON STRUCTURAL REJUVENATION OF A METALLIC GLASS DURING HIGH-TEMPERATURE DEFORMATION

The homogenous deformation behavior of metallic glasses at high temperature is related to key processes such as glass transition, aging and rejuvenation, which is an important support for understanding the nature of glassy state and improving the theoretical system of amorphous mechanics. Exploring the dynamic competition between aging and rejuvenation in the process of homogenous deformation is conducive to the quantitative control of the energetic state. Based on the stretched exponential equation and free volume model, the tension-stress relaxation cycle of Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ metallic glass under constant/decreasing strain rate was studied by dynamic mechanics analyzer. The total deformation in high-temperature homogenous deformation process is composed of elastic, anelastic and viscoplastic components, and the deformation completely changes from elastic and anelastic components to plastic components in stress relaxation process. Compared with traditional metallic glass systems, the high configurational entropy design induces a smaller activation volume involved in homogeneous deformation and a lower degree of deviation from Newtonian flow characteristics in the correlation between viscosity and strain rate. Three key physical parameters, i.e., peak stress of true stress-strain curve, stress relaxation strength and defect concentration, are used to elucidate the evolution of energetic state during deformation. The findings confirm that free volume theory can accurately describe the homogenous deformation behavior of metallic glasses, the anelastic component corresponds to the structural rejuvenation, and the viscoplastic strain corresponds to the structural relaxation. Notably, the energetic state of metallic glasses in the steady state deformation is only controlled by temperature and applied strain rate, and is independent on their macroscopic thermomechanical loading history. Furthermore, increasing the strain rate was found to induce a higher degree of structural rejuvenation, thus extending the dynamic heterogeneity and accelerating the relaxation rate, as confirmed by the evolution of the stretched exponent β and characteristic relaxation time τ from the Kohlrausch-William-Watts equation.