Competitive mechanism of stress-driven anelasticity recovery and viscoplastic accumulation in metallic glasses

The complex relaxation behavior of metallic glasses (MGs) and the microscopic dynamics of the evolution of microstructural heterogeneity during thermomechanical processing are yet to be fully understood. This study investigates the competition between viscoelastic recovery and viscoplastic accumulation in MGs during the two-step creep process, manifested as non-monotonic strain evolution. A two-parameter Kohlrausch-Williams-Watts (KWW) constitutive model was developed, and the anelastic and viscoplastic deformations were decoupled from the total creep processes. This phenomenon reveals the intrinsic dynamics of MGs as non-equilibrium systems, its physical essence can be interpreted as a dynamic competition between the thermally-assisted release of stored internal stress, which enhances collective atomic motion, and the reactivation of viscoplastic flow under sustained low stress. The strain recovery process should be related to the activation and motion of the localized soft domains constrained by the elastic matrix. This study provides important experimental evidence for improving the physical mechanism-based nonlinear creep constitutive theory and offers a fresh perspective for analyzing complex deformation behavior.