Impulse excitation as a unified probe of structural state evolution in bulk metallic glasses: Linking flexural damping to rejuvenation, annealing, and fatigue

The impulse excitation technique (IET) was used to examine structural-state evolution in Zr 55 Cu 30 Ni 5 Al 10 bulk metallic glass subjected to sub-T g annealing, elastostatic rejuvenation, and cyclic fatigue. Variations in flexural resonance frequency, damping, and calorimetric relaxation enthalpy were analyzed to relate changes in elastic stiffness to atomic-scale relaxation processes. The results showed that sub-T g annealing led to a progressive increas`e in elastic modulus and a marked reduction in relaxation enthalpy, while the damping response changed only slightly. Elastostatic rejuvenation resulted in moderate elastic softening accompanied by increased relaxation enthalpy, with minimal variation in damping. Cyclic fatigue showed a different evolution: early cycling produced gradual modulus degradation and a continuous increase in damping, whereas advanced cycling caused pronounced resonance broadening, peak asymmetry, and splitting associated with shear-band accumulation and microcrack formation. Mapping the coupled evolution of normalized modulus, internal friction, and relaxation enthalpy shows that annealing, rejuvenation, and fatigue follow distinct structural trajectories. The results indicate that flexural damping obtained from IET is particularly sensitive to fatigue-induced structural disorder, complementing elastic and calorimetric measurements in characterizing the structural state of metallic glasses.