Exploring dynamic heterogeneity of metallic glass via anomalous creep

The dynamic heterogeneity is an inherent nature of metallic glasses (MGs) due to their inhomogeneous structure down to the atomic scale. However, a quantitative relationship between the dynamic features and deformation modes of MGs is still not fully established. In this work, extensive creep experiments and dynamic mechanical analysis were conducted over a wide range of temperature, stress, time, and frequency to quantitatively explore the dynamic heterogeneity over multiple timescales. Creep is found to be governed by a diffusive-like mechanism with increasing activation Helmholtz free energy at longer times. Unexpectedly, the activation volume exhibits an increasing trend with temperature, in sharp contrast with the creep in crystalline materials, in which activation parameters remain constant with a unique creep mechanism. The state-of-the-art activation-relaxation technique unveils the correlation between the dynamic heterogeneity of MGs and the spatial distribution of the potential energy landscape. Activation barriers are overcome successively from small to large with increasing temperature, stress, or equivalently, longer times. A free energy barrier probability distribution model, considering both forward and backward activated fluxes of the deformation elements, is proposed for the whole creep process. This scenario of anomalous creep accommodated by the heterogeneous dynamics is consistently confirmed by the creep experiments and atomic-scale simulations. We thus propose a general creep description to quantitatively explore the dynamic heterogeneity of disordered materials. The consistent experimental, theoretical, and atomistic insights challenge the usual concepts of creep developed for crystals to comprehend the heterogeneous dynamics of amorphous metals.