Experimental observation and theoretical modeling of multi-stage power-law creep in metallic glass

Power-law creep, where the creep strain rate follows a power-law relationship with time, is ubiquitous in crystalline materials. However, this behavior typically exhibits multi-stage characteristics in amorphous materials due to the intrinsic structural and dynamic heterogeneity. In this study, we systematically performed high-temperature creep experiments on a Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ metallic glass. It is found each stage in multi-stage creep is governed by different deformation mechanisms, influenced by factors such as temperature, stress, and structural relaxation. Experimental results indicate that increasing temperature causes the power-law creep behavior to change from two stages to three stages, while increasing stress does not alter this behavior. After cyclic creep, the power-law creep behavior reverts from three stages to two stages. Based on the quasi-point defect theory, we propose a creep constitutive model that includes the contribution of structural relaxation to creep behavior in the generic metastable materials. Theoretical modelings show creep response is primarily driven by two deformation mechanisms: the activation of inherent deformation units (shear microdomains), which dominate the early stage of creep; and the mechanism related to structural relaxation, with atomic correlations significantly influenced by temperature and aging conditions. The constitutive model reveals the factors influencing the power-law creep and clarifies the intrinsic mechanism underlying the transition from two stages to three stages. These mechanisms align with the thermal and mechanical effects observed in the experiments.