Dynamic relaxation in metallic glasses: A unified view from quasi-point defects and fractional viscoelasticity

Amorphous solids are ubiquitous in nature, and their non-Debye relaxation behaviors are often modeled using the stretched exponential function or the power-law form. However, these empirical approaches lack a clear physical landscape and direct ties to the underlying microstructure. Dynamic mechanical relaxation is a key metric for understanding the mechanical and physical properties of amorphous solids with viscoelastic characteristics. This study focuses on dynamic mechanical relaxation behavior of Cu₅₀Zr₄₃Al₇ metallic glass, a typical representative of amorphous solids. We employ the simplified modified fractional-order model, combining the quasi-point defect theory and the fractional calculus, to investigate the mechanical relaxation spectrum of Cu₅₀Zr₄₃Al₇ metallic glass in temperature domain. Our findings demonstrate the convergence between mechanical (simplified modified fractional-order model) and physical (quasi-point defect theory) viewpoints. Molecular dynamics simulations reveal that variations of parameter χ (or α) in the models is closely related to changes in icosahedral clusters. Additionally, calculation of local pair entropy S₂ for atoms before and after annealing, along with analysis of the “entropy-rising” atoms during annealing, show a strong correlation with the quasi-point defects.