Viscoelasticity of Cu- and La-based bulk metallic glasses: Interpretation based on the quasi-point defects theory

The dynamic mechanical relaxation of metallic glasses is closely associated with the physical and mechanical properties. In the current work, the dynamic mechanical relaxation behaviors of Cu₄₆Zr₄₅Al₇Y₂ and La₆₅Al₁₄(Cu_5/6Ag_1/6)₁₁(Ni_1/2Co_1/2)₁₀ bulk metallic glasses are investigated by mechanical spectroscopy. In general, metallic glasses display two relaxation modes: main (α) relaxation and the slow secondary (β) relaxation. The α relaxation is linked to the dynamic glass transition phenomenon and viscous flow while the slow β relaxation is associated with many fundamental issues, such as diffusion and glass transition phenomenon. The experimental study shows La₆₅Al₁₄(Cu_5/6Ag_1/6)₁₁(Ni_1/2Co_1/2)₁₀ bulk metallic glass displays a noticeable slow β relaxation. Contrarily, the Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass relaxation process takes the form of an “excess wing”. In the framework of quasi-point defects (QPD) theory, the dynamic mechanical response of the metallic glasses is discussed.