Gamma relaxation in Dy-based metallic glasses and its correlation with plasticity

The discovery of secondary relaxation in metallic glass (MG) breaks the longstanding cognition that MG, as a simple glassy system, exhibits only α relaxation and contributes significantly to the understanding of the structure and mechanical properties of MG. In this work, two independent fast secondary relaxation peaks corresponding to γ and β′ relaxation were detected by dynamic mechanical measurement in several Dy-based MGs at temperatures far below the glass transition temperature. Compared with β′ relaxation, the novel γ relaxation is activated at lower temperatures and possesses smaller activation energy approximately 2/3 of that for β′ relaxation. By exciting γ relaxation, loosely packed regions evolve into vein-like patterns in the fracture surface, leading to unusual plasticity at cryogenic temperatures. Furthermore, a holistic relaxation spectrum including boson peak, fast γ and β′ relaxation, slow β relaxation and primary α relaxation in MG was depicted.