Reversible anelastic deformation mediated by β relaxation and resulting two-step deformation in a La₆₀Ni₁₅Al₂₅ metallic glass

The stress relaxation dynamics of a La60Ni15Al25 metallic glass were studied in ribbon and bulk samples. In both tensile and single cantilever testing modes, it is observed that the stress decay of deep glass is mediated by the beta relaxation, which contributes about 5% to the total stress. The characteristic time of stress relaxation near the glass transition coincides with that of the alpha relaxation, indicating that the two-step stress decay may correspond directly to the two dynamic relaxations. A possible atomic mechanism involving both relaxation and deformation is proposed based on the evolution of shear transition zone, which enables reconstruction of the two-step deformation theoretically. The present experimental and theoretical protocol further provides a strategy to detect the beta relaxation associated phenomena at room temperature and even lower, circumventing interference from physical aging or the alpha relaxation. These findings clarify the elusive roles of relaxation modes in the nonelastic deformation of amorphous matters and reveal the interrelationships between them