Creep in bulk metallic glasses. Transition from linear to non linear regime

Tensile creep is investigated in a La₆₀Al₂₅Ni₁₅ (at%) bulk metallic glass. Temperature and stress are chosen in a large range and tests are performed during long times (up to 10⁵ s). The compliance of the samples, i.e. the ratio between the induced strain and the applied stress, is deduced from the resulting strain. A transition from a linear regime to a non-linear regime is progressively observed when either temperature or stress level is increased. This transition indicates a modification of the physical mechanism involved in the deformation. The physical model initially proposed by Perez et al is used to describe this transition. When a stress is applied shear micro-domains (SMDs) are progressively formed in appropriate shear planes and when the stress or temperature is high enough a coalescence of these SMDs occurs progressively. The phenomenon becomes irreversible and then the viscoplasticity takes place. The transition is therefore linked to the onset of viscoplasticity.