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 10(5) 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.