The role of cryogenic treatment in the relaxation behavior of the elastically rejuvenated metallic glasses

Abstract

This research investigates how elastically pre-loaded Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ metallic glass (MG) subjected to cryogenic treatments (CT) affects its relaxation behavior and mechanical properties. The findings reveal that as the elasto-static compression loading (ECL) stress and duration increase, a noticeable improvement in structural rejuvenation will be induced due to the increase of the free volume. From the perspective of the atomic-level stress theory, the dilated atomic structure induced by ECL helps to achieve a synergy of strength and plasticity after CT. The shrinkage after cooling triggers the coalescence of the hard elastic matrix with the soft regions, which results in free volume annihilation and induces partial structural relaxation. Hence, high density regions with lower activation energy and higher yield strength are generated, manifesting an overcoming the strength-plasticity trade-off in MGs. Further investigations show that the β-relaxation activation that occurs after the activation of a small concentration of local low-viscosity regions is closely related to β′-relaxation. It is evidenced that with increasing of ECL stress and time that followed by CT process, the activation energy of β- and β′-relaxation and the viscosity of local liquid-like regions are decreased, while the concentrations of the defective flow units of β- and β′-relaxation are increased. Moreover, ECL and CT can induce structural modifications manifesting in the decrease of the activation energy and the increase of the shear transformation zones (STZs) volume, as compared with the as-cast state. The generalized Maxwell and free volume models serve as the frameworks for understanding the phenomena. These results offer insights into the relationship between the local liquid-like regions excitations and secondary relaxations with the mechanical properties, to develop advanced MGs with fascinating properties.