Cycle Deformation Enabled Controllable Mechanical Polarity of Bulk Metallic Glasses

Abstract

Tuning the anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing asymmetric oscillatory mechanical training method, we induce the mechanical polarity in a model bulk metallic glass effectively,without devastating the sample or inducing significant annealing or rejuvenation effect. Moreover, the polarized anelastic limit can be well controlled by regulating the deformation amplitude of asymmetric cycling. Through the atomic-level analysis of nonaffine displacement, we find that only the plastic atomic rearranged events corresponding to the training direction can be completely healed by cycle deformation and the survived anelastic events dominate the directional anelastic limit. The polarized distribution of local yield stress reveals that the mechanical polarity is attributed to the plastic-event-healing induced asymmetry of the local potential energy surface rather than the frozen-in anelastic strain. Furthermore, the healing of plastic events associated with the redistribution of local residual stress indicates the origin of polarity induced by asymmetric cycling. Our study is of fundamental importance, which further our understanding of the mechanical deformation of metallic glasses and shed some light on the prospects for improved properties through induced anisotropy.

Keywords: Metallic glasses, molecular dynamic simulation, mechanical anisotropy, asymmetric mechanical cycling