Cycle deformation enabled controllable mechanical polarity of bulk metallic glasses

TL;DR

This study demonstrates that asymmetric mechanical cycling can induce and control mechanical polarity in bulk metallic glasses without damage, revealing the atomic mechanisms behind anisotropy and offering new ways to optimize their properties.

Contribution

The paper introduces a novel method of using asymmetric mechanical cycling to controllably induce and analyze anisotropy in bulk metallic glasses at the atomic level.

Findings

Mechanical polarity can be effectively induced without damaging the sample.

The anelastic limit is controllable via cycling amplitude.

Polarity arises from plastic-event-healing and local potential energy surface asymmetry.

Abstract

Tuning 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 the quasi-elastic asymmetric mechanical cycling method, we effectively induce the mechanical polarity of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine displacement, we find that only plastic atomic rearranged events corresponding to the training direction can be exhausted by asymmetric cycling 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 local potential energy surface, rather than 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 furthers our understanding of the mechanical deformation of metallic glasses and shed some light on the prospects for improved properties through induced anisotropy.