Hidden order in serrated flow of metallic glasses

TL;DR

This study analyzes serrated stress-time curves in metallic glasses, revealing chaotic dynamics in less ductile alloys and self-organized criticality in more ductile ones, providing insights into their different plastic deformation mechanisms.

Contribution

It uncovers distinct dynamic regimes in metallic glasses, linking chaos to less ductility and criticality to higher ductility, enhancing understanding of their deformation behavior.

Findings

Less ductile alloy shows chaotic dynamics with positive Lyapunov exponent.

More ductile alloy exhibits power-law distributions indicating self-organized criticality.

Different deformation mechanisms are suggested for the two alloys based on their dynamic regimes.

Abstract

We report results of statistical and dynamic analysis of the serrated stress-time curves obtained from compressive constant strain-rate tests on two metallic glass samples with different ductility levels in an effort to extract hidden information in the seemingly irregular serrations. Two distinct types of dynamics are detected in these two alloy samples. The stress-strain curve corresponding to the less ductile $Zr_{65}Cu_{15}Ni_{10}Al_{10}$ alloy is shown to exhibit finite correlation dimension and a positive Lyapunov exponent, suggesting that the underlying dynamics is chaotic. In contrast, for the more ductile $Cu_{47.5}Zr_{47.5}Al_{5}$ alloy, the distributions of stress drop magnitudes and their time durations obey a power law scaling reminiscent of a self-organized critical state. The exponents also satisfy the scaling relation compatible with self-organized criticality. Possible physical mechanisms contributing to the two distinct dynamic regimes are discussed by drawing on the analogy with the serrated yielding of crystalline samples. The analysis, together with some physical reasoning, suggests that plasticity in the less ductile sample can be attributed to stick-slip of single shear band, while that of the more ductile sample could be attributed to the simultaneous nucleation of large number of shear bands and their mutual interactions.