Shear-band cavitation determines the shape of the stress-strain curve of metallic glasses

TL;DR

This study reveals that shear-band cavitation within metallic glasses influences their stress-strain response, linking internal micro-cracking to the variability in post-yielding behavior through x-ray tomography analysis.

Contribution

It introduces the first direct observation of shear-band cavitation evolution in metallic glasses, connecting microstructural changes to macroscopic mechanical variability.

Findings

Cavity growth follows a power-law during plastic flow.

Macroscopic strain-softening coincides with shear-band cavitation detection.

Fractal analysis of cavities aligns with surface roughness post-fracture.

Abstract

Metallic glasses are known to have a remarkably robust yield strength, admitting Weibull moduli as high as for crystalline engineering alloys. However, their post-yielding behavior is strongly varying, with large scatter in both flow stress levels and strains at failure. Using x-ray tomography we reveal for the first time how a strain-dependent internal evolution of shear-band cavities underlies this unpredictable post yielding response. We demonstrate how macroscopic strain-softening coincides with the first detection of internal shear-band cavitation. Cavity growth during plastic flow is found to follow a power-law, which yields a fractal dimension and a roughness exponent in excellent agreement with self-similar surface properties obtained after fracture. These findings demonstrate how internal micro-cracking coexists with shear-band plasticity along the plastic part of a stress-strain curve, rationalizing the large variability of plastic flow behavior seen for metallic glasses.