  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.
