Homogeneous ductile flow of metallic glasses is observed at the micrometer scale. It is shown that this unusual deformation mode of an otherwise brittle material depends on both specimen size and applied loading rate. The results are explained by intrinsic length-scale effects of nanometer-sized defects, and provide a rationale for the long term debated brittle-to-ductile transition of amorphous metals.

A statistical analysis of the rate-dependent pop-in behavior during spherical nanoindentation of a metallic glass is presented. Since the first pop-in of a test corresponds to the initiation of plasticity, this method provides insights into the fundamentals of shear-banding behavior. In this study, test series with different applied loading rates reveal that the initiation of a shear band is thermally activated with a rate-and stress-dependent activation volume. We further find a spatial inhomogeneity of the elastic modulus at the micrometer scale. This long-range structural heterogeneity does not strongly correlate with the shear-band initiation stress. V

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