Figure 3
Effect of size on strength and plastic deformation mode of MG nanowires.
(a), Deformation mechanism map giving normalized metric for energy of shear band propagation vs. specimen length for our measurements (green symbols) and various metallic glass small scale experiments14,16,17,20,22,23,24,32,38, shown in comparison to the prediction of a size-dependent transition to homogeneous flow12. See text for details. While this theory predicts the transition for previous reports (homogeneous flow shown as open symbols), it fails to describe the tensile ductility observed in our ion irradiated moulded nanowires (open green symbols), suggesting a distinct mechanism for accommodating plastic flow. Literature values are estimated by the mean stress for each deformation mode and lower and upper limits for the length of specimens showing heterogeneous and homogeneous flow, respectively. (b), Measured strength of MG nanowires as a function of size, (c), surface area and (d), volume. Closed, open and partially filled symbols represent as-moulded, ion irradiated and irradiated and subsequently annealed (below Tg) nanowires, respectively. Fracture strength is plotted for nanowires showing brittle response (as-moulded and irradiated and annealed), while 0.2% offset yield strength is shown for ductile nanowires (irradiated). No clear size effect is measured beyond the experimental uncertainty over the tested range (see supplementary information for calculation of error bars), irrespective of the processing condition. Colors of irradiated and irradiated and annealed data points in (b–d) correspond to those used in the stress strain curves of Figure 2a.
