Serrated flow during inhomogeneous bending deformation of bulk metallic glasses: From self-organized critical to chaotic dynamics

Abstract

In this research, the dynamic behavior of serrated flows observed in the flexural stress-deflection curves during three-point bending (3 PB) tests on Zr-, Ti- and La-based bulk metallic glasses (BMGs) is statistically analyzed. Furthermore, the effect of strain rate on the serrations is studied. Based on the ductility of alloy, two distinct types of dynamics are detected. For more ductile alloys (Zr- and Ti-based BMGs) the stress drop magnitude of serrations obeys a power-law distribution of shear avalanches, which is an indicator of the self-organized critical (SOC) state in dynamics. In this case, the size of avalanches has no characteristic scale. In contrast, the size of serrations corresponding to the less ductile alloy (La-based BMG) exhibits a characteristic length scale and implies that the underlying dynamics is chaotic. Results indicate that the plasticity in less ductile alloy can be related to the stick-slip process of a few shear bands, but in the case of more ductile alloys, it can be attributed to the simultaneous nucleation and interaction of a large number of shear bands. Above a critical strain rate, the serrations on flexural stress-deflection curves do not appear and a transition occurs from the serrated to non-serrated plastic flow. The comparison of apparent activation energy for the onset of serrated flow and the STZ activation energy indicates that these two processes are interrelated. Using these values, it is possible to determine the dynamic behavior of serrated flows in BMGs.