Intrinsic versus extrinsic effects on serrated flow of bulk metallic glasses

In this work, we systematically investigate the serrated flow behavior in the compression of bulk metallic glasses by varying the intrinsic composition and various extrinsic material and experimental factors including the sample size, the strain rate, and the testing machine stiffness. We find that the serrated flow, characterized by the amplitude of load serrations, can be suppressed for the higher Young's modulus, larger sample size, higher strain rate, and larger testing machine stiffness, respectively, and that it could completely disappear at certain critical strain rates. Meanwhile, the shape of serrated flow, which tends to become more "blunt", manifests as the increasing ratio of the duration time to the awaiting time of the serrated events. The dependence of the serrated flow on these various factors is interpreted from the stick-slip dynamics of a single dominant shear band in compression process and can be condensed into a unified theoretical parameter k/k_cr, where k is a parameter dependent on the Young's modulus, the sample size and the machine stiffness, and k_cr is expressed as a function of temperature and testing strain rate. The implication of the stick-slip shear band dynamics together with the tuning of these material factors and test parameters will lead to the design of ductile BMGs.