Effect of structural heterogeneity on serrated flow behavior of Zr-based metallic glass

Abstract

Physical correlation between structural heterogeneity and plastic flow of metallic glasses (MGs) is crucial for the understanding of MGs' deformation mechanism. In this work, different degrees of structural heterogeneity are introduced into Zr-based MGs through different cooling rates casting. The effect of structural heterogeneity on serrated flow behavior was studied. The findings demonstrate that there exists a tendency that serration flow dynamics of the MGs transforms from a chaotic state to a selforganized critical state with increased inhomogeneity. The established correlation between structural heterogeneity and serrated flow behavior shows that the higher degree of structural heterogeneity facilitates a higher frequency of interaction and multiplication of shear bands by increasing nucleation sites, and then promotes serrated flow behavior to be more homogeneous in time and space, thereby induces transformation of dynamics behavior and improves the plasticity. The obtained results shed light on deformation mechanism of plastic flow and provide a new insight into the plasticity of MGs.

A Review of the Serrated-Flow Phenomenon and Its Role in the Deformation Behavior of High-Entropy Alloys

“…Table 1 compares some of the different mechanisms responsible for the serrated flow in crystalline and amorphous alloys. These mechanisms include the flow defect unit and liquid-like site agglomeration, and shear band formation and propagation [197][198][199][200][201]. The activation and percolation of the flow units are typically caused by an applied stress or elevated temperature [202].…”

“…Amorphous Alloys (BMGs) Excess free volume generation, flow defect and liquid-like site agglomeration, shear band initiation and propagation. Figure 9 displays an illustration of the serration process that occurs due to the flow defect accumulation and subsequent shear-band initiation and propagation in a BMG [197]. At the beginning of a serration event, the applied stress leads to stress concentrations that arise from the modulus difference between the flow units and the glassy matrix.…”

“…An illustration of the serration process that occurs due to the flow defect accumulation in a BMG during compression. Each numbered section corresponds to the evolution of the flow unit and glassy matrix during the serration event as follows: (I) activation of flow units in liquid-like regions under an applied stress, (II) growth and coalescence of the liquid-like cites with adjacent cites with an increase in stress, (III) initiation of a shear band when a critical stress is reached, and (IV) a drop in the stress that is accompanied by shear-band arrest and subsequent restoration of the glassy matrix in the shear plane (adapted from Reference [197]). is typically dependent on the applied strain rate or test temperature during either tension or compression testing [8,9,133,153].…”

Near-Net Forming Complex Shaped Zr-Based Bulk Metallic Glasses by High Pressure Die Casting

“…In the EVP-HPDC process, the molten metal solidifies under a relatively lower cooling rate and higher solidification pressure compared with the suction casting in the laboratory. The lower cooling rate provided more time for the supercooling liquid to relax to an “ideal state” possessing less free volume [27,28]. Furthermore, the high solidification pressure also facilitates the forming of a denser structure [12].…”

“…Furthermore, the high solidification pressure also facilitates the forming of a denser structure [12]. Studies indicate that the decreasing free volume in the as cast BMGs results in the formation of less shear bands during deformation, thereby causing a decrease of plasticity [28,29]. Therefore, the BMGs fabricated by EPV-HPDC display a lower plasticity.…”