Spatial correlation of elastic heterogeneity tunes the deformation behavior of metallic glasses

Abstract

Metallic glasses (MGs) possess remarkably high strength but often display only minimal tensile ductility due to the formation of catastrophic shear bands. Purposely enhancing the inherent heterogeneity to promote distributed flow offers new possibilities in improving the ductility of monolithic MGs. Here, we report the effect of the spatial heterogeneity of elasticity, resulting from the inherently inhomogeneous amorphous structures, on the deformation behavior of MGs, specifically focusing on the ductility using multiscale modeling methods. A highly heterogeneous, Gaussian-type shear modulus distribution at the nanoscale is revealed by atomistic simulations in Cu 64 Zr 36 MGs, in which the soft population of the distribution exhibits a marked propensity to undergo the inelastic shear transformation. By employing a mesoscale shear transformation zone dynamics model, we find that the organization of such nanometer-scale shear transformation events into shear-band patterns is dependent on the spatial heterogeneity of the local shear moduli. A critical spatial correlation length of elastic heterogeneity is identified for the simulated MGs to achieve the best tensile ductility, which is associated with a transition of shear-band formation mechanisms, from stress-dictated nucleation and growth to structure-dictated strain percolation, as well as a saturation of elastically soft sites participating in the plastic flow. This discovery is important for the fundamental understanding of the role of spatial heterogeneity in influencing the deformation behavior of MGs. We believe that this can facilitate the design and development of new ductile monolithic MGs by a process of tuning the inherent heterogeneity to achieve enhanced ductility in these high-strength metallic alloys.

Effect of Hydrogen Charging on Pop-in Behavior of a Zr-Based Metallic Glass

“…In a simulation study by Wang et al [21], the mechanical properties of samples with the same potential energy distribution but different correlation lengths for the local shear modulus are compared. To first order, the correlation length simply describes the size and spacing of potential STZs (elastically soft sites) in the MG. Their results reveal that when the correlation length increases from 0.5 to 5 nm, a transition in deformation mechanism from "stress-dictated" shear band nucleation and growth to a "structural-dictated" strain percolation occurs [21]. This is associated with a decrease in the tendency for strain localization and an increase in the plastic strain to failure.…”

“…It has been proposed that hydrogen addition in MGs can introduce local structural heterogeneities which prevent single, catastrophic shear bands and promote the formation of multiple shear bands [16,18,20]. A recent work on elastic heterogeneity actually shows that the spatial correlation of the heterogeneities plays an important role in tuning ductility of MGs [21]. Since hydrogen addition is potentially useful in MG alloy design, the underlying mechanisms of how hydrogen addition improves ductility and stability of MGs deserve further investigation.…”

Notch Effect on Plastic Deformation of Metallic Glass: A Numerical Study by Revised Free‐Volume Theory

“…Instead of the three-dimensional model, two-dimensional FEM is used in this work in order to reasonably capture the key deformation mechanism without costing much computational resources [15][16][17]21]. In this framework, the strain localization is described by an internal state variable, i.e., the normalized free-volume v f , as shown in equation (6). e evolution of strain localization could represent for the shear banding process.…”

“…However, the vital shortcoming of monolithic metallic glass is the fast shear banding process, and it seldom exhibits noticeable plasticity once its yield strength has been reached. Although some scholars claimed that its plasticity could be enhanced by tuning structural or spatial heterogeneities [4][5][6], the low ductility is still its main weakness, which limits its wide application in engineering. erefore, many investigations have been dedicated to this field with the purpose of improving its ductility.…”

Heterogeneous structural changes correlated to local atomic order in thermal rejuvenation process of Cu-Zr metallic glass

“…The correlation between structural heterogeneity and deformability, especially in the shear banding behavior, has attracted significant attention in the field of metallic glasses [29][30][31][32]. Because rejuvenation changes the microstructure of metallic glasses, rejuvenation affects deformation behaviors [7].…”