Origin of Intermittent Plastic Flow and Instability of Shear Band Sliding in Bulk Metallic Glasses

Abstract

Intermittent or serrated plastic flow is widely observed in the deformation of bulk metallic glasses (BMGs) or other disordered solids at low temperatures. However, the underlying physical process responsible for the phenomena is still poorly understood. Here, we give an interpretation of the serrated flow behavior in BMGs by relating the atomic-scale deformation with the macroscopic shear band behavior. Our theoretical analysis shows that serrated flow in fact arises from an intrinsic dynamic instability of the shear band sliding, which is determined by a critical stiffness parameter in stick-slip dynamics. Based on this, the transition from serrated to nonserrated flow with the strain rate or the temperature is well predicted and the effects of various extrinsic and intrinsic factors on shear band stability can be quantitatively analyzed in BMGs. Our results, which are verified by a series of compression tests on various BMGs, provide key ingredients to fundamentally understand serrated flow and may bridge the gap between the atomic-scale physics and the larger-scale shear band dynamics governing the deformation of BMGs.

Serration Dynamics in a Zr-Based Bulk Metallic Glass

“…[21] The vein-patterned zone possesses most of the fracture surface. In a serration, the deforming band will undergo negligible (v ( v 0 ) and rapid (v ) v 0 ) sliding rates, [36] here v 0 is the compressive rate of the machine, and v is the rate of deforming band. As shear bands slide rapidly, the temperature can reach a value high enough to result in the melting of the material.…”

“…[37] In order for an atom to jump, there must be a nearest space larger than an atom. When the sample is subjected to a shear stress, the internal shear band will generate a rapid sliding rate [36] that even leads to the melting behavior of the surrounding tissue. The local zone is softening and benefits atoms jumping.…”

Progressive shear band propagation in metallic glasses under compression

“…Besides, sample dimension, and deformation history also affect the plastic deformation behavior. Decreasing the sample size can cause the propagation of shear bands to be more stable due to a slower energy release [11,27,[30][31]. However, so far, the experimental evidence is still insufficient to quantitatively determine the effect of sample size on the initiation and propagation of shear band.…”

“…To deal with this question, substantial researches have been conducted recently, including the investigations on the propagation dynamics of an individual shear band and/or the interactions between shear bands [23][24][25], effects of extrinsic factors like sample size, machine stiffness, testing temperatures and strain rates on shear banding behaviors [26][27][28][29][30][31], and in situ or quasi-in situ observations on shear band evolution [14,32,33], and so on. Theoretical models such as the stick-slip model [5,25,31,34], the shear instability model [26][27][28] and the quasi-phase transition model [11] have also been proposed and applied to account for the inherent mechanisms behind experimental observations. However, http concerning the propagation mode of shear band, although two modes of progressive shearing and simultaneous propagation have been assumed [4,35], only the simultaneous propagation mode has been experimentally confirmed so far.…”

The Self-Organized Critical Behavior in Pd-based Bulk Metallic Glass

“…However, their use as structural materials is severely limited because of their poor ductility and catastrophic failure at room temperature arising from the shear localization [3,4]. Lack of long-range atomic order, the underlying deformation mechanisms of BMGs are completely different from the crystalline alloys.…”