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Understanding the atomistic mechanisms of relaxation dynamics in metallic glasses remains a longstanding challenge. Here, using microsecond time scale molecular dynamics simulations, three main relaxation stages in metallic glasses are identified. At about 0.6T g , chemical composition plays a dominant role in the relaxation, manifested by stress accumulation and only minimal variations in structure. As T g approaches, the confluence of structural heterogeneity and chemical composition leads to the decoupling of relaxation mechanisms. At this temperature, the relaxation results in a structure with a lower energy state and a lower level of stress. In the supercooled liquid regime, an extensive increase in the number of closed-packed icosahedral clusters is responsible for accelerated structural relaxation while their packing frustration leads to the accumulation of intrinsic residual stresses in the glass. The atomistic origin of these dynamic relaxation modes is discussed in terms of structural, chemical composition and stress variations. [Display omitted] [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations, we provide an atomistic description of the shear band multiplication mechanisms in a heterogeneous metallic glass consisting of two distinct amorphous regions with different amounts of free volume and degrees of short-range order. The structural differences and elastic fluctuations encountered by the developing shear band while crossing the interface between the two regions alter the autocatalytic activation of the shear transformation zones (STZs) and, subsequently, lead to shear band branching. The two-unit STZ-vortex mechanism sheds light on the correlation between the strain distribution during tensile deformation and the directional characteristics of the STZ activation process. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The fast dynamics and localized nature of shear banding together with the disordered structure of metallic glasses make it difficult to gain an understanding of the mechanism of strain localization and shear band formation during deformation. The most widely accepted theory for the atomic-scale mechanisms of shear banding is related to the percolation of shear transformation zones (STZs). Recently we reassessed and clarified the atomistic details of STZs self-assembly mechanisms and provided a new two-unit model crucial in understanding STZs percolation and shear band formation. This manuscript attempts to provide a brief but up-to-date review on the STZ-Vortex mechanism and its applications in the areas of the shear band dynamics and, in general, in the atomistic description of deformation mechanisms in metallic glasses. The review also identifies a number of unsolved issues concerning deformation and relaxation mechanisms in metallic glasses where the STZ-Vortex model could be successfully applied. [Display omitted] [ABSTRACT FROM AUTHOR]

When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure. [ABSTRACT FROM AUTHOR]

[Display omitted] As the reverse process of relaxation, rejuvenation is the structural excitation process that can bring metallic glasses (MGs) to a higher energy state and usually increases their free volume. Here, using a dilution procedure conducted by randomly removing atoms from the modeled glass matrix, the degree of rejuvenation can be systematically controlled and the maximum rejuvenation threshold of MGs is identified. The structural relaxation is activated during the rejuvenation process and the dynamic balance between free volume creation and annihilation defines the rejuvenation ability of MGs. The highest degree of rejuvenation correlates to the flow strain of the materials and the structure is similar to that found in shear bands. [ABSTRACT FROM AUTHOR]