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A systematic study on the fracture surface of brittle Mg-, Fe-, and Co-based metallic glasses under compressive loading is approached and a fracture mechanism is proposed. Experimentally, the metallic glass samples are compressed into many small fragments, displaying an explosion fracture feature. Therefore, an energy equilibrium model is employed to describe the fracture processes of those brittle metallic glasses. Furthermore, some regular nanoscale steps, which were scarcely discovered, are found on the mirror region on their fracture surfaces. It is suggested that such nanoscale steps are associated with the energy distribution in metallic glasses and are created by the shear waves generated by the instability of crack propagation during the explosion rupture processes. Based on the comparison of experimental observations with numerical calculations, we recommend a novel model for interpreting the development of nanoscale steps on the dynamic fracture surfaces of these brittle metallic glasses, which appropriately describes the experimental findings. [ABSTRACT FROM AUTHOR]

Cellular bulk metallic glasses (BMGs) with macroscopic cellular structures were designed and fabricated. The cellular BMGs exhibited remarkable energy absorption capacity as compared with reported BMG foams and honeycombs. The enhanced energy absorption capability is attributed to the large plastic bending of the struts, the blunting of the cracks, and the large plastic deformation at the nodes. This work shows that, in cellular BMGs, the macroscopic cellular structures are more efficient in dissipating mechanical energy than microscopic cellular structures, opening a window for developing energy absorption devices using BMGs. [ABSTRACT FROM AUTHOR]

The plasticity of Ti-based metallic glasses with different aspect ratios can be improved by introducing two semicircular notches on the edges of the samples, owing to the interactions of shear bands (SBs) under conventional compression tests. The interaction of SBs can be ascribed to the easy initiation of SBs around the notches due to the large stress gradient, and the consequent blocking effect of notches on the propagation of shear bands. Additionally, the current findings provide a new way to understand the physical nature for the plastic deformation behavior of some brittle metallic glasses and supply an effective approach to enhance the plasticity to some extent. [ABSTRACT FROM AUTHOR]

The authors find that metallic glass can be controlled to create regularly arrayed fine multiple shear bands under small punch test, indicating that metallic glass essentially has a good plastic deformation ability and thus high ductility under suitable loading condition. The current findings imply that the initiation and propagation of shear bands in metallic glass strongly depends on the stress state and the small punch test can also be regarded as an effective method to characterize the shear deformation ability and distinguish ductile-brittle transition of different metallic glasses. [ABSTRACT FROM AUTHOR]

Dynamic instability is one of the typical cleavage fracture features in brittle materials. The authors find that dynamic instability of metallic glass starts to occur in the mirror region on the fracture surface through a wavy cracking propagation with the formation of periodic nanoscale steps. This kind of dynamic instability is associated with the early crack curving due to the intrinsic isotropic structure of metallic glass. Furthermore, they classify dynamic instabilities of cleavage fracture as crack curving at low velocity and crack branching at high velocity, corresponding to the mirror and hackle regions of metallic glass, respectively. [ABSTRACT FROM AUTHOR]

Cellular bulk metallic glasses (BMGs) have exhibited excellent energy-absorption performance by inheriting superior strength from the parent BMGs. However, how to achieve high energy absorption capacity in cellular BMGs is vital but mysterious. In this work, using step-by-step observations of the deformation evolution of a series of cellular BMGs, the underlying mechanisms for the remarkable energy absorption capacity have been investigated by studying two influencing key factors: the peak stress and the decay of the peak stress during the plastic-flow plateau stages. An analytical model of the peak stress has been proposed, and the predicted results agree well with the experimental data. The decay of the peak stress has been attributed to the geometry change of the macroscopic cells, the formation of shear bands in the middle of the struts, and the 'work-softening' nature of BMGs. The influencing factors such as the effect of the strut thickness and the number of unit cells have also been investigated and discussed. Strategies for achieving higher energy absorption capacity in cellular BMGs have been proposed. [ABSTRACT FROM AUTHOR]

The plastic stability of metallic glass composites (MGCs) under tension was investigated. There exists a critical normalized strain-hardening rate determining the plastic stability of MGCs: if the normalized strain-hardening rate is smaller than the critical normalized strain-hardening rate, the plastic instability occurs, thus, leading to localized plastic strain in MGCs; otherwise the plastic stability is in charge of the plastic deformation of the MGCs, so the strain localization or necking is effectively suppressed, which results in homogeneous elongation in MGCs. [ABSTRACT FROM AUTHOR]

The mechanical properties of Zr52.5Ni14.6Al10Cu17.9Ti5 and Ti40Zr25Ni3Cu12Be20 metallic glasses were investigated under uniaxial compressive loading and small punch loading, respectively. The Zr-based metallic glass displays higher density of shear bands, larger critical shear offsets and higher energy absorbing capability than the Ti-based metallic glass under the small punch tests. A concept of critical shear offset is proposed to explain the difference in shear deformation abilities or plasticity of different metallic glasses. The current experiments demonstrate that, in contrast with the small difference between the responses of the Zr- and Ti-based metallic glasses under uniaxial compressive loading, the biaxial tension produced by the small punch test is an effective way to evaluate the difference in shear deformation abilities and can be used to distinguish the brittleness or plasticity of various metallic glasses. [ABSTRACT FROM AUTHOR]

The quasi-static compressive deformation behavior of a Vitreloy 1 bulk metallic glass (BMG) with an aspect ratio of 0.25 was investigated. It is found that the friction and the confinement at the specimen-loading platen interface will cause the dramatic increase in the compressive load, leading to higher compressive strength. In particular, the BMG specimens show great plastic-deformation ability, and plenty of interacted, deflected, wavy, or branched shear bands were observed on the surfaces after plastic deformation. The formation of the strongly interacted, deflected, wavy, or branched shear bands can be attributed to the triaxial stress state in the glassy specimens with a very small aspect ratio. [ABSTRACT FROM AUTHOR]