Mechanical Behavior of Micronanoscaled Metallic Glasses

Abstract

In this paper, research on the mechanical behavior of micronanoscaled metallic glasses (MGs) is reviewed, with an emphasis on works achieved through in situ transmission electron microscope. It was found that the strength of micronanoscaled MGs has a nonlinear dependence on sample size. Corresponding to the transition of size-dependent strength, the deformation mechanism of MGs changes gradually from brittle to ductile with the critical transition size being affected by strain rate, e-beam irradiation and thermal history of the sample. Besides monotonic loading, the mechanical behaviors of MGs in response to cyclic loadings and fatigue tests are also reviewed. Keywords: Metallic Glasses, Micronanoscaled, Plasticity, Strength, Cyclic LoadingIntroduction Metallic glasses (MGs), also known as amorphous metals, are materials composed of metal components but without crystalline structure.[1-3] The lack of long-range order, that is, atoms do not register in periodic lattice sites, renders MGs unique in mechanical behaviors. [4][5][6][7] Unlike crystalline metals, MGs do not have dislocation or deformation twinning as plastic carriers. When the applied mechanical load exceeds their yield strength, bulk MGs usually deform through the formation of shear band, a thin band where large shear strains localized [8], usually in a catastrophic manner. The stress level required for the nucleation and propagation of shear band is much higher than that for dislocations or twins in bulk crystalline materials, usually on the GPa level. Without early yielding, the measured elastic limit for bulk MGs can be up to 2% [4,9], much larger than their crystalline counterparts. Even though the brittleness and high cost limit the commercialization of bulk MGs, recent studies [10][11][12] demonstrated that micronanoscaled (refer to samples with their size ranged from 10 nm to 10 μm [13]) MGs own outstanding strength and reasonable plastic deformability which make them attractive for applications in Micro/Nano electro-mechanical systems (M/NEMS). Consequently, a systematic study of the mechanical properties of

Mechanical Properties of Glassy Nanopillars: A Comparative, Computational Study of Size Effects in Nanoglasses and Homogeneous Bulk Glasses

“…These results are in agreement with previous MD simulation results which reported that sizeindependent shear banding until their dimensions approach the shear-band thickness which is about 5-20 nm (Adibi et al, 2016;Liontas et al, 2016;Shi, 2019). This transition appears in experiments at a lager sample diameter, between 100 and 400 nm, as compared with MD simulations (Tian et al, 2016). This difference in the sample size on the change of the deformation mode between experiments and simulations can be related to the different processing and testing conditions (Shi, 2019).…”

Revealing anelasticity and structural rearrangements in nanoscale metallic glass films using in situ TEM diffraction

“…showed that enhanced plastic deformation in Zr-based bulk metallic glasses is possible through the suppression of shear localization by using geometrical constraints [ 5 ]. Alternatively, researchers have shown that when sample dimensions are reduced to the nanoscale, homogeneous flow supersedes shear band propagation as the dominant mode of deformation and results in enhanced ductility [ 6 , 7 ]. Furthermore, molecular dynamics (MD) simulations have revealed that metallic glass films can deform plastically below a critical thickness by non-localized flow [ 8 ], providing further promise for increased ductility at the nanoscale.…”

Deformation Behavior of Bulk Metallic Glasses and High Entropy Alloys under Complex Stress Fields: A Review

“…Hufnagel et al [ 48 ] have indicated that although many previous studies have focused on the deformation behavior of BMGs under uniaxial stress states, the understanding of the deformation behavior as well as structural evolution under more complex stress states is urgently needed to uncover the shear-banding mechanisms, such as the shear localization process. The research progress on the formation mechanisms of shear bands in BMGs has been summarized in many review papers [ 4 , 27 , 30 , 34 , 35 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ], however, the formation of shear bands under complex stress fields has rarely been emphasized. Here, the initiation of shear bands under more complex stress fields is summarized.…”