Direct measurement of nanostructural change during in situ deformation of a bulk metallic glass

Abstract

To date, there has not yet been a direct observation of the initiation and propagation of individual defects in metallic glasses during deformation at the nanoscale. Here, we show through a combination of in situ nanobeam electron diffraction and large-scale molecular dynamics simulations that we can directly observe changes to the local short to medium range atomic ordering during the formation of a shear band. We observe experimentally a spatially resolved reduction of order prior to shear banding due to increased strain. We compare this to molecular dynamics simulations, in which a similar reduction in local order is seen, and caused by shear transformation zone activation, providing direct experimental evidence for this proposed nucleation mechanism for shear bands in amorphous solids. Our observation serves as a link between the atomistic molecular dynamics simulation and the bulk mechanical properties, providing insight into how one could increase ductility in glassy materials.

Ab initio modeling of the energy landscape for screw dislocations in body-centered cubic high-entropy alloys

“…Indeed, their disordered multiple-element compositions lead to a strong possibility of SRO, for example, the preference for certain types of bonds within the first few neighbor shells. This is not particularly rare in conventional alloys 52,53 and glasses 54 ; however, it could be argued that its existence would be even more likely in multiple principal element alloys 49,51,55 due to large number of elements and their equimolar concentrations. Recent DFT and MD simulations on the fcc CrCoNi alloy suggest that SRO can have a profound effect on critical parameters, notably the stacking-fault energy 55 and dislocation mobility 56 ; accordingly, such local order could be an important factor in controlling mechanical properties.…”

Impact of Severe Deformation by HPT at Room Temperature on the Relaxation of the Glassy and the Supercooled Liquid States of PdNiP

“…Low-temperature heat capacity measurements (PPMS) were performed in order to reveal changes in the atomic vibrational spectra which are related to the excess free volume distribution 18,19 and thus atomic arrangements. To investigate the corresponding amorphous structure in detail, fluctuation electron microscopy (FEM) was employed to determine the MRO fingerprint (size 7,20 , relative volume fraction 21,22 and types 23,24 ) of each materials' state 20,[25][26][27][28][29][30][31] . Finally, these findings are discussed in terms of a PEL scheme offering a new approach for MRO engineering of glasses.…”

Direct Visualization of the Earliest Stages of Crystallization

“…Recently, the 4D-STEM technique has been developed as a tool to study relative orientations while imaging nanoparticles at a low-dose; secondary phases in a glass matrix, polymers, and different beam-sensitive materials can also be studied (Bustillo et al, 2016; Ophus, 2019; Panova et al, 2019; Pekin et al, 2019; DeRocher et al, 2020). In this process, while scanning in the STEM mode, CBED information can also be recorded from each pixel.…”