Short-range structural origins of serration events in metallic glasses
M Kumar and E Nicholson and DW Kirk and SJ Thorpe and CV Singh, JOURNAL OF ALLOYS AND COMPOUNDS, 787, 840-850 (2019).
Plastic deformation of metallic glasses under compression proceeds through sudden stress drops and accumulations known as serration or avalanche events. Experimental studies have suggested that this occurs by stick-slip behaviour of weak spots, while the atomistic structural origins underlying this phenomenon have remained unclear. In this study, we investigate deformation mechanisms underpinning serrated flow in Cu- Zr metallic glasses using molecular dynamics simulations. We show that this behaviour is essentially dictated by the short-range structural order as defined by the relative population of full icosahedra and geometrically unfavourable motifs (GUMs). The slip of atoms belonging to GUMs causes stress drops whose magnitude is directly correlated to the number of atoms involved in the slip. Continued loading leads to the breakdown of full icosahedra into GUMs, causing severe serration behaviour during the later stages of deformation. More severe and frequent stress drops are observed at higher temperatures and lower strain rates, indicating the thermally activated nature of this phenomenon. The compositions with lower Cu content show enhanced serrated flow, suggesting that ductility can be compositionally tuned. The statistical analysis of stress drops exhibits good agreement with previous experimental findings. Insights gained from this study will assist in designing new metallic glasses with superior ductility. (C) 2019 Published by Elsevier B.V.
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