Slower icosahedral cluster rejuvenation drives the brittle-to-ductile transition in nanoscale metallic glasses

JG Yu and MC Wangy and SC Lin, COMPUTATIONAL MATERIALS SCIENCE, 140, 235-243 (2017).

DOI: 10.1016/j.commatsci.2017.08.038

The brittle-to-ductile transition (BDT) in nanoscale multi-element metallic glasses (MGs) has been shown to strongly depend on the element composition and sample aspect ratio. However, the inherent microstructural evolution at the atomic level that leads to such BDT, in particular, the impact from the population and distribution of the full icosahedral clusters, has been largely unexplored. In this paper, we systematically probe the inherent shear band and icosahedral cluster evolutions of CuxZr100-x (x = 25, 50 and 75) MGs under different aspect ratios using molecular dynamics simulations. During tensile loading, the initial full icosahedra with local fivefold high-symmetry in CuxZr100-x MGs gradually transform into low-symmetry ones before reaching the maximum stress, which leads to the stress softening. Upon further tensile loading, high-symmetry full icosahedra gradually rejuvenate from low-symmetry ones far away from the shear bands (SBs), accompanied by irreversible atomic rearrangements near the SBs, both resulting in the limited plasticity of MGs. We attribute the observed BDT behavior upon decreasing the aspect ratio primarily to the slower rejuvenation or reformation rates of major full icosahedra. This study provides fundamental guidance for the optimal design of the composition, aspect ratio, and size of MGs for structural materials with high strength and ductility. (C) 2017 Elsevier B.V. All rights reserved.

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