Origins and dissociation of pyramidal dislocations in magnesium
and its alloys
ZG Ding and W Liu and H Sun and S Li and DL Zhang and YH Zhao and EJ
Lavernia and YT Zhu, ACTA MATERIALIA, 146, 265-272 (2018).
DOI: 10.1016/j.actamat.2017.12.049
Alloying magnesium (Mg) with rare earth elements such as yttrium (Y) has
been reported to activate the pyramidal slip systems and improve
the plasticity of Mg at room temperature. However, the origins of such
dislocations and their dissociation mechanisms remain poorly understood.
Here, we systematically investigate these mechanisms using dispersion-
inclusive density-functional theory, in combination with molecular
dynamics simulations. We find that dislocations form more
readily on the pyramidal 1 plane than on the pyramidal II plane in Mg.
The addition of Y atoms in Mg facilitates the dissociation of
dislocations on pyramidal II, leading to the easier formation of the
pyramidal 11 than pyramidal 1 in Mg-Y alloy. Importantly, in pyramidal
II slip plane, a flat potential-energy surface (PES) exists around the
position of stable stacking fault energy (SFE), which allows cooperative
movement of atoms within the slip plane. Alloying Mg with Y atoms
increases the range of the PES, and ultimately promotes different
sliding pathways in the Mg-Y alloy. These findings are consistent with
experimentally observed activation of the pyramidal II slip
system in Mg-Y alloys, and provide important insight into the
relationship between dislocation structure and macroscopic enhancement
of plasticity. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd.
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