Molecular Dynamic Simulations Of {11-22}〈11-2-3 〉And {11-21}〈11-2-6〉Twining Modes In Hexagonal Close-Packed Metals
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Authors
Ombogo, Jamie T. M.
Issue Date
2018
Type
Thesis
Language
Keywords
atomistic , Classical , Dislocations , Simulations , Theory , Twinning
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Abstract
Deformation twinning is crucially important in the mechanical behavior of hexagonal close-packed (HCP) metals such as Mg, Ti, Co and Zr etc.. Classical twinning theory is able to predict the twinning elements of individual twinning modes; however, some predictions are unable to be verified in atomistic simulations. In this thesis, {11-22}〈11-2-3〉 and {11-21}〈11-2-6〉 twinning modes were investigated via molecular dynamic (MD) simulations. The results show that, for {11-22}〈11-2-3〉 mode, the second invariant plane K_2={11-2-4}, predicted by the classical twinning theory, did not occur. Instead, the K_2 plane is actually the (0002) basal plane which was considered to be the least possible in the classical theory. Twin boundary migration is mediated by single layer dislocations on each twinning plane, instead of the three-layered zonal dislocations as predicted in the classical theory. For {11-21}〈11-2-6 〉 twinning mode, the classical twinning theory predicted that K_2=(0002) and the twinning dislocations should be two-layer zonal dislocations, and no atomic shuffles are needed. However, no clearly defined dislocation lines are observed in the MD simulations. Instead, the twin boundary migrates as a four-layer zone with a Burgers vector twice the predicted elementary twinning dislocation in the classical theory. Possible mechanisms are discussed to account for these abnormal properties of the two twinning modes
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Creative Commons Attribution-ShareAlike 4.0 United States