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Abstract
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Atomistic simulations are used to study the effect of calcium (Ca) addition on plastic flow of nanocrystalline
hexagonal close-packed (hcp) magnesium (Mg) under uniaxial tensile deformation. The nanostructure materials
are constructed using the Voronoi tessellation method, and the plastic deformation behavior is studied by
molecular dynamics simulation. A second nearest neighbor modified embedded atom method (2NN-MEAM) is
applied to represent interatomic potential energy. Calcium atoms with different concentration of 0.0–1.3 wt%
are randomly distributed in the magnesium nanocrystal with mean grain size of 8.5 nm as substitution atoms.
Surprisingly, deformation twinning is not observed in the samples unlike the easy occurrence of twinning in Mg
nanocrystal with coarse-grained structure. Structural analysis demonstrated that plastic deformation occurred in
the studied Mg-Ca alloys via slip of partial dislocations, nucleation and growth of disordered atom segments
(DAS) inside grains. The continuous accumulation of stacking faults induces hcp to fcc (face centered cubic)
phase transformation. MD simulation results show that the tensile stress required for partial dislocation nucleation
decreases with increasing Ca concentration. The presence of Ca atoms as solid solution in the structure
of nanocrystalline Mg-Ca alloy influences the densities of stacking faults and DAS which promotes nucleation of
partial dislocations and DAS.
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