Abstract
We have investigated twin boundaries in double-lattice hexagonal close-packed metallic materials, focusing on their atomic geometry. Combining accurate ab-initio methods and large-scale atomistic simulations we address the following two fundamental questions: (i) What are the possible intrinsic twin boundary structures in hcp crystals? (ii) Are these structures stable against small distortions? In order to help end a decade-long controversy over the experimental observations of the atomic structures of twin boundaries, we have determined the energetics, spectra, and transition mechanisms of the twin boundaries. Our results confirm that the mechanical stability controls structures which are observed.
Highlights
The hexagonal close-packed structure is one of the three principal crystal structures for metallic materials.[1]
The low room-temperature deformability is believed to be caused by an insufficient number of active deformation modes and is associated with their highly anisotropic crystal structures
Gamma surfaces were previously employed to search for possible stable stacking faults on a slip plane.[18,19,20]
Summary
The hexagonal close-packed (hcp) structure is one of the three principal crystal structures for metallic materials (the other two are face-centered cubic, fcc, and body-centered cubic).[1]. In pure Mg, both our present and previous studies[12, 14, 15] using different total energy methods (empirical potentials as well as DFT with different exchange-correlation functionals) predict that glide TBEs are close to reflection TBEs with differences of smaller than 4% with respect to TBEs (see Table 2).
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