Abstract
Minimum-energy structures for the symmetric (11\(\bar 2\)1) and (11\(\bar 2\)2) twin grain boundaries (GBs), as well as for two nonsymmetric GBs that exhibit dislocations, are obtained for the hcp structure by computer modeling. Central force potentials constructed within the embedded-atom method are used to represent atomic interactions. Vacancy-formation energies and entropies for different sites are calculated, and the properties of various vacancy jumps are investigated. Unstable vacancy sites, located in the GB dislocation cores, are observed. The random-walk approach, combined with simulation results, is applied to study tracer diffusion by a vacancy mechanism in the twin GBs; higher diffusivity values than those for the lattice are obtained, in qualitative agreement with experiments. Correlation effects, taken into account by the matrix method, determine the main features of GB diffusion to be contributed by jumps in a narrow region.
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