Local topology and its effects on grain boundary and solute segregation in HCP magnesium

First principles simulations were carried out to study the energetics of ten special grain boundaries in pure magnesium. The relaxed systems were subjected to topological analysis which revealed correlation between grain boundary energy and local structures conforming to the Mg bulk symmetry. In addition, three different elements with various observed effects were selected from groups 4, 12 and lanthanides of the periodic table and energetic changes imparted by them were calculated for two boundaries with the lowest and higher interfacial energy, respectively. Local topological analysis based on Voronoi polyhedra was utilized to estimate the atomic volume of each segregant and the strain energy associated with it. The contributions of strain and chemical bonding to the grain boundary energetics were then assessed. It was found that while the variation of computed energetics can be justified by the cooperative and competitive role of the strain and chemical bonding respectively, topological analysis applied to the boundary served as an effective complementary method to explain segregation-induced energetic variations.