Abstract
Segregation at a triple junction of grain boundaries has not been explained much because the structure of a triple junction is very complicated. The present paper describes Monte Carlo simulations by which Y segregation was investigated at a triple junction of a {101¯1}–{101¯2} double twin in Mg. Y atoms segregated at the extension sites in the {101¯1} and {101¯2} twin boundaries. However, they were not necessarily more segregated at the triple junction of the double twin, although the free volumes at the extension sites of the triple junction were larger on average than those of the other boundaries. Thus, the Y segregation behavior at the triple junction cannot be explained only by the free volume. The anisotropic factor of the atomic Voronoi polyhedron was developed to explain the Y segregation behavior at the triple junction. In addition, the shortest interatomic distance and coordination number affected Y segregation at the triple junction. Also, segregation at the triple junction strongly depended on the Y concentration, which resulted from variations in the local atomic configuration. Thus, the Y segregation behavior at the triple junction was complicated, in contrast to those at twin boundaries, even when the size effect was predominant.
Highlights
Grain boundary segregation strongly affects material properties of polycrystallines
Similar Y segregation behavior at the twin boundary (TB) was obtained for 0.2 at.% Y, the number of segregated Y atoms was larger for 0.2 at.% Y than for 0.1 at.% Y
Y atoms segregated at the extension sites in the TBs
Summary
Grain boundary segregation strongly affects material properties of polycrystallines. Segregation at a triple junction (TJ) of grain boundaries has not been investigated much because the structure of a TJ is very complicated. Coincidence boundaries are convenient for investigating grain boundary segregation behavior from the atomistic view because atomic positions are known for many coincidence boundaries. There are many atomistic studies on grain boundary segregation at coincidence boundaries.[1,2,3] a TJ of coincidence boundaries is suggested to be suitable for investigating segregation at a TJ from the atomistic view. Mg has few activated slip systems at room temperature because of its anisotropic hexagonal closepacked structure, and twinning is enhanced during deformation in Mg.[4,5] There are some deformation twinning modes in Mg.[6,7,8,9,10,11] In particular, {101 ̄1} and {101 ̄2} twinning significantly affect the mechanical properties of Mg.[10,11,12,13,14,15] It has been found that the {101 ̄1}–{101 ̄2} double twin (DT), which is composed of secondary {101 ̄2} twins in a primary {101 ̄1} twin, is formed at a final stage of deformation and provides a fracture-initiation site.[11,16,17,18,19,20,21,22] There are four possible variants
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