Molecular dynamics study of migration mechanism of triple junctions of tilt boundaries in fcc metals

Abstract

The study of migration mechanism of triple junctions of tilt boundaries with misorientation axes 〈1 1 1〉 and 〈1 0 0〉 on the example of nickel was performed by the method of molecular dynamics. It was found that migration and elongation of low-angle 〈1 0 0〉 boundaries is realized through slipping of pair grain-boundary dislocations with the subsequent change of dislocations-partners. During the changing of dislocation-partners, the decomposed dislocations slipped, the climb of the dislocations was not observed. The migration of 〈1 1 1〉 tilt boundary occurred as a result of the combined action of two mechanisms: the mechanism described above and the mechanism consisting in the joint slipping of pair grain-boundary dislocations, which, in contrast to grain-boundary dislocations in 〈1 0 0〉 boundaries, have common slip planes. The second mechanism has relatively low activation energy, as a result of which 〈1 1 1〉 boundaries are much more mobile than 〈1 0 0〉 boundaries.During the triple junction migration, at an elongation of the low-angle boundary, a new geometrically necessary dislocation appeared, as a rule, from the migrating triple junction, after which the dislocation-partners are redistributed at the elongating boundary near the junction as a result of their split and subsequent merging with the formation of zigzag atomic displacements.