Formation of hexagonal close packing at a grain boundary in gold by the dissociation of a dense array of crystal lattice dislocations

Abstract

We analyze a thin (~1 nm) hexagonal-close-packed (HCP) intergranular layer at a 29° 〈110〉 tilt grain boundary in gold. Our analysis, which is based on HRTEM observations and atomistic calculations, shows that this boundary consists of a dense array of 60° 1/2〈110〉 crystal lattice dislocations that are distributed one to every two {111} planes. These dislocations dissociate into paired Shockley partial dislocations, creating a stacking fault on every other plane and thereby producing the …abab…, or HCP, stacking sequence. This distribution of dislocations is consistent both with the measured intergranular misorientation and with the calculated rigid-body translation along the tilt axis. By establishing the interfacial dislocation arrangement, we also show how the HCP layer at the 29° boundary observed here is geometrically related to that found previously at the 80.6° Σ = 43 〈110〉 boundary. This result helps to link dislocation-based descriptions for boundary structures between the high- and low-angle misorientation regimes.