THEORETICAL AND EXPERIMENTAL-ANALYSIS OF NEAR SIGMA-3 (211) BOUNDARIES IN SILVER

Two grain boundaries in Ag have been investigated by High Resolution Transmission Electron Microscopy (HRTEM), The orientations of the grains are tilted by 3.1 and 2.1-degrees from the ideal SIGMA3 orientation on the common tilt axis [110]. Both boundaries are found to be asymmetric. They are dissociated into two parallel sub-boundaries separated by a thin (approx. 1 nm) layer of faulted 9R character. One of the sub-boundaries contains two well defined types of structural units, which we refer to as kites and rhombuses. The other resembles a small angle boundary, consisting of a row of partial dislocations. We have atomistically simulated SIGMA3, symmetric SIGMA451 and asymmetric SIGMA451 boundaries using molecular dynamics and statics. On this basis we interpret the observed structures both in terms of structural units and DSC dislocations and we explain the occurrence and width of the faulted 9R phase.