Experimental observations of dislocation core structures in gold and iridium

Dislocation core structures are known to play an important role in determining the mechanical properties of metals and alloys. The ability to develop atomic level models of dislocation core structures that are based on first-principles or atomistic calculations has increased significantly in recent years, and in many ways these theoretical models have outpaced experimental observations. The HREM study outlined in this paper has been undertaken to provide an experimental benchmark for such models. In-situ TEM observations have been used to identify the presence of screw and 60° dislocations, and HREM images of these dislocations in both gold and iridium have been recorded. Computer-based image analyses have been employed to characterize subtle in-plane atomic level displacements, and direct comparisons with image simulations have been used to measure the separation distance between dissociated Shockley partial dislocations. The separations measured in this study have been found to be in good agreement with recently obtained theoretical predictions based on the first-principles calculations of Mryasov and colleagues.