Molecular-dynamics study of partial edge dislocations in copper and gold: Interactions, structures, and self-diffusion

Abstract

The interactions between the [112] partial dislocations (PD), the interactions of vacancies and interstitials with the PD and their structures near the PD, as well as self-diffusion along the PD's in copper and gold are studied by using constant-NTV (number of atoms, temperature, and volume) molecular dynamics and the Ackland-Tichy-Vitek-Finnis many-atom interaction model. The interaction energy between the PD's is found to agree accurately with the elastic-continuum energy beyond and at the equilibrium separation distance whereas the former energy grows much more strongly at smaller separation distances due to the increased core repulsion. This behavior indicates a small core overlap at the equilibrium. A vacancy at the edge of a PD is found to have a form of a distorted hexagon whereas an interstitial is found to form a long ⟨110⟩ crowdion in the (11¯1) plane in front of the edge of a PD for both metals. The self-diffusion activation energy for the vacancy mechanism is found to be at least 0.33 eV smaller than that for the interstitial mechanism in the region of the PD pair in gold whereas the corresponding activation energies are estimated to be equal in copper. We find that self-diffusion has nearly equal components along the edges of the PD's and the stacking fault ribbon. This can explain why self-diffusion in metals has a tendency to be weaker along PD pairs than along perfect dislocations.