Structural evolution of vacancy clusters in a-iron: A kinetic activation-relaxation technique study

MM Rahman and F El-Mellouhi and N Mousseau, PHYSICAL REVIEW MATERIALS, 7, 093602 (2023).

DOI: 10.1103/PhysRevMaterials.7.093602

The kinetics of vacancies in materials plays a significant role in determining their physical properties. In this work, we investigate diffusion of vacancies in alpha-iron using the kinetic activation- relaxation technique, an offlattice kinetic Monte Carlo method with on- the-fly catalog building based on the activation-relaxation technique nouveau coupled with an embedded atom method potential. We focus on the evolution of one to eight vacancies to provide a detailed picture of the energy landscape, overall kinetics, and diffusion mechanisms associated with these defects. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for the diffuse systems. This study points to an unsuspected dynamic richness, even for this simple system, that can only be discovered through comprehensive and systematic approaches such as the kinetic activation- relaxation technique. The complex energetic environment controlling the kinetics of small vacancy clusters, we find here, demonstrates that simple rules are not sufficient to develop a robust approach to predictive control and prevention of damage processes associated with vacancy clusters in structural metals.

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