Atomistic modelling of diffusional phase transformations with elastic strain

Abstract

Phase transformations in 2xxx series aluminium alloys (Al–Cu–Mg) are investigated withan off-lattice atomistic kinetic Monte Carlo simulation incorporating the effects of strainaround misfitting atoms and vacancies. Atomic interactions are modelled by Finnis–Sinclairpotentials constructed for these simulations. Vacancy diffusion is modelled bycomparing the energies of trial states, where the system is partially relaxed for eachtrial state. No special requirements are made about the description of atomicinteractions, making our approach suitable for more fundamentally based models such astight binding if sufficient computational resources are available. Only a limitedprecision is required for the energy of each trial state, determined by the value ofkBT. Since the change in the relaxation displacement field caused by a vacancy hop decays as1/r3, it is sufficient to determine the next move by relaxing only those atoms in a sphere offinite radius centred on the moving vacancy. However, once the next move has beenselected, the entire system is relaxed.Simulations of the early stages of phase separation in Al–Cu with elastic relaxation showan enhanced rate of clustering compared to those performed on the same system with arigid lattice.