Simulation of copper atom diffusion via the vacancy mechanism in a dilute Fe-Cu alloy

Atomic diffusion in pure alpha-Fe and Fe-1 at. % Cu crystals via vacancies is investigated by molecular-dynamics computer simulation. In order to generate a large statistical set, modeling is performed for the temperature range of 1000-1800 K. The migration energy and preexponential factors in diffusion coefficients of copper and iron atoms are estimated and compared with the results of a five-frequency model, using different approaches for the frequencies, and Monte Carlo studies, where the energy barriers are obtained by molecular statics. It is concluded that the five-frequency model is valid. The vacancy-copper atom cross-diffusion coefficient is estimated by both molecular-dynamics and Monte Carlo methods and is concluded to be negative over the entire temperature range studied, indicating that under irradiation conditions copper atoms migrate in the direction opposite to the vacancy flux. It has been observed that, at temperatures above 1500 K, about 0.5% of the vacancy jumps are double jumps, when two atoms move simultaneously in a < 111 > direction towards the vacancy.