Simulation of atomic jump features and carbon atom migration in α-Fe

In this paper we study features of atomic jumps and features of carbon atom migration in α-Fe by simulation. At first we present a new approach of the constant temperature Molecular Dynamics that fully takes into account the fluctuating character of this phenomenon. Then by the developed model, the diffusion mobility of carbon atoms at different temperatures is studied. Analysis of a large number of diffusion jump trajectories allowed us to find a correlation in moving jumping carbon atom and neighbor iron atoms and estimate the contribution of double jumps in the diffusion. We evaluated the influence of anharmonic effects on the carbon diffusivity at high temperatures. Isotope effect and its temperature dependence are considered. Also we study carbon diffusion under pressure.

In the second part, we study the effect of vacancies on the diffusion of carbon atoms using a model similar to that developed earlier [1]. An activation barrier set for different configurations of the carbon–vacancy complexes is simulated by the method of Molecular Static. Then we calculate atom jump rates for these configurations. The simulation of the carbon and vacancy migration in bcc metal is realized on the basis of obtained atom jump rates by using the Monte-Carlo method. In the result of that carbon atom diffusion coefficient is obtained at different temperatures. The carbon diffusivity is shown to be significantly modified by the formation of vacancy-carbon complexes.

We analyze the possible reasons for the acceleration of carbon diffusion in α-iron at high temperatures based on our results.

[1] L.V. Selezneva, A.V. Nazarov, Defect and Diffusion Forum, v.237-240, 1275 (2005).