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Y.V. Shan, J. Svoboda, F. Fischer, E. Kozeschnik:
"Diffusion of Interstitial Components in Systems with Traps";
Talk: Materials Science and Engineering - MSE 2012, Darmstadt; 2012-09-25 - 2012-09-27.

Diffusion of small atoms, like hydrogen, nitrogen, oxygen or carbon, in alloys has been studied thoroughly in literature. However, the relationship of the effective diffusion coefficient in alloys compared to the diffusion coefficient in pure metals, which are well known, is highly complex and only approximated by theoretical models. Using a Monte-Carlo framework, the diffusion of interstitial atoms in a rigid fcc-lattice in the presence of substitutional trapping sites is studied. In the present MC framework, interstitial jumps are performed according to the Metropolis algorithm. The interaction between atoms is defined by pairwise trapping enthalpies. Simulations are carried out to determine the equilibrium fraction of trapped interstitial atoms for various trap depths. Based on the results of charging and discharging simulations for interstitial components, the diffusion characteristics of the interstitials are investigated in detail. Depending on the repulsive or attractive nature of the traps, the results vary considerably: Whereas the former leads to a minor decrease of the effective diffusion coefficient, the latter causes substantial changes in the diffusion profiles. These consist of asymmetric profiles in charging and discharging simulations at higher trap depths and a significantly lower effective diffusion coefficient. The calculations are compared to a recent theoretical analysis of J. Svoboda and F.D. Fischer, who derived a general model for diffusion of an interstitial component in the presence of one kind of immobile trap. The Monte Carlo approach and the analytical model are in good quantitative agreement. The basic features of the two approaches are highlighted and discussed.

diffusion, Lattice-Monte-Carlo, interstitital trapping, charging and discharging asymmetry