The long-range tracer diffusion coefficient of interstitials, their jump rate and their distribution among different sites in one-, two- and three-dimensional lattices were determined by Monte Carlo calculations. In part of the study, traps or anti-traps were introduced with equilibrium site energies being lower or higher, respectively, and energies of the surrounding saddle points being higher or lower when compared with the normal sites. Already a small decrease of the saddle point energies around the trap sites, reduces the diffusion coefficient remarkably. For an overall constant saddle point energy the results could be compared with various trapping models, but for lower or higher energy barriers around the trap sites analytical solutions for the site occupancy and the diffusivity had to be derived which were in agreement with the computer calculations. According to the theoretical results the free energy of a site was also determined by its accessibility where lower saddle points decrease the free energy and vice versa. In a second part of this study a site energy distribution was constructed which corresponds to the elastic interaction energy between an interstitial solute and an edge dislocation. Again the segregation of solute atoms in trap sites of the dislocation was strongly dependant on the distribution of saddle point energies and remarkable deviations from the treatment of Cottrell and Bilby occurred if the saddle point energy was lowered in the same way as the energy of the equilibrium points.

Monte-Carlo Simulations of Interstitial Diffusion and Trapping-I. One Type of Traps and Dislocations. R.Kirchheim: Acta Metallurgica, 1987, 35[2], 271-80