The atomic-scale behaviour of an interstitial C atom in the core of a ½[111](1¯10) edge dislocation in α-Fe was simulated for the first time. The C sites with high binding energy to the dislocation were investigated and the critical stress, τc, for the dislocation to overcome a row of C atoms determined. The effects of temperature and strain rate on τc were studied. It was found that τc decreased rapidly as the temperature was increased to about 400K and became almost constant at higher temperatures. It decreased with decreasing strain-rate and was independent of the latter at above about 300K. The activation parameters in simulation conditions were obtained. The activation distance of some (0.2–0.3)b was consistent with point-obstacle strengthening. However, the activation energy was only about 5kT, where k was the Boltzmann constant, and some 20kT smaller than that realized in experimental conditions. This implied that the decline of τc over the range 0 to about 400K would occur over 0 to 80K in experiment, which was where C-edge dislocation effects would be influential. A few jumps of C occurred in the core before dislocation unpinning at above 800K and gave a small T-dependence of τc. Core diffusion of C occurred by ±½[111] jumps at 70.5° to [111]. The diffusivity in the absence of an applied stress was given by:

D (m2/s) = 4 x 10-9 exp[-0.2(eV)/kT]

and by:

D (m2/s) = 1.9 x 10-7 exp[-0.7(eV)/kT]

for the bulk diffusion of C in the same MD model. Hence, the edge dislocation provided a path for rapid diffusion of C, but net transport along the core could only occur by motion of the dislocation itself.

Computer Simulation of Interaction of an Edge Dislocation with a Carbon Interstitial in α-Iron and Effects on Glide. K.Tapasa, Y.N.Osetsky, D.J.Bacon: Acta Materialia, 2007, 55[1], 93-104