Computer simulation of interaction of an edge dislocation with a carbon interstitial in α-iron and effects on glide

The atomic-scale behaviour of a carbon (C) interstitial atom in the core of a 1 / 2 [1 1 1] (1 over(1, ̄) 0) edge dislocation in α-iron has been simulated for the first time. C sites with high binding energy to the dislocation have been investigated and the critical stress, τ_c, for the dislocation to overcome a row of C atoms determined. The effects of temperature, T, and applied strain rate, over(ε, ̇), on τ_c have been studied. τ_c decreases rapidly as T increases to ∼400 K and becomes almost constant at higher T. It decreases with decreasing over(ε, ̇) and is over(ε, ̇)-independent at T greater than ∼300 K. The activation parameters in simulation conditions have been obtained. The activation distance of ∼(0.2-0.3)b is consistent with point-obstacle strengthening. However, the activation energy is only ∼5k_BT, where k_B is the Boltzmann constant, and ∼20k_BT smaller than that realized in experimental conditions. This implies that the decline of τ_c over the range 0 to ∼400 K would occur over 0 to ∼80 K in experiment, which is where C-edge dislocation effects would be influential. A few jumps of C occur in the core before dislocation unpinning at T ≥ 800 K and give a small T-dependence of τ_c. Core diffusion of C occurs by ± 1 / 2 [1 1 over(1, ̄)] jumps at 70.5° to [1 1 1]. The diffusivity in the absence of applied stress is 4 × 10^-9exp(-0.2 eV/k_BT) m²/s compared with 1.9 × 10^-7exp(-0.7 eV/k_BT) m²/s for bulk diffusion of C in the same MD model. Hence, the edge dislocation provides a path for rapid diffusion of C, but net transport along the core can only occur by motion of the dislocation itself.