Atomistic modeling of carbon Cottrell atmospheres in bcc iron

Abstract

Atomistic simulations with an EAM interatomic potential were used to evaluate carbon–dislocation binding energies in bcc iron. These binding energies were then used to calculate the occupation probability of interstitial sites in the vicinity of an edge and a screw dislocation. The saturation concentration due to carbon–carbon interactions was also estimated by atomistic simulations in the dislocation core and taken as an upper limit for carbon concentration in a Cottrell atmosphere. We obtained a maximum concentration of 10 ± 1 at.% C at T = 0 K within a radius of 1 nm from the dislocation lines. The spatial carbon distributions around the line defects revealed that the Cottrell atmosphere associated with an edge dislocation is denser than that around a screw dislocation, in contrast with the predictions of the classical model of Cochardt and colleagues. Moreover, the present Cottrell atmosphere model is in reasonable quantitative accord with the three-dimensional atom probe data available in the literature.