[SY-N5] Understanding the impact of extended defects on the behaviour of C atoms: a multi technique approach
Invited
The interaction at the atomistic scale of interstitial solutes such as carbon or nitrogen with extended point defects has consequences at the macroscopic level. Typical examples are the yield peak and Lüders plateau, related to static strain aging or the Portevin-Le Chatelier effect (the presence of serrations on the plastic part of the stress-strain curve during tensile test) due to dynamic strain aging. In ferritic steels, these atypical behaviors are due to the interaction between dislocations and solute atoms (mainly C). Depending on aging time and temperature, solute atoms diffuse towards dislocations, forming Cottrell atmospheres, and reduce their mobility. Because of the time scale of C diffusion and the stresses created near the extended defects, typical atomistic approaches such as molecular dynamics (MD) or on-lattice atomistic kinetic Monte Carlo (on-lattice AKMC) approaches are not appropriate to investigate, at the atomistic level, these phenomena. In this talk, we will thus present the approach we have pursued to investigate the behavior of C atoms in the vicinity of extended defects (dislocations, dislocation loops …) in Fe. We have applied different complementary techniques. Calculations based on the density functional theory (DFT) as well as with an empirical FeC atomistic potential have been used extensively to determine the strength of the interaction between carbon atoms and the various defects in stable or metastable configurations. On-lattice static Monte Carlo as well as off-lattice kinetic Monte Carlo approaches have been applied to build Cottrell atmospheres and study dynamically the behavior of C atoms in the vicinity of extended defects (dislocations, …). Finally molecular dynamics (MD) simulations have been deployed to estimate the stress necessary to release the dislocations from the C atmospheres.