Interaction of dislocations with carbides in BCC Fe studied by molecular dynamics

In this study, the atomic processes involving the interaction of an edge dislocation with carbide precipitates in an iron matrix are investigated by molecular dynamics, utilizing two interatomic potentials (Hepburn, 2008 and Henriksson, 2013). The carbides investigated were.Fe3C and M23C6, where M was either Fe or Cr. The results from spherical precipitates were compared with rod shaped obstacles, to investigate the effect of climb in the unpinning process and the stress related to this process. The rod simulations showed a higher unpinning stress for all investigated sizes and temperatures, which indicates that climb will play a role in the unpinning phenomenon. The results showed, as previous studies, a decrease of the unpinning stress with increasing temperature and that a larger obstacle yields a higher unpinning stress. The Orowan process of dislocation unpinning was observed with both potentials as an increase in the needed unpinning stress in consecutive interactions with the same obstacle. The results showed that the structure of the obstacle does not affect the unpinning stress, as much as temperature, for obstacles >= 2 nm. Comparison of obstacles with the same structure but with different composition, Fe23C6 and Cr23C6, showed that the small shearable chromium carbides were stronger than the corresponding iron carbides, pointing to the importance of the chemical composition of the carbide. (C) 2015 Elsevier B.V. All rights reserved.