Atomistic Kinematics of Carbon Diffusion and Clustering in BCC Fe with Point Defects*

Carbon diffusion and clustering in iron are important phenomena as they closely link to processes of production of steels such as cementite formation, phase transition, and so on. Here, we studied these phenomena using multi-scale approach. First, the stability of carbon and its interaction with point defect were examined via total energy optimization using our own newly developed Fe-C potential. Then, the diffusion mechanisms for carbon interstitials were analyzed. By using kinetic Monte Carlo (kMC) simulations, diffusion coefficients of carbon depending on temperature were estimated to clarify the influence of vacancy on the diffusion and clustering processes. We found that in perfect lattice, carbon atoms tend to form stable C-C pairs, while the presence of vacancies leads to the formation of larger vacancy-carbon (VC_n) clusters with VC₂ as the most stable structure. In addition, due to the presence of vacancies, the diffusion paths of carbon are strongly modified. The kMC simulations show that diffusion coefficient is decreased as vacancy content increases. Therefore, it is suggested that vacancies may play an important role in the clustering process of carbon.