Theoretical and computational investigation on the radiation-induced point defects in cementite: Picosecond timescale

Abstract In this paper, we propose a novel time-dependent model for the displacement cascade in cementite. It consists of two terms, one of which depends on spherical-like inflation of the thermal spike stage and the other one on the recombination stage. The first term is obtained from spherical inflation of the cascade and the second term is resulted from solving the equation of heat conduction in spherical geometry in a uniform medium. The proposed model had a satisfactory agreement with those of resulted by molecular dynamics simulations based on employing Fe-C MEAM potential developed by Liyanage et al. (2014) for cementite. In the second goal of the current work, we determine the residual number of all types of radiation-induced point defects, including iron/carbon antisites, vacancies, and interstitials produced by primary knock-on atoms with energies of 0.5–9 keV in cementite by using molecular dynamics based on employing the potential developed by Liyanage et al. (2014). Then, the results are compared with those reported in the literature, the results of which were based on using the potential developed by Henriksson and Nordlund (2012). Surprisingly, the comparison showed fundamental differences. Thus, the molecular statics simulations were carried out for calculating the formation energies of all types of defects by using these two interatomic potentials and also the potential developed by Ruda et al. (2009). The results were used to analyze these discrepancies and to compare with those reported in the literature by using density functional theory calculations. It was concluded that the potential developed by Liyanage et al. (2014) has the best performance among two other ones for the study of radiation damage. Finally, the nudged elastic band calculations showed that the vacancies most probably migrate to the interstitial sites due to their much lower migration energies.