Molecular dynamics simulation of displacement cascades in B2 NiAl

This study is focused on the behavior of B2 NiAl alloy under irradiation. For achieving this aim, we performed a series of molecular dynamics simulations of displacement cascades with the primary knock-on atom (PKA) energy from 1 keV to 40 keV. To ensure that the boundary effects were not important, the simulation boxes contained from 60 x 60 x 60 to 112 x112 x112 unit cells with 432 000 to 2 809 856 atoms, depending on the PKA energy. To correctly reproduce atomic interactions at short distances, the Mishin EAM potentials were stiffened in a short range using polynomial regression to join the equilibrium part of the EAM potential to a short range of ZBL potential and intermediate interatomic distance with the corresponding pairwise energy based on the density function theory calculation. To obtain statistically meaningful results, 10 simulations were performed for each PKA energy. Each cascade simulation lasted approximately from 12 ps to 42 ps, depending on the PKA energy; in these time intervals the number of Frenkel pairs (FP) became stable. We discuss in detail the time evolution of Frenkel pairs, the avalanche effect in the sonic phase and the origin of the permanent defect. The results from our simulations, including the number of stable Frenkel pairs, chemical composition, clustering of the defect production are in good agreement with the reports from the literature.