Primary damage formation in molybdenum: a computer simulation study

The primary damage formation in Mo is investigated using molecular dynamics (MD) simulation with embedded-defect (ED) and embedded-atom method (EAM) interatomic potentials. The former is similar in spirit to the latter but includes an approximate treatment of bond directionality in the many-body interaction. MD simulations are used to calculate threshold displacement energy as function of crystallographic orientation and displacement cascade evolution resulting from primary knock-on atoms (PKAs) with energies ranging from 0.5 up to 50 keV. The defect structures produced with increasing PKA energy are analysed and the results obtained are compared for the two potentials and with simulations from the literature for other bcc materials. The impact of temperature and inelastic losses on the cascade characteristics are also discussed. The ED approach is in better agreement with the experimental findings on threshold energy. It also predicts larger vacancy clusters as well as a larger fraction of clustered vacancies than the EAM does; this seems to be more consistent with experiment, however, on statistical grounds a definite assessment is not possible with the number of simulations performed. Inelastic losses coupled with the thermal spike affect the defect production in subtle ways, especially at the higher energies considered here. This does not seem to have been realized before and deserves to be studied more comprehensively.