Evaluation of the Threshold Displacement Energy in Fe–Cr Ferritic-Martensitic Steels

Molecular dynamics (MD) simulations are applied to study primary damage formation in a Fe–10 at % Cr binary model alloy. 14 784 events of radiation defect formation are initiated by either Fe or Cr primary knock-on atoms (PKAs) with PKA energies 100 eV ≤ E_PKA ≤ 5 keV introduced along twenty-two nonequivalent crystallographic directions. The generated sample is used to calculate the average threshold displacement energies. It is shown that in the considered material the average threshold displacement energy of Fe and Cr atoms is the same and equals 〈E_d〉 = 24.5 ± 0.6 eV. It is also established that the dependence of E_d on E_PKA splits into two linear fragments determined by the governing defect formation mechanism. The formation of isolated point defects at low PKA energies E_PKA ≤ E_cc, where E_cc ≈ 0.84 keV, is replaced by defect formation in collision cascades initiated by PKAs with energy E_PKA ≥ E_cc. Using MD simulation results, we modified the cascade function in the Kinchin–Pease model to take into account the dependence of the threshold displacement energy on the PKA energy.