Molecular Dynamics Simulation on Irradiation-induced Defect Evolution in Titanium

Titanium base alloys can be used as potential candidate of structural materials in nuclear reactor due to their outstanding corrosion resistance and mechanical properties. By using molecular dynamics (MD) methods, this paper simulated the displacement cascade processes in α-Ti metal at various temperatures (T=300, 500, 700 and 900 K) with primary knock-on atom (PKA) (E_PKA=1, 5, 10 and 20 keV) incident in various directions (0001, 1010 and 1100). The displacement cascades were designed as follows, the model was initially relaxed at each specified temperature for 10 ps with periodic boundary conditions applied. Then, a PKA was randomly selected and assigned specific kinetic energy to initiate the displacement cascade. At length, the data production, defect analysis and visualization were done to elucidate the irradiation cascade processes. The results show that the defect number increases with the increase of PKA energy or temperature, whereas the incident directions of PKA does not affect the defect number during the evolution a lot. With the increase of temperature, the number of peak defects in α-Ti increase significantly, and the time required for the defect recombination process extends. With the increase of PKA energy, the number of defect in the entire defect evolution process increases significantly, and the steady-state defect number also shows an increasing tendency. However, the PKA incident direction has slightly effect on the defect evolution during the cascade process. The Norgett-Robinson-Torrens (NRT) model was used to calculate the trendency of defect number as functional of PKA energy and it is consistent with the MD calculations. Considering the simulated temperature and PKA energy, and the number of remaining defects after cascade collision accounted for about 30% of NRT. The results in this paper help to understand the primary irradiation defect and atomic effect evolution mechanisms in α-Ti from the perspective of theoretical calculations. Moreover, discussing how to enhance the radiation resistance of metallic titanium and titanium alloys under the current theoretical research content has certain guiding significance for the design of future nuclear reactor shell materials.