MD Simulations of Collision Cascades in α-Ti. The Residual Number of Radiation Defects, Cascade Relaxation Time, and Displacement Cascade Region Morphology

Molecular dynamics (MD) simulations were applied to study primary damage formation in collision cascades initiated by the recoil of primary knock-on atoms (PKAs) with PKA energies \({{E}_{{{\text{PKA}}}}}\) = 5, 10, 15, 20, and 25 keV in α-Ti at temperature T = 100, 300, 600, and 900 K. A statistical sample of 24 collision cascades per set of parameters \(\left( {{{E}_{{{\text{PKA}}}}},~T} \right)\) was generated in order to assure statistical reliability of the obtained results. The size of the sampling set was justified posteriori using a simple procedure. The number of Frenkel pairs, \({{N}_{{{\text{FP}}}}}\), and cascade relaxation time were obtained as functions of \(\left( {{{E}_{{{\text{PKA}}}}},~T} \right)\). It was found that the average \(\left\langle {{{N}_{{{\text{FP}}}}}\left( {{{E}_{{{\text{PKA}}}}},~T} \right)} \right\rangle \) values fit into ≈0.3NRT if the threshold displacement energy is selected in the range of 28–40 eV depending on the irradiation temperature. At high PKA energies/low temperatures, collision cascades in α-Ti tend to break up into subcascades elongated along the trajectories of high-energy recoil atoms and their relaxation time does not depend on \({{E}_{{{\text{PKA}}}}}\). At low PKA energies/high temperatures, equiaxed collision cascades dominate and their relaxation time increases monotonically with increasing PKA energy \({{E}_{{{\text{PKA}}}}}\).