Displacement cascades in the ordered compound CuTi studied by molecular-dynamics simulations

Abstract

The properties of displacement cascades of up to 5 keV in energy in the ordered intermetallic compound CuTi were investigated by molecular-dynamics simulations. Various aspects of the cascade evolution were examined, including the production of Frenkel pairs, “pure” replacements, and antisite defects, as well as the anisotropy of the displacement threshold energy. The minimum displacement threshold energy (15 eV) is found for the 〈100〉 recoil directions. The average threshold energy for displacement initiated by a Ti primary-knock-on atom (78 eV) is ∼ 1.7 times larger than that by a Cu primary-knock-on atom (47 eV). The damage function was analyzed, based on the average number of stable Frenkel pairs generated by both kinds of primary knock-on atoms in 18 directions. Multiple defect production is found for cascade energies ≥ 500 eV. Around this energy, ∼ 25 replacements are created for each stable Frenkel pair. Planar cascades occur in the (100), (010) and (110) planes under certain conditions, producing significantly more Frenkel pairs than in the case of three-dimensional cascades. Melting of the core of a 5 keV cascade during the first 5 ps causes efficient, local atomic mixing. After recrystallization at the end of the event, the impact region shows a high degree of chemical disorder, characterized by a chemical short-range order parameter of 0.49. The efficiency of Frenkel-pair production by a 5 keV recoil is estimated to be 0.14.