DISPLACEMENT CASCADES IN THE ORDERED COMPOUND CUTI STUDIED BY MOLECULAR-DYNAMICS SIMULATIONS

The properties of displacement cascades of up to 5 keV in energy in th e ordered intermetallic compound CuTi were investigated by molecular-d ynamics simulations. Various aspects of the cascade evolution were exa mined, including the production of Frenkel pairs, ''pure'' replacement s, and antisite defects, as well as the anisotropy of the displacement threshold energy. The minimum displacement threshold energy (15 eV) i s found for the [100] recoil directions. The average threshold energy for displacement initiated by a Ti primary-knock-on atom (78 eV) is si milar to 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 ene rgies greater than or equal to 500 eV. Around this energy, similar to 25 replacements are created for each stable Frenkel pair. Planar casca des occur in the (100), (010) and (110) planes under certain condition s, producing significantly more Frenkel pairs than in the case of thre e-dimensional cascades. Melting of the core of a 5 keV cascade during the first 5 ps causes efficient, local atomic mixing. After recrystall ization at the end of the event, the impact region shows a high degree of chemical disorder, characterized by a chemical short-range order p arameter of 0.49. The efficiency of Frenkel-pair production by a 5 keV recoil is estimated to be 0.14.